JP5288145B2 - Gear ratio control device and gear ratio control method - Google Patents

Description

  The present invention relates to a transmission ratio control device and a transmission ratio control method for controlling a transmission ratio of a transmission mechanism.

  In Patent Document 1, the engine output is transmitted to the wheels via the continuously variable transmission to drive the vehicle, and the vehicle can be driven by a drive motor arranged in parallel with the engine. Disclosed is a hybrid vehicle that is configured to temporarily stop an engine and drive a wheel by a drive motor to drive the vehicle.

  FIG. 9 is a schematic diagram showing a configuration of a power transmission device for a hybrid vehicle disclosed in Patent Document 1. As shown in FIG. As shown in FIG. 9, the hybrid vehicle includes a metal V-belt continuously variable transmission mechanism 20 that changes the rotation of the engine E, a forward clutch 14 that performs engagement / disengagement control between the engine E and the continuously variable transmission 20, and a reverse drive. The brake 15 and a second motor generator 50 capable of driving the wheels 36 in parallel with the engine E are configured, and the control device is driven by the engine-driven first hydraulic pump 3 and the pump driving electric motor 55. A second hydraulic pump 56 and a forward / reverse clutch control valve for switching and controlling the operating hydraulic pressure supply to the forward clutch 14 and the like are provided. When the engine E stops and travels, the control device releases the forward clutch 14 and the like by the forward / reverse clutch control valve, drives the second hydraulic pump 56 by the pump driving electric motor 55, and uses the hydraulic pressure thereof. Shift control of the continuously variable transmission 20 is performed according to the driving state at that time.

JP 2001-200920 A

  The control device described in Patent Document 1 described above sets the target speed ratio RT while the engine E is stopped while the hybrid vehicle is running with the driving force from the second motor generator 50 in a state where the engine E is stopped. It is determined from the vehicle speed V and the accelerator pedal opening AP. Further, the control device controls the speed ratio in the continuously variable transmission 20 according to the magnitude relationship between the difference between the target speed ratio RT and the actual speed ratio RA (speed ratio deviation RE = RT−RA) and a predetermined value. With this control, the fuel efficiency and drivability are improved when switching from traveling by the second motor generator 50 with the engine E stopped to traveling by the engine E. However, if the predetermined value to be compared with the gear ratio deviation RE is a fixed value, the fuel consumption deteriorates due to energy consumption accompanying unnecessary change of the gear ratio depending on the driving conditions.

  The object of the present invention is to change the speed ratio of the speed change mechanism in preparation for traveling by the power from the first power source when the first power source is stopped and traveling only by the power from the second power source. It is to provide a transmission ratio control device and a transmission ratio control method capable of minimizing the performance while maintaining a good state.

  In order to solve the above-described problems and achieve the object, a transmission ratio control device according to a first aspect of the present invention is a first power source (for example, in the embodiment) that generates power for a vehicle to travel. An internal combustion engine 103), a first transmission for transmitting power from the first power source to driving wheels of the vehicle (for example, driving wheels 119 in the embodiment), the first transmission, and the driving wheels. And a one-way clutch (for example, the one-way clutch 120 in the embodiment) that can transmit only the power from the power source to the drive wheel side, and the drive from the first power source A speed change mechanism (for example, continuously variable transmission 105 in the embodiment) that transmits power to the wheels, and a second power source that generates power for running the vehicle (for example, electric motor 101 in the embodiment) And a drive system comprising: A transmission ratio control device (for example, the management ECU 115 in the embodiment) that controls the transmission ratio of the transmission mechanism, and a transmission ratio that can be set in the transmission mechanism when traveling by power from the first power source. A second range of the gear ratio of the transmission mechanism that is set in a state where the first power source is stopped based on a first range and a change amount of the gear ratio that can be changed during startup of the first power source. The gear ratio range deriving unit (for example, the upper / lower limit ratio calculating unit 151 in the embodiment) and the gear ratio range deriving unit derive while the vehicle is traveling only by the power from the second power source. Only when the transmission ratio of the transmission mechanism does not fall within the second range, the transmission ratio control unit (for example, in the embodiment) controls the transmission mechanism so that the transmission ratio of the transmission mechanism is within the second range. Gear ratio control unit 153 It is characterized by having a and.

