DSG – Direct Shift Transmission (Dual Clutch)
Direct Shift Transmission (Dual Clutch)
The direct shift gearbox (German name: Direkt-Schalt-Getriebe), also known as DSG, is a multi-shaft, dual-clutch, electronically controlled manual gearbox that has a design called a “transaxle” unit one housing gearbox and differential), without a traditional clutch pedal and with full automatic or semi-manual control. The first true dual-clutch gearboxes were developed by Porsche in the 1980s for its Porsche 962 race car..
In simple terms, the DSG transmission is two separate mechanical gearboxes (and two clutches), combined in one housing and working as a single unit. It was designed by BorgWarner and was originally licensed to the Volkswagen Group with the support of IAV GmbH. The presence of two separate clutches allows you to speed up the process of gear shifting and eliminates the need to use a torque converter present in automatic planetary gearboxes.
Transverse DSG Transmission
During its market launch in 2003, it became the world’s first dual-clutch transmission, which was equipped with a production car – the Volkswagen Golf Mk4 R32, and shortly afterwards – the original Audi TT 3.2. In the early years of production, this original DSG transmission was only installed on vehicles with front-wheel drive front-wheel drive layout or on all-wheel drive systems manufactured by Haldex Traction.
The first DSG Transaxle transmission, which went into production for Volkswagen Group’s mass-produced automobiles, had six forward gears (and one reverse speed) and a wet multi-plate clutch (immersed in an oil bath) (Volkswagen Group internal code) : DQ250, catalog code prefix: 02E). Such a transmission was paired with engines developing up to 350 Nm (260 lb-ft) of torque, and the single-drive version weighs 93 kg (205 lbs). It is produced at the Volkswagen Group factory in Kassel, the daily output of which is 1,500 units.
At the beginning of 2008, another DSG transmission appeared in the Transax scheme, a seven-speed transmission weighing 70 kg (150 pounds) (Volkswagen Group internal code: DQ200, catalog code prefix: 0AM). It differs from the six-speed DSG in that it has two dry-clutch single-plate clutches (of the same diameter). Such a clutch was developed by LuK Clutch Systems, LLC. This seven-speed DSG is used in front-wheel drive cars with small engines and low torque output, such as the new Volkswagen Golf, Volkswagen Polo Mk5, and the new SEAT Ibiza. She is paired with engines developing up to 250 Nm (180 lb-ft) of torque. The filling capacity of the DQ200 box is 1.7 liters (0.37 English gallons; 0.45 US gallons) of transmission fluid, which is significantly lower than the six-speed DQ250.
In September 2010, Volkswagen launched the new seven-speed DSG, the DQ500, rated at 500 Nm (370 lb-ft) of torque. It was first used on the Audi TT-RS..
Longitudinally mounted transmission DSG (Audi)
At the end of 2008, the latest seven-speed version of the Transaxl DSG transmission called S-tronic (internal code for the Volkswagen Group: DL501, catalog code prefix: 0B5) went into series production. At first, from the beginning of 2009, it was used only on some Audi models, and only with longitudinally mounted engines. This drivetrain utilizes a wet-type concentric dual multi-plate clutch, as in the original six-speed DSG. However, it is in this version that there are much more clutch disks: a larger external clutch (for odd gears) has 10 clutch disks, and a smaller internal clutch has 12 disks.
Another notable difference from the original transverse DSG is the lubrication system: Audi now uses two completely separate oil circuits. One 7.5 liter (1.65 English gallons; 1.98 US gallons) circuit is designed to lubricate the hydraulic clutch and mechatronics unit with a special synthetic transmission fluid for automatic transmissions (ATF), while the second circuit is 4.3 liters (0.95 English gallons; 1.14 US gallons) lubricates the gears as well as the front and center differentials with normal hypoid oil. Such a dual-circuit lubrication system is aimed at improving overall reliability (of the system) by eliminating cross-contamination with waste and wear particles. It is designed to transmit torque of up to 600 Nm (440 lb-ft), and net engine power of up to 330 kW (450 PS (German PS); 440 bhp (British PS)). Its total weight, including lubrication and a two-section flywheel, is 141.5 kg (312 lbs).
