Driving force control device for hybrid vehicle

Abstract

To provide a driving force control device of a hybrid vehicle that can reduce a time after switching of a travelling range is requested until travelling is started, while suppressing driving force from decreasing at the time of backward travelling.SOLUTION: A driving force control device of a hybrid vehicle, which is configured so that torque, transmitted from an engine through a transmission mechanism to an output member when the engine is driven, corresponds to backward torque outputted from a second motor, when a first condition that the transmission mechanism sets a low mode and a backward travelling range is selected as a travelling range (a step S1 and a step S2: Yes), changes a starting determination value for determining that the engine is started to a value at which it is harder to start the engine than when the first condition is not satisfied (a step S3).SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a driving force control device for a hybrid vehicle equipped with a differential mechanism in which an engine and a first motor are connected, and a second motor connected to an output side member of the differential mechanism. [Background technology]

[0002] Patent Document 1 describes a hybrid vehicle equipped with a power split mechanism that splits the output torque of the engine between the first motor side and the output side. The power transmitted from the engine to the first motor in this way is converted into electric power by the first motor and supplied to the second motor. The vehicle runs by adding the torque output from the second motor to the torque transmitted from the engine to the drive wheels via the power split mechanism. The power split mechanism is equipped with two engagement mechanisms, and is configured to be able to set a low mode in which a relatively large proportion of the torque is transmitted to the output element of the power split mechanism by engaging one of the engagement mechanisms, and to set a high mode in which a smaller proportion of the torque is transmitted to the output element of the power split mechanism than in the low mode by engaging the other engagement mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6451524 Summary of the Invention [Problem to be solved by the invention]

[0004] The hybrid vehicle described in Patent Document 1 outputs a reaction torque by the first motor to suppress an increase in engine speed caused by driving the engine. By outputting the reaction torque from the first motor in this way, a part of the engine torque is transmitted to the drive wheels. Since the direction of the torque when driving the engine is limited to one direction, the direction of the torque transmitted to the drive wheels is also limited to one direction. Therefore, the power train is configured so that the direction of the torque transmitted from the engine to the drive wheels via the power split mechanism becomes the drive torque for forward driving. Therefore, when driving backward, the drive torque for reverse driving is output from the second motor, whereas when the engine is driven, the drive torque for reverse driving is reduced.

[0005] As described above, the proportion of torque transmitted from the engine to the drive wheels via the power split mechanism is smaller in the high mode than in the low mode, so it is preferable to set the high mode in order to suppress a decrease in drive torque for reverse driving. However, when driving forward at a low vehicle speed and requiring high drive force, the drive torque of the second motor alone may not be sufficient, and it is preferable to set the low mode in which a large torque is transmitted from the engine via the power split mechanism in order to reduce energy loss in the engine and each motor.

[0006] Therefore, if the driving mode is changed according to the driving range selected when the vehicle is stopped, the engagement mechanism is changed after the shift lever is operated to change the driving range. Therefore, for example, it takes time from when the shift lever is operated until the vehicle starts to drive, which may cause the driver to feel uncomfortable.

[0007] This invention has been made with an eye on the above-mentioned technical problems, and aims to provide a driving force control device for a hybrid vehicle that can reduce the decrease in driving force when driving in reverse while shortening the time from a request to switch driving ranges to the start of driving. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a transmission mechanism including an engine, a first rotating machine, a first rotating element connected to the engine, a second rotating element connected to the first rotating machine, and a third rotating element connected to an output member, which are connected to each other so as to be capable of differential rotation, and which transmits torque from the engine to the output member by outputting a reaction torque from the first rotating machine, and which is configured to be able to set a low mode in which a ratio of the torque output from the engine that is transmitted to the output member side is a first predetermined value, and a high mode in which the ratio is a second predetermined value that is smaller than the first predetermined value; a second rotating machine connected to the output member so as to be able to transmit torque; A driving force control device for a hybrid vehicle is configured to drive in reverse by outputting a reverse torque from the second rotating machine, and the torque transmitted from the engine to the output member via the transmission mechanism when the engine is running opposes the reverse torque. The driving force control device for a hybrid vehicle includes a controller that controls the engine, the first rotating machine, and the second rotating machine, and when a first condition is met in which the transmission mechanism sets the low mode and the driving range selects the reverse driving range, the controller changes a start determination value that determines whether to start the engine so that it is more difficult to start the engine than when the first condition is not met.

[0009] In this invention, the start-up judgment value includes an engine start-up threshold determined based on the required driving force or required driving power of the hybrid vehicle, and the controller is configured to start the engine when the required driving force or the required driving power becomes equal to or greater than the engine start-up threshold, and when the first condition is satisfied, the engine start-up threshold may be increased more than when the first condition is not satisfied.

[0010] In this invention, the first rotating machine is configured to convert power transmitted from the engine into electric power and supply the converted electric power to the power storage device, the start judgment value includes a charge start threshold for starting the engine based on the remaining charge of the power storage device, and the controller is configured to start the engine when the remaining charge becomes equal to or less than the charge start threshold, and when the first condition is satisfied, the charge start threshold may be lowered more than when the first condition is not satisfied.

[0011] In this invention, the controller is configured to determine the output power of the engine when the engine is running to be a total power which is the sum of the driving power for driving the hybrid vehicle and the charging power for charging the power storage device, and when a first condition is met in which the transmission mechanism is set to the low mode and the driving range selects the reverse driving range, the output torque of the engine may be reduced compared to when the first condition is not met.

[0012] The present invention also provides a power transmission mechanism comprising an engine, a first rotating machine, a first rotating element connected to the engine, a second rotating element connected to the first rotating machine, and a third rotating element connected to an output member, which are connected to each other so as to be capable of differential rotation, the power transmission mechanism transmitting torque from the engine to the output member by outputting a reaction torque from the first rotating machine, and capable of setting a low mode in which a ratio of the torque output from the engine that is transmitted to the output member side is a first predetermined value, and a high mode in which the ratio is a second predetermined value smaller than the first predetermined value, a second rotating machine connected to the output member so as to be capable of transmitting torque, and an electricity storage device electrically connected to the first rotating machine and the second rotating machine, and which runs in reverse by outputting reverse torque from the second rotating machine. In a driving force control device for a hybrid vehicle, the torque transmitted from the engine to the output member via the transmission mechanism when the engine is running opposes the reverse torque, and the driving force control device includes a controller that controls the engine, the first rotating machine, and the second rotating machine, and the controller is configured to determine the output power of the engine when the engine is running to a total power that is a sum of a driving power for driving the hybrid vehicle and a charging power for charging the power storage device, and when a first condition is met in which the transmission mechanism sets the low mode and the driving range selects the reverse driving range, the output torque of the engine is reduced compared to when the first condition is not met.

[0013] In this invention, when the first condition is satisfied, the controller may reduce the output torque of the engine by increasing the engine speed while maintaining the output power of the engine the same as when the first condition is not satisfied.

[0014] In this invention, when the first condition is satisfied, the controller may reduce the output power of the engine and thereby reduce the output torque of the engine by setting the charging power to be lower than when the first condition is not satisfied.

[0015] In this invention, the controller is configured to further control the transmission mechanism, and when a predetermined period of time has elapsed since the hybrid vehicle was traveling in reverse, the controller may switch the transmission mechanism from the low mode to the high mode, and may return the changed start-up judgment value to the start-up judgment value when the first condition is not satisfied.

[0016] In this invention, the controller is configured to further control the power transmission mechanism, and when a predetermined period of time has elapsed since the hybrid vehicle was traveling in reverse, the controller may switch the power transmission mechanism from the low mode to the high mode, and restore the reduced output torque of the engine to the output torque of the engine when the first condition is not satisfied.

[0017] In this invention, the controller may determine whether the hybrid vehicle is traveling in reverse on a high-load driving road where the driving force required when traveling in reverse is greater than a predetermined driving force, and may change the start-up judgment value when traveling on the high-load driving road.

[0018] In this invention, the controller may determine whether the hybrid vehicle is reversing on a high-load driving road where the driving force required when reversing is greater than a predetermined driving force, and may reduce the output torque of the engine when traveling on the high-load driving road.

[0019] In this invention, the controller determines whether the hybrid vehicle has approached a high-load driving road where the driving force required when reversing is greater than a predetermined driving force, and when the hybrid vehicle has approached the high-load driving road, increases the charging power of the storage device compared to when the hybrid vehicle is not approaching the high-load driving road.

[0021] In the present invention, when the engine is stopped at the time when the vehicle approaches the high-load driving road, the controller may start the engine to increase the charging power of the power storage device. Effect of the Invention

[0022] The power transmission mechanism of the present invention is configured such that the torque output from the engine is transmitted to the output member by outputting a reaction torque from the first rotating machine, and the torque opposes the reverse torque. Also, the torque transmitted to the output member side is configured to be larger when the low mode is set than when the high mode is set. In a hybrid vehicle equipped with such a power transmission mechanism, the torque transmitted from the engine to the output member during reverse running acts to reduce the driving force during reverse running. Therefore, in the present invention, when the power transmission mechanism is set to the low mode and the reverse running range is selected as the running range, the start determination threshold for determining whether to start the engine is changed so that the engine is difficult to start. That is, by changing the start determination threshold, the range in which the vehicle runs using the second rotating machine is expanded compared to when the start determination threshold is not changed. That is, the vehicle can run by outputting a larger driving force only from the second rotating machine than when the start determination threshold is not changed. As a result, the vehicle can run in reverse only with the power of the second rotating machine with the engine stopped and the low mode set, and the time from when the reverse running range is selected to when the vehicle starts running in reverse can be shortened.

