DE102022132491B3 - Braking system of a motor vehicle electrically driven by an electric machine - Google Patents

Abstract

The invention relates to a braking system (1) of a motor vehicle (3) that can be electrically driven by means of an electric machine (2), wherein the braking system (1) comprises a brake (4) with a brake disk (5) that can be subjected to a friction torque by means of a brake actuator (7), and the electric machine (2) has a rotor (8) that is coupled to at least one vehicle wheel (24) of the motor vehicle (3) in a torque-transmitting manner, wherein the brake (4) is accommodated in a brake housing (9) and the brake disk (5) is connected to the rotor (8) of the electric machine (2) in a torque-transmitting manner.

Description

The present invention relates to a braking system of a motor vehicle that can be electrically driven by means of an electric machine, wherein the braking system comprises a brake with a brake disc, which can be subjected to a friction torque by means of a brake actuator, and the electric machine has a rotor which is coupled to at least one vehicle wheel of the motor vehicle in a torque-transmitting manner,

Electric motors are increasingly being used to drive motor vehicles in order to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday suitability of electric drives and also to be able to offer users the usual driving comfort. A detailed description of an electric drive can be found, for example, in an article in the magazine ATZ 113th year, 05/2011, pages 360-365 by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold with the title: Highly integrated and flexible electric drive unit for electric vehicles. This article describes a drive unit for an axle of a vehicle, which includes an electric motor that is arranged coaxially to a bevel gear differential.

Such motor vehicles with a hybridized or electrified drive train can not only accelerate and brake with the help of an electric machine, but also. During braking, the electric machine is operated as a generator and the recuperated energy is used, for example, to charge the battery. For safety reasons, however, an additional mechanical braking device is still required. With drives close to the wheels, such as a wheel hub motor or an electric axle, this results in a more difficult installation space situation.

Particularly in vehicles with an electric wheel hub drive, a so-called E-Wheel Drive, brakes with discs are often used to slow the vehicle down. However, brakes in the form of disc brakes with floating calipers, disc brakes with fixed calipers, drum brakes and multiple disc brakes are also known.

From the EN 10 2019 120 409 A1 For example, a braking device for a wheel hub drive arrangement is known in which the brake partners that are fixed relative to the circumferential direction have cooling channels. The axially movable brake partner is actuated by brake cylinders. The brake partner that is movable in the circumferential direction is designed as a disk carrier.

There is also an increasing requirement to reduce or completely avoid emissions of brake dust, which often occurs as fine dust. WO 2016/ 146 625 A1 a braking system according to the preamble of claim 1 is disclosed. Further prior art is in the DE 11 60 319 B described.

It is therefore the object of the invention to provide an improved braking system with high braking torques, high operational reliability and low brake dust emissions with a small space requirement.

This object is achieved by a braking system of a motor vehicle that can be electrically driven by means of an electric machine, wherein the braking system comprises a brake with a brake disc, which can be subjected to a friction torque by means of a brake actuator, and the electric machine has a rotor which is coupled to at least one vehicle wheel of the motor vehicle in a torque-transmitting manner, wherein the brake is accommodated in a brake housing and the brake disc is connected to the rotor of the electric machine in a torque-transmitting manner.

This provides the advantage that the braking system according to the invention supplements the recuperation of the electric machine in generator mode in driving situations where this alone cannot provide the desired braking energy. These are, for example, driving situations with a low vehicle speed or speed of the electric machine or stopping at a standstill or braking at low temperatures.

The advantage of an additional, encapsulated brake is that the braking energy can be transferred to the thermal management of the vehicle as heat, without the energy having to be stored in the vehicle's battery, for example. In addition, brake dust particles are not released into the environment. If legal regulations allow this in the future, it may also be possible to dispense with the wheel brakes on one axle, for example.

Such a brake is sometimes referred to as a complementary brake.

