Spindle nut and linear actuator

Abstract

The invention relates to a spindle nut (8) for an electromechanical linear actuator (1), in particular a brake force generator or brake booster of a motor vehicle brake system, having a base body (12), which has an internal thread (9) for a spindle (7) and an external thread (15) for a drive motor (6). It is provided that the base body (12) is made of plastic, and a sleeve (17), which is stiffer in relation to the base body (12), is pushed onto the base body (12) at least substantially without play and is connected to the base body (12) in a form-fitting manner in the circumferential direction.

Description

[0001] R.409833

[0002] - 1 -

[0003] Description

[0004] Spindle nut and linear actuator

[0005] The present invention relates to a spindle nut for a linear actuator, in particular a brake force generator or brake booster of a motor vehicle braking system, with a base body having an internal thread for a spindle and an external thread for a drive motor.

[0006] The invention further relates to a linear actuator, in particular a brake booster or brake force generator for a motor vehicle braking system, with a controllable drive motor and with at least one displaceable actuator element, wherein the drive motor is operatively connected to the actuator element by means of a spindle drive, and wherein the spindle drive has a spindle connected to the actuator element and a spindle screw arranged on the spindle, wherein the spindle screw is connected to the drive motor.

[0007] State of the art

[0008] Spindle nuts for brake boosters, especially electromechanical brake boosters, are already known from the prior art. With the increasing electrification of motor vehicles, braking systems are also being electrified, for example, to eliminate the mechanical connection between the brake pedal and the wheel brake assembly or to enable the replacement of vacuum brake force generators, which can no longer be used due to the elimination of a brake force generator. Furthermore, electromechanical brake boosters can increase the functional versatility of braking systems and improve their control precision, regardless of the type of drive motor in a motor vehicle. The linear actuators typically used have an actuator element in the form of an R.409833

[0009] - 2 -

[0010] A piston either directly presses a brake pad against a brake disc or exerts pressure on a hydraulic medium of a hydraulic brake system. A spindle drive is frequently used to transmit power from a drive motor to the actuator element. This drive has a spindle that is fixed to the actuator element in the direction of displacement and a spindle nut that is rotatably mounted on the spindle and relative to the spindle. However, the spindle nut is fixed in the direction of displacement of the actuator element and is operatively connected to the drive motor. If the spindle nut is driven by the drive motor and set into a rotational movement, the spindle drive converts the rotational movement of the spindle nut into a translational movement of the spindle or the spindle shaft, thus displacing the actuator element in the direction of displacement.

[0011] Disclosure of the invention

[0012] The spindle nut according to the invention, with the features of claim 1, has the advantage of offering cost and functional benefits compared to conventional solutions without any disadvantages. According to the invention, the base body is made of plastic, and a sleeve, which is stiffer than the base body, is pushed onto it with at least substantially no play and is positively connected to the base body in the circumferential direction. The use of plastic for the base body initially offers significant cost advantages compared to conventional solutions that use a ball screw drive. The use of plastic also results in the spindle nut being comparatively lighter than known solutions.The sleeve, which is slid onto the base body and is stiffer than the base body itself, ensures that the spindle nut as a whole does not lose strength or robustness even at high temperatures. The sleeve supports and stiffens the base body. This stiffening allows the use of a less expensive plastic for the base body, which is inherently less temperature-resistant, as the sleeve provides sufficient support even at high temperatures without compromising its functionality. R.409833.

[0013] - 3 -

[0014] Preferably, the base body has a cylindrical axial projection onto which the sleeve is pushed. This means the sleeve does not extend over the entire base body, but rather only over the axial projection, so that the remaining part of the base body, particularly the external thread, is free of the sleeve or spaced apart from it. This provides support and stiffening to the base body, at least in the area of ​​the axial projection. Preferably, the internal thread extends through the entire base body and thus also through the axial projection.

[0015] In particular, the sleeve is positively connected to the base body in the circumferential direction. A positive-locking connection is thus formed between the sleeve and the base body, wherein preferably the base body and / or the sleeve itself are shaped or have such drive elements that an anti-rotation device is formed between the base body and the sleeve.

