Vehicle control system

Abstract

The present invention provides a vehicle control device that suppresses the temperature rise of the PCU when transitioning from ultra-high speed driving to an extremely low speed state, thereby ensuring driving performance such as restarting and re-engaging. [Solution] The electronic control unit 60 performs flow rate suppression control when the vehicle 10 transitions from ultra-high speed driving (UHS) to an extremely low speed state (ULS) which is stopped or just before stopping, and the first water temperature T1, which is the temperature of the coolant flowing out of the radiator 32, is equal to or greater than the second water temperature T2, which is the temperature of the coolant flowing out of the PCU 40, and the state in which the first water temperature T1 is equal to or greater than a predetermined water temperature TN continues for a first predetermined period BT1 or longer, by reducing the flow rate Mw of the coolant for a second predetermined period BT2. This prevents heat generated from the electric motor MG from being transmitted to the PCU 40 via the coolant. Therefore, the temperature rise of the PCU 40 is suppressed, and driving performance such as restarting and restarting from the extremely low speed state (ULS) is ensured.

Description

Technical Field

[0001] The present invention relates to a control device for a vehicle including a cooling circuit for cooling an electric motor and a PCU (Power Control Unit) that performs drive control of the electric motor.

Background Art

[0002] A control device for a vehicle including a PCU including an inverter that performs drive control of an electric motor and a cooling circuit that circulates cooling water from a radiator to the PCU and the electric motor in this order and returns it to the radiator is known. For example, the control device for a cooling water system described in Patent Document 1 is such a device. Patent Document 1 discloses controlling the flow rate of the cooling water and the operation of a fan that air-cools the radiator based on the temperature of the cooling water supplied from the radiator to the PCU and the temperature of the electric motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, when the aforementioned vehicle engages in ultra-high-speed driving, such as circuit driving where the average speed exceeds 200 km / h, which differs from normal driving, a problem occurs where the cooling capacity of the cooling circuit becomes insufficient when transitioning to a stop, such as during a pit stop, or to an extremely low speed state just before stopping. When transitioning to an extremely low speed state, the radiator's cooling capacity decreases sharply due to the reduction in cooling airflow (airflow from driving), and the heat generated by the PCU also decreases as the inverter switching stops. However, because the electric motor has a large heat capacity, a considerable amount of heat generation continues for a considerable period even in an extremely low speed state. As a result, the heat generated from the electric motor exceeds the cooling capacity of the radiator, and consequently, the temperature of the coolant rises. Due to this effect, the heat generated from the electric motor is transmitted to the PCU via the coolant, and when the temperature of the inverter in the PCU rises, the electric motor's drive may be restricted by the temperature protection function, potentially making it impossible to guarantee driving performance such as restarting and restarting from an extremely low speed state.

[0005] This invention was made against the above circumstances, and its objective is to provide a vehicle control device that can suppress the temperature rise of the PCU when transitioning from ultra-high speed driving to an extremely low speed state, and can ensure driving performance such as restarting and restarting. [Means for solving the problem]

[0006] The gist of the first invention is a control device for a vehicle comprising (a) a PCU including an inverter for controlling the drive of an electric motor, and a cooling circuit that circulates coolant from a radiator to the PCU and then to the electric motor, and returns it to the radiator, characterized in that (b) when the vehicle transitions from ultra-high-speed driving to an extremely low-speed state such as stopping or just before stopping, and the first water temperature, which is the temperature of the coolant flowing out of the radiator, is equal to or greater than the second water temperature, which is the temperature of the coolant flowing out of the PCU, and the state in which the first water temperature is equal to or greater than a predetermined water temperature continues for a first predetermined period of time or longer, the flow rate of the coolant is reduced for a second predetermined period of time, thereby performing flow rate suppression control. [Effects of the Invention]

