Drive device for a motor vehicle, method for operating a drive device, motor vehicle

Abstract

Drive device (1) for a motor vehicle (2) having at least two wheel axles (3, 4), with an internal combustion engine (5), with a first electric machine (6) and with a second electric machine (7), wherein the internal combustion engine (5) is coupled to the first electric machine (6), wherein the internal combustion engine (5) and the first electric machine (6) are assigned to a first of the wheel axles (3) and the second electric machine (7) is assigned to a second of the wheel axles (4), and wherein the first electric machine (6) is connectable to the first wheel axle (3) by a first actuatable clutch (8), characterized in that the internal combustion engine (5) and the first electric machine (6) are coupled to the first wheel axle (3) by the first clutch (8) with a transmission (9) having a fixed gear ratio.

Description

[0001] The invention relates to a drive device for a motor vehicle having at least two wheel axles, with an internal combustion engine, with a first electric machine and with a second electric machine, wherein the internal combustion engine is coupled to the first electric machine.

[0002] Furthermore, the invention relates to a method for operating such a drive device and to a motor vehicle with a corresponding drive device. State of the art

[0003] Drive devices, methods for operating them, and motor vehicles with such drive devices are known from the prior art, for example from DE 10 2010 033 431 A1 or WO 2008 / 142 076 A1. Hybrid drive devices are known as drive devices which, in addition to the conventional internal combustion engine, also have an electric machine, wherein both the electric machine and the internal combustion engine generate torque to drive the vehicle and jointly bring it onto the road. The electric machine can also be operated as a generator, so that by operating the internal combustion engine, which drives the electric machine, electrical energy can be generated and stored, for example, in a battery. At the same time, the electric machine can also be used as a starter motor for the internal combustion engine.Different topologies of hybrid drive devices are known, such as a series hybrid drive device or a parallel hybrid drive device. In a series hybrid drive device, a first electric machine is driven by the internal combustion engine to generate electricity, while a second electric machine uses the generated energy to provide torque to drive the motor vehicle. In a parallel hybrid drive device, at least one of the electric machines and the internal combustion engine each provide torque to drive the motor vehicle.

[0004] The technical object of the invention is to provide an improved drive device for a hybrid vehicle. Disclosure of the invention

[0005] The drive device according to the invention with the features of claim 1 solves this problem and has the advantage that the second electric machine cannot be directly coupled to the internal combustion engine and the first electric machine and can therefore be operated essentially independently of them. This results in further advantageous design options for controlling the drive device. According to the invention, it is provided for this purpose that the internal combustion engine and the first electric machine are assigned to a first of the wheel axles and the second electric machine is assigned to a second of the wheel axles. The second electric machine is therefore not a component of the combination of internal combustion engine and first electric machine and can therefore be operated essentially independently of them.Although feedback occurs via the road surface, the second electric machine can also be operated at a different speed, for example due to a different friction behavior of the wheels of the second wheel axle compared to the wheels of the first wheel axle.

[0006] According to the invention, the first electric machine can be connected to the first wheel axle by a first actuatable clutch. By coupling and uncoupling the first electric machine, the first electric machine can be decoupled as needed, so that it does not have to be dragged along when driving the motor vehicle, thereby avoiding corresponding power losses. Preferably, the internal combustion engine is coupled to the electric machine, so that when the first electric machine is decoupled from the first wheel axle by actuating or disengaging the clutch, the internal combustion engine is also decoupled from the first wheel axle. The first clutch thus represents the link between the first electric machine and the internal combustion engine to the first wheel axle. By actuating the first clutch, the entire combination of the first electric machine and the internal combustion engine can be coupled or uncoupled.

[0007] Furthermore, the invention provides that the internal combustion engine and the first electric motor can be coupled to the first wheel axle by means of the first clutch with a transmission having a fixed gear ratio. It is therefore provided that the drive device between the internal combustion engine and the first wheel axle is not a manual transmission or another transmission having a gear ratio that can be changed during driving. The drive device drives the motor vehicle with a gear ratio determined during design. Due to the electric motors, it is possible, for example, to drive electrically at low engine speeds and to engage the internal combustion engine at higher speeds.