  Furthermore, in the transmission ratio control apparatus according to the second aspect of the invention, the transmission ratio range deriving unit rotates the first power source when the vehicle travels using only the power from the first power source. The first range is derived based on a number range and a rotation speed range on the output side of the transmission mechanism.

  Furthermore, in the transmission ratio control apparatus according to claim 3, the second range adds the change amount to a lower limit of the first range from a lower limit value obtained by subtracting the change amount from the upper limit of the first range. It is characterized by being in the range up to the upper limit value.

  Further, in the transmission ratio control apparatus according to the invention of claim 4, the transmission ratio range deriving unit derives the second range when the vehicle is traveling only by power from the second power source. It is characterized by.

  Further, in the transmission ratio control apparatus according to the fifth aspect of the present invention, the first power source is an internal combustion engine, the second power source is an electric motor, and the drive system is driven from the second power source. A transmission ratio control device comprising a connecting / disconnecting portion (for example, clutch 109 in the embodiment) for connecting / disconnecting a power transmission path to a wheel.

  Furthermore, in the transmission ratio control method according to the sixth aspect of the present invention, a first power source (for example, the internal combustion engine 103 in the embodiment) that generates power for traveling of the vehicle, and the first power source. Is transmitted between the first transmission and the driving wheel, and is transmitted from the power source to the driving wheel of the vehicle (for example, the driving wheel 119 in the embodiment). A one-way clutch (for example, the one-way clutch 120 in the embodiment) that can transmit only the power to the drive wheel side, and a transmission mechanism that transmits power from the first power source to the drive wheel (for example, The speed change mechanism in a drive system including a continuously variable transmission 105) according to an embodiment and a second power source (for example, the electric motor 101 according to the embodiment) that generates power for the vehicle to travel. To control the gear ratio A control method comprising: a first range of a gear ratio that can be set in the speed change mechanism when traveling by power from the first power source; and a change in the gear ratio that can be changed during startup of the first power source. A second range of a transmission gear ratio of the transmission mechanism set in a state where the first power source is stopped based on the amount, and the vehicle is traveling only by power from the second power source, The transmission mechanism is controlled such that the transmission ratio of the transmission mechanism is within the second range only when the transmission ratio of the transmission mechanism does not fall within the second range derived by the transmission ratio range deriving unit. Yes.

  According to the transmission ratio control device of the inventions described in claims 1 to 5 and the transmission ratio control method described in claim 6, the first power source is stopped and the vehicle travels only with the power from the second power source. It is possible to minimize the change in the speed ratio of the speed change mechanism in preparation for traveling by power from one power source while maintaining the fuel consumption and drivability in a good state.

Block diagram showing the internal configuration of a parallel HEV Side sectional view of a part of the continuously variable transmission 105 viewed from the axial direction Flowchart when the management ECU 115 controls the ratio of the continuously variable transmission 105 Flowchart when the management ECU 115 calculates the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped. Graph showing BSFC and rotational speed NE of internal combustion engine 103 with respect to required output P The graph which shows an example of the relationship between the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped, and the lower limit imin and the upper limit imax of the ratio that can be set in the continuously variable transmission 105 when the engine is running. A graph showing an example of (a) the vehicle speed, (b) the calculated upper and lower limit ratio, the actual ratio of the controlled continuously variable transmission 105, and (c) the operating state of the internal combustion engine 103 when the vehicle is traveling. The block diagram which shows the internal structure of the other form of HEV of a parallel system Schematic which shows the structure of the power transmission device of the hybrid vehicle disclosed by patent document 1

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The transmission ratio control device of the present embodiment is mounted on a HEV (Hybrid Electrical Vehicle). The HEV includes an electric motor and an internal combustion engine, and travels by the driving force of the electric motor and / or the internal combustion engine according to the traveling state of the vehicle. There are two types of HEVs: a series method and a parallel method. The series-type HEV travels by the power of the electric motor. The internal combustion engine is used only for power generation, and the electric power generated by the power generator by the power of the internal combustion engine is charged in the capacitor or supplied to the electric motor.

  The parallel HEV travels by the power of one or both of the electric motor and the internal combustion engine. Hereinafter, traveling using only the driving force of the electric motor is referred to as “EV traveling”, traveling using only the driving force of the internal combustion engine is referred to as “engine traveling”, and both the driving force of the electric motor and the driving force of the internal combustion engine are referred to. The travel that is used is called “parallel travel”.

