JP7205502B2 - four wheel drive vehicle - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle capable of adjusting a main side distribution ratio, which is a ratio of driving force transmitted to main driving wheels to total driving force transmitted to main driving wheels and sub-driving wheels.

(a) a driving force source; (b) an automatic transmission having a plurality of engagement elements and connected to said driving force source and a drive shaft; and (c) from said drive shaft to main drive wheels and auxiliary drive wheels and the ratio of the driving force transmitted to the main driving wheels to the total driving force transmitted from the drive shaft to the main driving wheels and the auxiliary driving wheels Four wheel drive vehicles with adjustable rate drive power distribution systems are well known. For example, a four-wheel drive vehicle described in Patent Document 1 is one of them.

WO2011/042951

By the way, in the four-wheel drive vehicle of Patent Document 1 described above, when a coast downshift is performed in the automatic transmission, the torque fluctuation of the drive shaft caused by the coast downshift is transmitted through the driving force distribution device. There is a problem that the transmission is transmitted to the main driving wheels and the auxiliary driving wheels, and the shift shock is worsened depending on the main side distribution ratio.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a four-wheel drive vehicle that suppresses aggravation of shift shock while suppressing deterioration of shift response. .

The inventors of the present invention conducted various studies against the background of the above circumstances, and found that when the automatic transmission performs a coast downshift, the main-side distribution ratio is relatively small. When the distribution ratio of the driving force transmitted to the sub-driving wheels is adjusted to the equal (50:50) side by the driving force distribution device, the shift shock due to the torque fluctuations transmitted to the sub-driving wheels is increased. I found that it tends to get worse. The present invention has been made based on such findings.

That is, the gist of the first invention is (a) an automatic transmission having a driving force source, a plurality of engagement elements and connected to the driving force source and the drive shaft, and It is possible to transmit the driving force from the driving force source to the driving wheels and the sub-driving wheels, and the ratio of the driving force transmitted to the main driving wheels to the total driving force transmitted from the driving shaft to the main driving wheels and the sub-driving wheels A four-wheel drive vehicle comprising: a driving force distribution device capable of adjusting a main side distribution rate, which is a ratio; In this case, according to the main side distribution rate, the automatic transmission is controlled so that when the main side distribution rate is small, the shift time is longer than when the main side distribution rate is large. .

Further, the gist of the second invention is that in the first invention, the control device is arranged in accordance with the main-side distribution ratio, when the main-side distribution ratio is small, compared to when the main-side distribution ratio is large. To control the shift of the automatic transmission so that the coast downshift is performed on the low vehicle speed side.

The gist of the third invention is that in the first invention or the second invention, (a) the automatic transmission includes a plurality of friction engagement elements and a one-way clutch as the plurality of engagement elements. (b) the coast downshift includes switching one of the plurality of friction engagement elements from an engaged state to a released state and switching the one-way clutch from a disengaged state to an engaged state; It is downshifting.

Further, the gist of the fourth invention is that in the third invention, (a) the frictional engagement element is shifted from the engaged state to the above-described frictional engagement state by reducing the hydraulic pressure supplied to the frictional engagement element. (b) the control device, when performing the coast downshift, according to the main side distribution rate, when the main side distribution rate is small, the main side distribution rate; To perform speed change control of the automatic transmission so as to lower the reduction speed at which the hydraulic pressure is reduced in the hydraulic friction engagement device compared to when the side distribution ratio is large.

According to the four-wheel drive vehicle of the first aspect of the invention, when the automatic transmission performs a coast downshift, the control device determines, according to the main-side distribution ratio, the main-side shift when the main-side distribution ratio is small. The shift control of the automatic transmission is performed so that the shift time becomes longer than when the distribution ratio is large. Therefore, when the main-side distribution ratio is relatively small and the shift shock tends to worsen, the shift control of the automatic transmission is performed so as to lengthen the shift time, so the shift shock worsens. is suitably suppressed. Further, when the main-side distribution ratio is relatively large and the shift shock tends not to worsen, the shift control of the automatic transmission is performed so as not to lengthen the shift time. Deterioration of shift responsiveness is suitably suppressed. As a result, it is possible to suppress the deterioration of the shift shock while suppressing the deterioration of the shift responsiveness.

According to the four-wheel drive vehicle of the second aspect of the invention, the control device performs the coast downshift according to the main-side distribution ratio when the main-side distribution ratio is small compared to when the main-side distribution ratio is large. Since the shift control of the automatic transmission is performed so as to be performed on the low vehicle speed side, it is possible to suitably suppress the deterioration of the shift shock.

According to the four-wheel drive vehicle of the third invention, (a) the automatic transmission has a plurality of friction engagement elements and a one-way clutch as the plurality of engagement elements, and (b) the coastdown A shift is a coast downshift that switches one of the plurality of frictional engagement elements from an engaged state to a released state and switches the one-way clutch from a non-engaged state to an engaged state. Therefore, in the coast downshift, the shift shock caused by switching the one-way clutch from the non-engaged state to the engaged state is caused by, for example, the frictional engagement element switching from the released state to the engaged state instead of the one-way clutch. However, it is possible to suitably suppress the deterioration of the shift shock in this case.

According to the four-wheel drive vehicle of the fourth aspect of the invention, (a) the frictional engagement element is switched from the engaged state to the released state by reducing the hydraulic pressure supplied to the frictional engagement element. (b) when the coast downshift is performed, the control device is configured according to the main-side distribution ratio when the main-side distribution ratio is small and when the main-side distribution ratio is large; The speed change control of the automatic transmission is performed so as to lower the reduction speed at which the hydraulic pressure is reduced in the hydraulic friction engagement device compared to . Therefore, by reducing the speed at which the hydraulic pressure is reduced in the hydraulic friction engagement device, the shift time is lengthened in the shift control of the automatic transmission.

1 is a diagram showing a schematic configuration of a four-wheel drive vehicle to which the present invention is applied, and an outline of a control system including an electronic control device that controls the four-wheel drive vehicle; FIG. 2 is a skeleton diagram showing a schematic configuration of the transmission in FIG. 1; FIG. 3 is an engagement actuation table for the transmission of FIG. 2; FIG. 3 is a collinear diagram showing the relative relationship between the rotational speeds of the rotating elements in the continuously variable transmission and the stepped transmission of FIG. 2; FIG. 2 is a skeleton diagram for explaining the structure of the transfer in FIG. 1; FIG. 3 is a diagram showing an example of an AT gear shift map used for shift control of a stepped transmission and a power source switching map used for switching control between hybrid running and motor running, and also showing the relationship between them. FIG. 5 is a diagram showing release-side hydraulic pressure of a release-side frictional engagement element that changes according to a front-rear distribution ratio, that is, a rear-wheel-side distribution ratio when a coast downshift is performed to switch from AT 2nd gear to AT 1st gear; FIG. 5 is a diagram showing a downshift line of an AT gear shift map that changes according to a front/rear distribution ratio, that is, a rear wheel side distribution ratio when a coast downshift to switch from AT 2nd gear to AT 1st gear is determined. FIG. 2 is a flow chart for explaining the main part of the control operation of the electronic control unit of FIG. 1, for example, when performing a coast downshift to switch from AT 2nd gear to AT 1st gear, control operation of shift control of a stepped transmission; It is a flow chart for explaining. FIG. 5 is a skeleton diagram for explaining the structure of a transfer provided in a four-wheel drive vehicle according to another embodiment of the present invention;

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

FIG. 1 shows a schematic configuration of a four-wheel drive vehicle 10 to which the present invention is applied, and an overview of a control system including an electronic control device (control device) 200 that controls the four-wheel drive vehicle 10. FIG. As shown in FIG. 1, a four-wheel drive vehicle 10 includes an engine (driving force source) 12 as a main driving force source, a pair of left and right front wheels 14L and 14R, a pair of left and right rear wheels 16L and 16R, and an engine 12. and a power transmission device 18 for transmitting the driving force from the front wheels 14L, 14R and the rear wheels 16L, 16R, respectively. The rear wheels 16L and 16R (referred to as the rear wheels 16 unless otherwise distinguished) are main drive wheels that serve as drive wheels during two-wheel drive and four-wheel drive. The front wheels 14L and 14R (referred to as the front wheels 14 unless otherwise distinguished) are sub-driving wheels that become driven wheels during two-wheel drive running and drive wheels during four-wheel drive running. The four-wheel drive vehicle 10 is a front-engine rear-wheel drive (FR)-based four-wheel drive vehicle. The rear wheels 16 correspond to the main drive wheels of the invention, and the front wheels 14 correspond to the auxiliary drive wheels of the invention.

The power transmission device 18 includes a hybrid transmission 20 including a first rotating machine (driving force source) MG1 and a second rotating machine (driving force source) MG2, which will be described later, and a transfer (driving force distribution device) 22. , a front propeller shaft 24 and a rear propeller shaft 26, a front wheel side differential gear device 28, a rear wheel side differential gear device 30, a pair of left and right front wheel axles 32L and 32R, a pair of left and right rear wheel axles 34L, 34R and the like. In the power transmission device 18, the driving force from the engine 12 transmitted via the transmission 20 is sequentially transmitted from the transfer 22 through the rear propeller shaft 26, the rear wheel side differential gear device 30, the rear wheel axles 34L and 34R, and the like. are transmitted to the rear wheels 16L and 16R. In the power transmission device 18, when part of the driving force from the engine 12 transmitted to the transfer 22 is distributed to the front wheels 14L and 14R, the distributed driving force is transferred to the front propeller shaft 24 and the front wheels. The power is transmitted to the front wheels 14L, 14R through the differential gear device 28, the front wheel axles 32L, 32R, and the like.

