Brake system for motor vehicle driven by electric motor

Abstract

The invention relates to a brake system (1) of a motor vehicle (3) that can be electrically driven by an electric machine (2), comprising a drum brake (4) with a brake drum (5) to which a friction torque can be applied by means of at least one brake shoe (6), the invention relates to a drum brake (4) for a motor vehicle (3), comprising a brake drum (5), a brake shoe (6) which can be moved radially in the direction of the brake drum (5) by means of a brake actuator (7), an electric machine (2) equipped with a rotor (8) coupled in a torque-transmitting manner to at least one wheel (10) of the motor vehicle (3), and a drum brake (4) housed in a brake housing (9), the brake drum (5) is connected to the rotor (8) of the electric machine (2) in a torque-transmitting manner.

Description

Technical Field

[0001] The invention relates to a braking system for a motor vehicle which can be electrically driven by means of an electric motor, wherein the braking system comprises a drum brake with a brake drum, to which a friction torque can be applied by means of at least one brake shoe, which can be radially displaced in the direction of the brake drum by a brake actuator, and the electric motor has a rotor which is coupled to at least one wheel of the motor vehicle in a torque-transmitting manner. Background Art

[0002] Electric motors are increasingly being used to drive motor vehicles to create an alternative to internal combustion engines that require fossil fuels. Considerable effort has been made to improve the suitability of electric drives for everyday use and also to provide users with the driving comfort they are accustomed to. For example, a detailed description of electric drives can be found in an article published by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold in the German automotive magazine ATZ, May 2011, Volume 113, pages 360 to 365, entitled: Hochintegrativ und FlexibelElektrische Antriebseinheit für E-Fahrzeuge [Highly Integrative and Flexible Electric Drive Unit for E-Vehicles (Highly Integrated and Flexible Electric Drive Unit for Electric Vehicles)]. The article describes a drive unit for an axle of a vehicle, the drive unit comprising an electric motor arranged coaxially with a bevel gear differential.

[0003] Vehicles of this type with a hybrid or electrified drive train can not only accelerate, but also brake with the aid of the electric machine. For example, during braking, the electric machine operates as a generator and the recovered energy is used to charge the battery. However, for safety reasons, additional mechanical braking devices are still required. For drives near the wheels, such as wheel hub motors or electric axles, this leads to more difficult problems in terms of installation space.

[0004] In particular, vehicles with electric wheel hub drives, so-called electric wheel drives, usually use brakes with disks in order to decelerate the vehicle. However, disk brakes with floating calipers, disk brakes with fixed calipers, drum brakes and multi-disc brakes are also known.

[0005] For example, DE10 2019 120 409A1 discloses a braking device for a wheel hub drive assembly in which a braking mating part fixed relative to the circumferential direction has cooling channels. The axially movable brake mating part is actuated via a brake cylinder. The brake mating part movable in the circumferential direction is designed as a disk carrier.

[0006] There is also an increasing need to reduce or completely avoid brake wear emissions, which typically occur as particulate matter. SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to provide an improved braking system having a high braking torque, high operating safety, and low brake dust emissions.

[0008] This object is achieved by a braking system for a motor vehicle that can be electrically driven by a motor, wherein the braking system includes a drum brake with a brake drum, a friction torque can be applied to the brake drum by means of at least one brake shoe, the brake shoe can be radially displaced in the direction of the brake drum by a brake actuator, and the motor has a rotor that is torque-transmittingly coupled to at least one wheel of the motor vehicle, wherein the drum brake is accommodated in a brake housing, and the brake drum is torque-transmittingly connected to the rotor of the motor.

[0009] The advantage of this is that the braking system according to the invention supplements the recuperation of the motor in generator mode in driving situations where the desired braking energy cannot be provided separately. These are, for example, driving situations with a low vehicle speed or a low motor speed or driving situations where the vehicle is stopped or braked at low temperatures.

[0010] The advantage of the additionally encapsulated brake is that the braking energy can be transferred in the form of heat to the vehicle's thermal management system without having to store the energy, for example, in the vehicle's battery. Additionally, brake dust particles are not released into the environment. For example, if future laws and regulations permit, the wheel brakes on an axle can also be dispensed with.

[0011] This type of brake is sometimes referred to as a supplementary brake.

