FUEL CELL VEHICLE WITH ELECTRIC MOTOR OUTPUT TORQUE CONTROL

Abstract

Fuel cell vehicle (2) with a battery (4) and a fuel cell (3) which supply electrical current to an electric motor (6) for driving, wherein a controller (10) which controls the electric motor (6) is configured such that it sets a maximum increase rate of an output torque of the electric motor (6) for a predetermined time after the fuel cell (3) has started activation to a first upper limit rate and sets the maximum rate of increase after the elapse of the predetermined time to a second upper limit rate that is greater than the first upper limit rate.

Description

The technique disclosed herein relates to a fuel cell vehicle including a battery and a fuel cell that supply electric power to an electric motor for traveling, and more particularly to a fuel cell vehicle having a controller that controls an output torque of the electric motor.JP 2008-301 542 A, JP 2008-312 418 A, JP 2009-44 835 A and DE 10 2015 119 266 A1 disclose a fuel cell vehicle which contains a battery and a fuel cell. The fuel cell vehicle disclosed in these documents can also travel with only the electric current of the battery before activation of the fuel cell.The maximum power of the battery is smaller than the maximum power of the fuel cell. The output torque of the electric motor is limited when the fuel cell vehicle runs only with the electric current of the battery. When the fuel cell is activated, the upper limit of the output torque of the electric motor increases. When the fuel cell is activated while a driver depresses an accelerator pedal and the output torque of the electric motor suddenly increases, the driver may feel uncomfortable.JP 2009-44 835 A proposes limiting the power consumption of the electric motor when the fuel cell vehicle is driving only with the electric current of the battery, and to gradually cancel the power limitation as soon as the fuel cell is activated. DE 10 2015 119 266 A1 proposes that, after activation of the fuel cell, different threshold values for the power consumption of the electric motor be established.The fuel cell vehicle disclosed herein includes, according to claim 1, a controller that sets a maximum increase rate of an output torque of the electric motor to a first upper limit rate for a predetermined time after the fuel cell starts activation, and sets the maximum increase rate to a second upper limit rate that is greater than the first upper limit rate after the lapse of the predetermined time. By suppressing the maximum increase rate for the predetermined time after the fuel cell starts activation to be smaller than the upper limit rate (the second upper limit rate) at a normal time, a sudden increase in the output torque is suppressed, which can reduce the feeling of discomfort given to the driver.The first upper limit rate may be set as follows. A time during which the output torque of the electric motor reaches a second maximum output torque from a first maximum output torque at the first upper limit rate is longer than an activation time of the fuel cell. The first maximum output torque is the maximum output torque when the fuel cell vehicle is running only with the battery, and the second maximum output torque is the maximum output torque after activation of the fuel cell. When the activation time elapses, the electric motor may output the second maximum output torque. However, when the output torque of the electric motor is rapidly increased during the activation time, the driver feels uncomfortable to a greater extent. Therefore, by setting the first upper limit rate as described above, it becomes possible to reduce the feeling of discomfort given to the driver.When the driver largely depresses the accelerator pedal even during activation of the fuel cell, the feeling of discomfort given to the driver is small even if the increase rate is large. In other words, the feeling of discomfort given to the driver is small when a change in the accelerator operation amount is large, although a change in the output torque is large. Based on this, the controller can adopt the following control rule. When the accelerator operation amount immediately before activation of the fuel cell exceeds a predetermined first operation amount, the controller sets the maximum increase rate to the first upper limit rate during the predetermined time. When the accelerator operation amount immediately before the activation of the fuel cell falls below the first operation amount, the controller sets the maximum increase rate to a third upper limit rate during the predetermined time. The third upper limit rate is greater than the first upper limit rate and less than or equal to the second upper limit rate.Details of the technique disclosed herein and further improvements are discussed further below in the detailed description of the embodiments.Referring now to the accompanying drawings, wherein like reference numerals designate like elements, features, advantages, and technical and industrial significance of an exemplary embodiment of the invention will be described. The following shows: FIG. 1 is a block diagram of a fuel cell vehicle of the embodiment; FIG. 2A is a graph showing the maximum output torque of an electric motor; and FIG. 2B is a graph showing the maximum increase rate of the output torque of the electric motor.FIG. 1 shows a block diagram of a fuel cell vehicle 2 according to an exemplary embodiment. The fuel cell vehicle 2 travels by means of an electric motor 6 with