1.Function
A magnetic clutch is driven by engine through the drive belt. The magnetic clutch is a device to connect the engine and the compressor. The magnetic clutch stops and drives the compressor as necessary.
2.Construction
The magnetic clutch consists of a stator (electromagnet), pulley, center piece, and other components. The center piece is installed together with the compressor shaft and the stator is held on the front housing of the compressor.
3.Operation
When the magnetic clutch turns on, current passes through the stator coil, which makes the stator a strong electromagnet. As a result, the stator pulls the center piece with strong magnetic force so the compressor turns together with the pulley.
When the magnetic clutch is off, current doesn’t pass through the stator, which causes the center piece not to be pulled and only the pulley turns idle.

Condenser

1.Function
The condenser cools the gaseous refrigerant that reaches a high temperature and high pressure by being compressed by the compressor to change it into the high-temperature and high-pressure (mostly liquid state refrigerant but mixed with some gas) refrigerant.
2.Construction
The condenser consists of tubes and fins, and is installed on the front surface of the radiator.
3.Operation
The high-temperature and high-pressure gaseous refrigerant sent from the compressor separates out 3 passages of tubes to pass through the condenser to be cooled.

<1>While the engine cranks

When the clutch gear (outer) revolves faster than the spline shaft (inner), the clutch rollers are forced to the narrower section, and so the revolving force of the clutch gear is transmitted to the spline shaft.

<2>After the engine starts

When the spline shaft (inner) revolves faster than the clutch gear (outer), the clutch rollers are forced to the wider section, causing the clutch gear to revolve idly.

If the one-way clutch that works as the overrunning clutch slips, the engine cannot be cranked even though the starter revolves.

Clutch Release Cylinder

The clutch release cylinder moves the piston with hydraulic pressure from the master cylinder and operates the release fork through the push rod.

Self-adjusting release cylinder

The conical spring in the release cylinder constantly presses the push rod against the release fork with its spring force to hold the clutch pedal freeplay constant.

Adjustable release cylinder

When the diaphragm spring tip position has changed due to wear of the clutch disc, it is necessary to adjust the freeplay with the push rod.

Clutch Release Bearing

The clutch release bearing absorbs the rotational difference between the release fork (which is not turning) and the diaphragm spring (which is turning) to transmit the movement of the release fork to the diaphragm spring.

Self-centering release bearing

In transaxles for FF vehicles, the crankshaft and input shaft shift slightly. This results in noise caused by friction between the diaphragm spring and the release bearing. To prevent this noise, this mechanism supplies the center line of the diaphragm and release bearing to be aligned automatically

The clutches and brakes that operate the planetary gear unit are operated by hydraulic pressure. The hydraulic control unit generates and adjusts this hydraulic pressure and switches its passage. The illustration on the left shows the hydraulic circuitry for the A140E model. The hydraulic pressure operates through various hydraulic pressure passages.

HINT:

If the battery is dead, it is possible to start the engine of manual transaxle vehicles by push-starting it, but with automatic transaxle vehicles, this is not possible. During push-starting, since the oil pump is not operating, the operating hydraulic pressure of the planetary gear unit is not generated. In other words, the power from the tires is not transmitted to the engine. The hydraulic control unit has the following three functions.

1. To generate hydraulic pressure

The oil pump has the function of generating the hydraulic pressure. The oil pump generates the hydraulic pressure required for automatic transaxle operation by driving the torque converter case (engine).

2. To adjust hydraulic pressure

The hydraulic pressure compressed by the oil pump is adjusted with the primary regulator valve. Also, the throttle valve produces the hydraulic pressure appropriate to the engine output.

3. To shift gears (to make theclutches and brakes operate)

When the clutch and brake operations of the planetary gear unit are switched, the gears are shifted. The fluid passage is created in accordance with the shift position by the manual valve. When the vehicle speed rises, signals are sent to the solenoid valves from the Engine & ECT ECU (Electronic Control Unit). The solenoid valves operate each shift valve to shifting the gears. The major components of the hydraulic control unit are the following.

Oil pump

Valve body

Primary regulator valve

Manual valve

Shift valve

Solenoid valve

Throttle valve

The clutches connecting and disconnecting the power are C1 and C2. The clutch C1 acts to transmit power from the torque converter to the front ring gear via the input shaft. The discs and plates are lined up alternately. The discs are splined to the front ring gear and the plates are splined to the forward clutch drum. The front ring gear is splined to the ring gear flange and the forward clutch drum is splined to the direct clutch hub. The clutch C2 transmits power from the input shaft to the direct clutch drum (sun gear). The discs are splined to the direct clutch hub and the plates are splined to the direct clutch drum. The direct clutch drum meshes with the sun gear input drum and the sun gear input drum is splined to the front and rear sun gears. The structure is such that the three units of discs, plates, and drums turn together.

