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Replacements and upgrades for active, semi-active and adaptive suspension systems
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By Counterman
The standard automotive powertrain for the majority of the 20th century was the front engine, rear-wheel-drive (RWD) design. The rear axle assembly housed the differential and individual axles, and it is through this assembly that power was transferred to the wheels.
Even though both front-wheel-drive (FWD) and four-wheel-drive (4WD) cars were also designed and manufactured during the early years of the automobile, they didn’t flourish and the durability and simplicity of the typical RWD design made it the sole choice of automobile platforms for many manufacturers.
In a typical RWD vehicle, the power generated by the engine is transferred through the transmission to the driveshaft, differential and axles to the rear wheels. In a typical 4WD vehicle, a differential/axle assembly is located at the front of the vehicle, and to transfer power to the front, a transfer case is also installed after the transmission and a short driveshaft is installed between the transfer case and front axle.
You will also notice that the front differential/axle assembly is different in two ways. One, the differential location is offset for clearance since the engines were always mounted in the center and, two, since the front wheels must turn to steer the vehicle, the axles must have some type of articulating joint at the end, the most common of which is the traditional Universal Joint (U-Joint.)
The transfer case transfers the power that exits the transmission to either the rear wheels (RWD), or the front and rear wheels at the same time (4WD.) Another feature of a traditional transfer case is that it offers both high and low ranges in either RWD or 4WD positions, as well as a neutral position. This is so that if the vehicle must overcome particularly difficult terrain, it can be placed in the low range so the engine will operate at a higher RPM to provide additional torque to the wheels. The high range is 1:1, which means the output speed of the transfer case is the output speed of the transmission. The low range ratio varies depending on manufacturer.
An important aspect of all this is differential operation. The differential itself transfers the power from the driveshaft to the axles, and it is necessary because it allows power to be transferred to the wheels, but also allows them to travel at different speeds when turning a corner. A conventional differential is considered an “open” design. An operating characteristic of an open differential is that it transfers power to the wheel that spins the easiest.
As an example, if one wheel is on ice, that wheel will spin, resulting in minimal traction. The same affect is what causes a car under heavy acceleration to “burn rubber” with only one wheel. To combat this problem, there is another type of differential that is referred to as “limited slip.” There are many different names for this type of differential depending on the manufacturer, but their operation is the same.
A limited slip differential contains clutch packs built in between the side gears and the differential case. When one wheel begins to spin from loss of traction, the clutches will grab and transfer power to the other wheel. The same clutches will slip just enough to allow the wheel speeds to differ when going around a corner, so the normal differential action is still available.
The majority of cars and trucks on the road come standard with open differentials, due to the additional cost of limited slip. Limited slip differentials have always been an option, just not standard. So, on a four-wheel-drive vehicle equipped with open differentials, technically speaking, the maximum number of wheels that can put power to the ground at any given time is two…kind of funny on something known as a 4×4, but it’s still twice as much traction as RWD only, and for the most part it got the job done. Most people who were really going to be in some serious off-road situations would be sure they were equipped with limited-slip differentials.
4WD, as it was originally developed, was a rather primitive system that required input from the driver, from engaging to transfer case to engaging hubs on the front wheels in many cases. Technology was the eventual downfall of rudimentary 4WD systems as we know them, but the drive to utilize this technology came from the safety benefits of AWD.
The ability to transfer power to all four wheels has incomparable benefits for traction, vehicle stability and handling. Not only does this translate to the safety of daily driven vehicles, but it translates to performance, as well.
With the advancement of computer and electronic technology, antilock braking systems (ABS) and traction control systems (TCS) all of a sudden knew exactly what was happening at each wheel at all times. Was it losing traction, was it locking up under braking? All this data was now available, and engineers knew that the key to vehicle performance, safety and handling all together, was in the ability to precisely control what happened at each wheel at any given point in time.
