Service brake system in electrically driven vehicle having coupled cooling circuit of drive and brake

Abstract

The invention relates to a service brake system for a vehicle having at least one electric drive shaft (1), said service brake system having an independently controllable service brake device (6) for each wheel (5) for the drive shaft (1). The aim of the invention is to find an alternative solution for improving the reliable actuation of the service brake system for electric and hybrid vehicles in that each controllable service brake device (6) is designed as a multi-plate wet brake and has a hydraulic actuator (10), the invention relates to a hydraulic actuator for a controllable brake actuation by means of a pressure oil brake system (9). The pressure oil brake system (9) preferably comprises an electric pump for generating pressure and controlling brake power.

Description

Technical Field

[0001] The invention relates to a service brake system in a vehicle having at least one electrically driven axle, wherein the service brake system has an independently controllable brake device for each wheel, and the service brake system is particularly used for motor vehicles, such as passenger vehicles (Pkw), trucks, etc.

[0002] The field of application of the invention is in particular the automotive industry in the field of electric vehicles or hybrid vehicles, preferably for increasing the efficiency of the main operating components of electric vehicles. Background Art

[0003] Currently, the state of the art in service brake systems for passenger vehicles (Pkw) is - regardless of the drive concept (electric drive, hybrid drive or combustion drive) - an air-cooled disc brake close to the wheel is provided for each wheel. This has been the dominant type of service brake for electric vehicles as well, which operates independently of the drive concept. Disadvantages of such service brake systems are air cooling, particulate load, maintenance costs, influence on vehicle geometry, drag losses, etc.

[0004] For electric vehicles or hybrid vehicles, which are also often referred to as BEV-Battery Electric Vehicle or (P)HEV-(Plug-In) Hybrid Electric Vehicle, air cooling of disc brakes has undesirable side effects such as wear and dust emissions caused by friction, high maintenance requirements caused by friction and weather, and restrictions on vehicle design due to the necessary ventilation ducts. These are very important issues for the environmental friendliness pursued by electric vehicles (Pkw).

[0005] In addition, for disc brakes, drag losses need to be improved, which describe the delay in the action from the open state to the closed state of the brake pad or brake lining caused by primary influencing variables such as the medium in the air gap (gap), lining width, number and diameter of friction surfaces and secondary influences such as lining surface area and friction lining use. Therefore, the clearance (the distance between the brake pad and the brake disc in a disc brake system) is particularly important, because the distance between the brake lining and the brake disc is necessary for the (unbraked) rotation of the brake disc, but on the other hand, when braking, the clearance leads to a longer braking distance.

[0006] Furthermore, BEVs and HEVs / PHEVs should primarily improve the performance and range of the electric drive by better linking the service brake system with the drive system using energy recovery (regenerative braking) in order to charge the energy storage device (battery) or convert excess heat from the drive and brake systems or use it for other purposes.

[0007] Although nowadays it is mainly due to additional functions such as ESP (elektronisches -Programm, electronic stability program), ASR (Antischlupfregelung, anti-skid control), ABS (Antiblockiersystem, anti-lock braking system), etc. The service brakes in traditional PKW are no longer controlled electronically through the brake pedal with the help of mechanical connection. However, even for pure electric vehicles (BEV), the service brake system is still strictly separated from the electric drive system, and a peripheral brake device (air-cooled disc brakes at the vehicle wheels) is provided as an emergency brake.

[0008] The new approach away from this air-cooled dry disc approach is to move towards wet brakes close to the transmission, thereby eliminating, among other things, the dust load and the air cooling channels. However, since electric vehicles do not require hydraulic systems and hydraulic systems do not fit into the concept of clean electric vehicles, electromechanical actuation mechanisms are always preferred over additional hydraulic systems for operating wet brakes for reasons of easier laying of electrical control lines, overall installation space and overall weight, and cost.

[0009] However, for example, electromechanical actuation may be problematic due to the absolute failure reliability of the service brake, since additional battery control elements and / or redundant battery partitions must be installed for this purpose. In addition, electromechanical actuation also brings increased wear potential and maintenance workload. Summary of the invention

[0010] The object of the present invention is to find an alternative feasible solution for improving the reliable operation of the service brake system of an electric vehicle or a hybrid vehicle, which improves the reliability of operation and ease of maintainability of the service brake system while maintaining the sustainability brought by the wet brake solution and the advantages of the electric drive solution.

