Steering: Description and Operation
Steering
The steering rack is designed for a high level of variability. The angle at the center of the steering is smaller. As a result, the contact point is deeper in the pinion. The pinion pitch diameter is smaller, which means that the transmission ratio is higher. If the angle is increased, the pinion pitch diameter increases and the transmission ratio is lowered accordingly.
- Rack-and-pinion steering gear with variable steering ratio. Advantage: Driving stability at high speeds thanks to a higher steering ratio around the central position (i = 17.11:1). The steering ratio becomes more direct when the steering wheel is turned more sharply (I = 13.76:1). This makes driving around tight corners or parking easier. The turning circle is approx. 11.9 m.
NOTE: Repair instructions: Markings on the housing identify the central steering position.
Steering Wheel Adjustment
Steering wheel can be adjusted mechanically or electrically by approx. 60 mm (reach) and approx. 45 mm (height)
Mechanical steering-wheel adjustment is standard equipment on the Panamera S and 4S, while electric steering-wheel adjustment is standard equipment on the Panamera Turbo, and is optional on the Panamera S/4S.
Steering Controlled ZF Power Steering Pump
Power steering with controlled power-steering pump with a variable geometric flow rate. The demand-controlled flow rate reduces energy consumption and thus lowers fuel consumption.
Servotronic (speed-dependent steering assistance) is available as an option for all Panamera models. The steering is firm and precise with excellent steering comfort at high speeds. At low speeds, on the Servotronic makes manoeuvring and parking easier.
The pump delivers a constant volume flow to the hydraulic power steering when the engine is idling. An increasing change in engine speed causes the pump pressure, which is rising internally, to open the control valve (11), apply pressure on the curve ring (5) and reduce eccentricity to the rotor (3). As a result, the pump chambers become smaller and only produce a reduced flow rate.
The development objective of this type of pump was to support the automotive industry in its endeavour to achieve the CO2 and fuel consumption limit values,
particularly in top-of-the-range mid-size and luxury class vehicles. There is also room for improvement by reducing the steering oil temperature and protecting the pump from possible overload.
Design
Unlike normal ZF vane-type pumps, the curve ring (5) in the rotor set in the VARIOSERV pump can be adjusted and can generate a variable geometric flow rate thanks to the varying eccentricity. The curve ring is adjusted according to engine speed based on the pre-existing differential pressure between the left (12) and right chambers (13). A control valve (11) with integrated pressure control fitted at a right angle to the shaft (2) essentially controls how it works.
Function
Once the pump speed is reached, the pump delivers a constant volume flow to the hydraulic power steering when the engine is idling. An increasing change in engine speed causes the pump pressure, which is rising internally, to open the control valve (11), apply pressure on the curve ring (5) and reduce eccentricity to the rotor (3). As a result, the pump chambers become smaller and only produce a reduced geometric flow rate. This restricted pump function prevents an overproduction of pressure oil and as a result, significantly less energy is used at higher pump speeds due to reduced power consumption. This makes it possible to simplify cooling measures in the steering system. When the change in engine speed in the vehicle is falling, the pressure that exists between the left and right chambers increases the eccentricity between the rotors (3) and the curve ring (5). As a result, the geometric flow rate increases continuously again.
Steering Servotronic Control Unit Structure
The on-board computer control unit (BCM) receives information about speed and vehicle variant via the gateway. The Servotronic valve is controlled via a corresponding PWM signal. The steering remains fully functional in the event of an electrical malfunction. If the power supply fails, the converter valve opens to maximum, i.e. maximum hydraulic feedback or "high-speed characteristic".