Power unit for a vehicle and method for operating a power unit for a vehicle

Abstract

The invention relates to a power unit (1) for a vehicle (F), comprising: - an internal combustion engine (2), - at least one electric motor (3), and - a transmission (4) having a separate input shaft (E1, E2) for each of the internal combustion engine (2) and the electric motor (3), wherein the electric motor (3) is permanently coupled to an output unit (5) of the transmission (4) and the power flow between the electric motor (3) and the output unit (5) is interrupted when the transmission (4) is in a neutral position (N). The invention also relates to a method for operating such a power unit (1).

Description

Field of the Invention

[0001] The present invention relates to a drive unit for a vehicle. The present invention also relates to a method for operating such a drive unit. Background Art

[0002] Drive units for vehicles (such as hybrid drive units) and methods for operating them are generally known in the prior art. Summary of the Invention

[0003] The present invention is based on the object of specifying a particularly compact drive unit for a vehicle that is improved relative to the prior art. The present invention is also based on the object of specifying a suitable method for operating such a drive unit.

[0004] The object is achieved by means of a drive unit for a vehicle according to the present invention and a method for operating the drive unit.

[0005] Advantageous configurations of the present invention are the subject of preferred embodiments.

[0006] A drive unit for a vehicle according to the present invention includes an internal combustion engine, at least one electric motor, and a transmission, wherein the transmission has a separate input shaft for the internal combustion engine and for the electric motor in each case. Here, the electric motor is fixedly coupled to an output unit of the transmission, and the power flow between the electric motor and the output unit is not interrupted when the transmission is in the neutral position.

[0007] The drive unit is configured as a hybrid drive for a vehicle and allows pure electric operation of the vehicle when the internal combustion engine is functionally disengaged from the transmission. Due to the fact that the electric motor is fixedly coupled to the output unit, no clutch element is required for functionally coupling the electric motor to the transmission. In other words: the electric motor is directly coupled to the output unit with a reduction ratio, without the need for a disconnect unit. The transmission can thus be produced in a simple and compact form, so that the drive unit is more cost-effective than conventional drive units. In addition, the transmission requires less structural space than the transmission of a conventional hybrid drive.

[0008] According to an exemplary embodiment, the transmission is in the neutral position during each start-up process of the vehicle. Therefore, the vehicle must be electrically driven during each start-up process. This has the advantage that no so-called start clutch for functional access to the internal combustion engine is required during start-up of the vehicle. This further promotes the compact design of the transmission. In addition, when the vehicle is driven by the internal combustion engine at a certain speed or above, the torque generated by the electric motor can be superimposed on the torque generated by the internal combustion engine. In other words: the torque generated by the electric motor can be used to enhance - that is, assist - the internal combustion engine during the drive operation.

[0009] The transmission is specifically configured as a gear-driven automated manual transmission having multiple transmission gear ratios. The automated manual transmission is characterized by a relatively simple mechanical structure and good efficiency. In addition, compared to the prior art, the number of transmission gear ratios can be reduced. For a drive unit configured in this way, for example, compared to a conventional drive unit, a number of four transmission gear ratios is sufficient and there is no loss of any driving comfort. The number of two or three transmission gear ratios is also conceivable.

[0010] The transmission further includes a drive shaft which is functionally connected to, specifically kinematically connected to, an internal combustion engine. A countershaft is arranged parallel to the drive shaft and can be brought into engagement with the drive shaft, specifically by means of gears. By means of the parallel countershaft, the rotational speed of the drive shaft in the power flow of the transmission can be reduced and the torque can be increased. Here, the countershaft includes a gear-driven final transmission ratio by means of which an output unit can be directly driven. The output unit is, for example, a differential transmission which drives a wheel axle drive shaft for the drive wheels of a vehicle (e.g., front drive wheels).

[0011] The transmission further includes at least one dog clutch for shifting to at least one transmission gear ratio. The dog clutch can be produced in a simple and thus cost-effective form and promotes a simple and compact construction of the transmission of the drive unit.

[0012] In addition, an electric motor is connected to the output unit via the countershaft. The electric motor can thus drive the output unit independently of the drive shaft connected to the internal combustion engine.

