Cooling system for electric vehicle

Abstract

To suppress a sudden change in the temperature of a cooling medium due to heat generation associated with power waste control in a vehicle in which the power waste control for reducing the efficiency of a motor is performed when a regenerative brake is used.SOLUTION: The control device is configured to determine a ratio between an amount of braking caused by generation of the regenerative electric power and an amount of braking by the brake device based on a required amount of braking at the time of braking of the vehicle, predict a heat generation amount associated with waste electric power control for operating the power train device with reduced efficiency when the regenerative brake is used in a state in which a charge amount of the power storage device exceeds a charge amount given in advance, and control the cooling mechanism based on the predicted heat generation amount.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cooling system for an electric vehicle. [Background technology]

[0002] In recent years, as a measure against climate change such as global warming, the use of electric vehicles such as hybrid vehicles that use electric motors as their drive source and have low carbon dioxide emissions, and electric vehicles that run solely on electric motors, has become more widespread. These electric vehicles use regenerative braking, which generates braking force by making the motor that serves as the drive source function as a generator when braking the vehicle and using the regenerative power generated to charge the battery.

[0003] In these vehicles, braking force is usually primarily provided by regenerative braking, with mechanical brakes such as disc brakes used as a secondary brake. However, when the battery is nearly fully charged, the regenerative power cannot be fully consumed, and the proportion of mechanical brake use increases. For example, when this condition occurs while driving down a long slope, the amount of heat generated by the mechanical brakes increases, making them more susceptible to vapor lock and brake fade.

[0004] As a conventional countermeasure to such problems, for example, Patent Document 1 discloses a waste electricity control method that reduces the power generation efficiency of a motor used as a generator during braking, thereby discharging part of the energy obtained by regenerative braking as heat and controlling the amount of charge to the battery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-50099 Summary of the Invention [Problem to be solved by the invention]

[0006] In waste electricity control, part of the regenerative energy is discharged as heat from the motor. The heat generated by the motor is transported via a cooling medium such as water or oil. After cooling the motor, the cooling medium is cooled in a radiator and circulated to cool the motor again. Generally, the cooling medium is cooled by, for example, monitoring the temperature of the cooling medium and controlling grill shutters or the like in response to the temperature rise of the cooling medium, thereby adjusting the amount of air flowing into the radiator.

[0007] Therefore, if the temperature of the cooling medium rises suddenly due to factors such as frequent requests for regenerative braking, the cooling medium may not be cooled sufficiently, which may affect the operation of the powertrain.

[0008] In view of the problems in the prior art described above, an object of the present invention is to provide a cooling system that can maintain the temperature of the cooling medium that cools the motor at an appropriate level and can meet the demands of more regenerative braking. [Means for solving the problem]

[0009] In one preferred aspect, a cooling system for an electric vehicle according to the present invention includes a powertrain device that drives wheels provided on the vehicle and brakes the wheels with a regenerative brake that generates regenerative electric power using the rotational force of the wheels, an electric storage device that supplies electric power to the powertrain when the wheels are driven and is charged by the regenerative electric power, a cooling mechanism that circulates a coolant through the powertrain device to cool the powertrain device, and a control device that controls the powertrain device to control the braking and driving of the vehicle and controls the cooling mechanism to control the cooling state of the powertrain device. The control device is configured to determine, based on a required braking amount when braking the vehicle, a braking amount to be allocated to the regenerative brake and a braking device provided on the vehicle that brakes the wheels by mechanical frictional force, and, if the braking amount allocated to the regenerative brake exists and the charge amount of the electric storage device exceeds a predetermined charge amount, predict a heat generation amount associated with power waste control that reduces the efficiency of the powertrain device and operates the powertrain device, and control the cooling mechanism based on the predicted heat generation amount.

[0010] According to the present invention, the cooling capacity of the cooling system is controlled according to the amount of heat generated by waste electricity control, so that regenerative braking can be used while suppressing sudden changes in the temperature of the cooling medium. Other novel features of the present invention and the technical problems solved thereby will become apparent from the description and drawings of this specification. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a configuration of an electric vehicle equipped with a cooling mechanism according to an embodiment. [Figure 2] 4 is a flowchart showing the flow of cooling control in the first embodiment. [Figure 3] FIG. 2 is a schematic diagram showing the distribution of braking force between a regenerative brake and a mechanical brake. [Figure 4] FIG. 10 is a schematic diagram showing the relationship between the vehicle speed and the amount of cooled heat, with the airflow control amount used as a parameter. [Figure 5] 10 is a flowchart showing the flow of cooling control in the second embodiment. [Figure 6] 10 is a flowchart showing the flow of cooling control in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Representative embodiments of the present invention will be described below with reference to the drawings.

