COOLANT SUPPLY FOR AN ELECTRIC VEHICLE AXLE DRIVE

Description

[0001] The invention relates to an electric vehicle axle drive according to the preamble of claim 1.

[0002] Such a vehicle axle drive can have a wet-running electric machine in which the stator, in particular the winding heads of the stator windings, as well as the rotor are actively cooled.

[0003] In an exemplary coolant supply system for an electric vehicle axle drive, the electric motor has a housing in which a stator and rotor interact. The coolant supply system provides stator cooling, with the coolant being directed at least into a winding headspace of the electric motor. This winding headspace extends radially between the radially inner rotor shaft and a radially outer cylindrical wall of the electric motor housing. Axially, the winding headspace extends between an end wall of the cylindrical electric motor housing and an end face of the stator / rotor assembly. During operation, a coolant / air mixture circulates in an eddy current around the rotor shaft within the winding headspace.

[0004] A generic electric vehicle axle drive is known from DE 10 2019 117 893 A1. Another wet-running electric machine is known from US 2019 0199173 A1. US 2004 / 134693 A1 discloses a cooling system for the electric motor of a vehicle. A drive device and a vehicle drive system are known from WO 2020 / 213508 A1.

[0005] The object of the invention is to provide an electric vehicle axle drive that is structurally simpler compared to the prior art and / or, in particular, enables more effective cooling of the electric machine or transmission components compared to the prior art.

[0006] The problem is solved by the features of claim 1. Preferred embodiments of the invention are disclosed in the dependent claims.

[0007] The invention relates to an electric vehicle axle drive comprising a coolant supply system and an electric motor in whose motor housing a stator interacts with a rotor. The electric motor drives at least one vehicle wheel of the axle via a transmission arrangement. According to claim 1, a coolant separator is arranged in the motor housing. This divides the interior of the motor housing into a radially outer annular stator chamber, in which the stator with its stator windings is arranged, and a radially inner rotor chamber, largely separated from it by a fluid-tight or flow-tight seal, in which the rotor is arranged. In this way, the stator, which heats up considerably during operation of the electric motor, can be supplied with coolant in a more targeted manner. Furthermore, the coolant supply to the stator chamber is decoupled from the eddy current that forms in the rotor chamber.The rotor is therefore less in contact with the coolant. Instead, the stator winding ends in particular can be completely surrounded by coolant. In this case, the stator chamber can be essentially completely filled with coolant.

[0008] The coolant separation unit is a closed surface (i.e., nozzle-free) and in tight contact with the axially opposing end walls of the electric motor housing. A fluid-tight or flow-tight seal between the stator and rotor compartments does not necessarily mean a hermetic seal, i.e., a completely airtight seal. Rather, during operation of the electric motor, a small amount of coolant may leak through the sealing surfaces of the coolant separation unit into the rotor compartment. If necessary, the coolant separation unit can also be implemented as a so-called containment vessel, i.e., a tube (for example, made of plastic) that is inserted between the rotor and the stator and sealed axially to the housing.

[0009] In one technical implementation, the coolant supply system comprises a stator hydraulic circuit and a rotor hydraulic circuit, which are at least partially fluidically decoupled from each other. The stator chamber is integrated into the stator hydraulic circuit, while the rotor, particularly for internal rotor cooling, is integrated into the rotor hydraulic circuit.

[0010] According to the invention, the stator chamber has at least one drain point from which the coolant flowing out of the stator chamber can be returned to a coolant reservoir. The rotor chamber can have at least one drain point from which the coolant flowing out of the rotor chamber can be returned to the coolant reservoir. According to the invention, the coolant return is achieved by means of a return pump. Furthermore, the stator chamber can each have an inlet point into which the coolant can be supplied from the coolant reservoir to the stator chamber. The coolant supply can be supported, in particular, by means of a supply pump. It is especially important here that the stator chamber is completely filled with oil – for this, a pump is needed to deliver the oil into it, and the drain must be designed as an overflow, i.e., located at the top.To prevent oil from draining out of the stator chamber at high lateral accelerations, the drain must be throttled either by an orifice or by a pressure relief valve.

