Oil supply system and hybrid powertrain

Abstract

Oil supply system (10) for supplying oil to a hybrid powertrain (1), wherein the hybrid powertrain (1) comprises an internal combustion engine (2), an electric machine (4) and a switching element (6), wherein a drive connection between the internal combustion engine (2) and the electric machine (4) can be separated by means of the switching element (6) into a first drive section (3) connected to the internal combustion engine (2) and into a second drive section (5) connected to the electric machine (4), and wherein the switching element (6) can be hydraulically actuated by means of the oil supply system (10), wherein the oil supply system (10) comprises a first pump (11) driven by the first drive section (3) and a second pump (12) driven by the second drive section (5), wherein the oil supply system (10) has a high-pressure section (15), wherein a first pressure port (13) of the first pump (11) and a second pressure port (14) of the second pump (12) are connected or connectable to the high-pressure section (15), and wherein the second pressure port (14) is separable from the high-pressure section (15) by means of a pump changeover valve (16), characterized in that that the pressure in the high-pressure area (15) is limited to a high-pressure value by a first pressure relief valve (19), and that a coupling control valve (25) is connected between the pump switching valve (16) and the first pressure relief valve (19).

Description

[0001] The present invention relates to an oil supply system for supplying oil to a hybrid powertrain, wherein the hybrid powertrain comprises an internal combustion engine, an electric machine, and a switching element for disconnecting the drive connection between the internal combustion engine and the electric machine. The invention further relates to a hybrid powertrain with such an oil supply system.

[0002] From DE 10 2011 112 753 A1, a hybrid drivetrain with an internal combustion engine and an electric motor is known, which can also be operated, at least temporarily, as a series hybrid drive. The hybrid drivetrain comprises an internal combustion engine, an electric motor, and a planetary gear set arranged in the drive connection between the internal combustion engine and the electric motor. A braking system allows the ring gear of the planetary gear set to be locked in place, thus temporarily making it a stationary component of the planetary gear set. The braking system can be actuated, for example, by hydraulic pressure.

[0003] From DE 10 2019 100 617 A1, a hydraulic system with two mechanically driven pumps for controlling the drivetrain of a motor vehicle is known. Both pumps can be driven simultaneously, and one of the pumps is designed to pump fluid to actuate a disconnect clutch, which connects an input shaft and an output shaft of the drivetrain. The input shaft is connected to an internal combustion engine for torque transmission. The output shaft is connected to an electric drive motor for torque transmission. The first pump and / or the second pump are mechanically connected to the output shaft and / or the input shaft.

[0004] Finally, a pump system for a motor vehicle comprising a first and a second pump is known from DE 10 2020 204 675 A1. The first and second pumps can be driven by an electric motor and an internal combustion engine, respectively. The first and second pumps can be coupled via a coupling. Furthermore, a pressure line of the first pump and a pressure line of the second pump are connected via a connecting line. A hydraulic valve is installed between the pressure line of the second pump and the connecting line, which regulates the fluid flow through the connecting line.

[0005] The object of the present invention is to provide an improved oil supply system for supplying oil to a hybrid powertrain and a hybrid powertrain with such an oil supply system.

[0006] This problem is solved by an oil supply system according to claim 1 and by a hybrid powertrain according to claim 4. Advantageous embodiments are specified in the dependent claims.

[0007] An oil supply system for a hybrid powertrain is proposed. The hybrid powertrain comprises an internal combustion engine, an electric machine, and a switching element located in a drive connection between the internal combustion engine and the electric machine. During normal driving operation, the drive power of the internal combustion engine is transferred to the electric machine via this connection. In generator mode, the electric machine then produces electrical energy, which is used to power the vehicle with one or more electric drive motors. This type of drive arrangement is also known as a series hybrid drive. The electric machine can also be operated as an electric motor to start the internal combustion engine.The drive connection can include a gearbox in addition to the switching element, in particular a gearbox that provides a gear ratio between the rotational speeds of the internal combustion engine and the electric motor. The switching element can be structurally integrated into such a gearbox or attached to it.

[0008] The switching element allows the drive connection to be disconnected and connected. With this switching element, the drive connection can be divided into a first drive section connected to the combustion engine and a second drive section connected to the electric motor. The switching element can therefore be either closed or open. It is hydraulically actuated via the oil supply system. The switching element can be designed, in particular, as a hydraulically actuated brake or clutch.