The brake is preferably arranged in a brake housing. The brake housing encloses the brake. A brake housing can also accommodate one or more brake actuators. The brake housing can also Part of a cooling system and designed in such a way that cooling fluid is supplied to the brake system via the brake housing and/or the heat can be dissipated to the outside via the housing surfaces. In addition, the brake housing protects the complementary brake from external mechanical and/or chemical influences. A brake housing can in particular be made from a metallic material. The brake housing can advantageously be formed from a metallic cast material, such as gray cast iron or cast steel. In principle, it is also conceivable to form the brake housing entirely or partially from a plastic. It is also possible for the brake housing to be designed in one piece or in several parts. The brake housing can also be designed entirely or partially as part of a motor housing of an electrical machine or a transmission housing of a transmission coupled to the electrical machine. The brake housing and the motor housing or the transmission housing preferably form a structural unit. For this purpose, the brake housing can be screwed to the motor housing or the transmission housing, for example. The brake housing is preferably designed in such a way that abrasion that occurs during braking cannot escape from the brake housing. This prevents unwanted exposure of the environment to brake wear. Furthermore, this type of encapsulation of the braking system also reduces braking noise in the environment. Another advantageous aspect of this encapsulation is that the braking performance of the braking system is independent of the weather conditions outside the vehicle.

A brake actuator has the particular function of actuating the brake, i.e. putting it into a frictionally engaged operating state and an operating state released from the frictional engagement. For this purpose, the brake actuator can be actuated in particular pneumatically, hydraulically, by an electric motor, mechanically, electromagnetically or by any combination thereof.

The braking system according to the invention is preferably provided for a motor vehicle that can be driven electrically by means of an electric machine. Electric machines in the sense of this application serve to convert electrical energy into mechanical energy and/or vice versa, and generally comprise a stationary part referred to as a stator, stand or armature and a part referred to as a rotor or runner and arranged to be movable relative to the stationary part. In connection with this invention, an electric machine can be designed in particular as a rotary machine. In such rotary electric machines, a distinction is made in particular between radial flux machines and axial flux machines. A radial flux machine is characterized in that the magnetic field lines in the air gap formed between the rotor and stator extend in the radial direction, while in the case of an axial flux machine the magnetic field lines in the air gap formed between the rotor and stator extend in the axial direction. In connection with the present invention, an electric machine is intended in particular for use within a drive train of a hybrid or fully electrically driven motor vehicle. In particular, the electric machine 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 machine particularly preferably has an output of more than 30 kW, preferably more than 50 kW and in particular more than 70 kW. It is further preferred that the electric machine provides speeds of more than 5,000 rpm, particularly preferably more than 10,000 rpm, very particularly preferably more than 12,500 rpm.

The electric machine can have a housing, which is also referred to as a motor housing. The motor housing encloses the electric machine. A motor housing can also accommodate the control and power electronics, and preferably also at least parts of the braking system. The motor housing can also be part of a cooling system for the electric machine and can be designed in such a way that cooling fluid is supplied to the electric machine via the motor housing and/or the heat can be dissipated to the outside via the motor housing surfaces. In addition, the motor housing protects the electric machine and any electronics present from external mechanical and/or chemical influences. A motor housing of the electric machine can in particular be made of a metallic material. The motor housing can advantageously be formed from a metallic cast material, such as gray cast iron or cast steel. In principle, it is also conceivable to form the motor housing entirely or partially from a plastic. It is also possible for the motor housing of the electric machine to be made in one piece or in several parts.

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 laminations arranged on the rotor shaft in a rotationally fixed manner. The rotor shaft can be hollow, which on the one hand results in a weight saving and on the other hand enables the supply of lubricant or coolant to the Rotor body permitted. The rotor shaft can be coupled in particular with the brake shaft of the complementary brake.

The electric machine and/or the brake can preferably be coupled to a transmission which is designed in particular to generate a drive torque for the motor vehicle. The drive torque is particularly preferably a main drive torque, so that the motor vehicle is driven exclusively by the drive torque.

