WO2015159661A1

WO2015159661A1 - Hybrid vehicle

Info

Publication number: WO2015159661A1
Application number: PCT/JP2015/059011
Authority: WO
Inventors: Kensei Hata; Yuji Iwase; Hiroaki Ebuchi; Yosuke Suzuki; Koichi Kato; Seitaro NOBUYASU; Taro MOTEKI
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2014-04-17
Filing date: 2015-03-18
Publication date: 2015-10-22
Also published as: JP2015205526A

Abstract

A hybrid vehicle (Ve) is propelled by delivering torques of an engine (1) and a motor (2, 3, 20) to a drive shaft (5). In the hybrid vehicle (Ve), a clutch (7) having an outer race (7a) and an inner race (7b) is disposed between the engine (1) and the drive shaft (5), and the clutch (7) is brought into engagement by increasing a rotational speed of the second rotary member (7b) by the motor (2).

Description

DESCRIPTION

Title of Invention

HYBRID VEHICLE

Technical Field

The present invention relates to a hybrid vehicle powered by an engine and a motor. Background Art

One example of a hybrid vehicle is described in JP-A-8-295140. The hybrid vehicle taught by JP-A-8-295140 is comprised of an engine, a first motor adapted to generate electricity by an input torque, a second motor driven by an input current, an output shaft, a planetary gear unit, and a braking device. In the planetary gear unit, a sun gear is joined to the first motor, a ring gear is joined to the output shaft, and a carrier is joined to the engine. The braking device is brought into engagement to stop rotation of the engine 1.

According to the teachings of JP-A-8-295140, a clutch disposed between the engine and the braking device is brought into disengagement while applying a maximum current to the second motor under conditions that an opening degree of an accelerator is larger than 80% and a vehicle speed is lower than 30km/h.

Summary of Invention

Technical Problem

In the hybrid vehicle taught by JP-A-8-295140, the engine is allowed to be disconnected from a powertrain and the first motor is allowed to be stopped when the hybrid vehicle is powered by the second motor. According to the teachings of JP-A-8-295140, therefore, drag losses of the first motor and the planetary gear unit can be reduced to improve power transmission efficiency. In the hybrid vehicle of this kind, however, a hydraulic actuator or an electric actuator and a power source thereof is required to actuate the clutch. In addition, an additional space is required for the actuator and the power source and hence dimensions of the hybrid vehicle and a weight thereof are increased. Further, fuel consumption or an electric consumption is increased to actuate the clutch.

The present invention has been conceived noting the foregoing technical problems, and it is therefore an object of the present invention is to prevent an increment of a size and a weight of a hybrid vehicle having a clutch device for disconnecting an engine from a powertrain, and to improve an energy efficiency of the hybrid vehicle.

Solution to Problem

The present invention relates to a hybrid vehicle, which is propelled by delivering torques of an engine and a motor respectively serving as a prime mover to a drive shaft. In order to achieve the above-mentioned objectives, according to the present invention, a clutch having a first rotary member and a second rotary member rotated by the motor is disposed between the prime mover and the drive shaft. The clutch is adapted to be brought into engagement by increasing a rotational speed of the second rotary member.

Specifically, the first rotary member is connected to the engine or the drive shaft, and the second rotary member is connected to the motor. The clutch is brought into engagement by rotating the second rotary member at a speed higher than a predetermined speed so that the second rotary member comes into engagement with the first rotary member. The hybrid vehicle is further provided with a one-way clutch that is disposed in parallel to the clutch to unilaterally transmit torque of the prime mover to the drive shaft.

A rotational speed of the engine may be increased by bringing the clutch into engagement so that torque of the motor is applied thereto in a same rotational direction.

The hybrid vehicle is further provided with a controller that is configured to carry out a motoring of the engine by increasing a rotational speed of the clutch by the motor to bring the clutch into engagement, when the engine is required to be started during propelling the vehicle by the torque of the motor while stopping the engine.

The controller may be configured to maintain the clutch in partial engagement while establishing a predetermined torque transmitting capacity, by increasing a rotational speed of the motor to be higher than a threshold value and maintaining thereto.

The controller may also be configured to increase an output torque of the motor to cancel an inertia torque of the engine when the clutch starts to be brought into engagement to start the engine.

The controller may also be configured to increase a rotational speed of the engine after starting the engine, so as to rotate a rotary member of the one-way clutch of the prime mover side at a speed higher than that of a rotary member of the one-way clutch of the drive shaft side.

Alternatively, the controller may also be configured to control a rotational speed of the motor after starting the engine, so as to rotate the rotary member of the one-way clutch of the prime mover side at a speed higher than that of the rotary member of the one-way clutch of the drive shaft side.

According to the hybrid vehicle of the present invention, the motor includes at least a first motor and a second motor delivering torque to the output shaft. In addition, the hybrid vehicle further provided with a power distribution device that is interposed between the engine and the first motor to deliver torques of the engine and the first motor to the drive shaft while synthesizing or splitting those torques.

More specifically, the controller may be configured to carry out a motoring of the engine by increasing a rotational speed of the clutch by the first motor to bring the clutch into engagement, when the engine is required to be started during propelling the vehicle by the torque of the second motor while stopping the engine.

That is, the controller may be configured to increase an output torque of the second motor to cancel an inertia torque of the engine when the clutch starts to be brought into engagement to start the engine.

Advantageous Effects of Invention

According to the present invention, therefore, the hybrid vehicle is allowed by those clutches to be propelled under EV mode while disconnecting the engine from a powertrain, without using a friction clutch or dog clutch requiring an actuator. That is, since the actuator for actuating the friction clutch or the dog clutch and a power source can be eliminated, the hybrid vehicle can be downsized and a weight thereof can be reduced. In addition, a drag loss can be reduced under the EV mode by thus disconnecting the engine from the powertrains so that a power transmission efficiency of the hybrid vehicle can be improved. Further, the clutches employed in the hybrid vehicle of the present invention can be actuated without consuming energy so that fuel consumption and electric consumption can be reduced.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a schematic view showing a first example of the hybrid vehicle according to the present invention.

[Fig. 2] Fig. 2 is a schematic view showing a second example of the hybrid vehicle according to the present invention.

[Fig. 3] Fig. 3 is a nomographic diagram of a power distribution device of the hybrid vehicles shown in Figs. 1 and 2.

[Fig. 4] Fig. 4 is a schematic view showing a third example of the hybrid vehicle according to the present invention.

[Fig. 5] Fig. 5 is a nomographic diagram of a power distribution device of the hybrid vehicles shown in Fig. 4.

