Wheel brake device, brake system, method for operating a wheel brake device

Abstract

The invention relates to a wheel brake device (1) comprising a first and a second piston (2, 3), wherein the first piston (2) is axially displaceable within a piston chamber (4) which is filled with brake fluid, wherein the first piston (2) carries a brake pad (7) associated with a brake disc (6) on a first end face (5), and wherein the second piston (3) is fluidically connected to the piston chamber (4). It is provided that the first piston (2) has a recess (9) on a second end face (8) facing away from the first end face (5), which forms part of the piston chamber (4), and that the second piston (3) is axially displaceable within the piston chamber (4).

Description

[0001] The invention relates to a wheel brake device, comprising a first and a second piston, wherein the first piston is axially displaceable in a piston chamber which can be filled with brake fluid, wherein the first piston carries a brake pad associated with a brake disc on a first end face, and wherein the second piston is fluidly connectable to the piston chamber.

[0002] Furthermore, the invention relates to a braking system of a motor vehicle with such a wheel brake device and to a method for operating such a wheel brake device. State of the art

[0003] Wheel brake devices of the type mentioned above are known from the prior art. For example, German patent application DE 10 2023 108 135 A1 discloses an electro-hydraulic brake unit for a motor vehicle, comprising a pressure source designed as an actuator, at least one brake piston, and a brake circuit connecting the pressure source and the at least one brake piston, wherein the pressure source, the at least one brake piston, and the brake circuit are arranged in a wheel brake. In particular, the actuator has a piston, the brake circuit has a working chamber and a connecting line, the piston being movably arranged in the working chamber, and the connecting line connecting the working chamber to the brake piston.

[0004] Actuating the actuator results in a displacement of the piston, which is transmitted via the brake fluid in the brake system to the brake piston with a brake pad attached to it. This movement brings the brake pad into contact with the friction surface of a brake disc or drum, thereby braking the vehicle.

[0005] Furthermore, patent DE 10 2005 007 560 B3 discloses a master brake cylinder in which a first piston is axially displaceable within a recess formed in a second piston, the recess together with a further recess formed in the first piston forming a pressure chamber. The recess formed in the second piston thus acts as a kind of telescopic guide for the first piston, so that the overall volume of the master brake cylinder is advantageously reduced along its longitudinal axis. The first piston is displaced, in particular, by means of an electromechanically driven brake booster. Disclosure of the invention

[0006] The wheel brake device according to the invention, with the features of claim 1, is characterized in that the first piston has a recess on a second end face facing away from the first end face, which forms part of the piston chamber, and that the second piston is mounted to be axially displaceable within the piston chamber. To generate a braking force, the second piston is preferably moved translationally in the direction of the first piston, so that pressure is exerted on the brake fluid and the first piston with the brake lining is moved towards the brake disc. It should be noted, purely as a precaution, that this operating principle is also applicable to drum brakes, i.e., a brake drum can be provided instead of a brake disc. In this case, the end face with the brake lining lies outside the piston chamber, or the piston is partially displaced out of the piston chamber during braking.By using two pistons, an advantageous hydraulic transmission is achieved, and the arrangement within the same piston chamber and the recess simultaneously save valuable installation space. This discloses a special design of a wheel brake as a wheel module that can be directly mounted on a vehicle wheel, in which a hydraulic transmission is provided instead of the gear stages used, for example, in electromechanical wheel brakes. The wheel brake device is pre-filled, thus advantageously eliminating the need for filling, for example, by the vehicle manufacturer. The two pistons are therefore arranged in the same piston chamber, similar to the master brake cylinder mentioned above, in a space-saving manner, and are fluidically coupled to each other.In contrast, the pistons in the electro-hydraulic brake unit described above are arranged in separate chambers, connected only by a connecting line. The recess in the first piston is directly associated with the second piston, or at least forms part of its working chamber, so that overall, particularly along the axial extent of the piston, correspondingly less installation space is required. The second piston is preferably designed or arranged to be axially displaceable in the direction of the recess. In particular, each piston is assigned at least one circumferential sealing element to reliably seal the piston chamber to the outside.

