Transmissions

This section begins with a description of a Dual Clutch Transmission (DCT).

Presented in the subsections are some practical examples: BMW, Mercedes Benz

Brief History (Wikipedia)

This type of transmission was invented by Frenchman Adolphe Kégresse just before World War II, although he never developed a working model. The first development of the twin-clutch or dual-clutch transmission started in the early part of 1980 under the guidance of Harry Webster at Automotive Products (AP), Leamington Spa, with prototypes built into the Ford Fiesta Mk1, Ford Ranger, and Peugeot 205. Initially, the control systems were based on purely analogue/discrete digital circuitry. All of these early AP twin-clutch installations featured a single dry clutch and multiplate wet clutch. Following discussions with VW/Porsche, DCT work continued from Porsche in-house development, for Audi and Porsche racing cars later in the 1980s, when computers to control the transmission became compact enough: the Porsche Doppelkupplungsgetriebe (PDK) used in the Porsche 956 and 962 Le Mans race cars from 1983, and the Audi Sport Quattro S1.

Basic advantages

Shifts can be accomplished without interrupting torque distribution to the driven roadwheels, by applying the engine's torque to one clutch at the same time as it is being disconnected from the other clutch. Since alternate gear ratios can preselect an odd gear on one gear shaft while the vehicle is being driven in an even gear (and vice versa), DCTs are the fastest-shifting road car transmission available.

Some manufacturers

BorgWarner

Eaton (truck market)

FEV

Getrag

Oerlikon Graziano

LuK (clutches)

Ricardo

ZF

Click on the image below to open an explanatory Youtube video by Tremec:

Some other views to give other examples:

Next we look at a section of the gearbox with a very simplified diagram:

From a more representative diagram we can see that there are two concentric clutches, where the outer one is connected to an inner shaft (red) for odd gears, and the inner clutch is connected to a hollow shaft (green) for even gears. The relevant clutch and gear selectors are actuated in order to select the desired gear.

Below we can see a few more cross sections of clutches, the second one from a Honda motorcycle:

This cross section below belongs again to a Honda motorcycle rather than a passenger car, so the disposition of the clutches is slightly different but the concept is similar:

Highlighted in blue are various different parts of a DCT:

Honda have a useful diagram explaining some of the sensors and actuators:

• • No. 1 Linear Solenoid Valves

  • No. 1 Clutch Pressure Sensor

  • No. 2 Linear Solenoid Valves

  • No. 2 Clutch Pressure Sensor

  • Line Pressure Sensor

  • Line Temperature Sensor

  • Outer Main Shaft Speed Sensor

  • Inner Main Shaft Speed Sensor

  • Shift Spindle Angle Sensor

  • Neutral Switch

  • Shift Drum Angle Sensor

  • Speed Sensor

And in this sequence we can see how 1st and then 2nd gear is engaged:

Below we can see a split view of a synchroniser