DE4208060A1 - Electrohydraulic drive control system for vehicle double clutch transmission - uses three switching cylinders each with central neutral pressure space and two end gear switching pressure spaces - Google Patents

Abstract

The drive control system has three switching cylinders (11, 12, 13), each with a piston rod moved between three different switch positions, the two end positions corresponding to the switch positions for a respective gear and the middle position corresponding to the neutral position. The switching cylinders (11, 12, 13) each have three pressure spaces (42, 47, 44; 45, 48, 41; 46, 49, 43). The third pressure space (47, 48, 49) for the neutral position lies between the end pressure spaces (42, 44; 45, 41; 46, 43). All the pressure lines for the switching cylinders (11, 12, 13) are supplied via two blocking valves (31, 32) with a separate pressure suply for the neutral position pressure space (47, 48, 49) and for the gear switch positions of each switching cylinder (11, 12, 13). ADVANTAGE - Fail-safe characteristic, simplified design.

Description

The invention relates to an electro-hydraulic Transmission control system, especially for double clutch tion gearbox, according to the preamble of claim 1 they are used in particular for motor vehicles.

Electro-hydraulic transmission control systems are in different embodiments are known.

DE-OS 34 47 676 describes a method for Control of an automatic clutch, in which a so-called gear actuator an optional actuator and a switch actuator are provided. These are Hydraulic cylinder with three positions of the pistons, so with two end and one middle position. By corresponding on / off check valves are two End pressure chambers controlled, whereby by simultaneous Pressurizing both pressure rooms the new one in the middle tralposition of the ring piston or the shift rod is enough. One way if the magnet fails valves to shut all cylinders in neutral position ten, as well as protection against actuation of a Shift cylinder as long as the power flow in the corresponding Gear train is not interrupted, is not be here wrote.

In EP-B1-0 52 814 a transmission control for described a speed change group transmission in which in the shift control of the main transmission Shift cylinder is used, its double-acting Cylinder in a central position by a hydraulic actuated locking bolt can be fixed. Here is the locking bolt on each shift cylinder ne supply lines and valves fed or controlled,  where at the same time the locking pin is engaged Pressure supply to the gear change pressure rooms blocked becomes. Overall, this is a relatively complex tax system, which moreover does not provide adequate security if the solenoid valves fail.

In VDI reports No. 466, 1983, pages 101 ff. And in ATZ-Automobiltechnische Zeitschrift 89 (1987) 9, page 441, the Porsche PDK transmission is described in which three shift cylinders for shift rod actuation with three positions are provided. The gear positions are each via a solenoid valve, i.e. H. a total of six solenoid valves, and the middle positions through corresponding pressure springs in the depressurized state of the Cylinder switched or taken. Although here at Failure of the electronics, d. H. of the solenoid valves that Reset the switching cylinder using the Springs made, but the supply of the Sy stem pressure to the valves is not switched off, so that there is a relatively high level of leakage. Is also one Protection against actuation of a switching cylinder, see above as long as the power flow is not interrupted, do not be wrote. In addition, gear selection is not provided and the actuation of the shift cylinder is only over Ma solenoid valves possible.

The object of the invention is an electro-hydraulic Gearbox control system to be mentioned above ben, in a simple, economical embodiment, the is safe and economical in its function and different gait strategies with the appropriate gearshift Security allowed.

This object is achieved by an electrohy Draulic transmission control system with the features of claim 1 solved. Advantageous configurations  are contained in the subclaims.

Accordingly, the shift cylinders each have three pressures clean up, the third pressure room essentially in the middle between the two outer aisle pressure rooms is arranged and serves for the neutral position. To the Shift rods of the shift cylinders are mechanical over support elements attached to the gear change in Execute change gear. As below wrote, this mean pressure space is always normal under pressure so that when the two are depressurized Aisle pressure rooms automatically take the middle position men will.