[0007] According to a preferred embodiment of the invention, the second piston is aligned parallel, and in particular coaxially, to the first piston. Such an alignment of the pistons advantageously ensures that the wheel brake device is designed to be particularly space-saving.

[0008] It is particularly preferred that the second piston has a smaller diameter than the first piston. Such a difference in diameter results in a particularly advantageous hydraulic ratio. Preferably, the second piston has a diameter that is at least 10%, 25%, or 50% smaller than that of the first piston. The difference in diameter is compensated for by appropriately adjusted strokes, ensuring a constant displacement volume. In particular, the corresponding diameter ratio of the second piston to the first piston is in a range greater than 1:1 to 1:2, 1:2.5, or 1:3. The second piston is thus actuated with less force but a longer stroke than the first piston.

[0009] According to a preferred embodiment of the invention, the second piston is designed to be slidable into the recess, at least partially. This advantageously ensures that the second piston immerses in the recess, making the arrangement particularly space-saving.

[0010] It is particularly preferred that the wheel brake device has an electromechanical actuator, wherein the second piston is axially displaceable by the actuator, and in particular is operatively connected to the actuator by a gear arrangement. The corresponding actuator offers the advantage that the wheel brake device can be actuated with pinpoint accuracy. For example, the actuator is designed as an electric machine. The gear arrangement is preferably connected to a rotor shaft of the electric machine. In particular, the gear arrangement comprises a ball screw drive or a spindle drive. Particularly preferably, the gear arrangement includes a further gear stage as a transmission ratio, for example, a planetary gear stage or a worm gear.In particular, the gear ratio is directly coupled to the actuator, preferably a rotor shaft, for example arranged between the actuator and the ball screw drive or the spindle drive.

[0011] According to a preferred embodiment of the invention, the actuator, in particular a rotor shaft of the actuator, is aligned coaxially with at least one of the pistons. In particular, the rotor shaft is aligned coaxially with the second piston, and in particular with both the first and the second piston. This advantageously ensures that the actuator acts on the second piston without deflection.

[0012] It is particularly preferred that a control device associated with the actuator is arranged axially between the actuator and at least one of the pistons, wherein, in particular, a rotor shaft of the actuator axially penetrates the control device. This offers the advantage that the control device, the actuator, and the piston form a space-saving structural unit. Furthermore, this provides an advantageous means for the particularly simple direct connection of a pressure sensor associated with the piston chamber to the control device. In particular, a pressure sensor associated with the piston chamber and connected to and / or arranged on the control device is provided. Preferably, a rotor position sensor for a rotor shaft of the actuator is arranged on the control device, in particular on a printed circuit board.In particular, a pole pot of the actuator forms a cover for the control device, and / or encloses it at least partially, in particular completely, to protect it from environmental influences.

[0013] According to a preferred embodiment of the invention, the wheel brake device has a reservoir for brake fluid, and the piston chamber is fluidically connected to the reservoir via a fluid line. The reservoir and the corresponding connection advantageously ensure that the piston chamber is always supplied with brake fluid as needed. In particular, at least one further fluid line is provided, which is assigned to a circumferential sealing element of at least one of the pistons, for example, the second piston, in order to lubricate it.

[0014] It is particularly preferred that the reservoir and the piston chamber are arranged in a common housing. This arrangement of the reservoir and piston chamber in the same housing offers the advantage that the wheel brake device is designed as a space-saving, structurally integrated module. Consequently, the wheel brake device does not require any external hydraulic connections for supplying brake fluid.

[0015] According to a preferred embodiment of the invention, the reservoir is provided with a pressure equalization element, in particular a pressure equalization diaphragm or pressure equalization piston. The pressure equalization element advantageously ensures that the hydraulic pressure in the reservoir can be adjusted within a predetermined range, for example to compensate for expansion due to heating of the brake fluid.

[0016] It is particularly preferred that a sensor element, in particular a magnetic element, of a reservoir level sensor is arranged on the pressure equalization element. The corresponding arrangement of the sensor element has the advantage that an additional float for the level sensor is unnecessary. The pressure equalization element thus fulfills a dual function (pressure equalization and level measurement).

