Brake unit for an electric vehicle

Abstract

The invention relates to a brake unit (1) for a motor vehicle (1), comprising a cylindrical housing (2) which can be filled with a fluid and in which a plurality of first plates (4) protrude radially inward from a circumferential side (2a) of the housing (2) with respect to a longitudinal axis L of the housing (2), wherein a plurality of second plates (3) are arranged in the housing (2) so as to be axially movable with respect to the longitudinal axis L relative to the first plates (4). According to the invention, a central shaft (6) is guided along the longitudinal axis L through the housing (2) and is fastened thereto in a rotationally fixed manner, wherein the second plates (3) are arranged so as to protrude radially outward on a hollow shaft (5) and are connected thereto in a rotationally fixed manner, which hollow shaft (5) concentrically surrounds the central shaft (6) and which can be coupled to the central shaft (6) in a rotationally fixed manner.

Description

[0001] The invention relates to a brake unit and a motor vehicle with such a brake unit.

[0002] Wet multi-disk brakes are a special type of service brake commonly used in motor vehicles and machinery. They are generally constructed from multiple disc-like friction linings impregnated with a fluid, often a special brake oil. When the brakes are applied, the friction linings are pressed against a rotating brake disc, generating friction and slowing or stopping the vehicle. Wet multi-disk brakes are characterized by the following advantages: high braking performance, thermal stability, durability, and ease of maintenance. Wet multi-disk brakes operate on the same principle as wet multi-disk clutches, which are used, for example, in automatic transmissions in conventional powertrains.

[0003] In addition to the advantages mentioned, the use of wet multi-disk brakes also has disadvantages. A major disadvantage is that wet multi-disk brakes generate drag torque because the friction linings or friction plates rotate in the operating fluid (usually oil). This drag torque leads to increased energy consumption and a reduced range, which is considered particularly disadvantageous for battery-electric vehicles, i.e. vehicles with an electric motor as their drive. In battery-electric vehicles, the service brake is needed less frequently than in conventional motor vehicles, since braking torque can also be generated through recuperation. In other words, in many driving situations, the vehicle is decelerated by means of recuperation braking.The use of the service brake is only necessary during emergency braking (ABS emergency braking) or at very low ambient temperatures, when a vehicle battery cannot absorb the recuperated energy. A braking device according to the preamble of claim 1 is disclosed in DE 10 2010 039 448 A1. Further prior art is described in DE 11 2009 002 644 T5.

[0004] It is therefore an object of the invention to provide a braking device in which drag torque generation is significantly reduced.

[0005] This object is achieved by a braking device according to claim 1. Preferred embodiments are specified in the subclaims.

[0006] A brake unit for a motor vehicle according to embodiments of the invention comprises a cylindrical housing which can be filled with a fluid and in which a plurality of first plates protrude radially inward from a circumferential side of the housing with respect to a longitudinal axis L of the housing, wherein a plurality of second plates are arranged in the housing and are arranged to be axially movable relative to the first plates with respect to the longitudinal axis L in order to be able to be brought into and out of a braking position in which the first and second plates abut one another. According to the invention, a central shaft is guided through the housing along the longitudinal axis L, wherein the second plates are arranged to protrude radially outward on a hollow shaft which concentrically surrounds the central shaft and which can be coupled to the central shaft in a rotationally fixed manner.The first slats can be made of steel, which is advantageous in terms of load capacity and temperature resistance.

[0007] When terms such as “radial” or “axial” are used in the context of the invention, unless otherwise stated, these are to be understood as referring to the longitudinal axis L of the cylindrical housing, and therefore also to the central shaft which is aligned concentrically to the longitudinal axis L.

[0008] The brake unit according to the invention is a wet multi-disk brake in which the first and second disks are accommodated in a housing which, during use, is filled with a fluid, for example brake oil. The housing can have a closable inlet for filling. The first disks are spaced apart from one another in the axial direction, with the distances between the individual first disks being the same. The second disks are likewise spaced apart from one another in the axial direction, with the respective distances between the second disks being the same. Preferably, the first and second disks are arranged relative to one another such that a first disk is positioned between two second disks. To initiate a braking process, the hollow shaft is first connected to the central shaft.The brake unit is then moved into a braking position via an actuating device, for example, an electric actuator, in which the first and second plates rest against each other and are pressed against each other, thus creating a braking effect. After decoupling the hollow shaft and the axial shaft, the first and second plates can be spaced apart again, and the braking position is released.