  FIG. 1 is a block diagram showing an internal configuration of a parallel HEV. As shown in FIG. 1, a parallel HEV (hereinafter simply referred to as “vehicle”) includes an electric motor (Mot) 101, an internal combustion engine (ENG) 103, a continuously variable transmission 105 having a four-bar linkage mechanism, a differential, A gear 107, a clutch 109, a vehicle speed sensor 111, a rotation speed sensor 113, and a management ECU (MG ECU) 115 are provided. One embodiment of the gear ratio control apparatus according to the present invention corresponds to the management ECU 115. In FIG. 1, dotted arrows indicate value data, and solid lines indicate control signals including instruction contents.

  The electric motor 101 generates power for the vehicle to travel. The output of the electric motor 101 is transmitted to the axle 117 via the clutch 109 and the differential gear 107. The internal combustion engine 103 generates power for the vehicle to travel. The output of the internal combustion engine 103 is input to the continuously variable transmission 105.

  The continuously variable transmission 105 converts the rotational motion of the input shaft (drive shaft) into a swing motion, further converts the swing motion into a rotational motion, and outputs it from the output shaft (driven shaft). A continuously variable transmission (variable transmission) (hereinafter also referred to as “BD”). In the present embodiment, no clutch is required between the continuously variable transmission 105 and the internal combustion engine 103, and the output of the internal combustion engine 103 is input to the input shaft of the continuously variable transmission 105 as it is. In addition, the electric motor 101 is connected to the output side of the continuously variable transmission 105 via a clutch 109.

  FIG. 2 is a side sectional view of a part of the continuously variable transmission 105 as viewed from the axial direction. The continuously variable transmission 105 converts the rotary motion of the output shaft of the internal combustion engine 103 into a swing motion, and further converts the swing motion into a rotary motion. Therefore, in the continuously variable transmission 105, the gear ratio can be changed steplessly by adjusting the eccentricity r1, and the maximum value of the gear ratio can be set to infinity. In the continuously variable transmission 105, the output rotational speed is zero when the gear ratio is set to infinity. As shown in FIG. 2, the continuously variable transmission 105 includes an eccentric body driving device whose input shaft is directly connected to the crankshaft of the internal combustion engine 103, a one-way clutch 120 provided on the output side, an eccentric body driving device and a one-way And a connecting member 130 for connecting the clutch 120.

  The eccentric body drive device includes an input shaft 102 that rotates around the input center axis O <b> 1 by receiving rotational power from the internal combustion engine 103, and an eccentric disk 104 that rotates integrally with the input shaft 102. The transmission of power from the input member 122 to the output member 121 of the one-way clutch 120 is performed under the condition that the rotational speed of the input member 122 in the positive direction (the arrow RD1 direction in FIG. 2) exceeds the rotational speed of the output member 121 in the positive direction. Only done. In other words, in the one-way clutch 120, meshing (locking) occurs through the roller 123 only when the rotational speed of the input member 122 becomes higher than the rotational speed of the output member 121, and the swinging power of the input member 122 is output. It is converted into the rotational motion of the member 121. Therefore, in the vehicle shown in FIG. 1, the internal combustion engine 103 is driven only when the positive rotation speed of the input member 122 in the one-way clutch 120 by the output of the internal combustion engine 103 exceeds the positive rotation speed of the output member 121. Is transmitted to the drive wheels 119 via the continuously variable transmission 105.

  The differential gear 107 distributes the driving force transmitted from the electric motor 101 and / or the internal combustion engine 103 to the left and right axles 117. The clutch 109 opens and closes a driving force transmission path from the electric motor 101 to the differential gear 107. The clutch 109 is controlled by the management ECU 115.

  The vehicle speed sensor 111 detects the traveling speed (vehicle speed) of the vehicle. A signal indicating the vehicle speed detected by the vehicle speed sensor 111 is sent to the management ECU 115. The rotation speed sensor 113 detects the rotation speed (input rotation speed of the continuously variable transmission 105) NE of the internal combustion engine 103.