[0007] According to the first invention, the control device performs flow rate suppression control to reduce the flow rate of the coolant for a second predetermined period if the vehicle transitions from ultra-high-speed driving to an extremely low-speed state, such as being stopped or just before stopping, and the first water temperature, which is the temperature of the coolant flowing out of the radiator, is equal to or greater than the second water temperature, which is the temperature of the coolant flowing out of the PCU, and the state in which the first water temperature is equal to or greater than a predetermined water temperature continues for a first predetermined period or longer. This prevents the heat generated from the electric motor from being transmitted to the PCU via the coolant. Therefore, the temperature rise of the PCU is suppressed, and driving performance such as restarting and restarting from an extremely low-speed state is ensured. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram illustrates the schematic configuration of a vehicle to which the present invention is applied. [Figure 2] This diagram illustrates the detailed configuration and operation of the PCU. [Figure 3] This is a schematic diagram illustrating the detailed configuration and operation of the cooling circuit. [Figure 4] This diagram illustrates an example of the changes in heat absorption and dissipation under various driving conditions of a vehicle. [Figure 5] This is a flowchart illustrating the key aspects of the control operation of an electronic control unit. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0010] Figure 1 is a diagram illustrating the schematic configuration of a vehicle 10 to which the present invention is applied.

[0011] In Figure 1, the vehicle 10 comprises a pair of drive wheels 12, a drive unit 16 that drives the drive wheels 12 via a drive shaft 14, and a battery 18.

[0012] The drive unit 16 includes an electric motor MG, a reduction mechanism 20, a differential gear unit 22, a PCU (Power Control Unit) 40, etc. The vehicle 10 is an electric vehicle in which the driving force from the electric motor MG is transmitted to the drive wheels 12 via the reduction mechanism 20 and the differential gear unit 22.

[0013] The electric motor MG is a so-called motor generator. The battery 18 is a rechargeable DC power source, such as a nickel-metal hydride secondary battery or a lithium-ion battery. The battery 18 is connected to the PCU 40.

[0014] Figure 2 is a diagram illustrating the detailed configuration and operation of the PCU40.

[0015] The PCU40 includes a DC-DC converter 42, an electric motor control device 44, a boost converter 46, and an inverter 48. The PCU40 is a power control device that controls the power exchanged between the battery 18 and the electric motor MG.

[0016] The DC-DC converter 42 is connected to the battery 18. The DC-DC converter 42 functions as a charging device that steps down the voltage of the battery 18 to a voltage equivalent to that of the auxiliary battery 24 and charges the auxiliary battery 24. The auxiliary battery 24 supplies power to operate the auxiliary equipment, motor control device 44, electronic control device 60 (described later), etc., provided in the vehicle 10.

[0017] The boost converter 46 includes reactors and switching elements (not shown). The boost converter 46 is a buck-boost circuit that has the function of boosting the voltage of the battery 18 and supplying it to the inverter 48, and the function of stepping down the voltage converted to DC by the inverter 48 and supplying it to the battery 18.

[0018] The inverter 48 includes a power module 50. The power module 50 includes a plurality of transistors and the like that convert a direct current into a three-phase alternating current by being turned on and off as switching elements, and constitutes a three-phase bridge circuit for the U-phase, V-phase, and W-phase. The electric motor MG and the power module 50 (that is, the inverter 48) are electrically connected by a bus bar 52. The bus bar 52 is a power line that electrically connects the electric motor MG and the PCU 40, and includes a plurality of bus bars 52u, 52v, and 52w. The plurality of bus bars 52u, 52v, and 52w are three power lines through which three-phase alternating currents of the U-phase, V-phase, and W-phase flow. The electric motor MG is a three-phase alternating current synchronous motor driven by the inverter 48.

[0019] The inverter 48 converts the direct current from the boost converter 46 into an alternating current for driving the electric motor MG. The inverter 48 converts the alternating current generated by the electric motor MG by means of regenerative braking into a direct current.

[0020] The electric motor control device 44 controls the boost converter 46 and the inverter 48 based on commands from an electronic control device 60 described later, and controls the electric motor MG. For example, the electric motor control device 44 converts the direct current from the battery 18 into an alternating current used for the electric motor MG respectively. The electric motor control device 44 drives the electric motor MG to ensure the amount of power generation required for charging the battery 18. The electric motor control device 44 drives the electric motor MG or functions as a generator to generate a regenerative brake so as to realize a required drive torque Twfdem commanded from the electronic control device 60 described later.

