Suspension Control ( Automatic - Electronic ): Description and Operation
Vehicle Dynamic Suspension
COMPONENT LOCATION
INTRODUCTION
A continuously variable damping system, known as adaptive dynamics, is available on certain models. Adaptive dynamics is an electronically controlled suspension system which continuously adjusts the damping characteristics of the suspension dampers in reaction to the current driving conditions.
The system is controlled by an ADCM (adaptive damping control module). The ADCM receives signals from three accelerometers, four suspension height sensors and from other vehicle systems to determine vehicle state, body and wheel motions, and driver inputs. These signals are used by the ADCM to continuously control the damping characteristics of each damper to the appropriate level, to give the optimum body control and vehicle ride.
The ADCM also contains the controller for the electronic differential, if fitted.
DAMPERS
CAUTION: The dampers look identical to those on the CATS (computer active technology suspension) system of 4.2L vehicles, but have a different part number. Resistance across the solenoid pins of an adaptive dynamics damper should be 2 to 3.5 ohms; if more than 5 ohms, you should suspect that the damper is from a CATS system.
The adaptive dynamics dampers are monotube, nitrogen gas and oil filled units. The dampers are continuously variable, which allows the damping force to be electrically adjusted when the vehicle is being driven. The dampers provide the optimum compromise between vehicle control and ride comfort.
The dampers have an electrical connector on the end of the piston rod, in the center of the top mount.
In each damper, the damping adjustment is achieved by a solenoid operated variable orifice, which opens up an alternative path for oil flow within the damper. 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. In compression, oil flows from the lower portion of the damper through a hollow piston rod, a separate soft (comfort) valve, the slider housing and orifice and into the upper portion of the damper, 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, but when the bypass is opened by any amount the oil flows through both valves in 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 damper operates continuously between these two boundary conditions.
The solenoid in each damper is operated by a 526 Hz PWM (pulse width modulation) signal from the ADCM. The ADCM controls the PWM (pulse width modulation) duty ratio to provide 1.5 A to operate the damper in the soft setting. When de-energized (0.0 A) the damper is in the firm setting. The current varies continuously as required to increase and decrease the damping individually in each of the dampers.
Sectioned Views of Damper Operating States
ACCELEROMETERS
Three accelerometers are used in the adaptive dynamics system. The accelerometers are located as follows:
- One each on the front edge of the LH (left-hand) and RH (right-hand) A pillars.
- One in the luggage compartment, in the rear LH (left-hand) corner adjacent to the rear lamp assembly.
The accelerometers measure acceleration in the vertical plane and output a corresponding analogue signal to the ADCM. The algorithms in the ADCM calculate the heave, pitch and roll motions of the vehicle, which are used by the controller to control road induced body motion.
Each accelerometer is connected to the ADCM 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.
SUSPENSION HEIGHT SENSORS
Four suspension height sensors are used in the adaptive dynamics 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 subframes 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 RH (right-hand) suspension height sensors are dual output, with separate outputs for the adaptive damping system and for the AFS (adaptive front lighting system). The LH (left-hand) 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 ADCM. The algorithms in the ADCM 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 ADCM via three wires, which supply ground, 5 V supply and signal return.
The sensing element consists of an array 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 elements 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.
ADAPTIVE DAMPING CONTROL MODULE (ADCM)
The ADCM is installed on the right side of the passenger compartment rear bulkhead, behind the RH (right-hand) rear seat back (and behind the RH (right-hand) roll over protection hoop on convertible models).
System Fault Message
If a fault is detected by the ADCM, a message is sent via the high speed CAN (controller area network) to the instrument cluster and the message ADAPTIVE DYNAMICS FAULT is displayed. The ADCM also logs an appropriate DTC (diagnostic trouble code). The ADCM can be interrogated using a Jaguar approved diagnostic system.
When a fault is detected, the ADCM implements a strategy based on the type of fault. If there is an electrical power fault, or the ADCM cannot control the dampers, they default to the firm condition. If a sensor fails that only affects one or more control modes then an intermediate damper setting is used as the lower threshold and the remaining working modes can demand higher damping as required. In the event of a high speed CAN (controller area network) bus fault, the dampers are fixed at an intermediate setting (no control) or default to the firm condition, depending on the severity of the fault.