FIG. 2 is a skeleton diagram showing a schematic configuration of the transmission 20. As shown in FIG. The engine 12 controls an engine control device 36 (see FIG. 1) including an electronic throttle valve, a fuel injection device, an ignition device, etc. by an electronic control device 200, which will be described later. is controlled.

The transmission 20 includes a first rotary machine MG1 and a second rotary machine MG2. The first rotary machine MG1 and the second rotary machine MG2 are rotary electric machines having a function as an electric motor (motor) and a function as a generator (generator), and are so-called motor generators. The first rotary machine MG1 and the second rotary machine MG2 can serve as driving force sources for the four-wheel drive vehicle 10 to travel. The first rotary machine MG1 and the second rotary machine MG2 are each connected to a battery 40 (see FIG. 1) provided to the four-wheel drive vehicle 10 via an inverter 38 (see FIG. 1) provided to the four-wheel drive vehicle 10. )It is connected to the. Electronic control unit 200 controls inverter 38 of first rotary machine MG1 and second rotary machine MG2, so that MG1 torque Tg, which is the output torque of first rotary machine MG1, and output of second rotary machine MG2, respectively. MG2 torque Tm, which is torque, is controlled. For example, in the case of positive rotation, the output torque of the rotating machine is power running torque when the positive torque is on the acceleration side, and regenerative torque when the negative torque is on the deceleration side. Battery 40 is a power storage device that transfers electric power to and from each of first rotary machine MG1 and second rotary machine MG2. The first rotary machine MG1 and the second rotary machine MG2 are provided inside a case 42, which is a non-rotating member attached to the vehicle body. The first rotating machine MG1 and the second rotating machine MG2 correspond to the driving force source of the present invention.

The transmission 20 includes an electric continuously variable transmission 44 and a mechanical stepped transmission (automatic transmission) arranged in series on a common first rotation axis CL1 in a case 42 as a non-rotating member attached to the vehicle body. machine) 46 and the like. An electric continuously variable transmission 44 is provided in a power transmission path between the engine 12 and a mechanical stepped transmission 46 . The electric continuously variable transmission 44 is connected to the engine 12 directly or indirectly via a damper (not shown) or the like. A mechanical stepped transmission 46 is provided in a power transmission path between the electric continuously variable transmission 44 and the transfer 22 . The mechanical stepped transmission 46 is connected to the output side of the electric continuously variable transmission 44 . In the transmission 20 , the power output from the engine 12 and the second rotary machine MG2 is transmitted to the mechanical stepped transmission 46 and then transmitted from the mechanical stepped transmission 46 to the transfer 22 . Hereinafter, the electric continuously variable transmission 44 will be referred to as the continuously variable transmission 44 and the mechanical stepped transmission 46 will be referred to as the stepped transmission 46 . In addition, power is the same as torque and force unless otherwise specified. The continuously variable transmission 44 and the stepped transmission 46 are configured substantially symmetrically with respect to the first rotation axis CL1, and lower halves thereof are omitted from FIG. 2 with respect to the first rotation axis CL1.

The continuously variable transmission 44 serves as a power splitting mechanism that mechanically divides the power of the first rotary machine MG1 and the engine 12 to the first rotary machine MG1 and an intermediate transmission member 50 that is an output rotary member of the continuously variable transmission 44. and a differential mechanism 52. A second rotary machine MG2 is coupled to the intermediate transmission member 50 so as to be capable of power transmission. The first rotating machine MG1 is a rotating machine to which the power of the engine 12 is transmitted. The continuously variable transmission 44 is an electric continuously variable transmission in which the differential state of the differential mechanism 52 is controlled by controlling the operating state of the first rotary machine MG1. The continuously variable transmission 44 has a ratio of the engine rotation speed Ne, which is the same value as the rotation speed of the connecting shaft 48, which is the input rotation member, and the MG2 rotation speed Nm, which is the rotation speed of the intermediate transmission member 50 which is the output rotation member. It is operated as an electric continuously variable transmission in which the gear ratio γ0 (=Ne/Nm), which is a value, can be varied. The first rotary machine MG1 is a rotary machine capable of controlling an engine rotation speed Ne, which is the rotation speed of the engine 12 . Note that controlling the operating state of the first rotating machine MG1 means controlling the operation of the first rotating machine MG1.

The differential mechanism 52 is composed of a single pinion type planetary gear device, and includes a sun gear S0, a carrier CA0, and a ring gear R0. The engine 12 is connected to the carrier CA0 via a connecting shaft 48 so as to be able to transmit power, the first rotating machine MG1 is connected to be able to transmit power to the sun gear S0, and the second rotating machine MG2 is capable of transmitting power to the ring gear R0. connected to In differential mechanism 52, carrier CA0 functions as an input element, sun gear S0 functions as a reaction force element, and ring gear R0 functions as an output element.

The stepped transmission 46 is an automatic transmission that forms a power transmission path between the intermediate transmission member 50 and the transfer 22, and includes the engine 12, which is a driving force source for running, the first rotary machine MG1, and the second rotary machine MG1. It is an automatic transmission forming part of the power transmission path between the rotary machine MG2 and the drive wheels (14, 16). The intermediate transmission member 50 also functions as an input rotating member of the stepped transmission 46 . Further, the intermediate transmission member 50 is connected to the second rotary machine MG2 so as to rotate integrally therewith. The stepped transmission 46 includes, for example, a plurality of sets of planetary gear trains of a first planetary gear train 54 and a second planetary gear train 56, and a plurality of clutches C1, C2, brakes B1 and B2 including a one-way clutch F1. It is a known planetary gear type automatic transmission provided with an engagement device (engagement element). Hereinafter, the clutch C1, the clutch C2, the brake B1, and the brake B2 will simply be referred to as an engagement device CB unless otherwise specified.

The engagement device CB is a hydraulic friction engagement device (friction engagement element) composed of a multi-plate or single-plate clutch or brake pressed by a hydraulic actuator, a band brake tightened by a hydraulic actuator, or the like. The engagement device CB is in an engaged state or a disengaged state by each hydraulic pressure of the engagement device CB that is regulated and output from a hydraulic control circuit 58 (see FIG. 1) provided in the four-wheel drive vehicle 10. is switched.

In the stepped transmission 46, the respective rotating elements of the first planetary gear device 54 and the second planetary gear device 56 are connected directly or indirectly via an engagement device CB or a one-way clutch F1, or are connected via intermediate transmission. It is connected to the member 50 , the case 42 or the output shaft 60 . That is, the stepped transmission 46 has an engagement device CB and a one-way clutch F1 that are a plurality of engagement devices (engagement elements), and also includes the engine 12, the first rotary machine MG1, and the second rotary machine MG1 that are driving force sources. It is connected to the rotary machine MG2 and an input shaft (drive shaft) 66 of a transfer 22 (to be described later) connected to the output shaft 60 so that power can be transmitted. The rotating elements of the first planetary gear set 54 are the sun gear S1, the carrier CA1 and the ring gear R1, and the rotating elements of the second planetary gear set 56 are the sun gear S2, the carrier CA2 and the ring gear R2.

The stepped transmission 46 has a gear ratio (also referred to as a gear ratio) γat (=input rotation speed Ni/output rotation speed No) that differs depending on the engagement of any two of the plurality of engagement devices. It is a stepped transmission in which one of a plurality of gear stages (also referred to as gear stages) is formed. In other words, the stepped transmission 46 switches gear stages, that is, performs gear shifting by selectively engaging a plurality of engagement devices. The stepped transmission 46 is a stepped automatic transmission in which a plurality of gear stages are alternatively formed. In this embodiment, the gear stage formed by the stepped transmission 46 is called an AT gear stage. The input rotation speed Ni is the input rotation speed of the stepped transmission 46, which is the rotation speed of the input rotation member of the stepped transmission 46, and has the same value as the rotation speed of the intermediate transmission member 50. It has the same value as the MG2 rotation speed Nm, which is the rotation speed of the machine MG2. The input rotation speed Ni can be represented by the MG2 rotation speed Nm. The output rotation speed No is the rotation speed of the output shaft 60, which is the output rotation speed of the stepped transmission 46, and is the output rotation speed of the entire transmission 20 including the continuously variable transmission 44 and the stepped transmission 46. But also.

For example, as shown in the engagement operation table of FIG. 3, the stepped transmission 46 has a plurality of AT gear stages: AT 1st gear ("1st" in the figure)-AT 4th gear ("4th" in the figure). ”) are formed. The transmission gear ratio γat of the AT 1st gear stage is the largest, and the transmission gear ratio γat becomes smaller as the AT gear stage becomes higher. A reverse AT gear stage ("Rev" in the drawing) is formed, for example, by engagement of the clutch C1 and engagement of the brake B2. That is, when the vehicle is traveling in reverse, for example, the AT 1st gear is established. The engagement operation table in FIG. 3 summarizes the relationship between each AT gear stage and each operation state of a plurality of engagement devices. That is, the engagement operation table of FIG. 3 summarizes the relationship between each AT gear stage and a predetermined engagement device, which is an engagement device that is engaged with each AT gear stage. In FIG. 3 , “◯” indicates engagement, “Δ” indicates engagement during engine braking or during coast downshifting of the stepped transmission 46, and blank spaces indicate disengagement.

The stepped transmission 46 is controlled by an electronic control unit 200, which will be described later, to switch between AT gear stages according to the driver's accelerator operation, vehicle speed V, etc. In other words, a plurality of AT gear stages are selectively selected. formed in For example, in speed change control of the stepped transmission 46, so-called clutch-to-clutch speed change is executed by disengaging the release side engagement device CB and engaging the engagement side engagement device CB.

