Drive system for a hybrid vehicle and methods for operating such a drive system

Abstract

Drive system for a hybrid vehicle, with an internal combustion engine (12) which has an internal combustion engine shaft (14) and can drive, an automatic transmission (16) which has a transmission input shaft (18) arranged coaxially to the combustion engine shaft (14) on the drive side and a transmission output shaft (20) arranged coaxially to the combustion engine shaft (14) on the output side, a transmission coupling (22) for coupling or decoupling the transmission input shaft (18) and the transmission output shaft (20), a flywheel drive unit (24) which is arranged axially between the internal combustion engine (12) and the automatic transmission (16) and has an intermediate shaft (26) arranged coaxially to the internal combustion engine shaft (14), a first clutch (28) for coupling or uncoupling the internal combustion engine shaft (14) and the intermediate shaft (26), a second clutch (30) for coupling or uncoupling the intermediate shaft (26) and the transmission input shaft (18) as well as an electric machine (32) which sits on the gearbox input shaft (18) and can drive it in motor operation, characterized in that the electric motor (32) is integrated into the automatic transmission (16) is integrated.

Description

[0001] The invention relates to a drive system for a hybrid vehicle and a method for operating such a drive system.

[0002] To operate hybrid vehicles energy-efficiently, drive systems are already known from the prior art that, when the accelerator pedal is not depressed (i.e., when no active vehicle acceleration is desired), disengage the power transmission in the drivetrain while the combustion engine is running, in order to enter a state of so-called "idling coasting". It is also already known to switch off the combustion engine when the accelerator pedal is not depressed and power transmission in the drivetrain is present, thus establishing a mechanical coasting mode with optional brake recuperation.

[0003] DE 29 43 554 A1 discloses a hybrid drive for a vehicle, comprising an internal combustion engine, an electric motor, a transmission, and two disconnect clutches, wherein the internal combustion engine can be periodically switched off and on again during suitable operating phases by opening and closing the disconnect clutches. In this document, the internal combustion engine is designed without a flywheel. The required inertia is assigned to the electric motor, in particular, at least partially integrated into the rotating part of the electric motor. Due to the flywheel-free design of the internal combustion engine, it comes to a standstill almost instantly when the disconnect clutch between the internal combustion engine and the electric motor is disengaged, and can then be restarted essentially without jerking by re-engaging it with the rotating electric motor due to its low mass.In this way it is possible to start initially using only the electric machine and to start the combustion engine only after reaching a minimum speed, using the kinetic energy stored in the rotating masses and accelerating very quickly to the speed of the electric machine.

[0004] DE 199 17 665 A1 describes a hybrid drive for a motor vehicle, which is arranged in a drive train between an internal combustion engine and a vehicle transmission, a first electric machine and a second electric machine permanently connected to a transmission input shaft, wherein a switchable clutch is arranged between the electric machines and the internal combustion engine.

[0005] DE 10 2004 023 673 A1 discloses a method for controlling a powertrain of a hybrid vehicle, which has a parallel hybrid drive with a series arrangement of an internal combustion engine and an electric machine equipped with a flywheel S, as well as a drive transmission.

[0006] However, based on driving the hybrid vehicle with the combustion engine switched off, it became apparent that when the driver requests acceleration, there is a considerable delay before the vehicle responds. This sluggish behavior of the drive system negatively impacts driving comfort and can be perceived as annoying by the driver.

[0007] Therefore, the object of the invention is to provide a drive system for a hybrid vehicle and a method for its operation which enables a particularly rapid vehicle response to a request for acceleration from the driver, even when the combustion engine is switched off.

[0008] This problem is solved according to the invention by a drive system for a hybrid vehicle, comprising an internal combustion engine which has and can drive an internal combustion engine shaft, an automatic transmission which has, on the drive side, a transmission input shaft arranged coaxially to the internal combustion engine shaft and, on the output side, a transmission output shaft arranged coaxially to the internal combustion engine shaft, a transmission clutch for coupling or decoupling the transmission input shaft and the transmission output shaft, a flywheel drive unit which is arranged axially between the internal combustion engine and the automatic transmission and which has an intermediate shaft arranged coaxially to the internal combustion engine shaft, a first clutch for coupling or decoupling the internal combustion engine shaft and the intermediate shaft, a second clutch for coupling or decoupling the intermediate shaft and the transmission input shaft, and an electric machine.which sits on the transmission input shaft and can drive it in motor mode. The electric motor is integrated into the automatic transmission. This drive system design allows for a very rapid vehicle response, even with the combustion engine switched off, in the event of acceleration requested by the driver. When the accelerator pedal is pressed to actively accelerate the vehicle, the electric motor can be immediately switched to motor mode and coupled with the automatic transmission to accelerate the vehicle within the limits of the electric motor's power output. Simultaneously, a mechanical drag start of the switched-off combustion engine can be achieved via the flywheel drive unit. The time it takes for the combustion engine to start and provide the desired acceleration of the hybrid vehicle is reduced.The electric motor thus bridges the gap with electric vehicle acceleration. The drive system therefore reacts less sluggishly and provides the driver with the desired, rapid vehicle response.

