Method for operating a drive device for a motor vehicle, corresponding drive device and computer program product

Abstract

The invention relates to a method for operating a drive device (1) for a motor vehicle, which drive device has an electric traction machine (2) which is at least temporarily cooled by means of a coolant and has a rotor (3) and a stator (4) which is spaced apart from the rotor (3) by an air gap (6). According to the invention, if there is a brake request for providing a predefined braking torque by way of hydrodynamic braking, a specific amount of the coolant to be added is introduced into the air gap (6). The invention also relates to a drive device (1) for a motor vehicle and to a computer program product.

Description

[0001] Method for operating a drive device for a motor vehicle, corresponding drive device and computer program product

[0002] DESCRIPTION:

[0003] The invention relates to a method for operating a drive device for a motor vehicle, which has an electric traction machine, cooled at least temporarily by a coolant, with a rotor and a stator spaced from the rotor by an air gap. The invention further relates to a corresponding drive device and a computer program product.

[0004] For example, EP 0 641 499 B1 is known from the prior art. This describes an electric rotary motor vehicle drive motor with an inner stator and an outer rotor, on the outside of which a sealed housing is provided. A hydrodynamic brake that can be selectively activated and deactivated is to be formed between the outer rotor and the housing.

[0005] It is an object of the invention to propose a method for operating a drive device for a motor vehicle, which has advantages over known methods, in particular enables a reliable provision of a braking torque with the aid of the traction machine, preferably in the event of a malfunction of the motor vehicle or the drive device.

[0006] This is achieved according to the invention with a method for operating a drive device for a motor vehicle having the features of claim 1. It is provided that when a braking request occurs, a specific additional coolant quantity of the coolant is introduced into the air gap to provide a predetermined braking torque by hydrodynamic braking.

[0007] Advantageous embodiments with useful further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments explained in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are feasible.

[0008] The drive device serves to drive the motor vehicle, i.e., to provide a drive torque directed towards driving the motor vehicle. To provide the drive torque, the drive device has at least one drive unit, wherein the drive unit or one of several drive units is designed as an electric traction machine. The traction machine is at least temporarily drive-connected to at least one wheel axle of the motor vehicle, such that the motor vehicle can be directly driven by means of the traction machine, namely via the operative connection between the traction machine and the at least one wheel axle. For example, the traction machine is drive-connected to only one of several wheel axles of the motor vehicle or, alternatively, it is at least temporarily drive-connected to several wheel axles of the motor vehicle.In any case, a torque provided by the traction machine acts directly on at least one wheel axle.

[0009] The traction machine has the rotor and the stator, which are usually arranged coaxially with each other with respect to a rotational axis of the rotor. The rotor is rigidly connected to a machine shaft of the traction machine or is seated on the machine shaft, with the torque of the traction machine being provided via the machine shaft. In other words, the machine shaft is drive-connected, at least temporarily, to at least one wheel axle of the motor vehicle in the manner already explained. The air gap is located in the radial direction with respect to the rotational axis between the rotor and the stator. Ideally, the air gap is as small as possible in the radial direction in order to minimize magnetic losses of the traction machine. Conversely, however, it is large enough to compensate for a tolerance of the traction machine and / or dimensional changes of the rotor and / or stator that occur during operation of the traction machine.For example, the air gap in the radial direction has dimensions between 0.1 mm and 0.5 mm, between 0.2 mm and 0.4 mm or approximately or exactly 0.3 mm, inclusive of the values ​​mentioned.

[0010] The rotor is located within the stator. This means that the stator surrounds the rotor and, viewed axially relative to the rotational axis, overlaps the rotor. The space defined radially outward by the stator serves both to accommodate the rotor and to form the air gap. The air gap is defined radially inward by the rotor and radially outward by the stator.

[0011] During operation of the electric traction machine, heat is generated, which is at least temporarily dissipated by the electric machine, namely using the coolant. The coolant is preferably present in a coolant circuit in which the coolant is at least temporarily circulated. The coolant is supplied to the traction machine and absorbs heat there. The coolant is then removed from the traction machine, and the heat it contains is dissipated, in particular to the outside environment, preferably using a vehicle radiator. However, it can also be provided to actively control the temperature of the coolant, in particular using a refrigeration circuit.

