The invention concerns a shift device with a servo assistance device of a kind defined in more detail in the preamble of claim 1.
With such shift devices the rotary motion of the gearshift rod serves the purpose of reselection of the individual shift gutters and generally does not require high shift forces. The axial longitudinal motion of the gearshift rod serves the purpose of engagement of the desired gear and requires higher shift forces, especially with transmissions for heavy vehicles and vehicles where the driver seat is some distance away from the transmission.
In present commercial vehicles, such as buses and trucks with cab-over-engine or forward-control configuration, the transmission is necessarily installed some distance away from the driver seat. This distance is especially far in vehicles with under floor or rear engines. Precise gear changes are often made difficult by the long and occasionally stiff gearshift linkage in mechanically shifted transmissions.
For the driver of a motor vehicle to be able to fully focus his attention on the traffic, as much strain as possible must be taken off him, and he must be supported in all activities needed to operate a motor vehicle.
All drivers know how crucial perfect operation of a manual transmission can be in difficult traffic conditions. Pneumatic shift assistance for commercial vehicles of all sizes can put things right here.

Some servo assistance devices known so far are directly attached to the transmission and feature an externally accessible control rod and piston rod. The gearshift linkage is connected to the control rod. Assistance is activated via longitudinal motion of the control rod. This type of control is found in connection with dual-rod or cable-controlled shift mechanisms. Sealing of the control and piston rod by means of bellows and lack of lubrication represent drawbacks here. This area is exposed to significant fouling in trucks. A changed gearshift linkage ratio also changes the start of servo assistance; or it must be adjusted to the linkage ratio through modification of the valve. This is also the case with shift assistance systems composed of a control valve and a servo cylinder separated from each other. Valve and cylinder are linked by means of ball joints to the shift lever and a console, which in turn is mounted to the transmission. The additional drawback of this arrangement is that each shift results in the parts moving relative to the transmission and the vehicle frame, and that thus the airlines connecting valve and cylinder can be worn through.
Such pneumatic shift assistance systems of a disintegrated type are known which consist of a mechanical-pneumatic control section and a separate pneumatic force section. A shift assistance system of a disintegrated type is known from Lowman; Toothed Gearing; 2nd edition; Springer Verlag; 1988; p. 225. The control section is a mechanically actuated control valve actuated by the gearshift linkage. Transmission of the selection motion during gear change takes place through direct mechanical action on the transmission. Transmission of the shift motion involves actuation of the control valve and simultaneous mechanical transmission of the manual shift force to the transmission via a lever.

The manual shift force is additionally pneumatically supported by a compressed-air cylinder. As a two-position cylinder with integrated hydraulic shock absorber, this compressed-air cylinder constitutes the pneumatic force section. Direct proportional realization of manual shift force is not achieved here. The travel distances between control section and force section are far, and installation is space-consuming. Damage to the compressed-air lines between control section and force section cannot be avoided.
From DE 195 39 471 A1 a shift device is known with control valve and force section combined in a single component. Depending on the driver's shift force, the shift force is proportionally reinforced, with the same effects being achieved as with a manually shifted transmission. The driver does not lose the feeling for the shift system and can feel directly when a gear is engaged or how long the synchronization phase lasts. With this shift device, controllability of the pneumatic assistance device still needs improvement.
In the unpublished applications of the applicant with file number 10 2006 006 651.0 and 10 2006 006 652.9 a shift device with servo assistance device for an automotive transmission is disclosed which comprises means for selection and shifting of a gear step of the transmission and control rod of the servo assistance device, on which the manual shift force to be assisted acts. According to the unpublished application with the file number 10 2006 006 651.0, the shift device features elastic elements for modification or limitation of the manual shift force before it acts on the servo assistance device. According to the unpublished application with the file number 10 2006 006 652.9, spring elements are provided for modification of the manual shift force acting on the servo assistance device within the servo assistance device before and/or during generation of the servo assistance force, and thus to influence the effect of the servo assistance device.