[0011] The transmission assembly comprises a transmission housing in which, for example, an axle differential is arranged. Its input side can be connected to the electric motor, either directly or indirectly, for instance, at least via a gear stage designed for torque conversion. The output side of the axle differential is connected to at least one wheel of the vehicle axle.

[0012] Alternatively or additionally, the invention relates to the coolant supply system described below for an electric vehicle axle drive, which comprises an electric motor in whose motor housing a stator interacts with a rotor. The electric motor drives at least one vehicle wheel of the axle via a transmission arrangement. With a view to reducing the installation space of the coolant supply system and reducing the number of components, the invention provides that the coolant supply system does not have a separate coolant tank, but rather the transmission housing and, in particular, the stator housing also serve a dual function as a coolant reservoir. In this case, the return pump and / or the supply pump can also be positioned directly in the transmission housing.

[0013] According to the invention, the feed pump and the return pump are combined to form a dual pump, preferably with a common drive shaft. The common drive shaft is connected to an electric motor.

[0014] For a compact vehicle axle drive, it is preferable to install the electric motor transversely, so that its rotor shaft extends in the transverse direction of the vehicle, i.e., parallel to the vehicle's transverse axis. To further reduce installation space, the electric motor and the transmission assembly can be arranged side by side in the transverse direction of the vehicle. In addition, the transmission housing can be directly flanged to the electric motor housing.

[0015] In a gearbox housing designed in this way, an upwardly open hollow body, in particular a shell, can be arranged. The hollow body shields a coolant-free, upwardly open installation space from the coolant column located in the gearbox housing. A gearbox component, in particular the axle differential, can be arranged, at least partially, in the upwardly open installation space. In this way, it is prevented during normal operation that the gearbox component is immersed in the coolant column located in the gearbox housing.

[0016] In addition to the stator hydraulic circuit and the rotor hydraulic circuit, the coolant supply system can include a gearbox hydraulic circuit. The gearbox hydraulic circuit can supply coolant to at least one gearbox component located in the gearbox housing via dry sump lubrication or injection lubrication. In this case, the coolant is routed through a gearbox supply line to a lubrication point on the gearbox component. The gearbox component supplied with coolant via dry sump lubrication or injection lubrication can preferably project into the installation space provided by the hollow body. In this case, the coolant dripping from the gearbox component can collect at the bottom of the hollow body and be returned to the coolant reservoir via a bottom-side drain, particularly with the assistance of a return pump.Dry sump lubrication refers to a system where the oil draining from the engine is actively returned to a dry sump, typically by a pump. In contrast, a wet sump system uses gravity to drain the oil into a lower area (oil pan). Unlike dry sump lubrication, a wet sump system allows gears to be lubricated by immersion in the oil.

[0017] If injection lubrication proves insufficient, internal lubrication of the axle differential can be added. Preferably, an oil supply for internal lubrication is provided via a possible decoupling mechanism.

[0018] To ensure an emergency coolant supply to the transmission component even in the event of a pump failure of the return pump and / or the supply pump, the following measure can be provided: The hollow body can have an emergency inlet through which coolant from the coolant column located in the transmission housing can flow into the hollow body. In the event of a pump failure, this ensures an emergency coolant supply to the transmission component. The flow of coolant through the emergency inlet creates a coolant column within the hollow body, into which the transmission component is immersed, similar to splash lubrication.

