Powertrain and method of controlling powertrain

An ECU executes a program including the steps of: providing control over an engine coupled to a carrier for driving a first MG coupled to a sun gear in a power split device, and providing control over a second MG for allowing a ring gear to stop; expecting that a shift operation will be performed when a brake operation is performed; and stopping providing the control over the engine for driving the first MG and stopping providing the control over the second MG for allowing the ring gear to stop.

This nonprovisional application is based on Japanese Patent Application No. 2006-339784 filed with the Japan Patent Office on Dec. 18, 2006, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a powertrain and a method of controlling a powertrain, and in particular, to a technique of controlling a powertrain having an engine and a rotating electric machine as motive power sources.

2. Description of the Background Art

Conventionally, a hybrid vehicle having an internal combustion engine and a rotating electric machine as motive power sources is known. In such a hybrid vehicle, the internal combustion engine and the rotating electric machine are selectively used in accordance with a traveling state of the vehicle. For example, the internal combustion engine is mainly used for traveling at a high speed, and the rotating electric machine is mainly used for traveling at an intermediate or low speed. One such hybrid vehicle is provided with a differential mechanism that functions as a continuously variable transmission by means of a rotating electric machine.

Japanese Patent Laying-Open No. 2005-337491 discloses a control apparatus for a vehicular drive apparatus. The control apparatus includes: a continuous shift portion that has a differential mechanism constituted of a first element coupled to an engine, a second element coupled to a first motor (rotating electric machine), and a third element coupled to a second motor, and that functions as an electric continuously variable transmission; and a shift portion (shift mechanism) provided between the continuous shift portion and wheels. The control apparatus of Japanese Patent Laying-Open No. 2005-337491 includes a continuous shift control portion that executes, when the shift portion is shifted, shift of the continuous shift portion synchronizing with the shift of the shift portion so that the gear ratio implemented by the continuous shift portion and the shift portion is continuous.

According to the control apparatus disclosed in the publication, the gear ratio implemented by the continuous shift portion and the shift portion, i.e., a synthesis gear ratio implemented based on the gear ratio of the continuous shift portion and that of the shift portion is continuously changed. Thus, the engine speed (revolution speed) is changed continuously before and after the shift of the shift portion, whereby a shift shock is reduced.

Meanwhile, in a hybrid vehicle having a powertrain provided with two rotating electric machines such as the vehicular drive apparatus disclosed in Japanese Patent Laying-Open No. 2005-337491, for example when the shift lever is in P (parking) position, one of the rotating electric machines may be driven by the engine to generate power. In such a situation, in the vehicle provided with a stepwise transmission between a continuous shift portion, wherein an engine and two rotating electric machines are coupled via a differential mechanism, and wheels, such as the one disclosed in Japanese Patent Laying-Open No. 2005-337491, when the stepwise transmission in P (parking) range or the like is shifted to the neutral state, in order for the driving force of the engine to efficiently be transmitted to the rotating electric machine employed as a generator, it is desirable that a rotary element coupled to the rotating electric machine that does not generate power is stopped. Accordingly, when power is generated by one of the rotating electric machines, control is provided over the other rotating electric machine for allowing the rotary element coupled to the other rotating electric machine to stop. However, when control over the rotating electric machine for allowing the rotary element to stop is provided, if the vehicle is to be started, torque of the rotating electric machine must once be “0” so that transition to control for allowing the rotating electric machine to actuate as the drive source of the vehicle is realized. Here, since the rotary element having been stopped becomes freely rotatable, the load to the engine is abruptly reduced and the engine speed may abruptly be increased.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a powertrain and the like that is capable of preventing an abrupt increase in the engine speed.

A powertrain according to one aspect of the present invention includes: a differential mechanism having a first rotary element coupled to a first rotating electric machine, a second rotary element coupled to a second rotating electric machine, and a third rotary element coupled to an engine; a shift mechanism coupled to the second rotary element and transmitting torque being input from the second rotary element to a wheel; and an operation unit. The operation unit provides control, over the engine, for driving the first rotating electric machine, and provides control, over the second rotating electric machine, for allowing the second rotary element to stop. The operation unit expects a shift operation of a driver. The operation unit stops providing the control over the engine for driving the first rotating electric machine and stops providing the control over the second rotating electric machine for allowing the second rotary element to stop, when the shift operation is expected.