[0011] For a service brake system in a vehicle with at least one electrically driven axle, wherein the service brake system has an independently controllable service brake device for each wheel on the driven axle, this object is achieved in that the controllable service brake device is designed as an oil sump-based multi-disc wet brake and has a hydraulic actuator, which is used for controllable brake actuation by means of a pressurized oil brake system.

[0012] The hydraulic brake system advantageously comprises one or more electric pumps for generating pressure and controlling the braking power as a function of the brake pedal position.

[0013] The hydraulic actuator for the controllable actuation of the service brake device can additionally be designed to lock the parking brake in a form-fitting manner.

[0014] The service brake device is expediently designed as a fluid-cooled multi-disk wet brake which is connected to a cooling device in a cooling circuit.

[0015] In a preferred embodiment, each service brake device has a cooling device, which is connected to the cooling device of the drive unit via a common heat exchanger system, wherein the heat exchanger system is configured for intelligent thermal management of the drive unit and the service brake device and for controlling the thermal balance of the vehicle's heating system or cooling system.

[0016] The heat exchanger system can advantageously be connected to a mechanism for cross-system control of regenerative braking of the drive unit, brake control of the service brake device, a fluid-cooled service brake device and a thermal coupling of the drive unit, so as to execute the thermal operating point of the mobile drive unit via the heat exchanger system based on the increased heat production caused by the coupled control of the service brake device and the simultaneous increase in the power of the drive unit.

[0017] In this case, the hydraulic brake system appropriately controls the partial actuation of the service brake until the thermal operating point of the drive unit is shifted into a desired low-wear operating range by the waste heat generated in the service brake and the drive unit.

[0018] Advantageously, when the thermal operating point of the drive unit reaches the low-wear operating area, the pressure oil brake system continues to appropriately control the partial actuation of the service brake device and the heat exchanger system begins to transport the waste heat generated in the drive unit and the brake device for heating purposes and temperature adjustment purposes in the vehicle.

[0019] Suitably, the heat exchanger system can activate a mechanism for cross-system control of the regenerative braking and service brake devices to access at least one of the following factors: battery charge state, target temperature / actual temperature of the energy storage device, drive unit or vehicle interior, ambient temperature, overall condition of the service brake device, target braking power / actual braking power, driving speed, driving characteristics to date and route information.

[0020] The object is also achieved by a vehicle having at least one electrically driven axle, which comprises a service brake system according to one of the preceding embodiments.

[0021] The invention is based on the recognition that in modern motor vehicles with any drive technology, the service brake system already meets the basic requirements of further integrating the service brake system into the electric drive system and improving its sustainability with respect to wet brake concepts due to integrated safety functions such as electronic stability program (ESP), drive slip control (ASR), anti-lock braking system (ABS), etc. However, maintenance convenience and reliability in the event of an electrical accident must also be taken into account.

[0022] The object of the present invention is therefore to significantly reduce the wear and maintenance costs in the existing oil cooling circuit of the drive unit, in particular for a Pkw with so-called electric axles and a brake device designed as a wet brake, and to replace the hitherto preferred electromechanical actuation of the service brake device with an alternative actuation by means of a pressure hydraulic system. Such hydraulic actuation of the brake device is not conceivable for electric axles that are conventionally equipped with an oil circuit operating at low pressure, because the oil circuit of the brake device and / or the oil circuit of the heat exchanger of the drive assembly cannot be easily used together for hydraulic brake actuation of the wet brake. For reasons of installation space, weight and cost, replacing the electromechanical actuation of the wet brake by hydraulic pressure actuation in order to increase the reliability and ease of maintenance of the brake actuation has been explicitly rejected to date. However, if the pressure oil circuit can be operated by means of a small, high-performance electric pump or the pressure oil system is used, for example, for an automatic transmission, the pressure oil circuit required for the hydraulic actuation is considered a possible alternative. Pressure oil hydraulic actuation also offers proven advantages for electric vehicles in terms of ease of maintenance and better resistance to electrical failures of the service brake. Since electric vehicles cannot be operated without an oil circuit, actuating the service brakes with a pressurized oil hydraulic system is still the recommended alternative, especially if other oil pressure-controlled components (such as servo steering or similar components) can be used to create synergies.