[0016] Furthermore, it is preferably provided that the axial projection on its outer surface has several radial protrusions and / or radial recesses, each of which interacts positively in the circumferential direction with a radial recess or radial protrusion on the inner surface of the sleeve. The positive-locking connection between the sleeve and the base body, through the radial protrusions and the interacting radial recesses, thus achieves anti-rotation protection between the base body and the sleeve. In particular, at least one radial protrusion is located in each radial recess such that they interact positively, at least in the circumferential direction. Specifically, the radial protrusion and radial recess interact without play in the circumferential direction. This ensures that forces acting on the base body in the region of the axial projection are advantageously distributed by the sleeve to the axial projection and thus to the base body without overloading it.Additionally or alternatively, to form the anti-rotation device, the axial projection has at least one axial elevation and / or axial depression on its free end face, which corresponds to an axial depression or axial elevation of the sleeve or to a radial depression R.409833.

[0017] - 4 - or radial recession of the sleeve at the end of the sleeve facing the free end face.

[0018] Preferably, the radial depressions and / or radial ridges, as well as the axial depressions and / or axial ridges, are rib-shaped. This ensures that even large forces, particularly in the circumferential direction, can be transmitted. Preferably, these ribs run parallel to the central axis or axis of rotation of the sleeve or base body. Alternatively, the ribs run inclined to the central axis.

[0019] Particularly preferably, the external thread is arranged on a first axial section of the base body, wherein the axial projection is formed on a second axial section adjoining the first axial section, and wherein an outer diameter of the base body in the first axial section is larger than an outer diameter in the second axial section. The base body is thus, particularly in longitudinal section, T-shaped, with the external thread arranged, and in particular formed, on the first axial section with the larger diameter. The axial projection thus extends axially beyond the larger diameter external thread, and the sleeve can be pushed, for example, up to the first axial section or to the external thread in order to encompass the axial projection to the maximum extent.

[0020] Preferably, the axial projection has at least one elastically deformable locking element at its free end facing away from the first axial section. This locking element is designed to engage the sleeve positively at its end face adjacent to the free end. This allows the sleeve to be secured between the locking element and the first axial section. The elastic deformability of the locking element ensures, in particular, easy assembly of the sleeve and / or effortless sliding of the sleeve onto the axial projection. During sliding, the locking element is elastically retracted and then returns to its initial position due to its own elasticity, thereby positively engaging the end face of the sleeve. R.409833

[0021] - 5 -

[0022] It is further preferably provided that the sleeve has a radially inwardly projecting collar on its end face, designed to abut the free end of the axial projection. Thus, the sleeve is cup-shaped, with a shell wall radially surrounding the axial projection and a base forming the end face associated with the free end of the axial projection, and in particular having a central opening through which the spindle can pass. Specifically, the collar projects radially inward to a maximum extent equal to the thickness of the shell wall of the axial projection. The collar ensures that the sleeve has a secure contact with the axial projection, even if it does not extend to the first axial section. Furthermore, the collar provides an advantageous mating surface with which the locking element interacts.

[0023] The detent element is particularly preferably designed to preload the sleeve against the first axial section of the base body and / or against the end face of the axial projection. This ensures a clear positioning of the sleeve on the axial projection, which, in addition to an interference fit between the sleeve and the axial projection, increases the robustness of the spindle nut.

[0024] The linear actuator according to the invention, comprising the features of claim 10, is characterized by the design of the spindle nut according to the invention. This results in the advantages already mentioned above.

[0025] Further advantages and preferred features and combinations of features will become apparent in particular from the foregoing and from the claims. The invention will now be explained in more detail with reference to the drawing. To this end, we show...

[0026] Figure 1 shows an advantageous linear actuator in a schematic representation,

[0027] Figure 2 shows an advantageous spindle nut of the linear actuator in a perspective view, R.409833

[0028] - 6 -

[0029] Figure 3 shows an advantageous sleeve of the spindle nut in a further perspective view and

[0030] Figure 4 shows a sectional view of the linear actuator in the area of ​​the spindle nut.

[0031] Figure 1 shows a linear actuator 1 in the form of a conventional electromechanical brake booster in a simplified longitudinal section. Unlike a brake pressure generator, the brake booster is designed to exert an actuating force on the master brake cylinder 3 in addition to the actuating force applied to the brake pedal by the driver of the vehicle, which is transmitted to the master brake cylinder 3 via a connecting rod 2. The linear actuator 1 shown here has a spindle drive 4 for this purpose, which can apply a pressure force to an input rod of the master brake cylinder 3 independently of the pedal actuation by an actuator element 5. An electric drive motor 6, shown here only as an indication, is associated with the spindle drive.