The four-wheel drive vehicle 10 also includes a one-way clutch F0, a mechanical oil pump MOP 62, an electric oil pump (not shown), and the like.

The one-way clutch F0 is a lock mechanism that can fix the carrier CA0 so that it cannot rotate. That is, the one-way clutch F0 is a locking mechanism that can fix the connecting shaft 48 that is connected to the crankshaft of the engine 12 and rotates integrally with the carrier CA0 to the case 42 . The one-way clutch F0 is idly rotated in the forward rotation direction, which is the rotation direction when the engine 12 is running, and mechanically automatically engages in the rotation direction opposite to when the engine 12 is running. Therefore, when the one-way clutch F0 is idling, the engine 12 is allowed to rotate relative to the case 42 . On the other hand, when the one-way clutch F<b>0 is engaged, the engine 12 cannot rotate relative to the case 42 . That is, the engine 12 is fixed to the case 42 by engaging the one-way clutch F0. Thus, the one-way clutch F0 permits rotation of the carrier CA0 in the positive rotation direction, which is the rotation direction during operation of the engine 12, and prevents rotation of the carrier CA0 in the negative rotation direction. That is, the one-way clutch F0 is a lock mechanism that allows rotation of the engine 12 in the positive rotation direction and prevents rotation in the negative rotation direction.

The MOP 62 is connected to the connecting shaft 48 , rotates with the rotation of the engine 12 , and discharges hydraulic oil used in the power transmission device 18 . An electric oil pump (not shown) is driven when the engine 12 is stopped, that is, when the MOP 62 is not driven. Hydraulic oil discharged from the MOP 62 or an electric oil pump (not shown) is supplied to the hydraulic control circuit 58 as source pressure. The engagement device CB is switched between operating states by each hydraulic pressure regulated from the original pressure by the hydraulic control circuit 58 .

FIG. 4 is a collinear diagram showing the relative relationship between the rotational speeds of the rotating elements in the continuously variable transmission 44 and the stepped transmission 46. As shown in FIG. In FIG. 4, three vertical lines Y1, Y2, and Y3 corresponding to the three rotating elements of the differential mechanism 52 constituting the continuously variable transmission 44 indicate, from left to right, the sun gear S0 corresponding to the second rotating element RE2. The g-axis represents the rotational speed, the e-axis represents the rotational speed of the carrier CA0 corresponding to the first rotating element RE1, and the rotational speed of the ring gear R0 corresponding to the third rotating element RE3 (that is, the speed of the stepped transmission 46). input rotational speed). The four vertical lines Y4, Y5, Y6, and Y7 of the stepped transmission 46 indicate, in order from the left, the rotational speed of the sun gear S2 corresponding to the fourth rotating element RE4, and the rotational speed of the sun gear S2 corresponding to the fifth rotating element RE5. The rotation speed of the coupled ring gear R1 and carrier CA2 (that is, the rotation speed of the output shaft 60), the rotation speed of the mutually coupled carrier CA1 and ring gear R2 corresponding to the sixth rotating element RE6, corresponding to the seventh rotating element RE7 These axes represent the rotational speeds of the sun gear S1. The mutual intervals of the vertical lines Y1, Y2, Y3 are determined according to the gear ratio ρ0 of the differential mechanism 52. As shown in FIG. Further, the intervals between the vertical lines Y4, Y5, Y6 and Y7 are determined according to the respective gear ratios ρ1 and ρ2 of the first and second planetary gear units 54 and 56, respectively. If the distance between the sun gear and the carrier corresponds to "1" in the relationship between the vertical axes of the collinear chart, then the gear ratio ρ (=number of teeth of the sun gear/ring gear) of the planetary gear system between the carrier and the ring gear is number of teeth).

4, in the differential mechanism 52 of the continuously variable transmission 44, the engine 12 (see "ENG" in the drawing) is connected to the first rotating element RE1, and the second rotating element A first rotating machine MG1 (see "MG1" in the drawing) is connected to RE2, and a second rotating machine MG2 (see "MG2" in the drawing) is connected to a third rotating element RE3 that rotates integrally with the intermediate transmission member 50. , and is configured to transmit the rotation of the engine 12 to the stepped transmission 46 via the intermediate transmission member 50 . In the continuously variable transmission 44, straight lines L0e, L0m, and L0R crossing the vertical line Y2 indicate the relationship between the rotation speed of the sun gear S0 and the rotation speed of the ring gear R0.

In the stepped transmission 46, the fourth rotating element RE4 is selectively connected to the intermediate transmission member 50 via the clutch C1, the fifth rotating element RE5 is connected to the output shaft 60, and the sixth rotating element RE6 is It is selectively connected to the intermediate transmission member 50 via the clutch C2 and selectively connected to the case 42 via the brake B2, and the seventh rotating element RE7 is selectively connected to the case 42 via the brake B1. be. In the stepped transmission 46, the respective straight lines L1, L2, L3, L4, and LR crossing the vertical line Y5 by the engagement release control of the engagement device CB cause the output shaft 60 to be "1st", "2nd", and "3rd". , “4th” and “Rev” are shown.

A straight line L0e and straight lines L1, L2, L3, and L4 indicated by solid lines in FIG. The relative speed of each rotating element is shown. In this hybrid running mode, in the differential mechanism 52, MG1 torque Tg, which is a reaction torque of negative torque generated by the first rotary machine MG1, is input to the sun gear S0 with respect to the positive engine torque Te input to the carrier CA0. Then, an engine direct torque Td (=Te/(1+ρ0)=-(1/ρ0)×Tg) appears in the ring gear R0, which becomes a positive torque in forward rotation. Then, according to the required driving force, the total torque of the engine direct torque Td and the MG2 torque Tm is the driving torque in the forward direction of the four-wheel drive vehicle 10, which is one of the AT first gear stage to the AT fourth gear stage. The power is transmitted to the transfer 22 via a stepped transmission 46 having an AT gear stage. The first rotary machine MG1 functions as a generator when it generates negative torque in positive rotation. The electric power Wg generated by the first rotating machine MG1 is charged in the battery 40 or consumed by the second rotating machine MG2. The second rotary machine MG2 uses all or part of the generated power Wg, or uses power from the battery 40 in addition to the generated power Wg to output the MG2 torque Tm.

A straight line L0m indicated by a dashed dotted line in FIG. 4 and straight lines L1, L2, L3, and L4 indicated by solid lines in FIG. 1 shows the relative speed of each rotating element in forward running in a motor running (=EV running) mode in which motor running is possible using at least one of the rotary machines as a driving force source. Motor running in forward running in the motor running mode includes, for example, single-drive motor running in which only the second rotary machine MG2 is used as a driving force source, and single-drive motor running in which both the first rotary machine MG1 and the second rotary machine MG2 are used as driving force sources. There is a running both drive motor running. In single-drive motor running, the carrier CA0 is set to zero rotation, and the MG2 torque Tm, which becomes positive torque in forward rotation, is input to the ring gear R0. At this time, the first rotary machine MG1 connected to the sun gear S0 is brought into a no-load state and idled in a negative rotation. In single-drive motor running, the one-way clutch F0 is released and the connecting shaft 48 is not fixed to the case 42 .

In dual-drive motor running, when the carrier CA0 is set to zero rotation and MG1 torque Tg, which becomes negative torque at negative rotation, is input to the sun gear S0, the carrier CA0 is prevented from rotating in the negative rotation direction. , the one-way clutch F0 is automatically engaged. In a state where carrier CA0 is non-rotatably fixed by engagement of one-way clutch F0, reaction torque due to MG1 torque Tg is input to ring gear R0. In addition, in dual-drive motor running, MG2 torque Tm is input to ring gear R0 in the same manner as in single-drive motor running. When the MG1 torque Tg, which becomes a negative torque at negative rotation, is input to the sun gear S0 in a state where the carrier CA0 is set to zero rotation, if the MG2 torque Tm is not input, single-drive motor running by the MG1 torque Tg is also possible. is. In forward running in the motor running mode, the engine 12 is not driven, the engine rotation speed Ne is set to zero, and at least one of the MG1 torque Tg and the MG2 torque Tm is used to drive the four-wheel drive vehicle 10 in the forward direction. As torque, it is transmitted to the drive wheels (front wheels 14 and rear wheels 16) via a stepped transmission 46 in which any one of the AT 1st gear-AT 4th gear is formed. In forward running in the motor running mode, the MG1 torque Tg is power running torque of negative rotation and negative torque, and the MG2 torque Tm is power running torque of positive rotation and positive torque.

A straight line L0R and a straight line LR indicated by dashed lines in FIG. 4 indicate the relative speed of each rotating element during reverse travel in the motor travel mode. In reverse travel in this motor travel mode, MG2 torque Tm, which becomes negative torque at negative rotation, is input to the ring gear R0, and the MG2 torque Tm serves as a drive torque in the reverse direction of the four-wheel drive vehicle 10, and the AT 1st speed gear. The power is transmitted to the drive wheels (front wheels 14 and rear wheels 16) via a stepped transmission 46 having steps. In the four-wheel drive vehicle 10, the electronic control unit 200 sets a forward low-side AT gear stage among a plurality of AT gear stages, for example, an AT 1st gear stage. The second rotating machine MG2 outputs the reverse MG2 torque Tm, which is opposite in polarity to the MG2 torque Tm of the second rotary machine MG2, so that the vehicle can travel backward. In reverse running in the motor running mode, the MG2 torque Tm is power running torque of negative rotation and negative torque. Also in the hybrid running mode, it is possible to rotate the second rotary machine MG2 in the negative direction as in the straight line L0R, so that reverse running can be performed in the same manner as in the motor running mode.

