Fuel cell vehicle

Abstract

To provide a fuel cell vehicle that has a fuel cell system with a compressor and that can suppress increase in internal pressure difference of a compressor 100 at accelerator-off.SOLUTION: A fuel cell vehicle comprises: a fuel cell stack that generates power for a traveling motor; a compressor that supplies air to the fuel cell stack; and a controller. The compressor comprises a motor that rotates an impeller. The controller reduces the rotation number of the motor when detecting accelerator-off. The controller reduces the rotation number at a first deceleration rate when an outlet pressure of the compressor is higher than a pressure threshold, and reduces the rotation number at a second deceleration rate lower than the first deceleration rate when the outlet pressure is lower than the pressure threshold.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The technology disclosed in this specification relates to fuel cell vehicles. [Background technology]

[0002] The fuel cell system includes a fuel cell stack and a compressor that supplies air to the fuel cell stack. The compressor rotates an impeller with a motor to compress the air. The compression chamber (impeller chamber) of the compressor and the motor housing are isolated by a mechanical seal, but if the internal pressure difference between the compression chamber and the motor housing is large, air or lubricating oil may leak through the mechanical seal. The fuel cell system disclosed in Patent Document 1 includes a pressure relief valve that releases pressure inside the motor housing. The fuel cell system disclosed in Patent Document 2 includes a release pipe that releases pressure inside the motor housing. A filter is attached to the release pipe. If the filter becomes clogged, air may not be able to escape from the motor housing. Patent Document 2 discloses a technology for predicting when to replace the filter. Patent Documents 1 and 2 disclose automobiles (fuel cell vehicles) equipped with fuel cell systems. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-113169 A [Patent Document 2] JP 2022-120320 A Summary of the Invention [Problem to be solved by the invention]

[0004] Fuel cell vehicles drive the traction motor with the power generated by the fuel cell stack. The target output of the traction motor, i.e., the target output of the fuel cell stack, frequently changes depending on the driver's accelerator work. The flow rate of air supplied to the fuel cell stack also changes depending on the accelerator work. In other words, the rotation speed of the compressor motor also depends on the accelerator work. If the accelerator work changes suddenly, the rotation speed of the compressor motor also changes suddenly. A sudden change in the rotation speed of the motor increases the internal pressure difference between the compression chamber (impeller chamber) of the compressor and the motor housing (especially when the above-mentioned pressure relief valve and release pipe do not function). If the pressure inside the motor housing becomes lower than the pressure in the compression chamber, the air in the compression chamber may leak into the motor housing. Conversely, if the pressure inside the motor housing becomes higher than the pressure in the compression chamber, the lubricating oil inside the motor housing may leak into the compression chamber. If the lubricating oil leaked into the compression chamber enters the fuel cell stack, it may damage the fuel cell stack.

[0005] When the driver's release of the accelerator is detected, the target output drops sharply, so the controller drops the motor speed sharply. At this time, the internal pressure difference between the compressor's compression chamber (impeller chamber) and the motor housing can become large. If the compressor motor speed is slowly lowered when the accelerator is released, the increase in the internal pressure difference can be suppressed. However, if the compressor motor speed is slowly lowered even when the accelerator is released, this can cause the driver to feel uncomfortable. This is because the driver expects the vehicle noise to decrease when the accelerator is released, but if the motor speed does not decrease quickly, noise and vibration will be transmitted to the driver. This specification provides a technology that suppresses the increase in the internal pressure difference when the accelerator is released without causing the driver to feel uncomfortable, and without relying on the above-mentioned pressure relief valve or release pipe. [Means for solving the problem]

[0006] The fuel cell vehicle disclosed in this specification includes a fuel cell stack, a compressor, and a controller. The fuel cell stack generates electricity for the drive motor. The compressor supplies air to the fuel cell stack. The compressor includes an impeller and a motor that rotates the impeller. The controller reduces the motor rotation speed when it detects that the accelerator is off. The controller reduces the motor rotation speed at a first deceleration rate if the compressor outlet pressure is higher than a pressure threshold, and reduces the motor rotation speed at a second deceleration rate if the outlet pressure is lower than the pressure threshold. The second deceleration rate is lower than the first deceleration rate. The lower the "deceleration rate," the more gradually the rotation speed decreases.

