Hydraulic system for controlling the drivetrain of a motor vehicle

Abstract

Hydraulic system (7) for controlling a drive train (1) of a motor vehicle, comprising a pump (8) configured for cooling and / or lubricating a drive element (3, 4, 5) of the drive train (1) in a first delivery direction and for causing hydraulic positioning of an actuator (6, 15) of the drive train (1) in a second delivery direction, comprising a temperature measuring device for detecting the temperature of the hydraulic fluid, a pressure measuring device (27) for detecting the pressure of the hydraulic fluid at the actuator (6, 15), and a control unit (29) for controlling the pump (8), wherein the control unit (29) is configured for pressure- and temperature-dependent control of the pump (8), characterized in that the control unit (29) is configured to record a time-dependent pressure profile (32) of the pressure at the actuator (6, 15).15) to detect the applied pressure and to perform a comparison of the current temperature of the hydraulic fluid with a target temperature assigned to a specific pressure profile over time (32).

Description

[0001] The present invention relates to a hydraulic system for controlling a motor vehicle's drivetrain, in particular a hybrid drivetrain of a motor vehicle, comprising a pump configured for cooling and / or lubricating a drive element of the drivetrain in a first delivery direction and for hydraulically positioning an actuator of the drive in a second delivery direction, a temperature measuring device for detecting the temperature of the hydraulic fluid, a pressure measuring device for detecting the pressure of the hydraulic fluid at the actuator, and a control unit for controlling the pump. It also relates to a hybrid drive system with such a hydraulic system.

[0002] Hydraulic systems for hybrid drives are known from the prior art in which hydraulic fluid can be pumped in two directions by means of a reversing pump. In the first direction, hydraulic fluid is pumped through a cooling and / or lubrication circuit, which cools, for example, transmissions, bearings, and electric motors. In the second direction, hydraulic fluid is pumped to an actuator of the hybrid drive, for example, a clutch or a parking lock, thereby providing the pressure required to actuate the actuator. The hydraulic circuit is controlled by switchable directional control valves and check valves. In parallel hybrid operation with the clutch engaged, the reversing pump delivers hydraulic fluid in the first direction to the cooling and / or lubrication circuit.

[0003] German patent application DE 10 2004 033 439 A1 proposes a drive train for a motor vehicle, comprising a friction clutch for transmitting drive torque to the motor vehicle and an actuator arrangement for actuating the friction clutch. The actuator arrangement includes a first actuator designed for rapidly closing the friction clutch with minimal force, thus quickly bridging any play present when the friction clutch is open, and a second actuator designed to apply a large force with a small stroke to actuate the friction clutch, keeping it closed with minimal energy expenditure.

[0004] From DE 10 2014 105 168 A1, a coupling arrangement is known, in particular for a manual or automated motor vehicle transmission, comprising a wet friction clutch for arrangement between a drive motor and a transmission, a fluid actuator for actuating the friction clutch, a fluid supply device comprising an electric motor and a pump arrangement driven by the electric motor, wherein the pump arrangement is connected to the fluid actuator via a first branch, and a secondary branch through which a portion of the fluid volume flow provided by the pump arrangement can be directed to a low-pressure area. A branch arrangement is provided which can be controlled to reduce the secondary fluid volume flow directed to the secondary branch when an actuation pressure (P) in the fluid actuator exceeds a threshold pressure (PSW) and / or the fluid actuator exceeds a threshold travel (SSW).

[0005] Hydraulic systems with pump arrangements for actuating or cooling a clutch, a parking lock or a gearbox are known from the patent applications DE 10 2015 107 362 A1, DE 10 2016 215 225 A1, US 2006 / 0 223 670 A1, DE 10 2015 220 535 A1, DE 101 08 668 A1, DE 10 2012 202 162 A1, DE 10 2016 115 925 A1 and CN 109764132 A.

