12. Automatic transmission

Automatic transmission 4HP18 is the four-stage block including the hydrokinetic converter of rotation with the built-in torsion damper and planetary transfer.

Control of transmission is exercised of the 7-position selector lever installed on a floor. Transmission can function in various modes, depending on position of the lever of the selector.

At installation of the lever of the selector in situation "P" (parking) transmission is mechanically blocked, preventing a possibility of a provorachivaniye of wheels. For this reason situation "P" has to get out only at statement of the car to the parking.

At installation of the lever of the selector in situation "N" (neutral) transmission disunites the drive between the engine and the conducted wheels, also, as it becomes in the manual transmission. Such situation has to be chosen at the movement of the car. If the car is left on the parking in position of the lever of the selector "N", it is necessary to cock the emergency brake.

In position of the lever of the selector "D" (movement) transmission automatically switches between four forward transfers depending on the speed of the movement of the car and the provision of an accelerator. The first transfer is always chosen at start-off of the car from the place and in the course of a set of speed of transfer automatically switch on reaching the speed of the certain values caused in advance that provides optimum comfort, economy of fuel and maximum efficiency of operation of the engine.

Before installing the selector lever in situation "R" (backing) the movement of the car has to be completely stopped forward. The choice of "R" at the movement is prevented by the hydraulic blocking mechanism installed in transmission which provides a possibility of turning on of the reverse gear only after a full stop of the car.

Start of the engine can be carried out only in two provisions of transmission - "P" and "N".

Range of switching of transmission can be limited to the first three transfers, the first two transfers or even only the first transfer if it is demanded by road conditions. Installation of the lever of the selector in situation "3" allows automatic switching of transmission between the first three transfers, inclusion of the fourth transfer at the same time is impossible. At installation of the lever of the selector in situation "3" during the movement on the fourth transfer (the lever is installed in situation "D" (movement)) immediately there is a switching of transmission to the 3rd transfer. In order to avoid damage of the engine and transmission do not switch the selector lever to situation "3" at speeds of car more than 130 km/h.

Installation of the lever of the selector in situation "2" allows automatic switching of transmission between the first two transfers, inclusion of the third and fourth transfer at the same time is impossible. Such operating mode of transmission provides maximum efficiency of the movement of the car at the movement on the hilly area. When switching the lever of the selector in situation "2" during the movement of the car on the third transfer (at position of the D or 3 lever), switching of transmission to the second transfer is carried out only on reaching the car of speed of in advance established value that allows to avoid damage of the engine and transmission.

Installation of the lever of the selector in situation "1" blocks transmission in the provision of the first transfer, without giving the chance to the car to move at the second, third and fourth speeds. Such mode usually is the most optimum at the movement on the abrupt, hilly area and in particular, at towage. Besides, such mode excludes automatic switching of the transmission between the first and second transfers that usually causes an overheat of transmission liquid. At installation of the lever of the selector in situation "1" during the movement of the car on the second, third and fourth transfer (at position of the lever "D", "3" or "2") switching of transmission to the first transfer is carried out consistently on reaching the car of speed of in advance established values for the third and second transfers. It allows to avoid damages of the engine and transmission, and also sudden unexpected braking of the engine.

For ensuring the maximum acceleration during overtaking, when squeezing until the end of an accelerator pedal (further provisions of completely open throttle), turn on the device of decrease in transfer of transmission (kickdown). At the same time, if the transfer of transmission established at present is not optimum for ensuring the maximum acceleration at the current speed of the car, transmission will automatically switch to a low gear. The transfer chosen at the same time will remain included until the pedal of an accelerator is not released from situation Kick-down or until the maximum speed of the movement of the car for this transfer is reached; then there will be a switching to higher transfer.

In view of complexity of a design of transmission of the procedure of its general and capital repairs have to be made in representative office of SAAB at whose order there are necessary tools and the diagnostic equipment. Information provided in this Chapter, thus, is limited to the description of procedures of service of transmission which can be made without use of specialized tools, and also the test and repair equipment.