[0009] When the brake unit is used in a motor vehicle, one of the shafts, preferably the hollow shaft, is coupled to at least one wheel axle of the motor vehicle in such a way that it rotates together with the wheel axle. The central shaft is connected to both the output shaft of the transmission and to the wheel. According to the device described in the invention, the hollow shaft is coupled to the central shaft. Thus, the central shaft and hollow shaft rotate and the braking effect is transferred to the central shaft. When a braking process is initiated, the hollow shaft is moved in the axial direction so that the second plates move in the axial direction against the first plates and are ultimately pressed against them. The wheel axle is braked by the resulting friction between the first and second plates.

[0010] According to the invention, the hollow shaft can be coupled to the central shaft in a rotationally fixed manner. This means that the hollow shaft and the central shaft can be reversibly attached to each other so that both shafts rotate synchronously around the central axis. When the two shafts are coupled, a drag torque is generated because the hollow shaft, on which the second plates are located, rotates. Since the second plates, which can be friction plates, rotate between the first plates, a drag torque is generated. In contrast, when decoupled from each other, the hollow shaft and the central shaft are rotatable relative to each other, and the first plates and the second plates can move relative to each other in a circumferential direction. When the two shafts are decoupled, only the central shaft rotates. The hollow shaft, and thus also the friction plates, do not rotate. Thus, according to the invention, no drag torque is generated....

[0011] The housing serves to contain a fluid, in particular brake oil, to create a wet multi-disk brake. The housing can be formed, in particular, from a metallic material. For example, the housing can be formed from a metallic cast material, such as gray cast iron or cast steel. In principle, it is also conceivable to construct the housing entirely or partially from a plastic, provided the plastic has sufficient temperature resistance. Furthermore, the housing can be constructed in one piece or in multiple parts.

[0012] Preferably, the housing is designed in such a way that wear particles generated during braking cannot escape from the housing. This prevents unwanted exposure of the environment to brake wear particles. Furthermore, such encapsulation of the brake unit also reduces braking noise to the environment. A further advantageous aspect of this encapsulation is that the braking performance of the brake unit is independent of the weather conditions outside the vehicle.

[0013] According to the invention, the brake unit comprises a claw device for coupling the central shaft to the hollow shaft. The claw device serves to reversibly and non-rotatably couple the central shaft and the hollow shaft. This constitutes a positive, temporary connection between the two shafts. This achieves a simple, mechanically based coupling.

[0014] In particular, the claw device comprises a hollow ring which is provided on an inner side with radially inwardly projecting teeth, wherein a coupling section of the central shaft and a coupling section of the hollow shaft are each provided on their circumference with radial recesses which can be brought into engagement with the teeth of the hollow ring. The coupling section of the central shaft and the coupling section of the hollow shaft are thus both intended to be inserted into the hollow ring such that the teeth on the inner side of the hollow ring engage in the respective recesses of the coupling section of the hollow shaft and the coupling section of the central shaft. In other words, when the two shafts are coupled, the hollow ring encloses both the central shaft and the hollow shaft at their respective coupling sections.Because the coupling takes place via the respective outer circumferences of the two coupling sections, torque is transmitted evenly over the entire circumference.

[0015] According to the brake unit according to the invention, the coupling section of the central shaft comprises a region with an enlarged outer diameter D, and the coupling section of the hollow shaft comprises a region with an enlarged outer diameter d. In other words, the coupling section of the hollow shaft and the coupling section of the central shaft each form a thickened region that serves to engage the hollow ring. In this way, an enlarged coupling surface is achieved.

[0016] The outer diameter D of the coupling section of the central shaft can be equal to the outer diameter d of the coupling section of the hollow shaft. This ensures that the teeth of the hollow ring engage the same depth in the coupling section of the hollow shaft and the coupling section of the central shaft, thus achieving a particularly secure coupling.

[0017] Preferably, the coupling section of the central shaft of the brake unit and the coupling section of the hollow shaft of the brake unit can be inserted into the hollow ring by axial displacement. Particularly preferably, the hollow shaft can be moved. This results in a coupled state when both shafts are inserted or pushed into the hollow ring, and a decoupled state when at least one of the two shafts, i.e. the hollow shaft and / or the central shaft, is outside the hollow ring. The coupling section only serves to couple or decouple the two shafts, but not to press the first and second plates against each other during the braking process. As already mentioned, the two types of plates are pressed together exclusively via a separate actuator.

[0018] The claw device of the brake unit according to the invention can comprise a synchronizer ring, which is placed in the axial direction between the coupling section of the hollow shaft and the coupling section of the central shaft. The synchronizer ring is provided with recesses on an outer circumference that correspond to the recesses in the coupling section of the hollow shaft. Thus, the rotational speed of the hollow shaft can be adjusted to that of the central shaft via the synchronizer ring. Once the rotational speeds are adjusted, a rotationally fixed connection between the two shafts can be established via the hollow ring.