In particular, it can be provided that the electric machine and/or the brake and the transmission are arranged in a common drive train housing. Alternatively, it would of course also be possible for the electric machine to have a motor housing and the transmission to have a transmission housing, the structural unit then being able to be effected by fixing the transmission arrangement relative to the electric machine. This structural unit is sometimes also referred to as an electric axle. The drive train housing is preferably made of a metallic material, particularly preferably aluminum, gray cast iron or cast steel, in particular by means of a primary forming process such as casting or die casting. In principle, however, it would also be possible to form the drive train housing from a plastic. The drive train housing can particularly preferably have a pot-like basic shape, so that the electric machine and the transmission can be inserted into the drive train housing via the open front side of the drive train housing.

The electric machine preferably has a motor housing and/or the gearbox a gearbox housing, the structural unit then being able to be achieved by fixing the gearbox relative to the electric machine. The gearbox housing is a housing for accommodating a gearbox. Its job is to guide existing shafts via the bearings and to grant the wheels (possibly cam disks) the degrees of freedom they require under all loads without hindering their rotation and possible path movement, as well as to absorb bearing forces and support moments. A gearbox housing can be single- or multi-shell, i.e. undivided or divided. The gearbox housing should in particular also be able to dampen noise and vibrations and safely accommodate hydraulic fluid. The gearbox housing is preferably made of a metallic material, particularly preferably aluminum, gray cast iron or cast steel, in particular by means of a primary forming process such as casting or die casting.

The transmission can further preferably be configured as a planetary transmission or comprise a planetary transmission. The planetary transmission can preferably have a sun gear and a plurality of planetary gears that mesh with the sun gear and are rotatably mounted in a planetary gear carrier, which move in rotation around the sun gear, as well as a ring gear arranged coaxially to the sun gear, in which the planetary gears roll.

The transmission can also have a differential gear. A differential gear is a planetary gear with one input and two outputs. Its function is usually to drive two wheels of a motor vehicle so that they can turn at different speeds in curves but with the same propulsive force.

In order to implement different drive or operating modes for the motor vehicle, one or more separating clutches can be provided within the torque path between the electric machine and a vehicle wheel. A separating clutch can, for example, be arranged between the output of the electric machine and the input of the transmission, so that the electric machine can be decoupled from the transmission, thereby enabling the motor vehicle to coast. It would also be conceivable to arrange a separating clutch between the output of the transmission and a vehicle wheel or wheels, thereby also enabling the motor vehicle to coast. Finally, it is also possible to arrange a separating clutch between the input of the braking system and the output of the electric machine, whereby the braking system can be completely decoupled from the electric machine.

For the purposes of this application, motor vehicles are land vehicles that are moved by mechanical power without being tied to railway tracks. A motor vehicle can, for example, be selected from the group of passenger cars (PCs), lorries (HGVs), mopeds, light motor vehicles, motorcycles, buses (KOM) or tractors.

Advantageous embodiments of the invention are specified in the dependent claims. The features listed individually in the dependent claims can be combined with one another in a technologically meaningful manner and can define further embodiments of the invention. In addition, the features specified in the claims are specified and explained in more detail in the description, with further preferred embodiments of the invention being presented.

According to an advantageous embodiment of the invention, the brake system can have a brake cooling circuit to dissipate heat from the brake. The advantage of this embodiment is that the heat generated by the frictional energy of the brake can be dissipated and made available, for example, to a thermal management system of a motor vehicle. Furthermore, cooling the brake can increase its braking performance and, in particular, reduce so-called thermal fading, i.e. a loss of braking force due to heat.

In the context of this invention, the term thermal management refers to the needs-based and efficient control of thermal energy flows in a particularly battery-operated, electrically driven motor vehicle according to the prevailing operating or load condition.

The thermal management system of the motor vehicle can comprise a hydraulic control system. A hydraulic control system directs the volume flows within a thermal management system of a motor vehicle by means of switching elements that act hydraulically on a fluid, such as valves, slides, pumps and the like. For this purpose, the hydraulic control system can, for example, completely or partially throttle a volume flow and/or distribute it to the relevant heat sources and sinks in sub-circuits of the thermal management system of a motor vehicle. For this purpose, the hydraulic switching elements are controlled and switched by the electronic control unit.

