JP7582228B2 - Fuel tank pressure control device - Google Patents

Description

The present invention relates to a fuel tank pressure control device.

Fuel tank pressure control devices are known that control the internal pressure of a fuel tank in order to prevent vapor (evaporated fuel) generated in the fuel tank of a vehicle such as an automobile from being released into the atmosphere.

Patent document 1 discloses an internal pressure control device for a fuel tank, which includes a fuel tank with a fuel pump installed inside, a vapor conduit installed between the fuel tank and a canister to guide fuel vapor generated in the fuel tank to a canister, a control valve installed midway through the vapor conduit and controlling the opening and closing of the flow path of the vapor conduit, a surge tank located midway through the vapor conduit between the control valve and the fuel tank and for temporarily storing vapor generated in the fuel tank, a pressure sensor for detecting the pressure in the surge tank, a temperature sensor for detecting the fuel temperature in the fuel tank, an altitude sensor for detecting the altitude when driving at high altitudes, and a valve opening/closing means for normally opening the control valve and closing the control valve when the values detected by the altitude sensor and temperature sensor are equal to or greater than a predetermined value and the value detected by the pressure sensor is equal to or less than a predetermined value.

Japanese Patent Application Publication No. 2-99755

The technology described in Patent Document 1 closes the control valve between the surge tank and the canister to increase the internal pressure of the fuel tank when the internal pressure of the surge tank falls below a specified value during high altitude driving. This prevents the boiling point of the fuel in the fuel tank from dropping as the air pressure drops, resulting in the generation of a large amount of vapor.

However, in the technology described in Patent Document 1, when the control valve is closed when the internal pressure of the fuel tank is lower than a certain predetermined value, the predetermined value must be set sufficiently high to suppress vapor generation regardless of altitude or fuel temperature. This can result in the internal pressure of the fuel tank being increased more than necessary relative to the actual amount of vapor generated. This can result in a problem of risk of compromising the reliability of the fuel tank.

The present invention has been made to solve these problems, and aims to provide a fuel tank pressure control device that can ensure the reliability of the fuel tank while suppressing the generation of vapor.

The fuel tank pressure control device according to one embodiment includes a pump scavenging speed estimation unit that estimates a pump scavenging speed, which is the speed at which vapor is scavenged by a feed pump that scavenges vapor from fuel drawn into the fuel tank that stores the fuel; a vapor generation speed estimation unit that estimates a vapor generation speed, which is the speed at which vapor is generated in the fuel tank; and a control unit that controls at least one of the vapor generation speed and the pump scavenging speed so that the vapor generation speed is equal to or lower than the pump scavenging speed when it is predicted that the vapor generation speed will be greater than the pump scavenging speed.

The present invention provides a fuel tank pressure control device that can suppress vapor generation while ensuring the reliability of the fuel tank.

1 is a diagram showing a configuration of a vehicle on which a pressure control device according to a first embodiment is mounted; 4 is a flowchart illustrating a process of controlling the amount of vapor in the tank by the pressure control device. FIG. 4 is a diagram illustrating fuel vapor pressure characteristics before and after climbing a slope. FIG. 4 is a diagram illustrating a process for calculating a vapor generation rate. FIG. 13 is a diagram showing a map for calculating Vpump. 4 is a graph showing changes in feed fuel pressure over time. FIG. 4 is a diagram illustrating control of a pump rotation speed. 5A and 5B are diagrams illustrating a reduction control of the tank internal pressure. FIG. 2 is a vapor pressure curve of a fuel.

First embodiment
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment. In addition, in order to clarify the description, the following description and drawings are appropriately simplified. What is shown in the drawings is only a part of the whole, and in reality, many other configurations that are not shown are included. Furthermore, in the following description, the same or equivalent elements are given the same reference numerals, and duplicated descriptions are omitted.

As one preferred embodiment of the fuel tank pressure control device according to this embodiment, a pressure control device for a vehicle fuel tank that can be used to construct a closed tank system will be specifically described. The pressure control device according to this embodiment is installed in various vehicles that run using power from an internal combustion engine 22, hybrid vehicles that have a rotating electric machine in addition to the internal combustion engine 22, or plug-in hybrid vehicles.

First, the configuration of the fuel tank pressure control device according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a diagram showing the configuration of a vehicle in which the pressure control device according to the first embodiment is installed. Note that FIG. 1 shows the main parts of the vehicle related to the pressure control device.