electric power supplied from a fuel cell 3 and a main battery 4. The fuel cell 3 and the main battery 4 are connected in parallel. Powers from the fuel cell 3 and the main battery 4 are converted into AC power by a converter 5 and supplied to the electric motor 6 for traveling. A boost converter may be connected between the fuel cell 3 and the power converter 5 (or between the fuel cell 3 and the main battery 4). A bidirectional voltage converter may be connected between the main battery 4 and the power converter 5. The broken lines in FIG. 1 represent signal lines.To the main battery 4, an input end of a buck converter 7 is connected, and to an output end of the buck converter 7, a sub-battery 8 is connected. The output voltage of the main battery 4 is more than 100 volts and the output voltage from the sub-battery 8 is below 50 volts. The step-down converter 7 decreases the output electric power from the main battery 4 or the fuel cell 3 to charge the sub-battery 8.The electric current of the sub battery 8 is supplied to a device operating at a voltage of less than 50 volts. Devices powered by the electric power from the secondary battery 8 include small-sized consumers such as a radio 20 and various controllers (computers). Various accessories attached to the fuel cell 3 are also supplied with the electric power from the sub battery 8.The fuel cell 3 and the power converter 5 are controlled by a controller 10. To the controller 10, sensors such as a main switch 11, an accelerator sensor 12, and a vehicle speed sensor 13 of the fuel cell vehicle 2 are connected. The accelerator pedal sensor 12 measures an operation amount of the accelerator pedal (accelerator operation amount). The controller 10 activates the fuel cell 3 when the main switch 11 is turned on. In addition, the controller 10 determines the output torque of the electric motor 6 based on information such as the operation amount of the accelerator pedal or an operation amount of a brake pedal (not shown) and a vehicle speed.The fuel cell 3 takes a predetermined time to be activated. Although the fuel cell 3 requires time to be activated, the fuel cell vehicle 2 may start running with the electric current from the main battery 4 immediately after the main switch 11 is turned on. However, the maximum output of the main battery 4 is smaller than the maximum output of the fuel cell 3. When the fuel cell 3 has been activated, the maximum output torque of the electric motor 3 suddenly increases. When the fuel cell 3 is activated while the driver depresses the accelerator pedal with a constant force and the output torque of the electric motor 6 suddenly increases, the driver may feel uncomfortable. The fuel cell vehicle 2 suppresses a rate of increase in output torque of the electric motor 6 while the fuel cell 3 is activated, which can suppress the feeling of discomfort given to the driver.The controller 10 determines the rate of increase of the output torque corresponding to the accelerator operation amount. As the accelerator operation amount increases, the increase rate also increases. In the controller 10, an upper limit value (a maximum increase rate) of the increase rate is set. The controller 10 suppresses the increase rate of the output torque to be equal to or less than the maximum increase rate.FIG. 2A is a graph showing the maximum output torque of the electric motor 6, and FIG. 2B is a graph showing the maximum increase rate of the output torque. The vertical axis of FIG. 2A represents the output torque of the electric motor 6, and the horizontal axis represents time. The vertical axis of FIG. 2B represents the rate of rise and the horizontal axis represents time.The main switch 11 is turned on at time T 0. The preparation for activation of the fuel cell 3 takes some time for a while after the main switch 11 is turned on. In FIGS. 2A and 2B, the time from the time T 0 to the time T 1 is the time (activation preparation period Pr) required for the activation preparation. The fuel cell vehicle 2 can travel with the electric power from the main battery 4 until the fuel cell 3 starts activation. The maximum output torque of the electric motor 6 when the fuel cell vehicle 2 travels with only the main battery 4 is a first maximum output torque Tm 1. The maximum output torque after activation of the fuel cell 3 is a second maximum output torque Tm 2. In medium and high vehicle speed ranges, the maximum output torque of the electric motor 6 depends on the vehicle speed. The graphs of FIGS. 2A and 2B show changes in the maximum output torque in a low vehicle speed region in which the maximum output torque does not depend on the vehicle speed.Activation of the fuel cell 3 starts at time T 1. From the time T 1, supply of fuel gas and oxidizing gas to the fuel cell 3 starts, and electric current starts to be discharged from the fuel cell 3. When the electric current starts to be output from the fuel cell 3, the maximum output torque of the electric motor 6 also increases. The activation of the fuel cell 3 is completed at time T 2. The time from the time T 1 to the time T 2 is the activation time Ps of the fuel cell 3.The fuel cell vehicle 2 can start traveling with the electric current from the main battery 4 immediately from the time T 0. The maximum output torque (the first maximum output torque Tm 1) from the electric motor 6 when the fuel cell vehicle 2 travels only with the electric current from the main battery 4 is smaller than the maximum output torque (the second maximum output torque Tm 