  The management ECU 115 performs overall control of the electric motor 101, the internal combustion engine 103, the continuously variable transmission 105, and the like. For example, if the management ECU 115 determines that it is necessary to start the internal combustion engine 103 based on the AP opening and the vehicle speed VP while the vehicle is traveling on EV, the management ECU 115 performs start control of the internal combustion engine 103. The management ECU 115 also has a signal from the vehicle speed sensor 111 (a signal indicating the vehicle speed VP), a signal from the rotation speed sensor 113 (a signal indicating the rotation speed NE of the internal combustion engine 103), and an accelerator pedal operated by the driver. A signal indicating the opening (AP opening) is input. The management ECU 115 derives the required output P based on the vehicle speed VP and the AP opening, and determines the speed ratio (hereinafter referred to as “ratio”) of the continuously variable transmission 105 corresponding to the state of the internal combustion engine 103 corresponding to the required output P. Control.

  As shown in FIG. 1, the management ECU 115 includes an upper / lower limit ratio calculation unit 151 and a gear ratio control unit 153 related to the ratio control of the continuously variable transmission 105. The upper and lower limit ratio calculation unit 151 calculates the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped. The transmission ratio control unit 153 controls the ratio of the continuously variable transmission 105 based on the upper and lower limits of the ratio and the actual ratio calculated by the upper and lower limit ratio calculation unit 151.

  FIG. 3 is a flowchart when the management ECU 115 controls the ratio of the continuously variable transmission 105. As shown in FIG. 3, the management ECU 115 determines whether or not the internal combustion engine 103 is stopped based on the rotational speed NE of the internal combustion engine 103 indicated by the signal from the rotational speed sensor 113 (step S101). In the determination in step S101, if the rotational speed NE = 0, it is determined that the internal combustion engine 103 is stopped and the process proceeds to step S103. If the rotational speed NE ≠ 0, it is determined that the internal combustion engine 103 is operating and the process proceeds to step S121. move on.

  In step S103, the upper and lower limit ratio calculation unit 151 of the management ECU 115 calculates the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped. Details of the calculation method will be described later. Next, the gear ratio control unit 153 of the management ECU 115 determines whether or not the ratio i-1 (previous value) set at that time is less than the lower limit (lower limit ratio) of the ratio calculated in step S103. (Step S105) If ratio i-1 <lower limit ratio, the process proceeds to step S107, and if ratio i-1≥lower limit ratio, the process proceeds to step S109. The ratio i-1 uses a value measured by a ratio sensor (not shown) attached to the continuously variable transmission 105.

  In step S107, the gear ratio control unit 153 sets the ratio i (current value) of the continuously variable transmission 105 to the value of the lower limit ratio (ratio i = lower limit ratio). On the other hand, in step S109, the gear ratio control unit 153 determines whether the ratio i-1 (previous value) is larger than the upper limit (upper limit ratio) of the ratio calculated in step S103, and the ratio i-1> the upper limit ratio. If so, the process proceeds to step S111, and if ratio i-1 ≦ upper limit ratio, the process proceeds to step S113.

  In step S111, the gear ratio control unit 153 sets the ratio i (current value) of the continuously variable transmission 105 to the value of the upper limit ratio (ratio i = upper limit ratio). On the other hand, in step S113, the gear ratio control unit 153 sets the ratio i (current value) of the continuously variable transmission 105 to the value of the ratio i-1 that is the previous value (ratio i = ratio i-1).

  In step S121, which proceeds when it is determined in step S103 that the internal combustion engine 103 is operating, the management ECU 115 calculates the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is operating. The ratio is obtained by setting the target value of the rotational speed of the internal combustion engine 103 according to the required output P based on the vehicle speed VP and the AP opening to the rotational speed of the output member 121 of the continuously variable transmission 105 (= vehicle speed VP / circumference of the drive wheel 119 Obtained by dividing by the length L). Note that the target value of the rotational speed of the internal combustion engine 103 is the rotational speed when the internal combustion engine 103 is operated in a BSFC bottom. Next, the management ECU 115 sets the ratio i (current value) of the continuously variable transmission 105 to the ratio calculated in step S121 (step S123).

