COOLANT SUPPLY SYSTEM FOR AN ELECTRIC VEHICLE AXLE DRIVE

Description

[0001] The invention relates to a coolant supply system for 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 end windings of the stator windings, and the rotor are actively cooled with coolant (i.e., oil). The rotor is spaced from the stator by an air gap. The interior of the electric machine can be supplied with coolant for internal rotor cooling and / or stator cooling.

[0003] It has been shown that coolant-containing air in the air gap between the rotor and the stator leads to drag losses in the rotor, which reduces the efficiency of the electric machine.

[0004] Against this background, in a generic electric machine according to US 2021 / 0083555 A1, compressed air lines are integrated into the rotor and / or stator, which are in flow connection with the air gap. An air flow is generated for a compressed air source that flows through the air gap in the axial direction. In this way, the air gap is kept essentially free of coolant, thereby reducing rotor drag losses.

[0005] In US 2021 / 0083555 A1, the compressed air lines run inside the stator and / or rotor. The component geometry of the stator and / or rotor therefore differs from a conventional rotor / stator component geometry, which is complex to manufacture.

[0006] EP 3 193 434 B1 and EP 3 032 709 A1 disclose further electric machines. US 2005 / 023909 A1 discloses a generator for motor vehicles. WO 2019 / 008220 A1 discloses an electric machine. US 4 496 862 A discloses a high-speed generator vent for an air gap. GB 164 114 A discloses improvements to dynamoelectric machines. US 3 240 967 A discloses a cooling device for electric machines.

[0007] The object of the invention is to provide a coolant supply system for an electric vehicle axle drive in which the electric machine can be operated in a simple manner with a higher efficiency compared to the prior art.

[0008] The object is solved by the features of claim 1. Preferred developments of the invention are disclosed in the subclaims.

[0009] According to the invention, a coolant supply system is provided for an electric machine, in whose electric machine housing a stator interacts with a rotor that is spaced from the stator by an air gap. The electric machine is implemented as a wet-running, coolant-flow electric machine, in which the electric machine interior is supplied with coolant for internal rotor cooling and / or for stator cooling. The coolant supply system also has a flow unit by means of which an air flow can be generated. The air flow flows through the air gap in the axial direction. In this way, the air gap is kept substantially free of coolant-containing air, thereby reducing rotor drag losses. According to the characterizing part of claim 1, the rotor / stator arrangement has an air flow chamber on each axial side (that is, the rotor chamber in the specific exemplary embodiment).The two airflow chambers are in flow communication with the intermediate air gap. According to the invention, the airflow chambers (i.e., the rotor chambers) are divided into an air inlet-side airflow chamber and an air outlet-side airflow chamber. The airflow generated by the flow unit flows into the air inlet-side airflow chamber via the air inlet. The airflow then flows through the air gap into the outlet-side airflow chamber. From there, the airflow is discharged from the outlet-side airflow chamber via an air outlet.

[0010] According to the invention, no geometric adjustments to the rotor and / or stator are required to achieve air flow through the air gap. Rather, the invention allows for simple manufacturing using a conventional component geometry of the rotor or stator.

[0011] In a technical implementation, the two airflow chambers, the air gap, and the flow unit can be integrated into a closed air circuit. In the air circuit, the airflow generated by the flow unit flows through the air inlet into an inlet-side airflow chamber. From there, the airflow is guided axially through the air gap to the outlet-side airflow chamber. From the outlet-side airflow chamber, the airflow is returned via the air outlet to the flow unit.

[0012] In the electric machine housing, the stator-rotor arrangement has a free housing chamber on each axial end face on each of the two sides. The air flow chambers according to the invention are components of these housing chambers. Each of the two end face housing chambers is preferably divided by a coolant separation into a radially outer winding head chamber and a radially inner rotor chamber, which is largely separated from the latter in a fluid-tight manner and in which the rotor is arranged. In contrast, the stator, including the stator windings, is positioned in the radially outer winding head chamber. In this way, the stator, which heats up considerably during electric machine operation, can be supplied with coolant in a more targeted manner. In addition, the coolant supply to the winding head chamber is largely decoupled from the rotor chamber. In particular, the winding heads of the stator can preferably be completely surrounded by coolant. In this case, the winding head chamber can be essentially completely filled with coolant.