[Fig. 6] Fig. 6 is a schematic view showing a fourth example of the hybrid vehicle according to the present invention.

[Fig. 7] Fig. 7 is a nomographic diagram of a power distribution device of the hybrid vehicles shown in Fig. 6.

[Fig. 8] Fig. 8 is a schematic view showing a fifth example of the hybrid vehicle according to the present invention.

[Fig. 9] Fig. 9 is a nomographic diagram of a power distribution device of the hybrid vehicles shown in Fig. 8.

[Fig. 10] Fig. 10 is a schematic view showing a sixth example of the hybrid vehicle according to the present invention.

[Fig. 11] Fig. 11 is a flowchart showing a first control example of the hybrid vehicle. [Fig. 12] Fig. 12 is a time chart showing a situation of the hybrid vehicle during execution of the control examples.

[Fig. 13] Fig. 13 is a flowchart showing a second control example of the hybrid vehicle.

[Fig. 14] Fig. 14 is a flowchart showing a third control example of the hybrid vehicle. [Fig. 15] Fig. 15 is a flowchart showing a fourth control example of the hybrid vehicle. [Fig. 16] Fig. 16 is a flowchart showing a fifth control example of the hybrid vehicle. [Fig. 17] Fig. 17 is a flowchart showing a six control example of the hybrid vehicle.

Description of Embodiments

Next, preferred example of the present invention will be described in more detail with reference to the accompanying drawings. Referring now to Fig. 1, there is shown a first example of the hybrid vehicle. According to the first example, a prime mover of the hybrid vehicle Ve includes an engine 1 (abbreviated as "ENG" in the drawings), a first motor-generator (abbreviated as "MG1" in the drawings) 2, and a second motor-generator (abbreviated as "MG2" in the drawings) 3. A power of the engine 1 is distributed to the first motor-generator 2 side and to a drive shaft 5 side through a power distribution device 4. Meanwhile, an electric power generated by the first motor-generator 2 can be supplied to the second motor-generator 3 so that the second motor-generator 3 is driven to generate a torque for rotating the drive shaft 5.

The engine 1 is allowed to be adjusted, started and stopped electrically. Specifically, given that a gasoline engine is used as the engine 1, an opening degree of a throttle valve, an amount of fuel supply, a commencement and a termination of ignition, an ignition timing etc. are controlled electrically.

In the preferred examples, a permanent magnet type synchronous motor having a generating function is used individually as the first motor-generator 2 and the second motor-generator 3. Each of the first motor-generator 2 and the second motor-generator 3 is individually connected with a not shown battery through a not shown inverter to control a rotational speed and a torque thereof so that the motor-generators 2 and 3 can be operated selectively as a motor or a generator responsive to a current applied thereto.

In the example shown in Fig. 1, specifically, the power distribution device 4 is a single pinion type planetary gear unit adapted to perform a differential action among three rotary element such as a sun gear S, a ring gear R and a carrier C.

The planetary gear unit serving as the power distribution device 4 is arranged coaxially with a crankshaft la of the engine 1, and the first motor-generator 2 is situated on an opposite side of the engine 1 across the power distribution device 4. The sun gear S of the power distribution device 4 is connected with a rotor shaft 2a of the first motor-generator 2, and the ring gear R as an internal gear is situated concentrically with the sun gear S. A plurality of pinion gears are interposed between the sun gear S and the ring gear R while meshing with those gears, and those pinion gears are supported by the carrier C connected with an input shaft 4a of the power distribution device 4 in a rotatable and revolvable manner. The input shaft 4a is connected with the crankshaft la of the engine 1 through a one-way clutch 6 and a centrifugal clutch 7. Thus, the power distribution device 4 interposed between the engine 1 and the first motor-generator 2 to deliver torques of those power sources to the drive shaft 5 while synthesizing or splitting those torques.

The one-way clutch 6 is adapted to transmit engine torque unilaterally to the power distribution device 4. Specifically, the one-way clutch 6 is brought into engagement when the crank shaft la is rotated at a speed higher than the input shaft 4a to transmit power of the engine 1 to the power distribution device 4. By contrast, the one-way clutch 6 is brought into disengagement when the crankshaft la is rotated at a speed lower than the input shaft 4a to interrupt power transmission between the engine 1 and the power distribution device 4.

The centrifugal clutch 7 is comprised of an outer race 7a rotated integrally with the crankshaft la, an inner race 7b rotated integrally with the input shaft 4a, and a weight 7c that is moved centrifugally. Specifically, the weight 7c is fitted onto the inner race 7b and actuated centrifugally to connect the inner race 7b to the outer race 7a. That is, the centrifugal clutch 7 is brought into engagement to enable power transmission between the engine 1 and the power distribution device 4 by rotating the inner race 7b at a speed higher than a predetermined speed so that the weight 7c is subjected to a sufficient centrifugal force. By contrast, the centrifugal clutch 7 is brought into disengagement to interrupt the power transmission between the engine 1 and the power distribution device 4 when the rotational speed of the inner race 7b is lower than the predetermined speed and hence the centrifugal force applied the weight 7c is insufficient.

When the centrifugal clutch 7 is in engagement, an output torque of the first motor-generator 2 can be transmitted to the engine 1 through the power distribution device 4 and the input shaft 4a. That is, the centrifugal clutch 7 can be brought into disengagement by increasing a rotational speed of the inner race 7b by the output torque of the first motor 2 transmitted thereto through the power distribution device 4. Consequently, a rotational speed of the engine 1 can be increased by the output torque of the first motor 2.

Accordingly, the outer race 7a serves as the claimed first rotary member, the inner race 7b serves as the claimed second rotary member, the centrifugal clutch 7 serves as the claimed clutch and, the power distribution device 4 serves as the claimed power distribution device.

The one-way clutch 6 and the centrifugal clutch 7 are disposed parallel to each other between the engine 1 and the drive shaft 5. Specifically, the centrifugal clutch 7 is disposed between the crankshaft la and the input shaft 4a, and the one-way clutch 6 is disposed between the outer race 7a connected to the crankshaft la and the inner race 7b connected to the input shaft 4a. Accordingly, torque of the engine 1 is allowed to be transmitted to the drive shaft 5 upon engagement of the one-way clutch 6.