[0017] According to a preferred embodiment of the invention, a controllable valve, in particular a solenoid valve, is arranged in the fluid line. The valve provides a particularly advantageous way of connecting the reservoir to the piston chamber fluidically only as needed. The valve is specifically designed as a normally open solenoid valve. In the event of a malfunction, brake fluid can thus flow back into the reservoir unhindered to prevent further unintended braking of the corresponding wheel. For example, a solenoid coil of the valve is connected to the aforementioned control device.

[0018] It is particularly preferred that the second piston is designed to be moved away from the first piston when the valve is open, particularly by an actuator, to allow brake fluid to flow from the reservoir. When the second piston is retracted by the first piston within the piston chamber, brake fluid flows from the reservoir into the piston chamber because a corresponding vacuum is created. This occurs when the first piston retracts only with a delay or incompletely due to friction points, for example, at sealing elements, particularly due to imbalance of the brake disc. This advantageously compensates for brake pad wear in a particularly simple manner without requiring an increase in the piston stroke, as the wear is compensated for by the additional fluid volume from the reservoir.

[0019] The braking system of a motor vehicle with the features of claim 14 is characterized by the wheel brake device according to the invention. This results in the advantages already mentioned.

[0020] The method with the features of claim 15 for operating a wheel brake device with the features of claim 12 is characterized in that, when the valve is open, the second piston is moved away from the first piston, in particular by an actuator, to allow brake fluid to flow from the reservoir. For this purpose, the wheel brake device must include at least the aforementioned reservoir, the fluid line, and the valve arranged therein. As described above, this advantageously compensates for brake pad wear in a particularly simple manner.

[0021] Further preferred features and combinations of features will become apparent from the foregoing and from the claims. The invention will now be explained in more detail with reference to the drawings. These drawings show... Fig. 1 an advantageous wheel brake device, Fig. 2 a simplified view of the wheel brake device, Fig. 3 a detailed view of the wheel brake device, Fig. 4A to 4D show further detailed views of the wheel brake device, and Fig. 5 a method for operating the wheel brake device.

[0022] Fig. Figure 1 shows an advantageous wheel brake device 1 as part of a braking system of a motor vehicle, which is otherwise not shown in detail. In the Fig. Figure 2 shows a simplified, schematic view of the wheel brake device 1. The wheel brake device 1 has a first piston 2 and a second piston 3. The two pistons 2 and 3 are each axially displaceable within a piston chamber 4 that can be filled with or is filled with brake fluid. The second piston 3 is aligned and arranged parallel, and in this case also coaxially, to the first piston 2. The second piston 3 has a diameter that is smaller than that of the first piston 2, in particular by at least 10%, 25%, or 50%.

[0023] The first piston 2 carries a brake pad 7 associated with a brake disc 6 of the wheel brake device 1 on a first end face 5 and is thus designed as the actual brake piston. On a second end face 8 facing away from the first end face 5, the first piston 2 has a recess 9 which forms part of the piston chamber 4 and is associated with the second piston 3. The second piston 3 is fluidically connected to the same piston chamber 4 as the first piston 2. Preferably, the second piston 3 is designed to be slidable into the displacement 9, at least partially.

[0024] The wheel brake device 1 has a housing 10 in which the piston chamber 4 is formed. A brake caliper 11, which surrounds the brake disc 6 and on which a further brake pad 12 is arranged, is connected to the housing 10, in particular formed integrally with it, wherein the brake pad 7 is associated with a first side surface 13 of the brake disc 6, and the brake pad 12 is associated with a second side surface 14 of the brake disc 6 facing away from the first side surface 13.

[0025] The wheel brake device 1 further comprises an electromechanical actuator 15, which in this case is designed as an electric machine, and a gear assembly 16. The gear assembly 16 is operatively connected to a rotor shaft 17 of the actuator 15 and in this case comprises a spindle drive or a ball screw drive. The gear assembly 16 in this case comprises a gear spindle 18 and a spindle nut 19 encompassing it. The rotor shaft 17, the gear spindle 18, the spindle nut 19, and the two pistons 2, 3 are aligned or arranged coaxially with each other. The gear assembly 16 also comprises a further gear stage as a gear ratio 36, in this case a planetary gear stage. The gear ratio 36 is directly coupled to the rotor shaft 17 and thus arranged between the actuator 15 and the gear spindle 18 and the spindle nut.

