VEHICLE CONTROL UNIT

Abstract

A control device (80) for a vehicle (10) provided with a drive power source (14, MG2), drive wheels (28), and a step transmission (20) forming part of a power transmission path between the drive power source (14, MG2) and the drive wheels (28), and having a plurality of clutch devices (CB) selectively engaged to implement a selected one of a plurality of gear positions, the control device (80) comprising: a control section (88) configured to implement control of an input torque (Ti) of the stepped transmission (20) during an inertia phase of a downshift of the stepped transmission (20) by feedback compensation of a target value (Titgt) of the input torque corresponding to an operation amount (θacc) of an accelerator pedal by a driver of the vehicle such that a value (dNm / dt) representative of a rotational state of an input rotary element (30) of the stepped transmission (20) agrees with a target value (dNmtgt) at which a rotational speed (Nm) of the input rotary element (30) changes toward a post-shift synchronization value (Nmsyca) to be implemented after the downshift is completed; a state determining section (94) configured to determine whether the rotational speed of the input rotary element (30) is equal to the post-shift synchronization value (Nmsyca); an input torque reset control section (92) configured to implement input torque reset control for changing the input torque (Ti) of the stepped transmission (20) toward the target value (Titgt) when the state determining section (94) determines that the rotational speed of the input rotary element (30) is equal to the post-shift synchronization value (Nmsyca); a target input torque setting section (90) configured to operate when the operation amount (θacc) of the accelerator pedal is increased in the process of downshifting implemented in a power-off state of the vehicle (10) in which the accelerator pedal is in a non-operating state, wherein the target input torque setting section (90) sets the target value (Titgt) of the input torque according to the operation amount (θacc) of the accelerator pedal and limits an increase amount of the target value (Titgt) of the input torque with respect to an increase amount of a driver-required input torque value (Tidem) represented by the operation amount (θacc) of the accelerator pedal, such that the target value (Titgt) of the input torque is maintained at not greater than a predetermined upper limit value (Ti1) until the input torque reset control is terminated; and a real input torque increasing section (98) configured to operate when the operation amount of the accelerator pedal is increased before a timing of initiation of the inertia phase of the downshift in the off state, wherein the real input torque increasing section (98) implements input torque increasing control before the timing of initiation of the inertia phase of the downshift to control the input torque (Ti) of the stepped transmission (20) to be greater than the target value (Titgt).

Description

FIELD OF THE INVENTIONThe present invention relates to a control apparatus for a vehicle provided with a drive power source, drive wheels, and a step-change transmission forming part of a power transmission path between the drive power source and the drive wheels.BACKGROUND OF THE INVENTIONThere is known a control apparatus for a vehicle provided with an engine, drive wheels and a step-change transmission which forms part of a power transmission path between the engine and the drive wheels and has a plurality of clutch devices selectively engaged to establish a selected one of a plurality of speed positions. For example, JP2014-223888A discloses a control apparatus for controlling a hybrid vehicle. The controller disclosed in the above publication is configured to control an input torque of the stepped transmission such that a rate of change of a rotational speed of an input rotary element of the stepped transmission representing a rotational state of the input rotary element in the process of a shift operation of the stepped transmission matches a target value by implementing feedback compensation control of a target value of the input torque according to an operation amount of an accelerator pedal by a driver of the hybrid vehicle.The publication DE 11 2009 004 644 T5 discloses a further control device for a vehicle.SUMMARY OF THE INVENTIONWhen the input torque of the stepped transmission is feedback controlled during its shifting operation, as disclosed in JP2014-223888A, there is a possibility that the input torque of the stepped transmission may deviate from the target value when the rotational speed of the input rotary element has become equal to a post-shift synchronization value. In this case, a torque reset control is implemented to reset the input torque of the step-variable transmission to the target value after the rotation speed of the input rotary element becomes equal to the post-shift synchronization value. Incidentally, when the target value of the input torque of the stepped transmission is increased due to a request of the vehicle driver to accelerate the vehicle with an increase in the operation amount of the accelerator pedal or a re-operation of the accelerator pedal in the process of a power-off downshift operation of the stepped transmission in a non-operation state of the accelerator pedal, there is a risk of generation of a so-called "backlash elimination shock" due to the elimination of backlash in the power transmission path of the stepped transmission during its downshift operation. In order to avoid this risk, it is considered effective to restrict an increase amount of the target value of the input torque of the step-variable transmission with respect to an increase of a required value of the input torque represented by the operation amount of the accelerator pedal so that the target value of the input torque is limited to or lower than a predetermined value until the torque reset control is finished. However, limiting the increase amount of the target value of the input torque in the case of the driver's request to accelerate the vehicle before the initiation of an inertia phase results in a timing of the initiation of the inertia phase of the shift-down operation being delayed compared to the timing without limitation. This delay in the initiation of the inertia phase results in deterioration of the control behavior to the driver's vehicle acceleration request.The present invention has been made in view of the above-described prior art. It is therefore an object of the present invention to provide a control apparatus for a stepped transmission vehicle that enables improvement of the control behavior on the driver's vehicle acceleration request with increase of the operation amount of the accelerator pedal in the process of the step transmission power-off downshift operation, and at the same time reduces the risk of generation of the "backlash elimination shock".The above object is achieved according to the following modes of the present invention:According to a first mode of the invention, there is provided a control apparatus for a vehicle provided with a drive power source, drive wheels and a step-variable transmission (hereinafter) which constitutes a part of a power transmission path between the drive power source and the drive wheels and which has a plurality of clutch devices selectively engaged to implement a selected one of a plurality of gear positions (hereinafter) and the step-variable transmission, the control apparatus comprising: a control portion configured to implement control of an input torque of the step-variable transmission during an inertia phase of a shift-down operation of the step-variable transmission by feedback compensation of a target value of the input torque corresponding to an operation amount of an accelerator pedal by an operator of the vehicle so that a value indicative of, said speed of rotation of an input rotary element of said step-variable transmission coincides with a target value at which a speed of rotation of said input rotary element changes toward a post-shift synchronization value to be converted after completion of said shift-down operation; a state determining section configured to determine whether the speed of rotation of said input rotary element is equal to said post-shift synchronization value; an input torque reset control section configured to implement an input torque reset control for changing the input torque of said step-variable transmission toward said target value when said state determining section determines that the speed of rotation of said input rotary element is equal to said post-shift synchronization value; a target input torque setting section configured to be operated when the operation amount of the accelerator pedal is increased in the process of the downshift implemented in an off state of the vehicle in which the accelerator pedal is in a non-operation state, wherein the target input torque setting section sets the target value of the input torque corresponding to the operation amount of the accelerator pedal and limits an increase amount of the target value of the input torque with respect to an increase amount of a driver required input torque value represented by the operation amount of the accelerator pedal so that the target value of the input torque is kept not greater than a predetermined upper limit value until the input torque reset control is finished; and a real input torque increasing portion configured to be operated when the operation amount of the accelerator pedal is increased before a time of initiation of the inertia phase of the shift-down operation in the off state, wherein the real input torque increasing portion implements an input torque increasing control before the time of initiation of the inertia phase of the shift-down operation to control the input torque of the step-variable transmission to be larger than the target value.According to a second mode of the invention, the control apparatus according to the first mode of the invention further includes a shift control section configured to be operated when the input torque increase control is implemented by the real input torque increase section, wherein the shift control section controls a torque capacity of a release-side clutch device of the plurality of clutch devices to be brought into a released state for implementing the shift-down operation and a torque capacity of an engagement-side clutch device of the clutch devices to be brought into an engaged state for implementing the shift-down operation, wherein the shift control section reduces the torque capacity of the release-side clutch device at a timing earlier than when the shift control section increases the torque capacity of the engagement-side clutch device.According to a third mode of the invention, the control apparatus according to the first or second mode of the invention is configured such that the target input torque setting portion gradually changes the target value of the input torque toward the input torque value required by the driver after the input torque reset control implemented by the input torque reset control portion is finished.According to a fourth mode of the invention, the control apparatus according to any one of the first to third modes of the invention further includes a real input torque reducing portion configured to reduce the input torque of the step-variable transmission with a change in the rotational speed of the input rotational element of the step-variable transmission toward the post-shift synchronization value while the input torque is larger than the target value during the inertia phase of the shift-down operation.According to a fifth mode of the invention, the control apparatus according to any one of the first to fourth modes of the invention is configured such that the real input torque increasing section realizes the input torque increasing control when the operation amount of the accelerator pedal is increased by an amount not less than a predetermined value.According to a sixth mode of the invention, the controller according to any one of the first to fifth modes of the invention is configured such that the plurality of clutch devices are hydraulically operated friction clutch devices, and the real input torque increasing portion implements the input torque increasing control when a temperature of a working fluid used for operating the hydraulically operated friction clutch devices is not lower than a predetermined value.According to a seventh mode of the invention, the control apparatus according to any one of the first to sixth modes of the invention is configured to control the vehicle which is a hybrid vehicle provided with: an engine functioning as a drive power source; an electrically controlled transmission mechanism having a differential mechanism to which the engine is operatively connected in a power transmitting manner and a first motor generator to which the differential mechanism is operatively connected in a power transmitting manner so as to control a differential state of the differential mechanism by controlling an operating state of the first motor generator; and a second motor generator operatively connected to an output rotational element of the electrically controlled transmission mechanism and also functioning as a drive power source. In the seventh mode of the invention, the step-variable transmission is a mechanically operated transmission mechanism forming part of a power transmission path between the output rotational element of the electrically controlled transmission mechanism and the drive wheels, and the control portion is configured to control an output torque of the first motor generator and an output torque of the second motor generator during the inertia phase of a shift operation of the mechanically operated transmission mechanism based on an output torque of the engine and a torque transmitted by the mechanically operated transmission mechanism such that a value representative of a rotational state of the input rotational element of the mechanically operated transmission mechanism and a value representative of an operating state of the engine coincide with respective target values. Further, the input torque reset control portion is configured to implement the input torque reset control when the rotational speed of the input rotational element of the mechanically operated transmission mechanism has become equal to the post-shift synchronization value.As described above, the control apparatus according to the first mode of the invention is configured such that, when the operation amount of the accelerator pedal is increased in the process of the downshift implemented in the OFF state of the vehicle, the increase amount of the target value of the input torque is restricted with respect to the increase amount of the input torque value required by the driver, which is represented by the operation amount of the accelerator pedal, so that the target value of the input torque is kept not greater than the predetermined upper limit value until the input torque reset control is finished, so that the above-described risk of backlash elimination shock of the stepped transmission after completion of the downshift can be reduced. Further, when the operation amount of the accelerator pedal is increased before a time of initiating the inertia phase of the shift-down operation in the off state, the input torque increase control is implemented to control the input torque of the stepped transmission to be larger than the target value before the time of initiating the inertia phase of the shift-down operation. Accordingly, the present control apparatus enables early initiation of the inertia phase of the shift-down operation even when the target value of the input torque of the step-variable transmission is limited to or lower than the predetermined upper limit value. Thus, the present control apparatus enables improvement of the control behavior upon a driver's request to accelerate the vehicle with an increase in the operation amount of the accelerator pedal in the process of the step-change gear OFF-downshift, and at the same time, reduction of the risk of