[0019] In particular, the synchronizer ring can be provided with a profile on a side facing the hollow shaft, which can be brought into engagement with a counter-profile of the coupling section of the hollow shaft. In this way, the hollow shaft can be securely engaged with the synchronizer ring and coupled to the central shaft.

[0020] The invention also relates to a motor vehicle which has a drive, a transmission and at least one wheel driven by the drive, wherein a brake unit according to one of the above embodiments is placed between the drive and the at least one driven wheel.

[0021] According to the invention, it is possible to use a multi-disk brake, in particular a wet multi-disk brake, in such a motor vehicle without having to accept the increased drag torque of the brake that usually accompanies this. This is because, when the two shafts, i.e., the hollow shaft and the central shaft, are decoupled, the second discs located on the hollow shaft no longer have to rotate through a fluid within the housing of the wet multi-disk brake. This reduces the motor vehicle's energy consumption and increases its range.

[0022] The use of a wet multi-disk brake has the advantage of enabling effective and powerful braking, making it suitable for heavy loads and demanding applications. Furthermore, thanks to liquid cooling, it can withstand high thermal loads over extended periods. Furthermore, the discs are highly wear-resistant, ensuring a long service life. Last but not least, wet multi-disk brakes are relatively easy to maintain compared to other braking systems. These numerous advantages can be exploited by the present invention without having to accept the disadvantages of increased energy consumption due to the drag torque generated by the wet multi-disk brake.

[0023] In particular, the motor vehicle's drive system may be an electric motor. The brake unit according to the invention may be used as the motor vehicle's service brake.

[0024] Electric motors within the meaning of this application serve to convert electrical energy into mechanical energy and generally comprise a stationary part referred to as a stator, stand or armature and a part referred to as a rotor or runner which is arranged to be movable relative to the stationary part. In connection with the present invention, an electric motor is intended in particular for use within a drive train of a hybrid or fully electrically powered motor vehicle. In particular, the electric machine is dimensioned such that vehicle speeds of greater than 50 km / h, preferably greater than 80 km / h and in particular greater than 100 km / h can be achieved. The electric machine particularly preferably has an output of greater than 30 kW, preferably greater than 50 kW and in particular greater than 70 kW. It is further preferred that the electric machine has rotational speeds of greater than 5.000 rpm, particularly preferably greater than 10,000 rpm, most preferably greater than 12,500 rpm.

[0025] A rotor is the rotating part of an electrical machine. The rotor comprises, in particular, a rotor shaft and one or more rotor bodies formed from rotor cores, arranged in a rotationally fixed manner on the rotor shaft. The rotor shaft can be hollow, which, on the one hand, results in weight savings and, on the other hand, allows the supply of lubricant or coolant to the rotor body. The rotor shaft can be coupled, in particular, to the hollow shaft of the brake unit.

[0026] In battery-electric vehicles, i.e., vehicles with an electric motor, a service brake is required less frequently due to the use of a regenerative brake. The service brake is only necessary during emergency braking (ABS emergency braking) or very low ambient temperatures (the battery cannot absorb recuperated energy). In other braking situations, the service brake is optional. When a brake unit according to the invention is used as a service brake, the brake unit is therefore rarely applied, which means that the first and second discs do not engage each other for most of a journey. Without the use of the invention, the second discs would thus rotate almost continuously through the brake oil.Due to the possibility of coupling the central shaft with the hollow shaft on which the second plates are located, this rotation in a state of the brake being released and the associated drag torques are avoided.

[0027] Further features, advantages, and effects of the invention will become apparent from the following description of a preferred embodiment of the invention and the accompanying drawings. The drawings show: Fig. 1 is a schematic longitudinal sectional view through a brake unit according to the invention; Fig. 2a, Fig. 2b schematic longitudinal sectional views through a claw device which can be used in connection with the present invention; Fig. 2c a cross-sectional view through a coupling section of a central shaft of the claw device of the Fig. 2a and Fig. 2b; Fig. 2d a cross-sectional view through a hollow ring of a central shaft of the claw device of the Fig. 2a and Fig. 2b; Fig. 2e a cross-sectional view through a hollow ring of a central shaft of the claw device of the Fig. 2a and Fig. 2b; Fig. 2f a cross-sectional view through a hollow ring of a central shaft of the claw device of the Fig. 2a and Fig. 2b; and Fig. 3 a schematic view of a motor vehicle with a brake unit according to the invention.