[0012] For example, there are coolant channels in the traction machine through which the coolant flows to cool the traction machine. The coolant channels are preferably made in the stator and therefore primarily serve to cool the stator. Additionally or alternatively, the cooling channels are provided in the rotor. In this case, for example, they are fluidly connected to the coolant circuit via a coolant channel configured in the machine shaft. Additionally or alternatively, the coolant for cooling the traction machine is also supplied to the air gap, at least temporarily. However, since hydrodynamic losses occur here, in particular due to the rotor splashing in the coolant, the amount of coolant present in the air gap is usually limited to the minimum necessary to cool the traction machine.

[0013] Particularly in purely electrically powered motor vehicles, which, for example, have only the electric traction motor or multiple electric traction motors, the motor vehicle should be decelerated at least temporarily using the traction motor. For this purpose, the traction motor is operated as a generator. When a braking torque is provided to brake the motor vehicle, electrical current is generated. This current is typically temporarily stored in an energy storage device and used at a later time to operate the traction motor, thus driving the motor vehicle.

[0014] Providing the braking torque and generating the electrical current can also be referred to as recuperation. However, the energy storage device cannot absorb the electrical energy in every operating state of the drive system. In this case, the electrical energy would have to be dissipated in another way, for example by generating heat. However, this is not possible in every operating state and is generally only possible to a limited extent. It is also necessary to safely brake the vehicle, especially to a standstill, even in the event of a malfunction, for example, a partial or complete failure of the vehicle's electrical system.

[0015] For this reason, the invention provides for actively using the coolant to provide the braking torque, i.e., to brake the motor vehicle. To this end, when the braking request occurs, the specified additional coolant quantity is introduced into the air gap to provide the specified braking torque. As already explained, the coolant present in the air gap causes hydrodynamic losses, thus braking the rotor relative to the stator, so that the braking torque is generated hydrodynamically.

[0016] The additional coolant quantity of the coolant is understood to be the quantity of coolant that is introduced into the air gap during the introduction of the coolant into the air gap, in addition to the coolant already present in the air gap. For example, the quantity of coolant present before introduction into the air gap is referred to as the initial coolant quantity, which is increased by the introduction of the additional coolant quantity. It can be provided that the initial coolant quantity is zero, i.e. that there is no coolant in the air gap before the coolant is introduced. However, particularly in the case of a wet-running traction machine, an initial coolant quantity other than zero can already be present in the air gap.

[0017] The braking request is generated, for example, by a driver of the motor vehicle, in particular by actuating an operating element, preferably a brake pedal, by a driver assistance device of the motor vehicle, or by the drive device itself. In the former case, the driver specifies a preset braking torque, for example, by adjusting the operating element accordingly. The preset braking torque is determined from the position of the operating element. For example, it is provided that the preset braking torque is generated at least partially by introducing coolant into the air gap. In particular, for this purpose, the quantity of coolant present in the air gap is set to a specific preset coolant quantity, which is determined from the preset braking torque.

[0018] Particularly preferably, an actual torque of the motor vehicle corresponding to the specified braking torque, which causes the braking of the motor vehicle, is provided solely by means of the drive device and without the use of a service brake of the motor vehicle, in particular if the specified braking torque is less than a threshold value. If the specified braking torque exceeds the threshold value, i.e., is greater than it, the actual braking torque is only partially generated by means of the drive device through hydrodynamic braking, whereas a further portion, or the remainder, is provided using the service brake. This reliably prevents damage to the traction machine caused by the coolant present in the air gap.

[0019] The braking request can also be generated by the drive device itself, in particular automatically, for example, in the event of a failure of the motor vehicle's electrical system. In this case, the specified braking torque preferably corresponds to the maximum torque that can be achieved by hydrodynamic braking. Thus, the maximum available coolant quantity is introduced into the air gap, so that the additional coolant quantity is comparatively large. In other words, the coolant quantity present in the air gap is increased, for example, starting from zero or from a non-zero initial coolant quantity, in order to provide the braking torque through hydrodynamic braking of the traction motor.The described procedure has the advantage that, regardless of the state of other components of the drive device and / or the motor vehicle, a reliable provision of the braking torque is always possible, in particular in the event of a failure of one or more of the components.