generation of the backlash elimination shock.The control apparatus according to the second mode of the invention is configured such that when the input torque increase control is implemented by the real input torque increasing portion, the torque capacity of the release-side clutch device is reduced at a timing earlier than when the torque capacity of the engagement-side clutch device is increased, so that the input torque of the step-variable transmission is increased while the transmission torque of the step-variable transmission is relatively small or zero. Accordingly, the risk of generation of the backlash elimination shock of the stepped transmission can be reduced even when the vehicle is changed from its non-driving state to its driving state in the input torque increase control process.The control apparatus according to the third mode of the invention is configured such that the target value of the input torque is gradually changed toward the input torque value required by the driver after completion of the input torque reset control, so that the requirement of the driver for accelerating the vehicle can be satisfied and at the same time the risk of generating the backlash elimination shock can be reduced.The control apparatus according to the fourth mode of the invention is configured such that the input torque of the stepped transmission is reduced with the change in the rotational speed of the input rotational element of the stepped transmission toward the post-shift synchronization value while the input torque is larger than the target value during the inertia phase of the shift-down operation, so that the risk of generation of the backlash elimination shock of the stepped transmission after completion of the shift-down operation can be further reduced.The control apparatus according to the fifth mode of the invention is configured such that the input torque increase control is implemented by the real input torque increase section when the operation amount of the accelerator pedal is increased by an amount not less than the predetermined value, so that it is possible to appropriately improve the control behavior upon the driver's request for acceleration of the vehicle and at the same time to reduce the risk of generation of the backlash elimination shock when the driver has a comparatively high degree of request for the vehicle acceleration. If the driver has a comparatively low requirement degree for the vehicle acceleration, the risk of generation of the backlash elimination impact can be further reduced.The control apparatus according to the sixth mode of the invention is configured such that the real input torque increasing portion implements the input torque increasing control when the temperature of the working fluid used for operating the hydraulically operated friction clutch devices is not lower than the predetermined value. Namely, the input torque increasing control is not implemented at a relatively low temperature of the working fluid at which the hydraulic control characteristics of the clutch devices are low. Accordingly, it is possible to reduce the deterioration of controllability of the shift-down operation of the stepped transmission portion due to a balance loss between the engagement torques of the respective two friction clutch devices controlled to implement the shift-down operation and the input torque of the stepped transmission.The control apparatus according to the seventh mode of the invention is configured to control the hybrid vehicle provided with the electrically controlled transmission mechanism and the mechanically operated transmission mechanism arranged in series. The present control apparatus enables improvement of the control behavior to the driver's vehicle acceleration request and, at the same time, reduction of the risk of generation of the backlash elimination shock with increase of the accelerator pedal operation amount in the process of the power-off downshift operation of the mechanically operated transmission mechanism.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a schematic view showing an arrangement of a drive system of a vehicle to be controlled by a controller according to an embodiment of the present invention, and main control functions and control portions of the controller; FIG. 2 is a table indicating a relationship between AT gear positions of a mechanically operated stepped transmission portion shown in FIG. 1 and combinations of clutch devices placed in engagement states to realize the corresponding AT gear position; FIG. 3 is a collinear chart indicating a relationship between the rotational speeds of rotary elements of an electrically controlled continuously variable transmission portion and the stepped mechanically operated transmission portion; FIG. 4 is a table indicating an example of a plurality of total rotational speed positions of rotating elements of a transmission device with respect to the gear positions of the stepped transmission portion; FIG. 5 is a view indicating some examples of the gear positions of the stepped transmission mechanically operated portion and some examples of the total rotational speed positions of the transmission device in a collinear chart similar to FIG. 3 ; FIG. 6 is a view showing examples of an AT gear position shift map and an overall speed position shift map used for upshift and downshift of the transmission device; FIG. 7 is a time chart showing an example of changes of various parameters when transmission input torque control and input torque reset control of the stepped transmission portion are implemented at a vehicle acceleration request of a vehicle driver in the process of a power-off downshift operation of the stepped transmission portion; FIG. 8 is a flowchart showing a main control operation of an electronic control device provided for controlling the vehicle, a control routine performed for improving a control behavior on the driver's vehicle acceleration request with an increase in an operation amount of an accelerator pedal in the process of the power-off downshift operation of the stepped transmission portion, while reducing the risk of generating a so-called "backlash elimination shock" of the stepped transmission portion; and FIG. 9 is a timing chart showing an example of changes in the various parameters when the control routine shown in FIG. 8 is performed.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTSIn the present specification, it is understood that a rotation state of each rotating element is represented by, for example, a rotation speed N of the rotating element or a change rate dN / dt of the rotation speed N. Examples of the rotary elements include: an engine; a first motor generator; a second motor generator; each rotary element of a differential mechanism; an output rotary element of an electrically controlled transmission mechanism; and an input rotary element of a step-variable transmission referred to above with respect to the seventh mode of the invention. The rotational speed N of the rotating element corresponds to an angular speed of the rotating element. The rate of change dN / dt of the rotational speed N is a rate of change of the rotational speed N per unit time, namely, a time derivative of the rotational speed N, and an angular acceleration value of the rotary element. In a mathematical equation (1) given below, the rate of change dN / dt is represented by an N having a point (•) thereon.It is also understood that a gear ratio of each of the above-described stepped transmission and a transmission device consisting of the electrically controlled transmission mechanism and the mechanically operated stepped transmission mechanism arranged in series is a ratio of a rotational speed of an input rotational element of the transmission or the transmission device to a rotational speed of an output rotational element of the transmission or the transmission device. A gear position or speed position of the transmission or transmission device having a relatively low gear ratio is implemented or used to drive the vehicle at a relatively high driving speed. On the other hand, a gear position or speed position of the transmission or transmission device having a relatively high gear ratio is implemented or used to drive the vehicle at a relatively low running speed. For example, the gear position having the highest gear ratio is the gear position of the lowest speed.Referring now to the drawings, a preferred embodiment of the invention will be described in detail.First, reference is made to FIG. 1, which is the schematic view showing an arrangement of a drive system 12 of a vehicle 10 to be controlled by a controller according to the present invention, and main control functions and control portions of the controller. As shown in FIG. 1, the vehicle drive system 12 is provided with an engine 14 functioning as a vehicle drive power source, an electrically controlled continuously variable transmission portion 18, and a mechanically operated stepped transmission portion 20. The continuously variable transmission portion 18 and the stepped transmission portion 20 are disposed within a stationary member in the form of a transmission case 16 fixed to the body of the vehicle 10 in series such that the transmission portions 18 and 20 are coaxially disposed on a common axis. The electrically controlled continuously variable transmission portion 18 is directly or indirectly connected to the engine 14 through a damper (not shown), while the mechanically operated step-variable transmission portion 20 is connected to an output rotational element of the electrically controlled continuously variable transmission portion 18. The vehicle drive system 12 is additionally provided with a differential gear mechanism 24 connected to an output rotational member in the form of an output shaft 22 of the mechanically operated stepped transmission portion 20, and a pair of axles 26 connected to the differential gear mechanism 24. In the vehicle drive system 12, a driving force generated by the engine 14 and a second motor generator MG 2 (described below) is transmitted to the stepped mechanically operated transmission portion 20, and is transmitted from the stepped mechanically operated transmission portion 20 to left and right drive wheels 28 of the vehicle 10 through the differential gear mechanism 24 and other devices. The vehicle drive system 12 is suitably used in the vehicle 10 of an FR type (front engine rear wheel drive type) in which the axis of the engine 14 is parallel to the longitudinal direction of the vehicle 10. Note that the transmission case 16 will be hereinafter referred to simply as "case 16", and the electrically controlled continuously variable transmission portion 18 and the mechanically operated stepped transmission portion 20 will be hereinafter referred to simply as continuously variable transmission portion 18 and stepped transmission portion 20, respectively. It should also be noted that the driving force is considered to be equivalent to a torque or a power, unless expressly stated otherwise. It should be further noted that the continuously variable and stepped transmission portions 18 and 20 are constructed substantially symmetrically about the common axis indicated above, and that FIG. 1 does not show the lower halves of the transmission portions 18 and 20. A crankshaft of the engine 14 and a connecting shaft 34 described below are coaxial with the common axis indicated above.The engine 14 is the drive power source for driving the vehicle 10, which is a known internal combustion engine such as a gasoline engine or a diesel engine. In the present embodiment, the engine 14 is a gasoline engine using gasoline as fuel. Motor torque Te, which is an output torque of the motor 14, is controlled by a motor control device 50 controlled by an electronic control device 80 described below. The engine control device 50 includes an electronic throttle valve, a fuel injection device, and an ignition device provided in the vehicle 10. In the present embodiment, the engine 14 is connected to the continuously variable transmission portion 18 without a fluid-operated power transmission device such as a torque converter or a fluid clutch being disposed between the engine 14 and the continuously variable transmission portion 18.The continuously variable transmission portion 18 is provided with: a first motor generator MG 1; a power distributing mechanism in the form of a differential mechanism 32 configured to mechanically distribute the driving force of the engine 14 to the first motor generator MG 1 and an intermediate power transmitting member 30 that is the output rotating member of the continuously variable transmission portion 18. The second motor generator MG 2 is operatively connected to the intermediate power transmission member 30 in a power transmitting manner. The continuously variable transmission portion 18 is an electrically controlled continuously variable transmission, and a differential state of the differential mechanism 32 is controllable by controlling an operation state (torque, etc.) of the first motor generator MG 1. The first motor generator MG 1 functions as a differential motor generator that enables control of an engine speed Ne, namely, an operation speed of the engine 14. On the other hand, the second motor generator MG 2 is a motor generator that functions as a vehicle drive power source, namely, a vehicle drive electric motor. The vehicle 10 is a hybrid vehicle provided with the vehicle drive power source in the form of the engine 14 and the second motor generator MG 2. The operation state of the first motor generator MG 1 is controlled in a predetermined manner.Each of the first motor generator MG 1 and the second motor generator MG 2 is an electrically operated rotating device having the function of an electric motor and the function of an electric generator. The first motor generator MG 1 and the second motor generator MG 2 are connected to a power storage device in the form of a battery 54 through an inverter 52. The inverter 52 and the battery 54 are provided in the vehicle 10, and the inverter 52 is controlled by the above-mentioned electronic control device 80 to control an output torque of the first motor generator MG 1, namely, an MG 1 torque Tg, and an output torque of the second motor generator MG 2, namely, an MG 2 torque Tm. Positive values of the MG 1 torque Tg and the MG 2 torque Tm acting to accelerate the vehicle 10 are vehicle driving torques, while negative values of the MG 1 torque Tg and the MG 2 torque Tm acting to brake the vehicle 10 are regenerative torques. The battery 54 is the power storage device to and from which power is supplied and discharged from the first motor generator MG 1 and the second motor generator MG 2.The differential mechanism 32 is a single pinion type planetary gear set having a sun gear S 0, a carrier CA 0, and a ring gear R 0. The carrier CA0 is operatively connected to the engine 14 in a power transmitting manner through the connecting shaft 34, and the sun gear S0 is operatively connected to the first motor generator MG1 in a power transmitting manner, while the ring gear R0 is operatively connected to the second motor generator MG2 in a power transmitting manner. In the differential mechanism 32, the carrier CA 0 functions as an input rotational element, and the sun gear S 0 functions as a reaction rotational element, while the ring gear R 0 functions as an output rotational element.The stepped transmission portion 20 is a mechanically operated transmission mechanism that functions as a stepped transmission that forms part of a power transmission path between the intermediate power transmission member 30 and the drive wheels 28, namely, a mechanically operated transmission mechanism that forms part of a power transmission path between the continuously variable transmission portion 18 and the drive wheels 28. The intermediate power transmission member 30 also functions as an input rotating member of the stepped transmission portion 20, and the intermediate power transmission member 30 is connected to the second motor generator MG 2 so that the intermediate power transmission member 30 and a rotor of the second motor generator MG 