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DSC HU PART CONSTRUCTION/OPERATION

id041500100900

## Construction

• The ABS HU mainly consists of the pressure-retention/pressure reduction solenoid valves, pump motor (pump), stability control solenoid valves and traction switching solenoid valves.

### Function Of Main Component Parts

Part name | Function
--- | ---
Pressure-retention solenoid valve | • Adjusts the fluid pressure in each brake system according to DSC HU/CM signals.
Pressure-reduction solenoid valve | • Adjusts the fluid pressure in each brake system according to DSC HU/CM signals.
Stability control solenoid valve | • Switches the brake hydraulic circuits during and according to normal braking, ABS and EBD control, TCS control and DSC control.
Traction switching solenoid valve | • Switches the brake hydraulic circuits during and according to normal braking, ABS and EBD control, TCS control and DSC control.
Reservoir | • Temporarily stores brake fluid from the caliper piston to ensure smooth pressure reduction during ABS and EBD control, TCS control and DSC control.
Pump | • Returns the brake fluid stored in the reservoir to the master cylinder during ABS and DSC control. • Increases brake fluid pressure and sends brake fluid to each caliper piston during TCS control and DSC control.
Pump motor | • Operates the pump according to DSC HU/CM signals.

### Hydraulic Circuit Diagram

.

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Stability control solenoid valve
5 | Brake fluid pressure sensor
6 | Reservoir
7 | Caliper piston
8 | Traction switching solenoid valve
9 | Pump
10 | Pump motor

## Operation

### During normal braking

  • During normal braking, the solenoid valves are not energized and all of them are off. When the brake pedal is depressed, brake fluid pressure is transmitted from the master cylinder, through the traction switch solenoid valve and pressure-retention solenoid valves, and then to the caliper piston.

Solenoid valve operation table

Traction switching solenoid valve | Stability control solenoid valve | Pressure-retention solenoid valve | Pressure-reduction solenoid valve | Pump motor, pump
--- | --- | --- | --- | ---
LF-RR | RF-LR | LF-RR | RF-LR | LF | RF | LR | RR | LF | RF | LR | RR
OFF (open) | OFF (closed) | OFF (open) | OFF (closed) | Stopped

Hydraulic Circuit Diagram

.

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Stability control solenoid valve
5 | Reservoir
6 | Caliper piston
7 | Traction switching solenoid valve
8 | Pump
9 | Pump motor
10 | Pressure increase

### During ABS and EBD control

  • During ABS and EBD control, when wheel lock-up is about to occur, the traction switching solenoid valve and stability control solenoid valves are not energized, and the pressure-retention and pressure-reduction solenoid valves are energized and controlled in three pressure modes (increase, reduction or maintain), thereby adjusting brake fluid pressure. Brake fluid during pressure reduction is temporarily stored in the reservoir and afterwards the pump motor operates the pump to return the fluid to the master cylinder. (The following figure shows these conditions: right front wheel pressure increased, left front wheel pressure maintained, and both rear wheels pressure decreased.))

Solenoid valve operation table

| Traction switching solenoid valve | Stability control solenoid valve | Pressure-retention solenoid valve | Pressure-reduction solenoid valve | Pump motor, pump
--- | --- | --- | --- | --- | ---
LF-RR | RF-LR | LF-RR | RF-LR | LF | RF | LR | RR | LF | RF | LR | RR
During pressure increase mode | OFF (open) | OFF (closed) | OFF (open) | OFF (closed) | Stopped
During pressure maintain mode | OFF (open) | OFF (closed) | ON (closed) | OFF (closed) | Stopped
During pressure reduction mode | OFF (open) | OFF (closed) | ON (closed) | ON (open) | Operat-ing

Hydraulic Circuit Diagram

.

1 | Master cylinder
2 | Pressure-retention solenoid valve
3 | Pressure-reduction solenoid valve
4 | Stability control solenoid valve
5 | Reservoir
6 | Caliper piston
7 | Traction switching solenoid valve
8 | Pump
9 | Pump motor
10 | Pressure increase
11 | Pressure maintained
12 | Pressure reduction

### During DSC control (to suppress oversteer tendency) and TCS control

  • When a large oversteer tendency or driving wheel spin is determined, the traction switching solenoid and stability control solenoid valves are energized, switching the hydraulic circuits. At the same time, the pump motor is actuated to operate the pump, thereby increasing pressure by supplying brake fluid pressure to the caliper piston of the outer front wheel or the slipping driving wheel. Also at this time, the inlet solenoid valve of the inner rear wheel is energized and the hydraulic circuit of this wheel is closed.
  • After a pressure increase, brake fluid pressure is adjusted using the three pressure modes (reduction, maintain, increase) so that the target wheel speed is obtained. (The following figure shows a left turn, or control of right front wheel spin (during pressure increase mode).)

Solenoid valve operation table

| Traction switching solenoid valve | Stability control solenoid valve | Pressure-retention solenoid valve | Pressure-reduction solenoid valve | Pump motor, pump
--- | --- | --- | --- | --- | ---
LF-RR | RF-LR | LF-RR | RF-LR | LF | RF | LR | RR | LF | RF | LR | RR
During pressure increase mode | OFF (open) | ON (closed) | OFF (closed) | OFF (open) | ON (closed) | OFF (open) | OFF (closed) | Operating
During pressure maintain mode | OFF (open) | ON (closed) | OFF (closed) | OFF (open) | ON (closed) | OFF (open) | OFF (closed) | Stopped
During pressure reduction mode | OFF (open) | ON (closed) | OFF (closed) | OFF (open) | ON (closed) | OFF (open) | OFF (closed) | ON (open) | OFF (closed) | Operating

Hydraulic Circuit Diagram

.

1 | Pressure-retention solenoid valve
2 | Pressure-reduction solenoid valve
3 | Reservoir
4 | Traction switching solenoid valve
5 | Pump
6 | Pump motor
7 | Pressure increase

### During DSC control (to suppress understeer tendency)

  • When a large understeer tendency is determined, the traction switching solenoid and stability control solenoid valves are energized, switching the hydraulic circuits. At the same time, the pump motor is actuated to operate the pump, supplying brake fluid pressure from the reservoir to the inner rear wheel cylinder. Also at this time, the pressure-retention solenoid valve of the outer front wheel is energized and the hydraulic circuit of this wheel is closed.
  • After a pressure increase, brake fluid pressure is adjusted using the three pressure modes (reduction, maintain, increase) so that the target wheel speed is obtained. (The following figure shows control during a left turn during pressure increase mode.)

Solenoid valve operation table

| Traction switching solenoid valve | Stability control solenoid valve | Pressure-retention solenoid valve | Pressure-reduction solenoid valve | Pump motor, pump,
--- | --- | --- | --- | --- | ---
LF-RR | RF-LR | LF-RR | RF-LR | LF | RF | LR | RR | LF | RF | LR | RR
During pressure increase mode | OFF (open) | ON (closed) | OFF (closed) | OFF (open) | ON (closed) | OFF (open) | OFF (closed) | Operating
During pressure maintain mode | OFF (open) | ON (closed) | OFF (closed) | OFF (open) | ON (closed) | OFF (open) | OFF (closed) | Stopped
During pressure reduction mode | OFF (open) | ON (closed) | OFF (closed) | OFF (open) | ON (closed) | OFF (open) | OFF (closed) | ON (open) | OFF (closed) | Operating

Hydraulic Circuit Diagram

.

1 | Pressure-retention solenoid valve
2 | Pressure-reduction solenoid valve
3 | Reservoir
4 | Traction switching solenoid valve
5 | Pump
6 | Pump motor
7 | Pressure increase