The fuel tank 14 that stores the fuel F is a sealed pressure-resistant tank, and is made of, for example, a metal or resin tank. When refueling, the internal pressure of the fuel tank 14 (tank internal pressure) is reduced in advance to prevent vapor from being released into the atmosphere. The fuel tank 14 is connected to a fuel supply pipe 35 that has a fuel supply port at one end. The fuel tank 14 also includes a tank internal pressure sensor 34, a feed pump 36, and a fuel gauge 38.

The feed pump 36 pressure-feeds the fuel F through a fuel supply pipe 40 to an injector 42 for injecting the fuel F. The fuel F pressure-feeds to the injector 42 is supplied from the injector 42 to the internal combustion engine 22. The feed pump 36 has a fuel intake port that draws in the fuel F in the fuel tank 14 and the vapor in the fuel F, a fuel outlet port that discharges the fuel F drawn into the feed pump 36, and a vapor outlet port that discharges the vapor drawn into the feed pump 36.

At least a portion of the vapor sucked into the feed pump 36 is compressed in the feed pump 36 to become liquid-phase fuel F, which is then discharged from the fuel outlet. Vapor that is not compressed in the feed pump 36 is discharged from the vapor outlet into the fuel tank 14 as gas-phase vapor. In this way, the feed pump 36 supplies the fuel F sucked from the fuel tank 14 to the internal combustion engine 22, and scavenges the vapor sucked from the fuel tank 14. For example, the feed pump 36 is composed of a positive displacement pump such as a circumferential flow type pump. The drive of the feed pump 36 (pump rotation speed) is controlled by the control unit.

The fuel gauge 38 measures the remaining fuel volume in the fuel tank 14. The fuel gauge 38 is, for example, a float-type sender gauge.

The fuel supply pipe 40 is provided with a feed fuel pressure sensor that detects the pressure (feed fuel pressure) of the fuel F discharged from the feed pump 36, and a fuel temperature sensor that detects the temperature (fuel temperature) of the fuel F discharged from the fuel outlet of the feed pump 36.

The tank pressure sensor 34 is a sensor that measures the pressure inside the tank, and is, for example, a diaphragm-type pressure sensor. By providing the tank pressure sensor 34, not only can the tank pressure be ascertained, but also vapor leaks caused by partial damage to the fuel tank 14 can be detected.

The vapor pipe 16 has one end connected to the fuel tank 14 and the other end connected to the canister 44. The vapor pipe 16 functions as a passage for vapor in the fuel tank 14 during pressure reduction control of the fuel tank 14.

The vapor pipe 16 is provided at the end on the fuel tank 14 side with an ORVR valve 47 (Onboard Refueling Vapor Recovery Valve) and an RO valve 49 (Roll Over Valve). The ORVR valve 47 and the RO valve 49 are, for example, float valves. Both are normally open and are closed when the liquid level in the fuel tank 14 becomes high. Closing the valves prevents the fuel F from being released into the atmosphere via the vapor pipe 16 when the vehicle 12 rolls over, etc.

The valve unit 46 is provided in the vapor pipe 16 and switches the vapor pipe 16 between a connected state and a blocked state. The valve unit 46 includes a shutoff valve 28 and relief valves 48A and 48B.

The shutoff valve 28 opens and closes in response to an open/close command from the control unit. The shutoff valve 28 is composed of an electromagnetic valve, such as a solenoid valve. By closing the shutoff valve 28, a sealed tank system can be constructed.

The relief valves 48A, 48B are provided to forcibly eliminate pressure abnormalities that occur in the vapor piping 16 when the shutoff valve 28 fails. The relief valves 48A, 48B are normally closed and open when a pressure equal to or greater than a predetermined value is applied to a built-in spring. Of the two relief valves 48A, 48B, the valve 48A is configured to open when the canister 44 side becomes higher pressure than the fuel tank 14 side. The other valve 48B is configured to open when the fuel tank 14 side becomes higher pressure than the canister 44 side.

The inside of the canister 44 is filled with an adsorbent (e.g., activated carbon) capable of adsorbing vapor. The canister 44 is an adsorption means for adsorbing vapor. The canister 44 is provided at the branch point of the vapor pipe 16 and the vent pipe 20. The canister 44 is open to the atmosphere via the vent pipe 20.