[0009] The oil supply system comprises a first pump driven by the first drive section and a second pump driven by the second drive section. Both the first and second pumps are mechanically driven, preferably via gear connections. Mechanically driven pumps have the advantage over electrically driven pumps of functioning reliably even at very low temperatures. Each of the two pumps has sufficient pumping capacity to provide adequate oil pressure and flow rate on its own to actuate the switching element. This ensures that the switching element can be actuated in any operating condition, regardless of whether only the internal combustion engine is operating with the first drive section, only the electric motor with the second drive section, or both.

[0010] The proposed oil supply system features a high-pressure section to which a pressure port of both the first and second pumps is connected or connectable. Thus, a first pressure port of the first pump and a second pressure port of the second pump are connected or connectable to the high-pressure section. Furthermore, the second pressure port can be disconnected from the high-pressure section by means of a pump changeover valve. The pump changeover valve can be located within the high-pressure section.

[0011] The pump changeover valve ensures that the appropriate amount of oil is delivered to a main pressure valve in all operating conditions. During normal operation, the first and second drive sections, and thus the first and second pumps, are driven. The pumping capacities of both pumps are therefore added together. Since the required functionality, particularly for actuating the switching element, can already be ensured with just one of the two pumps, there is a hydraulic power surplus during normal operation. The pump changeover valve allows the second pump to stop delivering oil to the high-pressure section of the oil supply system. Instead, the flow from the second pump can be returned directly to an oil reservoir, such as an oil sump, with virtually no pressure or flow losses. This increases the overall efficiency of the hybrid drivetrain.The energy savings achieved by separating the second pump from the high-pressure area can be considerable, because the second pump is not required during the predominantly normal operating phases and can run at almost zero power during these predominant operating phases.

[0012] In the high-pressure section, the pressure is limited to a predetermined high-pressure value by a first pressure relief valve. A high-pressure value suitable for the specific application can be set. In this case, the high-pressure value should be at least high enough to reliably actuate the switching element hydraulically. For example, the first pressure relief valve can be set so that the high-pressure value is limited to approximately 20 bar.

[0013] The pump changeover valve can be controlled, in particular by means of a solenoid valve, and actuated depending on a first pressure generated by the first pump.

[0014] To regulate the pressure for actuating the switching element, a clutch control valve is connected in the high-pressure section between the pump changeover valve and the first pressure relief valve. The clutch control valve allows the switching element to be selectively actuated, thereby opening or closing it as desired. Particularly when the switching element is designed as a friction clutch or brake, the clutch control valve can also be used to precisely control its behavior, for example, to achieve a specific closing speed.

[0015] In the high-pressure section between the second pump and the pump changeover valve, a second pressure relief valve can be installed. This valve limits the maximum pressure in this section, with the set maximum pressure being higher than the high-pressure value mentioned above. By using this second pressure relief valve, the second pump can be operated with excess hydraulic power or a very high flow rate for a limited time, thus preventing an undesirable pressure drop in the high-pressure system under certain operating conditions. If the high-pressure value in the section between the second pump and the pump changeover valve is exceeded, the excess oil can then be discharged back into the tank or oil reservoir via the second pressure relief valve.

[0016] Such an operating condition can occur, for example, during a so-called generator start. First, the electric motor is ramped up to a target speed for starting the combustion engine. During this process, the second pump connected to the electric motor generates sufficiently high oil pressure to close the switching element when the clutch control valve opens. Thus, when the target speed is reached, the clutch control valve switches, closing the switching element. This closes the drive connection between the electric motor and the combustion engine, and the electric motor and the masses it is already driving accelerate the crankshaft of the combustion engine, initiating its start. After the switching element closes, the first pump also begins to pump oil.Consequently, the pump changeover valve can be switched to avoid operation with a high hydraulic power surplus. The pump changeover valve switches from a first position, in which the pressure ports of the first and second pumps are connected via the pump changeover valve, to a second position, in which the pressure port of the second pump is connected to the tank or oil reservoir. In the second position of the pump changeover valve, only the first pump delivers to the high-pressure area, and the oil flow generated by the second pump flows back into the tank. The pump changeover valve can, for example, be switched depending on the engine speed. It can be switched, for instance, as soon as the engine speed exceeds 1000 revolutions per minute.

[0017] To ensure that the pressure in the high-pressure range does not drop during the described switching process, the overlap at the pump changeover valve can be selected so that the second pump delivers a significantly higher pumping capacity and flow rate for a short time than would be necessary to maintain the high pressure. Due to the very high flow rate, the excessive pumping capacity might not be sufficiently reduced by the first pressure relief valve within this short time. Therefore, any excess pressure or the excess oil volume pumped can be reduced via the second pressure relief valve during this brief period. For example, the second pressure relief valve can be set so that the pressure between the second pump and the pump changeover valve is limited to a maximum pressure of approximately 30 bar, even during this short period.