[0020] A further development of the invention provides that a wet-running electric motor is used as the traction machine, and in order to provide the braking torque, a quantity of coolant present in the air gap is increased from an initial coolant quantity by introducing the additional coolant quantity. A wet-running electric motor is understood to be an electric motor in which, independent of the hydrodynamic braking, at least temporarily, in particular continuously, a quantity of coolant other than zero, namely the initial coolant quantity, is present in the air gap. The coolant present in the air gap serves to cool and / or lubricate the traction machine. In order to generate the braking torque in a targeted manner, the quantity of coolant corresponding to the initial coolant quantity is increased by the additional coolant quantity, so that there is subsequently more coolant in the air gap than before the braking torque is provided.This allows the aforementioned advantages to be achieved in a simple manner.

[0021] A further development of the invention provides that the additional coolant quantity is determined as a function of the specified braking torque. The braking torque corresponds, for example, to the aforementioned specified braking torque. In order to provide at least part of the braking torque or even the entire braking torque using hydrodynamic braking, the additional coolant quantity is determined from the specified braking torque, for example, using a mathematical relationship, a characteristic map, and / or a table. In any case, the additional coolant quantity depends directly on the specified braking torque. This allows the motor vehicle to be reliably braked in an emergency or even to at least partially replace a service brake of the motor vehicle.

[0022] A further development of the invention provides that the specified coolant quantity is used as a coolant quantity that is at least 2, at least 3, or at least 4 greater than the initial coolant quantity. To provide the braking torque through hydrodynamic braking, a coolant quantity is introduced into the air gap that is significantly greater than the coolant quantity previously present in the air gap. An even larger coolant quantity can also be used; for example, the specified coolant quantity is at least 10, at least 20, or at least 30 greater than the initial coolant quantity. This achieves a significant braking effect and reliably brakes the motor vehicle.A further development of the invention provides that the air gap is fluidly connected to a coolant circuit of the drive device and that the coolant is circulated in the coolant circuit at least temporarily by means of a coolant pump. Such a design of the drive device and such a procedure have already been mentioned. The coolant pump is operated at least temporarily to circulate the coolant in the coolant circuit and accordingly, at least temporarily, to supply it to the air gap of the traction machine and to discharge it again from it. In particular, the coolant pump is operated such that, apart from hydrodynamic braking, the amount of coolant in the air gap remains constant. This means that the same amount of coolant is discharged from the air gap as is withdrawn from it.This minimizes hydrodynamic losses outside of hydrodynamic braking, i.e. when hydrodynamic braking is not applied.

[0023] A further development of the invention provides that in order to increase the amount of coolant in the air gap, the delivery rate of the coolant pump is increased. In principle, there are various ways to increase the amount of coolant present in the air gap. On the one hand, more coolant can be supplied to the air gap per unit of time and / or the amount of coolant removed from the air gap per unit of time can be reduced. By increasing the delivery rate of the coolant pump, the coolant throughput into the air gap is increased, whereby the coolant throughput is understood to be a quantity of coolant, i.e. a mass or a volume, per unit of time. Increasing the delivery rate therefore represents a reliable way of introducing the coolant into the air gap for hydrodynamic braking.

[0024] Particularly preferably, the coolant pump is driven by an electric pump motor that is supplied with electrical power by multiple redundant power supplies. The pump motor is an electric motor and is drive-connected to the coolant pump. It can also be provided that the coolant pump and the pump motor are integrated, i.e., present as a structural unit. In any case, the pump motor is electrically connected to the multiple power supplies in order to compensate for the failure of one of the power supplies. This means that even if one of the power supplies fails, the coolant pump can be driven by the pump motor to introduce the coolant into the air gap, thus ensuring a high level of operational reliability.

