1、 附录 2 英文翻译 TRANSMISSION TYPES AND OPERATION Travel-speed-changing systems found in tractors vary considerably particularly with respect to the number of speeds, kinds of gears, and methods of shifting. Based on these factors, transmission types can be classified as (1) sliding spur gear, (2) constan
2、t-mesh with shifting collars, (3) Synchromesh, and (4) hydrostatic. Also with respect to changing speeds, it can be done manually with a hand-lever or automatically by hydraulic pressure. These variations will be explained in connection with the descriptions of different makes of tractor transmissio
3、ns. In general, the smaller sizes of tractors, 20 to 40 PTO hp use simpler transmissions with fewer travel speeds, while the larger sizes have speeds ranging from six or eight to twelve or sixteen. In such cases, provision is made for shifting from the low-range to the high-range speeds or vice vers
4、a while the tractor is in motion, and without disengaging the master clutch and coming to a dead stop. These advantages, in turn, permit a closer and more convenient adjustment and a quicker response of power, torque, and tractive ability of the tractor to the specific drawbar-load conditions and re
5、quirements. Plain Spur-Gear Transmission Figure 18-7 illustrates the design and operation of the type of transmission originally used in earlier tractors and still used in some small, current models. As shown, the different speeds are obtained by sliding gears of a certain size into me h with others
6、 of another size. Reverse requires an additional single gear on a separate short shaft. The entire mechanism operates in an oil bath in a special housing. The bearings may be plain or antifriction type. The different speeds are obtained by a manually operated lever attached to certain gears in such
7、a manner as to slide them into mesh with others that are stationary. These changes can only be made with the main clutch disengaged and the tractor stationary. Figure 18-8 shows a similar transmission used in a high-clearance row-crop tractor. Deere Horizontal Two-Cylinder Transmission Figure 18-9 s
8、hows a two-cylinder, horizontal engine equipped with a four-speed sliding gear transmission and spur-gear final drive for the axles and wheels. Allis-Chalmers Dual-Range Transmission The AUis-Chalmers dual-range (Fig. 18-10) consists of an eight-speed, constant-mesh unit with helical gears and shift
9、ing collars. A special double-unit, hand-lever-operated disk clutch that runs in oil has three positions: Low-range, High-range, and Neutral. The change from one range to the other can be made by means of this clutch and a hydraulic assist mechanism while the tractor is moving. Ford Dual-Power Trans
10、mission Figure 18-11 illustrates a manual shift transmission, which normally has eight forward speeds and two reverse speeds. However, if the tractor must operate at slower speeds and under heavier draft conditions, this transmission can be equipped with an optional gear assembly that will provide e
11、ight additional forward and four additional reverse speeds. The shift is made by a single lever without stopping the tractor. The travel speed is reduced, but the pulling power is increased to permit the handling of unexpected or difficult situations. Deere Hydraulic Hi-Lo Range Tractor Figure 18-12
12、 is a six-cylinder, 80 hp tractor having a two-range transmission with twelve forward and three reverse speeds. Table 18-1 gives the travel speeds for each range. International Harvester 60 hp Tractor Figure 18-13 shows the complete power transmission train for an International Harvester 60 hp tract
13、or having two travel speed ranges with four forward speeds for each one. This is a constant-mesh synchronized transmission. A Hi-Lo-Reverse range lever permits shifting between forward and reverse for shuttle-type operation on back-and-forth operations. The entire power train is pressure lubricated.
14、 The wet-disk brakes are hydraulic actuated and self-adjusting. Deere Four-Wheel-Drive Tractor Figure 18-14 illustrates the power train and transmission design for a four-wbeel-drive tractor. Power is first transmitted to two sets of primary master gears. These gears, in turn, transmit power to two
15、sets of change-speed gears by which the different ravel speeds are obtained. These gears then transmit the power to the front and rear final-drive gears and axles. Hydraulically operated front and rear differential locks simultaneously lock both axles. Both locks are operated by a single foot pedal
16、which can be engaged or disengaged on the go. Track-Type Tractor Transmissions The transmissions for the track-type tractors are not unlike those in wheel machines except that the steering mechanism is incorporated in them. That is, the ordinary wheel tractor s propelled by the rear wheels and guide
17、d by means of the front wheels, whereas the conventional track-type tractor, having but two traction members, must be both propelled and guided through them. Caterpillar Transmission Figure 18-15 shows the change-gear set for the Caterpillar tractor. The power is transmitted to a countershaft by mea
18、ns of bevel gears； then, through two steering clutches located on this countershaft on each side of the bevel gear, to the spur-type final-drive gears； and then to the sprocket. Steering is accomplished through the multiple-dry-disk steering clutches； that is, by means of hand levers, either clutch
19、can be disengaged, which obviously cuts off the power to that particular track and causes the tractor to make a turn. Each clutch is equipped with a foot-operated brake that acts on the outside of the clutch drum carrying the driven plates. If a quick, short turn is desired, not only is the clutch r
20、eleased but the brake for that particular clutch is actuated and the track movement virtually stopped on the one side. With all the power going to the other track, the machine obviously will turn very short. By pressing on both brakes at the same time, the machine can be stopped almost instantly. It
21、 should be noted that a differential is unnecessary in the Caterpillar transmission. Caterpillar Planetary Transmission Figure 18-16 shows a planetary transmission and power train for a track-type tractor. Power from the engine is first transmitted to the torque converter by the crankshaft, then to
22、the planetary power-shift transmission. This unit consists of a certainnumber of planetary units that vary in size. Large clutch packs surround each gear set and engage with special hydraulic modulation for smooth, cushioned shifting. The clutch plates and gears are cooled by oil. For operations tha
23、t do not require frequent direction changes this tractor can be equipped with a gear-type transmission. Hydrostatic Drives and Power Transmission The basic principles involved in the operation of hydrostatic drives are explained in Chap. 20. A hydrostatic drive mechanism consists essentially of two
24、major units, namely, a positive displacement pump driven by the original power unit and a positive displacement motor, which receives its energy from the pump. In other words, the tractor engine develops and transfers mechanical energy to the pump. The pump unit then converts this mechanical energy into hydraulic energy, which operates the motor unit and thus, in turn, produces mechanical energy to propel the tractor.