[0013] In a further embodiment, the electric motor is connected to the countershaft via a gear of a first transmission gear ratio, which gear is rotatably connected to the output shaft by means of the at least one dog clutch. The electric motor is thus connected to the countershaft by means of transmission components already existing for the internal combustion engine. The reuse of the transmission components in this way further reduces the structural space requirements of the transmission.

[0014] Here, when the at least one dog clutch is in the open state, the gear of the first transmission gear ratio is rotatable relative to the drive shaft. Specifically, when the dog clutch is open, power is not transmitted from the gear of the first transmission gear ratio to the drive shaft, and in this state the internal combustion engine is functionally disengaged from the transmission. This allows the gear of the first transmission gear ratio to be used both for connecting the internal combustion engine to the transmission and for connecting only the electric motor to the transmission. The electric motor can thus also perform the function of the drive assembly during a gearshift process in which the dog clutch is temporarily open. This allows gearshifting without interruption of the tractive power and eliminates an expensive synchronization unit.

[0015] The connection of the electric motor and the connection of the output unit are also realized by means of the so-called reduction ratio. In this case, the rotational speed in the direction of the power flow in the transmission is reduced, but the transmitted torque is increased. For this purpose, the magnitude of the transmission ratio between the rotational speed of the electric motor and the rotational speed of the output unit is greater than one. This allows the rotational speed of the electric motor to be increased to the wheel rotational speed required for optimal starting operation. In addition, during the gear ratio change, the torque drop can be compensated by the electric motor without interrupting the traction power.

[0016] In the case of the method for operating a drive unit according to the present invention, when the transmission is in the neutral position, the power for driving the output unit is transmitted only from the electric motor. Therefore, when the internal combustion engine is not functionally connected to the transmission, a pure electric drive of the vehicle is possible. Here, by directly connecting the electric motor to the output unit via the reduction ratio without the need for a disengaging unit, the functional disconnection of the internal combustion engine from the transmission and thus the exclusive access of the electric motor as a drive component can be achieved in a simple manner.

[0017] According to an embodiment of the present method, during each starting process, the transmission is placed in the neutral position, where the power for driving the output unit is transmitted from the internal combustion engine starting from a specified speed greater than zero. Since each starting process of the vehicle is electrically driven, the starting clutch for functionally connecting the internal combustion engine to the transmission can be omitted. This allows for a compact and simple design of the transmission, and compared to the prior art, the structural space requirements are reduced and thus the drive unit is more cost-effective.

[0018] After the starting process, for higher speeds, the internal combustion engine is used as a drive component. Here, starting from a specified speed greater than zero, the internal combustion engine is connected to the countershaft by means of the transmission gear ratio, so that the power for driving the output unit is transmitted additionally or only from the internal combustion engine. During the gearshift process, the electric motor can continue to perform the function of the drive component, so that the torque drop can be almost avoided during the gearshift. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Exemplary embodiments of the present invention will be discussed more specifically below with reference to the drawings.

[0020] Specifically:

[0021] Figure 1 A vehicle having a drive unit is schematically shown, and

[0022] Figure 2 A drive unit for a vehicle is schematically shown.

[0023] In all the drawings, corresponding parts are denoted by the same reference numerals. DETAILED DESCRIPTION

[0024] Figure 1 A vehicle F with a drive unit 1 is shown in a very simplified illustration. Figure 2 The drive unit 1 of the vehicle F is schematically shown and has an internal combustion engine 2, an electric motor 3, a transmission 4, and an output unit 5.

[0025] The drive unit 1 forms a hybrid drive for the vehicle F, specifically for a motor vehicle, and can for example be used as a front drive or as a rear drive with a front-mounted drive assembly mounted transversely or longitudinally. The vehicle F is for example a passenger car, an off-road vehicle, a multi-purpose vehicle, or a motorcycle.

[0026] In the exemplary embodiment shown, the drive unit 1 has an internal combustion engine 2 and an electric motor 3 as drive components. Both the internal combustion engine 2 and the electric motor 3 are coupled to the transmission 4 by means of dedicated input shafts E1, E2. The electric motor 3 is fixedly coupled to the output unit 5, where the power flow between the electric motor 3 and the output unit 5 is not interrupted when the transmission 4 is in the neutral position N.

