Electrohydraulic Suspension, Basic Function - GF32.50-P-1008A
Model all (CAR) with code 490 (Electrohydraulic suspension)
Schematic diagram of suspension strut with air spring and active damper
Schematic diagram of electrohydraulic suspension on front axle
Schematic diagram of electrohydraulic suspension on rear axle
Overview
This document contains information on:
- General
- Function requirements
- Function
General
The electrohydraulic suspension is a fully active suspension system based on the 48 V on-board electrical system technology. It combines an air suspension system with electrohydraulic dampers. The electrohydraulic suspension adapts both the springing and the damping at each individual wheel to suit the ambient conditions.
Function requirements
- Ignition ON (circuit 15)
Function
The electrohydraulic suspension supplements the air suspension with a semi-supporting hydropneumatic system. In this, the air suspension bears the basic load of the vehicle body and regulates the level. The hydropneumatic system produces dynamic forces which are superimposed on the forces of the air suspension. The vehicle body is thus actively supported and damped, e.g. under longitudinal and lateral acceleration or when driving on uneven roads.
At each of the four wheels, a hydraulic damper is installed inside the axle, which contains an adjustable throttle valve at both working chambers and a hydraulic accumulator. The hydraulic damper is connected through hydraulic lines to an electrohydraulic controller unit. The air suspension control unit actuates the electrohydraulic controller units at all four wheels. This control unit also actuates the valves and the compressor of the air suspension system.
When an electrohydraulic controller unit is actuated, the integrated hydraulic pump moves the hydraulic fluid between the annular space and the piston space in the connected hydraulic damper. A pressure difference can be set here inside the hydraulic damper. This pressure difference generates a force at the piston of the hydraulic damper, that is set to ensure that the required dampening effect is achieved on the vehicle body.
The system primarily uses information from the following sensors:
- Pressure sensors
- Body acceleration sensors
- Lateral acceleration sensor
- Level sensors at each wheel
With this sensor information, the air suspension control unit mainly actuates the following actuators:
- Damping valve units at each wheel
- Electrohydraulic controller units at each wheel
Influencing variable
The electrohydraulic suspension detects the driving situation and the vehicle load, and adapts the control accordingly. The adaptation is dependent on the following factors:
- Driving style, e.g. dynamic
- Road surface, e.g. surface undulations
- Vehicle load
The active lean-over in bends also has the following function requirements:
- Vehicle speed between 30 km/h and 160 km/h
If the Curve drive program is activated, the vehicle actively leans into the curve. This improves ride comfort when cornering. Active lean-over in bends is only available in a certain vehicle speed range. Outside this vehicle speed range, the Curve transmission mode is equivalent to the Comfort drive program.
When the vehicle drives into a curve, the air suspension control unit primarily actuates the following components:
- Left front electrohydraulic controller unit
- Right front electrohydraulic controller unit
- Left rear electrohydraulic controller unit
- Right rear electrohydraulic controller unit
Recovery mode
The recovery mode also has the following function requirements:
- Off-road program activated
- Vehicle speed below 15 km/h
Recovery mode is a function of the electrohydraulic suspension which can help the driver to free a vehicle which has become stuck on loose ground (e.g. sand or snow).
When recovery mode is activated, the body is moved in slow vertical oscillations. In this way, the wheels are intermittently more heavily loaded so that they have more grip, enabling the vehicle to be freed. In the following cases, recovery mode is deactivated automatically:
- A hard impact on the underbody of the vehicle is detected.
- After a period of 30 seconds.
- Vehicle speed above 15 km/h.
- A door is opened.
Individual wheel control
The individual wheel control also has the following function requirements:
- Vehicle speed below 15 km/h
Individual wheel control is a function of the electrohydraulic suspension with which the vehicle level can be adjusted at each wheel individually. This can help to improve the alignment of the body when driving off-road. In the following cases, individual wheel control is deactivated automatically:
- A hard impact on the underbody of the vehicle is detected.
- Vehicle speed above 15 km/h.
- A door is opened.
- Drive program, e.g. Comfort
Active lean-over in bends
Schematic diagram of visual road mapping
Visual road mapping
The visual road mapping also has the following function requirements:
- Engine in operation
- Vehicle speed between 7 km/h and 130 km/h
If the multifunction camera is installed, visual road mapping is available to the electrohydraulic suspension. With this, the road in front of the vehicle is captured by the camera. This information about the road surface enables the suspension struts to be actuated prior to surface undulations is such a way as to significantly reduce movements of the body when the undulations are driven over.
Visual road mapping may be impaired or inoperative in the following cases:
- With inadequate illumination of the road, e.g. in darkness.
- With snow, rain, fog, heavy slush, dazzle, direct sunlight or alternating light conditions.
- If the windshield in the area of the multifunction camera is soiled, fogged, damaged or covered.
- If the road surface has no visible structure or is reflective.
- If the distance to the preceding vehicle is too short.
- On stretches of road with very small curve radii.
| Function schematic | |||
| Function schematic for adaptive damping system | Model 167 with code 490 (Electrohydraulic suspension) | PE32.32-P-2500B | |
| Additional basic functions | |||
| Level control system, basic function | GF32.33-P-1002A | ||
| Control units | |||
| Air suspension control unit, basic function | Model 167 with code 490 (Electrohydraulic suspension) | GF32.22-P-9890A | |
| Components | |||
| Acceleration sensor, basic function | GF32.32-P-2001A | ||
| Active roll stabilization lateral acceleration sensor, basic function | GF32.34-P-2000A | ||
| Electrohydraulic controller unit, basic function | Model 167 with code 490 (Electrohydraulic suspension) | GF32.50-P-2002A |