TUBE AS 3356693 - Caterpillar

CARM System Components
Illustration 1 g03496821
Wheel Tractor Scraper seat suspension and the CARM system components (A) Controller (B) Sensor (C) DamperThe CARM system is comprised of four main components: The damper, the sensors, the controller, and the control program. Refer to Illustration 1 and the discussed detail in the following sections.Damper
The active component of the damper is the valve which is opened and closed using a voice coil.One of the main features of the CARM damper is that unlike most semiactive systems, the unenergized state is highly damped. This factor is significant in a malfunction of the electrical components on the seat. The damper will default to the highly damped state. The change in seat performance provides enough damping in the suspension to allow the operator to finish the shift. However, the increased discomfort indicates to the operator that something is wrong with the seat and must be reported for service. There are no serviceable parts inside the damper.Sensors
The valve assembly contains a position sensor which is used in the control feedback loop of the valve. Additionally, a temperature sensor is used to monitor the temperature in the system. These two sensors are used primarily for component level performance and monitoring. The two sensors are built into the damper and are not serviceable.In addition to the sensors inside the valve assembly, there is a displacement sensor built into the suspension to monitor the travel of the suspension. The displacement sensor is primarily used to establish the proximity of the endstops. This sensor is a 2-part sensor that is calibrated at the factory and must not be tampered with. If one of the two parts is moved, the calibration is no longer accurate and the performance of the seat will be compromised.Additionally, there is a pressure sensor that measures the pressure inside the air spring. This sensor is used with the displacement sensor to determine the weight of the operator. Both these sensors are instrumental in the control program that drives the behavior of the suspension and ultimately the ride perception of the operator. The pressure sensor is serviceable. The displacement sensor is not.Controller
The controller is housed in a small, sealed, weatherproof enclosure mounted inside the seat suspension. There are no serviceable parts inside the enclosure.Control Program
The control program is the key to a successful semiactive system. The control program reads the input signals from the various sensors. The control program creates an output current signal that adjusts the damping of the suspension up to 1000 times per second. The control program is built upon a number of independent control schemes that kick in depending on the conditions the sensors pick up. Below is a brief summary of the various control programs and functions:
Default state – the state where all current is shut off to the damper. The Default state is the fail-safe mode that the damper defaults to in case of malfunction or loss of power
Normal operation – the program that is active most of the time. Normal operation selects