In addition, all pressure supply lines leading to the switch cylinders, guided by two check valves, the via the clutch pressure of one of the two clutches lungs of the transmission double clutch are controlled. Here is one of the three shift cylinders of one of the two Couplings and the other two shift cylinders from the second clutch controllable or lockable. As a result one of the two clutches switched on, then rises the clutch pressure. If this exceeds a predetermined one Lower limit, then the corresponding blocking vein til the pressure oil flow to the assigned Schaltzylin locked off. This means that if one Solenoid valve or component, with clutch engaged, the switching state does not change. In addition, here is given by a switch fuse at the same time, since the Possibility of switching in the under load Gear part is prevented.

Furthermore, there is a separate pressure supply Neutral pressure rooms are provided. This is the big one Advantage that the neutral pressure chambers are always under pressure are maintained and the aisle pressure chambers only when required,  d. H. only apply pressure when changing gear be hit. The pressure supply line or are the / lines for the pressure supply of the aisle Optional pressure chambers of the switching cylinders via a solenoid valve switchable, the when the solenoid valve is not actuated Oil supply is prevented. It can only be used for Actuation of this solenoid valve with the help of additional ven tile or solenoid valves the switching state of the cylinder to change. The separate pressure supply for the gear shift positions and the central positions of the cylinders to change the preselection strategy of the switch positions. That means, in the transmission branch that is not in the power flow, can the next lower gear, neutral or next higher gear can be shifted.

According to a development of the inventive concept the three pressure chambers of the shift cylinders are designed or the piston area ratios of the three pressure chambers selected to each other so that the gear selection piston surfaces are larger than the neutral areas. So the middle one Pressure chamber should always be kept under pressure, because at Actuation of one of the two aisle pressure rooms anyway the appropriate gear selection can be made. are both aisle pressure rooms depressurized, then automa the middle position under pressure.

It is also of particular advantage if in the Pressure medium supply line, before the switching valve for the Change in the switching state of the cylinders (gear pressure spaces), a solenoid valve with a downstream slide Valve is provided, which is open when not actuated condition, the hydraulic pressure supply is not below binds. The pressure medium supply lines are for the middle position of the shift cylinder just behind branched off this valve, so that with targeted actuation supply of this solenoid valve the entire pressure medium supply  is switched off. Possible loss of pressure medium leakage is then only possible up to this valve Lich.

It is also an advantage if the position change the cylinder via solenoid valves with downstream Gate valves are controlled, one Shift cylinder, the gears of the corresponding clutch lung switches via a corresponding valve combination is switched, which in the pressure oil course above the arranged first clutch pressure controlled check valve is, while the other two shift cylinders, the ent shifting the gears of the other clutch, from two Ven one behind the other in the pressure medium inflow combinations are controllable. Here is the assignment Gear / valve combination designed so that in the event of failure the next higher gear of a solenoid valve is switched on. Thus, if a Sig nals, solenoid valve or gear sensor no undefined System state occur because either the means position of the shift cylinder or an uncritical one higher gear is set.

Furthermore, it is of particular advantage if everyone Solenoid valve assigned a hydraulic slide valve is that with the solenoid valve switched on via the Sy stem pressure is switchable. This brings the advantages to use standard solenoid valves with small to generate high switching forces against magnetic forces and when using solenoid valves with very small Flow rates high flow rates via the slide to be able to supply valves to the shift cylinders.

Finally, it is advantageous if each shift cylinder at least one sensor for the switching status check is assigned to the signals on the position of the  Passes shift rods to a microcomputer. On the Gait disturbance sensor is e.g. B. the defect of a magnetic vein tils recognizable since there is no change in the state of the switching cycle linder takes place. This is a variety of surveillance possibilities of the overall system.

The structure of the transmission control system according to the invention stems ensures that there is only one in each transmission branch set a switching position of the three-position cylinder can (according to the solenoid valve combination).

The invention based on an embodiment example explained in more detail with reference to the drawing.

