Fuel cell vehicle

A FC vehicle includes a long distance hill climbing detector for detecting long distance hill climbing and a controller for, in the case where the long distance hill climbing detector detects the long distance hill climbing, controlling the allocation amount of electric power outputted from an FC such that the allocation amount is larger than the allocation amount before the detection of the long distance hill climbing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-111033 filed on May 18, 2011, of which the contents are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell vehicle including a traction motor driven by use of a fuel cell and an energy storage device.

2. Description of the Related Art

Fuel cell vehicles including a traction motor by use of a fuel cell and a battery are known (U.S. Patent Application Publication No. 2009/0105895 (hereinafter referred to as “US 2009/0105895 A1”), Japanese Laid-Open Patent Publication No. 2009-046020 (hereinafter referred to as “JP 2009-046020 A”)).

In US 2009/0105895 A1, when the accelerator opening degree change rate ΔAcc is large, the amount of battery assist is increased, and when the change rate ΔAcc is small, the amount of battery assist is reduced (see “Abstract” therein). The amount of battery assist is continuously adjusted based on the change rate ΔAcc until the difference ΔP between the drive power demand Pdr* and the output Pfc of the fuel cell becomes substantially zero (see S150, S155, and S190 of FIG. 3 therein). Further, in US 2009/0105895 A1, in comparison with the case of the normal mode, when a sport mode is selected, the amount of battery assist is increased, and when an economy mode is selected, the amount of battery assist is reduced (see Abstract and FIG. 8 therein).

Further, in JP 2009-046020 A, in order to suppress increase in the temperature of the fuel cell during hill climbing, when the temperature of the fuel cell 6 becomes the threshold value or more, the output of an air conditioner device 21 is decreased. Thus, by decreasing the amount of waste heat from a capacitor 22 of the air conditioner device 21 provided in front of a radiator 9 of the fuel cell 6, improvement in the cooling efficiency of the radiator 9 is achieved (see Abstract therein).

SUMMARY OF THE INVENTION

As described above, in US 2009/0105895 A1, the amount of battery assist is adjusted depending on the accelerator opening degree change rate ΔAcc and the running mode. However, no consideration is given to the amount of battery assist (output from the battery) at the time of long distance hill climbing (in particular, high speed hill climbing). Assuming that the control of US 2009/0105895 A1 is applied at the time of long distance hill climbing, and a state where the difference ΔP between the drive power demand Pdr* and the output Pfc of the fuel cell does not become substantially zero continues for a long time, since a state where the amount of battery assist is large continues, the battery may run out of electric power undesirably. In this regard, there is no description in JP 2009-046020 A.

The present invention has been made taking the problems of this type into account, and an object of the present invention is to provide a fuel cell vehicle which makes it possible to ensure a desired assist from an energy storage device at the time of high speed hill climbing.

A fuel cell vehicle according to the present invention includes a traction motor, a fuel cell, an energy storage device, a power distribution apparatus, a long distance hill climbing detector, and a controller. The fuel cell supplies electric power to the traction motor. The energy storage device supplies electric power to the traction motor, and the energy storage device is capable of being charged with regenerative electric power of the traction motor or electric power generated in the fuel cell. The power distribution apparatus controls targets to which electric power generated in the fuel cell, electric power outputted from the energy storage device, and regenerative electric power of the traction motor are supplied. The long distance hill climbing detector detects long distance hill climbing of the fuel cell vehicle. In the case where the long distance hill climbing detector detects the long distance hill climbing, the controller controls an allocation amount of electric power outputted from the fuel cell such that the allocation amount of electric power outputted from the fuel cell is larger than the allocation amount before the detection of the long distance hill climbing.

In the present invention, in the case where long distance hill climbing is detected, control is implemented such that the allocation amount of electric power outputted from the fuel cell is larger than that before detection of the long distance hill climbing. Thus, since the allocation amount of electric power outputted from the energy storage device is decreased relatively, during the long distance hill climbing of the fuel cell vehicle, it becomes possible to prevent the SOC of the energy storage device from being decreased at an early stage due to discharging of electric power at the large output, and prevent assistance by the energy storage device from being disabled at an early stage.

The fuel cell vehicle may further include a cooling apparatus for cooling the fuel cell by a coolant. In the case where the long distance hill climbing detector detects the long distance hill climbing, the output of the air conditioner may be limited depending on increase in the temperature of the fuel cell. In this manner, during the long distance hill climbing of the fuel cell vehicle, by limiting the output of the air conditioner, excessive electric power can be utilized for the output of the traction motor. Additionally, for example, in the case where heat from the air conditioner raises the temperature of the fuel cell or the coolant, or in the case where the coolant for the fuel cell is also utilized for cooling the air conditioner, by limiting the output from the air conditioner to suppress heat produced in the air conditioner, even if the output of the fuel cell is increased, it becomes possible to suitably protect the fuel cell against heat. Further, it becomes possible to prevent the output and efficiency of the fuel cell from being lowered due to overheating of the fuel cell.