[0008] According to an advantageous further development of the invention, the second electric motor can be connected to the second wheel axle via a second actuatable clutch. When the second clutch is disengaged, the second electric motor is decoupled from the second wheel axle and is not dragged, for example, when the motor vehicle is driven by the internal combustion engine or the first electric motor. This prevents dragging of the electric motor, particularly at high speeds, and thus increases drive power.

[0009] The method according to the invention with the features of claim 3 has the advantage of achieving advantageous drive behavior of the drive device, which, on the one hand, offers a high level of driving safety and, on the other hand, efficiently implements a driver's command. According to the invention, the clutches are actuated depending on the current speed of the motor vehicle. It is therefore provided that, depending on the current speed, the first and second clutches are connected to the respective wheel axle for coupling or decoupling the respective drive unit comprising the first electric motor and the internal combustion engine, or the second electric motor, for driving the respective wheel axle.

[0010] It is preferably provided that the second clutch is closed in a first speed range from standstill up to a first limit value and opened in a second speed range from a second limit value up to a maximum speed. This results in the second electric machine being used for starting from standstill and being decoupled at higher speeds, i.e. in the second speed range, so that it no longer needs to be towed. In particular, it is provided that the first wheel axle is a front wheel axle and the second wheel axle is a rear wheel axle. Driving stability is thus also increased by the fact that the drive device assigned to the rear wheel axle, namely the second electric machine, is decoupled at high speeds and the drive device is thereby switched to a front wheel drive device.The second limit value is expediently selected such that it corresponds to the first limit value. Alternatively, it can also be provided that the second limit value is higher than the first limit value, so that there is an intermediate speed range within which the second clutch can be opened or closed depending on further predeterminable boundary conditions. Of course, it can be provided that in certain situations, such as in emergency situations, the second clutch can be opened in the first speed range and closed in the second speed range. During normal operation of the motor vehicle, however, the second clutch is controlled depending on the speed ranges, as described above.

[0011] Furthermore, the invention provides that the first clutch is engaged in a third speed range from a third limit value up to the maximum speed. In the third speed range up to the maximum speed, the first clutch is engaged, so that the maximum speed can be safely reached with the aid of the internal combustion engine. In particular, when the internal combustion engine can only be connected to the first wheel axle via the fixed gear ratio, the first clutch is disengaged in a speed range below the second limit value in order to prevent the internal combustion engine from operating in a speed range below an idling speed range. The third limit value is preferably selected such that it is higher than the first limit value.

[0012] According to an advantageous development of the invention, it is further provided that wheels of the second wheel axle are monitored for slippage during start-up, and that the first clutch is engaged when a predeterminable threshold is exceeded, and the internal combustion engine and / or the first electric motor are driven. When the motor vehicle starts moving, the drive device is in the first speed range, in which the first clutch is preferably disengaged and the second clutch is engaged.If, during starting off, it is detected that the wheels of the second wheel axle are spinning, which is recognized by the slippage exceeding a predefined threshold, the first clutch is engaged and additional torque is transferred to the road by the internal combustion engine and / or the first electric motor, whereby the motor vehicle or the drive device operates as an all-wheel drive, which enables safe starting off. In this case, a engaged state of the first or second clutch is understood in particular to also mean a slipping state of the clutches, so that in the case described above, the first clutch can be operated with slipping to assist starting off.

[0013] The motor vehicle according to the invention with the features of claim 6 is characterized by a control unit that implements the method according to the invention. This results in the advantages already mentioned. Further features and advantages emerge from the above description and from the claims.

[0014] The invention will be explained in more detail below with reference to the drawings. These show: Fig. 1 a drive device for a motor vehicle in a simplified representation, Fig. 2 a method for operating the drive device depending on a current driving speed, Fig. 3 a first embodiment of the method, Fig. 4 a second embodiment of the method and Fig. 5 a third embodiment of the method in a flow chart.