This transmission was first used in quattro all-wheel drive systems in Audi vehicles; it is very reminiscent of the new Porsche Doppel-Kupplung (PDK) gearboxes from ZF Friedrichshafen.
DSG Transmission Version List
|Name||Qty||Max Torque||A type|
An internal combustion engine drives two clutches. An external clutch controls gears 1, 3, and 5 (and 7, if any) and the reverse gear. External clutch is designed to transmit more torque due to the fact that its discs have a larger diameter compared to internal clutch discs. The internal clutch controls gears 2, 4 and 6. Unlike the standard large dry single-plate clutch, each six-speed DSG clutch is a collection of four small wet-type clutch discs (similar to a motorcycle wet multi-disc clutch). Due to space limitations, the two clutch sets are concentric and the shafts inside the gearbox are hollow. Due to the fact that the transmission prepares gears for the “waiting” clutch in advance (switching to the selected gear occurs through the currently unused transmission section), it is possible to avoid a break in the power flow during gear shifting, since the torque transmission is simply transferred from one clutch to the second . This means that the dual-clutch transmission can handle upshifts in just 8 milliseconds. For comparison, a sequential gearbox (SMT) in a Ferrari F430 Scuderia takes 60 milliseconds to shift, while a Ferrari Enzo takes 150 milliseconds. The mentioned upshift time is the time during which no power is supplied to the wheels.
DSG Gearbox Controls
The direct shift gearbox has a gear lever on the floor of the body, very similar to the one used for a traditional automatic transmission. The lever moves forward and backward (no displacements or curved paths of movement of the lever); it also has an additional button designed to prevent accidentally switching the lever to the wrong position.
If the floor gear lever is in the “P” position, this means that the transmission is in parking mode. In this position, both clutches are fully disengaged, all gears are disengaged, and the driven gear of the main gear is rigidly fixed by the gearbox lock. This mode can only be activated when the vehicle is stationary. In addition, the lever must be moved to this position before removing the ignition key..
If the floor gear lever is in the “N” position, this means that the transmission is in neutral mode. As in the “P” mode, both clutches are switched off and all gears are disengaged; however, the parking lock is also off.
While the vehicle is stationary and in neutral mode, the driver can shift the lever to the “D” (forward) position after depressing the brake pedal. The reverse gear engages on the first shaft K1 and the external clutch K2 engages. At the same time, the reverse gear clutch is prepared in advance on the shaft of the reverse gear, since the gearbox does not yet know if the driver wants to go forward or backward. The clutch package for second gear (K2) is getting ready for engagement. When the driver releases the brake pedal, the clutch pack K2 increases the closing force, resulting in a second gear; Thus, the torque is transmitted from the engine through the transmission to the drive shaft and the running wheels, which allows the car to move. As a result of pressing the accelerator pedal, the clutch engages and the forward speed increases. Pressing the gas pedal all the way (sharp acceleration) will force the gearbox to shift to first gear (“kickdown”) to provide acceleration at first speed, although there will be a short delay until the transmission turns off second gear and engages first.
As the vehicle accelerates, the transmission control unit decides when to use the second gear (which is secured to the second clutch). Depending on the speed of the car and the engine power needed by the driver (which is determined by the position of the accelerator pedal), the DSG box increases gears. During this process, the transmission disengages the first external clutch and simultaneously engages the second internal clutch (all engine power now passes through the second shaft), thereby performing a gear shift sequence. This process takes 8 milliseconds (thanks to the preliminary selection of gears) and can occur even when the throttle is fully open, therefore, as a result of power loss, there is practically no.
As soon as the transmission has finished switching to the second gear, the gear of the first gear is immediately disengaged and the gear of the third gear is prepared (which is on the same shaft as the gears of the first and fifth gears). When the time comes to switch to third gear, the second clutch disengages and the first engages again. The transmission continues to operate in the same manner for the remaining forward gears..