If the energy storage device is a battery, an upper limit value of remaining battery level (state of charge: SOC) of the battery for performing power generation of the fuel cell may be set. If the remaining battery level exceeds the upper limit value, power generation of the fuel cell may not be performed, and in the case where the long distance hill climbing detector detects the long distance hill climbing, the upper limit value of the remaining battery level may be increased. Thus, during the long distance hill climbing, even if the SOC of the battery is high, power generation of the fuel cell can be performed. Therefore, even if the required load is kept high for long distance hill climbing, since the output of the fuel cell is suitably regulated in accordance with the load, it becomes possible to prevent the SOC of the battery from being decreased at an early stage, and prevent assistance by the battery from being disabled at an early stage.

An output upper limit value of the fuel cell may be set depending on the remaining battery level (state of charge), and in the case where the long distance hill climbing detector detects the long distance hill climbing, in a region where the remaining battery level is low, the output upper limit value of the fuel cell may be set to be lower in comparison with the case where the long distance hill climbing detector does not detect the long distance hill climbing. In this manner, it becomes possible to suppress overheating of the fuel cell, and maintain a desired drivability.

That is, in the present invention, except the case where the SOC of the battery is low from a time point immediately after long distance hill climbing is started, the SOC may be lowered gradually during the long distance hill climbing (in particular, high speed hill climbing). In the case where the output limit value of the fuel cell is increased (the output limit of the fuel cell is relaxed) during long distance hill climbing, the fuel cell could be overheated due to power generation before the SOC becomes low (Since heat produced in the fuel cell is proportional to the square of the power generation current, as the current is higher, the amount of heat produced in the fuel cell is increased). In the case where the fuel cell is overheated, it may become necessary to take some actions, e.g., significantly limit power generation of the fuel cell, or stop power generation of the fuel cell. In the case where such actions are required, drivability may become significantly poor in the middle of hill climbing. Thus, according to the present invention, in the region where the SOC is low, in the case where long distance hill climbing is detected, the output limit value of the fuel cell is lowered. Therefore, even if the long distance hill climbing continues, it becomes possible to suppress overheating of the fuel cell, and maintain a desired drivability.

Further, in the case where the output of the fuel cell is increased in the state where the power generation efficiency is low, the fuel gas is consumed rapidly. In order to address the problem, in the above structure, the amount of consumption of the fuel gas is suppressed at the time of long distance hill climbing. Thus, it becomes possible to prevent the fuel gas from being used excessively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Description Regarding Overall Structure

FIG. 1is a diagram schematically showing a structure of a fuel cell vehicle10(hereinafter referred to as the “FC vehicle10” or “vehicle10”) according to an embodiment of the present invention. The FC vehicle10includes a vehicle power supply system12(hereinafter referred to as “a power supply system12”), a traction motor14, and an inverter (auxiliary device)16.

The power supply system12includes a fuel cell unit18(hereinafter referred to as the “FC unit18”), a battery20(energy storage device), a power distribution apparatus22, and an electronic control unit (control device)24(hereinafter referred to as the “ECU24”).

The motor14generates a driving force based on the electric power supplied from the FC unit18and the battery20, and rotates wheels28using the driving force through a transmission26. Further, the motor14outputs electric power generated by regeneration (regenerative electric power Preg) [W] to the battery20. The regenerative electric power Preg may be outputted to a group of auxiliary devices (including an air pump36, a water pump (cooling apparatus)68, an air conditioner130, and a group of low voltage auxiliary devices134as described later).

The inverter16has three phase full bridge structure, and carries out DC/AC conversion to convert direct current into alternating current in three phases. The inverter16supplies the alternating current to the motor14, and supplies the direct current after AC/DC conversion as a result of regeneration to the battery20or the like through a power distribution apparatus22.

It should be noted that the motor14and the inverter16are collectively referred to as a load30. The load30may include components (auxiliary device) such as an air pump (reactant gas supply apparatus)36, a water pump68, an air conditioner130, and a group of low voltage auxiliary devices, to described later.

The FC unit18includes a fuel cell stack32(hereinafter referred to as “a FC stack32” or “a FC32”). For example, the fuel cell stack32is formed by stacking fuel cells (hereinafter referred to as the “FC cells”) each including an anode, a cathode, and a solid polymer electrolyte membrane interposed between the anode and the cathode. A hydrogen tank34and the air pump36are connected to the fuel cell stack32through their respective passages38,40. Hydrogen (fuel gas) as one reactant gas is supplied from the hydrogen tank34, and a compressed air (oxygen-containing gas) as the other reactant gas is supplied from the air pump36. Electrochemical reactions of the hydrogen and the air supplied from the hydrogen tank34and the air pump36to the FC stack32occur in the FC stack32to generate electric power, and the electric power generated (FC electric power Pfc) [W] in the power generation is supplied to the motor14and the battery20.