Next, the transfer 22 will be explained. FIG. 5 is a skeleton diagram for explaining the structure of the transfer 22. As shown in FIG. The transfer 22 has a transfer case 64 as a non-rotating member. As shown in FIG. 5 , the transfer 22 includes an input shaft 66 , a rear wheel side output shaft 68 , a front wheel drive drive sprocket 70 , a high/low switching mechanism 72 , and a front wheel drive clutch 74 in a transfer case 64 . , about a common first rotation axis CL1. Note that the input shaft 66 is connected to the engine 12 via the transmission 20 so as to be able to transmit power. Further, the rear wheel output shaft 68 is connected to the rear propeller shaft 26 so as to transmit power, and the rear wheel output shaft 68 receives the driving force transmitted from the engine 12 to the input shaft 66 via the transmission 20. Output to the rear wheels 16L and 16R. The front-wheel drive drive sprocket 70 is supported by the rear-wheel output shaft 68 so as to be relatively rotatable with respect to the rear-wheel output shaft 68 . The high-low switching mechanism 72 also functions as an auxiliary transmission that changes the speed of the rotation of the input shaft 66 and transmits it to the rear wheel side output shaft 68 . The front-wheel drive clutch 74 is a multi-plate wet clutch, and the front-wheel drive clutch 74 transmits part of the driving force transmitted to the rear-wheel-side output shaft 68 to the front-wheel drive drive sprocket 70. The transmission torque transmitted from the rear-wheel output shaft 68 to the front-wheel drive drive sprocket 70 is adjusted.

As shown in FIG. 5, the transfer 22 includes a front-wheel output shaft 76 and a front-wheel drive driven sprocket 78 in a transfer case 64 around a common second rotation axis CL2. Further, the transfer 22 includes a front wheel drive chain 80 and a differential lock mechanism 82 . The front-wheel output shaft 76 is connected to the front propeller shaft 24 so as to be capable of power transmission. A driven sprocket 78 for driving the front wheels is provided integrally with the front-wheel output shaft 76 . The front-wheel drive chain 80 is respectively hung on the front-wheel drive drive sprocket 70 and the front-wheel drive driven sprocket 78, and connects the front-wheel drive drive sprocket 70 and the front-wheel drive driven sprocket 78 so that power can be transmitted. The differential lock mechanism 82 is a dog clutch that selectively connects the rear-wheel output shaft 68 and the front-wheel drive drive sprocket 70, and the differential lock mechanism 82 rotates between the rear propeller shaft 26 and the front propeller shaft 24. It selectively switches between a differential state with limited differential and a non-differential state with limited rotational differential therebetween.

The high-low switching mechanism 72 includes a single pinion type planetary gear device 84 and a high-low sleeve 86, as shown in FIG. The planetary gear device 84 includes a sun gear S connected to the input shaft 66 so as to be able to transmit power, a ring gear R connected to the transfer case 64 so as not to rotate about the first rotation axis CL1, and the sun gear S and the ring gear R. and a carrier CA that supports a plurality of meshed pinion gears P so that they can rotate on their own axis and revolve around the first rotation axis CL1. Therefore, in the high/low switching mechanism 72 , the rotational speed of the sun gear S is constant with respect to the input shaft 66 , and the rotational speed of the carrier CA is reduced with respect to the input shaft 66 . As shown in FIG. 5, high-side gear teeth 88 are formed on the inner peripheral surface of the sun gear S, and low-side gear teeth 90 having the same diameter as the high-side gear teeth 88 are formed on the carrier CA. It is

The high-low sleeve 86 is spline-fitted to the rear-wheel output shaft 68 so as to be movable relative to the rear-wheel output shaft 68 in the direction of the first rotation axis CL1 and to be non-rotatable relative to the rear-wheel output shaft 68. ing. 5, the high-low sleeve 86 is integrally provided with a fork connecting portion 86a and outer peripheral teeth 86b that can mesh with the high-side gear teeth 88 and the low-side gear teeth 90, respectively. . In the high-low switching mechanism 72, when the high-low sleeve 86 is moved in the direction of the first rotation axis CL1 with respect to the rear wheel side output shaft 68, and the outer peripheral teeth 86b of the high-low sleeve 86 mesh with the high side gear teeth 88, A high-speed side gear stage H is formed to transmit the rotation of the input shaft 66 and the rotation of the same speed to the rear wheel side output shaft 68 . In the high-low switching mechanism 72, when the high-low sleeve 86 is moved in the direction of the first rotation axis CL1 with respect to the rear wheel side output shaft 68 and the outer peripheral teeth 86b of the high-low sleeve 86 mesh with the low side gear teeth 90, A low-speed side gear stage L is formed to transmit the rotation reduced with respect to the rotation of the input shaft 66 to the rear wheel side output shaft 68 .

The differential lock mechanism 82 includes lock teeth 92 and a lock sleeve 94, as shown in FIG. The lock teeth 92 are formed integrally with the inner peripheral surface of the drive sprocket 70 for driving the front wheels. The lock sleeve 94 is spline-fitted to the rear-wheel output shaft 68 so as to be movable relative to the rear-wheel output shaft 68 in the direction of the first rotation axis CL1 but not relatively rotatable with respect to the rear-wheel output shaft 68. are combined. In addition, the lock sleeve 94 is formed with outer peripheral teeth 94 a that can mesh with the lock teeth 92 . Therefore, in the differential lock mechanism 82, when the lock sleeve 94 is moved in the first rotation axis CL1 direction with respect to the rear wheel side output shaft 68 and the outer peripheral teeth 94a of the lock sleeve 94 mesh with the lock teeth 92, the rear wheel The side output shaft 68 and the drive sprocket 70 for driving the front wheels rotate integrally.

The transfer 22 includes a coiled first spring 96 and a coiled second spring 98, as shown in FIG. The first spring 96 is arranged in a compressed state between the high-low sleeve 86 and the lock sleeve 94, and the first spring 96 is pushed in a direction to separate the high-low sleeve 86 and the lock sleeve 94 from each other. force. The second spring 98 is arranged in a compressed state between a projection 68a formed on the rear-wheel-side output shaft 68 and the lock sleeve 94, and the second spring 98 pushes the lock sleeve 94 into the lock teeth. It is biased away from 92 . In the transfer 22 , when the outer peripheral teeth 86 b of the high-low sleeve 86 mesh with the low-side gear teeth 90 , the lock sleeve 94 approaches the lock teeth 92 by the biasing force of the first spring 96 . , so that the outer peripheral teeth 94 a of the lock sleeve 94 mesh with the lock teeth 92 . In the transfer 22 , when the outer peripheral teeth 86 b of the high-low sleeve 86 mesh with the high-side gear teeth 88 , the lock sleeve 94 is moved away from the lock teeth 92 by the biasing force of the second spring 98 . , so that the outer peripheral teeth 94 a of the lock sleeve 94 move away from the lock teeth 92 .

The front wheel drive clutch 74 includes a clutch hub 100, a clutch drum 102, a friction engagement element 104, and a piston 106, as shown in FIG. The clutch hub 100 is connected to the rear wheel side output shaft 68 so as to be able to transmit power. Clutch drum 102 is coupled to drive sprocket 70 for driving the front wheels so as to be able to transmit power. The friction engagement element 104 includes a first friction plate 104a and a second friction plate 104b. The first friction plate 104a is arranged on the outer peripheral side of the clutch hub 100 so as to be movable in the direction of the first rotation axis CL1 with respect to the clutch hub 100 and not relatively rotatable about the first rotation axis CL1 with respect to the clutch hub 100. is provided. In addition, the second friction plate 104b is movable with respect to the clutch drum 102 in the direction of the first rotation axis CL1 and is not relatively rotatable with respect to the clutch drum 102 around the first rotation axis CL1. is provided in The piston 106 comes into contact with the frictional engagement element 104 and clamps the first friction plate 104a and the second friction plate 104b.

The transfer 22 operates the high-low switching mechanism 72, the front wheel drive clutch 74, and the differential lock mechanism 82. As shown in FIG. and a transmission mechanism 112 for transmitting the linear motion force in the screw mechanism 110 to the high-low switching mechanism 72, the front wheel drive clutch 74, and the differential lock mechanism 82, respectively.

