Hybrid vehicle and method for controlling running of the same

Abstract

To provide a hybrid vehicle that is configured so that a vehicle body can be avoided from vibrating in a state where an engine is dragged around, and a method for controlling running of the vehicle.SOLUTION: In a hybrid vehicle 100 which is equipped with a generator 103 connected to an engine 102 and a speed change gear 104 that transmits torque of the engine to a driving wheel, a control part 200 drives the driving wheel together with the torque of a motor 101 by making the generator 103 perform a powering operation to transmit the torque of the generator to the driving wheel through the speed change gear 104, and changes the change gear ratio of the speed change gear 104 so that the vibration frequencies of the engine caused by the rotation of the engine 102 depending on the rotation of the generator 103 avoid the resonance band of the vehicle.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a hybrid vehicle equipped with a transmission and its driving control technology.

Background Art

[0002] Generally, a hybrid vehicle includes a motor (electric motor), a generator (electric generator), and an engine (internal combustion engine), and can appropriately select driving modes such as series mode, parallel mode, and EV mode according to the driving situation. In the series mode, the motor is used as the power source for vehicle driving, and the engine is used as the power source for the generator. In the parallel mode, the motor and the engine are used as the power sources for vehicle driving. On the other hand, in the EV mode, only the motor is used as the power source for vehicle driving, and the engine is not used. Therefore, the EV mode is the quietest and is particularly suitable for driving in a low-noise environment where noise should be reduced. For example, Patent Document 1 discloses a driving control technology for ensuring the charge amount required for a hybrid vehicle to travel in the EV mode in a low-noise environment.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a hybrid vehicle, not only is it necessary to ensure the charge amount, but it may also be desirable to enhance the driving torque of the motor, for example, when starting on an uphill slope. However, in existing hybrid vehicles, it is not possible to improve the climbing performance without using the engine. Therefore, a method of making the generator perform a power running operation to enhance the driving force can be considered. However, since the generator and the engine are mechanically connected, the engine is rotated along with the rotation of the generator, resulting in the deterioration of drivability described below.

[0005] When an engine that is not operating is rotated by a generator, the pistons in the engine reciprocate. As a result, the air in the cylinder repeatedly compresses and expands, generating vibrations corresponding to the rotational speed. When this vibration frequency becomes the resonance frequency of the vehicle body, the vehicle body resonates and starts to shake violently, greatly deteriorating drivability. For example, resonance may occur during low-speed driving when the engine rotational speed is about 500 rpm, causing large shaking.

[0006] The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a hybrid vehicle and a driving control method thereof that can avoid vibrations of the vehicle body when the engine is being rotated.