The power generation voltage of the FC stack32(hereinafter referred to as the “FC voltage Vfc”) [V] is detected by a voltage sensor42, and the power generation current of the FC stack32(hereafter referred to as the “FC current Ifc”) [A] is detected by a current sensor44. The FC voltage Vfc and the FC current Ifc are outputted to the ECU24. Further, the power generation voltage of each FC cell of the FC stack32(hereinafter referred to as the “cell voltage Vcell”) [V] is detected by a voltage sensor46, and outputted to the ECU24.

A regulator50is provided in the passage38connecting the hydrogen tank34and the FC stack32. A passage52branches from the passage40connecting the air pump36and the FC stack32, and the passage52is connected to the regulator50. Compressed air from the air pump36is supplied through the passage52. The regulator50changes the opening degree of the valve depending on the pressure of the supplied compressed air, and regulates the flow rate of the hydrogen supplied to the FC stack32.

A purge valve58and a back pressure valve60are provided respectively in a hydrogen passage54and an air passage56provided on the outlet side of the FC stack32. The purge valve58discharges the hydrogen on the outlet side of the FC stack32to the outside of the vehicle10, and the back pressure valve60regulates the pressure of the air. Further, a passage62connecting the passage38on the inlet side of the hydrogen and the passage54on the outlet side of the hydrogen is provided. The hydrogen discharged from the FC stack32is returned to the inlet side of the FC stack32through the passage62. Pressure sensors64,66are provided in the passages54,56on the outlet side of the FC stack32, and detection values (pressure values) are outputted from the pressure sensors64,66to the ECU24, respectively.

Further, the water pump68for cooling the FC stack32is provided adjacent to the FC stack32. The water pump68circulates coolant water (coolant) in the FC stack32. The temperature Tw [° C.] of the coolant water is detected by a temperature sensor70, and outputted to the ECU24.

The battery20is an energy storage device (energy storage) containing a plurality of battery cells. For example, a lithium-ion secondary battery, a nickel hydrogen battery, or a capacitor can be used as the battery20. In the present embodiment, the lithium-ion secondary battery is used. The output voltage [V] of the battery20(hereinafter referred to as the “battery voltage Vbat”) is detected by a voltage sensor72, and the output current [A] of the battery20(hereinafter referred to as the “battery current Ibat”) is detected by the current sensor74. The battery voltage Vbat and the battery current Ibat are outputted to the ECU24. The ECU24calculates the remaining battery level (state of charge) (hereinafter referred to as the “SOC”) [%] of the battery20based on the battery voltage Vbat from the voltage sensor72and the battery current Ibat from the current sensor74.

The power distribution apparatus22controls targets to which the FC electric power Pfc from the FC unit18, the electric power [W] supplied from the battery20(hereinafter referred to as the “battery electric power Pbat”), and the regenerative electric power Preg from the motor14are supplied.

FIG. 2shows details of the power distribution apparatus22in the present embodiment. As shown inFIG. 2, the power distribution apparatus22includes a DC/DC converter78in which one side of the DC/DC converter78is connected to the primary side1S where the battery20is provided, and the other side of the DC/DC converter78is connected to the secondary side2S, which is connection points between the load30and the FC32.

The DC/DC converter78is a chopper type step up/down voltage converter for increasing the voltage on the primary side1S (primary voltage V1) [V] to the voltage on the secondary side2S (secondary voltage V2) [V] (V1≦V2), and decreasing the secondary voltage V2to the primary voltage V1.

As shown inFIG. 2, the DC/DC converter78includes a phase arm UA interposed between the primary side1sand the secondary side2S, and a reactor80.

The phase arm UA includes an upper arm element (an upper switching element82and a diode84) and a lower arm element (a lower arm switching element86and a diode88). For example, MOSFET or IGBT is adopted in each of the upper arm switching element82and the lower arm switching element86.

The reactor80is interposed between the middle point (common connection point) of the phase arm UA and the positive electrode of the battery20. The reactor80is operated to release and accumulate energy during voltage conversion between the primary voltage V1and the secondary voltage V2by the DC/DC converter78.

The upper arm switching element82is turned on when high level of a gate drive signal (drive voltage) UH is outputted from the ECU24, and the lower arm switching element86is turned on when high level of a gate drive signal (drive voltage) UL is outputted from the ECU24.

The ECU24detects primary voltage V1by a voltage sensor90provided in parallel with a smoothing capacitor92on the primary side, and detects electrical current on the primary side (primary current I1) [A] by a current sensor94. Further, the ECU24detects secondary voltage V2by a voltage sensor96provided in parallel with the smoothing capacitor98on the secondary side, and detects electrical current on the secondary side (secondary current I2) [A] by a current sensor100.