[0019] As mentioned previously, the coolant separation between the radially outer stator chamber and the radially inner rotor chamber cannot provide a hermetic seal, resulting in leakage losses where coolant from the stator chamber enters the rotor chamber. This leakage coolant collects at the bottom of the rotor chamber, particularly on the inside of the coolant separation. To remove the leakage coolant from the rotor chamber, at least one drain point is provided at the bottom of the rotor chamber, through which the leakage coolant can be returned to the coolant reservoir, particularly by means of a return pump. The rotor hydraulic circuit can be specifically designed for internal rotor cooling, in which the rotor shaft is designed as a hollow shaft. Its cavity can be at least partially filled with coolant. After internal rotor cooling, the coolant can be discharged into the rotor chamber, where it collects at the bottom.As already mentioned, at least one rotor chamber drain point can be formed at the bottom of the rotor chamber, through which the coolant can be returned to the coolant reservoir.

[0020] The invention provides a coolant supply system with reduced component costs, but with unchanged optimal efficiency and cooling performance.

[0021] Exemplary embodiments of the invention are described below with reference to the accompanying figures.

[0022] They show: Figures 1 and 2 each show a schematic representation of a coolant supply system, and Figure 3 shows a schematic representation of a comparative example not covered by the invention.

[0023] For a simpler understanding of the invention, reference is first made to the Figure 3The figure shows a roughly schematic representation of a drive device for one axle of a two-track vehicle. The drive device comprises an electric motor, which, by way of example, is mounted transversely, parallel to the flange shafts 3 that lead to the vehicle wheels. A stator 4 with a cooperating rotor 5 is arranged in a housing 2 of the electric motor. The rotor shaft 6 is rotatably supported in bearing openings on axially opposite housing walls 8, 9 of the electric motor housing 2, with intermediate arrangement of rotary bearings 13, 15.

[0024] The rotor shaft 6 of the electric machine is non-rotatably connected to a gearbox input shaft 17 of a gearbox assembly 19, which drives onto the two flange shafts 3. In the Figure 3 The transmission arrangement 19 consists of a transmission stage 18 and an axle differential 20.

[0025] In the Figure 3Stator 4 has a multitude of stator windings, of which in the Figure 1 Only two stator windings 21 are indicated. Each stator winding 21 has a winding head 23, 25 on both axial sides, which projects into a winding head chamber 27. Each winding head chamber 27 is integrated into an oil-hydraulic circuit described later, by means of which the respective winding head chamber 27 can be supplied with oil to cool the winding heads 23, 25 of the stator 4. In each of the electric motor chambers 27, an oil / air mixture moves in an eddy flow around the rotor shaft 5, which rotates at high speed.

[0026] In the Figure 3 In the right bearing arrangement, one shaft end of the rotor shaft 6 is rotatably supported in a hub section 31 via a rotary bearing 15.

[0027] The oil hydraulic circuit includes an oil tank 35, which is connected to a supply pump 37 via a suction line. A pressure line leads from the supply pump 37 to oil supply lines 41 and 43. Oil is fed into a radially outer annular gap 45 via supply line 41. From there, the oil is guided via radially outer stator channels 47 to another annular gap 49 in the right-hand winding head chamber 27. The two annular gaps 45 and 49 are separated from their respective winding head chambers 27 by oil spray rings 44. Each of the oil spray rings 44 has circumferentially distributed nozzles 46 through which oil can be injected into the respective winding head chamber 27. Oil is guided through the rotor shaft 6 via supply line 43 and, via a flow connection 51, into radially inner rotor channels 53 and into the right-hand winding head chamber 27. On the bottom of the electric motor housing, there is a Figure 3a suction port 54, through which oil collecting at the bottom of the housing can be returned to the oil tank 35 by means of a return pump 56.