[0007] The controller quickly reduces the motor rotation speed (at a first deceleration rate) while the outlet pressure is high, so that the driver does not feel uncomfortable immediately after the accelerator is released. After the outlet pressure drops to the pressure threshold, the controller slowly reduces the motor rotation speed (at a second deceleration rate). Therefore, the pressure inside the motor housing drops gradually, and the pressure difference between the compression chamber and the motor housing does not increase suddenly. The fuel cell vehicle disclosed in this specification can suppress the increase in the internal pressure difference (the internal pressure difference between the compression chamber and the motor housing) when the accelerator is released, without causing the driver to feel uncomfortable.

[0008] When the temperature of the lubricating oil in the compressor is lower than a predetermined temperature threshold, the controller reduces the rotation speed of the air compressor at a first deceleration rate if the outlet pressure of the air compressor is higher than the pressure threshold, and reduces the rotation speed at a second deceleration rate if the outlet pressure is lower than the pressure threshold. On the other hand, when the temperature of the lubricating oil is higher than the temperature threshold, the controller may reduce the rotation speed of the motor at the first deceleration rate even if the outlet pressure is lower than the pressure threshold. Lubricating oil with a high temperature has a lower viscosity. Lubricating oil with a low viscosity is more likely to release air bubbles. The released air bubbles escape through an open tube that releases pressure in the motor case. Therefore, the internal pressure of the motor case is less likely to increase. By reducing the motor rotation speed at the first deceleration rate at high temperatures when the internal pressure of the motor case is less likely to increase, the discomfort felt by the driver can be further reduced.

[0009] The pressure threshold may be determined to depend on the rotation speed of the compressor motor. If the pressure loss in the air flow path between the compressor and the fuel cell stack is large, the outlet pressure will be high even if the motor rotation speed is low. On the other hand, if the pressure loss in the air flow path is small, the outlet pressure is unlikely to be high even if the motor rotation speed is high. The relationship between the outlet pressure and the rotation speed changes depending on the pressure resistance of the air flow path. Therefore, an appropriate pressure threshold can be set by changing the pressure threshold depending on the motor rotation speed.

[0010] The first deceleration rate may be set to a maximum deceleration rate. By quickly reducing the motor rotation speed until the outlet pressure reaches the pressure threshold, the driver does not feel uncomfortable when the accelerator is released.

[0011] Details and further improvements of the technology disclosed in this specification are described in the following "Forms for Carrying Out the Invention". [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a block diagram of a power system of a fuel cell vehicle. [Diagram 2] FIG. [Diagram 3] 4 is a flowchart of a motor rotation speed control when the accelerator is released. [Figure 4] 4 is a time chart of the rotation speed, the flow rate, and the outlet pressure when the accelerator is released. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A fuel cell vehicle 2 according to an embodiment will be described with reference to the drawings. FIG. 1 shows a block diagram of the power system of the fuel cell vehicle 2. Hereinafter, for ease of explanation, "fuel cell" may be written as "FC." A "fuel cell vehicle" and a "fuel cell stack" will be written as "FC vehicle" and "FC stack," respectively.

[0014] The FC vehicle 2 drives a traction motor 13 with power generated by the FC stack 10. The output power of the FC stack 10 is boosted by a boost converter 11 and then supplied to an inverter 12. The inverter 12 converts the boosted DC power into AC power suitable for driving the traction motor 13.

[0015] A battery 14 is also connected to the DC terminal of the inverter 12. The battery 14 supplements the output power of the FC stack 10. The battery 14 is also charged with surplus power from the FC stack 10.

[0016] As is well known, the FC stack 10 generates electricity by reacting hydrogen (fuel) with oxygen (air). Hydrogen gas is supplied to the FC stack 10 from a hydrogen tank 20 through a fuel pipe 21. Hydrogen gas remaining from the reaction in the FC stack 10 is separated in a gas-liquid separator 23 and returned to the fuel pipe 21. The water and exhaust gas separated in the gas-liquid separator 23 are released outside the vehicle via a muffler 24. The fuel pipe 21 is equipped with several pressure sensors, various valves, and injectors, but these are not shown in the figure.

