YOKE 8R7756 - Caterpillar

Construction
Illustration 1 g03637843
Main pump
(1) Front pump regulator
(2) Rear pump regulator
(3) Front pump
(9) Rear pump
(13) Center manifold
(16) Negative flow control regulator
(17) Power shift pressure regulator
(18) Charge pump
(32) Minimum angle stop screw
(33) Maximum angle stop screw
(A) Outlet port (front pump)
(B) Outlet port (rear pump)
(CR (A)) Pump signal pressure from rear pump
(CR (B)) Pump signal pressure from front pump
(H3 (A)) Port (negative flow control signal pressure)
(H3 (B)) Port (negative flow control signal pressure)
(L5 (A)) Port (power shift pressure)
(L5 (B)) Port (power shift pressure)
(MA) Port (front pump pressure)
(MB) Port (rear pump pressure)
(M1A) Control signal pressure (front pump)
(M1B) Control signal pressure (rear pump)
(PA) Port (pilot pressure)
(PB) Port (pilot pressure)
(S) Inlet port
(T1) Case drain port
(T2) Case drain port The main pumps consist of front pump (3) and rear pump (9). The pumps are connected in series by center manifold (13). Both pumps are variable displacement piston pumps. The displacement is controlled by regulators (1) and (2). The front pump and the rear pump are identical in construction and operation. The front pump and the rear pump are equipped with a common charge pump (18) that is located within center manifold (13).Charge pump (18) is a fixed displacement pump that consists of an impeller. Charge pump (18) draws oil from inlet port (S) in center manifold (13). The charge pump delivers oil to the front pump and the rear pump. The front pump delivers oil through outlet port (A) in center manifold (13). The rear pump delivers oil through outlet port (B) in center manifold (13).The pump regulators (1) and (2) are mounted on center manifold (13). Both the front pump and the rear pump have a regulator as part of the pump control system. The control system is identical for both pumps.Two pressure inputs are supplied to each regulator. The pressure inputs to the regulators control the output of the pump. Power shift pressure and negative flow control signal pressure are inputs to the regulators.Each regulator consists of power shift pressure regulator (17) and negative flow control regulator (16). The power shift pressure signal flows through port (L5 (A)) and port (L5 (B)) to each regulator. The negative flow control signal pressure flows to the regulators through port (H3 (A)) and port (H3 (B)). In addition, oil from the pilot pump is delivered to each of the front and rear pumps through port (PA) and port (PB). Note: Pilot oil that is delivered to port (PA) and port (PB) are inputs for pump control. The pilot pressure is used when the system pressure is lower than the pilot system pressure.Operation
Illustration 2 g03396981
Main pumps (sectional view) (typical example)
(3) Front pump
(9) Rear pump
(11) Inlet port
(13) Center manifold
(19) Swashplate
(20) Slipper
(21) Plate
(22) Piston
(23) Barrel
(24) Passage
(25) Port plate
(26) Shaft
(27) Rod
(28) Actuator piston
(29) Impeller
(30) Inlet passage
(31) Coupling
(32) Minimum angle stop screw
(33) Maximum angle stop screw
(34) Guide
(35) Spring
(36) Rod
(37) Spring
(38) Actuator piston
(39) Barrel
(40) Swashplate
(41) Shaft
(42) Passage The engine crankshaft drives the hydraulic pumps. The engine is connected to shaft (26) through the coupling in the flywheel housing. Shaft (26) is connected to shaft