It shows:

Fig. 1 a schematic representation of the control system of the transmission,

Fig. 2 is a schematic block diagram of a Dop pelkupplungsgetriebes,

Fig. 3 is a table from which it can be seen for which gear which clutch and pressure chambers are applied, and

Fig. 4 is a schematic representation of the Lastschaltun gene.

As already mentioned, the invention was implemented on a double clutch transmission. Such a double clutch transmission is shown in Fig. 2 in a block diagram. The transmission essentially consists of two parts, namely a first transmission part 5 with a drive 3 and two clutches 1 and 2 which are operatively connected to it. The second transmission part 6 contains the gear shift elements such as gear wheels, clutches, syn chronizations, shift cylinders, etc. In a box-shaped block, the shift elements 7 for shifting gears 1 , 3 , 5 and R, which are in the power flow of clutch 1, are combined while in the further box-shaped representation, the gear wheels and shift elements for the gears 2 and 4 , which are in the power flow of the clutch 2, are shown. Depending on the gear engaged, the output 4 is connected to the transmission branch which contains the clutch 1 and the shifting elements 7 or the clutch 2 and the shifting elements 8 .

From FIG. 1, the basic structure of the fiction, modern electro-hydraulic transmission control system can be seen. It consists essentially of three Schaltzy alleviate 11 , 12 and 13 , five solenoid valves 21 , 22 , 23 , 24 and 25 , and seven mechanical sliding valves 31 , 32 , 33 , 34 , 35 , 36 and 37 and corresponding lines.

A line 14 leads from a hydraulic pressure supply 10 , from which branch lines 15 , 16 , 17 , 18 , 19 and 20 lead to the solenoid valves 21-25 . When the engine is started and the function of the hydraulic pressure supply 10 coupled therewith, the same system pressure is consequently present at the six valves shown. When the solenoid valves 21-25 are actuated, the system pressure is guided to the respective valve valves 33-37 coupled to them via respective control lines 26 , whereby the slide valves are each switched to their second slide position. When the solenoid valves 21-25 are switched off, a connection of the lines 26 to the gearbox sump 9 will take place in the solenoid valves, as a result of which the corresponding slide valves 33-37 are relieved. As a result, these are pushed back to their relieved position, after which connections from at least one pressure medium line to the sump 9 are also established, relieving the pressure in the corresponding lines. A pressure line 27 leads from the slide valve 33 to the slide valve 34 . From this pressure line 27 branches two pressure lines 28 and 29 leading to the check valves 31 and 32 . From the check valve 31 , the pressure medium coming from the line 28 is passed on to the switching cylinder 11 via a line 30 , while the pressure medium coming from the line 29 via the check valve 32 into a line 38 and via two branch lines 39 and 40 to the switching cylinders 12 and 13 forwarded.

Coming from clutch 1 , a control pressure line 51 leads to check valve 32 , while a control pressure line 50 leads from clutch 2 to check valve 31 . When the pressure in the control pressure lines 50 and 51 rises by a certain amount, the check valves 31 , 32 are shifted and block their passages.

A line 52 continues from the slide valve 34 and branches into lines 53 and 54 . The line 53 leads via the shut-off valve 31 into a line 55 and further via the slide valve 35 into lines 56 and 57 , which in turn open into the pressure chambers 42 and 44 of the shift cylinder 11 .

The pressure medium is conveyed from the pressure line 54 via the check valve 32 into a line 58 which leads to the slide valve 36 . Depending on the switching state of the slide valve 36 , the pressure medium is conducted into the lines 59 or 60 and via this into the slide valve 37 . Depending on the switching state of the slide valve 37 , the liquid pressure will propagate in the lines 61 and 62 , which lead to the pressure spaces 45 and 43 or in the pressure lines 63 and 64 , which in turn open into the pressure spaces 41 and 46 .