[0006] A problem encountered in known systems is that, in parallel hybrid driving mode with the clutch engaged, the oil pressure required for the clutch's function is maintained in its slave cylinder by a switchable check valve. However, this valve is not 100% leak-proof, so the pressure used to actuate the clutch gradually decreases over time. Consequently, the torque that can be transmitted via the clutch decreases, since the pressure and the transmissible torque of the clutch are proportional to each other. To maintain the pressure at the clutch, and thus the torque that can be transmitted, hydraulic fluid is periodically pumped in by the reversing pump in known systems. During continuous driving, the supply of hydraulic fluid as a cooling medium is interrupted, and the desired pressure at the clutch is set by the pump.For maximum possible torque transmission in the clutch, the pressure in the clutch slave cylinder should be as high as possible. Conversely, the pressure should not exceed a certain maximum value to prevent overloading the hydraulic system and ensure the longest possible service life.

[0007] Starting from the prior art described above, the object of the invention is to avoid or at least mitigate the disadvantages of the prior art and, in particular, to create a hydraulic system for a motor vehicle that is simple and easy to control compared to known conventional hydraulic systems, wherein, in particular, the hydraulic pressure generated by means of a pump can be reliably maintained and operated in a pressure-optimized manner, and wherein, in addition, leakage that goes beyond the system-related and temperature-dependent leakage can be detected more easily and accurately.

[0008] The object of the invention is achieved in a generic hydraulic system by configuring the control unit for pressure- and temperature-dependent control of the pump. The control unit is configured to detect and / or monitor the pressure profile of the pressure applied to the actuator over time. It is also configured to detect and / or monitor the temperature of the hydraulic fluid. Particularly advantageously, it compares the current temperature of the hydraulic fluid, especially the hydraulic fluid applied to the actuator, with a target temperature corresponding to a specific pressure profile over time. As a result of the pressure-dependent control, the hydraulic system can always be operated within the desired pressure range. This object is further achieved by a hybrid drive system with a hydraulic system according to the invention, particularly according to one of the appended claims.

[0009] It is ensured that the minimum pressure required for the actuator's operation is not undershot and that the system and its components are not subjected to a maximum permissible pressure. According to the invention, this pressure-dependent control is combined with a temperature-dependent control. To meet the requirements for optimal actuator function, the hydraulic fluid pressure that enables its actuation and operation should be as high as possible. However, the pressure should not exceed a maximum threshold, as otherwise the service life of the hydraulic system components may be impaired. For this purpose, the control unit can, for example, establish or control the pressure using a two-point controller. This controller cyclically switches the pump on and off to increase the pressure from the lower switch-on threshold (i.e., the minimum pressure) to the upper switch-off threshold (i.e., the maximum pressure).During normal operation of the system, this process repeats itself cyclically.

[0010] The pressure- and temperature-dependent control of the pump according to the invention, however, produces a synergistic effect that goes beyond the effects described above: as already explained, the pump operation and switching of the pump in the normal operating mode of the system are cyclical and constant. They depend essentially only on the viscosity of the fluid, and this in turn depends essentially on the temperature. Consequently, the frequency of the two-point controller (the switching frequency of the pump) is almost constant at a constant temperature. This is different if there is a leak in the hydraulic system in the steady-state range, because then the frequency increases at a substantially constant or inadequately rising temperature. If the pressure at the actuator drops faster than expected, the two-point controller / control unit switches the pump on earlier than usual to increase the pressure. The switching frequency for switching the pump therefore increases.This frequency can now be measured and compared with the recorded fluid temperature values. If the frequency does not match the temperature or is higher than expected, there is a high probability of a leak not caused by the system.

[0011] According to the invention, the hydraulic system is configured to control, or is part of, the powertrain of a motor vehicle. In particular, it can be configured to control, or be part of, a hybrid drive system of a motor vehicle. The hydraulic system comprises a pump configured to cool and / or lubricate a drive element of the powertrain in a first delivery direction. The pump is also configured to hydraulically actuate an actuator of the drive in a second delivery direction. A hybrid drive system within the meaning of the invention is understood to be, in particular, a hybrid powertrain for a motor vehicle.