[0009] According to one embodiment of the drive system, the electric motor is a low-voltage electric motor with an operating voltage of less than 60 V. Designing it as a low-voltage electric motor reduces the cost of the drive system. This is primarily because the lower electrical voltage in the system reduces the risk of damage, making the protection of the electrical system simpler and more cost-effective. Specifically, the electric motor used is a 48 V electric motor, as this can provide higher power output compared to a conventional 12 V electric motor, both in generator mode during recuperation and in motor mode. The higher power output of the electric motor is particularly beneficial when used to accelerate the hybrid vehicle, as the vehicle's response is more noticeable to the driver.

[0010] In particular, the automatic transmission can have a bell housing on the drive side, with the electric motor housed within this housing. The electric motor replaces the torque converter typically found in the bell housing of automatic transmissions, allowing a compact electric motor to be integrated into the automatic transmission without requiring additional installation space. This results in a particularly compact design of the drive system.

[0011] In another embodiment of the drive system, an electrical system is provided, wherein the electric machine is also designed as a generator and feeds electrical energy into the electrical system during generator operation. In this way, the electric machine can be used for recuperation with minimal effort, in which the vehicle's kinetic energy is converted into electrical energy.

[0012] The aforementioned task is also solved by a method for operating the drive system described above, which has an electrical control unit, and the method comprises the following steps: a) In an operating state of the drive system, the first clutch is opened and the internal combustion engine is switched off; b) A signal for active vehicle acceleration is transmitted to the electrical control unit; c) the second clutch is then opened by the electrical control unit, thereby decoupling the flywheel drive unit from the electric machine; d) then the first clutch and the transmission clutch are closed.

[0013] This process achieves a functional separation when active vehicle acceleration is desired with the combustion engine switched off (i.e., unfired and decoupled). The flywheel drive unit is decoupled from the electric motor and coupled to the combustion engine to perform a mechanical drag start. While the combustion engine is starting, the electric motor is already coupled to the automatic transmission, specifically its output shaft, to accelerate the hybrid vehicle. The driver's acceleration request can thus be advantageously fulfilled via the electric motor even before the combustion engine starts and is coupled to the transmission output shaft.

[0014] Preferably, after the first clutch is engaged in step d), the combustion engine is started by the flywheel drive unit. The flywheel drive unit acts as an energy storage device and is designed, in particular, such that the combustion engine can be started via a rotating flywheel of the flywheel drive unit. During operation of the hybrid vehicle, the flywheel of the flywheel drive unit is ideally always kept above the minimum speed required to start the combustion engine.

[0015] After the transmission clutch engages in step d), the transmission output shaft can be driven by the electric motor. In this way, a corresponding vehicle response, i.e., vehicle acceleration, can be generated with minimal effort after the driver's acceleration request has been detected.

[0016] According to one method variant, after the combustion engine is started in step d), the second clutch is closed again in a subsequent process step e). By closing the second clutch, the started combustion engine is connected to the automatic transmission, in particular the transmission output shaft of the automatic transmission, and can accelerate the hybrid vehicle as desired.

[0017] According to another variant of the procedure, the transmission clutch is closed before step b) and the electric motor is switched to generator mode. This puts the vehicle into a particularly energy-efficient operating state, also known as "engine-off coasting with recuperation." In this operating state, with the combustion engine switched off, the rolling hybrid vehicle is only slowed by friction effects and the adjustable resistance of the electric motor when operating as a generator.

[0018] Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawings. These show: - Fig. 1 a schematic sketch of a drive system according to the invention for a hybrid vehicle; - Fig. 2 a diagram showing the vehicle speed and the rotational speeds of the internal combustion engine and the flywheel drive unit plotted against time; and - Fig. 3 Another diagram showing the vehicle speed and the rotational speeds of the internal combustion engine and the flywheel drive unit over time.