[0015] Fig. 1 shows a simplified representation of a drive device 1 for a motor vehicle 2, not shown in detail. The drive device 1 has a first wheel axle 3 and a second wheel axle 4, wherein the first wheel axle 3 represents a front wheel axle of the motor vehicle 2 and the second wheel axle 4 represents a rear wheel axle of the motor vehicle 2.

[0016] The drive device 1 comprises an internal combustion engine 5, in particular in the form of a reciprocating piston engine, a first electric machine 6, and a second electric machine 7 as drive units. However, the electric machines 6, 7 can also, in principle, be operated as generators.

[0017] The internal combustion engine 5 and the first electric machine 6 together form a drive unit that is assigned to the first wheel axle 3. For this purpose, the internal combustion engine 5 is directly coupled to the electric machine 6, for which purpose, for example, an output shaft of the internal combustion engine 5 is rotationally fixedly coupled to a rotor of the electric machine 6. The electric machine 6 is further coupled to a first actuatable clutch 8. The clutch 8 connects the drive unit to a transmission 9, which has a fixed gear ratio i, and connects the clutch 8 to the first wheel axle 3, as needed. The wheel axle 3 is in Fig. 1 is only symbolically represented as a continuous axle. Of course, it can be provided that the wheel axle 3 has a separate drive shaft for each driven wheel 10, 11 of the wheel axle 3, which is connected to the transmission 9. The same applies to the wheel axle 4 and its wheels 12, 13, which are coupled to one another, in particular, by a differential gear 14.

[0018] The second electric motor 7 is assigned to the second wheel axle 4 and can be coupled thereto by a second actuatable clutch 15. The clutch 15 is preferably designed as a claw clutch, which enables a positive torque transmission from the electric motor 7 to the second wheel axle 4.

[0019] Furthermore, the drive device 1 has an electrical storage device 16, which is designed as a rechargeable high-voltage storage device and is connected to the first electric machine 6 and the second electric machine 7 via an inverter 17 and 18, respectively, for the energy supply. Furthermore, a control unit 19 is provided that controls the electric machines 6, 7, the clutches 8, 15, and the internal combustion engine 5. The control unit 19 is also connected to speed sensors 20, 21, 22, 23, each of which is assigned to a wheel 10, 12, 13, 11 of the drive device 1.

[0020] The transmission 9 has a gear ratio such that the motor vehicle reaches its maximum speed at the maximum power of the internal combustion engine. In particular, a gear ratio i is provided that corresponds to 5th gear or higher in conventional manual transmissions. Consequently, the minimum and still stable drivable speed of the motor vehicle 2 is, for example, 50 km / h, which then preferably corresponds to the idle speed of the internal combustion engine 5.

[0021] The electric machine 7 is coupled to the wheel axle 4 with a gear ratio when the clutch 15 is closed such that, with the same starting torque at the wheels 13, 12, the torque requirements of the electric machine 7 at 0 km / h or at a standstill are as small as possible, and at the same time there is still an overlap between the speed range of the electric machine 7 and the speed range of the internal combustion engine 5, so that the electric machine 7 can act to drive the motor vehicle 2 in the speed range in which the internal combustion engine 5 is no longer operable, and beyond that in the overlap range of the motor vehicle in which both the internal combustion engine 5 and the electric machine 7 are operable.At low driving speeds, the drive device 1 is preferably operated in series, so that the drive torque is generated only by the electric machine 7, but electrical energy is made available by the generator operation of the electric machine 6.

[0022] Based on Fig. 2, the method for operating the drive device 1 will be explained in more detail below. Fig. 2 shows a diagram of the operating range of the internal combustion engine 5 and the electric motor 7 plotted against the driving speed v of the motor vehicle 2. The upper bar represents the speed range of the internal combustion engine 5, and the lower bar represents the speed range of the electric motor 7. The speed values ​​are, of course, purely exemplary; depending on the embodiment of the drive device 1, other speed values ​​may also be used.