A drive gear 8 as an external gear is integrally formed around the ring gear R of the planetary gear unit, and a countershaft 9 is arranged parallel to a common rotational axis of the power distribution device 4 and the first motor-generator 2. A counter driven gear 10 is fitted onto one of the end portions of the countershaft 9 in a manner to be rotated integrally therewith while being meshed with the drive gear 8. Meanwhile, the counter drive gear 13 is fitted onto the other end portion of the countershaft 9 in a manner to be rotated integrally therewith while being meshed with a ring gear 12 of a deferential gear unit 11 serving as a final reduction. Thus, the ring gear R of the power distribution device 4 is connected with the drive shaft 5 through the gear train comprised of the drive gear 8, the countershaft 9, the counter driven gear 10, the counter drive gear 13, and the deferential gear unit 11. In the powertrain shown in Fig. 1, a torque of the second motor-generator 3 can be added to a torque transmitted from the power distribution device 4 to the drive shaft 5. To this end, the second motor-generator 3 is arranged parallel to the countershaft 9, and a pinion gear 14 connected with the rotor shaft 3a of the second motor-generator 3 is meshed with the counter driven gear 10. Here, a diameter of the pinion gear 14 is smaller than that of the counter driven gear 10 so that the torque generated by the second motor-generator 3 is transmitted to the counter driven gear 10 or to the countershaft 9 while being amplified.

In order to operate the engine 5 and the motor-generators 2 and 3, the vehicle Ve is provided with an electronic control unit (abbreviated as "ECU" hereinafter) 15 that serves as the claimed controller. The ECU 15 is comprised of a microcomputer configured to carry out a calculation based on input data and preinstalled data, and to transmit a calculation result in the form of a command signal.

Referring now to Fig. 2, there is shown a second example of the hybrid vehicle Ve. According to the second example, the second motor-generator 3 is connected to the above-explained gear train comprised of the drive gear 8, the countershaft 9, the counter driven gear 10 and the counter drive gear 13 through a reduction gear unit 16.

According to the second example, specifically, a single-pinion planetary gear unit is also used as the reduction gear unit 16 comprising a sun gear 16s, a ring gear 16r, and a carrier 16c. The sun gear 16s is joined to the rotor shaft 3a of the second motor-generator 3, and the ring gear 16r is connected to the ring gear R of the power distribution device 4 to be rotated integrally therewith. The drive gear 8 as an external gear is integrally formed around the ring gear R of the power distribution device 4 and the ring gear 16r. The carrier 16r is fixed to a fixed member 17 such as a housing in a manner not to rotate.

A gear ratio of the reduction gear unit 16 is set in a manner such that a rotational speed of the ring gear 16r is reduced to be lower than that of the sun gear 16s. Accordingly, torque of the second motor-generator 3 is delivered to the counter driven gear 10 and the countershaft 9 through the drive gear 8 while being amplified.

Fig. 3 is a nomographic diagram showing rotational states of the power distribution device 4 shown in Figs. 1 and 2. In Fig. 3, line LI represents a situation in which the vehicle Ve is powered by the second motor-generator 3 under an electric vehicle mode (abbreviated as the "EV mode" hereinafter) while stopping the engine 1. In the situation indicated by the line LI, the first motor-generator 2 is not rotated, and both the one-way clutch 6 and the centrifugal clutch 7 are brought into disengagement to disconnect the engine 1 from the power distribution device 4. If a rotational speed of the first motor-generator 2 is increased in the forward direction, a rotational speed of the carrier C joined to the input shaft 4a is increased in the forward direction as indicated by a broken line L2. Consequently, a rotational speed of the inner race 7b of the centrifugal clutch 7 is increased so that the inner race 7b is eventually engaged with the outer race 7a. That is, a transmission torque of the centrifugal clutch 7 is increased gradually so that a torque transmission between the input shaft 4a and the crankshaft la is enabled eventually. As a result, the rotational speed of the crankshaft la is increased so that the engine 1 is started. It is to be noted that the forward direction denotes a rotational direction of the engine 1, and a backward direction denotes a rotational direction opposite to the rotational direction of the engine 1.

Thus, in the vehicle Ve shown in Figs. 1 and 2, the engine 1 can be started under the EV mode by controlling the rotational speed of the first motor-generator 2. Specifically, when the engine 1 is required to be started, the rotational speed of the first motor-generator 2 is increased in the forward direction to increase the rotational speed of the carrier C connected to the inner race 7b of the centrifugal clutch 7 through the input shaft 4a. Consequently, the centrifugal clutch 7 is brought into engagement so that the rotational speed of the crankshaft la is increased to crank the engine 1. Then, when the rotational speed of the crankshaft la is increased to a predetermined speed, the engine 1 is ignited.

During the above-explained starting operation of the engine 1, the centrifugal clutch 7 is mainly involved in a torque transmission between the engine 1 and the power distribution device 4 until the completion of the starting operation of the engine 1. Then, when the starting operation of the engine 1 is completed and the rotational speed of the crankshaft la exceeds the rotational speed of the input shaft 4a of the power distribution device 4, the one-way clutch 6 is brought into engagement. Subsequently, the one-way clutch 6 is mainly involved in the torque transmission between the engine 1 and the power distribution device 4. Thus, according to the first and the second examples of the vehicle Ve, the clutch involved in the torque transmission is switched before and after the starting operation of the engine 1 between the centrifugal clutch 7 and the one-way clutch 6 arranged parallel to each other. That is, the centrifugal clutch 7 will not be involved in the torque transmission after the completion of the starting operation of the engine 1 so that a torque transmitting capacity of the centrifugal clutch 7 can be reduced to such an extent that the cranking of the engine 1 can be carried out. Therefore, the centrifugal clutch 7 can be downsized.

A third example and a fourth example of the vehicle Ve are shown in Figs. 4 and 6 respectively. In the vehicle Ve shown in Fig. 4, the one-way clutch 6 and the centrifugal clutch 7 are disposed between the rotor shaft 2a of the first motor-generator 2 and the sun gear S of the power distribution device 4.

According to the third example shown in Fig. 4, the one-way clutch 6 is adapted to transmit torque of the first motor-generator 2 only in a direction toward the power distribution device 4. Specifically, the one-way clutch 6 is brought into engagement when a rotational speed of the rotor shaft 2a side exceeds a rotational speed of the sun gear S side to transmit power of the first motor-generator 2 to the power distribution device 4. By contrast, the one-way clutch 6 is brought into disengagement when the rotational speed of the rotor shaft 2a side is lower than that of the sun gear S side to interrupt power transmission between the first motor-generator 2 and the power distribution device 4.

According to the third example, in the centrifugal clutch 7, the outer race 7a is joined to the sun gear S to be rotated integrally therewith, and the inner race 7b is joined to the rotor shaft 2a to be rotated integrally therewith. Accordingly, the centrifugal clutch 7 is brought into engagement to enable power transmission between the first motor-generator 2 and the power distribution device 4 by rotating the rotor shaft 2a at a speed higher than a predetermined speed so that the weight 7c is subjected to a sufficient centrifugal force. By contrast, the centrifugal clutch 7 is brought into disengagement to interrupt the power transmission between the first motor-generator 2 and the power distribution device 4 when the rotational speed of the rotor shaft 2a is lower than the predetermined speed and hence the centrifugal force applied the weight 7c is insufficient.

