Manual transaxles are located at the left end or right end of transversely mounted engines in FF vehicles. Manual transmissions are located to the rear of vertically mounted engines in FR vehicles.

1. Manual transaxle operation

Neutral

The motive power from the engine is not transmitted from the input shaft to the output shaft so that it is not done to the differential. Blue arrow: Transmission of power Red arrow: Direction of rotation

The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

1st gear

The gear of the output shaft rotating meshed with the 1st gear of the input shaft transmits power to the differential through the drive pinion. Blue arrow: Transmission of power Red arrow: Direction of rotation The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

3rd gear

The gear of the output shaft rotating meshed with the 3rd gear of the input shaft transmits power to the differential through the drive pinion. Blue arrow: Transmission of power Red arrow: Direction of rotation The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

Reverse

The reverse idler gear is meshed with the input shaft reverse gear. The output shaft gear meshed with the reverse idler gear transmits power for reverse rotation to the differential through the drive pinion.

Blue arrow: Transmission of power

Red arrow: Direction of rotation

Violet arrow: Direction of reverse

idler gear rotation

The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque. Blue arrow: Transmission of power Red arrow: Direction of rotation The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

Manual Transmission

For manual transmissions, the input shaft and the output shaft are located on the same axis and the counter gear integrates the input shaft and the output shaft to transmit power.

The drive train transmits the power of the engine to the wheels. It is broadly divided into the following classifications:

1. FF (Front engine-Front wheel drive vehicle)

The drive force from the engine is transmitted via the transaxle differential to the left and right drive shafts, wheels, and tires.

2. FR (Front engine-Rear wheel drive vehicle)

The drive force from the engine is transmitted from the transmission and then via the propeller shaft and differential to the right and left drive shaft (or axle shaft), axle shaft, wheels, and tires.

HINT:

The drive shaft and axle shaft combination is also called the drive shaft.

Differential Construction

The differential further increase the torque transmitted via the transmission and distributes the drive force to the left and right drive shafts. In addition, this is also a differential gear that generates the difference in the rotational speed between the inner wheel and outer wheel during cornering, and allows the smooth driving on curves.

1. Final gears

The final gears reduce the rotation from the transaxle (transmission) to increase the torque. The FR vehicle final gears increase the torque while changing its direction.

2. Differential gears

The differential gears create two different wheel turning speeds when the vehicle is driving on curves.

1. FF vehicle differential

The differential used in FF vehicles with transversely-mounted engines is integrated with the transmission. The differential assembly is mounted in between the transmission case and the transaxle case. A helical gear is used for the ring gear. This gear is integrated with the differential case and is mounted on the transaxle via two side bearings. The drive shaft meshes with the splines inside the side gear. There are ordinarily two pinion gears, but in differentials for high-power engines, four pinion gears are often used.

2. FR vehicle differential

The final gear and the differential gear in an actual product are assembled as a unit, as shown, and installed directly in the differential carrier, which is further fitted to the rear axle housing, body, or frame. The universal joint of the propeller shaft is fixed to the companion flange, and rotates the drive pinion through the companion flange. The drive pinion is fitted to the differential carrier by two tapered roller bearings. The ring gear and the differential case are integrally fitted to the differential carrier via two side bearings. The drive pinion and the ring gear are hypoid gears for which the shaft extensions are mutually offset, so special hypoid gear oil must be used to lubricate them. The side gear and the rear axle shaft are fitted to each other via splines.

3. Adjustment

(1) Side bearing preload adjustment

A taper roller bearing is used in the side bearing, so preload adjustment is required.

(2) Drive pinion preload adjustment

The preload of the drive pinion bearings is normally adjusted by changing the distance of the front and rear inner races while the outer races are fixed to the differential carrier. This can also be achieved by changing the total thickness of shims used, or applying pressure to the collapsible spacer (by tightening the nut) in order to alter its length.

(3) Hypoid gear backlash adjustment

The backlash adjustment performs to adjust the clearance of the contact surface between the drive pinion and ring gear. When the backlash is large, the differential case is adjusted toward to the drive pinion, and when the backlash is small, it is adjusted away from the drive pinion. The adjustment nut is used to make the adjustment.

(4) Hypoid gear tooth contact adjustment

The hypoid gear tooth contact is adjusted by offsetting the drive pinion and ring gear use the adjusting washer.

SERVICE HINT:

1. Side bearing preload

The thrust load is received from the ring gear, so if the preload adjustment is poor, the side bearing taper roller will wear causing unstable rotation. To prevent this, the preload adjustment using the adjusting shim or adjusting nut is required.