[0026] In particular, the gear spindle 18 is rotationally fixed to the rotor shaft 17, and the spindle nut 19 is axially displaceable on the gear spindle 18. If the rotor shaft 17 is rotated, the spindle nut 19, for example, shifts axially. The spindle nut 19 is in turn rotationally fixed to the second piston 3, so that the second piston 3 is then axially displaced by the actuator 15 because it is operatively connected to the actuator 15 via the gear arrangement 16.

[0027] The wheel brake device 1 has a control unit 20 associated with the actuator 15, with a printed circuit board 21, which is arranged axially between the actuator 15 and the gear arrangement 16 as well as the two pistons 2, 3, wherein the rotor shaft 17 of the actuator 15 penetrates the control unit 20 axially through a recess 22 in the printed circuit board 21, so that the rotor shaft 17 can be connected to the gear arrangement 16.

[0028] Furthermore, the wheel brake device 1 has a reservoir 23 for brake fluid, wherein the piston chamber 4 is supplied by means of a fluid line 24, which is located at least in the Fig. As can be seen directly, reservoir 23 is fluidly connected to / connected to reservoir 23. Reservoir 23 and piston chamber 4 are arranged in the common housing 10.

[0029] A controllable valve 25, in this case a solenoid valve, is arranged in the fluid line 24. The second piston 3 is designed to be moved away from the first piston 2 by the actuator 15 when the valve 25 is open, allowing brake fluid to flow from the reservoir 23. For this purpose, the fluid line 24 opens into the piston chamber 4 at an end region of the piston chamber 4 facing away from the first end face 5.

[0030] In the Fig. Figure 2 also shows that the reservoir 23 has a pressure equalization element 26, which is arranged, in particular, on an upper side of the reservoir 23. The pressure equalization element 26 is located in the Fig. 2 designed as a pressure equalization membrane 27.

[0031] In the Fig. 3 is one in the Fig. Figure 2, section A, shows the area outlined with a dashed line in the region of the pressure equalization element 26 as a detailed view, where an alternative design of the pressure equalization element 26 has been chosen. Thus, the pressure equalization element 26 is in the Fig. 3 designed as a pressure equalization piston 28. A sensor element 30, in particular a magnetic element, of a level sensor 31 of the reservoir 23 is arranged on the pressure equalization piston 28, in this case in a recess 29 of the pressure equalization piston 28. Thus, the pressure equalization element 26 fulfills an advantageous dual function.

[0032] The two pistons 2, 3 are each mounted in the piston chamber by two axially spaced sealing elements 32, in particular sealing rings, to seal it. A further fluid line 33, connected to the reservoir 23, is associated with the sealing elements 32 of the second piston 3 to lubricate them.

[0033] Finally, in the Fig. Figure 2 shows a rotor position sensor 34 associated with the actuator 15, as well as a pressure sensor 35 arranged in the fluid line 24. The sensors 34 and 35 are connected in particular to the control unit 20.

[0034] The following refers to Fig. 5 describes an advantageous method for operating the wheel brake device 1. For this purpose, the Fig. 5. The procedure is described using a flowchart. In particular, the procedure ensures that sufficient braking power is provided even with progressive wear of the brake pads 7, 12. Specifically, the procedure is carried out using the control unit 20.

[0035] The Fig. Figures 4A to 4D show corresponding process steps, each differing in the position of pistons 2 and 3, with one piston in each case being located in the Fig. 2 is shown as section B, the area outlined with a dashed line.

[0036] In step S1, the process begins with the detection of a brake request. The two pistons 2 and 3 are located in a position within the Fig. Figure 4A shows the initial position, which is withdrawn (moved as far away as possible from the brake disc 6). There is a corresponding air gap, the so-called clearance, between the brake disc 6 and the brake pad 7.

[0037] In step S2, the actuator 15 is now controlled to move the second piston 3 axially towards the first piston 2. Due to the hydraulic coupling via the brake fluid, the first piston 2, along with the brake pad 7, is also moved towards the brake disc 6. The two pistons 2 and 3 are located in a position within the Fig. 4B shown brake position, in which the air gap is overcome and the brake disc 6 is in contact with the brake pad 7 (as well as the brake pad 12).