2 are rotated as a unit. Further, the engine 14 is connected to an input rotating element of the continuously variable transmission portion 18. Accordingly, the stepped transmission portion 20 is a transmission that forms part of a power transmission path between the drive power source in the form of the second motor generator MG 2 and the engine 14 and the drive wheels 28. The intermediate power transmission member 30 is a power transmission member for transmitting the driving force of the driving power source to the driving wheels 28. The stepped transmission portion 20 is a known planetary gear type automatic transmission provided with a plurality of planetary gear sets in the form of a first planetary gear set 36 and a second planetary gear set 38 and a plurality of clutch devices in the form of a clutch C1, a clutch C2, a brake B1 and a brake B2, and a one-way clutch F1. Hereinafter, unless otherwise stated, the clutches C 1 and C 2 and the brakes B 1 and B 2 are simply referred to as "clutch devices CB".Each of the clutch devices CB is a hydraulically operated friction clutch device in the form of a multi-plate clutch or single-plate clutch or brake or band brake operated by a hydraulic actuator. The clutch devices CB are selectively placed in their engaged or released states, with their torque capacities or their engaged torques Tcb changed in accordance with the engaged hydraulic pressures PRcb acting thereon controlled by respective solenoid valves SL1-SL4 included within a hydraulic control unit 56. In order for an input torque Ti of the stepped transmission portion 20 to be transmitted between the intermediate power transmitting member 30 and the output shaft 22 without slipping operations of the clutch devices CB placed in their engaged states, a sum of the engaging torques Tcb of the clutch devices CB needs to be equal to the input torque Ti which is a sum of the torques to be transmitted by the respective clutch devices CB. In this regard, it should be noted that the maximum torques to be transmitted by the clutch devices CB are not increased by increasing the engagement torques Tcb after the torques to be transmitted by the clutch devices CB are increased to the maximum values. Namely, the required engaging torques Tcb are equal to the maximum torques actually transmitted through the clutch devices CB. Note also that the clutch devices CB are considered to be free from slipping when there is no difference between rotational speeds of two clutch rotating elements of each clutch device CB. The engagement torques Tcb and the engagement hydraulic pressures PRcb are substantially proportional to each other after the engagement hydraulic pressures PRcb are raised to fill the hydraulic actuators for the clutch devices CB.In the step-change transmission portion 20, selected rotating elements of the first and second planetary gear sets 36 and 38 are connected either directly or indirectly to each other or to the intermediate power transmitting member 30, the housing 16, or the output shaft 22 through the clutch devices CB or the one-way clutch F 1. The first planetary gear set 36 is provided with the rotating elements in the form of a sun gear S1, a carrier CA1 and a ring gear R1, while the second planetary gear set 38 is provided with the rotating elements in the form of a sun gear S2, a carrier CA2 and a ring gear R2.The stepped transmission portion 20 is shifted to a selected one of four speed positions (rotational speed positions) by engaging operations from selected ones of the clutch devices CB. These four gear positions each have different gear ratios γat (=AT input rotational speed Ni / output rotational speed No). Namely, the stepped transmission portion 20 is shifted up and down from one gear position to another by putting selected ones of the clutch devices CB in their engaged state. That is, the stepped transmission portion 20 is a stepped automatic transmission having a plurality of speed positions. In the present embodiment, the plurality of gear positions converted by the stepped transmission portion 20 are referred to as "AT gear positions". The AT input rotational speed Ni is a rotational speed of the input rotational element of the stepped transmission portion 20, i.e., an input rotational speed of the stepped transmission portion 20 that is the same as a rotational speed of the intermediate power transmitting member 30 and a MG 2 rotational speed Nm that is an operation rotational speed of the second motor generator MG 2. The AT input rotational speed Ni is represented by the MG 2 rotational speed Nm. On the other hand, the output rotational speed No is a rotational speed of the output shaft 22 of the stepped transmission portion 20, i.e., an output rotational speed of the stepped transmission portion 20, which is considered as an output rotational speed of a transmission device 40 consisting of the continuously variable transmission portion 18 and the stepped transmission portion 20. In the present embodiment, the transmission device 40 as a whole serves as an automatic transmission that forms the part of the power transmission path between the engine 14 and the drive wheels 28.Reference is now made to FIG. 2, which is the table indicating the relationship between the first to fourth AT gear positions of the stepped transmission portion 20 and combinations of the clutch devices CB that are in the engaged state to realize the respective AT gear positions. In the table of FIG. 2, the four AT gear positions are represented by "1.", "2.", "3." and "4." respectively. The first speed AT gear position "1st" has a highest gear ratio γat, and the gear ratios γatof the four AT gear positions decrease from the first speed AT gear position (lowest speed gear position) "1st" toward the fourth speed AT gear position (highest speed gear position) "4th". In the table, "O" indicates the engagement state of the clutch devices CB, "Δ" indicates the engagement state of the clutch device B 2 during application of an engine brake to the vehicle 10 or during an idle downshift of the stepped transmission portion 20 during idling of the vehicle 10 while the idle indicates the released state of the clutch devices CB. The above one-way clutch F 1 is disposed in parallel with the brake B 2 placed in the engaged state to realize the first speed AT speed position "1.". Accordingly, the AT speed position of the first speed "1st" is realized with the engagement operation of the brake B 2 or alternatively the engagement operation of the one-way clutch F 1. Therefore, the brake B 2 does not need to be placed in the engaged state at the start or acceleration of the vehicle 10. For example, the stepped transmission portion 20 performs the idle speed down shift operation during deceleration of the vehicle 10 in the accelerator non-operated position of which the operation amount θacc is zero or substantially zero. Note that the stepped transmission portion 20 is placed in its neutral state when all the clutch devices CB are placed in their released state. In this neutral state, a driving force cannot be transmitted through the step-change gear portion 20. Because the one-way clutch F 1 is an automatically engaged and disengaged clutch, the stepped transmission portion 20 is placed in its neutral state by the engagement operations of all the clutch devices CB. Note also that when it is determined that a shift-down operation of the stepped transmission portion 20 is to be performed, the stepped transmission portion 20 needs to be shifted down.The stepped transmission portion 20 is upshifted or downshifted to implement a newly selected one of the four AT speed positions according to the accelerator pedal operation amount θacc by a driver of the vehicle 10 and the running speed V of the vehicle 10 with a releasing operation of one of the clutch devices CB and a simultaneous engaging operation of another clutch device CB, the simultaneous releasing and engaging operations being controlled by the above-mentioned electronic control device 80. The above-mentioned one clutch device CB (referred to as "release-side clutch device CB") has been placed in the engaged state before the stepped transmission portion 20 is shifted to implement the newly selected AT speed position, while the above-mentioned other clutch device CB (referred to as "engagement-side clutch device CB") has been placed in the released state before the stepped transmission portion 20 is shifted to implement the newly selected AT speed position. Thus, the stepped transmission portion 20 is upshifted or downshifted from one to another of the AT speed positions by a so-called "clutch-to-clutch" shifting operation, namely, simultaneous releasing and engaging operations of the releasing-side and engaging-side clutch devices CB. For example, a shift-down operation of the stepped transmission portion 20 from the second speed AT speed position "2nd" to the first speed AT speed position "1st" is implemented by the simultaneous releasing and engaging operations of the respective brakes B1 and B2, as is apparent from the table of FIG. 2. In the shift-down operation, the transient hydraulic pressure of the brake B 1 (release-side clutch device CB) to be placed in its released state and the transient hydraulic pressure of the brake B 2 (engagement-side clutch device CB) to be placed in its engaged state are appropriately controlled. The release-side clutch device CB to be placed in its released state to realize the newly selected AT speed position has been placed in the engaged state before initiation of the shift-down operation, while the engagement-side clutch device CB to be placed in its engaged state to realize the newly selected AT speed position has been placed in the released state before initiation of the shift-down operation. Note that the shift-down operation from the second speed AT speed position "2nd" to the first speed AT speed position "1st" can also be implemented with the automatic engagement operation of the one-way clutch F 1 that is performed simultaneously with the release operation of the release-side clutch device CB in the form of the brake B 1.The collinear chart of FIG. 3 indicates a relationship between rotational speeds of the rotary elements of the continuously variable transmission portion 18 and the stepped transmission portion 20. In this collinear diagram of FIG. 3, three vertical lines Y1, Y2 and Y3 corresponding to the respective three rotary elements of the differential mechanism 32 of the continuously variable transmission portion 18 respectively indicate a "g" axis indicating the rotational speed of a second rotary element RE2 in the form of the sun gear S0, an "e" axis indicating the rotational speed of a first rotary element RE1 in the form of the carrier CA0, and an "m" axis indicating the rotational speed of a third rotary element RE3 in the form of the ring gear R0. Further, four vertical lines Y4, Y5, Y6 and Y7 corresponding to the respective four rotating elements of the stepped transmission portion 20 respectively indicate an axis indicating the rotational speed of a fourth rotating element RE4 in the form of the sun gear S2, an axis indicating the rotational speed of a fifth rotating element RE5 in the form of the ring gear R1 and the carrier CA2 which are fixed to each other, namely, the rotational speed of the output shaft 22, an axis indicating the rotational speed of a sixth rotating element RE6 in the form of the carrier CA1 and the ring gear R2 which are fixed to each other, and an axis indicating the rotational speed of a seventh rotating element RE7 in the form of the sun gear S1. The distances between the adjacent vertical lines Y 1, Y 2, and Y 3 are determined by a gear ratio ρ 0 of the differential mechanism 32, while the distances between the adjacent vertical lines Y 4-Y 7 are determined by gear ratios ρ 1 and ρ 2 of the respective first and second planetary gear sets 36 and 38. When the distance between the axis indicating the rotation speed of the sun gear S 0, S 1, S 2 and the axis indicating the rotation speed of the carrier CA 0, CA 1, CA 2 corresponds to "1", the distance between the axis indicating the rotation speed of the carrier CA 0, CA 1, CA 2 and the axis indicating the rotation speed of the ring gear R 0, R 1, R 2 corresponds to the gear ratio ρ of the planetary gear set (=number of teeth Zs of the sun gear / number of teeth Zr of the ring gear).As shown in the collinear chart of FIG. 3, the differential mechanism 32 of the continuously variable transmission portion 18 is arranged such that the engine 14 (shown as "ENG" in the collinear chart) is connected to the first rotating element RE 1, and the first motor generator MG 1 (shown as "MG 1" in the collinear chart) is connected to the second rotating element RE 2, while the second motor generator MG 2 (shown as "MG 2" in the collinear chart) is connected to the third rotating element RE 3, which is rotated together with the intermediate power transmitting member 30. Thus, a rotational movement of the motor 14 is transmitted to the stepped transmission portion 20 through the intermediate power transmission member 30. In a part of the collinear chart of FIG. 3 corresponding to the continuously variable transmission portion 18, straight lines L 0 and L 0R crossing the vertical line Y 2 indicate a relationship between the rotational speeds of the sun gear S 0 and the ring gear R 0.The stepped transmission portion 20 is arranged such that the fourth rotary element RE4 is selectively connected to the intermediate power transmitting member 30 through the clutch C1, the fifth rotary element RE5 is connected to the output shaft 22, the sixth rotary element RE6 is selectively connected to the intermediate power transmitting member 30 through the clutch C2 and is selectively connected to the housing 16 through the brake B2, and the seventh rotary element RE7 is selectively connected to the housing 16 through the brake B1. In a part of the collinear chart corresponding to the stepped transmission portion 20, straight lines L1, L2, L3, L4, and LR crossing the vertical line Y5 indicate the rotational speeds of the output shaft 22 in the respective AT gear positions of the first, second, third, and fourth speeds "1st", "2nd", "3rd", and "4th", and a reverse position "Rev".Solid straight lines L 0, L 1, L 2, L 3, and L 4 shown in the collinear chart of FIG. 3 indicate the relative rotational speeds of the rotary elements in a hybrid drive mode in which the vehicle 10 is driven in the forward direction with at least the engine 14 operated as a drive power source. In the differential mechanism 32 placed in the hybrid drive mode, the motor torque Te is applied to the carrier CA0, while a reaction torque (i.e., regenerative torque) which is a negative torque generated by the first motor generator MG1 is applied to the sun gear S0 so as to rotate the sun gear S0 in the positive direction. As a result, a direct transmitted motor torque Td (=Te / (1+p0)=-(1 / p0)×Tg) that is a positive torque is applied to the ring gear R 0 so as to rotate the ring gear R 0 in the positive direction. The vehicle 10 is driven in the forward direction with a vehicle driving torque which is a sum of the directly transmitted engine torque Td and the MG2 torque Tm and which is transmitted to the drive wheels 28 through the stepped transmission portion 20 selectively placed in an AT speed position of the first to fourth speeds according to a required vehicle driving force of the driver. At this time, the first motor generator MG 1 functions as an electric generator that operates in the positive direction to generate a negative torque. Electric power Wg generated by the first motor generator MG 1 is stored in the battery 54 or consumed by the second motor generator MG 2. The second motor generator MG 2 is operated to generate the MG 2 torque Tm with the total electric power Wg generated by the first motor generator MG 1, a part thereof, or a sum of the generated electric power Wg and the electric power supplied from the battery 54.In the differential mechanism 32 placed in a motor drive mode in which the vehicle 10 is driven with a driving force generated by the second motor generator MG 2 operated as a driving power source while the engine 