[0012] Brake housing

[0013] The brake is preferably arranged in a brake housing. The brake housing encloses the brake. The brake housing may also accommodate one or more brake actuators. The brake housing may also be part of a cooling system and may be designed such that cooling fluid can be supplied to the braking system via the brake housing and / or heat can be dissipated to the outside via the housing surface. The brake housing also protects the supplementary brake from external mechanical and / or chemical influences. The brake housing may in particular be formed from a metallic material. Advantageously, the brake housing may be formed from a metallic casting material such as grey cast iron or cast steel. In principle, it is also conceivable that the brake housing is formed completely or partly from plastic. The brake housing may also be designed as one piece or as a number of components. The brake housing may also be designed completely or partly as part of the motor housing of an electric motor or as part of the transmission housing of a transmission coupled to the electric motor. The brake housing and the motor housing or the transmission housing preferably form a single structural unit. For example, the brake housing may be screwed to the motor housing or the transmission housing. The brake housing is preferably designed such that wear emissions generated during braking cannot escape from the brake housing. This prevents undesired pollution of the environment by brake wear emissions. The braking noise can also be reduced by encapsulating the braking system in this way. Another advantageous aspect of this encapsulation is that the braking performance of the braking system is not affected by weather conditions outside the vehicle.

[0014] Brake actuator

[0015] In particular, the brake actuator has the function of enabling the brake, bringing the brake into a friction-operating state and releasing it from the friction connection. In particular, the brake actuator can be actuated pneumatically, hydraulically, by means of an electric motor, mechanically, electromagnetically or in any combination thereof.

[0016] Electric motor

[0017] The braking system according to the invention is preferably provided for a motor vehicle that is electrically driven by means of an electric motor. For the purposes of the present application, an electric motor serves to convert electrical energy into mechanical energy and / or mechanical energy into electrical energy, and generally comprises a fixed part known as a stator or stationary armature and a part known as a rotor or moving armature that is arranged movably relative to the fixed part. In connection with the present invention, the electric motor can in particular be designed as a rotary machine. In the case of such an electric rotary machine, a distinction is made between a radial flux type machine and an axial flux type machine. The radial flux type machine is characterized in that the magnetic field lines extend in the radial direction in the air gap formed between the rotor and the stator, while in the case of the axial flux type machine, the magnetic field lines extend in the axial direction in the air gap formed between the rotor and the stator. In connection with the present invention, the electric motor is in particular intended for use within the powertrain of a hybrid or fully electric motor vehicle. In particular, the electric motor is dimensioned such that vehicle speeds of more than 50 km / h, preferably more than 80 km / h, and in particular more than 100 km / h can be achieved. The electric motor particularly preferably has an output of more than 30 kW, preferably more than 50 kW, and in particular more than 70 kW. Furthermore, it is preferred that the electric motor provides a speed of more than 5000 rpm, particularly preferably more than 10,000 rpm, and very particularly preferably more than 12,500 rpm.

[0018] The electric motor can have a housing, which is also referred to as a motor housing. The motor housing encloses the electric motor. The motor housing can also accommodate control electronics and power electronics, and preferably can also accommodate at least a part of the braking system. The motor housing can also be part of a cooling system for the electric motor and can be designed such that cooling fluid can be supplied to the electric motor via the motor housing and / or heat can be dissipated to the outside via the motor housing surface. Additionally, the motor housing protects the electric motor and any electronics that may be present from external mechanical and / or chemical influences. The motor housing of the electric motor can in particular be formed from a metallic material. Advantageously, the motor housing can be formed from a metallic casting material such as grey cast iron or cast steel. In principle, it is also conceivable that the motor housing is formed completely or partly from plastic. The motor housing of the electric motor can also be designed as a single piece or as several components.

[0019] The rotor is the rotating (swirling) part of the electric motor. The rotor particularly comprises a rotor shaft and one or more rotor bodies formed by a rotor lamination stack that are arranged non-rotatably on the rotor shaft. The rotor shaft can be hollow, which on the one hand reduces the weight and on the other hand allows the supply of lubricant or coolant to the rotor body. In particular, the rotor shaft can be coupled to the brake shaft of a supplementary brake.