[0027] Furthermore, the drive shaft A of the transmission 4 (which is coupled to the input shaft E1 of the internal combustion engine 2 and runs coaxially with respect to E1) is coupled to an electric starter generator 6, which starts the internal combustion engine 2, aids synchronization, and acts as a generator during the operation of the vehicle F. Here, the drive unit 1 for example forms a parallel hybrid drive with a combination of a so-called P1 arrangement and a P3 arrangement.

[0028] The designation of the arrangement depends on the installation position of the electric motor 3 within the drive unit 1. Since the electric motor 3 in the exemplary embodiment shown is directly coupled to the output of the transmission 4 (see the more specific explanation below), there is a P3 arrangement. The combination with the P1 arrangement is produced by the additional electric starter generator 6, which is fixedly connected to the drive shaft A.

[0029] The transmission 4 described more specifically below is based on an automated manual transmission known from the prior art, specifically a multi-ratio spur gear transmission with positive engagement shift elements.

[0030] In the transmission 4 shown, a so-called countershaft V is arranged parallel to the drive shaft A, which at the same time forms the output shaft of the transmission 4 and directly drives the output unit 5 via a final gear ratio consisting of two gears Z1, Z2. The output unit 5 is for example a differential transmission, which drives the axle drive shaft for the drive wheels (for example, the front drive wheels) of a motor vehicle.

[0031] A plurality of gears Z3 to Z6 are arranged on the drive shaft A (the gears are continuously engaged in pairs with the gears Z7 to Z10 arranged on the countershaft V), and thus provide different transmission ratios for different gear ratios. In the exemplary embodiment shown, the transmission 4 has four transmission gear ratios G1 to G4. Alternatively, the transmission 4 can also have fewer than four transmission gear ratios G1 to G4, such as two or three transmission gear ratios G1 to G4. It is also conceivable to have more than four transmission gear ratios G1 to G4.

[0032] For each gear pair, in each case, one of the gears Z3 to Z10 is arranged rotatably connected to the corresponding shaft (that is, the drive shaft A or the countershaft V), and the other gears of the gears Z3 to Z10 are arranged on the corresponding shaft in a freely rotatable and axially fixed manner.

[0033] In the exemplary embodiment shown, the gear pair of the fourth transmission gear ratio G4 includes the gear Z6 (also referred to as the fixed gear) fixedly arranged on the drive shaft A and the gear Z10 (also referred to as the idler gear) loosely arranged on the countershaft V. The gear Z6 fixedly arranged on the drive shaft A also continuously engages with the gear Z11, which is connected to the input shaft E3 of the starter generator 6. The loosely arranged gear Z10 is specifically arranged on the shaft section V1 of the countershaft V, which is in the form of a hollow shaft, for example, and includes a first claw clutch K1, which is fastened to the countershaft V in a rotatably connected and axially displaceable manner.

[0034] The gear pair of the third transmission gear ratio G3 includes the gear Z5 fixedly arranged on the drive shaft A and the gear Z9 loosely arranged on the countershaft V. The loosely arranged gear Z9 is similarly arranged on another shaft section V2 of the countershaft V including the first claw clutch K1.

[0035] The gear pair of the second transmission gear ratio G2 includes the gear Z4, which is loosely arranged on the drive shaft A and is arranged on the drive shaft section A1 of the drive shaft A, for example, in the form of a hollow shaft. The drive shaft section A1 includes a second claw clutch K2. The gear pair of the second transmission gear ratio G2 also includes the gear Z8, which is fixedly arranged on the countershaft V.

[0036] The gear pair of the first transmission gear ratio G1 includes the gear Z3 and also includes the gear Z7. The gear Z3 is loosely arranged on the drive shaft A and is similarly arranged on another drive shaft section A2 of the drive shaft A. The other drive shaft section A2 includes the second claw clutch K2. The gear Z7 is fixedly arranged on the countershaft V.

[0037] The dog clutches K1, K2 are used for shifting the transmission gear ratios G1 to G4. Herein, the dog clutches K1, K2 each have a first dog element K1.1, K2.1, which are respectively rotatably connected and arranged on the drive shaft A or the countershaft V. Specifically, the first dog elements K1.1, K2.1 are arranged such that they rotate together with the drive shaft A or with the countershaft V but are axially displaceable relative to the drive shaft A or relative to the countershaft V, respectively.