[0017] The FC vehicle 2 takes in air from outside the vehicle and supplies the air (oxygen) to the FC stack 10. The compressor 100 compresses the outside air and supplies it to the FC stack 10. The compressor 100 is equipped with a motor 110 (electric motor 110). A refrigerant pipe 102 also passes through the compressor 100. The refrigerant passing through the refrigerant pipe 102 cools the lubricant oil inside the compressor 100. The refrigerant pipe 102 is equipped with a temperature sensor 101. The temperature sensor 101 measures the temperature of the refrigerant that has passed through the compressor 100. The measurement value of the temperature sensor 101 is used as the temperature of the lubricant oil (an approximation of the temperature of the lubricant oil). The structure of the compressor 100 will be explained in detail later with reference to FIG. 2.

[0018] An air pipe 31 is connected to the outlet of the compressor 100, and the air pipe 31 is equipped with a pressure sensor 39. The pressure sensor 39 measures the outlet pressure (compressed air pressure) of the compressor 100. The outlet of the compressor 100 is connected to the FC stack 10 via the air pipe 31. Air is supplied from the compressor 100 to the FC stack 10 via the air pipe 31. A stop valve 34 is provided in the air pipe 31. When the FC stack 10 is stopped, the stop valve 34 is closed.

[0019] An air pipe 32 is connected to the air outlet of the FC stack 10. The air pipe 32 is equipped with a pressure regulating valve 35. A bypass pipe 33 is connected to the air pipe 31, and the bypass pipe 33 is connected to the air pipe 32. The bypass pipe 33 is equipped with a flow dividing valve 36. When the flow dividing valve is opened, part of the air from the compressor 100 bypasses the FC stack 10 and flows to the muffler 24.

[0020] A pressure regulating valve 35 and a flow dividing valve 36 adjust the flow rate of air supplied to the FC stack 10. When the target output of the FC stack 10 (i.e. the target output of the traction motor 13) is high, the controller 40 increases the output of the compressor 100 and throttles the pressure regulating valve 35 to increase the air pressure inside the FC stack 10. Increasing the air pressure inside the FC stack 10 increases the reaction efficiency inside the FC stack 10. In other words, the output of the FC stack 10 increases.

[0021] When the target output of the FC stack 10 (i.e. the target output of the traction motor 13) is low, the controller 40 reduces the output of the compressor 100 and opens the diverter valve 36 to reduce the amount of air supplied to the FC stack 10.

[0022] By adjusting the pressure regulating valve 35 and the flow dividing valve 36, the internal pressure of the FC 10, that is, the outlet pressure of the compressor 100, changes.

[0023] 1 represent signal lines, and the measurement value (accelerator opening) of accelerator pedal sensor 41 is sent to controller 40. Controller 40 determines the target output of traction motor 13 (target output of FC stack 10) from the accelerator opening and vehicle speed, and controls FC stack 10, boost converter 11, inverter 12, and compressor 100 so as to realize the target output.

[0024] The measured values ​​of the pressure sensor 39 and the temperature sensor 101 are also sent to the controller 40. The controller 40 controls the compressor 100 based also on the measured values ​​of the pressure sensor 39 and the temperature sensor 101. In particular, when an "accelerator off" is detected, the controller 40 controls the motor 110 of the compressor 100 so as to prevent compressed air from being sucked into the motor housing of the compressor 100. "Accelerator off" is detected when the driver releases the accelerator pedal. "Accelerator off" means a state in which the accelerator opening is zero.

[0025] 2 shows a cross-sectional view of the compressor 100. The compressor 100 compresses air by rotating an impeller 120 with a motor 110 (electric motor 110). Air entering from an inlet 131 of the compressor is compressed by the impeller 120 and discharged from an outlet 132 of the compressor (compressed air outlet). The compressed air is supplied to the FC stack 10 through an air pipe 31.