As shown in FIG. 5, the screw mechanism 110 is arranged on the first rotation axis CL1, which is the same axis as the rear-wheel output shaft 68. The screw mechanism 110 includes a screw shaft member 114 and a nut member 116. It has The screw shaft member 114 is connected to the electric motor 108 via a worm gear 118 . The screw shaft member 114 is supported by the rear-wheel output shaft 68 so as to be rotatable relative to the rear-wheel output shaft 68 about the first rotation axis CL1. The nut member 116 is screwed onto the screw shaft member 114 so as to be movable in the direction of the first rotation axis CL1 relative to the screw shaft member 114 as the screw shaft member 114 rotates around the first rotation axis CL1. The worm gear 118 is a gear pair including a worm 120 integrally formed with the motor shaft of the electric motor 108 and a worm wheel 122 integrally formed with the screw shaft member 114 . With this configuration, the screw mechanism 110 converts the rotation from the electric motor 108 transmitted to the screw shaft member 114 via the worm gear 118 into linear motion in which the nut member 116 moves in the direction of the first rotation axis CL1. Convert to

As shown in FIG. 5, the transmission mechanism 112 includes a first transmission mechanism 112a, a second transmission mechanism 112b, and a third transmission mechanism 112c. The first transmission mechanism 112 a transmits the force of linear motion of the nut member 116 in the screw mechanism 110 in the direction of the first rotation axis CL<b>1 to the piston 106 of the front wheel drive clutch 74 . The first transmission mechanism 112a is a bearing arranged between the piston 106 and the nut member 116 of the front-wheel drive clutch 74. As shown in FIG. The second transmission mechanism 112 b transmits the force of linear motion of the nut member 116 in the screw mechanism 110 in the direction of the first rotation axis CL<b>1 to the high-low sleeve 86 of the high-low switching mechanism 72 . The second transmission mechanism 112b includes a coupling mechanism 124, a fork shaft 126, and a fork 128. In addition, the connection mechanism 124 connects the nut member 116 of the screw mechanism 110 and the fork shaft 126 so that power can be transmitted. Further, the fork shaft 126 is provided in the transfer case 64 so as to be relatively movable with respect to the transfer case 64 in the direction of the third rotation axis CL3 parallel to the first rotation axis CL1. Also, the fork 128 is connected to the fork shaft 126 and the fork connecting portion 86a of the high-low sleeve 86, respectively. The third transmission mechanism 112 c transmits the force of linear motion of the nut member 116 in the screw mechanism 110 in the direction of the first rotation axis CL<b>1 to the lock sleeve 94 of the differential lock mechanism 82 . The third transmission mechanism 112c includes the coupling mechanism 124, the fork shaft 126, the fork 128, the high-low sleeve 86, the first spring 96, and the second spring 98 described above.

In the transfer 22 configured as described above, the amount of rotation of the motor shaft of the electric motor 108 is controlled by the electric motor control command signal Sw supplied from the electronic control unit 200 to the electric motor 108. When the position of the member 116 in the direction of the first rotation axis CL1 is switched, the operating state of the transfer 22 is switched sequentially.

For example, when the electric motor 108 switches the position of the nut member 116 to the predetermined L4L position, the transmission mechanism 112 moves the outer peripheral teeth 86 b of the high-low sleeve 86 to a position where they mesh with the low-side gear teeth 90 . As described above, when the outer teeth 86b of the high-low sleeve 86 mesh with the low-side gear teeth 90, the biasing forces of the first spring 96 and the second spring 98 cause the outer teeth 94a of the lock sleeve 94 to engage the lock teeth 92. It is designed to mesh. Therefore, in the transfer 22, when the position of the nut member 116 is the L4L position, the high-low switching mechanism 72 forms the low-speed side gear stage L, and the differential lock mechanism 82 connects the front propeller shaft 24 and the rear propeller shaft 26. The rotational differential between is limited.

Further, when the position of the nut member 116 is switched to the predetermined H2 position by the electric motor 108, the outer peripheral teeth 86b of the high-low sleeve 86 mesh with the high-side gear teeth 88 and the piston 106 engages the frictional engagement of the front wheel drive clutch 74. It is moved to a position spaced apart from mating element 104 . Therefore, in the transfer 22, when the nut member 116 is at the H2 position, the high-low switching mechanism 72 sets the high-speed gear stage H and releases the front wheel drive clutch 74. .

Further, when the position of the nut member 116 is switched to the predetermined H4A position by the electric motor 108, the outer peripheral teeth 86b of the high-low sleeve 86 mesh with the high-side gear teeth 88, and the piston 106 engages the frictional engagement of the front wheel drive clutch 74. It is moved to a position where it presses the dowel element 104 . Therefore, in the transfer 22, when the nut member 116 is at the H4A position, the high-low switching mechanism 72 is set to the high-speed gear H and the front-wheel drive clutch 74 is slip-engaged. ing.

Also, when the position of the nut member 116 is switched to the predetermined H4L position by the electric motor 108, the outer peripheral teeth 86b of the high-low sleeve 86 mesh with the high-side gear teeth 88, and the piston 106 engages the frictional engagement of the front wheel drive clutch 74. It is moved to a position where it presses the dowel element 104 . Therefore, in the transfer 22, when the nut member 116 is at the H4L position, the high-low switching mechanism 72 is set to the high-speed gear stage H and the front-wheel drive clutch 74 is fully engaged. ing.

In the transfer 22 configured as described above, the driving force from the driving force source during running can be transmitted from the input shaft 66 to the rear wheels 16 as the main driving wheels and the front wheels 14 as the auxiliary driving wheels, and , by switching between the differential state and the non-differential state with the differential lock mechanism 82 or by adjusting the torque capacity of the front wheel drive clutch 74, the driving force Pr transmitted from the driving force source to the rear wheels 16 during running. The rear wheel side distribution ratio Xr (Xr = Pr/Ptotal), which is the ratio to the total driving force Ptotal (Ptotal = Pr + Pf) transmitted from the driving force source to the rear wheels 16 and the front wheels 14 during running, can be adjusted. . The above "Pf" is the driving force transmitted to the front wheels 14 from the driving force source during running. For example, when the nut member 116 is at the H2 position and the piston 106 does not press the friction engagement element 104, the torque capacity of the front wheel drive clutch 74 becomes zero. At this time, the front wheel drive clutch 74 is released and the rear wheel side distribution ratio Xr becomes 1.0. In other words, the front/rear distribution ratio of the driving force distributed to the front wheels 14 and the rear wheels 16 is 0 (front wheels):100 (rear wheels). On the other hand, when the nut member 116 is at the H4A position and the piston 106 presses the friction engagement element 104, the torque capacity of the front wheel drive clutch 74 becomes greater than zero, and the torque of the front wheel drive clutch 74 is As the capacity increases, the rear wheel side distribution ratio Xr decreases. When the nut member 116 is at the H4L position and the torque capacity is such that the front wheel drive clutch 74 is fully engaged, the rear wheel side distribution ratio Xr becomes 0.5. In other words, the front/rear distribution ratio of the driving force distributed to the front wheels 14 and the rear wheels 16 is 50:50. Further, when the position of the nut member 116 is the L4L position and the differential lock mechanism 82 limits the rotational differential between the front propeller shaft 24 and the rear propeller shaft 26, the rear wheel side distribution ratio Xr becomes 0.5. Become. In this manner, the transfer 22 is switched between the differential state and the non-differential state by the differential lock mechanism 82, or the torque capacity of the front-wheel drive clutch 74 is adjusted, so that the rear-wheel side distribution ratio Xr can be changed. The front/rear distribution ratio of the driving force distributed to the front wheels 14 and the rear wheels 16 can be adjusted between 1.0 and 0.5, that is, between 0:100 and 50:50. Note that the transfer 22 corresponds to the driving force distribution device of the present invention. Further, since the rear wheels 16 correspond to the main drive wheels, the rear wheel side distribution rate Xr corresponds to the main side distribution rate of the present invention.

Returning to FIG. 1, the four-wheel drive vehicle 10 includes an electronic controller as a controller including a control device of the four-wheel drive vehicle 10 related to control of the engine 12, the continuously variable transmission 44, the stepped transmission 46, the transfer 22, and the like. A control device 200 is provided. FIG. 1 is a diagram showing an input/output system of the electronic control unit 200, and is a functional block diagram for explaining main control functions of the electronic control unit 200. As shown in FIG. The electronic control unit 200 includes, for example, a so-called microcomputer having a CPU, a RAM, a ROM, and an input/output interface. Various controls of the four-wheel drive vehicle 10 are executed by performing signal processing. The electronic control unit 200 is configured separately for engine control, shift control, etc., as required. Note that the electronic control unit 200 corresponds to the control unit of the present invention.

The electronic control unit 200 includes various sensors provided in the four-wheel drive vehicle 10 (for example, engine rotation speed sensor 130, output rotation speed sensor 132, MG1 rotation speed sensor 134, MG2 rotation speed sensor 136, rotation angle sensor 138, Accelerator opening sensor 140, throttle valve opening sensor 142, differential lock selection switch 144, G sensor 146, battery sensor 148, oil temperature sensor 150, shift position sensor 152, yaw rate sensor 154, steering sensor 156, etc.). Various signals (for example, engine rotation speed Ne, output rotation speed No corresponding to vehicle speed V, MG1 rotation speed Ng that is the rotation speed of the first rotary machine MG1, MG2 rotation speed Nm that is the input rotation speed Ni, electric motor 108 The rotation angle θ of the motor shaft, the accelerator opening θacc as the driver's acceleration operation amount representing the magnitude of the driver's acceleration operation, the throttle valve opening θth being the opening of the electronic throttle valve, the rear propeller in the differential lock mechanism 82 An ON/OFF signal indicating whether or not the driver requests to select a non-differential state (differential lock state) in which the rotational differential between the shaft 26 and the front propeller shaft 24 is limited, the four-wheel drive vehicle 10. longitudinal and lateral accelerations Gx and Gy of the battery 40, the battery temperature THbat, the battery charging/discharging current Ibat and the battery voltage Vbat, the hydraulic oil temperature THoil which is the temperature of the hydraulic oil oil, the shift lever provided in the four-wheel drive vehicle 10 The operating position POSsh, the yaw rate Ryaw that is the rotational angular velocity of the four-wheel drive vehicle 10 about the vertical axis, the steering angle θsw of the steering wheel provided in the four-wheel drive vehicle 10, etc.) are supplied.