According to this configuration, for example when power is generated by the first rotating electric machine, control is provided, over the engine, for driving the first rotating electric machine, and control is provided, over the second rotating electric machine, for allowing the second rotary element to stop. Thus, reaction force can be received by the second rotary element and driving force output from the engine can efficiently be transmitted to the first rotating electric machine. Provision of the control over the engine for driving the first rotating electric machine is stopped and provision of the control over the second rotating electric machine for allowing the second rotary element to stop is stopped, when the shift operation is expected. Thus, provision of the control over the engine for driving the first rotating electric machine can be stopped and provision of the control over the second rotating electric machine for allowing the second rotary element to stop can be stopped, before the shift operation is actually performed. Thus, transition to control for reducing the output of the engine and for actuating in advance the rotating electric machine as the drive source of the vehicle can be made. As a result, a powertrain that is capable of preventing an abrupt increase in the engine speed can be provided.

Preferably, the operation unit expects the shift operation when a brake operation by the driver is performed.

According to this configuration, for example when the shift lever is shifted from P (parking) position to another position, a brake operation is performed. Therefore, when a brake operation is performed by the driver, a shift operation is expected. Thus, a shift operation can surely be expected.

Further preferably, the operation unit provides the control over the engine for driving the first rotating electric machine and provides the control over the second rotating electric machine for allowing the second rotary element to stop, when power is generated by the first rotating electric machine.

According to this configuration, when power is generated by the first rotating electric machine, control is provided over the engine for driving the first rotating electric machine, and control is provided over the second rotating electric machine for allowing the second rotary element to stop. Thus, when power is generated by the first rotating electric machine, driving force output from the engine can efficiently be transmitted to the first rotating electric machine. Therefore, power generation efficiency can be improved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, referring to the drawings, an embodiment of the present invention will be described. In the following description, identical components are denoted by identical reference characters. Their labels and functions are also identical. Accordingly, detailed description thereof will not be repeated.

Referring toFIG. 1, a hybrid vehicle incorporating a control apparatus according to the present embodiment will be described. The hybrid vehicle is an FR (Front engine Rear drive) vehicle. It is noted that the vehicle may not necessarily be an FR vehicle.

The hybrid vehicle includes an engine100, a transmission200, a propeller shaft500, a differential gear600, rear wheels700, and an ECU (Electronic Control Unit)800. The control apparatus according to the present embodiment is implemented by, for example, the execution of a program recorded in ROM (Read Only Memory)802of ECU800. A powertrain1000controlled by ECU800that is a control apparatus according to the embodiment of the present invention includes engine100and transmission200.

Engine100is an internal combustion engine that burns an air-fuel mixture of fuel injected from an injector102and air, inside a combustion chamber of a cylinder. A piston in the cylinder is pushed down by the combustion, and a crankshaft is rotated.

Transmission200is coupled to engine100. As described later, transmission200includes a first shift portion300and a second shift portion400. Torque output from transmission200is transmitted to right and left rear wheels700via propeller shaft500and differential gear600.

Connected to ECU800via a harness or the like are a position switch806of a shift lever804, an accelerator pedal position sensor810of an accelerator pedal808, a brake switch814of a brake pedal812, a throttle position sensor818of an electronic throttle valve816, an engine speed sensor820, an input shaft rotation speed sensor822, an output shaft rotation speed sensor824, an oil temperature sensor826, and a water temperature sensor828.

The position of shift lever804is detected by position switch806, and a signal representing the detection result is transmitted to ECU800. Corresponding to the position of shift lever804, shift in transmission200is achieved automatically.

Accelerator pedal position sensor810detects the position of accelerator pedal808, and transmits a signal representing the detection result to ECU800. Brake switch814detects a brake operation (an operation of brake pedal812by the driver), and transmits a signal representing the detection result to ECU800.

Throttle position sensor818detects the position of electronic throttle valve816having its position adjusted by an actuator, and transmits a signal representing the detection result to ECU800. The amount of air taken into engine100(an output of engine100) is adjusted by electronic throttle valve816.

It is noted that, instead of or in addition to electronic throttle valve816, an intake valve (not shown) or an exhaust valve (not shown) may have its lift amount or opening/closing phase changed so that the amount of air taken into engine100is adjusted.

Engine speed sensor820detects the rotation speed of an output shaft (crankshaft) of engine100, and transmits a signal representing the detection result to ECU800. Input shaft rotation speed sensor822detects an input shaft rotation speed NI of second shift portion400, and transmits a signal representing the detection result to ECU800. Output shaft rotation speed sensor824detects an output shaft rotation speed NO of transmission200(second shift portion400), and transmits a signal representing the detection result to ECU800.