The ECU24controls the motor14, the inverter16, the FC unit18, the battery20, and the power distribution apparatus22(DC/DC converter78) through a communication line102(seeFIG. 1). For implementing the control, programs stored in a memory (ROM) are executed, and detection values obtained by various sensors such as the voltage sensors42,46,72,90,96, the current sensors44,74,94,100, the pressure sensors64,66, and the temperature sensor70are used.

The various sensors herein include an opening degree sensor110, a motor rotation number sensor112, and a gradient sensor116(FIG. 1). The opening degree sensor110detects the opening degree [degrees] of an accelerator pedal118(hereinafter referred to as “an accelerator opening degree θ” or “opening degree θ”). The rotation number sensor112detects the rotation number [rpm] of the motor14(hereinafter referred to as “motor rotation number Nm” or “rotation number Nm”). The gradient sensor116detects the gradient A [°] of the road (gradient of the vehicle10in a longitudinal direction thereof). Further, a main switch120(hereinafter referred to as the “main SW120”) is connected to the ECU24. The main SW120switches between supply and non-supply of the electric power from the FC unit18and the battery20to the motor14. This main SW120can be operated by a user.

The ECU24includes a microcomputer. Further, as necessary, the ECU24has a timer and input/output (I/O) interfaces such as an A/D converter and a D/A converter. The ECU24may comprise only a single ECU. Alternatively, the ECU24may comprise a plurality of ECUs for each of the motor14, the FC unit18, the battery20, and the power distribution apparatus (DC/DC converter78)22.

The ECU24has a power generation control function (controller)122and a long distance hill climbing detection function (long distance hill climbing detector)124. The power generation control function122is a function of controlling power generation of the FC32. The long distance hill climbing detection function124is a function of detecting long distance hill climbing of the vehicle10. These functions122,124will be described in detail later.

As shown inFIG. 1, the vehicle10further includes an air conditioner130. A capacitor (not shown) of the air conditioner130is provided in front of a radiator (not shown) of the FC32. For example, detailed structure (including layout) of the capacitor and the radiator can be provided based on the description of JP 2009-046020 A.

The air conditioner130is operated in accordance with instructions from the ECU24. At this time, the air conditioner130obtains electric power from at least one of the FC32, the battery20, and the motor14.

[1-8. Downverter132and Group of Low Voltage Auxiliary Devices134]

As shown inFIG. 1, the vehicle10further includes a downverter132(hereinafter referred to as the “DV132”) and a group of low voltage auxiliary devices134. The output from the DV132may be outputted to a low voltage battery (not shown). The DV132decreases the primary voltage V1of the DC/DC converter78, and outputs the primary voltage V1to the group of low voltage auxiliary devices134. The group of low voltage auxiliary devices134includes, e.g., lamps (lights), various sensors, and the ECU24.

2. Control According to Present Embodiment

Next, control in the ECU24will be described.

FIG. 3is a flow chart showing basic control in the ECU24. In step S1, the ECU24determines whether or not the main SW120is in an ON state. If the main SW120is not in the ON state (S1: NO), step S1is repeated. If the main SW120is in the ON state (S1: YES), the control proceeds to step S2. In step S2, the ECU24calculates the load (system load Ls) [W] required by the power supply system12.

In step S3, the ECU24performs energy management of the power supply system12. The energy management herein is a process of calculating the power generation amount of the FC32(FC electric power Pfc) and the output of the battery20(battery output Pbat). The energy management is intended to suppress degradation of the FC stack32, and improve the efficiency in the output of the entire power supply system12.

Specifically, based on the system load Ls calculated in step S2, the ECU24determines allocation (shares) of a fuel cell's load (requested output) Lfc which should be assigned to the FC32, a battery's load (requested output) Lbat which should be assigned to the battery20, and a regenerative power supply's load Lreg which should be assigned to the regenerative power supply (motor14) through adjustment.

In step S4, based on the fuel cell's load Lfc or the like determined in step S3, the ECU24implements control (FC power generation control) of peripheral devices of the FC stack32, i.e., the air pump36, the purge valve58, the back pressure valve60, and the water pump68. In step S5, the ECU24implements torque control of the motor14, e.g., based on the motor rotation number Nm from the rotation number sensor112and the opening degree θ of the accelerator pedal118from the opening degree sensor110.

In step S6, the ECU24determines whether or not the main SW120is in an OFF state. If the main SW120is not in the OFF state (S6: NO), the control returns to step S2. If the main SW120is in the ON state (S6: YES), the current process is finished.

[2-2. Calculation of System Load Ls]

FIG. 4is a flow chart for calculating the system load Ls. In step S11, the ECU24reads the opening degree θ of the accelerator pedal118from the opening degree sensor110. In step S12, the ECU24reads the rotation number Nm [rpm] of the motor14from the rotation number sensor112.

