Electric vehicles

Abstract

To safely stop an electric vehicle even in the case that a power supply to a motor-driven vacuum pump is stopped.SOLUTION: An electric vehicle 100 comprises: a brake booster 23; a motor-driven vacuum pump 33; a motor 13; and a controller 50 which controls behavior of the motor 13 based on pressure PV of the brake booster 23, ambient pressure PA and vehicle speed. The controller 50 sets a vehicle speed limit based on differential pressure between the pressure PV of the brake booster 23 and the ambient pressure PA to regulate output of the motor 13 when the vehicle speed exceeds the vehicle speed limit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to vehicle speed control for an electric vehicle. [Background technology]

[0002] A vacuum-type brake booster is used in the braking system of a vehicle. In an electric vehicle, an electric vacuum pump is used as the vacuum source. This electric vacuum pump can be switched on and off as required (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a method for changing the vacuum level at which the electric vacuum pump of a vehicle's electric brake booster is stopped depending on the altitude, thereby preventing the electric vacuum pump from operating continuously when traveling at high altitudes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-522768 Summary of the Invention [Problem to be solved by the invention]

[0005] The electric vacuum pump is powered by the vehicle's battery. Therefore, if the power supply from the battery that drives the electric vacuum pump is stopped, the electric vacuum pump will stop. In this case, the brake pedal force cannot be amplified, and braking force may decrease.

[0006] Therefore, an object of the present disclosure is to safely stop an electric vehicle even when the power supply to an electric vacuum pump is stopped. [Means for solving the problem]

[0007] The electric vehicle disclosed herein is an electric vehicle comprising: a brake booster that amplifies the brake pedal force; an electric vacuum pump that evacuates the brake booster; a pressure sensor that detects the pressure of the brake booster; an atmospheric pressure sensor that detects atmospheric pressure; a motor for driving the vehicle; a vehicle speed sensor that detects vehicle speed; and a control unit that adjusts the operation of the motor based on the pressure of the brake booster detected by the pressure sensor, the atmospheric pressure detected by the atmospheric pressure sensor, and the vehicle speed detected by the vehicle speed sensor, wherein the control unit sets a vehicle speed limit based on the pressure difference between the pressure of the brake booster and the atmospheric pressure, and limits the output of the motor if the vehicle speed exceeds the vehicle speed limit.

[0008] This allows the vehicle speed to be controlled to a speed limit that corresponds to the braking force, and the electric vehicle can be stopped safely even if the power supply to the electric vacuum pump is cut off.

[0009] In the electric vehicle of the present disclosure, the control unit may set the vehicle speed limit lower as the pressure difference decreases.

[0010] As a result, when the pressure difference is small and the braking force is reduced, the vehicle speed is limited to a low level, so that the electric vehicle can be stopped safely even if the power supply to the electric vacuum pump is stopped.

[0011] In the electric vehicle of the present disclosure, a display may be provided, and when the atmospheric pressure drops and the differential pressure becomes smaller, and the control unit limits the output of the motor, the control unit may display on the display that the output of the motor is being limited due to high altitude driving.

[0012] This makes it possible to notify the driver that the motor output is being limited due to high altitude driving.

[0013] In the electric vehicle of the present disclosure, the control unit may include an electric vacuum pump control unit that adjusts the operation of the electric vacuum pump, and a motor control unit that is connected to the electric vacuum pump control unit and adjusts the operation of the motor, the electric vacuum pump control unit sets the vehicle speed limit based on the pressure of the brake booster detected by the pressure sensor and the atmospheric pressure detected by the atmospheric pressure sensor, and outputs the set vehicle speed limit to the motor control unit, the motor control unit limits the output of the motor when the vehicle speed exceeds the vehicle speed limit, and the electric vacuum pump control unit may set the vehicle speed limit so that the smaller the pressure difference is, the lower the vehicle speed limit.