Downshift is activated according to the same principle as upshifts, only in reverse and slower – it takes 600 milliseconds due to the fact that the electronic control unit (ECU) must open the throttle for a short time, so that the engine crankshaft rotates at a speed gear shaft rotation.
This happens when the control unit responds to a deceleration of the car or if an increase in power is required (during acceleration) – for this the control unit activates the lower gear on an unused shaft.
The switching moment is determined by the DSG transmission control unit, which controls the hydromechanical unit. The transmission control unit, combined with the hydromechanical unit, is called “mechatronic”. Since the so-called “fuzzy logic” is used in the DSG control unit, the DSG gearbox is considered adaptive, that is, it adapts to the driver’s driving style and will gradually adapt shift points to it.
On the dashboard of the car, between the speedometer and tachometer, the available positions of the gear lever are displayed, the current position of the lever is shown in bold, and the current gear ratio is displayed.
With “normal” increasing linear acceleration and deceleration, the DSG gearbox shifts gears sequentially, i.e. as follows: during acceleration – 1st> 2nd> 3rd> 4th> 5th> 6th, and in reverse when decelerating. However, the sequential method is not the only possible one; a transmission can also skip adjacent gears, skipping two or more steps at once. The latter is especially true in situations where when driving at moderate speeds in one of the highest gears with a slightly open throttle, the accelerator pedal is flushed to the floor, activating the kick-down function (switching to lower gear). In the kick-down mode, the box can jump to several gears of the steps, including the most suitable gear at once, depending on the speed and degree of opening of the throttle. The kick-down mode is activated when you press the accelerator pedal hard and is completely independent of the additional resistance of the pedal that can be felt when the kick-down function is turned on in manual control mode. In 2007 Audi cars, the seven-speed transmission does not automatically shift to seventh gear – instead, it remains in fifth to maintain a constant power supply at high speeds at medium operating speed.
When the floor shift lever is in the “D” position, the DSG dual-clutch gearbox operates in fully automatic mode, in which it is programmed to shift gears in such a way as to maximize fuel economy. This means that gear changes will occur at earlier revs. For example, on the Volkswagen Golf Mk5 GTI, sixth gear is engaged at a speed of approximately 52 km / h (32 mph), according to the default settings of the DSG transmission control unit, however, with an aggressive or sporty driving style, the adaptive gearbox will increase the speed at which sixth gear.
The floor shift lever also has an “S” position, which means the DSG transmission is in sport mode. The sport mode is fully automatic, this mode is comparable to the “D” mode, but up and down gears are made at higher speeds. This mode is convenient for a sporty driving style, since it uses much more available engine power and applies maximum engine braking. However, fuel consumption in this mode is markedly increased compared to mode “D”. This mode is not entirely suitable for a quiet ride or for driving on a slippery road (in rain, snow, ice), as tire grip may be lost (wheel slipping during acceleration or jamming of wheels when lowering gears at high speeds with the throttle closed ) On cars equipped with 4motion or quattro all-wheel drive systems, this can be compensated by the fact that in S mode the rear differential works continuously to more or less optimize power distribution in case of loss of front-wheel traction.
The “S” position is highlighted, the current gear ratio is also displayed on the dashboard, as in the “D” mode.
The “R” position of the gear lever indicates reverse gear. It works similarly to the “D” mode, but there is only one gear in reverse mode. In the “R” mode, the corresponding position is highlighted on the dashboard.
The DSG gearbox also has a manual control mode, for which there are spring-loaded “+” and “-” positions on the gear lever. This mode can be activated by moving the lever in the opposite direction from the driver (in cars with a driver’s seat on the right, the lever must be pushed to the left, and in cars with left-hand drive – the lever is moved to the right) from the “D” mode. When choosing manual mode, the box can be controlled as mechanical, although gear shifting is performed only sequentially.
In most VW vehicles, the indicator on the dashboard displays the number of the gear selected (from 1 to 6), and, as in automatic mode, the gear ratio used is highlighted. In other models (eg Audi TT), the “M” indicator lights up on the display, followed by the gear number, for example M1, M2, etc..
