Method for operating an electric traction motor of a vehicle and drive train of a vehicle

Abstract

Method for operating an electric traction motor (20) of a vehicle (10), comprising: Transmitting a driving movement of the vehicle (10) as a rotational movement to a rotor (22) of the traction motor (20), and Applying a negative pressure to the rotor (22) while the rotational movement moves the rotor (22), wherein the negative pressure is generated by pumping air out of a closed housing (21) surrounding the rotor (22) by means of a negative pressure source, characterized in that the vacuum source is a vacuum pump (40) which generates a vacuum in a brake booster (50) of the vehicle (10) during operation of the vehicle (10), and the application of the negative pressure to the rotor (22) is terminated when the electric traction motor (20) generates traction power for moving the vehicle (10).

Description

[0001] It is well known that electric motors or electric machines are used to power vehicles. Such machines are called electric traction motors.

[0002] Particularly in electric vehicles and hybrid vehicles, which have an electric motor as a drive unit, an electric machine converts electrical current into movement, with a rotor rotating relative to a stator.

[0003] While the electric motor is used for traction, it generates waste heat, which is dissipated by suitable ventilation measures or by liquid cooling.

[0004] However, there are some operating conditions in which the traction motor continues to move, albeit passively. For example, when the vehicle is in a so-called sailing or coasting mode, in which the vehicle rolls with only minimal assistance from the drive system or without any power, or when the vehicle is in a mode in which another component of the drivetrain generates traction power or propulsion, for example, when only one combustion engine of a hybrid vehicle is operating. In these cases, the rotating rotor generates air turbulence, which decelerates the vehicle, thereby worsening its energy balance.

[0005] US 3 574 325 A describes an electrical machine whose interior can be evacuated to reduce drag losses.

[0006] DE 10 2006 036 445 A1 discloses a method and a device for generating a negative pressure in a brake system of a vehicle equipped with a hybrid drive.

[0007] It is an object of the invention to show a possibility with which the losses resulting from turbulence due to the rotor (so-called drag losses) can be reduced in a simple manner. Disclosure of the invention

[0008] This object is achieved by the method and the drive train according to the independent claims. Further embodiments are provided by the features of the subclaims and the features set forth in the description.

[0009] The aim is to reduce turbulence losses in vehicle electrical machines, which arise when the vehicle's driving motion is transmitted to the electrical machine (i.e. to the electric traction motor), by creating a vacuum on the rotor. Since drag losses are directly linked to the pressure of the gas in which the turbulence losses occur, the drag losses caused by turbulence can be significantly reduced by creating a vacuum. In traction motors used to traction a vehicle, the drag loss at normal pressure is usually well above the sum of the drag losses at negative pressure and the power required to create the negative pressure, so that the overall energy balance when creating a negative pressure is improved compared to conventional systems.

[0010] The vacuum is generated using one of the numerous components already present in a vehicle (for example, a vacuum pump in a brake booster), so that implementation requires little effort.

[0011] A method for operating an electric traction motor of a vehicle is therefore proposed as follows. The vehicle is an electric vehicle or preferably a hybrid vehicle, in particular with an internal combustion engine connected to a vehicle's power take-off. First, a driving motion of the vehicle is transmitted as a rotational motion to the rotor of the traction motor. This occurs in particular during coasting operation or during sailing operation of the vehicle, or in a driving mode in which another traction component (e.g., the internal combustion engine) (primarily) drives the vehicle.For example, at high speeds, such as over 80, 120 or 140 km / h, hybrid vehicles may be designed to switch off the electric traction motor, as these speeds are linked to speeds that are outside the standard speed range of the traction motor while the combustion engine drives the vehicle.

[0012] Coasting mode is a vehicle operation in which the electric traction motor generates only minimal traction power, for example, to essentially maintain a speed without exerting significant acceleration. The drive power can typically be > 0% and < 10%, < 5%, < 1%, or < 0.5% of the nominal maximum power of the electric traction motor. Since the power is low, in this mode, a driving movement of the vehicle (10) is transmitted as a rotational movement to a rotor (22) of the traction motor and essentially determines the rotational movement of the rotor.

[0013] Coasting operation refers to an operating mode in which the electric traction motor does not generate any torque, i.e. is not supplied with power.

[0014] Since in both sailing and coasting modes the driving motion significantly determines the rotational movement of the rotor, while the torque generated by the rotor only insignificantly influences the driving movement or the rotor does not generate any torque that influences the driving movement, the terms sailing mode and coasting mode are to be regarded as synonymous and are interchangeable in the context of the method described here.

