LATEST MECHANICAL INVENTION

Robotic device has therapeutic potential for ankles and feet

A soft, wearable device that mimics the muscles, tendons and ligaments of the lower leg could aid in the rehabilitation of patients with ankle-foot disorders.

This is the claim of Yong-Lae Park, an assistant professor of robotics at Carnegie Mellon University. He worked with collaborators at Harvard University, the University of Southern California, MIT and Massachusetts-based BioSensics to develop an active orthotic (artificial support or brace) device using soft plastics and composite materials instead of a rigid exoskeleton.

The soft materials - combined with pneumatic artificial muscles (PAMs), lightweight sensors, and advanced control software - made it possible for the robotic device to achieve natural motions in the ankle.

The researchers reported on the development in the journal Bioinspiration & Biomimetics. In a statement, Park said the same approach could be used to create rehabilitative devices for other joints of the body or create soft exoskeletons that increase the strength of the wearer.

The robotic device would be suitable for aiding people with neuromuscular disorders of the foot and ankle associated with cerebral palsy, amyotrophic lateral sclerosis, multiple sclerosis or stroke. These gait disorders include drop foot, in which the forefoot drops because of weakness or paralysis, and equinus, in which the upward bending motion of the ankle is limited. Conventional passive ankle braces can improve gait, but long-term use can lead to muscle atrophy because of disuse. Active, powered devices can improve function and also help re-educate the neuromuscular system.

‘The limitation of a traditional exoskeleton is that it limits the natural degrees of freedom of the body,’ said Park. The ankle is naturally capable of a complicated three-dimensional motion, but most rigid exoskeletons allow only a single pivot point. The soft orthotic device enabled the researchers to mimic the biological structure of the lower leg. The device’s artificial tendons were attached to four PAMs, which correspond with three muscles in the foreleg and one in the back that control ankle motion. The prototype was capable of generating an ankle range of sagittal motion of 27 degrees, which is sufficient for a normal walking gait.

The soft device, however, is more difficult to control than a rigid exoskeleton. Park said it required more sophisticated sensing to track the position of the ankle and foot, and a more intelligent scheme for controlling foot motion. The device contains sensors made of a touch-sensitive artificial skin, and thin rubber sheets that contain long microchannels filled with a liquid metal alloy. When these rubber sheets are stretched or pressed, the shapes of the microchannels change, which cause changes in the electrical resistance of the alloy. These sensors were positioned on the top and at the side of the ankle.

Park said additional work will be necessary to improve the wearability of the device. This includes artificial muscles that are less bulky than the commercially produced PAMs used in this project.

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Filed Under: Mechanical Engineering, Robotics on Wednesday, February 5, 2014 2 Comments

Types and working of Power Steering

There are 2 types of power steering currently in use. These are integral and linkage booster types. Both are operated by hydraulic pressure produced by an engine driven pump to assist in turning the steering mechanism. The integral power steering is explained below :

Integral Power Steering : figure shows the integral power steering when the vehicle moves in the straight head position. the oil pump is belt driven from the engine crankshaft pulley. It consists of a solid cylinder with 2 grooves cut called valve spool which slides within the valve housing. The housing has three internal grooves is connected to the pump and the other are connected to the reservoir.

 

 

The two additional opening are connected to the two sides of the cylinder fitted with piston. When the valve spool is in the position as shown is figure , the pump delivers the oil in the central part of the housing which flows back to the reservoir by the passage shown by the arrows. In this position, there is no oil pressure in the cylinder and there is no tendency for the position to slide in any direction. There is no steering action and the vehicle moves in the straight-head position.

Figure 2nd shows that when the valve spool is moved towards right side, the direct return supply from the pump to the reservoir is closed. The oil flows into the cylinder by the right side passage and pushes the piston to the left side as shown in the figure. The oil on the left side of the piston flows back to the reservoir through the valve housing under this position. The left side outward movement of the piston rod turns towards left side of the road, the vehicle can be turned to the right side by reversing the steering operation.

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Filed Under: Steering Systems on Monday, February 3, 2014 2 Comments

Different types of Casting Process

1) Investment casting

2) Permanent mold casting

3) Centrifugal casting

4) Continuous casting

5) Sand casting

Investment casting

Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with lost wax process being one of the oldest known metal forming techniques. From 5000 years ago, when bees wax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity.

Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting it that the wax can be reused.

The process is suitable for repeatable production of net shape components, from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminum castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting it can be an expensive process, however the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so requiring little or no rework once cast.

Permanent mold casting

Permanent mold casting (typically for non-ferrous metals) requires a set-up time on the order of weeks to prepare a steel tool, after which production rates of 5-50 pieces/hr-mold are achieved with an upper mass limit of 9 kg per iron alloy item (cf., up to 135 kg for many nonferrous metal parts) and a lower limit of about 0.1 kg. Steel cavities are coated with a refractory wash of acetylene soot before processing to allow easy removal of the workpiece and promote longer tool life. Permanent molds have a limited life before wearing out. Worn molds require either refinishing or replacement. Cast parts from a permanent mold generally show 20% increase in tensile strength and 30% increase in elongation as compared to the products of sand casting.

The only necessary input is the coating applied regularly. Typically, permanent mold casting is used in forming iron, aluminum, magnesium, and copper based alloys. The process is highly automated.