In order to switch to a higher gear, the lever should be moved forward (overcoming the spring resistance) to the value “+”, and to engage the downshift, the lever must be moved back to the “-” position. Now the decision to shift gears in the DSG transmission is made mainly by the driver. This control method is called tiptronic. In order to protect the engine, when accelerating in manual mode (tipronic mode), the DSG transmission automatically increases gears to the cut-off, and when slowing down, it automatically reduces gears at very low revs before the engine starts to idle. In addition, if the driver selects a gear whose inclusion is currently inappropriate (for example, downshifting when the tachometer needle is close to the red line), the DSG box will not engage the gear selected by the driver.
Modern modifications of the DSG transmission still reduce gears to the lowest possible gear ratio after activating the kick-down button when the throttle is fully open in manual mode. In the manual control mode, the kick-down function is activated by an additional button under the accelerator pedal; if this button is not pressed, the DSG will not engage downshift, but simply provide acceleration with the throttle fully open in the gear that was used before.
Paddle shift paddles
Initially, paddle shift paddles were on certain high-power and sports cars, for example in cars with 2.0 TFSI engines and 3.2 / 3.6 VR6. However, today they are found (either as part of the standard package, or as an accessory to choose from at an additional cost) on virtually all machines equipped with DSG transmissions, on all model lines, including less powerful models such as the Volkswagen Golf Plus with engine power of 105 PS (German).
They work on the same principle as the floor gear lever when it is shifted across the wings to manual mode. The steering column switches have two distinct advantages: 1) the driver can keep his hands on the steering wheel without distracting attention from the road, in manual control mode / tiptronic mode; 2) “paddle shifters” allow the driver to temporarily take control of any of the automatic programs (“D” or “S”) and manually control the gearshift for some time (within the framework of the above limitations).
If the transition to manual control bypassing the automation by means of the flap switches in one of the automatic modes (“D” or “S”) is used periodically, the DSG transmission will return to the previously selected automatic mode after a predetermined period of time during which the switches will not be used, or after stopping the car. To return to fully automatic mode, it is enough for the driver to hold the “+” petal pressed for at least two seconds.
Advantages and disadvantages
• Lower fuel consumption (saving up to 15%) compared to a traditional planetary automatic transmission (due to reduced parasitic losses due to foaming of oil);
• There is no break in the flow of torque from the engine to the drive wheels during gear shifting;
• Quick upshift (8 milliseconds) when shifting to a gear selected in advance;
• Smooth gear changes;
• Downshift always takes 600 milliseconds, regardless of throttle position or transmission mode;
• It is difficult to provide driving without acceleration or overcoming the ascent, avoiding exceeding a certain limit of engine rotation speed (for example, 3000 or 4000 rpm), as this will require you to ensure that the kick-down activation mechanism does not work. To avoid kickdown activation, you need to feel the gas pedal well, but using the throttle fully open can still be achieved by slightly increasing the sensitivity of the gas pedal, since the kickdown button is at the very end of the pedal stroke.
• Somewhat worse overall mechanical efficiency compared to a conventional mechanical gearbox, especially on wet-type transmissions (due to electronics and hydraulic systems);
• The need for professional transmission fluids / oils with specialized additives that need regular replacement;
• Relatively expensive to manufacture, which leads to an increase in the purchase price of a car;
• Relatively slow gear shifting when shifting to a gear not prepared by the transmission (approximately 1100 ms, depending on the situation);
• Limitations of transmitted torque impose restrictions on engine modifications in the secondary market (although many tuners and motorists have already significantly exceeded the limit value of torque). Later modifications were delivered to more powerful cars, such as the 300 hp / 350 Nm VW R36 and 272 hp Audi TTS. / 350 Nm.
• The DSG weighs more than the comparable Getrag traditional mechanical gearbox (respectively: 75 kg (165 pounds) versus 47.5 kg (105 pounds));
• Fuel consumption up to 15% higher than when using a manual gearbox.
Volkswagen Group models equipped with a DSG dual clutch gearbox:
Audi originally used the DSG trademark, but subsequently renamed its dual-clutch transmission “S-tronic”
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