Means for Solving the Problem

[0007] According to an embodiment of the present invention for achieving the above object, a hybrid vehicle includes a motor that drives drive wheels, an engine, a generator connected to the engine, a transmission that transmits the torque of the engine to the drive wheels, and a control unit that controls the motor, the engine, the generator, and the transmission. The control unit causes the generator to perform a power running operation, transmits the torque of the generator to the drive wheels via the transmission to drive the drive wheels together with the torque of the motor, and changes the gear ratio of the transmission so that the engine vibration frequency caused by the rotation of the engine following the rotation of the generator avoids the resonance band of the vehicle. Also, according to an embodiment of the present invention, if the vehicle speed at which the engine vibration frequency at the first gear ratio reaches the lower limit value of the resonance band is defined as the first vehicle speed, and the vehicle speed at which the engine vibration frequency at the second gear ratio smaller than the first gear ratio reaches the lower limit value of the resonance band is defined as the second vehicle speed, the control unit can switch from the first gear ratio to the second gear ratio when the vehicle speed reaches the first vehicle speed, and then switch from the second gear ratio to the first gear ratio when the vehicle speed reaches the second vehicle speed. Further, according to an embodiment of the present invention, the vehicle speed at which the engine vibration frequency at the first gear ratio reaches the lower limit value of the resonance band is defined as the first vehicle speed, and the vehicle speed at which the engine vibration frequency at the second gear ratio smaller than the first gear ratio reaches the lower limit value of the resonance band is defined as the second vehicle speed. When the vehicle speed reaches the second vehicle speed from a vehicle speed lower than the first vehicle speed in the state of the second gear ratio, the control unit can switch from the second gear ratio to the first gear ratio. Further, according to an embodiment of the present invention, the first gear ratio and the second gear ratio can be set such that when switching from the second gear ratio to the first gear ratio when the vehicle speed reaches the second vehicle speed, the engine vibration frequency at the first gear ratio is equal to or higher than the upper limit value of the resonance band. Further, according to an embodiment of the present invention, the control unit can slide the second vehicle speed toward the higher speed side as the gradient of the traveling direction of the vehicle increases. Further, according to an embodiment of the present invention, the control unit can slide the second vehicle speed toward the higher speed side as the acceleration of the vehicle decreases. Further, according to an embodiment of the present invention, when the load weight of the vehicle is lighter than the reference value, the control unit can slide the first vehicle speed and the second vehicle speed toward the higher speed side, and when the load weight of the vehicle is heavier than the reference value, the control unit can slide the first vehicle speed and the second vehicle speed toward the lower speed side. Further, according to an embodiment of the present invention, a predetermined margin can be provided for the upper limit value and the lower limit value of the resonance band, respectively. According to an embodiment of the present invention for achieving the above object, there is provided a driving control method for a hybrid vehicle including: a motor for driving drive wheels; an engine; a generator connected to the engine; a transmission for transmitting the torque of the engine to the drive wheels; and a control unit for controlling the motor, the engine, the generator, and the transmission. The control unit causes the generator to perform a power running operation, drives the drive wheels together with the torque of the motor by transmitting the torque of the generator to the drive wheels via the transmission, and changes the gear ratio of the transmission so that the engine vibration frequency caused by the rotation of the engine dependent on the rotation of the generator avoids the resonance band of the vehicle.

Advantages of the Invention

[0008] According to an embodiment of the present invention, it is possible to avoid a situation where the engine vibration frequency caused by the rotation of the engine dependent on the rotation of the generator enters the resonance band by changing the gear ratio of the transmission. Also, according to an embodiment of the present invention, the resonance band can be avoided by switching the gear ratio using the vehicle speed as an index. Also, according to an embodiment of the present invention, resonance can be surely avoided by setting the first gear ratio and the second gear ratio so as to avoid the resonance band. Also, according to an embodiment of the present invention, by sliding the second vehicle speed to the higher speed side as the slope increases, it is possible to avoid a situation where the engine vibration frequency enters the resonance band due to a decrease in the vehicle speed when switching the gear ratio on a slope. Also, according to an embodiment of the present invention, by sliding the second vehicle speed to the higher speed side as the acceleration decreases, it is possible to avoid a situation where the engine vibration frequency enters the resonance band due to a decrease in the vehicle speed when switching the gear ratio on a slope. Also, according to an embodiment of the present invention, by sliding the first vehicle speed and the second vehicle speed to the higher speed side when the load weight is light and to the lower speed side when the load weight is heavy, respectively, it is possible to avoid a situation where the vehicle speed decreases due to the load during gear ratio switching and the engine vibration frequency enters the resonance band. Further, according to an embodiment of the present invention, by providing a margin in the resonance band, it is possible to effectively avoid a situation where the engine vibration frequency enters the resonance band due to factors such as road surface conditions and loading conditions.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0010] Hereinafter, a hybrid vehicle according to an embodiment of the present invention will be described in detail.

[0011] 1. Vehicle Configuration Referring to FIGS. 1 and 2, an example of the configuration and control system of a hybrid vehicle (hereinafter also simply referred to as "vehicle") according to an embodiment of the present invention will be described.

[0012] In FIG. 1, a hybrid vehicle 100 according to an embodiment of the present invention includes a motor 101, an engine 102, a generator 103, and a transmission 104. As is well known, the motor 101 functions as a generator during regeneration, and the generator 103 can function as a motor during power running.