Sub-types of permanent mold casting

1. Gravity Die Casting.

2. Low pressure die casting.(LPDC)

3. High pressure die casting.(PDC)

 

Centrifugal casting

Centrifugal casting is both gravity- and pressure-independent since it creates its own force feed using a temporary sand mold held in a spinning chamber at up to 900 N (90 g). Lead time varies with the application. Semi- and true-centrifugal processing permit 30-50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3-4.5 kg.

Industrially, the centrifugal casting of railway wheels was an early application of the method developed by German industrial company Krupp and this capability enabled the rapid growth of the enterprise.

Continuous casting

Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. Molten metal is poured into an open-ended, water-cooled copper mold, which allows a 'skin' of solid metal to form over the still-liquid centre. The strand, as it is now called, is withdrawn from the mold and passed into a chamber of rollers and water sprays; the rollers support the thin skin of the strand while the sprays remove heat from the strand, gradually solidifying the strand from the outside in. After solidification, predetermined lengths of the strand are cut off by either mechanical shears or travelling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimeters thick by about five metres wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut.

Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increases the quality of the final product. Metals such as steel, copper and aluminium are continuously cast, with steel being the metal with the greatest tonnages cast using this method.

 

Sand casting

Sand casting is one of the most popular and simplest types of casting that has been used for centuries. Sand casting allows for smaller batches to be made compared to permanent mold casting and a very reasonable cost. Not only does this method allow for manufacturers to create products for a good cost there are other benefits to sand casting such as there are very little size operations. From castings that fit in the palm of your hand to train beds (one casting can create the entire bed for one rail car) it can be done with sand casting. Sand casting also allows for most metals to be cast depending in the the type of sand used for the molds.

Sand casting requires a lead time of days for production at high output rates (1-20 pieces/hr-mold), and is unsurpassed for large-part production. Green (moist) sand has almost no part weight limit, whereas dry sand has a practical part mass limit of 2300-2700 kg. Minimum part weight ranges from 0.075-0.1 kg. The sand is bonded together using clays (as in green sand) or chemical binders, or polymerized oils (such as motor oil.) Sand in most operations can be recycled many times and requires little additional input.

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Filed Under: Casting, Mechanical Industry on Saturday, February 1, 2014 2 Comments

Why Manual Transmission Cars Make a Loud Whirring Noise in Reverse?

Manual transmissions use mostly helical gears, but reverse is a special situation that requires a different type of gear - a spur gear.

The gears that make up the forward gear ratios are all helical gears. The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement. This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears. Also, because of the angle of the gear teeth, more teeth are in engagement at any one time. This spreads the load out more and reduces stresses.

The only problem with helical gears is that it is hard to slide them in and out of engagement with each other. On a manual transmission the forward gears stay engaged with each other at all times, and collars that are controlled by the shift stick lock different gears to the output shaft (see How Manual Transmissions Work for details). The reverse gear on your manual transmission uses an idler gear (the large spur gear visible at the right side of the picture below), which has to slide into mesh with two other spur gears at the same time in order to reverse the direction of rotation.

Spur gears, which have straight teeth, slide into engagement much more easily than helical gears, so the three gears used for reverse are spur gears>
Each time a gear tooth engages on a spur gear, the teeth collide instead of gently sliding into contact as they do on helical gears. This impact makes a lot of noise and also increases the stresses on the gear teeth. When you hear a loud, whirring noise from your car in reverse, what you are hearing is the sound of the spur gear teeth clacking against one another!

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Filed Under: Automobile Industry, Mechanical Engineering on 5 Comments

10 reasons why Mechanical Engineering is the best

There has always been a debate and discussion among all engineering students about which engineering course is the best? Students always love discussing about the best branch of engineering. Though this is a proven fact and it needs no discussion that mechanical engineering is the best still I will be providing 10 reasons over here which make mechanical engineering The Best among all other branches of engineering.

10 reasons why Mechanical Engineering is the best

1) Evergreen Field: Mechanical engineering is an evergreen field. Applications of mechanical engineering have spread over such a wide spectrum that it has penetrated into almost every industry. Mechanical engineering got its application started right from the birth of this universe and it will continue till the end of this universe.

2) Mother Of All Engineering Disciplines: Yeah it’s mother of all engineering disciplines and you know it! Mechanical engineering links all engineering disciplines together and provides a base for all engineering education.

3) Everything Is Mechanical: Mechanical engineering has its application in all fields of life. May it be medicine, construction, automobile or even software and IT industry. Everything you see around you involves mechanical engineering to some extent.

4) Everlasting Scope: Scope of mechanical engineering is everlasting. Mechanical engineering graduates can find career placements in almost every sector, right from construction sector to steel industry and from automobile to software.

5) Best Job Offers: Mechanical engineers get best job offers after graduation. It’s one of the highest paid jobs all over the world.

6) Social Status: Mechanical engineers are respected in every society. They possess a respectful social status among masses. They are like global ambassadors. Wherever they go, they are treated with respect.

7) Most Interesting: Mechanical engineering involves study of some of the most interesting phenomena of science and engineering. The basic focus during study is on subjects such as thermal engineering, fluid sciences, machine design, industrial engineering and production engineering.

8) Even GOD Loves ME: Ever thought GOD also implemented mechanical engineering in nature? Motion of your body, arms, hands and feet involves mechanical engineering. Your heart pumps blood and it runs through all your veins. This is again application of mechanical engineering. The more you look into nature with the eye of a mechanical engineer, you will find more application of it.

9) Best Lifestyle: Do you need a best lifestyle to live in? Mechanical engineering offers you one of the best lifestyles. It’s like a dream come true.