[0013] In the above subdivision of the respective housing space into the radially outer winding head space and the radially inner rotor space, the radially inner rotor space specifically forms the air flow space according to the invention. In this case, the radially inner rotor spaces of the electric machine are specifically integrated into the air circuit. Against this background, the air inlet opens into the inlet-side rotor space, while the air outlet opens into the outlet-side rotor space.

[0014] To ensure reliable stator cooling, the winding head chamber can be part of a stator hydraulic circuit, which is preferably decoupled from the air circuit. The stator hydraulic circuit can have an inlet point at which coolant can be supplied from a coolant reservoir into the winding head chamber, in particular with the aid of a supply pump arranged in the coolant reservoir. Furthermore, the stator hydraulic circuit can have a drain point separate from the air outlet, from which coolant can be returned from the winding head chamber toward the coolant reservoir.

[0015] Alternatively and / or additionally, internal rotor cooling can be provided, in which the rotor is part of a rotor hydraulic circuit. The rotor hydraulic circuit can also be largely decoupled from the air circuit and the stator hydraulic circuit.

[0016] The aforementioned coolant separation between the winding head space and the radially inner rotor space forms a floor of the rotor space. During electric machine operation, leakage coolant escaping from the winding head space and / or leakage coolant escaping from the internal rotor cooling system or coolant escaping from the bearings can collect on the rotor space floor. It is preferred if the air outlet is located at the rotor space floor of the outlet-side rotor space. In this way, not only the air flow can be discharged via the air outlet, but also the leakage coolant can be discharged from the outlet-side rotor space. The mixture of air flow and leakage coolant can be returned to the coolant reservoir via a return line.

[0017] To prevent coolant-containing air from entering the air gap, it is preferable to install a separator directly or indirectly upstream of the air inlet. The separator can be used to remove coolant droplets from the air flow entering the electric machine housing via the air inlet.

[0018] In a first embodiment, the air outlet can be connected to the suction side of a return pump via a return line. The return pump acts as an air / coolant suction pump, with which the mixture of air flow and leakage coolant can be sucked out of the rotor chamber. In this way, a negative pressure is created in the rotor chamber, creating a pressure gradient between the gear chamber and the rotor chamber, which leads to the air flow. The return pump can preferably be positioned within the coolant reservoir and have a riser on its pressure side. The mixture of air flow and leakage coolant can flow into the coolant reservoir via the riser. In addition, the air inlet can open into the air-filled upper interior of the coolant reservoir without a direct pump connection.

[0019] Alternatively, in a second embodiment, an air supply pump can be arranged in the coolant reservoir, acting as an air pressure pump. The air supply pump can be in flow connection with its suction side to the air-filled upper interior of the coolant reservoir. In this case, the air supply pump can extract air from the air-filled upper interior of the coolant reservoir, which is conveyed via an air supply line to the air inlet and from there further through the electric motor. In this case, the air outlet can be connected to the coolant reservoir via a return line. The return line can open into the coolant reservoir without a direct pump connection. Preferably, the return line within the coolant reservoir can merge into a riser line, via which the mixture of air flow and leakage coolant flows into the coolant reservoir.

[0020] It is preferred if a separator is installed upstream of the air supply pump on its suction side, with which the extracted air flow is cleaned of coolant droplets.

[0021] A space-saving and structurally simple design is achieved when the flow unit is designed as a dual pump, in which the supply pump for stator cooling and / or for internal rotor cooling and the return pump or supply pump for the air flow are combined into a dual pump. In this case, the individual pumps installed in the dual pump can be driven by a common drive shaft.

[0022] The coolant separation is designed with a closed surface (i.e., nozzle-free) and is in sealing contact with the axially opposite end walls of the electric machine housing. A fluid-tight or flow-tight seal between the winding head space and the rotor space does not necessarily mean a hermetic seal, i.e., a completely tight seal. Rather, a slight coolant leakage through the sealing surfaces of the coolant separation into the rotor space may occur during electric machine operation.