[0015] A vacuum is applied to the rotor in order to reduce turbulence losses. The vacuum is applied while the rotational movement moves the rotor, i.e. while the traction motor is being towed by the vehicle. The vacuum is applied in particular to the interior of a housing of the traction motor, which housing seals off the traction motor (and in particular the rotor, optionally including the associated stator) from the environment, with the vacuum being provided in particular in an air gap between the rotor and an associated stator. The vacuum is usually not generated at the rotor itself, but only applied there, with the vacuum being provided by means of a vacuum source, in particular by means of a vacuum pump, by means of an intake tract, or also by means of a container in which a vacuum prevails. A vacuum pump can in turn be connected to such a container.

[0016] The application of negative pressure to the rotor does not necessarily mean that negative pressure exists only there. Rather, the negative pressure is applied not only in the immediate vicinity of the rotor, but preferably also to other components of the traction motor in order to avoid the need for complex sealing measures. In particular, the negative pressure can either be applied to the entire housing of the traction motor, which encloses all components of the traction motor (rotor, stator, electronics), or it can be applied to a module housing within the aforementioned housing. The module housing contains the rotor and stator, but not all other components of the traction motor. In particular, the electronics of the traction motor can be located outside the module housing.

[0017] The vacuum is preferably applied by pumping air (or another gas) out of a closed housing surrounding the rotor. This closed housing may be the same as the housing of the electric traction motor or the aforementioned module housing. The air or gas is pumped out using a vacuum source connected to the housing surrounding the rotor.

[0018] A vacuum pump is used as the vacuum source, so that the negative pressure is generated by means of the vacuum pump. The vacuum pump in this case is a vacuum pump of a brake booster of the vehicle. When the vehicle is in operation, the vacuum pump therefore generates a vacuum in a brake booster of the vehicle. The vacuum pump thus generates a vacuum in the brake booster and also on the rotor. For this purpose, the vacuum pump can be connected to both the brake booster and the rotor (i.e. the housing that surrounds the rotor) via a branch or a distributor. Negative pressure is generated by the vacuum pump when the vehicle is in operation, although this only applies in particular during operating phases while driving, for example when the vacuum pump is used as an additional pump alongside another vacuum source (such as an intake tract).The operation of the vacuum pump can overlap with the use of the additional vacuum source, or the vacuum pump and the additional vacuum source can be used alternately to generate the vacuum. Thus, the vacuum pump can be used in time multiplex mode (considering the vacuum pump as a vacuum resource) by the brake booster and to apply vacuum to the rotor.

[0019] The vacuum pump can in particular be an electric vacuum pump which supplies the brake booster with vacuum instead of or in combination with a further vacuum source. Such a further vacuum source is in particular the intake tract of an internal combustion engine or an intake line connected to it, since during operation of the internal combustion engine it usually generates vacuum there. This is used to supply the brake booster. In hybrid vehicles which comprise both an internal combustion engine and an electric traction motor, however, the internal combustion engine can be switched off during operation of the vehicle (i.e. while it is driving), so that the internal combustion engine or its intake tract is not available as a vacuum source.In such systems, in addition to tapping the intake tract as a vacuum source, an electric vacuum pump is usually provided, which is particularly active when the combustion engine is switched off but the brake booster is still to be supplied with vacuum.

[0020] Thus, such an electric vacuum pump serves an additional purpose, namely the generation of a vacuum that can be applied to the rotor of the electric traction motor. Thus, instead of just one function, the electric vacuum pump has two functions, requiring only a distributor or branch for the vacuum and, if necessary, a valve. Other vacuum sources or vacuum pumps can also be used as a vacuum source to apply a vacuum to the rotor, in particular the intake tract of an air compressor or the intake tract of a compressor of a supercharging device (i.e., a turbocharger) of the vehicle.

[0021] The negative pressure can be generated by means of an electrically driven vacuum pump, which is supplied, for example, by an on-board electrical system of the vehicle. The electrically driven vacuum pump can also be supplied by a generator that is driven by the driving movement of the vehicle, in particular by an alternator, a starter / generator or an electrical machine that has the exclusive purpose of generating electrical power for the vacuum pump and that is driven by the drive train, the rotating rotor or generally by the driving movement of the vehicle. The electrically driven vacuum pump can also be supplied with electrical power that is generated by the traction motor as an electrical generator from the rotational movement of the rotor. Since the traction motor is designed as an electrical machine, appropriate control orBy adjusting the operating mode of the electric machine, the traction motor itself can be used as a generator. While this slows down the rotor movement because the generator is running, this additional load on the rotor is less than the reduction in drag losses due to the negative pressure on the rotor. This results in an improved, positive energy balance.

