Shifting apparatus with power assistance device

The invention relates to a shifting apparatus having a power assistance device of the type defined in more detail in the preamble of claim 1.

Modern utility vehicles such as buses and heavy goods. vehicles, with their forward-control layout, have spatial conditions for the installation of the gearbox which are such that the gearbox inevitably has to be situated remote from the driver's seat. The remoteness is particularly great in vehicles with under-floor rear-mounted engines, A precise gearchange is often made difficult as a result of the long, sometimes taut shift linkage in the case of mechanically shifted gearboxes.

Pneumatic shift aids of said type which are of separated configuration are known which are composed of a mechanical-pneumatic control part and a separate pneumatic force part. A shift aid of separated configuration is known from Loomann; Zahnradgetriebe [Gear mechanisms]; 2nd edition; Springer Verlag; 1988; page 225. The control part is a mechanically actuated control valve which is actuated by the shift linkage. Here, the selector movement during a gearshift is transmitted mechanically directly to the gearbox. During the transmission of the shift movement, the control valve is actuated and, at the same time, the manual shift force is transmitted mechanically via a lever to the gearbox. Here, the manual shift force is additionally pneumatically assisted by a compressed-air cylinder. Here, said compressed-air cylinder, as a two-position cylinder with integrated hydraulic damper, forms the pneumatic force part. A direct proportional reproduction of the manual shift force is not obtained here. The paths between the control part and force part are long and the mounting takes up a large amount of space.

DE 10 2004 041 543 Al discloses a shifting apparatus having a power assistance device for a gearbox of a motor vehicle, which shifting apparatus comprises a central shift shaft, the axial movement of which results in a selector movement and the rotational movement of which results in a shift movement. In the event of a rotational movement of the central shift shaft, a control valve of the power assistance device is activated by means of pins for transmitting the manual shift force and a lever which is operatively connected to the pins. The pins for transmitting the manual shift force engage into longitudinal grooves in the circumference of the shift shaft and are arranged in the longitudinal grooves in such a way as to enable an axial movement of the shift shaft. To bypass the power assistance device in certain gears, corresponding transverse grooves are provided on the longitudinal grooves.

DE 10 2006 006 651 Al discloses a shifting apparatus having a power assistance device for a gearbox of a vehicle, which shifting apparatus comprises means for shifting and selecting a gear stage of a gearbox and comprises a control rod of the power assistance device, on which control rod a manual shift force to be assisted acts. Elastic elements are provided in the shifting apparatus in order to vary or limit the manual shift force acting on the power assistance device before said manual shift force is introduced into the power assistance device.

DE 10 2006 006 652 Al likewise discloses a shifting apparatus having a power assistance device for a gearbox of a motor vehicle, which shifting apparatus comprises means for shifting and selecting a gear stage of a gearbox and comprises a control rod of the power assistance device, on which control rod a manual shift

force to be assisted acts. Spring elements are provided in the shifting apparatus in order to vary the manual shift force acting on the power assistance device within the power assistance device before and/or during the generation of the power assistance force.

The present invention is based on the object of providing an embodiment of a shifting apparatus having a power assistance device by means of which a power assistance force can be limited in a gear-dependent or shift-lane-dependent fashion.

The object on which the invention is based is achieved by means of a generic shifting apparatus having a power assistance device which also has the characterizing features of the main claim.

The shifting apparatus having a power assistance device according to the invention, in particular for gearboxes of utility vehicles, comprises a shift housing, means for selecting and shifting a gear stage of the gearbox, and a transmission point for transmitting the manual shift force to the power assistance device. The transmission point for transmitting the manual shift force has a lever which is connected to an element of the power assistance device. In a preferred embodiment of the shifting device according to the invention, the element on which the manual shift force to be assisted acts is designed as a control rod of the power assistance device. Furthermore, means are provided for varying and/or limiting the manual shift force acting on the power assistance device.

In one advantageous refinement, said means may be designed as spring elements which interact with the control rod of the power assistance device, which spring elements for example have different elasticities in an actuating direction of the control rod in order
to vary the manual shift force acting on the power assistance device within the power assistance device before and/or during the generation of the power assistance force. An arrangement and effect of the spring elements is described for example in DE 10 2006 006 652 Al.

In another embodiment, the means for varying or limiting the manual shift force acting on the power assistance device are designed as elastic elements. An arrangement and effect of the elastic elements in the shifting apparatus is described for example in DE 10 2006 006 651 Al.

