Collision Repair Training | Australia
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Collision Repair Training | Australia
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Current Events/News: Advantage Online: 2004 Archives
This article may be distributed and reproduced, but only by following the requirements stated in Permission to Reproduce. WHAT'S IN A SEAT?
September 27, 2004 -There's more electromechanical equipment than ever built into seats on vehicles coming into collision repair facilities these days. Most technicians are probably familiar with power seats and all the applicable parts. Power seats have been around for quite a few years. If you're working on a newer model vehicle, there may be a lot more in that seat than you think (see Figure 1). Today's vehicles have seats that may contain such parts as:
Side AirbagsA seat-mounted side airbag is designed to limit the force a vehicle occupant experiences during a side-impact collision (see Figure 2). Depending on the physical dimensions of the airbag used, the occupant may have side-impact protection from their hips up to their head. These airbags may be located in both the front and rear seats, depending on the vehicle maker. The 2004 Audi A8 has rear seat-mounted airbags. As early as 1996, Mercedes-Benz began using rear seat-mounted airbags. Sensors may be located in the passenger seatback. Seat-mounted side airbags are either electronically or mechanically operated. A mechanical seat-mounted side airbag uses no electronics such as computers or crash sensors. The 1998–2003 Volvo C70 uses a mechanical side airbag in both front seats of the vehicle. Seat Position SensorsSeat position sensors determine the occupant's position in relationship to the airbag deployment zone and are used to determine which type of airbag deployment may be necessary. Seat position sensors are located on the seat track and will identify if the seat is forward or rearward of a threshold point. A seat position sensor may be located on either the driver or passenger seat. Occupant Classification SystemAn occupant classification system (OCS) can detect the presence of an occupant in the passenger seat and deploy the passenger airbag accordingly (see "Advancements in Passive Restraints" in the January 19th Advantage Online). This is done using a seat-occupied sensor. During a collision, if the passenger seat is occupied, the airbag will deploy. If it is not occupied, the airbag will not deploy. Depending on the occupant, seat position, and the use of seat belts, the OCS determines which passenger restraint system to deploy. The OCS uses various input information to determine which type of deployment, if any, should occur.
These measurements are determined by the occupant weight using either a pressure bladder or strain gauges in the passenger seat (see Figure 3). Similar to a pressure bladder, a strain gauge system determines occupant weight and communicates with the occupant classification module to activate or disarm the passenger airbag. Specific parts of a strain gauge OCS include four strain gauge sensors, located at each corner of the seat frame assembly. Anti-Whiplash SystemsEnergy-absorbing seats are designed to limit occupant injury, such as whiplash, during rear impacts. These seats provide head protection by the seat changing position with the occupant's rearward movement. On the Volvo and Jaguar systems, it is part of the hinge mechanism, called Whiplash Protection System (WHIPS). BMW uses a deforming floorpan under the seat. Energy-absorbing seats may move in two directions. The first direction of movement is up to protect the occupant's head, and the second direction of movement is backwards to help absorb the impact forces from the collision. Seat Positioning SystemsPower seat systems may have two-way, four-way, six-way, or eight-way adjustments. Depending on which option the vehicle is equipped with, the seat can be moved forward/backward, up/down, front and rear tilt, and recline. A motor, or motors, in the seat assembly control power seat movement. Multiple motor power seat systems use integrated gears to move the seats in a variety of directions. Memory SeatsMemory seats return seats to a preprogrammed setting. Most vehicle makers use the same type of operating system for memory seats. These systems operate using seat adjuster motors, controlled by a memory seat module and a seat adjuster switch. The memory seat module stores the motor positions by recording the feedback voltage of each position sensor. When the driver operates the memory recall switch, the memory module moves the motors until the feedback voltage of the position equals the feedback voltages stored in the computer memory. Lumbar SupportA motor may be used to provide lumbar support. Some systems use an air pump to pump air into a bladder located in the seat back. A typical power lumbar system consists of a lumbar switch, motorized air pump, and a bladder. Some power lumbar systems use a motor instead of an air bladder to roll the lumbar support. Heated SeatsSome seats are heated. To heat the seats, heater elements are placed in the lower seat cushions and seat backs. The heated seat element is typically a fabric-type or mesh design that is adhered to the seat cushion. Similar to defrosting grids on the back glass, when a switch is activated, power is supplied to the seat relay module, which in turn provides power to the heater element. Most systems contain a thermistor to monitor the element temperature. A thermistor is a temperature-sensitive variable resistor. The relay module determines the seat cushion temperature by monitoring the signal voltage supplied to the thermistor. Once the seat reaches maximum temperature, the voltage supply is turned off. Cooled SeatsAs early as the 2000 model year, seats with the capability to cool have been available (this was available as an option on the 2000-model Lincoln Navigator). A thermoelectric device provides the cooling effect. A fan in the base of the seat and a system of air channels along with perforation in the upholstery allow the cooled air to reach the occupant. ConclusionSo, do you know what's in that vehicle seat you are working on? There just may be a lot more than you think. Troubleshooting or repairing any of these electronic systems requires more than knowing that these systems are present on a seat. Vehicle-specific repair information is required. A vehicle-specific scan tool, generic scan tool, or at least a DVOM is also required. To learn more about systems found in today's vehicle seats, look for the I-CAR programs: Power Accessories (PWR01) and Advanced Restraint Systems (RES02).
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