14 is stopped, the carrier CA 0 is held stationary while the MG 2 torque Tm, which is a positive torque, is applied to the ring gear R 0 to rotate the ring gear R 0 in the positive direction. At this time, the first motor generator MG 1 connected to the sun gear S 0 is placed in an unloaded state and is freely operated in the negative direction. Namely, in the engine drive mode, the engine 14 is maintained in the non-operating state so that the engine speed Ne is substantially zero and the vehicle 10 is driven in the forward direction with the MG2 torque Tm (positive forward drive torque) transmitted to the drive wheels 28 as a forward drive torque through the stepped transmission portion 20 placed in an AT speed position of the first to fourth speeds.Broken straight lines L 0R and LR shown in the collinear chart of FIG. 3 show the relative rotational speeds of the various rotating elements of the continuously variable transmission portion 18 and the stepped transmission portion 20 during the backward travel of the vehicle 10 in the motor drive mode. During the backward direction running of the vehicle 10 in the engine drive mode, the MG 2 torque Tm, which is a negative torque, is applied to the ring gear R 0 so as to rotate the ring gear R 0 in the negative direction, and is transmitted to the drive wheels 28 as the backward drive torque through the stepped transmission portion 20 placed in the first speed AT speed position. The vehicle 10 can be driven in the reverse direction with the reverse drive MG 2 torque Tm, which is the negative torque generated by the second motor generator MG 2 under control of the electronic control device 80 and which is opposite to the forward positive drive torque generated while the stepped transmission portion 20 is placed in the AT speed position of the low forward speed, e.g., the AT speed position of the first speed "1.". The forward drive MG 2 torque Tm is the positive vehicle drive torque for rotating the drive wheels 28 in the positive direction, while the reverse drive MG 2 torque Tm is the negative vehicle drive torque for driving the drive wheels 28 in the negative direction. Thus, the vehicle 10 is propelled in the reverse direction with the generated MG2 negative torque Tm, while the step-change transmission portion 20 is placed in the correspondingly selected forward-drive AT gear position, which is also used to propel the vehicle 10 in the forward direction. Also in the hybrid drive mode, the second motor generator MG 2 may be operated in the negative direction as indicated by the straight line L 0R, so that the vehicle 10 may be driven in the reverse direction in both the hybrid drive mode and the motor drive mode.In the vehicle drive system 12, the continuously variable transmission portion 18 functions as an electrically controlled transmission mechanism provided with the differential mechanism 32 whose differential state is controlled by controlling the operating state of the first motor generator MG 1 and which has the three rotating elements, namely, the first rotating element RE 1 in the form of the carrier CA 0 to which the engine 14 is operatively connected in a power transmitting manner, the second rotating element RE 2 in the form of the sun gear S 0 to which the first motor generator MG 1 is operatively connected in a power transmitting manner, and the third rotating element RE 3 in the form of the ring gear R 0 to which the intermediate power transmitting element 30 is operatively connected in a power transmitting manner. The third rotation element RE 3 to which the intermediate power transmitting member 30 is connected may be regarded as the third rotation element RE 3 to which the second motor generator MG 2 is operatively connected in a power transmitting manner. Namely, the continuously variable transmission portion 18 provided in the vehicle drive system 12 includes the differential mechanism 32 to which the engine 14 is operatively connected in a power transmitting manner, and the first motor generator MG 1 to which the differential mechanism 32 is operatively connected in a power transmitting manner so as to control the differential state of the differential mechanism 32 according to the operating state of the first motor generator MG 1. The continuously variable transmission portion 18 is operated as an electrically controlled continuously variable transmission whose gear ratio γ0 (=Ne / Nm) is variable. The gear ratio is a ratio of the engine speed Ne that is equal to a speed of the connecting shaft 34 (which is the input rotational element of the continuously variable transmission portion 18) to the MG 2 speed Nm that is equal to the speed of the intermediate power transmitting member 30 (which is the output rotational element of the continuously variable transmission portion 18).In the hybrid drive mode, for example, the rotational speed of the sun gear S0 is increased or decreased by controlling an operating rotational speed of the first motor generator MG1 while the rotational speed of the ring gear R0 is determined by the rotational speed of the drive wheels 28, with the stepped transmission portion 20 being placed in one of the AT speed positions, so that the rotational speed of the carrier CA0 (namely, the engine rotational speed Ne) is increased or decreased accordingly. In the hybrid drive mode, therefore, the engine 14 can be operated in an efficient operating state. That is, the stepped transmission portion 20 to be placed in a selected one of the AT gear positions and the continuously variable transmission portion 18 functioning as a continuously variable transmission cooperate to provide the transmission device 40 in which the continuously variable transmission portion 18 and the stepped transmission portion 20 are arranged in series and which functions as a continuously variable transmission as a whole.Alternatively, the continuously variable transmission portion 18 may be shifted like a step-variable transmission. Accordingly, the transmission device 40 constituted by the stepped transmission portion 20 to be placed in one of the AT speed positions and the continuously variable transmission portion 18 that can be shifted like the stepped transmission can be shifted as a whole like a stepped transmission. That is, the stepped transmission portion 20 and the continuously variable transmission portion 18 can be controlled so as to selectively provide a plurality of speed positions (hereinafter referred to as "total speed positions") each having different values of a gear ratio γt (=Ne / No) which is a ratio of the engine speed Ne to the output speed No. The gear ratio γt is a total gear ratio of the transmission device 40 consisting of the continuously variable transmission portion 18 and the step-variable transmission portion 20 arranged in series. The total transmission ratio γt is equal to a product of the transmission ratio γ 0 of the continuously variable transmission portion 18 and the transmission ratio γat of the stepped transmission portion 20, namely, γt=γ 0×γat.At least one total speed position is provided for each of the four AT gear positions of the stepped transmission portion 20 with a combination of each AT gear position with at least one of the different gear ratio values γ0 of the continuously variable transmission portion 18. FIG. 4 is the table indicating an example of the total speed positions of the transmission device 40, wherein the first to third total speed positions are converted for the first speed AT gear position, the fourth to sixth total speed positions are converted for the second speed AT gear position, the seventh to ninth total speed positions are converted for the third speed AT gear position, and a tenth total speed position is converted for the fourth speed AT gear position.FIG. 5 is the view indicating, in a collinear chart similar to FIG. 3, some examples of the AT gear positions of the stepped transmission portion 20 and some examples of the total rotational speed positions of the transmission device 40. In the collinear chart of FIG. 5, solid lines indicate the fourth to sixth total rotational speed positions that are realized when the stepped transmission portion 20 is placed in the AT speed position of the second speed. In the transmission device 40, the continuously variable transmission portion 18 is controlled to control the engine speed Ne relative to the output speed No to convert the predetermined total gear ratio values γt, thereby converting the total speed position or positions for each of the AT gear positions. A broken line indicates the total seventh speed position that is realized when the stepped transmission portion 20 is placed in the third speed AT speed position. In the transmission device 40, the continuously variable transmission portion 18 is controlled according to the selected AT speed position for shifting the transmission device 40 from one of the total speed positions to the other.As shown in FIG. 1, the vehicle 10 is provided with the control apparatus of the present invention in the form of the electronic control device 80 configured to control various devices of the vehicle 10, e.g., the engine 14, the continuously variable transmission portion 18, and the stepped transmission portion 20. FIG. 1 is the view showing input and output signals of the electronic control device 80, and is a functional block diagram showing main control functions and control portions of the electronic control device 80. For example, the electronic control device 80 is a so-called microcomputer including a CPU, a ROM, a RAM, and an input-output interface. The CPU performs various controls of the vehicle 10 by implementing various input signal processings according to control programs stored in the ROM, using a temporary data storage function of the RAM. The electronic control device 80 may be constituted by two or more control units exclusively assigned to perform various controls, e.g., engine controls and transmission shift controlsThe electronic control device 80 receives various input signals such as: an output signal of an engine speed sensor 60 indicating the engine speed Ne; an output signal of an MG1 rotation speed sensor 62 indicating an MG1 rotation speed Ng that is the operation rotation speed of the first motor generator MG1; an output signal of an MG2 rotation speed sensor 64 indicating the MG2 rotation speed Nm that is the AT input rotation speed Ni; an output signal of an output rotation speed sensor 66 indicating the output rotation speed No that corresponds to the vehicle running speed V; an output signal of an accelerator pedal operation amount sensor 68 indicating the operation amount θacc of a vehicle accelerator element in the form of the accelerator pedal; an output signal of a throttle valve opening angle sensor 70 indicating an opening angle θth of the above-indicated electronic throttle valve; an output signal of a brake pedal sensor 72 indicative of an operation state of the brake pedal by the vehicle operator; an output signal of a G sensor 74 indicative of a longitudinal acceleration value G of the vehicle 10; an output signal of a shift position sensor 76 indicative of the currently selected operation position POSsh of a shift lever 58; output signals of a battery sensor 78 indicative of a temperature THbat, a charge / discharge current Ibat, and a voltage Vbat of the battery 54; and an output signal of an oil temperature sensor 79 indicative of a temperature THoil of a working fluid to be supplied to the hydraulic actuators of the clutch devices CB, the working fluid used to switch each clutch device CB between its engaged state and released state.The operation amount θacc of the accelerator pedal provided as the vehicle accelerator represents the degree of acceleration of the vehicle 10 required by the vehicle operator and therefore a vehicle driving force or output required by the vehicle operator. The vehicle driving force or output may be represented by the electronic throttle opening angle θth, a driver required vehicle driving torque Tdem described below, and so on, in addition to the accelerator pedal operation amount θacc.The electronic control device 80 generates various output signals such as: motor control command signals Se to be applied to a motor control device 50 for controlling the motor 14; motor generator control command signals Smg to be applied to the inverter 52 for controlling the first motor generator MG 1 and the second motor generator MG 2; and hydraulic command control signals Sat to be applied to the hydraulic control unit 56 for controlling the operation state of the clutch devices CB. The hydraulic command control signals Sat are command signals for controlling the solenoid valves SL1-SL4 to regulate the engaging hydraulic pressures PRcb to be applied to the respective hydraulic actuators of the clutch devices CB for shifting the step-change transmission portion 20. The electronic control device 80 operates to set a hydraulic pressure command value corresponding to the engagement hydraulic pressure PRcb to be applied to each of the hydraulic actuators to convert a desired amount of the engagement torque Tcb of the corresponding clutch device CB, and applies a current or voltage command signal corresponding to the hydraulic pressure command value to the hydraulic control unit 56.The electronic control device 80 calculates a state-of-charge value SOC[%] of the battery 54 (an amount of electric energy stored in the battery 54) based on the charge / discharge current Ibat and the voltage Vbat of the battery 54. These lower and upper limit values Win and Wout are calculated based on the battery temperature THbat and the state of charge value SOC %, for example. Charge and discharge controls of the battery 54 are implemented such that the battery power Pbat is within a range between the calculated lower and upper limit values Win and Wout. The range between the lower and upper limit values Win and Wout is narrowed when the battery temperature THbat is decreased below a lower limit value of a normal operation range of the battery 54 or when the battery temperature THbat is increased above an upper limit value of the normal operation range. The lower limit value Win is decreased with an increase in the state of charge value SOC above a predetermined upper limit value, while the upper limit value Wout is decreased with a decrease in the state of charge value SOC below a predetermined lower limit value.The electronic control device 80 includes a shift control device in the form of a step shift control section 82 and a hybrid control device in the form of a hybrid control section 84 for implementing various controls of the vehicle 10.The stepped shift control section 82 is configured to determine a shift operation of the stepped transmission section 20 according to a stored AT gear position shift map obtained experimentally or determined by a suitable design theory, and implement a shift control for controlling the stepped transmission section 20 to perform the determined shift operation. In this shift control, the step shift control section 82 applies the hydraulic command control signals Sat to the hydraulic control unit 56 to command the solenoid valves SL1-SL4 to bring the appropriate clutch devices CB into the released states and engaged states to automatically upshift or downshift the step transmission section 20. The above-mentioned AT gear position shift map represents a predetermined relationship between two variables in the form of the output rotational speed No and the accelerator operation amount θacc, the relationship being used to determine a shift operation of the stepped transmission portion 20 and being represented by upshift and downshift shift lines in a two-dimensional coordinate system in which the output rotational speed No and the accelerator operation amount θacc are removable along two respective axes. The output rotational speed No may be replaced by the vehicle running speed V, and the accelerator operation amount θacc may be replaced by a driver required vehicle driving torque Tdem or the throttle opening θth. The shift lines of the AT gear position shift map are composed of upshift lines for determining upshifts of the stepped transmission