Electric traction drive for propelling a vehicle using electrical energy

Abstract

Electric traction drive for propelling a vehicle by means of electrical energy, comprising a first drive component (1) which is an inverter and which is a heat-emitting drive component (2), and a cooling system for temperature control of the first and second drive components (1, 2), wherein the cooling system comprises a first cooling circuit (3) and a second cooling circuit (4) and a heat exchanger (5), the heat exchanger (5) is configured for heat exchange between the first and second cooling circuits (3, 4), the first cooling circuit (3) leads through the first drive component (1) to temperature control the first drive component (1), the second cooling circuit (4) leads through the second drive component (2) to temperature control the second drive component (2), characterized by a first valve (36) arranged in the first cooling circuit (3) for adjusting the coolant flow from the first cooling circuit (3) through the heat exchanger (5),and a control unit (6) for actuating the first valve (36), wherein the control unit (6) is configured to actuate the first valve (36) based on a temperature model stored in the control unit (6).

Description

The invention relates to an electric traction drive for propelling a vehicle, in particular a motor vehicle, by means of electrical energy. The traction drive comprises several drive components that emit heat during operation and a cooling system for cooling these drive components. The invention also relates to a method for setting a predetermined temperature at one or more of these drive components of the traction drive. Modern vehicle traction systems typically incorporate water cooling to cool the traction motor, such as an internal combustion engine, or the electric traction battery. This cooling system is often also used to cool the transmission or electronic components of the traction drive. This has the advantage of requiring only one pump system for the cooling water and allowing the use of an existing temperature control system for the cooling water. The flow rate of the cooling water in the cooling circuit is usually determined by the cooling requirements of the drive motor or battery. The transmission is primarily cooled by its integrated lubrication system. The transmission lubricant is generally circulated by a lubricant pump, which is mechanically driven by the traction motor.The flow rate of the lubricant in the transmission lubrication system and the flow rate of the cooling water in the water cooling system are usually independent of each other. To prevent the lubricant from overheating, it is common practice to thermally couple the lubrication circuit and the water cooling system via a heat exchanger. This results in disadvantages. Due to the now achievable high efficiencies of drive components, the amount of heat generated at low and medium loads is low. This can lead to the drive components no longer reaching their optimal operating temperature, e.g., 60-80°C, over long distances and instead operating in an unfavorable temperature range. Furthermore, with known cooling systems, it can happen that after the overall system has heated up, individual components of the drive system do not cool down as desired because the cooling water unintentionally heats these components. In addition, the heat transfer capacity of the heat exchanger is oversized for most driving situations, as it is designed for peak loads. Thus, a relatively large amount of heat transfer occurs even when this is undesirable. From EP 2 599 651 A1, a motor vehicle with a first and second heating / cooling circuit is known. The first heating / cooling circuit has a heat source / sink and a first pump, and the second heating / cooling circuit has a battery to be heated / cooled and a second pump. The two heating / cooling circuits can be connected via at least one valve such that the same liquid heat transfer medium flows through both heating / cooling circuits. A heat exchanger may be provided between the valve and the battery in the second heating / cooling circuit. From DE 10 2013 201 787 A1, a method and a device for improving the efficiency of a motor vehicle's drive system are known, in which heat energy generated in the vehicle's braking system is used to heat components of the drive system. For this purpose, it is provided that the heat energy generated in the braking system during braking is supplied to an axle drive intended for transmitting and distributing the drive power to the vehicle's drive wheels. From DE 42 22 088 A1, a cooling system for an internal combustion engine is known in which an external coolant circuit is formed by connecting a pump, oil cooler, charge air cooler, heat exchanger, and high-temperature regulator in series. The heat exchanger is arranged in a first control line of the high-temperature regulator, and a second control line leads to a part-load regulator. The first switching line of the part-load regulator is connected to the outlet of the heat exchanger and the inlet of the charge air cooler, and the second switching line enters the circuit downstream of the charge air cooler. The inlet of the high-temperature regulator is directly connected to the coolant outlet of the internal combustion engine, and the second switching line of the part-load regulator and the outlet of the charge air cooler are connected to the inlet of the pump. The oil cooler is arranged between the internal combustion engine and the pump. From DE 10 2018 118 045 A1, a computer-implemented method for controlling a coolant fluid in a cooling system for an internal combustion engine is known. In this method, a flow division requirement is calculated by a processing device, and a rotary valve is operated by the processing device based on this flow division requirement. From DE 10 2017 100 374 A1, a liquid bypass valve is known which includes a valve element arranged within a valve chamber. The valve element includes a temperature-based actuation mechanism that positions the valve element in a first position when the temperature of a liquid is equal to or less than a predetermined temperature, and positions the valve element in a second position when the temperature of the liquid is greater than the predetermined temperature. From DE 10 1018 209 340 B3, an electric drive unit for a motor vehicle is known. This unit comprises an electric machine with a stator and a rotor, an inverter with a first switching unit for energizing a first phase system of the stator, a gearbox connected to the rotor for torque transmission, a lubrication circuit for lubricating the gearbox and / or cooling the rotor, a first coolant circuit for cooling the first switching unit, a lubricant-coolant heat exchanger for thermal coupling of the first coolant circuit and the lubricant circuit, and a control device