Electric drive system with integrated brake unit having service brake and parking brake function

Abstract

The invention relates to an electric drive system (100) having at least one electric machine (EM) and having a wet-running brake unit (52) which is integrated into an electric drive and has multi-disc brakes (44) on the axle side shafts (48) of the driven axle, which multi-disc brakes can be activated by means of electric or hydraulic actuations, characterised in that the brake unit (52) comprises at least components for forming a service brake and components for forming a parking brake.

Description

[0001] Electric drive system with integrated brake unit with service brakes and parking brake function

[0002] 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.

[0003] State of the art

[0004] 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.

[0005] 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.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 in order 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.

[0006] 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.

[0007] DE 102021 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] The object of the invention is to develop a maintenance-free, wet-running braking system integrated into 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

[0013] 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.

[0014] The service brake is defined as the braking function during ferry operation until the vehicle comes to a standstill. The integrated brake unit allows two functions to be implemented in a small installation 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.

[0015] In one embodiment, the electric machine may also include a transmission and / or a differential.

[0016] 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.

[0017] The brake unit comprises a space in which a brake piston and at least one sleeve for the parking brake are axially movable relative to each other, thus forming pressure chambers that are pressurized or vented depending on their function as a service brake or parking brake. Nesting the components of the different functions creates pressure chambers 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.

[0026] Description of the characters

[0027] Figure 1 shows an embodiment of an electric drive system, Figure 2 shows an alternative embodiment of an electric

[0028] Drive system, Figure 3 shows a hydraulic circuit diagram for an electric drive system, Figure 4 shows an alternative embodiment of the hydraulic circuit, Figure 5 shows a further embodiment of the hydraulic circuit, Figure 6 shows a section through a multi-disk brake with parking brake, Figures 7-13 show the sequence of actuation of a multi-disk brake with parking brake,

[0029] Figure 14 shows an alternative embodiment of a multi-disk brake with parking brake,

[0030] Figures 15-20 show the operation of the multi-disk brake according to Figure 14,

[0031] Figure 21 shows a further alternative embodiment of the multi-disk brake, Figures 22 and 23 show a third embodiment of a multi-disk brake, Figures 24-29 show the operation of the multi-disk brake according to Figures 22 and 23,

[0032] Figure 30 shows an embodiment of a brake piston,

[0033] Figure 31 shows an embodiment of a parking piston,

[0034] Figure 32 shows the locking of the brake piston on the housing, Figure 33 shows the components after assembly.

[0035] Figure 1 schematically illustrates 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.

[0036] Multi-disk brakes 44 are mounted on the two axle side shafts. In this embodiment, the multi-disk brakes 44 are electrically actuated. This is done by an electric actuator 46, which applies force to the individual steel plates of the multi-disk brake 44 via a ball ramp 47.

[0037] 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.

[0038] In the embodiment shown in Figure 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.

[0039] 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 as an assembly also includes the multi-disk brake. 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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. Figure 5 shows an embodiment that serves 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 in the brake unit 52, preloaded with mechanical springs.

[0044] Figure 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The multifunctional sleeve 4 is in contact with preload springs 8.

[0049] A parking piston 15 is screwed to the secondary piston 2, which is not shown in detail in the figure.

[0050] The spring-loaded parking piston 15 works as an accumulator during braking.

[0051] In parking brake mode, the brake pistons 1 are pressed against the disc pack by the preload spring and the multi-function sleeve 4 and sleeve 5 for the mechanical parking brake. The sleeve 5 for the mechanical parking brake, which is pressureless during normal operation, is pressed against the housing-mounted web 3a by the accumulator pressure and is not in contact with the multi-function sleeve 4.

[0052] 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.

[0053] The exact sequence is described in Figures 7-13. 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Figure 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.

[0060] In Figure 12, this force connection is indicated by an arrow.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] Applying the parking brake is therefore different from systems and transmissions that engage without hydraulic energy.

[0065] Figure 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.

[0066] 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.

[0067] Figures 15-20 show the sequences when the multi-disk brake is actuated in this embodiment according to Figure 14. 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.

[0068] Figure 16 shows that the space C is pressurized via the reservoir inlet 19 and moves the sleeve 5a against the preload springs 8.

