Electric oil pump control apparatus for vehicle, electric oil pump control method for vehicle, and shift apparatus

When the shift position is changed to the drive position, the amount of oil that is supplied to an automatic shift unit is increased by a larger amount as the standby hydraulic pressure is lower. Therefore, even if the standby hydraulic pressure is decreased, the required hydraulic pressure is more easily achieved when the shift position is changed to the drive position. Therefore, it is possible to decrease the standby hydraulic pressure without slowing down the response to the automatic shift unit to the hydraulic pressure and reducing the useful life of the automatic shift unit. Thus, the amount of electricity consumed by the electric oil pump is reduced. As a result, it is possible to enhance the fuel efficiency.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2007-085734 filed on Mar. 28, 2007 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to an electric oil pump control apparatus for a vehicle, which includes an electric oil pump and a application device that is driven by a hydraulic pressure supplied from the electric oil pump, and with which the response of the application device provided in a shift mechanism to the hydraulic pressure and the useful life of the application device are improved, the invention also relating to an electric oil pump control method.

2. Description of the Related Art

Usually, a vehicle is provided with a shift apparatus that is directly or indirectly connected to an engine and that changes the rotational speed of the engine in a stepwise manner or continuously. An example of such shift apparatus is a stepped automatic transmission. The automatic transmission is formed of multiple planetary gear units, and a desired gear is selected by selectively connecting rotational elements of these planetary gear units to each other. The rotational elements are connected to each other by application devices provided in the automatic transmission. The application devices are driven by a hydraulic pressure. The application devices are applied or released by controlling the hydraulic pressure in an appropriate manner.

The hydraulic pressure of the hydraulic fluid supplied from an oil pump is used as the original pressure, and the original pressure is regulated to a desired hydraulic pressure in a hydraulic pressure control circuit of the shift apparatus. Then, the regulated hydraulic pressure is supplied to these application devices. In many cases, an oil pump is provided in the shift apparatus, and driven in accordance with an operation of the engine.

In recent years, hybrid vehicles in which two types of drive power sources, that is, an engine and an electric motor are used in combination, have come on the market. Because both the engine and the electric motor are used, it is possible to utilize the advantages and make up for the disadvantages of each of the engine and the electric motor. With this structure, hybrid vehicles provide good drivability, that is, the hybrid vehicles are driven smoothly and respond quickly to a control. In addition, the hybrid vehicles consume considerably smaller amount of fuel and emit far less exhaust gases than conventionally powered vehicles. If the shift apparatus is provided in such hybrid vehicles, it may be possible to further enhance the drivability and fuel efficiency. In such hybrid vehicles, the engine efficiency is usually low when the vehicle starts moving, when the vehicle is traveling at a low speed and when the vehicle is traveling at a low torque. In such a case, the engine is stopped and the vehicle travels using the drive power produced by the electric motor.

If only a mechanical oil pump that is driven in accordance with an operation of the engine is provided in the above-described hybrid vehicle, the hydraulic pressure is not supplied when the vehicle travels using the drive power produced by the electric motor. This is because the mechanical oil pump is not driven due to a stop of the engine. Especially, in the hybrid vehicle in which the above-described shift apparatus is provided, an appropriate hydraulic pressure is not supplied to the application devices of the shift apparatus. Therefore, the drive power is not transmitted to drive wheels, which makes it impossible for the vehicle to keep traveling. In order to avoid such inconvenience, in the hybrid vehicle provided with the shift apparatus, an electric oil pump is provided in addition to the mechanical oil pump. When the engine is stopped, the electric oil pump is driven to supply a hydraulic pressure to the application devices of the shift apparatus.

The electric oil pump may be provided not only in the hybrid vehicles but also in other types of vehicles. For example, in a control apparatus for a vehicle described in Japanese Patent Application Publication No. 2000-356148 (JP-A-2000-356148), an electric motor (motor generator) is provided between an engine and a torque converter. When the vehicle is traveling using the power from the electric motor, a hydraulic pressure is supplied from the electric oil pump to the shift apparatus.

When the shift position is in a stop position, for example, Neutral, at which the drive power is not transmitted to drive wheels, the control apparatus for a vehicle described in JP-A-2000-356148 stops the engine to stop the mechanical oil pump and drives the electric oil pump to reliably achieve the hydraulic pressure that is supplied to the shift apparatus. Then, when it is predicted that the vehicle will be placed in a stopped state, the output from the electric oil pump is reduced to reduce the amount of electric power consumed to drive the electric oil pump.

However, when the control apparatus described in JP-A-2000-356148 predicts that the vehicle will be maintained in the stop state and therefore keeps low output from the electric oil pump, if the shift position is changed from the stop position to the cruise position, the hydraulic pressure that is supplied to the application device of the shift apparatus does not rise quickly, and slippage of the application device may occur. As a result, the response of the shift apparatus to the hydraulic pressure may be slow down and the useful life of the shift apparatus may be reduced.

SUMMARY OF THE INVENTION

The invention provides an electric oil pump control apparatus for a vehicle, which includes an electric oil pump and a shift mechanism that is driven by a hydraulic pressure supplied from the electric oil pump, and with which the response of the shift mechanism to the hydraulic pressure is improved and reduction in the useful life of the shift mechanism is suppressed. The invention also provides an electric oil pump control method which is applied to the electric oil pump control apparatus.

A first aspect of the invention relates to an electric oil pump control apparatus for a vehicle that includes: an application device; an electric oil pump that supplies a hydraulic pressure to the application device; and a switching device in which the shift position is selectively changed between a drive position for placing a vehicle in the driven state and a non-drive position for placing the vehicle in the non-driven state. The electric oil pump control apparatus includes: a standby hydraulic pressure setting unit that presets at least one of a rotational speed of the electric oil pump and a standby hydraulic pressure which is supplied to the application device when the vehicle is at a standstill; and an oil amount adjustment unit that adjusts the amount of oil which is supplied to the application device when it is predicted or determined that the shift position is changed between the non-drive position and the drive position in the switching device. The oil amount adjustment unit adjusts the amount of oil that is supplied to the application device based on the standby hydraulic pressure.

With the electric oil pump control apparatus according to the first aspect of the invention, the amount of oil that is supplied to the application device is adjusted based on the standby hydraulic pressure when the shift position is changed to the drive position. Thus, even when the standby hydraulic pressure is increased or decreased, the required hydraulic pressure is more easily achieved when the shift position is changed. Therefore, it is possible to increase or decrease the standby hydraulic pressure without reducing the useful life of the application device and slowing down the response of the application device to the hydraulic pressure.

In the first aspect of the invention, when it is predicted or determined that the shift position is changed from the non-drive position to the drive position in the switching device, the oil amount adjustment unit may increase the amount of oil that is supplied to the application device by a larger amount as the standby hydraulic pressure is lower.

Thus, the amount of oil that is supplied to the application device is increased by a larger amount as the standby hydraulic pressure is lower. Therefore, even if the standby hydraulic pressure is low, it is possible to reliably achieve the required hydraulic pressure when the shift position is changed to the drive position.

In the first aspect of the invention, the oil amount adjustment unit may increase at least one of the rotational speed of the electric oil pump and the duration of time the electric oil pump is rotated at an increased rotational speed.

Because at least one of the rotational speed of the electric oil pump and the duration of time the electric oil pump is rotated at an increased rotational speed is increased, it is possible to easily increase the amount of oil that is supplied to the application device.

In the first aspect of the invention, the standby hydraulic pressure setting unit may decrease at least one of the rotational speed of the electric oil pump and the standby hydraulic pressure when there is a low possibility that the shift position is changed from the non-drive position to the drive position in the switching device.

When there is a low possibility that the shift position is changed from the non-drive position to the drive position in the switching device, the standby hydraulic pressure setting unit decreases at least one of the rotational speed of the electric oil pump and the standby hydraulic pressure. Thus, the output from the electric oil pump is suppressed. As a result, it is possible to suppress the electric power consumption.

In the first aspect of the invention, the standby hydraulic pressure setting unit may set at least one of the rotational speed of the electric oil pump and the standby hydraulic pressure based on at least one of the duration of time the selected shift position is maintained at the non-drive position and whether the brake is applied.

At least one of the rotational speed of the electric oil pump and the standby hydraulic pressure is set based on at least one of the duration of time the selected shift position is maintained at the non-drive position and whether the brake is applied. Therefore, it is possible to relatively accurately reflect the drive's intention on the control.

In the first aspect of the invention, the application device may be included in a shift mechanism, and the application state of the application device may be controlled based on the shift position selected in the switching device.

Thus, an appropriate hydraulic pressure is supplied to the application device based on the shift position selected in the switching device and the application state of the application device is appropriately controlled. Therefore, it is possible to appropriately control the operating state of the shift mechanism.

A second aspect of the invention relates to an electric oil pump control method for a vehicle that includes: an application device; an electric oil pump that supplies a hydraulic pressure to the application device; and a switching device in which a shift position is changed between a drive position for placing a vehicle in a driven state and a non-drive position for placing the vehicle in a non-driven state. The electric oil pump control method includes: presetting a standby hydraulic pressure that is supplied to the application device when the vehicle is at a standstill; predicting or determining whether the shift position is changed between the non-drive position and the drive position in the switching device; adjusting the amount of oil that is supplied to the application device depending on the result of prediction or determination as to whether the shift position is changed between the non-drive position and the drive position in the switching device; and adjusting the amount of oil that is supplied to the application device based on the standby hydraulic pressure.

With the electric oil pump control method according to the second aspect of the invention, the amount of oil that is supplied to the application device is adjusted based on the standby hydraulic pressure when the shift position is changed to the drive position. Thus, even when the standby hydraulic pressure is increased or decreased, the required hydraulic pressure is more easily achieved when the shift position is changed. Therefore, it is possible to increase or decrease the standby hydraulic pressure without reducing the useful life of the application device and slowing down the response of the application device to the hydraulic pressure.

A third aspect of the invention relates to a shift apparatus for a vehicle. The shift apparatus includes: an application device that changes the shift mode; an electric oil pump that supplies a hydraulic pressure to the application device; a switching device in which a shift position is selectively changed between a drive position for placing a vehicle in a driven state and a non-drive position for placing the vehicle in a non-driven state; and a controller that presets a standby hydraulic pressure which is supplied to the application device when the vehicle is at a standstill and that adjusts an amount of oil which is supplied to the application device based on the standby hydraulic pressure when it is predicted or determined that the shift position is changed between the non-drive position and the drive position in the switching device.