Traditional differentials, even limited slip, were mechanical devices. There was no external control of how they operated. With electronics and computer control, the traditional differential became a technologically advanced unit containing not only gearsets, but clutch packs like those in an automatic transmission, and their own pumps to pressurize the fluid.
The same technology is present in both front and rear differentials, as well as center differentials/transfer cases. AWD systems have the ability to precisely control the amount of torque that is transferred to any given wheel at any point in time, providing absolute control of the vehicle.
In conclusion, 4WD is functional, durable, rough and tough, but not user friendly. AWD, the product of technology, computers and electronics, is technologically superior, and provides the safety feature we rely on in today’s vehicles.
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By Counterman
link hidden, please login to viewreleased two new suspension bushing tool kits for on-vehicle R&I of single-wrap and double-wrap heavy-duty suspension bushings – Suspension Bushing Kit with Pump and Suspension Bushing Adapter Kit. Both tool kits replace worn-out, rusted and frozen heavy-duty suspension bushings faster and easier without risking heat or other damage by providing a 25-ton capacity, the company said. Each kit saves hours on each job by making quick work of Pivot and D-pin bushing R&I. OTC’s latest suspension bushing tool kits include:
4247-FR Suspension Bushing Kit with Pump: Includes air/hydraulic pump, 25-ton hydraulic cylinder, hose with couplers, complete puller leg/plates and adapter set for double-wrap leaf springs.
4254-FR Suspension Bushing Adapter Kit: For use with OTC service sets; 4247, 4275, 4261 or 4263 with 4106A 25-ton ram.
OTC said each suspension bushing kit features Hendrickson rear suspensions, including Primaax EX, Comfort Air and FCCC V-Ride Pivot and D-Pin suspension bushings, and freightliner rear suspensions, including double and single-wrapped FAS II Airliner rear suspension bushings. Both also include centering adapters to align tool and bushing for clean installation. Both are available through OTC distribution partners and resellers.
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By Counterman
Most active suspension systems come in many styles with fancy names like airmatic, dynamic or advanced. And, it doesn’t matter if it is a BMW, Mercedes or Jaguar, an active suspension must be able to react to three critical pieces of information.
First, it must act on information from the ABS and stability control system. Second, it must measure body movement. Third, it must detect the extent and rate of suspension movement. With these three pieces of information, the suspension can actively adjust the compression and rebound of the shock or strut.
Why would an engineer or automaker include this feature on a vehicle? An active dampener allows for a ride without compromise. The three inputs can be used to detect a rough road or an emergency situation where body roll could change the stability of the vehicle.
Electronic Shocks/Struts
Electronically adjustable shocks and struts use conventional mono-tube and twin-tube oil-filled dampeners. The rods, gas chambers and piston have the construction of passive units. Like a passive unit, they can fail if they leak, the gas escapes or the rods are bent. They can also wear out like a conventional unit as the oil inside breaks down and surfaces in the bore wear.
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What makes these units unique are the valves with their variable orifices. These valves regulate the flow between the chambers on either side of the piston. The piston in some units, however, does not have any valving.
The size of the orifices controlled by electromagnetic solenoids can control the valves very quickly. The electrical connections and solenoids are typically found outside the body and act on the valves inside the unit using magnetism. The signal to the solenoid is pulse-width modulated and varies the voltage to change the size of the orifice.
The valves and solenoids can’t be serviced or separated from the shock or strut. If a problem is detected with the system, the valves go into a fail-safe position that is fixed, and the system becomes passive. The driver is then alerted with a message or light on the instrument cluster or message center.
Most systems will perform a circuit check when the system wakes up. This typically involves sending a signal to fully open and close the valve. If the system detects an open, short or a voltage outside of the specifications, it will set a code.
Measuring Wheel Movement
Ride-height sensors not only measure the position of the suspension, but also the rate of movement. They are supplied with a voltage of around 5 volts. The signal voltage is changed as a magnet moves past a coil. Most sensors have three wires – ground, power and signal.
