Automatic transmission shift points are controlled by an electronic-hydraulic system (so-called EH control). This means that the hydraulic system of the gearbox is controlled by an electronic control unit, which, depending on the speed and load of the engine, selects the correct shift points.
To make gear selection even better suited to the driver's individual driving style and driving conditions, the automatic transmission is equipped with an adaptive control system (AGS). It takes into account when selecting gears apart from various conditions such as driving in mountains, towing a trailer, driving on slippery roads or driving in city mode (frequent stops) as well as the driving style of the driver. The AGS system analyzes for this the position and movement of the accelerator pedal, driving speed, lateral acceleration (cornering movement) and deceleration in corners.
Based on this information, the system determines the type of driving and enters it into one of the four preset main programs. These basic programs range from the extra economical XE program through the E and S programs to the XS sports program. A driver with a sporty driving style, if necessary, can switch on using selector lever position 4 «tough» sports program. On slippery roads, additional «winter» program to increase stability in motion.
Elements of automatic transmission ZF4HP22
1 - output shaft flange;
2 - screw plug;
3 - oil pan with control device;
4 — a shaft of the lever of management of switching;
5 - gas drive cable;
6 - air outlet from the box;
7 - parking lock gear;
8 - centrifugal regulator;
9 - planetary gear;
10 - lamellar (viscous) clutch;
11 - oil pump;
12 - torque converter;
13 - converter blocking clutch;
14 - connection of the slave disk.
STEPTRONIC - automatic with AGS and stepped gear shifting
Some models with the STEPTRONIC system have a second short channel next to the main channel for the selector (backstage) with the possibility of stepwise gear shifting. Stepped gear shifting is common on motorcycles, especially sport bikes.
In automatic mode, which is engaged for forward range D, automatic 5-speed shifts are normally performed using the adaptive shift control system (AGS). When the lever is in the left side of the gate, on the contrary, the driver can select gears at will. If he moves the selector lever to the left side (channel) from position D to position M, the previous gear is maintained. If the driver moves the selector lever forward in the direction «+», then the gearbox shifts to the next higher gear, and if in the direction «-», then to the next lower gear.
Unlike manual shifting, the STEPTRONIC system ensures comfortable driving and eliminates erroneous commands: illegal shifts, such as downshifting at very high speeds, are ignored by the system. When accelerating with the KICKDOWN system running (forced downshifting when the gas pedal is pressed hard) without operation of the selector, a downshift to the lowest possible gear is mandatory. When accelerating without manual intervention, the system shifts the gearbox to a higher gear when the engine speed is slightly below the limit value.
When coasting, STEPTRONIC automatically downshifts up to third gear to ensure sufficient traction when towing a trailer.
To check the operation of the automatic transmission and for the correct diagnosis, we find experience with automatic transmissions and special devices. Therefore, only the removal of the gearbox, the adjustment of the shift cable and the oil change are described here.
Automatic transmission shift levers ZF4HD22
1 - shift lever;
2 - the lower part of the shift lever;
3 - base plate;
4 - gasket;
5 - backstage;
6 - switching handle;
7 - push contact;
8 - switch;
9 - lever;
10 - switching rod;
11 - the lower part of the shift lever;
12 - switching control shaft;
13 — a disk of a choice of transfer;
14 - latch;
15 - cam;
16 - cable «kickdown»;
17 - mounting pin.