The electronic accelerator pedal actually means that the throttle opening is controlled by the motor, which cancels the throttle cable between the accelerator pedal and the throttle. In other words, the driver's acceleration intention will be transmitted to the engine controller through the position sensor of the accelerator pedal, and the engine controller will adjust the throttle body through the electric motor. At the same time, the electronic throttle opening sensor feeds back the detected opening signal to the ECU to realize the closed-loop control of the electronic throttle opening.

This principle sounds very simple, so how is it realized in technology? Today we will talk about how the electronic accelerator pedal works.

Basic principle of electronic accelerator pedal sensor

The electronic accelerator pedal sensor, in the final analysis, is a resistive sensor. It is no different from the slip line rheostat that we learned in middle school physics.

It may be more intuitive to look at the schematic diagram. Line 1 is connected to a 5V DC voltage (reference voltage), and line 2 is grounded. Then the different positions of the sliding pin P on the resistance will output 0~5V between the P lead and the ground terminal. Voltage difference (output voltage).

The single-chip microcomputer converts the output voltage (analog quantity) of 0~5V into a decimal number (digital quantity) such as 0~256 (reading 8 bits from AD) or 0~1024 (reading 10 bits) through AD conversion. The decimal number of this change is restored to the accelerator pedal opening (depressed angle) through a formula (the so-called algorithm), and then the engine throttle is controlled accordingly. In display life, most sensors are based on this principle. The temperature sensor is a thermistor, the brightness sensor is a photoresistor, and the air pressure sensor is a piezoresistor…..

Below are the resistors and brushes in the electronic accelerator pedal.

If you pay attention to observation, it is estimated that the readers have discovered why there are two brushes and coating resistors in the above picture? This is what we call a redundant design. The current electronic accelerator pedals all use two resistance sensors with two output voltages. Therefore, the electronic accelerator pedal connector that we usually see has six pins. They are two sets of completely independent reference voltages, output voltages, and grounding.

Similarly, the output voltage of the electronic accelerator pedal is naturally also two. It should be noted that the output voltage here has different slopes, so different algorithms need to be applied to the two voltages in the ECU to calculate the same accelerator opening.

●Test voltage (Vref): 5V± 0.2V, the same is true for vehicle voltage.

●The electronic accelerator pedal must adopt a redundant safety design. PPS1 and PPS2 must be completely independent output circuits, and their power supply and ground terminals must not be shared.

● ECU reads two signals at the same time. When both signals are normal, the acceleration and subtraction are based on PPS1.

●If there is a problem with only one signal, or the two signals are not synchronized, the ECU will alarm, and the vehicle can walk with the support of the other signal, but the speed is limited.

In addition to the basic requirements for the electronic accelerator pedal above, there are detailed performance requirements such as synchronization.

Electronic accelerator pedal performance requirements

Synchronization (Definition) The difference between the ratio of the first measured voltage to twice the reference voltage at any throttle position multiplied by 100 and the ratio of the second measured voltage to the reference voltage multiplied by 100. Allowable deviation of synchronization degree (definition) (calculation formula) Allowable value of synchronization degree deviation∣UA1/(2UB1)*100-UA2/UB2*100∣<0.5 Simplified: ∣UA1- 2UA2∣<0.05

Linearity (definition) (calculation formula) The ratio of the difference between the design voltage and the measured voltage at any throttle position and the reference voltage multiplied by 100. The allowable value of linearity deviation ︱(UA1nom-UA1)/UB1*100︱<1.5 after simplification: ︱(UA1nom design voltage-UA1 measured voltage) ︱<0.075

Sensor overvoltage test

The sensor should be able to withstand a power supply voltage of 5min, ± 15VDC continuously, after the power supply returns to normal, the sensor output meets the requirements. 5V V0=2.629 15V5min V0=8.218V

Ground terminal open circuit

When the sensor ground terminal is open, for APS1, Vsig≥91%Vref within 100ms; for APS2, Vsig≥50%Vref within 100ms. After the local line returns to normal, the sensor should resume normal operation within 100ms. (Vref is the 5V input voltage, and Vsig is the signal output voltage. If the throttle is at a certain angle, the output voltage is 4.5V). Under special circumstances, if the ground wire is in poor contact, the output signal will not change instantaneously and maintain a signal value greater than 50% to ensure that the engine does not have a sudden change in speed.

Power terminal open circuit

When the sensor power supply terminal is open, for APS1, Vsig≤15%Vref within 100ms; for APS2, Vsig≤7%Vref within 100ms. When the power supply returns to normal, the sensor should resume normal operation within 100ms. Under special circumstances, when the power supply terminal is open, the output signal will not change instantaneously, maintaining a value of less than 15% and 7%. After the power supply is restored, normal operation is mainly maintained by the capacitor during circuit design.

The signal output terminal is short-circuited to the ground terminal

When the sensor signal terminal is short-circuited to the ground terminal, for APS1, Vsig≤15%Vref within 100ms; for APS2, Vsig≤7%Vref within 100ms. When the signal is restored, the sensor should resume normal operation within 100ms.

The signal output terminal is shorted to the power terminal

When the sensor signal terminal is short-circuited to the power terminal, for APS1, Vsig≥91%Vref within 100ms; for APS2, Vsig≥50%Vref within 100ms. When the signal is restored, the sensor should resume normal operation within 100ms.

Linearity of output signal

Within the full range of the throttle, the maximum deviation from the linear regression line on the output signal curve is not greater than ±5﹪Vspan. (Vspan is the span voltage, such as the throttle from the initial position to fully open, 0.375---2.05V, then Vsig=1.675V)

Signal hysteresis

In the middle stroke position of the pedal, the signal output hysteresis ≤2﹪Vspan. Under special circumstances, if the ground wire is open, the power supply is open, the signal output terminal is short-circuited to the ground terminal, and the signal output terminal is short-circuited to the power terminal. Numerical value to ensure that the engine will not have a sudden change in speed due to the above conditions. When the sensor circuit is designed, the above conditions have been taken into account, and capacitors are used to buffer.

Other types of electronic accelerator pedal

The above is our common contact resistance sensing method, and now there are non-contact electronic accelerator pedals designed using Hall principle.

The working principle of the Hall type is the Hall effect. The relative movement of the magnet and the Hall sensor causes the change of the magnetic induction intensity acting on the Hall sensor, which causes the output signal to change. VH=KHISB, where KH is the sensitivity of the Hall element, and VH is the Hall potential.

kick down function

We may have this experience when driving. When we step on the accelerator deeply, the automatic transmission vehicle will take the behavior of downshifting and increasing torque. This is because the automatic gearbox is designed to adjust the gear according to the load of the engine and the depth of the throttle. When the vehicle is climbing or needs to accelerate quickly, the driver will step on the accelerator deeply. At this time, because the engine output torque is not enough, the automatic transmission will automatically lower a gear to increase the torque and increase the speed to assist the driver to accelerate the vehicle the goal of. Therefore, the action that allows the driver to step on the accelerator while climbing a hill or need to accelerate quickly and force the gearbox to automatically downshift is called the Kick down function.

In fact, Kick Down has no special change in the output voltage of the electronic accelerator. As long as the ECU judges that the output voltage reaches the downshift threshold, it will adopt the downshift strategy, and the change in pedal force is indeed more prominent. This is because at the end of the pedal stroke, the setting A KickDown mechanism increases the pedal force. As shown below.

When Kick Down gives the driver the feeling of floor oil, he will hear a "squeak" sound. At the same time, the vehicle downshifts, gains and accelerates in one go. Ha ha.