[0013] FIG. 1 is a schematic diagram showing the configuration of an embodiment of a vehicle to which the present invention is applied.

[0014] In the diagram, reference numeral 1 denotes a vehicle such as a passenger car or commercial vehicle, with the top of the diagram representing the front and the bottom representing the rear. 2 denotes wheels provided on the vehicle, 3 denotes a motor for driving wheels 2, 4 denotes an inverter for controlling motor 3, 5 denotes an in-wheel motor provided inside wheel 2 for driving wheel 2, 6 denotes a battery for supplying power for driving motor 3 and in-wheel motor 5, and 7 denotes high-voltage wiring for transmitting power from battery 6 to inverter 4. Each in-wheel motor 5 is equipped with an inverter (not shown) for controlling the motor. The motor 3, inverter 4, and in-wheel motor 5 constitute a powertrain device for braking and driving vehicle 1.

[0015] Reference numeral 8 denotes a radiator that cools the cooling medium, such as coolant or cooling oil, that has become hot after cooling the motor 3, inverter 4, in-wheel motor 5, and battery 6, 9 denotes a grille shutter that adjusts the amount of air flowing into the radiator 8, 10 denotes a radiator fan that adjusts the amount of air flowing into the radiator 8 in the same way as the grille shutter 9, 11 denotes a refrigerant flow path that circulates the cooling medium, and 12 denotes a pump that circulates the cooling medium between the motor 3, inverter 4, in-wheel motor 5, battery 6, and radiator 8. The radiator 8, grille shutter 9, radiator fan 10, refrigerant flow path 11, and pump 12 constitute the cooling mechanism of the vehicle 1.

[0016] Reference numeral 13 denotes a vehicle control device (vehicle ECU) that incorporates a microprocessor and executes various processes for the vehicle 1 according to programs stored in memory. Reference numeral 14 denotes an accelerator pedal, 15 denotes an accelerator pedal sensor that acquires the amount of operation of the accelerator pedal 14, 16 denotes a brake pedal, 17 denotes a brake pedal sensor that acquires the amount of operation of the brake pedal 16, 18 denotes a temperature sensor that acquires the temperature of the cooling medium, and 19 denotes a mechanical brake device that obtains braking force by pressing a friction material against a disc or drum that rotates together with the wheels 2. The brake device 19 may be a hydraulic type that presses a friction material using hydraulic pressure, or an electric type that presses a friction material using an electric actuator. In this specification, these are collectively referred to as mechanical brakes in contrast to regenerative brakes.

[0017] In the drawing, the dashed lines extending from the vehicle ECU 13 indicate control wiring for transmitting control signals and the like between the vehicle ECU 13 and each part of the vehicle 1.

[0018] In this embodiment, a synchronous motor driven by three-phase AC power is used as the motor 3. Based on a control signal sent from the vehicle ECU 13, the inverter 4 converts DC power supplied from the battery 6 into three-phase AC power and supplies it to the motor 3. When braking the vehicle 1, the motor 3 also operates as a generator to generate three-phase AC regenerative power. The three-phase AC power generated by the motor 3 is converted into DC power by the inverter 4 and used to charge the battery 6.

[0019] The vehicle ECU 13 receives the operation amount of the accelerator pedal 14 obtained by the accelerator pedal sensor 15 and the operation amount of the brake pedal 16 obtained by the brake pedal sensor 17, obtains the required driving force and braking force based on these operation amounts, and issues various commands to the inverter 4, the in-wheel motor 5, and the brake device 19 to control the running of the vehicle 1. For example, when driving the vehicle 1, the vehicle ECU 13 calculates the torque for driving the vehicle 1 based on the operation amount of the accelerator pedal 14 detected by the accelerator pedal sensor 15, and issues commands to the inverter 4 and the in-wheel motor 5 so that the motor 3 and the in-wheel motor 5 output that torque amount. When braking the vehicle 1, the vehicle ECU 13 calculates the required braking amount based on the operation amounts of the accelerator pedal 14 and the brake pedal 16 detected by the accelerator pedal sensor 15 and the brake pedal sensor 17, and allocates the calculated braking amount to the regenerative braking by the motor 3 and the in-wheel motor 5 and the brake device 19, thereby slowing down and stopping the vehicle 1. When the state of charge of the battery 6 prevents charging using regenerative power generated by regenerative braking, the vehicle ECU 13 performs electricity waste control to use regenerative braking by reducing the efficiency of the motor 3 and the in-wheel motor 5. Note that electricity waste control is not directly related to the present invention and can be realized using the technology described in Patent Document 1, for example, and therefore a detailed description thereof will be omitted in this specification.

