Control device for electric car

Abstract

An electric car (1) is capable of parallel travel in which a motor (4) and a drive shaft (9) are connected and disconnected by a motor clutch (6) in a state in which an engine (3) and the drive shaft (9) are directly connected. When the motor (4) and the drive shaft (9) are disconnected by the motor clutch (6), a vibration damping control unit (82) uses a generator (5) to apply cancellation torque (Tc) that cancels vibration of the drive shaft (9). The vibration damping control unit (82) suppresses the cancellation torque (Tc) in a sub-resonance region (frs).

Description

Control device for an electric vehicle

[0001] The present invention relates to a control device for an electric vehicle.

[0002] Conventionally, in an electric vehicle having an engine and a motor as drive sources, there is known one provided with an engine clutch for disconnecting the engine and the drive shaft, and a motor clutch for disconnecting the motor and the drive shaft (Patent Document 1).

[0003] Also, there is known an electric vehicle that performs parallel running using both an engine and a motor as drive sources. In parallel running, it is conceivable to connect or disconnect the motor and the drive shaft according to the necessity of assist by the motor while the engine is connected to the drive shaft.

[0004] In such parallel running, when the motor and the drive shaft are disconnected, it is conceivable to perform vibration damping control by a generator. However, there is a problem that the accuracy of detecting engine misfire deteriorates during parallel running.

[0005] Japanese Patent No. 7331936

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a control device for an electric vehicle that improves the accuracy of detecting engine misfire during parallel running.

[0007] To achieve the above objective, the electric vehicle control device according to the present invention is characterized as follows: an electric vehicle control device that controls an electric vehicle capable of parallel driving, wherein the motor and the drive shaft are connected by the clutch while the engine and the drive shaft are directly connected, and the motor and the drive shaft are connected and disconnected, the electric vehicle control device further comprises a vibration damping control unit that applies a cancellation torque to the drive shaft using the torque of the generator to cancel out vibrations of the drive shaft when the motor and the drive shaft are disconnected by the clutch, and the vibration damping control unit suppresses the cancellation torque in a predetermined frequency band.

[0008] The electric vehicle control device of the present invention has the effect of improving the accuracy of engine misfire detection during parallel driving.

[0009] The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by referring to the accompanying drawings and reading through the embodiments for carrying out the invention described below (hereinafter referred to as "embodiments").

[0010] Figure 1 is a block diagram of an electric vehicle to which the electric vehicle control device of the present invention is applied. Figure 2 is a functional block diagram of the control unit shown in Figure 1. Figure 3 shows the frequency characteristics of the gain G1 and phase θ1 of the vibration generated in the vehicle model in response to the vibration caused by the applied torque when a constant torque is applied to the vehicle model. Figure 4 shows the frequency characteristics of the gain G1 and phase θ1 of the output to the input of the vibration damping control unit of the present invention shown in Figure 1. Figure 5 is a flowchart showing the results of checking the misfire detection rate when the engine is artificially (forcibly) misfired in a conventional product when vibration damping control by the generator is not performed. Figure 6 is a flowchart showing the results of checking the misfire detection rate when the engine is artificially (forcibly) misfired in a conventional product when vibration damping control by the generator is performed. Figure 7 shows the frequency characteristics of the gain G1 and phase θ1 of the output to the input of the vibration damping control unit of a conventional product. Figure 8 is a flowchart showing the results of checking the misfire detection in the present invention when the engine is artificially (forcibly) misfired in a conventional product when vibration of the engine mount is occurring.

[0011] Specific embodiments of the present invention will be described below with reference to the figures.

[0012] Figure 1 is a block diagram of an electric vehicle to which the electric vehicle control device of the present invention is applied. The electric vehicle 1 is a plug-in hybrid vehicle (PHEV) or hybrid vehicle (HEV) that uses an engine 3 and a motor 4 as drive sources and is capable of external charging or external power supply. The electric vehicle 1 comprises a battery 2, an engine 3, a motor 4, a generator 5, an engine clutch 6, a motor clutch 7, and a control unit 8 as the "electric vehicle control device".