A hydraulic switching element can be a hydraulic pump, a switching valve, a controllable throttle valve and the like. A hydraulic switching element can preferably be controlled electrically. Furthermore, a hydraulic switching element preferably has at least two different, switchable operating states in which the hydraulic switching element acts in different ways on the corresponding fluid in a circuit.

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

According to an advantageous embodiment of the invention, it can be provided that the electric machine has an engine cooling circuit for dissipating or supplying heat from or to the electric machine, wherein the hydraulic control unit acts on the engine cooling circuit by means of at least one hydraulic switching element to influence the volume flows in the engine cooling circuit.

According to an advantageous embodiment of the invention, it can be provided that the thermal management system further comprises an inverter with an inverter cooling circuit for dissipating or supplying heat from or to the inverter, wherein the hydraulic control unit acts on the inverter cooling circuit by means of at least one hydraulic switching element in order to influence the volume flows in the inverter cooling circuit.

According to an advantageous embodiment of the invention, it can be provided that the vehicle battery has a battery cooling circuit for dissipating or supplying heat from or 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 volume flows in the battery cooling circuit.

According to a further preferred development of the invention, it can also be provided that the brake has an axially movable brake caliper, which can be brought into frictional engagement with the axially fixed brake disc by the brake actuator, which can bring about installation space advantages for given installation space situations.

Furthermore, according to the invention, it is provided that the brake actuator has a radially displaceable actuating means which interacts with the axially movable brake caliper in such a way that a radial offset of the actuating means causes an axial offset of the brake caliper, so that the brake caliper can be brought into frictional engagement with the brake disk. The advantageous effect of this design is based on the fact that it enables particularly compact axial brake systems to be implemented.

According to a further particularly preferred embodiment of the invention, it can be provided that the radially displaceable actuating means has a first ramp section which, in the event of a radial offset of the actuating means, runs against a corresponding second ramp section formed on the brake caliper, so that a radial offset of the actuating means via the ramp sections causes an axial offset of the brake caliper, thereby enabling a structurally simple and operationally reliable implementation of a radial into an axial actuation movement.

Furthermore, the invention can also be further developed in such a way that the radially displaceable actuating means is mounted so as to be axially displaceable, so that the brake disc can in particular also be contacted axially by the actuating means and subjected to friction.

In a likewise preferred embodiment variant of the invention, it can also be provided that the actuating means can be displaced from radially inside to outside or from radially outside to radially inside in order to produce a frictional connection. This makes it possible to provide an optimized arrangement in accordance with the given installation space conditions.

It may also be advantageous to further develop the invention in such a way that at least one cooling channel that can be connected to the brake cooling circuit is formed in or on the brake caliper. The advantage that can be achieved in this way is that the frictional heat generated can be dissipated from a non-rotating component of the brake. Since the brake caliper usually does not have a lot of mass, a hydraulic fluid in the cooling channels can be heated up quite quickly, so that such a system usually has good thermal dynamics.

According to a further preferred embodiment of the subject matter of the invention, it can be provided that a friction lining is fixed to at least one side, preferably both sides, of the end faces of the brake disc, which can be subjected to a friction torque by the brake caliper and/or the actuating means, and/or at least one friction lining is fixed to the brake caliper and/or the actuating means, which can be brought into frictional contact with one of the end faces of the brake disc. This can in particular improve the applied friction torques.

Finally, the invention can also be advantageously implemented such that the brake actuator is an electro-mechanical or an electro-hydraulic brake actuator.

Finally, the invention can also be advantageously designed such that the brake is configured as a dry-running brake. It is therefore preferred that the brake system is designed as a "dry" brake system that has cooling channels or cooling hoses in one of the brake components - preferably in the non-rotating one. A coolant, for example a water-glycol mixture or a cooling oil, is transported through these to the thermal management system of the motor vehicle. Compared to a "wet" (multi-disk) brake system, a "dry" brake system has the advantage that it generates significantly fewer losses when not actuated and the coefficient of friction and thus the braking torque is more constant.

