Electrohydraulic actuator for a brake system

Abstract

An electrohydraulic actuator (100) for a brake system comprises: a housing (1) which defines an interior (10) and has a first opening (11) and a second opening (12); a main brake cylinder (2) which is positioned in the first opening and is attached to the housing such that the first opening is sealed in a fluid-tight manner; an electric motor (4) arranged on the housing; and a transmission (3) which is received in the interior of the housing and is kinematically coupled to the main brake cylinder, wherein the transmission has a transmission intermediate part which can be moved along a longitudinal axis (L1) and which subdivides the housing, in relation to the longitudinal axis, into a first housing region (13), in which the main brake cylinder is arranged, and a second housing region (14), which faces the second opening. The actuator further comprises a compensating membrane (5) which closes the second opening in a fluid-tight manner and which is elastically deformable in order to reduce a pressure difference between the first and the second housing region in the event of an axial displacement of the transmission intermediate part.

Description

[0001] Description

[0002] Technical area

[0003] The present invention relates to an electrohydraulic actuator for a braking system, in particular of a vehicle.

[0004] State of the art

[0005] Electrohydraulic brake boosters are typically used to amplify the manually applied force on a brake pedal by actuating a master cylinder using an electric motor. In so-called "brake-by-wire" systems, in which a control signal is generated by actuating the brake pedal or by other means, and an electrohydraulic actuator is actuated based on the control signal to generate brake pressure, electrohydraulic brake boosters are also used as actuators.

[0006] DE 10 2013 213 888 B3 discloses a hydraulic actuator for a braking system comprising a master brake cylinder, an electric motor, and a transmission that couples the electric motor to the master brake cylinder to convert a movement of the motor into an actuation of the master brake cylinder. The transmission is housed in a housing, with the master brake cylinder positioned in an opening of the housing.

[0007] A particular advantage of such electro-hydraulic actuators is their ability to induce highly dynamic pressure changes in the braking system through rapid axial adjustment of the master brake cylinder via the transmission. However, in the housing, which is generally fluid-tight to the environment, rapid movement of components within the housing can temporarily lead to significant pressure differences between different areas of the housing, as pressure equalization within the housing is often inhibited by transmission components.

[0008] Disclosure of the invention

[0009] Against this background, the invention provides an electro-hydraulic actuator having the features of claim 1.

[0010] The electro-hydraulic actuator according to the invention for a brake system comprises a housing defining an interior space with a first opening and a second opening, a master brake cylinder positioned in the first opening, which is attached to the housing such that the first opening is sealed in a fluid-tight manner, an electric motor arranged on the housing and a gear accommodated in the interior space of the housing, which is kinematically coupled to the master brake cylinder, wherein the gear has an intermediate gear part which is movable along a longitudinal axis and which divides the housing with respect to the longitudinal axis into a first housing region in which the master brake cylinder is arranged, and a second housing region which is located facing the second opening.Furthermore, the actuator has a compensating membrane which closes the second opening in a fluid-tight manner, in particular in a liquid-tight manner and preferably also in a gas-tight manner, and which is elastically deformable in order to reduce a pressure difference between the first and the second housing region during an axial displacement of the intermediate transmission part.

[0011] One idea underlying the invention is to reduce the pressure differences within the housing caused by a rapid movement of at least part of the transmission within the housing by arranging an elastically deformable membrane in an opening of the housing. The membrane changes its deformation state as a result of a pressure change within the housing, thus increasing or decreasing the effective volume of the respective housing area.

[0012] The master brake cylinder can be actuated by the electric motor via the transmission. In particular, the transmission has a part that can be moved along a longitudinal axis and thereby actuates the master brake cylinder, e.g. by axially displacing a piston of the master brake cylinder. The transmission generally has an intermediate transmission part that divides the housing into a first and a second region with respect to the longitudinal axis. The first and the second region are fluidly connected to one another, e.g. by a gap between the housing and the intermediate transmission part. These passages defined between the intermediate transmission part and the housing between the first and the second housing region form a considerable flow resistance during rapid movement of the intermediate transmission part, so that a pressure difference arises between the first and second regions. According to the invention, this pressure difference is advantageously reduced with the aid of the diaphragm.