10) Vast Industry: Mechanical engineering industry is vast. Every industry needs mechanical engineers to run its business smoothly.

Do you have more reasons to say? Don’t forget to comment. Let us see how many reasons we can gather here in comments.

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Filed Under: Mechanical Engineering on 5 Comments

Ultrasonic Welding

Ultrasonic welding is represented as a friction welding method, where oxides and other contaminants present on the material surfaces are broken up and also the components to be welded are brought together under simultaneous pressure. Molecular bonding, just like the conventional cold-press welding, then takes place. Ultrasonic welding is the conversion of high frequency electrical energy into high frequency mechanical energy. In ultrasonic welding spot welds in thin steels are produced by the local application of high frequency vibrating energy to work pieces held together under pressure. The work pieces are clamped together under a moderate static force applied normal to their face and oscillating shear stresses of ultrasonic frequencies (1 KHz to 40 KHz) with a power ranging of 700 to 6000 watts are applied parallel to the interface. The vibrating probe called “a sonotrode” induces lateral vibrations and slip between the surfaces fracturing the brittle oxide layers and softening the asperities because of localized heating. The combined effects of pressure and vibrations cause movement of metal molecule bringing about a sound weld.

The bonding is achieved in solid state without application of external heat, filler rod or high pressure. There is also no need for any thorough cleaning before welding because all contaminants, oxides, moisture etc are removed by the vibrating motion.

Ultrasonic Welding Equipment:

The ultrasonic vibrating unit consists of following main components:

1. Frequency converter,
2. Booster,
3. Horn or sonotrode,
4. Pneumatic Press /Actuator,
5. Ultrasonic power supply, and
6. holding fixture

This converts 50 Hz – 60 Hz line power into high frequency electrical power and a transducer which changes the high frequency electrical power into ultrasonic vibratory motion that is transmitted to the joint. The weld is completed in 0.5 to 1.5 seconds.

Ultrasonic welding of plastics:

Plastics are typically engineered materials consisting of polymers. Polymers are shaped by polymerisation that may be a chemical action during which two or more molecules are combined to make a larger molecule. Polymers are often classified as either thermosets or thermoplastics. Thermosets aren’t appropriate for ultrasonic assembly because they degrade when subjected to intense heat. Thermoplastics on the opposite hand soften when heated and cool when hardened and are thus ideally fitted for ultrasonic assembly.

Materials for Ultrasonic Welding of Plastics:

Most of the thermoplastic materials can be ultrasonic weldable. Teflon with low coefficient of friction and high melting temperature is impossible to weld using this process. 

Welding Temperature Achieved:

Ultrasonic welding produces a localized temperature rise from the combined effects of elastic hysteresis, interfacial slip and plastic deformation. The weld interfaces reach roughly 1/3 the temperatures required to melt the metals. Since the temperature doesn’t reach the melting point of the material, the physical properties of the welded material are preserved. As the ultrasonic welding method is an exothermic reaction, as welding time will increases so does weld temperature.

 

The ultrasonic welding process has the advantage that since no bulk heating of the work pieces is involved and there is no danger of any mechanical or metallurgical bad effects. Although metals have up to 2.5 mm thick have been welded by this process. It is used mostly for welding foils. This process is suitable only for thermoplastics with the exception of thermosetting resins and Teflons. The process can be used on a variety of metals including the refractory metals. Even dissimilar metals can be welded because there is no fusion. The process can also be used on temperature sensitive materials because temperature rise is limited.

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Filed Under: Welding on 1 Comment

2 stroke engines in racing motorcycles

Although two stroke engines have long since been updated with four stroke racing bike engines, two stroke engines provide a lightweight and suitable solution for racing bikes, motocross and dirt bikes.
Earlier on, the two stroke engines in racing bikes were quite popular, but they have since then have been replaced with the four stroke version of the engine.

The two stroke engine was a much simpler design, therefore provided a low cost solution for racing teams.

The two stroke bike engine operates in two strokes, instead of the normal four stroke Otto cycle.
The stages in a two stroke engine are:

1. Power/exhaust stroke: This is the stroke that occurs right after the ignition of the charge, forcing the piston down. After sometime, the top of the piston goes over the exhaust port, with a large amount of the pressurized gases to escape. The downward movement of the piston continues to compress crankcase containing the air, fuel, oil mixture. The top of the piston having passed the transfer port, the charge that is compressed enters the cylinder with any exhaust being forced out.

2. Upon entering the cylinder, the air fuel mixture makes the piston move up, compressing the charge in the cylinder. This results in a vacuum being drawn in the crankcase, with drawing in more air, fuel and oil. The spark plug now ignites the compressed charge, and thereafter the cycle begins again.

The main variations of the two stroke engine types are found in the method of the fuel intake; this depends on the various different types of the cylinder arrangement.

The Reed valve type of configuration delivers power through a wider RPM range than the regular piston and port types, which is generally a suitable arrangement for dirt bikes, as a dirt bike course demands more power over the difficult jump sections.

A rotary inlet valve type of engine configuration has a thin disk attached to the crankshaft, which spins at the crankshaft speed. The fuel-air mixture is made to pass through the disk, with the disk having a section cut, opening if it passes the intake pipe, closing otherwise.

The advantage of the rotary valve arrangement is that it asymmetrically arranges the two stroke mechanism’s intake timing, not possible with piston port type of arrangements.

Cross flow engines are configured to house the transfer ports and exhaust ports on opposing sides, with on top of the piston being the deflector, directing the fresh intake charge on to the upper side of the cylinder.