[0025] Additionally or alternatively, it is provided that the coolant pump is driven at least temporarily via a mechanical connection from a drive shaft of the drive device and / or a machine shaft of the traction machine. The mechanical connection of the coolant pump to the drive shaft and / or the machine shaft represents a particularly fail-safe solution for introducing the coolant into the air gap. For example, it is provided that the coolant pump is normally driven by the electric pump motor, but in the event of a pump motor failure, it is driven temporarily via the mechanical connection.In this case, it can be provided that the coolant pump is connected to the drive shaft or the machine shaft, for example via a freewheel, so that only in the event of a pump motor failure is the coolant pump driven by the drive shaft or the machine shaft in order to introduce the coolant into the air gap.

[0026] Such a procedure has the advantage that the amount of coolant pumped by the coolant pump and accordingly the amount of coolant introduced into the air gap depends on the speed of the drive shaft or the engine shaft and thus on the speed of the motor vehicle. The faster the motor vehicle, the more coolant is pumped into the air gap for hydrodynamic braking by the drive device. This results in a self-regulating system whose braking torque depends on the speed of the motor vehicle. A further development of the invention provides that the air gap downstream of the coolant pump is connected to a pressure side of the coolant pump and, to increase the amount of coolant in the air gap, a switching valve located downstream of the air gap in the coolant circuit is at least partially closed. The air gap is connected to the pressure side of the coolant pump.More precisely, this applies to a coolant inlet of the air gap. Downstream of the air gap, however, is the switching valve, which is connected to a coolant outlet of the air gap. When the drive device is arranged as intended, the coolant inlet is preferably positioned higher than the coolant outlet, in particular geodetically or in a geodetic reference system. The switching valve is understood to be a valve that can be placed in different switching states, in which it has different flow cross-sectional areas. The different switching states of the switching valve are set electrically, for example. For this purpose, the switching valve is preferably implemented as a solenoid valve or the like.

[0027] In terms of flow, the switching valve is located between the air gap, in particular the coolant outlet of the air gap, and the coolant pump and / or the coolant pump is located between the switching valve and the air gap, in particular the coolant inlet of the air gap. By closing the switching valve, in particular while simultaneously keeping the delivery rate of the coolant pump constant or increasing, the amount of coolant in the air gap is increased in order to introduce the additional amount of coolant into the air gap. Preferably, the switching valve is completely closed for this purpose in order to increase the amount of coolant in the air gap particularly quickly. Particularly preferably, the measures already described for increasing the amount of coolant in the air gap are combined, i.e. both the delivery rate of the coolant pump is increased and the switching valve is at least partially or even completely closed.This allows the aforementioned advantages to be achieved particularly reliably. A further development of the invention provides for the use of a normally closed switching valve as the switching valve. The switching valve closes automatically as soon as it is no longer supplied with electrical current. This ensures that the additional coolant quantity is reliably introduced into the air gap, thus providing the braking torque, even in the event of a failure of the vehicle's electrical system.

[0028] A further development of the invention provides that the air gap is fluidically connected to a coolant reservoir, from which coolant is introduced into the air gap to increase the amount of coolant, in particular solely by the influence of gravity acting on the coolant. The coolant reservoir can be a separate reservoir or it is formed by at least one further device that is at least temporarily supplied with coolant, namely preferably by the coolant pump. For example, the said device and the traction machine are fluidically connected in parallel. Particularly preferably, the coolant reservoir is designed and arranged such that, in the event of a failure of the coolant pump, the coolant flows from the coolant reservoir into the air gap solely due to the influence of gravity on the coolant in order to effect hydrodynamic braking.This ensures a particularly high level of operational safety for the vehicle.

[0029] A further development of the invention provides that a magnetorheological coolant is used as the coolant, and a coolant flow rate of the coolant through the switching valve is adjusted by adjusting the field strength of a magnetic field. The coolant therefore has a magnetorheological component; in particular, it contains magnetic particles that can be influenced by applying a magnetic field. For example, the magnetic field is used to determine the orientation of the particles and, accordingly, also the viscosity of the coolant. For this purpose, the switching valve has means for generating the magnetic field with the specific field strength, so that the desired coolant flow rate through the switching valve is adjusted by adjusting the field strength of the magnetic field.