[0013] Battery 2 is charged with electricity generated by the generator 5 (described later) and electricity regenerated by the motor 4 (described later).

[0014] Engine 3 constitutes the power source in the electric vehicle and generates power by burning fuel. Engine 3 drives the drive shaft 9 attached to the drive wheel 10.

[0015] Motor 4 drives the drive shaft 9 by receiving power from battery 2. Motor 4 also has a regenerative function, recovering deceleration energy as electricity by being rotated along with the drive shaft 9 during deceleration. Motor 4 constitutes the power source in the electric vehicle 1.

[0016] The generator 5 generates electricity using the power of the engine 3 and also drives the drive shaft 9 by receiving power from the battery 2. The generator 5 constitutes the power source of the electric vehicle 1.

[0017] The engine clutch 6 engages and disengages the engine 3 and generator 5 from the drive shaft 9. The engine clutch 6 is provided to be movable from a disengagement position, where it disconnects the engine 3 and generator 5 from the drive shaft 9, to a connection position, where it connects the engine 3 and generator 5 from the drive shaft 9.

[0018] When the engine clutch 6 connects the engine 3 and generator 5 to the drive shaft 9, the power generated by the engine 3 and generator 5 is transmitted to the drive shaft 9. When the engine clutch 6 disconnects the engine 3 and generator 5 from the drive shaft 9, the power generated by the engine 3 and generator 5 is not transmitted to the drive shaft 9.

[0019] The motor clutch 7 connects and disconnects the motor 4 and the drive shaft 9. The motor clutch 7 is provided so as to be movable from a disconnection position that disconnects the motor 4 and the drive shaft 9 to a connection position that connects the motor 4 and the drive shaft 9. When the motor clutch 7 connects the motor 4 and the drive shaft 9, the power generated by the motor 4 is transmitted to the drive shaft 9. When the motor clutch 7 disconnects the motor 4 and the drive shaft 9, the power generated by the motor 4 is not transmitted to the drive shaft 9.

[0020] The control unit 8 consists of a storage unit that stores programs and the like, and a computer that operates according to the program. As shown in Figure 2, the control unit 8 includes a misfire detection unit 81, a vibration damping control unit 82, a passband filter 83, and an adder 84.

[0021] The misfire detection unit 81 receives the rotational speed of the drive shaft 9 detected by the rotational speed sensor 11. Based on the rotational speed, the misfire detection unit 81 determines the amount of variation (deviation) of the angular acceleration of the drive shaft 9, and detects a misfire in the engine 3 when the determined amount of variation is greater than or equal to a predetermined value.

[0022] The vibration damping control unit 82 controls the torque of the generator 5 to suppress torsional vibrations applied to the drive shaft 9 when the motor clutch 7 disconnects the motor 4 from the drive shaft 9. The rotational speed of the drive shaft 9 detected by the rotational speed sensor 11 is input to the vibration damping control unit 82 after passing through the passband filter 83. The vibration damping control unit 82 calculates a generator torque compensation value based on the change in rotational speed. The adder 84 adds the generator torque compensation value to the generator torque command and outputs it to the generator 5. This generator torque compensation value is output from the generator 5 as a cancellation torque Tc that cancels out torsional vibrations generated in the drive shaft 9, and the generator 5 can suppress vibrations of the drive shaft 9.

[0023] Next, the frequency characteristics of the gain and phase of the vehicle model will be described. Figure 3 shows the frequency characteristics of the gain G1 and phase θ1 of the vibration generated in the vehicle model in response to the vibration caused by the applied torque when a constant torque is applied to the vehicle model by the engine 3 and generator 5. As shown in the figure, the frequency characteristics of the gain G1 have two resonance regions: the main resonance region frm and the secondary resonance region frs.

[0024] The peak of the secondary resonance region frs is lower than the peak of the primary resonance region frm. The primary resonance region frm is the resonance region of torsional vibrations occurring in the drive shaft 9. The secondary resonance region frs is the resonance region of vibrations occurring in the engine mount. The primary resonance region frm and the secondary resonance region frs are determined in advance from the vehicle model.