[0018] In addition to hydraulically actuating the switching element, the oil supply system can also supply lubrication points in the hybrid powertrain with oil. For this purpose, a low-pressure section can be connected downstream of the first pressure relief valve. The pressure in this low-pressure section can be limited to a specific low pressure by a third pressure relief valve, for example, to a low-pressure value of 2 bar. Such a low-pressure value is sufficient to ensure the required lubrication of lubrication points 31.

[0019] Furthermore, the oil supply system can also provide pressurized oil for actuating other switching elements. For example, switchable power take-offs (PTOs) can be hydraulically actuated, or switched on or off, using the oil supply system. Suitable switching valves can be connected to the high-pressure section for this purpose.

[0020] The invention and its advantages will be explained in more detail below with reference to the exemplary embodiment shown in the accompanying figure.

[0021] This shows Fig. 1 a schematic representation of a hybrid powertrain and Fig. 2 a schematic circuit diagram of an oil supply system for a hybrid powertrain according to Fig. 1.

[0022] The one in Fig. The hybrid powertrain 1 shown in Figure 1 comprises an internal combustion engine 2, an electric machine 4, and a switching element 6 arranged in the drive connection between them. The drive connection between the internal combustion engine 2 and the electric machine 4 can be separated by means of the switching element 6 into a first drive section 3 connected to the internal combustion engine 2 and a second drive section 5 connected to the electric machine 4. "Separated" in this context means that no torque can be transmitted from the first drive section 3 to the second drive section 5 or vice versa. In the present embodiment, the switching element 6 is connected to a transmission element of a gearbox 7 arranged between the first drive section 3 and the second drive section 5. The switching element 6 can be structurally integrated into the gearbox 7, resulting in a very compact design.The transmission 7 is designed as a planetary gear set, wherein the ring gear of the planetary gear set is connected to the electric machine 4 and the planet carrier of the planetary gear set is connected to the internal combustion engine 2. The switching element 6 is connected to the sun gear of the planetary gear set. The switching element 6 is designed as a friction-fit multi-plate brake, wherein an outer plate carrier is fixedly connected to a stationary housing 20 and an inner plate carrier is connected to the sun gear of the planetary gear set.

[0023] The first drive section 3 drives a first pump 11 via a first gear pair 8. The second drive section 5 drives a second pump 12 via a second gear pair 9. The two pumps 11 and 12 are part of an oil supply system 10, which is located in the Fig. 2 is shown schematically and described in more detail below.

[0024] The switching element 6 is connected using the one in the Fig. The oil supply system 10 shown in Figure 2 is hydraulically actuated. The oil supply system 10 comprises a first pump 11 and a second pump 12, wherein the first pump 11 is driven by the first drive section 3 and the second pump 12 is driven by the second drive section 5. The first and second pumps 11 and 12 are driven mechanically via their respective associated gear pairs 8 and 9. A driving gear is arranged on a shaft of the associated drive section 3 or 5, and a driven gear is arranged on a pump drive shaft of the respective pump 11 or 12.

[0025] The one in Fig. The oil supply system 10 shown in Figure 2 comprises a high-pressure section 15, which is connected to the first pressure port 13 of the first pump 11. Only when the pump changeover valve 16 is in the first position shown is the second pressure port 14 of the second pump 12 also connected to the high-pressure section 15. The oil supply system 10 shown in Figure 2 comprises a high-pressure section 15, which is connected to the first pressure port 13 of the first pump 11. Fig. The high-pressure area 15, drawn as a rectangle using a dotted line, therefore corresponds approximately to the high-pressure area 15 when the pump switching valve 16 is in the spring-assisted first position.

[0026] The second pressure port 14 can be isolated from the high-pressure section 15 by means of a pump changeover valve 16, by switching the pump changeover valve 16 from a first position, in which the pressure ports 13, 14 of the first and second pumps 11, 12 are connected, to a second position. In the second position, the pressure port 14 of the second pump 12 is connected to the tank 18. The tank can, for example, contain an oil sump of the gearbox 7. In the second position of the pump changeover valve 16, only the first pump 11 pumps into the high-pressure section 15. The oil flow generated by the second pump 12 then flows almost without pressure through a first return line 23 from the pump changeover valve 16 into the tank 18.

[0027] The pump changeover valve 16 is pressure-operated and controlled by a solenoid valve 17. The pressure for operating the pump changeover valve 16 is generated by the first pump 11. In the unoperated state, the pump changeover valve 16 is held in its home position, the first position described above, by a spring.