[0023] In addition, when the power transmission mechanism is set to the low mode and the driving range is set to the reverse driving range, the engine output torque is reduced to suppress an increase in torque counteracting the torque for driving in reverse. Therefore, it is sufficient to drive in reverse with the power transmission mechanism set to the low mode, and the time from a request to switch the driving range to the start of driving can be shortened. In addition, even if the engine is driven to drive in reverse with the power transmission mechanism set to the low mode, the engine output torque is reduced to suppress a decrease in driving force during reverse driving.

[0024] Furthermore, by increasing the charge request amount when approaching a slope to promote charging of the power storage device, the SOC of the power storage device can be maintained high at the time when reverse running on an uphill road is started. Therefore, the power that can be output from the power storage device to the second rotating machine and the amount of power can be increased. In other words, a high driving force can be obtained during reverse running using only the second rotating machine as a driving force source, and the travelable time (or distance) can be extended. Therefore, reverse running on an uphill road can be performed with the engine stopped. In other words, reverse running can be performed without changing the mode set by the transmission mechanism, so the time from when the travel range is switched to the reverse travel range to when reverse running starts can be shortened. [Brief description of the drawings]

[0025] [Figure 1] 1 is a skeleton diagram for explaining an example of a hybrid vehicle according to the present invention; [Diagram 2] 1 is a table showing the clutch mechanism, the engaged and disengaged states of the brake mechanism, the operating state of the motor, and whether the engine is running in each driving mode. [Diagram 3] FIG. 4 is a collinear diagram for explaining an operating state in HV-Hi mode. [Figure 4] FIG. 4 is a nomographic diagram for explaining an operating state in an HV-Lo mode. [Diagram 5] FIG. 4 is a collinear diagram for explaining an operating state in a direct connection mode. [Figure 6] FIG. 4 is a collinear diagram for explaining the operating state in EV-Lo mode. [Figure 7] FIG. 4 is a collinear diagram for explaining the operating state in EV-Hi mode. [Figure 8] FIG. 4 is a collinear diagram for explaining an operating state in a single mode. [Figure 9] 10 is a flowchart illustrating an example of control for increasing the engine start threshold when a reverse drive range is selected and a Lo clutch mechanism is engaged. [Figure 10]10 is a time chart showing changes in the driving mode and the engine start threshold value when the control example shown in FIG. 9 is executed. [Figure 11] 10 is a flowchart illustrating an example of control for lowering a charge start threshold when a reverse drive range is selected and a Lo clutch mechanism is engaged. [Figure 12] 12 is a time chart showing changes in the driving mode and the charge start threshold value when the control example shown in FIG. 11 is executed. [Figure 13] 4 is a flowchart illustrating an example of a control for increasing the engine speed during reverse traveling. [Figure 14] 14 is a time chart showing changes in the driving mode, the flag for operating the engine, the engine speed, and the engine torque when the control example shown in FIG. 13 is executed. [Figure 15] 5 is a flowchart for explaining a control example for reducing a required charge amount during reverse traveling. [Figure 16] 16 is a time chart showing changes in the driving mode, the flag for operating the engine, the required charge amount, the engine speed, and the engine torque when the control example shown in FIG. 15 is executed. [Figure 17] 10 is a flowchart for explaining an example of control for returning an engine start threshold value; [Figure 18] 18 is a time chart showing changes in the driving mode and the engine start threshold value when the control example shown in FIG. 17 is executed. [Figure 19] 10 is a flowchart illustrating an example of control for returning a charge start threshold value. [Figure 20] 20 is a time chart showing changes in the driving mode and the charge start threshold value when the control example shown in FIG. 19 is executed. [Figure 21] 4 is a flowchart illustrating an example of control for returning the engine speed. [Figure 22] 22 is a time chart showing changes in the driving mode, the flag for operating the engine, the engine speed, and the engine torque when the control example shown in FIG. 21 is executed. [Figure 23] 10 is a flowchart illustrating an example of control for returning a requested charging amount. [Figure 24] 24 is a time chart showing changes in the driving mode, the flag for operating the engine, the required charge amount, the engine speed, and the engine torque when the control example shown in FIG. 23 is executed. [Diagram 25] 10 is a flowchart for executing the control example shown in FIG. 9 during reverse driving when a high driving force is required. [Figure 26] 10 is a flowchart for explaining an example of control for promoting charging of the power storage device when the vehicle approaches a slope. [Figure 27] 27 is a time chart showing changes in the SOC determination flag, the hill determination flag, the engine operation flag, the required charge amount, the engine speed, and the engine torque when the control example shown in FIG. 26 is executed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The driving force control device in this embodiment of the present invention is a driving force control device for a hybrid vehicle equipped with a power split mechanism that divides the torque output from the engine between a first motor side and a drive wheel side, and can set a low mode in which the torque output from the engine is relatively large and a high mode in which the torque transmitted to the drive wheel side is relatively small.

[0027] An example of this type of hybrid vehicle will be described with reference to FIG. 1. FIG. 1 shows a drive device 2 for driving front wheels 1R, 1L. The drive device 2 is a so-called two-motor type drive device equipped with an engine 3 and two motors 4, 5 as drive power sources, and the first motor 4 is configured by a motor with a power generating function (i.e., motor generator: MG1). The first motor 4 controls the rotation speed of the engine 3, and drives the second motor 5 with the power generated by the first motor 4, and the torque output by the second motor 5 is added to the torque for traveling. The second motor 5 can be configured by a motor with a power generating function (i.e., motor generator: MG2). The first motor 4 corresponds to the "first rotating machine" in the embodiment of the present invention, and the second motor 5 corresponds to the "second rotating machine" in the embodiment of the present invention.

[0028] A power split mechanism 6, which corresponds to the "transmission mechanism" in the embodiment of the present invention, is connected to the engine 3. This power split mechanism 6 is composed of a splitting unit 7, the main function of which is to split the torque output from the engine 3 between the first motor 4 side and the output side, and a speed change unit 8, the main function of which is to change the torque split ratio.

[0029] The dividing section 7 may be configured to perform a differential action by three rotating elements, and a planetary gear mechanism may be adopted. In the example shown in Fig. 1, it is configured by a single-pinion type planetary gear mechanism. The dividing section 7 shown in Fig. 1 is configured by a sun gear 9, a ring gear 10 which is an internal gear arranged concentrically with the sun gear 9, a pinion gear 11 arranged between the sun gear 9 and the ring gear 10 and meshing with the sun gear 9 and the ring gear 10, and a carrier 12 which holds the pinion gear 11 so that it can rotate and revolve. The sun gear 9 mainly functions as a reaction element, the ring gear 10 mainly functions as an output element, and the carrier 12 mainly functions as an input element.

[0030] Power output from the engine 3 is input to the carrier 12. Specifically, an input shaft 14 of the power split mechanism 6 is connected to an output shaft 13 of the engine 3, and the input shaft 14 is connected to the carrier 12. This carrier 12 corresponds to a "first rotating element" in the embodiment of the present invention. Instead of a configuration in which the carrier 12 and the input shaft 14 are directly connected to each other, the carrier 12 and the input shaft 14 may be connected to each other via a transmission mechanism such as a gear mechanism. Furthermore, a mechanism such as a damper mechanism or a torque converter may be disposed between the output shaft 13 and the input shaft 14.

[0031] The sun gear 9 corresponds to the "second rotating element" in the embodiment of the present invention, and the first motor 4 is connected to the sun gear 9. In the example shown in Fig. 1, the split unit 7 and the first motor 4 are arranged on the same axis as the central axis of rotation of the engine 3, and the first motor 4 is arranged on the opposite side of the split unit 7 to the engine 3. Between the split unit 7 and the engine 3, on the same axis as the split unit 7 and the engine 3, and aligned in the direction of the axial line, the transmission unit 8 is arranged.

[0032] The transmission unit 8 is configured by a single-pinion type planetary gear mechanism, and includes a sun gear 15, a ring gear 16 which is an internal gear arranged concentrically with the sun gear 15, a pinion gear 17 which is arranged between the sun gear 15 and the ring gear 16 and meshes with the sun gear 15 and the ring gear 16, and a carrier 18 which holds the pinion gear 17 so that it can rotate and revolve around its axis. This differential mechanism performs differential action using the three rotating elements of the sun gear 15, the ring gear 16, and the carrier 18. The ring gear 10 in the division unit 7 is connected to the sun gear 15 in the transmission unit 8. In addition, an output gear 19 is connected to the ring gear 16 in the transmission unit 8. The ring gear 16 corresponds to the "third rotating element" in the embodiment of the present invention, and the output gear 19 corresponds to the "output member" in the embodiment of the present invention.

[0033] A Lo clutch mechanism C_Lo is provided so that the dividing unit 7 and the transmission unit 8 constitute a compound planetary gear mechanism. The Lo clutch mechanism C_Lo is configured to selectively connect the carrier 18 in the transmission unit 8 to the carrier 12 in the division unit 7. This Lo clutch mechanism C_Lo may be a friction type clutch mechanism such as a wet multi-plate clutch, or a meshing type clutch mechanism such as a dog clutch. By engaging this Lo clutch mechanism C_Lo, the carrier 12 in the division unit 7 and the carrier 18 in the transmission unit 8 are connected to each other and become input elements, the sun gear 9 in the division unit 7 becomes a reaction element, and the ring gear 16 in the transmission unit 8 becomes an output element, forming a compound planetary gear mechanism.