[0028] Unlike the Figure 3 will be in the Figure 1 or 2 According to the invention, the stator 4 with its winding heads 23, 25 is no longer cooled by means of an air / oil vortex flow. Instead, the interior of the electric motor housing 2 is divided by means of a coolant partition 57 into a radially outer annular stator chamber 59 and a radially inner rotor chamber 61. The stator 4 with its stator windings 21 is positioned in the stator chamber 59, while the rotor 5 is arranged in a fluid-tight separation in the radially inner rotor chamber 61. According to the invention, the stator 4 therefore no longer comes into contact with a vortex flow forming in the rotor chamber 61. Instead, the cooling is achieved in the Figure 1The stator chamber 59 is completely filled with coolant during electric machine operation, so that the winding heads 23, 25 in particular are completely surrounded by coolant, resulting in a better efficiency compared to eddy current cooling. The core of the invention, however, consists firstly in locating the coolant in the unit at a point (i.e., in the stator chamber 59) where it is needed anyway. Secondly, the invention largely keeps the coolant away from the rotor chamber 61. When using the spray oil cooling known from the prior art... Figure 3 The problem is that, depending on the coolant temperature, very different amounts of coolant adhere to the winding. Therefore, a comparatively large amount of coolant must be added to provide a sufficient quantity for the pressure pump.

[0029] As from the Figure 1 As can be seen, the electric machine is analogous to the Figure 3 It is installed transversely in the vehicle, with a rotor shaft 6 running in the transverse direction y of the vehicle, i.e., parallel to the vehicle axis. Furthermore, in the Figure 1 The electric motor and the transmission assembly 19 are arranged side by side in the transverse direction y of the vehicle. The transmission housing 63 of the transmission assembly 19 is also directly flanged to the electric motor housing 2. The transmission assembly 19 is positioned in the transmission housing 63, which according to the Figure 3 The transmission stage 18 and the axle differential 20 are featured.

[0030] A key aspect of the invention is that a separate oil tank (reference number 35 in the Figure 3 ) is dispensed with and instead the gearbox housing 63 also serves a dual function as an oil tank or coolant reservoir, in which an oil column 65 forms. In addition, the components in the Figure 3The feed pump 37 and return pump 56 shown are combined into a common dual pump 64. In the dual pump 64, the feed and return pumps 37 and 56 are driven by an electric motor via a common (not shown) drive shaft.

[0031] As from the Figure 1 As further shown, a hollow shell 67, open at the bottom, is positioned in the gearbox housing 63. This shell shields a coolant-free, open-topped installation space 69 from the oil column 65. The axle differential 20 partially protrudes into the installation space 69. Normally, lubrication is provided by injection, with oil being supplied to the axle differential 20 via the gearbox supply line 42. Coolant dripping from the axle differential 20 collects at the bottom of the shell 67 and is then directed via a drain point 68 into a return line 73, which is connected to the suction side of the dual pump 64.

[0032] During electric motor operation, oil is fed into the stator chamber 59 via the supply line 41 at an inlet point 69 near the gearbox by means of the twin pump 64. The oil is discharged from the stator chamber 59 at an axially opposite outlet point 71 located further away from the gearbox. The stator chamber outlet point 71, located further away from the gearbox, can be implemented as an orifice or possibly as a pressure relief valve. The stator chamber outlet point 71 is also connected via a first return line 72 to the oil column 65 located in the gearbox housing 63, into which the first return line 72 opens. Additionally, oil can accumulate within the hub section 31 of the rotary bearing 15 located further away from the gearbox, which can also be directed into the first return line 73 via a further outlet point 80.

[0033] In the Figure 1 Internal rotor cooling is carried out using the coolant supply system, in which the components in the Figure 1The oil guide S shown in the sketch results. The oil guide S in the rotor shaft 6 is designed such that both the bearing 13 closest to the drive and the bearing 15 furthest from the drive are cooled from the inside. The aim of the oil guide S is to minimize the temperature difference between the inner and outer rings of the respective bearings 13 and 15.

[0034] According to the oil flow S, oil is fed into the cavity of the hollow rotor shaft 6 via the supply line 43, up to the axial height of the rotary bearing 15 furthest from the gearbox. From there, the oil is directed into the rotor channels 53 via a flow connection 76 furthest from the gearbox. Within the rotor channels 53, the oil flows in the opposite direction until it reaches a flow connection 77 near the gearbox, where it is returned to the cavity of the rotor shaft 6. The returned oil is guided from the rotor shaft 6 via a drain point 78 into the rotor chamber 61. There, the oil collects at the bottom of the rotor chamber, from where it is directed into the second return line 73 via rotor chamber drain points 79 located on both sides of the electric motor housing 2. This second return line is connected to the suction side of the twin pump 64.