According to the invention, the shifting apparatus has an apparatus for limiting the power assistance force, which apparatus is arranged directly adjacent to the transmission point for transmitting the manual shift force to the power assistance device and comprises a pin which is arranged in the shift shaft, which pin engages into at least one groove of a hollow shaft which surrounds the shift shaft, wherein a limitation of the power assistance force can be realized by means of the pin which engages into the groove of the hollow shaft. The pin is arranged in the shift shaft in such a way that a movement of the shift shaft generates an immediate movement of the pin. The pin is preferably arranged without play, or only with minimum play, in the shift shaft.

In one preferred embodiment of the shifting apparatus according to the invention, the groove in the hollow shaft is designed such that different rotational plays prevail between the pin, which is arranged in the shift shaft and engages into the groove of the hollow shaft, and the hollow shaft. The rotational plays may for example be configured such that a different rotational play prevails for each shift lane or for each gear stage, as a result of which a different limitation of the power assistance force can be realized for each shift lane or for each gear stage.

In one advantageous embodiment of the shifting apparatus according to the invention, the rotational plays are greater for relatively low gear stages than for relatively high gear stages, as a result of which a greater power assistance force is provided for the relatively low gear stages than for the relatively high gear stages. Taking for example the gear stage 3 as a starting point, a relatively low gear stage is to be understood here to mean for example the gear stage 2, and a relatively high gear stage is to be understood to mean for example the gear stage 4.

In one preferred embodiment of the shifting apparatus according to the invention, the pin, which is arranged in the shift shaft, for limiting the power assistance force is arranged symmetrically with respect to a groove in the shift shaft and therefore symmetrically with respect to pins for transmitting the manual shift force to the power assistance device.

In a further embodiment of the shifting apparatus according to the invention, the hollow shaft has, in the region of the pin for limiting the power assistance force, a second groove which is arranged in the hollow shaft so as to be offset by 180 degrees, that is to say opposite the first groove. Here, the pin for limiting the power assistance force is designed, and arranged in the shift shaft, in such a way as to engage both into the groove and also into the second groove of the hollow shaft, as a result of which the occurring loading is distributed between the two grooves of the hollow shaft.

In one preferred embodiment of the shifting apparatus according to the invention, the contact surfaces of the pin for limiting the power assistance force and the hollow shaft are designed such that optimum surface pressure can be obtained in the event of contact between the pin and the hollow shaft.

In one embodiment, the contact surfaces of the pin and hollow shaft are of conical design with respect to one another. In a further advantageous embodiment, the pin for limiting the power assistance force is designed, in the region of the hollow shaft, as a stepped pin, as a result of which two contact points are generated between the pin end hollow shaft. Other embodiments are also possible.

In a particularly preferred embodiment of the shifting apparatus according to the invention, it is possible for the pin for limiting the power assistance force to be axially secured along its longitudinal axis by means of the shift housing. Other embodiments are possible for realizing the axial securing of the pin. For example, the pin for limiting the power assistance force may be fixed in the shift shaft by means of at least one locking ring and/or a collar on the pin.

By means of the shifting apparatus according to the invention, it is therefore possible to realize a limitation of the power assistance force for each gear stage or each shift lane by means of an apparatus, which is directly adjacent to the transmission point for transmitting the manual shift force to the power assistance device, for limiting the power assistance force. By means of the arrangement according to the invention, it is possible for the problem of occurring tolerances to be kept correspondingly small, as a result of which the rotational plays between the pin, which is arranged in the shift shaft and engages into the groove of the hollow shaft, and the hollow shaft can be set very precisely, and the power assistance force can therefore be limited very precisely to the
desired value.

The basic principle of the invention, which permits numerous embodiments, will be explained in more detail below by way of an example on the basis of a drawing, in which:

figure 1 shows a shift system according to the prior art,
figure 2 shows a sectional illustration of an embodiment of the shifting apparatus
according to the invention,
figure 3 shows a plan view of the shifting apparatus according to the invention, and figure 4 shows a sectional illustration of an embodiment of the shifting apparatus according to the invention.

Figure 1 shows a sketch of a shift system 2 of a motor vehicle according to the prior art. A shift rod 6 leads from a shift lever 4 via a lever deflection 8 to a shifting apparatus 11 having a pneumatic power assistance device 10. The pneumatic power assistance device 10 has a connecting line 12 which leads to a storage tank 14 from which the pneumatic power assistance device 10 is supplied with compressed air. The lever deflection 8 has a first lever 16 which is preferably articulatedly connected to the shift rod 6. The lever deflection 8 has a second lever 18 which engages in turn into a control rod 20 which is arranged in the pneumatic power assistance device 10. Also provided in the pneumatic power assistance device 10 is a piston rod 22 into which a lever 24 engages which is connected via a rotatable shift shaft 26 to a lever 28 in the vehicle gearbox 30. The lever 28 engages into a shift rail 32 by means of which transmission ratios of the gearbox can be shifted in a known way. A movement of the lever 24 is converted via the shift shaft 26 into a movement of the lever 28, such that the lever 28 can set the shift rail 32 in an axial motion. During said movement, the shift rail 32 assumes preferably three positions, two axial end positions corresponding to in each case one selected transmission ratio, and a central position which is situated between the end positions and which corresponds to a neutral position of the gearbox.