Oil temperature sensor826detects the temperature (oil temperature) of oil (Automatic Transmission Fluid, ATF) used for actuation or lubrication of transmission200, and transmits a signal representing the detection result to ECU800.

Water temperature sensor828detects the temperature (water temperature) of coolant of engine100, and transmits a signal representing the detection result to ECU800.

ECU800provides control over various devices such that the vehicle attains a desired traveling state based on signals transmitted from position switch806, accelerator pedal position sensor810, brake switch814, throttle position sensor818, engine speed sensor820, input shaft rotation speed sensor822, output shaft rotation speed sensor824, oil temperature sensor826, water temperature sensor828and the like, as well as map and program stored in ROM802.

Referring toFIG. 2, transmission200is further described. Included in transmission200as coaxially arranged in a case202that is a non-rotary member are: an input shaft204being an input rotary member; a first shift portion300coupled directly or via a damper (not shown) to input shaft204; a second shift portion400serially coupled in a power transmitting route between first shift portion300and rear wheels700via a transmission member (transmission shaft)206; and an output shaft208being an output rotary member coupled to second shift portion400.

Transmission200is configured symmetrically relative to its axis. Accordingly, the lower part of transmission200is omitted inFIG. 2.

First shift portion300includes a power split device310, a first MG (Motor Generator)311, and a second MG312. First shift portion300further includes two frictional engagement elements of a C0 clutch314and a B0 brake316.

Power split device310splits the output of engine100being input to input shaft204for first MG311and transmission member206. Power split device310is constituted of a planetary gear320.

Planetary gear320includes a sun gear322, a pinion gear324, a carrier326supporting pinion gear324so that it can rotate on its own axis and revolve around sun gear322, and a ring gear328meshing with sun gear322via pinion gear324.

In power split device310, carrier326is coupled to input shaft204, i.e., to engine100. Sun gear322is coupled to first MG311. Ring gear328is coupled to second MG312via transmission member206.

Power split device310functions as a differential apparatus, by the relative rotation of sun gear322, carrier326, and ring gear328. By the differential function of power split device310, the output of engine100is divided for first MG311and for transmission member206.

First MG311generates power using part of the divided output of engine100, and/or second MG312rotates using the power generated by first MG311, whereby power split device310functions as a continuously variable transmission.

First MG311and second MG312are three-phase alternating current rotating electric machines. First MG311is coupled to sun gear322of power split device310. Second MG312is provided such that rotors integrally rotate with transmission member206.

First MG311and second MG312are controlled so as to satisfy target output torque of transmission200that is calculated from, for example, the accelerator pedal position and the vehicle speed, and to realize the optimum fuel efficiency in engine100.

C0 clutch314is provided so as to couple sun gear322and carrier326. B0 brake316is provided so as to couple sun gear322to case202.

Second shift portion400includes three single pinion type planetary gears411-413and five frictional engagement elements of a C1 clutch421, a C2 clutch422, a B1 brake431, a B2 brake432, and B3 brake433.

By the engagement of the frictional engagement elements of first shift portion300and second shift portion400in the combinations shown in the operation table ofFIG. 3, five forward gears of first to fifth gears are implemented in transmission200.

When C0 clutch314and B0 brake316are in a disengaged state, the relative rotation of sun gear322, carrier326and ring gear328is permitted. In this state, power split device310functions as a continuously variable transmission. That is, transmission200enters a continuous shift state.

When C0 clutch314is in an engaged state, the relative rotation of sun gear322, carrier326and ring gear328is prohibited. In this state, power split device310does not function as a continuously variable transmission. That is, a stepwise shift state in which gear ratio changes stepwise in transmission200is established.

When B0 brake316is in an engaged state, sun gear322is fixed to case202. In this state, power split device310does not function as a continuously variable transmission. That is, transmission200enters a stepwise shift state.

As shown inFIG. 3, when shift lever804is in P position and when it is in N (Neutral) position, all the frictional engagement elements are caused to enter a disengaged state. Accordingly, transmission200enters a state where it cannot transmit torque to wheels. In this state, ring gear328cannot receive the reaction force of the driving force being output from engine100.

Shift (including switching between a continuous shift state and a stepwise shift state) in transmission200is controlled based on the shift map shown inFIG. 4, for example. The shift map in the present embodiment is determined with the parameters of target output torque calculated from accelerator pedal position and/or vehicle speed, and the vehicle speed. It is noted that parameters of a shift map are not limited thereto.

