Improved electromagnetic compatibility of a drive system for an electrically powered vehicle

Abstract

Drive arrangement (1) for an electrically powered vehicle, with - an electric machine (10) designed to accelerate the vehicle, wherein the electric machine (10) has a rotor (11) arranged inside a stator with stator windings (8) and which is arranged on a rotor shaft (14); - a drive shaft (24) coupled to a drive wheel (29) of the vehicle; and - a shaft coupling (100) which transmits the torque delivered by the rotor shaft (14) so ​​that it can be directed to the drive shaft (24), wherein the shaft coupling (100) has a torque receiving element (102) which receives the torque delivered by the electric machine (10), and a torque delivery element (106) which is mechanically coupled to the torque receiving element (102) and delivers the torque in the direction of the drive shaft (24); wherein an electrically insulating grease (104) is arranged between the torque receiving element (102) and the torque delivery element (106), characterized in that the electrically insulating grease (104) comprises particles of an insulating solid (105).

Description

[0001] The invention relates to an improved drive arrangement for an electrically powered vehicle in which disturbances radiated from an electric machine via shafts to drive the motor vehicle are reduced.

[0002] Electric machines for powering motor vehicles are known in the prior art, for example in vehicles with a so-called hybrid drive, which comprises an internal combustion engine and an electric machine, and in fully electric vehicles powered solely by an electric machine. An electric machine typically comprises a stator with a plurality of stator windings. The rotor can consist of permanent magnets, electrically excited magnets, or a cage.

[0003] The stator windings are typically driven by an inverter. The inverter does not generate an ideal signal waveform, but rather one with jumps and interference spikes. These jumps and interference spikes cause so-called ripple currents or ripple voltages in the electric machine. These ripple currents can propagate through the gearbox to the drive shafts, emitting interference fields. It goes without saying that such interference fields are undesirable.

[0004] DE 11 2010 004 938 T5 discloses a retrofit kit for grounding a shaft, comprising a conductive ring element and a cylindrical spring with a diameter equal to that of the conductive ring element. The spring constant of the cylindrical spring is such that the spring keeps the conductive ring element in contact with the shaft and the housing within the housing.

[0005] DE 35 11 755 A1 discloses an arrangement for discharging shaft voltages, wherein on the shaft side of the electrodynamic machine, where the bearings are galvanically isolated from earth, mass and foundation by insulating gaps, a current path is provided with a contact device having at least one sliding contact and a capacitor connected in series thereto between the shaft and the machine mass or earth.

[0006] DE 60 2004 011 867 T2 discloses the reduction of wave voltages and wave currents by conductive bearing grease, insulating the bearings, and using copper-phosphorus brushes and a Faraday shield. Furthermore, an annular frame in an annular channel with several electrically conductive threads can be used to reduce ionization in the presence of an electric field.

[0007] DE 10 2013 200 356 A1 discloses a bearing system for a wind turbine with an insulating ring for electrically insulating a bearing ring from a wind turbine element.

[0008] DE 26 57 575 A1 discloses a parallel shaft drive, in particular for rail vehicles, with an electric motor arranged parallel to the drive axle and essentially next to it, which is connected to a gearbox via a gear coupling or the like.

[0009] The teachings of the prior art are not sufficient to guarantee the electromagnetic compatibility of a drive arrangement for an electrically powered vehicle.

[0010] The invention aims to create a drive arrangement for an electrically powered vehicle that has improved electromagnetic compatibility.

[0011] The object of the invention is achieved by a drive arrangement for an electrically powered vehicle according to claim 1. The dependent claims describe preferred embodiments.

[0012] A drive arrangement for an electrically powered vehicle comprises an electric machine configured to accelerate or decelerate the vehicle, the electric machine having a rotor arranged within a stator with stator windings and mounted on a rotor shaft. The drive arrangement further comprises a drive shaft coupled to a drive wheel of the vehicle. The drive arrangement also includes a shaft coupling that transmits the torque delivered by the rotor shaft so that it can be directed to the drive shaft, the shaft coupling having a torque receiving element that receives the torque delivered by the electric machine and a torque delivery element that is mechanically coupled to the torque receiving element and delivers the torque towards the drive shaft.An electrically insulating grease is arranged between the torque receiving element and the torque delivering element.

[0013] The electrically insulating grease prevents the shaft voltage and current from propagating further via the shaft coupling, thus increasing the electromagnetic compatibility of the drive assembly. The shaft currents and voltages are not conducted into the gearbox or the drive shaft of the electrically powered vehicle.

[0014] It is not necessary for the torque receiving element to be directly coupled to the rotor shaft. It is also not necessary for the torque delivering element to be directly coupled to the drive shaft.

[0015] The torque receiving element and the torque delivering element can be positively connected to each other. The insulating grease can be applied to the positively connected joint.

[0016] The torque receiving element and the torque output element can form a shaft-hub interface. The torque receiving element can be a splined shaft and the torque output element can be a hub with a broached internal profile. Alternatively, the torque receiving element can be a hub with a broached internal profile and the torque output element a splined shaft.

