Steering gear of rack-and-pinion steering, component description (MODEL 204.0/2 with Speed-sensitive power steering up to Model Year 8) - GF46.20-P-5137CWA

MODEL 204.0/2 with CODE (213) Speed-sensitive power steering up to Model Year 8

Location

The steering gear is mounted rigidly to the front axle's frame-type integral support.

Fig 1: Identifying Rack-And-Pinion Steering Gear

Courtesy of MERCEDES-BENZ USA

Overview

Fig 2: Identifying Center Positioning Marking On Rack-And-Pinion Steering

Courtesy of MERCEDES-BENZ USA

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

Transfer of steering movement

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, rack and pinion steering gear is wear-resistant and also has a very low noise level.

Fig 3: Identifying Drive Pinion And Toothed Rack

Courtesy of MERCEDES-BENZ USA

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. Regulation is effected over the speed-sensitive power steering solenoid valve, which is actuated by the Electronic Stability Program control unit (N30/4) in a speed-dependent manner.

Play compensator

The thrust piece (3a) ensures that the drive pinion (1a) and toothed rack (1b) mesh without any play.

Engine ON

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

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.

Fig 4: Identifying Thrust Piece, Drive Pinion and Toothed Rack

Courtesy of MERCEDES-BENZ USA

Shown on steering damping at left steer

Fig 5: Identifying Oil Flow Conditions (Pressurized, Unpressurized And Damped Return)

Courtesy of MERCEDES-BENZ USA

Pressurized steering damper (I)

Through 4 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 into the perforated disk via 4 further bores. 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.