Direct Steering Function - GF46.50-P-0002RR
Model 190
Function requirements in general
- Engine running
The ME-SFI [ME] control unit sends the "Engine running" signal to the AMG gateway control unit via the drive CAN, powertrain control unit and suspension CAN 1.
Direct-Steer system in general
The steering wheel's rotary motion is converted into horizontal movement through the steering gear of the rack-and-pinion steering. The rack-and-pinion steering gear has a variable gear ratio in the range of 5° to 150° steering angle. The steering force is supported hydraulically by the belt-driven power-steering pump.
The power steering is controlled by the rack-and-pinion steering's steering gear. The manual force required at the steering wheel is increased from vehicle stillstand up to the maximum vehicle speed. The hydraulic reaction is adapted via the Direct-Steer solenoid valve of the respective vehicle speed. The electronic control is integrated into the AMG gateway control unit.
To control the Direct-Steer system, the AMG gateway control unit evaluates the following signals:
- Wheel speeds
The ESP® control unit directly reads in the signals of the RPM sensors and sends them to the AM G gateway control unit via the suspension CAN 1.
- Steering wheel angle and steering speed
The steering wheel angle and the steering speed are detected by the steering wheel angle sensor. The steering column tube module control unit directly reads in the signals of the steering wheel angle sensor. It then sends information on the steering wheel angle and the steering speed to the AMG gateway control unit via chassis CAN 1 (up to 30.11.2018) or AMG FlexRay (as of 01.12.2018).
Additional scope for Model 190.381
A fine filter to keep the oil circuit clean is installed in the hydraulic system return line. It filters out minute particles that can lead to abrasive wear of the pump or steering. The filter is a maintenance-relevant component part that is subject to a change interval.
A separate oil cooler is installed directly upstream of the radiator for cooling the steering gear oil.
Steering angle
If the steering wheel is turned, the drive pinion supports itself on the toothed rack. The rotary valve is rotated against the stabilizer bar for the pilot bushing surrounding it, thereby changing the position of the control grooves in relation to one another.
The steering gear oil now flows into the right working cylinder (left steering movement) or into the left working cylinder (right steering movement) and supports the axial motion to the right or left.
The steering gear oil is pushed out of the unpressurized working cylinder and flows back into the expansion reservoir of the power-steering pump via the open return grooves of the pilot bushing.
The required steering wheel torque is regulated depending on the vehicle speed. It is controlled by the Direct-Steer system solenoid valve, which is actuated by the AMG gateway control unit.
A differentiation is made here between the following conditions:
- Vehicle stationary
- Vehicle speeds up to 200 km/h
- Vehicle speeds as of 200 km/h
Shown: steering movement to left
Shown: steering movement to left and vehicle stillstand
Vehicle stationary
The Direct-Steer system solenoid valve (Y10) is fully energized whereupon it is then closed against the force of the integrated compression spring. The pressure ratios in the reaction chambers are identical because the steering gear oil supply is suppressed. No force is exerted on the reaction balls (4); no additional torque acts on the surfaces of the rotary valve (12).
The steering is light because the steering torque to be applied by the driver, i.e. the force required to overcome the force of the torsion bar (10), is very low. The steering gear oil is conveyed to the expansion reservoir of the power-steering pump almost unpressurized via the constant constriction orifice (8).
Shown: steering movement to left and vehicle speed up to 200 km/h
Vehicle speeds up to 200 km/h
As the vehicle speed increases, energization of the Direct-Steer system solenoid valve (Y10) decreases continuously; the valve is opened by the force of the integrated compression spring. The controlled pressure is led to the reaction balls (4) via the regulating valve (9), causing the pressure applied to the surfaces of the rotary valve (12) to increase.
The force on the rotary valve (12) is increased further as a result, and the driver has to apply greater steering torque to operate the steering wheel. The constant constriction orifice (8) reduces the regulated pressure from the Direct-Steer system solenoid valve (Y10). This is then routed practically depressurized as a backflow to the power steering pump expansion reservoir.
Shown: steering movement to left and vehicle speed as of 200 km/h
Vehicle speeds as of 200 km/h
The Direct-Steer system solenoid valve (Y10) receives minimum energy. As a result, the highest possible pressure is fed from the Direct-Steer system solenoid valve (Y10) to the reaction balls via the regulating valve (9). The pressure application to the surfaces of the rotary valve (12) increases to a maximum.
The constant constriction orifice (8) reduces the regulated pressure from the Direct-Steer system solenoid valve (Y10). This is then routed in an almost depressurized state as a return flow to the expansion reservoir of the power steering pump.
The determined vehicle speed is assigned a specified current in the AMG gateway control unit via a characteristics map. This is then set in the Direct-Steer system solenoid valve (Y10) and influences the flow volume (hydraulic reaction) within the rack-and-pinion steering gear and thereby the manual force required at the steering wheel.
The Direct-Steer system solenoid valve (Y10) is pulse-actuated. The current is regulated by pulse-width modulation of these pulses.
Straight-ahead driving
When driving straight ahead (steering wheel in center position) the rotary valve (12) is in neutral position. The control grooves of the rotary valve (12) and the pilot bushing (11) are aligned such that the flow volume is routed directly back to the expansion reservoir via the return flow. The working cylinder (I, II) are thus unpressurized.
The torsion bar (10) is pinned on one side with the rotary valve (12) and on the other side with the drive pinion (14).
| Electrical function schematic for direct steering | PE46.50-P-2049-97HBA | ||
| Overview of system components for direct steering | GF46.50-P-9998RR |