[0013] The motor 101 is connected to a differential gear 106 via a motor clutch 105, and the torque of the motor 101 is transmitted to the drive wheels 107. The engine 102, the generator 103, and the transmission 104 are interconnected by a gear mechanism 108. More specifically, the crankshaft of the engine 102 is gear-connected to the shaft of the generator 103 and the input shaft of the transmission 104, respectively. Thereby, the torque of the engine 102 is transmitted to the transmission 104 and the generator 103, and the torque of the generator 103 is transmitted to the transmission 104 via the gear of the engine 102.

[0014] Note that the configuration of the gear mechanism 108 is not limited to FIG. 1. For example, the respective rotating shafts of the engine 102 and the generator 103 may be directly connected without using a gear, or further, the input shaft of the transmission 104 may also be directly connected without using a gear.

[0015] The transmission 104 transmits the rotation of the input shaft to the output shaft at a desired gear ratio (gear ratio). The transmission 104 may be a transmission using gears or a continuously variable transmission not using gears. The output shaft of the transmission 104 is connected to the differential gear 106, and the torque of the engine 102 or the generator 103 can be transmitted to the drive wheels 107.

[0016] Note that the transmission 104 shown in FIG. 1 may include an engine clutch. That is, by connecting the engine clutch, the torque of the engine 102 or the generator 103 can be transmitted to the drive wheels 107 through the transmission 104. Also, by disengaging the engine clutch, it is possible to use the engine 102 exclusively for power generation by the generator 103.

[0017] Furthermore, the hybrid vehicle 100 includes a battery 109, a control unit 200, and various sensors such as various operation amount sensors (not shown), a vehicle speed sensor that detects the traveling speed V, and an acceleration sensor that detects the gradient and acceleration. The control unit 200 controls the motor 101, the engine 102, the generator 103, the transmission 104, and the clutch 105, and executes various controls including the traveling control according to the present embodiment described below.

[0018] Also, if the hybrid vehicle 100 is a plug-in hybrid (PHEV) type, the battery 109 may be charged by power supplied from a commercial power supply for home use or a rapid charging power supply of a charging stand by providing an external charging unit (not shown), or an external power supply unit (not shown) may be provided to supply power from the battery 109 to home appliances or the like. The control system will be described below with reference to FIG. 2.

[0019] In FIG. 2, the control unit 200 includes a vehicle ECU (Electronic Control Unit) 201, an MCU (Motor Control Unit) 202, an engine (ENG) ECU 203, a transmission ECU 204, a GCU (Generator Control Unit) 205, a BMU (Battery Control Unit) 206, and other control units. The vehicle ECU 201 is connected to the MCU 201, the engine ECU 203, the transmission ECU 204, the GCU 205, and the BMU 202, and is in charge of the overall control of the vehicle 100 including the traveling control according to the present embodiment.

[0020] In this embodiment, the vehicle ECU 201 can realize the functions of the resonance band setting unit 210 and the gear ratio switching unit 211 by executing a program on a processor, for example. These functions may be activated when starting, especially when a large driving torque is required, such as when starting in a loaded state or on an uphill road. As will be described later, the resonance band setting unit 210 inputs the gear ratio (gear ratio) of the transmission 104, the driving force of the vehicle, the acceleration / deceleration detection value, and the gradient to set the resonance band, and outputs it to the gear ratio switching unit 211. The gear ratio switching unit 211 switches the gear ratio of the transmission 204 so that the engine vibration frequency avoids the resonance band based on the current vehicle speed V and the gear ratio (gear ratio). This will be described in detail below.

[0021] 2. Setting of the resonance band As shown in FIG. 3, if the load applied to the suspension of the vehicle 100 is m and the spring constant is k, the resonance frequency fn of the vehicle can be calculated by fn = √(k / m) / 2π. The magnitude of the vibration of the vehicle 100 due to resonance increases near the resonance frequency fn and reaches a maximum at fn. Therefore, a predetermined range of ±Δf centered on the resonance frequency fn is set as the resonance band 304. Therefore, by controlling the gear ratio of the transmission 104 so that the vibration frequency of the engine 102 does not enter the resonance band 304, large vehicle vibrations can be avoided. Note that the upper limit value f U and the lower limit value f L may be set to the vibration frequency when the magnitude of the vibration is small enough not to affect drivability. Such vehicle vibrations due to resonance occur at low speeds when the rotational speed of the engine 102 is low (for example, ~500 rpm).