In step S13, the ECU24calculates the estimated electric power Pm [W] consumed by the motor14based on the opening degree θ and the rotation number Nm. Specifically, in a map shown inFIG. 5, the relationship between the rotation number Nm and the estimated consumed energy Pm is stored for each opening degree θ. For example, in the case where the opening degree θ is θ1, a characteristic140is used. Likewise, in the cases where the opening degrees θ are θ2, θ3, θ4, θ5, and θ6, characteristics142,144,146,148, and150are used, respectively. After the characteristic indicating the relationship between the rotation number Nm and the consumed electric power Pm is determined based on the opening degree θ, based on the determined characteristic, the estimated consumed energy Pm in correspondence with the rotation number Nm is determined.

In step S14, the ECU24reads data of the current operating conditions from auxiliary devices. For example, the auxiliary devices herein include auxiliary devices operated at high voltage, such as the air pump36, the water pump68, and the air conditioner (not shown), and auxiliary devices operated at low voltage, such as the low voltage battery (not shown), the accessory, and the ECU24. For example, as for the operating conditions of the air pump36and the water pump68, the rotation number Nap [rpm] of the air pump36and the rotation number Nwp [rpm] of the water pump68are read respectively. As for the operating condition of the air conditioner, output settings of the air conditioner are read.

In step S15, the ECU24calculates the electric power Pa [W] consumed by the auxiliary devices depending on the present operating conditions of the auxiliary devices. In step S16, the ECU24calculates the estimated consumed electric power in the entire FC vehicle10(i.e., system load Ls) by summing the estimated electric power Pm consumed by the motor14and the electric power Pa consumed by the auxiliary devices.

[2-3. Output Limit of Air Conditioner130and FC32]

In the present embodiment, based on whether or not the vehicle10is in the middle of long distance hill climbing (in particular, in the middle of high speed hill climbing), limit values (upper limit values) are set on electric power consumed by the air conditioner130and electric power generated in power generation of the FC32. That is, the limit value for electric power consumed by the air conditioner130(hereinafter referred to as the “air conditioner electric power limit value Palim”) is used at the time of calculating the electric power Pa consumed by the auxiliary devices in step S2ofFIG. 3(more specifically, in step S15ofFIG. 4). Further, the upper limit value of the FC electric power Pfc (hereinafter referred to as the “FC output upper limit value Pfclim”) is used at the time of calculating the fuel cell's load Lfc in step S3ofFIG. 3.

FIG. 6is a flow chart for setting the air conditioner electric power limit value Palim and the FC output upper limit value Pfclim. In step S21, the ECU24(power generation control function122) calculates FC primary side supply electric power Psup. The FC primary side supply electric power Psup can be calculated by subtracting the output of the motor14and the electric power consumed by the air pump36from the power generation amount of the FC (i.e., FC output Pfc), and represents electric power that can be supplied to the load excluding the motor14and the air pump36.

In step S22, the ECU24determines whether or not the vehicle velocity V [km/h] is equal to or more than a vehicle velocity threshold THV1(hereinafter also referred to as the “threshold THV1”) for determining whether the vehicle10is in the middle of high speed hill climbing. The vehicle velocity threshold THV1is a first condition for determining whether or not the vehicle10is in the middle of high speed hill climbing (hereinafter referred to as the “high speed hill climbing condition1”). The vehicle velocity V is calculated by the ECU24based on the motor rotation number Nm. If the vehicle velocity V is less than the threshold value THV1(S22: NO), it is determined that the vehicle10is not in the middle of high speed hill climbing.

In step S23, the ECU24resets a counter C by inputting zero to the counter C. The counter C is used for fixing determination that the vehicle10is in the middle of high speed hill climbing. Then, in step S24, the ECU24calculates the air conditioner electric power limit value Palim based on the following expression (1).
Palim=FCprimary side supply electric powerPsup+battery output limit valuePblim−DVelectric power consumptionPdv(1)

In the above expression (1), the battery output limit value Pblim represents the output limit value (upper limit value) of the battery20, and the “DV electric power consumption Pdv” represents electric power consumed by the downverter132.

Then, in step S25, the ECU24sets the FC output upper limit value Pfclim based on the SOC of the battery20. More specifically, the FC output upper limit value Pfclim in correspondence with the SOC is determined based on an FC output upper limit value characteristic160during normal operation in an FC output upper limit value table shown inFIG. 7.

As shown inFIG. 7, according to the FC output upper limit value characteristic160during normal operation in the FC output upper limit value table, when the SOC is SOC1or more, the FC output upper limit value Pfclim is zero. This is because, in the case where the SOC is excessively large, it is advantageous to use electric power from the battery20, rather than to perform power generation of the FC32, for improving the power generation efficiency of the power supply system12as a whole. Further, in the FC output upper limit value characteristic160during normal operation, when the SOC is less than SOC1, as the SOC decreases, the FC output upper limit value Pfclim is increased. This is because, when the SOC is low, the output of the FC32is used to compensate for the shortage of the output of the battery20, and with excessive electric power, the battery20is charged.