[0021] Returning to FIG. 1, the vehicle 10 further includes a cooling circuit 30 that circulates cooling water from the radiator 32 to the PCU 40 and the electric motor MG in that order and then returns it to the radiator 32. The dashed line with an arrow in FIG. 1 indicates the circulation direction of the cooling water. The radiator 32 includes a cooling fan 32a and a fan drive motor 32b for driving the cooling fan 32a. The fan drive motor 32b controls the fan rotation speed Nf of the cooling fan 32a and the like based on a command from an electronic control unit 60 described later.

[0022] FIG. 3 is a schematic diagram for explaining the detailed configuration and operation of the cooling circuit 30. The cooling circuit 30 includes a water pump 34 and an oil cooler 36. The water pump 34 is a pump that circulates cooling water in the cooling circuit, and controls the flow rate Mw of the cooling water based on a command from an electronic control unit 60 described later. The oil cooler 36 is a device that performs heat exchange between oil (refrigerant) circulated in an electric motor cooling circuit 38 by an oil pump (not shown) to cool the electric motor MG and the cooling water in the cooling circuit 30, and controls the drive of the oil pump based on a command from an electronic control unit 60 described later.

[0023] In FIG. 3, the thick line indicates the cooling water passage WL, and the cooling water circulates counterclockwise in the drawing as indicated by the arrow in the figure. That is, the relatively low-temperature cooling water flowing out from the radiator 32 is first supplied to a water inlet provided in a case (not shown) of the PCU 40, cools the components and devices included in the PCU 40 by circulating through the cooling water passage in the case, and then is supplied from the drain port of the PCU 40 to the oil cooler 36 to cool the electric motor MG, and then is refluxed to the radiator 32 via the water pump 34. The reason for cooling the PCU 40 first is that the allowable upper limit Tup of the temperature of the power module 50 included in the PCU 40 is lower than the allowable upper limit Tum of the temperature of the electric motor MG.

[0024] The vehicle 10 further includes an electronic control unit 60 as a controller that includes a control device of the vehicle 10 related to the control of the PCU 40, the cooling circuit 30, and the like. The electronic control unit 60 is configured to include a so-called microcomputer.

[0025] The electronic control unit 60 is supplied with various signals based on values ​​detected by various sensors installed in the vehicle 10 (for example, the first water temperature T1, which is the temperature of the coolant flowing out of the radiator 32; the second water temperature T2, which is the temperature of the coolant flowing out of the PCU 40; the power module temperature Tp, which is the internal temperature of the power module 50; the MG temperature Tmg, which is the internal temperature of the electric motor MG; the MG rotation speed Nmg, which is the rotation speed of the electric motor MG corresponding to the vehicle speed V; the accelerator opening θacc, etc.).

[0026] The electronic control unit 60 outputs various command signals (for example, a fan control command signal Sf to control the fan rotation speed Nf of the cooling fan 32a, a water pump control command signal Sw to control the flow rate Mw of the coolant circulated by the water pump 34, an oil cooler control command signal Sc to control the oil pump in the oil cooler 36, and an MG control command signal Smg to control the electric motor MG) to each device installed in the vehicle 10.

[0027] The electronic control unit 60 calculates the driver's requested drive torque Twfdem for the vehicle 10 by applying, for example, the accelerator opening θacc and vehicle speed V to a predetermined drive request map, and outputs an MG control command signal Smg to the PCU 40 (motor control device 44) to realize the requested drive torque Twfdem.

[0028] The electronic control unit 60 calculates the fan rotation speed Nf and the flow rate Mw of the cooling fan 32a based on the vehicle speed V, first water temperature T1, second water temperature T2, power module temperature Tp, MG temperature Tmg, etc., and outputs a fan control command signal Sf to the radiator 32 (fan drive motor 32b) and a water pump control command signal Sw to the water pump 34 to achieve the fan rotation speed Nf and flow rate Mw.

