Electrohydraulic Suspension, Basic Function - GF32.50-P-1008A
Model all (CAR)
with code 490 (Electrohydraulic suspension)
Front axle electrohydraulic suspension, model 223
Rear axle electrohydraulic suspension, model 223
Front axle electrohydraulic suspension, model 167
Rear axle electrohydraulic suspension, model 167
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 (vehicle-specific)
- Drive program matrixes
- 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. The electrohydraulic suspension adapts both the springing and the damping at each individual wheel to suit the ambient conditions.
The proportional gas-filled shock absorber and the air bellows are integrated into the suspension struts on the front and rear axles. The system on the front and rear axle also has a torsion bar stabilizer bar.
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 media 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 ADS
- Electrohydraulic controller unit
- Automatic lowering through two stages at higher speeds
- Lowering function and adaptation of damping characteristic for the Sport/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 (2). The air bellows bear the basic load of the vehicle body and adjust the vehicle level. The hydropneumatic system (2) generates dynamic forces that are superimposed on the forces of the air bellows 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 to the electrohydraulic controller unit.
The air suspension control unit actuates the electrohydraulic controller units at the wheels. The valves and compressor for the air spring are also actuated through the air suspension control unit.
When an electrohydraulic controller unit is actuated, the integrated hydraulic pump moves the hydraulic fluid between the annular space and the piston space (3) 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
With this sensor information, the air suspension control unit mainly actuates the following actuators:
- Damping valve units at each wheel
- Electrohydraulic controller unit
Influencing variables
The electrohydraulic suspension detects the driving situation and the vehicle load, and adapts the control accordingly.
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 for active lean-over in bends:
- 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. 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 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
Individual wheel control (depending on equipment installed)
Additional function requirements for individual wheel control:
- 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.
Transmission modes
DYNAMIC SELECT enables the driver to change the properties of the following systems:
- 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 can be selected using a control on the media display.
When selecting a drive program, the driver receives acoustic and visual operation feedback. The selected drive program is displayed as a status and shown on the media display. Comfort drive program is the default setting. Vehicle models with plug-in HYBRID also have the Battery Level and Electric drive programs.
Further drive programs in model 167
Additional drive programs are available to the driver in model 167:
- Off-road/off-road+
- Recovery mode
Additional function requirements for the off-road/off-road+ drive program and recovery mode:
- Off-road program activated
- Vehicle speed below 15 km/h
Off-road/off-road+
The off-road/off-road+ drive programs provide suspension tuning for driving off-road, e.g. on dirt roads, gravel and sand. The off-road/off- road+ drive programs can be selected using the DYNAMIC SELECT switch in the center console.
Recovery mode
Recovery mode is a function of the electrohydraulic suspension which can help the driver to free a vehicle that has become stuck on loose ground (e.g. sand or snow).
When recovery mode is activated, the body is moved in slow vertical oscillations. More load is applied here intermittently to the wheels, so that they have more grip, enabling the vehicle to be freed.
In the following cases, recovery mode is deactivated automatically:
- If a hard impact is detected on the vehicle underbody.
- After a period of 30 seconds.
- If the vehicle speed is greater than 15 km/h.
- When a vehicle door is opened.
Drive program matrixes
| Transmission modes | Steering | Drive | ESP® | Chassis |
|---|---|---|---|---|
| ECO | Comfort | ECO | Comfort | Comfort/ECO |
| Curve | Comfort | Comfort | Comfort | Curve |
| Comfort | Comfort | Comfort | Comfort | Comfort |
| Sport | Sport | Sport | Sport | Sport |
| Sport+ | Sport | Sport | Sport | Sport+ |
| Individual | Comfort | Comfort | Comfort/sport | ECO/Comfort/Sport |
| Battery level | Comfort | Battery level | Comfort | Comfort |
| Electric | Comfort | Electric | Comfort | Comfort |
| Maybach | Comfort | Maybach | Comfort | Maybach |
| Transmission modes | Steering | Drive | ESP® | Chassis |
|---|---|---|---|---|
| ECO | Comfort | ECO | Comfort | Comfort |
| Curve | Comfort | Comfort | Comfort | Curve |
| Comfort | Comfort | Comfort | Comfort | Comfort |
| Sport | Sport | Sport | Sport | Sport |
| Sport+ | Sport | Sport+ | Sport+ | Sport+ |
| Individual | Comfort/sport | ECO/Comfort/Sport | Comfort/sport | Comfort/sport |
| Battery level | Comfort | Battery level | Comfort | Comfort |
| Electric | Comfort | Electric | Comfort | Comfort |
| Maybach | Comfort | Maybach | Comfort | Maybach |
| Off-road | Comfort | Off-road | Off-road/off-road+ | Off-road |
| Off-road+ | Comfort | Off-road+ | Off-road | Off-road+ |
Visual road mapping
Illustration shows visual road mapping
Visual road mapping (depending on equipment installed)
Additional function requirements for visual road mapping:
- 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. 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 schematics | |||
| Function schematic for ADS | Model 167 with code 490 (Electrohydraulic suspension) | PE32.32-P-2500-97B | |
| Model 223 with code 490 (Electrohydraulic suspension) | PE32.32-P-2500-97D | ||
| Additional base function | |||
| Level control system, basic function | Model all (CAR) with code 490 (Electrohydraulic suspension) |
GF32.33-P-1002A | |
| Control units | |||
| Air suspension control unit, basic function | Model all (CAR) with code 490 (Electrohydraulic suspension) |
GF32.22-P-9890A | |
| Components | |||
| Acceleration sensor, basic function | Model all (CAR) with code 490 (Electrohydraulic suspension) |
GF32.32-P-2001A | |
| Electrohydraulic controller unit, basic function | Model all (CAR) with code 490 (Electrohydraulic suspension) |
GF32.50-P-2002A |