Comparative characteristics of automatic transmission, CVT and robot

Preselective gearbox

(PKP) is the second generation of robotic gearboxes.

The most famous representative of this type is DSG (manufactured by Borg-Warner - DSG-6 (DQ250, wet clutches) and LUK - DSG-7 (DQ200 - dry[1] clutches, DQ500 - wet[2]). Boxes from other manufacturers are also known (for example, Getrag) under other names PDK, SST, DSG, PSG, S-tronic [3]. A special feature of this gearbox is that there are two separate shafts for even and odd gears, each of which is controlled by its own clutch. This allows pre-switch the gears of the next gear, and then almost instantly switch the clutches, while no torque gap occurs.

This type of robotic gearbox is currently the most advanced in terms of efficiency and shift speed.

Content

• 1 Classification 1.1 According to the method of power flow transmission
• 1.2 By the number of main shafts with gears
• 1.3 Classification of planetary gearboxes
• 1.4 By control method
• 1.5 By number of gears
• 1.6 Types of gearboxes
• 1.7 Example

Comparison of 6DCT and 7DCT

First of all, these boxes differ in the number of gears. A 7-speed robot, unlike a 6DCT, provides more dynamic acceleration and consumes 5-7% less fuel. But the differences don't end there.

If the 6DCT has quite a few disadvantages that the driver has to put up with during daily trips, then the 7DCT gearbox is devoid of these disadvantages. It behaves more adequately in traffic jams, when reversing, braking and in mountainous areas. It is difficult to say how the manufacturer eliminated these shortcomings, but there is no doubt that the box has been significantly improved. But this does not mean that with a 7-speed robot you can drag along unhindered in traffic jams, slowing down the movement with the brake pedal. Driving like this kills the box.

Classification[ | ]

Variable boxes

transmissions are classified according to several criteria.
Opened mechanical 16-speed (2x4x2) gearbox 16S181, 2, 4, 5 - divider ( 2x
4x2), 7 - 10 - main 4-speed gearbox with reverse gear Opened planetary range switch (range switch, English range, 2x4
x2
) boxes gear ZF 16S181

According to the method of power flow transmission[ | ]

• Mechanical
  - gearboxes that use mechanical transmissions, usually gears.
• With coaxial shafts
  - made using cylindrical and bevel gears.
• Planetary
  - made using planetary gears.
• Hydromechanical
  - gearboxes in which mechanical transmissions, usually planetary gears, are used in combination with a hydraulic transmission (fluid coupling, torque converter).
• CVTs
  are based on a continuously variable mechanical friction transmission - a variator, often in combination with a fluid coupling and planetary or simple gear transmissions.

According to the number of main shafts with gears[ | ]

• two-shaft axles with one stage of engagement - the simplest, but do not have direct transmission (most front-wheel drive and some rear-engine cars)
• three-shaft with two stages of engagement: coaxial - the primary and secondary shaft are coaxial - have direct transmission, are characterized by a reduced transverse dimension, but increased (insignificantly) longitudinal (most rear-wheel drive cars), allow you to obtain a larger reduction range in the same dimensions due to sequential torque conversion
• with misaligned shafts - do not have direct transmission (transfer boxes of all-wheel drive vehicles, tractor gearboxes)

By number of moves

(moving gears, carriages or couplings): two-, three-, four- and five-way.

According to the method of switching stages:

• with movable carriage gears (spur teeth only). They are used where switching is carried out with stopped shafts (machines that reduce tractor gearboxes);
• with face cam couplings and constant mesh gears (old types of tractors, motorcycles, multi-speed gearboxes of sports cars)
• with constant meshing of gears and shifting using gear couplings: without synchronizers (transfer boxes of modern [ when?
  ] cars)
• with synchronizers

Classification of planetary gearboxes[ | ]

According to the number of degrees of freedom

when all friction devices are turned off:

• with two degrees of freedom;
• with three degrees of freedom;
• with four or more degrees of freedom.

By type of planetary gears used:

Gearboxes with
epicyclic
and
attached
planetary gears of external or internal gearing.

By control method[ | ]

• With manual gear shift
  - the driver (operator) engages the gear.
  Direct acting
  - only operator effort is used.
  Direct acting drives are either mechanical
  or
  hydraulic
  .
• Servo drives
  - uses the force of the operator and the servo device, with the servo device doing most of the work, and the operator force is needed to control the operation of the servo device.
  Depending on the source (converter) of energy, servos are divided into hydraulic
  ,
  mechanical
  ,
  electrical
  ,
  vacuum
  ,
  mixed
  , etc. In automobile and tank construction, hydraulic servos are most widespread.

By number of gears[ | ]

The number of forward, reverse and neutral gears is indicated.

Types of gearboxes[ | ]

• Manual transmission
  is a multi-stage cylindrical gearbox, which provides manual gear shifting.
• Automated gearbox
  - provides automatic (without direct driver participation) selection of the gear ratio appropriate to the current driving conditions, depending on many factors.
• Robotic gearbox
  - is a manual gearbox in which the clutch release and gear shift functions are automated.