[0034] Furthermore, a Hi clutch mechanism C_Hi is provided for integrating the entire transmission unit 8. This Hi clutch mechanism C_Hi is for connecting at least two rotating elements in the transmission unit 8, such as connecting the carrier 18 to the ring gear 16 or the sun gear 15, or connecting the sun gear 15 to the ring gear 16, and can be formed of a friction or meshing clutch mechanism. In the example shown in Fig. 1, the Hi clutch mechanism C_Hi is configured to connect the carrier 18 to the ring gear 16 in the transmission unit 8.

[0035] The Lo clutch mechanism C_Lo and the Hi clutch mechanism C_Hi are disposed on the same axis as the engine 3, the dividing unit 7, and the transmission unit 8, and are disposed on the opposite side of the transmission unit 8 to the dividing unit 7. The clutch mechanisms C_Lo and C_Hi may be disposed side by side on the inner and outer periphery sides in the radial direction as shown in FIG. 1, or may be disposed side by side in the axial direction. When disposed side by side in the radial direction as shown in FIG. 1, the axial length of the drive unit 2 as a whole can be shortened. Furthermore, when disposed side by side in the axial direction, there are fewer restrictions on the outer diameter of the clutch mechanisms C_Lo and C_Hi, so that when a friction-type clutch mechanism is employed, the number of friction plates can be reduced.

[0036] A countershaft 20 is disposed parallel to the central axis of rotation of the engine 3, the dividing unit 7, or the transmission unit 8. A driven gear 21 meshing with the output gear 19 is attached to this countershaft 20. A drive gear 22 is attached to the countershaft 20, and this drive gear 22 meshes with a ring gear 24 in a differential gear unit 23, which is the final reduction gear.

[0037] Furthermore, a drive gear 26 attached to a rotor shaft 25 of the second motor 5 meshes with the driven gear 21. Therefore, the power or torque output by the second motor 5 is added to the power or torque output from the output gear 19 at the driven gear 21. The power or torque thus synthesized is output from the differential gear unit 23 to the left and right drive shafts 27, and the power or torque is transmitted to the front wheels 1R, 1L.

[0038] The drive device 2 shown in FIG. 1 is provided with a friction or meshing brake mechanism B that is configured to selectively fix the output shaft 13 or the input shaft 14 so that the drive torque output from the first motor 4 can be transmitted to the front wheels 1R and 1L. That is, by engaging the brake mechanism B to fix the output shaft 13 or the input shaft 14, the carrier 12 in the split unit 7 and the carrier 18 in the transmission unit 8 can function as reaction elements, and the sun gear 9 in the split unit 7 can function as an input element. This brake mechanism B is not limited to a configuration that completely fixes the output shaft 13 or the input shaft 14, as long as it can generate a reaction torque when the first motor 4 outputs a drive torque, and it is sufficient that the required reaction torque can be applied to the output shaft 13 or the input shaft 14. Alternatively, a one-way clutch that prohibits the output shaft 13 or the input shaft 14 from rotating in a direction opposite to the direction in which the engine 3 rotates when the engine 3 is driven may be provided as the brake mechanism B.

[0039] A first power control device 28 equipped with an inverter, a converter, etc. is connected to the first motor 4, and a second power control device 29 equipped with an inverter, a converter, etc. is connected to the second motor 5, and these power control devices 28, 29 are connected to an electricity storage device 30 composed of a lithium ion battery, a capacitor, etc. In other words, the motors 4, 5 are electrically connected to the electricity storage device 30 so as to be able to exchange electric power with them. In addition, the first power control device 28 and the second power control device 29 are configured to be able to supply electric power to each other. Specifically, when the first motor 4 functions as a generator by outputting a reaction torque, the power generated by the first motor 4 is configured to be able to be supplied to the second motor 5 without passing through the electricity storage device 30.

[0040] An electronic control unit (ECU) 31 is provided for controlling the inverters and converters in the power control devices 28, 29, the engine 3, the clutch mechanisms C_Lo, C_Hi, and the brake mechanism B. The ECU 31 corresponds to the "controller" in the embodiment of the present invention, and is mainly composed of a microcomputer. Based on input signals and pre-stored maps or arithmetic expressions, the ECU 31 outputs signals for controlling the power control devices 28, 29, the engine 3, the clutch mechanisms C_Lo, C_Hi, and the brake mechanism B. Examples of signals input to the ECU 31 include signals output from sensors for detecting the amount of operation of the accelerator pedal or the brake pedal, a sensor for detecting the vehicle speed, the state of charge (SOC) of the power storage device 30, the temperature of the power storage device 30, the temperature of the motors 4, 5, the rotation speed of the motors 4, 5, a sensor for detecting (receiving) a state outside the vehicle by a radar or the like, a navigation system, a GPS, and the like.

[0041] The drive device 2 described above can be set to an HV driving mode in which the vehicle travels by outputting driving torque from the engine 3, and an EV driving mode in which the vehicle travels by outputting driving torque from the first motor 4 and the second motor 5 without outputting driving torque from the engine 3. Furthermore, the HV driving mode can be set to an HV-Lo mode in which a large proportion (split ratio) of the torque output from the engine 3 is mechanically transmitted to the output gear 19 via the power split mechanism 6, an HV-Hi mode in which the split ratio of this torque is small, and a direct mode in which the torque output from the engine 3 is transmitted directly to the output gear 19.

[0042] Specifically, if the torque output from the engine 3 is Te, in the HV-Lo mode, the torque transmitted to the output gear 19 is (1 / (1-ρ1·ρ2))Te, in the HV-Hi mode, it is (1 / (1+ρ1))Te, and in the direct mode, it is Te. Here, ρ1 is the ratio between the number of teeth of the ring gear 10 and the number of teeth of the sun gear 9, and ρ2 is the ratio between the number of teeth of the ring gear 16 and the number of teeth of the sun gear 15, and ρ1 and ρ2 are values ​​smaller than "1". Therefore, when the HV-Lo mode is set, the torque mechanically transmitted to the output gear 19 via the power split mechanism 6 is larger than when the HV-Hi mode is set. Therefore, when the vehicle starts to travel forward, the HV-Lo mode is set. The HV-Lo mode corresponds to the "low mode" in this embodiment of the invention, and the ratio of torque transmitted to output gear 19 when the HV-Lo mode is set (1 / (1-ρ1·ρ2)) corresponds to the "first predetermined value" in this embodiment of the invention. Similarly, the HV-Hi mode corresponds to the "high mode" in this embodiment of the invention, and the ratio of torque transmitted to output gear 19 when the HV-Hi mode is set (1 / (1+ρ1)) corresponds to the "second predetermined value" in this embodiment of the invention.

[0043] In addition, the above-mentioned HV-Lo mode and HV-Hi mode are continuously variable transmission modes configured so that the rotation speed of the engine 3 can be controlled by controlling the rotation speed of the first motor 4, whereas in the direct drive mode, the rotation speeds of the engine 3 and the output gear 19 are the same.

[0044] Furthermore, the EV driving mode can be set to a dual mode in which driving torque is output from the first motor 4 and the second motor 5, and a single mode in which driving torque is output only from the second motor 5 without outputting driving torque from the first motor 4. Furthermore, the dual mode can be set to an EV-Lo mode in which the amplification factor of the torque output from the first motor 4 is relatively large, and an EV-Hi mode in which the amplification factor of the torque output from the first motor 4 is relatively small. Note that in the single mode, it is possible to run the vehicle by outputting driving torque only from the second motor 5 with the Lo clutch mechanism C_Lo engaged, to run the vehicle by outputting driving torque only from the second motor 5 with the Hi clutch mechanism C_Hi engaged, or to run the vehicle by outputting driving torque only from the second motor 5 with the clutch mechanisms C_Lo and C_Hi released.

[0045] Each of these driving modes is set by controlling the Lo clutch mechanism C_Lo, the Hi clutch mechanism C_Hi, the brake mechanism B, the engine 3, and the motors 4 and 5. FIG. 2 shows an example of these driving modes, the engaged and disengaged states of the Lo clutch mechanism C_Lo, the Hi clutch mechanism C_Hi, and the brake mechanism B, the operating states of the first motor 4 and the second motor 5, and the presence or absence of output of drive torque from the engine 3 in each driving mode, as a table. In the figure, the symbol "●" indicates an engaged state, the symbol "-" indicates a disengaged state, the symbol "G" means that the motor is mainly operated as a generator, the symbol "M" means that the motor is mainly operated as a motor, a blank space indicates a state in which the motor and the generator are not functioning, or the first motor 4 and the second motor 5 are not involved in driving, "ON" indicates a state in which the engine 3 is outputting drive torque, i.e., the engine 3 is driven as an energy source for driving the hybrid vehicle, and "OFF" indicates a state in which the engine 3 is not outputting drive torque, i.e., the engine 3 is not driven as an energy source for driving the hybrid vehicle.

[0046] The operation in the above-mentioned HV-Hi mode and HV-Lo mode will be explained using a nomographic diagram. The nomographic diagram shows straight lines representing each rotating element in the power split mechanism 6 drawn parallel to each other at intervals equal to the gear ratio, and the distance from a base line perpendicular to these lines is shown as the rotation speed of each rotating element. The direction of torque is indicated by an arrow on the line representing each rotating element, and the magnitude of the torque is indicated by the length of the arrow.

