Electric drive system with integrated brake unit including service brakes and parking brake function

Abstract

Electric drive system (100) with at least one electric machine (EM) and with a wet-running brake unit (52) integrated into an electric drive, with multi-disc brakes (44) on the axle side shafts (48) of the driven axle, which can be activated via electrical or hydraulic actuators, characterized in that the brake unit (52) comprises at least components for forming a service brake as well as components for forming a parking brake.

Description

[0001] The invention relates to an electric drive system with at least one electric machine comprising at least one transmission, and with a wet-running brake unit integrated in an electric drive with multi-disk brakes on the axle side shafts of the driven axle, which can be activated via electric or hydraulic actuations. State of the art

[0002] The current state of the art for service braking systems on vehicles, regardless of the drive concept (electric, hybrid, or combustion engine), is a close-coupled, air-cooled disc brake for each wheel. This remains the predominant type of service brake for electric vehicles, operating independently of the drive concept. Disadvantages of this service braking system include air cooling, particulate matter pollution, maintenance requirements, impact on vehicle geometry, drag losses, etc.

[0003] In a disc brake, drag losses, which describe the delay in action from the open to the closed state of the brake pad or disc, require improvement due to primary influencing factors such as the fluid in the air gap, pad width, number and diameter of the friction surfaces, and secondary influences such as pad surface and friction lining wear. The air gap is particularly important because a gap between the brake pad and the brake disc is essential for the unbraked rotation of the brake disc. On the other hand, the air gap leads to an increase in braking distance when the brakes are applied, which, in a hydraulic braking system, can amount to approximately 0.1 to 0.2 seconds as a brake response time.

[0004] In addition, the performance of electric vehicles is to be increased, particularly by better combining synergy effects between the service brake system and the drive system, utilising energy recovery through recuperation to recharge the energy storage system or to convert excess thermal energy from the drive and braking systems or to use it for heating purposes.

[0005] Although it is now state of the art that a service brake in a vehicle is no longer controlled by means of a mechanical connection but by means of electronically controlled pumps from the brake pedal, primarily due to additional functionalities such as ESP (electronic stability program), ASR (anti-skid control), ABS (anti-lock braking system), etc., the service brake system is still separate from the electric drive system, even for purely electric vehicles, and is connected to the peripheral braking devices (air-cooled disc brakes) on the vehicle's wheels via hydraulic brake circuits.

[0006] DE 10 2021 213 092 A1 discloses an electrically powered vehicle comprising a drive unit, a driven primary axle, and a non-driven secondary axle. The primary axle comprises a primary braking system, and the secondary axle comprises a secondary braking system. The primary braking system comprises at least one wet service brake, and the secondary braking system also comprises at least one wet service brake. The primary braking system and the drive unit share a common oil supply. The primary braking system and the secondary braking system are designed to communicate with a central control unit. This allows for optimal coordination of the primary braking system and the secondary braking system.

[0007] The at least one wet service brake of the secondary braking system forms a brake combination with a parking brake that locks a wheel assigned to it. In this way, the secondary braking system can be expanded to include a parking brake or parking lock.

[0008] The brake combination comprises an actuator which is adjustable between a service braking range, within which it is connected to the at least one wet-running service brake, a locking range in which it is connected to the parking brake, and a neutral range, between the service braking range and the locking range, in which the actuator is connected neither to the at least one wet-running service brake nor to the parking brake.

[0009] DE 10 2022 121 622 A1 shows an electric drive system with a drive arrangement, wherein the drive arrangement comprises an electric drive machine for generating a drive torque, with a friction brake for braking the vehicle, with a braking device for generating a braking torque for the vehicle, wherein the braking device is designed as a complementary brake and / or as a supplementary braking device to the friction brake.

[0010] DE 10 2004 055 960 A1 proposes a parking brake that is integrated into the transmission. The parking brake according to the invention is preferably designed as a multi-disk brake operating in an oil bath.

