POWER STEERING ASSEMBLY COMPRISING STEERING TORQUE OVERLAY

Abstract

The invention relates to a power steering assembly for a hydraulic power steering system of motor vehicles, comprising at least one hydraulic servo valve with a control member (3) for controlling the steering assistance in accordance with a relative rotation of an input shaft with respect to an output shaft (2), and at least one actuator (9) for the relative adjustment of the control member (3) with respect to the input shaft or output shaft (2) in order to influence the steering assistance characteristic. Further, the power steering assembly comprises a summation gearing having a first rotatable drive member (4) that is in operative engagement with the control member (3), and a second rotatable drive member (5) that is in operative engagement with an output element (8) of the actuator (9), and an output member (6). The summation gearing superposes a rotation of the first drive member (4) with a rotation of the second drive member (5) and drives, via the output member (6), an epicyclic gearing with at least one planetary gear (11), which is in operative engagement together with both the input shaft or output shaft (2) and with the control member (3) and can be rotated both about a planetary axis (14) fixed with respect to the frame and about its own axis of rotation (12) orbiting about the planetary axis (14), in such a way that a rotation of the first drive member (4) causes a rotation of the own axis of rotation (12) of the planetary gear (11) orbiting about the planetary axis (14) in such a way that no rotation of the planetary gear (11) about its own axis of rotation (12) occurs as a consequence, but a rotation of the second drive member (5) causes a rotation of the planetary gear (11) about its own axis of rotation (12), wherein the rotation of the planetary gear (11) about its own axis of rotation (12) causes a relative rotation of the input shaft or output shaft (2) with respect to the control member (3).

Claims

1. A power steering assembly for a hydraulic power steering system of motor vehicles, comprising at least one hydraulic servo valve with a control member (3) for controlling the steering assistance in accordance with a relative rotation of an input shaft with respect to an output shaft (2), and at least one actuator (9) for the relative adjustment of the control member (3) with respect to the input shaft or output shaft (2) in order to influence the steering assistance characteristic, characterized by a summation gearing having a first rotatable drive member (4) that is in operative engagement with the control member (3), and a second rotatable drive member (5) that is in operative engagement with an output element (8) of the actuator (9), and an output member (6), wherein the summation gearing superposes a rotation of the first drive member (4) with a rotation of the second drive member (5) and drives, via the output member (6), an epicyclic gearing with at least one planetary gear (11), which is in operative engagement together with both the input shaft or output shaft (2) and with the control member (3) and can be rotated both about a planetary axis (14) fixed with respect to the frame and about its own axis of rotation (12) orbiting about the planetary axis (14), in such a way that a rotation of the first drive member (4) causes a rotation of the own axis of rotation (12) of the planetary gear (11) orbiting about the planetary axis (14) in such a way that no rotation of the planetary gear (11) about its own axis of rotation (12) occurs as a consequence, but a rotation of the second drive member (5) causes a rotation of the planetary gear (11) about its own axis of rotation (12), wherein the rotation of the planetary gear (11) about its own axis of rotation (12) causes a relative rotation of the input shaft or output shaft (2) with respect to the control member (3).

2. The power steering assembly according to claim 1, characterized in that the epicyclic gearing is concentrically disposed around the input shaft or output shaft (2) and the control member (3) and has a first sun gear (15) non-rotatably connected to the control member (3) and has a second sun gear (16) non-rotatably connected to the input shaft or output shaft (2), wherein the planetary gear (11) is in rotational engagement with the two sun gears (15, 16).

3. The power steering assembly according to claim 1, characterized in that the planetary gear (11) is a cogwheel and the two sun gears (15, 16) of the epicyclic gearing have different external toothings.

4. The power steering assembly according to claim 1, characterized in that the at least one planetary gear (11) of the epicyclic gearing is rotatably retained by a planetary gear carrier (13) which is rotatable about the planetary axis (14) of the epicyclic gearing and is in rotational engagement with the output member (6) of the summation gearing.

5. The power steering assembly according to claim 1, characterized in that a secondary drive gear (10), which is in rotational engagement with the first drive member (4) of the summation gearing, is non-rotatably connected to the control member (3).

6. The power steering assembly according to claim 1, characterized in that the summation gearing is a planetary gearing with a sun gear (5), one or several planet gears (7) rotatably retained by a planet carrier (6) and a ring gear (4), wherein the ring gear (4) forms the first drive member, the sun gear (5) forms the second drive member and the planet carrier (6) forms the output member of the summation gearing.

7. The power steering assembly according to claim 5, characterized in that the planetary gearing is a toothed gearing, wherein the ring gear (4) has both an internal toothing, which is in rotational engagement with the one or several planet gears (7), and an external toothing, which is in rotational engagement with a toothing of the secondary drive gear (10).