[0013] One advantage of the invention is that the compensating diaphragm reduces pressure differences within the housing. This facilitates the dynamic actuation of the actuator. Furthermore, by reducing the pressure difference between the first and second housing sections, the force required to actuate the master brake cylinder can also be reduced, which has a positive effect on energy consumption and the dynamic behavior of the actuator. Furthermore, the compensating diaphragm offers a cost-effective way to seal the housing in a fluid-tight manner while still facilitating pressure equalization between the housing sections.

[0014] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures of the drawing.

[0015] According to some embodiments, the compensating membrane can have a flange portion that abuts the housing in the region of the second opening, and a curved portion that protrudes from the housing. The flange portion can, for example, at least partially abut an inner circumferential surface of the second opening. The second opening can generally be circular in shape, in particular. The curved portion can, in particular, be conical or frustoconical in shape, but is not limited thereto. For example, a spherical curvature or the like can also be provided. Since the curved portion protrudes from an outer surface of the housing, a space conflict with components located in the interior of the housing is advantageously avoided. Furthermore, the possible volume change of the second housing region is increased in this way.

[0016] According to some embodiments, it can be provided that the compensating membrane is formed from a plastic material, in particular a rubber material, such as ethylene propylene diene rubber, EPDM for short.

[0017] According to some embodiments, the compensating membrane can be designed as a closed body. Accordingly, the compensating membrane alone or exclusively closes the second opening. In particular, the compensating membrane can be designed without a through-opening connecting the interior of the housing to the environment. The compensating membrane therefore serves the sole purpose of increasing or decreasing the volume of the second housing region through its elastic deformation as a result of a pressure change, thereby reducing the pressure difference between the housing regions.

[0018] According to some embodiments, it can be provided that the transmission has an actuating part which is movable along the longitudinal axis and is kinematically coupled to the master brake cylinder, and a guide part which is coupled to the actuating part and guided along the longitudinal axis, wherein the guide part forms the transmission intermediate part.

[0019] According to some embodiments, the actuating part can be designed as a threaded spindle, wherein the gear has a spindle nut that engages with the threaded spindle, and an input shaft that is drivable by the electric motor and engages with the spindle nut to rotate it about the longitudinal axis. In this way, a space-saving design of the gear is realized.

[0020] According to some embodiments, it can be provided that the guide part is coupled to the threaded spindle in a rotationally fixed manner. The guide part thus prevents the spindle from rotating with the spindle nut due to its guidance along the longitudinal axis.

[0021] According to some embodiments, it can be provided that the threaded spindle is movable into at least one axial position in which it projects through the second opening. The first and the second opening can, for example, be arranged coaxially to one another along the longitudinal axis. The threaded spindle is displaceable along the longitudinal axis, e.g., can be moved back and forth, in order to move the piston of the master brake cylinder. In this case, the spindle can also be moved into positions in which it projects through the second opening. In this case, it is particularly advantageous if the compensating diaphragm, as described above, has a flange section and a curved section, since the spindle can thus project into the space delimited by the curved section. The compensating diaphragm can thus additionally contribute to realizing a more compact design of the housing with respect to the longitudinal axis.

[0022] According to some embodiments, the guide part can be designed as a disc having at least one first guide element, in particular a projection, on its outer circumference, which engages with a second guide element extending parallel to the longitudinal axis, in particular a guide groove of the housing. The second guide element, e.g., in the form of a groove, can be formed in particular in the housing.

[0023] According to some embodiments, the actuator may have an electrical interface signal-connected to the electric motor for connecting the electric motor to a voltage source and / or for receiving control signals for operating the electric motor. The actuator may be operated exclusively via signals received at the interface, in particular without a mechanical backup actuation interface. The actuator may thus be designed for exclusive "by-wire" actuation.