designed to provide a loss-increasing operating mode for the first switching unit to increase the power loss that heats a coolant of the first coolant circuit.In this case, the lubricant-coolant heat exchanger is designed to transfer heat from the heated coolant to the lubricant circuit in order to reduce the viscosity of a lubricant. A system for recovering heat from motor vehicle exhaust gases is known from DE 10 2019 104 747 A1. The system comprises a motor that receives a flow of coolant from a cooling pump, a coolant outlet head that receives the flow of coolant exiting the motor, a main rotary valve that receives the coolant exiting the coolant outlet head and selectively distributes the coolant to a heater core and a transmission oil heater, and an exhaust gas heat recovery device positioned to receive the coolant exiting the heater core and the transmission oil heater and positioned in a path for returning the coolant to the cooling pump during a cold start operation of the engine. From US Patent 2020 / 238818 A1, a thermal control device for a hybrid vehicle is known, comprising an engine cooling circuit through which coolant circulates to cool an internal combustion engine, a generator cooling circuit through which a refrigerant circulates to cool a motor-generator, and a heat exchanger that facilitates heat exchange between the coolant and the refrigerant. If, based on the state of charge (SOC) of a battery, it is determined that the battery can be charged, a charging control is performed to charge the battery with the electrical energy generated during regenerative braking. However, if it is determined that the battery cannot be charged, a heat dissipation control is performed, whereby the heat generated during regenerative braking is transferred to the engine cooling circuit via the heat exchanger. The object of the present invention is to improve the state of the art. This problem is solved by the measures specified in the main claims. Preferred embodiments thereof are described in the dependent claims. An electric traction drive is proposed for propelling a vehicle, particularly a motor vehicle such as a passenger car, truck, or bus, using electrical energy. The traction drive comprises a first drive component, an inverter, which emits heat during operation, and a second drive component that also emits heat during operation. In other words, these drive components generate waste heat during operation. A cooling system for the traction drive serves to regulate the temperature of these two drive components. The cooling system comprises a first cooling circuit, a second cooling circuit, and a heat exchanger. The heat exchanger thermally couples the two cooling circuits and is therefore designed for heat exchange between them. The first cooling circuit runs through the first drive component to regulate its temperature. The second cooling circuit runs through the second drive component to regulate its temperature. Thus, the two cooling circuits are designed to, during operation of the traction drive, either remove heat from the aforementioned drive components (cooling) or supply heat to them (heating), depending on the requirements. A first valve is provided in the first cooling circuit. This first valve is designed to regulate the coolant flow from the first cooling circuit through the heat exchanger. Specifically, the valve is located upstream of the heat exchanger in the first cooling circuit. This first valve thus allows adjustment of the coolant flow rate from the first cooling circuit through the heat exchanger. In this way, the amount of heat exchanged between the two cooling circuits can be regulated. The two cooling circuits and the drive components they regulate can therefore be thermally coupled and thermally decoupled from each other. This makes it possible to operate the drive components at nearly identical temperatures or at different temperatures. Each of the two drive components can be selectively cooled or heated. Via the two cooling systems, one drive component can selectively heat or cool the other as needed. This is achieved very simply through the first valve. A complex control system for the coolant pump speed is unnecessary. Simple mechanical pumps can be used. Thus, the pump of the first cooling circuit and / or the pump of the second cooling circuit can be mechanically driven by the traction motor of the traction drive to circulate the coolant within their respective circuits, with the pump speed then corresponding to the motor speed. This allows the heat exchanger to be configured so that, for example, coolant flows through it only above a coolant temperature of 90°C, either to cool the respective drive component or to heat it to more than 50°C. This enables the drive components to operate within an optimal temperature range. Furthermore, the high heat capacities of the cooling media in both cooling circuits can be fully utilized when short-term peaks in power and heat loss occur. The cooling media then absorb the corresponding amount of heat through a temporary temperature increase, for example, by briefly heating from 60°C to over 90°C. The temperature is then subsequently reduced again. Specifically, the first valve is designed to open the flow through the heat exchanger only when a temperature reduction in the first cooling circuit is required (i.e., to cool the first drive component) or when the second cooling circuit needs to be heated (i.e., to warm the second drive component). If both drive components have cooled down, or if the second drive component has reached its optimal operating temperature, or if the second drive component has not yet reached its optimal operating temperature and cannot be heated by the coolant in the first cooling circuit (because the necessary temperature is not present in the first cooling circuit), the flow through the heat exchanger is reduced to a minimum or completely stopped by the first valve. The traction drive serves to propel a vehicle. In other words, the traction drive provides the mechanical drive power required for propulsion during vehicle operation. The traction drive primarily comprises the traction motor, which is typically an electric motor. A combination of an internal combustion engine and an electric motor (hybrid drive) is also possible. In this case, the traction motor is the second drive component. Accordingly, the traction motor is then cooled by a separate cooling circuit. Preferably, the first cooling circuit is designed for operation with cooling water as the coolant, i.e., as a water cooling circuit. The cooling water may also contain additives to prevent, for example, freezing and / or corrosion. The second cooling circuit can then be designed for operation with a lubricant as both a cooling and lubricating medium, i.e., as a lubrication circuit. The lubricant is, in particular, gear oil. The