The switching cylinders 11 , 12 and 13 are Dreistellungszy cylinder. Their peculiarity is that they, seen abge from the respective two end pressure spaces 41-46 , each have a mean pressure space 47 , 48 and 49 respectively. The shift cylinders 11 , 12 , 13 have a stepped cylinder body 65 , the respective outer, smaller diameter ends forming the corresponding pressure chambers 41-46 , while the larger diameter middle parts form the middle pressure chambers 47-49 . The Kol ben 66 of the switching cylinder 11-13 have a cylindri's central part 67 , which is flanked by two end pistons 68 and 69 . These end pistons 68 and 69 work appropriately sealed in the end pressure spaces 42 , 45 , 46 and 44 , 41 , 43 . On the piston middle part 67 are axially displaceable two ring pistons 70 and 71 angeord net, the pressure in the middle pressure chambers 47-49 to the outside up to rest on the corresponding graduations of the cylinder body 65 and on the corresponding shoulders of the end pistons 68 and 69 . The corre sponding piston rods are designed as switching rods 72 , 73 and 74 . Each shift rod 72 , 73 , 74 is assigned a sensor 75 , 76 or 77 , which, for example, determine the switching positions of the shift cylinders or shift rods via corresponding profiles on the shift rods 72-74 and report them to a computer (not shown).

In Fig. 3 is shown in a table are for which gear which the clutch and which speed-pressure chamber is pressurized. For example, the clutch 1 is actuated for the first gear and the pressure chambers 41 of the cylinders 12 and 42 of the cylinder 11 are pressurized, while the clutch 2 and the pressure chamber 42 are pressurized for the second gear, etc.

Finally, Fig. 4 shows schematically the possible load circuits, the respective gear designation is entered in the circles standing for the different gears and, as is common practice, an arrangement according to train belonging to a transmission branch or controllability was made by one of the two clutches. Thus, the gears 1, 3, 5, R that can be blocked by clutch 1 are shown in the first horizontal gear row, and 2 and 4 that are lockable by clutch 2 are shown in the second row. It can be seen from the arrows that z. B. from the second and fourth gear can be switched to the next higher gear 3 or 5 ge, while in the next lower gear can only be switched from the fourth to the third or from the second to the first gear. The circuits from fourth to first gear and to reverse gear and from second gear to reverse gear are also possible from the hy draulic circuit arrangement (see dashed lines), but a backup is provided for this via the computer, so that, for example, the reverse gear can only be switched via the neutral position.

The electro-hydraulic transmission according to the invention control system works as follows:

The two slide valves 33 , 34 arranged essentially one behind the other in the feed lines are on / off valves ( 2/1 ). However, they have a reverse mode of operation, since the first valve 33 is open in the non-activated state, that is to say allows the pressure medium flow to pass through, while the slide valve 34 is closed in the non-activated state, that is to say the pressure lines leading to the respective end pressure chambers of the switching cylinders are blocked. However, since the branch lines 28 , 29 etc., which lead to the respective middle pressure spaces 47-49 of the switching cylinders 11-13 , branches off from the pressure line 27 between the two slide valves 33 and 34 and the lines 28 , 30 and 29 , 38 do not are guided over the slide valves 35 , 36 , 37 , but only over the check valves 31 and 32 , a separate pressure supply to the middle position or the gear-end switch positions of the shift cylinder is present, which has many advantages.

For example, when the engine is started, a hydraulic pressure will build up, so that via the Druckversor supply 10 and line 14 , the open slide valve 33 (when the slide valve 34 is not actuated and thus closed), the other lines 28 , 30 and 29 , 38 , 39 and 40 the pressure is passed to the middle pressure chambers 47 , 48 and 49 of the shift cylinders 11 , 12 , 13 , whereby their middle, ie zero position (neutral position) is switched. Of course, in this initial stage, the pressure lines 50 , 51 of the clutches 1 and 2 are practically depressurized by not actuating them, as a result of which the associated check valves 31 and 32 are not activated and are therefore open. So when starting the engine, there is no need to fear that one of the shift cylinders is in an engaged gear shift position, which must first be cleaned.

