Copyright Goodheart-Willcox Co., Inc. Heavy Equipment Power Trains and Systems 826 Caterpillar Differential Steering Joystick Controls Caterpillar differential steering controls use a single joystick control called a steering tiller for controlling the machine’s direction, speed, and steering. Refer to Figure 24-18. When the operator presses the tiller forward, the tractor steers to the left. The tractor steers to the right when the operator pulls the tiller backward. When the operator rotates the steering tiller grip forward, the tractor is propelled forward. The tractor is propelled in reverse when the operator rotates the tiller grip backward. Case, New Holland, and Fiat Power Steering The Case 1650K and 1850K (Series I, II, III), New Hol- land DC150, DC150.B, DC180, and DC180.B, and Fiat Kobelco D150 and D180 dozers are equipped with power steering, which is the term Case New Holland (CNH) uses to describe differential steering. Note that later CNH model dozers, such as Case 750M–2050M dozers, and the New Holland D125C, D150B, D150C, D180B, and D180C dozers are equipped with dual-path hydrostatic drives rather than differential steer. The steering differential receives input from the powershift transmission through the bevel gear set. The bevel gear set delivers input to the left and right ring gears. The hydrau- lic steering motor is linked to both sun gears through a series of spur gears and external- toothed shafts. Output to the left and right axles is provided by the planetary carriers. See Figure 24-19. Propel in reverse Propel forward Steer right Steer left Goodheart-Willcox Publisher Figure 24-18. A Caterpillar differential steering control joystick is called a steering tiller. The top push button is for upshifting the powershift transmission, and the lower push button is for downshifting the powershift transmission. Goodheart-Willcox Publisher Figure 24-19. In the CNH “power steering” differential steering system, two planetary gear sets receive ring gear input from the powershift transmission. The two sun gears receive input from the hydraulic steering motor. Output to the left and right axle shafts is delivered by the planetary carriers. The axle shafts drive a bull-and-pinion final drive that also drops down the power flow to the drive sprocket commonly used on low-sprocket crawlers (non-elevated dozers) as explained in Chapter 17, Final Drives. Sun gear long shaft Sun gear short shaft Right axle shaft Right planetary carrier Right ring gear Right sun gear Bevel ring gear Left sun gear Powershift transmission input Hydraulic steering motor Left ring gear Left planetary carrier Left axle shaft