For example, if the fuel tank 14 becomes highly pressurized while the internal combustion engine 22 is stopped, the shutoff valve 28 is opened to connect the vent pipe 20 to the fuel tank 14. At this time, vapor released from the fuel tank 14 is adsorbed into the canister 44. When the internal combustion engine 22 is running, the purge valve 30 is opened to release the vapor adsorbed in the canister 44 and draw it into the intake passage. This restores the adsorption capacity of the canister 44.

The purge pipe 18 is connected to an intake passage that leads to the vehicle's internal combustion engine 22. One end of the purge pipe 18 is connected to the vapor pipe 16 near the canister 44, and the other end is connected to a portion of the intake passage closer to the internal combustion engine 22 than the throttle valve.

The purge pipe 18 is provided with a purge valve 30. The purge valve 30 switches the purge pipe 18 between a connected state and a blocked state. The purge valve 30 is composed of an electromagnetic valve such as a solenoid valve.

One end of the vent pipe 20 is connected to the canister 44, and the other end is open to the atmosphere. The vent pipe 20 and the vapor pipe 16 form an air intake passage 54, one end of which is connected to the fuel tank 14 and the other end of which is open to the atmosphere.

The vent pipe 20 is provided with an air filter 56 and an OBD module 57. The air filter 56 absorbs dust particles in the air when the air is introduced. The OBD module 57 (on-board fault diagnosis module) is configured by housing a key-off pump and a switching valve in a module case.

The key-off pump applies internal pressure to the fuel tank 14, which is connected to the canister 44 via the vent pipe 20, the canister 44, and the vapor pipe 16. The vent pipe 20 is provided with a switching valve. The switching valve switches the vent pipe 20 between a connected state and a blocked state. The switching valve is composed of an electromagnetic valve, such as a solenoid valve.

By driving the key-off pump, internal pressure is applied to the canister 44 and fuel tank 14, and abnormalities (e.g., holes) in the canister 44, fuel tank 14, and surrounding components can be detected. The internal pressure applied to the fuel tank 14 by the key-off pump may be positive or negative.

The pressure control device is configured to include a vapor generation rate estimation unit, a pump scavenging rate estimation unit, a state detection unit, a target value calculation unit, a control unit, etc. The pressure control device is configured to include a so-called microcomputer equipped with, for example, a CPU (Central Processing Unit), a memory device, an input/output port, and a communication port. The memory device includes a RAM (Random Access Memory) as a working memory, a ROM (Read Only Memory) as a storage device, and a non-volatile flash memory.

The CPU reads out programs stored in the ROM, expands them into the RAM, and executes various processes according to the expanded programs to execute various controls performed by the pressure control device. Signals from various sensors, including the tank internal pressure sensor 34, the feed fuel pressure sensor, and the fuel temperature sensor, are input to the CPU via an input port, and various control signals based on the signals from the various sensors are output from the CPU via an output port. The storage device stores various programs, including a program for executing in-tank vapor amount control, and various maps and parameters for executing the in-tank vapor amount control.

The pressure control device controls the negative pressure in the fuel tank 14. Negative pressure control includes pressure reduction control and pressure increase control. In pressure reduction control, the tank internal pressure that has become equal to or higher than atmospheric pressure is reduced to a predetermined normal negative pressure. In pressure increase control, the tank internal pressure that has become excessively negative is increased to the normal negative pressure.

Pressure reduction control is performed when the internal combustion engine 22 is running and the intake passage is at negative pressure. When the shutoff valve 28 and purge valve 30 are opened in response to a command from the control unit, vapor in the fuel tank 14 is drawn into the intake passage via the vapor pipe 16 and purge pipe 18. The vapor drawn into the intake passage is combusted in the internal combustion engine 22 together with the fuel F injected from the injector 42. When the tank internal pressure reaches a predetermined normal negative pressure, the shutoff valve 28 and purge valve 30 are closed.

In pressure increase control, the control unit commands the shutoff valve 28 to open. This allows air to be drawn into the fuel tank 14 via the vent pipe 20 and the vapor pipe 16. When the tank internal pressure reaches a predetermined normal negative pressure, the shutoff valve 28 closes.