Referring back to step S22, if the vehicle velocity V is the threshold value THV1or more, and thus the high speed hill climbing condition1is satisfied (S22: Yes), then, in step S26, the ECU24determines whether or not a gradient A detected by a gradient sensor116is equal to or more than a gradient threshold value THA1(hereinafter referred to as the “threshold THA1”) for determining whether or not the vehicle10is in the middle of high speed hill climbing. The threshold THA1is a second condition for determining whether or not the vehicle10is in the middle of high speed hill climbing (hereinafter referred to as the “high speed hill climbing condition2”). If the gradient A is less than the threshold value THA1(S26: NO), it is determined that the vehicle10is not in the middle of high speed hill climbing. Then, the process proceeds to step S23for performing the procedures as described above.

If the gradient A is the threshold value THA1or more (S26: YES), then, in step S27, the ECU24determines whether or not determination that the vehicle10is in the middle of high speed hill climbing should be fixed. Specifically, it is determined whether or not the counter C is equal to or more than the counter threshold value THC1for fixing the determination. If the counter C is less than the threshold value THC1(S27: NO), then, in step S28, the ECU24increments the counter C by 1, and the process proceeds to step S24. If the counter C is the threshold value THC1or more (S27: YES), the determination that the vehicle10is in the middle of high speed hill climbing is fixed, and the process proceeds to step S29.

In step S29, the ECU24sets the air conditioner limit correction value α (hereinafter also referred to as the “correction value α”). The correction value α is a value for limiting the output of the air conditioner130during high speed hill climbing, and the correction value α is determined based on the water temperature Tw of the coolant water detected by the temperature sensor70. More specifically, in the air conditioner limit correction value table shown inFIG. 8, the air conditioner limit correction value α corresponding to the water temperature Tw of the coolant water is used.

As can be seen fromFIG. 8, in the air conditioner limit correction value table, if the water temperature Tw is the threshold value Tw1or less, the correction value α is constant. Further, if the water temperature Tw exceeds the threshold value Tw1, the correction value α is increased gradually. Therefore, if the water temperature Tw exceeds the threshold value Tw1, as the water temperature Tw increases, the output limit on the air conditioner130is increased. Thus, as the water temperature Tw becomes high, it becomes possible to further suppress the increase in the temperature of the FC32.

In step S30ofFIG. 6, the ECU24calculates the air conditioner electric power limit value Palim during high speed hill climbing based on the following expression (2).
Palim=FCprimary side supply electric powerPsup−air conditioner limit correction value α−DVelectric power consumptionPdv(2)

In contrast to the air conditioner electric power limit value Palim (see the above expression (1)) in the case where the vehicle is not in the middle of high speed hill climbing (during normal operation), in the air conditioner electric power limit value Palim in the case where the vehicle is in the middle of high speed hill climbing (see expression (2)), the air conditioner limit correct value α is subtracted (S30), and there is no addition of the battery output limit value Pblim. Thus, electric power consumed by the air conditioner130is suppressed, and by providing electric power for the output of the motor14, improvement in the drivability is achieved. Further, by suppressing the output from the battery20, it becomes possible to prevent excessive discharging electric power from the battery20during high speed hill climbing.

In step S31, the ECU24determines the FC output upper limit value Pfclim based on the SOC of the battery20. More specifically, using an FC output upper limit value characteristic162at the time of high speed hill climbing in the FC output upper limit value table shown inFIG. 7, the FC output upper limit value Pfclim is determined in correspondence with the SOC.

As can be seen fromFIG. 7, in the FC output upper limit value characteristic162at the time of high speed hill climbing, the FC output upper limit value Pfclim is zero when the SOC is the SOC2or more. In comparison with the FC output upper limit value characteristic160during normal operation, the SOC where the FC output upper limit value Pfclim is zero is higher, for preventing the SOC of the battery20from being decreased to the lowest value (e.g., zero) even if the required system load Ls is kept high for long distance hill climbing.

Further, in the FC output upper limit value characteristic162during high speed hill climbing, when SOC is less than SOC3, the FC output upper limit value Pfclim is lower in comparison with the FC output upper limit value characteristic160during normal operation. This is intended to suppress overheating of the FC32, and maintain a desired drivability.