  Hereinafter, the method of calculating the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped, shown in step S103 of FIG. 3, will be described in detail with reference to FIGS. FIG. 4 is a flowchart when the management ECU 115 calculates the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped. FIG. 5 is a graph showing the BSFC (Brake Specific Fuel Consumption) and the rotational speed NE of the internal combustion engine 103 with respect to the required output P. 5 indicates the BSFC of the internal combustion engine 103, and the dotted line indicates the rotational speed of the internal combustion engine 103. The vehicle according to the present embodiment performs engine running using only the driving force of the internal combustion engine 103 at the required output P between the lower limit and the upper limit shown on the horizontal axis of the graph of FIG. However, the rotational speed NE of the internal combustion engine 103 during engine running is limited to NEmin to NEmax shown on the right vertical axis of the graph of FIG. The management ECU 115 can read a table showing the graph shown in FIG. 5 from a memory (not shown).

  The upper / lower limit ratio calculation unit 151 of the management ECU 115 reads the vehicle speed range VPmin to VPmax during engine running set in the memory (step S201). Next, the upper and lower limit ratio calculation unit 151 calculates the rotation speed range VPmin / L to VPmax / L of the output member 121 of the continuously variable transmission 105 based on the vehicle speed range VPmin to VPmax and the circumferential length L of the drive wheel 119. Based on the vehicle speed VP obtained from the vehicle speed sensor 111 and the circumference L of the drive wheel 119, the current rotational speed VP / L of the output member 121 of the continuously variable transmission 105 is calculated (step S203). Next, the upper / lower limit ratio calculation unit 151 calculates the current rotation of the output member 121 of the continuously variable transmission 105 derived in step S203, the lower limit imin and the upper limit imax of the ratio that can be set in the continuously variable transmission 105 during engine running. It calculates from the number and NEmin, NEmax shown in the graph of FIG. 5 (step S205). Note that imin = NEmin / (VP / L) and imax = NEmax / (VP / L). As VP / L, a value in the range of VPmin / L to VPmax / L calculated in step S203 is used.

  Next, the upper and lower limit ratio calculation unit 151 uses the maximum change speed vi of the ratio to change the ratio ic of the ratio of the continuously variable transmission 105 that can be changed during the time Tes required for starting the internal combustion engine 103, to ic. = Vi × Tes is obtained from the calculation formula (step S207). Next, the upper and lower limit ratio calculation unit 151 uses the ratio lower limit imin and upper limit imax calculated in step S205 and the ratio change ic calculated in step S207 to continuously variable transmission 105 when the internal combustion engine 103 is stopped. The upper and lower limits (upper limit ratio and lower limit ratio) of the ratio are calculated (step S209). Note that the upper limit ratio = imin + ic, and the lower limit ratio = imax−ic.

  FIG. 6 is a graph showing an example of the relationship between the upper and lower limits of the ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped, and the lower limit imin and the upper limit imax of the ratio that can be set in the continuously variable transmission 105 when the engine is running. It is. 7 shows (a) the vehicle speed, (b) the calculated upper and lower limit ratio, the actual ratio of the continuously variable transmission 105, and (c) the operating state of the internal combustion engine 103 when the vehicle is traveling. It is a graph which shows an example.

  As described above, in the present embodiment, when the management ECU 115 derives the ratio of the continuously variable transmission 105 provided for the operation of the internal combustion engine 103 during EV travel using only the driving force from the electric motor 101, the management ECU 115 The upper limit ratio and the lower limit ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped based on the upper and lower limits imin, imax of the ratio during engine running and the change amount ic of the ratio that can be changed during startup of the internal combustion engine 103 Is calculated. Furthermore, the management ECU 115 controls the continuously variable transmission 105 so that the actual ratio of the continuously variable transmission 105 falls within the range of the lower limit ratio to the upper limit ratio calculated above. At this time, the management ECU 115 does not change the ratio if the ratio is within the range.

  As described above, the management ECU 115 of the present embodiment does not change the ratio with a large amount of change or frequent change of the ratio while the continuously variable transmission 105 during EV travel is set to the ratio prepared for the operation of the internal combustion engine 103. Not performed. As a result, fuel consumption and drivability can be maintained in a good state, and fuel consumption deterioration due to the ratio change can be suppressed. Further, since the ratio is not frequently changed, durability of the continuously variable transmission 105 can be improved.

  Further, the upper and lower limits imin and imax of the ratio during engine running are the range of the rotational speed of the internal combustion engine 103 (the rotational speed on the input side of the continuously variable transmission 105) and the rotational speed range on the output side of the continuously variable transmission 105. Therefore, the management ECU 115 can accurately calculate the upper limit ratio and the lower limit ratio of the continuously variable transmission 105 when the internal combustion engine 103 is stopped.

