A general description of torque converter operation when the shift lever is shifted into a “D”, “2″, “L” or “R” is given below.

1. Engine idling, vehicle stopped

When the engine is idling, the torque generated by the engine itself is at a minimum. If the brakes (parking brake and/or foot brake) are applied, the load on the turbine runner is great because it cannot rotate. Because the vehicle is stopped, however, the speed ratio of the turbine runner to the pump impeller is 0 while the torque ratio is at a maximum. Therefore, the turbine runner is always ready to be rotated with a higher torque than the torque generated by the engine.

2. Vehicle starting off

When the brakes are released, the turbine runner is able to rotate with the transaxle input shaft. Therefore, the turbine runner rotates with a torque greater than that generated by the engine by depressing the accelerator pedal. Thus, the vehicle starts to move.

3. Vehicle running at low speed

As the vehicle speed increases, the rotational speed of the turbine runner quickly approaches that of the pump impeller. Therefore, the torque ratio quickly approaches 1.0. When the ratio of the turbine runner speed to that of the pump impeller speed reaches the clutch point, the stator starts to rotate, and torque multiplication decreases. In other words, the torque converter starts to operate as a fluid coupling. Therefore, the vehicle speed increases almost in linear proportion to the engine speed.

4. Vehicle running constantly at medium or high

speed

The torque converter functions only as a fluid coupling. The turbine runner is rotating at a speed almost identical to that of the pump impeller.

HINT:

Under normal conditions when the vehicle starts off, the torque converter reaches the clutch point 2 to 3 seconds. However, if the load is heavy even while the vehicle is running at a medium or high speed, the torque converter may operate in the converter range.

When the brakes are released, even if the accelerator pedal is not depressed, the vehicle slowly starts to move. This is called creep phenomenon.

The torque converter both transmits and multiplies the torque from the engine using the ATF (Automatic Transaxle Fluid) into the transaxle (planetary gear unit) as the medium.

The torque converter consists of the pump impeller, turbine runner, one-way clutch and stator, and the converter case which contains all of these components. The converter is filled with the ATF, which is supplied by the oil pump. The engine rotates and the pump impeller rotates, then this fluid is forced out from the pump impeller in a powerful stream that rotates the turbine runner.

HINT:

For ATF, DEXRONII or Toyota type T-IV is used.

Construction Pump Impeller

The pump impeller is integrated with the converter case and is connected to the crankshaft via the drive plate. Many curved vanes are mounted on the inside of the pump impeller. A guide ring is installed on the inner edges of the vanes to provide a path for smooth fluid flow.

Turbine Runner

Many vanes are installed in the turbine runner, as in the pump impeller. The direction of the curvature of these vanes is opposite from that of the pump impeller vanes. The turbine runner is installed on the transaxle input shaft so that the vanes inside it oppose pump impeller vanes with a very small gap in between.

HINT:

The turbine runner rotates with the transaxle input shaft when the vehicle is running with the shift lever position in the “D”, “2″, “L” or “R” range. However, it is stopped rotating when the vehicle is stopped. When the shift lever position is in the “P” or “N” range, the turbine runner rotates freely with the rotation of the pump impeller.

Stator

The stator is located between the pump impeller and the turbine runner. It is mounted, via a one-way clutch on the stator shaft, which is fixed to the transaxle case.

1. Stator operation

The flow of the fluid returning from the turbine runner to the pump impeller is in the direction that impedes the rotation of the pump impeller. Therefore, the stator changes the direction of fluid flow so that it strikes the back of the vanes of the pump impeller, giving the pump impeller an added “boost” and thus increasing torque.

2. One-way clutch operation

The one-way clutch allows the stator to rotate in the same direction as the engine crankshaft. However, if the stator would start to rotate in the reverse direction, the one-way clutch locks the stator in order to prevent it from rotating.

Center Differential and Transfer

1. Transfer

This transfer is a two-speed (Low- High) type. This transfer is a compact and lightweight. Its main feature is the adoption of the torque sensing type center differential with mechanical locking type. In this transfer, a planetary gear train is used in the reduction mechanism and a silent chain is used to reduce noise for the front drive. The method for switching the modes of this transfer involves the operation of a 4WD control switch to actuate the two shift motors. Thus, the transfer shift lever has been discontinued and the ease of operation has been improved.

Transfer shift actuator

The transfer shift actuator, which contains “H”-”L” shift motor limit switch, center differential lock shift motor, “H”-”L” shift motor limit switch, center differential lock shift motor limit switch and center differential lock detection switch, cannot be disassembled. (1/3)

2. Power transmission

(1) “H” position The splines at the rear of the transfer input shaft mesh with the internal gear teeth of the high and low clutch sleeve. Also, the high and low clutch sleeve is meshed to the differential case. Thus, the rotation of the input shaft is transmitted to the high and low clutch sleeve, the differential case.

(2) “L” position The external teeth of the high and low clutch sleeve are meshed with the planetary spline piece, and the planetary ring gear is fixed. Thus, the rotation of the input shaft is transmitted in a reduce from to the planetary sun gear, planetary pinion gear, planetary pinion gear shaft, planetary carrier, planetary spline piece, high and low clutch sleeve, high and low clutch hub, and differential case.

3. Center differential

(1) Construction Torque sensing type center differential with mechanical locking type consists of a differential case, coupling, ring gear, 8 pinion gears, sun gear, and carrier.

(2) Principle of operation 1. Normal driving (front wheel speed = rear wheel speed) The driving force that is input by the differential case is transmitted by front: 40, rear: 60. When a rotational difference exists between front wheel and rear wheel, the torque distribution of the driving force (torque) that is input by differential case changes instantly by the pinion gear and clutch plate operation before the torque is transmitted. 2. Front wheel skid driving (front wheel speed > rear wheel speed) The center differential distributes more torque to the rear wheels.

4. Rear wheel skid driving (front wheel speed = rear wheel speed)

The center differential distributes more torque to the rear wheels.

Center differential lock mechanism

When the center differential lock switch is ON, the center differential lock shift motor within the transfer shift actuator operates. This slides the center differential lock shift fork and locks the center differential.