[0017] The electrically insulating grease contains particles of an electrically insulating solid. This grease may contain polytetrafluoroethylene (PTFE) particles, polytetrafluoroethylene flakes, or similar materials. PTFE is also known under the brand name Teflon. The addition of PTFE as an additive to the grease achieves an insulating effect because the PTFE particles can adhere to the torque receiving and torque delivering elements.

[0018] Preferred are particles, flakes, or additives that form an insulating film between and / or on the torque receiving element and the torque delivering element. The insulating film can form, for example, due to the mechanical forces acting on the grease and the particles, flakes, or additives.

[0019] Lubricating grease must be applied to both the torque receiving and torque delivering elements to prevent corrosion. Adding additives to the grease ensures both good corrosion protection and good electrical insulation.

[0020] The electrically insulating grease placed between the torque receiving element and the torque delivering element can create a contact resistance between the torque receiving element and the torque delivering element of at least 10 kΩ, preferably at least 100 kΩ, and most preferably at least 1 MΩ. With a contact resistance of approximately 1 MΩ, the electromagnetic compatibility of the drive arrangement improves by a factor of about 10, which corresponds to an attenuation of approximately 20 dB.

[0021] The torque receiving element can be integrally formed with the rotor shaft. For example, the rotor shaft can have a splined shaft profile or a hub profile with a cleared inner profile at one end. In this embodiment, the electrical isolation of the shaft currents or voltages occurs very close to the electric machine. The rotor shaft can be coupled to the drive shaft via a gearbox. The torque output element can be integrally formed with a gearbox shaft. This embodiment results in a compact drive arrangement and the isolation of the shaft currents or voltages close to the electric machine.

[0022] The invention will now be described in more detail and without limitation by means of an embodiment with reference to the attached figures, wherein Fig. 1 shows an equivalent circuit diagram of a drive arrangement for propelling a motor vehicle; Fig. 2a shows a cross-section through a shaft coupling; and Fig. 2b shows a longitudinal section through a rotor shaft and a transmission shaft in the area of ​​the shaft coupling.

[0023] It will be on Fig. 1 Reference is made to Figure 1, which shows a schematic view of a drive arrangement 1 of an electrically powered vehicle, in which an electrical equivalent circuit diagram for electromagnetic compatibility as well as for shaft voltages and shaft currents is also shown.

[0024] An inverter 2 is arranged in an inverter housing 6. The inverter 2 generates a three-phase alternating current from the DC voltage of a traction battery (not shown). The three-phase alternating current includes harmonics and pulses (so-called ripples). The three-phase alternating current is transmitted via a three-phase line 4 to an electric machine 10.

[0025] The electric machine 10 has three stator windings 8. The rotating magnetic field generated by the stator windings 8 causes a force to act on magnets 11 on the rotor shaft 14, which in turn causes the rotor shaft 14 to rotate. The rotor shaft is coupled via a shaft-hub interface 100 to the input shaft 18 of a gearbox 30 with a plurality of meshing gears 20, 22, which transmit the torque of the rotor shaft 14 to a drive shaft 24. A brake disc 26 and a wheel 29 are arranged on the drive shaft 26.

[0026] The electrical equivalent circuit is described below insofar as it concerns the electromagnetic compatibility of the drive arrangement 1. A ground strap 12 between the electric machine and the housing of the inverter 6 acts as a ground inductance L. GNDThe three-phase line 4 and / or the stator windings 8 exhibit a first parasitic capacitance 16 to the rotor shaft 14. The rotor windings 8 exhibit a second parasitic capacitance 9 to the housing of the electric machine 10. Furthermore, the brake disc 26 exhibits a third parasitic capacitance 27 to the body 28, for example via the brake pads. The oil in the gearbox 32 generates a parasitic resistance 32.

[0027] The following describes exemplary wave currents and wave voltages, insofar as they are essential for considering the electromagnetic compatibility of the drive arrangement 1. A first wave current 50 flows from the inverter 2 via the three-phase line 4, the first parasitic capacitances 16, the rotor shaft 14, the input shaft 18 of the gearbox 30, and via the gears 20 and 22 of the gearbox 30 to the drive shaft 24. This applies a wave voltage to the drive shaft 24, which is an alternating voltage, so that the drive shaft acts as an antenna and emits an interference signal. The first wave current 50 can flow to the body 28 via the brake discs and the third parasitic capacitance 27.

[0028] A second parasitic wave current 52 flows from the inverter 2 via the three-phase line 4, the first parasitic capacitances 16, the rotor shaft 14, the shaft-hub interface 100, the gearbox input shaft 18, at least one gear 20, 22 and the parasitic gearbox oil resistance 32 to the gearbox housing 30, from where it flows back to the inverter 2 via the housing of the electric machine 10, past the EMC seal 7, via the housing 6 of the inverter.

