Electromechanical brake pressure generator with screw drive

Abstract

The invention relates to an electromechanical brake pressure generator (14) for a hydraulic brake system (10) of a vehicle, the brake pressure generator having at least one threaded transmission. The threaded transmission comprises a hydraulic piston, a spindle and a spindle nut, which act together via a thread, and an electric drive, whereby the spindle and the spindle nut can rotate relative to each other. The hydraulic piston of a piston / cylinder unit at least partially radially surrounds the spindle and the spindle nut, the hydraulic piston being received in a hydraulic cylinder of the piston / cylinder unit, the hydraulic cylinder forming an anti-twist structure, the anti-twist structure being formed by a recess extending in the axial direction and forming a sliding surface, and a sliding element extending into the recess, and the sliding element being constructed in such a way that the sliding element abuts against a planar contact area of ​​the sliding surface, so that the hydraulic piston is protected against rotation and can be axially moved by rotation of the spindle or the spindle nut.

Description

Technical Field

[0001] The invention relates to an electromechanical brake pressure generator for a hydraulic brake system of a vehicle, which comprises in particular a screw transmission for converting a drive-side rotational movement into a translational movement for piston actuation of a piston / cylinder unit. Background Art

[0002] The driver's pedal force is usually not enough to brake the motor vehicle, so the motor vehicle is usually equipped with a brake booster. Conventional brake boosters usually work with the negative pressure generated by the combustion engine. The pressure difference between the engine pressure and the ambient pressure is used to apply a boosting force to the piston rod of the piston / cylinder unit in addition to the driver's pedal force.

[0003] For future drive concepts of motor vehicles, alternative brake pressure build-up devices are required, since negative pressure is no longer available for operating conventional vacuum brake boosters. For this purpose, electromechanical brake pressure generators have been developed, which are of interest here.

[0004] In this case, the actuating force is generated on the master brake cylinder by means of an electric motor. Such an electromechanical brake pressure generator can be used not only to provide an auxiliary force, but also in a brake-by-wire system for the sole provision of an actuating force. Electromechanical brake pressure generators are therefore particularly advantageous in autonomous driving.

[0005] A conventional electromechanical brake booster is known from WO 2017 / 045804 A1, which has a Figure 1 . In contrast, the present invention relates to an electromechanical brake pressure generator which is able to apply a braking force independently of the actuation of the brake pedal. The aforementioned brake booster 1 comprises a spindle nut 2 and an electric motor (not sketched), by means of which the spindle nut 2 can be set in rotation via a spur gear 3. The spindle nut 2 is in active engagement with a spindle 4, so that the spindle 4 can be set in a translational movement along its spindle axis 5 by means of the spindle nut 2 set in rotation. In order that the spindle 4 does not rotate along with the rotation of the spindle nut 2, the brake booster 1 has a bearing device 6, to which the spindle 4 is fixedly connected.

[0006] The bearing device 6 comprises a collar 6a, on the edge of which two plain bearings 6b are arranged. The plain bearings 6b run on a tie rod 7, which extends essentially parallel to the spindle axis 5. By means of this bearing device 6, the spindle 4 can be moved in the axial direction and is protected against rotation. Summary of the invention

[0007] The object of the present invention is to specify an electromechanical brake pressure generator having a threaded drive which ensures a technically simple but reliable protection against rotation.

[0008] This object is achieved by an electromechanical brake pressure generator for a hydraulic brake system. An electromechanical brake pressure generator for a hydraulic brake system of a vehicle, comprising: at least one threaded transmission for converting a drive-side rotational movement into a translational movement; a piston / cylinder unit for generating brake pressure that can be actuated by the threaded transmission, the piston / cylinder unit comprising a hydraulic piston, wherein the threaded transmission comprises a spindle and a spindle nut, the spindle and the spindle nut acting together via a thread; and an electric drive, by means of which the spindle and the spindle nut can be rotated relative to each other, the hydraulic piston of the piston / cylinder unit at least partially radially surrounding the spindle and the spindle nut, and the hydraulic piston being received in a hydraulic cylinder of the piston / cylinder unit, the hydraulic cylinder forming a torsion-proof structure, wherein the torsion-proof structure is formed by a recess extending in the axial direction and forming a sliding surface and a sliding element extending into the recess, and wherein the sliding element is designed such that it rests on a planar contact area of ​​the sliding surface, so that the hydraulic piston is protected against torsion and can be axially displaced by a rotation of the spindle or the spindle nut. Advantageous developments of the invention are reflected below.

