Toro Groundsmaster 4500-D Series Service Manual page 118

Forward Direction (continued)
Reverse Direction
Hydraulic System: Hydraulic Flow Diagrams
When in LOW mode position with the traction pedal pushed in the forward
direction, oil from the piston pump is directed to the front wheel motors and rear
axle motor through a parallel system. Oil flow to the front wheel motors drives
the motors in the forward direction and then returns to the piston pump. Oil flow
to the rear axle motor drives the motor in the forward direction. Oil returning from
the axle motor enters the rear traction manifold at the M8 port. Flow bypasses
the PR cartridge through the CV check valve, out manifold port P2 and returns to
the piston pump.
When going down a hill, the tractor becomes an over-running load that drives
the front wheel and rear axle motors. In this condition, the rear axle motor could
lock up as the oil pumped from the motor increases pressure as it returns to the
piston pump. To prevent rear wheel lock up, an adjustable relief valve (RV) in
the rear traction manifold reduces rear axle motor pressure created in down hill,
dynamic braking conditions.
The traction circuit operates essentially the same in reverse LOW mode as it
does in the forward direction. However, the flow through the circuit is reversed.
Oil flow from the piston pump is directed to the front wheel motors and also to
the rear traction manifold. The oil to the front wheel motors drives them in the
reverse direction and then returns to the piston pump. The oil to the rear traction
manifold enters the manifold at port P2 and flows through pressure reducing
valve (PR) which limits the down stream pressure to the rear axle motor to 27.6
bar (400 PSI) so the rear wheels will not scuff the turf during reverse operation.
This reduced pressure flow is directed out rear traction manifold port M8 to
drive the rear axle motor in reverse. Return oil from the rear motor returns to
the piston pump.
Page 5–16 Groundsmaster ® 4500-D/4700-D
19245SL Rev A