8. The power steering assembly according to claim 1, characterized in that the actuator (9) is an electric drive motor (9) and the output element (8) is an output shaft (8), which is driven by the drive motor (9) and is nonrotatably connected to the second drive member (5) of the summation gearing.

9. The power steering assembly according to claim 1, characterized in that the summation gearing is disposed eccentrically with respect to the input shaft or output shaft (2) and the control member (3).

10. The power steering assembly according to claim 6, characterized in that the planetary gearing is a toothed gearing, wherein the ring gear (4) has both an internal toothing, which is in rotational engagement with the one or several planet gears (7), and an external toothing, which is in rotational engagement with a toothing of the secondary drive gear (10).

Description

[0025] Other features and advantages of the invention become apparent from the following description of an exemplary embodiment of the invention, which is to be understood not to be limiting and which will be explained below with reference to the FIGURES. In this drawing, the FIGURES schematically show:

[0026] FIG. 1: a lateral sectional view of an exemplary embodiment of a power steering assembly according to the invention.

[0027] FIG. 1 constitutes a lateral sectional view of an exemplary embodiment of a power steering assembly 1 according to the invention.

[0028] The power steering assembly 1 substantially comprises a hydraulic servo valve, an actuator, a summation gearing and an epicyclic gearing.

[0029] The servo valve substantially comprises an input shaft (not shown), an output shaft 2 and a control member 3. The input shaft is connected to a steering wheel of a motor vehicle via a steering column, which is not shown. In turn, the output shaft 2 is indirectly connected to wheels of the motor vehicle that are to be rotated, which are not shown. In a known manner, the input shaft is connected to the output shaft 2 via a torsion bar (also not shown), wherein the torsion bar on its one end is non-rotatably connected to the input shaft and on its other end non-rotatably connected to the output shaft 2. Accordingly, the torsion bar establishes a coupling between the input shaft and the output shaft 2, wherein it permits a relative rotation between them. Moreover, the control member 3 is disposed concentrically with and around the input shaft. The control member 3 is mounted so as to be rotatable and/or displaceable relative to the input shaft.

[0030] The function and mode of action of the power steering assembly 1 described up to this point are generally known from the prior art.

[0031] As is also apparent from FIG. 1, the summation gearing comprises a first drive member 4, a second drive member 5 and an output member 6. The summation gearing of the illustrated power steering assembly 1 is configured as a planetary gear unit in which a ring gear forms the first drive member 4, a sun gear forms the second drive member 5 and a planet carrier forms the output member 6. The planet carrier 6 carries several planet gears 7, which are rotatably mounted on corresponding shafts and in rotational engagement with an internal toothing of the ring gear 4 and a toothing of the sun gear 5 in a known manner.

[0032] The second drive member 5 of the summation gearing is non-rotatably connected to an output element 8 of the actuator 9. In the exemplary embodiment of the power steering assembly 1 shown in FIG. 1, the actuator 9 is an electric drive motor with a driven output shaft forming the output element 8.

[0033] Furthermore, it can be seen in FIG. 1 that a secondary drive gear 10 is non-rotatably connected to the control member 3. Via the secondary drive gear 10, the control member 3 is in operative engagement with the first drive member 4, in particular with the ring gear 4, of the summation gearing. For this purpose, the ring gear 4 also has an external toothing via which the secondary drive gear 10, which is configured as a cogwheel, is in rotational engagement.

[0034] As is apparent from FIG. 1, the summation gearing of the power steering assembly 1 is disposed eccentrically with respect to the output shaft 2 and the control member 3.

[0035] Furthermore, the epicyclic gearing driven by the summation gearing can be recognized in FIG. 1. The former comprises a planetary gear 11, which is retained on a planetary gear carrier 13 so as to be rotatable about its on axis of rotation 12. The planetary gear carrier 13 is in operative engagement with the output member 6, in particular the planet carrier 6, of the summation gearing. In the power steering assembly 1 illustrated in FIG. 1, the planet carrier 6 of the summation gearing has a external toothing for this purpose, which is in rotational engagement with an external toothing of the planetary gear carrier 13 of the epicyclic gearing. Furthermore, the planetary gear carrier 13 is rotatably mounted about a planetary axis 14, which is a planetary axis fixed with respect to the frame with regard to the power steering assembly 1. Thus, the planetary gear 11 is able to rotate both about its own axis of rotation 12 as well as about the planetary axis 14. As is apparent from FIG. 1, the epicyclic gearing in the illustrated exemplary embodiment of the power steering assembly 1 is concentrically disposed around the output shaft 2 and the control member 3.