[0011] The object of the invention is to develop a maintenance-free, wet-running braking system integrated in an electric drive, which, due to its design, meets the power loss requirements required for electric vehicles, is open to existing braking systems with hydraulic control or, in the future, with electrically controlled brakes, and integrates a safety parking brake function as well as a parking lock function. Description of the invention

[0012] The object is achieved with an electric drive system with at least one electric machine and with a wet-running brake unit integrated in an electric drive with multi-disk brakes on the axle side shafts of the driven axle, which can be activated via electric or hydraulic actuations, wherein the brake units comprise at least components for forming a service brake as well as components for forming a parking brake.

[0013] A service brake is defined as the braking function during driving until the vehicle comes to a standstill. The integrated brake unit allows two functions to be implemented in a small space. Electric actuation is necessary for future operation of an electrically controlled brake. Hydraulic actuation can be simplified by integration into the electric drive system.

[0014] In one embodiment, the electric machine may also include a transmission and / or a differential.

[0015] The brake units can be actuated with hydraulic pressure diverted from a pump used in the electric drive system, which serves to cool the electric motor and the brakes. By using a single pump for cooling and to build up pressure for actuating the brake unit, components are eliminated.

[0016] The brake unit comprises a space in which a brake piston and at least one sleeve for the parking brake can be axially displaced against each other and thus form pressure chambers which are pressurised or vented depending on their function as a service brake or parking brake.

[0017] By nesting the components of the different functions within each other, pressure chambers are created that can be selectively controlled via the hydraulic control system.

[0018] A multifunctional sleeve is also axially movable within the installation space, defining an additional pressure chamber between the parking brake sleeve and the preload springs. This multifunctional sleeve represents a structural embodiment of the brake unit.

[0019] The parking brake can be engaged by applying force to a connection of inclined planes on the multifunctional sleeve and the sleeve for the parking brake.

[0020] The sleeve has a space for the parking brake in which a plunger is held by a lock nut and pre-tensioned with a locking spring.

[0021] The sleeve for the parking brake contains a pressure chamber which is pressurized by an inlet parking system.

[0022] The plunger can be moved radially outwards and fixes the brake piston.

[0023] The sleeve for the parking brake forms a structural unit with a parking piston, whereby a plunger from the housing of the brake unit can be inserted into a guide groove.

[0024] The parking piston and the brake piston overlap when the service brake is active.

[0025] The parking brake can only be activated by an energy input, so it does not engage automatically when the brake unit loses pressure. Description of the characters Fig. 1 shows an embodiment of an electric drive system, Fig. 2 shows an alternative embodiment of an electric drive system, Fig. 3 shows a hydraulic circuit diagram for an electric drive system, Fig. 4 shows an alternative embodiment of the hydraulic circuit, Fig. 5 shows another embodiment of the hydraulic circuit, Fig. 6 shows a section through a multi-disk brake with parking brake, Fig. 7-13 show the process of operating a multi-disk brake with parking brake, Fig. 14 shows an alternative embodiment of a multi-disk brake with parking brake, Fig. 15-20 shows the operation of the multi-disk brake after Fig. 14, Fig. 21 shows another alternative embodiment of the multi-disk brake, Fig. 22 and Fig. 23 show a third embodiment of a multi-disk brake, Fig. 24-29 show the operation of the multi-disk brake according to the Fig. 22 and Fig. 23, Fig. 30 shows an embodiment of a brake piston, Fig. 31 shows an embodiment of a parking piston, Fig. 32 shows the locking of the brake piston on the housing, Fig. 33 shows the components after assembly.

[0026] In Fig. 1 schematically shows an electric drive system 100 arranged on an axle of a vehicle. An electric machine EM is controlled by an inverter 40, which in turn is connected to a controller 41. The output of the electric machine EM is connected to a differential 43 via a transmission 42. The differential 43 drives two axle side shafts 48. The two axle side shafts 48 end at the wheels 45. Multi-disk brakes 44 are located on the two axle side shafts. In this exemplary embodiment, the multi-disk brakes 44 are electrically actuated. This is achieved by an electric actuator 46, which applies force to the individual steel plates of the multi-disk brake 44 via a ball ramp 47.