Figure 2 shows the shifting apparatus 40 according to the invention in a sectional illustration. The shifting apparatus 40 comprises a central shift shaft 36 which is mounted, so as to be rotatable about its axis 58, within a hollow shaft 38. The shift shaft 36 has longitudinal grooves 50 on its circumference in the longitudinal direction, that is to say along the axis 58, into which longitudinal grooves 50 pins '34 for transmitting the manual shift force engage, which pins 34 themselves are arranged in a lever 18, preferably rotatably mounted in needle bushes. Here, the pins 34 are arranged in the grooves 50 in such a way as to enable an axial movement of the shift shaft 3 6, that is to say the selector movement, with a rotation of the shift shaft 36 about the axis 58 causing a pivoting of the lever 18, which leads to an activation of the power assistance device 10 since the lever 18 engages into the control rod 20 (not illustrated here) of the power assistance device 10 (see figure 1) • The power assistance force generated by the power assistance device 10 is transmitted by the piston rod 22 (not shown here) to the lever 24 (see figure 1) . The lever 24 is rotationally fixedly connected to the hollow shaft 38, as a result of which the power assistance force generated by the power assistance device 10 is transmitted via the lever 24 to the hollow shaft 38.
The hollow shaft 38 is arranged in an axially fixed manner in the shifting apparatus and is arranged so as to be rotatable with the shift shaft 36 for shifting the shift rails 32.

According to the invention, the shifting apparatus 40 has an apparatus for limiting the power assistance force, which apparatus is arranged directly adjacent to the transmission point for transmitting the manual shift force to the power assistance device 10, that is to say directly adjacent to the lever 18 in which the pins 34 which engage into the grooves 50 of the shift shaft 36 are arranged. The apparatus for limiting the power assistance force comprises a pin 42 which is arranged in the shift shaft 36 and which engages here into a groove 4 6 of the hollow shaft 38. The groove 4 6 in the hollow shaft 38 is designed here such that corresponding rotational plays prevail between the groove 4 6 and the pin 42 and therefore between the hollow shaft 38 and the shift shaft 36. By means of a corresponding design of the groove 46 (see figure 3) , it is possible for the power assistance force to be correspondingly limited for each shift lane or each gear stage. The pin 42, which is arranged in the shift shaft 36, for limiting the power assistance force is arranged symmetrically with respect to a groove 50 in the shift shaft 36 and therefore symmetrically with respect to the pins 34 for transmitting the manual shift force to the power assistance device 10. Here, the pin 4.2 is axially secured along its longitudinal axis by the shift housing 44.

The shift shaft 36 can be actuated in rotation in order to transmit the manual shift force to the releasing lever 18 of the power assistance device 10 and to transmit the manual shift force to the shift rails 32 of the gearbox 30. Furthermore, the shift shaft 36 can be actuated axially in order to select the shift rail 32 to be shifted, that is to say for the selector movement.

Figure 3 shows the shift shaft 36, the hollow shaft 38 which surrounds the shift shaft 36, the groove 4 6 in the hollow shaft 38, the pin 42 which engages into the groove 46 and is arranged in the shift shaft 36, the lever 24 which is rotationally fixedly connected to the hollow shaft 38, and the lever 18 which is connected by means of pins 34 (See figure 2) to the shift shaft 36. The pin 42 is shown in the groove 46 in three different positions, but only one such pin 42 is provided in the groove 46. The left-hand position illustrated in figure 3 is the position of the pin 42 in the shift lane 52 for the gear stage 3/4 of a vehicle gearbox. The central position is the position of the pin 42 in the shift lane 54 for the gear stage 1/2, while the right-hand position is the position of the pin 42 in the shift lane 56 for the reverse gear and/or crawler gear. The groove 46 in the hollow shaft 38 is designed such that different rotational plays si - s6 prevail between the pin 42 and the hollow shaft 38. The groove 4 6 illustrated here is designed such that a greater rotational play si, s2 prevails in the shift lane 54 than in the shift lane 52 (rotational play s3, s4). The power assistance force is generated until the rotational play si - s6 between the pin 42 and the hollow shaft 38 and therefore between the shift shaft 36 and the hollow shaft 38 has been eliminated. When the rotational play si - s6 has been eliminated, then the manual shift force is transmitted directly to the hollow shaft 38 and the control rod 20 of the power assistance device 10 no longer travels relative to the piston rod 22 of the power assistance device 10. Since the rotational plays si - s6 are greater for relatively low gear stages than for relatively high gear stages, it is possible for a greater power assistance force to be provided for the relatively low gear stages than for the relatively high gear stages. For the reverse gear and/or crawler gear, the power assistance force can be correspondingly limited by the rotational plays s5, s6.