[0030] In particular, the coolant and the switching valve are designed such that when the magnetic field is generated using electric current, a higher viscosity is present, resulting in a lower coolant flow rate. However, if the switching valve is no longer supplied with electric current, for example, due to a failure of the vehicle electrical system, the viscosity decreases due to the changed field strength of the magnetic field, so that the coolant flow rate increases accordingly, and the additional coolant quantity is introduced into the air gap. This achieves the aforementioned high operational reliability of the motor vehicle.

[0031] The invention further relates to a drive device for a motor vehicle, in particular for carrying out the method according to the embodiments within the scope of this description, wherein the drive device has an electric traction machine, cooled at least temporarily by a coolant, with a rotor and a stator spaced from the rotor by an air gap. The drive device is provided and configured to introduce a specific additional coolant quantity into the air gap upon the occurrence of a braking request to provide a predetermined braking torque through hydrodynamic braking.

[0032] The advantages of such a procedure or such a design of the drive device have already been pointed out. Both the drive device and the method for its operation can be further developed according to the explanations in this description, so reference is made to these in this regard.

[0033] The invention also relates to a computer program product comprising instructions that cause the drive device to execute the explained method according to the embodiments of this description. Regarding the advantages and possible advantageous developments, reference is made to the entire description.

[0034] The features and feature combinations described in the description, in particular the features and feature combinations described in the following description of the figures and / or shown in the figures, can be used not only in the respective combination specified, but also in other combinations or on their own, without departing from the scope of the invention. Thus, embodiments are also considered to be encompassed by the invention that are not explicitly shown or explained in the description and / or the figures, but which follow from or can be derived from the explained embodiments.

[0035] The invention will be explained in more detail below with reference to the exemplary embodiments shown in the drawings, without limiting the invention.

[0036] Figure 1 is a schematic representation of a drive device for a motor vehicle with a traction machine and a coolant circuit for cooling the traction machine.

[0037] Figure 1 shows a schematic representation of a drive device 1 for a motor vehicle. The drive device 1 has an electric traction machine 2, which in turn has a rotor 3 and a stator 4, wherein the rotor 3 is mounted rotatably about a rotation axis 5 with respect to the stator 4. An air gap 6 is present in the radial direction with respect to the rotation axis 5 between the rotor 3 and the stator 4. This air gap 6 is fluidically connected to a coolant circuit 7 or is a component of the coolant circuit 7. For this purpose, the traction machine 2 has a coolant inlet 8 and a coolant outlet 9. The coolant can be supplied to the air gap 6 via the coolant inlet 8 and removed from it via the coolant outlet 9. The coolant is circulated at least temporarily in the coolant circuit 7 by means of a coolant pump 10.A pressure side of the coolant pump 10 is fluidically connected to the air gap 6, more precisely to the coolant inlet 8, via a coolant reservoir 11. On its suction side, the coolant pump 10 is also fluidically connected to the air gap 6, namely to the coolant outlet 9. A switching valve 12, by means of which a coolant flow rate can be adjusted, is located between the air gap 6, more precisely the coolant outlet 9, and the coolant pump 10 or its suction side.

[0038] The traction machine 2 shown here is a wet-running electric motor. This means that, during operation of the traction machine to provide a drive torque directed toward propelling the motor vehicle, a certain amount of coolant is present in the air gap 6, at least temporarily. This amount of coolant is also referred to as the initial coolant amount. It is intended that, at least temporarily, the traction machine 2 is used to brake the motor vehicle, namely by providing a predetermined braking torque. The braking torque is achieved by hydrodynamic braking, and for this purpose, the amount of coolant present in the air gap is increased, namely based on the initial coolant amount.

[0039] In other words, to provide the braking torque, a specific additional coolant quantity is introduced into the air gap 6, namely in addition to the initial coolant quantity already present therein. The additional coolant quantity is preferably greater than the initial coolant quantity, in particular by a factor of at least 2, at least 4, or at least 6. This ensures that a sufficient braking effect is achieved.