With the shift apparatus according to the third aspect of the invention, the amount of oil that is supplied to the application device is adjusted based on the standby hydraulic pressure when the shift position is changed to the drive position. Thus, even when the standby hydraulic pressure is increased or decreased, the required hydraulic pressure is more easily achieved when the shift position is changed. Therefore, it is possible to increase or decrease the standby hydraulic pressure without reducing the useful life of the application device and slowing down the response of the application device to the hydraulic pressure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENT

FIG. 1is a view schematically showing a shift mechanism10that constitutes part of a drive system of a hybrid vehicle to which a control apparatus according to an example embodiment of the invention is applied. As shownFIG. 1, the shift mechanism10includes an input shaft14, a differential unit11, an automatic shift unit20, and an output shaft22, all of which are coaxially arranged in tandem inside a transmission case12(hereinafter, simply referred to as “case12”) which is a non-rotating member that is attached to a vehicle body. The input shaft14serves as an input rotating member. The differential unit11is either directly connected to the input shaft14or connected to the input shaft14via a pulsation absorbing damper (vibration damping device), not shown. The automatic shift unit20functions as a stepped transmission. The automatic shift unit20is arranged in a power transmission path between the differential unit11and a pair of drive wheels38(seeFIG. 6), and is connected to the differential unit11via a transmitting member (transmitting shaft)18. The output shaft22is an output rotating member that is connected to the automatic shift unit20. The shift mechanism10is used in, for example, a FR (front-engine, rear-drive) vehicle in which an engine is longitudinally disposed. The shift mechanism10is provided between the drive wheels38and an engine8that is an internal combustion engine, for example, a gasoline engine or a diesel engine, which serves as a drive power source that produces a drive power used to drive the vehicle. The engine8is either directly connected to the input shaft14or connected to the input shaft14via a pulsation absorbing damper, not shown. This shift mechanism10transmits the drive power from the engine8to the drive wheels38via, for example, a differential gear unit (final reduction device)36and a pair of axles, in this order, which constitute part of the power transmission path.

As described above, the engine8and the differential unit11are directly connected to each other in the shift mechanism10of this example embodiment. That is, the engine8is connected to the differential unit11without provision of a fluid transmission device such as a torque converter or a fluid coupling between the engine8and the differential unit11. Therefore, for example, when the engine8is connected to the differential unit11via the above-mentioned pulsation absorbing damper, it is regarded that the engine8is directly connected to the differential unit11. Because the configuration of the shift mechanism10is symmetric with respect to the axis thereof, the lower portion of the shift mechanism10is not shown inFIG. 1. InFIG. 6as well, the lower portion of the shift mechanism10is not shown.

The differential unit11includes a first electric motor M1, a power split mechanism16, and a second electric motor M2. The power split mechanism16is a differential mechanism which distributes the drive power output from the engine8to the first electric motor M1and the transmitting member18. The second electric motor M2is provided so as to rotate together with the transmitting member18. The second electric motor. M2may be provided at any portion in the power transmission path between the transmitting member18and the drive wheels38. The first electric motor M1and the second electric motor M2in this example embodiment are both so-called motor-generators that also function as generators. The first electric motor M1functions as at least a generator (is able to generate electricity) that generates a reaction force, and the second electric motor M2functions as at least a motor (electric motor) that outputs drive power. The second electric motor M2serves as a drive power source that produces the drive power used to drive the vehicle.

The power split mechanism16mainly includes a single-pinion first planetary gear unit24having a predetermined gear ratio ρ1of, for example, approximately 0.418, a switching clutch C0, and a switching brake B0. The first planetary gear unit24includes rotating elements, that is, a first sun gear S1, first pinions P1, a first carrier CA1which supports the first pinions P1in such a manner that the first pinions are allowed to rotate about their axes and turn around the first sun gear S1, and a first ring gear R1that is in mesh with the first sun gear S1via the first pinions P1. When the number of teeth on the first sun gear S1is ZS1and the number of teeth on the first ring gear R1is ZR1, the gear ratio ρ1is expressed as ZS1/ZR1.

In the power split mechanism16, the first carrier CA1is connected to the engine8via the input shaft14, the first sun gear S1is connected to the first electric motor M1, and the first ring gear R1is connected to the transmitting member18. The switching brake B0is provided between the first sun gear S1and the case12, and the switching clutch C0is provided between the first sun gear S1and the first carrier CA1. Releasing both the switching clutch C0and the switching brake B0enables the three rotating elements of the first planetary gear unit24, that is, the first sun gear S1, the first carrier CA1, and the first ring gear R1to rotate relative to each other, thus placing the power split mechanism16in the differential mode in which the power split mechanism16performs differential operation. Therefore, the drive power output from the engine8is distributed to the first electric motor M1and the transmitting member18. Part of the drive power output from the engine8, which is distributed to the first electric motor M1, is used to run the first electric motor M1to generate electricity. The generated electricity is stored, or used to run the second electric motor M2. Accordingly, the differential unit11(power split mechanism16) functions as an electric differential device. For example, the differential unit11may be placed in the so-called continuously variable shift mode (electric CVT mode) and the rotational speed of the transmitting member18is continuously changed even when the engine8is operating at a constant speed. When the power split mechanism16is placed in the differential mode, the differential unit11is also placed in the differential mode. Accordingly, the differential unit11is placed in the continuously variable shift mode in which the differential unit11functions as an electric continuously variable transmission of which the gear ratio γ0(rotational speed of the input shaft14/rotational speed of the transmitting member18) is continuously changed within a gear ratio range from a minimum value γ0min to a maximum value γ0max. In this way, the ratio between the rotational speed of the input shaft14that is connected to the engine8and the rotational speed of the transmitting member18that serves as an output shaft is controlled by the first electric motor M1and the second electric motor M2.

When the switching clutch C0or the switching brake B0is applied, the power split mechanism16is placed in the non-differential mode (locked mode) in which the power split mechanism16cannot perform the differential operation. More specific description will be provided below. When the switching clutch C0is applied and therefore the first sun gear S1and the first carrier CA1are connected to each other, the power split mechanism16is placed in the locked mode in which the three rotating elements of the planetary gear unit24, that is, the first sun gear S1, the first carrier CA1, and the first ring gear R1are rotated together, in other words, the power split mechanism16is placed in the non-differential mode in which the power split mechanism16cannot perform the differential operation. As a result, the differential unit11is also placed in the non-differential mode. Also, the rotational speed of the engine8matches the rotational speed of the transmitting member18. Therefore, the differential unit11(power split mechanism16) is placed in the fixed shift mode, that is, the stepped shift mode, in which the differential unit11functions as a transmission of which the gear ratio γ0is fixed at 1. When the switching brake B0is applied instead of the switching clutch C0and therefore the first sun gear S1is locked to the case12, the power split mechanism16is placed in the locked mode in which the first sun gear S1is not allowed to rotate, in other words, the power split mechanism16is placed in the non-differential mode in which the power split mechanism16cannot perform the differential operation. As a result, the differential unit11is also placed in the non-differential mode. The first ring gear R1rotates faster than the first carrier CA1. Therefore, the power split mechanism16functions as a speed increasing mechanism, and the differential unit11(power split mechanism16) is placed in the fixed shift mode, that is, the stepped shift mode, in which the differential unit11functions as a speed increasing transmission of which the gear ratio γ0is fixed at a value less than 1, for example, approximately 0.7.

As described above, the switching clutch C0and the switching brake B0in this example embodiment function as differential mode switching devices that selectively switch the shift mode of the differential unit11(power split mechanism16) between the differential mode, i.e., the unlocked mode, and the non-differential mode, i.e., the locked mode. More specifically, the switching clutch C0and the switching brake B0function as differential mode switching devices that selectively switch the shift mode of the differential unit11(power split mechanism16) between i) the differential mode in which the differential unit11(power split mechanism16) functions as an electric differential device, for example, the continuously variable shift mode in which the differential unit11(power split mechanism16) functions as an electric continuously variable transmission of which the gear ratio is changed continuously, and ii) the shift mode in which the differential unit11(power split mechanism16) does not perform the electric continuously variable shift operation, for example, the locked mode in which the differential unit11(power split mechanism16) does not function as a continuously variable transmission and the gear ratio is fixed at a predetermined value, namely, the fixed shift mode (non-differential mode) in which the differential unit11(power split mechanism16) functions as a single-speed transmission having one gear ratio or a multi-speed transmission having multiple gear ratios, which cannot perform the electric continuously variable shift operation.

The automatic shift unit20constitutes part of the power transmission path from the differential unit11to the drive wheels38, and includes a single-pinion second planetary gear unit26, a single-pinion third planetary gear unit28, and a single-pinion fourth planetary gear unit30. The second planetary gear unit26includes a second sun gear S2, second pinions P2, a second carrier CA2which supports the second pinions P2in such a manner that the second pinions are allowed to rotate about their axes and turn around the second sun gear S2, and a second ring gear R2that is in mesh with the second sun gear S2via the second pinions P2. The second planetary gear unit26has a predetermined gear ratio ρ2of, for example, approximately 0.562. The third planetary gear unit28includes a third sun gear S3, third pinions P3, a third carrier CA3which supports the third pinions P3in such a manner that the third pinions P3are allowed to rotate about their axes and turn around the third sun gear S3, and a third ring gear R3that is in mesh with the third sun gear S3via the third pinions P3. The third planetary gear unit28has a predetermined gear ratio ρ3of, for example, approximately 0.425. The fourth planetary gear unit30includes a fourth sun gear S4, fourth pinions P4, a fourth carrier CA4which supports the fourth pinions P4in such a manner that the fourth pinions P4are allowed to rotate about their axes and turn around the fourth sun gear S4, and a fourth ring gear R4that is in mesh with the fourth sun gear S4via the fourth pinions P4. The fourth planetary gear unit30has a predetermined gear ratio ρ4of, for example, approximately 0.424. When the number of teeth on the second sun gear S2is ZS2, the number of the teeth on the second ring gear R2is ZR2, the number of teeth on the third sun gear S3is ZS3, the number of teeth on the third ring gear R3is ZR3, the number of teeth on the fourth sun gear S4is ZS4, and the number of teeth on the fourth ring gear R4is ZR4, the gear ratio ρ2is expressed as ZS2/ZR2, the gear ratio ρ3is expressed as ZS3ZR3, and the gear ratio ρ4is expressed as “ZS4/ZR4”.

In the automatic shift unit20, the second sun gear S2and the third sun gear S3are connected to each other, and selectively connected to the transmitting member18via the second clutch C2. Also the second sun gear S2and the third sun gear S3are selectively connected to the case12via the first brake B1. The second carrier CA2is selectively connected to the case12via the second brake B2. The fourth ring gear R4is selectively connected to the case12via the third brake B3. The second ring gear R2, the third carrier CA3, and the fourth carrier CA4are connected to each other, and selectively connected to the output shaft22. The third ring gear R3and the fourth sun gear S4are connected to each other, and selectively connected to the transmitting member18via the first clutch C1. In this way, the automatic shift unit20and the transmitting member18are connected to each other via one of the first clutch C1and the second clutch C2which are used to select the gear of the automatic shift unit20. In other words, the first clutch C1and the second clutch C2function as application devices that change the state of the power transmission path which extends between the transmitting member18and the automatic shift unit20, i.e., which extends between the differential unit11(transmitting member18) and the drive wheels38. The state of the power transmission path is changed between the power transmittable state in which the drive power is allowed to be transmitted along that power transmission path and the power transmission-interrupted state in which transmission of the drive power along that power transmission path is interrupted. That is, applying at least one of the first clutch C1and the second clutch C2places the power transmission path in the power transmittable state. Conversely, releasing both the first clutch C1and the second clutch C2places the power transmission path in the power transmission-interrupted state.

The switching clutch C0, the first clutch C1, the second clutch C2, the switching brake B0, the first brake B1, the second brake B2, and the third brake B3are hydraulic friction application devices (which may be regarded as application devices according to the invention) that are used in vehicle stepped automatic transmissions. The clutches may be wet multiple-disc clutches in which a plurality of stacked friction plates are pressed together by a hydraulic actuator, and the brakes may be band brakes in which one end of one or two bands that are wound around the outer peripheral surface of a rotating drum is pulled tight by a hydraulic actuator. Each hydraulic friction application device selectively connects members, located on both sides of the hydraulic friction application device, to each other.