That is, in the present embodiment, except the case where the SOC is low from a time point immediately after long distance hill climbing is started, during long distance hill climbing (in particular, during high speed hill climbing), the SOC may be decreased gradually. In the present embodiment, the FC output upper limit value Pfclim is high (the FC output upper limit is relaxed) during long distance hill climbing (in a region where the SOC is between the SOC3and the SOC2). Therefore, the FC32could be overheated by power generation before the SOC becomes low (Since heat produced in the FC32is proportional to the square of the FC current Ifc, as the electrical current is higher, the amount of heat produced in the FC32is increased). In the case where the FC32is overheated, it may become necessary to take some actions, e.g., significantly limit power generation of the FC32, or stop power generation of the FC32. In the case where such actions are required, drivability becomes significantly poor in the middle of hill climbing. In the present embodiment, in the region where the SOC is low (less than SOC3), the FC output limit value Pfclim for SOC recovery which is performed during the normal condition is not high (FC output limit is not relaxed). Thus, even if long distance hill climbing continues, it becomes possible to suppress overheating of the FC32, and maintain a desired drivability.

Further, in the case where the FC output Pfc is increased in the state where the power generation efficiency is low, the fuel gas is consumed rapidly. Therefore, it is required to suppress the amount of consumption of the fuel gas at the time of long distance hill climbing, and prevent excessive use of the fuel gas.

3. Advantages of the Present Embodiment

As described above, in the present embodiment, in the case where long distance hill climbing (in particular, long distance high speed climbing) has been detected, the fuel cell's load Lfc (allocation amount of electric power outputted from the fuel cell) is controlled to be larger than that before detection of the long distance hill climbing (InFIG. 7, if the SOC exceeds SOC3, the FC output upper limit value Pfclim is increased). Thus, since the battery's load Lbat is decreased relatively, during long distance hill climbing of the FC vehicle10, it becomes possible to prevent the SOC of the battery20from being rapidly decreased due to large output discharging, and prevent assistance by the battery20from being disabled (i.e., it becomes possible to prevent the battery20from running out of electric power).

In the present embodiment, if the ECU24(long distance hill climbing detection function124) detects long distance hill climbing, the output of the air conditioner130is limited depending on increase in the temperature Tw of the coolant water. Thus, by limiting the output of the air conditioner130during the long distance hill climbing of the FC vehicle10, excessive electric power can be utilized for the output of the motor14. Additionally, for example, in the case where heat from the air conditioner130raises the temperature of the FC32or the coolant, or in the case where the coolant for the FC32is also utilized for cooling the air conditioner130, by limiting the output of the air conditioner130to suppress heat produced in the air conditioner130, even if the FC output Pfc is increased, it becomes possible to suitably protect the FC32against the heat. Further, it becomes possible to prevent the output and the efficiency of the FC32from being lowered due to overheating of the FC32.

In the present embodiment, the upper limit values SOC1and SOC2for performing power generation of the FC32are set. If the SOC exceeds the upper limit values SOC1and the SOC2, power generation of the FC32is not performed. If the ECU24(long distance hill climbing detection function124) detects long distance hill climbing, the upper limit value of the SOC is increased. In this manner, during long distance hill climbing, even if the SOC is high, power generation of the FC32can be performed. Thus, even if the required system load Ls is kept high for long distance hill climbing, since the output of the FC32can be adjusted suitably in accordance with the system load Ls, it becomes possible to prevent the SOC from being lowered at an early stage, and prevent assistance by the battery20from being disabled at an early stage.

In the present embodiment, the FC output upper limit value Pfclim is set depending on the SOC, and if the ECU24(long distance hill climbing detection function124) detects long distance hill climbing, in a region where the SOC is low, the FC output upper limit value Pfclim is lower in comparison with the case where long distance hill climbing is not detected (FIG. 7). In this manner, overheating of the FC32can be suppressed, and a desired drivability can be maintained.

That is, in the present embodiment, except the case where the SOC is low from a time point immediately after long distance hill climbing is started, during the long distance hill climbing (in particular, during high speed hill climbing), the SOC may be decreased gradually. In the present embodiment, since the FC output upper limit value Pfclim during long distance hill climbing is increased (the FC output limit is relaxed), the FC32may be overheated before the SOC becomes low (Since heat produced in the FC32is proportional to the square of the FC current Ifc, as the electrical current is higher, the amount of heat produced in the FC32is increased). In the case where the FC32is overheated, it becomes necessary to take some actions, e.g., significantly limit power generation of the FC32or stop power generation of the FC32. If such actions are required, the drivability becomes significantly poor in the middle of hill climbing. In the present embodiment, when the SOC is low (less than SOC3), the FC output upper limit value Pfclim for SOC recovery which is performed during the normal condition is not high (the FC output upper limit is not relaxed). Thus, even if long distance hill climbing continues, it becomes possible to suppress overheating of the FC32, and maintain a desired drivability.

Further, in the case where the FC output Pfc is increased in the state where the power generation efficiency is low, the fuel gas is consumed rapidly. In order to address the problem, in the present embodiment, the amount of consumption of the fuel gas is suppressed during long distance hill climbing. Thus, it becomes possible to prevent the fuel gas from being used excessively.