second cooling circuit then serves not only to regulate the temperature of the second drive component but also to lubricate it. In the first cooling circuit, a water pump mechanically driven by the traction motor can be used to circulate the cooling water. Similarly, in the second cooling circuit, a lubricant pump mechanically driven by the traction motor can be used to circulate the lubricant. A water-oil heat exchanger can be provided as the heat exchanger.The aforementioned advantages are realized by using the aforementioned first valve in such a cooling system within the cooling water circuit. In particular, it is anticipated that the first drive component typically dissipates more heat during operation than the second drive component. Due to the higher heat capacity of the cooling water in the first cooling circuit compared to the lubricant in the second, the first cooling circuit can be used more effectively to regulate the temperature of the first drive component. This, in turn, allows for more precise temperature control of the second drive component, tailored to its specific needs. Preferably, the first valve is a 4 / 2-way valve or a 6 / 2-way valve. Preferably, the first valve is configured so that in its first position it is open towards the heat exchanger and in its second position it is closed towards the heat exchanger, starting from the coolant pump. In the first position, coolant from the first cooling circuit flows through the valve to the heat exchanger and from the heat exchanger back through the valve into the rest of the first cooling circuit. In this respect, the valve is fluidically positioned both upstream and downstream of the heat exchanger. In its second position, the valve closes the heat exchanger to the coolant from the first cooling circuit. No coolant then flows from the first cooling circuit into the heat exchanger or from the heat exchanger into the first cooling circuit.In other words, the first valve is designed to open the heat exchanger to a coolant flow from the first cooling circuit in its first valve position and to close the heat exchanger to this coolant flow in its second valve position. The first drive component can be connected in parallel with the first valve in terms of flow characteristics. Preferably, the first cooling circuit has a first cooling circuit section through which the first drive component is cooled, and a second cooling circuit section in which the heat exchanger is located. The first cooling circuit section thus passes at least or only through the first drive component, and the second cooling circuit section passes at least or only through the heat exchanger. The first valve is located within the second cooling circuit section. In particular, the first cooling circuit branches into the aforementioned cooling circuit sections downstream of a coolant pump of the first circuit, and these sections rejoin downstream of the first drive component and the heat exchanger.A device may be provided to adjust the distribution of the flow rate through the two cooling circuit sections, for example at least one additional valve or an adjustable throttle. Preferably, when the first drive component and the first valve are arranged in parallel, a restrictor is provided in the second cooling circuit section. The restrictor is therefore also arranged parallel to the first drive component in terms of flow direction. The first valve is then configured so that, in its second valve position, it directs the coolant from the first cooling circuit through the restrictor instead of the heat exchanger. This ensures that, in the second valve position, the pressure in the first cooling circuit section does not rise too high due to the closed-off heat exchanger. In the first valve position, i.e., when it is open towards the heat exchanger, it closes the path through the restrictor.In other words, the first valve is configured to open one flow path for coolant through the heat exchanger in its first position and to open an alternative flow path for coolant through the throttle in its second position, blocking the other flow path. The coolant flow therefore passes either through the heat exchanger or the throttle. The throttle is specifically a fixed throttle (in particular, a fixed throttle or constant throttle), meaning its opening width cannot be changed during operation. Preferably, under normal operating conditions, the flow path through the throttle and the alternative flow path through the heat exchanger exhibit essentially the same flow resistance for the coolant. In particular, the differences in flow resistance between the flow paths are less than 10%. This results in simpler adjustment and control of the coolant flow in the first cooling circuit, since the valve position of the first valve has only a minor effect on the flow in the rest of the cooling circuit. The first drive component can also be connected in series with the first valve in terms of flow characteristics. In this case, the first drive component is arranged upstream of the first valve. Thus, in the first cooling circuit, the coolant flows from the coolant pump first through the first drive component and then through the first valve. When the first valve is open in its first valve position towards the heat exchanger, the coolant flows from the valve to the heat exchanger. Preferably, the coolant flows from the heat exchanger back to the first valve, where it is further routed in the first circuit, particularly to an air cooler of the first cooling circuit. Preferably, a second valve is arranged in the second cooling circuit, particularly upstream of the heat exchanger. This second valve is designed to regulate the coolant flowing through the heat exchanger from the second cooling circuit. This allows for even more flexible temperature control of the first and / or second drive component. In particular, this prevents coolant from the second cooling circuit from constantly flowing through the heat exchanger, thus preventing unwanted heat transfer (heating or cooling) at the heat exchanger even when the first valve is closed. The second valve is preferably designed as a 4 / 2-way valve. The explanations in the paragraph above regarding the first valve, which is designed as a 4 / 2-way valve, then also apply analogously to the second valve and the second cooling circuit if the second valve is designed as a 4 / 2-way valve. According to the invention, the first drive component is an inverter. The drive component, designed as an electric machine, forms in particular the traction motor of the traction drive. The inverter converts direct current, especially from the traction battery, into alternating current, particularly for the motor operation of the electric machine. If required, this conversion can also be reversed by the inverter, i.e., from alternating current to direct current, for example, to