[0047] As shown in Fig. 3 and Fig. 4, in the HV-Hi mode and the HV-Lo mode, a driving torque is output from the engine 3, either the Lo clutch mechanism C_Lo or the Hi clutch mechanism C_Hi is engaged, and a reaction torque is output from the first motor 4. In this case, the rotation speed of the first motor 4 can be controlled so that the efficiency of the drive device 2 as a whole (a value obtained by dividing the amount of consumed energy by the amount of energy of the front wheels 1R, 1L) is optimal, taking into consideration the fuel efficiency of the engine 3 and the driving efficiency of the first motor 4. The rotation speed of the first motor 4 can be changed continuously, and the engine rotation speed is determined based on the rotation speed of the first motor 4 and the vehicle speed. Therefore, the power split mechanism 6 functions as a continuously variable transmission.

[0048] When the first motor 4 functions as a generator by outputting a reaction torque from the first motor 4 as described above, a part of the power of the engine 3 is converted into electric energy by the first motor 4. Then, the power of the engine 3 minus the power converted into electric energy by the first motor 4 is transmitted to the ring gear 16 in the transmission 8. The ratio of the torque transmitted to the first motor 4 side to the torque transmitted to the ring gear 16 (or output gear 19) side differs between the HV-Lo mode and the HV-Hi mode. That is, when the HV-Lo mode is set as described above, the torque transmitted to the ring gear 16 is larger than when the HV-Hi mode is set, and conversely, when the HV-Lo mode is set, the reaction torque to be output from the first motor 4 is smaller than when the HV-Hi mode is set.

[0049] The electric power generated by the first motor 4 is then supplied to the second motor 5 and the power storage device 30. Specifically, when the first motor 4 generates electric power equal to or greater than the electric power corresponding to the output (power) required of the second motor 5, the surplus electric power is supplied to the power storage device 30 in addition to the second motor 5. On the other hand, when the electric power generated by the first motor 4 is less than the electric power corresponding to the output (power) required of the second motor 5, electric power is supplied from the power storage device 30 to the second motor 5 in addition to the first motor 4.

[0050] In the direct connection mode, the clutch mechanisms C_Lo, C_Hi are engaged, so that the rotating elements in the power split mechanism 6 rotate at the same rotation speed as shown in FIG. 5. That is, all of the power of the engine 3 can be output from the power split mechanism 6. In this case, a part of the power of the engine 3 is not converted into electrical energy by the first motor 4 or the second motor 5. Therefore, there is no loss due to electrical resistance that occurs when converting into electrical energy, and the efficiency of power transmission can be improved. Note that even when the direct connection mode is set, the first motor 4 or the second motor 5 can be made to function as a generator to charge the power storage device 30.

[0051] When the above-mentioned HV running mode is set, the engine 3 is configured to output a total power obtained by adding together the driving power required to drive the hybrid vehicle and the charging power required to charge the power storage device 30. This is the same when the vehicle is running in reverse, which will be described later. When the output (power) of the engine 3 is set in this manner, the rotation speed of the first motor 4 is controlled so that the rotation speed of the engine 3 becomes a rotation speed that provides good fuel economy.

[0052] As shown in Figs. 6 and 7, in the EV-Lo mode and the EV-Hi mode, the brake mechanism B is engaged and the motors 4 and 5 output driving torque to travel. As shown in Figs. 6 and 7, the ratio between the rotation speed of the first motor 4 and the rotation speed of the ring gear 16 in the transmission unit 8 is greater in the EV-Lo mode than in the EV-Hi mode. That is, the reduction ratio is greater in the EV-Lo mode than in the EV-Hi mode. Therefore, a large driving force can be obtained by setting the EV-Lo mode. In addition, in the single mode, as shown in Fig. 8, the driving torque is output only from the second motor 5, and the clutch mechanisms C_Lo and C_Hi are released, so that each rotating element of the division unit 7 can be stopped. Therefore, the power loss caused by the rotation of the engine 3 and the first motor 4 can be reduced.

[0053] 3 and 4, when torque is output from the engine 3, a reaction torque is output from the first motor 4 to suppress an excessive increase in engine speed. As a result, part of the torque output from the engine 3 is transmitted to the front wheels 1R, 1L via the power split mechanism 6 in a direction to move the hybrid vehicle forward. Therefore, when traveling backward, it is preferable to set the single mode and travel using the power of the second motor 5.

[0054] On the other hand, when the output power required of the second motor 5 for traveling backward is relatively large and the power of the power storage device 30 alone cannot satisfy the output power required of the second motor 5, power is supplied from the first motor 4 to the second motor 5 in addition to the power storage device 30. Specifically, the Lo clutch mechanism C_Lo or the Hi clutch mechanism C_Hi is engaged and the engine 3 is driven, at least a part of the power output from the engine 3 is converted into power by the first motor 4, and the converted power is supplied to the second motor 5. That is, the output power of the engine 3 is determined so that the first motor 4 can generate power that is insufficient with the power of the power storage device 30. In this case, the torque transmitted from the engine 3 via the power split mechanism 6 acts against the torque output from the second motor 5 for traveling backward (reverse torque). Therefore, during traveling backward, which requires a relatively large driving force, it is preferable to set the HV-Hi mode in which the torque transmitted via the power split mechanism 6 is relatively small.

[0055] As described above, when the hybrid vehicle starts to travel forward, the HV-Lo mode is set. Therefore, when the hybrid vehicle stops, the HV-Lo mode is usually set. Therefore, when the vehicle stops from forward travel and then the shift lever is operated to travel backward, more specifically, when traveling backward on a high-load travel road that requires a relatively large driving force such as an uphill road, it is preferable to switch the travel mode from the HV-Lo mode to the HV-Hi mode in order to reduce the torque that opposes the reverse torque of the second motor 5. In this case, the travel mode is switched to the HV-Hi mode after the driver switches the shift lever from the drive position to the reverse position. Therefore, it takes time to start traveling backward because the travel mode needs to be switched between the shift operation and the hybrid vehicle starting to travel backward. In addition, when the Lo clutch mechanism C_Lo and the Hi clutch mechanism C_Hi are meshing engagement mechanisms, engagement noise such as dog teeth contacting each other may be generated at the time when the Hi clutch mechanism C_Hi is engaged to switch to the HV-Hi mode. In particular, since the Hi clutch mechanism C_Hi is engaged when the vehicle is stopped, the driver may feel uneasy (unpleasant) if an engagement noise occurs.

[0056] Therefore, the driving force control device in the embodiment of the present invention is configured to change the determination threshold value for starting the engine 3 so that the engine 3 is difficult to start, thereby enabling the vehicle to travel backward with the engine 3 stopped. In other words, the driving force control device is configured to expand the region in which the vehicle can travel only with the power of the second motor 5. That is, the driving force control device is configured to shorten the time from a request to switch the travel range to the start of travel by not starting the engine 3 and not switching the clutch mechanism to be engaged. A flow chart for explaining an example of the control is shown in FIG. 9. In the example shown in FIG. 9, first, it is determined whether the travel range is the reverse travel range (R range) (step S1). This step S1 can be determined based on whether the shift lever is operated to the reverse position.

[0057] If the drive range is not the reverse drive range and therefore the negative determination is made in step S1, the routine is terminated. On the other hand, if the drive range is the reverse drive range and therefore the positive determination is made in step S1, then it is determined whether or not only the Lo clutch mechanism C_Lo is engaged (step S2). In other words, it is determined whether or not the drive mode in the case where the engine 3 is driven is the HV-Lo mode. This step S2 can be determined based on, for example, whether or not a signal for engaging the actuator for operating the Lo clutch mechanism C_Lo is output and a signal for releasing the actuator for operating the Hi clutch mechanism C_Hi is output, and whether or not the operating positions of these actuators are in a position for engaging only the Lo clutch mechanism C_Lo. The conditions in the above steps S1 and S2 correspond to the "first condition" in the embodiment of the present invention.

[0058] If the Lo clutch mechanism C_Lo is not engaged, or if the Hi clutch mechanism C_Hi is engaged in addition to the Lo clutch mechanism C_Lo, and thus a negative determination is made in step S2, the routine is terminated. On the other hand, if only the Lo clutch mechanism C_Lo is engaged and thus a positive determination is made in step S2, the engine start threshold is increased by a predetermined value (step S3), and the routine is terminated. This engine start threshold is a threshold for determining whether to switch from the EV driving mode to the HV driving mode, and parameters that can be used include the accelerator opening, and a required driving force or required power determined based on the accelerator opening and the vehicle speed. This engine start threshold corresponds to the "start determination value" in this embodiment of the present invention.

[0059] Here, the region in which the EV driving mode is set is determined to be a range of power smaller than the power that can be output from the second motor 5. In other words, the region in which driving is possible in the EV driving mode is determined to be a region that is a predetermined margin less than the maximum output of the second motor 5. The power that can be output from the second motor 5 changes based on the temperature of the power storage device 30 or the second motor 5, the remaining charge of the power storage device 30, etc. Therefore, the engine start threshold in step S3 may be a variable value that changes based on the temperature of the power storage device 30 or the second motor 5, the remaining charge of the power storage device 30, etc.

[0060] The predetermined value can be appropriately determined within the above-mentioned margin, and may be a fixed value determined in advance, or may be a variable value depending on the magnitude of the required driving force, etc.

[0061] Fig. 10 is a time chart showing the change in the driving mode and the engine start threshold when the control example shown in Fig. 9 is executed. At time t0 shown in Fig. 10, the shift range is in the parking range (P) when the vehicle is stopped. Therefore, since the result of step S1 in Fig. 9 is negative, the engine start threshold is set to a predetermined value. Note that, since the range is frequently switched to the drive range when the vehicle is stopped, the Lo clutch mechanism C_Lo is engaged.