[0025] The vibration damping control unit 82 outputs a generator torque compensation value that suppresses the cancellation torque Tc in the sub-resonance region frs (a predetermined frequency band). Specifically, the vibration damping control unit 82 has frequency characteristics of gain G2 and phase θ2 as shown in Figure 4. Figure 4 shows the frequency characteristics of gain G1 and phase θ1 of the output (= generator torque compensation value) of the vibration damping control unit 82 in response to the input.

[0026] As shown in Figure 4, the gain G2 increases from a frequency lower than the main resonance region frm as it approaches the main resonance region frm. This allows the cancellation torque Tc of the main resonance region frm output from the generator 5 to be increased. Furthermore, the gain G2 remains constant from the main resonance region frm to the sub-resonance region frs. This allows the cancellation torque Tc of the sub-resonance region frs output from the generator 5 to be set to 0. By suppressing the cancellation torque Tc of the main resonance region frm in this way, the accuracy of misfire detection by the misfire detection unit 81 during parallel driving can be improved.

[0027] Next, we will explain the background to the present invention. As explained in the background technology section, conventional electric vehicle control devices (hereinafter referred to as "conventional products") had a problem in that the accuracy of misfire detection deteriorated during parallel driving. In order to investigate the cause of the deterioration in misfire detection accuracy, the inventors conducted the following Test 1 on the conventional product.

[0028] Test 1: Multiple engine power ratios and multiple engine speeds were combined, and for each combination, engine 3 was simulated (forcibly) to misfire, and the misfire detection rate was checked. Test 1 was performed while the vehicles were moving in parallel and when motor 4 and drive shaft 9 were disconnected by motor clutch 7.

[0029] The results of Test 1 showed that when the engine power ratio was high, the misfire detection rate was high regardless of engine speed. When the engine power ratio was low, the misfire detection rate was found to be low in the engine speed range of 2000 rpm to 3000 rpm. Furthermore, the inventors conducted Tests 2 and 3, described below, to investigate the cause of the deterioration in misfire detection accuracy.

[0030] Test 2: In the conventional product, when vibration damping control by the generator 5 is not performed, the engine 3 is simulated (forcibly) to misfire, and the misfire detection rate is checked.

[0031] Test 3: While vibration damping control is being performed by the generator 5 in the conventional product, the engine 3 is simulated (forcibly) to misfire, and the misfire detection rate is checked.

[0032] Tests 2 and 3 were conducted with reduced engine output and an engine speed of 3000 rpm. Similar to Test 1, Tests 2 and 3 were performed during parallel driving and with the motor 4 and drive shaft 9 disconnected by the motor clutch 7. The results of Test 2 are shown in Figure 5, and the results of Test 3 are shown in Figure 6.

[0033] Figures 5(A) and 6(A) are time charts of the misfire detection results. Figures 5(B) and 6(B) are time charts of the torque (cancellation torque) output from the generator 5. Figures 5(C) and 6(C) are time charts of the forced misfire signal, showing the timing at which the engine 3 was forcibly misfired. Figures 5(D) and 6(D) are time charts of the angular acceleration of the drive shaft 9.

[0034] As shown in Figure 5, when vibration damping control by the generator 5 is not performed, misfire detection can be performed for all four forced misfire signals. When vibration damping control by the generator 5 is not performed, as shown in Figure 5(B), no cancellation torque Tc is output from the generator 5. Therefore, it was found that the disturbance in the angular acceleration of the drive shaft 9 due to the cancellation torque Tc is small, and the misfire detection rate is high.

[0035] As shown in Figure 6, when vibration damping control was performed by the generator 5, misfire detection was only possible for the latter two out of four forced misfire signals. When vibration damping control is performed by the generator 5, as shown in Figure 6(B), a cancellation torque Tc with a nearly constant period is output from the generator 5. This cancellation torque Tc disrupts the angular acceleration of the drive shaft 9. As a result, it becomes difficult to distinguish whether the fluctuation in angular acceleration is due to a misfire or vibration damping control, and it was found that the misfire detection rate deteriorates.