[0022] Finally, it is possible for the vacuum to be generated using a mechanically driven vacuum pump. This vacuum pump is driven by the rotational movement of the rotor, by the vehicle's driving motion, or by a drivetrain component that transfers traction power to a vehicle's output. As already mentioned, the intake tract of an internal combustion engine (an air compressor or a turbocharger of an internal combustion engine) can also be used as a compressed air source.

[0023] The use of an electric vacuum pump as a vacuum source, which also generates a vacuum in a brake booster, has the advantage that it remains essentially unused during operation of the internal combustion engine. Thus, at high speeds, where the electric traction motor is only towed along, the electrically driven vacuum pump, which is already present, can essentially only be used to generate the vacuum to be applied to the rotor. Thus, the operation of the brake booster remains unaffected by the inventive use of an electric vacuum pump that supplies the brake booster to generate the vacuum to apply it to the rotor or to the electric traction motor.

[0024] Furthermore, the strength of the vacuum, and thus the power of the vacuum source or the vacuum pump, can be adapted to the vehicle speed (and in particular to the temperature inside the traction motor). At a first vehicle speed, the vacuum is generated with less power (or taken to a lesser extent from the vacuum source) than at a second vehicle speed that is greater than the first vehicle speed. Since turbulence losses are significantly higher at high speeds than at lower speeds, the strength of the vacuum can be reduced if the vehicle speed is already relatively low. Instead of a first and second vehicle speed, a first and a second speed of the electric machine can also be used to adjust the vacuum as described above.

[0025] Furthermore, it can be provided that the negative pressure is generated at a first temperature within the electric traction motor with a lower power than at a second temperature, which is lower than the first temperature. This applies in particular to air-cooled electric traction motors, especially to self-cooling electric traction motors, in which the movement of the rotor directly generates a coolant flow. Since a lower negative pressure (i.e., a higher pressure) is required for better heat dissipation at high temperatures than at low temperatures, the negative pressure applied to the rotor decreases with increasing temperature.The coolant flow can be guided past a cooling surface on the inside of the housing of the traction motor, so that the heat is first transferred from the coolant flow to the inside of the housing, then from the inside to the outside of the housing, where it can be dissipated into the environment.

[0026] According to the invention, the generation of the negative pressure on the rotor is terminated when the electric traction motor generates traction power to move the vehicle. Since heat is also lost in the traction motor when traction power is generated, heat dissipation should be increased so that the pressure on the rotor is increased or the negative pressure is reduced in order to be able to dissipate heat more effectively via the air as a cooling fluid. The application of the negative pressure is terminated by switching off the vacuum pump connected to the traction motor or at least reducing its power by isolating the negative pressure source, in particular by opening a valve connected between the negative pressure source and the traction motor, or by opening a valve that fluidically connects the rotor to the environment of the traction motor.This allows atmospheric air to enter the traction motor, reducing the negative pressure until atmospheric pressure is reached.

[0027] Repeating this process—creating a vacuum and ventilating the rotor chamber—several times creates a kind of breathing mechanism, allowing the hot air generated during normal operation to be easily blown out and replaced with fresh, cool air. This increases the maximum cooling capacity and could potentially even increase the continuous power of the electric motor, since the rotor is the most thermally critical part of an electric motor (especially in an ASM - asynchronous motor).

[0028] In order to achieve reduced turbulence losses as described here and also to dissipate heat from the motor, the negative pressure can be applied to the rotor, ended and then reapplied in order to introduce fresh air into the traction motor and at the same time to apply a negative pressure to the rotor at least temporarily. The periods in which the negative pressure is applied and in which no negative pressure is applied can alternate, in particular in a duty cycle. This duty cycle results, for example, from the temperature of the traction motor, from the heat to be dissipated or from the traction power generated by the traction motor. In particular, not only is a driving movement in the form of a rotational movement transferred to the rotor, but the traction motor itself generates traction power, for example to support another drive, so that heat loss also occurs in the traction motor.The above-mentioned duty cycle is greater the greater the traction power generated by the traction motor or the greater the heat power generated by the traction motor.

[0029] The duty cycle is the ratio of the time during which no vacuum is applied to the time during which vacuum is applied. In particular, the time during which vacuum is applied is greater than zero. The duty cycle can also depend on the outside temperature or on other operating parameters that reflect the required degree of cooling, in particular the temperature inside the traction motor or the temperature of the stator or rotor.

