![]() This helps to increase engine’s breathing which also improves its ‘ volumetric efficiency’ to a large extent. At high speed, the Inlet valves open quite earlier so that more air-fuel mixture or ‘charge’ enters the cylinders. The VVT varies the timing of opening and closing of valves for multiple engine speeds. To overcome this deficiency, the engineers developed VVT or ‘Variable Valve Timing’ mechanism. However, as the engine speed increases, it considerably reduces the time required to fill the cylinders fully.As a result, the engine would receive less amount of charge (air-fuel mixture) which causes power-loss especially when the engine runs at high speed. In older conventional engines, the time for which the valves remained open was optimised only for single engine speed. This is because to produce more power, it needs to suck more air-fuel mixture (charge) for burning. Similarly, when the engine runs at high speed it needs to open its inlet valves earlier, faster & for a longer period. Thus, it causes faster breathing and/or wider opening of the mouth to receive more air. This is because when the human body is subjected to heavy work, it increases the need for air-intake. Besides, while carrying out activities like swimming or lifting a weight the persons also need to open the mouth to get more air. For e.g., if the person/s are sitting or sleeping, they will breath slowly as compared to when they are walking or running. The rate at which humans breathe mainly depends upon the work carried out by humans. Note, the engine may stall during this test.Let’s try to understand in the begining, why to vary the Valve Timing/VVT?įirstly, read here first what is ‘ Engine valve-timing’? An automotive engine actually ‘breaths’ (inhales/exhales) thru’ its valves just like the humans do. Thus movement equates to approximately 30 degrees of crankshaft rotation. The waveform below, image 5, shows the change in camshaft position when the variable valve timing solenoid is supplied with a constant live. It must be noted that the solenoid valve has a constant ground and is controlled on the positive side. The table below shows the signal being displayed on each channel:įrom the waveform above we can see the variable valve timing solenoid valve has a low duty cycle, approximately 10% actuation. Image 4 shows the expecting waveform with the engine idling. This test can be used to inspect the valve timing as well as detecting issues with cylinder sealing. Which is key to testing the dynamic valve timing of the engine.Ī pressure transducer can be used to analyze the in-cylinder conditions with the engine running. ![]() The waveform can be used to validate the operation of the entire variable valve timing circuit, not only electrically but also mechanically and hydraulically. The waveform, Image 3 below, shows the same trace during the actuator test. The phonic wheel for detecting the crankshaft speed and position has 34 teeth with two missing teeth to indicate crankshaft position with respect to Top Dead Center (TDC). With the engine at operating temperature and the engine idling, the ignition advance angle will be approximately 6 to 8° of crank angle rotation before Top Dead Center. The ignition coil trace is used as a trigger to capture the waveform and to reference cylinder position. The table below shows the signal being displayed on each channel:ġ-Yellow-Ignition coil cylinder 1 control Image 2 presents a waveform that shows a trace at idle with 0 percent actuation of the exhaust solenoid. Using an oscilloscope the technician can view the actual change in camshaft position with respect to the crankshaft and the camshaft which hasn’t been actuated. See image 1 below:ĭuring actuation of the solenoid valve it can be seen that the engine speed dropped to 587 revolutions per minute (RPM), the electronic throttle control system increased the engine speed to prevent a stall so the engine speed increased to 812 RPM before stabilizing at 737 RPM when the actuator test finished. During the functional test, the technician is presented with data. For the purpose of this article the exhaust camshaft timing control solenoid has been actuated. This particular Toyota Auris (Corolla) with a 1NR-FE engine has variable valve timing on both intake and exhaust camshafts. To demonstrate let’s take a look at an example. Using an actuator test, a technician can actuate a variable valve timing solenoid and observe a change in the audible note of the engine and/or a change in engine speed. ![]() By altering when the valves open and close you can optimize the performance of the engine. The purpose of variable valve timing (VVT) is to help increase the engine’s volumetric efficiency and limit the exhaust gasses produced by the vehicle. Such conditions can be difficult to diagnose without the correct equipment. ![]() Sometimes a vehicle will suffer from driveability issues and fault codes relating to valve timing. ![]()
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