[0036] Next, the frequency characteristics of the gain G1 and phase θ1 of the conventional vibration damping control unit will be explained with reference to Figure 7. As shown in Figure 7, the gain G2 increases from frequencies lower than the main resonance region frm as it approaches the main resonance region frm. Also, the gain G2 decreases from the main resonance region frm to the sub-resonance region frs. As a result, in the conventional product, the cancellation torque Tc output from the generator 5 is large in both the main resonance region frm and the sub-resonance region frs. Furthermore, the frequency of the cancellation torque Tc generated from the generator 5 of the conventional product shown in Figure 6(B) is in the sub-resonance region frs.

[0037] Therefore, conventional products detect vibrations in the engine mount and output a cancellation torque Tc in a large sub-resonance region frs to counteract those vibrations. This cancellation torque Tc in the sub-resonance region frs is thought to be one of the reasons why misfire detection accuracy deteriorates.

[0038] In this embodiment, as shown in Figure 2, an engine clutch 6 is provided at one end of the drive shaft 9, and the engine 3 and generator 5 are located near the engine clutch 6. A motor clutch 7 is provided at the other end of the drive shaft 9, and the motor is located near the motor clutch 7. In such an engine mount structure, vibrations from the engine mount are easily transmitted to the drive shaft 9.

[0039] In this embodiment, by suppressing the cancellation torque Tc in the sub-resonance region frs, the disturbance of the angular acceleration of the drive shaft 9 caused by the cancellation torque Tc in the sub-resonance region frs is reduced, and the misfire detection accuracy is improved. In the vibration of the engine mount, torsional vibration of the drive shaft 9 hardly occurs.

[0040] Next, in order to confirm the effects of the present invention, the following Test 4 was conducted.

[0041] Test 4: In the control unit 8 of the electric vehicle 1 of this embodiment, when vibration of the engine mount occurs, the engine 3 is pseudo (forcedly) misfired, and misfire detection is confirmed.

[0042] Similar to Tests 2 and 3, Test 4 was also conducted with the engine output lowered and the engine speed set to 3000 rpm. Also, similar to Tests 2 and 3, Test 4 was conducted during parallel running and when the motor 4 and the drive shaft 9 were disconnected by the motor clutch 7. The results are shown in FIG. 8.

[0043] (A) of FIG. 8 is a time chart of the misfire detection result. (B) of FIG. 8 is a time chart of the torque output from the generator 5. (C) of FIG. 8 is a time chart of the forced misfire signal indicating the timing when the engine 3 is forcedly misfired. (D) of FIG. 8 is a time chart of the angular acceleration of the drive shaft 9.

[0044] As shown in (B) of FIG. 6, in the conventional product, vibration of the engine mount is detected, and a large cancellation torque Tc in the sub-resonance region frs is output. As shown in (D) of FIG. 6, a large disturbance occurs in the angular acceleration due to this cancellation torque Tc.

[0045] On the other hand, as is clear from the comparison between (B) of FIG. 6 and (B) of FIG. 8, in the product of the present invention, even when vibration of the engine mount occurs, the cancellation torque Tc in the sub-resonance region frs is not output. As shown in (D) of FIG. 8, a large disturbance of the angular acceleration due to the cancellation torque Tc does not occur. According to the control unit 8 of the electric vehicle 1 of this embodiment, five misfire detections could be performed for the output of six forced misfire signals. That is, the control unit 8 of the electric vehicle of this embodiment was able to improve the misfire detection accuracy compared to the conventional product.

[0046] According to the above-described embodiment, the vibration control unit 82 suppresses the cancellation torque Tc in the main resonance region frm. Thereby, it is possible to improve the misfire detection accuracy of the engine 3 during parallel running.

[0047] According to the above-described embodiment, the cancellation torque Tc in the main resonance region frm is 0. Thereby, it is possible to further improve the misfire detection accuracy of the engine 3.