[0022] Also, the vibration distribution 301 of the resonance frequency fn with the load m slides toward the higher vibration frequency as the load m decreases (distribution 302), and slides toward the lower vibration frequency as the load m increases (distribution 303). Therefore, the resonance band 304 also varies depending on the load m. Since the load m changes depending on the loading weight including the number of passengers and the amount of luggage in the hybrid vehicle 100, the resonance band 304 also changes depending on the loading weight.

[0023] Note that the load m can be estimated by detecting the acceleration of the vehicle with respect to the driving force of the drive wheels 107, and when the vehicle 100 is on a slope, it may be estimated in consideration of the slope.

[0024] As shown in FIG. 4, when the resonance band 304 of the engine 102's vibration frequency is set, the vehicle speed V corresponding to the resonance band 304 can be determined according to the gear ratio. Here, the low gear 401 with a large gear ratio and the high gear 402 with a smaller gear ratio are exemplified. The respective gear ratios of the low gear 401 and the high gear 402 are relative. As will be described later, the change amounts of these gear ratios are selected such that, for example, after switching from the low gear 401 to the high gear 402, the vehicle speed increases, and when switching from the high gear 402 to the low gear 402 at a certain vehicle speed, the vibration frequency of the engine 102 can avoid the resonance band 304.

[0025] Hereinafter, when the drive wheels 107 are driven by the torque of the motor 101 and the torque of the generator 103 during parking, for example, starting on an uphill road is assumed. In this case, the hybrid vehicle 100 starts in the low gear 401 with a large gear ratio. As an example, the vehicle speed corresponding to the lower limit value f of the resonance band 304 in the low gear 401 is defined as the first vehicle speed V1, and the vehicle speed corresponding to the same lower limit value f in the high gear 402 is defined as the second vehicle speed V2. By switching the gear ratio at either the first vehicle speed V1 and the second vehicle speed V2 or by using the second vehicle speed V2 as an opportunity, it is possible to avoid the engine's vibration frequency from entering the resonance band 304. Hereinafter, the gear ratio switching control according to the embodiment of the present invention will be described using the control system shown in FIG. 2 as an example. L corresponding to is defined as the first vehicle speed V1, and the vehicle speed corresponding to the same lower limit value f L corresponding to is defined as the second vehicle speed V2. By switching the gear ratio at either the first vehicle speed V1 and the second vehicle speed V2 or by using the second vehicle speed V2 as an opportunity, it is possible to avoid the engine's vibration frequency from entering the resonance band 304. Hereinafter, the gear ratio switching control according to the embodiment of the present invention will be described using the control system shown in FIG. 2 as an example.

[0026] 3. Embodiment 3.1) First Embodiment 5, the resonance band setting unit 210 of the vehicle ECU 201 sets the amount of change in the gear ratio (the difference between low gear 401 and high gear 402) that can avoid the resonance band 304, and the first vehicle speed V1 and the second vehicle speed V2 as described above. When the vehicle speed V at low gear 401 reaches the first vehicle speed V1, the gear ratio switching unit 211 switches the gear ratio of the transmission 104 from low gear 401 to high gear 402. This reduces the vibration frequency of the engine to the vibration frequency at high gear 402, i.e., a frequency that is sufficiently lower than the lower limit value of the resonance band 304.

[0027] Next, when the vehicle speed V of the hybrid vehicle 100 increases in the high gear 402 and reaches the second vehicle speed V2, the gear ratio of the transmission 104 is switched from the high gear 402 to the low gear 401. This causes the engine vibration frequency to increase to the vibration frequency in the low gear 401, i.e., to a frequency higher than the upper limit value of the resonance band 304. By switching the gear ratio of the transmission 104 as shown in the curve 403 at the first vehicle speed V1 and the second vehicle speed V2 in this way, vibration due to resonance of the vehicle 100 can be effectively avoided.

[0028] Furthermore, since the resonance band setting section 210 can estimate the load m using the acceleration and the inclination relative to the driving force, it can set the resonance band 304A according to the increase or decrease in the load m, as exemplified in FIG.