InFIG. 4, the solid line represents the up-shift line, and the dashed line represents the down-shift line. The range enclosed by the bold solid line inFIG. 4represents a range where the vehicle travels using only the driving force of second MG312and without using the driving force of engine100. The alternate long and short dash line inFIG. 4is a switch line for switching from the continuous shift state to the stepwise shift state. The alternate long and two short dashes line is a switch line for switching from the stepwise shift state to the continuous shift state.

When shift is implemented, C0 clutch314, B0 brake316, C1 clutch421, C2 clutch422, B1 brake431, B2 brake432and B3 brake433actuate by hydraulic pressure. In the present embodiment, as shown inFIG. 5, the hybrid vehicle is provided with a hydraulic control apparatus900feeding and exhausting hydraulic pressure to and from each frictional engagement element to control each element to engage and disengage.

Hydraulic control apparatus900includes a mechanical oil pump910and an electric motor driven oil pump920, and a hydraulic circuit930that adjusts hydraulic pressure generated at oil pumps910and920to be a line pressure and also uses the line pressure as an initial pressure to provide an adjusted hydraulic pressure and feed and exhaust the adjusted hydraulic pressure to and from each frictional engagement element, and also supplies an appropriate portion with oil for lubrication.

Mechanical oil pump910is a pump driven by engine100to generate hydraulic pressure. Mechanical oil pump910is for example arranged coaxially with carrier326, and receives torque from engine100to operate. That is, rotation of carrier326drives mechanical oil pump910and hydraulic pressure is generated.

In contrast, electric motor driven oil pump920is a pump driven by a motor (not shown). Electric motor driven oil pump920is attached at an appropriate location such as an exterior of a case202. Electric motor driven oil pump920is controlled by ECU800to generate hydraulic pressure as desired. For example, the rotation speed or the like of electric motor driven oil pump920is feedback-controlled.

Electric motor driven oil pump920is actuated by electric power supplied from a battery942via a DC/DC converter940. The electric power of battery942is supplied to first MG311and second MG312besides electric motor driven oil pump920.

Hydraulic circuit930includes a plurality of solenoid valves, switching valves or pressure adjustment valves (all not shown) and is configured to be capable of electrically controlling pressure adjustment, and hydraulic pressure to be fed and exhausted. It is controlled by ECU800.

Note that oil pumps910and920are provided at their respective discharging sides with check valves912and922, which are opened by pressures respectively caused as oil pumps910and920discharge, and are closed for a direction opposite to that of the pressures. Oil pumps910and920are connected parallel to each other relative to hydraulic circuit930. Furthermore a valve (not shown) that adjusts line pressure is configured to control the line pressure to have two states. More specifically, it increases an amount discharged and thus provides increased line pressure and, in contrast, decreases an amount discharged and thus provides decreased line pressure.

Referring toFIG. 6, the function of ECU800that is a control apparatus according to the present embodiment will be described. It is noted that the function of ECU800described below may be implemented by hardware or software.

ECU800includes a power generation control portion840, a shift operation expecting portion850, and a stopping portion860. While the shift range is P range, if power is generated by means of first MG311, power generation control portion840provides control over engine100for driving first MG311and provides control over second MG312for allowing ring gear328in power split device310to stop. For example, by supplying power only to d axis of second MG312, control is provided over second MG312for allowing ring gear328in power split device310to stop.

Shift operation expecting portion850expects that, when there is a brake operation by the driver, a shift operation will be performed. When a shift operation is expected, stopping portion860stops the control over engine100for driving first MG311and also stops the control over second MG312for allowing ring gear328to stop.

Referring toFIG. 7, a control structure of a program executed by ECU800that is a control apparatus according to the present embodiment will be described. It is noted that the program described in the following is repeatedly executed in predetermined cycles.

In step (hereinafter step is abbreviated as S)100, ECU800determines whether or not shift lever804is in P position, based on a signal transmitted from position switch806. If shift lever804is in P position (YES in S100), the process goes to S110. Otherwise (NO in S100), this process ends.

In S110, ECU800determines whether or not a brake operation is performed, based on a signal transmitted from brake switch814. If a brake operation is performed (YES in S110), the process goes to S140. Otherwise (NO in S110), the process goes to S120.

In S120, ECU800provides control over engine100for driving first MG311, and provides control over second MG312for allowing ring gear328in power split device310to stop. In S130, ECU800provides control over first MG311for allowing first MG311to actuate as a power generator.

In S140, ECU800expects that a shift operation will be performed. In S150, ECU800determines whether or not it is a state where the control is provided over engine100for driving first MG311for power generation by first MG311and the control is provided over second MG312for allowing ring gear328to stop. If it is the state where the control is provided over engine100for driving first MG311and the control is provided over second MG312for allowing ring gear328to stop (YES in S150), the process goes to S160. Otherwise (NO in S150), the process ends.

