Description And Operation
DESCRIPTION
The Electronic Shift Module (ESM) is part of the shifter assembly called the Shift Lever Assembly (SLA). If it is necessary to service the ESM, the entire shifter must be replaced.
OPERATION
This is a shift-by-wire engagement control system which means:
- there is no mechanical connection between the transmission and the shift lever
- the shift lever is a device that detects the drivers requests
- there is no mechanical backup
- the hydraulically actuated parking lock is managed by the Transmission Control Module (TCM). There is always a backup device for manually unlocking it so that the vehicle can be moved if necessary.
Using a shift-by-wire device simplifies the installation and assembly, improving the passenger compartment sound proofing due to the lack of connection cables between the transmission and the shift lever.
The shifter assembly incorporates an electronic control module called an ESM. The ESM communicates with the TCM and other modules on the Controller Area Network-Chassis (CAN-C) network.
The innovation introduced by the shift-by-wire technology is that the shift lever is no longer forced to follow a selection grid to achieve a given transmission condition but, not unlike a joystick, always returns to the starting position, named "Central Position".
This behavior means that the shift lever position and the gearbox condition no longer correspond. To allow the shift control to be used intuitively, a logical control system that refers to the classic R, N, D, TIP selection grid was developed.
From the central position the shift lever may move at most two positions forwards and at most two positions backwards.
The shift lever has an ergonomic design and it has three key elements built into the top for gear shift management and driver information:
- lever release button
- parking lock engagement button
- transmission condition display device
| 1 | Stable position |
| 2 | Unstable Position |
| 3 | Mechanical lock |
| 4 | Locked by software |
| 5 | Movement made by the lever |
The lever release button (1) must be pressed together with the brake pedal whenever the driver wants to engine the reverse gear. Press the Parking button (2) to engine Parking mode. The vehicle speed must be at zero speed.
| FROM | A | CLICKS FORWARD | CLICKS BACKWARD | MOVE THE LEVER TO THE LEFT | RELEASE BUTTON | BRAKE PEDAL | ||
|---|---|---|---|---|---|---|---|---|
| P | R | 2 | no | pressed | pressed | |||
| P | N | 1 | no | pressed | pressed | |||
| P | D | 1 | no | pressed | pressed | |||
| D | R | 2 | no | pressed | pressed | |||
| D | N | 1 | no | not pressed | not pressed | |||
| D | M | none | none | yes | not pressed | not pressed | ||
| N | R | 1 | no | pressed | pressed | |||
| N | D | 1 | no | not pressed | pressed | |||
| R | N | 1 | no | not pressed | not pressed | |||
| R | D | 2 | no | not pressed | pressed | |||
To activate manual shifting, put the lever to the D position and move it to the left (- and +). Each forward or backward movement of the lever corresponds to a gear shift requests. The ESM sends the shift message to the TCM and if the engine load and vehicle speed allow, the TCM will engage the requested gear. The display will also show the gear selected.
Since the shift-by-wire solution has no selection grid, there is an element at the top of the shift lever that allows the driver to see the current transmission condition. Dedicated high-power Light Emitting Diodes (LED) provide backlighting for the symbols on the lever.
To protect the shift-by-wire lever electronics from overvoltages, there is an electric circuit inside that conducts Electro-Static Discharges (ESD) from the driver to the ESM through a separate ground connection.
- In the Key ON condition with the engine off, all the LEDs are on.
- In the Parking position with the engine on, the two P LEDs will be on
- In all the other positions, the corresponding gear LED (R - N - D - M +/-) will turn on
The ESM has the shift lever position sensor inside it. This ESM registers the drivers command, assesses the signal, communicates with the TCM and performs all the shift-by-wire control and diagnosis functions.
The ESM sensor control unit performs the following tasks:
- Determines the engagement travel and the position of the shift lever;
- Transmits the shift lever position signal to the TCM
- Communicates with the TCM through the CAN bus
- Processes the reverse unlock button signal and transmits the information to the TCM
- Processes the shift lever parking lock button signal and transmits the information to the TCM
- Controls the display device on the shift lever according to the transmission conditions transmitted by the TCM
The sensor built into the ESM detects the shift levers movements and position. This information is sent to the TCM. On the basis of this information, the TCM determines the transmission condition (P. R, N, D TIP) and sends it to the ESM. This information is used to control the operating strategies of the lever and the LED display at the top of the shift lever.