[0012] The hybrid drive system according to the invention can, in particular, comprise an electric motor and an internal combustion engine for powering the motor vehicle and for converting chemical energy into rotational and / or electrical energy. Such a hybrid drive system can, in particular, form a powertrain for a motor vehicle or be part of such a powertrain and combines the advantages of a series and a parallel hybrid. The components are connected in series, with two subsystems being directly connected via the disconnect clutch or able to be operated independently of one another. Specifically, the hybrid drive system of the invention can comprise an internal combustion engine, a first electric machine, and a second electric machine. The first electric machine can, in particular, be an electric motor or generator, preferably an electric motor directly connected to the internal combustion engine.A generator serves as the energy source for the second electric machine. This machine can be, in particular, an electric motor, integrated into the hybrid drive system in series via a coupling and connected to the driven wheels by means of a single gear ratio. The hybrid drive system can have a second such electric machine for each driven wheel of the vehicle.

[0013] The drive concept according to the invention is characterized in that, compared to a fully electric vehicle, the energy carried is not only stored in a battery and directly available as electricity, but is also carried in the form of fuel (diesel, gasoline, gas) and is chemically available. This additional energy can be converted into electrical energy for use in the electric drive. It can also be stored in a battery or accumulator for short periods and is available as needed to extend the vehicle's range. The storage capacity of the battery or accumulator can be smaller compared to the storage system of a fully electric vehicle, thus saving costs and weight. Preferably, however, it is sufficiently large to enable emission-free driving in urban areas.The advantage of the drive train of the invention is a high efficiency of the electric drive at low speeds, especially in combination with the simple gearbox with only one gear ratio stage.

[0014] In the hybrid drive system of the invention, the pump actuates the actuator and also pumps hydraulic fluid as a cooling medium in the gearbox. When the pump is operating in the first direction of rotation, hydraulic fluid is pumped through a cooling circuit and used to cool and / or lubricate components of the drive system, in particular the electric motor(s), bearings, and / or gearbox. When the pump is operating in the other direction of rotation, hydraulic fluid is pumped to the actuator to generate the pressure required to perform the respective function of the actuator.

[0015] Advantageous embodiments are claimed in the dependent claims and are explained below.

[0016] The control unit can be configured, in particular, to maintain the pressure applied to the actuator between a predetermined minimum and a predetermined maximum pressure. These pressure limits are determined and predefined based on the characteristics and typical operating parameters of the hydraulic system and are stored in the control unit or in a data storage device connected to it via communication technology.

[0017] The control unit can, in particular, initiate the pump to deliver hydraulic fluid in the second delivery direction if the pressure applied to the actuator drops below the predetermined minimum pressure. Alternatively or additionally, if the pressure applied to the actuator exceeds the predetermined maximum pressure, it can initiate the pump to deliver hydraulic fluid in the first delivery direction. In this way, the pressure applied to the actuator can be easily maintained within a parameter range suitable for the intended operation of the hydraulic system.

[0018] According to one embodiment of the invention, the control unit is configured to detect and / or monitor the time interval between reaching the maximum pressure and reaching the minimum pressure, and / or the time interval between reaching the minimum pressure and reaching the maximum pressure. It can also be configured to generate an error message and / or store an error message in an error memory if a limit value for deviation from the setpoint temperature is exceeded. Within the scope of the invention, the time interval or duration between reaching two or more successive maximum pressure limits or minimum pressure limits can also be detected.

[0019] The pump is preferably a reversible pump, in particular an electrically operated reversible pump. This allows for the simplest possible pumping of hydraulic fluid in both directions by switching or reversing the pump.

[0020] Another embodiment of the invention is characterized in that the system has a hydraulically acting check valve between the pump and the actuator. The check valve is preferably arranged in a bypass line. This bypass line can branch off from the line leading from the pump to the actuator. Additionally, it can be connected to a reservoir for hydraulic fluid. This enables particularly simple and effective pressure relief of the actuator combined with simple return of hydraulic fluid to the hydraulic system.

[0021] The hydraulic system can also include a directional control valve. This can, in particular, be a two-way valve. The directional control valve can advantageously be hydraulically arranged in the line leading from the pump to the actuator. Furthermore, the directional control valve can be configured for the selective hydraulic connection of a first actuator, such as a clutch, or a second actuator, such as a parking brake. The invention also includes embodiments with more than two actuators, wherein the directional control valve provides a corresponding number of switching options. The pressure measured within the scope of the invention is preferably the pressure applied to the actuator for actuation, i.e., for example, the pressure acting on a clutch slave cylinder. The measured temperature is preferably the temperature of the hydraulic fluid flowing to the actuator.