Example[ | ]

The gearbox of the T-72 tank can be classified as follows: planetary, with three degrees of freedom, with an attached external gear planetary gear and three epicyclic planetary gears. Gear engagement is frictional using hydraulic control servo drives. Provides seven forward gears and one reverse gear.

Typical "diseases"

DSG-6 oil changes must be carried out strictly according to the manufacturer’s regulations - they can be seen in the instructions for the car. Almost all typical breakdowns occur due to untimely change of transmission fluids.

The multi-plate friction clutch wears out very often. Most often this manifests itself in the periodic lack of loading of the reverse gear and in jerks when changing even gears. The gearbox can go into emergency mode. In this case, it is impossible to engage odd-numbered gears. DSG repair in this case means replacing the entire friction clutch or replacing individual discs. Next, basic setup and adaptation is performed.

Also, one of the problems with these boxes is the wear of the solenoids that regulate the pressure in the mechatronics. In this case, you may feel jerking when switching. The breakdown does not cause errors. The problem can be solved by replacing the solenoids. In some cases, mechatronics are also completely replaced.

Certain problems may arise with the mechatronics electronic unit. They are usually detected during a cold engine start. The DSG-6 box will go into emergency mode once. Sometimes, for the same reason, the gearbox may periodically go into emergency mode. Operation can be restored by replacing the mechatronics or repairing the unit.

Often, technicians diagnose wear on the input shaft bearing and other bearings. Differentials also fail. This is manifested by increased noise when driving, braking, and accelerating. The problem can be solved by overhauling the DSG using high-quality used spare parts.

Gearboxes with design specifics[ | ]

Shaftless gearbox[ | ]

Locomotive 8-speed (+4;-4) 4-row shaftless gearbox of the Maybach Mekydro K-104 model, the first three rows are responsible for 4 gears, the fourth row is a reverse gearbox
. This gearbox does not have common shafts for a set of gears, hence the name of the scheme “ shaftless." The cylindrical gears are arranged in pairs in rows on two parallel axes (as if there were shafts after all). Each pair of gears in the same row is in constant mesh with each other. All coaxially located gears are connected to each other by means of locking clutches, and every two clutches of two gears of the same row are engaged according to a mutually exclusive principle: when one clutch is on, the other is off. The drive shaft here is rigidly connected to its first row gear. The driven shaft is similar with its last row gear. Both shafts can be positioned coaxially or non-coaxially; this in some way affects the calculation of transmission ratios, but is not of fundamental importance, except that in a coaxial arrangement, direct transmission is possible.

From the point of view of the mechanics of work, in this scheme for each of the two gears of any row except the first and last there is no strictly fixed role, such as a driver-driven one. When forming different gear ratios, the same intermediate gear can be driving in one case and driven in another. This feature allows you to obtain a larger number of available gear ratios, and in general, their number is always an exponential function of the form 2 to the power of x-1, where x is the number of rows. Each gear ratio can be formed by more than one row, up to the simultaneous use of all rows. The gear clutches here can be engaged in groups, which may require the use of some kind of auxiliary automation and various central synchronization devices.

Regarding the scheme on shafts, the shaftless scheme allows not only to increase the number of gears in both directions, but to increase the power range of the gearbox while reducing the dimensions, which will be more noticeable the greater the number of rows of gears. For example: 4 rows of gears - 8 gears (either 8 forward, or 4 forward and 4 reverse); 5 rows of gears - 16 gears (+16;0 or +8;-8). The fatal disadvantages of the scheme are the difficulty (or even impossibility) of obtaining an arbitrary breakdown of the power range according to the required gear ratios, as well as the impossibility of creating a gearbox in a purely mechanical form without auxiliary automation.

The shaftless gearbox was developed and promoted by the German company Maybach. Three models became famous: Variorex, Olvar and Mekydro. The first two were used in different versions on German tanks and armored personnel carriers of the war period. The Mekydro gearbox assembled with a torque converter was used on German mainline diesel locomotives with hydromechanical transmission. They experimented with shaftless gearboxes in the USSR after the war [ when?

], but it did not come to practical application.
An extremely rare scheme to use, in modern [ when?
] transmissions is not used due to its shortcomings.

Unsynchronized CP[ | ]

Multi-stage non-synchronized gearbox of an American truck tractor
This means a mechanical gearbox, the design of which does not have synchronizers (moreover, it can be either a scheme with sliding gears, in which synchronizers are impossible in principle, or a scheme with constant mesh gears). Changing gears on such a gearbox requires the driver to have certain skills in independently synchronizing the angular speeds of the clutches and gears by determining the duration of the process of switching from one gear to another and parallelly adjusting the speed of the gas pedal. Both are usually done based on the sensations of driving speed and engine speed based on applied experience of driving a particular car, with the tachometer providing additional assistance.

Almost all pre-war manual gearboxes were unsynchronized. In modern [ when?

] transport equipment is equipped with non-synchronized gearboxes on American-made truck tractors and dump trucks, motorcycles, some tractors and racing cars.
On some gearboxes, synchronizers may not be present in all gears, but only in some gears. Terms such as “over-throttle” and “double clutch release” are related to the operation of unsynchronized gearboxes, although in fact they are modern [ when?
] non-synchronized gearboxes allow you to change gears without using the clutch.

