Oil pump system of a hybrid vehicle and method for controlling it

Abstract

Oil pump system of a hybrid vehicle which supplies a working hydraulic pressure to an automatic transmission (50) of the hybrid vehicle, wherein the oil pump system comprises: a transmission control device (90) which controls the operation of the automatic transmission (50); an electric oil pump (60) which pumps oil to generate the working hydraulic pressure which is supplied to the automatic transmission (50);and an oil pump control device (70) which receives information regarding a state of the automatic transmission (50) from the transmission control device (90) and controls the operation of the electric oil pump (60), wherein the working hydraulic pressure supplied to the automatic transmission (50) is generated only by means of the electric oil pump (60), which is electrically operated, wherein, if a fault occurs in the hydraulic pressure supply to the automatic transmission (50), the oil pump control device (70) performs a control to maintain the working hydraulic pressure of the automatic transmission (50) at a constant working hydraulic pressure, which is generated by means of the electric oil pump (60), and wherein, if the working hydraulic pressure of the automatic transmission (50) is controlled to a substantially constant pressure, the transmission control device (90) performs a control to reduce the output torque required for the automatic transmission (50).

Description

The invention relates to an oil pump system of a hybrid vehicle and a method for controlling it, and in particular an oil pump system of a hybrid vehicle which is designed to supply hydraulic pressure to an automatic transmission by means of only one electric oil pump, and a method for controlling it. Generally, an automatic transmission is connected to an oil pump system to supply hydraulic pressure to the transmission. The oil pump system comprises one or more oil pumps. Traditionally, an oil pump system was primarily used, supplying a working hydraulic pressure to an automatic transmission via a mechanical and an electric oil pump. Hybrid vehicles, in particular, have primarily employed a method for controlling an oil pump system that divides a vehicle's driving state into a stop range, a low-speed range, and a high-speed range, and selectively operates either a mechanical or an electric oil pump. According to this method, only the electric oil pump can operate during the stop range, the mechanical and electric oil pumps can operate simultaneously during the low-speed range, and only the mechanical oil pump can operate during the high-speed range. However, using two or more oil pumps, such as a mechanical and an electric pump, can excessively increase manufacturing costs. Furthermore, a mechanical pump driven by the engine's torque can negatively impact the vehicle's fuel efficiency. Omitting either the mechanical or electric pump can result in an unstable supply of hydraulic pressure to the automatic transmission. In particular, using only an electric pump makes it difficult to troubleshoot and correct faults caused by a solenoid malfunction or similar issue affecting the transmission's hydraulic pressure supply.Furthermore, if the hydraulic pressure required for the electric oil pump is set in such a way that it is fixed at an excessively high hydraulic pressure at the time a hydraulic pressure supply fault occurs, power may be wasted driving the electric oil pump, and parts may be damaged by overcurrent. US 5,944,632 A describes an oil pump system of a hybrid vehicle which supplies a working hydraulic pressure to an automatic transmission of the hybrid vehicle, comprising a transmission control unit that controls the operation of the automatic transmission, an electric oil pump that pumps oil to generate the working hydraulic pressure supplied to the automatic transmission, and an oil pump control unit that receives information regarding a state of the automatic transmission from the transmission control unit and controls the operation of the electric oil pump, wherein the working hydraulic pressure supplied to the automatic transmission is generated only by means of the electric oil pump, which is electrically operated. DE 38 41 400 A1 describes a method for controlling an automatic transmission. The invention provides an oil pump system for a hybrid vehicle, which is suitable for supplying a stable working hydraulic pressure to an automatic transmission using only one electric oil pump and for minimizing power loss even in the event of a fault in supplying hydraulic pressure to an automatic transmission, and a method for controlling the same. According to the invention, this is achieved by an oil pump system according to the features of claim 1 and a method for controlling an oil pump system according to the features of claim 5. Advantageous embodiments are described in the dependent claims. According to one aspect of the invention, an oil pump system for a hybrid vehicle is provided, which supplies a working hydraulic pressure to an automatic transmission of the hybrid vehicle. The oil pump system comprises: a transmission control unit that controls the operation of the automatic transmission, an electric oil pump that pumps oil to generate the working hydraulic pressure to be supplied to the automatic transmission, and an oil pump control unit that receives information regarding the state of the automatic transmission from the transmission control unit and controls the operation of the electric oil pump. The hydraulic pressure supplied to the automatic transmission is generated solely by means of the electric oil pump, which