CONTROL DIAGRAM
NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus; N = Medium speed CAN (controller area network) bus
PRINCIPLES OF OPERATION
The ADCM uses a combination of information from other system modules and data from the accelerometers and suspension height sensors to measure the vehicle and suspension states and driver inputs. Using this information, the ADCM applies algorithms to control the dampers for the current driving conditions.
The ADCM receives the following signals on the high speed CAN (controller area network) bus from the stated system components:
- Brake Pressure - ABS (anti-lock brake system) module.
- Brake Pressure Quality Factor - ABS (anti-lock brake system) module.
- Car Configuration Parameters - AJB (auxiliary junction box).
- Center Differential Range Actual - ECM (engine control module).
- Engine Speed - ECM (engine control module).
- Engine Speed Quality Factor - ECM (engine control module).
- Engine Torque Flywheel Actual - ECM (engine control module).
- Engine Torque Flywheel Actual Quality Factor - ECM (engine control module).
- Gear Position Target - TCM (transmission control module).
- Lateral Acceleration - ABS (anti-lock brake system) module.
- Power Mode (Ignition Signal) - CJB (central junction box).
- Power Mode Quality Factor - CJB (central junction box).
- Roll Stability Control Mode - ABS (anti-lock brake system) module.
- Steering Wheel Angle - ABS (anti-lock brake system) module.
- Steering Wheel Angle Speed - ABS (anti-lock brake system) module.
- Steering Wheel Angle Status - ABS (anti-lock brake system) module.
- Terrain Mode Requested - JaguarDrive selector.
- Torque Converter Slip - TCM (transmission control module).
- Vehicle Information Parameters HS - AJB (auxiliary junction box)
- Vehicle Speed - ABS (anti-lock brake system) module.
- Vehicle Speed Quality Factor - ABS (anti-lock brake system) module.
- Front Left Wheel Speed - ABS (anti-lock brake system) module.
- Front Left Wheel Speed Quality Factor - ABS (anti-lock brake system) module.
- Front Right Wheel Speed - ABS (anti-lock brake system) module.
- Front Right Wheel Speed Quality Factor - ABS (anti-lock brake system) module.
- Rear Left Wheel Speed - ABS (anti-lock brake system) module.
- Rear Left Wheel Speed Quality Factor - ABS (anti-lock brake system) module.
- Rear Right Wheel Speed - ABS (anti-lock brake system) module.
- Rear Right Wheel Speed Quality Factor - ABS (anti-lock brake system) module.
The ADCM also outputs information on the high speed CAN (controller area network) bus for use by other systems as follows:
- Fault Message - instrument cluster.
- Terrain Mode Change Status - JaguarDrive selector.
- Terrain Mode - JaguarDrive selector.
The ADCM monitors the input signals and operates the damper solenoids. The input signals are used in control functions and a force required for each damper, for each function, is calculated. An arbitrator monitors the force requirements from each function and apportions a force to a damper. The force is converted to the appropriate current and sent to the damper.
The control functions are as follows:
- Body Control - Uses CAN (controller area network) and accelerometer inputs. Calculates road induced body motions 100 times a second and sets each damper to the appropriate level to maintain a flat and level body.
- Roll Rate Control - Uses CAN (controller area network) inputs. Predicts vehicle roll rate due to driver steering inputs 100 times a second and increases damping to reduce roll rate.
- Pitch Rate Control - Uses CAN (controller area network) inputs. Predicts vehicle pitch rate due to driver throttle and braking inputs 100 times a second and increases damping to reduce pitch rate.
- Bump Rebound Control - Uses suspension height sensor inputs. Monitors the position of the wheel 500 times a second and increases the damping rate as the damper approaches the end of its travel.
- Wheel Hop Control - Uses suspension height sensor and CAN (controller area network) inputs. Monitors the position of the wheel 500 times a second and detects when the wheel begins to vibrate at its natural frequency and increases the damping to reduce vertical wheel motion.
Under normal road conditions when the vehicle is stationary with the engine running, the dampers are set to the firm condition to reduce power consumption.
The ADCM receives its power supply via a relay and fuse in the CJB (central junction box). The relay remains energized for a period of time after the ignition is off. This allows the ADCM to record and store any DTC (diagnostic trouble code) relating to adaptive dynamics system faults.