portion 20 and downshift lines for determining downshifts of the stepped transmission portion 20, Each of the shift lines is defined by a series of shift points determined so that the stepped transmission portion 20 should be upshifted or downshifted when the output rotational speed No becomes higher or lower than the shift point at a predetermined value of the accelerator pedal operation amount θacc, or when the accelerator pedal operation amount θacc becomes higher or lower than the shift point at a predetermined value of the output rotational speed No.The hybrid control portion 84 has a function of a motor control means or a portion for controlling the motor 14 and a function of a motor generator control means or a portion for controlling the first motor generator MG 1 and the second motor generator MG 2 through the inverter 52. The hybrid control section 84 is configured to calculate a vehicle driving power Pdem required by the driver, for example, on the basis of the accelerator operation amount θacc and the vehicle running speed V and according to a predetermined relationship in the form of a driving force map. In other words, the hybrid control section 84 calculates the driver required vehicle driving torque Tdem at the current vehicle running speed V. The hybrid control section 84 generates the motor control command signals Se for controlling the motor 14 and the motor generator control command signals Smg for controlling the first motor generator MG 1 and the second motor generator MG 2 to provide the driver required vehicle driving power Pdem, taking into account the upper and lower limit values Wout and Win. For example, the engine control command signals Se represent an engine output Pe which is the torque Te of the engine 14 at its present operating speed Ne. For example, the motor generator control command signals Smg represent the electric power Wg to be generated by the first motor generator MG 1 to generate the reaction torque with respect to the motor torque Te, namely, the MG 1 torque Tg at the present MG 1 rotation speed Ng, and an amount of electric power Wm to be consumed by the second motor generator MG 2 to generate the MG 2 torque Tm at the present MG 2 rotation speed Nm.For example, when the transmission device 40 is operated as a continuously variable transmission as a whole while the continuously variable transmission portion 18 is operated as the continuously variable transmission, the hybrid control portion 84 controls the engine 14 and the electric power Wg to be generated by the first motor generator MG 1 to convert the engine rotational speed Ne and the engine torque Te to obtain the engine power Pe, to convert the vehicle driving power Pdem required by the driver in consideration of a highest fuel efficiency point of the engine 14 so as to control the gear ratio γ 0 of the continuously variable transmission portion 18 to continuously change. As a result, the gear ratio γt of the transmission device 40 is controlled while the continuously variable transmission portion 18 is operated as the continuously variable transmission.When the transmission device 40 is shifted as a whole as a stepped transmission while the continuously variable transmission portion 18 is shifted as a stepped transmission, the hybrid control portion 84 determines a shifting operation of the transmission device 40 according to an overall speed position shift map, and performs shift control of the continuously variable transmission portion 18 to implement a selected one of the plurality of overall speed positions in cooperation with the stepped shift control portion 82 for selectively shifting the stepped transmission portion 20 to the AT speed positions. The plurality of total speed positions may be implemented by controlling the first motor generator MG 1 to control the engine speed Ne according to the output speed No so as to maintain the respective gear ratio values γt. Each of the gear ratio values γt of the total rotational speed positions may not be constant over the entire range of the output rotational speed No and may have different values in respective ranges of the output rotational speed No, or may be limited depending on upper and lower limit values of the rotational speeds of different parts of the stepped transmission portion 20. Thus, the hybrid control portion 84 can control the transmission device 40 to be shifted to the selected one of the total speed positions by controlling the engine speed Ne.Like the AT gear position shift map, the above-mentioned total speed position shift map represents a predetermined relationship between the output speed No and the accelerator operation amount θacc. FIG. 6 shows an example of the total speed position shift map. In FIG. 6, solid lines indicate upshift boundary lines, while broken lines indicate downshift boundary lines. The transmission device 40, which is composed of the continuously variable transmission portion 18 and the stepped transmission portion 20 arranged in series, is shifted from one of the total speed positions to another according to the total speed position shift map as if the transmission device 40 as a whole were shifted like a stepped transmission. This overall speed shift control for controlling the shift operations of the transmission device 40 as the overall speed transmission may preferably be implemented in the continuously variable shift control of the transmission device 40 as the overall continuously variable transmission only when a sport running mode or other high drivability running mode is selected by the vehicle operator, or only when the vehicle driving torque Tdem required by the operator is comparatively large, but may be implemented basically unless the overall speed shift control is restricted or inhibited.The total speed position shift control by the hybrid control portion 84 and the step shift control by the step shift control portion 82 are implemented in cooperation with each other. In this embodiment, the ten total speed positions, i.e., the first to tenth total speed positions, are implemented for the four AT speed positions, i.e., the AT speed positions of the first to fourth speeds. The AT gear position shift map is defined such that an AT gear position shift operation is performed in synchronization with an overall speed position shift operation. Described in more detail, the upshift lines for upshifting the transmission device 40 from the third total speed position to the fourth total speed position (3→4), from the sixth total speed position to the seventh total speed position (6→7), and from the ninth total speed position to the tenth total speed position (9→10) are consistent with the respective upshift lines for upshifting the stepped transmission portion 20 from the first speed AT speed position to the second speed AT speed position (1→2), from the second speed AT speed position to the third speed AT speed position (2→3), and from the third speed AT speed position to the fourth speed AT speed position (3→4). For example, the total speed position upshift line 3→4 coincides with the AT speed position upshift line AT 1→2 as indicated in FIG. 6. Further, the downshift lines for downshifting the transmission device 40 from the fourth total speed position to the third total speed position (3←4), from the seventh total speed position to the sixth total speed position (6←7), and from the tenth total speed position to the ninth total speed position (9←10) coincide with the respective downshift lines for downshifting the stepped transmission portion 20 from the second speed AT speed position to the first speed AT speed position (1←2), from the third speed AT speed position to the second speed AT speed position (2←3), and from the fourth speed AT speed position to the third speed AT speed position (3←4). For example, the total speed position downshift line 3 ← 4 agrees with the AT speed position downshift line AT 1 ← 2 as indicated in FIG. 6. Alternatively, a command to shift the stepped transmission portion 20 may be applied to the stepped shift control portion 82 in response to a determination corresponding to the total speed position shift map of FIG. 6 that the transmission device 40 is to be shifted from one total speed position to another. Thus, an upshift operation of the transmission device 40 as a whole takes place in an upshift operation of the stepped transmission portion 20 and a downshift operation of the transmission device 40 as a whole takes place in a downshift operation of the stepped transmission portion 20. The stepped shift control portion 82 commands the stepped transmission portion 20 to perform a shift from one AT gear position to another to perform the transmission device 40 from one total speed position to another. Because the AT speed position shift operation is performed in synchronization with the total speed position shift operation, the shift operation of the stepped transmission portion 20 is performed with a change in the engine speed Ne, so that the vehicle operator is less likely to feel a shift shock of the stepped transmission portion 20 unpleasant.The hybrid control portion 84 selectively establishes the motor drive mode or the hybrid drive mode depending on the running state of the vehicle 10. For example, the hybrid control portion 84 selects the motor drive mode when the vehicle drive power Pdem required by the driver is lower than a predetermined threshold value, i.e., within a predetermined motor drive mode range, and selects the hybrid drive mode when the vehicle drive power Pdem required is equal to or higher than the threshold value, i.e., within a predetermined hybrid drive mode range. Further, even when the vehicle drive required power Pdem is within the motor drive mode range, the hybrid control portion 84 selects the hybrid drive mode when the amount of electric energy SOC stored in the battery 54 is less than a predetermined motor start threshold. In the motor drive mode, the vehicle 10 is driven with a driving torque generated by the second motor generator MG 2 while the engine 14 is stopped. In the hybrid drive mode, the engine 14 is operated as needed. The above-mentioned engine start threshold is predetermined as a lower limit value of the amount of electric energy SOC below which the battery 54 should be charged by starting the engine 14.The overall speed position shift control of the transmission device 40 implemented in a shift operation of the stepped transmission portion 20 will be described in detail. In order to implement the overall speed position shift control of the transmission device 40 in the shifting operation of the stepped transmission portion 20, the hybrid control portion 84 includes: target value setting means in the form of a target value setting portion 86; control means in the form of a control portion 88; target input torque setting means in the form of a target input torque setting portion 90; and input torque reset control means in the form of an input torque reset control portion 92. The electronic control device 80 further includes state determination means in the form of a state determination portion 94.The target value setting section 86 is configured to set a target value of a MG2 speed change rate dNm / dt, which is a change rate of the MG2 speed Nm, namely, a change rate of the AT input speed Ni, during an inertia phase of a shift operation of the stepped transmission section 20 controlled by the stepped shift control section 82. The target value setting section 86 sets, from time to time, the target value of the MG2 speed change rate dNm / dt such that the MG2 speed Nm changes in a predetermined pattern toward a post-shift synchronization speed to be converted after completion of the shift operation of the stepped transmission section 20. This MG2 speed change rate dNm / dt represents a rotation state of the input rotary element of the stepped transmission portion 20. the target value setting portion 86 is further configured to set a target value of an engine speed change rate dNe / dt that is a change rate of the engine speed Ne during the inertia phase of the shift operation of the stepped transmission portion 20 controlled by the stepped shift control portion 82. The target value setting section 86 sets, from time to time, the target value of the engine speed change rate dNe / dt such that the engine speed Ne changes in a predetermined pattern toward a target value to be converted after completion of the shifting operation of the stepped transmission section 20. The engine speed change rate dNe / dt represents an operation state of the engine 14. as described above, the AT speed position shift operation is performed in synchronization with the total speed position shift operation, so that the target value of the engine speed Ne to be converted after the completion of the shift operation of the stepped transmission portion 20 is considered to be equivalent to a post-shift synchronization value of the engine speed Ne to be converted after the total speed position shift operation of the transmission device 40. In the following description of the present embodiment, the post-shift synchronization value of the MG 2 rotational speed Nm to be converted after completion of the shift operation of the stepped transmission portion 20 is represented by "Nmsyca" (=No x yata). The value yata is a gear ratio of the stepped transmission portion 20 in its AT speed position which is converted after its shifting operation. Further, the target value of the MG2 rotation speed change rate dNm / dt is represented by "dNmtgt", while the target value of the engine rotation speed change rate dNe / dt is represented by "dNetgt".The control section 88 is configured to implement controls of the MG 1 torque Tg and the MG 2 torque Tm in the process of a shift operation of the stepped transmission section 20, i.e., during the inertia phase of the shift operation, based on the motor torque Te and the transmission torque of the stepped transmission section 20 such that the MG 2 speed change rate dNm / dt and the motor speed change rate dNe / dt coincide with the respective target values dNmtgt and dNetgt set by the target value setting section 86. A sum of the MG 2 torque Tm and the direct-transmitted motor torque Td transmitted to the ring gear R 0 due to the MG 1 torque Tg acting as reaction torque with respect to the motor torque Te is the same as the AT input torque Ti of the step-variable transmission portion 20.The stepped transmission portion 20 has four kinds of shift operations: an on-step-up operation in an on-state of the vehicle 10; an on-step-down operation in an on-state of the vehicle 10; an off-step-up operation in an off-state of the vehicle 10; and an off-step-down operation in an off-state of the vehicle 10. On the other hand, the turn-off switching operation is required due to a decrease in the accelerator pedal operation amount θacc, or due to a decrease in the vehicle running speed V in the accelerator non-operating state, or in a state in which the accelerator pedal operation amount θacc is maintained at a value low enough to cause the vehicle 10 to decelerate. When the AT input rotational speed Ni and the MG 2 rotational speed Nm are not controlled, the AT input rotational speed Ni (=MG 2 rotational speed Nm) increases in the process of the power-on switching operation, and the MG 2 rotational speed Nm decreases in the process of the power-off switching operation while no torque for the switching operation is transmitted through the engagement-side and release-side clutch devices CB. Therefore, in the on-shift upshift and off-shift downshift in which the MG 2 rotation speed cannot be changed toward the post-shift synchronization rotation speed Nmsyca without control of the MG 2 rotation speed Nm, it is desirable that torque be transmitted through the engagement-side clutch device CB to be placed in its engaged state to establish the selected AT gear position to enable a rapid process of the shift operation. On the other hand, in the power-off upshift operation and the power-on downshift operation in which the MG 2 rotation speed can be changed toward the post-shift synchronization rotation speed Nmsyca without the control of the MG 2 rotation speed Nm, it is desirable that