[0026] The motor 110 is composed of a shaft 111, a rotor core 112, and a stator 113. The motor 110 is accommodated in a motor housing 130. The stator 113 is fixed inside the motor housing 130. The rotor core 112 is fixed to the shaft 111. The shaft 111 is rotatably supported by the motor housing 130 via a bearing 137.

[0027] An oil pump 150 is attached to the rear end of the shaft 111. The oil pump 150 pumps up the lubricating oil accumulated at the bottom of the motor housing 130 and supplies it to the oil passage 135. Several nozzles 136 are provided in the oil passage 135. The nozzles 136 are located above the motor 110. The lubricating oil pumped up by the oil pump 150 is sprayed onto the motor 110 to cool it.

[0028] The oil pump 150 rotates in synchronization with the shaft 111. That is, as the rotation speed of the motor 110 increases, the amount of oil discharged from the oil pump 150 also increases. When the motor 110 stops, the oil pump 150 also stops.

[0029] Another type of motor 110 pumps lubricating oil inside the shaft 111 to cool the rotor core 112 .

[0030] The shaft 111 extends into the compression chamber 134 through a through hole 133 of the motor housing 130. An impeller 120 is fixed to an end of the shaft 111 in the compression chamber 134. A gap between the shaft 111 and the through hole 133 is sealed by a mechanical seal 140. The mechanical seal 140 includes a fixed ring 142 and a rotating ring 141. The fixed ring 142 is attached to the inner peripheral surface of the through hole 133, and the rotating ring 141 is attached to the shaft 111. The rotating ring 141 is a rubber disk, and rotates together with the shaft 111 while the outer peripheral edge of the rotating ring 141 contacts the inner peripheral surface of the fixed ring 142. The mechanical seal 140 seals the gap between the shaft 111 and the through hole 133 while allowing the shaft 111 to rotate.

[0031] The mechanical seal 140 separates the internal space of the compression chamber 134 from that of the motor housing 130. However, the rotating ring 141 may be deformed due to the internal pressure difference between the compression chamber 134 and the motor housing 130, and a gap may occur between the rotating ring 141 and the fixed ring 142. Due to the internal pressure difference (the internal pressure difference between the compression chamber 134 and the motor housing 130), air in the compression chamber 134 may leak into the motor housing 130 through the mechanical seal 140. In addition, when the internal pressure of the motor housing 130 becomes higher than the internal pressure of the compression chamber 134, lubricating oil may leak from the motor housing 130 to the compression chamber 134 through the mechanical seal 140. In the following, for ease of explanation, the "internal pressure difference between the compression chamber 134 and the motor housing 130" may be simply referred to as the "internal pressure difference."

[0032] A group of gears may be provided between the shaft 111 and the impeller 120. Since it is desired to provide lubricating oil to the group of gears, the group of gears is also housed in the motor housing 130. Even when the group of gears is provided, the mechanical seal 140 separates the compression chamber 134 from the internal space of the motor housing 130. When the group of gears is disposed next to the mechanical seal 140, the lubricating oil sprayed onto the group of gears also adheres to the mechanical seal 140. In this case in particular, the lubricating oil is likely to leak into the compression chamber 134 when the internal pressure of the motor housing 130 is high.

[0033] A breather pipe 160 is provided in the motor housing 130. The breather pipe 160 communicates between the inside and outside of the motor housing 130. When the internal pressure of the motor housing 130 becomes excessively high, air is released from the breather pipe 160. The breather pipe 160 is provided with a filter 161 that prevents foreign matter from entering the motor housing 130.

[0034] The internal pressure of the motor housing 130 is maintained close to atmospheric pressure because air can enter and exit through the breather pipe 160. However, the internal pressure difference may increase due to clogging of the filter 161 or a sudden change in the internal pressure of the motor housing 130.

[0035] Since the rotating ring 141 slides against the fixed ring 142 of the mechanical seal 140 described above, air and lubricating oil may pass between the compression chamber 134 and the motor housing 130. If the rotation speed of the motor 110 is constant, the internal pressure of the compression chamber 134 and the internal pressure of the motor housing 130 are balanced, and little air or lubricating oil flows in or out. If the rotation speed of the motor 110 changes slowly, the internal pressure difference also changes slowly, and little air or lubricating oil passes through the mechanical seal 140.