recharge the traction battery (generator operation of the electric machine). The inverter thus serves in particular to supply the electric machine with alternating current. The electric machine is therefore designed in particular as a rotating field machine, such as a synchronous machine, asynchronous machine, or reluctance machine. The first drive component, designed as an inverter, generates a relatively large amount of waste heat during operation, especially at peak loads, and this heat must be cooled accordingly. The first cooling circuit is suitable for this purpose, particularly if it is a water cooling circuit. The second drive component is typically the electric motor, the gearbox, or a combination of both. These components also usually require lubrication during operation, making the second cooling circuit, designed as a lubrication circuit, particularly suitable for temperature control and lubrication. The traction drive can additionally include an electric traction battery. In this case, the first cooling circuit can also run through the traction battery for temperature control. The first drive component and the traction battery can be connected in series or parallel to each other in the first cooling circuit. According to the invention, the traction drive is an electric traction drive for propelling a vehicle using electrical energy. The first drive component is the inverter, and the second drive component is the electric motor, the transmission, or a combination of both. The transmission serves to translate the drive torque provided by the electric motor so that the vehicle's drive wheels can be driven by the electric motor. Preferably, an air cooler is located within the first cooling circuit. This cooler is designed to cool the coolant in the first cooling circuit using air. The air cooler acts as an additional heat exchanger for the cooling system. It serves to transfer heat from the coolant in the first cooling circuit to the surroundings. This allows heat to be easily dissipated from the first cooling circuit. By thermally coupling the two cooling circuits as needed via the heat exchanger, the air cooler can also indirectly dissipate heat from the second cooling circuit. Preferably, a thermostat is arranged upstream of the air cooler of the first cooling circuit. The thermostat is configured to partially or completely close the coolant flow through the air cooler and partially or completely open a bypass that bypasses the air cooler when the coolant temperature in the first cooling circuit falls below a predetermined temperature threshold. Furthermore, the thermostat is configured to partially or completely reopen the coolant flow through the air cooler and partially or completely close the coolant bypass when the coolant temperature in the first cooling circuit rises above the predetermined temperature threshold. The thermostat operates automatically via a heat-activated actuator, for example, based on a bimetallic strip, a wax motor, or a shape-memory alloy.Below the predetermined temperature threshold, the coolant bypasses the air cooler. This allows the primary cooling circuit to heat up faster. Above the predetermined temperature threshold, the thermostat deactivates the bypass, so heat from the primary cooling circuit is drawn away from the air cooler. According to the invention, the traction drive has a control unit. This unit is configured to actuate at least the first valve. A temperature model of the traction drive is stored in the control unit, which actuates the valve based on this temperature model, i.e., opens or closes it. This allows the valve, and thus the heat transfer between the two cooling circuits, to be adjusted precisely as needed. In particular, information about the current state of the traction drive is fed into the temperature model, from which it determines the corresponding temperature values ​​of the drive components. By selectively opening and closing at least the first valve, and optionally also the second valve, the drive components can then be temperature-controlled accordingly, ensuring they always operate within their optimal temperature range.In particular, the electrical energy supplied to the traction drive (e.g., current, voltage, power) forms an input variable for the temperature model, on the basis of which it determines the temperature of one or more components of the traction drive, such as the inverter and / or the electric machine. By using the temperature model, some or all of the (usually present) temperature sensors in the cooling circuits can be omitted. In particular, the first and / or second cooling circuit is therefore free of temperature sensors that output a corresponding measurement (for example, for regulating or controlling the respective coolant temperature). Independently of this, one or more temperature sensors can be provided in the area of ​​the electric traction battery for the traction drive, serving to monitor this traction battery. The control unit can perform several functions for the traction drive. In particular, the control unit also actuates the aforementioned second valve in the second cooling circuit. Thus, the first and second valves can be advantageously actuated based on the temperature model stored in the control unit. This allows for particularly efficient temperature control of the two drive components. The control unit can also actuate the first and / or second drive component, specifically controlling the respective drive component. Actuation of each valve is achieved using a suitable actuator, such as an electromagnet or servo motor, which is controlled by the control unit. The control unit can alternatively or additionally be configured to actuate at least the first valve based on a measured temperature of the coolant in the first cooling circuit and / or the coolant in the second cooling circuit and / or the first drive component and / or the second drive component, i.e., to open or close it. Here, too, the control unit can optionally be configured to actuate the second valve based on this measured temperature. In this way, the temperature model can be bypassed, for example, if the actual temperature is too high or too low contrary to the calculation of the temperature model. For temperature measurement, a temperature sensor is provided, particularly in the respective cooling circuit or on the respective drive component, which outputs the measured temperature or a corresponding measured value to the control unit. Preferably, the control unit is configured to maintain the first and second drive components within a predetermined temperature range by actuating at least the first valve, and in particular also the second valve. This can be achieved by heating the drive components through heat extraction from the other cooling circuit, and by cooling them through heat transfer to the other