  In the above embodiment, the case where the internal combustion engine 103 and the continuously variable transmission 105 are a combination of the motor 101 and the motor 101 is described as an example of the configuration of the vehicle. However, as illustrated in FIG. Instead of the clutch 109, the present invention can also be applied to a vehicle having a configuration in which an internal combustion engine 203 similar to the internal combustion engine 103 and a continuously variable transmission 205 similar to the continuously variable transmission 105 are provided. However, in this case, EV travel is read as “travel by driving force from one of the internal combustion engines”, and engine travel is read as “travel by driving force from the other internal combustion engine”.

102 Input shaft 104 Eccentric disc 120 One-way clutch 121 Output member 122 Input member 123 Roller (engagement member)
130 Connecting member 101 Electric motor (Mot)
103 Internal combustion engine (ENG)
105 Continuously variable transmission (BD)
107 Differential gear 109 Clutch 111 Vehicle speed sensor 113 Speed sensor 115 Management ECU (MG ECU)
117 Axle 119 Drive Wheel 151 Upper / Lower Limit Ratio Calculation Unit 153 Gear Ratio Control Unit

Claims (6)

A first power source that generates power for the vehicle to travel;
A first transmission for transmitting power from the first power source to the drive wheels of the vehicle; and disposed between the first transmission and the drive wheels, wherein only the power from the power source is on the drive wheel side A one-way clutch capable of transmitting to the transmission, and a transmission mechanism for transmitting power from the first power source to the drive wheels,
In a drive system comprising a second power source that generates power for traveling of the vehicle, a speed ratio control device that controls a speed ratio of the speed change mechanism,
Based on a first range of a gear ratio that can be set in the speed change mechanism during traveling by power from the first power source, and an amount of change in the gear ratio that can be changed during startup of the first power source, A speed ratio range deriving unit for deriving a second range of the speed ratio of the speed change mechanism set in a state where the first power source is stopped;
While the vehicle is traveling only with the power from the second power source, the gear ratio of the transmission mechanism is changed only when the gear ratio of the transmission mechanism does not fall within the second range derived by the gear ratio range deriving unit. A transmission ratio control unit for controlling the transmission mechanism so as to be within the second range;
A gear ratio control apparatus comprising: The transmission ratio control device according to claim 1,
The speed ratio range deriving unit is provided in a range of the rotational speed of the first power source and a range of the rotational speed on the output side of the transmission mechanism when the vehicle travels using only the power from the first power source. A transmission ratio control device, wherein the first range is derived based on the first range. The transmission ratio control device according to claim 1 or 2,
The gear ratio control characterized in that the second range is a range from a lower limit value obtained by subtracting the change amount to the upper limit of the first range to an upper limit value obtained by adding the change amount to the lower limit of the first range. apparatus. The transmission ratio control device according to any one of claims 1 to 3,
The gear ratio control device, wherein the gear ratio range deriving unit derives the second range when the vehicle is traveling only by power from the second power source. The transmission ratio control device according to any one of claims 1 to 4,
The first power source is an internal combustion engine, and the second power source is an electric motor;
The gear ratio control apparatus according to claim 1, wherein the drive system includes a connection / disconnection portion that connects / disconnects a power transmission path from the second power source to the drive wheel. A first power source that generates power for the vehicle to travel;
A first transmission for transmitting power from the first power source to the drive wheels of the vehicle; and disposed between the first transmission and the drive wheels, wherein only the power from the power source is on the drive wheel side A one-way clutch capable of transmitting to the transmission, and a transmission mechanism for transmitting power from the first power source to the drive wheels,
A drive ratio control method for controlling a speed ratio of the speed change mechanism in a drive system including a second power source that generates power for traveling of the vehicle,
Based on a first range of a gear ratio that can be set in the speed change mechanism during traveling by power from the first power source, and an amount of change in the gear ratio that can be changed during startup of the first power source, Deriving a second range of the gear ratio of the transmission mechanism set in a state where the first power source is stopped;
While the vehicle is traveling only with the power from the second power source, the gear ratio of the transmission mechanism is changed only when the gear ratio of the transmission mechanism does not fall within the second range derived by the gear ratio range deriving unit. A speed ratio control method, wherein the speed change mechanism is controlled to be within the second range.

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