[0023] The total speed range extends from the standstill of the motor vehicle 2 at v=0 km / h to the maximum possible driving speed v max. In a first speed range I from the standstill of the motor vehicle 2 v0 up to a first limit value v1, the clutch 15 is closed and the motor vehicle is driven by the electric machine 7. In a second speed range II from the limit value v1 to v max the second clutch 15 is opened, so that the electric machine 7 is decoupled from the wheel axle 4. As a result, the motor vehicle 2 is no longer driven by the electric machine 7. In a third speed range III, which extends from a third limit value v2 to the maximum speed v maxextends, the motor vehicle or the drive device 1 is driven by the internal combustion engine 5. This results in an overlap range of the speed ranges I and III, in which the motor vehicle 2 is driven both by the electric machine 7 and by the internal combustion engine 5. At speeds below the limit value v2, the internal combustion engine 5 is separated from the wheel axle 3, in particular by opening the clutch 8, so that in this speed range IV, from the standstill of the vehicle at v0 up to the limit value v2, the motor vehicle 2 is driven only by the electric machine 7. The limit value v2 is selected, as described above, as a function of the idling speed of the internal combustion engine 5. The internal combustion engine 5 thus covers the speed range III from approximately 50 km / h up to the maximum speed.The overlap range can be individually determined; a small overlap range reduces the torque requirements but makes switching between different operating modes more difficult. In principle, the drive device 1 can be operated as a parallel-connected hybrid drive device or as a series-connected hybrid drive device, depending on how the clutches 8, 15 are connected and the electric machines 6, 7 are driven. For operation as a parallel hybrid drive device, the clutches 8, 15 and both electric machines 6, 7 are operated as motors to generate torque. If necessary, the electric machine 6 can also be operated as a generator to generate electrical energy for the electric machine 7.For serial operation of the hybrid drive system, clutch 8 is opened and electric motor 6 is driven as a generator by internal combustion engine 5, generating electrical energy that is made available to the motor-driven electric motor 7. In this case, motor vehicle 2 is driven only at the rear wheel axle, whereas in the other, previously described, all-wheel drive is provided. While a relatively large overlap range facilitates switching between the two operating modes, it places greater demands on the torque required.

[0024] The drive device 1 also offers the advantage that the motor vehicle can drift thanks to its rear-wheel drive, which emphasizes the vehicle's sporty character. Thanks to the all-wheel drive function, the vehicle can utilize the electric power very effectively during boost and high acceleration. At high speeds, the vehicle also drives very stably because it is then front-wheel drive.

[0025] Fig. 3 shows a flowchart of a functional sequence of the method according to a first exemplary embodiment. After the motor vehicle has started in a first step S1, the current driving speed v of the motor vehicle is compared with the limit value v1 in a step S2. If the comparison shows that the current driving speed exceeds the limit value v1 (j), the clutch 15 is opened in a subsequent step S3, so that the drive device switches from the previous parallel hybrid driving mode to front-wheel drive. If the current driving speed is below the limit value v1 (n), the clutch 15 is closed in a step S4. The electric machine 7 is thus decoupled from the wheel axle 4 at high speeds by opening the second clutch 7, which results in driving dynamics advantages, in particular an increase in driving stability due to the front-wheel drive.In addition, the electric machine 7 does not have to be dragged along at high speeds, thereby increasing the efficiency of the drive device 1 by reducing mechanical and electrical losses.

[0026] A further embodiment of the method is illustrated by the flow chart in Fig. 4. It is preferably assumed that the clutch 8 is designed or constructed as a starting clutch, so that slipping operation of the clutch 8 is possible on multiple occasions. After the start in step S1, the data recorded by the speed sensors 21 and 22 of the wheel axle 4 are evaluated in step S5 in order to detect slippage at the wheels 13, 12. If slippage at the wheels 13, 12 is detected (j) when the vehicle starts moving by means of the electric machine 7, the clutch K1 is closed or slipped and the internal combustion engine 5 and the electric machine 6 are operated as a motor, so that torque is transmitted to the wheel axle 3. This implements an all-wheel drive function that enables starting and driving up steep inclines even with poor wheel ratio conditions. If it is detected that there is no wheel slip (n), the clutch 8 is opened or kept open in a step S6.If wheel slip is detected (y), a check is performed in step S7 to determine whether the internal combustion engine 5 and / or the electric motor 6 are producing a positive torque. If this is not the case (n), the internal combustion engine 5 is started and the electric motor 6 is switched to motor operation in step S8. Subsequently, in step S9, the clutch 8 is operated with slipping to achieve a desired drive torque M. s , which is set by the vehicle control 19, in particular depending on a driver's desired torque.