cooling circuit. The temperature range is a range in which the drive components operate optimally, such as an optimal operating temperature. A common temperature range can be specified for both drive components, or a separate temperature range can be specified for each. The control unit then actuates the valve(s) in such a way that the (respective) predetermined temperature range is maintained as closely as possible during operation of the traction drive. However, it is also possible that the first and / or second valve actuates itself automatically based on the coolant temperature. In this case, actuation is not carried out by the control unit, but independently by the valve, particularly by a heat-activated actuator on the valve. This can significantly simplify the design of the cooling system. The proposed method also serves to set a predetermined temperature (target temperature) at one or more of the drive components of the proposed traction drive. In this process, at least the first valve, and optionally the second valve as well, is actuated to regulate the coolant flow from the first cooling circuit (and, with the second valve, also from the second cooling circuit) through the heat exchanger. This then sets the predetermined temperature at the drive component. In other words, the actual temperature of the drive component is selectively adjusted to the target temperature by actuating the aforementioned valve(s) of the cooling system. This process primarily takes place on the traction drive's control unit. The predetermined temperature can, for example, be stored in the control unit or determined by it. Preferably, the method determines the temperature change of the actual temperature of the respective drive component and uses this change to actuate the valve(s). The temperature change then influences the actuation of the respective (first and / or second) valve. This allows the temperature profile of the drive component to be anticipated over time. The valve(s) can thus be actuated proactively to set the desired temperature of the respective drive component more quickly and precisely. Overshoot in temperature setting, for example due to temporarily excessive or insufficient cooling, can be avoided in this way. The temperature change is primarily defined as the change in temperature per unit of time (ΔT / t). Alternatively or additionally, the acceleration of the temperature change can also be used.To determine the temperature change, the temperature model of the traction drive is used in particular. This allows the temperature of the respective drive component to be determined in real time, even before the coolant temperature of the first and / or second cooling circuit shows a change. The invention is explained in more detail below with reference to figures, from which further preferred embodiments of the invention can be derived. Figure 1 shows a schematic representation of a first variant of a traction drive with a cooling system, Figure 2 shows an unloaded second variant of a traction drive with a cooling system, Figure 3 shows a third variant of a traction drive with a cooling system, and Figure 4 shows a fourth variant of a traction drive with a cooling system. In the figures, functionally identical components are labelled with the same reference symbols. Fig. 1 shows a purely electric traction drive for propelling a vehicle using electrical energy. The traction drive comprises an electric machine 2, which serves as a traction motor and can be coupled to a gearbox or have a gearbox integrated into it. The traction drive also includes an inverter 1, which supplies the electric machine 2 with three-phase alternating current. The electrical energy is drawn from a traction battery (not shown). For recuperation, the electric machine 2 can be operated as a generator, with electrical energy being fed back into the traction battery via the inverter 1. The inverter 1 forms a first drive component of the traction drive, which dissipates heat during operation. The electric machine 2 forms a second drive component of the traction drive, which also dissipates heat during operation.To prevent components 1 and 2 from overheating and to ensure their optimal operation, this heat must be dissipated. The optimal operating temperature range for components 1 and 2 is, for example, 60–80°C. It is therefore desirable to reach and maintain this temperature range as quickly as possible. The traction drive has a cooling system for temperature control of components 1 and 2. The cooling system comprises a first cooling circuit 3 for the inverter 1 and a second cooling circuit 4 for the electric motor 2. The first cooling circuit 3 is a water cooling circuit. The coolant circulating in it is therefore cooling water. The second cooling circuit 4 is a lubrication circuit. The coolant circulating in it is therefore a lubricant, such as oil, which simultaneously serves to lubricate the electric motor 2 and, optionally, the gearbox. The preferred flow direction of the coolants in the two circuits 3 and 4 is indicated by arrows in Fig. 1. Check valves can be provided at suitable locations to prevent coolant from flowing in the wrong direction within the cooling system. Cooling circuit 3 includes a pump 33 for circulating the coolant within the cooling circuit 3. The pump 33 can be designed as a separate component. The pump 33 is preferably driven mechanically by the electric motor 2. The speed of the pump 33 (pump speed) is therefore always coupled to the speed of the electric motor 2 (motor speed). In particular, the pump 33 is a pump with a constant delivery volume per revolution, for example, a gear pump, such as an external gear or internal gear pump. Downstream of pump 33, cooling circuit 3 splits into two parallel cooling circuit sections 31 and 32. The first section 31 passes through inverter 1 to absorb heat from it and, if necessary, also transfer heat to it. The second section 32, which is flow-parallel to inverter 1, runs through the heat exchanger 5 of the cooling system. The heat exchanger 5 transfers heat between the coolants of the first and second cooling circuits 3 and 4. Such heat exchangers 5 are already known. The heat exchanger 5 can, for example, be designed as a plate heat exchanger. The two sections 31 and 32 are reconnected downstream of inverter 1 and heat exchanger 5 and upstream of an air cooler 34. The air cooler 34 is thus connected in series with the two cooling circuit sections 31 and 32 from a fluid dynamics perspective. The air cooler 34 serves to dissipate heat from the coolant of the first cooling circuit 3 to the ambient air, for example, through airflow, convection, or a fan. From the air cooler 34, the coolant returns to the coolant pump 31. The first cooling circuit 3 has an expansion tank 37 at a suitable location. This is, for example, arranged between the air cooler 34 and