[0036] As is further apparent from FIG. 1, the planetary gear 11, which is configured as a cogwheel in the illustrated power steering assembly 1, is further in operative engagement, in particular in rotational engagement, with one sun gear 15 and one sun gear 16, respectively. The sun gear 15 is non-rotatably connected to the control member 3. The sun gear 16 is non-rotatably connected to the output shaft 2. The two sun gears 15 and 16 have a different number of teeth, so that a rotation of the planetary gear 11 common to both sun gears 15 and 16 about its own axis of rotation 12 results in a relative rotation of the output shaft 2 relative to the control member 3. A rotation of the planetary gear 11 is caused by a rotation of the planetary gear carrier 13 about the planetary axis 14. This rotation can be caused through the drive by the summation gearing. Accordingly, it is possible, by means of a rotation of the planetary gear 11 about its own axis of rotation 12, i.e. in the case of a relative rotation of the planetary gear carrier 13 with respect to the output shaft 2, in which the planetary gear 11 rolls on the sun gears 15 and 16, to adjust a difference angle between the output shaft 2 and the control member 3 in order thus to alter the steering assistance characteristics.

[0037] If no difference angle between the two sun gears 15 and 16 is to be adjusted, it is necessary to rotate the planetary gear carrier 13 about the planetary axis 14 with the same angular velocity with which the output shaft 2 rotates. In this case, the planetary gear 11 itself cannot rotate about its own axis of rotation 12.

[0038] In the exemplary embodiment of the power steering assembly 1 according to the invention shown in FIG. 1, the planetary gear carrier 13 is rotated by rotating the planet carrier 6.

[0039] In the case in which the output element 8 of the actuator 9 or the output shaft 9 of the drive motor 9 stands still but the output shaft 2 rotates, the summation gearing is driven by means of the secondary drive wheel 10 connected to the control member 3. In this case, the gear ratio of the summation gearing is chosen such that the rotation of the first drive member 4 or of the ring gear 4 causes an angular velocity of the output member 6 or of the planet carrier 6 in such a way that the planetary gear carrier 13, due to it being coupled to the planet carrier 6 of the summation gearing, rotates with the same angular velocity as the output shaft 2. Thus, the planetary gear 11 does not rotate about its own axis of rotation 12, so that no difference angle between the sun gears 15 and 16 is generated.

[0040] In the case where the output shaft 2 stands still but the output element 9 of the actuator 9 or the output shaft 9 of the drive motor 9 rotates, a rotation of the output member 6 or of the planet carrier 6 is initiated through the rotation of the first drive member 5 or of the sun gear 5 of the summation gearing. Since in that case, the output shaft 2 stands still and the planetary gear carrier 13 is rotated about the planetary axis 14 due to it being coupled to the planet carrier 6, and the planetary gear 11 now rolls on both sun gears 15 and 16, a difference angle is generated between the sun gears 15 and 16, and thus between the output shaft 2 and the control member 3.

[0041] The case where both the output shaft 2 and the output shaft 8 of the drive motor 9 rotate, results in a superposition of the two previously described cases, due to the function of the summation gearing of superposing a rotation of the first drive member 4 or of the ring gear 4 with a rotation of the second drive member 5 or of the sun gear 5.

[0042] An essential advantage of the power steering assembly 1 described herein over the prior art is that, in order to obtain a clearance-free or almost clearance-free transmission of the gear ratio between the two sun gears 15 and 16, only the planetary gear 11 and the two sun gears 15 and 16 must be designed with a high toothing quality. The eccentrically mounted summation gearing can be configured with toothing parts of a lower quality because the clearances produced there have only a marginal effect on the gear ratio between the control member 3 and the output shaft 2.

[0043] Another advantage is that the clearance between the sun gears 15 and 16 and the planetary gear 11 can be reduced by bringing the planetary gear 11 close up to the sun gears 15 and 16.

[0044] If the eccentric summation gearing is used, the required construction space of the power steering assembly can also be reduced and the packaging can be optimized.

[0045] The power steering assembly according to the invention was explained in more detail with reference to an exemplary embodiment illustrated in the FIGURE. However, the power steering assembly is not limited to the embodiment described herein, but also includes embodiments having the same effects.

[0046] In a preferred embodiment, the power steering assembly according to the invention is used for a hydraulic power steering system with a steering torque superposition in a motor vehicle.

LIST OF REFERENCE NUMERALS

[0047] 1 Power steering assembly [0048] 2 Output shaft [0049] 3 Control member [0050] 4 First drive member, ring gear [0051] 5 Second drive member, sun gear [0052] 6 Output member, planet carrier [0053] 7 Planet gear [0054] 8 Output element, output shaft [0055] 9 Actuator, electric drive motor [0056] 10 Secondary drive gear [0057] 11 Planetary gear [0058] 12 Own axis of rotation of 11 [0059] 13 Planetary gear carrier [0060] 14 Planetary axis [0061] 15 Sun gear [0062] 16 Sun gear