The Beauty of Having Two Separate Gear Sets - Transmission Digest

Main Navigation

Advertisement
Social Connect
Resources
Our Brand Family
Transmission Digest
Helping transmission shops achieve successful and profitable operation.
Manual Transmission

The Beauty of Having Two Separate Gear Sets

In last month’s article, we began to study the dual-clutch transmission, looking at its potential to eventually replace the common torque converter-planetary automatic transmission. In this chapter, we will look at the mechanical theory of operations on how these gear boxes work. We will be using illustrations from VW and Audi who were the first to mass market this design in 2003, in the Audi TT and VW Golf models.

Avatar
By Mike Weinberg

Up To Standards

  • Author: Mike Weinberg, Contributing Editor
  • Subject Matter: Dual clutch transmissions
  • Issue: Mechanical theory

Second in a series

In last month’s article, we began to study the dual-clutch transmission, looking at its potential to eventually replace the common torque converter-planetary automatic transmission. In this chapter, we will look at the mechanical theory of operations on how these gear boxes work. We will be using illustrations from VW and Audi who were the first to mass market this design in 2003, in the Audi TT and VW Golf models.

Related Articles

BorgWarner designed and created the wet-clutch systems and the computer-controlled electronic modules that make the system work. BorgWarner’s brand name for these transmissions is Dual Tronic, while VW/Audi calls these transmissions DSG or Direct Shift Gear Box. We will be looking at the front-wheel-drive transaxle design here, but these units are available by different manufacturers in rear-wheel-drive and four-wheel-drive variations also.

The theory of operation of any design will transcend to any variation of that design, so understanding the basic operation will help to diagnose issues requiring repair. The dual-clutch transmission provides an improvement at present of 5% to 15% better fuel efficiency, quicker acceleration and reduced emissions. The BorgWarner Dual Tronic systems will be found in AUDI/VW, Bugatti Veyron, Nissan GT-R, Audi S Tronic 7 speed, the Mitsubishi Lancer Evolution X, Ford, Volvo, and BMW models, with more to come as other manufacturers move to these designs.

Perhaps the easiest way to look at a dual-clutch design is to realize that basically it is two separate transmissions combined in one unit operating independently. The gear train is basically a manual transmission and each of the transmissions have two multi-plate wet clutches. There are three input shafts that are housed within each other. The innermost shaft is a solid drive shaft that is splined into a dual-mass flywheel bolted to the engine crank shaft and to a crescent-type of oil pump to provide the hydraulic pressure to operate the dual-wet clutches, shift the synchronizers, and cool the transmission through an oil to radiator trans cooler.

On the Audi/VW trans, the outer wet clutch is the K1 clutch and provides power to 1st, 3rd, 5th, and reverse gears. These wet clutches function exactly as a typical automatic clutch drum. The K2 clutch, which is the inner pack, powers 2nd, 4th, and 6th gears, as it splined to the middle input shaft. Both shafts have the gear sets mounted on them as well as a tone wheel that measures rpm so that the computer control can match the shaft speeds for very fast synchronization of the shifts. Keeping in mind that we are combining two separate transmissions within one housing, we now look at the output shafts of which there are two.

Output shaft 1 has 1st, 3rd, 4th, 2nd, and an output shaft gear to transfer torque to the final drive gear on the differential. Output shaft 2 contains 5th gear, 6th gear, reverse gear and an output shaft gear that sends torque to the final drive gear on the differential. Now we have to add one more shaft so that we can create a reverse rotation, so there is a reverse shaft, which meshes with 1st and reverse gears. Park mode is accomplished with a park-lock gear mounted on the differential carrier that operates with a typical parking-pawl setup to achieve a positive park position.

Synchronization on these units is achieved by using moly-coated rings in triple-, double-, and single-cone designs as is commonly found on most late-model manual transmissions today. The beauty of having two separate gear sets is that the transmission can preselect the next gear, which will not apply until one clutch pack releases and the other applies. This creates the lightning quick shifts possible with this design, without a major drop in rpm, and provides a transmission that will shift automatically through the computer-controlled module, or can be manually shifted through paddles or the stick, with no clutch pedal needed.

In our next chapter we will look at the mechanics and electronics that make these units shift.

You May Also Like

Manual Transmission

Lubricants: Understanding the Mysteries

Lubricating oils or lubricants have been around since the invention of the wheel, and every class or type of machinery uses and needs them. But, how much do we really understand about these products and about the amazing amount of engineering that is found in a can?

Avatar
By Mike Weinberg

Up To Standards

Author: Mike WeinbergSubject Matter: LubricantsIssues: History, additives

Technical Training

Lubricating oils or lubricants have been around since the invention of the wheel, and every class or type of machinery uses and needs them. But, how much do we really understand about these products and about the amazing amount of engineering that is found in a can?

Read Full Article

More Manual Transmission Posts
Tires Vastly Improved, but Check the Specs

The advancement of technology in the automotive field is rapid and unrelenting. Forces that shape the marketplace, state and federal regulations, the need to attract new customers, and the need to be different and at the same time profitable are driving the car makers to develop technology at a pace never seen before.

By Mike Weinberg
Are We Speaking the Same Language?

If you are repairing transmissions for a living, you will invariably spend some time on the phone ordering parts and speaking with technical hotlines to assist in your diagnosis of problems. Having been on both ends of a tech line for over half a century and an equal amount of time buying parts, I have learned a whole new language. To be successful communicating with those entities, one must understand the language and be speaking about the same correct topic with whoever is on the other end of the conversation.

By Mike Weinberg
Electronics In Dual Clutch Units

This article is the final segment of our exploration of the dual-clutch transmission, or direct shift gear box (VW and Audi) or DualTronic in BorgWarner’s brand. We have included several schematics from a VW Touran model, as VW has the largest amount of these transmissions in use. VW using its VAS 5051 diagnostic system provides for, as they say, “guided fault finding,” which means that a test schedule is available for the unit and provides testing for sensors, actuators and the mechatronic (computerized) valve body.

By Mike Weinberg
Hydraulic & Fluid Controls in Dual-Clutch Units

To recap, we have looked at how the dual-clutch transmission functions, essentially two gear boxes in one with the input shafts driven by hydraulically applied clutch packs that drive three concentric shafts that are one inside the other. The innermost shaft drives a gerotor-type of fluid pump that provides pressurized fluid to actuate the dual clutches, lubricate and cool the components, and shift the transmission into the selected gear. The next two shafts are driven by the two clutch packs with one shaft shifting the even-number gears and one shifting the odd-numbered gears.

By Mike Weinberg

Other Posts

Transmission Tech: Dual Clutch Operation Part 1

In this episode of Transmission Tech, Mike Riley begins a video series on DCT design, diagnostics and repair.

By Transmission Digest
TDTG 042320 DCT Part1
Controls Make Shifts Happen in Milliseconds

If you have been following the previous chapters of this series of articles, you are starting to understand the function of dual-clutch transmissions. We have used illustrations from the VW Direct Shift Gear Box (DSG) as VW has about 2 million of these units on the road at present.

By Mike Weinberg
Dual Clutch Transmissions: Are They the End of the Torque Converter?

We have enjoyed two major designs of transmissions for many years. The manual transmission where the driver disconnected the power flow from the engine to the transmission by stepping on the clutch pedal and manually moving the shift lever from the present gear to the next gear to be selected.

By Mike Weinberg
The New Year: It Will Be As Good As We Make It

Note: Mike Weinberg wrote this new-year outlook piece 10 years ago. Looking back to that time is instructive as it shows how business owners have endured tough times and how they must persevere in the same fashion going forward.

By Mike Weinberg