The hydrostatic power train is a dual path hydrostatic transmission with high pressure, closed drive loops. The dual path system allows the machine to perform a pivot turn and the dual path system allows the machine to counterrotate.
Each drive loop consists of a separate piston pump for each track and of a separate piston motor for each track. The piston pumps are overcenter pumps and the piston pumps provide oil flow for forward travel and for reverse travel. Travel direction is determined by the direction of flow from the piston pump. The piston motors are infinitely variable and the piston motors provide a range of ground speeds. The piston pumps also affect the machine's ground speed. First, the pumps upstroke in order to provide the desired speed. The motors will destroke if more speed is commanded.
 | |
| Illustration 1 | g01839605 |
(1) Cooler Group (2) Hydraulic oil filters (3) Final drives (4) Hydrostatic pressure taps and hydraulic taps (5) Hydrostatic motors (6) Left side hydrostatic pump (7) Hydraulic block (8) Hydraulic Tank (9) Charge Pump (10) Right side hydrostatic pump | |
 | |
| Illustration 2 | g01946357 |
(11) Machine ECM (12) Backup alarm (13) Parking brake solenoid (14) Override solenoid (15) Right pump, forward solenoid (16) Left pump, forward solenoid (17) Left pump, reverse solenoid (18) Right pump, reverse solenoid (19) Left motor solenoid (20) Right motor solenoid (21) Brake pedal position sensor (22) "G-Port" pressure sensor (23) Engine speed sensor (24) Speed sensor for the right motor (25) Speed sensor for the left motor (26) Sensor for the left steering pedal (27) Sensor for the right steering pedal (28) Throttle position switch (29) Armrest switch (30) Operator presence switch (31) Parking brake switch (32) Transmission control lever (33) Speed select switch (34) Transmission control lever (joystick) (if equipped) (35) Forward and reverse control (36) N/O (37) N/C (38) Service brake pedal switch (39) Implement ECM (40) Can "A" (41) Engine ECM (42) Cat Data Link (CDL) (43) Signal "A" (44) Signal "B" (45) Hydraulic oil temperature sensor | |
The electronic hystat control system controls the hydrostatic transmission functions. The hydrostatic transmission responds to inputs from the operator. Also, the hydrostatic transmission responds to inputs from the sensors. The electronic hystat control system controls the following items:
- The displacements of the hydrostatic drive pumps and motors
- The output for the backup alarm
- The state of the hydrostatic transmission override valve
- The state of the parking brake valve
The system also provides engine overspeed and underspeed protection. In an overspeed condition, the system automatically adjusts the current that is supplied to the hydrostatic transmission pumps and motors in order to slow the machine. Engine underspeed protection is provided by decreasing the control currents to the hydrostatic transmission pumps and to the motors. This is in response to the low engine speeds and to the engine lug.
Operator Presence Determination
Machine operation will be enabled or machine operation will be disabled based on the operator presence status. The operator presence status will be set to "Operator Not Present" if one of the following conditions is true:
- The left armrest is tilted upward.
- If the operator is not sensed in the seat, the brake pedal is not depressed and the travel speed is zero.
In all other situations, the operator presence status will be set to "Operator Present".
If the operator presence status is "Operator Not Present", the transmission and implement controls will be inoperable.
If the operator presence status changes from "Operator Not Present" to "Operator Present", the parking brake switch must be engaged and then disengaged in order to allow the transmission and implements to be activated.
If the operator presence status changes from "Operator Present" to "Operator Not Present" while the machine is in motion, the machine will not stop. If the machine is in motion, the machine will stop immediately when the left armrest is raised.