GENERAL
The transmission provides five forward speeds and one reverse speed and utilizes a floor shift lever design for gear selection. All forward gears are provided with synchromesh mechanisms that utilize inertial lock-key designs.
The transmission is unitized with the differential and housed in an aluminum case which is unitized with the clutch housing. The aluminum case is divided into left and right halves. Major features of the transmission are as follows: The clutch shaft has been extended to form a mainshaft, the countershaft combines the function of the final reduction drive pinion shaft, and the hypoid gear is "offset" to form a compact power train design. The forward gears are helical and feature high tooth-face strength, high engagement ratios and quiet operation. Reverse direction is achieved by engaging a selective-sliding reverse idler gear with the drive gear on the mainshaft and the driven gear on the 1st-2nd synchronizer hub of the drive pinion shaft. The 1st gear on the pinion side utilize sub-gear to reduce noise.
It is a compact, "full-time" transmission that utilizes a center differential provided with a viscous coupling at the rear of a transfer unit. The viscous coupling serves as a differential-action control.
The center differential utilizes a highly reliable, bevel gear. It not only delivers an equal amount of drive power to both the front and rear, but controls the difference in rotating speed between the front and rear wheels. A vicious coupling and center differential gears are located in the center differential case to connect the front and rear wheel drive shafts. With this arrangement, the transfer system realized a compact construction.
In addition, the viscous-coupling serves as a differential-action control to eliminate a mechanical lock mechanism.
Identifying Manual Transmission Case & Components. Scheme 325
Construction
The reverse check sleeve is bolted to the transfer case. The reverse accent shaft is inserted in the reverse check sleeve. On the smaller-diameter side of this reverse accent shaft, the reverse check cam is loosely mounted so that it can rotate, and the reverse check sleeve holds the reverse check cam in place with its stepped part.
The reverse return spring, which is inserted in the reverse accent shaft presses the shaft to the left. Further, the reverse check spring is placed in between the reverse check cam and reverse check sleeve, which forces the reverse check cam to the left and in the direction of rotation. Both springs are held down with the reverse check plate that is attached to the reverse check sleeve with the snap ring. The reverse accent shaft has a groove for reverse accent, in which the ball and reverse accent spring are put through a hole drilled in the reverse check sleeve.
Identifying Reverse Check Mechanism. Scheme 326
When 5th And Reverse Side Is Selected
The selector arm pushes the reverse accent shaft and reverse check cam simultaneously and moves to the 5th and reverse side.
Reverse Check Mechanism Operation (When 5th And Reverse Side Is Selected). Scheme 327
When Shift Is Made To 5th
The selector arm moves to the 5th side pushing the reverse accent shaft. When the selector arm pulls out of the reverse check cam, the reverse check cam is returned to the original position by the reverse check spring.
Reverse Check Mechanism Operation (When Shift Is Made To 5th). Scheme 328
When Shift Is Made From 5th To Reverse
The selector arm moves to the reverse side pushing the reverse accent shaft and runs against the selector cam that has already returned. The reverse check cam has a stopper, which hits against the reverse check plate. Thus, the reverse check cam cannot rotate further. Accordingly, the selector arm comes to a stop at a point where it has turned the reverse check cam to a certain degree (i.e., (N) position), and the reverse check cam is pushed back to the (N) position by the reverse accent shaft (i.e., the reverse return spring).
Reverse Check Mechanism Operation (When Shift Is Made From 5th To Reverse). Scheme 329
The center differential is composed of a mechanical differential and a viscous coupling and transmits the power from the transfer drive gear to the drive pinion shaft and the driven shaft.
The center differential has in general two functions; distributing engine torque to the front and rear wheel drive shafts equally, and absorbing the difference in rotating speed between the front and rear wheels during turns.
The differential with a viscous coupling, however, has the following function in addition to the above-mentioned functions. It generates viscous torque when spinning front or rear wheels have caused a rotating speed difference between the front and rear axles, limiting the differential action so that the optimum drive torque distribution may be attained.
Identifying Center Differential Components. Scheme 330
Mechanism Of Viscous Coupling
The viscous coupling housing contains a number of inner and outer plates which are arranged alternately. The inner plate has its internal perimeter fitted to the external side gear (rear) splines while the outer plate has its external perimeter fitted to the internal center differential case splines. A spacer ring is provided to position the perimeter of the outer plate. The inner plate has no spacer ring and moves slightly between the adjacent outer plates, along the side gear (rear) splined in the axial direction.
A mixture of silicone oil and air is sealed in the space inside the center differential case. An "X" seal ring prevents silicone oil from entering the transmission. This could occur when silicone oil is highly pressurized due to an increase in rotating speed difference between the front and rear wheels.
Identifying Mechanism Of Viscous Coupling. Scheme 331
"Hump" Phenomenon
Silicone oil is heated and expands as differential action continues. This crushes air inside the viscous coupling so that the silicone oil "charging rate" will increase. As differential action continues, internal pressure will abruptly increase so that inner and outer plates (alternately arranged) come in contact. This causes quick torque transmission to occur, which is called a "hump" phenomenon.
The "hump" phenomenon eliminates the rotating speed difference between the center differential case and side gear (rear) (which results in a state similar to "direct coupling"). This in turn decrease internal pressure and temperature. The viscous coupling returns to the normal operation. (The "hump" phenomenon does not occur under normal operating conditions.)
During normal driving (when there is no speed difference between the front and rear wheels), the center differential delivers drive power to the front and rear wheels at a torque ratio of 50:50.
When a rotating speed difference occurs between the front and rear wheels, the center differential action is controlled by viscous coupling so that optimum drive forces are automatically distributed to the two.
During Normal Driving
During normal straight driving (on flat roads at constant speed), all four wheels rotate at the same speed. The center differential delivers engine torque to the front and rear drive axles. The viscous coupling does not perform the differential-action control because there is no rotating speed difference between the front and rear drive shafts.
Center Differential Delivering Engine Torque To Front & Rear Drive Axles. Scheme 332
During Turns At Low Speeds
During turns at low speeds, a rotating speed difference occurs between the front and rear wheels, as well as the left and right wheels. In other words, the front wheels rotate faster than the rear wheels. When there is a small rotating speed difference (when vehicle speed is low), the center differential acts to absorb the rotating speed difference, making it possible to drive smoothly.
Although a slight rotating speed difference is transmitted to the viscous coupling, less torque transmission occurs because of the small rotating speed difference.
Center Differential Acting To Absorb Rotating Speed Difference. Scheme 333
Scheme 334
Scheme 335
- When front wheel is on slippery surface When the front wheels begins to spin during rough-road driving, the rotating speed difference between the shafts is increased by the differential's action. At this point, the viscous coupling delivers large torque to the differential on the side which is not spinning. In this way, driving stability on rough roads is increased. (Scheme 334): Viscous Coupling Delivering Large Torque To The Differential On The Side Which Is Not Spinning
- When rear wheel is on slippery surface During rapid acceleration from standing starts on a slippery (low "mu") road, front and rear wheel weight distribution changes. When the rear wheels begin to spin, the rotating speed difference between the two shafts increase simultaneously. This causes the viscous coupling to activate so that more torque is transmitted to the front wheels than to the rear. In addition, the center-differential's action is also restricted. In this way, acceleration performance during standing starts on low "mu" roads is greatly enhanced. (Scheme 335): Viscous Coupling Activating So That More Torque Is Transmitted To The Front Wheels Than To The Rear