[0014] In this way, the electric vacuum pump and the motor are controlled by two control units, so the control units can be distributed. [Effects of the Invention]

[0015] The present disclosure makes it possible to safely stop an electric vehicle even if the power supply to an electric vacuum pump is stopped. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a system diagram showing the configuration of an electric vehicle according to an embodiment; [Figure 2] 2 is a map that defines a vehicle speed limit relative to a pressure difference, which is stored in a memory of a control unit shown in FIG. 1; [Figure 3] 2 is a flowchart showing the operation of a control unit shown in FIG. [Figure 4] 2 is a graph showing the change in differential pressure and the change in vehicle speed limit with respect to time when the supply of power to the electric vacuum pump shown in FIG. 1 is stopped. [Figure 5] 2 is a graph showing changes in differential pressure and speed limit with respect to the altitude at which the electric vehicle shown in FIG. 1 travels. [Figure 6] FIG. 10 is a system diagram showing the configuration of an electric vehicle according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] An electric vehicle 100 according to an embodiment will be described below with reference to the drawings. As shown in Fig. 1, the electric vehicle 100 includes a battery 11, a power control unit 12 (hereinafter referred to as PCU 12), a motor 13 for driving the vehicle, and a control unit 50.

[0018] Battery 11 outputs DC power to PCU 12 for driving motor 13. PCU 12 converts the DC power input from battery 11 into AC power to drive motor 13. The output of motor 13 is transmitted to wheels 15 via axles 14. Control unit 50 is a computer that includes a CPU 51 that processes information and a memory 52 that stores control programs and control data. Control unit 50 operates PCU 12 to adjust the AC power supplied to motor 13 and adjust the output of motor 13.

[0019] A brake disc 16 is attached to the axle 14. A braking device 17 is disposed near the brake disc 16 to clamp the brake disc 16 and stop the electric vehicle 100. A vehicle speed sensor 18 is attached to the axle 14 to detect the vehicle speed V of the electric vehicle 100. The vehicle speed V detected by the vehicle speed sensor 18 is input to the control unit 50.

[0020] The electric vehicle 100 also includes a display 19 that displays information. The display 19 operates in response to a command from the control unit 50.

[0021] 1, the electric vehicle 100 has a brake system 20. The brake system 20 is composed of a brake pedal 21, a brake booster 23, a master cylinder 26, a reservoir tank 27, a vacuum tank 31, an electric vacuum pump 33, a pressure sensor 35, and an atmospheric pressure sensor 36.

[0022] The brake booster 23 is a vacuum booster that amplifies the force applied to the brake pedal 21 by using a vacuum generated by an electric vacuum pump 33. The brake booster 23 includes a diaphragm 24, an operating rod 22A, and a push rod 22B. The diaphragm 24 is provided inside the brake booster 23 and divides the interior of the brake booster 23 into a vacuum chamber 25A and an atmospheric chamber 25B. The operating rod 22A is located on the atmospheric chamber 25B side of the diaphragm 24 and is connected to the brake pedal 21. One end of the push rod 22B is connected to the operating rod 22A, and the other end is connected to a piston 26A located inside a master cylinder 26. The master cylinder 26 is connected to the braking device 17 by hydraulic piping 29. A reservoir tank 27 that stores hydraulic oil is attached to the top of the master cylinder 26.

[0023] A vacuum tank 31 is connected to the vacuum chamber 25A of the brake booster 23 via a vacuum tank connecting pipe 30. Furthermore, the vacuum tank 31 is connected to an electric vacuum pump 33 via a vacuum pump connecting pipe 32. The electric vacuum pump 33 is connected to an auxiliary battery 34. The electric vacuum pump 33 is supplied with driving power from the auxiliary battery 34. A pressure sensor 35 is attached to the vacuum tank connecting pipe 30. The pressure sensor 35 detects the pressure PV of the vacuum chamber 25A of the brake booster 23. An atmospheric pressure sensor 36 detects the atmospheric pressure PA. The voltage of the auxiliary battery 34, the pressure PV of the vacuum chamber 25A of the brake booster 23 detected by the pressure sensor 35, and the atmospheric pressure PA detected by the atmospheric pressure sensor 36 are input to a control unit 50. Furthermore, the electric vacuum pump 33 operates in response to commands from the control unit 50.

