Advances in ride control: Getting up-to-speed on electronic suspension control
Once upon a time, ride control simply referred to providing a vehicle with a comfortable driving experience while limiting excess body roll. This was primarily addressed by the automakers by the selection of the appropriate springs, shock absorbers that would dampen spring movement and anti-roll bars that somewhat tamed, or limited, excess body lean during turns or steering maneuvers.
A properly controlled suspension system, or “ride control” system, is enlisted with the responsibilities of controlling spring and suspension movement, enhancing tire life, providing consistent and predictable handling and braking, maintaining wheel alignment, and minimizing excessive body lean and body dive.
It should come as no surprise that with today’s ever-advancing and ever-encroaching computer control and management systems, the once mechanically operated suspension systems have now entered the management-by-ECU realm.
Generically, suspension systems that are “controlled” or “managed” by means of electronic aid may be referred to as “adaptive” or “active” suspensions.
Examples of vehicles that feature some sort of adaptive suspension system include such models as the 2008 Lexus GS350 with its adaptive ride control (this uses small electric motors attached to the upper tips of the shock rods to rotate the rods, changing damping characteristics much in the way that was once handled by manual adjustment on some adjustable performance shocks), 2002 and later Cadillac STS, GMC Yukon and Corvette with GM’s MagneRide system that uses a magnetic fluid approach, 2003 Volkswagen Phaeton’s continuous damping control, 2003 and later Mercedes Benz Airmatic, 2004-2007 Volvo 4-C active chassis system, Audi’s magnetic ride, just to name a few.
Basically, everyone’s getting into the act in terms of offering advanced ride control systems that may still be mechanically operated, but electronically controlled.
As this trend continues, shops, both dealer and independent, will begin to see more vehicles that are equipped with these systems.
Here, we’ll provide an overview of select systems in order to offer a bit of insight into their workings.
Magnetic ride control
Magnetic ride control, also known as “magneto rheological” technology, involves shock absorber units that feature electromagnetic oils within the shock’s piston, and are filled with a very sophisticated magnetic particle-infused polymer liquid. An electrical charge is delivered to the liquid (timed and controlled by an ECU that receives input data from a series of sensors), causing the magnetic particles within the fluid to change their shape, or density, which quickly changes the liquid’s viscosity (thinner when the system wants freer movement, thicker when damping needs to be more firm). The special “magnetic fluid” can change from a relatively thin viscosity to an almost plastic state faster than you can flick your finger. This altering of the state of viscosity changes (or is capable of changing) at an astonishing rate of up to 1,000 times per second as commanded by the system’s ECU.
Rather than pouring through every system out there, let’s take a look at the CES (Continuously Controlled Electronic Suspension) system developed by Tenneco for the OEM market. This is a semi-active system that is triggered by a dedicated ECU that receives and interprets data from a range of sensors including front and rear mounted acceleration sensors that detect body up/down movement, a steering angle sensor, vehicle speed sensor, brake pressure sensor and sensors that detect lateral body movement.
Considering the advanced (and ever-evolving) electronic-hydraulic and magnetic suspension control system technology, the capabilities of these systems may very well do away with the need for anti-sway bars, as these systems become more capable of controlling lateral body movement in relation to the suspension.
As these systems become more incorporated into mainstream vehicles, the aftermarket is beginning to respond with direct replacement shock absorber units. The trend of OE control systems will continue to proliferate beyond applications for high-end luxury and performance vehicles.
Vehicle-specific example: Lexus AVS
A specific example of an adaptive variable suspension (AVS) is the 2008 Lexus GS350. This system approach features control actuators that are mounted to the top of the struts/shocks. By monitoring the various vehicle sensors, the absorber ECU controls the actuators, varying the damping control of the hydraulic shocks/struts.
Monitoring and actuating components for the system include front and rear acceleration sensors, yaw rate sensor, steering angle sensor, skid control ECU, and the ECM (which sends a drive torque signal to the absorber control ECU).
The AVS, as a system, includes each shock’s absorber control actuator, a front acceleration sensor which detects vertical acceleration of the left front of the vehicle, a rear acceleration sensor, a yaw rate sensor that monitors lateral (side to side) and longitudinal movement, a steering angle sensor, and a dedicated shock absorber ECU. By the way, the absorber control ECU houses the right-front acceleration sensor. The skid control ECU and the front steering control ECU send data that is incorporated into the ECM’s decision-making process to control damping.
Where are these system sensors located? The front LH acceleration sensor is located under the left side of the dash, requiring removal of the instrument panel undercover, the instrument side panel, the LH door scuff plate and front door opening trim cover, behind the carpet.
NOTE: In order to inspect the front LH acceleration sensor, connect three 1.5-volt dry batteries in series. Connect terminal 3 (SGB) to battery positive and terminal 2 (SGG) to battery negative (do not test this with the vehicle’s 12V system — you must use three 1.5V batteries connected in series). With the batteries connected to the sensor terminals, connect a voltmeter between terminals 1 (SGFL) and 2 (SGG). With the sensor stationary on a workbench, voltage should read approximately 2.3V. Next, hold the sensor in a vertical position and vibrate it. The voltage reading should change between about 0.9 and 3.6V.