[0036] When the rotation speed of the motor 110 suddenly drops and the internal pressure of the motor housing 130 becomes excessively lower than the internal pressure of the compression chamber 134, compressed air leaks from the compression chamber 134 to the motor housing 130 through the mechanical seal 140. If the internal pressure of the motor housing 130 then becomes higher than the internal pressure of the compression chamber 134 for some reason, lubricating oil may leak from the motor housing 130 to the compression chamber 134 through the mechanical seal 140 together with the air. The lubricating oil that has entered the compression chamber 134 enters the FC stack 10 together with the compressed air. The lubricating oil may damage the FC stack 10. Typical cases in which the internal pressure of the motor housing 130 becomes higher than the internal pressure of the compression chamber 134 are when the rotation speed of the motor 110 suddenly increases and during the latter half of the accelerator-off period. The change in the internal pressure difference when the accelerator is off will be explained later.

[0037] As described above, when the rotation speed of the motor 110 changes gradually, the internal pressure difference between the compression chamber 134 and the motor housing 130 does not become large. The internal pressure difference becomes large when the rotation speed of the motor 110 changes suddenly. Conventionally, when the accelerator is released and the controller 40 detects that the accelerator is off, the controller 40 stops the motor 110 of the compressor 100 to stop the output of the FC stack 10. When the motor 110 is stopped, the oil pump 150 stops and the internal pressure of the motor housing 130 drops suddenly. On the other hand, the compression chamber 134 is connected to the FC stack 10 via the air pipe 31, and the internal pressure of the compression chamber 134 does not drop suddenly. When the motor 110 is suddenly stopped, the internal pressure of the motor housing 130 becomes significantly lower than the internal pressure of the compression chamber 134, and compressed air flows from the compression chamber 134 into the motor housing 130 through the mechanical seal 140.

[0038] If the breather pipe 160 is clogged, the internal pressure of the motor housing 130 is maintained at a level higher than atmospheric pressure. In the latter half of the accelerator-off period, the internal pressure of the compression chamber 134 drops to atmospheric pressure. Then, the internal pressure of the motor housing 130 becomes higher than the internal pressure of the compression chamber 134, and lubricating oil together with air may leak from the motor housing 130 to the compression chamber 134 through the mechanical seal 140.

[0039] One method of suppressing the increase in the internal pressure difference (the internal pressure difference between the compression chamber 134 and the motor housing 130) when the accelerator is released is to gradually reduce the rotation speed of the motor 110 when the accelerator is released. However, when the driver releases the accelerator, he or she expects the motor (the travel motor 13 and the motor 110 of the compressor 100) to quickly quiet down. However, if the rotation speed of the motor 110 does not quickly decrease when the accelerator is released, vibrations and noise are transmitted to the driver, which may cause the driver to feel uncomfortable. In other words, the driving feeling of the FC vehicle 2 is deteriorated. The FC vehicle 2 of the embodiment can suppress the increase in the internal pressure difference when the accelerator is released while minimizing the discomfort felt by the driver.

[0040] When the rotation speed of the motor 110 is gradually reduced, vibration and noise occur when the internal pressure of the air pipe 31, i.e., the outlet pressure of the compressor 100, is high. On the other hand, there is a time lag between the time when the rotation speed of the motor 110 is rapidly reduced and the time when the internal pressure difference starts to increase. Therefore, when the controller 40 detects the accelerator being released, if the outlet pressure of the compressor is higher than the pressure threshold, the controller reduces the rotation speed at a first deceleration rate. When the outlet pressure becomes lower than the first threshold, the controller reduces the rotation speed at a second deceleration rate lower than the first deceleration rate. The higher the deceleration rate, the faster the rotation speed decreases. By reducing the rotation speed quickly while the outlet pressure is high, noise and vibration can be suppressed. By reducing the rotation speed slowly after the outlet pressure becomes low, air leakage from the compression chamber 134 to the motor housing 130 (i.e., the increase in the internal pressure difference) can be suppressed.

