With electronic valve operation, it will be possible to control engine speed by regulating valve lift. BMW attempted to get around this on their V-10 powered M5, which had individual throttle butterflies for each cylinder, placed just before the intake valves. When a car is run at part throttle, this interruption in the airflow causes excess vacuum, which causes the engine to use up valuable energy acting as a vacuum pump. Another even more significant advancement will be the elimination of the conventional throttle. Cylinder deactivation, for instance, could be made much more fuel efficient if the intake valve could be opened on every downstroke and the exhaust valve opened on every upstroke of the deactivated cylinder or "dead hole". Once more fully developed, electronic valve operation will yield even more benefits. A significant portion of the power that an engine actually produces is used up just driving the valve train, compressing all those valve springs thousands of times a minute. The elimination of cams, lifters, rockers, and timing set reduces not only weight and bulk, but also friction.
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This is impossible with a normal camshaft, of course, which opens the valve for the whole intake period and always to full lift. The optimal opening and timing are always reached and combustion is as precise as possible.
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For the next stroke, the ECU calculates the engine load at the new, higher RPM and decides how to open the valve: early or late, wide-open, or half-open. Under a sudden increase in throttle, the valve opens in the same intake stroke and a greater amount of fuel is injected. The ECU then decides how much fuel should be injected to optimize combustion.Īt steady load conditions, the valve opens, fuel is injected, and the valve closes. The valves can open several times per intake stroke, based on engine load. Basically, the valves are opened by hydraulic pumps, which are operated by the ECU. Their Multiair engines use electronic valve control, which dramatically improves torque and horsepower while reducing fuel consumption as much as 15%. The first production engine of this type was invented (in 2002) and introduced (in 2009) by Italian automaker Fiat in the Alfa Romeo MiTo. Such a static-start engine would provide the efficiency and pollution-reduction improvements of a mild hybrid-electric drive, but without the expense and complexity of an oversized starter motor. Such engines can be started and run without a starter motor for certain multi-cylinder engines equipped with precision-timed electronic ignition and fuel injection. This can increase the flow of air into the cylinder, increasing power and fuel economy.Įxperimental engines have been made and tested that have no camshaft, but have full electronic control of the intake and exhaust valve opening, valve closing, and area of the valve opening. The valves are usually opened sooner at higher speed than at lower speed. In such an engine, the ECU controls the time in the engine cycle at which the valves open. It also monitors the ECU section for reliability.Ĭontrol of variable valve timing
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Effective idle speed control must anticipate the engine load at idle.Ī full authority throttle control system may be used to control idle speed and provide cruise control functions and top-speed limitation. Early throttle body injection (TBI) systems used an idle air control stepper motor. Early carburettor-based systems used a programmable throttle stop using a bidirectional DC motor. Idle speed is controlled by a programmable throttle stop or an idle air bypass control stepper motor. The engine RPM is monitored by the crankshaft position sensor, which plays a primary role in the engine timing functions for fuel injection, spark events, and valve timing.
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Most engine systems have idle speed control built into the ECU. If the engine is still cool, additional fuel will be injected.Īir–fuel mixture control of carburettors with computers is designed with a similar principle, but a mixture control solenoid or stepper motor is incorporated in the float bowl of the carburettor. The engine coolant temperature sensor measures whether the engine is warmed up or cool. The mass air flow sensor measures the amount of air flowing into the engine through the throttle plate. The throttle position sensor tells the ECU how far the throttle plate is opened when the accelerator ( gas pedal) is pressed down. Oxygen sensors tell the ECU whether the engine is running rich (too much fuel or too little oxygen) or running lean (too much oxygen or too little fuel) as compared to ideal conditions (known as stoichiometric).
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The ECU determines the amount of fuel to inject based on a number of sensor readings. Most modern engines use some type of fuel injection to deliver fuel to the cylinders.