[0038] The dog clutches K1, K2 also each have two second dog elements K1.2, K2.2, which are respectively arranged coaxially and opposite to the first dog elements K1.1, K2.1 on the drive shaft A and the countershaft V. In addition, the second dog elements K1.2 and K2.2 are integrally formed with the gears Z9, Z10 and Z3, Z4, respectively. That is to say, for example, the second dog element K2.2 of one dog clutch K2 is integrally formed with the gear Z3 of the first transmission gear ratio G1. The other second dog element K2.2 of the dog clutch K2 is integrally formed with the gear Z4 of the second transmission gear ratio G2, and the second dog element K1.2 of the other dog clutch K1 is integrally formed with the gear Z9 of the third transmission gear ratio G3. The other second dog element K1.2 of the other dog clutch K1 is integrally formed with the gear Z10 of the fourth transmission gear ratio G2.

[0039] Those surfaces of the first dog element K2.1 facing the gears Z3, Z4 each have a plurality of dog teeth (not shown in more detail). Similarly, a plurality of corresponding dog teeth are formed on those surfaces of the second dog element K2.2 that each face the first dog element K2.1 in each case, so that the dog teeth can be brought into engagement with each other.

[0040] In Figure 2 the exemplary embodiment shown, both dog clutches K1, K2 are illustrated as being in the open state. That is to say, the transmission 4 is in the neutral position N, in which the shiftable gears Z3, Z4 are not connected to the drive shaft A and the shiftable gears Z9, Z10 are not connected to the countershaft V. Therefore, no power is transmitted from the internal combustion engine 2 to the drive shaft A. Therefore, the internal combustion engine 2 is not functionally connected to the transmission 4, or is not kinematically connected to the transmission 4.

[0041] For a gear shift to the first transmission gear ratio G1, the second claw clutch K2 moves in the direction of the gear Z3 of the first transmission gear ratio G1. As a result, the claw teeth of the first claw element K2.1 and the claw teeth of the second claw element K2.2 (which are formed as a single piece with the gear Z3 of the first transmission gear ratio G1) are brought into engagement with each other. Thus, the gear Z3 of the first transmission gear ratio G1 is rotationally connected to the drive shaft A by means of the second claw clutch K2, so that the countershaft V is functionally connected to the gears Z1, Z2 and is thus coupled to them in terms of movement by means of the gear pair of the first transmission gear ratio G1. The transmission 4 has now been shifted to the first gear ratio position.

[0042] For a gear shift to the second transmission gear ratio G2, for example, the following situation occurs: the first claw element K2.1 of the second claw clutch K2 moves in the direction of the gear Z4 of the second transmission gear ratio G2 while the vehicle F is in motion, and the claw teeth of the first claw element K2.1 and the claw teeth of the second claw element K2.2 (which are formed as a single piece with the gear Z4 of the second transmission gear ratio G2) are brought into engagement with each other. Thus, the gear Z4 of the second transmission gear ratio G2 is rotationally connected to the drive shaft A by means of the second claw clutch K2, so that the countershaft V is functionally connected to the gears Z1, Z2, in particular is coupled to them in terms of movement by means of the gear pair of the second transmission gear ratio G2. The transmission 4 has now been shifted to the second gear ratio position.

[0043] For a gear shift to the third and fourth transmission gear ratios G3, G4, the above procedure is carried out in a manner similar to the first claw clutch K1.

[0044] In the case of a conventional drive unit 1, a synchronizing unit (for example in the form of synchronizing rings which are arranged transversely on the claw clutches K1, K2) is used to achieve a smooth gear shift process. Before the engagement of the gear ratio, the synchronizing unit adjusts the rotational speed of the corresponding gears Z1 to Z13 to the rotational speed of the corresponding shaft. In the case of the drive unit 1 according to the invention, such a synchronizing unit can be omitted.

[0045] Furthermore, since it is fixedly connected to the drive unit 1, the electric motor 3 drives the vehicle F during the gear shift process, whereby the drop in torque which usually occurs during the gear shift process can be compensated for. For this purpose, the electric motor 3 can be directly connected to the countershaft V and thus directly to the gears Z1, Z2, which include the final transmission ratio of the transmission 4 and drive the output unit 5. This will be explained in more detail below.