[0023] The functional connection of the wet-running service brake to the drive unit offers the following advantages overall:

[0024] - the closed wet brake housing and the possible integration into the drive housing avoids particulate emissions and enables a low-wear, maintenance-free actuator ("lifetime brake"),

[0025] - the friction lining is designed as a ring, which improves the dimensioning of the service brake, so that the brake size can be easily scaled as required depending on the vehicle weight and the drive assembly,

[0026] - Design of wet brakes in an efficiency-optimized manner through rotationally symmetrical friction linings (coaxial brakes), release springs, etc.,

[0027] - Active cooling of the service brakes via the oil cooling circuit of the drive unit,

[0028] - Integration of the control / regulation of the service brake system into the existing controller of the drive system (system integration, e.g. central electronic controller), better adjustability of the wet brake and direct combination with the regenerative torque of the drive system,

[0029] - Intelligent thermal management of the drive system and service brake system via a common heat exchanger,

[0030] -Electrical control of the service brakes by utilizing the proven advantages of hydraulic pressure cylinders in a pressure oil circuit with a small, high-performance electric pump.

[0031] In addition to the direct use of the electrohydraulically actuated service brake to expand the brake control of the regenerative brake with emergency braking procedures, the coordinated control or regulation of the oil circuit via a common heat exchanger system is also of great importance, whereby other measures can also be monitored and controlled across the system, such as the common thermal management of the drive unit and service brake system, as well as the temperature control of the battery (accumulator) pack and the interior of the electric vehicle (Pkw).

[0032] The unified control of the common heat balance produces a special effect for the entire electric axle consisting of the drive unit with wet brakes.

[0033] Due to the control possibilities provided by the centralized heat exchanger system, as a result of the integration of the cooling circuits of the service brake system and the drive unit, the control module responsible for the switch between engine operation and generator operation (regeneration) of the drive unit can additionally be used for new thermal management functions. Synergy means that the operating state of the drive system (including the battery system) can be adjusted so that when starting the vehicle in winter or on long journeys without significant high terrain, a low-wear, temperature-controlled operating range of the electric axle is reached, which would not be reached without the synergy effect. Thus, when the load on the drive unit is low and / or when the outside temperature is low, the load on the drive unit can be increased by means of a defined operation of the service brake system to raise the too low operating point of the drive system, so that additional heat is generated in both the drive system and the service brake system, so that a faster shift of the operating point is achieved, especially when starting from a cold start.

[0034] In this interaction, the electrohydraulic actuation of the service brake system also enables low-wear actuation of the service brake device and a more reliable functioning of the service brake device.

[0035] The present invention provides an alternative approach to improving the reliable actuation of a service brake system for an electric vehicle or hybrid vehicle, which increases the reliability of actuation and ease of maintenance of the service brake system by means of a wet brake approach in a coordinated thermal and control coupling with the electric drive system while maintaining sustainability. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be explained in more detail below according to embodiments. As shown in the figure:

[0037] Figure 1 : Schematic diagram of a drive axle of an electrically driven motor vehicle with a wet service brake unit and a hydraulically actuated actuator,

[0038] Figure 2 : The operating state of a hydraulically operated actuator regarding the brake pressure at the hydraulic piston and the braking effect, taking the left-hand driving brake unit as an example. DETAILED DESCRIPTION

[0039] Figure 1 The schematic structure of a drive shaft 1 of an electric vehicle (BEV, HEV or PHEV) is shown, which includes a drive unit 2 (hereinafter also referred to as an electric machine 2), which generates torque, which is transmitted to the drive shaft with drive wheels 5 via a transmission stage 4 and then via a differential 3. The electric machine 2 can include one or more electric motors, which can be presented as a separate drive or work as part of a hybrid drive. The electric machine 2 includes all necessary electronic devices for its control and operation as well as necessary or optional sensor mechanisms.

[0040] A service brake device 6 is arranged on the drive shaft 1 on both sides of the differential 3 , which is designed as a wet-running multi-plate brake and can decelerate the electric vehicle by generating a braking torque.

[0041] A braking system with the same structure is respectively provided in the two service brake devices 6, which consists of a multi-plate wet brake, an electro-hydraulic actuator 10 and a return spring 8. For the left brake BL, the return spring places the corresponding actuator 10 in the left zero position NL, and for the right brake BR, the return spring places the corresponding actuator in the right zero position NR.