In the shift mechanism10structured as described above, gear is selected from among forward gears from first gear through fifth gear, reverse gear, and neutral. The desired gear is selected by selectively applying the switching clutch C0, the first dutch C1, the second clutch C2, the switching brake B0, the first brake B1, the second brake B2, and the third brake B3in the combination shown in the operation chart inFIG. 2. Thus, the gear ratio γ(=rotational speed NINof the input shaft/rotational speed NOUTof the output shaft) at each gear is achieved. The ratios between the gear ratios γ of the adjacent gears are substantially equal to each other. In this example embodiment, the power split mechanism16is provided with the differential mode switching devices (C0, B0), i.e., the switching clutch C0and the switching brake B0. The power split mechanism16may be placed in the continuously variable shift mode in which the power split mechanism16functions as a continuously variable transmission. Alternatively, the power split mechanism16may be placed in the fixed shift mode in which the power split mechanism16functions as a transmission having a fixed gear ratio, by applying one of the switching clutch C0and the switching brake B0. Accordingly, the shift mechanism10may be placed in the stepped shift mode in which the shift mechanism10operates as a stepped transmission using the automatic shift unit20and the differential unit11that is placed in the fixed shift mode by applying one of the differential mode switching devices (C0, B0). Alternatively, the shift mechanism10may be placed in the continuously variable shift mode in which the shift mechanism10operates as an electric continuously variable transmission using the automatic shift unit20and the differential unit11that is placed in the continuously variable shift mode by keeping both of the differential mode switching devices (C0, B0) released. In other words, the shift mechanism10is placed in the stepped shift mode by applying one of the differential mode switching devices (C0, B0), and placed in the continuously variable shift mode by keeping both of the differential mode switching devices (C0, B0) released. The differential unit11may also be regarded as a transmission that is switched between the stepped shift mode and the continuously variable shift mode.

For example, when the shift mechanism10functions as a stepped transmission, one of the gears described below is selected as shown in the operation chart inFIG. 2. First gear that has the highest gear ratio γ1, for example, approximately 3.357, is selected by applying the switching clutch C0, the first clutch C1, and the third brake B3. Second gear that has a gear ratio γ2lower than that of first gear, for example, approximately 2.180, is selected by applying the switching clutch C0, the first clutch C1, and the second brake B2. Third gear that has a gear ratio γ3lower than that of second gear, for example, approximately 1.424, is selected by applying the switching clutch C0, the first clutch C1, and the first brake B1. Fourth gear that has a gear ratio γ4lower than that of third gear, for example, approximately 1.000, is selected by applying the switching clutch C0, the first clutch C1, and the second clutch C2. Fifth gear that has a gear ratio γ5lower than that of fourth gear, for example, approximately 0.705, is selected by applying the first clutch C1, the second clutch C2, and the switching brake B0. Reverse gear that has a gear ratio γR between the gear ratio of first gear and the gear ratio of second gear, for example, approximately 3.209, is selected by applying the second clutch C2and the third brake B3. When the automatic shift unit20is placed in Neutral, all of the clutches and brakes are released.

However, when the shift mechanism10functions as a continuously variable transmission, both the switching clutch C0and the switching brake B0are released as shown in the operation chart inFIG. 2. Thus, when the differential unit11functions as a continuously variable transmission and the automatic shift unit20, which is arranged in tandem with the differential unit11, functions as a stepped transmission, the rotational speed of the transmitting member18, that is, the rotational speed that is input to the automatic shift unit20, which is at one of first gear, second gear, third gear, and fourth gear, is continuously changed so that gear ratio of each gear is allowed to change continuously. Accordingly, the gears are changed while the gear ratio is continuously changed. As a result, the total gear ratio γT, which is achieved by the entire shift mechanism10, is continuously changed. The ratio of the gear ratio at a gear to a gear ratio at an adjacent higher gear (i.e., step) is shown in the section “STEP” inFIG. 2. As shown in the section “TOTAL” inFIG. 2, the ratio of the gear ratio at first gear to the gear ratio at the fifth gear is 4.76.

FIG. 3is a collinear diagram that shows, using straight lines, the correlative relationships among the rotational speeds of the various rotating elements of the shift mechanism10. The connection states of the rotating elements vary depending on the selected gear. The shift mechanism10includes the differential unit11that functions as a continuously variable transmission and the automatic shift unit20that functions as a stepped transmission. The collinear diagram inFIG. 3is a two-dimension coordinate system in which the abscissa axis represents the relationship among the gear ratios ρ of the planetary gear units24,26,28, and30, and ordinate axis represents the relative rotational speeds. Among three horizontal lines, the lower horizontal line X1represents a rotational speed of zero, the upper horizontal line X2represents a rotational speed of 1.0, i.e., the rotational speed NEof the engine8that is connected to the input shaft14, and the horizontal line XG represents the rotational speed of the transmitting member18.

Also, the three vertical lines Y1, Y2, and Y3which correspond to the three elements of the power split mechanism16that forms the differential unit11represent, in order from left to right, the relative rotational speeds of the first sun gear S1that is regarded as a second rotating element (second element) RE2, the first carrier CA1that is regarded as a first rotating element (first element) RE1, and the first ring gear R1that is regarded as a third rotating element (third element) RE3. The interval between the vertical lines Y1and Y2, and the interval between the vertical lines Y2and Y3are determined based on the gear ratio ρ1of the first planetary gear unit24. Further, the five vertical lines Y4, Y5, Y6, Y7, and Y8for the automatic shift unit20represent, in order from left to right, the relative rotational speeds of the second sun gear S2and the third sun gear S3which are connected to each other and which are regarded as a fourth rotating element (fourth element) RE4, the second carrier CA2which is regarded as a fifth rotating element (fifth element) RE5, the fourth ring gear R4which is regarded as a sixth rotating element (sixth element) RE6, the second ring gear R2, the third carrier CA3, and the fourth carrier CA4which are connected to each other and which are regarded as a seventh rotating element (seventh element) RE7, and the third ring gear R3and the fourth sun gear S4which are connected to each other and which are regarded as an eighth rotating member (eighth element) RE8. The interval between the vertical lines Y4and Y5, the interval between the vertical lines Y5and Y6, the interval between the vertical lines Y6and Y7, and the interval between the vertical lines Y7and Y8are determined based on the gear ratio ρ2of the second planetary gear unit26, the gear ratio ρ3of the third planetary gear unit28, and the gear ratio ρ4of the fourth planetary gear unit30. In the relationships among the intervals between the vertical lines in the collinear diagram, when the interval between the vertical line corresponding to the sun gear and the vertical line corresponding to the carrier is expressed by “1”, the interval between the vertical line corresponding to the carrier and the vertical line corresponding to the ring gear is expressed by the gear ratio ρ of the planetary gear unit. That is, in the coordinate system for the differential unit11, the interval between the vertical lines Y1and Y2is set to an interval corresponding to 1, and the interval between vertical lines Y2and Y3is set to an interval corresponding to the gear ratio ρ1. Similarly, in the coordinate system for the automatic shift unit20, the interval between the vertical line corresponding to the sun gear and the vertical line corresponding to the carrier is set to an interval corresponding to 1, and the interval between the vertical line corresponding to the carrier and the vertical line corresponding to the ring gear is set to an interval corresponding to the gear ratio ρ, at each of the second, third, and fourth planetary gear units26,28, and30.

As illustrated in the collinear diagram inFIG. 3, the shift mechanism10in this example embodiment is structured so that the power split mechanism16(differential unit11) transmits the rotation of the input shaft14to the automatic shift unit (stepped transmission)20via the transmitting member18when the first rotating element RE1(first carrier CA1) of the first planetary gear unit24is connected to the engine8via the input shaft14and is selectively connected to the second rotating element RE2(first sun gear S1) via the switching clutch C0, the second rotating element RE2is connected to the first electric motor M1and is selectively connected to the case12via the switching brake. B0, and the third rotating element RE3(first ring gear R1) is connected to the transmitting member18and the second electric motor M2. The relationship between the rotational speed of the first sun gear S1and the rotational speed of the first ring gear R1at this time is shown by the sloped straight line L0that passes through the point of intersection of Y2and X2.

When the switching clutch C0and the switching brake130are both released, the power split mechanism16is placed in the continuously variable shift mode (differential mode). In this case, when the rotational speed of the first sun gear S1, represented by the point of intersection of the straight line L0and the vertical line Y1, is increased or decreased by controlling the rotational speed of the first electric motor M1, if the rotational speed of the first ring gear R1, which depends on the vehicle speed V, is substantially constant, the rotational speed of the first carrier CA1represented by the point of intersection of the straight line L0and the vertical line Y2is increased or decreased. When the first sun gear S1and the first carrier CA1are connected to each other by applying the switching clutch C0, the power split mechanism16is placed in the non-differential mode in which the three rotating elements RE1, RE2, and RE3rotate together. Therefore, the straight line L0matches the horizontal line X2, and the transmitting member18rotates at the same speed as the engine speed NE. Alternatively, when the rotation of the first sun gear S1is stopped by applying the switching brake B0, the power split mechanism16is placed in the non-differential mode in which the power split mechanism16functions as a speed increasing mechanism. Therefore, the straight line L0is brought into the state shown inFIG. 3, and the rotational speed of the first ring gear R1represented by the point of intersection of the straight line L0and the vertical line Y3, i.e., the rotational speed of the transmitting member18, is input in the automatic shift unit20. At this time, the rotational speed of the transmitting member18is higher than the engine speed NE.

In the automatic shift unit20, the fourth rotating element RE4is selectively connected to the transmitting member18via the second clutch C2, and selectively connected to the case12via the first brake B1. The fifth rotating element RE5is selectively connected to the case12via the second brake B2. The sixth rotating element RE6is selectively connected to the case12via the third brake B3. The seventh rotating element RE7is connected to the output shaft22. The eighth rotating element RE8is selectively connected to the transmitting member18via the first clutch C1.

When the switching clutch C0, the first clutch C1and the third brake B3are applied, first gear is selected. As illustrated inFIG. 3, in the coordinate system for the automatic shift unit20, the rotational speed of the output shaft22in first gear is shown at the point of intersection of i) the sloped straight line L1that is defined by application of both the first clutch C1and the third brake B3and that passes through both the point of intersection of the horizontal line X2and the vertical line Y8which represents the rotational speed of the eighth rotating element RE8and the point of intersection of the horizontal line X1and the vertical line Y6which represents the rotational speed of the sixth rotating element RE6, and ii) the vertical line Y7that represents the rotational speed of the seventh rotating element RE7which is connected to the output shaft22. When the switching clutch C0, the first clutch C1and the second brake B2are applied, second gear is selected. The rotational speed of the output shaft22in second gear is shown at the point of intersection of the sloped straight line L2, which is defined by application of both the first clutch C1and the second brake B2, and the vertical line Y7that represents the rotational speed of the seventh rotating element RE7which is connected to the output shaft22. When the switching clutch C0, the first clutch C1and the first brake B1are applied, third gear is selected. The rotational speed of the output shaft22in third gear is shown at the point of intersection of the sloped straight line L3, which is defined by application of both the first clutch C1and the first brake B1, and the vertical line Y7that represents the rotational speed of the seventh rotating element RE7which is connected to the output shaft22. When the switching clutch C0, the first clutch C1and the second clutch C2are applied, fourth gear is selected. The rotational speed of the output shaft22in fourth gear is shown at the point of intersection of the horizontal straight line L4, which is defined by application of both the first clutch C1and the second clutch C2, and the vertical line Y7that represents the rotational speed of the seventh rotating element RE7which is connected to the output shaft22. When each of first-gear, second gear, third gear, and fourth gear is selected, the switching clutch C0is applied. Therefore, the rotation having the same speed as the engine speed NEis transmitted from the differential unit11, i.e., the power split mechanism16to the eighth rotating element RE8. However, if the switching brake B0is applied instead of the switching clutch C0, the rotation having a speed higher than the engine speed NEis transmitted from the differential unit11to the eighth rotating element RE8. Therefore, the rotational speed of the output shaft22in fifth gear is shown at the point of intersection of the horizontal straight line L5, which is defined by application of all the first clutch C1, the second clutch C2, and the switching brake B0, and the vertical line Y7that represents the rotational speed of the seventh rotating element RE7which is connected to the output shaft22.

