Patent Application
20150308527
The present invention relates to a transmission device. In addition, the present invention relates to an electromotive brake booster.
A power transmission assembly is described in DE 10 2009 027 468 A1. The power transmission assembly includes a drive, a worm shaft connected to the drive, two worm gears, which mesh with the worm shaft, and two pinions, each of which is rotatable together with an associated worm gear of the two worm gears. In addition, the power transmission assembly includes a double toothed element having a first row of teeth and a second row of teeth, each of which meshes with one of the two pinions.
The present invention makes a transmission device possible, the static and dynamic tolerances (the tolerance chain) of which can be compensated for without tensioning of the transmission device. The static tolerances are, for example, those that arise after assembly of the transmission and/or that do not change during an operation of the transmission device. Such static tolerances are, for example, an angular offset between the worm gear and the toothing of the pinion and/or an axial offset between the two toothed racks formed on the adjustable piston, which mesh with the two pinions. Dynamic tolerances are, for example, those that take effect during an operation of the transmission device and/or are a function of the actuating travel of the transmission device. Such dynamic tolerances can, for example, be concentricity deviations and pitch errors of all involved tooth gears, worms and/or toothed racks. The present invention is therefore reliably suited for eliminating functional impairments that traditionally occur in a transmission.
At the same time, two load paths are formed on the transmission device so that an advantageous power split occurs. The power split results in a compact transmission that is able to transfer comparatively high forces. As explained below in greater detail, in an example embodiment, undesirable partial meshing forces in the transmission device from the two engagements between the two pinions and the toothed racks associated with them cancel each other out in such a way that only one force oriented in a desired adjustment direction of the adjustable piston is exerted on the piston. This effectuates an advantageous, excellent adjustability of the adjustable piston in the desired adjustment direction.
The adjustable piston is preferably adjustable perpendicularly to the adjustment axis by a floating travel of at least 0.8 mm. The static and dynamic tolerances described above can, given such a large floating travel, be reliably compensated for without tensioning of the transmission device.
In particular, the adjustable piston can be guided in a floating manner between the first pinion and the second pinion in such a way that a center distance offset of at least ±0.3 mm is formed between the first pinion and the adjustable piston and between the second pinion and the adjustable piston. A center distance offset of ±0.3 mm in this case means that from the “initial position” of the pinion teeth and toothed rack teeth on block, the two sets of teeth are spaced 0.3 mm apart from each other. This results in a backlash, which is significantly greater than in the case of a conventional meshing configuration having a center distance offset of ±0.1 mm.
A center distance offset of at least ±0.4 mm can also be formed between the first pinion and the adjustable piston and between the second pinion and the adjustable piston. The advantageous formation of the comparatively large floating travel on both sides of the adjustable piston perpendicular to the adjustment axis allows for the advantageous compensation of tolerances with no additional components and with no additional installation space requirement.
In one advantageous example embodiment, a pinion center plane is definable, which intersects centrically the first pinion and the second pinion, respectively, the adjustable piston being guided in a floating manner in the pinion center plane exclusively with the aid of a first tooth engagement of the first pinion with a first row of teeth of the adjustable piston, and with the aid of a second tooth engagement of the second pinion with a second row of teeth of the adjustable piston. As explained in greater detail below, this permits an advantageous self-adjustment of the adjustable piston in a central position relative to the two pinions.
In addition, a first coverage of the first tooth engagement can be greater than or equal to 1 or a second coverage of the second tooth engagement can be greater than or equal to 1. In particular, the first coverage of the first tooth engagement can be greater than or equal to 1.05 or the second coverage of the second tooth engagement can be greater than or equal to 1.05. In this way, an overloading of the toothing and an uneven toothing sequence can be avoided.
In one preferred example embodiment, a function of a force balance is formed on the transmission device. Due to the thus implementable automatic self-adjustment of the adjustable piston, the tension-free action of the transmission device is ensured during its entire operation.
The above enumerated advantages are also ensured in the case of an electromotive brake booster including such a transmission device, whose adjustable piston is designed as a booster piston.
In one advantageous refinement of an example embodiment, the adjustable piston designed as a booster piston is guided with the aid of a radial clearance in at least one guide plane oriented at an angle to the pinion center plane in a housing bore of a brake booster housing of the electromechanical brake booster. A design including thrust surfaces on the brake booster housing suitable for this purpose can be easily implemented.
Additional features and advantages of the present invention are explained below with reference to the figures.
a-1e show schematic general and partial representations of an example embodiment of a transmission device.
a-2c show partial representations of various transmissions,
a-1e show general and partial representations of a transmission device according to an example embodiment of the resent invention.