[0020] The vehicle ECU 13 also controls the cooling mechanism to manage the temperature of the cooling medium. Specifically, the vehicle ECU 13 controls the grille shutter 9 and the radiator fan 10 to control the amount of air flowing into the radiator 8, and the pump 12 to control the amount of refrigerant circulation, thereby performing cooling control to keep the temperature of the cooling medium within a predetermined range.

[0021] In this embodiment, two types of motors, the motor 3 and the in-wheel motor 5, are used as the drive device, but it is not necessary to provide both of them, and only one of them may be provided. Also, in Fig. 1, the vehicle 1 is shown as a type in which only the front wheels are driven, but the vehicle may also be a type in which a drive mechanism similar to that for the front wheels is provided on the rear wheel side, so that both the front and rear wheels are driven, or a vehicle in which only the rear wheels are driven.

[0022] Fig. 2 is a flowchart showing the flow of cooling control performed by the vehicle ECU 13. The cooling control shown in Fig. 2 is repeatedly performed at predetermined time intervals while the vehicle 1 is in operation. Here, the cooling control during braking will be explained, and the normal cooling control in other cases will not be explained as it is the same as the conventional one.

[0023] When cooling control is started, the vehicle ECU 13 acquires a required braking amount based on the operation amount of the accelerator pedal 14 and the brake pedal 16 acquired by the accelerator pedal sensor 15 and the brake pedal sensor 17. In addition, when a braking request is issued from a driving assistance system such as a cruise control device or a safety brake device, the vehicle ECU 13 acquires a required braking amount based on the braking request (step S100).

[0024] Next, the ratio of the regenerative brake amount to the mechanical brake amount to be used is determined from the acquired brake request amount, and the brake amount to be allocated to each brake is acquired.

[0025] FIG. 3 is a schematic diagram showing an example of the allocation of braking force to regenerative brakes and mechanical brakes. The solid line shows the change in braking force required from when a braking request is made until vehicle 1 stops, and the dashed line shows the change in braking force allocated to the regenerative brakes. The difference between the solid and dashed lines is the braking force allocated to the mechanical brakes. As shown in the figure, at the beginning of braking, most of the braking force required is allocated to the regenerative brakes, and the braking force allocated to the mechanical brakes increases midway through, and the proportion of braking force allocated to the regenerative brakes is controlled to increase towards the end of braking.

[0026] The method for determining the allocation of the braking amount between the regenerative brake and the mechanical brake is not directly related to the content of the present invention and publicly known techniques can be used, so a detailed explanation thereof will be omitted here (step S110).

[0027] Next, the vehicle ECU 13 determines whether regenerative braking is required based on whether there is a braking amount allocated to the regenerative braking. If there is no request for regenerative braking, the vehicle ECU 13 ends the cooling control process (step S120).

[0028] If there is a braking amount allocated to the regenerative brakes, the vehicle ECU 13 obtains the charge amount of the battery 6 and determines whether the charge amount exceeds a predetermined threshold value. The threshold value can be a value at which the charge amount is at or near full charge, at which the battery 6 can no longer accept the power generated by the regenerative brakes, and power discard control is initiated. If the charge amount is below the threshold value, the battery 6 can still accept the power generated by the regenerative brakes, and power discard control is not performed, so the vehicle ECU 13 ends the cooling control (step S130).

[0029] When the charge amount exceeds the threshold value, the vehicle ECU 13 acquires a predicted heat generation amount, which is a predicted value of the amount of heat generated by the power waste control. The predicted heat generation amount can be calculated, for example, from the power loss caused by reducing the output efficiency of the motor 3 by the power waste control. Alternatively, the relationship between the amount of heat generated by the power waste control and the power waste control amount may be acquired in advance, and stored as a map in the vehicle ECU 13, and the predicted heat generation amount may be acquired from the map (step S140).

[0030] The vehicle ECU 13 also acquires the vehicle speed from a vehicle speed sensor or the like (step S150).

[0031] Next, the vehicle ECU 13 acquires control variables for the cooling mechanism based on the acquired predicted heat generation amount and vehicle speed. In this embodiment, the control variables for the cooling mechanism are control variables for the inflow airflow, specifically, control variables for the grille shutter 9 and the radiator fan 10.

[0032] FIG. 4 is a schematic diagram showing the relationship between the predicted heat generation amount acquired in step S140, the vehicle speed acquired in step S150, and the control amount of the inflow air flow.