the pump 33 in terms of flow characteristics. Upstream of the air cooler 34, a thermostat (see Fig. 2) can be provided that bypasses the cooler 34 when the coolant temperature there falls below a temperature threshold. This prevents heat from being dissipated via the cooler 34 if the heat exchanger 1 has not yet reached its optimal temperature. To prevent the coolant of the first cooling circuit 3 from constantly passing through the heat exchanger 5 and absorbing or releasing heat, a first valve 36 is provided in the second part 32 of the cooling circuit 3. This valve allows the flow rate of coolant through the heat exchanger 5 to be adjusted. The components 1 and the valve 36 are thus connected in parallel from a flow perspective. Preferably, the valve 36 is a 4 / 2-way valve, as shown in Fig. 1. In its second valve position, which is shown in Fig. 1, the first valve 36 blocks the flow of coolant from the first circuit 3 through the heat exchanger 5 and releases it again in its first valve position. The flow path through the heat exchanger 5 is completely blocked in the second valve position of the valve 36. The flow of coolant through the heat exchanger 5 is thus largely stopped. Alternatively, the valve 36 can be designed such that, in its second position, it switches the flow path of the heat exchanger 5 through the valve 36 as a separate circuit. This is implemented, for example, in Figures 3 and 4. In the second position of the valve 36, a separate circuit is then created, consisting of the heat exchanger 5 and the passage through the valve 36. This allows a certain coolant flow through the heat exchanger 5 in the second position of the valve 36, for example by convection, although it is thermally separated from the first circuit 3. Optionally, one or both of the valves 36, 41 can assume intermediate positions. This allows for fine adjustment of the respective flow rate through the heat exchanger 5 and thus the amount of heat transferred from the heat exchanger 5 between the cooling circuits 3, 4. Preferably, the valves 36, 41 are each electrically actuated by an electromagnet. Cooling circuit 4 also has a pump for circulating the coolant within cooling circuit 3. This pump is not shown in Fig. 1 for clarity. It is integrated, in particular, into the electric motor 2. This pump is also preferably driven mechanically by the electric motor 2. In this case, the pump speed is always coupled to the motor speed. This pump also has a constant delivery volume per revolution and is, for example, a gear pump. Cooling circuit 4 runs through electric motor 2 to absorb heat from it and, if necessary, also to transfer heat to it. Downstream of electric motor 2, cooling circuit 4 passes through heat exchanger 5. As explained above, heat exchanger 5 serves to transfer heat between the two circuits 3 and 4. A second valve 41 (second valve) is also provided in the second circuit 4 to prevent coolant from this cooling circuit 4 from constantly passing through the heat exchanger 5 and absorbing or releasing heat. This second valve 41, analogous to the first valve 36, allows the flow rate of coolant from the second circuit 4 through the heat exchanger 5 to be adjusted. One or both of the valves 36, 41 are actuated by a control unit 6 of the traction drive. The control unit 6 thus issues corresponding commands to open and close the respective valve 36, 41. For this purpose, the control unit 6 processes information from the traction drive, such as, in particular, power information and / or information on the temperature of the coolants in circuits 3, 4 and / or the drive components 1, 2. According to the invention, a temperature model of the traction drive is stored in the control unit 6, based on which it actuates the respective valve 36, 41. Preferably, an additional pressure relief valve (pressure limiting valve) is provided in one or both of the circuits 3, 4, which limits the pressure in the respective circuit 3, 4 and / or at the pump of the respective circuit 3, 4 to a specific pressure level. Such a pressure relief valve can be particularly useful when the valve 36 or 41 is at least partially closed and thus the flow resistance is correspondingly increased. In order to better adjust the distribution of the coolant flow rates through the two parts 31, 32 of the first cooling circuit 3 when valve 36 is open, an additional limiting valve or throttle can be provided in one or both of the two circuits 31, 32, see for example Fig. 3 . The traction drive shown can also include an electric traction battery to supply at least the inverter 1 and the electric motor 2 with electrical energy. The battery is not shown in Fig. 1. This battery should also advantageously be temperature-controlled. For this purpose, it can be integrated into the first cooling circuit 3, for example, by being arranged in parallel or in series with the electric motor 2 in the cooling circuit 3. Fig. 2 shows an unloaded traction drive for propelling a vehicle, at least intermittently, by means of an internal combustion engine 1*. The internal combustion engine 1* therefore serves as the traction motor of the traction drive. A transmission 2* is coupled to the internal combustion engine 1*. This is, in particular, a multi-stage transmission, i.e., one with several selectable gears, such as an automatic transmission or an automated manual transmission. The internal combustion engine 1* and the transmission 2* constitute drive components of the traction drive. The traction drive shown in Fig. 2 has a cooling system designed analogously to that shown in Fig. 1. Here, the internal combustion engine 1* is cooled by the first cooling circuit 3, and the transmission 2* by the second cooling circuit 4. The above explanations regarding the cooling system shown in Fig. 1 therefore also apply analogously to the cooling system shown in Fig. 2. In the cooling system shown in Fig. 2, unlike in Fig. 1, the thermostat 38 is shown upstream of the radiator 34 in the first cooling circuit 3. As explained above, the thermostat 38 bypasses the air cooler 34 when the coolant temperature falls below the predetermined temperature threshold. To do this, it directs the coolant through a bypass 39 arranged parallel to the air cooler 34 in terms of flow flow, instead of through the radiator 34. The bypass opens upstream of the pump 33 into the line running between the radiator 34 and the pump 33. Fig. 3 shows a modification of the traction drive from Fig. 1. The explanations for Fig. 1 also apply to the variant in Fig. 3, except for the differences mentioned below. In the variant shown in Fig. 3, a throttle 310 is provided in the second cooling circuit section 32 of the first cooling circuit 3. This throttle is connected in parallel with the first drive component 1 and the heat exchanger 5, and in series with the valve 36. The first valve 36 is specifically designed