[0023] The rotor hydraulic circuit can be specifically designed for internal rotor cooling, where the rotor shaft is designed as a hollow shaft. Coolant can flow through its hollow space, at least partially. After the internal rotor cooling has been completed, the coolant can be discharged into the rotor chamber, where it collects at the bottom of the rotor chamber. As already mentioned, at least one rotor chamber drain point can be provided at the bottom of the rotor chamber, through which the coolant can be returned to the coolant reservoir.

[0024] Two embodiments of the invention are described below with reference to the attached figures.

[0025] They show: Figs. 1 and 2 are schematic representations of a first and a second exemplary embodiment of a coolant supply system, respectively; and Fig. 3 is a schematic representation of a comparative example not covered by the invention.

[0026] For easier understanding of the invention, reference is first made to the Figure 3 , in which a drive device for a vehicle axle of a two-track vehicle is indicated in a roughly schematic representation. The drive device has an electric machine which, for example, is arranged transversely mounted axially parallel to the flange shafts 3 leading to the vehicle wheels. A stator 4 with a cooperating rotor 5 is arranged in a housing 2 of the electric machine. The rotor shaft 6 is rotatably mounted on axially opposite housing walls 8, 9 of the electric machine housing 2 in bearing openings with pivot bearings 13, 15 interposed.

[0027] The rotor shaft 6 of the electric machine is connected in a rotationally fixed manner to a transmission input shaft 17 of a transmission arrangement 19, which drives the two flange shafts 3. In the Figure 3 the transmission arrangement 19 is composed of a transmission stage 18 and an axle differential 20.

[0028] In the Figure 3 The stator 4 has a plurality of stator windings, of which Figure 1 Only two stator windings 21 are indicated. Each stator winding 21 has a winding head 23, 25 axially on both sides, which protrudes into a free housing space 27 at the front. Each housing space 27 is integrated into an oil-hydraulic circuit described later, with the aid of which the respective winding head space 27 can be supplied with oil in order to cool the winding heads 23, 25 of the stator 4. In each of the housing spaces 27, an oil / air mixture moves in a vortex flow around the rotor shaft 5, which rotates at high speed.

[0029] In the in the Figure 3 In the right-hand bearing arrangement, one shaft end of the rotor shaft 6 is rotatably mounted in a hub section 31 via the pivot bearing 15.

[0030] The oil-hydraulic circuit has an oil tank 35, which is connected to a feed pump 37 via a suction line. A pressure line leads from the feed pump 37 to oil supply lines 41, 43. Oil is fed into a radially outer circumferential annular gap 45 via the supply line 41. From there, the oil is guided via radially outer stator channels 47 to another annular gap 49 in the right-hand housing chamber 27. The two annular gaps 45, 49 are separated from the respective housing chamber 27 by oil spray rings 44. Each of the oil spray rings 44 has nozzles 46 distributed in the circumferential direction, through which oil can be injected into the respective housing chamber 27.

[0031] By means of the supply line 43, oil is guided through the rotor shaft 6 and via a flow connection 51 in radially inner rotor channels 53 into the right housing chamber 27. At the housing bottom of the electric machine housing, in the Figure 3a suction device 54, through which oil collecting at the bottom of the housing can be returned to the oil tank 35 with the aid of a return pump 56.

[0032] In contrast to Figure 3 is 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. Rather, the housing space 27 of the electric machine housing 2 is divided by means of a coolant separation 57 into a radially outer annular winding head space 59 and a radially inner rotor space 61. The stator 4 with its stator windings 21 is positioned in the winding head space 59, while the rotor 5 is arranged in a fluid-tight manner in the radially inner rotor space 61. According to the invention, therefore, the stator 4 no longer comes into cooling contact with a vortex flow forming in the rotor space 61. Rather, in the Figure 1the winding head space 59 is completely filled with the coolant during electric machine operation, so that the winding heads 23, 25 in particular are completely surrounded by coolant, which may result in a better efficiency compared to eddy current cooling.

[0033] A core of the invention is, firstly, to accommodate the coolant in the unit at a location (i.e., in the winding head space 59) where it is needed anyway. Secondly, the invention largely keeps the coolant away from the rotor space 61. When using the spray oil cooling system known from the prior art, Figure 3 One problem is that, depending on the coolant temperature, very different amounts of coolant cling to the winding. Therefore, to provide a sufficient amount of coolant for the pressure pump, a comparatively large amount of coolant must be added.