[0022] In a further embodiment, a check valve can be arranged in the line leading from the pump to the actuator. This valve can, in particular, allow the flow of hydraulic fluid from the pump to the actuator, but block it in the opposite direction. This prevents a pressure drop at the actuator due to the pump drawing in fluid.

[0023] It can also be said that the invention actuates a parking lock, a disconnect clutch, and a cooling system using an electrically driven reversing pump. In parallel hybrid driving mode, the disconnect clutch is engaged to allow the combustion engine torque to be transmitted directly to the wheels. The necessary oil pressure in the clutch slave cylinder is maintained by a switchable check valve. However, since this valve is not 100% airtight, the pressure decreases slowly but steadily over time. Therefore, during continuous driving, the pump must interrupt the cooling process to increase the pressure in the clutch slave cylinder again. The pressure and the transmissible torque of the clutch are proportional and are stored in the software control via a characteristic curve measured at the end of the manufacturing process. This characteristic curve is also adapted during operation.To maximize the clutch's torque capacity, the pressure can be maintained within a specific range using a two-point controller. The hydraulic pump can be cyclically switched on and off between a lower and an upper threshold. At a constant temperature, the frequency of the two-point controller remains nearly constant. However, if the pressure drops faster than expected, the frequency increases. This frequency, along with the fluid temperature, can be measured by the software control. If the frequency and temperature do not match, there is a high probability of a non-system-related leak, i.e., a fault.

[0024] The invention is explained in more detail below with the aid of two figures. These are merely schematic and serve solely to illustrate the invention. They show: Fig. 1 in a schematic representation a hybrid drive system according to the invention, Fig. 2 a schematic representation of the hydraulic system according to the invention and Fig. 3. An example pressure curve in a pressure-time diagram.

[0025] Fig. Figure 1 shows a schematic overview of an embodiment of a hybrid drive system 1 according to the invention. The hybrid drive system 1 serves to propel a motor vehicle, of which only one driven wheel 2 is shown by way of example in the figure. It comprises an internal combustion engine 3, a first electric machine 4 in the form of a generator 4, a second electric machine 5 in the form of an electric motor 5, and a clutch 6. The clutch 6 is arranged between the electric motor 5 and the generator 4 and effectively divides the hybrid drive system 1 into two subsystems. The clutch 6 is connected to the driven wheel 2 by means of a gear reduction stage, which is not shown in the figures.

[0026] The hybrid drive system 1 uses the electric motors 4, 5 and the internal combustion engine 3 to propel the vehicle, and the internal combustion engine 3 also to convert chemical energy (in the form of fuel such as gasoline, gas, or diesel) into rotational and / or electrical energy. Normally, the vehicle is driven by the electric motor 5, which draws its energy from a battery (not shown in the figure). If the energy available from this source is insufficient to operate the vehicle, the internal combustion engine 3 drives the generator 4, which then serves as the energy source for the electric motor 5. The drive train 1 thus combines the advantages of a series and a parallel hybrid. The electric motor 5, the generator 4, and the internal combustion engine 3 are connected in series via the coupling 6.The subsystems located on both sides of the coupling 6 can be directly connected to each other via the coupling 6 or operated independently of each other.

[0027] Fig. Figure 2 shows an embodiment of the hydraulic system 7 of the hybrid drive system 1 according to the invention. Fig. Figure 1 shows an enlarged view. The core component of the hydraulic system 7 is a pump 8, which is designed as a reversing pump and can be operated in two opposite directions of flow. The pump 8 is driven by a motor 9. A cooling and lubrication line 10 and an actuator line 11 are connected to the pump 8. A two-way valve 12 is arranged in the actuator line 11. In a first switching position of the two-way valve 12, the pump 8 can be hydraulically connected to a clutch slave cylinder 13 of the clutch via an actuator line 11a. In a second switching position of the two-way valve 12, it can be hydraulically connected to an actuating piston 14 of a parking lock 15 via an actuator line 11b. The clutch 6 and the parking lock 15 each form an actuator 6, 15, according to the invention.

