Electrohydraulic Suspension, Basic Function - GF32.50-P-1008A
Model All (CAR) With Code 490 (Electrohydraulic suspension)
Example illustration of front axle electrohydraulic suspension
Example illustration of rear axle electrohydraulic suspension
Example showing suspension strut with air spring and active damper
Overview
This document contains information on:
- General
- Function requirements
- Function
- Influencing variables
- Active lean-over in bends
- Individual wheel control
- Transmission modes
- Visual road mapping
General
The electrohydraulic suspension is a fully active suspension and provides soft basic suspension with low natural ride frequency.
The electrohydraulic suspension combines the air suspension system with electrohydraulic dampers, and it adapts both the suspension and dampening on a wheel-specific basis to the ambient conditions.
The proportionally adjustable gas-filled shock absorbers and the air bellows (1) are integrated into the suspension struts (2, 4) at the front and rear axles.
The electrohydraulic suspension offers the following advantages, e.g.:
- The vehicle level remains constant, irrespective of the given load. This ensures an optimum distance between the wheel and the wheel cutout contour of the fender.
- If necessary, the vehicle level can be raised by the driver using the central display to increase the ground clearance.
- To reduce air resistance and fuel consumption, the vehicle level is lowered automatically at higher vehicle speeds.
- The complete spring travel is available permanently on loaded vehicles.
- When driving along a curve, the active roll and pitch support function takes effect.
- The body is raised prior to an imminent side impact.
Function requirements
- Ignition ON (circuit 15)
Function
The electrohydraulic suspension basically consists of:
- Air suspension with level control and adaptive damping system (ADS)
- Electrohydraulic controller unit (7)
- Automatic lowering through two stages at higher speeds
- Lowering function and adaptation of damping characteristic for the "Sport" and "Sport+" drive program
- Option to set a raised driving level up to a speed of 60 km/h (ground clearance irrespective of load)
The electrohydraulic suspension supplements the air bellows (1) with a semi-supporting hydropneumatic system (9). The air bellows (1) bear the base load of the vehicle body and adjust the vehicle level.
The hydropneumatic system (9) generates dynamic forces that are superimposed on the forces of the air bellows (1) and actively support and dampen the vehicle body. This is the case, for example, with longitudinal and lateral acceleration or when driving on uneven roads.
A hydraulic damper is installed at each wheel, which contains an adjustable throttle valve and a hydraulic accumulator at both working chambers. The hydraulic damper is connected through hydraulic lines (5) to the electrohydraulic controller unit (7).
The air suspension control unit (6) actuates the electrohydraulic controller units (7) on the wheels. The valves and compressor for the air spring are also actuated through the air suspension control unit (6).
When an electrohydraulic controller unit (7) is actuated, the integrated hydraulic pump moves the hydraulic fluid between the annular space and the plunger chamber (10) in the connected hydraulic damper.
This enables a pressure difference to be set 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
Regulation adaptation is dependent on the following factors:
- Driving style, e.g. dynamic
- Road surface, e.g. surface undulations
- Vehicle load
- Drive program, e.g. "Comfort"
Active lean-over in bends
Additional 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 bend. This improves ride comfort when cornering. Outside this vehicle speed range, the "Curve" drive program corresponds to the "Comfort" drive program.
When the vehicle drives into a curve, the air suspension control unit (6) primarily actuates the following component parts:
- Left front electrohydraulic controller unit
- Right front electrohydraulic controller unit
- Left rear electrohydraulic controller unit
- Right rear electrohydraulic controller unit
Individual wheel control
Additional function requirements:
- Vehicle speed below 15 km/h
Individual wheel control is - depending on the equipment involved - a function of the electrohydraulic suspension with which the vehicle level can be adjusted on 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.
Transmission modes
DYNAMIC SELECT enables the driver to change the properties of the following systems:
With this sensor information, the air suspension control unit (6) mainly actuates the following actuators:
- Damping valve units at each wheel
- Electrohydraulic controller unit (7)
Influencing variables
The electrohydraulic suspension detects the driving situation and the vehicle load, and adapts the control accordingly.
- Drive
- ESP®
- Steering
- Chassis
Various properties are assigned to each system. The driver is able to select specified drive programs or to arrange single sub-programs individually.
The drive program is selected using a control element on the central display.
When selecting a drive program, the driver receives acoustic and visual operation feedback. The selected drive program is indicated as a status and shown on the central display. The "Comfort" drive program is the default setting.
Vehicle models with plug-in HYBRID are also equipped with the "Battery Level" and "Electric" drive programs.
The "Offroad" and "Offroad+" drive programs are also available to the driver depending on the model.
Exemplary illustration of visual road mapping
Visual road mapping
Additional function requirements for visual road mapping (8):
- Engine in operation
- Vehicle speed between 7 km/h and 130 km/h
If the multifunction camera is installed, visual road mapping is also available to the electrohydraulic suspension (equipment dependent). With this, the road in front of the vehicle is captured by the camera.
This information about the road surface enables the suspension struts (2, 4) to be actuated prior to surface undulations in 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.
- In the case of snow, rain, fog, heavy slush, dazzle, direct sunlight or varying 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 schematics | |||
| Function schematic for adaptive damping system | Model 167 | PE32.32-P-2500-97B | |
| Model 223 | PE32.32-P-2500-97D | ||
| Additional basic functions | |||
| Electrohydraulic suspension, detailed information | Model 167 | GF32.50-P-1010A | |
| Model 223 | GF32.50-P-1010B | ||
| Level control system, basic function | GF32.33-P-1002A | ||
| Air suspension control unit, basic function | GF32.22-P-9890A | ||
| Acceleration sensor, basic function | GF32.32-P-2001A | ||
| Active roll stabilization lateral acceleration sensor, basic function | All models (cars) with code 465 (Electric active roll stabilization (EARS)) | GF32.34-P-2000A | |
| Electrohydraulic controller unit, basic function | GF32.50-P-2002A |