[0046] The electric motor 3 is, for example, an electric traction machine. The electric motor 3 is mechanically connected to the transmission 4 via a separate input shaft E2. For this purpose, the transmission 4 includes an intermediate gear pair that includes gears Z12, Z13. The gear Z13 is constantly engaged with the gear Z3 of the first transmission gear ratio G1 (this gear Z3 is arranged on the drive shaft A) and thus is constantly engaged with the gear Z7 of the first transmission gear ratio G1 (which is arranged on the countershaft V).

[0047] If the second claw clutch K2 is in the open state, the transmission 4 is in the neutral position N and the internal combustion engine 2 is not functionally connected to the transmission 4. That is to say, the power transmission occurs directly from the electric motor 3 to the countershaft V, and the countershaft V drives the output unit 5 via the final gear ratio by means of the gears Z1, Z2. In other words: As long as the internal combustion engine 2 is not functionally connected to the transmission 4, the electric motor 3 directly drives the output unit 5.

[0048] The electric motor 3 is thus fixedly connected (that is to say, has a fixed gear ratio) to the transmission 4, and as long as only the electric motor 3 is connected to the transmission 4 as the drive component, the shifting of the transmission gear ratios G1 to G4 is not possible.

[0049] The gear ratio is defined as the quotient of the rotational speed of the drive component (in the case of the electric motor 3) and the rotational speed of the output unit 5. If the magnitude of the gear ratio is greater than one, this is called the so-called reduction ratio. In this case, the rotational speed decreases in the transmission 4 in the direction of the power flow, but the transmitted torque increases. In the exemplary embodiment of the drive unit 1 shown, the electric motor 3 is connected to the output unit 5 by means of a reduction ratio.

[0050] As can also be seen in the exemplary embodiment shown, the transmission 4 does not have a starting clutch. Therefore, during the starting process, the vehicle F must be driven by the electric motor 3. From a certain driving speed, the first transmission gear ratio G1 can be engaged so that the internal combustion engine 2 is functionally connected to the transmission 4. Since it is fixedly connected to the transmission 4, the electric motor 3 is always connected to the said transmission and can thus be temporarily used as the drive component of the vehicle F not only during the starting process but also during the shifting process. In addition, the reverse process of the vehicle F is driven by the electric motor 3, so that the reverse gear ratio in the transmission 4 can also be omitted.

[0051] Omitting the starting clutch and expensive transmission components such as a synchronization unit and a reverse gear ratio allows the drive unit 1 to have a particularly compact design. Specifically, the transmission 4 can be produced in a simplified and thus more cost-effective form compared to the prior art. By temporarily using the electric motor 3 as a drive component, driving comfort is hardly restricted or not restricted at all. This is especially because the electric motor 3 allows for electric operation of the vehicle F, a starting process that can be experienced as comfortable, and gear shifting with little to no torque drop.

[0052] The compact design is further promoted by the fact that the electric motor 3 can be connected to the output unit 5 via a gear pair of the first transmission gear ratio G1. Specifically, the gear Z3, which is arranged loosely on the drive shaft A, is used both as a shifting element of the transmission 4 and as an intermediate gear for coupling the electric motor 3 to the output unit 5. This transmission component that already exists for the internal combustion engine 2 can thus be used for power transmission from the electric motor 3 to the output unit 5.

[0053] Furthermore, since the gears Z3, Z4 are arranged loosely on the drive shaft A and the output unit 5 is located opposite, the gearbox width of the vehicle F can be reduced. This also allows the use of the gear Z3 as an intermediate gear for the electric motor 3.

[0054] Due to reasons of structural space and for the purpose of achieving the necessary transmission ratios of the transmission 4, the arrangement of the gears Z9, Z10, which are arranged loosely on the countershaft V, of the third and fourth transmission gear ratios G3, G4 allows for the direct connection of the starter generator 6.

[0055] The drive unit 1 can alternatively also be used as a series hybrid drive. Here, when the transmission 4 is in the neutral position N with the internal combustion engine 2 operating and running (where the internal combustion engine 2 is disengaged from the output unit 5 and the battery of the vehicle F (not shown) is charged by the starter generator 6), the power flow between the electric motor 3 and the output unit 5 is not interrupted. As an alternative or additionally, the starter generator 6 can also directly supply energy to the electric motor 3.

