TUBE ASSEM. 7N4807 - Caterpillar

Background
The main purpose of the seat is to support the machine operator. The seat should provide a level of comfort that allows the operator to operate a machine in a safe and comfortable environment. A safe and comfortable environment has been shown to impact the productivity and the job satisfaction of the operator. A safe and comfortable environment plays a significant role in the first impression a customer gets when operating a new machine.Suspension System Background
Earthmoving machines have a seat suspension for two reasons:
Keep the operator isolated from the harsh machine inputs
Keep the operator connected to the machine controls and the machine as a wholeThe three main components of a suspension system are:
the Mass
the Spring
the DamperMass
The mass represents the object to be isolated from an input excitation (in this case the operator).Spring
The spring is a device that is used to hold up the weight of the mass (in this case is an air spring).The characteristic property of a spring is stiffness. Stiffness is a measure of energy storage. The act of compressing a spring stores energy in the spring which can later be released when the compressing force is removed. A spring-mass system would keep bouncing if not for the damper. Damper
The damper is used to limit the amount of motion of the system (in this case is a hydraulic damper).The characteristic property of a damper is damping. Damping is a measure of energy dissipation. The act of compressing a damper dissipates energy which cannot be recovered when the compressing force is removed. The damper keeps the spring-mass system from bouncing excessively. A hydraulic damper works on the principle that fluid is forced from one chamber to another through a series of restrictive passages. As the fluid passes through the passages, the kinetic energy of the system is dissipated and transformed into viscous heating of the damper fluid.
Illustration 1 g03496617
Illustration of the influence of damping on ride performanceA common misconception is that changing a damper affects stiffness. Changing a damper may increase the damping. Changing a damper may result in a harsher ride (or "stiffer" ride) but the stiffness of the system has not changed. The only way to affect stiffness is by changing the spring.Suspension System Types
There are three types of suspension system: passive, active, and semiactive suspension. The passive suspension is the type of suspension that most people are familiar with. Most automobiles, motorcycles, trucks, trains, busses, and similar machines. have a passive suspension at each wheel. What makes a suspension passive is the fact that the stiffness and damping cannot be changed in real time in response to the input excitation. A passive system has no means of adding energy to the system and merely dissipates the energy that the system is exposed to. A passive system must be tuned for the harshest conditions. This tuning often leads to less than ideal ride performance in everyday operation.The polar opposite of a passive suspension system is the active suspension. In an active suspension, the damper (and sometimes