Fig. 5 is a nomographic diagram showing rotational states of the power distribution device 4 shown in Fig. 4. In Fig. 5, line Lll represents a situation in which the vehicle Ve is powered by the second motor-generator 3 under the EV mode while stopping the engine 1. In the situation indicated by the line Lll, the first motor-generator 2 is not rotated, and both the one-way clutch 6 and the centrifugal clutch 7 are brought into disengagement to disconnect the first motor-generator 2 from the power distribution device 4. In this situation, the sun gear S of the power distribution device 4 is rotated backwardly at a predetermined speed.

In the situation indicated by the line Lll, a rotational speed of the inner race 7b can be increased by increasing a rotational speed of the first motor-generator 2 in the forward direction so that the inner race 7b is eventually engaged with the outer race 7a. That is, a transmission torque of the centrifugal clutch 7 is increased gradually so that a torque transmission between the first motor-generator 2 and the sun gear S of the power distribution device 4 is enabled eventually. In addition, a rotational speed of the carrier C joined to the input shaft 4a is increased in the forward direction as indicated by a broken line L12. Consequently, a rotational speed of the crankshaft la is increased so that the engine 1 is started.

Thus, in the vehicle Ve shown in Fig. 4, the engine 1 can be started under the EV mode by controlling the rotational speed of the first motor-generator 2. Specifically, when the engine 1 is required to be started, the rotational speed of the first motor-generator 2 is increased in the forward direction to increase the rotational speed of the inner race 7b of the centrifugal clutch 7. Consequently, the centrifugal clutch 7 is brought into engagement so that the rotational speed of the sun gear S connected to the first motor-generator 2 through the centrifugal clutch 7 is increased in the forward direction. Eventually, the rotational speed of the carrier C is increased so that the rotational speed of the crankshaft la is increased to crank the engine 1. Then, when the rotational speed of the carrier C is increased to a predetermined speed, the engine 1 is ignited.

According to the fourth example shown in Fig. 6, the one-way clutch 6 and the centrifugal clutch 7 are disposed between the ring gear R of the power distribution device 4 and the drive gear 8. Specifically, a first hollow shaft 18 is formed around the ring gear R to be rotated therewith, and a second hollow shaft 19 is formed concentrically with the first hollow shaft 18. The drive gear 8 is fitted onto the second hollow shaft 19, and the second hollow shaft 19 is adapted to be rotated relatively with the first hollow shaft 18. That is, the one-way clutch 6 and the centrifugal clutch 7 are disposed between the first hollow shaft 18 and the second hollow shaft 19.

According to the fourth example shown in Fig. 6, the one-way clutch 6 is adapted to transmit torque only in a direction from the power distribution device 4 to the drive shaft 5. Specifically, the one-way clutch 6 is brought into engagement when a rotational speed of the ring gear R side exceeds a rotational speed of the drive gear 8 side to transmit power from the power distribution device 4 to the drive shaft 5. By contrast, the one-way clutch 6 is brought into disengagement when the rotational speed of the ring gear R side is lower than that of the drive gear 8 side to interrupt power transmission between the power distribution device 4 and the drive shaft 5.

According to the fourth example, in the centrifugal clutch 7, the outer race 7a is joined to the second hollow shaft 19 to be rotated integrally therewith, and the inner race 7b is joined to the first hollow shaft 18 to be rotated integrally therewith. Accordingly, the centrifugal clutch 7 is brought into engagement to enable power transmission between the power distribution device 4 and the drive shaft 5 by rotating the ring gear R at a speed higher than a predetermined speed so that the weight 7c is subjected to a sufficient centrifugal force. More specifically, the centrifugal clutch 7 is brought into engagement by rotating the ring gear R and the inner race 7b in the backward direction at a speed higher than the predetermined speed. By contrast, the centrifugal clutch 7 is brought into disengagement to interrupt the power transmission between the power distribution device 4 and the drive shaft 5 when the rotational speed of the ring gear R is lower than the predetermined speed and hence the centrifugal force applied the weight 7c is insufficient.

Fig. 7 is a nomographic diagram showing rotational states of the power distribution device 4 shown in Fig. 6. In Fig. 7, line L21 represents a situation in which the vehicle Ve is powered by the second motor-generator 3 under the EV mode while stopping the engine 1. In the situation indicated by the line L21, the first motor-generator 2 is not rotated, and the ring gear R is also not rotated so that both the one-way clutch 6 and the centrifugal clutch 7 are brought into disengagement to disconnect the second motor-generator 3 from the power distribution device 4.

In the situation indicated by the line L21, a rotational speed of the sun gear S can be increased in the forward direction by increasing a rotational speed of the first motor-generator 2 in the forward direction. Consequently, the carrier C connected to the engine 1 serves as a fulcrum so that rotational speeds of the ring gear R and the inner race 7b are increased in the backward direction and the inner race 7b is eventually engaged with the outer race 7a. That is, a transmission torque of the centrifugal clutch 7 is increased gradually so that a torque transmission between the second motor-generator 3 and the ring gear R is enabled eventually. In this situation, rotational speeds of the carrier C of the power distribution device 4 and the input shaft 4a are increased in the forward direction by generating a torque for cranking the engine 1 by the first motor-generator 2 while establishing a reaction torque counteracting to the cranking torque by the second motor-generator 3. Consequently, as indicated by a broken line L22, a rotational speed of the crankshaft la is increased so that the engine 1 is started. To this end, the second motor-generator 3 generates a total torque of the drive torque and the reaction torque.

Thus, in the vehicle Ve shown in Fig. 6, the engine 1 can be started under the EV mode by controlling the rotational speed of the first motor-generator 2. Specifically, when the engine 1 is required to be started, the rotational speeds of the first motor-generator 2 and the ring gear R of the power distribution device 4 are increased in the forward direction to increase the rotational speed of the inner race 7b of the centrifugal clutch 7 in the backward direction. Consequently, the centrifugal clutch 7 is brought into engagement so that the rotational speed of the ring gear R connected to the second motor-generator 3 through the centrifugal clutch 7 is increased in the forward direction. Eventually, the rotational speed of the carrier C is increased so that the rotational speed of the crankshaft la is increased to crank the engine 1. Then, when the rotational speed of the carrier C is increased to a predetermined speed, the engine 1 is ignited.