2. Drive pinion preload (FR)

The thrust load is received from the ring gear, so if the preload adjustment is poor, the taper roller bearings on both ends of the drive pinion will wear causing unstable rotation. To prevent this, the preload adjustment using the adjusting shim or collapsible spacer is required.

3. Hypoid gear backlash (FR)

The ring gear generates a thrust load, which is received by the drive pinion, so if the backlash adjustment is poor, an excessive force will be applied, causing damage to the teeth of both gears and seizing. It is required to adjust the adjusting nut or adjusting shim, and adjust the backlash.

4. Hypoid gear tooth contact (FR)

The ring gear generates a thrust load, which is received by the drive pinion, so if the tooth contact adjustment is poor, an excessive force will be applied, causing damage to the teeth of both gears and seizing or noise to occur be generated. Not only the backlash, but also the mutual tooth contact must be adjusted with the adjusting washer.

Operation

1. When driving straight

When driving straight, an even resistance is applied to both the right and left wheels, so the ring gear, pinion gear, and side gear rotate as a single unit so that the drive force is transmitted to both wheels.

2. When driving on a curve

When driving on a curve, the rotational speed is different between the outer tire and inner tire. In other words, inside the differential the inner B side gear turns slowly and the pinion gear rotates so that the outer A side gear rotates faster. This is how the differential allows the vehicle to drive smoothly through curves.

HINT:

The operation of the differential works to apply the same torque to both the right and left wheels. So while this has the advantage of making driving through curves smooth, it has the disadvantage of reducing the drive force to both wheels when the drive force is reduced to one wheel.

A manual transaxle (manual transmission) is a device that increases and decreases the engine speed by the gear and converts it to appropriate torque in order to transmit it to the drive wheels.

Refer to the “Drive Train” for the differential contained in the manual transaxle.

Roles of the transaxle

(1) To engage/disengage the driving power from the engine by operating the shift lever.

(2) To increase the torque when starting off and climbing hills.

(3) To drive the wheels at high speed during high-speed driving.

(4) To drive the wheels in reverse.

Necessity of Shifting Gears

The diagram on the left shows driving performance curves, which indicate the relationship between the driving force and the vehicle speed for the 1st through 6^th gears.

Driving performance curves

Ideally speaking, the curved line of the engine driving force should be changed continuously as A in the diagram. However, the driving force of actual manual transaxle changes discontinuously, as 1st though 6^th gear.

Therefore, the engine driving force is transmitted effectively when narrowing the shaped area in the graph to keep close to the ideal curved line. It can be guessed to be close to the ideal curved line A of driving force as the number of shift gear increases. However, the design of the transaxle

becomes complicated or it causes the driver to be complicated for shift operation.For these reasons, the number of the shift gear consists of 4th to 6th gear. 5th gear is used largely.

(1) Starting off

When the vehicle starts off, a large amount of power is required, so the 1st gear, which has the largest driving force, is used.

(2) Driving

After starting off, the 2nd and 3rd gears are used to increase the vehicle speed. These gears are used because there is an upper limit to the vehicle speed in 1st gear and that not as much driving force is required.

(3) High-speed driving

For high-speed driving, the 4th, 5th, and 6th gears areused to further increase the vehicle speed. Using gears with small driving force and lowering the engine speed improves fuel consumption.

(4) Backing up

When the reverse gear is used, the reverse idler gear is added, the reverse gear turns in reverse, and the vehicle backs up.

Reduction Ratio

The reduction ratio is expressed as:

Number of teeth of driven gear

Number of teeth of drive gear

If the driven gear has 38 teeth and the drive gear has 12 teeth, for example, the reduction ratio of this 1^st gear is 38/12 = 3.166.

When the rotation and torque of the input shaft is transmitted to the output shaft, the speed of the rotation decreases and the torque increases according to the reduction ratio of the gears.

Output torque = Input torque x Gear ratio Input rpm = Output rpm x Gear ratio This indicates that the torque increases and rpm becomes smaller with a greater reduction ratio. That is to say, the vehicle may be driven at a higher speed the smaller the reduction ratio is, although the driving power decreases.

Operating Mechanisms

1. Remote control type

This type connects between the shift lever and the transaxle with a cable or links, etc. This is used in FF vehicles, and there are characteristics such vibration and noise are difficult to be generated and the shift lever position can be designed freely.

2. Direct control type

This type installs the shift lever directly on the transmission. This type is used on FR vehicles because shift operations are quick and has good handling.