[0035] The twin pump 64 features in the Figure 1On its pressure side, a riser line 66 is provided, through which the returned oil is fed into the gearbox housing 63. In addition, a suction line 74 is connected to the suction side of the twin pump 64, which is fluidically connected to the oil column 65.

[0036] As from the Figure 1 As further shown, an emergency inlet 81 is formed on one wall of the shell 67, through which oil can flow from the coolant column 65 located in the gearbox housing 63 into the shell 67. In the event of a pump failure, this ensures an emergency coolant supply to the axle differential 20, whereby a coolant column forms in the shell 67 into which the axle differential 20 can immerse itself, similar to an immersion lubrication system. Figure 1 The emergency inlet 81 is a bottom-side opening in the bowl 67. Alternatively, the emergency inlet 81 can also be implemented as an upper overflow edge of the bowl 67.

[0037] In the Figure 2An example (not encompassed by the invention) is shown, the structure and function of which essentially correspond to the structure and function of the first embodiment. In the Figure 2 The oil flow direction in the stator hydraulic circuit is reversed. This means that the return line 73 is connected to a stator chamber drain point 71 located near the gearbox. This line is connected to the suction side of the twin pump 64. Conversely, a suction line 74 is connected to the stator chamber inlet point 69 located furthest from the gearbox, through which the oil is drawn from the oil column 65 located in the gearbox housing 63.

[0038] The gearbox housing 63 can be designed to be so narrow in the transverse direction y of the vehicle that, during lateral acceleration, the suction line 74 is always immersed in the coolant column 65, thus ensuring oil intake. The coolant supply system is designed such that the dual pump 64 draws oil from the gearbox housing 63 via only a single suction point (i.e., suction line 74). The suction point is positioned in the longitudinal direction x of the vehicle such that oil is reliably drawn in during positive or negative longitudinal acceleration and, with the opposite sign of the acceleration, sloshes into the tray 67 below the differential chamber.

[0039] In the Figure 1 and 2 The electric machine is additionally integrated into a cooling water circuit K, in which the cooling water flows around the outer circumference of the electric machine housing 2. REFERENCE MARK LIST:

[0040] 2 Electric machine housing 3 Flange shafts 4 Stator 5 Rotor 6 Rotor shaft 8, 9 Housing wall 11 Bearing opening 13, 15 Rotary bearing 17 Gearbox input shaft 18 Gearbox stage 19 Gearbox assembly 20 Axle differential 21 Stator winding 23, 25 Winding head 27 Electric machine compartment 31 Hub section 33 Sealing element 35 Coolant tank 37 Feed pump 41, 42, 43 Supply lines 44 Oil spray ring 45 Annular gap 46 Nozzles 47 Radial outer stator channel 49 Annular gap 51 Flow connection 53 Radial inner stator channel 54 Suction 56 Return pump 57 Coolant separation 59 Stator compartment 61 Rotor compartment 63 Gearbox housing 64 Dual pump 65 Coolant column 66 Riser pipe 67 Hollow body 68 Hollow body drain point 69 Stator compartment inlet point 71 Stator compartment drain point 72 Additional return line 73 Return line 74 Suction line 76 Flow connection far from gearbox 77 Flow connection near gearbox 78 Drain point 79 Rotor compartment drain point 80 Hub section drain point 81 Emergency inlet S Oil guide for internal rotor cooling K Cooling water circuit