is electrically operated. If a fault occurs in the hydraulic pressure supply to the automatic transmission, the oil pump control unit performs a control operation to keep the working hydraulic pressure of the automatic transmission constant, which is generated by the electric oil pump. The constant working hydraulic pressure can be set equal to or greater than a working hydraulic pressure generated by normal operation of the electric oil pump. When the working hydraulic pressure of the automatic transmission is controlled to be fixed at a constant level, the transmission control unit performs a control operation to reduce the output torque required for the automatic transmission. The electric oil pump can be controlled to a speed corresponding to the required working hydraulic pressure of the automatic transmission, which is reduced according to the reduced output torque of the automatic transmission. The speed of the electric oil pump can be set by a map based on a relationship between the oil temperature, the hydraulic pressure and the speed of the electric oil pump, which is stored in the oil pump control unit. According to another aspect of the invention, a method for controlling an oil pump system is provided, which supplies a working hydraulic pressure to an automatic transmission of a hybrid vehicle by means of an electric oil pump. The method comprises: determining whether a fault in the hydraulic pressure supply to the automatic transmission has occurred or not, fixing the working hydraulic pressure supplied to the automatic transmission, reducing the output torque required for the automatic transmission, and controlling the speed of the electric oil pump. If it is determined that no fault has occurred in the hydraulic pressure supply to the automatic transmission, the electric oil pump can be operated normally. If it is determined that a fault has occurred in the hydraulic pressure supply to the automatic transmission, the working hydraulic pressure supplied to the automatic transmission is fixed. If the hydraulic pressure supplied to the automatic transmission is fixed, the output torque required for the automatic transmission can be reduced. The required working hydraulic pressure of the automatic transmission can decrease according to the reduced output torque of the automatic transmission, and the speed of the electric oil pump can be controlled as the required working hydraulic pressure of the automatic transmission decreases. The speed of the electric oil pump can be controlled to a speed set by a map based on a relationship between the electric oil pump, the oil temperature, and the hydraulic pressure. The invention is explained in more detail with reference to the drawing. In the drawing: Fig. 1 shows a schematic of an oil pump system of a hybrid vehicle according to an exemplary embodiment of the invention; and Fig. 2 shows a flowchart to explain a method for controlling an oil pump system of a hybrid vehicle according to an exemplary embodiment of the invention. As shown in Fig. 1, an oil pump system of a hybrid vehicle according to an exemplary embodiment of the invention comprises an automatic transmission 50, a transmission control unit (TCU) 90, an electric oil pump (EOP) 60, and an oil pump control unit (OPU) 70. Furthermore, a powertrain system of the hybrid vehicle comprises an internal combustion engine 20, a hybrid starter generator (HSG) 22, an electric motor 40, a battery 10, an internal combustion engine clutch 30, an automatic transmission 50, and an axle 80. The power transmission of the hybrid vehicle is carried out as follows. The power generated by the internal combustion engine 20 or the electric motor 40 is selectively transmitted to a drive shaft 52 of the automatic transmission 50, and the power delivered to an output stage 54 of the automatic transmission 50 is transmitted to the axle 80 via a final reduction device 84 and a differential gear device 86. Furthermore, when the axle 80 rotates wheels 82, the hybrid vehicle is operated by means of the power generated by the internal combustion engine 20 or the electric motor 40. The battery 10 supplies a drive voltage to the electric motor 40. This means that the battery 10 stores a high voltage. Furthermore, the HSG 22 operates as a motor to start the combustion engine 20, or as a generator when the combustion engine 20 is running, thereby charging the battery 10. The battery 10 can also be charged by energy regenerated by the engine 40 during coasting of the hybrid vehicle. Additionally, the combustion engine clutch 30 selectively connects the combustion engine 20 to the electric motor 40. That is, the power of the combustion engine 20 and the power of the electric motor 40 are connected or disconnected by the combustion engine clutch 30. The power transmission and regenerative braking of the hybrid vehicle, as well as a fluid coupling (not shown) for selectively blocking the power transmitted to the automatic transmission 50, are obvious to a technically skilled professional. Therefore, a detailed description is omitted. The automatic transmission 50 serves to change the rotational speed by altering the gear ratio of the input shaft 52 to the output stage 54. Furthermore, the automatic transmission 50 changes the rotational speed according to the operation of a plurality of friction elements, comprising one or more brakes (not shown) and one or more clutches (not shown). The plurality of friction elements are operated in such a way that they can be engaged or disengaged by a working hydraulic pressure supplied to the automatic transmission 50. The TCU 90 serves to control the torque of the automatic