[0062] When the shift lever is operated to switch to the reverse drive range (R) at time t1, an affirmative determination is made in step S1 in Fig. 9. In addition, since the Lo clutch mechanism C_Lo has been engaged continuously since time t0, an affirmative determination is also made in step S2. As a result, the engine start threshold is increased by a predetermined value at time t1.

[0063] As described above, when the reverse drive range is selected and the Lo clutch mechanism C_Lo is engaged, by increasing the engine start threshold, the region in which the vehicle travels in the EV drive mode is expanded compared to when the engine start threshold is not increased. That is, the vehicle can travel by outputting a larger driving force only by the second motor 5 than when the engine start threshold is not increased. As a result, the vehicle can travel in reverse only by the power of the second motor 5 with the engine 3 stopped and the Lo clutch mechanism C_Lo engaged, and the time from when the reverse drive range is selected to when reverse drive starts can be shortened. In addition, when the Hi clutch mechanism C_Hi is configured as a meshing clutch mechanism, the Hi clutch mechanism C_Hi can be prevented from being engaged when the vehicle is stopped, and therefore the driver can be prevented from feeling uncomfortable due to the engagement sound.

[0064] FIG. 11 is a flow chart for explaining another example of the driving force control device in the embodiment of the present invention, and executes steps similar to steps S1 and S2 in FIG. 9. Then, when the Lo clutch mechanism C_Lo is engaged and the result of the affirmative determination in step S2 is affirmative, the charging start threshold is lowered by a predetermined value (step S13), and this routine is temporarily terminated. This charging start threshold is a predetermined remaining amount at which the engine 3 is started to start charging the power storage device 30 in order to prevent the SOC of the power storage device 30 from being depleted. That is, it is set to a value higher than the lower limit value of the SOC by a predetermined margin. Therefore, the predetermined value in step S13 can be appropriately set within the margin range, and may be a predetermined fixed value or a variable value that varies based on the discharge power corresponding to the required driving force. This charging start determination value corresponds to the "start determination value" in the embodiment of the present invention.

[0065] Fig. 12 is a time chart showing changes in the driving mode and the charge start threshold when the control example shown in Fig. 11 is executed. At time t10 shown in Fig. 12, the shift range is in the parking range (P) when the vehicle is stopped. Therefore, since the result of step S1 in Fig. 11 is negative, the charge start threshold is set to a predetermined SOC value. Note that, since the vehicle is frequently switched to the drive range when the vehicle is stopped, the Lo clutch mechanism C_Lo is engaged.

[0066] At time t11, when the shift lever is operated to switch to the reverse drive range (R), a positive determination is made in step S1 in Fig. 11. In addition, since the Lo clutch mechanism C_Lo has been engaged continuously since time t10, a positive determination is also made in step S2. As a result, the charge start threshold is reduced by a predetermined value at time t11.

[0067] As described above, when the reverse travel range is selected and the Lo clutch mechanism C_Lo is engaged, by lowering the charge start threshold, it is possible to suppress the engine 3 from starting before the reverse travel range is selected, for example, when the SOC drops when the vehicle is stopped and charging starts. As a result, it is possible to suppress the torque of the engine 3 from acting on the front wheels 1R, 1L at the time when the reverse travel range is selected, and it is possible to start reverse travel without switching the clutch mechanism to be engaged. In other words, it is possible to shorten the time from when the reverse travel range is selected to when reverse travel starts. In addition, even if the SOC drops due to traveling only with the power of the second motor 5, it is possible to suppress the engine 3 from starting, and it is possible to suppress a decrease in driving force during reverse travel.

[0068] The driving force control device in the embodiment of the present invention is not limited to changing the engine start threshold or the charge start threshold, but may change various parameters that cause the engine 3 to start so as to make it difficult to start the engine 3. Also, the control example shown in Fig. 9 and the control example shown in Fig. 11 may be combined and executed. That is, the engine start threshold may be increased and the charge start threshold may be decreased during reverse driving. By configuring in this way, it is possible to prevent the engine 3 from starting when either one of the conditions is satisfied.

[0069] Next, a control example will be described in which the torque output from the engine 3 is reduced to suppress a reduction in driving force during reverse driving without switching the clutch mechanism to be engaged. FIG. 13 is a flow chart for explaining this control example, and steps similar to steps S1 and S2 in FIG. 9 and FIG. 11 are executed. Then, if the Lo clutch mechanism C_Lo is engaged so that the answer in step S2 is YES, it is determined whether the engine 3 is running (step S23). This step S23 can be determined based on an output signal to a fuel injection device or the like that supplies fuel to the engine 3.

[0070] If the engine 3 is stopped and therefore the answer is negative in step S23, the routine is terminated. On the other hand, if the engine 3 is driven and therefore the answer is positive in step S23, the engine speed is increased (step S24) while maintaining the output power of the engine 3, and the routine is terminated. In other words, the output torque of the engine 3 is reduced while maintaining the output power of the engine 3. Specifically, the engine speed is increased, and the engine speed in step S24 is determined so that the torque transmitted to the front wheels 1R, 1L via the power split mechanism 6 with the Lo clutch mechanism C_Lo engaged is equivalent to the torque transmitted to the front wheels 1R, 1L via the power split mechanism 6 when the engine speed is controlled to a speed at which the fuel economy of the engine 3 is good and the HV-Hi mode is set.

[0071] Fig. 14 is a time chart showing changes in the driving mode, the flag for operating the engine 3, the engine speed, and the output torque of the engine 3 when the control example shown in Fig. 13 is executed. At time t20 shown in Fig. 14, the shift range is the parking range (P). Therefore, since a negative determination is made in step S1 in Fig. 13, the routine shown in Fig. 13 ends as it is. Note that the engine 3 is stopped at time t20.

[0072] At time t21, when the shift lever is operated to switch to the reverse drive range (R), a positive determination is made in step S1 in Fig. 13. Also, in the example shown in Fig. 14, a flag for starting the engine 3 is switched on at the same time as the change in the shift range. Therefore, the engine speed and engine torque start to increase from time t22.

[0073] Since the engine 3 is operated in this manner, an affirmative determination is made in step S23 in Fig. 13. As a result, the engine speed is increased to a higher speed than the engine speed (dashed line) in the case where the control example in Fig. 13 is not executed, and in order to maintain the output power of the engine 3, the engine torque is maintained lower than the engine torque (dashed line) in the case where the control example in Fig. 13 is not executed.

[0074] When the engine speed is increased in this way, the speed of the first motor 4 also increases, and the reaction torque by the first motor 4 decreases due to the reduction in the engine torque. Therefore, the power generated by the first motor 4 does not vary significantly depending on whether the engine speed is increased or not.

[0075] As described above, when the reverse travel range is selected and the Lo clutch mechanism C_Lo is engaged, the engine 3 is controlled to a higher rotation speed than that at which fuel economy is good, and the engine torque is reduced while maintaining the output power of the engine 3, thereby suppressing an increase in torque countering the torque for reverse travel. Therefore, reverse travel can be performed with the Lo clutch mechanism C_Lo engaged, and the time from a request to switch the travel range to the start of travel can be shortened. Furthermore, even if the engine 3 is driven to travel in reverse with the Lo clutch mechanism C_Lo engaged as described above, a reduction in the drive force during reverse travel can be suppressed by reducing the output torque of the engine 3.

[0076] As described above, in the HV running mode in which the engine 3 is driven, a total power obtained by adding together the power required to drive the hybrid vehicle and the power required to charge the power storage device 30 is output from the engine 3. In other words, by temporarily reducing the power required to charge the power storage device 30, the output power required of the engine 3 can be reduced, and as a result, even if the engine 3 is operated at a rotation speed at which the fuel efficiency of the engine 3 is good, the output torque of the engine 3 can be reduced compared to the case in which the power required to charge the power storage device 30 is not reduced.

[0077] Therefore, the driving force control device in the embodiment of the present invention may reduce the power required to charge the power storage device 30 when traveling backward with the Lo clutch mechanism C_Lo engaged. A flowchart for explaining an example of such control is shown in Fig. 15. In the example shown in Fig. 15, steps S1 and S2 are executed similarly to the control examples shown in Figs. 9, 11, and 13, and if the answer to step S2 is affirmative, it is determined whether or not the engine 3 is running (step S23) similarly to the control example shown in Fig. 13.

[0078] If the engine 3 is stopped and therefore the answer is negative in step S23, the routine is terminated. On the other hand, if the engine 3 is running and therefore the answer is positive in step S23, the charge request amount required to charge the power storage device 30 is reduced (step S34), and the routine is terminated. In other words, the output power of the engine 3 is reduced. Specifically, when the engine 3 is operated with a total power obtained by adding the power required to drive the hybrid vehicle and the charge request amount reduced in step S34, the engine speed is controlled to a speed at which the fuel economy of the engine 3 is good.

[0079] Fig. 16 is a time chart showing changes in the driving mode, the flag for operating the engine 3, the required charge amount, the engine speed, and the output torque of the engine 3 when the control example shown in Fig. 15 is executed. At time t30 shown in Fig. 16, the shift range is the parking range (P). Therefore, since the result of step S1 in Fig. 15 is negative, the routine shown in Fig. 16 ends as it is. Note that the engine 3 is stopped at time t30.

[0080] At time t31, when the shift lever is operated to switch to the reverse drive range (R), a positive determination is made in step S1 in Fig. 15. On the other hand, in the example shown in Fig. 16, the flag for starting the engine 3 is off when the shift range is changed. Therefore, at time t31, the engine 3 remains stopped.