Internally, it is difficult to damage one of these sensors. Externally, however, the linkage that connects the sensor to the suspension arm can be damaged. Additionally, the connector can be damaged and cause a short or open that sets a code. If one of these sensors is replaced, it must be calibrated after it is installed.
Ride-height sensors are sometimes called suspension-position or wheel-displacement sensors. The data from the sensor is used to measure the movement of the suspension. By knowing how far and fast the suspension is moving, the module can use the information to determine the size of the orifice in the dampener to control compression and rebound. These sensors should be calibrated if a sensor is replaced, a module is reprogrammed or if the battery dies.
Measuring Body Movement
Accelerometers mounted to the body measure changes in the ride. These accelerometers are typically mounted to the strut towers. These sensors output information as gravitational forces, or “G-force,” to a module. Changes in body roll due to cornering will produce lower G-force than a pothole would.
Information from the accelerometers is coupled with data from the ride-height sensor, steering sensor and other inputs by a computer processor in a module. The module can determine if the vehicle is going around a corner or traveling down a bumpy road. With this datastream, the valving inside the dampener can be adjusted in milliseconds for the best control and ride quality.
The accelerometers on the body differ from vehicle to vehicle. Some manufacturers mount the sensors under the headlights, on strut towers and near the taillights. More sophisticated systems use more than two accelerometers mounted in various locations.
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The control module for the electronic dampeners needs more than the movement of the wheels and body to determine the correct settings for the dampeners. The module uses and shares information with the anti-lock braking system, engine control module and instrument cluster. This information is typically shared on the high-speed CAN serial data bus. On some BMW 7 Series models, the information is shared on the fiber-optic Flex Ray bus.
With all this information, the module can do some amazing things with the adjustable dampeners. Problems like nosedive under braking, torque steer and understeer on FWD vehicles can be minimized. If the vehicle has air ride, the volume and pressure inside the air springs can also be tuned along with the valving in the dampeners to optimize ride quality and control.
Most active suspension systems will perform a circuit check when the system wakes up. The system will send 5 to 12 volts to the actuators and ride height sensors. The system is also looking at the resistance in the circuit, and the amount of voltage dropped. If the system detects an open, short or voltage outside of the specifications, it will set a code. Next, the control module will fully open and close the valves in the struts. If the system does not detect any irregularities, the system will go into an active mode.
Looking for these self-diagnostic signals can be performed using a meter. You may have to use a bypass harness or back probe the connector. If the system detects any problems, the system will go into a passive mode.
Sometimes servicing an active suspension is like rebuilding an engine with a new crankshaft and reusing the old bearings and valve springs. When a new active strut is reassembled with the old and tired spring and strut plate, the results can be less than desirable.
Upper strut mounts and bearings can be hammered to death. The upper strut mount essentially supports the vehicle weight and counters both braking and acceleration torque. Most mounts are sandwiches of rubber, metal and bearings. Over time, the rubber can lose its ability to isolate the suspension from the body. Bearings can also seize and bind, causing the vehicle to have steering problems.
Look up the ride height specifications and measure ride height front and rear, and on both sides of the vehicle. If ride height is less than specifications, the problem is most likely one or more weak springs that should be replaced. Springs should typically be replaced in pairs to maintain the same ride height side-to-side.
Weak springs also are more likely to fail. The springs on many late-model vehicles are thinner to reduce weight and have an outer plastic coating to protect the metal from corrosion. If this outer coating is cracked or damaged, corrosion can form a hot spot that eats into the spring, weakens it and eventually causes the spring to break.
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By Counterman
Westar Distribution LLC, a leading aftermarket supplier of engine & transmission mounts and air suspension components announces the release of 40 new Air Suspension Components, Engine & Transmission Mounts, Torque Strut Mounts, and Center Support Bushings servicing in excess of 35,000,000 vehicles in operation today in the US & Canada covering Acura, BMW, Dodge Truck, Ford Sport Utility, GMC Trucks, Honda, Hyundai, Jeep, Lexus, and Toyota vehicles. These newly released items are all in stock and ready for immediate shipment.
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