BODY A-PISTON 1S8417 - Caterpillar

Illustration 1 g03650667
Main control valve
(1) Left travel control valve
(3) Right travel control valve
(4) Straight travel PHMV Straight travel control valve maintains straight travel even though there is a swing operation or implement operation during travel. The straight travel control valve also improves pipelayer control or placement of timbers.When the machine travels without swing operation or implement operation, the pressure sensor for left travel and the pressure sensor for right travel are ON. The right joystick and left joystick are in the NEUTRAL position. The oil delivery from the front pump flows through left travel control valve (1) to the left travel motor. The oil delivery from the rear pump flows through straight travel control valve and right travel control valve (3) to the right travel motor. Because both travel circuits are separated, the machine continues to travel straight, unless a difference in travel resistance occurs between the right and left tracks.The straight travel system ensures the straight travel of the machine when other circuits are operated during travel. The rear pump and the front pump supply oil to the travel motors. During travel, if an implement operation or a swing operation occurs the oil supply to each travel motor will differ. This oil difference would cause the right travel motor and the left travel motor to rotate at different speeds. The different speeds will cause the machine to turn.The following actions occur when the straight travel control valve is activated.
The pressure sensor for left travel and the pressure sensor for right travel are ON.
The machine ECM senses an input signal from the left joystick or right joystick.
The swing circuit and implement circuits receive oil from the rear pump. When the machine is traveling, the swing circuit and implement circuits do not require a large amount of oil flow. The swing circuit and implement circuits are operated at speeds that are low enough for stable machine operation. The remainder of the oil is shared by the right travel circuit and the left travel circuit.
Illustration 2 g03400940
Section view of straight travel control valve (NEUTRAL position)
(1) Left travel control valve
(2) Straight travel control valve
(3) Right travel control valve
(4) Straight travel PHMV
(6) Pilot passage
(8) Passage
(9) Line (oil delivery from the front pump)
(11) Passage
(12) Line (oil delivery from the rear pump)
(13) Rear pump
(14) Front pump
(15) Passage
(16) Passage Pilot oil pressure is sent from the pilot oil manifold to straight travel PHMV (4). When only the travel levers/pedals are activated, straight travel PHMV (4) is not energized. Pilot oil flows to pilot passage (6) and straight travel control valve (2). The pilot oil pressure in spring chamber is high and straight travel control valve (2) is shifted by the combined force of the spring and pilot oil pressure in spring chamber. The oil delivery from the rear pump and the front pump flows in the following manner.
The oil delivery from the rear pump flows through line (12) to passage (11) in the center manifold section. The oil delivery from the rear pump separates into two flow