To be able to realize a different servo assistance force for each gear, a different resilience or elasticity is required for each gear. Depending on the design, this can be a complex task and require installation space often not available.
This invention is based on the task to demonstrate a shift device which permits an appropriate servo assistance force to be assigned to each gear without additional installation space and without different resilience’s being required.
The task on which this invention is based is solved by means of a generic shift device which also possesses the characteristic features of the main claim.
A shift device with a servo assistance device for an automotive transmission comprises means for selection and shifting of a gear step of the transmission and a control rod of the servo assistance device, on which a manual shift force to be assisted acts. According to the invention, a travel limit is provided in the control of the servo assistance device for the purpose of influencing the effect of the servo assistance device. The travel limit permits limitation of the relative motion between the control rod and a piston rod of the servo assistance device. The travel limit functions in such a manner that conditional use of a servo characteristic and therefore of a servo assistance force is possible, as a result of which a corresponding servo assistance force can be realized for each gutter or each gear. The servo characteristic used here is generated by a resilience in the components before or in the servo assistance device, or their combination. Resilience can, for example, be realized by means of a spring element arranged on the control rod of the servo assistance device.

A first embodiment of the invention involves implementation of a groove in a hollow shaft in such a manner that different backlashes are present between the groove and a pin passing through the groove in axial direction of the hollow shaft. The pin passing through the groove is supported on a lever, by means of which the control rod of the servo assistance device is actuated. This embodiment involves arrangement of hollow shaft and lever in such a manner that they are axially displaceable relative to each other. The angle of rotation of the gearshift shaft relative to the hollow shaft is limited by the groove in the hollow shaft, thus the lever can cover a limited travel distance only before the pin engages with the groove in the hollow shaft. Consequently, the lever-displaceable control rod of the servo assistance device can be actuated relative to the piston rod by a limited travel only, as a result of which the servo assistance force generated is limited accordingly.
Another embodiment involves a pin passing through the groove of the hollow shaft and being supported or arranged in the gearshift shaft. The pin is designed in such a manner that it engages with a groove of the lever, as a result of which the lever rotates together with the gearshift shaft and actuates the control rod of the servo assistance device. Travel limitation is also realized through different backlashes between the pin and the groove in the hollow shaft. This embodiment involves arrangement of gearshift shaft and hollow shaft in such a manner that they are axially displaceable relative to each other, preferably with the gearshift shaft being arranged axially displaceable and the hollow shaft axially non-displaceable.

Another embodiment involves implementation of a groove in a gearshift shaft in such a manner that different backlashes are present between the groove and a pin engaging with or passing through the groove in axial direction of the gearshift shaft. The pin is arranged or supported in a lever by means of which the control rod of the servo assistance device is actuated. When the gearshift shaft rotates, contact between the gearshift shaft and the pin is delayed by the respective backlash, so that actuation of the servo assistance device takes place only after the backlash. Then the lever is turned by the gearshift shaft and thus the control rod of the servo assistance device actuated. Therefore, the lever-displaceable control rod of the servo assistance device can be actuated relative to the piston rod by a correspondingly limited travel distance only.
Perferably, the groove in the hollow shaft or the gearshift shaft is designed in such a manner that the magnitude of the backlash between the pin and the groove is different for each gutter or gear. Limitation of the actuation of the control rod by the groove is greater in one direction of actuation than in the other direction of actuation. In combination with the servo characteristic, this results in different servo assistance forces.
Another embodiment involves realization of the limitation of the relative motion between the control rod and the piston rod of the servo assistance device by means of a bore in the gearshift shaft, for example a radial bore. The clearances arising between the gearshift shaft and a pin arranged in the bore result in corresponding backlashes between the gearshift shaft and the hollow shaft, as a result of which the servo assistance force can be limited accordingly.