[0020] Transmission

[0021] The electric machine and / or the brake can preferably be coupled to a transmission which is specifically designed to generate a drive torque for a motor vehicle. The drive torque is particularly preferably a main drive torque such that the motor vehicle is driven solely by this drive torque.

[0022] In particular, it can be provided that the electric machine and / or the brake and the transmission are arranged in a common powertrain housing. Alternatively, the electric machine can of course also have a motor housing, and the transmission can of course also have a transmission housing, whereupon a structural unit can then be produced by fixing the transmission relative to the electric machine. This structural unit is sometimes also referred to as an electric axle. The powertrain housing is preferably formed from a metallic material, particularly preferably from aluminum, gray cast iron or cast steel, in particular by means of a one-piece forming process such as casting or die-casting. However, in principle, the powertrain housing can also be formed from a plastic material. The powertrain housing can particularly preferably have a cup-shaped basic shape such that the electric machine and the transmission can be inserted into the powertrain housing via the open end face of the powertrain housing.

[0023] The electric machine preferably has a motor housing and / or the transmission has a transmission housing, whereupon the structural unit can then be realized by fixing the transmission relative to the electric machine. The transmission housing is a housing for accommodating the transmission. The transmission housing has the following tasks: guiding the existing shafts via bearings and giving the wheels (cam disks, where applicable) the degrees of freedom required under all loads without impeding the rotation of the wheels and possible path movements and absorbing bearing forces and support torques. The transmission housing can be designed as a single housing or a multi-housing, i.e., non-separated or separated. In particular, the transmission housing should be able to suppress noise and vibrations and safely absorb hydraulic fluid. The transmission housing is preferably formed from a metallic material, particularly preferably from aluminum, gray cast iron or cast steel, in particular by means of a one-piece forming process such as casting or die-casting.

[0024] Furthermore, the transmission can preferably be configured as a planetary transmission or include a planetary transmission. The planetary transmission can preferably have a sun gear and a plurality of planet gears and a ring gear, the plurality of planet gears meshing with the sun gear and being rotatably mounted in a planet gear carrier, the planet gears rotating around the sun gear, and the ring gear being arranged coaxially with the sun gear and the planet gears rolling in the ring gear.

[0025] The transmission can also have a differential gear. The differential gear mechanism is a planetary transmission having one drive end and two output ends. The differential gear mechanism generally has the following function: driving the two wheels of a motor vehicle such that the wheels can rotate at different speeds when turning, but with the same driving force.

[0026] Disengaging clutch

[0027] In order to implement different driving or operating modes for a vehicle, one or more disengaging clutches can be arranged in the torque path between the electric motor and the wheels. For example, a disengaging clutch can be arranged between the output of the electric motor and the input of the transmission, such that the electric motor can be disconnected from the transmission, thereby allowing the vehicle to operate in a coasting mode. It is also conceivable to arrange the disengaging clutch between the output of the transmission and one or more wheels, which can also achieve the coasting operation of the motor vehicle. Finally, the disengaging clutch can also be arranged between the input of the braking system and the output of the electric motor, which allows the braking system to be completely disconnected from the electric motor.

[0028] Motor vehicle

[0029] For the purposes of the present application, a motor vehicle is a land vehicle that is moved by machine power and is not restricted by railway tracks. Motor vehicles can be selected, for example, from the group consisting of passenger cars, trucks, scooters, light motor vehicles, motorcycles, buses / coaches or tractors.

[0030] Advantageous embodiments of the present invention

[0031] Advantageous embodiments of the present invention are specified in the dependent claims. The features listed separately in the dependent claims can be combined with each other in a technically meaningful way and can define other embodiments of the present invention. Additionally, the features indicated in the claims are described and explained in more detail in the specification, where other preferred embodiments of the present invention are shown.

[0032] According to an advantageous embodiment of the present invention, it can be provided that the braking system has a brake cooling circuit for dissipating heat from the drum brake. The advantage of this design is that the heat generated by the frictional energy of the brake can be dissipated and can be used, for example, in the thermal management system of the motor vehicle. Furthermore, cooling the brake can improve its braking performance and, in particular, reduce heat fade, i.e., the heat-related loss of braking force.

[0033] Thermal management system

[0034] In the context of the present invention, the term thermal management refers to the demand-oriented and effective control of the heat flow in an electric vehicle, especially a battery-powered vehicle, according to the main operating or load conditions.