Figure 4 shows the pin 42 which is arranged in the shift shaft 36 and which engages into the groove 4 6 of the hollow shaft 38. Here, the pin 42 is of stepped design, as a result of which two contact points 60, 62 are generated between the pin 42 and the hollow shaft 38. In the event of a rotation of the pin 42 by the shift shaft 36, said pin 42 comes into contact with the hollow shaft 38 firstly by means of the contact point 60. If wear, for example, occurs at the contact point 60, then the contact point 62 also comes into contact with the hollow shaft 38 in the event of a rotation of the pin 42. By means of the embodiment illustrated in figure 4, it is possible to realize optimum surface pressure between the pin 42 and hollow shaft 38.

Reference numerals
2 Shift system
4 Shift lever
6 Shift rod
8 Lever deflection
10 Power assistance device
11 Shifting apparatus
12 Connecting line
14 Storage tank
16 Lever
18 Lever
20 Element, control rod
22 Piston rod .
24 Lever
26 Shift shaft
28 Lever
30 Vehicle gearbox
32 Shift rail
34 Pin
36 Shift shaft
38 Hollow shaft
40 Shifting apparatus
42 Pin
44 Shift housing
4 6 Groove in the hollow shaft
50 Groove in the shift shaft
52 Shift lane, gear stage 3/4
54 Shift lane, gear stage 1/2
56 Shift lane, reverse gear and/or crawler gear
58 Axis
60 Contact point
62 Contact point

Patent claims

1. A shifting apparatus (11, 40) having a power assistance device (10) for a gearbox (30) of a vehicle, having a shift housing (44), having means for selecting and shifting a gear stage of the gearbox (30), having a transmission point for transmitting the manual shift force to the power assistance device (10) and having means for varying and/or limiting the manual shift force acting on the power assistance device (10), with the transmission point of the manual shift force having a lever (18) which is connected to an element (20) of the power assistance device (10), characterized in that the shifting apparatus (11, 40) has an apparatus for limiting the power assistance force, which apparatus is arranged directly adjacent to the transmission point for transmitting the manual shift force to the power assistance device (10) and comprises a pin (42) which is arranged in the shift shaft (36), which pin (42) engages into at least one groove (46) of a hollow shaft (38) which surrounds the shift shaft (36).

2. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in claim 1, characterized in that the groove (46) in the hollow shaft (38) is designed such that different rotational plays (s1 - s6) prevail between the pin (42) and the hollow shaft (38).

3. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in claim 2, characterized in that the rotational plays (s1 - s6) are greater for relatively low gear stages than for relatively high gear stages, as a result of which a greater power assistance force is provided for the relatively low gear stages than for the relatively high gear stages.

4. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in at least one of claims 1 to 3, characterized in that the pin (42), which is arranged in the shift shaft (36), for limiting the power assistance force is arranged symmetrically with respect to a groove (50) in the shift shaft (36) and therefore symmetrically with respect to pins (34) for transmitting the manual shift force to the power assistance device (10).

5. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in at least one of the preceding claims, characterized in that the hollow shaft (38) has, in the region of the pin (42) , a second groove which is arranged offset by 180 degrees with respect to the groove (46) in the hollow shaft (38), and the pin (42) is designed, and arranged in the shift shaft (36) , in such a way as to engage both into the groove (46) and also into the second groove of the hollow shaft (38).

6. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in one of the preceding claims, characterized in that the contact surfaces of the pin (42) and hollow shaft (38) are designed such that optimum surface pressure can be obtained in the event of contact.

7. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in claim 6, characterized in that the contact surfaces of the pin (42) and hollow shaft (38) are of conical design with respect to one another.

8. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in claim 6, characterized in that the pin (42) is designed, in the region of the hollow shaft (38), as a stepped pin, as a result of which two contact points (60, 62) are generated between the pin (42) and hollow shaft (38) .

9. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in at least one of the preceding claims, characterized in that it is possible for the pin (42) to be axially secured along its longitudinal axis by means of the shift housing (44) .

10. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in at least one of claims 1 to 8, characterized in that it is possible for the pin (42) to be axially secured along its longitudinal axis by means of at least one locking ring and/or a collar on the pin (42).

11. The shifting apparatus (11, 40) having a power assistance device (10) as claimed in at least one of the preceding claims, characterized in that the element (20) is designed as a control rod of the power assistance device (10) .