FIG. 4shows examples of signals input in (received by) and output from an electronic control unit40that controls the shift mechanism10in this example embodiment. The electronic control unit40includes a so-called microcomputer that has a CPU, a ROM, a RAM, an input interface, an output interfaces, etc. The electronic control unit40executes drive controls such as shift control over the automatic shift unit20and hybrid drive control related to the engine8and the first and second electric motors M1and M2, by processing the signals according to programs prestored in the ROM while using the temporary storage function of the RAM.

Various signals are transmitted to the electronic control unit40from various sensors and switches shown inFIG. 4. These signals include a signal indicating an engine coolant temperature TEMPW, a signal indicating a shift position PSH, a signal indicating an engine speed NEwhich is the rotational speed of the engine8, a signal indicating a gear ratio combination setting value, a signal indicating a command to select the M-mode (manual shift running mode), a signal indicating operation of an air-conditioner, a signal indicating a vehicle speed V that corresponds to the rotational speed NOUTof the output shaft22, an AT fluid temperature signal indicating a temperature of the oil in the automatic shift unit20, a signal indicating operation of an emergency brake, a signal indicating operation of a footbrake, a catalyst temperature signal indicating a catalyst temperature, and an accelerator depression amount signal indicating an accelerator depression amount ACCwhich corresponds to the amount of drive power required by a driver, a cam angle signal, a snow mode setting signal indicating a snow mode setting, an acceleration signal indicating a longitudinal acceleration of the vehicle, an auto-cruise signal indicating auto-cruise running, a vehicle weight signal indicating a vehicle weight, wheel speed signals indicating wheel speeds, a signal indicating whether a stepped shift mode selection switch, which is used to place the differential unit11(power split mechanism16) in the stepped shift mode (locked mode) to have the shift mechanism10function as a stepped transmission, has been operated, a signal indicating whether a continuously variable shift mode selection switch, which is used to place the differential unit11(power split mechanism16) in the continuously variable shift mode (differential mode) to have the shift mechanism10function as a continuously variable transmission, has been operated, a signal indicating a rotational speed NM1of the first electric motor M1(hereinafter, simply referred to as “first electric motor rotational speed NM1”), a signal indicating a rotational speed NM2of the second electric motor M2(hereinafter, simply referred to as “second electric motor rotational speed NM2”), and a signal indicating an air-fuel ratio A/F in the engine8.

The electronic control unit40transmits various control signals to an engine output control apparatus43(seeFIG. 5) to control the drive power output from the engine8. These control signals include a drive signal provided to a throttle actuator97that controls the opening amount θTHof an electronically-controlled throttle valve96arranged in an intake pipe95of the engine8, a fuel supply amount signal based on which the amount of fuel supplied into the cylinders of the engine8from a fuel injection device98is controlled, an ignition signal that indicates the ignition timing at which the air-fuel mixture is ignited by an ignition device in the engine8, and a boost pressure adjusting signal based on which the boost pressure is adjusted, an electric air-conditioner drive signal based on which an electric air-conditioner is operated, command signals based on which the electric motors M1and M2are operated, a shift position (operating position) indication signal based on which a shift range indicator is operated, a gear ratio indication signal based on which the gear ratio is indicated, a snow mode indication signal based on which the fact that the vehicle is being operated in the snow mode is indicated, an ABS activation signal based on which an ABS actuator that prevents the wheels from slipping when brakes are applied is actuated, an M-mode indication signal which indicates that the M-mode has been selected, valve command signals based on which electromagnetically-controlled valves in a hydraulic pressure control circuit42(seeFIG. 5) are actuated to control hydraulic actuators for the hydraulic friction application devices in the differential unit11and the automatic shift unit20, a drive command signal based on which a mechanical oil pump44which is a hydraulic pressure source for the hydraulic pressure control circuit42and an electric oil pump46are operated, a signal based on which an electric heater is driven, and a signal that is provided to a computer used to execute a cruise control.

FIG. 5shows an example of a shift operation device48that serves as a switching device that is used to manually select a shift position from among multiple shift positions PSHThis shift operation device48is arranged, for example, at the side of the driver's seat, and is provided with a shift lever49that is operated to select a desired shift position from among multiple shift positions PSH. The shift operation device48in this example embodiment may be regarded as a switching device according to the invention.

The shift lever49is manually operated to a desired position from among the following positions. These positions include the park position “Park”, the reverse position “Reverse”, the neutral position “Neutral”, the automatic shifting forward running position “Drive”, and manual shifting forward running position “Manual”. When the shift lever49is in Park, the neutral state, in which the power transmission path in the automatic transmission of the shift mechanism10is interrupted, is achieved, and the output shaft22of the automatic shift unit20is locked. When the shift lever49is in Reverse, the vehicle is allowed to go in reverse. When the shift lever49is in Neutral, the shift mechanism10in the neutral state in which the power transmission path therein is interrupted. When the shift lever49is in Drive, the automatic shift mode, in which the automatic shift control is executed, is achieved. In the automatic shift control, the total gear ratio γT is changed within a certain range. The total gear ratio γT is determined based on the gear ratio of the differential unit11and the gear ratio of the automatic shift unit20at each gear. The gear ratio of the differential unit11is continuously changed in a certain range. The gear of the automatic shift unit20is selected from among first gear to fifth gear by the automatic shift control. When the shift lever49is in Manual, the manual shift mode (manual mode) is selected to set so-called shift ranges by restricting the use of the high gear(s) of the automatic shift unit20that is (are) used in the automatic shift control.

When the shift lever49is manually shifted to the selected shift position PSHfrom among the above-described positions, for example, the state of the hydraulic pressure control circuit42is electrically switched to select one of Reverse, Neutral and Drive shown in the operation chart inFIG. 2.

Among the positions Park to Manual, each of the positions Park and Neutral is a non-running position that is selected to stop the vehicle from running. When the shift lever49is in Park or Neutral, both of the first clutch C1and the second clutch C2are released, as shown in the operation chart inFIG. 2. That is, each of Park and Neutral is a non-drive position. When the shift lever49is in Park or Neutral, the power transmission path in the automatic shift unit20is placed in the power-transmission interrupted state by releasing the first clutch C1and the second clutch C2so that the transmission of the power through the power transmission path is interrupted and therefore the vehicle is not allowed to run. Each of Reverse Drive, and Manual is a running position that is selected to cause the vehicle to run. When the shift lever49is in Reverse, Drive, or Manual, at least one of the first clutch C1and the second clutch C2is applied as shown in the operation chart inFIG. 2. That is, each of Reverse, Drive and Manual is a drive position. When the shift lever49is in Reverse, Drive or Manual, the power transmission path in the automatic shift unit20is placed in the power-transmission permitted state by applying the first clutch C1and/or the second clutch C2so that the transmission of power through the power transmission path is permitted and the vehicle is allowed to run.

More specifically, when the shift lever49is manually shifted from Park or Neutral to Reverse, the state of the power transmission path in the automatic shift unit20is switched from the power-transmission interrupted state to the power-transmission permitted state by applying the second clutch C2. When the shift lever49is manually shifted from Neutral to Drive, the state of the power transmission path in the automatic shift unit20is switched from the power-transmission interrupted state to the power-transmission permitted state by applying at least the first clutch C1. When the shift lever49is manually shifted from Reverse to Park or Neutral, the state of the power transmission path in the automatic shift unit20is switched from the power-transmission permitted state to the power-transmission interrupted state by releasing the second clutch C2. When the shift lever49is manually shifted from Drive to Neutral, the state of the power transmission path in the automatic shift unit20is switched from the power-transmission permitted state to the power-transmission interrupted state by releasing the first clutch C1and the second clutch C2. Note that, each of Neutral and Park in this example embodiment may be regarded as a non-drive position according to the invention, and each of Drive, Reverse and Manual may be regarded as a drive position according to the invention. The term “positions” means not only gears and shift positions but also shift ranges such as Drive and Reverse.

FIG. 6is a functional block diagram illustrating the main part of the control operation executed by the electronic control unit40. As shown inFIG. 6, a stepped shift control unit54functions as a shift control unit that changes gears of the automatic shift unit20. For example, the stepped shift control unit54determines whether the gears of the automatic shift unit20should be changed, based on the vehicle condition indicated by the vehicle speed V and the required torque Tour that should be output from the automatic shift unit20, using the relationships indicated by solid lines and alternate long and short dash lines (shift diagram, shift map) inFIG. 7prestored in a storage unit56. That is, the stepped shift control unit54determines the gear to which the automatic shift unit20should be shifted, based on the vehicle condition, using the shift diagram. Then, the stepped shift control unit54executes an automatic shift control so that the automatic shift unit20is shifted to the determined gear. At this time, the stepped shift control unit54provides a command to a hydraulic pressure control circuit70to apply and/or release the hydraulic frictional application devices other than the switching clutch C0and the switching brake B0so that the automatic shift unit20is shifted to the determined gear according to, for example, the operation chart inFIG. 2.

When the shift mechanism10is in the continuously variable shift mode, that is, when the differential unit11is in the differential mode, a hybrid control unit52operates the engine8efficiently, and controls the gear ratio γ0of the differential unit11that functions as an electric continuously variable transmission, by optimizing the ratio between the drive power supplied from the engine8and the drive power supplied from the second electric motor M2, and optimizing the reaction force borne by the first electric motor M1while the first electric motor M1generates electricity. For example, the hybrid control unit52calculates the target (required) drive power used to drive the vehicle based on the accelerator-pedal operation amount Acc, which indicates the amount of output required by the driver, and the vehicle speed V; calculates the total target drive power based on the target drive power used to drive the vehicle and the required value for charging an electricity storage device; calculates the target drive power output from the engine so that the total target drive power is output from the engine, taking into account a transfer loss, loads placed on auxiliary machines, art assist torque supplied from the second electric motor M2, and the like; and controls the engine speed NEand the engine torque TEof the engine8to obtain the target drive power, and controls the amount of electricity generated by the first electric motor M1.

