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 6th 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 6th 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 1st 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.