2) when the fuel cell vehicle 2 travels with the electric current from the fuel cell 3. From the time T1 to the time T2, the maximum output torque of the electric motor 6 increases from the first maximum output torque Tm1 to the second maximum output torque Tm2. However, the controller 10 limits the rate of increase of the output torque of the electric motor 6 after the fuel cell 3 starts activation for a while.As shown in FIG. 2B, the controller 10 sets the maximum increase rate of the output torque of the electric motor 6 to a first upper limit rate dBt 1 for the predetermined time P 1 after the fuel cell 3 starts activation (time T 1). The controller 10 also sets the maximum increase rate during traveling with the electric current from only the main battery 3 to the first upper limit rate dVl 1. After the lapse of the predetermined time P 1, the controller 10 changes the maximum increase rate from the first upper limit rate dTm 1 to a second upper limit rate dTm 2. The second upper limit rate dVl 2 is greater than the first upper limit rate dVl 1.As described above, the fuel cell 3 starts activation at time T 1 and completes activation at time T 2. When no upper limit value is provided for the output torque, the output torque of the electric motor 6 can be increased at the second upper limit rate dTm 2 at the maximum (see curve G 2 in FIG. 2A ). When the driver largely depresses the accelerator pedal at the start of activation of the fuel cell 3 (time T1), the output torque of the electric motor 6 starts to largely increase from the time T1. When the output torque suddenly increases although the operation amount of the accelerator pedal is constant, the driver feels uncomfortable. The controller 10 limits the increase rate of the output torque of the electric motor 6 to the first upper limit rate dHc 1 or less after the fuel cell 3 starts activation for the predetermined time P 1. Therefore, the output torque of the electric motor 6 increases maximally along the curve G 1 in FIG. 2A. The fuel cell vehicle 2 according to the embodiment can suppress the feeling of discomfort given to the driver when the fuel cell 3 is activated.In FIG. 2A, the increase rate limited upon activation of the fuel cell 3 is represented by the second upper limit rate dTm 2. The second upper limit rate dSm 2 is the maximum increase rate after the fuel cell 3 is activated. Therefore, the second upper slew rate dTm 2 is not necessarily consistent with the curve G 2 in FIG. 2A. However, the second upper limit rate dVl 2 is larger than the first upper limit rate dVl 1.The first upper limit rate dTm 1 is set such that the time (time P 1 in FIG. 2A ) during which the torque of the electric motor 6 reaches the second maximum torque Tm 2 from the first maximum torque Tm 1 at the first upper limit rate dTm 1 is longer than the activation time Ps of the fuel cell 3. The fuel cell 3 has the capability of increasing the maximum output torque from the first maximum output torque to the second maximum output torque during the activation time Ps. However, the maximum increase rate of the electric motor 6 is set to the first upper limit rate dVl 1 (which is less than the second upper limit rate dVl 2), thereby suppressing the feeling of discomfort given to the driver.The predetermined time P 1 is set to the time required for the torque of the electric motor 6 to reach the second maximum torque Tm 2 from the first maximum torque Tm 1 at the first upper limit rate dTm 1. When the accelerator operation amount at the start of activation of the fuel cell 3 (time T 1) is 100%, the maximum output torque of the electric motor 6 reaches the second maximum output torque Tm 2 during the predetermined time P 1. Even when the accelerator operation amount is 100%, the increase rate of the output torque is kept constant until the output torque reaches the second maximum output torque Tm2.When the accelerator operation amount immediately before activation of the fuel cell 3 falls below a predetermined first operation amount, the controller 10 sets the maximum increase rate to a third upper limit rate dTm 3 during the predetermined time P 1. FIGS. 2A and 2B show the case where the curve G 3 indicated by the alternate long and short dash line is the third upper limit rate dTm 3. As shown in FIGS. 2A and 2B, the third upper limit rate dTm 3 is greater than the first upper limit rate dTm 1 and is equal to or less than the second upper limit rate dTm 2. The reason for increasing the upper limit rate when the gas operation amount immediately before the activation of the fuel cell 3 falls below the predetermined first operation amount will now be described.When the driver largely depresses the accelerator pedal during the activation of the fuel cell 3, the feeling of discomfort given to the driver is small even if the increase rate is large. In other words, the feeling of discomfort given to the driver is small when a change in the accelerator operation amount is large, although a change in the output torque is large. Therefore, when the accelerator operation amount immediately before activation of the fuel cell 3 falls below the predetermined first operation amount, the controller 10 sets the maximum increase rate to the third upper limit rate dDc 3 during the predetermined time. When the change in the accelerator operation amount is large, the acceleration of the vehicle can be improved. The first operation amount is set to 60%, for example.The electric motor 6 operates with the electric current supplied from the