The residual gas is pushed down the deflector’s other side, out of the exhaust port. The 235 hp 2.6 L V6 crossflow till date has some of the highest output, coming from a low weight engine.

For motocross bikes, such as the 125 SX, bought out in 2007, being ultra light is a key feature. The two stroke engines are competitive, and preferred by racers who do not want to indulge in complicated four stroke machinery.

This bike has a displacement of 124.8cc with bore and stroke 54/54.5, with a TVC power valve.
This 6 gear, premix fuel run two stroke has a front suspension of WP USD 48 mm, with a total weight being about 89.5 kg. Bikes such as this one have a multi-disc hydraulically operated clutch system, with an ignition through a Kokusan digital magneto CDI.

The basic advantage over such two stroke dirt bikes over their four stroke counterparts is that they provide a much more hassle free, yet powerful transmission solutions.

The 250 SX 2007 is a two stroke bike that is powerful enough to give the four stroke category bikes a run for their money. Added to this it is light, making it ideal for motocross racers.

The single cylinder, two stroke engine calls for easy maintenance, and the fantastic suspension, with PDS geometry means that it is a beast on the tough dirt circuit.

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Filed Under: Automobile Engineering on 6 Comments

Common Rail Type Fuel Injection System

 

Electronic control common rail type fuel injection system drives an integrated fuel pump at an ultrahigh pressure to distribute fuel to each injector per cylinder through a common rail.

 

This enables optimum combustion to generate big horsepower, and reduce PM* (diesel plume) and fuel consumption.

Bosch will supply the complete common-rail injection system for the high-performance 12-cylinder engine introduced by Peugeot Sport for its latest racing car. The system comprises high-pressure pumps, a fuel rail shared by all cylinders (i.e. a common rail), piezo in-line injectors, and the central control unit which compiles and processes all relevant sensor data.

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Filed Under: Automobile Engineering on Friday, January 31, 2014 1 Comment

DISI Turbo or Direct Injection Spark Ignition Technology

DISI includes a whole new set of innovations for gasoline engines. To mention a few, direct injection (including cooling the air-gasoline mixture), a new combustion chamber geometry, variable timing technology, and nanotechnology for the catalyst. This all makes the engines consume 20 percent less while getting 15 to 20 percent better performance.

Further developments for its diesels: new direct injection technology (most European automakers are switching to piezoelectric injectors), making the engine lighter, DPF, and urea technology to reduce NOx emissions

Mazda’s DISI* engines balance sporty driving with outstanding environment performance. With the next generation engine in the series, we are aiming for a 15% ~ 20% improvement in dynamic performance and a 20% increase in fuel economy (compared with a Mazda 2.0L gasoline engine). Based on the direct injection system, we aim to reduce all energy losses (see figure on the right) and improve thermal efficiency through innovative engineering in a variety of technological areas. Among these technologies we are paying particular attention to direct injection, combustion control, variable valve system technology and catalyst technology. Also, among the various fuels on the market, we are studying the use of flex-fuel.

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Filed Under: Automobile Engineering on No Comments

Variable Turbochargers Geometry (VTG)

Variable geometry turbochargers (VGTs) are a family of turbochargers, usually designed to allow the effective aspect ratio (sometimes called A/R Ratio) of the turbo to be altered as conditions change. This is done because optimum aspect ratio at low engine speeds is very different from that at high engine speeds. If the aspect ratio is too large, the turbo will fail to create boost at low speeds; if the aspect ratio is too small, the turbo will choke the engine at high speeds, leading to high exhaust manifold pressures, high pumping losses, and ultimately lower power output. By altering the geometry of the turbine housing as the engine accelerates, the turbo’s aspect ratio can be maintained at its optimum. Because of this, VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. VGTs do not require a waste gate.

Most common designs
The two most common implementations include a ring of aerodynamically-shaped vanes in the turbine housing at the turbine inlet. Generally for light duty engines (passenger cars, race cars, and light commercial vehicles) the vanes rotate in unison to vary the gas swirl angle and the cross sectional area. Generally for heavy duty engines the vanes do not rotate, but instead the axial width of the inlet is selectively blocked by an axially sliding wall (either the vanes are selectively covered by a moving slotted shroud, or the vanes selectively move vs a stationary slotted shroud). Either way the area between the tips of the vanes changes, leading to a variable aspect ratio.

Actuation
Often the vanes are controlled by a membrane actuator identical to that of a waste gate, however increasingly electric servo actuation is used. Hydraulic actuators have also been used in some applications.

Main suppliers

Several companies supply the rotating vane type of variable geometry turbocharger, including Garrett (Honeywell), Borg Warner and MHI (Mitsubishi Heavy Industries). The rotating vane design is mostly limited to small engines and/or to light duty applications (passenger cars, race cars and light commercial vehicles). The only supplier of the sliding vane type of variable geometry turbocharger is Cummins Turbo Technologies (Holset), who are effectively the sole supplier of variable geometry turbochargers for applications involving large engines and heavy duty use (i.e. trucks and off highway applications).

Other common uses
In trucks, VG turbochargers are also used to control the ratio of exhaust re-circulated back to the engine inlet (they can be controlled to selectively increase the exhaust manifold pressure exceeds the inlet manifold pressure, which promotes exhaust gas recirculation (EGR)). Although excessive engine back pressure is detrimental to overall fuel economy, ensuring a sufficient EGR rate even during transient events (e.g. gear changes) can be sufficient to reduce nitrogen oxide emissions down to that required by emissions legislation (e.g. Euro 5 for Europe and EPA 10 for the USA).