[0041] The controller 40 uses the measured values ​​of the pressure sensor 39 and the temperature sensor 101 to suppress the increase of the internal pressure difference when the accelerator is released. As described above, the air pipe 31 is connected to the outlet of the compression chamber 134, and the air pipe 31 is provided with the pressure sensor 39. The pressure sensor 39 measures the air pressure (outlet pressure) at the outlet 132 of the compressor 100. As described above, the refrigerant pipe 102 passes through the compressor 100, and the temperature sensor 101 is provided on the refrigerant pipe 102. The temperature sensor 101 measures the temperature of the refrigerant that cools the lubricant. However, the measured value of the temperature sensor 101 is used as the temperature of the lubricant (an approximation of the temperature of the lubricant). In FIG. 2, the temperature sensor 101 is drawn in the lubricant accumulated at the bottom of the motor housing 130 to indicate that the measured value of the temperature sensor 101 corresponds to the temperature of the lubricant.

[0042] 3 shows a flowchart of the motor rotation speed control executed by the controller 40 when the controller 40 detects the accelerator release. The process of FIG. 3 is started when the controller 40 detects the accelerator release. The controller 40 detects the accelerator release from the measurement value of the accelerator pedal sensor 41.

[0043] If the temperature of the lubricant is higher than the temperature threshold, the controller 40 reduces the rotation speed of the motor 110 at a first deceleration rate (step S2: YES, S4). The first deceleration rate corresponds to the maximum deceleration rate of the motor 110.

[0044] When the temperature of the lubricating oil is high, the viscosity of the lubricating oil decreases, and the lubricating oil is more likely to release air bubbles. The released air bubbles escape through the pressure relief pipe. Therefore, when the temperature of the lubricating oil is high, the internal pressure of the motor housing 130 is less likely to become high. In such a case, the controller 40 reduces the rotation speed at the first deceleration rate regardless of the value of the outlet pressure.

[0045] If the temperature of the lubricant is lower than the temperature threshold and the outlet pressure is higher than the predetermined pressure threshold, the controller 40 reduces the rotation speed at the first deceleration rate (steps S2: NO, S3: YES, S4). On the other hand, if the temperature of the lubricant is lower than the temperature threshold and the outlet pressure is lower than the predetermined pressure threshold, the controller 40 reduces the rotation speed at the second deceleration rate (steps S2: NO, S3: NO, S5). The second deceleration rate is set to a value lower than the first deceleration rate. As described above, while the outlet pressure is high, the rotation speed is quickly reduced at the first deceleration rate. This makes it difficult for vibration and noise to occur, and does not give the driver a sense of discomfort. When the outlet pressure becomes low, the rotation speed is gradually reduced at the second deceleration rate. This prevents the internal pressure difference between the compression chamber 134 and the motor housing 130 from increasing.

[0046] It is preferable to employ step S2, but it is not necessary.

[0047] The controller 40 continues to reduce the rotation speed until the accelerator is pressed again (step S6: YES) or until the rotation speed of the motor 110 becomes zero (step S7: NO). After the accelerator is pressed again, the controller 40 controls the rotation speed of the motor 110 of the compressor 100 according to the target output of the travel motor 13 (the target output of the FC stack 10).

[0048] An example of changes in the rotation speed, flow rate, and outlet pressure of the compressor 100 when the accelerator is released is shown with reference to Fig. 4. Fig. 4 also shows the internal pressure of the motor housing 130 and the internal pressure difference (internal pressure difference between the compression chamber 134 and the motor housing 130). The solid line graph in Fig. 4 shows the results of control based on the flowchart in Fig. 3. The dashed line in Fig. 4 shows the results (comparative example) when the rotation speed is always reduced at the first deceleration rate when the accelerator is released.

[0049] Fig. 4(1) shows the change in accelerator opening. Fig. 4(2) shows the change in the rotation speed of the motor 110 (i.e., the rotation speed of the impeller 120). Fig. 4(3) shows the change in the amount of compressed air (discharge amount) discharged by the compressor 100. Fig. 4(4) shows the change in the outlet pressure of the compressor 100. Fig. 4(5) shows the internal pressure of the motor housing 130.