[0029] 6, as the load m decreases, the resonance band slides in the direction of higher vibration frequency, i.e., toward corrected resonance band 304A, so that resonance band setting unit 210 can set first vehicle speed V1 and second vehicle speed V2 that can avoid resonance band 304A. As the load m increases, the resonance band slides in the direction of lower vibration frequency, so that first vehicle speed V1 and second vehicle speed V2 that can avoid the corrected resonance band can be set in the same way. Once the first vehicle speed V1 and second vehicle speed V2 that can avoid the resonance band and the amount of change in the gear ratio are set, the subsequent gear ratio switching control (curve 403A) is as described above.

[0030] As described above, according to the first embodiment of the present invention, a resonance band corresponding to the load m is set, and the gear ratio of the transmission 104 is switched so as to avoid the resonance band according to the vehicle speed. In this way, when only the motor 101 and the generator 103 generate torque at the start when driving force is required, resonance of the vehicle caused by the vibration of the engine 102 being rotated can be effectively avoided.

[0031] 3.2) Second Embodiment As described above, in the first embodiment, starting in the low gear 401 and switching the gear ratio of the transmission 104 from the low gear 401 to the high gear 402 when the vehicle speed V reaches the first vehicle speed V1. However, the present invention is not limited to this, and it is also applicable when starting in the high gear 402.

[0032] As illustrated in FIG. 7, according to the second embodiment of the present invention, when starting in the high gear 402 and the vehicle speed V increases and reaches the second vehicle speed V2, the gear ratio of the transmission 104 is switched from the high gear 402 to the low gear 401. As a result, the vibration frequency of the engine increases to a vibration frequency in the low gear 401, that is, a vibration frequency higher than the upper limit value of the resonance band 304. By switching the gear ratio of the transmission 104 as shown by the curve 403B with the second vehicle speed V2 as an opportunity in this way, vibration due to resonance of the vehicle 100 can be effectively avoided.

[0033] 3.3) Third Embodiment As described above, the resonance band can be avoided by switching the gear ratio of the transmission 104. However, various factors of change can be considered, such as when the loaded weight changes outside the measurement period of the load m, or when the speed decreases during the gear ratio switching. Therefore, it is desirable to avoid resonance of the vehicle even in the presence of such changes. Therefore, according to the third embodiment of the present invention, by providing margins at the upper and lower limits of the resonance band 304, it is possible to surely avoid the situation of entering the resonance band during gear ratio switching. Hereinafter, the third embodiment will be described with reference to FIG. 8. Here, the gear ratio switching control based on the first embodiment illustrated in FIG. 5 is illustrated. However, the present invention is not limited to this, and the gear ratio switching control based on the second embodiment illustrated in FIG. 7 is similarly applicable.

[0034] As shown in FIG. 8, an upper margin 304 is provided at the upper limit of the above-described resonance band 304 U and a lower margin 304 is provided at the lower limit L respectively. The upper limit of the upper margin 304 U is f Um and the lower limit of the lower margin 304 L is f Lm . The resonance band setting unit 210 treats the upper limit f Um and the lower limit f Lm of the resonance band 304 with margins as the upper limit value f U and the lower limit value f L of the first embodiment. That is, the vehicle speed corresponding to the lower limit f Lm in the low gear 401 is set as the first vehicle speed V1, and the vehicle speed corresponding to the same lower limit f Lm in the high gear 402 is set as the second vehicle speed V2.

[0035] When the first vehicle speed V1 and the second vehicle speed V2 are set by providing such margins in this way, the subsequent gear ratio switching control (curve 403A1) is as described in the first embodiment. That is, when the vehicle speed V in the low gear 401 reaches the first vehicle speed V1, the gear ratio switching unit 211 switches the gear ratio of the transmission 104 from the low gear 401 to the high gear 402. Subsequently, when the vehicle speed V of the hybrid vehicle 100 increases in the high gear 402 and reaches the second vehicle speed V2, the gear ratio of the transmission 104 is switched from the high gear 402 to the low gear 401. As a result, the engine vibration frequency rises to a high vibration frequency equal to or higher than the upper limit f U of the upper margin 304 Um .