[0009] The invention discloses an electromechanical brake pressure generator for a hydraulic brake system of a vehicle. The electromechanical brake pressure generator has at least one screw transmission for converting a rotational movement into a translational movement for generating brake pressure. The screw transmission comprises a spindle and a spindle nut, wherein the spindle and the spindle nut cooperate via a thread and can be rotated relative to each other by a drive, and a hydraulic piston, which at least partially radially surrounds the spindle and the spindle nut and can be axially moved by rotation of the spindle or the spindle nut.

[0010] In addition, the threaded transmission comprises a housing, which forms a hydraulic cylinder corresponding to the hydraulic piston, in which the hydraulic piston is received. In addition, the threaded transmission comprises an anti-twist structure formed by the hydraulic cylinder and the hydraulic piston, by which the hydraulic piston is protected from twisting when the spindle or the spindle nut rotates. The anti-twist structure is formed by a recess extending in the axial direction and forming a sliding surface, and a sliding element extending into the recess. The sliding element is configured so that the sliding element is flat against the sliding surface in the contact area.

[0011] The invention includes not only pure spindle drives but also ball screw drives, in which the spindle nut is in direct contact with the spindle. Ball screw drives are screw drives with balls inserted between the spindle and the spindle nut. The two components each have a helical groove, which together form a helical tube filled with balls. The form-fitting connection in the thread transverse to the helix is ​​not between the thread groove and the thread bar, as in a pure spindle drive, but rather via the balls.

[0012] The hydraulic piston is directly in contact with the brake fluid, so that the brake fluid can be loaded with pressure via the hydraulic piston. The hydraulic piston is preferably configured in a pot shape. Preferably, a part of the spindle and a part of the spindle nut are engaged in the pot-shaped recess.

[0013] In the sense of the invention, "torsion" is understood to mean a rotational movement about the axial axis of the element to be protected in each case. In the present invention, both the spindle and the spindle nut can be protected against torsion. Depending on whether the spindle or the spindle nut is driven, the non-driven element is thus protected against torsion, so that a rotational movement can be converted into a translational movement. As a result, the non-driven element can be moved axially.

[0014] The recess extending in the axial direction extends along the axis of movement of the axially moving element. A form-fitting connection is preferably formed in the direction of rotation by means of the recess and the sliding element extending into the recess, thereby preventing rotation. The sliding surface is in particular a surface which is particularly designed for sliding movement. For example, the sliding surface is particularly smooth and has no protrusions. Good sliding properties can thus be provided.

[0015] The contact area refers in particular to the area in which the sliding element is in direct contact with the sliding surface. This contact area is not formed as a point structure (so that a linear contact is formed with the movement), but this contact area is constructed as a surface structure. The surface contact forms a strip-shaped contact with the sliding surface with the movement. The surface pressure is reduced by the surface contact. As a result, the force is not concentrated on the point contact, but is distributed on the surface contact. As a result, the wear between the sliding surface and the sliding element is also reduced.

[0016] Preferably, two anti-twist structures are respectively constructed, which have an angle of 180° between each other, that is, are opposite each other. By the anti-twist structures arranged in this way, it is sufficient to protect the element (to be protected against rotation) from rotation.

[0017] In a preferred embodiment of the invention, the spindle is connected to the hydraulic piston in a rotationally fixed manner, so that the hydraulic piston and the spindle can be moved axially with the rotation of the spindle nut. In another preferred embodiment of the invention, the hydraulic piston is connected to the spindle nut in a rotationally fixed manner, so that the hydraulic piston and the spindle nut can be moved axially with the rotation of the spindle. Thus, two different solutions can be provided, so that the best system can be selected for the respective application.