[0027] This embodiment is particularly suitable for use with an electric brake pedal "brake-by-wire." The electric motor EM with its transmission 42 and inverter 40, as well as the differential 43 and the multi-disk brakes 44, and their actuation, form a common assembly 300.

[0028] In the embodiment of the Fig. 2, the electric motor EM is connected to the wheels 45 via the transmission 42 and the differential 43. The multi-disk brakes 44 are actuated by hydraulic actuators 50. The hydraulic connection is established via a brake line 51 to brake components 49, which operate the hydraulic connection with pressure.

[0029] Fig. Figure 3 shows an embodiment of a hydraulic system for assembly 300 and thus also for the multi-disk brake 44, or rather, the brake unit 52, which also includes the multi-disk brake as an assembly. A pump 53, which in this embodiment is designed as a tandem pump, supplies a volume flow for cooling both the electric motor EM and the multi-disk brake 44 via the cooling mode valve V6. At the same time, the pump 53 also supplies the pressure circuit for the multi-disk brakes via the mode switching valve V1.

[0030] The brake units 52 as well as the brake valves V2L and V2R and the parking brake valve V4 are operated via the brake line 51.

[0031] In this embodiment, brake pressure modulation is achieved by applying pressure to a brake piston 1 in the brake unit 52 via the brake valves V2L and V2R, and reducing and emptying via the release valves V3L and V3R. Both valve groups are controlled in a clocked manner and are designed as slide valves.

[0032] The parking brake valve V4 controls and actuates a parking brake, which will be discussed later. The pressure relief valve V5 is a main relief valve.

[0033] In Fig. Figure 4 shows an alternative embodiment of the hydraulic actuation. In this embodiment, the brake valves V2L and V2R are designed as proportional valves. The parking brake valve V4 again serves to control a parking brake.

[0034] In Fig. Figure 5 shows an embodiment designed to overcome an air gap in the multi-disk brake particularly quickly and efficiently. Pressure pistons 55 are used for this purpose. These are controlled via a pressure reduction valve 56a. The multi-disk brake 44 is connected to brake components 49 and a hydraulic accumulator circuit preloaded by mechanical springs in the brake unit 52.

[0035] Fig. 6 shows an arrangement in the brake unit 52 which includes a combination of a service brake, a mechanical parking brake and an additional mechanical safety locking device.

[0036] A housing 13 comprises an output shaft 14 and serves as a receptacle for all the above-mentioned parts of the multi-disk brake 44.

[0037] A friction pack carrier 12 is mounted in the housing 13, rotatably mounted on the output shaft 14, and carries friction plates 9. The friction plates 9 interact with steel plates 10, which are arranged axially displaceably within the housing 13. Wave springs 11 are arranged between the steel plates 10. A brake piston 1 is mounted in direct contact with a first steel plate 10a. The brake piston 1 moves on a stationary inner cover 3, on which a sleeve 5 for a mechanical parking brake is also arranged.

[0038] Furthermore, the stationary inner cover 3 carries a multifunctional sleeve 4 for the parking brake. A mechanical lock 6 and a locking spring 7 are housed within the multifunctional sleeve 4.

[0039] The multifunctional sleeve 4 is in contact with preload springs 8.

[0040] A parking piston 15 is screwed to the secondary piston 2, which is not shown in detail in the figure.

[0041] The spring-loaded parking piston 15 works as an accumulator during braking.

[0042] In parking brake mode, the brake pistons 1 are pressed against the disc pack by the preload spring and the multifunctional sleeve 4 and sleeve 5 for the mechanical parking brake.

[0043] The sleeve 5 for the mechanical parking brake, which is pressureless during normal operation, is pressed against the housing-fixed web 3a by the accumulator pressure and is not in contact with the multifunctional sleeve 4.

[0044] When switching to the parking brake mode, the sleeve 5 for the mechanical parking brake is pressed and, through its stroke to the right, activates the multifunctional sleeve 4 in order to establish the flow of force from the preload springs 8 to the brake piston 1.

