Brake Control System: Overview Nissan Quest IV

System Description

1. The system switches fluid pressure of each brake caliper to increase, to hold or to decrease according to signals from control unit in ABS actuator and electric unit (control unit). This control system is applied to VDC function, TCS function, ABS function, EBD function and brake limited slip differential (BLSD) function.
2. Fail-safe function is available for each function and is activated by each function when system malfunction occurs.

Scheme 1

Under Normal Brake Operation

Since power is not supplied to the ABS IN valve and the ABS OUT valve, the ABS IN valve port is open and the ABS OUT valve port is closed. This allows the master cylinder fluid pressure to be sent to the front RH caliper and blocks the brake fluid passage to the reservoir.

OPERATION CHARACTERISTICS

VDC Function That Prevents Oversteer Tendency

Scheme 2

Scheme 3

1. During a cornering, brake force (brake fluid pressure) is applied on front wheel and rear wheel on the outer side of turn. Moment directing towards the outer side of turn is generated. Oversteer is prevented.
2. Changing driving lane on a slippery road, when oversteer tendency is judged large, engine output is controlled as well as brake force (brake fluid pressure) of 4 wheels. Oversteer tendency decreases.

VDC Function That Prevents Understeer Tendency

Scheme 4

Scheme 5

1. During a cornering, brake force (brake fluid pressure) is applied on front wheel and rear wheel on the inner side of turn. Moment directing towards the inner side of turn is generated. Understeer is prevented.
2. Applying braking during a cornering on a slippery road, when understeer tendency is judged large, engine output is controlled as well as brake force (brake fluid pressure) of four wheels. Understeer tendency decreases.

Scheme 6

1. Wheel spin status of drive wheel is detected by wheel sensor of 4 wheels. Engine output and transmission shift status is controlled so that slip rate of drive wheels is in appropriate level. When wheel spin occurs on drive wheel, ABS actuator and electric unit (control unit) perform brake force control of LH and RH drive wheels (apply brake force by increasing brake fluid pressure of drive wheel) and decrease engine torque by engine torque control. Wheel spin amount decreases. Engine torque is controlled to appropriate level.
2. TCS function can be switched to non-operational status (OFF) by operating VDC OFF switch. In this case, VDC OFF indicator lamp turns ON.
3. VDC warning lamp blinks while TCS function is in operation and indicates to the driver that the function is in operation.
4. CONSULT can be used to diagnose the system diagnosis.
5. Fail-safe function is adopted. When a malfunction occurs in TCS function, the control is suspended for VDC function, TCS function and brake limited slip differential (BLSD) function. The vehicle status becomes the same as models without VDC function, TCS function and brake limited slip differential (BLSD) function. However, ABS function and EBD function are operated normally. Refer to " «FAIL-SAFE»(ref-672633-S27765677952014112400000) ".

ABS FUNCTION: System Description

1. By preventing wheel lock through brake force (brake fluid pressure) control that is electronically controlled by detecting wheel speed during braking, stability during emergency braking is improved so that obstacles can be easily bypassed by steering operation.
2. During braking, control units calculates wheel speed and pseudo-vehicle speed, and transmits pressure increase, hold or decrease signals to actuator portion according to wheel slip status.
3. The following effects are obtained by preventing wheel lock during braking. Vehicle tail slip is prevented during braking when driving straight. Understeer and oversteer tendencies are moderated during braking driving on a corner. Obstacles may be easily bypassed by steering operation during braking.
4. CONSULT can be used to diagnose the system diagnosis.
5. Fail-safe function is adopted. When a malfunction occurs in ABS function, the control is suspended for VDC function, TCS function, ABS function and brake limited slip differential (BLSD) function. The vehicle status becomes the same as models without VDC function, TCS function, ABS function and brake limited slip differential (BLSD) function. However, EBD function is operated normally. Refer to " «FAIL-SAFE»(ref-672633-S27765677952014112400000) ".

Note. ABS has the characteristic as described here, but it is not the device that helps reckless driving. To stop vehicle efficiently, ABS does not operate and ordinary brake operates at low speed [approx. 10 km/h (6.2 MPH) or less, but differs subject to road conditions). Self-diagnosis is performed immediately after when engine starts and when vehicle initially is driven [by vehicle speed approx. 15 km/h (9.3 MPH)]. Motor sounds are generated during self-diagnosis. In addition, brake pedal may be felt heavy when depressing brake pedal lightly. These symptoms are not malfunctions.

Scheme 7

Scheme 8

BRAKE LIMITED SLIP DIFFERENTIAL (BLSD) FUNCTION: System Description

1. LH and RH driving wheel spin is always monitored. If necessary, appropriate brake force is independently applied to LH or RH driving wheel so that one-sided wheel spin is avoided and traction is maintained. Mainly starting ability is improved.
2. Brake limited slip differential (BLSD) function operates while VDC function is in non-operational status (OFF) by VDC OFF switch.
3. VDC warning lamp blinking while brake limited slip differential (BLSD) function is in operation and indicates to the driver that the function is in operation.
4. Slight vibrations are felt on the brake pedal and the operation noises occur, when brake limited slip differential (BLSD) function operates. This is not a malfunction because it is caused by brake limited slip differential (BLSD) function that is normally operated.
5. CONSULT can be used to diagnose the system diagnosis.
6. Fail-safe function is adopted. When a malfunction occurs in brake limited slip differential (BLSD) function, the control is suspended for VDC function, TCS function and brake limited slip differential (BLSD) function. The vehicle status becomes the same as models without VDC function, TCS function and brake limited slip differential (BLSD) function. However, ABS function and EBD function are operated normally. Refer to " «FAIL-SAFE»(ref-672633-S27765677952014112400000) ".

ECU IDENTIFICATION

ABS actuator and electric unit (control unit) part number can be read.

Description

1. In general, customers have their own criteria for a problem. Therefore, it is important to understand the symptom and status well enough by asking the customer about his/her concerns carefully. To systemize all the information for the diagnosis, prepare the interview sheet referring to the interview points.
2. In some cases, multiple conditions that appear simultaneously may cause a DTC to be detected.

Scheme 9

When replaced the ABS actuator and electric unit (control unit), Perform steering angle sensor neutral position. Refer to " WORK PROCEDURE ".

Always adjust the neutral position of steering angle sensor before driving when the following operation is performed.

CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN-H line, CAN-L line) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only.

CAN (Controller Area Network) is a serial communication line for real time application. It is an on-vehicle multiplex communication line with high data communication speed and excellent error detection ability. Many electronic control units are equipped onto a vehicle, and each control unit shares information and links with other control units during operation (not independent). In CAN communication, control units are connected with 2 communication lines (CAN-H line, CAN-L line) allowing a high rate of information transmission with less wiring. Each control unit transmits/receives data but selectively reads required data only.

VDC function, TCS function, ABS function, EBD function and brake limited slip differential (BLSD) function operates in excessive operation frequency.

A malfunction of brake pedal feel (height or others) is detected when brake pedal is depressed.

Brake stopping distance is long when ABS function is operated.

VDC function, TCS function, ABS function, EBD function and brake limited slip differential (BLSD) function does not operate.

1. Brake pedal vibrates and motor sound from ABS actuator and electric unit (control unit) occurs, when the engine starts.
2. Brake pedal vibrates during braking.

The vehicle jerks when VDC function, TCS function, ABS function, EBD function or brake limited slip differential (BLSD) function operates.

Scheme 10

Note. Front RH wheel sensor is symmetrically opposite of LH.