[0038] Once the braking demand is met, the second piston 3 is moved away from the first piston 2 again by the actuator 15 in a step S3. Preferably, this occurs with the valve 25 initially open. The resulting vacuum draws brake fluid from the reservoir 23 into the piston chamber 4. This compensates for wear on the brake pads 7, 12 and the brake disc 6. This is in the Fig. 4C is shown. The valve 25 is preferably closed again after a predetermined time and / or a predetermined displacement of the piston 2, in particular depending on a hydraulic pressure in the piston chamber 4, an expected and / or actual degree of wear.

[0039] The additional fluid volume ensures that the stroke of the second piston 3 is sufficient to move the first piston 2 far enough to achieve the desired braking effect when braking is next required. The corresponding new brake position is shown in the Fig. 4D representation. The first piston 2 has a greater stroke than in the Fig. 4B, while the stroke of the second piston 3 in particular remains constant. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2023 108 135 A1

[0003] DE 10 2005 007 560 B3

[0005]

Claims

[1] Wheel brake device (1), comprising a first and a second piston (2, 3), wherein the first piston (2) is axially displaceable in a piston chamber (4) which can be filled with brake fluid, wherein the first piston (2) carries a brake pad (7) associated with a brake disc (6) on a first end face (5), and wherein the second piston (3) is fluidly connectable to the piston chamber (4), characterized by , that the first piston (2) has a recess (9) on a second end face (8) facing away from the first end face (5), which forms the piston chamber (4), and that the second piston (3) is mounted axially displaceable in the piston chamber (4). [2] Wheel brake device according to claim 1, characterized by that the second piston (3) is aligned parallel, in particular coaxially, to the first piston (2). [3] Wheel brake device according to one of the preceding claims, characterized by, that the second piston (3) has a smaller diameter than the first piston (2). [4] Wheel brake device according to one of the preceding claims, characterized by , that the second piston (3) is designed to be inserted into the recess (9) at least in part. [5] Wheel brake device according to one of the preceding claims, characterized by an electromechanical actuator (15), wherein the second piston (3) is axially displaceable through the actuator (15), in particular by means of a gear arrangement (16) connected to the actuator (15). [6] Wheel brake device according to claim 5, characterized by , that the actuator (15), in particular a rotor shaft (17) of the actuator (15), is aligned coaxially to at least one of the pistons (2,3). [7] Wheel brake device according to one of claims 5 and 6, characterized by, that a control device (20) associated with the actuator (15) is arranged axially between the actuator (15) and at least one of the pistons (2,3), wherein in particular a rotor shaft (17) of the actuator (15) axially penetrates the control device (20). [8] Wheel brake device according to one of the preceding claims, characterized by a reservoir (23) for brake fluid, wherein the piston chamber (4) is fluidly connectable / connected to the reservoir (23) by means of a fluid line (24). [9] Wheel brake device according to claim 8, characterized by , that the reservoir (23) and the piston chamber (4) are arranged in a common housing (10). [10] Wheel brake device according to one of claims 8 and 9, characterized by that the reservoir has a pressure equalization element (26), in particular a pressure equalization membrane (27) or a pressure equalization piston (28). [11] Wheel brake device according to claim 10, characterized by, that a sensor element (29), in particular a magnetic element, of a level sensor (30) of the reservoir (23) is arranged on the pressure equalization element (26). [12] Wheel brake device according to one of claims 8 to 11, characterized by , that a controllable valve (25), in particular a solenoid valve, is arranged in the fluid line (24). [13] Wheel brake device according to claim 12, characterized by , that the second piston (3) is designed to be moved away from the first piston (2) when the valve (25) is open, in particular by an actuator (15), to allow brake fluid to flow from the reservoir (23). [14] Braking system of a motor vehicle, characterized by a wheel brake device (1) according to one of the preceding claims. [15] Method for operating a wheel brake device (1) according to claim 12, characterized by, that the second piston (3) is moved away from the first piston (2) when the valve (25) is open, in particular by an actuator (15), to allow brake fluid to flow from the reservoir (23).

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