In S160, ECU800stops providing the control over engine100for driving first MG311, and also stops providing the control over second MG312for allowing ring gear328to stop.

In step S170, ECU800provides control over second MG312to actuate as a drive source of the vehicle. For example, by supplying power to d axis and q axis of second MG312, control is provided over second MG312to actuate as a drive source of the vehicle.

A description will now be given of an operation of ECU800that is the control apparatus according to the present embodiment based on the above-described structure and flowchart.

During a vehicle system is activated, whether or not shift lever804is in P position is determined, based on a signal transmitted from position switch806. When shift lever804is in P position (YES in S100), if the state of charge of battery942is low, it is necessary to charge battery942by actuating first MG311as a generator.

In order for first MG311to be actuated as a generator, first MG311must be driven by means of the driving force of engine100. On the other hand, as described above, when shift lever804is in P position, all the frictional engagement elements are in a disengaged state. Thus, the reaction force of the driving force output from engine100cannot be received by ring gear328of power split device310.

Accordingly, when a brake operation is not performed (NO in S110), control is provided over engine100for driving first MG311, and also control is provided over second MG312for allowing ring gear328to stop (S120). In this state, control is provided over first MG311for allowing first MG311to actuate as a generator (S130).

Thus, the reaction force can be received by ring gear328and the driving force output from engine100can efficiently be transmitted to first MG311. Accordingly, the power generation efficiency of first MG311can be improved.

Meanwhile, when shift lever804is shifted from P position to, for example D (Drive) position or R (Reverse) position and the vehicle is started, control for allowing second MG312to actuate as a drive source must be entered.

However, in order for the control for allowing second MG312to actuate as a drive source to be entered from the state where the control is provided over second MG312for allowing ring gear328to stop, torque of second MG312once becomes “0”. Here, ring gear328cannot receive the reaction force of the driving force output from engine100, and the engine speed may abruptly be increased.

Therefore, based on that a brake operation will be performed if a shift operation in which shift lever804is shifted from P position to D position or to R position is performed, when a brake operation by the driver is performed (YES in S110), it is expected that a shift operation will be performed (S140).

Here, if it is a state where the control is provided over engine100for driving first MG311and the control is provided over second MG312for allowing ring gear328to stop (YES in S150), the control over engine100for driving first MG311and the control over second MG312for allowing ring gear328to stop are stopped (S160). Control is provided over second MG312to actuate as a drive source of the vehicle (S170).

Thus, before a shift operation is actually performed, transition from the control for stopping ring gear328by second MG311to the control for employing second MG312as a drive source of the vehicle can be realized, without increasing the engine speed. Thus, the engine speed is prevented from being abruptly increased when the vehicle is started where a shift operation is performed.

As above, according to the ECU that is the control apparatus according to the present embodiment, when the shift lever is in P position and a brake operation is not performed, control is provided over the engine for driving the first MG for power generation by first MG, and also control is provided over the second MG for allowing the ring gear to stop. Based on that a brake operation will be performed when a shift operation in which the shift lever is shifted from P position to, for example, D position or R position is performed, it is expected that, if a brake operation by the driver is performed, then a shift operation will be performed. If it is expected that a shift operation will be performed, then the control over the engine for driving the first MG and the control over the second MG for allowing the ring gear to stop are stopped. Thus, before a shift operation is actually performed, transition from the control for stopping the ring gear by the second MG to the control for employing the second MG as a drive source of the vehicle can be realized, without increasing the engine speed. Thus, the engine speed is prevented from being abruptly increased when the vehicle is started where a shift operation is performed.

It is noted that, instead of five forward gears, four forward gears of first to fourth gears may be allowed to be implemented in transmission200. When transmission200is configured to be capable of implementing four forward gears, as shown inFIG. 8, second shift portion400includes two single pinion type planetary gears441and442and four frictional engagement elements of a C1 clutch451, a C2 clutch452, a B1 brake461, and a B2 brake462. By the engagement of the frictional engagement elements in the combinations shown in the operation table ofFIG. 9, four forward gears of first to fourth gears are implemented.

It is noted that, instead of switching between the continuous shift state and the stepwise shift state based on a switching line defined in the shift map, it is also possible to switch between the continuous shift state and the stepwise shift state based on the map having output torque of engine100and engine speed NE as parameters, as shown inFIG. 10.