[0028] When the pump 8 is operating in the second delivery direction, the clutch slave cylinder 13 of the clutch 6 is supplied with hydraulic fluid and pressure via the actuator lines 11, 11a. When the pump 8 is operating in the first delivery direction, the cooling and lubrication line 10, a hydraulically connected heat exchanger 16, and hydraulically connected cooling and lubrication units 17 for vehicle components, such as the electric motors 4, 5 and / or their bearings, can be supplied with a specific volume flow of hydraulic fluid.

[0029] The hydraulic system 7 also includes a collection or storage reservoir 18 for hydraulic fluid. This reservoir is connected to the cooling and lubrication line 10 via suction lines 20 and 20a, each equipped with a filter element 19, and to the actuator line 11 via suction lines 20 and 20b. A check valve 21, 22 is arranged in each of the suction lines 20a and 20b, so that, due to the pumping action of the pump 6, hydraulic fluid can flow from the collection and storage reservoir 18 towards the hydraulic lines 10, 11, but a partial flow in the opposite direction is not possible. Another check valve 23 is arranged in the cooling and lubrication line 10 between the pump 8 and the heat exchanger 16.

[0030] To allow hydraulic fluid to flow back from the clutch slave cylinder 13 via a drain line 24 into the collection and storage reservoir 18 when the clutch 6 is released, a shut-off valve 25 is arranged in the actuator line 11a. In a first switching position, the valve opens the drain line 24, and in a second switching position, it closes it. A further check valve 26 is arranged between the drain line 24 and the two-way valve 12. The pressure present in the actuator line 11a can be detected by means of a pressure sensor 27.

[0031] The motor 9, the two-way valve 12, the shut-off valve 25, the pressure sensor 27 and a holding magnet 28 of the parking locking device 15 are connected via in Fig. 2 indicated data lines connected to a control unit 29.

[0032] In parallel hybrid driving mode, the clutch 6 is fully engaged to transmit the torque of the internal combustion engine 3 to the wheel 2. The required oil pressure in the clutch slave cylinder 13 is maintained by the switchable check valve 25. However, this valve is not 100% leak-proof. Therefore, the pressure gradually decreases over time. To increase the pressure in the clutch slave cylinder 13, fluid is pumped into the actuator lines 11 and 11a by the pump 8. The pressure and the transmissible torque of the clutch 6 are proportional. According to the invention, the pressure acting on the clutch 6 in the clutch slave cylinder 13 is detected by the pressure sensor 27 and monitored by the control unit 29. This unit contains a characteristic curve that is measured at the end of the manufacturing process. This characteristic curve is also adapted during operation. Fluid can be routed via a drain / bypass 30 if necessary.A non-return valve 31 may also be used.

[0033] Fig. Figure 3 illustrates the combined pressure and temperature monitoring within the scope of the invention in a time-pressure diagram. The diagram shows the pressure curve (ordinate 39) as a function of time (abscissa 40) using graph 32. The control unit 29 contains limit values ​​for a minimum pressure 33 and a maximum pressure 34, between which the pressure acting on the clutch slave cylinder 13 is maintained. During normal operation of the system (normal operation, characterized by section 35), the duration 37 of the pressure drop from the maximum value 34 to the minimum value 33 is essentially constant. During this duration 37, the pump 8 delivers in the first delivery direction.When the pressure at the clutch slave cylinder 13 reaches the minimum pressure limit 33 stored in the control unit 29, the control unit 29 causes the pump 8 to switch direction. The pump then pumps in the first delivery direction until the pressure at the clutch slave cylinder 13 reaches the maximum pressure limit 34 stored in the control unit 29. At this point, the control unit 29 switches the pump 8 from the first delivery direction to the second delivery direction. In normal operation 35, the time required for the pressure at the clutch slave cylinder 13 to drop again to the minimum value 33 is essentially the same as the duration of the previous drop. In other words, in normal operation, the time 37 for the drop from the maximum value 34 to the minimum value 33 is essentially constant, but depends on the temperature of the hydraulic fluid.

