Traction Circuits - Toro Groundsmaster 360 Service Manual

Traction Circuits

Forward Direction
Groundsmaster 360
16225SL Rev C
The traction system of the Groundsmaster 360 machines consists of a
transmission that is directly connected to, and driven by a coupler attached to
the engine flywheel. The traction components include a transmission with 2
independent closed loop circuits, 2 rear wheel motors, 2 front wheel motors,
and CrossTrax™ traction manifold assembly. Each of the closed loop circuits
includes a variable displacement, slipper foot design piston pump which provides
hydraulic flow for 2 wheel motors. One piston pump provides flow to the right
rear and left front wheel motor, and the other piston pump supplies flow to the left
rear and right front wheel motor. The swash plate in each of these piston pumps
is controlled by the operator traction pedal through a linkage system.
The angle of the swash plate determines the pump flow and ultimately traction
speed. When a traction pedal is moved a small amount, a small swash plate
rotation results in low pump output and lower traction speed. When the traction
pedal is moved fully, the pump swash plate rotates fully to provide maximum
pump output flow and traction speed.
With the engine running and the traction pedal in the N
swash plates of the piston pump are held in the vertical position, providing no
flow to either of the wheel motors and the machine remains stationary. The
transmission reverse check valves include an orifice which makes it easier to
locate the transmission neutral position.
When the traction pedal is pushed forward, the rod connected to the traction
linkage positions the swash plates in the piston pumps to provide hydraulic fluid
flow from the transmission (port A and C). This fluid flows to the rear wheel
motors and then to the opposite front wheel motor (e.g., right rear then left front)
and turns the motors in the forward direction. The fluid flow from the front wheel
motor returns to the transmission (port B or D) and is continuously pumped
while the traction pedal is pushed forward. As the traction load increases, the
forward traction circuit pressure can increase to the relief-valve setting of 27,600
kPa (4,000 psi). If the circuit pressure is more than the relief-valve setting, fluid
flows through the forward relief valve in the transmission to the low-pressure
side of the closed loop traction circuit.
The piston pumps use a small amount of hydraulic fluid for internal lubrication.
The fluid is designed to leak across the pump parts into the transmission case
drain. This leakage results in the loss of hydraulic fluid from the closed loop
traction circuits that must be replaced. A charge pump in the transmission
supplies hydraulic flow for maintaining 810 to 850 kPa (117 to 123 psi)
to the low-pressure side of the 2 traction circuits. The charge pump also
provides pressure for the transmission PTO drive system. The charge pump
replenishes the closed loop traction circuits with fluid from the hydraulic tank.
The charge-relief valve in the transmission maintains sufficient pressure so that
the charge-pump flow is guided past check valves to the low-pressure side of
each traction circuit. The charge-pump flow in excess of system requirements is
released through the charge-relief valve back to the hydraulic tank.
When operating the machine in a forward, straight direction (not turning),
transmission fluid flow to the 2 traction circuits routes from a rear wheel motor to
the opposite front wheel motor. Both the traction circuits require similar flow to
drive the wheel motors so minimal circuit flow change is provided through the
traction manifold assembly and balancing fluid lines.
When turning the machine in a forward direction, the 4 wheel motors require
different flows due to different wheel distances traveled going around the corner.
The balancing lines and the traction manifold assembly allow the 2 traction
circuits to be connected so differences in the wheel motor flows can be achieved.
Page 4–15 Hydraulic System: Hydraulic Flow Diagrams
position, the
EUTRAL