Steering on Cayenne S Hybrid

Steering On Cayenne S Hybrid

Since power assistance is also required for the steering when driving with electric power, the Cayenne S Hybrid is equipped with electro-hydraulic power assistance. The required hydraulic pressure is provided by a demand-controlled hydraulic pump, which is powered via the 12 V vehicle electrical system.

Steering gear

The Cayenne S Hybrid comes with a variable rack-and-pinion steering gear with hydraulic support and Servotronic valve as standard. The steering ratio is i = 16.7:1 in the center position and becomes more direct as the steering angle increases (up to i = 13.3:1). For further adaptation of the steering dynamics, the effective piston diameter was reduced along with the hydraulic control design.

Steering hydraulics

The scope of the steering hydraulics includes the reservoir (1), electric pump (2), suction line (3) and pressure line (4). The system is filled with Pentosin.







Hydraulic pump







The hydraulic pressure is delivered by an electrically driven gear pump integrated in the front left wheel housing. The demand-controlled pump only generates the energy required for power assistance in response to a steering command from the driver and otherwise remains in standby mode, e.g. when driving straight ahead. This contributes to a reduction in fuel consumption of more than 80% compared with purely hydraulic systems. The electrification of the unit means that the function is guaranteed even in driving modes with the combustion engine switched off. The Servotronic thus also functions when maneuvering in purely electric mode.

The pump drive power is controlled for optimum fuel consumption according to the vehicle speed, steering angle and, most importantly, the steering angle dynamics. Efficient control means that cooling of the power-steering fluid is not required.

Control unit structure







The system adapts to the requirements of the driving situation for efficient energy usage and delivers the boost pressure currently required for steering. It starts as soon as terminal 15 is switched on and the drive unit sends the driving readiness information.

The vehicle speed, steering angle and steering angle speed signals are evaluated in order to determine the defined speed for delivery of the required hydraulic pressure or flow using a programmed map.

Diagnosis, safety







The control unit diagnoses its internal components and checks the incoming CAN signals for plausibility. If the vehicle speed or steering angle sensor data is not received, the missing value is replaced by a predefined basic value in emergency operation mode in order to guarantee basic power assistance. In this emergency mode, higher forces are sometimes required for steering. For all faults, the steering wheel symbol and corresponding text message are displayed in the instrument cluster.