How to use cruise control in a car

1. Definition of cruising

The car's cruise control is used to control the car's constant speed. Once the car is set to cruise mode, the engine's fuel supply is controlled by the computer. The computer will continuously adjust the fuel supply according to road conditions and the car's driving resistance, so that the car always maintains the set speed without operating the accelerator.

2. Cruising main circuit

2.1. FAW Toyota Crown Cruise

in:

SW1 is the main switch (CMS); SW2 is the cancel switch (CS); SW3 is the set deceleration switch (SET/-); SW4 is the resume acceleration switch (RES/+)

2.2. Ford Focus Cruise

in:

SW1 is the reset switch (RES); SW2 is the acceleration switch (+); SW3 is the deceleration switch (-); SW4 is the cancel switch (CS); SW5 is the main switch (CMS)

2.3. Cruise circuit matching, design and calculation

Take Ford Focus car cruise control as an example, and Infineon TC1728 as the MCU

2.3.1. Controller and cruise sensor interface circuit

2.3.2.R11/R12/R13/C1/C2/C3 design and calculation

Reasonable values ​​can be set according to the design and calculation of [Introduction to Analog Input Interface Circuit 1]

Among them, the current limiting specifications of TC1728 are as follows, and the two indicators of single channel and all channels must not be exceeded.

3.3. Cruise and controller interface circuit matching design and calculation

Focus on matching design and calculation

3.3.1. Dual-channel MCU ADC redundancy design

Since the cruise signal is an important signal that endangers life, the design needs to consider that the failure of one MCU ADC cannot cause the cruise function to fail or operate randomly. Therefore, two MCU ADCs are designed to collect the original voltage value, and redundant verification can be performed on the two MCU ADCs to ensure the integrity and correctness of the input.

3.3.2. MCU ADC voltage calculation (R11=1000ohm)

V(ADC)=VCCRx/(Rx+R11)-Ioz1R12

in

Ioz1R12(max)=600nA10k=6mA, the impact is small (of course, this part can be taken into account in accurate calculation);

Rx is the resistance of the cruise resistor network when the switch is closed

R11=1000ohm

The above resistors are all involved in the calculation, and you need to choose resistors with an accuracy of less than or equal to 1%

The following simplified calculation (without taking into account the error on VCC/R)

V(ADC)=VCC*Rx/(Rx+R11)

V(ADC) can be calculated

1) From the table above, it can be found that the level of short circuit to ground is the same as that of canceling the switch, which can be understood as giving priority to exiting the cruise control in the case of short circuit.

2) When SW1~SW5 are pressed at the same time, SW4 has the highest priority, that is, exiting the cruise has the highest priority

3) When SW1~SW3 are pressed at the same time, SW3 has the highest priority, that is, the deceleration priority is the highest

4) When SW1 and SW2 are pressed at the same time, SW2 has the highest priority, that is, acceleration has the highest priority.

5) Open circuit and short circuit to VCC/VBAT cannot be distinguished, but during the power-on process (all cruise switches are not working at this moment), if the detection voltage is not between 3V-3.8V but above 4.5V, it is judged as open circuit or short circuit to VCC/VBAT.

6) Short circuit and SW4 closing cannot be distinguished, but during the power-on process (at this moment all cruise switches are not working), if the detection voltage is not between 3V-3.8V but below 0.2V, it is judged as a short circuit to ground.

3.3.3. MCU ADC voltage calculation (R11=600ohm)

When R11=600ohm, the voltage is more separated and easier to distinguish

The power calculation of the resistor value needs to refer to [Introduction to Analog Input Interface Circuit 1] to calculate whether it meets the requirements. This parameter must be calculated (the power consumption of R11 is the largest when VBAT is short-circuited in the WORSE CASE), otherwise the resistor may burn out. If the power consumption of R11 is not sufficient, consider using a power resistor or several resistors in parallel.