1. Engaged (C1)

When pressurized fluid flows into the piston cylinder, it pushes the piston check ball, causing it to close off the check valve. This in turn causes the piston to move inside the cylinder, forcing the plates into contact with the discs. Because of the high frictional force between plates and discs, the drive side plates and driven discs rotate at the same speed. This means that the clutch is engaged, the input shaft is connected to the ring gear, and the power from the input shaft is transmitted to the ring gear.

2. Disengaged (C1)

When the hydraulic pressurized is released, the fluid pressure in the cylinder decreases. This allows the check ball to move away from the check valve, which it attempts to do due to the centrifugal force that is applied to it, and the fluid in the cylinder is drained out through the check valve. As a result, the piston is returned by the return spring to it its original position, disengaging the clutch.

HINT:

The number of clutch discs and plates differs depending on the automatic transaxle model. Even in automatic transaxles of the same model, the number of discs may differ depending on the engine the transaxle is combined with.

NOTICE:

When replacing clutch discs with new discs, soak the new discs in the ATF for 15 minutes or longer before installation.

3. Centrifugal fluid pressure canceling

clutch

In the conventional clutch mechanism, to prevent the generation of pressure by the centrifugal force that is applied to the fluid in the piston fluid pressure chamber when the clutch is released, a check ball is provided to discharge the fluid. Therefore, before the clutch can be subsequently applied, it took time for the fluid to fill the piston fluid pressure chamber. During shifting, in addition to the pressure that is controlled by the valve body, the pressure that is applied on the fluid in the piston fluid pressure chamber also exerts influence, which is dependent upon engine speed fluctuations. In order to eliminate this influence, a canceling fluid pressure chamber is provided opposite to the piston fluid pressure chamber. By utilizing the lubrication fluid such as that of the shaft, the same amount of centrifugal force is applied, thus canceling the centrifugal force that is applied to the piston itself. Accordingly, it is not necessary to discharge the fluid through the use of a check ball, and a highly responsive and smooth shifting characteristic has been achieved.

One-way Clutch

When the planetary gear unit is designed without considering shifting shock, B2, F1, and F2 are not necessary. Just C1, C2, B1, and B3 are adequate. Also, it is difficult to make the fluid pressure is applied on the brake simultaneous with the moment that the clutch operating fluid pressure is released. Therefore, the No.1 one-way clutch (F1) operates via the B2 brake to prevent the front and rear sun gears from turning counterclockwise. The No.2 one-way clutch (F2) prevents the rear planetary carrier from turning counterclockwise. The outer race of the No.2 one-way clutch is fixed to the transaxle case. It is assembled so that it locks when the inner race (rear planetary carrier) is turning counterclockwise and turns freely when the inner race is turning clockwise. In this way, using one-way clutches switches the gears by always applying or releasing the fluid pressure on one element. That is, the function of the one-way clutch in the planetary gear unit is to ensure smooth gear shifting.

The lock-up clutch mechanism connects the engine power directly and mechanically to the automatic transaxle. Since the torque converter uses the fluid flow to transmit the power indirectly, there are power losses. Therefore, the clutch is attached in the torque converter to connect the engine and transaxle directly to reduce power loss. When the vehicle reaches a certain speed, the lock-up clutch mechanism is used to raise the power performance and fuel efficiency. The lock-up clutch is installed on the turbine runner hub, in front of the turbine runner. The damper spring absorbs the torsional force upon clutch engagement to prevent the generation of shock. A friction material (the same type that is used in the brakes and on the clutch disc) is bonded to the converter case or lock-up piston of the torque converter to prevent slippage at the time of clutch engagement.

Operation

When the lock-up clutch is actuated, it rotates together with the pump impeller and turbine runner. Engaging and disengaging of the lockup clutch is determined by changes in the direction of the hydraulic fluid flow in the torque converter when the vehicle reaches a certain speed.

1. Disengaging

When the vehicle is running at low speeds, the pressurized fluid (converter pressure) flows to the front of the lock-up clutch. Therefore, the pressure on the front and rear sides of the lock-up clutch become equal, so the lock-up clutch disengages.