[0034] As from the Figure 1As can be seen, the electric machine is analogous to the Figure 3 installed transversely in the vehicle, with a rotor shaft 6 running in the vehicle's transverse direction y, i.e. parallel to the vehicle axis. In addition, Figure 1 The electric machine and the transmission assembly 19 are arranged side by side in the vehicle transverse direction y. The transmission housing 63 of the transmission assembly 19 is also flanged directly to the electric machine housing 2. The transmission assembly 19 is positioned in the transmission housing 63, which is arranged according to the Figure 3 which has gear stage 18 and axle differential 20.

[0035] Another core of the invention is that a separate oil tank (reference number 35 in the Figure 3 ) is omitted and instead the gearbox housing 63 has a dual function as an oil tank or coolant reservoir in which an oil column 65 is formed. In addition, the Figure 3The feed pump 37 and return pump 56 shown are combined to form a common dual pump 64. In the dual pump 64, the feed and return pumps 37, 56 are driven by an electric motor with a common drive shaft (not shown).

[0036] As from the Figure 1As can be seen further, a hollow body, open at the top, is positioned in the bottom of the transmission housing 63, which shell 67 shields a coolant-free, open-top installation space 69 from the oil column 65. The axle differential 20 partially protrudes into the installation space 69. Normally, injection lubrication takes place, in which oil is guided via the transmission supply line 42 towards the axle differential 20. The coolant dripping from the axle differential 20 collects at the bottom of the shell 67 and from there is guided via a drain point (not shown) into the return line 89, which is connected to the suction side of the dual pump 64. Alternatively, it may be sufficient if the gear of the differential throws the coolant out of the shell 67. It would also be possible to form a small oil inlet bore in the shell 67 in order to ensure emergency lubrication of the gear in the event of a pump failure.

[0037] During electric machine operation, oil is fed into the winding head chamber 59 via the supply line 41 by means of the dual pump 64 at an inlet point 69 near the gearbox. The oil is drained from the winding head chamber 59 at an axially opposite outlet point 71 away from the gearbox. The winding head chamber outlet point 71, remote from the gearbox, can be implemented as an orifice plate, possibly also as a pressure relief valve. The orifice plate or pressure relief valve is necessary to keep the oil in the winding head chambers 59 even during very high accelerations, particularly lateral accelerations. The winding head chamber outlet point 71 is also in flow connection via a first return line 72 with the oil column 65 located in the gearbox housing 63, into which the first return line 72 opens. In addition, an oil supply line 80 branches off from the return line 72. The bearing 15 in the hub section 31 is supplied with oil via the oil supply line 80.The oil then passes through the bearing 15 into the rotor chamber 61, from where it is sucked out via a return line 89.

[0038] In the Figure 1 With the help of the coolant supply system, an internal rotor cooling is carried out, in which a Figure 1 The oil guide in the rotor shaft 6 is designed so that both the bearing 13 closest to the gearbox and the bearing 15 far from the gearbox are cooled from the inside. The aim of the oil guide is to minimize the temperature difference between the inner and outer rings of the respective bearings 13 and 15.

[0039] According to the oil guide, the oil is fed via the supply line 43 into the cavity of the rotor shaft 6, which is designed as a hollow shaft, up to the axial height of the pivot bearing 15 remote from the gearbox. From there, the oil is guided into the rotor channels 53 via a flow connection 76 remote from the gearbox. The oil then flows in the opposite direction in the rotor channels 53 until it reaches a flow connection 77 near the gearbox, where the oil is returned to the cavity of the rotor shaft 6.

[0040] A further core of the invention is that the coolant supply system has an additional closed air circuit. The following components are integrated into the closed air circuit: the dual pump 64, an air inlet 83, the inlet-side rotor chamber 61, an air gap 85 between the rotor 5 and the stator 4, and an air outlet 87 at the outlet-side rotor chamber 61. The air outlet 87 at the outlet-side rotor chamber 61 is positioned at the bottom of the coolant separator 57. During electric machine operation, leakage coolant collects on the bottom of the coolant separator 57, which escapes from the winding head chamber 59 and from the bearings 13 and 15, both of which are oil-lubricated. In addition, leakage coolant from the internal rotor cooling system collects.Not only the leakage coolant is discharged via the air outlet 87, but also an air flow L, described later, which is circulated in the closed air circuit.