Another use for the sliding vane type of turbocharger is as downstream engine exhaust brake (non-decompression type), so that an extra exhaust throttle valve isn’t needed. Also the mechanism can be deliberately modified to reduce the turbine efficiency in a predefined position. This mode can be selected to sustain a raised exhaust temperature to promote "light-off" and "regeneration" of a diesel particulate filter (this involves heating the carbon particles stuck in the filter until they oxidize away in a semi-self sustaining reaction – rather like the self-cleaning process some ovens offer). Actuation of a VG turbocharger for EGR flow control or to implement braking or regeneration modes generally requires hydraulic or electric servo actuation.

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Turbocharger

 

A turbocharger is actually a type of supercharger. Originally, the turbocharger was called a "turbo super charger." Obviously, the name was shortened out of convenience.

A turbocharger’s purpose is to compress the oxygen entering a car’s engine, increasing the amount of oxygen that enters and thereby increasing the power output. Unlike the belt-driven supercharger that is normally thought of when one hears the word "supercharger," the turbocharger is powered by the car’s own exhaust gases. In other words, a turbocharger takes a by-product of the engine that would otherwise be useless, and uses it to increase the car’s horsepower.

Cars without a turbocharger or supercharger are called normally aspirated. Normally aspirated cars draw air into the engine through an air filter; the air then passes through a meter, which monitors and regulates the amount of air that enters the system. The air is then delivered to the engine’s combustion chambers, along with a controlled amount of fuel from the carburetor or fuel injectors.

In a turbocharged engine, however, the air is compressed so that more oxygen will fit in the combustion chamber, dramatically increasing the burning power of the engine. The turbocharger is composed of two main parts: the compressor, which compresses the air in the intake; and the turbine, which draws the exhaust gases and uses them to power the compressor. Another commonly used term in relation to turbochargers is boost, which refers to the amount of pressure the air in the intake is subjected to; in other words, the more compressed the air is, the higher the boost.

Although the increase in power is advantageous to the car — and likely a source of enjoyment for the driver — a turbocharger has its drawbacks. First and foremost, a turbocharged engine must have a lower compression ratio than a normally aspirated engine. For this reason, one cannot simply put a turbocharger on an engine that was intended for normal aspiration without seriously undermining the life and performance of the engine. Also, a lower compression ratio means the engine will run less efficiently at low power.

Another major drawback of a turbocharger is the phenomenon known as turbo lag. Because the turbocharger runs on exhaust gases, the turbine requires a build-up of exhaust before it can power the compressor; this means that the engine must pick up speed before the turbocharger can kick in. Additionally, the inlet air grows hotter as it is compressed, reducing its density, and thereby its efficiency in the combustion chamber; a radiator-like device called an intercooler is often used to counter this effect in turbocharged engines.

Turbo lag

Turbo lag is the time required to change power output in response to a throttle change, noticed as a hesitation or slowed throttle response when accelerating from idle as compared to a naturally aspirated engine. This is due to the time needed for the exhaust system and turbocharger to generate the required boost. Inertia, friction, and compressor load are the primary contributors to turbo lag. Superchargers do not suffer this problem, because the turbine is eliminated due to the compressor being directly powered by the engine.
Turbocharger applications can be categorized into to those that require changes in output power (such as automotive) and those that do not (such as marine, aircraft, commercial automotive, industrial, engine-generators, and locomotives). While important to varying degrees, turbo lag is most problematic in applications that require rapid changes in power output. Engine designs reduce lag in a number of ways:

• Lowering the rotational inertia of the turbocharger by using lower radius parts and ceramic and other lighter materials
• Changing the turbine's aspect ratio
• Increasing upper-deck air pressure (compressor discharge) and improving wastegate response
• Reducing bearing frictional losses (e.g., using a foil bearing rather than a conventional oil bearing)
• Using variable-nozzle or twin-scroll turbochargers
• Decreasing the volume of the upper-deck piping
• Using multiple turbos sequentially or in parallel
• Using an Antilag system
• Using a turbo spool valve to increase exhaust gas flow speed to the (twin-scroll) turbine

Boost threshold

The boost threshold of a turbo system is the lower bound of the region within which the compressor operates. Below a certain rate of flow, a compressor produces insignificant boost. This limits boost at a particular RPM, regardless of exhaust gas pressure. Newer turbocharger and engine developments have steadily reduced boost thresholds.
Electrical boosting ("E-boosting") is a new technology under development. It uses an electric motor to bring the turbo up to operating speed quicker than possible using available exhaust gases. An alternative to e-boosting is to completely separate the turbine and compressor into a turbine-generator and electric-compressor as in the hybrid turbocharger. This makes compressor speed independent of turbine speed. In 1981, a similar system that used a hydraulic drive system and overspeed clutch arrangement accelerated the turbocharger of the MV Canadian Pioneer (Doxford 76J4CR engine)^.
Turbochargers start producing boost only when a certain amount of kinetic energy is present in the exhaust gasses. Without adequate exhaust gas flow to spin the turbine blades, the turbo cannot produce the necessary force needed to compress the air going into the engine. The boost threshold is determined by the engine displacement, engine rpm, throttle opening, and the size of the turbo. The operating speed (rpm) at which there is enough exhaust gas momentum to compress the air going into the engine is called the "boost threshold rpm". Reducing the "boost threshold rpm" can improve throttle response.