[0019] The Fig. Figure 1 shows a drive system 10 for a hybrid vehicle, with an internal combustion engine 12 which has and can drive an internal combustion engine shaft 14, an automatic transmission 16 which has a transmission input shaft 18 arranged coaxially to the internal combustion engine shaft 14 on the drive side and a transmission output shaft 20 arranged coaxially to the internal combustion engine shaft 14 on the output side, and a transmission clutch 22 for coupling or decoupling the transmission input shaft 18 and the transmission output shaft 20.Furthermore, the drive system 10 comprises a flywheel drive unit 24, which is arranged axially between the internal combustion engine 12 and the automatic transmission 16 and is located on an intermediate shaft 26 arranged coaxially to the internal combustion engine shaft 14, a first clutch 28 for coupling or decoupling the internal combustion engine shaft 14 and the intermediate shaft 26, a second clutch 30 for coupling or decoupling the intermediate shaft 26 and the transmission input shaft 18, and an electric machine 32, which is located on the transmission input shaft 18 and can drive it in motor operation of the electric machine 32.

[0020] The flywheel drive unit 24 is according to Fig. 1 is exemplified as a dual-mass flywheel, with the flywheel forming an energy storage device. Regardless of the specific design of the flywheel drive unit 24, its flywheel mass, together with the first clutch 28, enables a mechanical drag start of the disengaged internal combustion engine 12 when the vehicle is stationary or rolling. Consequently, an electric starting device for the internal combustion engine 12 is not required.

[0021] According to Fig. 1 Furthermore, an electrical on-board network 34 is provided, wherein the electric machine 32 is also designed as a generator and feeds electrical energy into the electrical on-board network 34 in generator mode.

[0022] In the present embodiment, only a low-voltage electrical system 34 with an operating voltage of less than 60 V is provided. Accordingly, the electric motor 32 is also a low-voltage electric motor, in particular a 48 V electric motor. By designing the electrical system 34 as a low-voltage electrical system with a low-voltage electric motor 32, the costs of the drive system 10 can be reduced, since the lower electrical voltage in the system reduces the risk of damage and thus simplifies and reduces the cost of protecting the electrical system 34.

[0023] The use of a 48 V electric motor 32 offers the advantage of increased performance compared to conventional 12 V electric motors. This is particularly noticeable when the electric motor 32 is used in its motor mode to accelerate the hybrid vehicle, but also during recuperation, when the electric motor 32 generates electrical energy in its generator mode and feeds it into the vehicle's electrical system 34.

[0024] The electric machine 32 is according to Fig. 1 is integrated into the automatic transmission 16 of the drive system 10. In particular, it is indicated that the automatic transmission 16 has a clutch housing 36 on the drive side, wherein the electric motor 32 is housed in the clutch housing 36 and replaces a torque converter that is usually provided there.

[0025] According to Fig. 1 also includes an electrical control unit 38 for controlling the internal combustion engine 12, the electric machine 32, and the hybrid vehicle transmission designed as an automatic transmission 16. The electrical control unit 38 is further connected to an actuator 40 for actuating the first clutch 28, an actuator 42 for actuating the second clutch 30, and an actuator 44 for actuating the transmission clutch 22. Furthermore, in Fig. 1 an accelerator pedal 46 is indicated, by the actuation of which the driver of the hybrid vehicle indicates an active acceleration request, whereby the electrical control unit 38 can detect an actuation of the accelerator pedal 46.

[0026] The electrical control unit 38 is connected to both the electric machine 32 and the electrical on-board network 34 and can switch the electric machine 32, for example, from motor operation to generator operation, or vice versa.

[0027] The following will be based on the Fig. 2 and Fig. 3. Procedure variants for operating the drive system 10 described above for a hybrid vehicle were discussed.

[0028] The Fig. 2 and Fig. Figure 3 each shows a diagram in which a vehicle speed 48, a rotational speed 50 of the internal combustion engine 12 and a rotational speed 52 of the flywheel drive unit 24 are plotted against time t, with the diagrams each being divided into time intervals 1 to 7.

[0029] According to Fig. Figure 2 depicts an operating state of the drive system 10 during time interval 1, in which the hybrid vehicle is driven by the internal combustion engine 12 and, accordingly, both the transmission clutch 22 and the first clutch 28 and the second clutch 30 are engaged. In the illustrated embodiment, the drive of the internal combustion engine 12 merely compensates for friction effects during time interval 1, so that the vehicle speed 48 remains essentially constant. Accordingly, the rotational speeds 50, 52 of the internal combustion engine 12 and the flywheel drive unit 24 also exhibit a constant profile during this time interval 1 and are, in particular, identical due to the engaged first clutch 28.