[0040] Particularly preferably, the coolant reservoir 11 has a volume corresponding to the volume of the additional coolant quantity of the coolant. The additional coolant quantity is thus completely stored in the coolant reservoir 11 during operation of the drive device 1, so that it can be introduced into the air gap 6 particularly quickly. This is achieved in particular by at least partially closing the switching valve 12 and / or by increasing the delivery capacity of the coolant pump 10.

[0041] Particularly preferably, the coolant reservoir 11 is arranged and designed such that even in the event of a failure of the coolant pump 10 and / or a vehicle electrical system of the motor vehicle that supplies the coolant pump 10 with electrical power, the coolant flows from the coolant reservoir 11 into the air gap 6, namely due to the influence of gravity acting on the coolant. Additionally or alternatively, the switching valve 12 is designed as a normally closed switching valve, so that in the event of a failure of the vehicle electrical system, the switching valve 12 closes and the coolant is forced from the coolant reservoir 11 into the air gap 6 to effect hydrodynamic braking there. In this way, the braking torque is provided in a reliable manner, in particular even in the event of a malfunction of the motor vehicle, in particular of the vehicle electrical system and / or the drive device 1.

[0042] LIST OF REFERENCE SYMBOLS:

[0043] 1 drive device

[0044] 2 Traction machine 3 Rotor

[0045] 4 Stator

[0046] 5 axis of rotation

[0047] 6 Air gap

[0048] 7 Coolant circuit 8 Coolant inlet

[0049] 9 Coolant outlet

[0050] 10 Coolant pump

[0051] 11 Coolant reservoir

[0052] 12 switching valve

Claims

PATENT CLAIMS:

1. Method for operating a drive device (1) for a motor vehicle, which has an electric traction machine (2) which is at least temporarily cooled by means of a coolant and has a rotor (3) and a stator (4) which is spaced from the rotor (3) by an air gap (6), characterized in that when a braking request occurs in order to provide a predetermined braking torque by hydrodynamic braking, a certain additional coolant quantity of the coolant is introduced into the air gap (6).

2. Method according to claim 1, characterized in that a wet-running electric motor is used as the traction machine (2) and, in order to provide the braking torque, a quantity of coolant present in the air gap (6) is increased starting from an initial quantity of coolant by introducing the additional quantity of coolant.

3. Method according to one of the preceding claims, characterized in that the amount of additional coolant is determined as a function of the predetermined braking torque.

4. Method according to one of the preceding claims, characterized in that a coolant quantity which is greater than the initial coolant quantity by a factor of at least 2, at least 3 or at least 4 is used as the default coolant quantity.

5. Method according to one of the preceding claims, characterized in that the air gap (6) is fluidically connected to a coolant circuit (7) of the drive device (1) and the coolant is circulated in the coolant circuit (7) at least temporarily by means of a coolant pump (10).

6. Method according to one of the preceding claims, characterized in that in order to increase the quantity of coolant in the air gap (6), a delivery capacity of the coolant pump (10) is increased.

7. Method according to one of the preceding claims, characterized in that the air gap (6) downstream of the coolant pump (10) is connected to a pressure side of the coolant pump (10) and in order to increase the amount of coolant in the air gap (6), a switching valve (12) present downstream of the air gap (6) in the coolant circuit (7) is at least partially closed.

8. Method according to one of the preceding claims, characterized in that the air gap (6) is fluidically connected to a coolant reservoir (11) from which coolant is introduced into the air gap (6) to increase the amount of coolant.

9. Drive device (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device (1) has an electric traction machine (2) which is at least temporarily cooled by means of a coolant and has a rotor (3) and a stator (4) spaced from the rotor (3) by an air gap (6), characterized in that the drive device (1) is provided and designed to introduce a specific additional coolant quantity of the coolant into the air gap (6) when a braking request occurs in order to provide a predetermined braking torque by hydrodynamic braking.

10. Computer program product comprising instructions which cause the drive device (1) according to claim 9 to carry out the method according to one or more of claims 1 to 8.

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