[0036] As described above, according to the third embodiment of the present invention, by providing the upper margin 304 U and the lower margin 304 L in the resonance band, even if the gear ratio switching timing is deviated due to a variation factor, the resonance band 304 can be effectively avoided as long as it is within the margin range. The same gear ratio switching control is also applicable when starting in the high gear 402 as in the second embodiment and switching the gear ratio of the transmission 104 from the high gear 402 to the low gear 401 when the vehicle speed V reaches the second vehicle speed V2.

[0037] 3.4) Fourth Embodiment As described above, the resonance band can be avoided by switching the gear ratio of the transmission 104. However, as is well known, it may take time in seconds (for example, several seconds) to switch the gear ratio of the transmission 104. Therefore, when the acceleration is small or when the vehicle is moving at a low speed on an uphill road, the speed may drop significantly while the gear ratio is being switched, and the vehicle may reverse. In such a situation, the possibility of entering the resonance band when switching the gear ratio is high. For example, in FIG. 8 described above, when the vehicle speed has increased to the second vehicle speed V2 in the high gear 402 and is switched to the low gear 401, if it is an uphill road or the like, the vehicle speed may drop significantly from the second vehicle speed V2. In this case, even if it is switched to the low gear 401, the engine vibration frequency may enter the resonance band 304.

[0038] Therefore, according to the fourth embodiment of the present invention, margins are provided at the upper and lower limits of the resonance band 304, and the second vehicle speed V2 is slid toward the high-speed side within a range where it does not enter the resonance band as the slope increases. This avoids the situation of entering the resonance band when switching the gear ratio even when the acceleration is small or when starting on an uphill road with a large slope. Hereinafter, the fourth embodiment will be described with reference to FIG. 9. Here, the gear ratio switching control based on the first embodiment illustrated in FIG. 5 is exemplified. However, it is not limited thereto, and the gear ratio switching control based on the second embodiment illustrated in FIG. 7 can be similarly applied.

[0039] As shown in FIG. 9, an upper margin 304 U and a lower margin 304 L are provided for the above-described resonance band 304. The upper limit of the upper margin 304 U is f Um and the lower limit of the lower margin 304 L is f Lm Let it be. The resonance band setting unit 210 sets the lower limit f as described above LmThe first vehicle speed V1 and the second vehicle speed V2 corresponding thereto are set respectively. However, when the acceleration is less than a predetermined value or the gradient is greater than a predetermined value, a new second vehicle speed V2c is set by sliding the second vehicle speed V2 by a predetermined value ΔV2 to the higher speed side in anticipation of a decrease in the vehicle speed. Note that since the first vehicle speed V1 does not enter the resonance band 304 even if there is a decrease in the vehicle speed, it is not always necessary to change it.

[0040] The setting conditions for the new second vehicle speed V2c are as follows. Condition 1) In the high gear 402, the lower limit f of the resonance band 304 L is less than and the vehicle speed corresponding to the frequency as close as possible to the lower limit f L ; and Condition 2) Even if there is an assumed speed reduction 404, the engine vibration frequency when switching to the low gear 401 exceeds the upper limit f U of the upper margin 304 Um .

[0041] If the second vehicle speed V2c is set in this way, the subsequent shift ratio switching control is as shown by the curve 403A2. That is, even if the vehicle speed significantly decreases from the second vehicle speed V2c on an uphill road or the like, the engine vibration frequency exceeds the upper limit f U of the upper margin 304 Um when switching from the high gear 402 to the low gear 401, so the possibility of entering the resonance band 304 can be surely excluded. The same shift ratio switching control is also applicable when starting in the high gear 402 as in the second embodiment, the vehicle speed V increases, and when reaching the second vehicle speed V2c, the shift ratio of the transmission 104 is switched from the high gear 402 to the low gear 401.

