CONSTRUCTION AND OPERATION
The construction and operation presented here is based on a single forward-and-reverse speed PTO for driving a vehicle front winch. This assembly has a forward, reverse, and neutral shift position.
A cast-iron case provides the housing and mounting for all of the shafts and gearing of the assembly. A large, flanged opening on the side of the gearbox provides the mounting surface. The mounting flange will match the mounting surface made on the side of the transmission or transfer assembly that is to mount the PTO. Machined openings in the front and rear of the case provide mounting points for the shafts. Some cases contain a drain plug for the lubricant.
All shafts in the gear case are mounted in line with the vehicle power train or from front to rear of the vehicle. Output shafts may extend outside the front or rear of the PTO case. Those driving the front winch will extend from the front. Tapered or straight roller bearings may be used to mount shafts in the case. Shift shafts are made to slide forward and rearward in a drilled passage in the case as in the manual transmission. The shifter fork is bolted or pinned to the shifter shaft, and a recess or detent is made into the shifter shaft for each shift position. A steel ball under pressure is mounted in a passage at a right angle to the shifter shaft and fits into the recesses.
The PTO idler gear is mounted very near the large flange on the side of the case. This method of mounting causes the idler gear to extend outside the PTO case. When the PTO is bolted to a transmission or transfer, the idler gear extends into the larger gearbox to mesh with a driving gear. The idler gear is a double gear with two sets of gear teeth. One set of gear teeth is designed to mesh with a drive gear in the transmission, and the other will mesh with the reverse gear. The reverse gear is a double gear that is mounted to one side and is in constant mesh with the idler gear. Straight roller bearings are used to mount the reverse gear to the shaft. The sliding gear, which is made to mesh with both the idler reverse gears, is mounted on the spline of the output shaft. Tapered roller bearings at each end mount (support) the output shaft in the PTO case. The sliding gear can slide to the front or rear on the output shaft. A part of the output shaft extends to the outside of the case. An oil seal and retainer prevents loss of lubricating oil where the output shaft passes through the case. A propeller shaft drive yoke is mounted on the end of the output shaft, outside the PTO case, and is secured by a metal key which fits into a slot in the shaft.
When the PTO is mounted on the side of the transmission, the shift lever extends up into the cab of the vehicle.
A slot cut into the cab floor allows the lever to be moved back and forth.
A latch for holding the lever in the neutral position, when the PTO is not in use, is mounted to the cab floor.
In the neutral position, the PTO idler gear is in constant mesh with a gear on the transmission countershaft. The PTO reverse gear is in constant mesh with the idler gear. The sliding gear is in the neutral position between the idler and reverse gears. When the vehicle clutch is engaged by the operator, the transmission countershaft will drive the idler and reverse gears of the PTO. Since the sliding gear is not in mesh with any driving gear, no power reaches the output shaft.
Now let's see what happens when a PTO used to operate a winch is put into operation.
To wind in the cable, the vehicle operator releases (disengages) the clutch and moves the PTO control lever. As the top of the shift lever moves forward, the lever pivots on the mounting pin and the lower end of the lever moves rearward. The shift shaft, which is connected to the lower end of the control lever, moves to the rear. At the same time, the shift fork mounted on the shift shaft is moving the sliding gear inside the PTO to the rear. The sliding gear moves along the splines of the output shaft into mesh with the idler gear. When the shift is complete, the steel ball under spring pressure moves into the recess on the shift shaft to hold the gears in position. As the engine clutch is engaged, the transmission countershaft drives the PTO idler gear, sliding gear, and output shaft. The output shaft drives the winch propeller shaft in the proper direction to cause the winch to wind in the cable.
To drive the winch so that the cable will unwind from the drum, the vehicle operator releases the engine clutch and moves the PTO control lever to the rear. This forces the shifter shaft, fork, and sliding gear to move forward so that the gear meshes with the reverse gear. The steel ball under spring pressure holds the shifter shaft in the selected position. As the engine clutch is engaged, the transmission countershaft drives the idler, reverse, and sliding gears. Since the sliding gear is splined to the output shaft, the shaft is driven in the same direction as the gear. The winch propeller shaft is driven by the output shaft in the proper direction to unwind the cable from the winch drum.
PTO assemblies mounted low on the side of a larger gearbox are below the level of the lubricating oil. This construction allows the transmission lubricant to flow freely in and out of the PTO. Proper lubrication is assured for all PTO parts in operation below the level of the gear oil. On those PTO assemblies mounted above the level of the lubricant, oil is splashed into the assembly by the transmission countershaft.
The heavy-duty-type PTO is designed to mount on a standard six-hole or six-stud PTO opening and is designed to mount on the left or right side of the driving mechanism. The shifter shaft extends through each end of the case so that the shifting control linkage may be attached at either end. The output shaft extends from the front of the case and is provided with a woodruff key for mounting the winch propeller shaft companion flange. Boots are installed over the ends of the shifter shaft to protect the surface of the shaft. The PTO input gear is a cluster composed of a helical gear, which is constantly in mesh with the helical gear of the transmission reverse idler gear, and the driving gear, which is of spur-tooth construction.
The PTO has two forward speeds, neutral, and one reverse speed. A shifting mechanism provides selection of the desired speed and direction of rotation of the output shaft. The neutral position of the shifting mechanism disengages the output shaft gears from the driving gear. |