Another advantage of the special arrangement and reverse function of the two slide valves 33 and 34 and the separate pressure supply to the middle positions (or neutral pressure chambers) and the gearshift positions (or end pressure chambers) can be seen in the fact that in the event of electronics failure, whereby all solenoid valves fall in the non-switched-on state, the slide valve 33 is permeable, while the slide valve 34 blocks. This also switches the center position (neutral) of the shift cylinder via the hydraulic pressure. Of course, due to the electronics failure, the clutch pressure is zero or so low that the check valves 31 and 32 are both not activated and are therefore permeable.

By actuating the solenoid valve 21 and the associated control of the slide valve 33 , the system pressure supply to all three switching cylinders is completely interrupted. Thus, the leakage current can be kept very low in phases without changing the system.

If the solenoid valve 22 is actuated and thus the slide valve 34 is controlled, then the lines 53 , 54 , etc. continue to be pressurized. If none of the other three solenoid valves 23 , 24 , 25 and thus the associated three slide valves 35 , 36 , 37 are actuated or controlled, then pressure is passed to the pressure chamber 44 via lines 53 , 55 , 57 , as a result of which Shift cylinder 11 or the shift rod 72 assumes the position for the fourth gear. At the same time, the pressure chamber 45 is applied via the lines 54 , 58 , 59 and 61 , as a result of which the fifth gear is shifted via the shift cylinder 12 or the shift rod 73 . Depending on whether clutch 1 or clutch 2 is actuated, the check valve 31 or 32 is actuated so that one of the two locks. By locking the valves 31 or 32 is th in the accordingly further branches of the system, the t cylinder 11 or the switching cylinders 12 and 13 contain, locked, so that each gear can no longer be changed. So can not be unwanted in the gear train under power, a gear change can be made, which can lead to possible Ge gear damage. At the same time, however, any gear selection, that is, a gear selection, can be made in the other gear train that is not under load. However, this only comes into play when the assigned shut-off valve is activated, ie locked and the other shut-off valve is relieved at the same time, ie opened by the appropriate clutch actuation.

If, for example, the blocking valve 31 is activated, that is to say the switching state of the switching cylinder 11 is blocked, the switching state of the switching cylinders 12 and 13 can be selected via the open blocking valve 32 by optionally actuating the solenoid valves 24 and 25 and thus the downstream slide valves 36 and 37, optionally the first, third, fifth or reverse gear can be selected. So, as described above, when the Ven tile is not actuated, the fifth gear will be selected via the shift cylinder 12 . When the solenoid valve 24 is actuated via the line 54 , the shutoff valve 32 , the line 58 , the switched slide valve 36, the line 60 , and line 62 , the pressure chamber 43 is pressurized, where it is pushed to the left by the switching rod 74 and the third Gear is switched on. Of course, this happens with simultaneous pressure relief of the pressure chamber 46 via the lines 64 and 59 , which are connected by the slide valve 36 to the sump 9 (= shift from fifth to third gear, with fourth gear engaged).

If only the valve 25 is actuated, then the pressure liquid from the line 54 via the check valve 32 , line 58 , the unactuated slide valve 36 , line 59 , the actuated slide valve 37 , line 64 , the pressure chamber 46 is applied, whereby Kol ben and shift rod 74 of the cylinder 13 perform a right movement and the reverse gear could be selected.

When actuating both solenoid valves 24 and 25 , the pressure medium is again applied via the shut-off valve 32 , line 58 , the operated slide valve 36 , line 60 , the operated slide valve 37 , and line 63 , the pressure chamber 41 , whereby piston and switching rod 73rd turn left and select first gear.