With automatic transaxle/transmission vehicles, the driver does not need to judge when shifting up and down. The gears are shifted automatically according to the vehicle speed and the amount that the accelerator pedal is depressed. A unit in which automatic gear shifting is controlled by an ECU (Electronic Control Unit) is called an ECT (Electronically- Controlled Transaxle/transmission) and a unit that does not use an ECU is called a full hydraulically-controlled automatic transaxle.

Currently, almost all vehicles use ECTs. In some models, the gear shifting pattern can be selected according to the driver’s preference and road conditions. This provides improved fuel economy and driving performance.

Types of Automatic Transaxle

Automatic transaxles can be basically divided into two types, those used in FF (Front-engine, Front wheel-drive) vehicles and those used in FR (Frontengine, Rear-wheel-drive) vehicles. Transaxles for FF vehicles have an internal final drive unit, but those for FR vehicles have a final drive unit (differential) mounted externally. The type of automatic transaxle used with FR vehicles is

called a transmission.

In the transversely-mounted automatic transaxle, the transmission and the final drive unit are housed integrally in the same case. The final drive unit consists of a pair of reduction gears (the drive and driven gears), and differential gears.

ECT (Electronically Controlled Transaxle)

An ECT (Electronically Controlled Transaxle) consists of following components:

1. Torque converter

Transmitting and multiplying the torque generated by the engine.

2. Planetary gear unit

Shifting such as deceleration,reverse, acceleration, and neutral.

3. Hydraulic control unit

Controlling the hydraulic pressure so that the torque converter and planetary gear unit operate smoothly.

4. Engine & ECT ECU

Controlling the solenoid valves and the hydraulic control unit to provide the optimum driving condition. It uses hydraulic pressure to automatically shift gears in accordance with ECU

control signals. The ECU controls the solenoid valves according to the condition of the engine and vehicle detected by the sensors, thus controlling the hydraulic pressure.

Full Hydraulically-controlled Automatic Transaxle

The construction of the full hydraulicallycontrolled automatic transaxle is basically the same as the ECT. However, this transaxle mechanically controls shifting by detecting the vehicle speed hydraulically from the governor valve and detecting the accelerator opening from the throttle valve via the amount of movement of the throttle cable.

4WD is the abbreviation for 4-Wheel Drive and drives all four tires using transfer, etc. There are two types of 4WD, full-time 4WD and part-time 4WD. 4WD vehicles can also be classified into those based on FF (Front-engine, Front-wheel-drive) and those based on FR (Front-engine, Rear-wheel-drive). Furthermore, 4WD vehicles can also be classified into those for driving off-road and those for driving on-road.

1. Operation of differential

The vehicle uses the differential to absorb the rotational difference during cornering. With full-time 4WD, there is a center differential in addition to the front differential and the rear differential in order to absorb the rotational difference between the front and rear wheels. Providing three different differentials makes smooth driving possible by ensuring the equal transmission of power to all four wheels, even during cornering – this is the major advantage of full-time 4WD.

When part-time 4WD vehicles, which do not have a differential to absorb the rotational difference between the front and rear wheels, turn sharply in the 4WD mode, the tight corner braking phenomenon occurs and smooth cornering becomes impossible. For this reason, with part-time 4WD, switching between 2WD and 4WD in response to driving conditions becomes necessary.

2. Tires and installing tire chains

All four tires mounted on a 4WD vehicle must be of the same size and type. If the front and rear tires are of different diameters, the center differential will have to operate at all times, even on a straight, level road. And if the diameters of the left and right tires are different, the front or rear differential will have to operate at all times (depending on whether the tires that are of different sizes are in the front or rear). Full-time 4WD offers outstanding drive-through performance on rough and snowy roads, but in some cases, it is necessary to install tire chains. At such times, the following point should be considered. When a 4WD vehicle is based on an FF model, tire chains should be mounted on the front tires. When the 4WD vehicle is based on an FR model, the tire chains should be mounted on the rear tires.  If a mistake is made, the tire chains could hit the body and damage it, so exercise caution at all times.

Types of 4WD

4WD can be classified into the following types according to differences in the drive type and control.

1. Part-time 4WD

With this type of 4WD system, the driver switches between 2WD and 4WD in accordance with road conditions by the transfer. Ordinarily, the vehicle is driven in 2WD, and 4WD is used for rough roads and snowy roads, etc. However, because the part-time 4WD system has the front and rear drive trains connected directly together, the tight corner braking phenomenon occurs during cornering, and the vehicle cannot be turned smoothly. For this reason, it is necessary to switch from 4WD to 2WD when driving on ordinary roads.