[0024] The invention is explained below with reference to the figures of the drawings. The figures show:

[0025] Fig. 1 is a perspective sectional view of an electro-hydraulic actuator according to an embodiment of the invention;

[0026] Fig. 2 is a side view of the sectional representation of the actuator shown in Fig. 1;

[0027] Fig. 3 is a plan view of a first opening of the actuator shown in Fig. 1, with a master brake cylinder omitted; and

[0028] Fig. 4 is a perspective view of a compensating diaphragm of the actuator shown in Fig. 1.

[0029] In the figures, the same reference symbols denote identical or functionally identical components, unless otherwise stated.

[0030] Fig. 1 shows an example of an electrohydraulic actuator 100 for a braking system, e.g., for a braking system of a motor vehicle. Fig. 2 shows the actuator from Fig. 1 in a side view. As shown in Figs. 1 and 2, the actuator 100 comprises a housing 1, a master brake cylinder 2, a gear 3, an electric motor 4, and a compensating diaphragm 5.

[0031] The housing 1 generally defines an interior space 10. For example, the housing 1 can have a plurality of walls 1A that delimit the interior space 10. The housing 1 has, in particular, a first opening 11 and a second opening 12. The openings 11, 12 form a connection between the interior space 10 and the surroundings. The openings 11, 12 can, for example, have a circular circumference, as can be seen in Fig. 3, for example, for the first opening 11. In principle, however, other circumferential shapes of the openings 11, 12 are also conceivable. As shown by way of example in Figs. 1 and 2, the first and second openings 11, 12 can be arranged opposite one another. In particular, the first and second openings 11, 12 can be arranged coaxially to one another. For example, the first and second openings 11, 12 can be arranged coaxially to a longitudinal axis L1. The housing 1 can, in particular, be a cast housing, e.g.made of a metal material or a plastic material.

[0032] The master brake cylinder 2 is designed to convey a hydraulic fluid to and from a hydraulic consumer, e.g., a wheel brake cylinder, in order to build up and release hydraulic pressure. For this purpose, the master brake cylinder 2 can, in particular, have a cylinder 20 in which at least one piston 21 is mounted for axial displacement. Figures 1 and 2 show, purely by way of example, a tandem master brake cylinder 2 with a directly actuable first piston 21A and a floating piston 21B.

[0033] 1 and 2, the master brake cylinder 2 is positioned in the first opening 11 of the housing 1. In particular, the master brake cylinder 2 projects through the first opening 11 into the interior 10 of the housing 1. The master brake cylinder 2, in particular the piston(s) 21, is / are preferably positioned coaxially to the longitudinal axis L1. The cylinder 20 of the master brake cylinder 2 is arranged in a stationary manner on the housing 1, in particular fastened thereto, e.g. screwed thereto. For example, a flange 22 can be formed on the cylinder 20, which is centered in the first opening 11 and completely covers it, as shown by way of example in Figs. 1 and 2. Sealing elements (not shown) can provide additional sealing of the first opening 11. In general, the master brake cylinder 2 is attached to the housing 1 in such a way that it seals the first opening 11 in a fluid-tight manner.

[0034] The electric motor 4 is shown only in a simplified manner in Figs. 1 and 2 and can, for example, be arranged on the outside of the housing 1 and fixed to the housing 1. The electric motor 4 can in particular be oriented such that a rotation axis A4, around which a drive shaft of the motor 4 rotates, extends transversely or perpendicularly to the longitudinal axis L1. The transmission 3 couples the master brake cylinder 2 kinematically to the electric motor 4, in particular such that a rotation of the motor 4 causes a movement of the piston 21 or the pistons 21A, 21B of the master brake cylinder 2 along the longitudinal axis L1. As shown in Figs. 1 and 2, the transmission 3 is accommodated in the interior 10 of the housing 1. As shown by way of example in Figs. 1 and 2, the transmission 3 can have an actuating part 30 and a guide part 31. In general, the actuating part 30 is kinematically coupled to the piston 21, in particular the piston 21 A of the master brake cylinder 21, e.g.via a connecting rod 35, and movable along the longitudinal axis L1 by the electric motor 4. The guide part 31 is connected to or coupled to the actuating part 30 and guided along the longitudinal axis L1, e.g., on the housing 1.