[0018] The anti-twist structure is preferably formed by a tongue-and-groove connection. A tongue-and-groove connection is characterized in particular by grooves that are precisely coordinated with one another and by a tongue that can be received therein. The groove and the tongue fit into one another in a form-fitting manner. The tongue-and-groove connection can be designed as a groove and a tongue on the components to be protected relative to one another, for example. The tongue-and-groove connection can be produced, for example, by stamping, broaching, cutting, milling, slotting or, in particular, cold forming. Such a tongue-and-groove connection can thus be produced easily and economically.

[0019] In an advantageous development, the sliding element is designed as a protruding structure in at least one axial edge region in the axial direction of the spindle. This means that the axial edge region arranged in the axial direction has a smaller thickness in the peripheral direction than in the core region of the sliding element. As a result, the correspondingly protrudingly formed axial edge region does not rest against the sliding surface. In the case of a corresponding tilting of the piston, no edge loads thus occur. As a result, even when the piston is tilted, a planar contact between the sliding element and the sliding surface can be ensured.

[0020] The sliding element is advantageously designed as a protruding structure in at least one radial edge region in the axial direction of the spindle. This means that the radial edge region arranged in the radial direction has a smaller thickness in the peripheral direction than in the core region of the sliding element. As a result, the correspondingly protruding radial edge region does not rest against the sliding surface. In the case of a corresponding tilting of the piston, no edge loads thus occur. Similarly, for the axial edge region, a planar contact between the sliding element and the sliding surface can thus be ensured even when the piston is tilted.

[0021] According to an advantageous embodiment of the invention, the sliding element additionally has a contact shoe, which is arranged on the outside and is in contact with the sliding surface. The contact shoe preferably lies flat against the sliding surface, thereby establishing a sliding contact with the sliding surface. The surface pressure is reduced by the flat contact with respect to the sliding surface. The contact shoe is preferably made of a material different from that of the hydraulic piston. Preferably, the contact shoe completely surrounds the sliding element. The contact shoe makes it possible to select the material of the hydraulic piston independently of the sliding properties. The material of the contact shoe is advantageously selected in this case so as to ensure a good sliding pairing between the material of the sliding surface and the contact shoe.

[0022] In a preferred development, the contact shoe is made of a plastic material. In addition, any desired shapes can be easily produced. This makes it possible to easily and economically construct such a contact shoe. In addition, the plastic is lightweight and inexpensive. In the field of plastics, there is also a great choice of plastics with specific properties, so that a suitable plastic can be found for the desired application.

[0023] The contact shoe and the inner sliding element part of the sliding element advantageously abut against each other along the axial direction of the main shaft via a flat surface and a convex surface. In other words, the surface on the sliding element or the contact shoe is convexly configured and points to the other component. The surface of the other component that abuts against the convex surface is flatly configured. The flat surface is preferably configured parallel to the sliding surface. The convex or flat surface is arranged on the two sides of the sliding element that are directed toward the sliding surface.

[0024] The convex and flat surfaces ensure that the hydraulic piston can be tilted without edge loading. The sliding element and the contact shoe thus also bear against each other in a planar manner during tilting. Accordingly, the surface pressure and thus the wear are reduced. The loads acting on the sliding element and the contact shoe are thus reduced.

[0025] In another advantageous embodiment, the sliding surface is formed by a slide rail inserted into the recess. The material of the recess formed by the housing is preferably different from the material of the slide rail. The slide rail can thus preferably be inserted into the recess as an additional component. By means of different materials, it is possible to use for the housing a material which has the best properties for the function of the housing, for example in terms of strength. However, the function of the slide rail must have good sliding properties. The material for the slide rail can thus be selected in such a way that the best sliding properties are guaranteed. Since the slide rail is supported by the housing, the requirements for the strength of the slide rail are much lower.

[0026] The slide rail is preferably constructed from plastic. Any known plastic can be used as the plastic. Such a slide rail made of plastic is preferably introduced into the recess as a separate component. It is also conceivable that the slide rail is manufactured by spraying plastic onto the wall of the recess. As the plastic, in particular, a plastic with good sliding properties is used. This allows sufficient sliding properties to be provided even during oil-free operation or dry operation, i.e., in the absence of lubricant. Plastic has the advantage, in particular, that it is lightweight and inexpensive.