Various command signals (for example, for controlling the engine 12) are sent from the electronic control unit 200 to each device (for example, the engine control unit 36, the inverter 38, the hydraulic control circuit 58, the electric motor 108, etc.) provided in the four-wheel drive vehicle 10. , a rotary machine control command signal Smg for controlling the first rotary machine MG1 and the second rotary machine MG2, a hydraulic control command signal Sat for controlling the operating state of the engagement device CB, an electric electric motor control command signal Sw for controlling the motor 108) are respectively output. The hydraulic control command signal Sat is also a hydraulic control command signal for controlling the speed change of the stepped transmission 46. For example, the hydraulic control command signal Sat is applied to each hydraulic actuator (clutch C1, clutch C2, brake B1, brake B2) of the engagement device CB. It is a command signal for driving each solenoid valve or the like for adjusting the supplied hydraulic pressures Pc1, Pc2, Pb1 and Pb2. The electronic control unit 200 sets hydraulic pressure command values corresponding to the values of the hydraulic pressures Pc1, Pc2, Pb1, and Pb2, and outputs a drive current or drive voltage to the hydraulic control circuit 58 according to the hydraulic pressure command values.

In order to realize various controls in the four-wheel drive vehicle 10, the electronic control unit 200 includes a stepped transmission control section 160 functioning as a stepped transmission control means, a hybrid control section 162 functioning as a hybrid control means, and a four-wheel drive vehicle. and a four-wheel drive control unit 164 that functions as drive control means.

The stepped transmission control section 160 operates the stepped transmission using an AT gear shift map such as that shown in FIG. 46, and outputs a hydraulic control command signal Sat to the hydraulic control circuit 58 for executing shift control of the stepped transmission 46 as required. The AT gear stage shift map is a predetermined relationship having a shift line for judging the shift of the stepped transmission 46 on two-dimensional coordinates having, for example, the vehicle speed V and the required driving force Frdem as variables. Here, instead of the vehicle speed V, the output rotational speed No or the like may be used. Also, the required drive torque Trdem, the accelerator opening θacc, the throttle valve opening θth, and the like may be used instead of the required driving force Frdem. Each shift line in the AT gear shift map is an upshift line for determining an upshift as indicated by a solid line, and a downshift line for determining a downshift as indicated by a dashed line.

The hybrid control unit 162 functions as an engine control means, that is, an engine control unit, for controlling the operation of the engine 12, and a rotary machine control means for controlling the operations of the first rotary machine MG1 and the second rotary machine MG2 via the inverter 38. That is, it includes a function as a rotary machine control unit, and executes hybrid drive control and the like by the engine 12, first rotary machine MG1, and second rotary machine MG2 by these control functions. The hybrid control unit 162 calculates a required drive force Frdem as a required drive amount by applying the accelerator opening θacc and the vehicle speed V to a required drive amount map, for example, which has a predetermined relationship. In addition to the required drive force Frdem [N], the required drive amount includes a required drive torque Trdem [Nm] at each drive wheel (front wheels 14 and rear wheels 16), a required drive power Prdem [W] at each drive wheel, A requested AT output torque or the like at the output shaft 60 can also be used.

Hybrid control unit 162 issues a command to control engine 12 so as to realize required driving power Prdem based on required driving torque Trdem and vehicle speed V, taking into account chargeable power Win and dischargeable power Wout of battery 40. It outputs an engine control command signal Se, which is a signal, and a rotary machine control command signal Smg, which is a command signal for controlling the first rotary machine MG1 and the second rotary machine MG2. The engine control command signal Se is, for example, a command value of the engine power Pe, which is the power of the engine 12 that outputs the engine torque Te at the engine rotation speed Ne at that time. The rotary machine control command signal Smg is, for example, a command value of the generated electric power Wg of the first rotary machine MG1 that outputs the MG1 torque Tg at the MG1 rotation speed Ng at the time of the command output as the reaction torque of the engine torque Te, and It is a command value of the power consumption Wm of the second rotary machine MG2 that outputs the MG2 torque Tm at the MG2 rotation speed Nm when the command is output.

The chargeable power Win of the battery 40 is the input power that defines the limit of the input power of the battery 40 , and the dischargeable power Wout of the battery 40 is the output power that defines the limit of the output power of the battery 40 . The chargeable power Win and the dischargeable power Wout of the battery 40 are calculated by the electronic control unit 200 based on, for example, the battery temperature THbat and the state of charge value SOC [%] corresponding to the amount of charge of the battery 40 . The state-of-charge value SOC of the battery 40 is a value indicating the state of charge of the battery 40, and is calculated by the electronic control unit 200 based on, for example, the battery charge/discharge current Ibat and the battery voltage Vbat.

The hybrid control unit 162 operates, for example, the continuously variable transmission 44 as a continuously variable transmission so that the entire compound transmission 63 in which the continuously variable transmission 44 and the stepped transmission 46 are arranged in series as a continuously variable transmission. When operating, the engine 12 is controlled and the first rotating machine is controlled so that the engine rotation speed Ne and the engine torque Te at which the engine power Pe that realizes the required driving power Prdem is obtained, considering the engine optimum fuel consumption point. By controlling the generated electric power Wg of MG1, continuously variable transmission control of the continuously variable transmission 44 is executed to change the gear ratio γ0 of the continuously variable transmission 44 . As a result of this control, the gear ratio γt (γt=γ0×γat) of the compound transmission 63 when operated as a continuously variable transmission is controlled.

For example, when the continuously variable transmission 44 is shifted like a stepped transmission and the entire compound transmission 63 is shifted like a stepped transmission, the hybrid control unit 162 uses a predetermined relationship, such as a shift map. is used to determine the shift of the compound transmission 63, and in cooperation with the shift control of the AT gear stage of the stepped transmission 46 by the stepped transmission control unit 160, a plurality of gear stages are selectively established. Shift control of the stepped transmission 44 is executed.

The hybrid control unit 162 selectively establishes the motor driving mode or the hybrid driving mode as the driving mode according to the driving state. For example, when the required driving power Prdem is in the motor running region smaller than the predetermined threshold, hybrid control unit 162 establishes the motor running mode, while the required driving power Prdem is greater than or equal to the predetermined threshold. is in the hybrid running region, the hybrid running mode is established. A dashed-dotted line A in FIG. 6 is a boundary line for switching between at least the engine 12 and only the second rotary machine MG2 as the driving force source for running the four-wheel drive vehicle 10 . That is, the dashed-dotted line A in FIG. 6 is the boundary line between the hybrid driving region and the motor driving region for switching between the hybrid driving and the motor driving. A predetermined relationship having a boundary line as indicated by the dashed-dotted line A in FIG. 6 is an example of a driving force source switching map composed of two-dimensional coordinates with vehicle speed V and required driving force Frdem as variables. In FIG. 6, for the sake of convenience, this driving force source switching map is shown together with the AT gear shift map.

Hybrid control unit 162 establishes the hybrid driving mode when state of charge value SOC of battery 40 is less than a predetermined engine start threshold value even when required driving power Prdem is in the motor driving region. . The motor driving mode is a driving state in which driving torque is generated by the second rotary machine MG2 while the engine 12 is stopped. The hybrid driving mode is a driving state in which the vehicle is driven while the engine 12 is in operation. The engine start threshold is a predetermined threshold for determining the state of charge value SOC at which it is necessary to forcibly start the engine 12 and charge the battery 40 .

The hybrid control unit 162 performs starting control for starting the engine 12 when the hybrid running mode is established when the operation of the engine 12 is stopped. When starting the engine 12, the hybrid control unit 162 increases the engine rotation speed Ne by the first rotary machine MG1, and ignites the engine when the engine rotation speed Ne reaches or exceeds a predetermined rotation speed at which ignition is possible. Start 12. That is, the hybrid control unit 162 starts the engine 12 by cranking the engine 12 with the first rotary machine MG1.

The four-wheel drive control unit 164 controls the ratio (Pr/ (Ptotal) is adjusted. For example, the four-wheel drive control unit 164 controls the electric motor 108 according to the running state of the four-wheel drive vehicle 10 determined from the output rotation speed sensor 132, the G sensor 146, and the like, to operate the front wheel drive clutch 74, for example. By adjusting the torque capacity, the rear wheel side distribution ratio Xr is adjusted to an appropriate value.

For example, when traveling straight ahead, the four-wheel drive control unit 164 releases the front wheel drive clutch 74 to set the rear wheel side distribution ratio Xr to 1.0 (that is, the driving force distributed to the front wheels 14 and the rear wheels 16). are controlled so that the front/rear distribution ratio is 0:100). Further, the four-wheel drive control unit 164 calculates a target yaw rate Ryaw* based on the steering angle θsw during cornering, the vehicle speed V, etc., and the yaw rate Ryaw detected by the yaw rate sensor 154 at any time follows the target yaw rate Ryaw*. The rear wheel side distribution ratio Xr is adjusted so that Further, the four-wheel drive control unit 164 controls the rotational differential between the rear propeller shaft 26 and the front propeller shaft 24 by the differential lock mechanism 82 when the driver operates the differential lock selection switch 144, for example. , the rear wheel side distribution ratio Xr is controlled to 0.5 (that is, the front/rear distribution ratio of the driving force distributed to the front wheels 14 and the rear wheels 16 is 50:50).

As shown in FIG. 1, the stepped shift control section 160 includes a downshift determination section 160a that functions as downshift determination means, and the downshift determination section 160a functions as coast downshift determination means. A coast downshift determining section 160b is provided. Further, the electronic control unit 200 is provided with a front/rear distribution ratio determination section 166 that functions as front/rear distribution ratio determination means.

The downshift determining unit 160a determines whether or not the stepped transmission 46 has determined to downshift. For example, as shown in FIG. 6, the downshift determining unit 160a determines that the stepped transmission 46 is downshifted when the point indicating the vehicle state obtained from the actual required driving force Frdem and the vehicle speed V crosses the dashed downshift line. It is determined that a shift has been determined.