A fifth example of the vehicle Ve is shown in Fig. 8. In the vehicle Ve shown in Fig. 8, the engine 1 is connected to the first motor-generator 2 through the one-way clutch 6 and the centrifugal clutch 7.

According to the third example shown in Fig. 8, the one-way clutch 6 is adapted to transmit torque of the engine 1 only in a direction toward the power distribution device 4. Specifically the one-way clutch 6 is brought into engagement when a rotational speed of the crankshaft la side exceeds a rotational speed of the carrier C side to transmit power of the engine 1 to the power distribution device 4. By contrast, the one-way clutch 6 is brought into disengagement when the rotational speed of the crankshaft la side is lower than that of the carrier C side to interrupt power transmission between the engine 1 and the power distribution device 4.

According to the fifth example, in the centrifugal clutch 7, the outer race 7a is joined to the crankshaft la to be rotated integrally therewith, and the inner race 7b is joined to the carrier C through the input shaft 4a to be rotated integrally therewith. Accordingly, the centrifugal clutch 7 is brought into engagement to enable power transmission between the engine 1 and the power distribution device 4 by rotating the input shaft 4a together with the carrier C at a speed higher than a predetermined speed so that the weight 7c is subjected to a sufficient centrifugal force. By contrast, the centrifugal clutch 7 is brought into disengagement to interrupt the power transmission between the engine 1 and the power distribution device 4 when the rotational speed of the input shaft 4a is lower than the predetermined speed and hence the centrifugal force applied the weight 7c is insufficient.

Thus, according to the fifth example, the rotor shaft 3a of the second motor-generator 3 is connected to the carrier C of the power distribution device 4 to be rotated integrally therewith, and the rotor shaft 3a is also connected to the inner race 7b of the centrifugal clutch 7 to be rotated integrally therewith through the input shaft 4a. Therefore, the centrifugal clutch 7 can be brought into engagement by increasing a rotational speed of the second motor-generator 3 to increase a rotational speed of the inner race 7b.

Fig. 9 is a nomographic diagram showing rotational states of the power distribution device 4 shown in Fig. 8. In Fig. 8, line L31 represents a situation in which the vehicle Ve is powered by at least one of the motor-generators 2 and 3 under the EV mode while stopping the engine 1. In the situation indicated by the line L31, a rotational speed of the first motor-generator 2 rotating the input shaft 4a and the carrier C of the power distribution device 4 is lower than the predetermined speed to bring the centrifugal clutch 7 into engagement. In this situation, therefore, the engine 1 is disconnected from power distribution device 4.

In the situation indicated by the line L31, a rotational speed of the inner race 7b can be increased by increasing a rotational speed of the second motor-generator 3 in the forward direction so that the inner race 7b is eventually engaged with the outer race 7a. That is, a transmission torque of the centrifugal clutch 7 is increased gradually so that a torque transmission between the engine 1 and the carrier C of is enabled eventually. Consequently, a rotational speed of the crankshaft la is increased as indicated by a broken line L32 and the engine 1 is started when the rotational speed of the crankshaft la reaches a starting speed.

Thus, in the vehicle Ve shown in Fig. 8, the engine 1 can be started under the EV mode by controlling the rotational speed of the second motor-generator 3. Specifically, when the engine 1 is required to be started, the rotational speed of the second motor-generator 3 is increased in the forward direction to increase the rotational speed of the inner race 7b of the centrifugal clutch 7. Consequently, the centrifugal clutch 7 is brought into engagement so that the rotational speed of the crankshaft la connected to the second motor-generator 3 through the centrifugal clutch 7 is increased to crank the engine 1. Then, when the rotational speed of the carrier C is increased to a predetermined speed, the engine 1 is ignited.

A sixth example of the vehicle Ve is shown in Fig. 10. In the vehicle Ve shown in Fig. 10, the prime mover includes the engine 1 and a motor-generator 20, and a transmission (abbreviated as T/M in Fig. 10) 22 is disposed between the motor-generator 20 and a driveshaft 21. Specifically, the engine 1, the motor-generator 20 and the transmission 22 are arranged coaxially with the crankshaft 22a of the engine 1, and a rotor shaft 20a of the motor-generator 20 is connected to an input shaft 22a of the transmission 22. According to the sixth example, the one-way clutch 6 and the centrifugal clutch 7 are disposed between the engine 1 and the motor-generator 20.

According to the sixth example shown in Fig. 10, the one-way clutch 6 is adapted to transmit torque of the engine 1 only in a direction toward the motor-generator 20. Specifically, the one-way clutch 6 is brought into engagement when a rotational speed of the crankshaft la side exceeds a rotational speed of the rotor shaft 20a side to transmit power of the engine 1 to the motor-generator 20. By contrast, the one-way clutch 6 is brought into disengagement when the rotational speed of the crankshaft la side is lower than that of the rotor shaft 20a to interrupt power transmission between the engine 1 and the motor-generator 20.

According to the sixth example, in the centrifugal clutch 7, the outer race 7a is joined to the crankshaft la to be rotated integrally therewith, and the inner race 7b is joined to the rotor shaft 20a to be rotated integrally therewith. Accordingly, the centrifugal clutch 7 is brought into engagement to enable power transmission between engine 1 and the motor-generator 20 by rotating the rotor shaft 20a at a speed higher than a predetermined speed so that the weight 7c is subjected to a sufficient centrifugal force. By contrast, the centrifugal clutch 7 is brought into disengagement to interrupt the power transmission between the engine 1 and the motor-generator 20 when the rotational speed of the rotor shaft 20a is lower than the predetermined speed and hence the centrifugal force applied the weight 7c is insufficient.

Thus, in the vehicle Ve shown in Fig. 10, the engine 1 can be started under the EV mode by controlling the rotational speed of the motor-generator 20. Specifically, when the engine 1 is required to be started, the rotational speed of the motor-generator 20 is increased in the forward direction to increase the rotational speed of the inner race 7b of the centrifugal clutch 7. Consequently, the centrifugal clutch 7 is brought into engagement so that the rotational speed of the crankshaft la connected to the motor-generator 20 through the centrifugal clutch 7 is increased to crank the engine 1. Then, when the rotational speed of the crankshaft la is increased to a predetermined speed, the engine 1 is ignited.

In order to improve energy efficiency depending on a running condition, a drive mode of the vehicle Ve is selected from a hybrid mode (abbreviated as the "HV mode" hereinafter) in which the vehicle Ve is powered at least by the engine 1, and the EV mode in which the vehicle Ve is powered at least one of the motor-generators 2, 3 and 20 while stopping the engine 1.