The hybrid control unit52executes the hybrid control to improve the power performance, the fuel efficiency, and the like, taking into account the gear of the automatic shift unit20. During this hybrid control, the differential unit11functions as an electric continuously variable transmission to coordinate the engine speed NEand the vehicle speed V, which are set to operate the engine8efficiently, and the rotational speed of the transmitting member18, which is set by the gear of the automatic shift unit20. That is, the hybrid control unit52sets the target value of the total gear ratio γT of the shift mechanism10so that the engine8operates according to the optimum fuel efficiency curve (fuel efficiency map, relational diagram). The optimum fuel efficiency curve is empirically determined in advance in a two-dimension coordinate that uses the engine speed NEand the torque TEoutput from the engine8(engine torque TE) as parameters so that high drivability and high fuel efficiency are achieved when the vehicle is driven in the continuously variable shift mode. The optimum fuel efficiency curve is stored in the hybrid control unit52. For example, the hybrid control unit52sets the target value of the total gear ratio γT of the shift mechanism10so that the engine torque TEand the engine speed NE, at which the drive power output from the engine matches the target drive power (the total target drive power, or the required drive power), are achieved. Then, the hybrid control unit52controls the gear ratio γ0of the differential unit11so that the target drive power is obtained, thereby controlling the total gear ratio γT within a range, for example, from 0.5 to 13, in which the total gear ratio γT is allowed to be changed.

At this time, the hybrid control unit52supplies the electric energy generated by the first electric motor M1to an electricity storage device60and the second electric motor M2through an inverter58. Therefore, although a large part of the drive power output from the engine8is mechanically transmitted to the transmitting member18, the other part of the drive power output from the engine8is consumed by the first electric motor M1to generate electricity. That is, the other part of the drive power output from the engine8is converted into electric energy in the first electric motor M1. The electric energy is supplied to the second electric motor M2through the inverter58, and the second electric motor M2is driven. Thus, mechanical energy is transmitted from the second electric motor M2to the transmitting member18. The devices related to the process from generation of the electricity to consumption of the electricity in the second electric motor M2constitute an electric path in which part of the power output from the engine8is converted into the electric energy, and the electric energy is converted to the mechanical energy.

Also, the hybrid control unit52has a function as an engine output control unit that executes an output control over the engine8so that the engine8generates the required amount of drive power, by outputting at least one of an instruction for controlling opening/closing of the electronically-controlled throttle valve96using the throttle actuator97, an instruction for controlling the amount of fuel injected by the fuel injection device98, and timing at which the fuel is injected by the fuel injection device98and an instruction for controlling timing at which the air-fuel mixture is ignited by the ignition device99such as an igniter, to the engine output control apparatus43. For example, the hybrid control unit52basically executes a throttle control to drive the throttle actuator97based on the accelerator-pedal operation amount Ace according to a prestored relational diagram (not shown). That is, the hybrid control unit52basically executes the throttle control to increase the throttle-valve opening amount θTHas the accelerator-pedal operation amount Acc increases.

The solid line A inFIG. 17is the boundary line between the engine-power cruise range and the motor-power cruise range. The boundary line is used to determine whether the drive power source, which generates the drive power used to start and drive the vehicle, should be changed between the engine8and a motor, for example, the second electric motor M2. In other words, the boundary line is used to determine whether the cruise mode should be changed between so-called engine-power cruise mode in which the vehicle is started and driven using the engine8as a drive power source, and so-called motor-power cruise mode in which the vehicle is driven using the second electric motor M2as a drive power source. The pre-stored relational diagram, shown inFIG. 7, which includes the boundary line (indicated by the solid line A) used to determine whether the cruise mode should be changed between the engine-power cruise mode and the motor-power cruise mode, is an example of a drive power, source switching diagram (drive power source map) that is formed of a two-dimensional coordinate system that uses the vehicle speed V and the output torque Tour which is a value related to drive power as parameters. This drive power source switching diagram is prestored along with, for example, the shift diagram (shift map) indicated by the solid lines and the alternate long and short dash lines inFIG. 7in the storage unit56.

For example, the hybrid control unit52determines whether the vehicle condition indicated by the vehicle speed V and the required torque Tour is within the motor-power cruise range or the engine-power cruise range using the drive power source switching diagram shown inFIG. 7. Then, the hybrid control unit52drives the vehicle in the motor-power cruise mode or the engine-power cruise mode. As evident fromFIG. 7, for example, the hybrid control unit52drives the vehicle in the motor-power cruise mode in a low output torque TOUTrange, that is, in a low engine torque TErange where the engine efficiency is generally lower than that in a high torque range, or in a low vehicle speed range where the vehicle speed V is low, that is, a low load range.

Even when the vehicle is driven in the engine-power cruise mode, the hybrid control unit52can perform a so-called torque-assist operation to assist the engine8, by supplying electric energy to the second electric motor M2from the first electric motor M1via the electric path, and/or from the electricity storage device60, and by driving the second electric motor M2. Therefore, the term “engine-power cruise” in this example embodiment also includes the situation where the vehicle is driven by the drive power from the engine and the drive power from the motor.

Also, the hybrid control unit maintains the operating state of the engine8using the electric CVT function of the differential unit11, even when the vehicle is not driven (stopped) or running at a low speed. For example, if the state-of-charge (SOC) of the electricity storage device60is reduced and electricity needs to be generated by the first electric motor M1when the vehicle is not driven (is at a standstill), the first electric motor M1is driven by the engine8to generate electricity and the rotational speed of the first electric motor M1is increased. Therefore, even if the second electric motor rotational speed NM2which is determined by the vehicle speed V becomes zero (or substantially zero) because the vehicle is at a standstill, the engine speed NEis maintained at or above the speed that enables the engine8to operate under its own power, by using the differential operation of the power split mechanism16.

A speed-increasing gear determination unit62determines whether the gear into which the shift mechanism10should be shifted is a speed-increasing gear, for example, fifth gear, according to the shift diagram shown inFIG. 7prestored in the storage unit56, based on, for example, the vehicle condition in order to determine which of the switching clutch C0and the switching brake B0should be applied when placing the shift mechanism10in the stepped shift mode. When the speed-increasing gear is selected, the rotational speed of the output shaft22is higher than the rotational speed of the engine8.

A differential mode switch control unit50selectively switches the shift mode between the continuously variable shift mode, i.e., the differential mode, and the stepped shift mode, i.e., the locked mode, by switching the application/release state of the differential mode switching devices (C0, B0) based on the vehicle condition. For example, the differential mode switch control unit50determines whether to switch the shift mode of the shift mechanism10(differential unit11) based on the vehicle condition indicated by the required output shaft torque TOUTand the vehicle speed V using the relationship (shift diagram, shift map) indicated by the broken line and the double-chain dash line inFIG. 7, which is prestored in the storage unit56. That is, the differential mode switch control unit50determines the shift mode into which the shift mechanism10should be shifted by determining whether the vehicle condition is within the continuously variable control range (differential range) in which the shift mechanism10should be placed in the continuously variable shift mode, or in the stepped control range (locked range) in which the shift mechanism10should be placed in the stepped shift mode. Then, the differential mode switch control unit50switches the shift mode to places the shift mechanism10into either the continuously variable shift mode (differential mode) or the stepped shift mode (locked mode), based on the result of determination.

More specifically, if it is determined that the vehicle condition is within the stepped control range, the differential mode switch control unit50transmits a signal, based on which the hybrid control or the continuously variable transmission control is not permitted, i.e. prohibited, to the hybrid control unit52. At the same time, the differential mode switch control unit50transmits a signal based on which gears of the automatic shift unit20are allowed to be changed, to the stepped shift control unit54. Then, the stepped shift control unit54executes the automatic shift control over the automatic shift unit20according to, for example, the shift diagram shown inFIG. 7that is prestored in the storage unit56. For example, the operation chart inFIG. 2that is prestored in the storage unit56shows the combinations of the hydraulic friction application devices, i.e., C0, C1, C2, B0, B1, B2, and B3, that are selectively applied to change the gears of the automatic shift unit20. That is, the entire shift mechanism10, i.e., the differential unit11and the automatic shift unit20, functions as a so-called stepped automatic transmission, and is shifted to the selected gear according to the operation chart shown inFIG. 2.

For example, when the speed-increasing gear determination unit62determines that the shift mechanism10should be shifted to fifth gear, a speed-increasing gear, i.e., a so-called overdrive gear, that has a gear ratio of lower than 1.0 should be selected by the entire shift mechanism10. Therefore, the differential mode switch control unit50transmits a command to the hydraulic pressure control circuit42to release the switching clutch C0and apply the switching brake B0so that the differential unit11functions as an auxiliary transmission that has a fixed gear ratio γ0of, for example, 0.7. On the other hand, when the speed-increasing gear determination unit62determines that the shift mechanism10should be shifted to a gear other than fifth gear, a speed-decreasing gear or a speed-maintaining gear that has a gear ratio of equal to or higher than 1.0 should be selected by the entire shift mechanism10. Therefore, the differential mode switch control unit50transmits a command to the hydraulic pressure control circuit42to apply the switching clutch C0and release the switching brake B0so that the differential unit11functions as an auxiliary transmission that has a fixed gear ratio γ0of, for example, 1. In this way, the differential mode switch control unit50places the shift mechanism10in the stepped shift mode, and changes the operating states of the switching clutch C0and the switching brake B0so that the speed-increasing gear or the speed-decreasing gear (speed-maintaining gear) in that stepped shift mode is selected. Thus, the differential unit11functions as an auxiliary transmission. In addition, the automatic shift unit20that is connected in tandem with the differential unit11functions as a stepped transmission. As a result, the entire shift mechanism10functions as a so-called stepped automatic transmission.

However, if it is determined that the vehicle condition is within the continuously variable transmission control range in which the shift mechanism10should be shifted to the continuously variable shift mode, the differential mode switch control unit50transmits a command to the hydraulic pressure control circuit42to release both the switching clutch C0and the switching brake B0. If both the switching clutch C0and the switching brake B0are released, the differential unit11is shifted to the continuously variable shift mode and the entire shift mechanism10is shifted to the continuously variable shift mode. At the same time, the differential mode switch control unit50transmits a signal to the hybrid control unit52to allow the hybrid control unit52to execute the hybrid control. Also, the differential mode switch control unit50provides the stepped shift control unit54with a signal to fix the gear at the predetermined gear for the continuously variable shift mode, or a signal to allow the stepped shift control unit54to automatically change the gears of the automatic shift unit20according to, for example, the shift diagram shown inFIG. 7which is prestored in the storage unit56. In this case, the stepped shift control unit54executes the automatic shift control by applying or releasing the clutches and the brakes other than the switching clutch C0and the switching brake B0according to the operation chart shown inFIG. 2. When the differential unit11that is shifted to the continuously variable shift mode by the differential mode switch control unit50functions as a continuously variable transmission and the automatic shift unit20that is arranged in tandem with the differential unit11functions as a stepped transmission, an appropriate amount of drive power is obtained. In addition, the rotational speed that is input to the automatic shift unit20, which is at one of first gear, second gear, third gear, and fourth gear, is continuously changed so that gear ratio of each gear is allowed to change continuously. Accordingly, the gears are changed while the gear ratio is continuously changed. As a result, the total gear ratio yT which is achieved by the entire shift mechanism10is continuously changed.

FIG. 7will be described in detail below.FIG. 7shows the relational diagram (shift diagram, shift map) which is prestored in the storage unit56and based on which whether the gears of the automatic shift unit20should be changed is determined. This shift diagram is formed of a two-dimensional coordinate system that uses the vehicle speed V and the required output torque TOUT, which is a value related to the drive power, as parameters. The solid lines inFIG. 7are upshift lines and the alternate long and short dash lines are downshift lines.