power converter 5. Suppressing the rate of increase of the electric current supplied to the electric motor 6 can therefore suppress the rate of increase of the output torque of the electric motor 6. A rate of increase dPm of the electric current supplied to the electric motor 6 can be obtained by using the rate of increase (for example, the first upper limit rate dTm 1) of the output torque based on Equation 1 below.The symbols used in Equation 1 mean the following.dt: Control cycle of power converter 5Pm 1: Electric current supplied to the electric motor 6 in the current control cyclePm 2: Electric current supplied to the electric motor 6 in the next control cycleNm 1: Instantaneous rotational speed of the electric motor 6Nm2: Scheduled rotational speed of the electric motor 6 in the next control cycledNm: Rate of rise of the rotational speed of the electric motor 6Tm1: Instantaneous output torque of the electric motor 6Tm2: Scheduled output torque of the electric motor 6 in the next control cycledTm 1: Rate of Increase of Output Torque of Electric Motor 6 (First Upper Limit Rate)Setting the maximum increase rate of the output torque of the electric motor 6 to the first upper limit rate is equivalent to providing the increase rate of the electric current supplied to the electric motor 6 according to Equation 1.The points regarding the technique described in the embodiment to be noted will now be explained. The controller 10 limits the rate of increase of the output torque of the electric motor 6 to the first upper limit rate (or the second upper limit rate or the third upper limit rate) or less. In other words, the controller 10 changes the increase rate according to the accelerator operation amount and sets the maximum increase rate to the first upper limit rate (or the second upper limit rate or the third upper limit rate). The increase rate when the accelerator operation amount is small may be less than the first upper limit rate (or the second upper limit rate or the third upper limit rate).The controller 10 limits the increase rate of the output torque of the electric motor 6 to the first upper limit rate dHc 1 or less for the predetermined time P 1 after the fuel cell 3 starts activation. In other words, the controller 10 sets the maximum increase rate of the output torque of the electric motor 6 to the first upper limit rate dTm 1 for the predetermined time P 1 after the fuel cell 3 starts activation. The controller 10 limits the increase rate after the lapse of the predetermined time P 1 to the second upper limit rate dLn 2 or less that is larger than the first upper limit rate dLn 1. In other words, the controller 10 sets the maximum increase rate after the lapse of the predetermined time P 1 to the second upper limit rate dLn 2 that is larger than the first upper limit rate dLn 1.In other words, the control of the controller 10 is as follows. For the predetermined time P 1 after the fuel cell 3 starts activation, the controller 10 sets the increase rate of the output torque of the electric motor 6 to the first upper limit rate dVl 1 when the accelerator operation amount is 100%. When the accelerator operation amount at this time is less than 100%, the increase rate of the output torque is less than or equal to the first upper limit rate dTm 1. After the lapse of the predetermined time P 1, the controller 10 limits the increase rate of the output torque to the second upper limit rate dLn 2 that is larger than the first upper limit rate dLn 1 when the accelerator operation amount is 100%. When the accelerator operation amount at this time is less than 100%, the increase rate of the output torque is less than the second upper limit rate dVl2.While a specific embodiment of the invention has been described in detail above, this is only an example that is not intended to limit the scope of the claims.

Claims

A fuel cell vehicle (2) including a battery (4) and a fuel cell (3) that supplies electric power to an electric motor (6) for running, wherein a controller (10) that controls the electric motor (6) is configured to set a maximum increase rate of an output torque of the electric motor (6) to a first upper limit rate for a predetermined time after the fuel cell (3) starts activation, and set the maximum increase rate to a second upper limit rate that is larger than the first upper limit rate after the lapse of the predetermined time.The fuel cell vehicle (2) according to claim 1, wherein the controller (10) is configured to set the first upper limit rate such that a time during which the output torque of the electric motor (6) from a maximum output torque when the fuel cell vehicle (2) travels only with the battery (4) reaches a maximum output torque at the first upper limit rate after the activation of the fuel cell (3) is longer than an activation time of the fuel cell (3).The fuel cell vehicle (2) according to claim 1 or 2, wherein the controller (10) is configured to set the maximum increase rate for the predetermined time to the first upper limit rate when an operation amount immediately before activation of the fuel cell (3) exceeds a predetermined first operation amount, and set the maximum increase rate for the predetermined time to a third upper limit rate when the operation amount immediately before activation of the fuel cell (3) falls below the first operation amount, the third upper limit rate being greater than the first upper limit rate and less than the second upper limit rate.

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