Key components of a turbocharger

The turbocharger has three main components:

1. The turbine, which is almost always a radial inflow turbine
2. The compressor, which is almost always a centrifugal compressor
3. The center housing/hub rotating assembly

Many turbocharger installations use additional technologies, such as wastegates, intercooling and blow-off valves.

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Supercharger

Engines combust (burn) fuel and use the energy of that combustion to do work. The more fuel that is combusted in any given time then the more energy is available to carry out the engines task. Fuel requires air (or the oxygen contained within air) to burn so if there isn’t enough air mixed with the fuel it will not burn. This also means that the amount of air entering an engine determines how much fuel can be burnt and consequently how much energy (or power) an engine can produce. Superchargers are essentially an air pump designed to cram extra air into an engine allowing it to combust more fuel than would otherwise be possible.

Mercedes pioneered automotive superchargers on their race cars during the 1920’s. These were simple reciprocating compressors attached to the engine by an electrically operated clutch. A switch activated by the accelerator pedal turned the pump on when extra power (full throttle) was required. A flurry of engineering endeavor ensued in order to reign in Mercedes advantage on the racetrack. Within a few short years most of the basic designs for modern superchargers had appeared.

During the 1930’s superchargers were largely the preserve of marine engines, aircraft and race vehicles but gradually found their way into commercial diesel engines by the 1950’s. It has been common for truck engines to be turbo supercharged (a.k.a. turbocharged) for decades but car engines originally had difficulty in effectively employing this technology.

Superchargers mostly fall into one of two categories, mechanically driven superchargers and turbo superchargers driven by exhaust gasses. A third category is starting to make an appearance and that is electrically powered superchargers.

Turbo superchargers (a.k.a. turbochargers or turbo’s) are relatively compact, lightweight and efficient but suffer from turbo lag and heat stress. By turbo lag we mean the amount of time it takes for the turbo’s rotor to speed up to full efficiency. Some of the earliest turbo charged vehicles took so long for the turbo to produce a usable amount of boost that they were all but useless. Modern turbo chargers are much better in this regard but turbo lag is still a problem. Heat is another bane of turbo chargers. Exhaust gasses are extremely hot and can cause so much heat to build up in the turbo that oil will burn and congeal within its galleries leading to a bearing failure. This is why many turbo chargers have a turbo timer. The timer will cause an engine to continue idling for a few minutes after it is switched off allowing excess heat to be dissipated.

Mechanically driven superchargers usually don’t suffer from turbo lag and can often produce more boost than an exhaust driven charger (turbo). On the negative side they are generally bulky, heavy, and have a cumbersome drive mechanism (usually belt drive). Furthermore most chargers of this type have to supply air at all engine speeds and loads making them difficult to match various engine conditions precisely.

As our supercharger is electrically driven we have devoted an entire article to the advantages and disadvantages of this type.

Heat exchangers (intercoolers) are frequently used in conjunction with superchargers. Compressing air increases its temperature thus making it less dense. By re-cooling the compressed volume of air before it enters, density is increased allowing even more air to be forced into the engine. Intercoolers are more important for turbo superchargers as there are two heating sources present, the act of compression and heat from exhaust gasses both increase air temperature.

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Filed Under: Automobile Engineering on Thursday, January 30, 2014 2 Comments

Working of Fuel Cell Car

Fuel Cell Stacks

This is the heart of the hydrogen fuel cell car—the fuel cell stacks. Their maximum output is 86 kilowatts, or about 107 HP. Because hydrogen fuel cell stacks produce power without combustion, they can be up to twice as efficient as internal combustion engines. They also produce zero carbon dioxide and other pollutants. For more information on the stacks.

Fuel Cell Cooling System

This has several parts. Perched at an angle at the front of the vehicle is a large radiator for the fuel cell system, while two radiators for the motor and transmission lie ahead of the front wheels below the headlights. The car also has a cooling pump located near the fuel cell stacks to stabilize temperature within the stacks.

Ultra capacitor

This unit serves as a supplementary power source to the fuel cell stack. Like a large battery, the ultra capacitor recovers and stores energy generated during deceleration and braking. It uses this energy to provide a "power assist" during startup and acceleration.

Hydrogen Tanks

Space in a car is limited, yet hydrogen is the most dispersive element in the universe and normally requires lots of room. A challenge for manufacturers is how to compress the gas into tanks small enough to fit in a compact car and yet still provide enough fuel for hundreds of miles of driving between refueling. The two high-pressure hydrogen tanks in this vehicle can hold up to 3.75 kilograms of hydrogen compressed to roughly 5,000 PSI—enough to enable an EPA-rated 190 miles of driving before refueling, the manufacturer says.

Electric Motor

(General area only—motor not visible) The electric motor offers a maximum output of 80 kilowatts, enabling a top speed of about 93 miles per hour. The manufacturer says this vehicle can also start in subfreezing temperatures (down to about -4°F), a perennial problem in fuel cell prototypes. Being electric, the engine and the car as a whole are quiet, with none of the vibration or exhaust noise of a gas-powered automobile.

Air Pump

(General area only—air pump not visible) Run by a high-voltage electric motor, this pump supplies air at the appropriate pressure and flow rate to the fuel cell stacks. The air, in turn, mixes with the stored hydrogen to create electricity.

Humidifier

The humidifier monitors and maintains the level of humidity that the fuel cell stack needs to achieve peak operating efficiency. It does this by recovering some of the water from the electrochemical reaction that occurs within the fuel cell stack and recycling it for use in humidification.