[0081] Next, at time t32, the flag for starting the engine 3 is switched to ON. Therefore, the determination in step S23 in Fig. 15 is affirmative. As a result, although the required charge amount increases from 0, the required charge amount (solid line) is set lower than the required charge amount (dashed line) in the case where the control example in Fig. 15 is not executed. Therefore, although the engine speed and engine torque increase from time t33, the engine speed and engine torque are maintained lower than the engine speed and engine torque in the case where the control example in Fig. 15 is not executed.

[0082] As described above, when the reverse travel range is selected and the Lo clutch mechanism C_Lo is engaged, by reducing the required charge amount, the engine torque can be reduced even if the engine 3 is controlled at a rotation speed at which the engine 3 has good fuel efficiency. Therefore, an increase in torque countering the torque for reverse travel can be suppressed. As a result, it is sufficient to perform reverse travel with the Lo clutch mechanism C_Lo engaged, and the time from a request to switch the travel range to the start of travel can be shortened. Furthermore, even if the engine 3 is driven to perform reverse travel with the Lo clutch mechanism C_Lo engaged as described above, a reduction in the drive force during reverse travel can be suppressed by reducing the output torque of the engine 3.

[0083] The control examples shown in Fig. 9 and Fig. 11 are configured to make it difficult to start the engine 3 by changing the judgment threshold that is a factor in starting the engine 3, whereas the control examples shown in Fig. 13 and Fig. 15 are configured to reduce the output torque of the engine 3 after the engine 3 has started, compared to when the front wheels are traveling or when the Hi clutch mechanism C_Hi is engaged. Therefore, the control examples shown in Fig. 13 and Fig. 15 may be configured to change the judgment threshold for starting the engine 3 based on the control examples shown in Fig. 9 and Fig. 11, and to execute the control examples shown in Fig. 13 and Fig. 15 when the requested driving force or SOC changes beyond the changed judgment threshold. Alternatively, the control examples shown in Fig. 13 and Fig. 15 may be executed in parallel with the control examples shown in Fig. 9 and Fig. 11.

[0084] 9, 11, and 15, the power output from the power storage device 30 is larger or the SOC of the power storage device 30 is reduced compared to normal times, and if the Lo clutch mechanism C_Lo is kept engaged for a long period of time, the durability of the power storage device 30 may be reduced. Furthermore, in the control example shown in Fig. 13, the engine 3 is driven at an operating point (rotation speed and torque) that is deviated from an operating point that provides good fuel economy, and fuel economy may be deteriorated. Therefore, after the vehicle has been traveling in reverse for a predetermined period of time, the clutch mechanism to be engaged may be switched from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi.

[0085] 17, 19, 21, and 23 are flow charts for explaining the control example. In the control example shown in FIG. 17, the engine start threshold is increased by a predetermined value (step S3) in the same manner as in the control example shown in FIG. 9. Then, after a predetermined period of time has elapsed, the clutch mechanism to be engaged is switched from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi (step S4). Specifically, first, the Lo clutch mechanism C_Lo is released. Then, the rotation speed of the first motor 4 is controlled to reduce the rotation speed difference between the carrier 18 and the ring gear 16 to a predetermined difference or less. When the vehicle is traveling backward with the Lo clutch mechanism C_Lo engaged, the first motor 4 rotates in the opposite direction to the engine 3, and the carrier 18 rotates in the opposite direction to the ring gear 16 accordingly. Therefore, by rotating the first motor 4 in the same direction as the engine 3, the rotation speed difference between the carrier 18 and the ring gear 16 can be reduced. Then, the Hi clutch mechanism C_Hi is engaged at the point in time when the difference in rotation speed between the carrier 18 and the ring gear 16 becomes equal to or less than a predetermined difference. Note that, as described above, the clutch mechanism to be engaged is switched to the Hi clutch mechanism C_Hi in order to suppress a decrease in durability of the power storage device 30, and therefore the predetermined period is the period during which the hybrid vehicle is traveling in reverse and excludes the period during which the vehicle is stopped.

[0086] By switching the clutch mechanism to be engaged from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi as described above, even if the engine 3 starts and outputs torque, the torque transmitted to the front wheels 1R, 1L via the power split mechanism 6 can be reduced compared to when the Lo clutch mechanism C_Lo is engaged. Therefore, following step S4, the increased engine start threshold is returned to the normal value α (step S5), and this routine is temporarily terminated. In other words, the engine start threshold is set to the same value as when the determination in step S1 or step S2 above is negative. Note that the engine start threshold is also returned to the normal value α when the shift range is switched to the drive range.

[0087] Fig. 18 is a time chart showing changes in the traveling mode and the engine start threshold when the control example shown in Fig. 17 is executed. In the example shown in Fig. 18, the engine start threshold is increased (time t1) as in the example shown in Fig. 10. Then, when a predetermined period of time has elapsed after the engine start threshold is increased (time t2), the above-mentioned step S4 is executed, whereby the Lo clutch mechanism C_Lo is disengaged and the Hi clutch mechanism C_Hi is engaged. That is, the traveling mode is switched to the Hi mode. Then, at time t3, the engine start threshold is lowered to the normal value α.

[0088] As described above, by returning the engine start threshold to a normal value after traveling in reverse for a predetermined period of time, the load on the power storage device 30 can be reduced, and as a result, a decrease in the durability of the power storage device 30 can be suppressed. Even if the engine 3 starts by returning the engine start threshold to a normal value, the torque transmitted via the power split mechanism 6 can be reduced, and a decrease in driving force can be suppressed. Furthermore, if the Hi clutch mechanism C_Hi is configured as a meshing clutch mechanism, the Hi clutch mechanism C_Hi is engaged during traveling, and therefore, even if an engagement sound is generated, the driver's discomfort can be suppressed.

[0089] Fig. 19 is a flowchart for explaining a control example in which, after traveling backward for a predetermined period, the clutch mechanism to be engaged is switched to the Hi clutch mechanism C_Hi and the lowered charge start threshold is returned to the normal value. The control example shown in Fig. 19 lowers the charge start threshold by a predetermined value (step S13) in the same manner as the control example shown in Fig. 11. Then, after a predetermined period has elapsed, the clutch mechanism to be engaged is switched from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi (step S14). This step S14 is the same as the above-mentioned step S4.

[0090] By switching the clutch mechanism to be engaged from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi as described above, even if the engine 3 starts and outputs torque, the torque transmitted to the front wheels 1R, 1L via the power split mechanism 6 can be reduced compared to when the Lo clutch mechanism C_Lo is engaged. Therefore, following step S14, the reduced charge start threshold is returned to the normal value (step S15), and this routine is temporarily ended. In other words, the charge start threshold is set to the same value as when the above step S1 or step S2 is determined to be negative. Note that the charge start threshold is also returned to the normal value when the shift range is switched to the drive range.

[0091] FIG. 20 is a time chart showing changes in the traveling mode and the charge start threshold when the control example shown in FIG. 19 is executed. In the example shown in FIG. 20, the charge start threshold is lowered (time t11) in the same way as in the example shown in FIG. 12. Then, when a predetermined period of time has elapsed after the charge start threshold is lowered (time t12), step S14 is executed, whereby the Lo clutch mechanism C_Lo is disengaged and the Hi clutch mechanism C_Hi is engaged. That is, the traveling mode is switched to the Hi mode. Then, at time t13, the charge start threshold is increased to the normal value α.

[0092] As described above, by returning the charge start threshold to the normal value after traveling in reverse for a predetermined period of time, the load on the power storage device 30 can be reduced, and as a result, a decrease in durability of the power storage device 30 can be suppressed. Even if the engine 3 starts by returning the charge start threshold to the normal value, the torque transmitted via the power split mechanism 6 can be reduced, and a decrease in driving force can be suppressed. Furthermore, if the Hi clutch mechanism C_Hi is configured as a meshing clutch mechanism, the Hi clutch mechanism C_Hi is engaged during traveling, and therefore, even if an engagement sound occurs, the driver's discomfort can be suppressed.

[0093] Fig. 21 is a flowchart for explaining a control example in which, after traveling backward for a predetermined period of time, the clutch mechanism to be engaged is switched to the Hi clutch mechanism C_Hi, and the increased engine speed is returned to the normal speed. The control example shown in Fig. 21 increases the engine speed (step S24) in the same manner as the control example shown in Fig. 13. Then, after a predetermined period of time has elapsed, the clutch mechanism to be engaged is switched from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi (step S25). This step S25 is similar to the above steps S4 and S14.

[0094] By switching the clutch mechanism to be engaged from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi as described above, the torque transmitted to the front wheels 1R, 1L via the power split mechanism 6 can be reduced compared to when the Lo clutch mechanism C_Lo is engaged. Therefore, following step S25, the increased engine speed is returned to the normal speed (step S26), and this routine is temporarily ended. In other words, the engine speed is controlled to a speed at which the fuel economy of the engine 3 is good. The same applies when the shift range is switched to the drive range. Engine RPM Return to normal value.

[0095] FIG. 22 is a time chart showing changes in the traveling mode, the flag for operating the engine 3, the engine speed, and the output torque of the engine 3 when the control example shown in FIG. 21 is executed. In the example shown in FIG. 22, the engine speed starts to increase at time t22, as in the example shown in FIG. 14. Then, at time t23, the engine speed increases to a target speed that is higher than the normal engine speed. Then, when a predetermined period of time has elapsed since the engine speed increases to the target speed (at time t24), the above-mentioned step S25 is executed, whereby the Lo clutch mechanism C_Lo is released and the Hi clutch mechanism C_Hi is engaged. That is, the traveling mode is switched to the Hi mode. Then, at time t25, the engine speed is reduced to the normal speed. Note that, in order to maintain the output power of the engine 3, the engine torque increases with the reduction in the engine speed.