[0028] With reference to the presentation of the Fig. Figure 1 shows a brake unit 1 according to the invention in longitudinal section along a longitudinal axis L of a housing 2. As can be seen in the figure, first plates 4 protrude radially inward from a peripheral side 2a of the housing 2. These plates can be attached to the housing 2 or formed integrally therewith. The housing 2 can be filled with a fluid, for example an oil, in particular a brake oil. Without connection to the housing 2, a central axis 6 extends coaxially to the longitudinal axis L of the housing 2.

[0029] A hollow shaft 5 is guided radially outside the central shaft 6, concentric with it, and carries a set of second plates 3, which are designed here with regular distances from one another. When the hollow shaft 5 and the central shaft 6 are decoupled, the central shaft 6 can rotate relative to the hollow shaft 5, while the latter is not carried along for rotation in the housing 2 and remains at rest in the fluid therein. Thus, no drag torque is generated in this state. In addition, the hollow shaft 5 can be displaced in the axial direction, i.e., in the direction of the longitudinal axis L, relative to the housing 2, for example by actuating an actuator (not shown). Thus, the second plates 3 can also be displaced in the axial direction relative to the first plates 4, wherein, in a braking position of the braking device 1, they bear against the first plates 4, thereby creating a frictional force that brings about braking.

[0030] In order to prevent the second plates 3 from rotating through the fluid in the housing 2 and thereby generating a drag torque when the brake unit 1 is not in the braking position, i.e. in a brake-released state, the invention accordingly proposes a possibility of coupling and decoupling the hollow shaft 5 with the central shaft 6.

[0031] For this purpose, a claw device 7 can be used, as shown in the longitudinal section of the Fig. 2a and Fig. 2b. Fig. 2a a representation of the hollow shaft 5 and the central shaft 6 in coupled state, while Fig. 2b shows the hollow shaft 5 and the central shaft 6 in a decoupled state. Both figures show a continuation of the hollow shaft 5 and the central shaft 6 laterally to the left with respect to the representation of the Fig. 1. The claw device 7 comprises a hollow ring 8, into which a coupling section 5a of the hollow shaft 5 and a coupling section 6a of the central shaft 6 can each be inserted in the axial direction with respect to the longitudinal axis L. As shown in the Fig. 2a and Fig. As can be seen in Figure 2b, the coupling sections 5a, 6a are regions with an enlarged outer diameter D, d, where D is the enlarged outer diameter of the coupling section 6a of the central shaft 6 and d is the enlarged diameter of the coupling section 5a of the hollow shaft 5.

[0032] As can be seen in the cross-sectional views of the Fig. 2c to 2e, radial recesses 6b are provided on the coupling section 6a of the central shaft 6, which are distributed circumferentially evenly over an outer circumference of the coupling section 6a ( Fig. 2c). These radial recesses 6b are a counterpart to radial teeth 8b, which project inwards from an inner side 8a of the hollow ring 8 ( Fig. 2d). If the central shaft 6, as shown in the Fig. 2a and Fig. 2b, is inserted into the hollow ring 8, the teeth 8b of the hollow ring 8 engage in the radial recesses 6b on the outer circumference of the coupling section 6a of the central shaft 6. Likewise, the coupling section 5a of the hollow shaft 5 comprises radial recesses 5b on its outer circumference ( Fig. 2e), into which the teeth 8b of the hollow ring 8 ( Fig. 2d) also engage when the hollow shaft 5 is inserted with its coupling section 5a into the hollow ring 8, as shown in Fig. 2a. In this way, the hollow shaft 5 and the central shaft 6 are in the Fig. 2a, are wedged together in a rotationally fixed manner via the hollow ring 8.

[0033] In order to align the respective speeds of the two shafts when coupling the hollow shaft 5 with the central shaft 6, a synchronizer ring 9 is provided, which is inserted into the Fig. 2a, Fig. 2b in longitudinal section and in Fig. 2f is shown in cross-section. The synchronizer ring 9 is on an outer circumference 9a, as shown in the cross-sectional view of Fig. 2f, is provided with radial recesses 9b, which also allow it to engage with the teeth 8b of the hollow ring 8 ( Fig. 2d). Furthermore, the synchronizer ring 9 is provided on one of the sides 9c facing the coupling section 5a of the hollow shaft 5 with a profile 9d, which is designed here in the form of bevels in a radially outer region of the synchronizer ring 9 and into which a counter-profile 5c formed on the coupling section 5a, which is also designed in the form of bevels in a radially outer region of the coupling section 5a, fits (see Fig. 2b).