[0041] The air outlet 87 is in the Fig. 1connected via a return line 89 to a suction side of the return pump integrated in the dual pump 64. By means of the return pump integrated in the dual pump 64, the mixture of the air flow L and the leakage coolant is sucked out of the outlet-side rotor chamber 61, creating a negative pressure in the outlet-side rotor chamber 61, whereby a pressure gradient arises between the gear chamber 63 and the rotor chamber 61, which leads to the air flow. The return pump integrated in the dual pump 64 has a riser line 91 on its pressure side, through which the mixture of air flow L and leakage coolant flows into the gear housing 63. This occurs with the creation of overpressure in the gear housing 63.

[0042] As from the Fig. 1As can be seen further, the air inlet 83 opens freely, i.e. without a direct pump connection, into the air-filled upper interior of the gear housing 63. In this way, a pressure gradient arises between the air-filled upper interior of the gear housing 63 and the inlet-side rotor chamber 61, whereby the air flow L is formed.

[0043] In the Fig. 2 An alternative embodiment is shown in which an air supply pump (not shown) is integrated into the dual pump 64. This pump sucks air from the air-filled upper interior of the gear housing 63, which is connected to the air inlet 83 via an air supply line 93. In addition, Fig. 2 The air outlet 87 is connected to the gearbox housing 63 via a return line 89. The return line 89 opens into the Fig. 2without a direct pump connection into the gearbox housing 63. Rather, the return line 89 ends with a riser line 99, via which the mixture of air flow L and coolant is fed into the gearbox housing 63.

[0044] As can be seen from the Fig. 1 and 2 As can be seen, an oil separator 97 is directly or indirectly connected upstream of the air inlet 87. With the aid of the oil separator 97, the air flow L is cleaned of coolant droplets before the air flow L enters the inlet-side rotor chamber 61.

[0045] In the Figure 1 and 2 the electric machine is additionally integrated in a cooling water circuit K in which the cooling water flows around the outer circumference of the electric machine housing 2. LIST OF REFERENCE SYMBOLS:

[0046] 2Electric machine housing 3Flange shafts 4Stator 5Rotor 6Rotor shaft 8, 9Housing wall 11Bearing opening 13, 15Pivot bearing 17Gearbox input shaft 18Gear stage 19Gearbox arrangement 20Axle differential 21Stator winding 23, 25Winding head 27Electric machine compartment 31Hub section 33Sealing element 35Coolant tank 37Supply pump 41, 42,43 Supply lines 44 Oil splash ring 45 Annular gap 46 Nozzles 47 Radial outer stator channel 49 Annular gap 51 Flow connection 53 Radial inner stator channel 54 Extraction 56 Return pump 57 Coolant separation 59 Winding head chamber 61 Rotor chamber 63 Gearbox housing 64 Dual pump 65 Coolant column 66 Riser 67 Hollow body 68 Hollow body drain point 69 Winding head chamber inlet 71 Winding head chamber drain point 72 Additional return line 76 Flow connection away from the gearbox 77 Flow connection near the gearbox 80 Coolant supply line 83 Air inlet 85 Air gap 87 Air outlet 89 Return line 91 Riser 93 Air supply line 97 Oil separator 99Rising pipe LAir flow KKooling water circuit,

Claims

1. Coolant supply system for an electric vehicle axle drive having a wet-running electric machine which is passed through by a coolant flow and in the electrical machine housing (2) of which a stator (4) interacts with a rotor (5) separated from the stator (4) via an air gap (85), wherein the electric machine interior is impinged with coolant for rotor internal cooling and / or for stator cooling, and wherein the coolant supply system has a flow unit (64), which is incorporated into a closed air circuit, and by means of which an air flow (L) flowing in the axial direction through the air gap (85) can be generated, as a result of which the air gap (85) is kept substantially free of coolant to reduce rotor drag losses, characterized in that located axially on both sides of the rotor / stator assembly is in each case an air flow chamber (61), in that the two air flow chambers (61) are fluidically connected to the air gap (85), and in that the two air flow chambers (61) are subdivided into an inlet-proximal air flow chamber (61) into which the air flow (L) flows by way of an air inlet (83), and into an outlet-proximal air flow chamber (61) having an air outlet (87) out of which the air flow (L) flows.