transmission 50 and the operation of the friction elements. Since the operation of the TCU 90 and the automatic transmission 50 is obvious to a technically skilled professional, a detailed description is omitted. The oil pump system of the hybrid vehicle can adequately supply a working hydraulic pressure to operate the friction elements of the automatic transmission 50 in order to carry out the power transmission of the hybrid vehicle smoothly. The electric oil pump 60 is connected to the automatic transmission 50. Alternatively, the electric oil pump 60 can be integrated into the automatic transmission 50. The electric oil pump 60 pumps oil to supply the automatic transmission 50 with working hydraulic pressure. In the oil pump system of the hybrid vehicle according to the exemplary embodiment of the invention, only the electric oil pump 60 generates working hydraulic pressure and supplies this pressure to the automatic transmission 50. The OPU 70 is connected to the electric oil pump 60 and controls the drive of the electric oil pump 60. In addition, the OPU 70 is connected to the TCU 90 and controls the drive of the electric oil pump 60 according to information about the state of the automatic transmission 50, which is received by the TCU 90. The following describes, with reference to Fig. 2, a method for controlling an oil pump system of a hybrid vehicle according to an exemplary embodiment of the invention. When the hybrid vehicle's oil pump system is operating (S100), the TCU 90 determines whether a hydraulic pressure supply fault has occurred in the automatic transmission 50 (S110). For example, a hydraulic pressure supply fault could be a malfunction of a solenoid (not shown) that supplies hydraulic pressure to the friction elements. If it is determined that no fault has occurred in the hydraulic pressure supply to the automatic transmission 50, the TCU 90 transmits information about the normal state of the automatic transmission 50 to the OPU 70. Furthermore, the OPU 70 controls the electric oil pump 60 for normal operation (S130). The normal operation of the electric oil pump 60 can be set by a technically skilled person based on the generated working hydraulic pressure. If a hydraulic pressure supply fault is detected in the automatic transmission 50, the TCU 90 transmits information about the fault condition of the automatic transmission 50's hydraulic pressure supply to the OPU 70. Furthermore, the OPU 70 controls the drive of the electric oil pump 60 to maintain a constant working hydraulic pressure (S120) supplied by the electric oil pump 60 to the automatic transmission 50. The constant working hydraulic pressure is set equal to or greater than the working hydraulic pressure generated by the normal operation of the electric oil pump 60. For example, if the working hydraulic pressure generated by the normal operation of the electric oil pump 60 varies between 11 bar and 16 bar, the working hydraulic pressure in the fault condition of the automatic transmission 50's hydraulic pressure supply can be fixed at 16 bar or more. However, if the working hydraulic pressure is continuously fixed at a higher level than that generated by the normal operation of the electric oil pump 60 for a predetermined time, a higher than necessary working hydraulic pressure may be supplied, power may be wasted to drive the electric oil pump 60, and parts may be damaged by overcurrent. Therefore, if the working hydraulic pressure supplied to the automatic transmission 50 is fixed at a constant level (S120), the TCU 90 performs a control operation to reduce the output torque of the automatic transmission 50 (S140). Reducing the output torque of the automatic transmission 50 allows for a corresponding reduction in the required working hydraulic pressure. The reduced output torque and the reduced required working hydraulic pressure are set by a technically qualified professional. The reduced output torque is referred to below as the limit torque, and the reduced required working hydraulic pressure is referred to as the limit hydraulic pressure. The limit torque is set within a range in which the power transmission of the automatic transmission 50 is smooth. Furthermore, the limit hydraulic pressure, set according to the limit torque, is set within a range in which the electric oil pump 60 is driven smoothly. When the output torque of the automatic transmission 50 is reduced (S140) and the limit torque and limit hydraulic pressure are set, the OPU 70 extracts information from a map (S150). The OPU 70 controls the speed of the electric oil pump 60 according to the information extracted from the map (S160). The map stores information about the relationship between the oil temperature, the hydraulic pressure, and the speed of the electric oil pump 60. That is, when the information from the map is used, the speed of the electric oil pump 60 can be set according to the limit hydraulic pressure and the current oil temperature. When the speed of the electric oil pump is controlled to 60 (S160), the hybrid vehicle is operated in an emergency running mode (S170), and the control for the oil pump system of the hybrid vehicle is terminated (S180). According to the exemplary embodiment of the invention, since only the electric oil pump 60 is used, manufacturing costs can be reduced and fuel efficiency can be improved. Furthermore, since the map is used to monitor the oil temperature, hydraulic pressure, and speed of the electric oil pump 60, the hydraulic pressure can be supplied stably even if a fault occurs in supplying the hydraulic pressure to the automatic transmission 50, and the power loss can be minimized.

