TipTronic® Gearboxes


If you've owned a VW or Audi in the last few years it might have come with a TipTronic® gearbox. To you, the driver, it looks like a regular automatic gearbox but with with an H-gate for the gearshift. In normal operation, you use the gearbox just like an automatic, putting it in 'D' for Drive and just letting it go about its business. But if you click the gearstick over into the H-gate it becomes a discreet automatic, meaning you can then click it fowards and backwards like a sequential gearchange. In this mode you are basically telling the gearbox when you want it to shift rather than allowing it to shift for you. When you click it forwards for example, you're indicating a desire to go up a gear. The ECU looks at the engine speed, road speed, torque and load and if all the planets align, it shifts up by activating the relevant solenoid valves in the automatic hydraulic system.
Most TipTronic® designs do have a certain amount of idiot-proofing though, and if you try to rev the **** off the engine in first, it will override you and automatically shift up to second to save the engine. These types of gearboxes often have steering-wheel shifters either as buttons or triggers on the steering wheel (like the Mazda MX-5) or paddle-shifters. TipTronic® is actually a design from Porsche and they simply license it to other vendors, typically German manufacturers. Because it was one of the first designs to come to the mass market, this type of discreet automatic automatic gearbox is now often referred to as TipTronic® even if it isn't one of the VW/Audi/Porsche ones. Here's a non-comprehensive list of some of the manufacturers and their TipTronic® type shifts:
Acura: Sequential SportShift. Audi: Tiptronic, Multitronic (CVT). BMW: Steptronic. Chrysler/Dodge: AutoStick. Citroën: Sensodrive. Ford (Australia): Sequential Sports Shift. Honda: iShift, S-matic, MultiMatic. Hyundai: Shiftronic, H-Matic. Infiniti: Manual Shift Mode. Jaguar: Bosch® Mechatronic. Lexus: E-Shift. Mazda: Sport AT. Mercedes-Benz: TouchShift. MG-Rover: Steptronic. Mitsubishi: INVECS, INVECS II, Sportronic, Tiptronic. Nissan: Tiptronic. Vauxhall/Opel: Easytronic. Peugeot: 2Tronic. Pontiac: TAPshift. Saab : Sentronic. Subaru: Sportshift (system developed and name used under license from Prodrive Ltd.). Smart : Softip. Volkswagen : Tiptronic. Volvo: Geartronic

Semi-automatic Gearboxes

Despite the name, these are actually an advanced type of manual gearbox. It's better to refer to them clutchless manual gearboxes because that more accurately describes what they are. Semi-automatics do not use planetary gearsets and torque converters; they use layshafts, output shafts, clutches and selector forks just like a manual. They come in three flavours, all of which have the same internal mechanisms. Two of those use the familiar paddle-shifters or up-down gearstick for changing gears. (This begins to explain why you cannot simply look at a gearstick or paddle-shifter and tell what the gearbox is. Up/down gearsticks or paddleshifters can both control sequential manual, clutchless manual or TipTronic® type gearboxes.) The third type has a pure manual gearstick. None of the three types have a clutch pedal though so how do they work? Well in the case of the first type, when you click the gearstick up or down, or press one of the paddleshifters, a hydromechanical system disengages the clutch and then moves the gearbox selector forks into the position for the next gear before re-engaging the clutch. Because the system takes inputs from load- and torque-sensors as well as road speed, throttle position and engine demand sensors, and because it's all computer controlled, it can shift more quickly and more smoothly that you or I ever could.
The third type uses the same hydromechanical system underneath but has additional sensors coupled to the gearstick. With this type, the action of moving the gearstick out of the gate for one of the gears (for example pulling it back from first) passes a hall effect sensor which tells the clutch to disengage. When you push the gearstick into the gate for the new gear, another hall effect sensor detects the final position of the gearstick and tells the clutch to re-engage. Effectively it's identical to driving a manual car only without a clutch pedal.
Clutchless manual gearboxes have appeared under many different names such as Saxomat and Olymat (Fiat 1800, Saab 93, some BMWs and Opels).

DSG / DCT Gearboxes - what, why and how?

How does this sound? A manual gearbox that's always in two gears at the same time. Sounds impossible, right? Scroll back up to the top of the page and look at how a manual gearbox works - how can this happen? Enter stage left the dual clutch transmission (DCT) or direct-shift gearbox (DSG). Two different names for essentially the same design. The most famous / common of these currently is the DSG as fitted to the Audi TT and some of the newer VW Golfs. The DSG is licensed technology from BorgWarner, which despite sounding like a horrible accident between a Star Trek character and a large movie studio, is an automotive parts supplier known until this point for its automatic gearboxes.
The principle is really simple even if the engineering is really complex. The idea is that when you're going up through the gears, increasing in speed, one clutch has the current gear engaged and a second clutch has the next gear up pre-engaged ready to use in the blink of an eye. Technically, that's not even true because a DSG can shift gears in 8 milliseconds. At 400 milliseconds it takes you 50 times longer than that to blink. That in essence is the key benefit to the DSG - blisteringly fast gearchanges. Plus, because one clutch engages as the other one disengages, the time that the gearbox is not driven under power is minimised.
So how does this work? Well a DSG gearbox has one layshaft like a normal gearbox, but two output shafts that mesh to a third shaft which goes to the differential. One output shaft has 1st, 3rd and 5th gears on it whilst the other has 2nd, 4th and 6th. The layshaft is actually two shafts one inside the other connected to two concentric 4-plate basket-type clutches at the end. In first gear, one clutch is engaged and the central layshaft is connected to the engine. Selector forks have the first dog-gear engaged with the first helical gear and the car is moving forwards. At the same time though, on the second output shaft, the second dog gear is already engaged with the second helical gear. Because the outer clutch on the layshaft is disengaged though, there is nothing driving this second gear and the outer layshaft is simply spinning freely. At the point when the gearbox needs to shift up, it simply engages the second clutch at the same moment it disengages the first and the outer layshaft is now being driven from the engine. Because second gear was already engaged there is literally no delay in shifting so the gearchange is near instantaneous. Once in second gear, the inner layshaft is now freewheeling as the selector forks engage third gear on the first output shaft and so on and so forth.
The three images below show my typical manual gearbox example modified into a 5-speed DSG. In this first image, first gear is engaged and second gear is pre-selected. The transmission of power from the engine to the output shaft is shown with the green components. The dual clutch (shown in cutaway) has engaged the inner set of friction plates which are connected to the outer layshaft. The first dog-gear is engaged with the first helical gear.
http://www.carbibles.com/images/dsginfirst.jpg

In this second image, second gear is selected and third gear is pre-selected. Again, the transmission of power is shown with the green components. This time the dual clutch has engaged the outer set of friction plates that are connected to the inner layshaft. The second dog-gear was already engaged with the second helical gear and so is now driving the output shaft.
http://www.carbibles.com/images/dsginsecond.jpg

This final image shows a cutaway of a simplified dual-clutch, dual-layshaft so you can see how the friction plates, layshaft and gears all relate to each other. The green inner layshaft has the drive gears for second and fourth whilst the outer red layshaft has drive gears for first, third and fifth. The grey clutch housing contains all the springs and hydraulics used to engage the various clutch plates, although they're not rendered in this view.
http://www.carbibles.com/images/dsglayshaft.jpg