[0048] In addition, according to the above-described embodiment, the sub-resonance region frs has been described as being derived from the vibration of the engine mount, but it is not limited to this. The sub-resonance region frs may occur due to another reason.

[0049] According to the above-described embodiment, the cancellation torque Tc in the sub-resonance region frs has been set to 0, but it is not limited to this. The cancellation torque Tc in the sub-resonance region frs may be suppressed to a magnitude that does not affect the detection accuracy of the misfire detection unit 81, and may be greater than 0. More specifically, in the present embodiment, the misfire detection unit 81 detects misfire of the engine 3 when the amount of change in the angular acceleration of the drive shaft 9 is greater than or equal to a predetermined value. If the fluctuation in the angular velocity of the drive shaft generated by the cancellation torque Tc in the sub-resonance region frs is less than the predetermined value, it may be greater than 0.

[0050] In the embodiment described above, the vibration damping control unit 82 constantly suppressed the cancellation torque Tc of the sub-resonance region frs to 0, but it is not limited to this. As explained in Test 1 described above, when the output ratio of the engine 3 is high, the misfire detection accuracy does not deteriorate even with the conventional product. Therefore, when the output ratio of the engine is above a predetermined ratio, the vibration damping control unit 82 is set to the frequency characteristics of the conventional product's gain G2 and phase θ1 shown in Figure 7. Alternatively, when the output ratio of the engine 3 is below a predetermined ratio, the vibration damping control unit 82 may be set to the frequency characteristics of the gain G2 and phase θ2 shown in Figure 4 to suppress the cancellation torque Tc of the sub-resonance region frs. In this case, when the output ratio of the engine 3 is high, the cancellation torque Tc of the sub-resonance region frs can be increased. As a result, vibration of the drive shaft 9 can be suppressed even further while improving the misfire detection accuracy.

[0051] Furthermore, when the output ratio of the engine 3 is above a predetermined ratio, the vibration damping control unit 82 sets the amount of suppression of the cancellation torque Tc in the sub-resonance region frs to be larger as the output ratio approaches the predetermined ratio. This further improves the accuracy of misfire detection.

[0052] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0053] The present invention aims to provide a control device for electric vehicles that improves the accuracy of engine misfire detection during parallel driving. This invention, which achieves this effect, is useful for electric vehicle control devices.

[0054] 1 Electric vehicle 2 Battery 3 Engine 4 Motor 5 Generator 7 Motor clutch (clutch) 8 Control unit (control device for electric vehicle) 9 Drive shaft 81 Misfire detection unit 82 Vibration damping control unit frs Sub-resonance band (predetermined frequency band) Tc Cancellation torque

Claims

1. A control device for an electric vehicle that controls an electric vehicle capable of parallel driving, wherein the engine and the drive shaft are directly connected and the motor and the drive shaft are connected and disconnected by the clutch, the control device further comprises a vibration damping control unit that applies a cancellation torque using the generator to cancel out vibrations of the drive shaft when the motor and the drive shaft are disconnected by the clutch, and the vibration damping control unit suppresses the cancellation torque in a predetermined frequency band.

2. A control device for an electric vehicle according to claim 1, wherein the cancellation torque in the predetermined frequency band is 0.

3. A control device for an electric vehicle according to claim 1, further comprising a misfire detection unit that detects a misfire state of the engine when the amount of fluctuation of the angular acceleration of the drive shaft is greater than or equal to a predetermined value, wherein the cancellation torque in the predetermined frequency band is suppressed to such an magnitude that the amount of fluctuation of the angular acceleration of the drive shaft generated by the cancellation torque is less than the predetermined value.

4. A control device for an electric vehicle according to claim 1, wherein the vibration damping control unit suppresses the cancellation torque in the predetermined frequency band when the output ratio of the engine is less than a predetermined ratio.

5. A control device for an electric vehicle according to claim 4, wherein the vibration damping control unit sets the amount of suppression of the cancellation torque to be larger as the output ratio of the engine approaches the predetermined ratio when the output ratio is greater than or equal to a predetermined ratio.

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