[0042] 3.5) Fifth Embodiment As described in the first embodiment, if the load m decreases, the resonance band slides in the direction of higher frequency, and if the load m increases, the resonance band slides in the direction of lower frequency. By sliding the first vehicle speed V1 and the second vehicle speed V2 set corresponding to the resonance band to the low speed side or the high speed side in response to such a change in the load m, resonance can be avoided. Hereinafter, as a fifth embodiment of the present invention, a case where the acceleration decreases due to loading will be described with reference to FIG. 10. Here, the gear ratio switching control based on the first embodiment illustrated in FIG. 5 will be exemplified. However, the present invention is not limited thereto, and the gear ratio switching control based on the second embodiment illustrated in FIG. 7 can be similarly applied.

[0043] As shown in FIG. 10, it is assumed that the load m increases and the resonance band 304 marginally set as described above slides to the lower frequency side. The upper margin of the resonance band 304d at that time is 304 U , the upper limit thereof is f Um , and the lower margin is 304 L , the lower limit thereof is f Lm . Further, the increase in the load m can be detected by an acceleration sensor.

[0044] The resonance band setting unit 210 sets the first vehicle speed V1 and the second vehicle speed V2 corresponding to the lower limit of the lower margin of the resonance band 304 as described above. When an increase in the load is detected due to a decrease in acceleration from this reference state, a new first vehicle speed V1d is set by sliding the first vehicle speed V1 by a predetermined value ΔV1 to the low speed side according to the increased load, and a new second vehicle speed V2d is set by sliding the second vehicle speed V2 by a predetermined value ΔV2 to the low speed side.

[0045] The setting conditions for the first vehicle speed V2d are as follows. Condition a) The engine vibration frequency is less than the lower limit f L of the resonance band 304d in the high gear 402; and Condition b) The engine vibration frequency when switching from the high gear 402 to the low gear 401 is equal to or higher than the upper limit f U of the upper margin 304 Um .

[0046] Note that the first vehicle speed V1d is such that the engine vibration frequency is less than the lower limit f of the resonance band 304d in the low gear 401, desirably less than the lower limit f of the lower margin 304 L as described below. L of the lower margin 304 Lm That's all that is required.

[0047] By setting the first vehicle speed V1d and the second vehicle speed V2d in this way, the subsequent shift ratio switching control is as shown by the curve 403A3. That is, even if the load increases significantly on an uphill road or the like, the engine vibration frequency does not exceed the upper limit f of the upper margin 304 U when switching from the high gear 402 to the low gear 401, so the possibility of entering the resonance band 304 can be reliably eliminated. The same shift ratio switching control is also applicable when starting in the high gear 402 as in the second embodiment, the vehicle speed V increases, and when the second vehicle speed V2d is reached, the shift ratio of the transmission 104 is switched from the high gear 402 to the low gear 401. Um

[0048] 4. Effects As described above, according to the above embodiment of the present invention, a resonance band corresponding to the load m is set, and the shift ratio of the transmission 104 is switched so as to avoid the resonance band according to the vehicle speed. In this way, when only the motor 101 and the generator 103 generate torque at the start when driving force is required, the resonance of the vehicle caused by the vibration of the engine 102 being rotated can be effectively avoided.

Explanation of Reference Numerals

[0049] 100 Hybrid vehicle 101 Motor 102 Engine 103 Generator 104 Transmission 105 Motor clutch 106 Differential gear 107 Drive wheel 108 Gear mechanism 200 Control unit 201 Vehicle ECU 210 Resonance band setting unit 211 Shift ratio switching unit​ 304 resonance band 304 U Upper margin 304 L Lower margin 401 Low gear (large gear ratio) 402 High gear (small gear ratio) V1 First vehicle speed V2 Second vehicle speed

Claims

1. A hybrid vehicle comprising a motor for driving a driving wheel, an engine, a generator connected to the engine, a transmission for transmitting the torque of the engine to the driving wheel, and a control unit for controlling the motor, the engine, the generator, and the transmission, wherein the control unit operates the generator in a power running mode, and drives the driving wheel together with the torque of the motor by transmitting the torque of the generator to the driving wheel via the transmission, changes the gear ratio of the transmission so that the engine vibration frequency caused by the rotation of the engine following the rotation of the generator avoids the resonance band of the vehicle. A hybrid vehicle characterized by the above.