[0035] The thermal management system of a vehicle may include a hydraulic control system. The hydraulic control system guides the volumetric flow within the thermal management system of a motor vehicle by means of switching elements that act hydraulically on the fluid, such as valves, sliders, pumps, etc. For example, the hydraulic control system can throttle the volumetric flow completely or partially and / or distribute the volumetric flow to relevant heat sources and radiators in sub-circuits of the thermal management system of the motor vehicle. For this purpose, the hydraulic switching elements are controlled and switched by an electronic control unit.

[0036] The hydraulic switching elements can be hydraulic pumps, switching valves, controllable throttle valves, etc. The hydraulic switching elements can preferably be electrically controlled. In addition, the hydraulic switching elements preferably have at least two different switchable operating states, in which the hydraulic switching elements act on the corresponding fluid in the circuit in different ways.

[0037] According to an advantageous embodiment of the invention, it can thus be provided that the brake has a brake cooling circuit for dissipating heat from or supplying heat to the brake, wherein the hydraulic control unit acts on the brake cooling circuit by means of at least one hydraulic switching element to influence the volumetric flow in the brake cooling circuit.

[0038] According to an advantageous embodiment of the invention, it can be provided that the electric motor has a motor cooling circuit for dissipating heat from or supplying heat to the electric motor, wherein the hydraulic control unit acts on the motor cooling circuit by means of at least one hydraulic switching element to influence the volumetric flow in the motor cooling circuit.

[0039] According to an advantageous embodiment of the invention, it can be provided that the thermal management system further includes an inverter that has an inverter cooling circuit for dissipating heat from or supplying heat to the inverter, wherein the hydraulic control unit acts on the inverter cooling circuit by means of at least one hydraulic switching element to influence the volumetric flow in the inverter cooling circuit.

[0040] According to an advantageous embodiment of the invention, it can be provided that the vehicle battery has a battery cooling circuit for dissipating heat from or supplying heat to the vehicle battery, wherein the hydraulic control unit acts on the battery cooling circuit by means of at least one hydraulic switching element to influence the volumetric flow in the battery cooling circuit.

[0041] According to another preferred further development of the invention, it can also be provided that at least one first cooling channel that can be connected to the brake cooling circuit is formed in or on the brake drum, whereby heat can be dissipated from the brake drum. The invention can also be advantageously designed such that the first cooling channel extends in the region of the friction surface of the brake drum and the brake shoe, which further improves the dissipation from the region that is subject to a certain degree of thermal stress.

[0042] Furthermore, according to an equally advantageous embodiment of the present invention, it may be provided that at least one second cooling channel which can be connected to a brake cooling circuit is formed in or on the brake housing, whereby the cooling effect can be further improved.

[0043] According to another particularly preferred embodiment of the present invention, it may be provided that a hydraulic transition region is formed between the first cooling channel of the brake drum and the second cooling channel of the brake housing, and the cooling fluid can flow from the first cooling channel into the second cooling channel via this transition region, and vice versa, the cooling fluid can flow from the second cooling channel into the first cooling channel via this transition region. This has a particular effect that the brake cooling circuit can be routed from the brake drum to the brake housing in a defined path, i.e., from a rotating component to a fixed component during operation.

[0044] Furthermore, the present invention can be further developed such that the transition region is designed as an annular disk-shaped gap which is sealed on the radially inner side by a first sealing element and on the radially outer side by a second sealing element, whereby a particularly advantageous transition region in terms of flow can be provided.

[0045] In an equally preferred embodiment of the present invention, it may also be provided that the first cooling channel is designed as an annular cross-sectional shape or an annular groove opening towards the gap in the region of the gap. This allows for a further improved hydraulic transition.

[0046] It may also be advantageous to further develop the present invention such that the second cooling channel is formed as an annular cross-sectional shape or an annular groove opening towards the gap in the region of the gap, which further improves the hydraulic transition between the brake drum and the brake housing.

[0047] According to another preferred embodiment of the subject matter of the present invention, the first sealing element and / or the second sealing element is designed as a labyrinth seal.

[0048] This can provide a particularly low-friction and substantially wear-free seal for the gap.