[0096] As described above, by returning the engine speed to the normal speed after traveling in reverse for a predetermined period of time, it is possible to suppress deterioration in fuel efficiency of the engine 3. Furthermore, even if the engine torque increases as the engine speed is returned to the normal speed, the torque transmitted via the power split mechanism 6 can be reduced, so that a decrease in driving force can be suppressed. Furthermore, if the Hi clutch mechanism C_Hi is configured as a meshing clutch mechanism, the Hi clutch mechanism C_Hi is engaged during traveling, so that even if an engagement sound is generated, it is possible to suppress the driver from feeling uncomfortable.

[0097] FIG. 23 shows a state in which, after the vehicle has been driven in reverse for a predetermined period of time, the clutch mechanism to be engaged is switched to the Hi clutch mechanism C_Hi, and the reduced required charging amount is increased to the normal Request amount23 is a flowchart for explaining a control example in which the charging request amount is returned to the Lo clutch mechanism C_Lo. The control example shown in FIG. 23 reduces the charging request amount by performing the same steps as in the control example shown in FIG. 15 (step S34). Then, after a predetermined period of time has elapsed, the clutch mechanism to be engaged is switched from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi (step S35). This step S35 is the same as the above steps S4, S14, and S25.

[0098] By switching the clutch mechanism to be engaged from the Lo clutch mechanism C_Lo to the Hi clutch mechanism C_Hi as described above, the torque transmitted to the front wheels 1R, 1L via the power split mechanism 6 can be reduced compared to when the Lo clutch mechanism C_Lo is engaged. Therefore, following step S35, the reduced required charging amount is returned to the normal required amount (step S36), and this routine is temporarily ended. In other words, the required charging amount is set to the same as when the above step S1 or step S2 is determined to be negative. Note that the required charging amount is also returned to the normal value when the shift range is switched to the drive range.

[0099] FIG. 24 is a time chart showing changes in the traveling mode, the flag for operating the engine 3, the charge request amount, the engine speed, and the output torque of the engine 3 when the control example shown in FIG. 23 is executed. In the example shown in FIG. 24, the engine speed starts to increase at time t33, as in the example shown in FIG. 16. Then, at time t34, the engine speed increases to a target speed that is lower than the normal engine speed. Then, when a predetermined period has elapsed since the engine speed increases to the target speed (at time t35), the above-mentioned step S35 is executed, whereby the Lo clutch mechanism C_Lo is released and the Hi clutch mechanism C_Hi is engaged. That is, the traveling mode is switched to the Hi mode. Then, at time t36, the charge request amount is returned to the normal request amount, so that the engine speed is increased to the normal speed. Note that, in order to drive the engine 3 at a driving point where the fuel efficiency of the engine 3 is good, the engine torque increases with the increase in the output power of the engine 3.

[0100] As described above, by returning the required charge amount to the normal required amount after the vehicle has been traveling backward for a predetermined period of time, it is possible to prevent the remaining charge amount of the power storage device 30 from excessively decreasing. Request amount Even if engine torque increases as a result of returning the Hi clutch mechanism C_Hi to its original position, the torque transmitted via the power split mechanism 6 can be reduced, thereby preventing a decrease in driving force. Furthermore, if the Hi clutch mechanism C_Hi is configured as a meshing clutch mechanism, the Hi clutch mechanism C_Hi is engaged during driving, so that even if an engagement sound is generated, the driver will not feel uncomfortable.

[0101] 3 to 23 are controls for suppressing a decrease in driving force caused by the torque in the forward direction transmitted from the engine 3 to the front wheels 1R, 1L via the power split mechanism 6 countering the torque output from the second motor 5 for traveling backwards. The engine 3 is started due to the low SOC of the power storage device 30 and the associated low power that can be output from the power storage device 30. Therefore, each of the above controls needs to be executed only during traveling backwards when a high driving force is required.

[0102] FIG. 25 shows a flow chart for explaining an example of the control. The control example shown in FIG. 25 is configured to execute the control example shown in FIG. 9 when traveling backward on an uphill road. Specifically, first, it is determined whether the current position is a slope road or not (step S6). This step S6 is a step for determining whether a situation in which a high driving force is required when traveling backward is present. Therefore, in step S6, it is determined whether the road will be an uphill road if traveling backward. In other words, a situation in which the road will be an uphill road if traveling forward is excluded. This step S6 may be determined based on detection values ​​of various sensors provided in the hybrid vehicle, such as an acceleration sensor or a radar, or may be determined based on position information such as a GPS or an IP address. In addition, in step S6, it is determined whether the current position is a slope road or not, but it may be determined whether there is an uphill road to travel by traveling backward within a predetermined distance. Furthermore, it may be determined whether the environment is not limited to a slope road, but for example, whether the environment is one in which a high driving force is required, such as going over a step by traveling backward.

[0103] If the current position is not on a slope and therefore the answer to step S6 is negative, this routine is temporarily terminated without executing the control example shown in Fig. 9. On the other hand, if the current position is on a slope and therefore the answer to step S6 is positive, then the control example shown in Fig. 9 is executed. That is, the process proceeds to step S1, where it is determined whether the driving range is the reverse driving range.

[0104] In this way, when high driving force is required, such as for traveling on a slope, or when there is a possibility that high driving force will be required, by changing judgment values ​​such as the engine start threshold, the engine speed, or the required charging amount, it is possible to prevent the durability of the storage device 30 from decreasing, or to prevent fuel efficiency from worsening.

[0105] Furthermore, if the SOC of the power storage device 30 is maintained high at the time when reverse running is started, the power that can be output from the power storage device 30 to the second motor 5 and the amount of power can be increased. In other words, a high driving force can be obtained when running backwards using only the second motor 5 as a driving force source, and the running time (or distance) can be extended. For this reason, the driving force control device in the embodiment of the present invention is configured to increase the SOC when there is a possibility of running uphill while running backwards.

[0106] A flow chart for explaining an example of this control is shown in Fig. 26. In the control example shown in Fig. 26, first, it is determined whether or not the current position is a position where there is a possibility of traveling uphill in reverse. That is, it is determined whether or not the vehicle is approaching a slope (step S41). This step S41 can be determined based on position information such as GPS or IP address, or based on the past travel history stored in ECU 31. Note that in this control example, it does not matter whether the hybrid vehicle is traveling forward or backward.

[0107] If the answer to step S41 is negative because the vehicle is not approaching a slope, the routine is immediately terminated. On the other hand, if the answer to step S41 is positive because the vehicle is approaching a slope, the routine determines whether the SOC is less than a predetermined SOC value (step S42). The predetermined SOC value in step S42 is a value greater than the charge start threshold value in step S13 in FIG. 11, and more specifically, is an SOC value required for parking by traveling backward on an uphill road using only the second motor 5 as a driving force source. The SOC can be determined based on a signal from a sensor that detects the SOC, the output voltage of the power storage device 30, etc.

[0108] If the SOC is equal to or greater than the predetermined SOC value and therefore the answer to step S42 is NO, this means that the power storage device 30 is charged with sufficient electric power for running backwards using only the second motor 5 as a driving force source, and so this routine is immediately terminated. On the other hand, if the SOC is less than the predetermined SOC value and therefore the answer to step S42 is YES, then it is determined whether the engine 3 is running (step S43). This step S43 is the same as step S23 described above.

[0109] If the engine 3 is running and the answer to step S43 is affirmative, the charge request amount is increased by a predetermined amount (step S44), and this routine is temporarily terminated. That is, by increasing the output power of the engine 3, the power generated by the first motor 4 is increased, and charging of the power storage device 30 is promoted. That is, the charging power of the power storage device 30 is increased. Note that the predetermined amount may be a variable value that varies depending on the difference between the current SOC value and a predetermined SOC value, the distance to a slope, etc.

[0110] On the other hand, if the engine 3 is not running and therefore the answer to step S43 is NO, the engine 3 is started (step S45), and the process proceeds to step S44.

[0111] After the charging request amount is increased and the power storage device 30 is charged as described above, if the SOC becomes sufficiently high or if the driving range is switched to the R range, the engine 3 may be stopped.

[0112] Fig. 27 is a time chart showing changes in SOC determination, hill road determination, whether or not the engine 3 is driven, the required charge amount, the engine speed, and the engine torque when the control example shown in Fig. 26 is executed. Note that Fig. 27 shows an example in which, from a state in which the engine 3 is stopped and the vehicle is traveling, the engine 3 is started by executing step S45, and the power storage device 30 is charged.

[0113] Therefore, at time t40, the engine 3 is stopped, so that the engine speed and engine torque are maintained at 0. Also, at time t40, a flag for determining whether the vehicle is on a slope (hereinafter, referred to as a slope determination flag) is turned off because the vehicle is not close to a slope. Furthermore, at time t40, the SOC is sufficiently high, so that the SOC determination flag for determining whether the SOC is higher than the predetermined SOC value in step S42 is set to Hi.

[0114] At time t41, the hill road determination flag is switched on due to the approach of a hill road. However, at time t41, the SOC determination flag remains Hi, so the answer in step S42 is NO, and the engine 3 remains stopped.

[0115] At time t42, the SOC determination flag is switched to Lo. Therefore, the above step S42 is determined as YES. On the other hand, at time t42, the engine 3 is stopped, so the above step S43 is determined as NO. Therefore, the engine 3 starts (at time t43). As a result, the engine speed and engine torque start to increase at time t43. In addition, the required charge amount for determining the output power of the engine 3 is increased from the required charge amount during normal operation by executing the above step S44.