Claims

1. Electric vehicle axle drive with a coolant supply system and with an electric machine, in the electric machine housing (2) of which a stator (4) interacts with a rotor (5), wherein the electric machine has a drive output by way of a transmission assembly (19) to at least one vehicle wheel of the vehicle axle, and wherein a coolant separator (57) is disposed in the electric machine housing (2), which divides the interior of the electric machine housing (2) into a radially outer stator chamber (59), in which the stator (4) with its stator windings (21) is disposed, and into a radially inner rotor chamber (61) which is separated therefrom in a largely fluid-tight manner and in which the rotor (5) is disposed, and wherein the stator chamber (59) has a drain point (71) from which the coolant flowing from the stator chamber (59) can be recirculated to a coolant reservoir, characterized in that the coolant recirculation is carried out by means of a recirculation pump (56), and in that the transmission assembly (19) has a transmission housing (63), and in that the transmission housing (63) forms the coolant reservoir in which a coolant column (65) is located, and in that a feed pump (37) and the recirculation pump (56) are combined so as to form a common dual pump (64), and in that oil is able to be fed into the stator chamber (59) by means of the dual pump (64) by way of a supply line (41) at a transmission-proximal supply point (69), and in that the oil is able to be discharged from the stator chamber (59) at an axially opposite transmission-distal drain point (71).

2. Electric vehicle axle drive according to Claim 1, characterized in that the stator chamber (59) is part of a stator hydraulic circuit, and the rotor chamber (61) is part of a rotor hydraulic circuit, and in that in particular the stator hydraulic circuit is at least partially fluidically decoupled from the rotor hydraulic circuit.

3. Electric vehicle axle drive according to Claim 1 or 2, characterized in that an axle differential (20) is disposed in the transmission housing (63), the input side of which is connected to the electric machine, specifically either directly or indirectly, for example by way of a gear stage (18) for torque conversion, and the output side of which is connected to at least one vehicle wheel of the vehicle axle.

4. Electric vehicle axle drive according to Claim 3, characterized in that the recirculation pump (56) and / or the feed pump (37) are disposed in the transmission housing (63).

5. Electric vehicle axle drive according to Claim 3 or 4, characterized in that an open-top hollow body (67), in particular bowl, which shields a coolant-free, open-top installation space (69) from the coolant column (65) located in the transmission housing (63), is disposed in the transmission housing (63), and in that in particular a transmission component, such as the axle differential (20), protrudes into the installation space (69).

6. Electric vehicle axle drive according to one of the preceding claims, characterized in that the coolant supply system has a gear / hydraulic circuit in which at least one transmission component (20) disposed in the transmission housing (63) is able to be supplied with coolant by dry sump lubrication or injection lubrication, in particular by means of the feed pump (37), and in that, in particular during injection lubrication, the coolant is fed from a transmission supply line (42) to a transmission component lubrication point, and in that in particular the coolant dripping from the transmission component (20) accumulates at the bottom of the hollow body (67), and in that in particular a drain point (68) is formed at the bottom of the hollow body (67), by way of which the coolant is able to be recirculated in the direction of the coolant reservoir, specifically in particular by means of the recirculation pump (56).

7. Electric vehicle axle drive according to Claim 5 or 6, characterized in that the hollow body (67) has an emergency supply (81), by way of which coolant flows from the coolant column (65) located in the transmission housing (63) into the hollow body (67), so that, in particular in the event of a pump failure, a coolant emergency supply of the transmission component (20), in which a coolant column is formed in the hollow body (67), into which the transmission component (20) is immersed, is guaranteed.

8. Electric vehicle axle drive according to one of the preceding claims, characterized in that a leaking coolant escaping from the stator chamber (59) and / or a coolant discharged from an internal cooling of the rotor accumulates at the bottom of the rotor chamber (61), in particular on the coolant separator (57), and in that in particular at least one rotor chamber drain point (79) is formed at the bottom of the rotor chamber (61), by way of which the coolant is able to be recirculated into the coolant reservoir, in particular by means of the recirculation pump (56).

9. Electric vehicle axle drive according to one of the preceding claims, characterized in that the stator chamber (59) is substantially completely filled with coolant, and / or in that the rotor hydraulic circuit causes internal cooling of the rotor, in which the rotor shaft (6) is formed as a hollow shaft, the cavity of which is at least partially passed through by a flow of coolant.