[0032] The spindle drive 4 has a spindle 7 which extends parallel to, or in alignment with, the input rod 5 in its longitudinal direction. The spindle drive 4 also has a spindle nut 8 which is fixed along the longitudinal direction of the spindle nut 7 and rotatably mounted. The spindle nut 8 has an internal thread 9 which engages with the thread 10 of the spindle 7. When the spindle nut 8 is set into rotation by the electric motor 6, the rotational movement of the spindle nut 8 is converted into a translational movement of the spindle 7 along its longitudinal axis 11, thereby moving the input rod 5 towards the master brake cylinder 3. To prevent the spindle 4 from rotating along with the spindle nut 8, the linear actuator 1 has a bearing arrangement 12 to which the spindle 7 is non-rotatably connected. The spindle 7 is only axially movable, and the spindle nut 8 is only rotatable. R.409833

[0033] - 7 -

[0034] Figure 2 shows a perspective view of an advantageous embodiment of the spindle nut 8. The spindle nut 8 has a base body 12 made of plastic. The base body 12 has a first axial section 13 with a first diameter and a second axial section 14 with a second diameter, which are adjacent to each other, the first diameter being larger than the second diameter.

[0035] The axial section 13 has an external thread 15 that interacts with the electric motor 6, in particular with a pinion of the electric motor 6. The external thread 15 extends axially only over the first axial section 13 of the base body 12. An axial projection 16 extends from the external thread 15, or the first axial section 13, along the second axial section 14. The spindle nut 8 shown in Figure 1 is designed accordingly. In contrast to the embodiment shown in Figure 1, however, the internal thread 9 advantageously extends through the entire base body 12, as shown in Figure 2.

[0036] A substantially cup-shaped sleeve 17 is slid onto the axial projection 16. The sleeve 17 is made of a material that is stiffer than the plastic of the base body 12. In particular, the sleeve 17 is generally stiffer than the base body 12 and is slid onto the axial projection 16 with at least substantially no play. At its front end, facing the external thread 15, the sleeve 17 has a radially outwardly projecting collar 18, which serves to abut the external thread 15 or an end face of the external thread 15. At its other end, the sleeve 17 has a radially inwardly projecting collar 19, which is associated with the free end of the axial projection 16. The collar 19 projects radially inward to such an extent that it radially overlaps the free end of the axial projection 16, at least partially.

[0037] Optionally, the collar 19 has several radial recesses 20 distributed around its circumference, the recesses 20 preferably being arranged evenly distributed around the circumference of the sleeve 17. Optionally, several axial recesses 20 are also provided at the free end of the axial projection 16.

[0038] - 8 - the projecting locking elements 21 are arranged and, in particular, formed integrally with the base body 12, wherein the locking elements 21 have an elastically deformable lever arm 22 that projects substantially axially from the free end of the axial projection 16. The respective lever arm 22 has a width that is smaller than the width of the respective radial recess 20 of the sleeve 17. Furthermore, the locking elements are arranged around the circumference of the axial projection 16 in accordance with the arrangement of the radial recesses 20 in the sleeve 17. When the sleeve 17 is pushed onto the axial projection 16, as shown in Figure 8, the lever arms 22 lie in the radial recesses 20 of the sleeve 17. At their free end, the lever arms 22 each have a radially outwardly projecting locking lug 23 which, in the assembled state, engages axially behind the end face or collar 19 of the sleeve 17 in a form-fitting manner.When the sleeve 17 is slid onto the axial projection 16, the locking elements 21, in particular the locking lugs 23, are elastically forced radially inwards so that, upon reaching the mounting position and overcoming the collar 19, they snap back into their initial position and thereby engage the collar 19 in a specific area. This ensures a captive arrangement of the sleeve 17 on the axial projection 16 or on the base body 12.

[0039] Furthermore, the axial projection 16 has several axially extending radial recesses 24. The recesses 24 are also preferably arranged evenly distributed around the circumference of the axial projection 14. In this case, four radial recesses 24 and four radial recesses 20 are provided. However, the number can also be chosen differently.

[0040] Figure 3 shows the sleeve 17 in a perspective view. The sleeve 17 preferably has several radial projections 25 on its inner surface. Because these are formed on the inner surface, they project radially inwards. The radial projections 25, like the radial recesses 24, are rib-like and extend axially along the sleeve 17. In cross-section, the radial projections 25 are only slightly smaller than the radial recesses 24, so that during assembly, one radial projection 25 is inserted into each radial recess 24 with almost no play or no play at all. Optional R.409833

[0041] - 9 - the radial protrusions 25 inserted into the radial recesses 24 each create an interference fit.

