Steering Gear: Description and Operation

GF46.20-P-5137RCB Steering gear of rack-and-pinion steering, component description
- with CODE (213) Speed-sensitive power steering

Component Identification:

Location
The steering gear is installed on the frame-type integral support of the front axle with rubber mounts.

Component Identification:

Function
The steering gear enables the following functions to be performed:
^ Transfer of steering movement
^ Steering assistance control
^ Variable steering force support (speed-dependent)
^ Play compensator
^ Steering damping

The DIRECT SERVO Vario steering has the following advantages compared to the previous speed-sensitive power steering:
^ Agile turning behavior, especially in urban traffic, when maneuvering or on twisty roads.
^ Improved comfort due to less steering-wheel turns lock to lock, especially when parking.

Transfer of steering movement

Component Identification:

The drive pinion (1a) transmits the movement of the steering wheel to the toothed rack (1b) and then via the tie rods to the wheels.

The drive pinion has spiral splines. Since several teeth are always engaged at the same time, the rack and pinion steering gear is wear-resistant and has a very low noise level.

Steering assistance control
If the steering wheel is turned, then the drive pinion is supported on the toothed rack. A rotary valve is twisted against the pilot bushing surrounding it via the stabilizer bar and this changes the position of the control grooves in relation to one another.

Now the oil flow is supplied by the power steering pump to the right working cylinder (left steer) (I) or the left working cylinder (right steer) (II) and supports the axial movement of the toothed rack to the right or left.

Variable steering force support
Steering force support is regulated to match vehicle speed. It is controlled via the SPS [PML] solenoid valve, which is actuated by the ESP and BAS control unit (N47-5) according to vehicle speed.

Play compensator
A thrust piece guarantees a zero clearance meshing of the drive pinion and toothed rack.

With engine ON:

Because the hydraulic steering assistance starts immediately, no steering play is noticeable.

With engine OFF:

When steering, only a slight, gradually increasing torque is noticeable for a travel distance of approx. 50 mm. This is due to the slewing range of the torsion bar in the rotary valve and should not be confused with play in the rack-and-pinion steering gear. Only when the steering wheel is turned further does the drive pinion begin to roll across the toothed rack, this can be felt on the steering wheel in the form of a slight pressure point and a more rapid torque increase.

Component Identification:

Pressurized steering damper (I)
Through four holes in the perforated disk, the high-pressure oil is routed unthrottled at the return stroke plate against the force of the return stroke spring to one of the working cylinders.

Dampened return pressure (II)
The oil flowing out of the opposite working cylinder is forced via four further holes in the perforated disk. As a result the disk spring is pressed on and the oil is delivered into the return line. This restricted pressure provides the required damping effect.