[0045] The exact procedure is described in the Fig. 7-13 described. Fig. Figure 7 shows the brake unit 52 or the multi-disk brake 44 in its initial state. The preload springs 8 are relaxed, and the brake piston 1 is also not pressing against the steel plates 10 and the wave springs 11.

[0046] Fig. Figure 8 shows the state of the multi-disk brake 44 while the battery is being charged. For this purpose, oil is poured into the installation space A between the multi-function sleeve 4 and the sleeve 5 for the parking brake via a parking system inlet 18. The multi-function sleeve 4 slides against the preload springs 8 and preloads them.

[0047] The multifunctional sleeve 4 on the secondary piston 2 is arranged radially inward with the locking spring 7 and has no contact with the secondary piston 2. The parking brake valve V4 is pressurized and moves the sleeve 5 for the parking brake to the right until it reaches a stop in the brake piston 1.

[0048] The filling volume for this comes from the accumulator. If the accumulator pressure is not further reduced, the movement stops and further pressure reduction occurs via the release valves V3R, V3L.

[0049] Fig. Figure 9 shows the multi-disk brake 44 in normal braking operation. For this purpose, oil is pressed from chamber A into chamber B. Additionally, the oil from the brake components of the brake circuit presses the brake piston 1 against the steel plates 10.

[0050] Fig. Figure 10 shows the multi-disk brake when the parking brake is activated. For this purpose, the pressure in chamber B is released, and the chamber C between the parking brake sleeve 5 and the housing-fixed web 3a of the housing is pressurized. This causes the parking brake sleeve 5 to slide against the multi-function sleeve 4. The multi-function sleeve 4 runs along the bevels of the sleeve 5 and is pressed radially outward from the axis.

[0051] Fig. 11 shows the multi-disk brake when the parking brake is engaged. The parking brake sleeve 5 engages the multi-function sleeve 4, thereby actuating the mechanical lock 6, preloading the locking spring 7. The preload springs 8 exert a force on the multi-function sleeve 4. This force is transferred via the secondary piston 2 to the brake piston 1. The brake piston 1 presses the steel plates 10 of the multi-disk brake together.

[0052] In Fig. 12 this force connection is indicated by an arrow.

[0053] Fig. Figure 13 shows the state of the multi-disk brake upon reaching the parking position, with no oil pressure applied to brake unit 52. The parking brake is engaged, and the multi-disk brake is closed.

[0054] To release the parking brake, oil must again be introduced into the chamber A in order to move the sleeve 5 for the parking brake away from the multifunctional sleeve 4 and to release it.

[0055] This parking brake function can be problematic because, in order to move sleeve 5, the accumulator must still have some residual charge, or the system pump must be active. At the very least, the parking brake valve V4 must be electrically functioning to move sleeve 5 for the parking brake.

[0056] Applying the parking brake is therefore different from systems and transmissions that engage without hydraulic energy.

[0057] Fig. 14 shows an alternative embodiment of the multi-disk brake 44. In this embodiment, there are no separate sleeves, multifunctional sleeve 4 and sleeve 5 for the parking brake, but a combined embodiment with a sleeve 5a. The sleeve 5a is movably arranged within the installation space of the brake piston 1. The sleeve 5 has a space in which the locking spring 7 is installed around a plunger 16. The plunger 16 is held in the sleeve 5a by a lock nut 17.

[0058] The Fig. 15-20 show the processes when operating the multi-disk brake in this embodiment according to Fig. 14. In Fig. Figure 15 shows the multi-disk brake in its neutral state, ready for actuation. The various chambers A, B, and C of the multi-disk brake are supplied with oil via an inlet 18 for the parking system, a reservoir inlet 19, and a brake inlet 20. In Fig. 16 shows that the space C is pressurized via the inlet reservoir 19 and moves the sleeve 5a against the preload springs 8.