When downshift determination section 160a determines that a downshift has been determined, coast downshift determination section 160b determines whether or not the downshift determined by stepped transmission 46 is a coast downshift. For example, the coast downshift determination unit 160b determines that the driver has not stepped on the accelerator pedal based on the accelerator opening θacc detected by the accelerator opening sensor 140 when the downshift determination unit 160a determines that the downshift has been performed. , it is determined that the downshift determined by the stepped transmission 46 is the coast downshift.

When downshift determination unit 160a determines that a downshift has been performed, front/rear distribution ratio determination unit 166 determines the ratio between front wheels 14 and rear wheels 16 when downshift determination unit 160a determines that a downshift has been performed. The front/rear distribution ratio of the driving force to be distributed, that is, the rear wheel side distribution ratio Xr when it is determined that the downshift is determined by the downshift determination unit 160a is determined. For example, the front/rear distribution ratio determining unit 166 determines the rear wheel side distribution ratio Xr from the position of the nut member 116 in the direction of the first rotation axis CL1 when the downshift determining unit 160a determines that the downshift has been performed. The position of the nut member 116 in the direction of the first rotation axis CL1 is calculated from changes in the rotation angle θ of the motor shaft of the electric motor 108 detected by the rotation angle sensor 138 at each sampling time. .

When a predetermined first condition CD1 and a predetermined second condition CD2 are satisfied, the stepped transmission control unit 160 adjusts the rear wheel side distribution ratio Xr determined by the front/rear distribution ratio determination unit 166. When the rear wheel side distribution ratio Xr is small, the stepped transmission 46 is controlled so that the shift time T [sec] becomes longer than when the rear wheel side distribution ratio Xr is large. Note that the first condition CD1 is established when the coast downshift determination section 160b determines that the downshift determined by the downshift determination section 160a is a coast downshift. Further, the second condition CD2 is established when the front/rear distribution ratio determining section 166 determines the rear wheel side distribution ratio Xr.

For example, when the first condition CD1 and the second condition CD2 are satisfied, the stepped transmission control unit 160 sets the rear wheel distribution ratio Xr to 0.5 and the rear wheel distribution ratio Xr to be 0.5 as shown in FIG. When the rear wheel side distribution ratio Xr is relatively small, the rate at which the release side hydraulic pressure Pb1 is reduced in the brake B1, which is the release side friction engagement device, is lower than when the rear wheel side distribution rate Xr is 1.0 and the rear wheel side distribution rate Xr is relatively large. The speed change control of the stepped transmission 46 is performed so as to lower Vd [Pa/sec]. FIG. 7 shows the process of switching the brake B1, which is the release side frictional engagement device, from the engaged state to the released state and switching the one-way clutch F1 from the non-engaged state to the engaged state. 3 is a diagram showing changes in release side hydraulic pressure Pb1 [Pa] of the release side brake B1 that is changed according to the front/rear distribution ratio, that is, the rear wheel side distribution ratio Xr. The solid line LJ shown in FIG. 7 indicates when the front/rear distribution ratio determination unit 166 determines that the rear wheel side distribution ratio Xr is 1.0, that is, when the front/rear distribution ratio determination unit 166 determines that the front wheels 14 and the rear wheels 16 10 is a line showing the change in the release side hydraulic pressure Pb1 of the brake B1 when the front/rear distribution ratio of the driving force distributed to 1 is determined to be 0:100. Further, the dashed line LH shown in FIG. 7 indicates that when the front/rear distribution ratio determination unit 166 determines that the rear wheel side distribution ratio is 0.5, that is, when the front/rear distribution ratio determination unit 166 determines the front wheels 14 and the rear wheels 16 The line shows the change in the release side hydraulic pressure Pb1 of the brake B1 when the front/rear distribution ratio of the distributed driving force is determined to be 50:50. Further, time t1 shown in FIG. 7 is when the stepped transmission 46 outputs a shift output. The decreasing speed Vd is the speed at which the releasing hydraulic pressure Pb1 decreases from the predetermined hydraulic pressure P1 per unit time in the brake B1, which is the releasing frictional engagement device. As shown in FIG. 7, the stepped shift control unit 160 reduces the disengagement side hydraulic pressure Pb1 of the brake B1, which is the disengagement side engagement element, to a predetermined hydraulic pressure P1 when the shift output is output. .

Further, for example, when the first condition CD1 and the second condition CD2 are respectively satisfied, the stepped transmission control unit 160 may control the disengagement side engagement as the rear wheel side distribution ratio Xr determined by the front/rear distribution ratio determination unit 166 becomes smaller. The shift control of the stepped transmission 46 is performed so that the decreasing speed Vd becomes low at the brake B1, which is a device. For example, when the front/rear distribution ratio determining section 166 determines that the rear wheel side distribution rate Xr is 0.6, the decreasing speed Vd is It is lower than the lowering speed Vd when it is determined that there is, and higher than the lowering speed Vd when the front/rear distribution ratio determination unit 166 determines that the rear wheel side distribution ratio Xr is 0.5.

Further, when the first condition CD1 and the second condition CD2 are respectively satisfied, the stepped transmission control unit 160 adjusts the rear wheel side distribution ratio according to the rear wheel side distribution ratio Xr determined by the front/rear distribution ratio determination unit 166. When Xr is small, shift control of the stepped transmission 46 is performed so that the coast downshift is performed on the low vehicle speed side compared to when the rear wheel side distribution ratio Xr is large.

For example, when the first condition CD1 and the second condition CD2 are satisfied, the stepped transmission control unit 160 sets the rear wheel distribution ratio Xr to 0.5 and the rear wheel distribution ratio Xr to When it is relatively small, the downshift line of the AT gear shift map is changed to the low vehicle speed side compared to when the rear wheel side distribution ratio Xr is 1.0 and the rear wheel side distribution ratio Xr is relatively large. It should be noted that the more the downshift line of the AT gear shift map changes toward the lower vehicle speed side, the more the coast downshift is performed at the lower vehicle speed side. FIG. 8 shows a downshift line of an AT gear shift map that changes according to the front/rear distribution ratio, that is, the rear wheel side distribution ratio Xr when a coast downshift to switch from AT 2nd gear to AT 1st gear is determined. It is a figure which shows. The dashed line LH1 shown in FIG. 8 indicates when the front/rear distribution ratio determination unit 166 determines that the rear wheel side distribution ratio Xr is 1.0, that is, when the front/rear distribution ratio determination unit 166 determines whether the front wheels 14 and the rear wheels 16 are equal to each other. 1 is a downshift line used in an AT gear shift map when the front/rear distribution ratio of the driving force distributed to 1 is determined to be 0:100. The dashed line LH2 shown in FIG. 8 indicates when the front/rear distribution ratio determination unit 166 determines that the rear wheel side distribution ratio is 0.5, that is, when the front/rear distribution ratio determination unit 166 determines that the front wheels 14 and the rear wheels 16 FIG. 10 is a downshift line used in an AT gear shift map when the front/rear distribution ratio of distributed drive power is determined to be 50:50; FIG.

Further, for example, when the first condition CD1 and the second condition CD2 are respectively satisfied, the stepped transmission control unit 160 can perform AT gear shift as the rear wheel side distribution ratio Xr determined by the front/rear distribution ratio determination unit 166 becomes smaller. Change the downshift line on the map to the low vehicle speed side. For example, when the front/rear distribution ratio determination section 166 determines that the rear wheel side distribution rate Xr is 0.6, the downshift line is 1.0. When the downshift line (broken line LH1) is determined to be lower than the downshift line (broken line LH1), and when the front/rear distribution ratio determination unit 166 determines that the rear wheel side distribution ratio Xr is 0.5. The downshift line (broken line LH2) is changed to the high vehicle speed side.

FIG. 9 is a flow chart for explaining the main part of the control operation of the electronic control unit 200. For example, shift control of the stepped transmission 46 when coasting downshifting from AT 2nd gear to AT 1st gear is performed. is a flow chart for explaining the control operation of . In the flow chart of FIG. 9, the operation is started when the downshift determining unit 160a determines that the stepped transmission 46 should downshift.

First, in step S10 corresponding to the function of the front/rear distribution ratio determination unit 166 (hereinafter, step is omitted), the front/rear distribution ratio of the driving force distributed to the front wheels 14 and the rear wheels 16, that is, the rear wheel side distribution ratio Xr is determined. Next, in S20 corresponding to the function of the coast downshift determining section 160b, it is determined whether or not the shift is a coast downshift. If the determination in S20 is negative, that is, if it is not a coast downshift, this routine is terminated. If the determination in S20 is affirmative, that is, if both the first condition CD1 and the second condition CD2 are satisfied, S30 corresponding to the function of the stepped shift control unit 160 is executed. In S30, the shift control of the stepped transmission 46 is changed according to the front/rear distribution ratio determined in S10, that is, the rear wheel side distribution ratio Xr. That is, in S30, when the rear wheel side distribution ratio Xr is small, the shift time T becomes longer than when the rear wheel side distribution ratio Xr is large. Shift control of the stepped transmission 46 is performed so that the coast downshift is performed on the low vehicle speed side compared to when the ratio Xr is large.

