System Components: EHPS

All models and derivatives are equipped with Electro Hydraulic Power Steering (EHPS). This system uses an electric motor to drive the hydraulic pump. This replaces the customary design whereby the pump is permanently driven from the engine via the auxiliary belt.

Fig 1: EHPS Motor Assembly

Courtesy of BMW OF NORTH AMERICA, INC.

The EHPS motor weighing 5.5 kg is mounted by four rubber insulators and is positioned in front of the steering rack.

The hydraulic pump displaces 1.25cm 3/revolution developing a pressure of 105 bar at a maximum pump motor speed of 4,200 rpm. The hydraulic pump has an incorporated pressure relief valve. The smaller metal pipe from the aluminum bodied pump is the high pressure side and the flexible pipe fitted to the plastic reservoir on the pump is the low pressure side. There is a small reservoir fitted to the end of the pump with a remote reservoir fitted to the bulkhead. The system is filled with Pentosin CHF 11 S. For top-up and refill use the same oil.

Fig 2: EHPS Motor/Pump Housings

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: Identifying EHPS Motor/Pump Internal Components

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 4: Remote Reservoir

Courtesy of BMW OF NORTH AMERICA, INC.