[0030] Furthermore, a drive train of a vehicle is described, wherein the drive train has an electric traction motor, in particular a traction motor as described above, and a vacuum source, in particular a vacuum source as described above. The vacuum source is fluidly connected to a rotor of the traction motor. In particular, the vacuum source is connected to a region within the traction motor in which the rotor is located. The vacuum source can be connected to the interior of a housing that surrounds the rotor and is closed.

[0031] The drive train has a brake booster connected to the vacuum source. The vacuum source is embodied as a vacuum pump. A distributor or junction can be connected to the vacuum pump, to which, in turn, the brake booster and the traction motor, in particular an area around the rotor, are connected. Valves can also be provided that control the connection between the junction and the brake booster or between the junction and the traction motor (or its housing).

[0032] The vacuum source may be configured as an electric vacuum pump. The vacuum pump has a supply connection configured to be connected to the vehicle's electrical system.

[0033] Furthermore, the vacuum source can be designed as an electric vacuum pump connected to an electric generator of the drive train (for example, an alternator or a starter / generator). The generator has a drive shaft that is directly or indirectly connected to an output of the drive train, in particular to a component that is connected to the output in a motion-transmitting manner.

[0034] Furthermore, the vacuum source can be designed as an electric vacuum pump having an electrical supply connection connected to an electrical connection of the traction motor. In this case, the traction motor is configured to also be operated as a generator and is particularly designed to convert a movement transmitted to the rotor into electrical power, which can be output at the electrical connection. This configuration can be provided in the form of power electronics that controls not only the current flowing to the traction motor but also the current flowing from the traction motor.

[0035] Furthermore, the vacuum source can be designed as a mechanical vacuum pump. This has a drive shaft that is connected to an output of the drive train, or to the rotor of the traction motor, or to another drive component, which in turn is connected to the output.

[0036] Finally, a tap in the intake tract of an internal combustion engine within the drivetrain, or the intake tract itself, can be used as a vacuum source. Furthermore, the intake tract of an air compressor of the vehicle in which the drivetrain is located, or the intake tract of a supercharging device of the internal combustion engine of the drivetrain, can be used as a vacuum source. A line, preferably equipped with a controllable valve, can be provided between the respective intake tract and the traction motor or the area around the rotor.

[0037] Finally, the traction motor can have a controllable valve that fluidically connects the rotor to the surroundings of the traction motor. This allows the application of the negative pressure to be terminated or the negative pressure to be reduced, in particular to allow a higher pressure for the cooling medium of the rotor or the traction motor. The controllable valve is opened in particular when a high temperature prevails inside the traction motor (which exceeds a predetermined threshold) or when the traction motor itself generates heat losses because it generates traction power for the drive.

[0038] Negative pressure is defined as a pressure below atmospheric pressure (under standard conditions). In particular, the negative pressure is at least 10 hPa, 30 hPa, 50 hPa, or at least 100, 200, or 400 hPa. Preferably, the negative pressure is not more than 500, 200, 100, 50 hPa, or 20 hPa. It may be provided that the negative pressure is not more than 15, 10, 5, or 2 hPa. Short description of the drawing The Fig. 1 shows an example of a vehicle designed according to the procedure described here. Detailed description of the drawings

[0039] The Fig. 1 shows a vehicle 10 with an electric traction motor 20, which includes a rotor 22 and a stator 24 surrounding the rotor. A drive shaft 26 is connected to the rotor 22 and extends from the traction motor 20 to transmit traction power to the output 30 (in the form of wheels). Depending on the operating mode, motion is also transmitted from the output to the drive shaft 26 of the traction motor 20, thereby also rotating the rotor 22 and generating turbulence losses as described herein.

[0040] The traction motor 20 has a housing 21. This encloses the interior of the traction motor 20 and in particular the rotor 22 (as well as the stator 24). The housing is completely closed (except for valve-controlled passages). The traction motor 28 further has an electrical supply connection 28, which is electrically connected to the stator or rotor. The supply connection serves to supply power to the traction motor and can also be used to output electrical power generated by the traction motor in generator mode.

[0041] To reduce drag losses when transmitting motion from the output 30 to the traction motor 20, negative pressure from a vacuum source 40 is applied or generated via a passage 23. A valve 52 is provided between the vacuum pump 40 and the passage 23, which leads through the housing 21 into the interior of the traction motor 20. Furthermore, the vacuum pump 40 is connected via a further valve 54 to a brake booster 50, which acts on the drive 30 as shown by the horizontal double arrows. For clarity, the braking devices located between the brake booster 50 and the output 30 are not shown.