The EV mode can be selected from a "disconnecting EV mode" in which both the one-way clutch 6 and the centrifugal clutch 7 are brought into disengagement so that the engine 1 is completely disconnected from the power train, and a "connecting EV mode" in which the centrifugal clutch 7 is brought into engagement at least partially so that the engine 1 is rotated by an external torque without supplying fuel thereto. Specifically, the connecting EV mode is selected when an engine braking force is required, or when the vehicle speed is high and the engine 1 is required to be restarted. If the vehicle is propelled under the connecting EV mode at high speed, the rotational speed of the engine 1 can be maintained at a desired speed to shorten a required time to be restarted. Therefore, the engine 1 can be restarted smoothly under the EV mode to generate a required driving force.

The ECU 15 is configured to shift the drive mode of the vehicle Ve smoothly from the disconnecting EV mode to the connecting EV mode by starting the engine 1 smoothly while suppressing a torque change.

A first example of such control to be carried out by the ECU 15 will be explained with reference to a flow chart shown in Fig. 11, and the routine shown therein is repeated at predetermined intervals. At step SI, it is determined whether or not the vehicle Ve is propelled under the disconnecting EV mode.

If the current drive mode is not the disconnecting EV mode so that the answer of step SI is NO, the routine is returned without carrying out any specific control.

By contrast, if the vehicle Ve is being propelled under the disconnecting EV mode so that the answer of step SI is YES, the routine advances to step S2 to determine a presence of a command signal for starting the engine 1 to shift the drive mode from the disconnecting EV mode to the HV mode.

If the command signal for starting the engine 1 has not yet been transmitted so that the answer of step S2 is NO, the routine is returned without carrying out subsequent controls.

By contrast, if the command signal for starting the engine 1 has been transmitted so that the answer of step S2 is YES, a rotational speed of the motor-generator is increased at step S3 so that the centrifugal clutch 7 is brought into engagement to increase a rotational speed of the engine 1. To this end, in the vehicle Ve shown in Fig. 1, 2, 4 or 6, the rotational speed of the first motor-generator 2 is increased in the forward direction. Likewise, in the vehicle Ve shown in Fig. 8, the rotational speed of the second motor-generator 3 is increased in the forward direction, and in the vehicle Ve shown in Fig. 10, the rotational speed of the motor-generator 20 is increased in the forward direction.

In addition, when the rotational speed of engine 1 is raised to be higher than an ignition speed, the engine 1 is ignited while spraying fuel within a combustion chamber of the engine 1. That is, a starting control of the engine 1 is carried out.

Then, at step S4, it is determined whether or not the starting control of the engine 1 has been completed. In other words, it is determined whether or not a self-sustaining condition of the engine 1 has been achieved.

If the engine starting control has not yet been completed so that the answer of step S4 is NO, the routine is returned to step S3 to repeat the engine starting control until the self-sustaining condition of the engine 1 is achieved.

By contrast, if the engine starting control has already been completed so that the answer of step S4 is YES, the routine is returned.

Temporal changes in behaviors of elements of the vehicle Ve shown in Fig. 1 or 2 during execution of the control shown in Fig. 11 will now be explained with reference to the time chart shown in Fig. 12.

In the situation shown in Fig. 12, the vehicle Ve is propelled under the disconnecting EV mode before point tl. When a command to start the engine 1 is transmitted at the point tl, an engine starting flag is turned on and a rotational speed of the first motor-generator 2 is gradually increased in the forward direction. Consequently, a rotational speed of the input shaft 4a connected to the carrier C of the power distribution device 4 is also increased gradually in the forward direction.

As a result, a rotational speed of the inner race 7b of the centrifugal clutch 7 is raised to be brought into engagement with the outer race 7a so that the torque transmitting capacity of the centrifugal clutch 7 starts increasing at point t2.

The rotational speed of the first motor-generator 2 is increased until point t3. During increasing the rotational speed of the first motor-generator 2, an output torque thereof is applied to the crankshaft la of the engine 1 through the power distribution device 4 and the centrifugal clutch 7. Consequently, the rotational speed of the engine 1 is gradually increased from the point t2 at which the centrifugal clutch 7 starts to be brought into engagement. Then, when the rotational speed of the engine 1 reaches the ignition speed, the engine 1 is ignited.

Then, when a determination of completion of the engine starting control is made at point t4, the rotational speed of the first motor-generator 2 is gradually lowered and the rotational speed of the engine 1 in the self-sustaining condition is gradually increased. In this situation, the rotational speed of the input shaft 4a is also changed in response to a change in the speed of the first motor-generator 2.

When the rotational speed of the engine 1 reaches the rotational speed of the input shaft 4a at point t5, the one-way clutch 6 is brought into engagement to deliver the torque of the engine 1 to the input shaft 4a. Consequently, the drive mode of the vehicle Ve is shifted to the HV mode at the point t5 so that the vehicle Ve is powered by the engine 1.

Here will be explained a second control example with reference to a flowchart shown in Fig. 13. In the second example, steps Sll and S12 are similar to steps SI and S2 of the first control example shown in Fig. 11. According to the second control example shown in Fig. 13, if the command signal for starting the engine 1 has been transmitted so that the answer of step S12 is YES, the routine advances to step S13 to crank the engine 1 as the aforementioned step S3 of the first control example shown in Fig. 11.

Then, at step S14, it is determined whether or not a rotational speed of the motor-generator being increased to crank the engine 1 is higher than a threshold value a. For example, in the vehicle Ve shown in Fig. 1, 2, 4 or 6, a rotational speed of the first motor-generator 2 is compared to the threshold value a. Likewise, in the vehicle Ve shown in Fig. 8, the rotational speed of the second motor-generator 3 is compared to the threshold value a, and in the vehicle Ve shown in Fig. 10, the rotational speed of the motor-generator 20 is compared to the threshold value a.

Specifically, the threshold value a is set to a value at which the centrifugal clutch 7 is allowed to be maintained in partial engagement while establishing a predetermined torque transmitting capacity.

If the rotational speed of the motor-generator being increased is still lower than the threshold value a so that the answer of step S14 is NO, the routine is returned to step S13 to repeat the cranking of the engine 1. That is, steps S13 and S14 are repeated until the rotational speed of the motor-generator exceeds the threshold value a.

By contrast, if the rotational speed of the motor-generator being increased is higher than the threshold value a so that the answer of step S14 is YES, the routine advances to step S15. At step S15, specifically, the rotational speed of the motor-generator is maintained when exceeds the threshold value a. In addition, the ignition control of the engine 1 is executed as the aforementioned step S3 of the first example shown in Fig. 11.