NOTE: If the sensor is tilted, a different voltage value may be output. Don’t apply more than 6V to the sensor, and don’t drop it. If dropped, chances are the sensor will be damaged and must be replaced. Also, never place the sensor upside down at any time.
The rear acceleration sensor is located in the right side of the trunk, just ahead of the right hinge, behind the trim cover. As with the front sensor, it’s advised not to place the sensor upside-down, and avoid dropping it.
The procedure for testing the rear acceleration sensor is similar to testing the left front sensor. With the sensor removed and laying on a workbench, connect three 1.5V batteries in series, with the positive connected to the sensor’s terminal 3 (SGV) and negative to terminal 2 (SGND). Connect the voltmeter to terminals 1 (SGRR) and 2 (SGND). With the sensor stationary, voltage should read approximately 2.3V. While holding the sensor in its normal vertical position and while vibrating the sensor, the reading should change between about 0.9 and 3.6V.
The absorber control ECU (which includes the right front acceleration sensor) is located under the right side of the dash, mounted vertically. Here’s a tip: Don’t simply begin to remove this ECU. After turning the ignition switch off, disconnect the vehicle battery negative cable, and then wait at least 90 seconds in order to disable the airbag (SRS) system. By the way, if this ECU is being replaced, you’ll need to perform a registration of vehicle identification information.
Vehicle identification information is automatically acquired when the system enters its test mode.
The yaw rate and acceleration sensor is located in its traditional location, under the center console box.
The shock absorber actuators are mounted atop each shock’s rod, under the upper shock absorber cap. The actuator engages to the top of the shock’s rod, keyed to an internal damping adjustment driver. This is similar to an aftermarket shock that’s manually adjustable. In this case, electronic actuators turn the adjusters, commanded by the ECU as a result of information provided by the system’s vertical, lateral and longitudinal sensors.
Use a jumper wire to connect terminals 12 (TS) and 4 (CG) of the DLC3 diagnostic port. Turn the ignition switch to the on position. The “SPORT S+” indicator in the information display should blink in the Test Mode blinking pattern, blinking once every 0.125 seconds. If the display does not blink, there’s a problem with the indicator light.
Check the absorber control actuator operation. Starting with the SOFT position, depress the brake pedal. Using the appropriate scan tool, determine if the absorber actuator position increases by two steps, every time the brake pedal is depressed. You should see the actuator position move from SOFT to 3, to 5, to 7, to 9, to 11, to 15, to 17 (the HARD position). Bounce the vehicle and confirm that the shock absorber(s) is getting stiffer on compression.
Every time the brake pedal is depressed, the absorber control actuator rotates in 15-degree increments to a maximum angle of 120 degrees. If the actuator does not rotate, suspect the actuator circuit.
Once the inspection is complete, turn the ignition switch to the off position, and then disconnect the jumper wire from the DLC3. Then you can turn the ignition switch to the on position. If the ignition switch remains on after the jumper wire has been removed, the vehicle will remain in the Test Mode.
In order to remove the shock absorber control actuator, remove the shock cap and disconnect the actuator wire connector. Turn the actuator counterclockwise 40 degrees.
In order to inspect the control actuator, use a multimeter to measure the actuator resistance. Citing the front actuators as an example, note that connections on the right front differ from that of the left front actuator.
In order to install the actuators, engage the actuator to the shock rod and turn the actuator clockwise 40 degrees. ●
Computer-controlled adaptive suspension glossary
Absorber control actuator
Small actuator motor connected to the top of the shock piston rod in an adaptive system where a signal from the ECU adjusts shock damping. An example of this is found in the 2008 Lexus G350.
Absorber control ECU
Dedicated ECU for an adaptive suspension system.
Lexus term for their Adaptive Vehicle Suspension system.
Tenneco’s Continuously Controlled Electronic Suspension system developed for a variety of OEM applications.
Continuous damping control. This is the term used for many of Ford Motor Corp.’s European applications.
4-C active chassis
Volvo’s terms for the active suspension featured in the S60R and V70R models.
The term used by Opel for their active suspension.
Detects the vertical acceleration of the body.
Front steering control ECU
This ECU sends the VGRS (variable gear ratio steering) operation angle signal to the absorber control ECU.
GM’s name for their magneto-rheological systems.
A magneto-rheological fluid (generally called MR fluid) is a highly specialized type of fluid containing dense magnetic particles that quickly changes viscosity when subjected to a magnetic field. This fluid can change from free-flowing to an almost solid plastic state by varying the strength of the magnetic field. When used to control shock absorber damping, it reacts very quickly, as fast as 1,000 times per second.
Rear acceleration sensor
Detects the vertical acceleration of the rear of the body.
Skid control ECU (brake actuator assembly)
This ECU sends the vehicle speed signal to the absorber control ECU as part of the data used to determine suspension damping. It also sends the brake pedal depressed signal to the absorber ECU. It sends a request for damping force control to the absorber ECU.
Detects the steering direction and the angle of the steering wheel. Another aspect of input information used by the adaptive suspension system to control shock damping.
Yaw rate sensor
Detects the vehicle’s longitudinal and lateral acceleration and deceleration. This is another integral bit of data fed to the adaptive suspension system in terms of detecting body movement.