It is of particular advantage that the combination was made by the special magnet arrangement, particularly with respect to the slide valves 36 and 37 , that a higher gear or the middle position (new tralposition) is switched on when the solenoid valves fail when a gear is switched on. For example, if the third gear is to be switched, the solenoid valve 24 is actuated, as described above. If the solenoid valve 24 fails, then the slide valve 36 is relieved, so that pressure medium no longer lines 60 and 62 in the pressure chamber 43 for the third gear, but via the pressure lines 59 and 61 in the pressure chamber 45 for the fifth gear is routed so that the fifth gear, that is a higher gear, is selected. This avoids that due to component failure, a lower gear, with corresponding negative consequences, is preselected and then engaged.

As already mentioned, the separate Druckver supply of the middle positions and the Gangschaltstellun conditions of the shift cylinders 11 , 12 , 13 to change the pre-selection strategy of the shift positions. That means in the gearbox branch, which is not loaded with torque, the next lowest gear, neutral, or the next higher gear can be shifted or preselected. For example, when the fourth gear is switched on (clutch 1 under pressure, ie check valve 31 activated or closed) and the fifth gear was pre-selected, but if the third gear is to be engaged, then the solenoid valve 24 must be actuated to engage the third gear. For this purpose, clutch 2 must now be opened and clutch 1 closed at the same time, which fixes the third gear. At the same time, fourth or second gear can then be preselected or switched on, depending on whether solenoid valve 23 is actuated or not.

Another peculiarity, with corresponding advantages, can be seen in the fact that with each gear selection that can be carried out after switching on the solenoid valve 22 , the three cylinders are actuated with the middle or neutral position already activated, without an additional pressure switch-off of the neutral position would be necessary. This is possible because the piston surface ratios of the annular pistons 70 , 71 of the pressure chambers 47 , 48 , 49 for the neutral position and the pistons 68 and 69 of the end pressure chamber 42-46 are selected such that the pressure surfaces of the gear pistons 68 , 69 are larger than the surfaces of the neutral annular pistons 70 , 71 .

As already mentioned, the switching rods 72 , 73 , 74 are each assigned sensors 75 , 76 , 77 , which report whether the associated switching rod is in the middle position (neutral) or whether one of the two end positions has been reached. The signals are sent from the sensors to a computer, not shown, which compares the actual with the target status. If a fault turns out, the computer switches off the solenoid valves and thus the solenoid valve 22 . As a result, only the neutral position is automatically pressurized and a safe gear condition is achieved.

The structure of the electrohydraulic according to the invention Transmission control system ensures that in every  Gearbox branch only one switch position of the three digits can adjust itself (according to the Solenoid valve combination).

The system according to the invention can easily be geared to other number of gears, or number of shift rods be turned. So z. B. use in commercial vehicles driven to derive easily.  

Reference symbol list

1 clutch A
2 clutch B
3 drive
4 downforce
5 First gear part
6 Second gear part
7 gear shift elements
8 gear shift elements
9 line in swamp
10 Hydr. Pressure supply
11 shift cylinders
12 shift cylinders
13 shift cylinders
14 line
15 line
16 line
17 line
18 management
19 management
20 line
21 solenoid valve
22 solenoid valve
23 solenoid valve
24 solenoid valve
25 solenoid valve
26 control line
27 pressure line
28 pressure line
29 pressure line
30 pressure line
31 slide valve
32 slide valve
33 slide valve
34 slide valve
35 slide valve
36 slide valve
37 slide valve
38 line
39 Management
40 line
41- gang pressure room
42- gang pressure room
43- gang pressure room
44- gear pressure room
45- gear pressure room
46 aisle pressure room
47 Neutral pressure room
48 Neutral pressure room
49 Neutral pressure room
50 control pressure line
51 Control pressure line
52 line
53 line
54 line
55 line
56 line
57 line
58 line
59 line
60 line
61 line
62 management
63 line
64 line
65 cylinder body
66 pistons
67 middle part
68 end pistons
69 end pistons
70 ring pistons
71 ring pistons
72 shift rod
73 shift rod
74 shift rod
75 sensor
76 sensor
77 sensor

