If HECU determines there's no lock-up in the wheel, HECU cuts voltage to solenoid valve. So voltage is not supplied
to each solenoid valve, brake fluid passes through the inlet valve to wheel cylinder, resulting in pressure increase.
TRACTION CONTROL SYSTEM (TCS) OPERATION
1. NORMAL MODE
Solenoid valve
State
Valve
Motor pump
TC valve
IN (NO)
OFF
OPEN
OFF
OFF
OUT (NC)
OFF
CLOSE
• In the normal driving condition, TC valve (normally open) is the passage between the master cylinder and the each
wheel cylinder.
• When brake pedal is applied, brake pressure is delivered to the wheel cylinders via NO-TC valve and all solenoid
valves inside the hydraulic unit are deactivated.
• In case of TCS malfunction it does not affect brake operation.
2. PRESSURE INCREASE MODE
Solenoid valve
State
Valve
Motor pump
TC valve
IN (NO)
FRONT: OFF
REAR: ON
FRONT: OPEN
REAR: CLOSE
ON
ON
OUT (NC)
OFF
CLOSE
• If a front wheel spin is detected, TCS begins a brake control to decrease a wheel spin.
• Hydraulic shuttle valve (HSV) is opened.
Brake fluid is supplied from the master cylinder by motor operation to the spin wheel via HSV.
• TC valve is closed (ON).
Brake pressure generated from motor pump is delivered only to the front wheel.
• Inlet valve remains open to deliver the brake pressure generated from motor pump to the spinning wheels.
3. PRESSURE DUMP MODE
Solenoid valve
State
Valve
Motor pump
TC valve
IN (NO)
ON
CLOSE
ON
ON
OUT (NC)
FRONT: ON
REAR: OFF
FRONT: OPEN
REAR: CLOSE
• When the wheel deceleration is under the threshold and the wheel spin is reduced under a slip threshold, applied
brake pressure is reduced to get a optimum traction force.
• Outlet valve is open to release the brake pressure and inlet valve is closed to block the pressure increase from the
motor pump.
• Hydraulic shuttle valve (HSV) remains opened, TC valve is ON.
• Motor is ON, to dump the brake fluid being released from the lock-up wheel.
4. PRESSURE HOLD MODE
Solenoid valve
State
Valve
Motor pump
TC valve
IN (NO)
ON
CLOSE
ON
ON
OUT (NC)
OFF
CLOSE
TRACTION CONTROL SYSTEM (TCS) FUNCTION
1. Main performance
Page 4 of 6
24.04.2008
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