Vehicle Dynamic Suspension (G1895520): Description: Notes
Shock Absorbers
The adaptive shock absorbers are nitrogen gas and oil filled monotube units. The shock absorbers are continuously variable, which allows the damping force to be electrically adjusted when the vehicle is being driven. The shock absorbers provide the optimum compromise between vehicle control and ride comfort.
The shock absorbers have an electrical connector on the end of the piston rod, in the center of the top mount.
In each shock absorber, the damping adjustment is achieved by a variable orifice operated by a solenoid. The orifice is used to open up alternative paths to allow oil-flow within the shock absorber. When de-energized the bypass is closed and all the oil flows through the main (firm) piston. When energized the solenoid moves an armature and control blade, which work against a spring. The control blade incorporates an orifice which slides inside a sintered housing to open up the bypass as required. When the shock absorber is compressed the oil flows from the lower portion of the shock absorber then through a hollow piston rod, which is a separate soft (comfort) valve. The oil then flows through the slider housing and orifice and into the upper portion of the shock absorber, thereby bypassing the main (firm) valve. In rebound the oil flows in the opposite direction.
In the firm setting oil flows through the main (firm) valve only, although when the bypass is opened by variable amounts, the oil flows through both valves to provide a pressure balance. When fully energized the solenoid moves the armature and therefore the slider to the maximum extension and opens the orifice completely. The shock absorber operates continuously between these two boundary conditions.
The solenoid in each shock absorber is operated by a 526 Hz Pulse Width Modulation (PWM) signal from the SUM. The SUM controls the PWM duty ratio to provide 1.5 A to operate the shock absorber in the soft setting. When de-energized (0.0 A) the shock absorber is in the firm setting. The current varies continuously as required to increase and decrease the damping individually in each of the shock absorbers.
Sectioned Views of Shock Absorber Operating States
| ITEM | DESCRIPTION |
|---|---|
| A | Firm setting |
| B | Soft setting |
| C | Main oil flow |
| D | Bypass oil flow |
| 1 | Bypass valve (open) |
| 2 | Main valve |
| 3 | Tube |
| 4 | Bypass valve (closed) |
| 5 | Piston and rod assembly |
Accelerometers
Three accelerometers are used in the adaptive damping system; two at the front of the vehicle and one at the rear.
The accelerometers measure acceleration in the vertical plane and output a corresponding analogue signal to the SUM. The algorithms in the pulse width modulation calculate the heave, pitch and roll motions of the vehicle, which are used by the SUM. to control body motion.
Each accelerometer is connected to the SUM via three wires, which supply ground, 5 V supply and signal return.
The sensing element comprises a single parallel plate capacitor, one plate of which moves relative to the other dependant on the force (acceleration) applied. This causes the capacitance to change as a function of applied acceleration. This capacitance is compared with a fixed reference capacitor in a bridge circuit and the signal is processed by means of a dedicated integrated circuit to generate an output voltage that varies as a function of applied acceleration. The sensors output a signal voltage of approximately 1 V/g ± 0.05 V/g. When the vehicle is stationary, each accelerometer outputs approximately 2 volts.
Height Sensors
Four height sensors are used in the adaptive damping system, two for the front suspension and two for the rear suspension. A front suspension height sensor is attached to each side of the front subframe and connected by a sensor arm and sensor link to the related lower lateral-arm of the front suspension. A rear suspension height sensor is attached to each side of the rear subframe and connected by a sensor arm and sensor link to the related upper control-arm of the rear suspension.
The right suspension height sensors are dual output, with separate outputs for the adaptive damping system and for the Adaptive Front Lighting (AFS) system. The left suspension height sensors are single output, for the adaptive damping system only.
On each suspension height sensor, the sensor arm and sensor link convert linear movement of the suspension into rotary movement of the sensor shaft. The suspension height sensors measure suspension displacement at each corner of the vehicle and output a corresponding analogue signal to the SUM. The algorithms in the SUM calculate the position, velocity and frequency content of the signals and use the results for wheel control.
Each suspension height sensor is connected to the SUM via three wires, which supply ground, 5 V supply and signal return.
The sensing element consists of Hall effect devices arranged to measure the direction of the magnetic field of a small magnet attached to the end of the sensor shaft. As the sensor shaft rotates, so do the lines of magnetic flux from the magnet. The signals from the Hall effect devices are processed by means of a dedicated integrated circuit to generate an output voltage that varies as the sensor shaft is rotated. The sensor has a measurement range of ± 40° around its nominal position and the nominal sensitivity is 57 mV/° of shaft rotation.
Suspension Control Module (SUM)
The SUM is installed at the rear of the vehicle.