2. Full-time 4WD

The vehicle which can be used at all times under all road conditions and driving conditions, from ordinary roads to rough roads to low coefficient-of-friction roads, is full-time 4WD. Also, the full-time 4WD vehicles are equipped with the center differential.

3. V-Flex full-time

4WD V-Flex full-time 4WD system enables the vehicle to operate practically in the 2WD mode during normal travel when there is almost no rotational difference between the front and rear wheels. When a rotational difference is created between the front and rear wheels, such as during cornering or driving on a snowy road, this system transmits the drive force to the rear wheels. Thus, it ensures stable maneuverability while driving in various roads and driving conditions.

(3) Rib-and-lug pattern

This pattern combines the rib and lug patterns to provide stable driving performance on both paved and unpaved roads.

The rib pattern running along the center of the tire stabilizes the vehicle by minimizing tire side-slipping, while the lug pattern on the edges of the tire enhances driving and braking performance. The lug portion of the pattern is more susceptible to uneven wear.

(4) Block pattern

In this pattern, the tread is divided into independent blocks. Used on most snow tires and studless tires, the block tread pattern is now coming to be used on radial-ply tires for passenger cars as well.

The block pattern provides better driving and braking performance.

The block pattern reduces slipping and skidding on muddy or snow-covered roads.

The tires tend to wear faster than those with the rib and lug patterns.

Rolling resistance is slightly greater.

The tread is susceptible to unusual wear, especially on hard surfaces.

Unidirectional Pattern Tires

These are tires with a tread pattern, which has directionality with respect to the direction of rotation. Lateral grooves in the tire tread are given directionality in order to improve performance on wet roads, making it easier for the tires to drain off water. The performance of these tires on wet roads worsens if they are mounted in the wrong direction.

2. Pattern noise

Pattern noise is the most distinctive operating sound of the tire. The tread grooves coming into contact with the road surface contain air, which is trapped and compressed between the grooves and the road surface. When the tread leaves the road surface, the compressed air bursts out of the grooves, generating noise. Pattern noise increase if tread design is such that air is more liable to be trapped in the grooves.

The block or lug tread pattern, for example, is more likely to generate noise than the rib pattern. The pitch (frequency) of the noise rises as the vehicle speed increases. Since pattern noise thus depends on tread pattern, the pattern can be designed to minimize this. What appears to be a simple repetitive lug and zigzag pattern, for example, may contain subtle variations in pattern spacing.

Tires are installed on the vehicle together with disc wheels. Vehicles ride on pneumatic tires filled with pressurized air. Tires are the only vehicle components that come into direct contact with the road surface. If the tire air pressure is improper, this can cause abnormal wear and lower the driving performance. Tires perform the following functions:

The tires support the overall weight of the vehicle.

The tires directly contact the road surface and therefore transmit the vehicle’s driving and braking forces to the road, thus controlling starting, acceleration, deceleration, stopping, and turning.

The tires attenuate (reduce) shock caused by irregularities in the road surface.

Outline Construction

Construction

(1) Tires The types of tires are tubed tires and tubeless tires. Also, there are radial tires and bias tires, both of which comprise the following parts.

<1>Tread

<2>Belt (rigid breaker)/Breaker

<3>Carcass (cross plies)

<4>Inner liner

<5>Bead wire There are also other types, such as compact spare tires (temporary tire types) used for punctures and other emergencies, and run-flat tires on which you can drive a certain distance even with a puncture.

(2)Tire size The size, performance, and the construction of the tire are indicated on the sidewall of a tire. The diagram on the left shows the names of the sizes of the various areas of a tire.

(3)Disc wheels

Tread Patterns

1. Types of tread patterns

A wide variety of patterns are molded into the tread both to help drain away water, and to cope with various factors dictated by the conditions of the road surface and the type of the vehicle being used.

(1)Rib pattern

The rib pattern consists of several parallel zigzag grooves that run along the circumference of the tire. This pattern is best suited for traveling on paved surfaces at high speeds and is used for a wide variety of automobiles, from passenger cars to buses and trucks.

The rib pattern minimizes the resistance of the tire to rolling.

Greater resistance to side-slipping provides good vehicle controllability.

Tire noise is reduced.

Traction is somewhat inferior to that of tires with the lug pattern.

(2) Lug pattern

The grooves in the lug pattern run at roughly right angles to the tire circumference. Frequently used on construction machinery and truck tires, this tread pattern is suited for driving on unpaved roads.

The lug pattern provides good traction.

Tire rolling resistance is somewhat high.

Resistance to side-slipping is smaller.

Tread in the lug area is susceptible to uneven wearing.