2. Engaging

When the vehicle is running constantly at medium or high speed (generally above 60 km/h), the pressurized fluid flows to the rear of the lock-up clutch. Therefore, the converter case and lock-up clutch are directly connected. As a result, the lock-up clutch and converter case rotate together (For example, the lock-up clutch is engaged).

The primary purpose of the clutch cover is to connect and disconnect engine power. It must be well balanced while it is rotating, and radiate heat efficiently at the time of clutch engagement. The clutch cover has a spring to push the pressure plate against the clutch disc. These springs may be either coil springs or a diaphragm spring. The latter is used in most clutches today.

1. Diaphragm spring type clutch

The diaphragm spring is made of spring steel. It is riveted or bolted to the clutch cover. A pivot ring is located at each side of the diaphragm spring and functions as a pivot while the diaphragm spring is operating. The retracting springs are used to connect the diaphragm springs to the pressure plate.

Recent models have adopted a DST (Diaphragm Spring Turn-over) type clutch cover. In this type of clutch cover, the tips of the clutch cover are turned over to hold the diaphragm spring at proper position directly. The straps are connected in a chordal (tangential) direction to transmit the torque.

2. Characteristics of diaphragm springs

The graph on the left shows the movement of the pressure plate along the horizontal axis and the pressure plate along the vertical axis. The solid line indicates the characteristics of the diaphragm spring, and the dotted line indicates the characteristics of the coil spring.

(1) Normal condition (When the clutch disc is brand new)

When the pressure applied to the pressure plate (P0) is equal for both types: coil spring type and diaphragm spring type, each pressure becomes P2 and P’2 with the clutch pedal fully depressed.

This means that for the diaphragm spring type, the force needed to depress the clutch pedal is smaller than that for the coil spring type by the amount shown by “a”.

(2) When wear on the contact surface of clutch disc exceeds the allowable limit

The pressure applied to the pressure plate of the coil spring type clutch decreases to P’1.

On the other hand, the pressure applied to the pressure plate of the diaphragm spring type clutch is P1, and the same as P0. That is, the power transmission ability of the diaphragmspring type clutch does not decrease till thedisc wear limit.Conversely, the pressure applied to the pressure plate of the coil spring type clutch decreases to P’1. As a result, the transmission ability decreases, causing the clutch to slip.

Automotive Clutch Disc

The clutch disc contacts the friction surface of the pressure plate and the flywheel uniformly to transmit motive power smoothly. It also consists to soften the impact of clutch engagement.

1. Torsion rubber

The torsion rubber is incorporated in the clutch hub and softens the rotational impact of clutch engagement by moving slightly in the circumferential direction.

2. Cushion plate

The cushion plate is riveted sandwiched between the clutch facings.

When the clutch is engaged suddenly, the impact is absorbed by this curved section to soften the shock of gear changing and allow power to be transmitted smoothly.

SERVICE HINT:

Wear of the torsion rubber and breakage of the cushion plate causes a large amount of impact shock and noise when the clutch is engaged.

The direction of the fluid entering the stator from the turbine runner depends on the difference in the rotational speeds between the pump impeller and turbine runner.

1. When the rotation speed difference is large

The fluid strikes the front surfaces of the stator vanes, causing the stator to rotate in the direction opposite that of the direction in which the pump impeller rotates. However, the pump impeller cannot rotate in the opposite direction because the stator is locked by the one-way clutch. Therefore, the direction of the fluid flow is changed.

2. When the rotation speed difference is small

Some of the fluid flowing from the turbine runner flows into the rear surface of the stator vanes. When the speed difference is at minimum, much of the fluid sent from the turbine runner contacts the rear surface of the stator vanes. In such a case, the stator vanes interfere with the fluid flow. The one-way clutch makes the stator idle in the same direction that the pump impeller is rotating and the fluid returns smoothly to the pump impeller.

SERVICE HINT:

When the stator cannot be locked, symptoms of acceleration failure occur due to the system being in the coupling range. On the other hand, when the stator cannot rotate freely, the system remains in converter range and the symptom occurs such the speed does not increase above a certain speed. Inspection of One-way Clutch

Inspection of One-way Clutch

One-way clutch inspection method

(1) Insert the SST in the inner race of the one-way clutch.

(2) Install the SST so that it fits in the notch of the converter hub and other race of the one-way clutch. (3) With the torque converter standing on its side, the clutch should lock when turned counterclockwise, and should rotate freely and smoothly when turned clockwise. If necessary, clean the converter and retest the clutch. Replace the converter if the clutch still fails the test.