[0027] Fig.5 shows a further exemplary embodiment in a further flow chart. This exemplary embodiment differs from the previous one in that the clutch 8 does not have to be designed as a starting clutch or operated with slip. For this purpose, the wheel slip of the wheels 12, 13 is first monitored in step S5, as before, when starting off. If it is then detected that there is no wheel slip (n), the torque of the electric machine 6 is set to zero in a step S10, or the electric machine 6 is placed in a neutral state, and the clutch 8 is opened in a step S11. If it is detected that wheel slip is present (j), the clutch 8 is closed in a step S12 and, depending on the desired drive torque M sIn a step S13, the electric machine 6 is controlled to adjust the torque. In this case, the torque at the wheel axle 3 is provided solely by the electric machine 6. The internal combustion engine 5 is thereby dragged along by the electric machine 6. However, it can also be provided to provide an additional clutch between the internal combustion engine 5 and the electric machine 6, so that the internal combustion engine 5 can also be decoupled from the electric machine 6 and does not have to be dragged along in the situation described above. An all-wheel drive function can nevertheless be realized using the electric machine 6 and the closed clutch 8, wherein, since the wheel axle 3 is driven solely by the electric machine 6, slipping operation of the clutch 8 is not necessary, whereby the clutch 8 is more cost-effective and easier to manufacture.

Claims

[1] Drive device (1) for a motor vehicle (2) having at least two wheel axles (3, 4), with an internal combustion engine (5), with a first electric machine (6) and with a second electric machine (7), wherein the internal combustion engine (5) is coupled to the first electric machine (6), wherein the internal combustion engine (5) and the first electric machine (6) are assigned to a first of the wheel axles (3) and the second electric machine (7) to a second of the wheel axles (4), and wherein the first electric machine (6) is connectable to the first wheel axle (3) by a first actuatable clutch (8), characterized by that the internal combustion engine (5) and the first electric machine (6) are coupled to the first wheel axle (3) by the first clutch (8) with a transmission (9) having a fixed gear ratio. [2] Drive device according to one of the preceding claims, characterized bythat the second electric machine (7) can be connected to the second wheel axle (4) by a second actuatable clutch (15). [3] A method for operating a drive device (1) for a motor vehicle (2), which has at least two wheel axles (3, 4), a first internal combustion engine (5), a first electric machine (6), and a second electric machine (7), wherein the internal combustion engine (5) is coupled to the first electric machine, wherein the internal combustion engine (5) and the first electric machine (6) are assigned to a first of the wheel axles (3), and the second electric machine (7) is assigned to a second of the wheel axles (4), and are operated as a function of a current driving speed of the motor vehicle (2), wherein the first electric machine (6) is connectable to the first wheel axle (3) by a first actuatable clutch (8), and the second electric machine (7) is connectable to the second wheel axle (4) by a second actuatable clutch (15), wherein the clutches (8, 15) are actuated as a function of the current driving speed, characterized bythat the first clutch (8) in a third speed range (III) from a third limit value (v2) up to the maximum speed (v max ) is closed. [4] Method according to claim 3, characterized by that the second clutch (15) is closed in a first speed range (I) from the standstill of the motor vehicle up to a first limit value (v1) and in a second speed range (II) from a second limit value (v1) up to a maximum speed (v max ) of the motor vehicle (2) is opened. [5] Method according to one of claims 3 to 4, characterized by that when starting off, wheels (12, 13) of the second wheel axle (4) are monitored for slippage, and that when a predeterminable threshold is exceeded, the first clutch (8) is closed and the internal combustion engine (5) and / or the first electric machine (6) are operated as a motor. [6] Motor vehicle (2) with a drive device (1) according to one of claims 1 to 2, characterized by a control device (19) which carries out the method according to one of claims 3 to 5.

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