760432 Caterpillar "G" Series Motor Grader Transmissions and Transmission Controls W. W. Blake and J. M. Gorreil Caterpillar Tractor Co. A decision was made to redesign the motor grader line to incorporate articulation and hydraulic implements. Fig. 1 shows the new models with their horsepower, weight, and length. Fig. 2 shows a photograph of the final vehicle design for one of these - the 120G. Transmission design objectives for these vehicles included: 1. Precise ground speed control 2. Efficient power transmission 3. Smooth power shifts 4. "Inching" capability 5. Meet 40 Km/hr (24.9 mph) European travel speed 6. Easy operation 7. Meet field determined rimpull require­ ments 8. Good reverse speed selection 9. Provide integral parking/emergency brake 10. Parts and/or tooling commonality between models 11. Minimize cases and covers 12. Provide good serviceability 13. Meet cost targets 14. Provide acceptable sound levels Because of precise ground speed control, overall efficiency, ease of operation, and This paper describes the concept and de­ sign of the Caterpillar "G" series motor grader transmission and transmission controls. Com­ ments on vehicle performance, power train, and oil system requirements are included. Countershaft directional clutches are combined with six or eight speed planetary 1524 ranges for this family of articulated motor graders. The pilot-operated hydraulic control pro­ vides smooth rapid gear ratio changes and "inching" modulation for the pressure lubed directional clutches. ABSTRACT Downloaded from SAE International by North Carolina State Univ, Wednesday, September 19, 2018operator acceptance, direct drive power shifts are ideally suited for this application. Marketing and field research studied exten­ sively the market and performance requirements for motor graders. This study, along with a European 40 Km/hr (24.9 mph) travel speed requirement, and extensive previous experience in six speed direct drive power shift transmis­ sions in 125 and 150 hp (93 - 112 Kw) machines and a nine speed 200 hp (149 Kw) motor grader, were instrumental in speed ratio selections. Six forward and reverse speeds were decided upon for the four models between 125 hp (93 Kw) and 150 hp (112 Kw). They were to adhere to the 40 Km/hr (24.9 mph) travel speed and provide second forward as the primary or "optimum" working range. Second forward ground speed was targeted at 4 mph (6.44 Km/hr) for the standard machine on the basis of engine torque rise, implement response, tire size options, rimpull requirements for a variety of functions and ground condition, operator preferences, and vehicle weight variations (due to options, etc.). With 2F and 6F established, the remaining speed ratios were evenly spaced to provide good ground speed coverage and responsive engine recovery for working shifts. Therefore, a six speed transmis­ sion with 60% steps was required. The two larger models have generally higher rimpull requirements because of more severe applications. This, coupled with the need for good engine response for these higher loaded shifts and a wider range of rimpull requirements, resulted in a broader range eight speed with 40-50% step ratios. Second and third forward were targeted as the primary working speeds and, via the same reasoning used on the six speed, yielded 3.3 mph (5.3 Km/hr) for second forward and 4.5 mph (7.2 Km/hr) for third forward for the standard machine. The 40-50% steps result in a lower ground speed in IF (compared to the six speed) and a higher top speed. Another requirement for motor grader transmissions is the ability to "inch." Fine 1525 grading and close quarter operation are integral functions for this machine, and the transmission must perform this operation. All vehicles, except the 180 hp (134 Kw) model (which has faster reverse speeds) have equal forward and reverse speeds. The transmission reductions (fro