Power Control Unit

(General area only—power control unit not visible) This controls the vehicle’s electrical systems, including the air and cooling pumps as well as output from the fuel cell stacks, electric motor, and ultra capacitor.

Cabin

With the fuel cell stacks hidden beneath the floor and the hydrogen tanks and the ultra capacitor beneath and behind the rear seats, respectively, the four-passenger cabin is isolated from all hydrogen and high-voltage lines. Hydrogen gas is colorless and odorless, and it burns almost invisibly. In case of a leak, therefore, the manufacturer has placed hydrogen sensors throughout the vehicle to provide warning and automatic gas shut-off. Also, in the event of a collision, the electrical source power line shuts down.

Hydrogen Filler Mouth

(Not visible—located on other side of vehicle) Drivers would fill the car with hydrogen just as they do with gasoline, through an opening on the side of the vehicle. The main difference is that a fuel cell car must be grounded before fueling to rid the car of hazardous static electricity. For this reason, this model has two side-by-side openings, with the latch to open the hydrogen filler mouth located inside the opening for the grounding wire. The manufacturer says filling up this model’s two tanks at a hydrogen filling station would take about three minutes.

Note

The limited-production vehicle seen in this feature is a Honda 2005 FCX, which is typical of the kinds of hydrogen fuel cell automobiles that some major automakers are now researching and developing. With such vehicles at present costing about $1 million apiece, none is currently for sale, though hundreds of fuel cell cars are now undergoing tests on the world’s roads.

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Kinetic Energy Recovery System (KERS) in F1

The introduction of Kinetic Energy Recovery Systems (KERS) is one of the most significant technical introductions for the Formula One Race. Formula One have always lived with an environmentally unfriendly image and have lost its relevance to road vehicle technology. This eventually led to the introduction of KERS.

KERS is an energy saving device fitted to the engines to convert some of the waste energy produced during braking into more useful form of energy. The system stores the energy produced under braking in a reservoir and then releases the stored energy under acceleration. The key purpose of the introduction was to significantly improve lap time and help overtaking. KERS is not introduced to improve fuel efficiency or reduce weight of the engine. It is mainly introduced to improve racing performance.

KERS is the brainchild of FIA president Max Mosley. It is a concrete initiative taken by F1 to display eco-friendliness and road relevance of the modern F1 cars. It is a hybrid device that is set to revolutionize the Formula One with environmentally friendly, road relevant, cutting edge technology.

Components of KERS

The three main components of the KERS are as follows:

• An electric motor positioned between the fuel tank and the engine is connected directly to the engine crankshaft to produce additional power.
• High voltage lithium-ion batteries used to store and deliver quick energy.
• A KERS control box monitors the working of the electric motor when charging and releasing energy.

A – Electric motor

B – Electronic Control Unit

C – Battery Pack

Working Principle of KERS

Kinetic Energy Recovery Systems or KERS works on the basic principle of physics that states, “Energy cannot be created or destroyed, but it can be endlessly converted.”

When a car is being driven it has kinetic energy and the same energy is converted into heat energy on braking. It is the rotational force of the car that comes to stop in case of braking and at that time some portion of the energy is also wasted. With the introduction of KERS system the same unused energy is stored in the car and when the driver presses the accelerator the stored energy again gets converted to kinetic energy. According to the F1 regulations, the KERS system gives an extra 85 bhp to the F1 cars in less than seven seconds.

This systems take waste energy from the car’s braking process, store it and then reuse it to temporarily boost engine power. This and the following diagram show the typical placement of the main components at the base of the fuel tank, and illustrate the system’s basic functionality – a charging phase and a boost phase. In the charging phase,

kinetic energy from the rear brakes (1)

is captured by an electric alternator/motor (2),

controlled by a central processing unit (CPU) (3),

which then charges the batteries (4).

 

In the boost phase, the electric alternator/motor gives the stored energy back to the engine in a continuous stream when the driver presses a boost button on the steering wheel. This energy equates to around 80 horsepower and may be used for up to 6.6 seconds per lap. The location of the main KERS components at the base of the fuel tank reduces fuel capacity (typically 90-100kg in 2008 ) by around 15kg, enough to influence race strategy, particularly at circuits where it was previously possible to run just one stop. The system also requires additional radiators to cool the batteries. Mechanical KERS, as opposed to the electrical KERS illustrated here, work on the same principle, but use a flywheel to store and re-use the waste energy.

Types of KERS

There are basically two types of KERS system:

Electronic KERS

Electronic KERS supplied by Italian firm Magneti Marelli is a common system used in F1 by Red Bull, Toro Rosso, Ferrari, Renault, and Toyota.

The key challenge faced by this type of KERS system is that the lithium ion battery gets hot and therefore an additional ducting is required in the car. BMW has used super-capacitors instead of batteries to keep the system cool.
With this system when brake is applied to the car a small portion of the rotational force or the kinetic energy is captured by the electric motor mounted at one end of the engine crankshaft. The key function of the electric motor is to charge the batteries under barking and releasing the same energy on acceleration. This electric motor then converts the kinetic energy into electrical energy that is further stored in the high voltage batteries. When the driver presses the accelerator electric energy stored in the batteries is used to drive the car.

Electro-Mechanical KERS

The Electro-Mechanical KERS is invented by Ian Foley. The system is completely based on a carbon flywheel in a vacuum that is linked through a CVT transmission to the differential. With this a huge storage reservoir is able to store the mechanical energy and the system holds the advantage of being independent of the gearbox. The braking energy is used to turn the flywheel and when more energy is required the wheels of the car are coupled up to the spinning flywheel. This gives a boost in power and improves racing performance.