However, when the fuel tank 14 is exposed to a high temperature or low pressure environment, evaporation of the fuel F in the fuel tank 14 is accelerated, which can generate vapor. For example, in a vehicle filled with fresh fuel F, the fuel F may boil under reduced pressure while climbing a hill in summer, generating vapor. Fresh fuel F is particularly prone to vapor generation due to its high volatility. As a result, when vapor is taken in and accumulates in the feed pump 36, the accumulated vapor reduces the feed fuel pressure, making it more likely that vapor lock will occur, in which fuel F is not supplied from the feed pump 36 to the internal combustion engine 22.

Regarding the mechanism by which vapor lock occurs, the quantitative relationship between the various factors involved in the occurrence of vapor lock was unclear. Therefore, the inventors discovered that vapor lock occurs when the scavenging capacity of the feed pump 36 is insufficient relative to the amount of vapor generated Qvap in the fuel tank 14.

Here, FIG. 9 is a diagram of the vapor pressure curve of fuel. In FIG. 9, the vapor pressure curve C of fuel F is shown by plotting the fuel temperature on the horizontal axis and the saturated vapor pressure on the vertical axis for the fuel F used (fuel used). In this vapor pressure curve diagram, when the usage environment (fuel temperature and tank internal pressure) is in a region above the vapor pressure curve C, the fuel F is maintained in a liquid phase. On the other hand, when the usage environment is in a region below the vapor pressure curve C, the fuel F is in a gas phase, and vapor is generated. In other words, the region above the vapor pressure curve C is a vapor non-generation region where no vapor is generated, and the region below the vapor pressure curve C is a vapor generation region where vapor is generated.

The vapor generation amount Qvap can be calculated by the following formula (1) using a vapor pressure curve.
Qvap=kS×ΔP...Formula (1)
where k is the fuel temperature (° C.), S is the tank liquid area (cm ² ), and ΔP is the gap (kPa). That is, the vapor generation amount Qvap is proportional to the gap between the vapor pressure curve C of the fuel F and the usage environment.

Furthermore, as shown in the following formula (2), it is possible to calculate the vapor generation speed Vvap by dividing the vapor generation amount Qvap by the vapor generation time Tvap, which is the period during which the vapor is generated.
Vvap=Qvap/Tvap...Formula (2)

In the example shown in Figure 9, a point E is plotted in the vapor generation region for a usage environment where the fuel temperature is k1 (45°C) and the tank internal pressure is P1 (70 kPa). On the other hand, a point S is plotted on the vapor pressure curve C shown in Figure 9 for a saturated vapor pressure of P2 (100 kPa) when the fuel temperature is k (45°C). That is, as shown in the following formula (3), the gap ΔP is a value obtained by subtracting P1 from P2.
ΔP=P2-P1...Formula (3)

On the other hand, the scavenging capacity of the feed pump 36 can be expressed by the pump scavenging speed Vpump, which is the speed at which the vapor is scavenged by the feed pump 36. This pump scavenging speed Vpump correlates with each of the pump rotation speed, fuel pressure, and fuel temperature.

When the pressure control device of this embodiment predicts that the vapor generation rate Vvap will be greater than the pump scavenging rate Vpump (Vvap>Vpump) when the internal combustion engine 22 is running, it executes in-tank vapor amount control to control at least one of the vapor generation rate Vvap and the pump scavenging rate Vpump so that the vapor generation rate Vvap is equal to or less than the pump scavenging rate Vpump (Vvap≦Vpump).

This makes it possible to suppress the generation of vapor within the fuel tank 14. In addition, the period during which the tank internal pressure is higher than necessary is shortened, which suppresses damage to the fuel tank 14 and ensures the reliability of the fuel tank 14.

Next, a series of process flows for controlling the amount of vapor in the tank described above will be described with reference to FIG. 2. FIG. 2 is a flowchart explaining the process of controlling the amount of vapor in the tank by the pressure control device.

When the series of processes for controlling the amount of vapor in the tank is started, the first process is to estimate (calculate) the vapor generation rate Vvap and the pump scavenging rate Vpump.

In step S10, the vapor generation rate estimation unit performs a process to estimate the vapor generation rate Vvap. In this step, the vapor pressure characteristic map of fuel F is referenced to estimate the vapor generation rate Vvap corresponding to the current usage environment. The vapor pressure characteristic map of fuel F is determined in advance through experiments and analysis as the relationship between the fuel temperature of the fuel used and the tank internal pressure (saturated vapor pressure of the fuel used), and is stored in a storage device. The vapor pressure characteristic map can be estimated from the history of the usage environment.

