Transmission

The term "transmission" usually refers to a manual or range-change transmission. Its role in the powertrain is to transfer power, and therefore to adapt the varying output P (kW) and torque M (Nm) of the (internal combustion) engine to the chang­ing parameters of weight, gradient/acceleration resistance, roll resistance and aerodynamic drag. Manual transmissions are usually of the gear-only type.

Manual transmission types

Constant mesh transmission

In a constant mesh transmission, there are no synchronising components (synchronising rings or packages) installed between the gear wheels and the shift sleeves. A force-locked connection (= engaged gear) between the meshing gear wheels and shift sleeves is only possible if both components are moving at the same speed or are at standstill. Ensuring that they move at the same speed was once the task of the driver (double-declutching, blipping the throttle). Nowadays this is done by engine and trans­mission control systems.

Synchromesh transmission

As in a constant mesh transmission, a force-locked connection between the meshing gear wheels and shift sleeves is only possible if both components are moving at the same speed or are at standstill. Ensuring that this is the case is the task of the synchromesh.

Planetary gear set

Gear set with equal input and output axes which distributes the torque and can be shifted under load. Power is distributed via at least three planetary gears. All the ratios are achieved by selective activation of the individual moving components. Major components: centre gear, planetary gears (with planetary carrier), ring gear (internal teeth).

Transmission principle

Gear-ratio steps

Direct drive transmission

The ratio of the highest gear is 1 to 1. The input torque is transferred to the drive axle differential without conversion, and therefore without losses.

Overdrive transmission

The input torque is reduced and the rpm is increased in one (or more) stage(s).

Ratio range

Describes the ratio between the highest and lowest gear.

Layshaft brake

Braking mechanism on the layshaft of the main gearbox. Function: the flywheel mass of the clutch is braked as it enters the transmission, so as to achieve faster synchronicity between the input and output.

Clutch brake

Acts on the clutch shaft. Action: see Layshaft brake.

Gearshift systems

Direct shift: shift lever is directly on the transmission cover, with purely manual transfer of gear shifting force (muscle power).
Remote-control shift: the transmission and shift lever are spatially separated; transfer of gear shifting force is manual (muscle power via linkages/cables), hydraulic/pneumatic (usually muscle power with servo assistance) or by external means (shift by wire).