The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

• 1 einen Achsantriebsstrang mit einem Bremssystem in einer schematischen Axialschnittansicht,
• 2 eine Bremse in einer schematischen Axialschnittdarstellung,
• 3 ein Bremssystem eines Kraftfahrzeugs in einer schematischen Blockschaltdarstellung.

It shows:

• 1 an axle drive train with a braking system in a schematic axial sectional view,
• 2 a brake in a schematic axial section,
• 3 a braking system of a motor vehicle in a schematic block diagram.

The 1 shows a braking system 1 of a motor vehicle 3 that can be driven electrically by means of an electric machine 2, as is also shown by way of example in the 3 The braking system 1 has in the embodiment of the 3 furthermore, a service brake system 27 for wheel-selective braking torque application to the vehicle wheels 24 of the first vehicle axle and the second vehicle axle.

The braking system 1 also has a brake 4 with a brake disk 5, which can be subjected to a friction torque by means of a brake actuator 7. The electric machine 2 accommodated in the motor housing 21 has a rotor 8, which can be coupled to the brake 4 and to at least one vehicle wheel 24 in a torque-transmitting manner. For this purpose, the rotor shaft 17 is connected to the brake shaft 23 in a rotationally fixed manner.

It is clear from the 1 furthermore, that the brake 4 comprises a brake cooling circuit 10, by means of which heat can be dissipated from the brake 4 and fed to a thermal management system of the motor vehicle 3 via the heat exchanger 22.

The electric machine 2, the brake 4 and the transmission 19 form a structural unit, which is also referred to as the axle drive train 20. In order to enable the motor vehicle to coast, for example, the separating clutch 18 is arranged between the vehicle wheel 24 and the electric machine 2. It can be seen from the 1 good that closing the brake 4 immediately applies a deceleration torque to the rotor 8 of the electric machine 2 and also to the vehicle wheel 24. The brake 4 is in a brake housing 9 on which forms a structural unit with the electrical machine 2.

In this configuration, three different deceleration moments can act on one or more of the vehicle wheels 24: the deceleration moment generated by the brake 4, the deceleration moment generated by the electric machine 2 and/or the deceleration moment generated by the service brake system 27. Depending on the driving situation and deceleration requirement, these three available deceleration moments can be combined with one another and applied in a controlled manner.

The 2 it can be seen that the brake 4 has an axially movable brake calliper 11, which can be brought into frictional engagement with the axially fixed brake disk 5 by the brake actuator 7. The axial displaceability is indicated by the corresponding dashed arrow. The brake actuator 7 also has a radially displaceable actuating means 12, which interacts with the axially movable brake calliper 11 in such a way that a radial offset of the actuating means 12 causes an axial offset of the brake calliper 11, so that the brake calliper 11 can be brought into frictional engagement with the brake disk 5. Here too, the radial movement of the actuating means 12 is indicated by a dashed arrow.

The radially displaceable actuating means 12 has a first ramp section 13 which, when the actuating means 12 is radially displaced, runs against a corresponding second ramp section 14 formed on the brake caliper 11, so that a radial displacement of the actuating means 12 via the ramp sections 13, 14 causes an axial displacement of the brake caliper 11. The radially displaceable actuating means 12 is also mounted so as to be axially displaceable.

The actuating means 12 is in the embodiment shown of the 3 Can be moved radially from the inside to the outside to create a frictional connection.

At least one cooling channel 15 that can be connected to the brake cooling circuit 10 is formed in or on the brake caliper 11. To connect the cooling channel 15, a channel section 26 that is flexible in the axial direction can be used, which can compensate for the axial offset of the brake caliper 11 relative to the brake housing 9.

A friction lining 16 is fixed on both sides of the front surfaces of the brake disc 5, which can be subjected to a friction torque by the brake caliper 11 and/or the actuating means 12.