If the usage environment is below the vapor pressure curve, the fuel F will be in a gaseous state and will wither. More specifically, the vapor pressure of the fuel F is determined by the lowest boiling point component among the components contained in the fuel F, so if the usage environment is below the vapor pressure curve of the low boiling point component in the fuel F, after the low boiling point component vaporizes, the vapor pressure characteristics of the fuel F will sequentially change to the vapor pressure curve of the low boiling point component with the next lowest boiling point after the vaporized low boiling point component.

These changes in the vapor pressure characteristics of fuel F will be explained using a specific example when climbing a slope. Figure 3 is a diagram that explains the vapor pressure characteristics of fuel before and after climbing a slope. The left side of Figure 3 shows the conditions when climbing a slope, and the right side shows the vapor pressure characteristics of fuel F before and after climbing a slope. As shown in the conditions when climbing a slope, for example, when climbing a slope from an altitude of 0 m (atmospheric pressure: 100 kPa) to an altitude of 3000 m (atmospheric pressure: 70 kPa), the atmospheric pressure decreases as the altitude increases.

Comparing the vapor pressure curves C1 and C2 of fuel F before and after the climb in the graph on the right, it can be seen that the vapor pressure curve C1 before the climb changes to the vapor pressure curve C2 after the climb. This change is caused by the vaporization of low-boiling point components in fuel F that have vapor pressure characteristics between the vapor pressure curves C1 and C2 due to the drop in atmospheric pressure that accompanies the climb. Therefore, the vapor pressure characteristics of fuel F can be determined based on the maximum fuel temperature and minimum pressure in the history of the usage environment.

In step S10, the vapor pressure characteristics of fuel F are estimated according to the flow shown in FIG. 4, and the vapor generation rate Vvap is estimated from the estimated vapor pressure characteristics and the current usage environment. FIG. 4 is a diagram explaining the process of calculating the vapor generation rate. As shown in FIG. 4, when calculating the vapor generation rate Vvap, first, the usage environment up to the previous time is plotted from the usage environment history (S10-1).

Next, a vapor pressure curve passing through the plotted points is created for each previous usage environment. The vapor pressure curve created here is given by the Clausius-Clapeyron equation. Then, from the vapor pressure curves for each previous usage environment, the lowest vapor pressure curve is extracted, and the extracted vapor pressure curve is estimated as the current vapor pressure curve C for fuel F (S10-2).

Next, the current operating environment UE is obtained from the fuel temperature sensor and the tank internal pressure sensor 34, and the vapor generation rate Vvap is calculated using equations (1) and (2) described in FIG. 9 based on the gap ΔP between the obtained current operating environment UE and the current vapor pressure curve C of the fuel F (S10-3).

Meanwhile, in step S20, the pump scavenging speed estimation unit performs a process to estimate the pump scavenging speed Vpump. The pump scavenging speed Vpump can be estimated based on at least one of the pump rotation speed, the fuel pressure, and the fuel temperature. Therefore, a method for estimating the pump scavenging speed Vpump will be described using an example in which estimation is based on the pump rotation speed.

Figure 5 shows a Vpump calculation map. The Vpump calculation map shown in Figure 5 is determined in advance through experiments and analysis as the relationship between the pump rotation speed and the pump scavenging speed Vpump, and is stored in a storage device. When estimating the pump scavenging speed Vpump, the Vpump calculation map created in advance is referenced to determine the pump scavenging speed Vpump that corresponds to the current pump rotation speed.

Next, in step S30, the state detection unit performs a process to detect the state of vapor generation rate - pump scavenging rate (Vvap - Vpump state). Here, the change trend of the feed fuel pressure associated with vapor generation will be specifically explained with reference to Figure 6. Figure 6 is a graph showing the change in the feed fuel pressure over time.

When the vapor generation rate Vvap becomes greater than the pump scavenging rate Vpump (Vvap>Vpump), the vapor that cannot be scavenged by the feed pump 36 accumulates in the feed pump 36. When vapor accumulates in the feed pump 36, the discharge rate of the feed pump 36 decreases, and the feed fuel pressure decreases.

In the example shown in FIG. 6, vapor begins to be generated from time t1 when Vvap>Vpump, and as the amount of vapor accumulated in the feed pump 36 gradually increases, the feed fuel pressure gradually decreases. After that, when the amount of vapor accumulation exceeds a certain level at time t2, the feed fuel pressure suddenly decreases. Furthermore, when the amount of vapor accumulation reaches a critical point at time t3, the feed pump 36 becomes unable to discharge.