as a 6 / 2-way valve. The throttle 310 is located in an alternative flow path, which is activated when the flow path via the heat exchanger 5 is closed for the coolant flow. The valve 36 is thus configured so that, in its second valve position shown in Fig. 3, it directs the coolant flow from the first circuit 3 through the throttle 310 instead of the heat exchanger 5. In its first valve position, the valve 36 blocks the coolant flow of the first cooling circuit 3 through the throttle 310 and, conversely, opens the heat exchanger 5. This configuration has the advantage that, even with heat exchanger 5 disconnected, a certain amount of coolant continues to flow through the second cooling circuit section 32 via the throttle 310 and the valve 36, without this coolant flow transferring heat from or absorbing it from heat exchanger 5. This prevents an excessive pressure increase in the first cooling circuit section 31 due to the disconnection of heat exchanger 5 by valve 36. It also ensures that a sufficient amount of coolant always flows through the first component 1 and that the flow resistance in the first cooling circuit 3 remains sufficiently low. To simplify the controllability of the coolant flow in the first cooling circuit 3, the flow path through the heat exchanger 5 that can be released by the valve 36 has as much flow resistance as possible as the flow path through the throttle 310 that can alternatively be released by the valve 36. As shown in Fig. 3, the valve 36, in its second position, can be designed so that it does not completely block the flow path through the heat exchanger 5 (as shown in Fig. 1), but rather opens it to a separate circuit. The coolant in the heat exchanger 5 and the associated flow path can thus circulate through the valve 36 to a limited extent, for example by convection, without affecting the coolant flow in the rest of the cooling circuit 3. This allows a certain amount of heat absorption and release via the heat exchanger 5 even when the valve 36, in its second position, fluidically separates the heat exchanger 5 from the second cooling circuit section 32. This can be advantageous if the heat exchanger 5 is to serve to a limited extent as a heat source or heat sink for the second cooling circuit 4, while at the same time no heat is to be transferred to or absorbed from the rest of the first cooling circuit 3. Fig. 4 shows a further modification of the traction drive from Fig. 1. The explanations for Fig. 1 also apply to the variant in Fig. 4, except for the differences mentioned below. As shown in Fig. 4, the first drive component 1 is connected in series with the first valve 36 in terms of fluid flow. Thus, in contrast to the variant shown in Figs. 1, 2 to 3, two cooling circuit sections 31, 32 are not required for the second circuit 3 – a single section suffices. Here, too, the valve 36 is specifically designed as a 4 / 2-way valve. In the second valve position of the valve 36 shown, the heat exchanger 5 is disconnected for the coolant flow of the first cooling circuit 3. Instead, the coolant then flows through the first valve 36, bypassing the heat exchanger 5. Analogous to Fig. 3, in the second valve position, the valve 36 does not completely block the flow path of the heat exchanger 5, but rather creates a separate circuit encompassing the passage through the first valve 36 and the heat exchanger 5. This allows the advantages already mentioned above to be achieved here as well. Alternatively, in its second valve position, the valve 36 can completely interrupt the flow path through the heat exchanger 5, analogous to the variant in Fig. 1, thereby largely stopping the flow of coolant through the heat exchanger 5. In the cooling systems shown in the figures, the coolant flow in the first cooling circuit 3 is adjusted so that flow through the heat exchanger 5 is only provided when the temperature of the drive components 1, 2 needs to be specifically raised or lowered. In particular, the flow through the heat exchanger 5 is reduced to a minimum or stopped completely when the traction drive has cooled down, when it has already reached the desired temperature range (optimal operating temperature), or when the drive components 1, 2 are currently warming up but have not yet reached the desired temperature range. This makes it possible to minimize the losses of the pumps 33 and to operate the entire drive system within the temperature range of optimal efficiency. The use of the temperature model for the traction drive allows threshold values ​​for switching the coolant flow on and off to be adjusted or stored in the control unit 6 according to local ambient conditions, thus achieving suitable settings for all climate zones. Optionally, the temperature of the traction battery can be taken into account when actuating valves 36 and 41. The temperature model can therefore be linked to one or more temperature sensors of the traction battery via software. If corresponding maps are available in the control unit 6, the cooling can then also be set directly based on these maps, i.e., without temperature sensors in the two cooling circuits 3 and 4, or without considering temperature readings from such sensors.The setting of the valve position of the first and / or second valve 36, 41 is then carried out by at least one characteristic map, wherein the temperature model provides one of several input variables of the characteristic map or the only input variable of the characteristic map. One or more valves 36, 41 are preferably actuated based on the coolant temperature in the first cooling circuit 3 or the temperature of the first drive components 1, 1* compared to the coolant temperature in the second cooling circuit 4 or the temperature of the second drive components 2, 2*. The respective valve 36, 41 opens when there is a sufficient temperature difference between these temperatures, as this indicates a sufficient temperature gradient in the heat exchanger 5. This temperature gradient is used to achieve the desired temperature of components 1, 1*, 2, 2*. The respective temperature can be measured by appropriate sensors or calculated by the temperature model in the control unit 6. Since the valve(s) 36, 41 are operated by the temperature model, temperature sensors in the cooling circuits 3, 4 and / or the drive components 1, 1*, 2, 2* are not required. It is also possible that pump 33 for the first cooling circuit 3 and / or the pump for the second cooling circuit 4 is operated in such a way that the respective specified temperature range of the drive components 1, 1*, 2, 2* is reached as quickly as possible. In this case, the pumping action is switched off if the specified temperature range has not yet been reached. For example, the respective pump can be disconnected or switched off, or its flow rate can be minimized. Once the specified temperature range is reached, the