[0069] 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.

[0070] Figure 18 shows how the parking brake is applied. 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.

[0071] 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.

[0072] In Figure 20, the final state and chamber A are depressurized via the parking system inlet 18. The preload springs 8 with the plunger 16 and the brake piston 1 tension the disk pack.

[0073] Figure 21 shows some details in which the multi-disk brake is improved according to the embodiment of Figure 14.

[0074] The simplified brake piston 1 should be mentioned, which is shorter than the first embodiment and requires one less seal.

[0075] The seals 56 are limited to a seal against the stationary inner cover 3, the housing 23 and the sleeve 5a.

[0076] 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.

[0077] Figures 22 and 23 show a third embodiment of the multi-disk brake. This uses a special sleeve 5c integrated into the parking piston 15.

[0078] 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.

[0079] 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.

[0080] Figures 24-29 show the sequence of actuation of the multi-disk brake with the embodiment according to Figure 22. 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 can be seen.

[0081] 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.

[0082] Figure 25 shows the state 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 plunger 16a is no longer located above the guide groove 15a.

[0083] Figure 26 depicts 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 the 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.

[0084] Figure 27 depicts the situation when the parking brake is applied. Starting from the situation in Figure 24, chamber C is pressurized via the reservoir inlet 19, causing the parking piston 15 to disengage from the brake piston 1 by axial displacement. At the same time, the tappet 16a is moved radially inward within the housing under pressure and inserted into the guide groove 15a.

[0085] 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.

[0086] Figure 29 shows the state in which the multi-disk brake system relaxes and becomes depressurized, with the pressure being reduced via the reservoir inlet 19 and the brake inlet 20.

[0087] Figures 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.

[0088] Reference symbol

[0089] 1 brake piston

[0090] 1 a gradation

[0091] 2 secondary pistons

[0092] 3 Stationary inner lid

[0093] 3a housing-fixed bridge

[0094] 4 multifunctional sleeve

[0095] 5, 5a, 5c sleeve

[0096] 6 Mechanical lock

[0097] 7 locking spring

[0098] 8 preload springs

[0099] 9 friction plates

[0100] 10 steel plates

[0101] 10a first steel plate

[0102] 11 wave springs

[0103] 12 friction pack carriers

[0104] 13 housings

[0105] 14 Output shaft

[0106] 15 parking pistons

[0107] 15a Guide groove

[0108] 15b, 15c gradation

[0109] 16, 16a tappet

[0110] 17 Lock nut

[0111] 18 Parking system inlet 19 Reservoir inlet

[0112] 20 Brake inlet

[0113] 23 housings

[0114] 26 Differential

[0115] 40 inverters

[0116] EM electric machine

[0117] 41 controllers

[0118] 42 gearboxes

[0119] 43 Differential

[0120] 44 multi-disk brake

[0121] 45 wheels

[0122] 46 Electric actuator

[0123] 47 Ball ramp

[0124] 48 axle side shaft

[0125] 49 brake components

[0126] 50 hydraulic actuators

[0127] 51 brake line

[0128] 52 brake unit

[0129] 53 Pump

[0130] 54 pressure switches

[0131] 55 pressure pistons

[0132] 56a Pressure reducing valve

[0133] 56 Seal

[0134] 57 Bearing solution 58 Brake housing

[0135] 58a radial groove

[0136] 100 Electric drive system

[0137] 300 assembly

[0138] 400 cooling unit

[0139] A, B, C room

[0140] V1 mode switching valve

[0141] V2L, V2R brake valve

[0142] V3L, V3R release valve

[0143] V4 parking brake valve

[0144] V5 pressure relief valve

[0145] V6 cooling mode valve

Claims

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 in 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 in that 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 in 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 in that the 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 in that the sleeve (5a) for the parking brake has a space in which a plunger (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 in 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 in that the plunger (16) is movable radially outwards and fixes the brake piston (1).

8. Electric drive system (100) according to claim 1, characterized in 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 in that the parking piston (15) and the brake piston (1) overlap with each other when the service brake is active.

10. Electric drive system (100) according to one of the preceding claims, characterized in that the parking brake can only be actuated via an energy input.

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