a torque to be transmitted through the release-side clutch device CB that is placed in the engaged state before the shift operation be decreased to enable a fast process of the shift operation. Thus, in the on-shift upshift operation and the off-shift downshift operation, the engagement-side clutch device CB is a shift proceeding clutch device whose transmission torque is controlled to achieve a rapid process of the shift operation. In the power-off upshift operation and the power-on downshift operation, on the other hand, the release-side clutch device CB is the shift proceeding clutch device. The shift proceeding clutch device is one of the release-side and engagement-side clutch devices CB whose torque is controlled to achieve a quick progress of the shift operation of the stepped transmission portion 20.Described in more detail, the control section 88 calculates the MG1 torque Tg and the MG2 torque Tm based on the target value dNmtgt of the MG2 speed change rate dNm / dt, the target value dNetgt of the engine speed change rate dNe / dt, the engine torque Te and an AT transmission torque Tat (described below), and according to the following mathematical equation (1). The control section 88 applies the motor generator control command signals Smg to the inverter 52 to convert the calculated MG1 torque Tg and the MG2 torque Tm. For example, the following mathematical equation (1) derives from the kinetic equations of inertia, speed change rate, and torque values along or on the axes "g", "e", and "m" of the continuously variable transmission section 18 in the collinear diagram of FIG. 3 and relationship equations based on the degree of freedom of the continuously variable transmission section 18 that the speeds of two of the three axes "g", "e", and "m" determine the speed on the remainder of these three axes. Accordingly, each of the values a11,..., a22, b11,....., b22, c11,....., and c22 of each of the 2×2 matrices is determined by a combination of the inertia of each rotating element of the continuously variable transmission portion 18, the gear ratio ρ0 of the differential mechanism 32, etc. Mathematical EquationIn the above mathematical equation (1), the target values dNmtgt and dNetgt are used as the respective MG2 speed change rate dNm / dt and engine speed change rate dNe / dt. For example, the target value setting section 86 sets the MG2 speed change rate target value dNmtgt and the engine speed change rate target value dNetgt such that the MG2 speed Nm and the engine speed Ne change in desired or predetermined manners during the inertia phase of a corresponding shift operation of the stepped transmission section 20. The target value setting section 86 sets the MG2 speed change rate target value dNmtgt and the engine speed change rate target value dNetgt depending on the corresponding type of shift operation of the stepped transmission section 20, the corresponding two AT speed positions between which the shift operation will take place, the corresponding two total speed positions between which the transmission device 40 will take place, a particular operating state of the engine 14, and any other condition. Therefore, the control section 88 can be considered to implement control of the AT input torque Ti in the process of the shift operation of the stepped transmission section 20 so that the MG2 rotational speed Nm changes in the desired manner during the inertia phase of the shift operation, in other words, so that the MG2 rotational speed change rate dNm / dt coincides with the target value dNmtgt so that the MG2 rotational speed Nm changes toward the post-shift synchronization value Nmsyca. In the present embodiment, this control implemented by the control section 88 during the inertia phase of the shift operation may also be referred to as "MG 2 speed control".For example, the engine torque Te in the mathematical equation (1) is a value to be generated at the engine speed Ne at which the engine output Pe for converting the vehicle driving power Pdem required by the driver is obtained.The AT transmission torque Tat in the mathematical equation (1) is a sum of torques to be transmitted by the respective release-side and engagement-side clutch devices CB in the process of the shift operation of the stepped transmission portion 20, the sum being converted into a torque value acting on the intermediate power transmitting member 30, a value of torque to be transmitted by the stepped transmission portion 20, the value being converted into a torque value acting on the intermediate power transmitting member 30. Because the above mathematical equation (1) is a model equation that enables a rapid progress of the shift operation of the stepped transmission portion 20, the torque to be transmitted by the engagement-side shift proceeding clutch device CB serving mainly to enable a rapid progress of the shift operation, wherein the torque is converted into the torque value acting on the intermediate power transmitting member 30, is used as the AT transmission torque Tat in the mathematical equation (1) in the present embodiment. The transmission torque of the engagement-side shift proceeding clutch device CB used as the AT transmission torque Tat in the mathematical equation (1) is a feedforward value.For example, the stepped shift control portion 82 sets the transmission torque of the shift proceeding clutch device CB on the basis of a target input torque value Titgt corresponding to the driver required vehicle driving power Pdem and according to a certain one of various predetermined relationships for respective various types of shifts of the stepped transmission portion 20, as represented by the certain type of shift and the corresponding two AT gear positions between which the shift is taking place, so that a good balance is obtained between the reduction or prevention of the shift shock and a reduction of a required shift time of the stepped transmission portion 20.The target input torque setting section 90 sets the target input torque Titgt corresponding to the accelerator operation amount θacc. Described in more detail, the driver required vehicle driving power Pdem and the driver required vehicle driving torque Tdem are calculated based on the accelerator operation amount θacc, and a change in the accelerator operation amount θacc is directly reflected in the vehicle driving power and the torques Pdem and Tdem. In order to reduce a change amount of the target input torque Titgt due to a change in the accelerator operation amount θacc, it is appropriate or preferable to use, as the target input torque Titgt, a smoothed value of a driver required input torque value Tidem that is the driver required vehicle drive torque Tdem converted into a torque acting on the intermediate power transmitting member 30. The target input torque setting section 90 sets, as the driver required input torque value Tidem, the driver required vehicle drive torque Tdem corresponding to the accelerator operation amount θacc, and the drive torque Tdem is converted into the torque acting on the intermediate power transmitting member 30. The target input torque setting section 90 sets, as the target input torque Titgt, the smoothed value of the driver required input torque value Tidem corresponding to the accelerator operation amount θacc.The control section 88 terminates the MG2 speed control (AT input torque control) when the MG2 speed Nm has become equal to a post-shift synchronization value Nmsyca during the inertia phase of the shift operation of the stepped transmission section 20. In the MG 2 speed control implemented by the control section 88, the AT input torque Ti is controlled so as to implement the MG 2 speed change target rate dNmtgt and the engine speed change target rate dNetgt. In other words, the AT input torque Ti is controlled by implementing control for canceling the target input torque Titgt. Accordingly, there is a possibility that the AT input torque Ti is deviated from the target input torque Titgt upon termination of the MG2 speed control. In this case, the AT input torque Ti deviating from the target value Titgt is reset to the target value Titgt after the MG 2 rotation speed Nm becomes equal to a post-shift synchronization value Nmsyca.When the MG2 rotation speed Nm has become equal to a post-synchronization value Nmsyca as a result of the MG2 rotation speed control (AT input torque control), the input torque reset control section 92 implements an AT input torque reset control to gradually change the AT input torque Ti toward the target value Titgt at a predetermined rate Rti so that the AT input torque Ti deviating from the target value Titgt is reset to the target value Titgt. In order to reset the AT input torque Ti to the target value Titgt, the input torque reset control portion 92 controls the MG 1 torque Tg and the MG 2 torque Tm. When the AT input torque Ti agrees with the target value Titgt, i.e., has been reset to the target value Titgt, the input torque reset control section 92 terminates the AT input torque reset control. When the target input torque Titgt at the initiation of the AT input torque reset control is larger than the AT input torque Ti, the rate Rti has a positive value. On the other hand, when the target input torque Titgt at the initiation of the AT input torque reset control is smaller than the AT input torque Ti, the rate Rti has a negative value. The AT input torque reset control by the input torque reset control section 92 corresponds to the input torque reset control of the present invention.For example, the input torque reset control section 92 sets the rate Rti on the basis of the type of shift operation of the stepped transmission section 20 performed immediately before the initiation of the AT input torque reset control and the corresponding two AT gear positions of this shift operation. The predetermined rate Rti is a predetermined rate of change dTi / dt of the AT input torque Ti that enables a good trade-off or balance between rapidly resetting the AT input torque Ti to the target value Titgt within a predetermined period of time and reducing the shift shock. This predetermined period is a predetermined maximum allowable period required to reset the AT input torque Ti to the target value Titgt. Note that relatively high and low values of the rate Rti are considered to be equivalent to relatively large and small amounts of the rate of change dTi / dt of the AT input torque Ti, respectively.The state determination section 94 is configured to determine whether the MG 2 rotation speed Nm during the inertia phase of the shift operation of the stepped transmission section 20 is equal to the post-shift synchronization value Nmsyca, for example, in the process of the shift-down operation of the stepped transmission section 20.FIG. 7 is the time chart showing an example of changes in various parameters when the MG 2 speed control and the AT input torque reset control are implemented with an increase in the operation amount θacc of the accelerator pedal by the vehicle driver for accelerating the vehicle 10 in the process of a power-off downshift operation of the stepped transmission portion 20. As indicated in FIG. 7, the driver required input torque value Tidem (AT input torque Ti indicated by a broken line in FIG. 7 ) is increased as a result of an operation of the accelerator pedal. However, in order to reduce the risk of generation of the above-described backlash elimination impact after completion of the shift-down operation, the increase amount of the AT target input torque value Titgt (AT input torque Ti indicated by a one-dot chain line in FIG. 7 ) with respect to the increase amount of the driver required input torque value Tidem is limited to keep the target value Titgt not greater than a predetermined upper limit value Ti 1 until the AT input torque reset control is completed, as indicated by a mark "A" in FIG. 7. As the shift-down progresses, the inertia phase is initiated at a time t 1, and the AT input torque Ti is controlled during the inertia phase. A command value of the AT input torque Ti (AT input torque Ti indicated by a solid line) agrees with the target value Titgt before the time of initiation of the inertia phase, and is controlled to deviate from the target value Titgt during the inertia phase. After the MG 2 rotation speed Nm is increased to the post-shift synchronization value Nmsyca, the AT input torque reset control is implemented so that the AT input torque Ti deviated from the target value Titgt is gradually decreased toward the target value Titgt (during a period between the times t 2 and t 3) as indicated by a mark "B". When the AT input torque Ti has been reset to the target value Titgt, the AT input torque reset control is ended (at time t3). After the AT input torque reset control is finished, the AT input target torque Titgt is gradually increased toward the driver required AT input torque value Tidem, as indicated by a mark "C", to satisfy the driver's request to accelerate the vehicle 10 and, at the same time, reduce the risk of generating the backlash elimination shock.As described above, the control section 88 implements the control of the AT input torque Ti by feedback compensating the target value Titgt during the inertia phase of the shift-down operation of the stepped transmission section 20 so that the MG2 speed change rate dNm / dt coincides with the target value dNmtgt at which the MG2 speed Nm changes toward the post-shift synchronization value Nmsyca.The input torque reset control section 92 is configured to implement the AT input torque reset control when the state determination section 94 has determined that the MG 2 rotation speed Nm has become equal to the post-shift synchronization value Nmsyca.When the accelerator pedal operation amount θacc is increased in the process of the turn-off downshift, the target input torque setting section 90 limits an increase amount of the target input torque value Titgt with respect to an increase amount of the driver required input torque value Tidem as a result of the increase of the accelerator pedal operation amount θacc so that the target input torque value Titgt is not greater than the predetermined upper limit value Ti 1 until the AT input torque reset control is finished. For example, the predetermined upper limit value Ti 1 is an upper limit value of the target input torque value Titgt at or below which the backlash elimination impact is likely not generated after the completion of the downshifting operation, namely, the risk of generating the backlash elimination impact is reduced. As the target input torque value Titgt increases from the value in the accelerator non-operating state to the predetermined upper limit value Ti1, the vehicle 10 can be switched from its non-driving state in which the AT input torque Ti has a negative value to its driving state in which the AT input torque Ti has a positive value. In this regard, note that a rate of increase of the target input torque value Titgt is a smoothed value of a rate of increase of the driver required input torque value Tidem, and the predetermined upper limit value Ti 1 is a small value. Accordingly, limiting the target input torque Titgt to the upper limit value Ti 1 enables reduction of the risk of generation of the backlash elimination impact while the vehicle 10 is being switched from its non-driving state to its driving state.Further, the target input torque setting section 90 is configured to gradually change the target input torque value Titgt toward the driver required input torque value Tidem after the termination timing of the AT input torque reset control.As shown in FIG. 7, the command value of the AT input torque Ti is reduced during the inertia phase of the downshift with a decrease in the MG 2 rotational speed Nm toward the post-shift synchronization value Nmsyca, so that the risk of generation of the backlash elimination impact after completion of the downshift is further reduced. Namely, the hybrid control section 84 further includes a real input torque reducing means in the form of a real input torque reducing section 96 configured to reduce the real AT input torque Ti with the decrease of the MG2 rotational speed Nm toward the post-shift synchronization