The broken line inFIG. 7represents the reference vehicle speed V1and the reference output torque T1used by the differential mode switch control unit50to determine whether the vehicle condition is within the continuously variable control range or the stepped control range. That is, the broke line inFIG. 7includes both a high vehicle speed determination line and a high output determination line. The high vehicle speed determination line indicates the reference vehicle speed V1which is a predetermined value that is used to determine whether the vehicle is traveling at a high vehicle speed. The high output determination line indicates the reference output torque T1which is a predetermined value that is used to determine whether the value related to the drive power required by the hybrid vehicle is high, for example, whether the output torque TOUTfrom the automatic shift unit20should be high. Moreover, there is provided a hysteresis range indicated by the alternate long and two short dash line and the broken line inFIG. 7. The hysteresis range is between the stepped control range and the continuously variable control range. Therefore, the hysteresis effect is produced in the determination as to whether the vehicle condition is within the stepped control range or the continuously variable control range. That is,FIG. 7shows a prestored switching diagram (switching map, relational diagram), which includes the reference vehicle speed V1and the reference output torque T1, which uses the vehicle speed V and the output torque TOUTas parameters, and which is used when the differential mode switch control unit50determines whether the vehicle condition is within the stepped control range or the continuously variable control range. A shift map that includes this switching diagram may be prestored in the storage unit56. The switching diagram may include at least one of the reference vehicle speed V1and the reference output torque T1, or may include a prestored switching line that uses the vehicle speed V or the output torque TOUTas a parameter.

The above-described shift diagram, switching diagram, drive power source switching diagram or the like may be stored in the form of a determination expression for comparing the actual vehicle speed V with the reference vehicle speed V1and a determination expression for comparing the output torque TOUTwith the reference output torque T1instead of in the form of a map. In this case, the differential mode switch control unit50places the shift mechanism10in the stepped shift mode, for example, when the actual vehicle speed V (value indicating the vehicle condition) has exceeded the reference vehicle speed V1. Also, the differential mode switch control unit50places the shift mechanism10in the stepped shift mode when the output torque TOUT(value indicating the vehicle condition) that should be output from the automatic shift unit20has exceeded the reference output torque T1.

There may be a failure or a decrease in function of electric control equipment, for example, an electric motor, which is used to have the differential unit11function as an electric continuously variable transmission. For example, there may be a decrease in the function of equipment related to the electrical path from generation of electrical energy in the first electric motor M1to conversion of the electricity into mechanical energy. That is, there may be a failure in the first electric motor M1, the second electric motor M2, the inverter58, the electricity storage device60, or the transmission path that connects these devices with each other. Also, the function of the vehicle may be decreased due to a failure or low temperature. In these cases, even if the vehicle condition is within the continuously variable control range, the differential mode switch control unit50may preferentially place the shift mechanism10in the stepped shift mode in order to reliably keep the vehicle running.

The value related to the drive power described above is a parameter that corresponds one-to-one with the drive power required by the vehicle. This value is not limited to the drive torque or drive power required by the drive wheels38, but may also be the actual value of, for example, the output torque Tour from the automatic shift unit20, the vehicle acceleration, or the engine torque TEthat is calculated based on the accelerator depression amount or the throttle valve opening amount θTH(or the intake air amount, the air-fuel ratio, or the fuel injection quantity) and the engine speed NE, or an estimated value of, for example, the required drive power, the required (target) output torque TOUTfrom the automatic shift unit20, or the required (target) engine torque TEthat is calculated based on, for example, the accelerator pedal depression amount achieved by the driver or the throttle opening amount. The drive torque may be calculated based on, for example, the output torque TOUTwith the differential ratio, the radius of the drive wheels38, etc. taken into account, or may be directly detected using, for example, a torque sensor. The other values may also be calculated or detected in this way.

If the shift mechanism10is placed in the continuously variable shift mode when the vehicle is traveling at a high vehicle speed, the fuel efficiency is decreased. In order to avoid such a situation, the reference vehicle speed V1is set. If the vehicle speed is higher than the reference vehicle speed V1, the shift mechanism10is placed in the stepped shift mode. The reference output torque T1is set based on, for example, the characteristics of the first electric motor M1, which are exhibited when the maximum value of the electric energy is appropriately decreased. In this way, when a large amount of drive power is required to drive the vehicle, a reaction torque from the first electric motor M1is not required for an engine torque within a high torque range. As a result, the size of the first electric motor M1is reduced.

FIG. 8is a switching diagram (switching map, relational diagram) that is prestored in the storage unit56. The switching map uses the engine speed NEand the engine torque TEas parameters, and includes an engine output line that is a boundary line which is used when the differential mode switch control unit50determines whether the vehicle condition is within the stepped control range (locked range) or the continuously variable control range (differential range). The differential mode switch control unit50may determine, based on the engine speed NEand the engine torque TE, according to the switching diagram inFIG. 8instead: of the switching diagram inFIG. 7, whether the vehicle condition indicated by the engine speed NEand the engine torque TEis within the continuously variable control range (differential range) or the stepped control range (locked range).FIG. 8is also a schematic diagram used to form the broken line inFIG. 7. In other words, the broken line inFIG. 7is a switching line that is formed on the two-dimensional coordinate system that uses the vehicle speed V and the output torque TOUTas parameters, based on the relational diagram (map) inFIG. 8.

As shown inFIG. 7, the high torque range in which the output torque TOUTis equal to or higher than the predetermined reference output torque T1, and the high vehicle speed range in which the vehicle speed V is equal to or higher than the predetermined reference vehicle speed V1, are used as the stepped control range. Therefore, the shift mechanism10is placed in the stepped shift mode when the torque from the engine8is relatively high and when the vehicle speed is relatively high. On the other hand, when the torque from the engine8is relatively low and when the vehicle speed is relatively low, namely, when the engine8is required to produce a drive power within a regular drive powers range, the shift mechanism10is placed in the continuously variable shift mode.

Similarly, as shown inFIG. 8, the high torque range in which the engine torque TEis equal to or higher than a predetermined reference value TE1, a high speed range in which the engine speed NEis equal to or higher than a predetermined reference value NE1, and a high drive power range in which the drive power output from the engine, which is calculated based on the engine torque TEand the engine speed NE, is equal to or greater than a predetermined reference value are used as the stepped control range. Therefore, the shift mechanism10is placed in the stepped shift mode when the torque output from the engine8is relatively high, when the speed of the engine8is relatively high, and when the drive power output from the engine8is relatively large. On the other hand, when the torque output from the engine8is relatively low, when the speed of the engine8is relatively low, and when the drive power output from the engine8is relatively small, namely, when the engine8is required to produce a drive power within the regular drive power range, the shift mechanism10is placed in the continuously variable shift mode. The boundary line between the stepped control range and the continuously variable control range inFIG. 8corresponds to the high vehicle speed reference line that indicates the values used to determine whether the vehicle is traveling at a high speed and the high output reference line used to determine whether a high engine torque is required to be output.

Accordingly, for example, when the vehicle is running at a low or medium speed and when a small or medium amount of drive power is required to drive the vehicle, the shift mechanism10is placed in the continuously variable shift mode to maintain favorable fuel efficiency. However, when the vehicle is running at a high speed, for example, when the actual vehicle speed V is higher than the reference vehicle speed V1, the shift mechanism10is placed in the stepped shift mode in which it operates as a stepped transmission. In this case, the drive power output from the engine8is transmitted to the drive wheels38along the mechanical power transmission path. Therefore, it is possible to suppress loss due to conversion between drive power and electric energy, which occurs when the shift mechanism10operates as an electric continuously variable transmission. As a result, the fuel efficiency is improved. When a large amount of drive power is required to drive the vehicle, for example, when the value related to the drive power, for example, the output torque TOUT, exceeds the reference output torque T1, the shift mechanism10is placed in the stepped shift mode in which it operates as a stepped transmission. In this case, the drive power output from the engine8is transmitted to the drive wheels38along the mechanical power transmission path. Therefore, the shift mechanism10is operated as an electric continuously variable transmission only when the vehicle is traveling at a low or medium speed and when a small or medium amount of drive power is required to drive the vehicle. Accordingly, it is possible to decrease the maximum value of the electricity that should be generated by the first electric motor M1, that is, the maximum value of the electricity that should be supplied from the first electric motor M1. As a result, it is possible to further reduce the size of the first electric motor M1or the vehicle drive system that includes that first electric motor M1. From another perspective, when a large amount of drive power is required to drive the vehicle, more emphasis is placed on the requirement for the drive power made by the driver than the requirement for the fuel efficiency. Accordingly, the shift mode is switched from the continuously variable shift mode to the stepped shift mode (fixed shift mode).

The hybrid control unit52changes a hydraulic pressure supply source, which supplies a hydraulic pressure to the hydraulic pressure control circuit42, between the mechanical oil pump44and the electric oil pump46. The mechanical oil pump44is arranged between the differential unit11and the engine8, and is driven in accordance with the operation of the engine8. Meanwhile, the electric oil pump46is arranged separately from the mechanical oil pump44. As described above, when the required torque is relatively high or when the vehicle is traveling at a relatively high speed, the vehicle is driven using the engine8as a drive power source. At this time, the mechanical oil pump44is driven in accordance with the operation of the engine8. Therefore, the hybrid control unit52selects the mechanical oil pump44as the hydraulic pressure supply source, which supplies a hydraulic pressure to the hydraulic pressure control circuit42of the automatic shift unit20. On the other hand, when the required torque is relatively low or when the vehicle is traveling at a relatively low speed, the engine8is stopped and the vehicle is driven using the second electric motor M2as a drive power source. At this time, the mechanical oil pump44is not operated because the engine8is at a standstill. Therefore, the hybrid control unit52selects the electric oil pump46as the hydraulic pressure supply source, which supplies a hydraulic pressure to the hydraulic pressure control circuit42.

In the shift mechanism10including the automatic shift unit20according to the example embodiment of the invention, the gears of the automatic shift unit20are changed while the vehicle is traveling using the second electric motor M2as a drive power source. In such a case, even when the engine8is at a standstill, a hydraulic pressure needs to be supplied to the hydraulic pressure control circuit42. Also, even when the vehicle is at a standstill, the electric oil pump46may be driven to supply a predetermined standby hydraulic pressure to the hydraulic pressure control circuit42of the automatic shift unit20in preparation for a subsequent movement of the vehicle or a movement caused by performing an operation of the shift operation device48with the accelerator pedal released, that is, a so-called garage shift operation. Because a torque converter is not provided in the shift mechanism10that includes the differential unit11according to the example embodiment of the invention, it is not possible to cause the vehicle to creep with the accelerator pedal released. Therefore, for example, the second electric motor M2is driven to simulate creeping.

A standby hydraulic pressure setting unit102presets (determines) the value of a standby hydraulic pressure that is supplied to the hydraulic pressure control circuit42of the automatic shift unit20in preparation for a subsequent movement of the vehicle or a movement caused by performing an operation of the shift operation device48with the accelerator pedal released, that is, a so-called garage shift operation, when the vehicle is at a standstill (not driven). The standby hydraulic pressure setting unit102sets the standby hydraulic pressure based on the results of determinations made by an engine stop determination unit104, a shift position determination unit106, and a brake operation determination unit108. The predetermined standby hydraulic pressure is empirically determined in advance. The predetermined standby hydraulic pressure is set to an appropriate value so that a hydraulic pressure is promptly supplied to the hydraulic friction application device of the automatic shift unit20, which is applied when a garage-shift operation is executed, and the amount of electricity consumed to drive the electric oil pump46is suppressed. The standby hydraulic pressure is supplied, via a regulator valve (not shown), and used as the line pressure of the hydraulic pressure control circuit42. When the standby hydraulic pressure is increased, the line pressure is also increased.