The transmission device depicted schematically in
In addition, the transmission device includes a first worm gear 12a, which is connected to a first pinion 16a via a first pinion shaft 14a. A second worm gear 12b of the transmission device is connected to a second pinion 16b via a second pinion shaft 14b. First worm gear 12a and second worm gear 12b contact worm shaft 10 in such a way that, with the aid of worm shaft 10 set into rotation about its longitudinal axis, first worm gear 12a and first pinion 16a are rotatable about a shared first rotation axis 18a, and second worm gear 12b and second pinion 16b are rotatable about a shared second rotation axis 18b. First rotation axis 18a and second rotation axis 18b are preferably aligned in parallel to each other. First rotation axis 18a and/or second rotation axis 18b can, in particular, be aligned perpendicularly to the longitudinal axis of worm shaft 10. However, the design of the transmission device is not limited to a particular alignment of the longitudinal axis of worm shaft 10 or of rotation axes 18a and 18b relative to each other.
The transmission device also includes an adjustable piston 20, which is guided in a floating manner between first pinion 16a and second pinion 16b. Adjustable piston 20 is adjustable along an adjustment axis 22 with the aid of first pinion 16a rotated about first rotation axis 18a and of second pinion 16b rotated about second rotation axis 18b. The adjustable piston is preferably adjustable by at least 0.5 cm along adjustment axis 22. Adjustment axis 22 of adjustable piston 20 can, in particular, be aligned in parallel to the longitudinal axis of worm shaft 10, perpendicular to first rotation axis 18a and/or perpendicular to second rotation axis 18b. (In
The floating travel of at least 0.6 mm of adjustable piston 20 perpendicular to adjustment axis 22 means that sufficient free space is formed between the two pinions 16a and 16b, so that adjustable piston 20 situated a minimal distance from first pinion 16a is able to float by at least 0.6 mm perpendicularly to adjustment axis 22 in the direction of second pinion 16b; and so that adjustable piston 20 situated a minimal distance from second pinion 16b can be moved toward first pinion 16a by a floating travel of at least 0.6 mm perpendicularly to adjustment axis 22. Adjustable piston 20 is therefore free for being guided perpendicularly to adjustment axis 22 in an adjustment movement between pinions 16a and 16b.
The floating travel preferably includes free space besides for that which allows for a potential heat expansion and/or swelling of adjustable piston 20 and/or pinions 16a and 16b due to absorption of liquid. Thus, the floating travel of adjustable piston 20 of at least 0.6 mm perpendicular to its adjustment axis 22 preferably still exists, even when operating the transmission device in an environment with a maximal onset temperature of the transmission device and/or when adjustable piston 20 and/or pinions 16a and 16b are in contact with liquid or air moisture for several days/weeks/months.
The comparatively free guidance of adjustable piston 20 between the two pinions 16a and 16b with a floating travel of at least 0.6 mm aligned perpendicularly to adjustment axis 22 ensures an advantageous ability to compensate for static and/or dynamic tolerances of the tolerance chain of the transmission device without tensioning. Static tolerances are identifiable as tolerances which arise after assembly of the transmission. In particular, tolerances that do not change during an operation of the transmission device can be described as static tolerances. The static tolerances include, for example, the tolerances of the positions of roller bearings 23a of worm shaft 10 from their setpoint positions and/or the tolerances of the positions of roller bearings 23b of pinion shafts 14a and 14b from their setpoint positions. The transmission device depicted in
Dynamic tolerances can be tolerances that take effect during an operation of the transmission device. In addition, dynamic tolerances can be a function of an actuating travel of the transmission device. Such dynamic tolerances can, for example, be concentricity deviations and pitch errors of the tooth gears, of the worm shaft and/or of a toothed rack. Such dynamic tolerances can also be reliably compensated for with the aid of the comparatively large floating travel of at least 0.6 mm of adjustable piston 20 perpendicular to its adjustment axis 22.
A compactness of the transmission device depicted in
As explained in greater detail below, a self-adjustment of the individual components of the transmission device during an operation is automatically implementable. The transmission device is therefore comparatively easy to assemble.
The advantages explained above can be implemented without attaching additional components to the transmission device. In addition, in a design of a floating travel of adjustable piston 20 of at least 0.6 mm aligned perpendicularly to adjustment axis 22, there are no additional installation space requirements for compensating for the tolerances of the tolerance chain of the transmission device.