Limitations of KERS

Though KERS is one of the most significant introductions for Formula One it has some limitations when it comes to performance and efficiency. Following are some of the primary limitations of the KERS:

• Only one KERS can be equipped to the existing engine of a car.
• 60 kw is the maximum input and output power of the KERS system.
• The maximum energy released from the KERS in one lap should not exceed 400 kg.
• The energy recovery system is functional only when the car is moving.
• Energy released from the KERS must remain under complete control of the driver.
• The recovery system must be controlled by the same electronic control unit that is used for controlling the engine, transmission, clutch, and differential.
• Continuously variable transmission systems are not permitted for use with the KERS.
• The energy recovery system must connect at one point in the rear wheel drive train.
• If in case the KERS is connected between the differential and the wheel the torque applied to each wheel must be same.
• KERS can only work in cars that are equipped with only one braking system.

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Chasis Frame

Chassis is a French term and was initially used to denote the frame parts or Basic Structure of the vehicle. It is the back bone of the vehicle. A vehicle with out body is called Chassis. The components of the vehicle like Power plant, Transmission System, Axles, Wheels and Tyres, Suspension, Controlling Systems like Braking, Steering etc., and also electrical system parts are mounted on the Chassis frame. It is the main mounting for all the components including the body. So it is also called as Carrying Unit.

The following main components of the Chassis are:

• Frame: it is made up of long two members called side members riveted together with the help of number of cross members.
• Engine or Power plant: It provides the source of power
• Clutch: It connects and disconnects the power from the engine fly wheel to the transmission system.
• Gear Box
• U Joint
• Propeller Shaft
• Differential

FUNCTIONS OF THE CHASSIS FRAME:

1. To carry load of the passengers or goods carried in the body.
2. To support the load of the body, engine, gear box etc.,
3. To withstand the forces caused due to the sudden braking or acceleration
4. To withstand the stresses caused due to the bad road condition.
5. To withstand centrifugal force while cornering

VARIOUS LOADS ACTING ON THE FRAME:
1. Short duration Load – While crossing a broken patch.
2. Momentary duration Load – While taking a curve.
3. Impact Loads – Due to the collision of the vehicle.
4. Inertia Load – While applying brakes.
5. Static Loads – Loads due to chassis parts.
6. Over Loads – Beyond Design capacity.

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Gorilla Glass Touch Screen

Touch screen technology in fast few years has grown drastically in various applications, in order to overcome the difficulties faced by the touch screen; a new frontier technology has to take its part to revitalize the use of touch screen. In this counterpart gorilla glass has thrown a flash light focus on touch screen technology. Gorilla Glass has taken an apt plays in touchscreen technology. This scratch repellent glass is used to form touchscreen panel for portable gadgets like ATM machines, android mobile phones, tablets, personal computers and MP3 Players. It’s designed to protect display screens from scratches, sticky oils, fractures, etc,.

Characteristics of Gorilla Glass:

• Scratch resistance
• Slimness / Thinner
• Stronger
• Improved Touch Sensitivity

Comparatively perfect fit for today’s abundance touch-screen handsets.

 

Difference between ‘Scratch- Proof ‘ and ‘Scratch Resistant’ glass:

A Scratch- screen proof is impermeable resistant to scratches. This kind of technology is not on the market however – any glass may break if it is placed under enough stress. Gorilla Glass is NOT a scratch-proof.

A Scratch- screen resistant is much stronger than most screens. It is less probable to smash/crack if dropped, and less probably to scratch if scratched. Extreme force, sharp objects, and continual exposure to abrasive oils may leave scratches.

History of Gorilla Glass:

The Gorilla Glass is the trade name of “Corning”, an United States of America Glass maker. They form the toughened glass (Alkali – Alumino Silicate Sheet) for the portable electronic gadgets. This idea generated in the 60s period as a project name, “Project Muscle”. The glass invented was called as “Chemcor” glass, which are ultra strong and light weight. The product is developed for windshield glass for cars, But the product is very costly so they are not succeeding on that time.

In the period of 2005, they again started researching with the project name of “Gorilla Glass”. In this period touch screen cell phones are popular, and the product needs a resilient, scratch resistant cell phone cover glass. At that time, the company take the idea from Chemcor glass and they start building the Gorilla glass.

After completing the research, first production starts at the period of 2007 and they got the first order in the period of 2008. At that period nearly 200 million users (about 20% of Devices) uses the gorilla glass for their cell phones. 

 

In 2012, the second generation of gorilla glass they built and launched, achieved a goal of one billion devices.

In 2013, the Third generation Gorilla Glass they launched, which are three times more resistant and stronger; 40% scratches which occur will not be visible to naked eye.

Currently Used Gorilla Glass products:

Phones

• Iphone
• HTC
• LG
• Motorolla
• Nokia
• Samsung

Tablets

• Samsung
• Blackberry
• Lenovo

Laptops

• Dell
• Sony
• Lenovo

TV’s

• Sony

Cameras

• Leica

BENEFITS:
• Glass designed for a high degree of chemical strengthening
- High compressive stress
- Deep compression layer
• High retained strength after use
• High resistance to scratch damage
• Superior surface quality
APPLICATIONS:
• Ideal protective covering for displays in
- Smart phones
- Laptop / Portable Computers and tablet computer screens
- Mobile devices
• Touchscreen devices
• Optical components
• High strength glass articles

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