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Three Technologies Work Together to Reduce Combustion Engine Noise and Vibration
Combustion engines have always been useful tools with built-in trade-offs: speed and convenience versus noise, vibration, and pollution. Over the years, we have learned to minimize the negatives and accentuate the positives as much as possible, but combustion engines are still things of compromise.
Virtually every engine-related problem can be attributed to the need for power. More horsepower meant more combustion, more torque, and more vibration. These in turn led to more noise, more pollution, and more discomfort. Look a little closer, and you´ll see that most of these drawbacks can be controlled by controlling torque, which has never been easy. Let´s take a closer look.
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Torque fluctuation is an inherent problem with combustion engines because torque is generated by the piston rods connected to the crankshaft. Torque, by definition being force applied over distance, fluctuates as the piston rods change position relative to the crankshaft. The farther away from the center of the shaft, the less torque. Torque fluctuation is a major contributor to vibration in the drive train which, in turn, is distributed to other parts of the vehicle, potentially contributing to a rough ride. Vibration also increases wear and tear on a vehicle, contributing to increase maintenance costs and shortened vehicle life-span. Decrease torque fluctuation and we go a long way to solving a lot of problems.
Hitachi has developed a way to do this by coming up with a method of harnessing a vehicle´s generator (alternator) to create counter torque against torque fluctuation as described above. Sensors in the vehicle´s main power transmission system monitor crankshaft rotational speed variations with each combustion cycle and then use the previous cycle´s information to provide the right amount of counter torque to the crankshaft. By absorbing the torque fluctuation, the rotational speed variation is kept at nearly zero and vibration disappears. Using this technology Hitachi is able to eliminate additional, costly add-on components used to dampen torque-related vibration.
To further smooth out the ride, Hitachi has engineered an acceleration rate-of-change sensor and control system designed to eliminate the characteristic "jerk" that follows vehicle acceleration, particularly from a stand-still. Known in the industry as the derivative of acceleration, the telltale jerk that comes with stepping on the gas has avoided elimination until now. Utilizing a sensor comprised of a pendulum and electromagnetic actuator, Hitachi´s process precisely measures the rate of acceleration by using relative movement to generate an electric current; the amount of voltage across the coil provides a direct measurement of the derivative of acceleration. This data is then fed to a controller which compensates for the derivative, smoothing out the rate of acceleration for a better ride.
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The third in this suite of technologies from Hitachi has to do with the development of a non-fouling gasoline fuel injector that promises to reduce emissions while improving performance.
Carbon dioxide (CO2) is the chief culprit in the global-warming phenomenon. Nearly 20% of the CO2 produced by human activity is exhausted from automobiles tailpipes. The Direct-Injection Spark-Ignition (DI-SI) gasoline engine is one of the most promising engine designs for reducing CO2 because of its advantages of reduced fuel consumption and reduced emissions. Hopes run high that the technology will become widespread in the automotive industry.
eposit build-up and fouling present a significant challenge to the DI-SI injector. However, Hitachi has developed a new technology that enables gasoline to be injected directly into the combustion chamber by introducing new injector tip materials and designs that substantially reduce or even eliminate deposit formation and buildup.
The key to this new concept is where the fouling takes place. Usually deposits inside the combustion chamber are not an issue because they actually improve combustion efficiency by increasing the insulating efficiency of the chamber. However, when deposits become attached to the fuel injection nozzle itself, it changes the shape of the opening and consequently affects both the spray shape and the size of the fuel particles sprayed into the chamber. As a result, combustion efficiency can drop off dramatically.
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To counter this problem, Hitachi has come up with a novel in-cylinder fuel injection device that features a fuel nozzle comprising a valve member for opening the fuel passage and a fuel swirl member to provide a swirl to the fuel spray for more efficient and even combustion. The nozzle itself has an enlarged surface area formed by projections or depressions and has a surface vapor-deposited layer for increasing thermal conductance. The nozzle is protected by a concave cover made of brass or an aluminum alloy shaped to further increase surface area, enhancing the heating process and virtually doubling the nozzle temperature from 550°C to 1050°C. By making the nozzle assembly hotter, deposits are burned off before they can build up to distort the spray and reduce combustion efficiency. For even greater efficiency, the injector design and swirl-controlled spray pattern can be adjusted under varying engine operating conditions. As a result, engine performance is enhanced and emissions reduced, resulting in a smoother, safer, and cleaner ride.
Hitachi´s suite of technologies for improving the performance of gasoline and diesel combustion engines is available for use in a wide range of transportation and power generation applications. The spray technology has further applications in the paint and aerosol industries. The shaft torque technology offers improved power performance to any application utilizing shaft-driven motion.
The motion control systems using jerk information will lead to drastic improvements in vehicle performance, comfort, and safety.