Temporal changes in the rotational speed of the first motor-generator 2 and the torque transmitting capacity of the centrifugal clutch 7 during execution of the second control example are also indicated in Fig. 12. When the rotational speed of the first motor-generator 2 being increased from the point tl reaches the threshold value a at the point t3, the rotational speed of the first motor-generator 2 is kept to the threshold value a. Consequently, the torque transmitting capacity of the centrifugal clutch 7 being increased from the point t2 is also kept constant after the point t3. Specifically, the centrifugal clutch 7 is maintained in the partial engagement so that the torque transmitting capacity thereof is kept approximately to 50%. In this situation, the cranking and the ignition of the engine 1 are carried out.

In case of thus maintaining the centrifugal clutch 7 into partial engagement, the centrifugal clutch 7 is allowed to serve as a damper to dampen torque pulses and fluctuations resulting from starting the engine 1. In this case, therefore, torque pulses and fluctuations resulting from starting the engine 1 will not propagate to the powertrain from the input shaft 4a to the drive shaft 5.

Referring back to Fig. 13, after carrying out the ignition control of the engine 1 while maintaining the rotational speed of the motor-generator, the routine advances to step S16 to determine whether or not the starting control of the engine 1 has been completed. In other words, it is determined whether or not the self-sustaining condition of the engine 1 has been achieved.

If the engine starting control has not yet been completed so that the answer of step S16 is NO, the routine is returned to step S15 to repeat the engine starting control while maintaining the rotational speed of the motor-generator until the self-sustaining condition of the engine 1 is achieved.

By contrast, if the engine starting control has already been completed so that the answer of step S16 is YES, the routine is returned.

Here will be explained a third control example with reference to a flowchart shown in Fig. 14. In the third example, steps S21 and S22 are similar to steps SI and S2 of the first control example shown in Fig. 11.

According to the third control example shown in Fig. 14, if the command to start the engine 1 is transmitted so that the answer of step S22 is YES, the routine advances to step S23 to crank the engine 1 as the aforementioned step S3 of the first control example shown in Fig. 11.

Then, at step S24, it is determined whether or not an engagement of the centrifugal clutch 7 has been started so that the centrifugal clutch 7 starts transmitting torque. To this end, for example, transmission torque of the centrifugal clutch 7 can be estimated by measuring rotational speeds of the crankshaft la and the input shaft 4a.

If the centrifugal clutch 7 has not yet transmitted torque so that the answer of step S24 is NO, the routine is returned to step S23 to repeat the cranking of the engine 1. That is, steps S23 and S24 are repeated until the centrifugal clutch 7 starts transmitting torque.

By contrast, if the centrifugal clutch 7 has already started to transmit torque so that the answer of step S24 is YES, the routine advances to step S25 to increase an output torque of the motor-generator in the forward direction. Specifically, in the vehicle Ve shown in Fig. 1, 2, 4 or 6, the output torque of the first motor-generator 2 is increased in the forward direction. Likewise, in the vehicle Ve shown in Fig. 8, the output torque of the second motor-generator 3 is increased in the forward direction, and in the vehicle Ve shown in Fig. 10, the output torque of the motor-generator 20 is increased in the forward direction.

That is, at step S25, the output torque of the motor-generator is increased to counteract to an inertia torque of the engine 1 applied to the centrifugal clutch 7 when bringing into engagement (i.e., a torque compensation). Consequently, an impact resulting from bringing the centrifugal clutch 7 can be suppressed. Temporal changes in the output torque of the first motor-generator 2 and the torque transmitting capacity of the centrifugal clutch 7 during execution of the third control example are also indicated in Fig. 12. During a period from the point tl to the point t2, the output torque of the first motor-generator 2 is increased to keep increasing the rotational speed thereof to increase the rotational speed of the centrifugal clutch 7. When the centrifugal clutch 7 starts to be brought into engagement at the point t2, the output torque of the first motor-generator 2 is further increased until the transmission torque of the centrifugal clutch 7 is stabilized at the point t3. After the point t3, the impact of the inertia torque is reduced and hence the output torque of the first motor-generator 2 is reduced to a level at which the transmission torque of the centrifugal clutch 7 can be maintained to a steady level.

When the centrifugal clutch 7 is brought into engagement to transmit torque by increasing a rotational speed thereof, the rotational speed of the centrifugal clutch 7 would be lowered by the inertia torque of the engine 1. However, such reduction in the transmission torque and the rotational speed of the centrifugal clutch 7 can be prevented by thus increasing the output torque of the motor-generator to counteract to the inertia torque of the engine 1.

Referring back to Fig. 14, after thus increasing the output torque of the motor-generator at step S25, the ignition control of the engine 1 is executed at step

526 as the aforementioned step S3 of the first example shown in Fig. 11.

After increasing the output torque of the motor-generator to counteract to the inertia torque of the engine 1 and then carrying out the ignition control of the engine 1, the routine advances to step S27 to determine whether or not the starting control of the engine 1 has been completed. In other words, it is determined whether or not the self-sustaining condition of the engine 1 has been achieved.

If the engine starting control has not yet been completed so that the answer of step

527 is NO, the routine is returned to step S26 to repeat the engine starting control until the self-sustaining condition of the engine 1 is achieved.

By contrast, if the engine starting control has already been completed so that the answer of step S27 is YES, the routine is returned.

Here will be explained a fourth control example with reference to a flowchart shown in Fig. 15. In the fourth example, steps S31, S32, S33 and S34 are similar to steps SI, S2, S3 and S4 of the first control example shown in Fig. 11.

According to the fourth control example, if the engine starting control has already been completed so that the answer of step S35 is YES, the routine advances to step S36 to increase a rotational speed of the engine 1 in the forward direction. In this case, since the engine 1 has already been brought into the self-sustaining condition, the rotational speed of the engine 1 can be increased by the ECU 15.

Then, at step S37, it is determined whether or not the one-way clutch 6 is in engagement to transmit torque of the engine 1 to the input shaft 4a. To this end, for example, the engagement state of the one-way clutch 6 can be estimated by measuring rotational speeds of the crankshaft la and the input shaft 4a.

If the one-way clutch 6 is still in disengagement so that the answer of step S37 is NO, the routine is returned to step S36 to repeat augmentation of the engine speed until the one-way clutch 6 is brought into engagement to transmit torque.

By contrast, if the one-way clutch 6 has already been brought into engagement so that the answer of step S37 is YES, the routine is returned.

Temporal changes in the rotational speed of the engine 1 and the transmission torque of the one-way clutch 6 during execution of the fourth control example are also indicated in Fig. 12. When the determination of completion of the engine starting control is made at point t4, the rotational speed of the engine 1 is gradually increased until the point t5 at which the rotational speed of the engine 1 reaches the rotational speed of the input shaft 4 so that the one-way clutch 6 is brought into engagement.