[0050] FIG. 4(6) shows the internal pressure difference. In FIG. 4(6), in the region above zero, the internal pressure of the compression chamber 134 is lower than the internal pressure of the motor housing 130. In the region below zero, the internal pressure of the compression chamber 134 is higher than the internal pressure of the motor housing 130. Below zero, there is a first limit point. When the internal pressure difference is lower than the first limit point (indicated by arrow A in FIG. 4(6)), air can leak from the compression chamber 134 to the motor housing 130. Above zero, there is a second limit point. When the internal pressure difference is higher than the second limit point (indicated by arrow B in FIG. 4(6)), air can leak from the motor housing 130 to the compression chamber 134.

[0051] Even during normal operation, air leaks from the compression chamber 134 to the motor housing 130. The leaked air is discharged to the outside through the breather pipe 160, so that the internal pressure difference is unlikely to become large during normal operation.

[0052] When the accelerator is released, the internal pressure in the motor housing 130 increases rapidly, causing a large internal pressure difference, which may exceed the sealing capacity of the mechanical seal 140. That is, the internal pressure difference exceeds the second limit point. When the internal pressure difference reaches the second limit point, a mixture of air and lubricating oil leaks into the compression chamber 134. By gradually reducing the rotation speed of the motor 110 of the compressor 100 (that is, by reducing the rotation speed at the second deceleration rate), it is possible to prevent the internal pressure difference from reaching the second limit point.

[0053] It should be noted that the graph in FIG. 4 is a schematic representation of the change in the internal pressure difference between the compression chamber 134 and the motor housing 130, and is not an experimental result.

[0054] In the example of Fig. 4, the controller 40 detects that the accelerator is off at time T1. Until time T1, the controller 40 controls the rotation speed of the motor 110 of the compressor 100 in accordance with changes in the accelerator opening. If the accelerator opening changes slowly, the rotation speed of the motor 110 also changes slowly, and the internal pressure difference between the compression chamber 134 and the motor housing 130 also changes slowly. In other words, before time T1, the graph in Fig. 4(6) is maintained near zero.

[0055] After time T1 when accelerator release is detected, the controller 40 reduces the rotation speed of the motor 110 at a first deceleration rate. As the rotation speed decreases, the air discharge amount (FIG. 4(3)) and the outlet pressure (FIG. 4(4)) also decrease. When the rotation speed decreases, the rotation of the oil pump 150 also decreases, and the internal pressure of the motor housing 130 decreases.

[0056] At time T2, the outlet pressure drops to the pressure threshold value. In the comparative example, even if the outlet pressure drops below the pressure threshold value, the rotation speed of the motor 110 continues to be reduced at the first deceleration rate. If the rotation speed of the motor 110 continues to be reduced at the first deceleration rate, the rotation speed will reach zero at time T3 (dashed line graph in FIG. 4(2)). The air discharge amount becomes zero at time T3 (dashed line graph in FIG. 4(3)). Meanwhile, as described above, due to the large pressure loss in the flow path from the compression chamber 134 to the FC stack 10 (pressure regulating valve 35), the outlet pressure drops to atmospheric pressure at time T4.

[0057] When the outlet pressure falls to the pressure threshold, the controller 40 of the embodiment reduces the rotation speed of the motor 110 at a second deceleration rate. The solid line graph in Figure 4 shows the change at this time. After time T2, the rotation speed gradually decreases, and the amount of air discharged also gradually decreases. Since the air continues to be compressed in the compression chamber 134 after time T2, the outlet pressure decreases even more gradually.

[0058] If the accelerator is pressed again after the accelerator is released and before the rotation speed of the motor 110 reaches zero, the rotation speed of the motor 110 increases, causing an increase in the internal pressure of the motor housing 130. Therefore, in this case as well, the compressor 100 of the embodiment can be expected to have the effect of suppressing the increase in the internal pressure difference.

[0059] Points to note regarding the technology described in the embodiment are as follows: The outlet pressure may be measured in units of Pascals [Pa] or as a ratio to atmospheric pressure.