The embodiment shown is essentially a disk brake with a floating brake calliper 11, which is actuated radially against an inclined, additional ramp section 13, 14. In the vicinity of these ramp sections 13, 14 and the friction surfaces to the brake calliper 11 runs the cooling channel 15, through which a cooling liquid can flow and which is hydraulically connected to the brake cooling circuit 10.

The brake calliper is mounted so as to be axially displaceable via a plurality of guide pins 25. This bearing is part of the indicated brake housing 9 or is firmly connected to the brake housing 9.

Deviating from the 3 In the embodiment shown, it would also be conceivable for the actuating means 12 to be displaceable from radially outside to inside. This requires a passage through the brake calliper 11. It is also conceivable to reverse the ramp sections 13, 14 so that the brake actuator 7 does not press the wedge-shaped actuating means 12 against the ramp section 14 of the brake calliper 11, but rather pulls it.

The invention is not limited to the embodiments shown in the figures. The above description is therefore not to be regarded as restrictive, but as explanatory. The following patent claims are to be understood in such a way that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the patent claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a ranking.

List of reference symbols

1

Braking system

2

electric machine

3

Motor vehicle

4

brake

5

Brake disc

7

Brake actuator

8th

rotor

9

Brake housing

10

Brake cooling circuit

11

Brake caliper

12

Actuating means

13

Ramp section

14

Ramp section

15

Cooling channel

16

Friction lining

17

Rotor shaft

18

Separating clutch

19

transmission

20

Axle drive train

21

Engine housing

22

Heat exchanger

23

Brake shaft

24

Vehicle wheel

25

Guide pin

26

Canal section

27

Service brake system

Claims (8)

Brake system (1) of a motor vehicle (3) that can be electrically driven by means of an electric machine (2), wherein the brake system (1) comprises a brake (4) with a brake disk (5) that can be subjected to a frictional torque by means of a brake actuator (7), and the electric machine (2) has a rotor (8) that is coupled to at least one vehicle wheel (24) of the motor vehicle (3) in a torque-transmitting manner, wherein the brake (4) is accommodated in a brake housing (9) and the brake disk (5) is connected to the rotor (8) of the electric machine (2) in a torque-transmitting manner, wherein the brake (4) has an axially movable brake caliper (11) that can be brought into frictional engagement with the axially fixed brake disk (5) by the brake actuator (7) , characterized in that the brake actuator (7) has a radially movable actuating means (12) that interacts with the axially movable brake caliper (11) in such a way that a radial offset of the Actuating means (12) causes an axial offset of the brake calliper (11) so that the brake calliper (11) can be brought into frictional engagement with the brake disc (5). Braking system (1) according to Claim 1 , characterized in that the braking system (1) has a brake cooling circuit (10) for dissipating heat from the brake (4). Brake system (1) according to one of the preceding claims, characterized in that the radially displaceable actuating means (12) has a first ramp section (13) which, in the event of a radial offset of the actuating means (12), runs against a corresponding second ramp section (14) formed on the brake calliper (11), so that a radial offset of the actuating means (12) via the ramp sections (13, 14) causes an axial offset of the brake calliper (11). Braking system (1) according to one of the preceding claims, characterized in that the radially displaceable actuating means (12) is mounted axially displaceably. Braking system (1) according to one of the preceding claims, characterized in that the actuating means (12) can be displaced from radially inside to outside or from radially outside to radially inside in order to produce a frictional connection. Braking system (1) according to one of the preceding claims, characterized in that at least one cooling channel (15) connectable to the brake cooling circuit (10) is formed in or on the brake calliper (11). Brake system (1) according to one of the preceding claims, characterized in that at least one friction lining (16) is fixed to the end faces of the brake disc (5) on one side, preferably on both sides, which friction lining can be subjected to a frictional moment by the brake caliper (11) and/or the actuating means (12), and/or at least one friction lining (16) is fixed to the brake caliper (11) and/or the actuating means (12), which friction lining can be brought into frictional contact with one of the end faces of the brake disc (5). Braking system (1) according to one of the preceding claims, characterized in that the brake actuator (7) is an electro-mechanical or an electro-hydraulic brake actuator (7).

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