[0030] As soon as the electrical control unit 38 detects that the conditions for switching to an energy-saving operating mode are met, in a first process step a) the first clutch 28 is opened and the internal combustion engine 12 is switched off. For this operating state, also referred to as "engine-off coasting", the accelerator pedal 46 must be released. Furthermore, the vehicle speed 48 is preferably above a predetermined speed threshold, which is ideally selected such that the resulting rotational speed of the flywheel drive unit 24, or the energy stored in the flywheel drive unit 24, is sufficient to start the internal combustion engine 12.

[0031] Apart from the aforementioned requirements, the electrical control unit 38 can receive further signals that prevent switching to the "engine-off coasting" operating state. Such signals can be generated, for example, by an excessively low coolant temperature in the engine cooling circuit, a low battery charge level, an excessive longitudinal gradient of the road, or activated optional equipment such as driving in sport mode.

[0032] However, if all conditions for the energy-saving operating mode are met, the combustion engine 12 is shut down, i.e., switched off and disconnected from the drivetrain by opening the first clutch 28. The rotational speed 50 of the combustion engine 12 therefore drops rapidly to zero within time interval 2.

[0033] During time interval 3, the transmission clutch 22 and the second clutch 30 are closed, so that the hybrid vehicle rolls largely freely and is only slowed down by friction losses.

[0034] To prevent the rotational speed 52 of the flywheel drive unit 24 from falling below a predetermined minimum speed, the flywheel drive unit 24 can be driven by the electric motor 32 during time interval 4. For this purpose, the transmission clutch 22 is opened and the electric motor 32 is switched to motor operation. The hybrid vehicle continues to essentially roll freely, although friction losses still lead to a decrease in vehicle speed 48.

[0035] The electric machine 32, on the other hand, actively drives the flywheel of the flywheel drive unit 24 and ensures at least energy conservation in the flywheel drive unit 24. In other words, the electric machine 32 keeps the flywheel of the flywheel drive unit 24 above the minimum speed sufficient for a mechanical tow start of the decommissioned combustion engine 12.

[0036] At the end of the time interval 4, a signal for active vehicle acceleration is transmitted to the electrical control unit 38 in a process step b), for example by the driver pressing the accelerator pedal 46.

[0037] Subsequently, according to process step c), the second clutch 30 is opened by the electrical control unit 38, so that the electric machine 32 and the flywheel drive unit 24 are decoupled.

[0038] Subsequently, in process step d), the first clutch 28 is closed. At the same time, the transmission clutch 22 is also closed (or held closed), so that the electric machine 32 is connected to the transmission output shaft 20 in a rotationally fixed manner.

[0039] By closing the first clutch 28, the rotational speed 50 of the internal combustion engine 12 and the rotational speed 52 of the flywheel drive unit 24 rapidly equalize within a time interval 5, whereby the internal combustion engine 12 is started by the flywheel drive unit 24 by a mechanical drag start.

[0040] Furthermore, after the transmission clutch 22 is engaged in process step d), the transmission output shaft 20 is driven by the electric motor 32. Consequently, in time interval 5, vehicle acceleration generated by the electric motor 32 occurs immediately after the driver activates the accelerator pedal 46. This is demonstrated by the electric motor 32 already present in time interval 5. Fig. 2 increasing vehicle speed 48 clearly.

[0041] After the combustion engine 12 is started in process step d), the second clutch 30 is closed again in a subsequent process step e) (time interval 6), whereby the electric machine 32 continues to provide vehicle acceleration.

[0042] The started and ignited combustion engine 12 is, at the beginning of time interval 7, rotationally fixed to the transmission output shaft 20 via the closed first clutch 28, the closed second clutch 30, and the closed transmission clutch 22, and can accelerate the hybrid vehicle as desired. As a result, during time interval 7, both the vehicle speed 48 and the rotational speeds 50, 52 of the combustion engine 12 and the flywheel drive unit 24 increase.

[0043] Due to the limited power output of the electric motor 32, the vehicle acceleration in time intervals 5 and 6 is lower than the acceleration provided by the combustion engine 12 in time interval 7. Nevertheless, the driver receives the desired vehicle feedback in the form of noticeable acceleration as early as time intervals 5 and 6, i.e., immediately after pressing the accelerator pedal 46. The drive system 10 thus reacts less sluggishly and provides the driver with a better driving experience.