[0028] The pressure in the high-pressure area 15 is limited to a predetermined high-pressure value by a first pressure relief valve 19. The first pressure relief valve 19 effectively separates the high-pressure area 15 from a low-pressure area, which primarily serves to lubricate and cool elements of the hybrid powertrain 1 at various lubrication points 31.

[0029] For the hydraulic pressure actuation of the switching element 6, a clutch control valve 25 is provided in the high-pressure section 15. The clutch control valve 25 is connected between the pump changeover valve 16 and the first pressure relief valve 19. In the same section or pressure branch, two additional pressure ports 27 and 28 are provided in this embodiment. These pressure ports 27 and 28 can be used, for example, for switching auxiliary drives 29, so-called PTOs.

[0030] A second pressure relief valve 26 is arranged between the second pump 12 and the pump changeover valve 16. The second pressure relief valve 26 limits the pressure in this area to a maximum pressure value that is higher than the high-pressure value limited by the first pressure relief valve 19. The second pressure relief valve 26 can also be referred to as a safety valve. It ensures that in operating conditions where the second pump 12 delivers into the high-pressure area 15 with excess hydraulic power due to high drive speeds, the maximum pressure is limited and excess flow can drain directly into the tank 18.

[0031] In the pressure lines of both pumps 11 and 12, a check valve 21 or 22 is arranged to ensure that the required pressure or high pressure can be built up in the operating conditions in which a pump 11 or 12 is stationary and the solenoid valve 17 is not switched.

[0032] The pressure in the low-pressure area can be limited to a specific low-pressure value by a third pressure relief valve 30. A suitable low-pressure value is, for example, 2 bar to adequately supply the lubrication points 31 in the hybrid drive train 1 with oil. The third pressure relief valve 30 thus determines the lubrication pressure and can therefore also be called a lubrication pressure valve. The third pressure relief valve 30 directs unused flow through a second return line 24 directly to an intake area of ​​the first pump 11. This further improves efficiency and reduces the tendency for cavitation in the first pump 11.

[0033] In the low-pressure area, a heat exchanger 32 is provided. A bypass valve 33 protects the heat exchanger 32 from excessively high flow rates and, especially at low temperatures, also from excessively high pressures. Reference sign 1 Hybrid powertrain 2 Internal combustion engine 3 first drive section 4 electric machine 5 second drive section 6 switching element 7 gearboxes 8 gear pairs 9 gear pair 10 Oil supply system 11 first pump 12 second pump 13 first pressure connection 14 second pressure port 15 High-pressure area 16 Pump changeover valve 17 Solenoid valve 18 Tank 19 first pressure relief valve 20 cases 21 Check valve 22 Check valve 23 first return line 24 second return line 25 Clutch control valve 26 second pressure relief valve 27 Pressure connection 28 Pressure connection 29 Power take-off 30 third pressure relief valve 31 lubrication points 32 heat exchangers 33 Bypass valve

Claims

[1] Oil supply system (10) for supplying oil to a hybrid powertrain (1), wherein the hybrid powertrain (1) comprises an internal combustion engine (2), an electric machine (4) and a switching element (6), wherein a drive connection between the internal combustion engine (2) and the electric machine (4) can be separated by means of the switching element (6) into a first drive section (3) connected to the internal combustion engine (2) and into a second drive section (5) connected to the electric machine (4), and wherein the switching element (6) can be hydraulically actuated by means of the oil supply system (10), wherein the oil supply system (10) comprises a first pump (11) driven by the first drive section (3) and a second pump (12) driven by the second drive section (5), wherein the oil supply system (10) has a high-pressure section (15), wherein a first pressure port (13) of the first pump (11) and a second pressure port (14) of the second pump (12) are connected or connectable to the high-pressure section (15), and wherein the second pressure port (14) is separable from the high-pressure section (15) by means of a pump changeover valve (16), characterized by , that the pressure in the high-pressure area (15) is limited to a high-pressure value by a first pressure relief valve (19), and that a coupling control valve (25) is connected between the pump switching valve (16) and the first pressure relief valve (19). [2] Oil supply system (10) according to claim 1, characterized by, that the pump switching valve (16) can be controlled by means of a solenoid valve (17) and can be actuated depending on a pressure generated by the first pump (11). [3] Oil supply system (10) according to claim 1 or 2, characterized by , that in the high-pressure area (15) between the second pump (12) and the pump changeover valve (16) a second pressure relief valve (26) is arranged, and that the second pressure relief valve (26) limits the pressure in this area to a maximum pressure value, the maximum pressure value being higher than the high-pressure value. [4] Hybrid powertrain (1) with an oil supply system (10) according to one of the preceding claims.

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