Claims

Oil pump system of a hybrid vehicle which supplies a working hydraulic pressure to an automatic transmission (50) of the hybrid vehicle, wherein the oil pump system comprises: a transmission control device (90) which controls the operation of the automatic transmission (50); an electric oil pump (60) which pumps oil to generate the working hydraulic pressure which is supplied to the automatic transmission (50);and an oil pump control device (70) which receives information regarding a state of the automatic transmission (50) from the transmission control device (90) and controls the operation of the electric oil pump (60), wherein the working hydraulic pressure supplied to the automatic transmission (50) is generated only by means of the electric oil pump (60), which is electrically operated, wherein, if a fault occurs in the hydraulic pressure supply to the automatic transmission (50), the oil pump control device (70) performs a control to maintain the working hydraulic pressure of the automatic transmission (50) at a constant working hydraulic pressure, which is generated by means of the electric oil pump (60), and wherein, if the working hydraulic pressure of the automatic transmission (50) is controlled to a substantially constant pressure, the transmission control device (90) performs a control to reduce the output torque required for the automatic transmission (50). Oil pump system according to claim 1, wherein the constant working hydraulic pressure is set equal to or greater than a working hydraulic pressure generated by normal operation of the electric oil pump (60). Oil pump system according to claim 1, wherein the electric oil pump (60) is controlled to a speed corresponding to a required working hydraulic pressure of the automatic transmission, which is reduced according to the reduced output torque of the automatic transmission (50). Oil pump system according to claim 3, wherein the speed of the electric oil pump (60) is set by a map on a relationship between the oil temperature, the hydraulic pressure and the speed of the electric oil pump (60), which is stored in the oil pump control device (70). Method for controlling an oil pump system which supplies a working hydraulic pressure to an automatic transmission (50) of a hybrid vehicle by means of an electric oil pump (60), wherein the method comprises: determining whether a fault in the hydraulic pressure supply to the automatic transmission (50) has occurred or not (S110); fixing the working hydraulic pressure supplied to the automatic transmission (50) when it is determined that a fault in the hydraulic pressure supply to the automatic transmission (50) has occurred (S120); reducing the output torque required for the automatic transmission (50) (S140); and controlling a speed of the electric oil pump (60) (S160). Method according to claim 5, wherein, when it is determined that no fault in the hydraulic pressure supply has occurred in the automatic transmission (50), the electric oil pump (60) is operated normally (S130). Method according to claim 5, wherein, when the working hydraulic pressure supplied to the automatic transmission (50) is fixed, the output torque required for the automatic transmission (50) is reduced. Method according to claim 5, wherein: the required working hydraulic pressure of the automatic transmission (50) decreases according to the reduced output torque of the automatic transmission (50), and the speed of the electric oil pump (60) is controlled as the required working hydraulic pressure of the automatic transmission (50) decreases. Method according to claim 5, wherein the speed of the electric oil pump (60) is controlled to a speed set by a card via a relationship between the electric oil pump (60), the oil temperature and the hydraulic pressure (S150).

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