[0116] Therefore, in order to suppress the deterioration of fuel efficiency that accompanies the increase in the output power of the engine 3, the engine speed and engine torque are controlled to target values ​​(solid lines) that are higher than the target speed (dashed lines) and target torque (dashed lines) that would be achieved if the required charging amount were not increased.

[0117] As described above, by increasing the charge request amount when approaching a slope and promoting the charging of the power storage device 30, the SOC of the power storage device 30 can be maintained high at the time when reverse running on an uphill road is started. Therefore, the power that can be output from the power storage device 30 to the second motor 5 and the amount of power can be increased. In other words, a high driving force can be obtained during reverse running using only the second motor 5 as a driving force source, and the travelable time (or distance) can be extended. Therefore, reverse running on an uphill road can be performed with the engine 3 stopped. In other words, reverse running can be performed without switching the engaged clutch mechanism, so the time from when the travel range is switched to the reverse travel range until reverse running begins can be shortened.

[0118] Even if the control example shown in FIG. 26 is executed to increase the SOC, if the distance (or time) of reverse driving is long or the driving force required during reverse driving is greater than expected, the engine 3 will be started. Therefore, the control examples shown in FIGS. 3 to 25 may be executed in addition.

[0119] The present invention is not limited to the above-described embodiments, and may be modified as appropriate within the scope of the object of the present invention. Accordingly, the hybrid vehicle that can be the subject of the present invention can be a hybrid vehicle that can set at least two driving modes in which the ratio of the torque transmitted to the first rotating machine (first motor) side to the torque transmitted to the output member (drive wheels) side is different, and the torque transmitted to the output member side via the power split mechanism acts in a direction to reduce the driving force during reverse driving. Specifically, the present invention can be applied to a hybrid vehicle that can set at least two driving modes in which the ratio of the torque transmitted to the first rotating machine (first motor) side to the torque transmitted to the output member side via the power split mechanism acts in a direction to reduce the driving force during reverse driving. Specifically, the present invention can be applied to a hybrid vehicle that can be configured to have a first differential mechanism in which a first rotating element and a second rotating element, which are two rotating elements among a rotating element to which an engine is connected, a rotating element to which a first motor is connected, and a rotating element to which a drive wheel is connected, and a third rotating element are differentially rotatably connected; a second differential mechanism in which a fourth rotating element, which is the other rotating element among a rotating element to which an engine is connected, a rotating element to which a motor is connected, and a rotating element to which a drive wheel is connected, a fifth rotating element connected to the third rotating element, and a sixth rotating element are differentially rotatably connected; the first engagement mechanism sets a low mode in which the torque transmitted from the engine to the drive wheels is large by engaging one of a first rotating element pair, which is a pair of rotating elements consisting of either the fourth rotating element, the fifth rotating element, and the sixth rotating element, and a second rotating element pair, which is a pair of rotating elements consisting of the fourth rotating element, the fifth rotating element, and the sixth rotating element, and a second engagement mechanism sets a high mode in which the torque transmitted from the engine to the drive wheels is smaller than the low mode by engaging the other rotating element pair of the first rotating element pair and the second rotating element pair. [Explanation of symbols]

[0120] 1R,1L front wheel 2. Drive unit 3 Engine 4,5 Motor 6 Power split mechanism 30 Energy storage device 31 Electronic Control Unit (ECU) C_Lo Lo clutch mechanism C_Hi Hi clutch mechanism

Claims

1. The engine, A first rotating machine; a transmission mechanism in which a first rotating element connected to the engine, a second rotating element connected to the first rotating machine, and a third rotating element connected to an output member are connected to be capable of differential rotation, and a reaction torque is output from the first rotating machine to transmit torque from the engine to the output member, and a low mode in which a ratio of the torque output from the engine that is transmitted to the output member is a first predetermined value, and a high mode in which the ratio is a second predetermined value smaller than the first predetermined value, is set; a second rotating machine connected to the output member so as to be capable of transmitting torque; an electricity storage device electrically connected to the first rotating machine and the second rotating machine; Equipped with a reverse torque is output from the second rotating machine to cause the vehicle to travel in reverse, A driving force control device for a hybrid vehicle, wherein a torque transmitted from the engine to the output member via the transmission mechanism when the engine is driving opposes a reverse torque, a controller for controlling the engine, the first rotating machine, and the second rotating machine; The controller: When a first condition is satisfied in which the power transmission mechanism is set to the low mode and the reverse drive range is selected as the drive range, a start determination value for determining whether to start the engine is changed so that the engine is more difficult to start than when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

2. 2. A driving force control device for a hybrid vehicle according to claim 1, the start determination value includes an engine start threshold value determined based on a required driving force or a required driving power of the hybrid vehicle, The controller: The engine is started when the required driving force or the required driving power becomes equal to or greater than the engine start threshold value, When the first condition is satisfied, the engine start threshold is increased more than when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

3. 2. A driving force control device for a hybrid vehicle according to claim 1, the first rotating machine is configured to convert power transmitted from the engine into electric power and to supply the converted electric power to the power storage device; the start determination value includes a charge start threshold value for starting the engine based on a remaining charge amount of the power storage device, The controller: The engine is started when the remaining charge amount becomes equal to or less than the charge start threshold value, When the first condition is satisfied, the charge start threshold is lowered to a value lower than when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

4. A driving force control device for a hybrid vehicle according to any one of claims 1 to 3, The controller: an output power of the engine when the engine is driven is determined to be a total power obtained by adding together a driving power for driving the hybrid vehicle and a charging power for charging the power storage device, When a first condition is satisfied in which the power transmission mechanism is set to the low mode and the reverse drive range is selected as the drive range, the output torque of the engine is reduced compared to when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

5. The engine, A first rotating machine; a transmission mechanism in which a first rotating element connected to the engine, a second rotating element connected to the first rotating machine, and a third rotating element connected to an output member are connected to be capable of differential rotation, and a reaction torque is output from the first rotating machine to transmit torque from the engine to the output member, and a low mode in which a ratio of the torque output from the engine that is transmitted to the output member is a first predetermined value, and a high mode in which the ratio is a second predetermined value smaller than the first predetermined value, is set; a second rotating machine connected to the output member so as to be capable of transmitting torque; an electricity storage device electrically connected to the first rotating machine and the second rotating machine; Equipped with a reverse torque is output from the second rotating machine to cause the vehicle to travel in reverse, A driving force control device for a hybrid vehicle, wherein a torque transmitted from the engine to the output member via the transmission mechanism when the engine is driving opposes a reverse torque, a controller for controlling the engine, the first rotating machine, and the second rotating machine; The controller: an output power of the engine when the engine is driven is determined to be a total power obtained by adding together a driving power for driving the hybrid vehicle and a charging power for charging the power storage device, When a first condition is satisfied in which the power transmission mechanism is set to the low mode and the reverse drive range is selected as the drive range, the output torque of the engine is reduced compared to when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

6. A driving force control device for a hybrid vehicle according to claim 4 or 5, The controller: When the first condition is satisfied, the output torque of the engine is reduced by increasing the rotation speed of the engine while maintaining the output power of the engine at the same level as when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

7. A driving force control device for a hybrid vehicle according to claim 4 or 5, The controller: When the first condition is satisfied, the charging power is set to be lower than when the first condition is not satisfied, thereby reducing the output power of the engine and reducing the output torque of the engine. A driving force control device for a hybrid vehicle.

8. A driving force control device for a hybrid vehicle according to any one of claims 1 to 4, The controller: configured to further control the transmission mechanism; When a predetermined period of time has elapsed since the hybrid vehicle started to travel in reverse, the power transmission mechanism is switched from the low mode to the high mode, and the changed start determination value is returned to the start determination value when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

9. A driving force control device for a hybrid vehicle according to any one of claims 4 to 7, The controller: configured to further control the transmission mechanism; When a predetermined period of time has elapsed since the hybrid vehicle started to travel in reverse, the power transmission mechanism is switched from the low mode to the high mode, and the reduced output torque of the engine is restored to the output torque of the engine when the first condition is not satisfied. A driving force control device for a hybrid vehicle.

10. A driving force control device for a hybrid vehicle according to any one of claims 1 to 4 or 8, The controller: determining whether the hybrid vehicle is traveling backward on a high-load road where a driving force required when traveling backward is greater than a predetermined driving force; When traveling on the high-load road, the start determination value is changed. A driving force control device for a hybrid vehicle.

11. A driving force control device for a hybrid vehicle according to any one of claims 4 to 7 or 9, The controller: determining whether the hybrid vehicle is traveling backward on a high-load road where a driving force required when traveling backward is greater than a predetermined driving force; When traveling on the high-load road, the output torque of the engine is reduced. A driving force control device for a hybrid vehicle.

12. A driving force control device for a hybrid vehicle according to any one of claims 1 to 11, The controller: determining whether the hybrid vehicle has approached a high-load roadway where a driving force required when the hybrid vehicle is traveling in reverse is greater than a predetermined driving force; When the vehicle is close to the high-load road, the charging power of the power storage device is increased more than when the vehicle is not close to the high-load road. A driving force control device for a hybrid vehicle.

13. A driving force control device for a hybrid vehicle according to claim 12, The controller: When the engine is stopped at the time when the vehicle approaches the high-load road, the engine is started to increase the charging power of the power storage device. A driving force control device for a hybrid vehicle.

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