[0027] Likewise, such a guide rail made of plastic can be produced easily and therefore economically.

[0028] The sliding element is preferably formed from a light metal alloy. A light metal alloy is defined here as having a density of less than 5 g / cm 3 The light metal alloy is characterized by high strength at low dead weight. As the light metal alloy, for example, an aluminum alloy, a magnesium alloy, a titanium alloy or a beryllium alloy is used.

[0029] The sliding element is preferably made of an aluminum alloy. The hydraulic piston, on which the sliding element is formed, is particularly preferably made of the same aluminum alloy. Components made of an aluminum alloy have the advantage that they are lightweight and ensure good heat dissipation. The sliding element also forms an advantageous material pairing, especially in combination with a guide rail made of plastic, which is improved in particular with regard to wear and dry operation.

[0030] In addition, the invention describes a vehicle with an electromechanical brake pressure generator for a hydraulic brake system. With such a vehicle, the advantages mentioned with respect to the electromechanical brake pressure generator can be achieved. In a preferred embodiment, such a vehicle can be an automated or fully autonomous vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the present invention are shown in the drawings and explained in detail in the following description.

[0032] Figure 1 A diagram of an electromechanical brake booster known from the prior art is shown;

[0033] Figure 2 shows a schematic diagram of a hydraulic brake system for a vehicle having an electromechanical brake pressure generator;

[0034] Figure 3 A longitudinal section through an exemplary embodiment of the threaded drive according to the invention of the electromechanical brake pressure generator is shown.

[0035] Figure 4 Shown in accordance with Figure 3 The cross section of the screw drive,

[0036] Figure 5 A view showing an embodiment of a sliding element, and

[0037] Figure 6 A view showing another embodiment of a sliding element is shown. DETAILED DESCRIPTION

[0038] exist Figure 2 2 shows a schematic diagram of a hydraulic brake system 10 for a vehicle with an electromechanical brake pressure generator 14. The hydraulic brake system 10 comprises the electromechanical brake pressure generator 14. This brake pressure generator 14 comprises a piston / cylinder unit 18, which is supplied with brake fluid via a brake fluid reservoir 12.

[0039] The piston / cylinder unit 18 can be actuated by a brake pedal 26 actuated by the driver and the resulting brake pedal travel is measured by a pedal travel sensor 30 and transmitted to a control unit 34. Figure 2 In principle, a brake booster is shown, but it is important here that the brake pedal travel is measured by pedal travel sensor 30. Braking pressure can also be generated without a brake pedal travel, so that the vehicle can also be braked in an autonomous driving state.

[0040] The controller 34 generates a control signal for an electric motor 38 of the brake pressure generator 14 as a function of the measured brake pedal travel. The electric motor 38, which is connected to a gear mechanism (not shown) of the brake pressure generator 14, amplifies the braking force input by the brake pedal 26 within the scope of the decoupled system as a function of the control signal. To this end, a screw gear 40 arranged in the brake pressure generator 14 is actuated by the electric motor 38 as a function of the actuation of the brake pedal 26, so that the rotational movement of the electric motor 38 is converted into a translational movement.

[0041] By actuating the brake pedal 26, the brake fluid in the piston / cylinder unit 18 is put under pressure by means of the brake pressure generator 14. This brake pressure is conducted to a brake hydraulic system 46 via a brake line 42. The brake hydraulic system 46, which is shown here only as a block, is formed by various valves and other components for the formation of, for example, an electronic stability program (ESP). The brake hydraulic system 46 is additionally connected to at least one wheel brake mechanism 50, so that a braking force can be applied to the wheel brake mechanism 50 via corresponding lines of valves.

