Manual Transmission/Transaxle: Description and Operation
1. 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 inertia 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 toothface 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 subgear 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 viscous 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.
2. REVERSE CHECK MECHANISM
A: Construction
The sleeve (1) is bolted to the transmission case. The shaft (2) is inserted in the sleeve (1). On the smaller-diameter side of this shaft (2), the cam (3) is loosely mounted so that it can rotate, and the sleeve (1) holds the cam in place with its stepped part.
The spring (4), which is inserted in the shaft (2) presses the shaft to the left. Further, the spring is placed in between the cam (3) and sleeve (1), which forces the cam (3) to the left and in the direction of rotation. Both springs are held down with the plate (6) that is attached to the sleeve (1) with the snap ring (7). The shaft (2) has a groove for reverse accent, in which the ball (9) and spring are out through a hole drilled in the sleeve (1).
B: Operation
The sleeve and shaft have a notch, and the arm is placed between the notches. The position of the arm shown is the neutral position (hereafter referred to as (N) position). The point where the arm stops when moved to the left is the 1st and 2nd position. Opposite this, the point where the arm stops when moved to the right is the 5th and reverse position.
When 5Th And Reverse Side Is Selected
The arm pushes the shaft and cam simultaneously and moves to the 5th and reverse side.
When Shift Is Made To 5Th
The arm moves to the 5th side pushing the shaft. When the arm pulls out of the cam, the cam is returned to the original position by the spring.
When Shift Is Made From 5Th To Reverse
The arm moves to the reverse side pushing the shaft and runs against the cam that has already returned. The cam has, as shown in figure [Arrow view "Z"], a stopper, which hits against the plate Thus, the cam cannot rotate further. Accordingly, the arm comes to a stop at a point where it has turned the cam to a certain degree (i.e., (N) position), and the cam is pushed back to the (N) position by the shaft (i.e., the spring).
When Shift Is Made To Reverse
The arm again moves to the 5th and reverse side. When the shift is made to reverse, the arm (11) moves to the reverse position while pushing the shaft and cam together.
3. CENTER DIFFERENTIAL
A: Construction
The center differential utilizes a "shaft-to-shaft" design which connects the front-wheel drive pinion shaft and the rear-wheel drive transfer drive gear shaft via viscous coupling to achieve compact construction. With this arrangement, viscous torque is generated by a difference in rotating speed between the two shafts so that both differential action and drive torque distribution are properly controlled.
The center differential provides a means of distributing engine torque (transmitted to the tubular driven shafts by way of the clutch, mainshaft and various gears) to the front-and rear-wheel drive shafts equally, as well as absorbing the difference in rotating speed between the front and rear wheels during turns.
When the front and/or rear wheels spin on muddy roads, etc., viscous coupling controls the differential action so that the optimum drive torque is automatically distributed to these wheels.
B: 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 hub splines while the outer plate has its external perimeter fitted to the internal housing 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 hub spliced in the axial direction.
A mixture of silicone oil and air is sealed in the space inside the viscous coupling housing. 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.
Torque Characteristics
When a difference in rotating speed between the viscous coupling housing and the hub occurs, a viscous shearing force is generated in the silicone oil placed between the outer and inner plates. The torque is then transmitted by the silicone oil between the housing and the hub.
The greater the difference in rotating speed between the viscous coupling housing and the hub, the greater the shearing force of the silicone oil. The relationship between the torque transmission and rotation speed difference is shown in the figure. As can be seen from the figure, the smaller the rotating speed difference, the lesser the torque transmission and the differential-action.
"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 housing and hub (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.)
C: Function
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.
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.
Acceleration During Standing Starts On A Low "u" Road
During rapid acceleration from standing starts on a slippery (low "u" ) 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 to 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 "u" roads is greatly enhanced.
Driving On Rough Roads
When one of the 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 spin ring. In this way, driving stability on rough roads is increased. (The figure shows an example of front wheel slip.)