[0024] The basic operation of the brake system 20 will be briefly described below. The electric vacuum pump 33 is driven to evacuate the air in the vacuum tank 31, creating a vacuum in the vacuum tank 31. This creates a vacuum in the pressure PV of the vacuum chamber 25A and the atmospheric chamber 25B of the brake booster 23. When the driver depresses the brake pedal 21, an atmospheric valve (not shown) opens, allowing air to enter the atmospheric chamber 25B of the brake booster 23. This causes the pressure in the atmospheric chamber 25B to rise to atmospheric pressure PA. A pressure difference ΔP is then generated between the atmospheric pressure PA of the atmospheric chamber 25B and the pressure PV of the vacuum chamber 25A. This pressure difference ΔP applies a force to the push rod 22B that is greater than the pedal force. This force is then applied to the piston 26A of the master cylinder 26, increasing the internal hydraulic pressure. The pressurized hydraulic oil is sent to the brake device 17 through the hydraulic piping 29 and presses the brake pads of the brake device 17 against the brake disc 16. This slows down and stops the electric vehicle 100.

[0025] Next, with reference to FIG. 2, the map 55 stored in the memory 52 by the control unit 50 will be described. As shown in FIG. 2, the control unit 50 stores a map 55 that defines the vehicle speed limit VL relative to the pressure difference ΔP. Here, the vehicle speed limit VL is the speed at which the electric vehicle 100 can be stopped by the braking force of the brake system 20. As the pressure difference ΔP decreases, the amplification of the depression force of the brake pedal 21 by the brake booster 23 decreases, and the braking force decreases. Therefore, in the map 55 shown in FIG. 2, the vehicle speed limit VL decreases as the pressure difference ΔP decreases. As shown in FIG. 2, when the pressure difference ΔP is equal to or greater than a threshold value ΔP1, the vehicle speed limit VL is the maximum speed VL0 at which the electric vehicle 100 can travel. Therefore, when the pressure difference ΔP is equal to or greater than a threshold value ΔP1, the vehicle speed V is not limited. When the pressure difference ΔP is less than the threshold value ΔP1, the vehicle speed limit VL decreases as the pressure difference ΔP decreases.

[0026] Next, the operation of the control unit 50 will be described with reference to Fig. 3. As shown in step S101 of Fig. 3, the control unit 50 detects the atmospheric pressure PA using the atmospheric pressure sensor 36. Then, in step S102 of Fig. 3, the control unit 50 detects the pressure PV of the vacuum chamber 25A of the brake booster 23 using the pressure sensor 35. Then, in step S103 of Fig. 3, the control unit 50 calculates the differential pressure ΔP using the following equation 1. Differential pressure ΔP = atmospheric pressure PA - pressure in vacuum chamber 25A PV (Equation 1)