[0049] Finally, the present invention can also be advantageously implemented such that the brake is configured as a dry-running brake. Therefore, preferably, the braking system is designed as a "dry" braking system, and this "dry" braking system has cooling channels or cooling hoses in one of the brake components - preferably in a non-rotating component. Through these channels or hoses, a coolant such as a water-glycol mixture or cooling oil is conveyed to the vehicle's thermal management system. Compared with a "wet" (multi-disc) braking system, the advantage of the "dry" braking system is that it generates significantly less loss when not actuated, and the friction coefficient and thus the braking torque are more constant. Description of the Drawings

[0050] The present invention will now be explained in more detail with reference to the accompanying drawings without restricting the general concept of the invention.

[0051] In the drawings:

[0052] Figure 1 There is shown in a schematic block diagram view an electrically drivable motor vehicle having a braking system,

[0053] Figure 2 There is shown in a schematic axial sectional view the axle drive of a motor vehicle having a braking system,

[0054] Figure 3 There is shown in a schematic axial sectional view a drum brake,

[0055] Figure 4 There is shown in an axial sectional view a detailed view of the gap of the drum brake. Detailed Description

[0056] Figure 1 There is shown a braking system 1 of an electrically drivable motor vehicle 3 which can be driven by means of an electric motor 2, as illustrated by way of example in Figure 2 . In the Figure 2 illustrated embodiment, the braking system 1 also has a service brake system 27 for applying a wheel-selective braking torque to the wheels 10 of the first and second vehicle axles.

[0057] The braking system 1 further includes a drum brake 4 with a brake drum 5, to which a frictional torque can be applied by means of at least one brake shoe 6, which can be radially displaced in the direction of the brake drum 5 by a brake actuator 7. The electric motor 2 accommodated in the motor housing 23 has a rotor 8 which is torque-transmittingly coupled to at least one wheel 10 of the motor vehicle 3.

[0058] The drum brake 4 is accommodated in a brake housing 9, and the brake drum 5 is torque-transmittingly connected to the rotor 8 of the electric motor 2 via a brake shaft 28 and a rotor shaft 22. In this configuration, three different deceleration torques can thus act on one or more of the wheels 10: the deceleration torque generated by the drum brake 4, the deceleration torque generated by the electric motor 2 and / or the deceleration torque generated by the service brake system 27. Depending on the driving situation and the deceleration requirements, these three available deceleration torques can be combined and applied in a controllable manner.

[0059] The electric motor 2, the transmission 26, and the drum brake 4 form a structural unit, which is also referred to as the axle driveline 24. A disengaging clutch 25 is installed between the electric motor 2 and the wheel 10, and the electric motor 2 can be disengaged from the torque path via the disengaging clutch, so that the axle driveline 24 can be set, for example, to a coasting mode.

[0060] The brake system 1 also has a brake cooling circuit 11 for dissipating heat from the drum brake 4. A heat exchanger 21 is arranged in the brake cooling circuit 11, and the heat dissipated from the drum brake 4 can be transferred to the thermal management system of the motor vehicle 3 by means of this heat exchanger. At least one first cooling channel 12 that can be connected to the brake cooling circuit 11 is formed in or on the brake drum 5. As Figure 3 can be clearly seen, the first cooling channel extends in the region of the friction surface of the brake drum 5 and the brake shoe 6. In addition, at least one second cooling channel 13 that can be connected to the brake cooling circuit 11 is formed in or on the brake housing 9. A hydraulic transition region 14 is formed between the first cooling channel 12 in the brake drum 5 and the second cooling channel 13 in the brake housing 9. The cooling fluid 15 can flow from the first cooling channel 12 into the second cooling channel 13 via this hydraulic transition region, and conversely, the cooling fluid can flow from the second cooling channel into the first cooling channel via this hydraulic transition region. This is explained in more detail below with reference to Figure 4 which.

[0061] In the illustrated embodiment, the transition region 14 is designed as an annular disk-shaped gap 16, which is sealed on the radially inner side by a first sealing element 17 and on the radially outer side by a second sealing element 18. The first sealing element 17 and the second sealing element 18 are designed as non-contact labyrinth seals. The first cooling channel 12 is formed in the region of the gap 16 as an annular cross-sectional or ring-shaped groove 19 that opens towards the gap 16. Similarly, the second cooling channel 13 is also designed as an annular cross-sectional or ring-shaped groove 20 that opens towards the gap 16 in the region of the gap 16.