[0042] The radial projections 25, which engage in the radial recesses 24, facilitate advantageous force transmission. As soon as an axial force acts on the spindle 7 in the spindle nut 8, it is transmitted to the spindle nut 8. Within the thread, the axial force is then converted into radial-tangential and radial forces. This may deform the plastic of the base body 12, causing it to expand radially due to the predominantly axial load. Furthermore, forces also arise that act circumferentially on the spindle nut 8, potentially causing it to twist.The rigid design of the sleeve 17 prevents the expansion and flow of the plastic base part 12, and the ribbing by means of the radial protrusions 25 and the radial recesses 24 prevents twisting and tilting of the base body 12 relative to the spindle 7, as shown in Figure 4 in a simplified detail view of a longitudinal section of the linear actuator 1.

[0043] The greater the forces attempting to expand the spindle nut 8, the greater the radial reaction forces that compress the spindle nut and align it axially via the rib-shaped anti-rotation feature. Furthermore, this advantageous solution ensures a uniform application of torque across the entire circumference and length of the base body 12. This uniform load distribution allows for optimal utilization of the component's load-bearing capacity, resulting, for example, in smaller required installation spaces or the use of more cost-effective materials, particularly those with lower strength.

[0044] The advantageous anti-rotation feature between sleeve 17 and base part 12 enables a wide variety of material combinations. This allows for the combination of functionally suitable materials to achieve an optimum balance between the requirements of function, installation space, and cost.

[0045] While in the present embodiment the radial protrusions 25 and radial recesses 24 are each axially aligned, in a further embodiment, not shown here, it is provided that the R.409833

[0046] - 10 -

[0047] The ribs are inclined to the axial extent, aligned in the manner of a thread.

Claims

R.409833 - 11 - Claims 1. Spindle nut (8) for an electromechanical linear actuator (1), in particular a brake force generator or brake booster of a motor vehicle braking system, with a base body (12) having an internal thread (9) for a spindle (7) and an external thread (15) for a drive motor (6), characterized in that the base body (12) is made of plastic and that a sleeve (17) which is stiffer in relation to the base body (12) is pushed onto the base body (12) at least substantially without play and is positively connected to the base body (12) in the circumferential direction.

2. Spindle nut according to claim 1, characterized in that the base body (12) has a cylindrical axial projection (16) onto which the sleeve (17) is pushed.

3. Spindle nut according to one of the preceding claims, characterized in that the sleeve (17) is positively connected to the base body (12) in the circumferential direction. 4 Spindle nut according to claim 3, characterized in that the axial projection (16) has several radial protrusions (25) and / or radial recesses (24) on its outer surface, each of which interacts positively in the circumferential direction with a radial recess (24) or radial protrusion (25) on the inner surface of the sleeve (17).

5. Spindle nut according to one of the preceding claims, characterized in that the radial recesses (24) and / or radial protrusions (25) are rib-shaped. R.409833 - 12 - 6. Spindle nut according to one of the preceding claims, characterized in that the radial recesses (24) and / or radial protrusions (25) extend axially.

7. Spindle nut according to one of the preceding claims, characterized in that the external thread (15) is arranged on a first axial section (13) of the base body (12), and that the axial projection (16) is formed on a second axial section (14) adjoining the first axial section (13), wherein an outer diameter of the base body in the first axial section is larger than an outer diameter in the second axial section.

8. Spindle nut according to one of the preceding claims, characterized in that the axial projection (16) has at least one elastically deformable locking element (21) at its free end facing away from the first axial section (13), which is designed to engage the sleeve (17) in a form-fitting manner at its end face associated with the free end.

9. Spindle nut according to one of the preceding claims, characterized in that the sleeve (17) has a radially inwardly projecting collar (19) on its end face, which is designed to abut the free end of the axial projection (16).

10. Spindle nut according to one of the preceding claims, characterized in that the respective detent element (21) is designed to preload the sleeve (17) against the first axial section (13) of the base body (12).

11. Electromechanical linear actuator (1), in particular brake booster or brake force generator, for a motor vehicle braking system, comprising a controllable drive motor (6) and at least one displaceable actuator element (5), wherein the drive motor (6) is operatively connected to the actuator element (5) by means of a spindle drive (4), and wherein the spindle drive (4) comprises a spindle connected to the actuator element (5). R.409833 - 13 - (7) and has a spindle nut (8) arranged on the spindle 70, wherein the spindle nut (8) is connected to the drive motor (6), characterized in that the spindle nut (8) is designed according to one of claims 1 to 10.

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