[0027] In step S104 of FIG. 3, the control unit 50 sets the vehicle speed limit VL corresponding to the pressure difference ΔP calculated in step S103 by referring to the map 55 shown in FIG. 2. Then, in step S105 of FIG. 3, the control unit 50 detects the vehicle speed V of the electric vehicle 100 from the vehicle speed sensor 18. In step S106 of FIG. 3, the control unit 50 determines whether the vehicle speed V exceeds the vehicle speed limit VL. If the control unit 50 determines YES in step S106 of FIG. 3, the control unit 50 proceeds to step S107 of FIG. 3. In step S107 of FIG. 3, the control unit 50 adjusts the PCU 12 to limit the power supplied to the motor 13 and reduces the output of the motor 13. Then, the control unit 50 proceeds to step S108 of FIG. 3. On the other hand, if the control unit 50 determines NO in step S106 of FIG. 3, the control unit 50 skips step S107 of FIG. 3 and proceeds to step S108 of FIG. 3 without reducing the output of the motor 13. The control unit 50 determines whether the electric vehicle 100 has stopped in step S108 of Fig. 3. If the control unit 50 determines YES in step S108 of Fig. 3, it ends the processing. On the other hand, if the control unit 50 determines NO in step S108 of Fig. 8, it returns to step S101 of Fig. 3 and repeatedly executes the operations of steps S101 to S108 of Fig. 3. In this way, the control unit 50 repeatedly executes the operations of steps S101 to S108 shown in Fig. 3 at every predetermined control period Δt until the electric vehicle 100 stops.

[0028] The output reduction rate of the motor 13 in one control period Δt can be set freely, but may be set to a constant rate relative to the output of the motor 13 at that time. Also, when the difference between the vehicle speed V and the limited vehicle speed VL is large, the output reduction rate may be set to be large, and when the difference between the vehicle speed V and the limited vehicle speed VL is small, the output reduction rate may be set to be small.

[0029] When the vehicle speed V exceeds the limit vehicle speed VL due to the above-described operation, the control unit 50 reduces the output of the motor 13 every control period Δt. Then, when the vehicle speed V becomes equal to or less than the limit vehicle speed VL, the control unit 50 stops reducing the output of the motor 13. In this way, the control unit 50 limits the output of the motor 13 so that the vehicle speed V becomes equal to or less than the limit vehicle speed VL.

[0030] Next, with reference to FIG. 4, the operation of the control unit 50 and changes in the pressure difference ΔP and vehicle speed limit VL when the power supply to the electric vacuum pump 33 is stopped will be described. When the power supply to the electric vacuum pump 33 is stopped, the electric vacuum pump 33 stops. If the vehicle continues to travel in this state, the pressure in the vacuum tank 31 increases and the degree of vacuum decreases each time the brake pedal 21 is depressed. Then, the pressure PV in the vacuum chamber 25A of the brake booster 23 increases. Meanwhile, the atmospheric pressure PA does not change. Therefore, as shown by the solid line A in FIG. 4, the pressure difference ΔP gradually decreases over time. However, until the pressure difference ΔP becomes less than the threshold value ΔP1 at time t1 shown in FIG. 4, the vehicle speed limit VL is maintained at the maximum speed VL0, and the control unit 50 does not limit the output of the motor 13.

[0031] When the pressure difference ΔP becomes less than the threshold value ΔP1 at time t1 shown in FIG. 4, the control unit 50 refers to the map 55 in FIG. 2 and starts to reduce the vehicle speed limit VL from the maximum speed VL0. Then, as shown by the dashed line B in FIG. 4, the control unit 50 sets the vehicle speed limit VL lower as the pressure difference ΔP decreases over time. Then, the control unit 50 limits the output of the motor 13 so that the vehicle speed V is equal to or less than the vehicle speed limit VL. For example, if the pressure difference ΔP becomes ΔP2 which is smaller than the threshold value ΔP1 at time t2, the control unit 50 sets the vehicle speed limit VL to VL2 which is lower than VL0. Then, the control unit 50 limits the output of the motor 13 so that the vehicle speed V is equal to or less than the vehicle speed limit VL2.

[0032] In this way, when the power supply to the electric vacuum pump 33 is stopped, the control unit 50 limits the output of the motor 13 so that the vehicle speed V of the electric vehicle 100 is equal to or lower than the limit vehicle speed VL that corresponds to the braking force. Therefore, the electric vehicle 100 can be stopped safely even when the power supply to the electric vacuum pump 33 is stopped.

