Koenigsegg’s Light Speed Transmission – Revolutionary

Gearboxes have been used in automobiles for quite a while now, ranging from the use of simple chains with gears to commonly used torque converters by most cars on the road today. Although their function has remained the same throughout history, gearboxes have been through quite a few variations, application-dependent.

The Torque Converter

A torque converter is a type of fluid coupling, which allows the engine to spin somewhat independently of the transmission. Hence it does not require a clutch to disconnect the engine from the transmission. Its main characteristic is to allow the engine to spin “somewhat” independently of the transmission. In addition, the torque converter pressurizes the transmission fluid (which is an incompressible oil) and this pressurization provides the force that is necessary to shift gears. Although it is suitable for low-power applications, it is not the best when quick-shifting is required.

Dual Clutch Transmission

Dual Clutch Transmission (DCT) uses two clutches in conjunction to assist with gear changes. The idea of a DCT started in the early 1930s in France but it never saw traction at that time. However, in the 1980s, Porsche created the Porsche Doppelkupplungsgetriebe (PDK) and like most automotive inventions, it was born out of racing requirements. The Porsche 962 was successful at Monza in 1986 with the PDK.

Yet, the PDK did not last long as the dry clutches available at that time did not provide the “smoothness” Porsche desired to put the PDK into road use. Porsche then began to develop its own wet clutches; however, this wasn’t a feasible option either. Fast forward to 2009, the interest in DCTs grew around the globe, and Porsche along with ZF produced the PDK 1. DCTs, like the PDK, provide almost instantaneous shifts, as the dual-clutches always have the next gear pre-selected and ready to shift. These transmissions are insanely quick and used in most supercars today. However, they can only pre-select one gear at a time and show some stubbornness while shifting multiple gears at once.

The Koenigsegg LST

Imagine a gearbox with the lightning-quick speed of the DCT but without the restriction of only achieving those quick shifts to the adjacent gears. Swedish manufacturer, Koenigsegg, has produced a revolutionary transmission that features just that called the Light Speed transmission. The Gearbox is a 9-speed and features seven clutches (yes, seven!). The differential is also a part of the transaxle and the whole package, along with fluids, only weighs 90 kilograms. This transmission is used in the Koenigsegg Jesko which has 1600 HP. Unlike a dual-clutch, the LST has no selector forks, collars, or synchronizers to engage each individual gear. Instead, the selection is executed purely by opening and closing clutches. These clutches can open or close in under two milliseconds. So technically, there is no shifting; there is only clutching between the gears. The transmission is able to jump from any forward gear to another in under 2 ms and shift to adjacent gears even quicker. Six clutches are designated for the forward gears and one for the reverse. The image below depicts how the combination of the clutches works to change between gears. The gears are arranged in three shafts, with the top one being the input shaft and the bottom one being the output shaft. Each clutch has its own pressure sensors and hydraulic actuators.

Due to this multi-clutch configuration, the LST delivers what Koenigsegg calls “ultimate power on demand”, or UPOD, by simultaneously opening and closing the respective clutches when switching gears. This instantaneous gear changing (literally), coupled with the flat-plane V8 of the Jesko makes it one of the few cars in the world that can cross the 300 MPH mark. Although open-clutches may not work their way into normal road cars due to their inefficiency, they are an optimal solution for high torque and power applications.

References:

• https://www.yutakagiken.co.jp/en/products/drive/
• https://www.roadandtrack.com/car-culture/a38269537/porsches-pdk-gearbox-traces-its-roots-to-the-962/
• https://www.caranddriver.com/features/a28927301/koenigsegg-new-transmission-promises-ultraquick-shifts/

The following blog post has been written by Aamir Ghare. An Instrumentation Engineer deeply engaged in cars all his life. Aamir loves watching motorsport and hopes to be involved in it in the near future.

This post has been edited for grammar and other inconsistencies. To learn how you can contribute to content creation at Formula Bharat, visit www.formulabharat.com/careers.

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