[0034] When using the brake unit 1 according to the invention, before initiating a braking process, the hollow shaft 5 in the illustration of Fig. 1 is shifted to the left. This causes the hollow shaft 5 to reach a state which is Fig. 2a. In other words, the two shafts 5, 6 are coupled together. Conversely, when no braking operation is carried out, the hollow shaft 5 can be moved into the Fig. 2b, in which it is decoupled from the central shaft 6, since it is located outside the hollow ring 8

[0035] The braking device 1 according to the invention described above can, as already mentioned, be used in a motor vehicle 10 which is Fig.3 is shown schematically by way of example. The motor vehicle 10 has a central drive train, which is constructed from a drive 11, in the present case an electric motor, and a transmission 12 coupled to the drive 11. The drive train further comprises a braking device 1 according to the invention, which in the present case is connected downstream of the transmission 12, although the positions of the braking device 1 and the transmission 2 can also be interchanged. The braking device 1 acts here as a service brake on the central drive train, which means that a braking torque is generated directly on a shaft that is coupled to a rotor shaft of the drive 11. List of reference symbols 1 brake unit 2 housings 2a peripheral side 3 first brake discs 4 second brake discs 5 hollow shaft 5a Coupling section hollow shaft 5b radial recess hollow shaft 5c Counter profile 6 Central Shaft 6a Coupling section central shaft 6b radial recess central shaft 7 Claw device 8 hollow ring 8a inside 8b radial teeth 9 Synchronizer ring 9a Outer circumference 9b radial recess synchronizer ring 9c page 9d profile 10 motor vehicle 11 Drive 12 gears 13 Driven wheel L Longitudinal axis

Claims

[1] Brake unit (1) for a motor vehicle (1), comprising a cylindrical housing (2) which can be filled with a fluid and in which a plurality of first plates (4) project radially inwards from a circumferential side (2a) of the housing (2) with respect to a longitudinal axis L of the housing (2), wherein a plurality of second plates (3) are arranged in the housing (2) so as to be axially movable relative to the first plates (4) with respect to the longitudinal axis L in order to be able to be brought into and out of a braking position in which the first and second plates (4, 3) abut one another, where a central shaft (6) is guided along the longitudinal axis L through the housing (2), and that the second lamellae (3) are arranged radially outwardly projecting on a hollow shaft (5) and are connected to it in a rotationally fixed manner, which concentrically surrounds the central shaft (6) and which can be coupled to the central shaft (6) in a rotationally fixed manner, it has a claw device (7) for coupling the central shaft (6) to the hollow shaft (5), that the claw device (7) has a hollow ring (8) which is provided on an inner side (8a) with radially inwardly projecting teeth (8b), wherein a coupling section (6a) of the central shaft (6) and a coupling section (5a) of the hollow shaft (5) are each provided on the circumference with radial recesses (6b, 5b) which are connected to the teeth (8b) of the hollow ring (8) can be brought into engagement, characterized bythat the coupling section (6a) of the central shaft (6) comprises a region with an enlarged outer diameter D and that the coupling section (5a) of the hollow shaft (5) comprises a region with an enlarged outer diameter d. [2] Brake unit (1) according to claim 1, characterized by that the outer diameter D of the coupling section (6a) of the central shaft (6) is equal to the outer diameter d of the coupling section (5a) of the hollow shaft (5). [3] Brake unit (1) according to claim 1 to 2, characterized by that the coupling section (6a) of the central shaft (6) and the coupling section (5a) of the hollow shaft (5) can be inserted into the hollow ring (8) by axial displacement. [4] Brake unit (1) according to one of claims 1 to 2, characterized byin that the claw device (7) comprises a synchronizer ring (9) which is placed in the axial direction between the coupling section (5a) of the hollow shaft (5) and the coupling section (6a) of the central shaft (6), wherein the synchronizer ring (9) is provided on an outer circumference (9a) with recesses (9b) which correspond to the recesses (5b) of the coupling section (5a) of the hollow shaft (5). [5] Brake unit (1) according to claim 4, characterized by that the synchronizer ring (9) is provided on a side (9c) facing the hollow shaft (5) with a profile (9d) which can be brought into engagement with a counter-profile (5c) of the coupling section (5a) of the hollow shaft (5). [6] Motor vehicle (10), comprising a drive (11), a transmission (12) and at least one wheel (13) driven by the drive (11), characterized by that a braking unit according to one of the preceding claims is placed between the drive (11) and the at least one driven wheel (13). [7] Motor vehicle (10) according to claim 6, characterized by that the drive (11) is an electric motor.

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