The clearances can be such that the same backlash is generated on both sides, or that different backlashes are generated between gearshift shaft and hollow shaft. The radial bore through the gearshift shaft, in which the pin is located, can also be an elongated hole, by means of which clearances of different magnitudes can be realized in axial direction of the gearshift shaft. Furthermore, a groove may be provided in the gearshift shaft instead of a radial bore in order to realize different magnitudes of clearances between gearshift shaft and pin, with the pin being split in this case. Suitable design of the elongated hole or the groove permits the appropriate servo assistance force to be generated for each gutter or each gear. As a result of the implementation of travel limitation by the elongated hole or the groove, the selection motion is not transmitted by the gearshift shaft to means for selection of a gear step but by a further element.
Limitation of the travel of the control rod of the servo assistance device can also be realized in some other place in the shift device or the shift system, and can therefore be of a different design.
Owing to the invention-defined travel limitation in the control of the servo assistance device, limitation of the actuation of the control rod of the servo assistance device relative to the piston rod can be travel or gear-dependent, as a result of which travel or gear-dependent servo assistance force can be realized.
The following figures represent detailed descriptions of the basic principle of the invention, which permits various embodiments.

Fig. 1 A state-of-the-art shift system.
Fig. 2 A sectional view of an embodiment of the shift device.

Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7

A sectional view of another embodiment of the shift
device.
A sectional view of another embodiment of the shift
device.
Details of an embodiment. Details of another embodiment. A servo characteristic.

Fig. 1 sketches a state-of-the-art automotive shift system 2. A gearshift rod 6 leads from a shift lever 4 via a relay lever system 8 to a shift device 11 with a pneumatic servo assistance device 10. The pneumatic servo assistance device 10 features a connection line 12 leading to a reservoir 14 from which the pneumatic servo assistance device 10 is supplied with compressed air. The relay lever system 8 features a first lever 16 linked to the gearshift rod 6 preferrably in a hinged manner. The relay lever system 8 features a second lever 18 which engages with a control rod 20 arranged in the pneumatic servo assistance device 10. In addition, the pneumatic servo assistance device 10 features a piston rod 22 in which a lever 24 engages which is linked to a lever 28 in the automotive transmission 30 by a rotatable gearshift shaft 26. The lever 28 engages with a gearshift rail 32 by means of which transmission ratios of the transmission can be shifted in the familiar manner. Motion of the lever 24 is relayed via the gearshift shaft 26 into motion of the lever 28, so that the lever 28 can cause axial motion of the gearshift rail 32.

When performing this motion, the gearshift rail 32 preferrably assumes three positions, two axial end positions, each corresponding to a shifted ratio, and a center position between the end positions, which corresponds to a neutral position of the transmission.
Fig. 2 represents a sectional view of the shift device 40 according to the invention. A gearshift shaft 44 rotating around Its axis is supported within a hollow shaft 52. The hollow shaft 52 swiveling around the axis of the gearshift shaft 44 is supported within the shift device 40. The gearshift shaft 44 features grooves 54 on its circumference alongside its axis. Pins 56 rotatably supported in needle bushes 58 in the lever 18 engage with these grooves 54 in the gearshift shaft 44. The pins 56 are arranged in the grooves 54 in such a manner that axial displacement of the gearshift shaft 44 along its axis is possible, and rotation of the gearshift shaft 44 around its axis triggers swiveling of the lever 18.
With a roll 60, arranged for example easily rotatable on a bolt, the lever 18 engages with a pocket 70 in the control rod 20, thus permitting low-friction transmission of the manual shift force to the pneumatic servo assistance device 10. A servo assistance force generated by the servo assistance device 10 is transmitted by the piston rod 22 to the lever 24 (see Fig. 1) and from there to the hollow shaft 52.
Travel limitation in the control of the servo assistance device 10 pennits generation of different servo assistance forces. Travel limitation functions in such a manner that backlashes present between the gearshift shaft 44 and the hollow shaft 52 are realized by means of a groove 48 in the hollow shaft 52 and the pins 56.

