Transmission overload protection - RA27057229320X(27-9320)
Function
A transmission overload protection is integrated in the EZL/AKR control unit in order to protect the shift elements of the automatic transmission from thermal stresses during gearshifts under load in the top engine speed range.
The transmission overload protection retards the ignition point to 5° CS before TDC (reduced engine torque) for approx. 400 ms during 1 → 2 and 2 → 3 upshifts.
As this retardation of the ignition point also improves the gearshift action during the shift phase, this measure is also employed during 3 → 2 full load downshifts.
The ignition point is retarded provided the following conditions are met simultaneously:
- engine speed >4000 rpm (reference value)
- vacuum in intake manifold <300 mbar (reference value)
- switching signal sent by transmission overload protection switch, brake band B1 (S65).
The transmission overload protection switch, brake band B1 (S65) is designed as a hydraulic pressure switch and is connected to the working pressure circuit of brake band B1 of the automatic transmission.
The switching function of the transmission overload protection switch, brake band B1 (S65) is dependent on the working pressure which exists at B1.
Working pressure <1.8 bar: S65 open.
Working pressure >1.8 bar: S65 closed.
The opening and closing of the transmission overload protection switch, brake band B1 (S65) is detected by the EZL/AKR control unit as a switching signal.
Transmission 722.362
This transmission has two transmission overload protection switches, brake band B1 and brake band B2 (S65, S65/1). Both have a resistance of 1kΩ and send the transmission-side signal for retarding the ignition to the EZL control unit.
| Selector lever/gear | Transmission overload protection switch, brake band B1, brake band B2(S65, S65/1). | Signal to EZL control unit |
|---|---|---|
| N, R and 4th gear | No transmission overload protection switch, brake band B1, brake band B2 (S65, S65/1) closed. | 5 V |
| 1st and 3rd gear | Transmission overload protection switch, brake band B2 (S65/1) closed. | 2.5 V |
| 2nd gear | Transmission overload protection switch, brake band B1, brake band B2 (S65, S65/1) closed. | 1.67 V |
The transmission overload protection is effective from an engine speed of >3000 rpm. During an upshift, the control time of the transmission overload protection is approx. the same as the shift time for a gear change. The control time is approx. 50 milliseconds for the 4 → 3 and 3 → 2 downshift.
Transmission overload protection emergency operating mode
If the EZL/AKR control unit does not receive a shift signal from the automatic transmission when driving, whether this is the result of a fault at the transmission overload protection switch, brake band B1 (S65) or its wiring, the EZL/AKR control unit switches to the emergency operating mode. The transmission overload protection is effective with restrictions in the emergency operating mode.
If no shift signal is received from the automatic transmission, the EZL/AKR control unit detects the commencement of a gear shift by a change in engine speed of a defined magnitude. If the transmission overload protection is operating in the emergency mode, this may be noticeable by the ignition point being briefly retarded at high speed.
If the complaint "misfiring at high speed" is received, the transmission overload protection switch, brake band B1 (S65) and the wiring must be checked.