Therefore, in step S30, the Vvap-Vpump state is detected from the change in the feed fuel pressure. In other words, vapor generation is detected from the change in the feed fuel pressure. Specifically, if the current feed fuel pressure obtained from the feed fuel pressure sensor remains below the target feed fuel pressure (target feed fuel pressure) for a predetermined period of time or more, it is determined that the Vvap>Vpump state is met.

Another method for detecting the Vvap-Vpump state is to detect it from a change in the integral term, which is the command amount for the drive current (or drive voltage) for the feed pump 36. Figure 7 is a diagram for explaining the control of the pump speed. Figure 7 shows the behavior of the feed fuel pressure, pump speed, and command amount when demand control is being performed to control the pump speed so as to obtain the target feed fuel pressure.

As shown in FIG. 7, when Vvap>Vpump and the feed fuel pressure drops, control is performed to increase the pump scavenging speed Vpump by increasing the pump rotation speed. Through this control, the feed fuel pressure can be maintained at the target feed fuel pressure. The Vvap-Vpump state can be detected by the increasing tendency of the command amount of the drive current (or drive voltage) for the feed pump 36 at this time. The command amount corresponds to the shortage of the scavenging capacity of the feed pump 36 relative to the vapor generation amount Qvap.

If it is determined that Vvap>Vpump, in step S40, the target value calculation unit performs a process of calculating a target value for at least one of the vapor generation speed Vvap and the pump scavenging speed Vpump. In this step, based on the difference between the estimated vapor generation speed Vvap and the pump scavenging speed Vpump, a target value is calculated at which the vapor generation speed Vvap is equal to or less than the pump scavenging speed Vpump. Then, control of at least one of the vapor generation speed Vvap and the pump scavenging speed Vpump is performed so as to obtain the calculated target value. If the vapor generation speed Vvap is to be controlled, proceed to step S50, and if the pump scavenging speed Vpump is to be controlled, proceed to step S60.

In step S50, the control unit performs a process to control the vapor generation rate Vvap. Here, for example, in the case of a closed tank system, when the vehicle is climbing a slope with the fuel temperature kept constant, the vapor generation rate Vvap is proportional to the tank internal pressure depressurization rate. Also, when the vehicle is warming up with the tank internal pressure kept constant, the vapor generation rate Vvap is proportional to the warm-up rate of the internal combustion engine 22. Therefore, when climbing a slope, the vapor generation rate Vvap can be controlled by adjusting the tank internal pressure depressurization rate. Also, when the vehicle is warming up, the vapor generation rate Vvap can be controlled by adjusting the warm-up rate of the internal combustion engine 22.

Here, we will explain the control of the vapor generation rate Vvap by taking the case of adjusting the tank internal pressure decompression rate as an example. The tank internal pressure decompression rate is adjusted, for example, by opening and closing the shutoff valve 28. In this step, a decompression rate calculation map is referenced to determine the target tank internal pressure decompression rate (target tank internal pressure decompression rate) that corresponds to the Vvap-Vpump state.

Figure 8 is a diagram explaining the pressure reduction control of the tank internal pressure. The left side of Figure 8 shows a vapor pressure curve diagram of fuel F. On the vapor pressure curve diagram shown in Figure 8, the Vvap-Vpump state according to the tank internal pressure when the fuel temperature is constant is shown as points ST1 to ST4. The tank internal pressure at points ST1 to ST4 is point ST1 > point ST2 > point ST3 > point ST4. Point ST1 is located in the non-vapor generation region, point ST2 is on the vapor pressure curve C, and points ST3 and ST4 are in the vapor generation region.

The right side of Figure 8 shows a map for calculating the decompression rate. The decompression rate calculation map shown in Figure 8 is determined in advance through experiments and analysis as the relationship between the Vvap-Vpump state and the tank internal pressure decompression rate, and is stored in a storage device. The solid line in the decompression rate calculation map shown in Figure 8 represents the tank internal pressure decompression rate required to achieve the Vvap=Vpump state.

For example, at point ST1 where Vvap<Vpump, the tank internal pressure depressurization rate is maintained at the current level. At point ST2 where Vvap=Vpump, the tank internal pressure depressurization rate is slightly reduced to control it to the target tank internal pressure depressurization rate. At points ST3 and ST4 where Vvap>Vpump, the tank internal pressure depressurization rate is reduced to control it to the target tank internal pressure depressurization rate. The greater the speed difference between Vvap and Vpump, the greater the degree of reduction in the tank internal pressure depressurization rate.