[0042] As a specific embodiment of the service brake device 6, a multi-disc wet brake is used, which is characterized in that it is a full-disc brake in which the entire brake disc surface is used as a friction surface for deceleration and runs completely in the oil groove. In this case, in the oil groove, a plurality of inner and outer plates are pressed axially against each other, thereby generating the required braking friction. By changing the number and size of the plates, an optimal option is provided for designing the size of the brake according to the vehicle weight and the drive unit 2, etc., and applying a modular system.

[0043] In the case of the two service brake devices 6 which are equipped with multi-disk wet brakes, the braking effect is produced by a braking action caused by hydraulic actuators 10 , wherein the actuators 10 are electrohydraulically controlled by a pressure oil system 9 .

[0044] exist Figure 2 The two figures show the force action at the actuator 10 and the braking effect of the service brake device 6 qualitatively and schematically using a curve that changes over time, taking the left brake as an example, and show a good conversion from the force increase at the piston of the actuator to the braking effect on the drive shaft 1 or the wheel 5.

[0045] The embodiment of a wet, low-wear, maintenance-free multi-disc brake (Life-Time-Bremse) also offers the following advantages, such as reduced influence of the brake on the driving characteristics due to the coaxial brake (rotationally symmetrical friction linings), optimization of efficiency by arranging the release spring and adjusting its size as well as the type, number and diameter of the friction linings, elimination of environmental influences (such as water, dirt, salt, etc.) on the braking characteristics, and avoidance of damage due to long periods of non-use This often happens with dry disc brakes.

[0046] In addition to the improved adjustment capability of the service brake device 6 due to the wet brake, the control of the service brake device 6 cooperating with the drive unit 2 can also be improved, in particular due to the short adjustment path and the low susceptibility to interference of the hydraulic pressure oil actuation of the service brake device 6.

[0047] Furthermore, it is particularly advantageous when the brake is designed as a wet brake that the friction heat is removed by the volume flow of the coolant. The waste heat can therefore also be particularly advantageously conveyed via the heat exchanger system 7 to a further location in the vehicle (not shown), where it can be used, for example, to heat the interior, to adjust the temperature of the battery pack, etc., or released to the environment.

[0048] like Figure 1 As shown by the middle dashed line, it is advantageous to use the same cooling medium as that used for the drive unit 2 when dissipating the braking energy converted into heat.

[0049] In this supplementary embodiment of the drive shaft 1 , a unification of the drive cooling and the brake cooling is achieved by means of a common heat exchanger system 7 , which provides for an optimized thermal management.

[0050] The common heat balance via the heat exchanger system 7 provides strategic energy recovery. A wet-running service brake system with service brake device 6 provides the possibility of using the braking energy to heat the cooling / lubricating medium (e.g. oil) of the common heat balance instead of simply releasing this energy into the environment. The heat energy thus obtained is used for the main heat balance (heat exchanger system 7) or optionally for a peripheral heat balance (e.g. battery cell heating or interior heating).

[0051] Furthermore, the problem of a very mild, uneven heating characteristic of the electric drive unit 2 including the vehicle cooling circuit of the heat exchanger system 7 is solved by the fact that it is now possible to move the operating point of the electric drive unit 2 and at the same time return heat energy to the vehicle system (components and cooling circuit) via the thermal coupling of the cooling device 71 of the electric drive unit 2 with the service brake device 6.

[0052] The advantageous function of the thermal coupling of the drive unit 2 and the service brake device 6 is achieved in the following manner, that is, when the load on the drive unit 2 is low and / or the external temperature is low, the service brake device 6 is operated in a defined manner while the driving speed of the Pkw is kept constant (for example, the speed is controlled) to increase the load on the drive unit 2, thereby raising the too low operating point of the drive unit 2, so that additional heat is generated in both the drive unit 2 and the service brake device, which heats the drive unit 2 to the desired operating temperature in the low-wear operating range, and continues to maintain this forced increased load state when there is an additional heating demand for the battery pack and / or the interior of the Pkw. The operating mode defined in this way accelerates the movement of the operating point when the electric drive axle 1 is cold started in winter, especially by means of cross-system controlled thermal management and the advantageous thermal coupling of the drive unit 2 and the service brake device 6. This heating method can also be used for long-distance travel on flat routes in cold weather to ensure an optimal, low-wear operating state or for vehicle heating.

