AHB System Operation Principals: Notes

Initial Status

Fig 1: AHB System Operation Diagram - Initial Status
Courtesy of KIA MOTORS AMERICA, INC.

High pressure (180 bar) between the PSU and the IBAU is generated consistently. Therefore, before removing the PSU or the IBAU, high pressure between them should be reduced for safety by conducting "High pressure release mode" of GDS connected.
Brake operation

Fig 2: AHB System Operation Diagram - PSU And IBAU
Courtesy of KIA MOTORS AMERICA, INC.

Apply Mode: During normal braking, IN valve becomes ON and opens; then, the high pressure generated by PSU is supplied to a caliper on each wheel by IBAU and the brake operation is engaged. Release Mode: During discharging brake, OUT valve opens and IN valve closes; then, the high pressure of brake oil return back to reservoir. At this time, CUT valve is ON and it prevents back flow of brake oil to master cylinder.
Brake malfunction

Fig 3: AHB System Operation Diagram - IN Valve ON And Opens

Courtesy of KIA MOTORS AMERICA, INC.

If the PSU or the IBAU is broken, IN valve and OUT valve are closed, and CUT valve is off. Therefore, the brake force is generated by only pressing a brake pedal manually by a driver.