[0033] The graph in the figure conceptually shows the relationship between vehicle speed and the amount of cooling heat when the airflow control amount is changed between 5% and 25% of the maximum airflow. Normally, when the vehicle speed is the same, the greater the control amount of the inflow airflow (the increase in the inflow airflow), the greater the amount of heat (cooling heat) that can be removed from the cooling medium. Also, even with the same airflow control amount, the higher the vehicle speed, the greater the amount of cooling heat. In this embodiment, the cooling airflow is controlled so that the amount of cooling heat is approximately equal to the predicted heat generation amount. To achieve this, the vehicle ECU 13 stores a map of the relationship between the predicted heat generation amount, vehicle speed, and airflow control amount, as shown in FIG. 4, which is acquired in advance, and obtains an appropriate airflow control amount based on the predicted heat generation amount and vehicle speed (the airflow control amount that is close to the intersection of the predicted heat generation amount and vehicle speed in the graph in FIG. 4) (step S160).

[0034] Then, the vehicle ECU 13 controls the cooling mechanism to achieve the acquired air volume control amount; specifically, it sets the opening degree of the grille shutter 9 and the rotation speed of the radiator fan 10 to increase by the control amount acquired by the above processing, and controls the grille shutter 9 and the radiator fan 10 to control the air volume flowing into the radiator 8 (step S170).

[0035] In addition, if this process is executed again after an increase in the control amount of the cooling mechanism is set in step S170, and the judgment results in steps S120 and S130 are negative, the setting of the increase in the control amount is canceled before the process ends.

[0036] According to this embodiment, when power dissipation control is performed while regenerative braking is in use, the amount of heat generated by the power dissipation control is obtained in advance and the amount of air sent to the radiator 8 is controlled, thereby suppressing a sudden increase in the temperature of the cooling medium and keeping the temperature change range small, thereby suppressing the impact on the powertrain.

[0037] In this embodiment, the control variables for the grille shutter 9 and radiator fan 10 are obtained from the control variable for the inflow air volume and then controlled, but it is also possible to store a map that shows the relationship between the control variables for the grille shutter 9 and radiator fan 10 and the predicted heat generation amount and vehicle speed, so that the control variables for the grille shutter 9 and radiator fan 10 can be obtained directly from the predicted heat generation amount and vehicle speed. Furthermore, the cooling mechanism may be controlled for both the grille shutter 9 and the radiator fan 10, or it may be controlled for only one of them depending on the predicted heat generation amount.

[0038] FIG. 5 is a flowchart showing the flow of cooling control in the second embodiment. In this embodiment, the flow rate of the cooling medium is controlled to suppress sudden local temperature changes associated with waste electricity control. Note that the configuration of the vehicle 1 in this embodiment is the same as that in the first embodiment, and therefore a description thereof will be omitted here. Furthermore, processes similar to those in the first embodiment shown in FIG. 2 are assigned the same reference numbers as those used in FIG. 2, and descriptions thereof will be omitted in the following description unless particularly necessary.

[0039] In this embodiment, the vehicle ECU 13 calculates the predicted heat generation amount in step S140, and then obtains the circulation amount, which is the increase in the flow rate per unit time of the cooling medium flowing into / out of the inverter, based on the predicted heat generation amount. The increased circulation amount of the cooling medium can be set in advance in the form of a map corresponding to the predicted heat generation amount, for example, and obtained from the map based on the predicted heat generation amount obtained in step S140. Alternatively, the increased circulation amount may be obtained by calculation using known constants such as the specific gravity and specific heat of the cooling medium (step S200).

[0040] Then, the vehicle ECU 13 controls the pump 12 by setting the amount of cooling medium discharged from the pump 12 to increase by the acquired circulation amount, thereby increasing the circulation amount of the cooling medium (step S210).

[0041] In addition, in step S210, if the control amount of pump 12 is set so as to increase the circulation amount and then this process is executed again, if the judgment results in steps S120 and S130 are negative, the setting of the increase in the control amount is canceled before the process ends.

[0042] According to this embodiment, when power dissipation control is performed during the use of regenerative braking, the amount of heat generated by the power dissipation control is predicted in advance and the amount of circulating cooling medium is controlled, thereby preventing sudden local temperature increases due to power dissipation control, minimizing the impact on vehicle components, and enabling stable temperature management of the cooling medium.

[0043] In this embodiment, as in the first embodiment, instead of a map of predicted heat generation amount and circulation amount, a map of predicted heat generation amount and control amount of pump 12 may be stored in vehicle ECU 13, so that the control amount of pump 12 can be obtained without having to calculate the circulation amount of the cooling medium.