[0059] In Fig. Figure 17 shows how the preloaded arrangement performs an actuation of the multi-disk brake 44. For this purpose, the pressure in chamber C is pressed into chamber B and the brake piston 1 is displaced toward the steel plates 10.

[0060] In Fig. Figure 18 shows how the parking brake is actuated. For this purpose, pressure is applied to space C and space A below the plunger 16 in an annular space of the sleeve 5a. The sleeve 5a moves axially against the preload springs 8, releasing the plunger 16. The plunger 16 is pressed radially outward via the installation space A and the filling via the parking system inlet 18 and the locking springs 7.

[0061] In Fig. Figure 19 shows how the multi-disk brake is secured. To do this, the preload springs 8 are released and exert force on the sleeve 5a and the plunger 16 contained therein. The plunger 16 displaces the brake piston 1 toward the steel plates 10.

[0062] In Fig. 20 is the final state, and chamber A is depressurized via the parking system inlet 18. The preload springs 8 with the plunger 16 and the brake piston 1 tension the disk pack.

[0063] Fig. 21 shows some details by showing the multi-disk brake according to the embodiment of Fig. 14 is improved.

[0064] One example is the simplified brake piston 1, which is shorter than the first embodiment and requires one less seal.

[0065] The seals 56 are limited to a seal against the stationary inner cover 3, the housing 23 and the sleeve 5a.

[0066] Bearing solution 57 includes ball bearings and a radial seal opposite the output shaft 14 to ensure better lubrication. The differential 26 is attached to the multi-disk brake via a special connection point, providing slip contact between the components and a built-in lubrication and cooling oil supply.

[0067] The Fig. 22 and Fig. 23 shows a third embodiment of the multi-disk brake. This uses a special sleeve 5c, which is integrated into the parking piston 15.

[0068] The parking piston 15 has a guide groove 15a. A tappet 16a is installed outside the installation space of the brake piston 1, radially above the parking piston 15, in the housing 23. The tappet 16a is secured in the housing 23 by a lock nut 17 and enclosed by a locking spring 7.

[0069] The parking piston 15 is movable within the installation space of the brake piston 1, wherein the parking piston 15 has a step 15b which can come into contact with a corresponding step 1a of the brake piston 1.

[0070] The Fig. 24-29 show the sequence of operation of the multi-disk brake with the embodiment according to Fig. 22. In the Fig. Figure 24 shows the state of the multi-disk brake in the deactivated state. On the right side of the figures, a top view of the parking piston 15 and the brake piston 1 is visible.

[0071] The parking piston 15 features a guide groove 15a in which the tappet 16a can run. The two pistons, the parking piston 15 and the brake piston 1, are separated from each other, and the tappet 16a is located above the guide groove 15a and does not engage.

[0072] In the Fig. Figure 25 shows the condition in which the accumulator is pressurized. For this purpose, oil is poured into chamber C and the sleeve 5c with the parking piston 15 is pressed against the preload springs 8. The gap between the parking piston 15 and the brake piston 1 is thereby enlarged, and the tappet 16a is no longer located above the guide groove 15a.

[0073] Fig. Figure 26 describes the situation when the normal brake is applied. Then, pressure is applied to chamber B via chamber C, while the preload springs 8 are simultaneously released. This builds up pressure on brake piston 1 and pressurizes the disc pack. The plunger 16a remains positioned above the parking piston 15. The two pistons, the parking piston 15 and the brake piston 1, are now engaged with each other.

[0074] Fig. Figure 27 describes the situation when the parking brake is applied. Based on the situation of Fig. 24, the chamber C is pressurized via the reservoir inlet 19, so that the parking piston 15 is released from the brake piston 1 by axial displacement. At the same time, the plunger 16a is moved radially inward in the housing under pressure and inserted into the guide groove 15a.

[0075] Fig. Figure 28 shows the final locking of the multi-disk brake. The pressure on the sleeve 5c and in the parking piston 15 is reduced via the reservoir inlet 19, so that the parking piston 15 is displaced toward the brake piston 1 with the aid of the preload springs 8. The parking piston 15 exerts a force on the brake piston 1, keeping the multi-disk brake closed.