The clutch is located between the engine and the manual transaxle (manual transmission) and connects and disconnects the engine power by operating the clutch pedal. Thus, the clutch can gradually transmit power from the engine to the drive wheels in order to start the automobile smoothly, and smoothly change the transmission gears according to the conditions under which the vehicle is traveling.

Requirements of the clutch

(1) It must engage the transmission and the engine smoothly.

(2) Once it engages the transmission, it must transmit power entirely without slipping.

(3) It must disengage the transmission quickly and with precision.

The clutch consists of a portion that operates mechanically to transmit power, and a portion that utilizes hydraulic pressure to transmit power.

Cable type clutch

There are also cable type clutches that connect the clutch pedal and the release fork by cable.

Clutch Pedal

The clutch pedal generates hydraulic pressure from the master cylinder with the force from depressing the pedal.

This hydraulic pressure is applied to the release cylinder and the clutch is finally engaged and disengaged.

Clutch pedal freeplay

The clutch pedal freeplay is the distance that the pedal can be depressed until the release bearing presses against the diaphragm spring. As the clutch disc wears, the freeplay is reduced. If the disc wears further and there is no more freeplay, this causes the clutch to slip. Therefore, it is necessary to adjust the length of the release cylinder push rod and hold the freeplay constant. Therefore, it is necessary to adjust the length of the release cylinder push rod and hold the freeplay constant. In current models, self-adjusting release cylinders are used, so the clutch pedal freeplay does not change. The clutch pedal height is adjusted with the pedal stopper bolt and the pedal freeplay is adjusted with the push rod length.

Turn-over Type Clutch Pedal

Turn-over type clutch pedals are clutch pedals that utilize spring force to reduce the operating force.

When the pedal is depressed and goes beyond a certain position, the spring force operating direction changes and is added with the force to be depressed. The spring is installed between the

clutch pedal and pedal support and force works on the spring to keep it constantly

extended. There are various types of turn-over type clutch pedals with different constructions.

TFT (Toyota Free-Tronic)

The TFT (Toyota Free-Tronic) has no clutch pedal and consists of the parts in the diagram on the left in addition to the conventional clutch construction. By performing the shift operation, the TFT ECU controls the hydraulic actuator based on the signals from the sensors and switches to send hydraulic pressure to the release cylinder and automatically operate the clutch. Since it is equipped with protection control, it warns the driver with a buzzer and the indicator

(1) Clutch pedal depressed

The piston is moved to the left via the push rod when the clutch pedal is depressed. The brake fluid in the cylinder flows through the inlet valve to the reservoir and at the same time to the release cylinder.

When the piston moves further to the left, the connecting rod is separated from the spring retainer, and the inlet valve closes the passage into the reservoir by the conical spring, as a result, a build up of a hydraulic pressure in chamber A occurs which is transmitted to the release cylinder piston.

(2) Clutch pedal released

When the clutch pedal is released, the piston is pushed back to the right by the compression spring and hydraulic pressure decreases. As the piston returns completely, the connecting rod is pulled to the right by the spring retainer. The inlet valve thus opens the passage to the reservoir and chamber A and B are connected.

SERVICE HINT:

If air is mixed into the fluid line, air is pressurized and sufficient amount of oil pressure is not generated. Then, it causes poor clutching or the gears unable to shift.

1. Stall point

The stall point refers to the situation in which the turbine runner is motionless. The difference in rotation speeds between the pump impeller and the turbine runner is at a maximum. The maximum torque ratio of the torque converter is at the stall point. (It is generally in a range between 1.7 and 2.5.) The transmission efficiency is 0.

HINT:

In the stall test described later, the performance of the torque converter and engine output are tested by the engine being run at full throttle (full load) at this stall point.

2. Clutch point

As the turbine runner starts to rotate and the speed ratio increases, the difference in rotational speed between the turbine runner and pump impeller starts to decrease. However at this time, the transmission efficiency increases. The transmission efficiency is at its maximum just before the clutch point. When the speed ratio reaches a specified level, the torque ratio becomes almost 1:1. In other words, the stator starts to rotate at the clutch point and the torque converter to operate as the fluid coupling in order to prevent the torque ratio from falling

below 1.

SERVICE HINT:

Stall test

This test is used to check the overall performance of the engine and transaxle (the clutches and brakes of the planetary gear unit). It is carried out by rendering the vehicle immovable, then measuring the engine rpm while shifting to the “D” or “R” range and depressing the accelerator pedal all the way.