The engine stop determination unit104determines whether the engine8has been stopped. Whether the engine8has been stopped is determined based on, for example, an engine output control command that is output from the hybrid control unit52. When the engine8is stopped, the electric oil pump46is driven because the mechanical oil pump44is not driven. For example, when the garage-shift operation is performed at a decreased engine speed or immediately after the engine is started after the end of the motor-power cruise, the flow rate of the oil supplied from the mechanical oil pump44may be insufficient. Accordingly, the electric oil pump46is driven to make up for a shortage in the flow rate of the oil. In such a case, the engine stop determination unit104determines that the engine8is stopped.

The brake operation determination unit108determines whether a foot brake pedal68has been depressed (brakes have been applied). Whether the foot brake pedal68has been depressed is determined based on a foot brake pedal operation signal (on-signal) BONindicating the fact, detected by a brake switch70, that foot brakes (wheel brakes), which are service brakes, have been applied. The brake operation determination unit108determines whether the duration of the time the foot brake pedal68is not depressed brakes are released) is shorter than a predetermined duration. More specifically, a timer (not shown) starts counting the time that has elapsed since it is determined that the foot brake pedal68is released. Then, the brake operation determination unit108determines whether the elapsed time is shorter than the predetermined duration. The predetermined duration is empirically determined in advance, and stored in the storage unit56.

When the engine stop determination unit104determines that the engine8has been stopped, the shift position determination unit106determines that the shift lever49is in Neutral, which is the non-drive position, and the brake operation determination unit106determines that the foot brake pedal68has been depressed (brakes are applied) or that the duration of time the foot brake pedal68is not depressed (brakes are released) is shorter than the predetermined duration, the standby hydraulic pressure setting unit102sets (determines) a regular standby hydraulic pressure.

FIG. 9shows the relationship between the duration of time the shift position selected in the shift operation device48is maintained at Neutral (N-range duration) and the rotational speed of the electric oil pump46, which is required to achieve the standby hydraulic pressure (hereinafter, referred to as “standby rotational speed of the electric oil pump46”). The standby rotational speed and the standby hydraulic pressure are in a proportional relationship. Therefore, the standby hydraulic pressure increases as the standby rotational speed of the electric oil pump46increases. InFIG. 9, the solid line indicates the above-described relationship when the brakes are released, and the dashed line indicates the relationship when the brakes are applied. When the N-range duration is short, that is, immediately after the shift position selected in the shift operation device48is changed to Neutral, there is only a low possibility that the garage-shift operation for changing the shift position from Neutral to Drive or Reverse is performed. Therefore, when the N-range duration is shorter than the predetermined duration T1, the standby rotational speed is set to a low value. When the brakes are applied, it is considered that the driver has an intention to perform the garage-shift operation. Therefore, the standby hydraulic pressure is set to a value that is higher than that when the brakes are released. Thus, a higher standby hydraulic pressure is achieved when the brakes are applied than when the brakes are released. More specifically, during the predetermined duration T1that starts immediately after the selected shift position is changed to Neutral, the possibility that the garage shift operation will be performed is considerably low when the brakes are released. Therefore, the standby rotational speed is set to zero. On the other hand, when the brakes are applied, it is considered that the driver has an intention to perform the garage-shift operation although the possibility that the garage-shift operation will be performed is low. Therefore, the standby rotational speed is maintained at the standby rotational speed N1that is higher than that when the brakes are released. Each of the predetermined duration T1and the standby rotational speed N1is set to an appropriate value that is empirically determined in advance.

Regardless of whether brakes are applied or released, the possibility that the garage-shift operation will be performed increases as the N-range duration increases. Accordingly, the standby rotational speed is increased in proportional to the N-range duration. More specifically, when the brakes are applied, the standby rotational speed is controlled to change from N1to N2during the period from the end of the predetermined duration T1to the end of the predetermined duration J2. When the brakes are released, the standby rotational speed is controlled to change from zero to N2during the period from the end of the predetermined duration T1to the end of the predetermined duration T3. Thus, the standby rotational speed N2is achieved more quickly when the brakes are applied than when the brakes are released. Therefore, if the garage-shift operation is performed within the predetermined duration13, the hydraulic friction application device of the automatic shift unit20is applied more quickly. As described above, the standby hydraulic pressure setting unit102sets the standby hydraulic pressure based on the duration of time the selected shift position is maintained at Neutral. The standby rotational speed N2is set so that, when the standby rotational speed N2is achieved, the predetermined standby hydraulic pressure, at which the hydraulic friction application device is quickly applied when the garage-shift operation is performed, is reliably achieved. The predetermined durations T2and T3, and the standby rotational speed N2, etc. are set to appropriate values that are empirically determined in advance.

An oil amount adjustment unit110increases the amount of oil supplied to the hydraulic pressure control circuit42by a larger amount as the standby hydraulic pressure is lower when the garage-shift operation is performed. More specifically, the oil amount adjustment unit110increases the amount of oil supplied to the hydraulic pressure control circuit42by increasing the rotational speed of the electric oil pump46and/or the duration of time the electric oil pump42is driven at an increased rotational speed. The amount of oil correlated with the standby hydraulic pressure is set to an appropriate value that is determined empirically in advance. Then, the amount of increase in the rotational speed of the electric oil pump46and the duration of time the electric oil pump46is driven at an increased rotational speed are controlled so that the predetermined amount of oil is supplied to the hydraulic pressure control circuit42.

FIG. 10is a time chart showing the relationship between the instructed rotational speed of the electric oil pump46to the brake operation performed when Neutral is selected. The relationship shown inFIG. 10is derived so that the standby hydraulic pressure set by the standby hydraulic pressure setting unit102is achieved. If the brakes are applied at T10, it is considered that the driver has an intention to perform the garage-shift operation. Therefore, the instructed rotational speed of the electric oil pump46is maintained at, for example, the standby rotational speed N2to reliably achieve a predetermined standby hydraulic pressure. Thus, the line pressure of the hydraulic pressure control circuit42of the automatic shift unit20is gradually increased. If the brakes are released at T11, there still is a possibility that the garage shift operation will be performed immediately after the brakes are released. Therefore, within a predetermined duration after the brakes are released, the rotational speed of the electric oil pump46is maintained at the standby rotational speed N2to reliably achieve the standby hydraulic pressure. Then, when the duration of time the brakes are released is equal to or longer than the predetermined duration, the possibility that the garage-shift operation will be performed is reduced. Therefore, the standby hydraulic pressure is decreased. More specifically, in the example embodiment of the invention, the standby hydraulic pressure is decreased to zero by stopping the electric oil pump46to decrease the standby rotational speed to zero. In this way, the amount of electricity consumed by the electric oil pump46is suppressed. The line pressure starts decreasing at T12. However, when the brakes are applied at T13, the instructed rotational speed of the electric oil pump46is returned to the standby rotational speed N2, which is set at T10, and the line pressure is increased. As described above, the standby hydraulic pressure setting unit102sets the standby hydraulic pressure based on the brake operation performed by the driver. The duration of time from when the brakes are released until when the electric oil pump46is stopped (predetermined duration) is empirically determined in advance.

FIG. 11is a time chart showing the state where the garage-shift operation is performed when a control is executed over the standby hydraulic pressure produced by the electric oil pump46in Neutral range, and the state where the garage-shift operation is performed when the electric oil pump46at a standstill in Neutral range. InFIG. 11, the dashed line shows the state where the standby control is executed so that the instructed rotational speed of the electric oil pump46is adjusted to the standby rotational speed N2(N-range standby control). The N-range standby control corresponds to the control that is executed by the standby hydraulic pressure setting unit102when the brakes are applied or within the predetermined duration after the brakes are released. The solid line shows the state where the electric oil pump46is stopped and the instructed rotational speed thereof is adjusted to zero (N-range stop control). The N-range stop control corresponds to the control that is executed by the standby hydraulic pressure setting unit102when the duration of time the brakes are released is equal to or longer than the predetermined duration.

Until T20inFIG. 11, the shift range is maintained at Neutral regardless of whether the N-range standby control or the N-range stop control is executed. In the N-range standby control, the instructed rotational speed of the electric oil pump46is maintained at the standby rotational speed N2. Therefore, the line pressure of the hydraulic pressure control circuit42is maintained at a predetermined standby hydraulic pressure. This state until T20inFIG. 11corresponds to the state after the end of the predetermined duration T2indicated by the dashed line inFIG. 9. In the N-range stop control, the instructed rotational speed of the electric oil pump46is zero because the electric oil pump46is at a standstill. Therefore, the line pressure is maintained at zero. This state until T20inFIG. 11corresponds to the state until the end of the predetermined duration T1indicated by the solid line inFIG. 9.

Next, when a so-called garage-shift operation for changing the shift position from Neutral to Drive or Reverse is started at T20, a so-called fast application control for abruptly increasing the instructed rotational speed of the electric oil pump46is started. In the N-range stop control, because the line pressure is zero, the response of the hydraulic friction application devices of the automatic shift unit20to the hydraulic pressure is slower than that in the N-range standby control. Therefore, the hydraulic pressure adjustment unit110sets the instructed rotational speed of the electric oil pump46that should be achieved by the fast application control in the N-range stop control to a value higher than the instructed rotational speed N4of the electric oil pump46that should be achieved by the fast application control in the N-range standby control. In other words, the hydraulic pressure adjustment unit110increases the instructed rotational speed of the electric oil pump46by a larger amount as the standby hydraulic pressure is lower, for example, as in the N-range stop control, to increase the amount of oil that is supplied to the hydraulic pressure control circuit42, thereby causing the hydraulic friction application devices of the automatic shift unit20to respond to the hydraulic pressure more quickly. The oil amount adjustment unit110may increase the amount of oil supplied to the hydraulic pressure control circuit42by not only increasing the rotational speed of the electric oil pump46but also increasing the duration of time the electric oil pump46is rotated at an increased rotational speed (duration from T20to T21inFIG. 11), namely, increasing the increased-rotational speed duration. Thus, even when the N-range stop control is executed, the hydraulic friction application devices are allowed to respond to the hydraulic pressure more quickly by raising the line pressure more quickly. The instructed rotational speeds N3and N4, and the duration of time the electric oil pump46is rotated at an increased rotational speed (duration from T20to T21) are set to appropriate values that are empirically determined in advance.

When the garage-shift operation is started while the N-range stop control is executed, the line pressure rises slowly. Therefore, issuance of a command on the application pressure for applying the target hydraulic friction application device is retarded, whereby slippage of the hydraulic friction application device is suppressed. More specifically, for example, when the garage-shift operation for changing the shift position to Drive is performed, first gear is usually selected. Therefore, the first clutch C1is applied according to the operation chart inFIG. 2. In this case, the application pressure (instructed pressure) for applying the first clutch C1is output later when the N-range stop control is executed than when the N-range standby control is executed. Retarding the output of the instructed pressure for applying the first clutch C1allows the first clutch C1to be applied after the line pressure is raised to an appropriate value. Therefore, it is possible to supply the application pressure at which slippage of the first clutch C1does not occur. To select first gear, in addition to the first clutch C1, the third brake B3is also applied. The similar control is executed on the third brake B3.