In the transmission device, the first worm gear 12a and the first pinion 16a can be situated at a first distance from a definable center plane 24, which centrically intersects worm shaft 10, the distance being (virtually) the same as a second distance of second worm gear 12b and of second pinion 16b from center plane 24. Thus, the transmission device can be (virtually) symmetrically designed with respect to center plane 24 extending centrically through worm shaft 10. In particular, adjustable piston 20 (present in a center position between the two pinions 16a and 16b) can also be symmetrically designed with respect to center plane 24. This ensures an advantageous power split of the power generated by the electric motor via a first path along first worm gear 12a and first pinion 16a and along a second path via second worm gear 12b and second pinion 16b. As a result of this power split, comparatively high forces can be transmitted by the electric motor to adjustable piston 20. However, the transmission device is not limited to such a symmetrical design.
In one advantageous example embodiment of the transmission device, adjustable piston 20 is guided in a floating manner between first pinion 16a and second pinion 16b, such that a center distance offset of at least ±0.3 mm is formed between first pinion 16a and adjustable piston 20, and between second pinion 16b and adjustable piston 20, respectively. The advantageous floating travel of at least 0.6 mm can thus be formed via a backlash. Preferably, the two pinions 16a and 16b are designed symmetrically with respect to their backlash. This results in an advantageous power split in spite of the comparatively large floating travel of adjustable piston 20 of at least 0.6 mm perpendicular to its adjustment axis 22.
In one advantageous example refinement, adjustable piston 20 can be adjustable perpendicularly to adjustment axis 22 by a floating travel of at least 0.8 mm, preferably of at least 0.9 mm, in particular, of at least 1.0 mm. This is implemented in a preferred manner by guiding adjustable piston 20 in a floating manner between first pinion 16a and second pinion 16b in such a way that a center distance offset of at least ±0.4 mm, preferably of at least ±0.45 mm, in particular of at least ±0.5 mm, is formed between first pinion 16a and adjustable piston 20, and between second pinion 16b and adjustable piston 20, respectively. This permits a reliable implementation of the advantages described above.
Adjustable piston 20 is preferably guided in a floating manner between the two pinions 16a and 16b in such a way that the maximal floating travel of adjustable piston 20 perpendicular to adjustment axis 22 is less than 1.3 mm, in particular less than 1.2 mm, preferably less than 1.1 mm. A value range for the maximum floating travel of adjustable piston 20 perpendicular to adjustment axis 22 of between 0.8 mm to 1 mm is preferred. The advantages of a limitation of the maximum floating travel of adjustable piston 20 perpendicular to adjustment axis 22 will also be explained below.
In addition, a pinion center plane 26 is also definable for the transmission device in
Preferably, a first coverage of the first tooth engagement (of first pinion 16a on the first row of teeth of adjustable piston 20) is greater than or equal to 1 or a second coverage of the second tooth engagement (of second pinion 16b on the second row of teeth of adjustable piston 20) is greater than or equal to 1. In particular, the first coverage of the first tooth engagement can be greater than or equal to 1.05 or the second coverage of the second tooth engagement can be greater than or equal to 1.05. Thus, the advantageously large floating travel of adjustable piston 20 perpendicular to adjustment axis 22 can be formed via the backlash of the two pinions 16a and 16b (or the rows of teeth associated with them). In this way, advantageously large distance tolerances can be formed for compensating for the above described tolerance chain. With the coverages of at least 1, an excessively high tooth stress of the teeth of pinions 16a and 16b and of the rows of teeth of adjustable piston 20 is prevented. In this way, an advantageously long service life/operating time of the transmission device may be ensured.
The transmission device depicted in
Also merely exemplary is the guiding of adjustable piston 20 designed as a booster piston in at least one guide plane 30 aligned at an angle, in particular, perpendicularly, to pinion center plane 26, with the aid of a radial clearance, which is formed via the thrust surfaces 36 in a housing bore 32 of a brake booster housing 34. The design of thrust surfaces 36 on housing bore 32 permits a reliable guiding of adjustable piston 20 designed as a booster piston, but it is not required.
A force balance is formed in the transmission device of
In
Meshing forces Fr1 and Fr2 are aligned orthogonally relative to the respective tooth flanks. If meshing forces Fr1 and Fr2 exerted on adjustable piston 20 are equally great/exhibit the same absolute values, then the components of meshing forces Fr1 and Fr2 aligned perpendicularly to adjustment axis 22 cancel each other out. In this case, meshing forces Fr1 and Fr2 add up to a total force Fges, which is aligned in parallel to adjustment axis 22. Thus, given the same meshing forces/absolute values of meshing forces Fr1 and Fr2, the desired linear adjustability of adjustable piston 20 along adjustment axis 22 is reliably ensured without a jamming occurring.