2. Coolant supply system according to Claim 1, characterized in that the two air flow chambers (61), the air gap (85) and the flow unit (64) are incorporated into an air circuit in which the air flow (L) generated by the flow unit (64) flows through the air inlet (83) into the inlet-proximal air flow chamber (61), is able to be guided axially through the air gap (85) and is able to be returned from the outlet-proximal air flow chamber (61) via the air outlet (87) to the flow unit (64).

3. Coolant supply system according to one of Claims 1 and 2, characterized in that the rotor / stator assembly has in each case axially on both sides a frontal housing space (27), and in that the air flow chamber (61) is a constituent part of the frontal housing space (27), and in that disposed in the electrical machine housing (2) is a coolant separation (57) which divides each housing space (27) into a radially outer winding head space (59) and a radially inner rotor space (61) which is separated from the latter in a largely fluid-tight manner and in which the rotor (5) is disposed and which forms the air flow chamber (61).

4. Coolant supply system according to Claim 3, characterized in that the air inlet (83) opens into the inlet-proximal rotor space (61), while the air outlet (83) opens into the outlet-proximal rotor space (61).

5. Coolant supply system according to one of Claims 3 and 4, characterized in that the winding head space (59) is a constituent part of a stator hydraulic circuit which has an infeed point (69) at which coolant from a coolant reservoir (63) is able to be fed into the winding head space (59), in particular by means of a feed pump, and in that the stator hydraulic circuit has an outfeed point (71) from which coolant from the winding head space (59) is able to be returned in the direction of the coolant reservoir (63).

6. Coolant supply system according to Claim 3, 4 or 5, characterized in that the coolant separation (57) forms a base of the rotor space (61) on which a leakage coolant escaping from the winding head space (59) and / or a leakage coolant escaping from the rotor internal cooling and / or a coolant escaping from the bearings (13, 15) collects, and in that the air outlet (87) is disposed on the rotor space base of the outlet-proximal rotor space (61) by way of which both leakage coolant as well as the air flow (L) are able to be discharged.

7. Coolant supply system according to one of the preceding claims, characterized in that a separator (97), by means of which coolant droplets are able to be removed from the air flow (L), is disposed indirectly or directly upstream of the air inlet (83).

8. Coolant supply system according to one of Claims 6 and 7, characterized in that the air outlet (87) is connected via a return line (89) to a suction side of a recirculation pump which extracts the mixture of air flow (L) and leakage coolant from the outlet-proximal rotor space (61), specifically by forming a vacuum in the rotor space (61), which causes a pressure gradient between the coolant reservoir (63) and the rotor space (61), causing the air flow, and in that in particular the recirculation pump has on its pressure side a riser line (91) by way of which the mixture of air flow (L) and leakage coolant flows into the coolant reservoir (63), and / or in that in particular the air inlet (83) opens into the air-filled upper interior of the coolant reservoir (63) without a direct pump connection so that the air flow (L) through the air inlet (83) is the result of a pressure gradient between the coolant reservoir (63) and the rotor space (61).

9. Coolant supply system according to Claim 6 or 7, characterized in that an air feed pump, which extracts air from the air-filled upper interior of the coolant reservoir (63) and is connected to the air inlet (83) via an air supply line (93), is disposed in the coolant reservoir (63), and in that the air outlet (87) is connected to the coolant reservoir (63) via a return line (89) which opens into the coolant reservoir (63) without a direct pump connection.

10. Coolant supply system according to one of Claims 5 to 9, characterized in that the feed pump for stator cooling and / or the rotor internal cooling as well as the return pump or feed pump for the air flow (L) are combined so as to form a double pump (64) which forms the flow unit and in which the pumps are able to be driven by a common drive shaft.