[0033] Next, with reference to Figure 5, the operation of the control unit 50 when the elevation of the road on which the electric vehicle 100 travels increases will be described. As the elevation of the road on which the electric vehicle 100 travels increases, the atmospheric pressure PA decreases. For this reason, as shown by solid line C in Figure 5, the differential pressure ΔP decreases as the elevation increases. As with the operation previously described with reference to Figure 4, the vehicle speed limit VL is maintained at the maximum speed VL0, and the control unit 50 does not limit the output of the motor 13, until the differential pressure ΔP becomes less than the threshold value ΔP1 at the elevation H1 shown in Figure 5.

[0034] When the pressure difference ΔP becomes less than the threshold value ΔP1 at altitude H1 shown in FIG. 5, the control unit 50 starts reducing the vehicle speed limit VL, as indicated by the dashed line D in FIG. 5. Since the pressure difference ΔP becomes smaller as the altitude increases, the control unit 50 sets the vehicle speed limit VL lower as the altitude increases. Then, the control unit 50 limits the output of the motor 13 so that the vehicle speed V is equal to or less than the vehicle speed limit VL. For example, when the pressure difference ΔP becomes ΔP2 at altitude H2, the control unit 50 sets the vehicle speed limit VL to VL2. Then, the control unit 50 limits the output of the motor 13 so that the vehicle speed V is equal to or less than the vehicle speed limit VL2.

[0035] In this way, when the altitude at which the electric vehicle 100 is traveling increases and the atmospheric pressure PA decreases, causing the pressure difference ΔP to decrease, the control unit 50 limits the output of the motor 13 so that the vehicle speed V of the electric vehicle 100 is equal to or lower than the speed limit VL that matches the braking force. Therefore, the electric vehicle 100 can be stopped safely even when traveling on a road at a high altitude.

[0036] Furthermore, when the altitude at which the electric vehicle 100 is traveling becomes higher than H1 and the output of the motor 13 is limited, the control unit 50 may display on the display 19 that the output of the motor 13 is being limited due to traveling at high altitude. The display may be, for example, a message such as "Motor output limited due to traveling at high altitude," or a mark that evokes the image of high altitude and a speed limit. This notifies the driver that the output of the motor 13 is being limited, and draws the driver's attention.

[0037] As described above, the control unit 50 limits the output of the motor 13 so that the vehicle speed V is equal to or less than the limit vehicle speed VL that corresponds to the braking force. Therefore, even if the power supply to the electric vacuum pump 33 is stopped or the electric vehicle 100 is traveling at high altitude, the electric vehicle 100 can be stopped safely.

[0038] Next, an electric vehicle 200 according to another embodiment will be described with reference to Fig. 6. The same parts as those in the electric vehicle 100 previously described with reference to Figs. 1 to 5 will be assigned the same reference numerals, and description thereof will be omitted.

[0039] 6 is configured such that the control unit 50 of the electric vehicle 100 described above is made up of two control units: an electric vacuum pump control unit 60 and a motor control unit 65. The electric vacuum pump control unit 60 and the motor control unit 65 are connected via a CAN 70 to exchange information with each other.

[0040] As shown in Figure 6, the electric vacuum pump control unit 60 is a computer equipped with a CPU 61 for performing information processing and a memory 62 for storing control programs and control data. Data is input to the electric vacuum pump control unit 60 from the pressure sensor 35, atmospheric pressure sensor 36, and auxiliary battery 34. The electric vacuum pump control unit 60 adjusts the operation of the electric vacuum pump 33. The electric vacuum pump control unit 60 stores the map 55 shown in Figure 2 in the memory 62.

[0041] The motor control unit 65 is a computer that includes a CPU 66 that performs information processing and a memory 67 that stores control programs and control data. Data from the vehicle speed sensor 18 is input to the motor control unit 65. The motor control unit 65 adjusts the operation of the PCU 12 to adjust the operation of the motor 13. The motor control unit 65 also adjusts the display on the display 19.