[0029] During normal operation of the vehicle 10, the following relational equation (1) holds true in the cooling circuit 30 controlled by the electronic control unit 60. Heat absorption Qr ≧ Heat radiation Qw1 + Heat radiation Qw2 (1) Here, the heat absorption Qr is the amount of heat [J] per unit time that the radiator 32 absorbs from the coolant as it cools the coolant. The heat dissipation Qw1 is the amount of heat [J] per unit time that the PCU 40 dissipates into the coolant. The heat dissipation Qw2 is the amount of heat [J] per unit time that the oil cooler 36 (motor MG) dissipates into the coolant. When equation (1) is true, the heat dissipation Qw1 from the PCU 40 and the heat dissipation Qw2 from the oil cooler 36 (motor MG) are all absorbed by the radiator 32, so the following relationship (2) also holds true. 1st water temperature T1 ≦ 2nd water temperature T2 (2)

[0030] Incidentally, in a scenario where vehicle 10 performs ultra-high-speed driving (UHS) that differs from normal driving, such as circuit driving where the average vehicle speed AV is 200 [Km / h] or more, if the vehicle transitions from ultra-high-speed driving (UHS) to a stopped state (ULS) such as during a pit stop or just before stopping, the cooling capacity of the cooling circuit 30 may become insufficient, and the above equations (1) and (2) may not hold true.

[0031] Figure 4 illustrates examples of the changes in heat absorption Qr, heat dissipation Qw1, and heat dissipation Qw2 for each driving state of vehicle 10. Note that the values ​​shown in the figure are convenient settings for illustrative purposes and do not necessarily correspond to actual values. Furthermore, the oil cooler 36 (motor MG) will be referred to as motor MG from now on.

[0032] Row a of Figure 4 shows an example of vehicle 10 in normal driving conditions, for example, when driving at a vehicle speed V = 100 [Km / h]. The cooling capacity of the radiator 32, i.e., the maximum value of the heat absorption Qr, is 300 [J], while the heat dissipation amounts Qw1 and Qw2 of the PCU 40 and electric motor MG are 100 [J], respectively, and equations (1) and (2) hold true.

[0033] Row b of Figure 4 shows an example where vehicle 10 transitions from normal driving (row a) to the extremely low-speed state ULS (Ultrasonic Load System) at a vehicle speed V ≤ 15 [Km / h]. The cooling capacity of the radiator 32, i.e., the heat absorption Qr, decreases with the reduction in cooling airflow (driving airflow), for example, to a maximum of 100 [J] due to forced air cooling by the cooling fan 32a. Also, the heat dissipation Qw1 of the PCU 40 decreases to 10 [J] or less as the switching of the inverter 48 (power module 50) stops. Because the electric motor MG has a large heat capacity, the heat dissipation Qw2 of the electric motor MG remains at a reasonable 90 [J] for a reasonable period even in the extremely low-speed state ULS, but even in this case, equations (1) and (2) hold true. In other words, the cooling circuit 30 is configured to ensure that the cooling performance of the radiator 32 always holds true during normal driving of vehicle 10.

[0034] Column c of Figure 4 shows an example of vehicle 10 operating at a super-high speed (UHS) with an average speed AV = 200 [Km / h], which is different from normal operation. With super-high speed operation (UHS), the heat dissipation Qw1 and Qw2 of the PCU 40 and electric motor MG increase to 200 [J], which is larger than in normal operation (column a). However, the cooling capacity of the radiator 32, i.e., the heat absorption Qr, also increases to a maximum of 450 [J] due to the increase in cooling air (airflow). Therefore, although this is not normal operation, equations (1) and (2) hold true.