2. The vehicle speed at which the engine vibration frequency at the first gear ratio reaches the lower limit value of the resonance band is defined as the first vehicle speed, and the vehicle speed at which the engine vibration frequency at the second gear ratio smaller than the first gear ratio reaches the lower limit value of the resonance band is defined as the second vehicle speed. The control unit switches from the first gear ratio to the second gear ratio when the vehicle speed reaches the first vehicle speed, and then switches from the second gear ratio to the first gear ratio when the vehicle speed reaches the second vehicle speed. The hybrid vehicle according to Claim 1, characterized by the above.

3. The vehicle speed at which the engine vibration frequency at the first gear ratio reaches the lower limit value of the resonance band is defined as the first vehicle speed, and the vehicle speed at which the engine vibration frequency at the second gear ratio smaller than the first gear ratio reaches the lower limit value of the resonance band is defined as the second vehicle speed. The control unit switches from the second gear ratio to the first gear ratio when the vehicle speed reaches the second vehicle speed from a vehicle speed lower than the first vehicle speed in the state of the second gear ratio. The hybrid vehicle according to Claim 1, characterized by the above.

4. The first gear ratio and the second gear ratio are set such that when switching from the second gear ratio to the first gear ratio when the vehicle speed reaches the second vehicle speed, the engine vibration frequency at the first gear ratio is equal to or higher than the upper limit value of the resonance band. The hybrid vehicle according to Claim 2 or 3, characterized by the above.

5. The control unit slides the second vehicle speed toward the higher speed side as the gradient of the traveling direction of the vehicle increases. The hybrid vehicle according to Claim 4, characterized by the above.

6. The control unit slides the second vehicle speed toward the higher speed side as the acceleration of the vehicle decreases. The hybrid vehicle according to Claim 4, characterized by the above.

7. When the load weight of the vehicle is lighter than the reference value, the control unit slides the first vehicle speed and the second vehicle speed to the higher speed side, and when the load weight of the vehicle is heavier than the reference value, the control unit slides the first vehicle speed and the second vehicle speed to the lower speed side. The hybrid vehicle according to claim 4, characterized in that.

8. The hybrid vehicle according to any one of claims 1 to 3, characterized in that predetermined margins are provided for the upper limit value and the lower limit value of the resonance band, respectively.

9. A driving control method for a hybrid vehicle including a motor that drives drive wheels, an engine, a generator connected to the engine, a transmission that transmits the torque of the engine to the drive wheels, and a control unit that controls the motor, the engine, the generator, and the transmission, wherein the control unit operates the generator in a power running mode, and drives the drive wheels together with the torque of the motor by transmitting the torque of the generator to the drive wheels via the transmission, and changes the gear ratio of the transmission so that the engine vibration frequency caused by the rotation of the engine dependent on the rotation of the generator avoids the resonance band of the vehicle. A driving control method characterized by that.

10. The vehicle speed at which the engine vibration frequency at the first gear ratio reaches the lower limit value of the resonance band is defined as the first vehicle speed, and the vehicle speed at which the engine vibration frequency at the second gear ratio smaller than the first gear ratio reaches the lower limit value of the resonance band is defined as the second vehicle speed. The driving control method according to claim 9, characterized in that when the vehicle speed reaches the first vehicle speed, the control unit switches from the first gear ratio to the second gear ratio, and then when the vehicle speed reaches the second vehicle speed, the control unit switches from the second gear ratio to the first gear ratio.

11. The vehicle speed at which the engine vibration frequency at the first gear ratio reaches the lower limit value of the resonance band is defined as the first vehicle speed, and the vehicle speed at which the engine vibration frequency at the second gear ratio smaller than the first gear ratio reaches the lower limit value of the resonance band is defined as the second vehicle speed. The driving control method according to claim 9, characterized in that when the vehicle speed reaches the second vehicle speed from a vehicle speed lower than the first vehicle speed in the state of the second gear ratio, the control unit switches from the second gear ratio to the first gear ratio.

12. The first gear ratio and the second gear ratio are set such that when the vehicle speed reaches the second vehicle speed and is switched from the second gear ratio to the first gear ratio, the engine speed at the time of the first gear ratio becomes equal to or higher than the upper limit value of the resonance band. The running control method according to claim 10 or 11, characterized in that.

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