[0042] Figure 3 1 shows a longitudinal section through an exemplary embodiment of a screw drive 40 according to the invention of the electromechanical brake pressure generator 14. The screw drive 40 comprises a housing 64 which forms a pot-shaped hydraulic cylinder 68. The housing 64 is formed from metal in this exemplary embodiment. The screw drive 40 additionally comprises a spindle nut 72 which is supported relative to the housing 64 via a bearing 76. The spindle nut 72 is supported by a bearing 76. Figure 2 The spindle nut 72 is driven by the electric motor 38 shown in the figure, which forms the drive device. The spindle nut 72 thus performs a rotational movement about its longitudinal axis. Similarly, in an embodiment not shown, a spindle 80 (see Figure 4 ).

[0043] exist Figure 4 The following is shown in Figure 3 The cross section of the threaded drive 40 of the spindle 80 is shown in FIG. The spindle 80 is formed with a thread 84, on which the spindle nut 72 is arranged and is in engagement with the spindle 80. The spindle nut 72 is essentially formed as a hollow cylindrical body. The spindle nut 72 is surrounded by a pot-shaped hydraulic piston 88, which is arranged in the hydraulic cylinder 68. In contrast to the spindle nut 72, the hydraulic piston 88 is not in engagement with the thread 72 of the spindle 80. In this embodiment, the hydraulic piston 88 is connected to the spindle 80 in a rotationally fixed manner.

[0044] On two opposite sides of the hydraulic piston 88, radially outwardly extending sliding elements 92 are arranged, which engage in recesses 96 of the housing 64 and form a rotationally fixed structure of the spindle 80, which is connected to the hydraulic piston 88 in a rotationally fixed manner. The recess 96, which is designed as a groove, is designed as a longitudinal groove in the housing 64.

[0045] The width of the sliding element 92 of the hydraulic piston 88 in the circumferential direction is slightly smaller than the width of the recess 96 of the housing 64 in the circumferential direction. The length of the sliding element 92 in the axial direction is much smaller than the length of the recess 96 of the housing 64. By rotating the spindle nut 72, the spindle 80 is held by the anti-twist structures 92, 96 of the hydraulic piston 88 and the housing 64, so that the hydraulic piston 88 can move in the axial direction in the housing 64 within the length of the recess 96 of the housing 64 with the sliding element 92.

[0046] like Figure 4 As shown, seals 100a, 100b are arranged between the hydraulic piston 88 and the hydraulic cylinder 68, so that pressure can be generated in the working chamber 104 of the hydraulic cylinder 68. By rotating the spindle nut 72, the hydraulic piston 88 can be moved axially on the spindle 80 in the direction of the working chamber 104, so that the brake fluid in the working chamber 104 can be squeezed. Figure 4 It is additionally shown that a slide rail 108 made of plastic is introduced into the recess 96 of the housing 64 , which slide rail forms a slide surface 110 for the slide element 92 .

[0047] Figure 5 A view of an embodiment of the sliding element 92 is shown. The sliding element 92 is shown in the guide rail 108. The sliding element 92 is flatly abutted against the sliding surface 110 of the guide rail 108 in the contact area 112. This results in a smaller surface pressure. Compared to a linear contact with a higher surface pressure, wear is reduced. The sliding element 92 is configured as a convex structure on the axial edge area 116 along the axial direction of the main shaft 80. As a result, no edge load occurs when the hydraulic piston 88 is tilted, so that a small surface pressure can be permanently guaranteed. The sliding element 92 is also configured as a convex structure on the radial edge area 120 along the radial direction of the main shaft 80. Edge load is also avoided in this way.

[0048] exist Figure 6 Another embodiment of a sliding element 92 is shown in FIG. The sliding element 92 is shown in this figure inside the recess 96, which forms the sliding surface 110. This embodiment is similar to Figure 5The difference from the embodiment in is that the sliding element 92 additionally has a contact shoe 124, which in this embodiment is made of plastic. Correspondingly, the sliding element 92 is formed by an inner sliding element part 128 and the contact shoe 124. The contact shoe 124 surrounds the inner sliding element part 128 on the outside. In the contact area 112 with respect to the sliding surface 110, the contact shoe 124 has a flat surface, through which the contact shoe 124 is flatly attached to the sliding surface 110.