As described above, according to the four-wheel drive vehicle 10 of the present embodiment, the electronic control unit 200 controls the rear wheels according to the rear wheel side distribution ratio Xr when the stepped transmission 46 performs a coast downshift. When the side distribution ratio Xr is small, the speed change control of the stepped transmission 46 is performed so that the speed change time T becomes longer than when the rear wheel side distribution ratio Xr is large. Therefore, when the rear-wheel-side distribution ratio Xr is relatively small and the shift shock tends to worsen, the shift control of the stepped transmission 46 is performed so that the shift time T becomes longer. is suitably suppressed. Further, when the rear wheel side distribution ratio Xr is relatively large and the shift shock tends not to worsen, the shift control of the stepped transmission 46 is performed so as not to lengthen the shift time T. Deterioration of speed change responsiveness in shifting is preferably suppressed. As a result, it is possible to suppress the deterioration of the shift shock while suppressing the deterioration of the shift responsiveness.

Further, according to the four-wheel drive vehicle 10 of the present embodiment, the electronic control unit 200 can be adjusted according to the rear wheel distribution ratio Xr when the rear wheel distribution ratio Xr is small and when the rear wheel distribution ratio Xr is large. Since the speed change control of the stepped transmission 46 is performed so that the coast downshift is performed on the low vehicle speed side, the deterioration of the speed change shock can be preferably suppressed.

Further, according to the four-wheel drive vehicle 10 of the present embodiment, the stepped transmission 46 has a plurality of engagement devices CB and a one-way clutch F1, and the coast downshift is performed by a plurality of engagement devices CB This is a coast downshift in which the brake B1 is switched from the engaged state to the released state and the one-way clutch F1 is switched from the non-engaged state to the engaged state. Therefore, in the coast downshift, the shift shock caused by switching the one-way clutch F1 from the non-engaged state to the engaged state is caused by, for example, the one-way clutch F1 instead of the engaging device CB being disengaged from the disengaged state. Although it tends to be larger than in the case of switching to the engaged state, it is possible to suitably suppress the deterioration of the shift shock in this case.

Further, according to the four-wheel-drive vehicle 10 of the present embodiment, the brake B1 is a hydraulic friction coefficient that is switched from the engaged state to the released state by lowering the release-side hydraulic pressure Pb1 supplied to the brake B1. When the coast downshift is performed, the electronic control unit 200 is controlled according to the rear wheel distribution ratio Xr when the rear wheel distribution ratio Xr is small compared to when the rear wheel distribution ratio Xr is large. Then, the speed change control of the stepped transmission 46 is performed so as to decrease the decreasing speed Vd at which the release side hydraulic pressure Pb1 is decreased in the brake B1. For this reason, the shift time T in the shift control of the stepped transmission 46 is lengthened by lowering the decrease speed Vd at which the release side hydraulic pressure Pb1 is decreased in the brake B1.

Another embodiment of the present invention will now be described. In the following description, parts common to the embodiments are denoted by the same reference numerals, and descriptions thereof are omitted.

FIG. 10 is a diagram illustrating a four-wheel drive vehicle according to another embodiment (embodiment 2) of the present invention, that is, a diagram illustrating a transfer (driving force distribution device) 202 provided in the four-wheel drive vehicle. . The four-wheel drive vehicle of this embodiment differs from the transfer 22 provided in the four-wheel drive vehicle 10 of the first embodiment in that the structure of the transfer 202 is different. It is substantially the same as the vehicle 10 . That is, unlike the transfer 22 of the first embodiment, the transfer 202 does not include the high-low switching mechanism 72, differential lock mechanism 82, second transmission mechanism 112b, and third transmission mechanism 112c. It is integrally connected with the output shaft 68 .

In the transfer 202 configured as shown in FIG. 10, the driving force from the driving force source during running can be transmitted from the input shaft 66 to the rear wheels 16 as the main driving wheels and the front wheels 14 as the auxiliary driving wheels. Also, by adjusting the torque capacity of the front wheel drive clutch 74, the rear wheel side distribution ratio Xr can be adjusted. For example, when piston 106 does not press friction engagement element 104, the torque capacity of front wheel drive clutch 74 is zero. At this time, the front wheel drive clutch 74 is released and the rear wheel side distribution ratio Xr becomes 1.0. On the other hand, when the piston 106 presses the friction engagement element 104, the torque capacity of the front wheel drive clutch 74 becomes greater than zero, and the rear wheel side distribution ratio Xr increases as the torque capacity of the front wheel drive clutch 74 increases. decreases. Then, when the torque capacity becomes such that the front wheel drive clutch 74 is fully engaged, the rear wheel side distribution ratio Xr becomes 0.5. Thus, the transfer 202 can adjust the rear wheel side distribution ratio Xr between 1.0 and 0.5 by adjusting the torque capacity of the front wheel drive clutch 74 .

Although the embodiments of the present invention have been described in detail above with reference to the drawings, the present invention is also applicable to other aspects.

For example, in the first embodiment described above, the four-wheel drive vehicle 10 is a hybrid vehicle that uses the engine 12, the second rotary machine MG2, and the first rotary machine MG1 as driving force sources. It is not limited to hybrid type vehicles. For example, the present invention can be applied to an electric vehicle using only a rotating machine as a driving force source or a vehicle using only an engine as a driving force source.

Further, in the first embodiment described above, the four-wheel drive vehicle 10 is based on the front engine rear wheel drive (FR), but the present invention is not necessarily limited to this. For example, it may be a four-wheel drive vehicle based on a front engine front wheel drive (FF). In the case of a four-wheel drive vehicle based on a front engine front wheel drive, the front wheels are the main drive wheels and the rear wheels are the auxiliary drive wheels. Further, the four-wheel drive vehicle 10 was a part-time four-wheel drive vehicle in which two-wheel drive and four-wheel drive can be switched according to the running state, but the present invention does not necessarily apply to a part-time four-wheel drive vehicle. The vehicle is not limited, and may be a full-time four-wheel drive vehicle. For example, it may be a full-time four-wheel drive vehicle with a central differential gearing (center differential) having a differential limiting clutch.

In the above-described first embodiment, when the electric motor 108 rotates, the piston 106 of the front wheel drive clutch 74 provided in the transfer 22 is frictionally moved via the screw mechanism 110 that converts rotary motion into linear motion. Although configured to press against engagement element 104, the invention is not necessarily limited to this configuration. For example, it may be configured such that when the electric motor 108 rotates, the piston 106 presses the friction engagement element 104 via a ball cam. Also, the piston 106 may be driven by a hydraulic actuator.

Further, in the above-described first embodiment, when the first condition CD1 and the second condition CD2 are satisfied in the stepped transmission control section 160, when the rear wheel side distribution ratio Xr is small, when the rear wheel side distribution ratio Xr is large, In addition, when the rear wheel side distribution ratio Xr is small, the downshift line is changed to the low vehicle speed side compared to when the rear wheel side distribution ratio Xr is large. , the speed change control of the stepped transmission 46 was performed. For example, even if the first condition CD1 and the second condition CD2 are satisfied, the stepped transmission control unit 160 does not necessarily change the downshift line according to the rear wheel side distribution ratio Xr.

It should be noted that what has been described above is just one embodiment, and the present invention can be implemented in aspects with various modifications and improvements based on the knowledge of those skilled in the art.

10: Four-wheel drive vehicle 12: Engine (driving force source)
14: Front wheel (auxiliary driving wheel)
16: Rear wheel (main driving wheel)
22, 202: Transfer (driving force distribution device)
46: Stepped transmission (automatic transmission)
66: Input shaft (drive shaft)
160: Stepped transmission control section 160a: Downshift determination section 160b: Coast downshift determination section 166: Front/rear distribution ratio determination section 200: Electronic control device (control device)
B1: Brake (engagement element, friction engagement element, hydraulic friction engagement device)
CB: engagement device (engagement element, friction engagement element, hydraulic friction engagement device)
F1: One-way clutch (engagement element)
MG1: First rotating machine (driving force source)
MG2: Second rotating machine (driving force source)
Pb1: release side hydraulic pressure (hydraulic pressure)
Pr: Driving force Ptotal: Total driving force T: Shift time Vd: Decreasing speed Xr: Rear wheel side distribution ratio (main side distribution ratio)

Claims (4)

a driving force source, an automatic transmission having a plurality of engagement elements and connected to the driving force source and a drive shaft, and driving force from the driving force source to the main driving wheels and the auxiliary driving wheels from the driving shaft and capable of adjusting a main side distribution ratio, which is a ratio of the driving force transmitted to the main driving wheels to the total driving force transmitted from the drive shaft to the main driving wheels and the auxiliary driving wheels. and a control device, wherein
When coast downshifting is performed in the automatic transmission, the control device lengthens a shift time according to the main-side distribution ratio when the main-side distribution ratio is small compared to when the main-side distribution ratio is large. A four-wheel drive vehicle characterized in that the shift control of the automatic transmission is performed so as to The control device controls the automatic transmission so that the coast downshift is performed at a lower vehicle speed side when the main-side distribution ratio is smaller than when the main-side distribution ratio is large, according to the main-side distribution ratio. 2. The four-wheel drive vehicle according to claim 1, wherein shift control is performed. The automatic transmission has a plurality of friction engagement elements and a one-way clutch as the plurality of engagement elements,
The coast downshift is a coast downshift that switches one of the plurality of frictional engagement elements from an engaged state to a released state and switches the one-way clutch from a non-engaged state to an engaged state. The four-wheel drive vehicle according to claim 1 or 2. The frictional engagement element is a hydraulic frictional engagement device that is switched from the engaged state to the released state by reducing hydraulic pressure supplied to the frictional engagement element,
When the coast downshift is performed, the control device controls the hydraulic friction engagement device according to the main-side distribution ratio when the main-side distribution ratio is small compared to when the main-side distribution ratio is large. 4. The four-wheel drive vehicle according to claim 3, wherein shift control of said automatic transmission is performed so as to reduce a reduction speed at which said hydraulic pressure is reduced.

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