[0029] A third parasitic wave current 54 flows from the inverter 2 via the three-phase line 4, the first parasitic capacitances 16, the rotor shaft 14, the shaft-hub interface 100, the input shaft 18 of the gearbox 30 and via the parasitic resistance 32 of the gearbox oil to the gearbox housing 30. From the gearbox housing 30, the third parasitic wave current 54 flows to the housing of the electric machine 2 and via the ground strap 12, which forms a parasitic inductance, to the housing 6 of the inverter 2 and finally to the inverter 2.

[0030] A fourth parasitic wave current 56 flows from the inverter 2 via the three-phase line 4, the stator windings 8 and the second parasitic capacitance 9 to the housing of the electrical machine 10, from where the fourth parasitic wave current flows past the EMC seal 7 to the housing 6 of the inverter 2 and finally to the inverter 2.

[0031] It will be on Fig. 2a and Fig. 2b referred to, whereby Fig. 2a a cross-section through the shaft-hub interface 100 and Fig. Figure 2b shows a longitudinal section through the shaft-hub interface 100. The rotor shaft 14 comprises a plurality of radially extending teeth 102. The input shaft 18 of the gearbox 30 comprises a hub 110 with a plurality of recesses 106 extending radially. The teeth 102 of the rotor shaft 14 are arranged within the recesses 106 of the hub 110, which is attached to the input shaft 18 of the gearbox 30. The shaft-hub interface 100, which forms a shaft coupling, also includes a housing 108, which may be made of plastic.

[0032] A film of grease 104 is located between the teeth 102 and the recesses 106. This film of grease is necessary to prevent corrosion of the teeth 102 and the recesses 104.

[0033] The inventors of the present invention have discovered that the first wave current 50, the second wave current 52, and the third wave current 54 can be significantly attenuated if an electrically insulating grease 104 is used in the shaft-hub interface 100. The insulating grease 104 can, for example, comprise polytetrafluoroethylene particles and / or polytetrafluoroethylene flakes. Polytetrafluoroethylene is also known as Teflon. The inventors of the present invention have found that the wave currents can be reduced by a factor of 10 by using the insulating grease 104, which corresponds to an attenuation of approximately 20 dB at, for example, 25 MHz.

[0034] The polytetrafluoroethylene particles and / or polytetrafluoroethylene flakes are added to the insulating grease 104 as an additive. They form an insulating polytetrafluoroethylene layer, which is created, for example, at the transition from the teeth 102 to the recesses 104. In contrast, a conventional grease allows a conductive contact point to form on the surface roughness of a tooth 102 and / or a recess 106.

[0035] The insulating grease 104 creates a shaft-hub interface 100 with a contact resistance of at least 10 kΩ, preferably at least 100 kΩ, and most preferably at least 1 MΩ. This contact resistance allows shaft currents to be reduced by a factor of 10 or attenuated by 20 dB.

Claims

[1] Drive arrangement (1) for an electrically powered vehicle, with - an electric machine (10) designed to accelerate the vehicle, wherein the electric machine (10) has a rotor (11) arranged inside a stator with stator windings (8) and which is arranged on a rotor shaft (14); - a drive shaft (24) coupled to a drive wheel (29) of the vehicle; and - a shaft coupling (100) that transmits the torque delivered by the rotor shaft (14) so ​​that it can be directed to the drive shaft (24), wherein the shaft coupling (100) has a torque receiving element (102) that receives the torque delivered by the electric machine (10), and a torque delivering element (106) that is mechanically coupled to the torque receiving element (102) and delivers the torque in the direction of the drive shaft (24); wherein an electrically insulating grease (104) is arranged between the torque receiving element (102) and the torque delivering element (106), characterized by , that the electrically insulating grease (104) contains particles of an insulating solid (105). [2] Drive arrangement (1) according to claim 1, characterized by , that the torque receiving element (102) and the torque delivering element (106) are positively connected to each other. [3] Drive arrangement (1) according to claim 1 or 2, characterized by, that the torque receiving element (102) and the torque delivering element (106) form a shaft-hub interface (100). [4] Drive arrangement (1) according to one of claims 1 to 3, characterized by , that the torque receiving element (102) is a toothed shaft and the torque delivering element (104) is a hub with a cleared internal profile or the torque receiving element is a hub with a cleared internal profile and the torque delivering element is a toothed shaft. [5] Drive arrangement (1) according to claim 1, characterized by , that the insulating fat (104) has at least one of the following: - Polytetrafluoroethylene particles (105); - Polytetrafluoroethylene flakes (105). [6] Drive arrangement (1) according to any one of claims 1 to 5, characterized by, that the electrically insulating grease (104) arranged between the torque receiving element (102) and the torque delivering element (104) has a contact resistance between the torque receiving element (102) and the torque delivering element (104) of at least 10 kΩ. [7] Drive arrangement (1) according to any one of claims 1 to 6, characterized by , that the torque receiving element (102) is integrally formed with the rotor shaft (14). [8] Drive arrangement (1) according to any one of claims 1 to 7, characterized by a gearbox (30) that is coupled to the rotor shaft (14) and the drive shaft (24). [9] Drive arrangement (1) according to claim 8, characterized by , that the torque output element (106) is integrally formed with a transmission shaft (18).

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