[0042] Also symbolically depicted is an internal combustion engine 60, the intake tract of which is connected to the brake booster 50. This connection can also be controlled by a valve. Furthermore, the dash-dotted line shows that the intake tract 60 can serve as a vacuum source that can supply negative pressure to the passage 23. The connection between the intake tract of the internal combustion engine 60 and the passage 23 can also run via a connection that connects the intake tract 23 to the vacuum pump 40 and / or to the brake booster 50. The connection between the intake tract and the passage 23 is preferably provided with a controllable valve, which for reasons of clarity is shown in the Fig. 1 is not shown.

[0043] Alternative vacuum sources are shown in dashed lines, wherein a vacuum pump 42 can be designed as an electric vacuum pump that is connected to the electrical connection 28 of the traction motor 20 in order to be supplied with electrical power, which the traction motor 20 generates as a generator. For this purpose, the electric vacuum pump 42 can have a connection 43 that is connected to the electrical connection 28 of the traction motor. Since the connection 43 of the electric vacuum pump 42 only serves to supply the vacuum pump with electrical power, the connection 43 can also be referred to as a supply connection. As an alternative source of supply power, an on-board electrical system 80 can be provided, which can also be connected to the supply connection of the electric vacuum pump 42. In this case, the electric vacuum pump 42 can use the on-board electrical system 80 and the electrical connection 28 of the traction motor 20 alternatively or in combination.

[0044] As a further alternative to the design of the vacuum source, an (optional) mechanical vacuum pump 44 is shown, which has a drive source 45. This is connected to the drive shaft 26 of the traction motor 22, preferably via an (optional) coupling 46, with which the mechanical vacuum pump 44 can be decoupled from the traction motor 20 or its drive source 26 in a controlled manner. A gear can also be provided at the location of the coupling 46. Both the electric vacuum pump 42 and the mechanical vacuum pump 44 are connected to the passage 23 and thus to the interior of the traction motor 20 in order to apply a vacuum to the motor located there.

[0045] Thus, the negative pressure of the following components can be applied to the rotor 22 (preferably via the passage 23) (in any combination or individually): - by an electric vacuum pump 40, which also supplies a brake booster 50 with negative pressure; - from an intake tract of an internal combustion engine 60, which may also generate negative pressure for the brake booster 50; - by an electric vacuum pump 42, which is electrically driven in particular by the traction motor or by an on-board network 80, or - by a mechanical vacuum pump 44, which is driven by the drive shaft 26 (or also by the output 30), by the components of the drive train which are connected to the output, or by an electric motor.

[0046] Finally, it should be noted that the valves shown and not shown here can be controlled by means of a control unit which, for the sake of clarity, is shown in Fig.1 is not shown. Such a control unit comprises an input via which a signal can be input which can detect the operating state of the traction motor and / or the combustion engine (active or inactive), and via which the temperature within the traction motor 20 can also preferably be detected, for example by means of a temperature sensor in the traction motor 20.

[0047] The temperature can be determined using a thermal electric motor model of the traction motor 20, wherein the electric motor model is present, for example, in the control unit, for example in a program of the control unit. This thermal model would reuse other existing measured variables from the system, such as voltages and currents, thus eliminating the need for a separate temperature sensor. Furthermore, temperature determination through a combination of a measurement and a calculation using a model is also conceivable, so that, for example, the temperature profile of the most thermally critical parts (usually the rotor) could be predicted in order to find the optimal time for generating or applying the vacuum.

Claims

[1] A method for operating an electric traction motor (20) of a vehicle (10), comprising: Transmitting a driving movement of the vehicle (10) as a rotational movement to a rotor (22) of the traction motor (20), and Applying a negative pressure to the rotor (22) while the rotational movement moves the rotor (22), wherein the negative pressure is generated by pumping air out of a closed housing (21) surrounding the rotor (22) by means of a negative pressure source, characterized by , that the vacuum source is a vacuum pump (40) which generates a vacuum in a brake booster (50) of the vehicle (10) during operation of the vehicle (10), and the application of the negative pressure to the rotor (22) is terminated when the electric traction motor (20) generates traction power for moving the vehicle (10). [2] The method of claim 1, wherein the vacuum is generated at a lower power at a first vehicle speed than at a second vehicle speed that is greater than the first vehicle speed. [3] Drive train of a vehicle (10) in which a method according to one of the preceding claims can be carried out, wherein the drive train has an electric traction motor (20) and a vacuum source which is fluidly connected to a rotor (22) of the traction motor (20), wherein the drive train further has a brake booster (50) which is connected to the vacuum source designed as a vacuum pump (40). [4] Drive train according to claim 3, wherein the traction motor (20) has a controllable valve (70) which fluidically connects the rotor (22) to the environment of the traction motor (20).

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