Depending on the design of the groove 48 in the hollow shaft 52 (Fig. 5), different backlashes may be present between the gearshift shaft 44 and the hollow shaft 52. The servo assistance force is generated until the backlash between the gearshift shaft 44 and the hollow shaft 52 is neutralized. The manual shift force is then transmitted directly to the hollow shaft 52, and there is no longer any travel of the control rod 20 relative to the piston rod 22 of the servo assistance device 10. This embodiment involves arrangement of the hollow shaft 52 and the lever 18 in such a manner that they are axially displaceable relative to each other. The embodiment of Fig. 2 shows the shift device in the gutter for the 1st and 2nd gear steps. The groove 48 in the hollow shaft 52 is designed in such a manner that the control rod 20 in the 1st gear step can cover the travel distance s1*, whereas in the 2nd gear step it can only cover the shorter travel distance s2*.
Fig. 3 shows another embodiment of the shift device 40. In contrast to the embodiment in Fig. 2, this embodiment features a pin 38 arranged in the gearshift shaft 44 either in a fixed manner or in bearings 62. The lever 18 features two continuous axial grooves 46 and a bore 42. The pin 38 is arranged in the grooves 46 in such a manner that axial displacement of the gearshift shaft 44 along its axis is possible, and that rotation of the gearshift shaft 44 around its axis triggers swiveling of the lever 18. Assembly of the pin 38 is made possible via the bore 42. The hollow shaft 52 and the gearshift shaft 44 are arranged in such a manner that they are axially displaceable relative to each other, with the gearshift shaft 44 preferably being arranged axially displaceable and the hollow shaft 52 axially non-displaceable. Travel limitation in the control of the servo assistance device 10 is such that backlashes present between the gearshift shaft 44 and the hollow shaft 52 are realized by the groove 48 in the hollow shaft 52 and the pin 38.