Cam gearbox[ | ]

Cam tooth profile in comparison with a conventional one
This means a non-synchronized mechanical gearbox on shafts and gears of constant mesh with gears engaged by clutches with a cam tooth profile. The difference between similar gearboxes and the same ones, but with gears engaged by clutches with different tooth profiles, is that the cam profile allows rougher operation during switching, both in terms of synchronizing angular velocities and in terms of force action. At the same time, all such gearboxes are noisier, since with each alternating acceleration the clutch can rotate slightly relative to the locked gear. Due to the fact that racing cars are often equipped with such gearboxes, where the constant presence of noise is a certain norm, spur gears are often used here, which produces even more noise, but increases the efficiency of the gearbox itself.

Sequential CP[ | ]

Sequential gearbox
Sequential gearbox means a gearbox in which the gear shift mechanism does not allow arbitrary selection of the next gear relative to the one that is currently engaged, but limits the range of available gears to only one gear higher and one gear lower. Switching to neutral on such a gearbox is usually possible only from two gears - first and reverse (on motorcycles it is possible from first and second). Some sequential gearboxes can be equipped with mechanisms for quickly entering neutral from any gear, but this is not a rule.

In their canonical form, sequential gearboxes are used on racing cars and any motorcycles. The gear shift mechanism here is usually a drum with grooves that transforms the single-stroke reciprocating movement of the gear lever rod into rotation. The design of the mechanical transmission in a sequential gearbox can be almost any and has nothing to do with the sequentiality of the gear shift mechanism, although most often the sequential gearbox assumes a scheme on constant mesh gears with gear engagement by cam clutches. There are planetary sequential command posts (Chieftain tank). The design of the unit responsible for selecting and shifting gears can also be different here: purely mechanical (cam gearboxes of motorcycles), hydraulic (some tank planetary gearboxes), electronic-hydraulic (gearboxes of most modern [ when?

] racing cars). Gear shifting here is possible either with a one-way handle, which has only two non-locking positions, upshift and downshift, or with a foot pedal with similar operating mechanics. Electronically controlled semi-automatic gearboxes of Formula 1 racing cars with gear shifting using buttons on the steering wheel can also probably be considered sequential. An imitation of a sequential gearbox can be considered automatic gearboxes of the Tiptronic-Porsche type and all similar automatic gearbox systems with the presence of an optional sequential gear shift mode at the driver’s command.

Preselective CP[ | ]

Gear selection selector for the pre-selective gearbox of the pre-war MG Magna car.
This means a gearbox in which the selection of the next gear occurs before switching to it.

In historical retrospect, this term is usually used in relation to the developments of the interwar period of the last century, and implies a planetary or shaftless gearbox, complemented by various mechanisms to simplify the gear shifting process. At that time, in the absence of both synchronized manual gearboxes and automatic gearboxes, this direction of gearbox development was relevant. The preselective gearbox was controlled using a gear preselection selector. The selector was set to the desired gear, and the moment of engagement was determined either by pressing the clutch pedal or by briefly pushing the selector to a non-locking position (in the case of using a centrifugal clutch on passenger cars). No qualifications or specific skills were required from the driver. Preselective gearboxes were used on completely diverse vehicles: German shaftless Maybach Variorex gearboxes of SdKfz 250 armored personnel carriers and PzKpfw III tanks; shaftless gearbox Maibach Olvar of Tiger and Royal Tiger tanks; German planetary gearboxes for racing Auto Union and executive Maybachs; British planetary Wilson gearboxes for Matilda II tanks, AEC RT-type buses, Armstrong Siddeley, Deimler, MG, Riley passenger cars; French planetary gearboxes Cotal and Talbot for passenger cars Delage, Delahaye, Talbot, Bugatti; American planetary gearboxes for Cord and Tacker machines.

scheme of modern[
when?
] preselective gearbox with two clutches

In modern [ when?

] moment preselective are any
gearboxes with two clutches
, since here the auxiliary automatic equipment always pre-selects an up or down gear depending on the current driving mode, regardless of whether the moment of transition to a new gear is determined automatically or by the driver.
In their original form, preselective planetary and shaftless gearboxes on modern [ when?
] do not apply to cars.
On modern multi-speed gearboxes [ when?
] truck tractors, a number of gears can be engaged through preselection using a switch button on the main gearbox lever, but such a gearbox is not called preselective.

Process steps

First of all, the machine is lifted on a lift or installed on a pit. It is recommended to install the gearbox selector in parking. Next, unscrew the drain plug on the gearbox housing. First, a liter of liquid will pour out of the box. Then you need to unscrew the control tube - about five more liters will flow out. If chips leak out along with the oil, then this is a reason to contact a service center to repair the box.

Next, the filter is replaced. On many cars (including Skoda) with DSG-6 the filter is located higher. To access it, you need to remove the battery along with the platform, the air filter housing and the air ducts. Then you can unscrew the filter.