Oerlikon Graziano, Vocis Driveline develop Independent Shift Rail transmission; DCT speed in a smaller, lightweight package

Italian transmission specialist Oerlikon Graziano and UK partner Vocis Driveline Controls, itself part-owned by Oerlikon Graziano, developed an innovative 7-speed automated manual transmission (AMT) that combines the dual-clutch principle of a DCT with the lightweight and compactness that is possible with an AMT when no manual option is required.

Designed for application in the new Aventador, the next generation supercar from Lamborghini, the 79kg gearbox is substantially lighter than its predecessor yet provides an extra ratio, handles more torque and maximizes cabin space by packaging into an exceptionally narrow transmission tunnel.

The new, 6.5 liter Lamborghini engine delivers 700 bhp (515 kW) at 8,250 rpm and 509 lb ft (690 N&iddot;m) at 5,500 rpm, which would normally require a substantial transmission. A conventional AMT, with external control systems, would not fit the available space, neither would a dual clutch transmission (DCT), which would need bulky wet clutches to meet the power handling requirements.

An AMT uses the established “H” pattern gearshift of a manual gearbox, in which the various gears are selected by sliding selector rails that lie parallel to each other. The jump from one rail to another corresponds to the dogleg in the middle of the H and is called “cross-gate” movement. Two actuators power the automatic shift; the actuator engaging the desired gear has to wait until the cross-gate actuator has selected the correct rail. Vocis and Oerlikon Graziano devised a strategy called independent shift rail (ISR) technology that eliminates this constraint.

In the ISR transmission, there is no cross-gate motion and consequently no cross-gate actuator. Instead, each rail is operated directly by its own actuator. One rail selects either 1st or reverse, one 3rd or 5th, one 2nd or 4th and one 6th or 7th. This means that no two sequential gears are on the same shift rail until the last change into 7th (top) gear. As a result, the system can begin to move the rail for the next gear while still withdrawing the previous one, allowing the shift to be accomplished faster.

The gearchange paddles are hard-wired into the Vocis-designed Transmission Control Unit (TCU), eliminating the time required for the CAN bus to poll the system. Very accurate measurement and control of the actuation current ensures precise and progressive control of the high-precision hydraulic valves, also specified by Vocis and designed uniquely for this application, that are critical not just to a fast change but also to shift quality.

Vocis points out that even with this new architecture, the ultra-fast shift speed would not be possible without careful optimization of the entire system.

Control systems are often designed after the gearbox hardware. By designing ours in parallel, using a small, highly integrated engineering team, we were able to eliminate a lot of the traditional compromises on both sides.

— Vocis managing director Mike Everitt

Packaging volume was minimized by refinement of every component and subsystem, including integrating the major hydraulic connections into the casing, developing a compact end-mounted valve block and using advanced analytical techniques to allow substantially reduced center distances between the shafts and reduced clearances between the transmission and the vehicle body.

Lamborghini claims a 50ms shift time for the new transmission.

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