Automatic gearbox - Jatco (Description): Description and operation

Description

General

The JATCO JF506E automatic gearbox is an electronically controlled, five speed gearbox which incorporates software to enable the gearbox to operate as a semi-automatic 'Steptronic' gearbox.

The gearbox can be operated as a conventional automatic gearbox by selecting P, R, N, D, 4, 2 or 1 on the selector lever. Moving the selector mechanism across the gate to the 'S/M' position, sends a signal to the Electronic Automatic Transmission (EAT) ECU and puts the gearbox into sport/manual mode.

In sport mode, the gearbox still operates as a conventional automatic transmission, but the unit becomes more responsive to driver demands. Lower gears will be held longer and the transmission will downshift more readily. This gives increased acceleration and improves vehicle response.

When in sport mode, if the selector lever is moved to the + or - positions, the system will automatically change to operate in manual mode. Manual gear changes can be performed sequentially using the selector lever. Movement of the selector lever in the forward (+) direction changes the gearbox up the ratios and movement in a rearward (-) direction changes the gearbox down the ratios.

Gearbox operation is controlled by the EAT ECU and the Engine Control Module (ECM) which communicate via a Controller Area Network (CAN) Bus. The EAT ECU receives information from the ECM and gearbox sensors to calculate the appropriate gear ratio for the conditions and controls solenoid valves to operate the gearbox as required.

The advantages gained with the electronically controlled gearbox are smoother gear changes, quicker and more accurate gear change scheduling and reduced fuel consumption through improved engine/gearbox speed matching.

Steptronic JATCO Automatic Gearbox

The JATCO five speed automatic gearbox is similar to conventional electronically controlled transmissions but provides the driver with an additional manual mode feature. Manual mode allows the driver to electronically select the five forward gear ratios and operate the gearbox as a semi-automatic manual gearbox.

The individual gear ratios are achieved through three planetary gear sets. The components of the planetary gear sets are driven or locked by means of four multi-plate clutches, two multi-plate brakes, one brake band and two one-way clutch assembles. Torque is transmitted from the gearbox to the final drive through a reduction gear.

Gearbox Casing Refer to JATCO Automatic Gearbox illustration.

The gearbox casing contains the input shaft transmitting the power into the drive train. The drive train is made up of the planetary gear sets and clutches.

The clutches and brake bands control which elements of the planetary gear sets are engaged and their direction of rotation, to produce the P and N selections, five forward ratios and one reverse gear ratio. Power output is from the drivetrain through a reduction gear into a differential.

Gear Ratios