Principle analysis of waveform failure of engine c

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Principle analysis of waveform fault of automobile engine control valve (I)

1 Idle speed control (IAC) solenoid valve

idle speed controller is designed in many mechanical and electromechanical devices. In the electronic engine management system, electronic control replaces the old-fashioned automatic thermostat plug, paraffin wax, vacuum tank and other similar devices. Electronically controlled idle speed solenoid valve and sold in bancassurance channel since February 16 can prevent idle speed stall, enhance the stability of idle speed, and reduce HC emissions by means of staged deceleration during deceleration. The idle solenoid valve can keep the idle speed as low as possible without going out, and can maintain the possible stability even when the air conditioner, generator, power steering and other auxiliary equipment are turned on to increase the load on the engine

some idle speed controllers are solenoid valves (most Ford cars), some are rotary motors (Bosch in Europe), and others are gear reduction DC stepping motors (most applicable to Chrysler cars). However, this feature makes it possible to use in orthopedics. In all cases, the control computer changes the amplitude or pulse width of the signal conditioning clamping speed knob to finally control the operation of idle speed

idle speed is detected by the engine speed sensor, and the idle speed is adjusted within the holding period set by the predetermined program. The control computer receives the input signals of digital switches from auxiliary devices such as the switch of air conditioning compressor, battery charging indication, power steering switch and neutral/parking gear switch. Each switch will trigger the preset idle speed compensation command and transmit it to the idle speed controller. When the throttle is closed and the engine speed reaches the minimum, in a short time, the spot may continue to rise below the value or the vehicle speed is stable, The idle speed control system usually starts to work, and the electronically controlled idle valve allows air to flow around the throttle, producing an effect similar to opening the throttle

test method:

idle the engine and turn on or off the auxiliary equipment (air conditioner, fan, wiper). If the vehicle is equipped with automatic transmission, switch between parking and forward gear. This will change the engine load and cause the output command signal from the engine control computer to the idle valve to change

waveform results:

confirm that the amplitude, frequency, shape, pulse width and other decisive scales of various idle speed compensation mode waveforms are within the correct range, and have repeatability and consistency

confirm that when the command signal of the control computer changes, the solenoid valve reacts, and the engine speed also changes. Observe the following conditions:

when the auxiliary electrical equipment switch is opened and closed or the transmission is out of gear, the idle speed control output command of the control computer will change. When the idle speed changes, the idle control valve should open and close the throttle bypass hole. If the idle speed does not change, it should be suspected that the idle valve is damaged or the bypass channel is blocked

before diagnosing the idle control valve and control circuit, make sure to check the vacuum leakage or improper air leakage, which will cause problems in the idle control system

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