[0035] Row d of Figure 4 shows an example where vehicle 10 transitions from the ultra-high-speed driving state UHS (row c) to the extremely low-speed state ULS (vehicle speed V ≤ 15 km / h). Similar to row b of Figure 4, the cooling capacity of the radiator 32, i.e., the heat absorption Qr, decreases to a maximum of 100 J as the cooling air (driving air) decreases. Also, the heat dissipation Qw1 of the PCU 40 decreases to 10 J or less as the switching of the inverter 48 (power module 50) stops, but the heat dissipation Qw2 of the electric motor MG remains at a considerable 180 J for a considerable period due to its large heat capacity. Since this heat dissipation Qw2 of 180 J exceeds the maximum value of 100 J of the heat absorption Qr, which is the cooling capacity of the radiator 32, equations (1) and (2) do not hold, and the temperature of the coolant rises. As a result, heat generated from the electric motor is transferred to the PCU 40 via the cooling water, causing the temperature of the inverter 48 (power module 50) in the PCU 40 to rise. If the temperature of the power module 50 exceeds the permissible upper limit Tup, the PCU 40 (electric motor control device 44) will restrict the operation of the electric motor MG, potentially making it impossible to guarantee driving performance such as restarting and restarting from the extremely low-speed state ULS.

[0036] Therefore, the electronic control unit 60 suppresses the temperature rise of the PCU 40 by performing flow rate suppression control as explained in the flowchart of Figure 5. Figure 5 is a flowchart illustrating the main parts of the control operation of the flow rate suppression control performed by the electronic control unit 60.

[0037] In Figure 5, each step in the flowchart corresponds to a function of the electronic control unit 60. First, in step S10 (the step will be omitted hereafter), it is determined whether or not ultra-high-speed driving (UHS) of the vehicle 10 has been detected. This determination is made, for example, by checking whether the average vehicle speed AV over a predetermined driving distance LN is equal to or greater than a first predetermined value V1 (for example, V1 = 200 [Km / h]). The predetermined driving distance LN and the first predetermined value V1 are thresholds that are set in advance to detect ultra-high-speed driving (UHS) scenes, such as driving on a circuit.

[0038] If the judgment in S10 is affirmative, in S20 it is determined whether the vehicle 10 has transitioned to the extremely low-speed state ULS. This determination is made, for example, by checking whether the vehicle speed V is below a second predetermined value V2 (e.g., V2 = 15 [Km / h]) which is the value at or just before stopping, and whether that state has continued for a third predetermined period BT3 or longer. The second predetermined value V2 and the third predetermined period BT3 are threshold values ​​that are set in advance to detect the transition to the extremely low-speed state ULS.

[0039] If the judgment in S20 is affirmed, in S30 it is determined whether the amount of heat dissipated by the cooling circuit 30 is equal to or greater than the cooling performance of the radiator 32. This determination is made, for example, by determining whether the state in which the first water temperature T1 is equal to or greater than the second water temperature T2 (T1≧T2) and the first water temperature T1 is equal to or greater than a predetermined water temperature TN (T1≧TN) has continued for a first predetermined period BT1 or longer.

[0040] If the judgment in S30 is affirmed, in S40 a water pump control command signal Sw is sent to the water pump 34 to reduce the cooling water flow rate Mw for the second predetermined period BT2, and this routine is terminated. By reducing the cooling water flow rate Mw, the heat generated from the electric motor MG is prevented from being transmitted to the PCU 40 via the cooling water, thereby suppressing the temperature rise of the PCU 40. If the judgments in S10 to S30 are denied, in S50 the cooling water flow rate Mw is not reduced and this routine is terminated. The predetermined water temperature TN, the first predetermined period BT1, the second predetermined period BT2, and the reduction value of the flow rate Mw are determined and set in advance through design or experimentation to suppress the temperature rise of the PCU 40.

[0041] Preferably, the larger the difference between the average vehicle speed AV and the first predetermined value V1, the smaller at least one of the predetermined water temperature TN and the first predetermined period BT1 is. As a result, the larger the difference between the average vehicle speed AV and the first predetermined value V1, the earlier the timing at which the cooling water flow rate Mw is reduced, and thus the earlier the temperature rise of the PCU 40 is suppressed. The predetermined water temperature TN and the first predetermined period BT1 are calculated, for example, by a method determined in advance through design or experimentation, for example, by referencing the difference between the average vehicle speed AV and the first predetermined value V1 on a map.