[0049] The contact shoe 124 has convex surfaces 132 on both sides facing the inner sliding element part 128 in the axial direction relative to the main axis 80. These convex surfaces 132 are in contact with the flat surfaces 136 of the inner sliding element 128. As a result, no edge loads occur when the hydraulic piston 80 is tilted. Nevertheless, a flat contact state is ensured between the sliding surface 110 and the contact shoe 124, so that a low surface pressure can be permanently ensured.

[0050] In an exemplary embodiment (not shown), it is also possible for the inner sliding element part 128 to have a convex surface 132, while the contact shoe 124 rests against the convex surface via a flat surface 136. This results in the same advantages as described above.

Claims

1. An electromechanical brake pressure generator (14) for a hydraulic brake system (10) of a vehicle, comprising: at least one threaded transmission (40) for converting a rotational movement on the drive side into a translational movement; a piston / cylinder unit (18) for generating brake pressure which can be actuated by the threaded transmission (40), the piston / cylinder unit comprising a hydraulic piston (88), wherein the threaded transmission (40) comprises a spindle (80) and a spindle nut (72), the spindle and the spindle nut acting together via a thread (84); and an electric drive (38) by means of which the spindle (80) and the spindle nut (72) can be rotated relative to each other, It is characterized in that The hydraulic piston (88) of the piston / cylinder unit (18) at least partially radially surrounds the spindle (80) and the spindle nut (72), and the hydraulic piston (88) is received in a hydraulic cylinder (68) of the piston / cylinder unit (18), which has an anti-rotation structure (92, 96), wherein the anti-rotation structure (92, 96) is formed by a recess (96) extending in the axial direction and forming a sliding surface (110) and a sliding element (92) extending into the recess (96), and wherein the sliding element (92) is constructed so that it abuts against a planar contact area (110) of the sliding surface (110). 112), so that the hydraulic piston (88) is protected against rotation and can be axially moved by rotation of the spindle (80) or the spindle nut (72), wherein the spindle (80) is connected to the hydraulic piston (88) in a rotationally fixed manner, and the hydraulic piston (88) and the spindle (80) can be axially moved as the spindle nut (72) rotates, and wherein the sliding surface (110) has two flat surfaces facing each other, and wherein each of the two flat surfaces of the sliding surface (110) contacts the corresponding surface of the sliding element (92) at a protruding section in the middle of the corresponding surface of the sliding element (92).

2. The electromechanical brake pressure generator (14) according to claim 1, characterized in that The anti-twist structures (92, 96) are constructed in the manner of a tongue-and-groove connection.

3. The electromechanical brake pressure generator (14) according to claim 1 or 2, characterized in that: The sliding element (92) is configured as a protruding structure in at least one axial edge region (116) along the axial direction of the spindle (80).

4. The electromechanical brake pressure generator (14) according to claim 1 or 2, characterized in that: The sliding element (92) is configured as a convex structure in at least one radial edge region (120) along the radial direction of the main shaft (80).

5. The electromechanical brake pressure generator (14) according to claim 1 or 2, characterized in that: The sliding element (92) additionally has a contact shoe (124) which is arranged on the outside and is in contact with the sliding surface (110).

6. The electromechanical brake pressure generator (14) according to claim 5, characterized in that The contact shoe (124) is constructed from a plastic material.

7. The electromechanical brake pressure generator (14) according to claim 5, characterized in that The contact shoe (124) and the inner sliding element part (128) of the sliding element (92) bear against each other in the axial direction of the spindle (80) via a flat surface (136) and a convex surface (132).

8. The electromechanical brake pressure generator (14) according to claim 1 or 2, characterized in that The sliding surface (110) is formed by a sliding rail (108) which is inserted into the recess (96).

9. The electromechanical brake pressure generator (14) according to claim 8, characterized in that The installed slide rail (108) is constructed of plastic.

10. The electromechanical brake pressure generator (14) according to claim 1 or 2, characterized in that The sliding element (92) is constructed from a light metal alloy.

11. Vehicle comprising an electromechanical brake pressure generator (14) for a hydraulic brake system (10) according to any one of claims 1 to 10.

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