pumping action is switched on accordingly, so that cooling of the drive components 1, 1*, 2, 2* begins. For example, the respective pump can be connected or switched on, or its flow rate can be increased. A method for setting a predetermined temperature of one or more of the drive components 1, 1*, 2, 2* of the traction drive involves actuating the first valve 36 and, optionally, the second valve 41 to adjust the coolant flowing through the heat exchanger 5 from the respective cooling circuit 3, 4, and thus to achieve the predetermined temperature of the drive component 1, 1*, 2, 2*. This method is executed primarily by means of the control unit 6. The predetermined temperature is stored in the control unit 6 or is determined by the control unit 6 based on the specific situation. Preferably, the method utilizes a temperature change in the respective drive components 1, 1*, 2, 2* to actuate the first and / or second valve 36, 41. Accordingly, this temperature change is incorporated into the actuation of the respective valve 36, 41. This allows the temperature profile of the drive components 1, 1*, 2, 2* to be anticipated and the setting of the predetermined temperature to be improved. Reference sign 1 Inverter, drive components 1* Internal combustion engine, traction drive, drive components 2 Electric motor, traction motor, drive component 2* Transmission, drive components 3 Cooling circuit 31 Cooling circuit section 32 Cooling circuit section 33 Pump 34 Air cooler 36 Valve 37 Expansion tank 38 Thermostat 39 Bypass 310 Throttle 4 Cooling circuit 41 Valve 5 Heat exchanger 6 Control unit

Claims

Electric traction drive for propelling a vehicle by means of electrical energy, comprising a first drive component (1) which is an inverter and which is a second drive component (2) which is a heat emitter during operation, and a cooling system for temperature control of the first and second drive components (1, 2), wherein the cooling system comprises a first cooling circuit (3) and a second cooling circuit (4) and a heat exchanger (5), the heat exchanger (5) is configured for heat exchange between the first and second cooling circuits (3, 4), the first cooling circuit (3) leads through the first drive component (1) to temperature control the first drive component (1), the second cooling circuit (4) leads through the second drive component (2) to temperature control the second drive component (2), characterized by a first valve (36) arranged in the first cooling circuit (3) for adjusting the coolant flow from the first cooling circuit (3) through the heat exchanger (5),and a control unit (6) for actuating the first valve (36), wherein the control unit (6) is configured to actuate the first valve (36) based on a temperature model stored in the control unit (6). Electric traction drive according to claim 1, wherein the first cooling circuit (3) is designed for operation with cooling water as the coolant and the second cooling circuit (4) is designed for operation with lubricant as the cooling and lubricating medium. Electric traction drive according to claim 1 or 2, wherein the first valve (36) is configured to open the heat exchanger (5) to a coolant flow of the first cooling circuit (3) in its first valve position and to close the heat exchanger (5) to this coolant flow in its second valve position. Electric traction drive according to claim 3, wherein the first valve (36) is configured to open the heat exchanger (5) for the coolant flow of the first cooling circuit (3) in its first valve position instead of a throttle (310) connected in parallel to the heat exchanger (5) and to close the heat exchanger (5) for this coolant flow and to open the throttle (310) for this coolant flow in its second valve position. Electric traction drive according to one of the preceding claims, wherein the first drive component (1) is connected in parallel with the first valve (36) in terms of flow technology. Electric traction drive according to one of claims 1 to 4, wherein the first drive component (1) is fluidically connected in series with the first valve (36). Electric traction drive according to one of the preceding claims, with a second valve (42) arranged in the second cooling circuit (4) for adjusting the coolant supplied by the second cooling circuit (4) through the heat exchanger (5). Electric traction drive according to claim 7, wherein the second valve (41) is a 4 / 2-way valve, wherein the second valve (41) is configured to open in its first valve position for a coolant flow of the second cooling circuit (4) through the heat exchanger (5) and to close in its second valve position through the heat exchanger (5). Electric traction drive according to one of the preceding claims, wherein the second drive component (1, 2) is an electric machine (2) or a gearbox. Electric traction drive according to one of the preceding claims, wherein an air cooler (34) is arranged in the first cooling circuit (3) for cooling the coolant of the first cooling circuit (3) by means of air. Electric traction drive according to claim 10, wherein a thermostat (37) is arranged upstream of the air cooler (34) in the first cooling circuit (3), wherein the thermostat (37) is configured to at least partially close a path of the coolant through the air cooler (34) and to at least partially open a bypass (39) that bypasses the air cooler (34) when the temperature of the coolant of the first cooling circuit (3) is below a predetermined temperature threshold, and to at least partially open the path of the coolant through the air cooler (34) and to at least partially close the bypass (39) when the temperature of the coolant of the first cooling circuit (3) is above the predetermined temperature threshold. Electric traction drive according to one of the preceding claims, wherein the control unit (6) is configured to actuate the first valve (36) on the basis of a measured temperature of the coolant of the first cooling circuit (3) and / or second cooling circuit (4) and / or the first drive components (1) and / or the second drive components (2). Electric traction drive according to one of the preceding claims, wherein the control unit (6) is configured to maintain the first and second drive components (1, 2) within a predetermined temperature range by actuating at least the first valve (36). Method for setting a predetermined temperature of one or more drive components (1, 2) of the traction drive according to one of the preceding claims, wherein at least the first valve (36) is actuated to adjust the coolant supplied by the first cooling circuit (3) through the heat exchanger (5) and thus the predetermined temperature of the drive component (1, 2). Method according to claim 14, wherein a temperature change of the drive components (1, 2) is used for actuating the at least first valve (36).

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