Fig. 4 shows a cut through the gearshift shaft 44 in the area of the lever 28, which by means of extensions 74 engages with gearshift rails 32 not shown here (cf. Fig. 1}. Lever 28, hollow shaft 52 and gearshift shaft 44 are passed through by at least one pin 66. The hollow shaft 52 features two elongated holes 64 in this area. The width of the elongated holes 64 in circumferential direction of the hollow shaft 52 nearly corresponds to the diameter of the pin 66. The pin 66 is retained in its position by circlips 72, for example. The gearshift shaft 44 features a bore in this area, for example a radial bore. Owing to the radial bore, clearances s, s' arise between the gearshift shaft 44 and the pin 66. These clearances s, s' result in backlashes 68, 68' between the gearshift shaft 44 and the hollow shaft 52. The clearances s, s' can be such that the same backlash 68, 68' is created on both sides or that different backlashes 68, 68' are created between the gearshift shaft 44 and the hollow shaft 52. The clearances s, s' can therefore also be used for travel-dependent limitation of the servo assistance force.
The radial bore through the gearshift shaft 44, in which the pin 66 is located, can also be an elongated hole, by means of which clearances s, s' of different magnitudes can be realized in axial direction of the gearshift shaft 44. Furthermore, a groove may be provided in the gearshift shaft 44 instead of the radial bore in order to realize clearances s, s' of different magnitudes between gearshift shaft 44 and pin 66, with the pin 66 being split in this case. Designing the elongated hole or the groove in a particular manner pennits generation of a corresponding servo assistance force for each gutter or each gear, with the selection motion not being transmitted to the lever 28 by the gearshift shaft 44 but by an element not shown here.
Fig. 5 shows the groove 48 in the hollow shaft 52. Here, the pin 56 is shown in the groove 48 in three different positions, but it is provided in the groove 48 only once.
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The lower position in Fig. 5 represents the position of the pin 56 in the shift gutter for the 1st and 2nd gear step in a 6-speed main transmission. The center position represents the position of the pin 56 in the shift gutter for the 3rd and 4th gear step, while the upper position represents the position of the pin 56 in the shift gutter for the 5th and 6th gear step. Owing to the groove 48 in the hollow shaft 52, a different backlash s1, s2, s3, s4, s5, s6 between groove 48 and pin 56 or hollow shaft 52 and gearshift shaft 44 is realized for each gear. The groove 48 is designed in such a manner that the backlashes s1, s3, s5 of one side of the groove 48 are of different magnitudes than the backlashes s2, s4, s6 on the opposite side of the groove 48 for realization of different servo assistance forces with different shift positions in the same shift gutter of the transmission. The backlashes in shift gutters with lower gear steps are of greater magnitude than in shift gutters with higher gear steps. The backlash si is of the greatest magnitude and thus assigned to the 1st gear step, while the backlash s6 is of the smallest magnitude and therefore assigned to the 6th gear step. The greater the backlash s1, s2, s3, s4, s5, s6 between the groove 48 in the hollow shaft 52 and the pin 56 passing through the hollow shaft 52, the greater the servo assistance force. If, for example, the same servo assistance force is desired for the 1st and 2nd gear step, then the groove 48 must be such that the backlashes si, s2 between pin 56 and hollow shaft 52 are of the same magnitude. Contact between the pin 56 and the hollow shaft 52 results in the manual shift force being transmitted directly to the hollow shaft 52, as a result of which the shift force acting on a gearshift rail 32 (Fig. 1) not shown here results from addition of the servo assistance force and the manual shift force.
Fig. 6 shows another embodiment of the invention. In contrast to the embodiment described in Fig. 5, travel limitation is realized by a groove 54 in the gearshift shaft 44. Here, too, the pin 56 is shown in the groove 54 in three different positions, but it is provided in the groove 54 only once.
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The lower position in Fig, 6 represents the position of the pin 56 in the shift gutter for the 5th and 6th gear step in a 6-speed main transmission. The center position represents the position of the pin 56 in the shift gutter for the 3rd and 4th gear step, while the upper position represents the position of the pin 56 in the shift gutter for the 1st and 2nd gear step. The backlashes s1, s2, s3, s4, s5, s6 of the shift gutters with lower gear steps are of a smaller magnitude than those of the shift gutters with higher gear steps. Servo assistance force is generated with this embodiment only when the gearshift shaft 44 has contact with the pin 56 and thus actuates the control rod 20 of the servo assistance device 10 via the lever 18. The greater the backlash s1, s2, s3, s4, s5, s6 between the groove 54 in the gearshift shaft 44 and the pin 56 engaging with the gearshift shaft 44 or passing through the gearshift shaft 44, the later the rotation of the gearshift shaft 44 will be transmitted to the lever 18, as a result of which the actuation travel of the control rod 20 of the servo assistance device 10 and therefore the servo assistance force are correspondingly minimal. The backlash si is of the greatest magnitude and therefore assigned to the 6th gear step, while the backlash s6 is of the smallest magnitude and therefore assigned to the 1st gear step. As a result, the servo assistance force provided for the lower gears is greater than that provided for the higher gears.