[0062] In order to increase the frictional force between the brake shoe 6 and the brake drum 5, a friction lining 29 is applied to the radially outer surface of the brake shoe. Of course, a friction lining can also be provided alternatively or additionally on the radially inner surface of the brake drum 5.

[0063] The present invention is not limited to the embodiments shown in the drawings. Therefore, the above description should not be considered restrictive, but rather illustrative. The appended claims should be understood to mean that the stated features are present in at least one embodiment of the present invention. This does not exclude the presence of other features. Where the claims and the above description define a "first" feature and a "second" feature, such designations are used to distinguish between two features of the same type and do not define a priority order.

[0064] List of reference numerals

[0065] 1 Brake system

[0066] 2 Electric motor

[0067] 3 Motor vehicle

[0068] 4 Drum brake

[0069] 5 Brake drum

[0070] 6 Brake shoe

[0071] 7 Brake actuator

[0072] 8 Rotor

[0073] 9 Brake housing

[0074] 10 Wheel

[0075] 11 Brake cooling circuit

[0076] 12 Cooling channel

[0077] 13 Cooling channel

[0078] 14 Transition region

[0079] 15 Cooling fluid

[0080] 16 Clearance

[0081] 17 Sealing element

[0082] 18 Sealing element

[0083] 19 Groove

[0084] 20 Groove

[0085] 21 Heat exchanger

[0086] 22 Rotor shaft

[0087] 23 Motor housing

[0088] 24 Axle drive train

[0089] 25 Separation clutch

[0090] 26 Transmission

[0091] 27 Service brake system

[0092] 28 Brake shaft

[0093] 29 Friction lining.

Claims

1. A braking system (1) for a motor vehicle (3) that can be electrically driven by means of an electric motor (2), wherein, The braking system (1) includes a drum brake (4) with a brake drum (5), which is capable of applying a frictional torque to the brake drum by means of at least one brake shoe (6). The brake shoe can be radially displaced in the direction of the brake drum (5) by a brake actuator (7), and the motor (2) has a rotor (8) that is torque-transmittingly coupled to at least one wheel (10) of the motor vehicle (3). It is characterized in that the drum brake (4) is accommodated in a brake housing (9), and the brake drum (5) is torque-transmittingly connected to the rotor (8) of the motor (2).

2. The braking system (1) according to claim 1, It is characterized in that the braking system (1) has a brake cooling circuit (11) for dissipating heat from the drum brake (4).

3. The braking system (1) according to claim 1 or 2, It is characterized in that at least one first cooling channel (12) that can be connected to the brake cooling circuit (11) is formed in or on the brake drum (5).

4. The braking system (1) according to any one of the preceding claims, It is characterized in that at least one second cooling channel (13) that can be connected to the brake cooling circuit (11) is formed in or on the brake housing (9).

5. The braking system (1) according to claim 4, It is characterized in that a hydraulic transition region (14) is formed between the first cooling channel (12) of the brake drum (5) and the second cooling channel (13) of the brake housing (9). The cooling fluid (15) can flow from the first cooling channel (12) into the second cooling channel (13) via the transition region, and vice versa, the cooling fluid can flow from the second cooling channel into the first cooling channel via the transition region.

6. The braking system (1) according to claim 5, It is characterized in that the transition region (14) is formed as an annular disk-shaped gap (16), which is sealed by a first sealing element (17) on the radially inner side and by a second sealing element (18) on the radially outer side.

7. The braking system (1) according to any one of claims 3 to 6, It is characterized in that the first cooling channel (12) is formed as an annular cross-section or annular groove (19) that opens towards the gap (16) in the region of the gap (16).

8. The braking system (1) according to any one of claims 4 to 7, It is characterized in that the second cooling channel (13) is formed as an annular cross-section or annular groove (20) that opens towards the gap (16) in the region of the gap (16).

9. The braking system (1) according to any one of claims 6 to 8, It is characterized in that the first sealing element (17) and / or the second sealing element (18) are designed as labyrinth seals.

10. The braking system (1) according to any one of the preceding claims 3 to 9, characterized in that, the first cooling channel (12) extends in the region of the friction surface of the brake drum (5) and the brake shoe (6).

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