[0035] 1 and 2 show, purely by way of example, a gear mechanism 3 in which the actuating part 30 is designed as a threaded spindle 30A with an external thread 30B and the guide part 31 is designed as a disk 31A guided on the housing 1. Furthermore, the gear mechanism 3 shown as an example in FIGS. 1 and 2 has a spindle nut 32 with an internal thread 32B, which engages with the external thread 30B of the threaded spindle 30A, and an input shaft 33. The spindle nut 32 is mounted in the housing 1 so as to be rotatable about the longitudinal axis L1, e.g. by means of a rolling bearing 34, as shown by way of example in FIGS. 1 and 2. Furthermore, the input shaft 33 can be designed, for example, as a worm shaft, which engages with external teeth (not shown) of the spindle nut 32. The input shaft 33 can, for example, be connected directly to the drive shaft (not shown) of the electric motor 4.

[0036] The guide part 31 or the disk 31A is coupled to the threaded spindle 30A in a rotationally fixed manner and thus forms a rotation lock for the threaded spindle 30A. As shown by way of example in Fig. 3, the disk 31A can have at least one first guide element 31B on its outer circumference, designed in Fig. 3 purely by way of example as a projection, which engages with a second guide element 1B extending parallel to the longitudinal axis L1. In Fig. 3 it is shown purely by way of example that the second guide element 1B can be designed as a guide groove of the housing 1 running parallel to the longitudinal axis L1. By rotating the spindle nut 32 by means of the input shaft 33 driven by the electric motor 4, the threaded spindle 30A is thus displaced together with the disc 31A along the longitudinal axis L1, so that the threaded spindle 30A moves the piston 21A, which in turn causes a displacement of the floating piston 21B by displacing hydraulic fluid.Figs. 1 and 2 show, by way of example, a position of the threaded spindle 30A in which it is in a maximally retracted position. This means that the pistons 21A, 21B of the master brake cylinder 21 are in an initial position and can be moved along the longitudinal axis L1 to build up pressure. As shown by way of example in Figs. 1 and 2, the threaded spindle 30A can, for example, protrude through the second opening 12 of the housing 1 in this position. In general, the threaded spindle 30A can be movable into at least one axial position in which it protrudes through the second opening 12.

[0037] In general, the master brake cylinder 2 can be actuated by moving the actuating part 30 along the longitudinal axis L1 by means of the electric motor 4. The guide piece 31 is also moved in the process. In this case, the guide piece 31 forms an intermediate gear part, which divides the housing 1 with respect to the longitudinal axis L1 into a first housing region 13, in which the master brake cylinder 2 is arranged, and a second housing region 14, which faces the second opening 12. In the actuator 100 shown as an example in Figs. 1 and 2, in particular the spindle nut 32 and the bearing 34 as well as the spindle 30A are located in the second housing region 14.

[0038] As symbolically indicated by a rectangle in Fig. 1, the actuator 100 can have an electrical interface 6 that is signal-connected to the electric motor 4. This interface 6 can be designed for the electrical connection of the electric motor 4 to a voltage source and / or for receiving control signals for operating the electric motor 4. For example, the interface 6 can be designed as a plug socket with connection contacts. Optionally, it can be provided that the electric motor 4 and thus the actuator 100 can be operated exclusively via signals received at the interface 6. As shown in Figs. 1 and 2, a mechanical coupling between the transmission 3 and a pedal or the like can be dispensed with. The actuator 100 can thus generally be designed for exclusive "by-wire" operation.