After the fast application control is completed at T21, the rotational speed of the electric oil pump46is maintained at a predetermined rotational speed regardless of whether the N-range standby control or the N-range stop control is executed. Then, a sweep control is executed on the first clutch C1during a period from T21to T22, whereby the first clutch C1is smoothly applied. The start timing of the sweep control may be later when the N-range stop control is executed than when the N-range standby control is executed. Thus, it is possible to suppress slippage of the first clutch C1due to slow rising of the line pressure. As a result, the useful life of the first clutch C1is increased by suppressing such slippage.

FIG. 12is a flowchart illustrating the main portion of the control executed by the electronic control unit40, that is, the control routine executed over the electric oil pump46when the garage-shift operation is executed. The control routine is periodically executed at considerably short time intervals of, for example, several milliseconds to several tens of milliseconds.

First, in step (hereinafter, referred to as “S”)1, the engine stop determination unit104determines whether the engine8has been stopped. For example, when the engine is driven, the control over the electric oil pump46is not executed because the required amount of oil is obtained by the mechanical oil pump44. If it is determined that the engine is driven, a negative determination is made in S1, and the routine ends.

On the other hand, if an affirmative determination is made in S1, S2is executed by the shift position determination unit106. In S2, it is determined whether shift lever49of the shift operation device48is in Neutral, which is the non-drive position. If a negative determination is made in S2, the control routine ends.

On the other hand, if an affirmative determination is made in S2, S3is executed by the brake operation determination unit108. In S3, it is determined whether the foot brake pedal68has been depressed, that is, the brakes have been applied. If an affirmative determination is made in S3, S6is executed by the standby hydraulic pressure setting unit102. In S6, the electric oil pump46is rotated at the standby rotational speed to reliably achieve the standby hydraulic pressure, whereby a decrease in the line pressure during the garage-shift operation is suppressed (N-range standby control is executed), because there is a high possibility that the garage-shift operation will be performed. On the other hand, if a negative determination is made in S3, S4is executed by the brake operation determination unit108. In S4, it is determined whether the duration of time the brakes are released is shorter than the predetermined duration. If it is determined that the duration of time the brakes are released is shorter than the predetermined duration, there is a high possibility that the garage-shift operation will be performed. Therefore, an affirmative determination is made in S4, and the N-range standby control is executed in S6.

On the other hand, if a negative determination is made in S4, that is, if it is determined that the duration of time the brakes are released is equal to or longer than the predetermined duration, there is only a low possibility that the garage-shift operation will be performed. Therefore, S5is executed by the standby hydraulic pressure setting unit102to suppress the amount of electricity consumed by the electric oil pump46. In S5, the N-range stop control for stopping the electric oil pump46is executed. Then, S7is executed by the shift position determination unit106. In S7, it is determined whether the garage-shift operation for changing the shift position from Neutral to Drive or Reverse has been performed. If a negative determination is made in S7, S3is executed again.

On the other hand, if an affirmative determination is made in S7, S8is executed by the oil amount adjustment unit110. In S8, the fast application control is executed. In the fast application control, the fast application instructed rotational speed is determined based on the instructed rotational speed of the electric oil pump46to increase the amount of oil. More specifically, when Neutral is selected, the line pressure rises more slowly when the N-range stop control is executed than when the N-range standby control is executed. Therefore, if the N-range stop control is executed, the instructed rotational speed of the electric oil pump46is set to a higher value to allow the hydraulic friction application devices to respond to the hydraulic pressure more quickly. Also, the duration of time the fast application control is executed may be increased to allow the hydraulic friction application devices to respond to the hydraulic pressure further quickly.

As described above, according to the example embodiment of the invention, when the garage-shift operation is performed, the amount of oil supplied to the hydraulic friction application devices of the automatic shift unit20is adjusted based on the standby hydraulic pressure. In this way, even if the standby hydraulic pressure is increased or decreased, it is possible to achieve the hydraulic pressure required in the garage-shift operation more easily. Therefore, it is possible to increase or decrease the standby hydraulic pressure without reducing the useful life of the automatic shift unit20and slowing down the response of the automatic shift unit20to the hydraulic pressure. Thus, it is possible to reduce the amount of electric power consumed by the electric oil pump46, thereby enhancing the fuel efficiency.

According to the example embodiment of the invention, the amount of oil that is supplied to the application devices is increased by a larger amount as the standby hydraulic pressure is lower. Therefore, even when the standby hydraulic pressure is low, it is possible to reliably obtain a sufficient amount of oil that is required when the drive position is changed.

According to the example embodiment of the invention, it is possible to easily increase the amount of oil that is supplied to the application devices of the automatic shift unit20by increasing the rotational speed of the electric oil pump46and/or the duration of time the electric oil pump46is rotated at an increased rotational speed.

In addition, according to the example embodiment of the invention, the output from the electric oil pump46is suppressed by decreasing the standby hydraulic pressure when there is only a low possibility that the shift position will be changed from Neutral to Drive or Reverse. As a result, it is possible to suppress electric power consumption.

According to the example embodiment of the invention, it is possible to relatively accurately reflect the drive's intention on the control, because the standby hydraulic pressure is set based on the duration of time the selected shift position is maintained at Neutral and/or the brake operation performed by the driver.

According to the example embodiment of the invention, it is possible to appropriately control the operating state of the shift mechanism10, because an appropriate hydraulic pressure is supplied to the application devices based on the shift position selected in the shift operation device48to appropriately control the applied state of the application devices.

The example embodiment of the invention has been described in detail with reference to the accompanying drawings. However, the invention may be implemented in the following modified examples of the embodiment of the invention.

For example, the shift mechanism10according to the example embodiment of the invention is formed of a transmission including the differential unit11and the automatic shift unit20. However, the structure of the transmission is not limited to this. The invention may be applied to a transmission having a structure in which, for example, a belt-type continuously variable transmission is connected to the differential unit11. In other words, the invention may be applied to any structures including the electric oil pump46and a transmission that is driven by the hydraulic pressure supplied from the electric oil pump46.

In the example embodiment of the invention, the standby rotational speed of the electric oil pump46is controlled to zero, when the duration of time the brakes are released is equal to or longer than the predetermined duration. However, it is not absolutely necessary to decrease the standby rotational speed of the electric oil pump46to zero. The standby rotational speed may be decreased to an appropriate rotational speed.

In the example embodiment of the invention, the oil amount adjustment unit110increases the amount of oil that is supplied to the application devices based on a decrease in the standby hydraulic pressure. Alternatively, the oil amount adjustment unit110may decrease the amount of oil that is supplied to the application devices, if the standby hydraulic pressure is high.

In the example embodiment of the invention, the predetermined duration of time the electric oil pump46rotated at an increased standby rotational speed is set to an appropriate value empirically determined in advance. Alternatively, the duration of time may be changed on an as needed basis by a learning control.

In the example embodiment of the invention, the second electric motor M2is directly connected to the transmitting member18. However, the position of the second electric motor M2is not limited to this. For example, the second electric motor M2may be connected to the power transmission path, at any position, from the differential unit11to the drive wheels38directly or via, for example, a transmission.

In the example embodiment of the invention, the differential unit11functions as an electric continuously variable transmission of which the gear ratio γ0is continuously changed within the gear ratio range from the minimum value γ0min to the maximum value γ0max. However, the invention may be applied even when the gear ratio γ0is changed not continuously but in a stepwise manner using a differential effect.

In the power split mechanism16according to the example embodiment of the invention, the first carrier CA1is connected to the engine8, the first sun gear S1is connected to the first electric motor M1, and the first ring gear R1is connected to the transmitting member18. However, the manner in which these members are connected to each other is not limited to this. The engine8, the first electric motor M1and the transmitting member18may be connected to any of the three rotating elements CA1, S1and R1of the first planetary gear unit24.

In the example embodiment of the invention, the engine8is directly connected to the input shaft14. However, the engine need not be directly connected to the input shaft14. For example, the engine8may be operatively connected to the input shaft14via a gear or a belt. In addition, the engine8need not be provided coaxially with the input shaft14.

In the example embodiment of the invention, the first electric motor M1and the second electric motor M2are provided coaxially with the input shaft14, the first electric motor M1is connected to the first sun gear S1, and the second electric motor M2is connected to the transmitting member18. However, these members need not be arranged in this way. For example, the first electric motor M1may be connected to the first sun gear S1via a gear, a belt or a reducer, and the second electric motor M2may be connected to the transmitting member18via a gear, a belt or a reducer.

In the example embodiment of the invention, the automatic shift unit20is connected in tandem with the differential unit11via the transmitting member18. Alternatively, a counter shaft may be provided in parallel with the input shaft14, and the automatic shift unit20may be provided coaxially with the counter shaft. In this case, the differential unit11and the automatic shift unit20may be connected to each other via paired counter gears, paired transmitting members that are a sprocket and a chain, which serve as the transmitting member18so that drive power is transmitted from the differential unit to the automatic shift unit20.

The power split mechanism16, which serves as a differential mechanism according to the example embodiment of the invention, may be a differential gear unit in which pinions that are rotated by the engine and paired bevel gears meshed with the pinions are operatively connected to the first electric motor M1and the transmitting member18(second electric motor M2).

The power split mechanism16according to the example embodiment of the invention is formed of one set of planetary gear unit. Alternatively, the power split mechanism16may be formed of two or more sets of planetary gear units, and may function as a transmission having three or more gears in the non-differential mode (fixed shift mode). In addition, the planetary gear unit is not limited to a single pinion planetary gear unit, and may be a double pinion planetary gear unit. Even when the power split mechanism16is formed of two or more sets of planetary gear units, the engine8, the first and second electric motors M1and M2, and the transmitting member18(and the output shaft22when a certain structure is employed) are connected to the rotating elements of the planetary gear units so that drive power is transmittable, and the shift operation is changed between the stepped shift operation and the continuously variable shift operation by controlling the clutch C and the brake B that are connected to the rotating elements of the planetary gear units.

In the example embodiment of the invention, the engine8and the differential unit11are directly connected to each other. However, the engine8and the differential unit11need not be directly connected to each other. The engine8and the differential unit11may be connected to each other via a clutch.

The shift operation device48according to the example embodiment of the invention is provided with the shift lever49that is operated to select a shift position PSHfrom among multiple shift positions PSH. However, instead of the shift lever49, a switch, for example, a push-button switch or a slide switch that selects a shift position PSHfrom among multiple shift positions PSH, a device that changes multiple shift positions PSHin response to voice of the driver instead of being manually operated, or a foot-operated device that changes multiple shift positions PSHmay be employed. A shift range is set by operating the shift lever49to Manual. Alternatively, gear may be set, namely, the highest gear within each shift range may be set by operating the shift lever49to Manual. In this case, the gears of the automatic shift unit20is changed to shift the automatic shift unit20to a desired gear. For example, when the shift lever49is manually operated to the upshift position “+” or the downshift position “−” in Manual, the automatic shift unit20is shifted to one of first gear to fourth gear in accordance with the operation of the shift lever49.

The example embodiment of the invention that has been disclosed in the specification is to be considered in all respects as illustrative and not restrictive. The invention may be implemented in various other embodiments that are derived based on the knowledge of those who are skilled in the art.