[0076] Fig. 29 shows the state in which the multi-disk brake system relaxes and becomes pressureless, whereby the pressure is reduced via the reservoir inlet 19 and the brake inlet 20.

[0077] Fig.30-33 show, by way of example, an embodiment for the dimensioning and shape of a brake piston 1 and a parking piston 15 with the guide groove 15a and the step 15b. A further step 15c is suitable for securing the parking piston 15 in the brake housing 58 within radial grooves 58a. Reference symbol 1 brake piston 1a gradation 2 secondary pistons 3 Stationary inner lid 3a housing-fixed bridge 4 multifunctional sleeve 5, 5a, 5c sleeve 6 Mechanical lock 7 locking spring 8 preload springs 9 friction plates 10 steel plates 10a first steel plate 11 wave springs 12 friction pack carriers 13 housings 14 Output shaft 15 parking pistons 15a Guide groove 15b, 15c gradation 16, 16a tappet 17 Lock nut 18 Inlet parking system 19 Reservoir inlet 20 Brake inlet 23 housings 26 Differential 40 inverters EM electric machine 41 controllers 42 gearboxes 43 Differential 44 multi-disk brake 45 wheels 46 Electric actuator 47 Ball ramp 48 axle side shaft 49 brake components 50 hydraulic actuators 51 brake line 52 brake unit 53 Pump 54 pressure switches 55 pressure pistons 56a Pressure reducing valve 56 Seal 57 storage solution 58 brake housing 58a radial groove 100 Electric drive system 300 assembly 400 cooling unit A, B, C room V1 mode switching valve V2L, V2R brake valve V3L, V3R release valve V4 parking brake valve V5 pressure relief valve V6 cooling mode valve

Claims

[1] Electric drive system (100) with at least one electric machine (EM) and with a wet-running brake unit (52) integrated into an electric drive with multi-disk brakes (44) on axle side shafts (48) of a driven axle, which can be activated via electric or hydraulic actuations, characterized by that the brake unit (52) comprises at least components for forming a service brake as well as components for forming a parking brake, wherein the brake unit (52) comprises a construction space in which a brake piston (1) and at least one sleeve (5, 5a, 5c) for the parking brake are axially displaceable relative to one another and thus form pressure chambers (B, C) which are pressurized or vented depending on the function as a service brake or parking brake. [2] Electric drive system (100) according to claim 1 characterized bythat the brake units (52) can be subjected to hydraulic pressure which is branched off from a pump (53) used in the electric drive system, which serves to cool the electric machine (EM) and the multi-disk brakes (44). [3] Electric drive system (100) according to claim 1, characterized by that a multifunctional sleeve (4) is also arranged axially displaceably in the installation space, which delimits a further pressure chamber (A) between the sleeve (5) for the parking brake and preload springs (8). [4] Electric drive system (100) according to claim 1, characterized by that a parking lock can be engaged by force at a connection of inclined planes on the multifunctional sleeve (4) and the sleeve (5) for the parking brake. [5] Electric drive system (100) according to claim 1, characterized bythat the sleeve (5a) for the parking brake has a space in which a tappet (16) is held by a lock nut (17) and installed with a locking spring (7). [6] Electric drive system (100) according to claim 5, characterized by that the sleeve (5a) for the parking brake comprises a pressure chamber (A) which is acted upon by an inlet parking system (18). [7] Electric drive system (100) according to claim 6, characterized by that the plunger (16) can be moved radially outwards and fixes the brake piston (1). [8] Electric drive system (100) according to claim 1, characterized by that the sleeve (5c) for the parking brake forms a structural unit with a parking piston (15), wherein a plunger (16a) from a housing (23) of the brake unit (52) can be immersed into a guide groove (15a). [9] Electric drive system (100) according to claim 8, characterized bythat the parking piston (15) and the brake piston (1) overlap when the service brake is active. [10] Electric drive system (100) according to one of the preceding claims, characterized by that the parking brake can only be activated via an energy input.

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