Analysis of Double Clutch: From Wet to Dry
Introduction: With the mass production of the 7-speed DSG gearbox equipped with LuK dry dual clutch, the DSG gearbox has entered a new stage, and the dual clutch of the dual clutch transmission DSG took five years from wet to dry.
With the mass production of the 7-speed DSG gearbox equipped with LuK dry dual clutch, the DSG gearbox has entered a new stage, and the dual clutch of the dual clutch transmission DSG took five years from wet to dry.
The latest 7-speed DSG gearbox is instructive for the future development of automobile dual clutch system, which brings convenience, movement and comfortable driving experience. Since Volkswagen put into the market in 2003, the six-speed DSG dual-clutch automatic transmission has opened a new era of transmission, which is inseparable from the vigorous investment of Volkswagen in new technology and the vigorous expansion of parts manufacturers in the field of new technology. Standing behind Volkswagen’s first-generation DSG is Borg Warner, who is providing wet dual clutches for Volkswagen DSG, and who will stand behind the second-generation DSG?
In the spring of this year, Volkswagen released a 7-speed DSG gearbox. Except for adding a gear, the biggest difference with the 6-speed DSG is that it adopts a dry dual clutch. This time, which component manufacturer provided the core component-dry dual clutch for the public? That is LuK Company, headquartered in Buehl, Baden, Germany. As an expert in clutch and gearbox system in the industry, it has developed this latest dry dual clutch through close cooperation with Volkswagen. In terms of fuel economy, it is better than the gearbox equipped with wet double clutch, and compared with the traditional manual gearbox, it can save fuel consumption by about 6%.
Wet dual clutch produced by Borgwarner
The birth of double clutch makes the phenomenon of power interruption and passengers "nodding" when shifting gears become history. As the heart of DSG gearbox, the working principle of LuK dry dual clutch is simple: LuK’s dual clutch consists of two clutches. One of the clutches is connected with the odd gear input shaft of the gearbox: 1st gear, 3rd gear, 5th gear and 7th gear; The other clutch controls the input shaft of even gears: 2nd gear, 4th gear, 6th gear and reverse gear. For example, when the vehicle is driving in 2nd gear, 3rd gear is already in gear (only the 3rd gear clutch is not engaged). Therefore, the whole shift process can be carried out quickly, smoothly and without torque interruption. The shift is completed by electro-hydraulic control mechanism, and the driver can hardly feel the instantaneous shift and the opening and closing of a single clutch.
The 6-speed DSG’s multi-plate dual clutch runs in the cooling oil tank in a "wet" way, while the LuK’s dual clutch has a dry structure. The torque transmission of wet dual clutch is realized by wet clutch friction plate immersed in oil, while the torque transmission of dry clutch is realized by friction plate on clutch driven plate. Because of saving the high efficiency of torque transmission of related hydraulic system and dry clutch itself, dry system greatly improves fuel economy. The same 1.9 TDI(105 PS/ 77 kW) engine with 7-speed DSG gearbox can save more than 10% fuel compared with 6-speed wet dual clutch transmission.
The design of "dry" double clutch has brought many benefits, the most important of which is to significantly improve the efficiency of the gearbox system. In addition, the new generation DSG gearbox eliminates the suction filter, oil cooler and high-pressure oil pipe in the gearbox housing. Like the ordinary manual gearbox, gearbox oil is only used for lubrication and cooling of gearbox gears and bearings. Therefore, the 7-speed DSG transmission oil only needs 1.7 liters of transmission oil, while the 6-speed DSG transmission oil needs 6.5 liters. Although "dry" dual clutch has many benefits, it is limited in torque transmission. The new generation DSG gearbox is suitable for all "small" engines with maximum torque less than 250 Nm.
Generally speaking, the dimension of dry double clutch is slightly larger than that of wet double clutch. This is determined by the layout of the double clutch and the friction material selected. Because the external dimensions of the dry dual clutch of the 7-speed DSG gearbox are slightly larger, the rest parts should be designed to be more compact, so that it can be equipped on Polo-class small cars.
Since 2004, LuK has started close cooperation with Volkswagen in the development of DSG damping parts. The torsional vibration absorber in this DSG technology gearbox-dual-mass flywheel is also LuK’s product. LuK’s double clutch has been shipped to Volkswagen’s transmission factory in Kassel, Germany since the beginning of 2008. LuK’s factory in Buehl has been fully prepared for mass production (about Schaeffler Group: the German-headquartered Schaeffler Group has three famous brands: INA, LuK and FAG, and is a leading manufacturer in the global automobile industry and rolling bearing industry).
A set of numbers about DSG gearbox
* 0.4 liter: Golf sedan with 122 horsepower TSI engine and 7-speed DSG.
The fuel consumption of the model is 0.4 liters less than that of the model equipped with a 6-speed manual transmission.
* 1.7 liters: 1.7 liters of transmission oil is required for the 7-speed DSG transmission.
* 6.5 liters: 6.5 liters of transmission oil is required for the 6-speed DSG transmission.
* 6 models: At present, Volkswagen has 6 models that can be equipped with a 7-speed DSG gearbox.
* 70kg: The 7-speed DSG gearbox weighs 70kg.
* 93kg: The 6-speed DSG gearbox weighs 93kg.
* 105 HP: At present, the "minimum" engine power matching DSG gearbox is 105 HP.
* 300 HP: At present, the "maximum" engine power matching DSG gearbox is 300 HP.
* 140℃: The maximum working environment (transmission oil) of electromechanical control module of 6-speed DSG gearbox is 140℃.
* 250Nm: The maximum torque of the engine matched with the 7-speed DSG gearbox is 250 nm.
* 350Nm: The maximum torque of the engine matched with the 6-speed DSG gearbox is 350 nm.
The main reason for the difference in the above data is the adoption of dry/wet dual clutch.
(Author: Weidong)