[0056] The starter generator 6 is similarly used here to synchronize the rotational speed of the internal combustion engine 2 during a gear shift operation. Thus, a mechanical synchronization element can also be omitted here, so that the structural space can be reduced, the cost of the transmission 4 can be reduced, and the transmission losses can also be reduced.

[0057] Furthermore, by means of the starter generator 6, both the crankshaft starter (specifically the crankshaft starting motor) and the conventional alternator can be omitted. Specifically, since the starter generator 6 is connected to the drive shaft A of the internal combustion engine 2 via the gear Z6 fixedly arranged on the drive shaft A with the fourth transmission gear ratio G4, considering the necessary transmission ratio and structural space, the starter generator 6 can be integrated into the transmission 4 with a minimum number of additional components.

[0058] List of reference numerals:

[0059] 1 drive unit

[0060] 2 internal combustion engine

[0061] 3 electric motor

[0062] 4 transmission

[0063] 5 output unit

[0064] 6 electric starter generator

[0065] A drive shaft

[0066] A1, A2 drive shaft sections

[0067] E1, E2, E3 input shafts

[0068] F vehicle

[0069] G1 to G4 transmission gear ratios

[0070] K1, K2 dog clutches

[0071] K1.1, K1.2 first dog elements

[0072] K2.1, K2.2 second dog elements

[0073] N neutral position

[0074] V countershaft

[0075] V1, V2 shaft sections

[0076] Z1 to Z13 gears.

Claims

1. A drive unit (1) for a vehicle (F), comprising: - an internal combustion engine (2), - at least one electric motor (3), and a transmission (4) having in each case a separate input shaft (E1, E2) for the internal combustion engine (2) and for the electric motor (3), wherein the electric motor (3) is fixedly coupled to the output unit (5) and the power flow between the electric motor (3) and the output unit (5) is not interrupted when the transmission (4) is in a neutral position (N), wherein the transmission ratio between the rotational speed of the electric motor (3) and the rotational speed of the output unit (5) is greater than one, wherein the transmission (4) is configured as a gear-driven automated manual transmission having a plurality of transmission gear ratios (G1 to G4), and The gear (Z3) of the first transmission gear ratio (G1) among the multiple transmission gear ratios (G1 to G4) is used both for connecting the internal combustion engine (2) to the transmission device (4) and for connecting only the electric motor (3) to the transmission device (4).

2. The drive unit (1) according to claim 1, During each starting process of the vehicle (F), the transmission (4) is in the neutral position (N).

3. The drive unit (1) according to claim 1, wherein the transmission device (4) further comprises: - a drive shaft (A) functionally coupled to said internal combustion engine (2), a layshaft (V) arranged parallel to the drive shaft (A) and capable of being brought into engagement therewith and comprising a gear-driven final drive ratio by means of which the output unit (5) can be driven directly, and - at least one dog clutch (K1, K2) for shifting into at least one transmission gear ratio (G1 to G4).

4. The drive unit (1) according to claim 3, The electric motor (3) is coupled to the output unit (5) via the secondary shaft (V).

5. The drive unit (1) according to claim 3 or 4, The electric motor (3) is connected to the countershaft (V) via the gear (Z3) of the first transmission gear ratio (G1), and the gear (Z3) is rotatably connected to the drive shaft (A) by means of the at least one dog clutch (K2).

6. The drive unit (1) according to claim 5, It is characterized in that The gear wheel (Z3) of the first transmission gear ratio (G1) is rotatable relative to the drive shaft (A) when the at least one dog clutch (K2) is in an open state.

7. Drive unit (1) according to claim 3 or 4, wherein the drive shaft (A) is coupled to an electric starter generator (6).

8. A method for operating a drive unit (1) according to any one of claims 1 to 7, wherein power for driving the output unit (5) is transmitted only from the electric motor (3) when the transmission (4) is in a neutral position (N).

9. The method according to claim 8, wherein - during each starting process the transmission (4) is placed in a neutral position (N), and, - Starting from a specified speed greater than zero, the internal combustion engine (2) is switched in via the transmission gear ratio (G1), and power for driving the output unit (5) is transmitted from the internal combustion engine (2).

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