[0034] If a leak occurs in system 7, it can be detected by the combined pressure and temperature monitoring according to the invention. Such a case exists in Fig. Section 36 presents a fault operating condition. The duration 37 required in Section 36 for the pressure to drop from the maximum value 34 to the minimum value 33 is significantly shorter than the duration 38 required for the same pressure change during normal operation (Section 35). If this pressure profile persists and the temperature of the hydraulic fluid recorded during Section 36 does not correspond to a temperature limit stored in the control unit for a specific pressure drop duration, a leak must be assumed. The control unit can store a corresponding entry in a fault memory or output a fault signal. Reference symbol list 1 Hybrid drive system 2 wheel 3 Internal combustion engine 4. Electric machine, generator 5 electric machine, electric motor 6 Actuator, clutch 7 Hydraulic system 8 Pump, reversing pump 9 engine 10 Cooling and lubrication line 11 Actuator line 11a Actuator line 11b Actuator line 12 Two-way valve 13 Clutch slave cylinders 14 actuating pistons 15 Actuator, parking lock device 16 heat exchangers 17 cooling and lubrication units 18 Collection or storage reservoir 19 filter element 20 Suction line 20a Suction line 20b Suction line 21 Check valve 22 Check valve 23 Check valve 24 Drain pipe 25 shut-off valve 26 Check valve 27 Pressure sensor 28 Holding magnet 29 Control unit 30 Drain, Bypass 31 Check valve 32 Graph of the pressure curve 33 Minimum pressure 34 Maximum pressure 35 Normal operation 36 Fault case operation 37 Duration of pressure change from maximum pressure to minimum pressure 38 Duration of pressure change from maximum pressure to minimum pressure 39 ordinates, print 40 Abscissa, Time

Claims

[1] Hydraulic system (7) for controlling a drive train (1) of a motor vehicle, comprising a pump (8) configured for cooling and / or lubricating a drive element (3, 4, 5) of the drive train (1) in a first delivery direction and for causing a hydraulic positioning of an actuator (6, 15) of the drive train (1) in a second delivery direction, comprising a temperature measuring device for detecting the temperature of the hydraulic fluid, a pressure measuring device (27) for detecting the pressure of the hydraulic fluid at the actuator (6, 15) and a control unit (29) for controlling the pump (8), wherein the control unit (29) is configured for pressure- and temperature-dependent control of the pump (8), characterized by, that the control unit (29) is set up to detect a pressure profile over time (32) of the pressure applied to the actuator (6, 15) and to perform a comparison of a current temperature of the hydraulic fluid with a target temperature assigned to a specific pressure profile over time (32). [2] Hydraulic system (7) according to claim 1, characterized by , that the control unit (29) is configured to maintain the pressure applied to the actuator (6, 15) between a predetermined minimum pressure (33) and a predetermined maximum pressure (34). [3] Hydraulic system (7) according to claim 2, characterized by , that the control unit (29) causes the pump (8) to deliver hydraulic fluid in the second delivery direction when the pressure applied to the actuator (6, 15) drops below the predetermined minimum pressure (33). [4] Hydraulic system (7) according to claim 2 or 3, characterized by, that the control unit (29) causes the pump (8) to deliver hydraulic fluid in the first delivery direction when the pressure applied to the actuator (6, 15) exceeds the predetermined maximum pressure (34). [5] Hydraulic system (7) according to any one of the preceding claims, characterized by , that the control unit (29) is configured to detect a time interval (37, 38) between the occurrence of the maximum pressure (34) and the reaching of the minimum pressure (33) and / or a time interval between the occurrence of the minimum pressure (33) and the reaching of the maximum pressure (34). [6] Hydraulic system (7) according to any one of the preceding claims, characterized by , that the control unit (29) is configured to issue an error message and / or store an error message in an error memory when a limit value for the deviation from the target temperature is exceeded. [7] Hydraulic system (7) according to any one of the preceding claims, characterized by , that the pump (8) is a reversing pump (8), in particular an electrically operated reversing pump (8). [8] Hybrid drive system (1) with a hydraulic system (7) according to one of the preceding claims. [9] Hybrid drive system (1) according to claim 8, characterized by , that the actuator (6, 15) of the drive (7) is a clutch (6) and / or a parking lock (15).

Images