Fig. 7 is a schematic representation of the travel-dependent servo assistance force Fs for the travel distance s* of the control rod 20 of the servo assistance device 10. The design-specified servo characteristic 50 is linear, with the slope of the characteristic 50 resulting from a resilience or elasticity in the components before or in the servo assistance device 10, or from their combination. The characteristic can also be nonlinear. Owing to the travel limitation in the control of the servo assistance device 10, the rotation angle of the gearshift shaft 44 is subject to different limitation, as a result of which the control rod 20 can cover a gear-dependent travel distance s1*, s2*, s3*, s4*, s5*, s6*. By using the servo characteristic 50, a specific servo assistance force Fsl, Fs2, Fs3, Fs4, Fs5, Fs6 can therefore be assigned to each travel distance si *, s2*, s3*, s4*, s5*, s6*.
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Limitation of the rotation angle of the gearshift shaft 44 by the backlashes s1, s2, s3, s4, s5, s6 thus causes limitation of the actuation travel s1 *, s2*, s3*, s4*, s5*, s6* of the control rod 20 of the servo assistance device 10. As a result, the servo assistance force Fs1, Fs2, Fs3, Fs5, Fs6 can be limited in a travel or gear-dependent manner, so that the servo assistance force Fs1, Fs2, Fs3, Fs4, Fs5, Fs6 does not exceed specified values.
Owing to the invention, a corresponding servo assistance force can be assigned to each gutter or each gear without additional Installation space and without different resiliences being required; and individual limitation of the maximum permitted servo assistance force can be realized for each synchronization In the transmission. A precisely defined control rod travel, here via a precisely defined backlash, can be assigned to each gutter or each gear, as a result of which servo assistance can be adjusted within a range including maximum servo assistance force.
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Patent Claims
1. Shift device (11,40) with servo assistance device (10) for a transmission (30) of a vehicle, which comprises means for selection and shifting of a gear step of the transmission (30) and an element (20) on which a manual shift force to be assisted acts, characterized in that travel limitation is provided in the control of the servo assistance device (10) and at least one resilience before and/or in the servo assistance device (10) for travel-dependent limitation of a servo assistance force (Fs1, Fs2, Fs3, Fs4, Fs5, Fs6) for each gutter or each gear.
2. Shift device (11,40) with servo assistance device (10) according to claim 1, characterized in that the element (20) is realized as a control rod of the servo assistance device (10).
3. Shift device (11, 40) with servo assistance device (10) according to claim 1 or 2, characterized in that the servo assistance device (10) comprises a piston rod (22) which cooperates with means for the shifting of a variable-speed transmission, a gearshift shaft (44) with openings (68, 68"), and a hollow shaft (52).
4. Shift device (11,40) with servo assistance device (10) according to one of the claims 1 thru 3, characterized in that travel limitation is realized by means of different backlashes (s1, s2, s3, s4, s5, s6) between pins (56, 38) and a groove (48) in the hollow shaft (52).
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6. Shift device (11, 40) with servo assistance device (10) according to claim 4, characterized in that the backlashes (s1, s2, s3, s4, s5, s6) are of greater magnitude with lower gear steps than with higher gear steps, with the backlash (s1) for the lowest gear step being of the greatest magnitude and the backlash (s6) for the highest gear step being of the smallest magnitude.
6. Shift device (11,40) with servo assistance device (10) according to one of the claims 1 thru 3, characterized in that travel limitation is realized by different backlashes (s1, s2, s3, s4, s5, s6) between pins (56) and a groove (54) in the gearshift shaft (44).
7. Shift device (11, 40) with servo assistance device (10) according to claim 6, characterized in that backlashes (s1, s2, s3, s4, s5, s6) with lower gear steps are of a smaller magnitude than with higher gear steps, with the backlash (si) for the highest gear step being of the greatest magnitude and the backlash (s6) for the lowest gear step being of the smallest magnitude.
8. Shift device (11, 40) with servo assistance device (10) according to one of the claims 4 thru 7, characterized in that the backlashes (s1, s3, s5) of one side of the groove (48, 54) are of different magnitude than the backlashes (s2, s4, s6) of the opposite side of the groove (48, 54) for realization of different servo assistance forces with different shift positions in the same shift gutter of the transmission (30).
9. Shift device (11,40) with servo assistance device (10) according to one of the claims 1 thru 3, characterized in that travel limitation is realized through clearances (s, s') between the gearshift shaft (44) and a pin (66), with corresponding backlashes (68,68') resulting between the gearshift shaft (44) and the hollow shaft (52).

10. Shift device (11, 40) with servo assistance device (10) according to claim 9, characterized in that the clearances (s, s') between the gearshift shaft (44) and the pin (66) are realized by means of an elongated hole or a groove in the gearshift shaft (44).

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