In the case of unequal meshing forces/absolute values of meshing forces Fr1 and Fr2, a force component aligned perpendicularly to adjustment axis 22 remains, which is directed from the high force side (of the greater meshing force Fr1 or Fr2) to the low force side (of the smaller meshing force Fr1 or Fr2). Adjustable piston 20 is moved (automatically) from the high force side to the low force side by the force component aligned perpendicularly to adjustment axis 22. In this way, the tooth engagement on the originally high force side (automatically) tends increasingly toward disengagement, so that the tooth engagement on the originally lower force side becomes stronger. In this way, adjustable piston 20 is displaced until meshing forces Fr1 and Fr2 are equally great/exhibit the same absolute values.
Thus, a force balance on the transmission device is formed in this way. This ensures a symmetrical load distribution of the force transmitted from the motor to adjustable piston 20 via a first load path implemented using a first worm gear 12a and first pinion 16a, and via a second load path implemented using a second worm gear 12b and second pinion 16b.
The tolerance compensation on the transmission device is explained in the following with reference to
In the depiction of
Since “overlap” 46 depicted in
However, since the (slight) displacement 52 of adjustable piston 20 is not linked to a simultaneous rotation of first pinion 16a about first rotation axis 18a, the (slight) displacement 52 of adjustable piston 20 causes an increase of the mesh clearance between first pinion 12a and adjustable piston 20. Tooth engagement 54 between first pinion 16a and adjustable piston 20 is therefore force-free.
Meshing force Fr2, which is exerted by second pinion 16b on adjustable piston 20, is therefore not compensated for at least in part by a counterforce. The effect of this is that the force component of meshing force Fr2 aligned perpendicularly to adjustment axis 22 exerted by second pinion 16b on adjustable piston 20 causes an adjustment movement of adjustable piston 20, until a force equilibrium between meshing forces Fr1 and Fr2 is restored. Thus, the function of the force balance described above can also be utilized in order to compensate for an off-center position of worm shaft 10. The desired counter-directional rotations 56 of pinions 16a and 16b for adjusting adjustable piston 20 along its adjustment axis 22 may be implemented without a jamming Thus, the comparatively large floating travel of at least 0.6 mm results in the possibility of an axial offset of adjustable piston 20, as a result of which every tolerance chain can be compensated for.
a-2c show partial representations of different transmissions,
It is expressly noted at this point that those skilled in the art must overcome many conventional preconceptions before they recognize the advantages of the transmission device depicted in
Moreover, to ensure the comparatively large 0.8 mm floating travel of adjustable piston 20 perpendicular to its adjustment axis 22, those skilled in the art are forced to meet contradictory boundary conditions when designing the toothing of pinions 16a and 16b and the toothed racks associated with them. For the floating travel of 0.8 mm, there should be a center distance offset on pinions 16a and 16b, respectively, of ±0.4 mm. A center distance offset of ±0.4 mm may be understood to mean that from the “initial position” of pinion teeth/toothed rack teeth on block, the two sets of teeth are spaced apart by 0.4 mm from one another. This results in an oversized backlash. (A conventional toothing design usually has a center distance offset of ±0.1 mm.)
In the case of a transmission device, however, those skilled in the art generally also prefer a preferably high transmission ratio, which is why they select a diameter for pinions 16a and 16b which is often comparatively small as compared to the diameter of worm gears 12a and 12b. However, a reduction of the diameter of pinions 16a and 16b in the case of a center distance offset of ±0.4 mm (on both sides) results in a coverage of tooth engagements of less than 1, which is associated with an irregular run of the transmission and high bending stresses at the tooth base. Pinions 16a and 16b with a larger diameter increases the coverage, but results in a lower transmission ratio. The implementation of the transmission device partially depicted in
Frequently, those skilled in the art also prefer preferably large teeth on pinions 16a and 16b and on the rows of teeth. For this reason, those skilled in the art traditionally shy away from designing a floating travel of at least 0.6 mm on a transmission device.
The transmission device partially schematically depicted in
The transmission depicted schematically in
Thus, when developing the transmission device, those skilled in the art must solve the problem that an excessively large floating travel may result in a significant decrease of the coverage, as a result of which the tooth stressing increases sharply. Those skilled in the art must overcome multiple difficulties in order to arrive at the transmission depicted in
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 222 949.3 | Dec 2012 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/072122 | 10/23/2013 | WO | 00 |