[0039] The compensating membrane 5 is shown in Fig. 4 by way of example in a perspective view. Generally, the compensating membrane 5 is formed from an elastically deformable but gas-impermeable material, in particular a plastic material. For example, the compensating membrane 5 can be formed from a plastic material, in particular a rubber material, such as ethylene propylene diene rubber, EPDM for short. Generally, the compensating membrane 5 is designed as a flat body. As shown purely by way of example in Fig. 4, the compensating membrane 5 can, for example, have a flange section 51 and a curved section 52. The flange section 51 is designed for attachment in and / or on the second opening 12 of the housing 1.

[0040] As shown by way of example in Fig. 4, the flange section 51 can, for example, have a base or frame section 51A adapted to the inner circumference of the second opening 12, which is annular in Fig. 4 corresponding to the circular realization of the second opening 12. Alternatively or additionally, the flange section 51 can have a collar 51B designed to bear against a region of the housing 1 surrounding the second opening 12. For example, the collar 51B can protrude radially from the base section 51A, as shown by way of example in Fig. 4.

[0041] The curved portion 52 extends from the flange portion 51 and defines an open interior receiving space 53. As shown by way of example in Fig. 4, the curved portion 52 can, for example, have the shape of a truncated cone. However, the invention is not limited to this; other curved shapes, such as spherical shapes or the like, are also conceivable.

[0042] 1 and 2, the compensating membrane 5 closes the second opening 12 of the housing 1 in a fluid-tight manner. As shown in particular in Fig. 2, the compensating membrane 5 can be partially inserted into the second opening 12. In particular, the base section 51A can bear against the inner circumferential surface 12 of the second opening 12, while the collar 51B bears against the region of the housing 1 surrounding the second opening 12. The flange section 51 thus bears against the housing 1 in the region of the second opening 12, and the curved section 52 protrudes from the housing 1. As shown by way of example in Figs. 1 and 2, the actuating part 30, here the threaded spindle 30A, for example, can protrude into the receiving space 53 defined by the curved section 52 of the membrane 5. The compensating membrane 5 can, for example, be integrally connected to the housing 1, e.g. glued to it.Alternatively, a mechanical fixation of the compensating membrane 5 to the housing 1 can be provided, e.g. via a clamping ring (not shown), which clamps the collar 51 B of the flange section 51 between itself and the housing 1.

[0043] As shown in Figs. 1, 3 and 4, the compensating membrane 5 can be designed as a closed body, in particular without a through-opening, e.g. in the curved section 52. The compensating membrane 5 is therefore preferably not intended to have components passed through it and to act as a type of sleeve, but rather serves to vary an effective internal volume of the housing 10, as will be explained in more detail below.

[0044] The compensating membrane 5 closes the second opening 12 of the housing 1 in a fluid-tight manner. In the same way, the first opening 11 of the housing 1 is closed in a fluid-tight manner by the master brake cylinder 2. The interior 10 of the housing 1 is thus essentially closed in a fluid-tight manner and the actuator 100, in particular its housing 1, can thus be regarded as immersion-tight. The intermediate gear part, in the example of Figs. 1 and 2 the guide part 31 or the disc 31A, divides the interior 10 of the housing 10 into the first and second housing regions 13, 14, as explained above. When the actuating part 30 or the spindle 30A is moved quickly along the longitudinal axis L1, e.g. in order to achieve a dynamic pressure build-up or pressure reduction by means of the master brake cylinder 2, the intermediate gear part displaces the air in front of it in the interior 10 of the housing 1 with respect to the direction of movement.Between the intermediate gear section and the inner surface of the housing 1, only a narrow gap S exists, through which air exchange can take place between the first and second housing sections 13, 14. In the example of Figs. 1 and 2, the bearing 34 and the spindle nut 32 further inhibit the gas exchange. A possible flow path F between the first and second housing sections 13, 14 is symbolically shown in Fig. 2.