[0044] Fig. 6 is a flowchart showing the flow of cooling control in the third embodiment. The cooling control in this embodiment controls the amount of air flowing into the radiator 8 during power waste control, and also controls the amount of cooling medium circulating, thereby suppressing localized rapid temperature increases as the temperature of the cooling medium increases. In Fig. 6, the same reference numerals are used to designate parts that perform the same processes as those in the cooling control shown in Figs. 2 and 5.

[0045] In the cooling control of this embodiment, in steps S100 to S170, the grille shutter 9 and the radiator fan 10 are controlled to control the amount of air sent to the radiator by the same processing as in the first embodiment. Thereafter, in the same manner as in the second embodiment, the vehicle ECU 13 acquires the circulation amount of the cooling medium based on the predicted heat generation amount acquired in step S140 (step S200), and controls the discharge amount of the pump 12 based on the acquired circulation amount, thereby controlling the circulation amount of the cooling medium (step S210).

[0046] In this embodiment, if this process is performed again after the control amount of the cooling mechanism is set in steps S170 and S210, and the judgment results in steps S120 and S130 are negative, the setting of the control amount is canceled before the process ends.

[0047] According to this embodiment, when power dissipation control is performed during regenerative braking, the amount of heat generated by the power dissipation control is predicted in advance, and the amount of air flowing into the radiator 8 as well as the amount of circulating cooling medium are controlled. This makes it possible to suppress sudden temperature increases and sudden partial temperature changes in the cooling medium, enabling more stable temperature management of the cooling medium.

[0048] According to each of the embodiments described above, when power dissipation control is performed when regenerative braking is in use, the amount of heat generated by the power dissipation control is predicted and the cooling mechanism is controlled, so that the temperature of the cooling medium can be kept at an appropriate level and more regenerative braking demands can be met.

[0049] Furthermore, when an in-wheel motor is used as a drive source, if the use of regenerative braking is restricted and mechanical braking is used more frequently, the heat generated by the brake will increase the temperature inside the wheel, significantly affecting the in-wheel motor. According to the above-described embodiment, the temperature of the cooling medium can be appropriately managed and regenerative braking can be used efficiently through power waste control, thereby reducing the possibility that the use of regenerative braking will be restricted, suppressing the use of mechanical braking and preventing heat generated by the mechanical brake from adversely affecting the operation of the in-wheel motor.

[0050] While the present invention has been described above using representative embodiments as examples, the present invention is not limited to these, and can be embodied in various forms without departing from the spirit of the invention as set forth in the claims. For example, the above embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations. [Explanation of symbols]

[0051] 1: Vehicle, 2: Wheel, 3: Motor, 4: Inverter, 5: In-wheel motor, 6: Battery, 7: High-voltage wiring, 8: Radiator, 9: Grille shutter, 10: Radiator fan, 11: Refrigerant flow path, 12: Pump, 13: Vehicle ECU, 14: Accelerator pedal, 15: Accelerator pedal sensor, 16: Brake pedal, 17: Brake pedal sensor, 18: Temperature sensor, 19: Brake device

Claims

1. a powertrain device that drives wheels provided on a vehicle and brakes the wheels by a regenerative brake that generates regenerative electric power by utilizing the rotational force of the wheels; an electric storage device that supplies electric power to the powertrain device when the wheels are driven and receives the regenerative electric power to be charged; a cooling mechanism that circulates a cooling medium through the powertrain device to cool the powertrain device; a control device that controls the powertrain device to control braking and driving of the vehicle and controls the cooling mechanism to control the cooling state of the powertrain device; the control device determines, based on a required braking amount when braking the vehicle, a braking amount to be allocated to each of the regenerative brake and a braking device provided on the vehicle that applies braking to the wheels by mechanical friction force; When a braking amount allocated to the regenerative braking is present by the determination and the charge amount of the power storage device exceeds a predetermined charge amount, a heat generation amount associated with power waste control that reduces the efficiency of the power train device and causes the power train device to operate is predicted; A cooling system for an electric vehicle configured to obtain a control amount for the cooling mechanism based on the predicted heat generation amount and control the cooling mechanism.

2. the cooling mechanism includes a radiator that cools the cooling medium and an air volume control device that controls the amount of air flowing into the radiator, The cooling system for an electric vehicle according to claim 1 , wherein the control device is configured to control the air volume control device based on the control amount to control the amount of air flowing into the radiator.

3. the cooling mechanism has a pump that circulates the cooling medium, The cooling system for an electric vehicle according to claim 1 , wherein the control device is configured to control the pump based on the control amount to control the flow rate of the cooling medium per unit time.

Images