Claims (10)

1. Electro-hydraulic transmission control system, especially for double clutch transmissions,

• - With three shift cylinders, the piston rods formed as a shift rod can each take three positions, the two end positions each representing shift positions for one gear and can be controlled by solenoid valves and the middle positions represent the neutral positions, and with the pressure in the non-pressurized state of both gear spaces a shift cylinder is in the neutral position,
• - and with a double clutch to establish the power flow in the two transmission branches,

characterized

• - That the switching cylinder ( 11 , 12 , 13 ) each have three pressure chambers ( 42, 47, 44; 45, 48, 41; 46, 49, 43 ), with the third pressure chamber ( 47 , 48 , 49 ) being essentially in the middle between the end pressure chambers arranged pressure chamber is provided for the neutral position,
• - That all pressure supply lines to the switching cylinders ( 11 , 12 , 13 ) are guided via two check valves ( 31 , 32 ), which are switchable via the pressure of one of the two couplings ( 1 , 2 ), a switching cylinder ( 11 ) from Clutch pressure of one clutch ( 2 ) and the two further shift cylinders ( 12 , 13 ) are controlled by the second clutch ( 1 ),
• - That a separate pressure supply to the pressure chambers ( 47 , 48 , 49 ) of the neutral position and the pressure chambers ( 41-46 ) of the gear shift position of the shift cylinders ( 11 , 12 , 13 ) is provided.

2. Electro-hydraulic transmission control system according to claim 1, characterized in that the pressure supply of the gear pressure chambers ( 41-46 ) is controlled via a valve ( 22 , 34 ) which switches off the pressure supply in the unactuated state, while the pressure supply of the neutral pressure chambers ( 47- 49 ) is not influenced by this valve ( 22 , 34 ). 3. Electro-hydraulic transmission control system according to claim 1, characterized in that the pressure supply of both the middle positions and the gear shift positions of the shift cylinders is controlled by a valve ( 21 , 33 ) which has opened the pressure medium supply in the non-actuated state (normal of fen). 4. Electro-hydraulic transmission control system according to claims 1 to 3, characterized in that the pressure medium supply lines to the neutral positions of the shift cylinders are branched from a line ( 27 ) connecting the valves ( 21 , 33 ) and ( 22 , 34 ). 5. Electro-hydraulic transmission control system according to claim 1, characterized in that the shift cylinders ( 11 , 12 , 13 ) are designed with respect to the piston area ratio of the respective three pressure chambers so that the piston areas of the gear pressure spaces ( 41-46 ) are always larger than the piston surfaces of the neutral pressure chambers ( 47 , 48 , 49 ). 6. Electro-hydraulic transmission control system according to claim 1, characterized in that the gear selection for the first shift cylinder ( 11 ) is carried out with the aid of a valve ( 23 , 35 ), while the gear selection for the two further shift cylinders ( 12 , 13 ) via two in the line course successively arranged valves ( 24 , 36 ) and ( 25 , 37 ) are controlled or can be taken before. 7. Electro-hydraulic transmission control system according to claims 2, 6, characterized in that the control valves for gear selection and for switching off the pressure medium supply to the cylinders each from a solenoid valve ( 21-25 ) and from a mechanical slide valve ( 33-37 ) consist. 8. Electro-hydraulic transmission control system according to claim 6, characterized in that the valves for controlling the gears are designed so that in the event of failure of one of the associated Magnetven tile ( 21-25 ) or the associated slide valve, a higher gear is switched. 9. Electro-hydraulic transmission control system according to claim 1, characterized in that the shift rods ( 72 , 73 , 74 ) sensors ( 75 , 76 , 77 ) are assigned, which transmit shift position signals to a computer which switches off the solenoid valve ( 22 ) in the event of a fault , whereby all three shift cylinders ( 11 , 12 , 13 ) assume the middle neutral position.