[0045] A rapid displacement of the intermediate gear part along the longitudinal axis L1 therefore leads to a transient pressure build-up in one of the housing areas 13, 14 and to a transient pressure reduction in the other of the housing areas 13, 14. As a result, a pressure difference arises between the housing areas 13, 14, which is only slowly reduced, e.g. via the flow path F. The compensating diaphragm 5 advantageously reduces the building-up of pressure difference due to its elastic deformability. If the intermediate gear part, in this case the disk 31A, is moved together with the spindle 30A, e.g. in the direction of the second opening 12, this leads to a pressure build-up in the first housing area 13 and a pressure reduction in the second housing area 14. The reduced pressure in the second housing area 14 causes the compensating diaphragm 5 to deform in such a way that it reduces the effective volume of the interior space 10.such that the effective volume of the second housing region 14 remains essentially constant. Figuratively speaking, the deformation of the diaphragm 5 follows the movement of the intermediate transmission part. In this way, a pressure difference between the first and second housing regions 13, 14 is reduced upon axial displacement of the intermediate transmission part.

[0046] Although the present invention has been explained above using exemplary embodiments, it is not limited thereto but can be modified in a variety of ways. In particular, combinations of the above embodiments are also conceivable.

Claims

Claims 1. Electro-hydraulic actuator (100) for a brake system, comprising: a housing (1) defining an interior space (10) with a first opening (11) and a second opening (12); a master brake cylinder (2) positioned in the first opening (11), which is attached to the housing (1) such that the first opening (11) is fluid-tightly sealed; an electric motor (4) arranged on the housing (1); a transmission (3) received in the interior space (10) of the housing (1), which is kinematically coupled to the master brake cylinder (2), wherein the transmission (3) has a transmission intermediate part movable along a longitudinal axis (L1), which divides the housing (1) with respect to the longitudinal axis (L1) into a first housing area (13) in which the master brake cylinder (2) is arranged, and a second housing area (14) which faces the second opening (12);and a compensating membrane (5) that seals the second opening (12) in a fluid-tight manner and is elastically deformable in order to reduce a pressure difference between the first and second housing areas (13, 14) during axial displacement of the intermediate gear section.

2. Actuator (100) according to claim 1, wherein the compensating membrane (5) has a flanged section (51) which abuts the housing (1) in the area of ​​the second opening (12) and a curved section (52) which projects from the housing (1).

3. Actuator (100) according to claim 1 or 2, wherein the compensating membrane (5) is made of a plastic material, in particular a rubber material, such as ethylene propylene diene monomer rubber. Actuator (100) according to one of the preceding claims, wherein the compensating membrane (5) is designed as a closed body, in particular without a through-opening connecting the interior (10) of the housing (1) to the environment. Actuator (100) according to one of the preceding claims, wherein the transmission (3) is an actuating element movable along the longitudinal axis (L1). (30), which is kinematically coupled to the master brake cylinder (2), and has a guide part (31) which is coupled to the actuating part (30) and guided along the longitudinal axis (L1), wherein the guide part (31) forms the intermediate transmission part. Actuator (100) according to claim 5, wherein the actuating part (30) is designed as a threaded spindle (30A), wherein the transmission (3) has a spindle nut (32) which engages with the threaded spindle (30A), and an input shaft (33) which can be driven by the electric motor (4) and engages with the spindle nut (32) to rotate it about the longitudinal axis (L1). Actuator (100) according to claim 6, wherein the guide part (31) is rotationally fixed to the threaded spindle (30A). Actuator (100) according to claim 6 or 7, wherein the threaded spindle (30A) is movable into at least one axial position in which it protrudes through the second opening (12).Actuator (100) according to one of claims 5 to 8, wherein the guide part. (31) is designed as a disk (31A) which has at least one first guide element (31B), in particular a projection, on its outer circumference, which engages with a second guide element (1B), in particular a guide groove of the housing (1), extending parallel to the longitudinal axis (L1). Actuator (100) according to one of the preceding claims, further comprising: an electrical interface connected to the electric motor (4) (6) for connecting the electric motor (4) to a voltage source and / or for receiving control signals for operating the electric motor (4), wherein the actuator (100) can be operated exclusively via signals received at the interface (6), in particular without a mechanical substitute actuation interface.

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