value Nmsyca while the AT input torque Ti is larger than the target value Titgt during the inertia phase in the process of the shift-down operation of the stepped transmission section 20. Accordingly, as a result of the MG 2 speed control implemented by the control section 88, the AT input torque Ti is limited to or lower than the value to which it is reduced by the real input torque reducing section 96.When the accelerator operation amount θacc is increased in the process of the power-off downshift operation of the stepped transmission portion 20, it is desirable to quickly finish the downshift operation, thereby improving a control behavior upon the driver's request to accelerate the vehicle 10. However, the AT input torque Ti is controlled to coincide with the target value Titgt while the MG2 speed control and the AT input torque reset control are not implemented, so that the limitation or limitation of the increase of the target value Titgt to or below the predetermined upper limit value Ti 1 for reducing the risk of generation of the backlash elimination shock results in a delay of initiation of the inertia phase and deterioration of the control behavior upon the driver's request for acceleration of the vehicle 10 when the accelerator operation amount θacc is increased before the time of initiation of the inertia phase of the downshift operation. It is desirable to improve the control performance upon the driver's request to accelerate the vehicle 10 while enabling the reduction of the risk of generating the backlash elimination impact.The hybrid control section 84 further includes a real input torque increasing means in the form of a real input torque increasing section 98 for improving the control response to the driver's request to accelerate the vehicle 10 while enabling the reduction of the risk of generating the backlash elimination shock.The state determination section 94 is configured to determine whether the step-change transmission section 20 is in the process of a power-off downshift. This determination is made based on the hydraulic command control signals Sat. After the state determination section 94 determines that the step-change transmission section 20 is in the process of the power-off downshift, the state determination section 94 determines whether the accelerator pedal is further operated, i.e., whether the accelerator pedal operation amount θacc is increased before the time of initiation of the inertia phase of the downshift.When the state determination portion 94 determines that the accelerator operation amount θacc is increased before the time of initiation of the inertia phase of the power-off downshift of the stepped transmission portion 20, the real input torque increasing portion 98 implements input torque increasing control before the time of initiation of the inertia phase of the downshift to control the AT input torque Ti to be larger than the target value Titgt.When the vehicle 10 is changed from its non-driving state to its driving state in the process of the input torque increasing control, there is a risk of generation of the backlash elimination impact of the stepped transmission portion 20. In the input torque increasing control implemented by the real input torque increasing section 98, the step-shifting control section 82 applies the hydraulic command control signal Sat to the hydraulic control unit 56 to reduce the engagement torque Tcb of the release-side clutch device CB before increasing the engagement torque Tcb of the engagement-side clutch device CB in the process of the shift-down operation. That is, the step-shifting control portion 82 reduces the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB at an earlier time when the input torque increase control is implemented than when the input torque increase control is not implemented than when normal clutch-to-clutch shift controls of the engagement-side and release-side clutch devices CB are implemented. The above-mentioned "increase in the engagement torque Tcb of the engagement-side clutch device CB" is interpreted as an increase in the engagement torque Tcb of the engagement-side clutch device CB from zero or a small value near zero.When the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB is reduced by the step-shifting control portion 82 at the earlier time as described above, the state determination portion 94 determines that the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB has been reduced to or below a predetermined value at which the engagement torque Tcb of the release-side clutch device CB is zero or substantially zero.When the state determination portion 94 has determined that the accelerator operation amount θacc is increased before the time of initiation of the inertia phase of the power-off downshift of the stepped transmission portion 20 and the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB that is reduced earlier has been reduced to the predetermined value, the real input torque increasing portion 98 implements the input torque increase control.When an increase amount of the accelerator operation amount θacc is relatively small, failure or lack of improvement of the control behavior to the driver required acceleration of the vehicle 10 is not considered a serious problem. In this regard, the input torque increase control may be implemented only when the increase amount of the accelerator operation amount θacc is relatively large. The state determination section 94 is further configured to determine whether the accelerator operation amount θacc is increased by an amount not less than a predetermined value θacc 1. The real input torque increasing section 98 implements the input torque increasing control when the state determining section 94 determines that the increase amount of the accelerator pedal operation amount θacc is equal to or greater than the predetermined value θacc 1. This predetermined value θacc 1 is a threshold above which deterioration of the control behavior upon the driver's request to accelerate the vehicle 10 is considered to be a serious problem.When the working fluid has a low temperature THoil at which a hydraulic pressure control behavior is deteriorated in the process of shifting operations of the clutch devices CB, a balance between the engagement torque Tcb of the clutch device CB and the AT input torque Ti is lost and the control behavior of the shift-down operation of the stepped transmission portion 20 may be deteriorated. In this regard, it is desirable not to implement the input torque increase control when the temperature THoil of the working fluid is relatively low. In the present embodiment, the real input torque increasing portion 98 is configured to implement the input torque increasing control only when the working fluid temperature THoil is not lower than a predetermined value THoil 1. This predetermined value THoil1 is a lower limit value of the working fluid temperature THoil over which the hydraulic pressure control performance is considered satisfactory.FIG. 8 is the flowchart showing a main control operation of the electronic control device 80, namely, a control routine executed to improve the control behavior on the driver's vehicle acceleration request with an increase in the accelerator pedal operation amount θacc in the process of the power-off downshift operation of the stepped transmission portion 20 and, at the same time, reduce the risk of generation of the backlash elimination shock of the stepped transmission portion 20. This control routine is repeatedly performed during the driving of the vehicle 10. FIG. 9 is the timing chart showing an example of changes in the various parameters when the control routine shown in the flowchart of FIG. 8 is executed.The control routine of FIG. 8 is initiated with a step S10 corresponding to the function of the state determination section 94 to determine that the step-change transmission section 20 is in the process of a power-off downshift. If a negative determination is obtained in step S10, one cycle of execution of the control routine is terminated. If an affirmative determination is obtained in step S 10, the processing proceeds to step S 20, which also corresponds to the function of the state determination portion 94, to determine whether the accelerator pedal is operated before the initiation of the inertia phase in the process of downshifting the stepped transmission portion 20. When an affirmative determination is obtained in step S 20, the processing proceeds to step S 30 corresponding to the function of the step-shifting control portion 82 to reduce the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB at the earlier time, as described above. Step S 30 is followed by step S 40 also corresponding to the function of the state determination portion 94 to determine whether the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB has been reduced to the predetermined value. When an affirmative determination is obtained in step S 40, the processing proceeds to step S 50 corresponding to the function of the real input torque increasing portion 98 to implement the input torque increasing control for increasing the AT input torque Ti at a relatively high rate before the time of initiation of the inertia phase of the turn-off downshift. If a negative determination is obtained in step S40, the processing returns to step S30. On the other hand, when a negative determination is obtained in step S 20, the processing returns to step S 60 corresponding to the functions of the step-shifting control portion 82 and the hybrid control portion 84 to implement normal control of the power-off downshift operation of the step-shifting transmission portion 20.As shown in the timing chart of FIG. 9 showing the changes of the various parameters of the control routine of FIG. 8, when the accelerator pedal is operated in the process of the power-off downshift of the stepped transmission portion 20, the hydraulic command control signal Sat in the power-off state is generated at a time t 1, so that the stepped transmission portion 20 is downshifted from the (n+1)-th AT speed position to the n-th AT speed position. When the accelerator pedal is operated in the process of the power-off downshift, the target input torque value Titgt is increased at a relatively low rate as indicated by a mark "A" in FIG. 9 to reduce the risk of generation of the backlash elimination impact. A one-dot chain line represents the target input torque value Titgt in the present embodiment and a comparative example, while a two-dot chain line represents the target input torque value Titgt in the comparative example. Because the rate of increase of the target input torque value Titgt is relatively low, the initiation of the inertia phase of the shift-down operation is delayed as indicated by a broken line mark "B" in the comparative example, so that the control behavior on the driver's vehicle acceleration request is deteriorated. In the present embodiment of the invention represented by solid lines, on the other hand, the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB is reduced at an accelerator pedal operation in the process of the power-off downshift at an earlier time as indicated by a mark "C", and the input torque increase control is implemented so that the AT input torque Ti is controlled to be larger than the target value Titgt before the time of the initiation of the inertia phase as indicated by a mark "D", so that the inertia phase is initiated at an earlier time t2 than in the comparative example as indicated by a mark "E", thereby improving the control performance on the driver's vehicle acceleration request. The reduction of the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB at the earlier time causes the transmission torque Tat of the stepped transmission portion 20 to be considerably small or zero and the absolute value of the deceleration torque of the vehicle 10 is reduced upon operation of the accelerator pedal, so that the vehicle operator is less likely to feel unpleasant as a result of the earlier reduction of the command value of the engagement hydraulic pressure PRcb of the release-side clutch device CB.As described above, the present embodiment is configured such that, when the operation amount θacc of the accelerator pedal is increased before the initiation of the inertia phase in the process of the power-off downshift operation of the stepped transmission portion 20, the increase amount of the target value Titgt of the AT input torque Ti is restricted with respect to the increase amount of the driver required input torque value Tidem, so that the target value Titgt of the AT input torque Ti is kept not greater than the predetermined upper limit value Ti 1 until the input torque reset control is finished, so that the risk of the backlash elimination shock of the stepped transmission portion 20 after the completion of the downshift operation can be reduced. Further, upon an increase in the operation amount θacc of the accelerator pedal before the time of initiation of the inertia phase of the power-off downshift, the input torque increase control is implemented to control the input torque Ti of the stepped transmission portion 20 to be larger than the target value Titgt before the time of initiation of the inertia phase of the downshift. Accordingly, the electronic control device 80 enables the inertia phase of the shift-down operation to be initiated early even when the target value Titgt of the input torque Ti of the stepped transmission portion 20 is limited to or lower than the predetermined upper limit value Ti 1. Thus, the electronic control device 80 enables improvement of a control behavior upon the driver's request to accelerate the vehicle 10 with increase of the operation amount θacc of the accelerator pedal in the process of the power-off downshift operation of the stepped transmission portion 20 and simultaneously reduces the risk of generation of the backlash elimination shock with respect to the related-art control device.The present embodiment is further configured such that, upon implementation of the input torque increasing control by the real input torque increasing portion 98, the engagement torque Tcb of the release-side clutch device CB is reduced at the earlier time than when the engagement torque Tcb of the engagement-side clutch device CB is increased, so that the AT input torque Ti is increased while the transmission torque Tat of the stepped transmission portion 20 is relatively small or zero. Accordingly, the risk of generation of the backlash elimination impact of the stepped transmission portion 20 can be reduced even when the vehicle 10 is switched from its non-driving state to its driving state in the process of the input torque increase control.The present embodiment is further configured such that the target value Titgt of the input torque Ti is gradually changed toward the driver required input torque value Tidem after completion of the input torque reset control implemented by the input torque reset control portion 92, so that the driver's request to accelerate the vehicle 10 can be satisfied and at the same time the risk of generation of the backlash elimination shock can be reduced.The present embodiment is further configured such that the AT input torque Ti is reduced with the change in the MG 2 rotational speed Nm toward the post-shift synchronization value Nmsyca while the AT input torque Ti is larger than the target value Titgt during the inertia phase of the shift-down operation, so that the risk of generation of the backlash elimination shock of the stepped transmission portion 20 after completion of the shift-down operation can be further reduced.The embodiment is further configured such that the input torque increase control is implemented by the real input torque increasing section 98 when the operation amount θacc of the accelerator pedal is increased by the amount not less than the predetermined value θacc 1, so that it is possible to appropriately improve the control behavior upon the driver's request for acceleration of the vehicle 10 and, at the same time, to reduce the risk of generation of the backlash elimination shock when the driver has a comparatively high request