The present invention is not limited to the above described embodiment. The present invention can adopt various structures based on the description herein. For example, the following structure may be adopted.

[4-1. Application of Power Supply System]

Though the power supply system12is mounted in the FC vehicle10in the above described embodiment, the present invention is not limited in this respect. The power supply system12may be mounted in other objects. For example, the power supply system12may be used in movable objects such as electric power-assisted bicycles, ships, or air planes.

[4-2. Structure of Power Supply System12]

In the embodiments, the FC32and the battery20are arranged in parallel, and the DC/DC converter78is provided on the near side the battery20. However, the present invention is not limited in this respect. For example, as shown inFIG. 9, the FC32and the battery20may be provided in parallel, and a step-up, step-down, or step-up/step-down DC/DC converter170may be provided on the near side of the FC32. Alternatively, as shown inFIG. 10, the FC32and the battery20may be provided in parallel, the DC/DC converter170may be provided on the near side of the FC32, and the DC/DC converter78may be provided on the near side of the battery20. Alternatively, as shown inFIG. 11, the FC32and the battery20may be provided in series, and the DC/DC converter78may be provided between the battery20and the motor14.

[4-3. Determination of Long Distance Hill Climbing (High Speed Hill Climbing)]

In the above embodiment, determination of whether the FC vehicle10is in the middle of long distance hill climbing (in particular, high speed hill climbing) is made based on the vehicle velocity V calculated based on the motor rotation number Nm and the gradient A from the gradient sensor116(S22and S26ofFIG. 6). However, the present invention is not limited in this respect. For example, determination of whether the FC vehicle10is in the middle of long distance hill climbing may be made using the vehicle velocity V determined based on position information from a navigation apparatus (not shown). Alternatively, gradient information of roads may be stored in the navigation apparatus, or the gradient information may be obtained from an external apparatus (e.g., server) through wireless communication means (not shown) to use the gradient information.

Alternatively, in the case of determining whether or not the FC vehicle is in the middle of long distance hill climbing regardless of the vehicle velocity V, for example, step S22ofFIG. 6may be omitted, and the determination can be made by steps S26and S27. Alternatively, whether or not the FC vehicle is in the middle of long distance hill climbing can be determined based on map information of the navigation apparatus. Stated otherwise, in the case of using the counter C in step S27, determination of the long distance hill climbing is made based on continuation of hill climbing. In the case where determination is made based on the map information, it becomes possible to determine (predict) whether or not the FC vehicle10will run uphill a long distance.

[4-4. Output Limit of FC32]

In the above embodiment, in comparison with the case where the FC vehicle10is not in the middle of high speed hill climbing, in a range where the SOC exceeds SOC3, the FC output upper limit value Pfclim during high speed hill climbing is increased (the FC output upper limit is relaxed). However, the range where the FC output upper limit value Pfclim is increased is not limited to this range. For example, as shown inFIG. 12, even in the region where the SOC is low, an FC output upper limit value characteristic182during high speed hill climbing may exceed an FC output upper limit value characteristic180during normal operation. Further, instead of increasing the FC output upper limit value Pfclim, during the high speed hill climbing, the FC output Pfc during normal operation may be multiplied by a predetermined coefficient or a predetermined value may be added to the FC output Pfc during normal operation.

In the above embodiment, in comparison with the case where the FC vehicle10is not in the middle of high speed hill climbing, in the case where the FC vehicle10is in the middle of high speed hill climbing, the upper limit value of the SOC for performing power generation of the FC32is set to be high (normal state: SOC1→high speed hill climbing state: SOC2). However, the upper limit value of the SOC for performing power generation of the FC32may be set in a different manner. For example, during high speed hill climbing, the upper limit value may not be provided. Alternatively, the same upper limit value may be used regardless of whether the FC vehicle10is in the middle of high speed hill climbing or not.

[4-5. Output Limit of Air Conditioner130]

In the above embodiment, during high speed hill climbing, the air conditioner electric power limit value Palim is set depending on the temperature Tw of the coolant water for cooling the FC32(FIG. 8). However, the manner of limiting the output of the air conditioner130during high speed hill climbing is not limited in this respect. For example, during high speed hill climbing, as the system load Ls increases or the fuel cell's load Lfc increases, the air conditioner electric power limit value Palim may be set to be large. Alternatively, in the case where the FC vehicle10is in the middle of high speed hill climbing, as the gradient A is larger, or as the vehicle velocity V is higher, the air conditioner electric power limit value Palim may be set to be large. Alternatively, in the case where the FC vehicle10is in the middle of high speed hill climbing, the output of the air conditioner130may be adjusted to a predetermined lowest value (including zero).

In the above embodiment, the air conditioner electric power limit value Palim is provided during high speed hill climbing. Alternatively, the air conditioner electric power limit value Palim may not be provided.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the spirit of the invention as defined by the appended claims.