[0042] As described above, according to the electronic control device 60 of this embodiment, when the vehicle 10 transitions from ultra-high-speed driving (UHS) to an extremely low-speed state (ULS) that is stopped or just before stopping, and the first water temperature T1, which is the temperature of the coolant flowing out of the radiator 32, is equal to or greater than the second water temperature T2, which is the temperature of the coolant flowing out of the PCU 40, and the state in which the first water temperature T1 is equal to or greater than a predetermined water temperature TN continues for a first predetermined period BT1 or longer, flow rate suppression control is performed to reduce the flow rate Mw of the coolant for a second predetermined period BT2. This prevents heat generated from the electric motor MG from being transmitted to the PCU 40 via the coolant. Therefore, the temperature rise of the PCU 40 is suppressed, and driving performance such as restarting and restarting from the extremely low-speed state (ULS) is ensured.

[0043] Furthermore, according to the electronic control device 60 of this embodiment, if the average vehicle speed AV over a predetermined travel distance LN is greater than or equal to a first predetermined value V1 which is an ultra-high speed, it is determined to be an ultra-high speed travel (UHS), and if the vehicle speed remains below a second predetermined value, which is a stop or just before stopping, for a third predetermined period of time or longer, it is determined to be an extremely low speed state (ULS). In this way, the same effects as described in the previous section can be obtained by performing flow rate suppression control.

[0044] Furthermore, according to the electronic control device 60 of this embodiment, the larger the difference between the average vehicle speed AV and the first predetermined value V1, the smaller at least one of the predetermined water temperature TN and the first predetermined period BT1 becomes. As a result, the larger the difference between the average vehicle speed AV and the first predetermined value V1, the earlier the timing at which the cooling water flow rate Mw is reduced, and thus the earlier the temperature rise of the PCU 40 is suppressed.

[0045] Although embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is also applicable to other embodiments.

[0046] For example, in the above-described embodiment, the vehicle 10 was an electric vehicle equipped with an electric motor MG as a power source, but the present invention is not limited to this embodiment. For example, even a hybrid vehicle equipped with an engine and an electric motor as power sources can be applied to the present invention as long as it has the same cooling circuit configuration as in the above-described embodiment.

[0047] It should be noted that the above-described embodiment is merely one example, and the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art. [Explanation of Symbols]

[0048] 10: Vehicle 30: Cooling circuit 32: Radiator 40: PCU (Power Control Unit) 48: Inverter 60: Electronic control unit (control device) AV: Average vehicle speed BT1: First predetermined period BT2: Second predetermined period BT3: Third predetermined period LN: Predetermined mileage MG: Electric motor Mw: Flow rate T1: First water temperature T2: Second water temperature TN: Predetermined water temperature UHS: Ultra-high speed running ULS: Extremely low speed state V: Vehicle speed V1: First predetermined value V2: Second predetermined value

Claims

1. A control device for a vehicle comprising a PCU including an inverter for controlling the drive of an electric motor, and a cooling circuit that circulates coolant from a radiator to the PCU and then to the electric motor, and returns it to the radiator, If the vehicle transitions from ultra-high-speed driving to an extremely low-speed state, such as being stopped or just before stopping, and the first water temperature, which is the temperature of the coolant flowing out of the radiator, is equal to or greater than the second water temperature, which is the temperature of the coolant flowing out of the PCU, and the state in which the first water temperature is equal to or greater than a predetermined water temperature continues for a first predetermined period of time or longer, then flow rate suppression control is performed to reduce the flow rate of the coolant for a second predetermined period of time. A vehicle control device characterized by the following features.

2. The control device determines that the vehicle is traveling at an extremely high speed if the average vehicle speed over a predetermined distance is greater than or equal to a first predetermined value, and determines that the vehicle is traveling at an extremely low speed if the vehicle speed remains below a second predetermined value, which is the speed at which the vehicle is stopped or just before stopping, for a period of three predetermined times or longer. The vehicle control device according to feature 1.

3. The control device reduces at least one of the predetermined water temperature and the first predetermined period as the difference between the average vehicle speed and the first predetermined value increases. The vehicle control device according to feature 2.

Images