[0042] When the electric vehicle 200 starts traveling, the electric vacuum pump control unit 60 executes steps S101 to S104 in Fig. 3 to set the vehicle speed limit VL, and then outputs the set vehicle speed limit VL to the motor control unit 65 via the CAN 70 (vehicle data bus).

[0043] The motor control unit 65 executes steps S105 to S108 in FIG. 3 based on the vehicle speed limit VL input from the electric vacuum pump control unit 60, and limits the output of the motor 13 when the vehicle speed V exceeds the vehicle speed limit VL.

[0044] The electric vacuum pump control unit 60 and the motor control unit 65 operate in cooperation with each other to perform operations similar to those of the control unit 50 of the electric vehicle 100. As a result, the electric vacuum pump control unit 60 and the motor control unit 65 can safely stop the electric vehicle 200 even when the power supply to the electric vacuum pump 33 is stopped or when the electric vehicle 200 is traveling at high altitude.

[0045] Furthermore, in the electric vehicle 200, the electric vacuum pump control unit 60 and the motor control unit 65 can be arranged separately, which increases the degree of freedom in layout design. [Explanation of symbols]

[0046] 11 battery, 12 PCU (voltage control unit), 13 motor, 14 axle, 15 wheel, 16 brake disc, 17 brake device, 18 vehicle speed sensor, 19 display, 20 brake system, 21 brake pedal, 22A operating rod, 22B push rod, 23 brake booster, 24 diaphragm, 25A vacuum chamber, 25B atmospheric chamber, 26 master cylinder, 26A piston, 27 reservoir tank, 29 hydraulic piping, 30 vacuum tank connecting pipe, 31 vacuum tank, 32 vacuum pump connecting pipe, 33 electric vacuum pump, 34 auxiliary battery, 35 pressure sensor, 36 atmospheric pressure sensor, 50 control unit, 51, 61, 66 CPU, 52, 62, 67 memory, 55 map, 60 electric vacuum pump control unit, 65 motor control unit, 100, 200 electric vehicle.

Claims

1. A brake booster that amplifies the force applied to the brake pedal, an electric vacuum pump for evacuating the brake booster; a pressure sensor for detecting the pressure of the brake booster; an atmospheric pressure sensor for detecting atmospheric pressure; a motor for driving the vehicle; a vehicle speed sensor for detecting a vehicle speed; a control unit that adjusts operation of the motor based on the pressure of the brake booster detected by the pressure sensor, the atmospheric pressure detected by the atmospheric pressure sensor, and the vehicle speed detected by the vehicle speed sensor, the control unit sets a vehicle speed limit based on a pressure difference between the pressure in the brake booster and the atmospheric pressure, and limits the output of the motor when the vehicle speed exceeds the vehicle speed limit; An electric vehicle characterized by:

2. The electric vehicle according to claim 1, the control unit sets the vehicle speed limit lower as the pressure difference becomes smaller; An electric vehicle characterized by:

3. The electric vehicle according to claim 2, Equipped with a display, when the control unit limits the output of the motor due to the decrease in the atmospheric pressure causing the pressure difference to become smaller, it displays on the display that the output of the motor is being limited due to high altitude traveling; An electric vehicle characterized by:

4. The electric vehicle according to claim 1, the control unit includes an electric vacuum pump control unit that adjusts the operation of the electric vacuum pump, and a motor control unit that is connected to the electric vacuum pump control unit and adjusts the operation of the motor, the electric vacuum pump control unit sets the vehicle speed limit based on the pressure of the brake booster detected by the pressure sensor and the atmospheric pressure detected by the atmospheric pressure sensor, and outputs the set vehicle speed limit to the motor control unit; the motor control unit limits the output of the motor when the vehicle speed exceeds the limited vehicle speed; the electric vacuum pump control unit sets the vehicle speed limit so that the smaller the pressure difference is, the lower the vehicle speed limit becomes; An electric vehicle characterized by:

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