[0053] By using the above-mentioned embodiment of the present invention, the principle of using dry brakes as service brake systems is further broken away from by using a wet-running brake in the form of a wet multi-disc brake as a service brake unit 6, which is actuated by a hydraulic actuator 10 with the aid of an electro-hydraulic controlled pressure oil brake system 9. By using the oil tank of each service brake unit 6, its cooling device 71 can be further combined into a common heat exchanger system 7 so as to cooperate with the cooling device 71 of the drive unit 2, thereby generating a synergistic effect between the service brake unit 6 of the electric axle 1 according to the present invention and the drive unit 2 and the heat exchanger 7 and generating optimized thermal management.

[0054] List of reference numerals:

[0055] 1 drive shaft (electric shaft)

[0056] 2 drive unit (motor)

[0057] 3 Differential

[0058] 4 speed levels

[0059] 5. Wheels

[0060] 6. Service brake system (multi-disc wet brake)

[0061] 7 Heat exchanger system

[0062] 71 Cooling device

[0063] 8 Return spring

[0064] 9. Pressure oil brake system (pressure oil hydraulic system)

[0065] 10 (Hydraulic) actuator.

Claims

1. A service brake system in a vehicle having at least one electrically driven axle (1), wherein: The service brake system has an independently controllable service brake device (6) for each wheel (5) on the drive shaft (1), characterized in that the controllable service brake device (6) is constructed as a multi-disc wet brake based on an oil tank and has a hydraulic actuator (10), which is used to perform controllable braking operation with the help of a pressure oil brake system (9).

2. The service brake system according to claim 1, characterized in that: The pressure oil brake system (9) includes an electric pump for generating pressure and controlling the braking power according to the position of the brake pedal.

3. The service brake system according to claim 1, characterized in that: The hydraulic actuator (10) is designed to actuate the service brake device (6) in a controllable manner in addition to positively locking the parking brake.

4. The service brake system according to claim 1, characterized in that: The service brake device (6) is constructed as a fluid-cooled multi-plate wet brake.

5. The service brake system according to claim 1, characterized in that: Each service brake device (6) has a cooling device (71), which is connected to the cooling device (71) of the drive unit (2) via a common heat exchanger system (7), wherein the heat exchanger system (7) is configured for intelligent thermal management of the drive unit (2), the service brake device (6) and for controlling the thermal balance of a heating system or a cooling system of the vehicle.

6. The service brake system according to claim 5, characterized in that: The heat exchanger system (7) is connected to a mechanism for cross-system control of the regenerative braking of the drive unit (2), the brake control of the service brake device (6), the fluid-cooled service brake device (6) and the thermal coupling of the drive unit (2), so as to execute the shifting of the thermal operating point of the drive unit (2) via the heat exchanger system (7) based on the increased heat generation by the coordinated operation of the service brake device (6) and the simultaneous increase of the power of the drive unit (2).

7. The service brake system according to claim 6, characterized in that: The pressure oil brake system (9) appropriately controls the partial actuation of the service brake device (6) until the thermal operating point of the drive unit (2) is moved into a desired low-wear operating range by the waste heat generated in the service brake device (6) and the drive unit (2).

8. The service brake system according to claim 6, characterized in that: When the thermal operating point of the drive unit (2) reaches the low-wear operating area, the pressure oil brake system (9) continues to appropriately control the partial actuation of the service brake device (6), and the heat exchanger system (7) begins to transport the waste heat generated in the drive unit (2) and the service brake device (6) for heating purposes and temperature adjustment purposes in the vehicle.

9. The service brake system according to claim 8, characterized in that: The heat exchanger system (7) activates a mechanism for cross-system control of regenerative braking and the service brake device (6) to access at least one of the following factors: battery charge state, target temperature / actual temperature of the energy storage device, the drive unit (2) or the vehicle interior, ambient temperature, overall condition of the service brake device (6), target braking power / actual braking power, driving speed, driving characteristics to date and route information.

10. Vehicle having at least one electrically driven axle (1), the vehicle comprising a service brake system according to any of the preceding claims.

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