[0060] The outlet of the compressor 100 is connected to air pipes 31 and 32 and the FC stack 10, and the air pipe 32 is equipped with a pressure regulating valve 35. The pressure loss in the flow path beyond the outlet of the compressor 100 can change depending on the opening degree of the pressure regulating valve 35. Therefore, even if the rotation speed of the motor 110 is constant, the outlet pressure can change. The pressure threshold value may be determined to change depending on the rotation speed of the motor 110.

[0061] The compressor 100 of the embodiment includes a compression chamber 134 in which an impeller 120 is housed and in which air is compressed by the rotation of the impeller 120, and a motor housing 130 in which a motor 110 is housed. The compression chamber 134 and the motor housing 130 are in communication with each other, and a shaft 111 passes through the communication portion. A gap between the compression chamber 134 and one of the through holes of the motor housing 130 and the shaft is sealed with a seal part (mechanical seal 140). The compressor 100 may be of any of a turbo type, a centrifugal type, and a scroll type. In the case of a scroll type, the impeller 120 of the embodiment corresponds to the scroll.

[0062] The compressor 100 includes an oil pump 150 that operates in synchronization with the motor 110. As the output of the oil pump 150 increases (as the rotation speed increases), the internal pressure of the motor housing 130 increases.

[0063] The term "traction motor" refers to an electric motor that is driven by the output power of the fuel cell stack 10 and is used to drive the wheels.

[0064] The controller 40 reduces the rotation speed of the motor 110 at a first deceleration rate if the outlet pressure of the compressor 100 is higher than a pressure threshold, and reduces the rotation speed at a second deceleration rate (<first deceleration rate) if the outlet pressure is lower than the pressure threshold. There is a predetermined relationship between the outlet pressure and the rotation speed. Therefore, "if the outlet pressure is higher than the pressure threshold" is equivalent to the expression "if the rotation speed of the motor 110 is higher than a predetermined rotation speed threshold." Similarly, "if the outlet pressure is lower than the pressure threshold" is equivalent to the expression "if the rotation speed of the motor 110 is lower than a predetermined rotation speed threshold."

[0065] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. The technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0066] 2: Fuel cell vehicle 10: Fuel cell stack 11: Boost converter 12: Inverter 13: Driving motor 14: Battery 20: Hydrogen tank 21: Fuel pipe 23: Gas-liquid separator 24: Muffler 31, 32: Air pipe 33: Bypass pipe 34: Stop valve 35: Pressure regulator valve 36: Flow divider valve 39: Pressure sensor 40: Controller 41: Accelerator pedal sensor 100: Compressor 101: Temperature sensor 110: Electric motor 111: Shaft 112: Rotor core 113: Stator 120: Impeller 130: Motor housing 131: Inlet 132: Outlet 133: Through hole 134: Compression chamber 135: Oil passage 136: Nozzle 137: Bearing 140: Mechanical seal 141: Rotating ring 142: Fixed ring 150: Oil pump 160: Breather pipe 161: Filter

Claims

1. a fuel cell stack that generates power for the drive motor; a compressor for supplying air to the fuel cell stack, the compressor including an impeller and a motor for rotating the impeller; a controller that reduces the rotation speed of the motor when it detects that the accelerator is off; Equipped with The controller reduces the rotational speed at a first deceleration rate if the outlet pressure of the compressor is higher than a pressure threshold, and reduces the rotational speed at a second deceleration rate lower than the first deceleration rate if the outlet pressure is lower than the pressure threshold.

2. The controller: When the temperature of the lubricating oil of the compressor is lower than a predetermined temperature threshold, the rotation speed is reduced at the first deceleration rate if the outlet pressure is higher than the pressure threshold, and the rotation speed is reduced at the second deceleration rate if the outlet pressure is lower than the pressure threshold; The fuel cell vehicle according to claim 1 , wherein when the temperature of the lubricant oil is higher than the temperature threshold, the rotation speed is reduced at the first deceleration rate even if the outlet pressure is lower than the pressure threshold.

3. 3. The fuel cell vehicle according to claim 1, wherein the pressure threshold value depends on a rotation speed of the motor when the accelerator release is detected.

4. 3. The fuel cell vehicle according to claim 1, wherein the first deceleration rate is set to a maximum deceleration rate.

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