In other words, when Vvap > Vpump, the opening of the shutoff valve 28 is controlled in the direction to open the tank internal pressure reduction rate to ease the rate at which the tank internal pressure is reduced, drawing air into the fuel tank 14 and reducing the vapor generation rate Vvap until it reaches the target value. This controls the vapor generation rate Vvap so that Vvap ≦ Vpump is achieved. When the vapor generation rate Vvap reaches the target value, control of the opening of the shutoff valve 28 is terminated and the tank internal pressure reduction rate is maintained.

On the other hand, in step S60, the control unit performs a process to control the pump scavenging speed Vpump. The pump scavenging speed Vpump can be controlled by adjusting at least one of the pump speed, the fuel pressure, and the fuel temperature.

For example, the case where the pump scavenging speed Vpump is controlled by adjusting the pump rotation speed is as described in FIG. 7. Specifically, when Vvap>Vpump, the pump rotation speed is increased to increase the pump scavenging speed Vpump until it reaches the target value. This controls the pump scavenging speed Vpump so that Vvap≦Vpump is satisfied. When the pump scavenging speed Vpump reaches the target value, the control to increase the pump rotation speed is terminated.

The series of processing flows from steps S10 to S60 described above are repeatedly executed at a predetermined control period while the internal combustion engine 22 is running. In this way, the pressure control device of this embodiment can raise the tank internal pressure to an appropriate level in response to changes in the vapor generation amount Qvap by controlling the vapor generation rate Vvap to be equal to or lower than the pump scavenging rate Vpump. This makes it possible to reduce the period during which the tank internal pressure is higher than necessary for the actual amount of vapor generated.

Therefore, the fuel tank pressure control device of this embodiment makes it possible to ensure the reliability of the fuel tank 14 while suppressing the generation of vapor.

The present invention is not limited to the above embodiment, and can be modified as appropriate without departing from the spirit of the present invention. For example, the above embodiment has been described with reference to an example of a fuel tank pressure control device capable of constructing a sealed tank system in which a valve unit 46 including a shutoff valve 28 is provided between the fuel tank 14 and the canister 44, but the present invention is not limited to this. For example, the present invention may be configured as a fuel tank pressure control device capable of constructing an unsealed tank system in which a valve unit 46 (shutoff valve 28) is not provided between the fuel tank 14 and the canister 44.

In the case of a non-sealed tank system, when the vehicle is climbing a slope with the fuel temperature kept constant, the vapor generation speed Vvap is proportional to the vehicle speed. Also, when the vehicle is warming up with the tank internal pressure kept constant, the vapor generation speed Vvap is proportional to the warm-up speed of the internal combustion engine 22. Therefore, the vapor generation speed Vvap can be controlled by adjusting the vehicle speed when climbing a slope. Also, when the vehicle is warming up, the vapor generation speed Vvap can be controlled by adjusting the warm-up speed of the internal combustion engine 22.

14 Fuel tank 16 Vapor piping 18 Purge piping 20 Vent piping 22 Internal combustion engine 28 Shut-off valve 30 Purge valve 34 Tank internal pressure sensor 35 Fuel supply pipe 36 Feed pump 38 Fuel gauge 40 Fuel supply piping 42 Injector 44 Canister 46 Valve unit 47 ORVR valves 48A, 48B Relief valve 49 RO valve 54 Atmospheric air introduction passage 56 Air filter 57 OBD module C, C1, C2 Vapor pressure curve F Fuel UE Operating environment Vpump Pump scavenging speed Vvap Vapor generation rate ΔP Gap

Claims (1)

a pump scavenging speed estimation unit that estimates a pump scavenging speed, which is a speed at which vapor is scavenged by a feed pump that scavenges vapor in fuel sucked from a fuel tank that stores fuel;
a vapor generation rate estimation unit that estimates a vapor generation rate, which is a rate at which the vapor is generated in the fuel tank;
a control unit that, when predicting that the vapor generation rate will be greater than the pump scavenging rate, controls at least one of the vapor generation rate and the pump scavenging rate so that the vapor generation rate is equal to or less than the pump scavenging rate;
A fuel tank pressure control device having a pressure sensor.

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