degree for the vehicle acceleration. If the driver has a comparatively low requirement degree for the vehicle acceleration, the risk of generation of the backlash elimination impact can be further reduced.The present embodiment is further configured such that the input torque increase control is implemented only when the temperature THoil of the working fluid used to operate the hydraulically operated friction clutch devices CB is not lower than the predetermined value THoil 1. Namely, the input torque increasing control is not implemented at the relatively low temperature THoil of the working fluid at which the hydraulic control behavior of the clutch devices CB is low. Accordingly, it is possible to reduce the deterioration of controllability of the shift-down operation of the stepped transmission portion 20 due to a balance loss between the engagement torques Tcbs of the respective two friction clutch devices CB controlled to implement the shift-down operation and the AT input torque Ti.Although the preferred embodiment of the invention has been described in detail with reference to the drawings, it is to be understood that the present invention may be practiced otherwise.For example, the increase amount of the AT input torque Ti may be decreased with a decrease in the working fluid temperature THoil by the input torque increase control, that is, the AT input torque Ti may be brought closer to the target value Titgt with a decrease in the working fluid temperature THoil.In the illustrated embodiment, the mathematical equation (1) is the model equation for the shift control of the stepped transmission portion 20 in which the MG2 speed change rate dNm / dt is used as a value indicating the rotation state of the input rotational element of the stepped transmission portion 20, while the engine speed change rate dNe / dt is used as a value indicating the operation state of the engine 14. The rotational state of the input rotational member of the stepped transmission portion 20 and the operating state of the engine 14 may be represented by the rotational speed of the input rotational member and the operating rotational speed Ne of the engine 14, respectively. In this case, the shift control of the stepped transmission portion 20 for controlling the AT input torque Ti according to the mathematical model equation (1) based on the MG2 rotation speed Nm and the engine rotation speed Ne can be implemented by a known PI control in which control amounts of the MG2 rotation speed Nm and the engine rotation speed Ne are calculated based on a difference between target and real values of the MG2 rotation speed Nm and the engine rotation speed Ne.In the illustrated embodiment, the vehicle 10 is provided with the transmission device 40. However, the control apparatus according to the present invention is equally applicable to a parallel type hybrid vehicle provided with an engine, a motor generator operatively connected to the drive wheels in a power transmitting manner, and a step-change transmission forming part of a power transmission path between the engine and the drive wheels. Further, the control apparatus according to the present invention is applicable to a series type hybrid vehicle provided with: an engine; a power generating motor generator operated with the driving force of the engine; a vehicle drive motor generator operated by an electric power generated by the power generating motor generator and / or an electric power supplied from a battery; and a step transmission constituting a part of a power transmission path between the vehicle drive motor generator and driving wheels. Further, the present control apparatus is applicable to a vehicle provided with an engine functioning as a vehicle drive power source and a stepped transmission forming part of a power transmission path between the engine and drive wheels. Further, the present control apparatus is applicable to a vehicle provided with a motor generator functioning as a vehicle drive power source and a stepped transmission constituting a part of a power transmission path between the motor generator and drive wheels. In essence, the present control apparatus is applicable to a vehicle provided with a vehicle drive power source and a step-change transmission forming part of a power transmission path between the vehicle drive power source and drive wheels.In the illustrated embodiment, the vehicle 10 is provided with the electrically controlled transmission mechanism in the form of the continuously variable transmission portion 18 having the differential mechanism 32 which is the single pinion type planetary gear set. However, the continuously variable transmission portion 18 may be replaced with a transmission mechanism whose differential function is limited by controlling a clutch or brake connected to a rotational element of the differential mechanism 32. Further, the differential mechanism 32 may be a differential mechanism that is composed of a plurality of planetary gear sets connected to each other and that has four or more rotating elements. Alternatively, the differential mechanism 32 may be replaced with a differential gear device having a pinion rotated by the engine 14 and a pair of bevel gears engaged with the pinion, and the first motor generator MG 1 and the intermediate power transmitting member 30 are connected to the pinion and the bevel gears, respectively. Furthermore, the differential mechanism 32 may alternatively be replaced by a mechanism consisting of two or more planetary gear sets having interconnected rotational elements and operatively connected to the engine, motor generator, and vehicle drive wheels, respectively, in a power transmitting manner.In the illustrated embodiment, the planetary gear type step-change gear portion 20 is provided as the step-change gear that constitutes a part of the power transmission path between the drive power source and the drive wheels. However, the stepped transmission portion 20 may be replaced with any other type of stepped transmission, for example, a known DSG (Dual Clutch Transmission) which is a two-axis synchronous engaged parallel automatic transmission having two input shafts connected to respective clutch devices (clutches) to realize respective even and odd gear positions. In the DSG, one of a plurality of clutch devices or a clutch device for controlling a shift operation of the DSG corresponds to the clutch device connected to each of the two input shafts.In the illustrated embodiment, the ten total speed positions are selectively implemented for the four AT gear positions. However, the numbers of the total speed positions and the AT gear positions are not limited to those of the illustrated embodiment. The number of the total speed positions is preferably equal to or greater than that of the AT speed positions, more preferably greater than that of the AT speed positions. For example, the number of the total rotational speed positions is preferably twice as large as the number of the AT gear positions or more. The stepped transmission portion 20 is shifted from one of the AT gear positions to the other so that the rotational speed of the intermediate power transmitting member 30 and the operating rotational speed of the second motor generator MG2 connected to the intermediate power transmitting member 30 are maintained within predetermined ranges. On the other hand, the transmission device 40 is shifted from one of the total speed positions to another so that the engine speed Ne is maintained within a predetermined range. In view of this, the number of AT gear positions and the number of total speed positions are determined accordingly.Although the preferred embodiment and its modifications have been described above for exemplary purposes only, it is to be understood that the present invention may be practiced with various other changes and modifications not described that will be apparent to those skilled in the art.LIST OF REFERENCE CHARACTERS10 Vehicle (hybrid vehicle) 14 Engine (drive power source) 18 Electrically controlled continuously variable transmission portion (electrically controlled transmission mechanism) 20 Mechanically operated stepped transmission portion (stepped transmission; mechanically operated transmission mechanism) 28 Drive wheels 30 Intermediate power transmission element (input rotation element of the stepped transmission; output rotation element of the electrically controlled transmission mechanism) 32 Differential mechanism 80 Electronic control device (control device) 82 Stepped shift control portion (shift control portion) 88 Feedback portion 90 Target input torque setting portion 92 Input torque reset control portion 94 State determination portion 96 Real input torque reduction portion 98 Real input torque increase portion CB Clutch devices (friction clutch devices) MG 1 First motor generator MG 2 Second motor generator (drive power source; motor generator)

Claims

A control apparatus (80) for a vehicle (10) provided with a drive power source (14, MG2), drive wheels (28) and a step-change transmission (20) forming part of a power transmission path between the drive power source (14, MG2) and the drive wheels (28) and having a plurality of clutch devices (CB) selectively engaged to realize a selected one of a plurality of gear positions, the control apparatus (80) comprising: a control portion (88) configured to:, that implements feedback compensation of a target value (Titgt) of the input torque according to an operation amount (θacc) of an accelerator pedal by a driver of the vehicle during an inertia phase of a shift down operation of the step shift (20) such that a value (dNm / dt) representative of a rotation state of an input rotation element (30) of the step shift (20) coincides with a target value (dNmtgt) at which a rotation speed (Nm) of the input rotation element (30) changes toward a post-shift synchronization value (Nmsyca) to be converted after completion of the shift down operation; a state determination section (94) configured to determine whether the rotational speed of the input rotary element (30) is equal to the post-shift synchronization value (Nmsyca); an input torque reset control section (92) configured to implement an input torque reset control for changing the input torque (Ti) of the step-variable transmission (20) toward the target value (Titgt) when the state determination section (94) determines that the rotational speed of the input rotary element (30) is equal to the post-shift synchronization value (Nmsyca); a target input torque setting section (90) configured to be operated when the operation amount (θacc) of the accelerator pedal is in the process of the shift-down operation implemented in an off state of the vehicle (10), in which the accelerator pedal is in a non-operating state, the target input torque setting section (90) sets the target value (Titgt) of the input torque corresponding to the operation amount (θacc) of the accelerator pedal and limits an increase amount of the target value (Titgt) of the input torque with respect to an increase amount of a driver required input torque value (Tidem) represented by the operation amount (θacc) of the accelerator pedal so that the target value (Titgt) of the input torque is kept not greater than a predetermined upper limit value (Ti1) until the input torque reset control is finished; A real input torque increasing portion (98) configured to be operated when the operation amount of the accelerator pedal is increased before a time of initiating the inertia phase of the shift-down operation in the off state, wherein the real input torque increasing portion (98) implements input torque increasing control to control the input torque (Ti) of the step-variable transmission (20) to be larger than the target value (Titgt) before the time of initiating the inertia phase of the shift-down operation.The control apparatus (80) according to claim 1, further comprising a shift control section (82) configured to be operated when the input torque increase control is implemented by the real input torque increase section (98), wherein the shift control section (82) controls a torque capacity of a release-side clutch device of the plurality of clutch devices (CB) to be brought into a released state for implementing the shift-down operation and a torque capacity of an engagement-side clutch device of the clutch devices (CB) to be brought into an engaged state for implementing the shift-down operation, wherein the shift control section (82) reduces the torque capacity of the release-side clutch device at an earlier time than when the shift control section (82) increases the torque capacity of the engagement-side clutch device.The control apparatus (80) according to claim 1 or 2, wherein the target input torque setting section (90) gradually changes the target value (Titgt) of the input torque (Ti) toward the driver required input torque value (Tidem) after the input torque reset control converted by the input torque reset control section (92) is finished.The control apparatus (80) according to any one of claims 1 to 3, further comprising a real input torque reducing portion (96) configured to reduce the input torque (Ti) of the stepped transmission (20) with a change in the rotational speed (Nm) of the input rotational member (30) of the stepped transmission (20) toward the post-shift synchronization value (Nmsyca) while the input torque is larger than the target value (Titgt) during the inertia phase of the shift down operation.The control apparatus (80) according to any one of claims 1 to 4, wherein the real input torque increasing section (98) implements the input torque increasing control when the operation amount (θacc) of the accelerator pedal is increased by an amount not less than a predetermined value (θacc1).The control apparatus (80) according to any one of claims 1 to 5, wherein the plurality of clutch devices (CB) are hydraulically operated friction clutch devices, and the real input torque increasing portion (98) implements the input torque increasing control when a temperature (THoil) of a working fluid used for operating the hydraulically operated friction clutch devices is not lower than a predetermined value (THoil1).The control apparatus (80) according to any one of claims 1 to 6, wherein the vehicle is a hybrid vehicle (10) provided with: an engine (14) functioning as a drive power source; an electrically controlled transmission mechanism (18) having a differential mechanism (32) to which the engine is operatively connected in a power transmitting manner and a first motor generator (MG1) to which the differential mechanism is operatively connected in a power transmitting manner such that a differential state of the differential mechanism is controlled by controlling an operation state of the first motor generator (MG1); and a second motor generator (MG2) operatively connected to an output rotational element of the electrically controlled transmission mechanism (18) and also functioning as a drive power source, and wherein the step-variable transmission (20) is a mechanically operated transmission mechanism, which forms part of a power transmission path between the output rotational element of the electrically controlled transmission mechanism (18) and the drive wheels (28), wherein the control portion (88) is configured to control an output torque (Tg) of the first motor generator (MG1) and an output torque (Tm) of the second motor generator (MG2) during the inertia phase of a shift operation of the mechanically operated transmission mechanism based on an output torque (Te) of the engine (14) and a torque transmitted by the mechanically operated transmission mechanism so that a value (dNm / dt) representative of a rotational state of the input rotational element (30) of the mechanically operated transmission mechanism and a value (dNe / dt) representative of an operating state of the engine (14), When the rotational speed (Nm) of the input rotational element of the mechanically operated transmission mechanism has become equal to the post-shift synchronization value (Nmsyca), the input torque reset control section (92) implements the input torque reset control.

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