[0044] The Fig. 3 illustrates analogously to Fig. 2 a method variant for operating the drive system 10 described above for a hybrid vehicle.

[0045] The in Fig. The third depicted procedure variant differs from the procedure variant according to Fig. 2. This is achieved simply by the fact that, prior to the signal for active vehicle acceleration in process step b), the transmission clutch 22 is closed (or held closed) and the electric machine 32 is switched to generator mode. In other words, recuperation takes place during time intervals 3 and 4, meaning that the kinetic energy of the vehicle is converted into electrical energy by the electric machine 32 operating in generator mode.

[0046] The resistance of the electric machine 32 in generator mode results in a greater vehicle deceleration, so that the vehicle speed 48 in time intervals 3 and 4 according to Fig. 3 decreases more sharply than the vehicle speed 48 in time intervals 3 and 4 according to Fig. 2.

[0047] Since the electric machine 32 is in the time interval 4 according to Fig. 3 is in generator mode, it cannot drive the flywheel drive unit 24.

[0048] In this case, the speed 52 of the flywheel drive unit 24 falling below the specified minimum speed is prevented by a transmission shift strategy of the automatic transmission 16. If the minimum speed of the flywheel drive unit 24 is reached, the speed of the transmission input shaft 18, and, via the engaged second clutch 30, also the speed of the intermediate shaft 26, and thus the speed 52 of the flywheel drive unit 24, are abruptly increased by downshifting the automatic transmission 16 to a lower gear (see Fig. 3 in the transition area of ​​time intervals 3 and 4). This ensures that the rotational speed 52 or the energy stored in the flywheel drive unit 24 is sufficient to perform a mechanical drag start of the internal combustion engine 12.

Claims

[1] Drive system for a hybrid vehicle, with an internal combustion engine (12) which has an internal combustion engine shaft (14) and can drive, an automatic transmission (16) which has a transmission input shaft (18) arranged coaxially to the combustion engine shaft (14) on the drive side and a transmission output shaft (20) arranged coaxially to the combustion engine shaft (14) on the output side, a transmission coupling (22) for coupling or decoupling the transmission input shaft (18) and the transmission output shaft (20), a flywheel drive unit (24) which is arranged axially between the internal combustion engine (12) and the automatic transmission (16) and has an intermediate shaft (26) arranged coaxially to the internal combustion engine shaft (14), a first clutch (28) for coupling or uncoupling the internal combustion engine shaft (14) and the intermediate shaft (26), a second clutch (30) for coupling or uncoupling the intermediate shaft (26) and the transmission input shaft (18) as well as an electric machine (32) which sits on the gearbox input shaft (18) and can drive it in motor operation, characterized by , that the electric motor (32) is integrated into the automatic transmission (16) is integrated. [2] Drive system according to claim 1, characterized by , that the electric machine (32) is a low-voltage electric machine with an operating voltage of less than 60 V. [3] Drive system according to one of the preceding claims, characterized by , that the automatic transmission (16) has a clutch bell (36) on the drive side, wherein the electric motor (32) is housed in the clutch bell (36). [4] Drive system according to one of the preceding claims, characterized by, that an electrical on-board network (34) is provided, wherein the electric machine (32) is also designed as a generator and feeds electrical energy into the electrical on-board network (34) in generator mode. [5] Method for operating a drive system (10) according to one of the preceding claims, which has an electrical control unit (38), wherein the method comprises the following steps: a) In an operating state of the drive system (10) the first clutch (28) is opened and the internal combustion engine (12) is switched off; b) a signal for active vehicle acceleration is transmitted to the electrical control unit (38); c) the second clutch (30) is then opened by the electrical control unit (38), thereby decoupling the flywheel drive unit (24) from the electric machine (32); d) then the first clutch (28) and the transmission clutch (22) are closed. [6] Method according to claim 5, characterized by , that the internal combustion engine (12) is started by the flywheel drive unit (24) after the first clutch (28) is closed in step d). [7] Method according to claim 5 or 6, characterized by , that the transmission output shaft (20) is driven by the electric machine (32) after the transmission clutch (22) is closed in step d). [8] Method according to any one of claims 5 to 7, characterized by , that after the combustion engine (12) is started in step d) the second clutch (30) is closed again in a subsequent process step e). [9] Method according to any one of claims 5 to 8, characterized by , that the transmission clutch (22) is closed before step b) and the electric machine (32) is switched to generator operation.

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