Rear Axle Steering, Detailed Information - GF46.80-P-0020B
Model 206, 214, 223, 236, 254, 295, 296, 297
with code 201 (Rear axle steering)
Model 223, 294, 295, 296, 297
with code 216 (Rear axle steering with large angle)
Rear axle steering, shown on model 223
Rear axle steering gear, shown on model 223
Detailed view of belt drive, shown on model 223
Overview
This document contains information on:
- General
- Function requirements
- Function
- Steering strategies
- Further steering strategies
General
Rear axle steering (1) is installed instead of the standard tie rods and tie rod adapters. It essentially comprises the following component parts:
- Electric motor (1.1)
- Travel sensor (1.3)
- Rear axle steering control unit (1.6)
- Tie rods with tie rod end (1.5)
Function requirements
- Ignition on (circuit 15).
- Drive unit active.
- Vehicle is in the corresponding vehicle speed range.
Function
A distinction is made between the following variants:
- 2.5° steering angle (code 201 (rear axle steering))
- 4.5° steering angle (code 201 (rear axle steering))
- 10° steering angle (code 216 (rear axle steering with large angle))
Steering originates from an electric motor (1.1) which drives the central spindle (4) via a belt (2). The central spindle (4) moves the tie rods (1.5) that are attached to the wheel carriers via joints.
Depending on the direction of rotation of the electric motor (1.1), the tie rods (1.5) move and, accordingly, the tie rod ends also shift left or right.
The travel sensor (1.3) records the stroke using a magnet installed on the long screw-on pin (6). The recorded stroke is transmitted to the rear axle steering control unit (1.6). This compares the values and uses them to calculate the steering angle.
The electric motor (1.1) is actuated accordingly via the rear axle steering control unit (1.6) and the integrated power driver.
The motor pinion (1.2) on the electric motor (1.1) drives (2) the belt pulley (3) through a belt. The belt pulley (3) moves the central spindle (4) via the spindle nut. The central spindle (4) is designed as a self-locking trapezoidal screw thread.
The rear axle steering control unit (1.6) receives signals for adjusting the steering via the following control units:
- ESP® control unit
- Parking control unit
- Rear axle steering control unit (internal)
In the event of failure, the system is self-locking and cannot be moved.
Steering strategies
Input signals:
- Speed signal from ESP® control unit
- Steering wheel angle, transmission position from steering column tube module
- Variant of electronic ignition lock
- Selected drive program from DYNAMIC SELECT switch
Maneuvering and parking:
- Up to 10° steering angle is implemented at the rear axle.
- The control strategy is active up to approx. 20 km/h, even when reversing.
- Advantages also during forward parking.
- The Parking Pilot also serves narrower parking spaces.
- If the transmission is in position "P", the steering is moved to 0°.
City agility:
- Steering angle adjustments between 3.5 and 4.5°.
- The control strategy is active between 20 and 60 km/h.
Vehicle dynamics increase:
- Small angle adjustments between 2.5 and 2.0°.
- The control strategy is active between 60 and 120 km/h.
High-speed stabilization:
- Small angle adjustment ≤ 2.0°.
- The control strategy is active as of approx. 120 km/h.
- The lane changes are perceived as being very safe and stable.
- The yaw angle is dampened.
| Vehicle speed | Steering strategy | Steer angle |
|---|---|---|
| < 60 km/h wheel angle against front axle | Maneuvering and parking | Up to 10° steering angle |
| City agility | Up to 4.5° steering angle | |
| > 60 km/h wheel angle with front axle | Vehicle dynamics increase | Up to 2.5° steering angle |
| High-speed stabilization | Up to 2.5° steering angle |
| Steering angle | 206 | 214 | 223 | 236 | 254 | 294 | 295 | 296 | 297 |
|---|---|---|---|---|---|---|---|---|---|
| 2.5° | x | - | x | x | - | x | x | x | x |
| 4.5° | - | x | x | - | x | x | x | x | x |
| 10.0° | - | - | x | - | - | x | x | x | x |
Further steering strategies
- The steering angle is restricted to 4.5° in trailer mode.
- Blockage detection takes place via the power consumption and the disabling of the steering angle adjustment. The disabling of the steering angle adjustment is only possible in the blocking direction and is canceled at a speed of > 2 km/h.
- In partially autonomous driving operation, e.g. DISTRONIC with Steer Assist, a control strategy with a maximum permissible steering angle of 4.5° is implemented.
- In roll mode, the angle is set to 0°.
- Obstacles are detected during parking. The steering angle is restricted accordingly.