In this case, the engine torque can be delivered promptly to the drive shaft 5 side after the completion of the engine starting control by thus increasing the rotational speed of the engine 1 until the one-way clutch 6 is brought into engagement.

Here will be explained a fifth control example with reference to a flowchart shown in Fig. 16. In the fifth example, steps S41, S42, S43 S44 and S45 are similar to steps SI, S2, S3, S4 and S5 of the first control example shown in Fig. 11.

According to the fifth control example, if the engine starting control has already been completed so that the answer of step S45 is YES, the routine advances to step S46 to control a rotational speed of the motor-generator in the backward (i.e., negative) direction. Consequently, the rotational speed of the motor-generator rotated in the forward direction to start the engine 1 is reduced gradually. For example, in the vehicle Ve shown in Fig. 1, 2, 4 or 6, the rotational speed of the first motor-generator 2 is reduced gradually. Likewise, in the vehicle Ve shown in Fig. 8, the rotational speed of the second motor-generator 3 is reduced gradually, and in the vehicle Ve shown in Fig. 10, the rotational speed of the motor-generator 20 is reduced gradually.

Then, at step S47, it is determined whether or not the one-way clutch 6 is in engagement to transmit torque of the engine 1 to the input shaft 4a. To this end, for example, the engagement state of the one-way clutch 6 can be estimated by measuring rotational speeds of the crankshaft la and the input shaft 4a.

If the one-way clutch 6 is still in disengagement so that the answer of step S47 is NO, the routine is returned to step S46 to repeat the control of the rotational speed of the motor-generator in the backward direction until the one-way clutch 6 is brought into engagement to transmit torque.

By contrast, if the one-way clutch 6 has already been brought into engagement so that the answer of step S47 is YES, the routine is returned.

Temporal changes in the rotational speed of the motor-generator and the transmission torque of the one-way clutch 6 during execution of the fifth control example are also indicated in Fig. 12. When the determination of completion of the engine starting control is made at point t4, the rotational speed of the first motor-generator 2 is gradually reduced until the point t5 at which the rotational speed of the engine 1 reaches the rotational speed of the input shaft 4 so that the one-way clutch 6 is brought into engagement.

In this case, the engine torque can be delivered promptly to the drive shaft 5 side after the completion of the engine starting control by thus lowering the rotational speed of the first motor-generator 3 until the one-way clutch 6 is brought into engagement.

Thus, the advantages of the fourth control example shown in Fig. 15 achieved by increasing the rotational speed of the engine 1 may also be achieved by reducing the rotational speed of the motor-generator. In addition, the control response of the motor-generator is quicker than that of the engine 1 so that the rotational speed of the motor-generator can be changed quickly. Further, those control of increasing the rotational speed of the engine 1 and control of reducing the rotational speed of the motor-generator may be switched according to need.

Here will be explained a sixth control example to be carried out in the vehicles Ve shown in Figs. 1, 2, 4 and 6, with reference to a flowchart shown in Fig. 17. In the sixth example, steps S51 and S52 are similar to steps SI and S2 of the first control example shown in Fig. 11.

According to the six control example shown in Fig. 17, if the command signal for starting the engine 1 has been transmitted so that the answer of step S52 is YES, the routine advances to step S53 to crank the engine 1 as the aforementioned step S3 of the first control example shown in Fig. 11.

Then, at step S54, it is determined whether or not an engagement of the centrifugal clutch 7 has been started so that the centrifugal clutch 7 starts transmitting torque. To this end, for example, transmission torque of the centrifugal clutch 7 can be estimated by measuring rotational speeds of the crankshaft la and the input shaft 4a.

If the centrifugal clutch 7 has not yet transmitted torque so that the answer of step S54 is NO, the routine is returned to step S53 to repeat the cranking of the engine 1. That is, steps S53 and S54 are repeated until the centrifugal clutch 7 starts transmitting torque.

By contrast, if the centrifugal clutch 7 has already started to transmit torque so that the answer of step S54 is YES, the routine advances to step S55 to increase an output torque of the second motor-generator 3 in the forward direction.

That is, at step S55, the output torque of the second motor-generator 3 is increased to counteract to an inertia torque of the engine 1 applied to the centrifugal clutch 7 when bringing into engagement. Consequently, an impact resulting from bringing the centrifugal clutch 7 can be suppressed. Temporal changes in the output torque of the second motor-generator 3 and the torque transmitting capacity of the centrifugal clutch 7 during execution of the sixth control example are also indicated in Fig. 12. During a period from the point tl to the point t2, the second motor-generator 3 generates torque to propel the vehicle Ve. When the centrifugal clutch 7 starts to be brought into engagement at the point t2, the output torque of the second motor-generator 3 is increased until the engine starting control is completed at the point t4.

During the period from the commencement of engagement of the centrifugal clutch 7 to the completion of the starting control of the engine 1, the inertia torque of the engine 1 is transmitted to the drive shaft 5 through the centrifugal clutch 7 and the input shaft 4a. However, the inertia torque of the engine 1 can be cancelled by thus increasing the output torque of the second motor-generator 3 when starting the engine 1.

Referring back to Fig. 17, after thus increasing the output torque of the second motor-generator 3 at step S55, the ignition control of the engine 1 is executed at step S56 as the aforementioned step S3 of the first example shown in Fig. 11.

After increasing the output torque of the second motor-generator 3 to counteract to the inertia torque of the engine 1 and then carrying out the ignition control of the engine 1, the routine advances to step S57 to determine whether or not the starting control of the engine 1 has been completed. In other words, it is determined whether or not the self-sustaining condition the engine 1 has been achieved. If the engine starting control has not yet been completed so that the answer of step S57 is NO, the routine is returned to step S56 to repeat the engine starting control until the self-sustaining condition of the engine 1 is achieved.

By contrast, if the engine starting control has already been completed so that the answer of step S57 is YES, the routine is returned.

Claims

[Claim 1]

A hybrid vehicle (Ve), which is propelled by delivering torques of an engine (1) and a motor (2, 3, 20) respectively serving as a prime mover to a drive shaft (5), characterized by:

a clutch (7) having a first rotary member (7a) and a second rotary member (7b) rotated by the motor (2), that is brought into engagement by increasing a rotational speed of the second rotary member (7b), and that is disposed between the prime mover and the drive shaft (5).

[Claim 2]

The hybrid vehicle (Ve) as claimed in claim 1,

wherein the first rotary member (7a) is connected to the engine (1) or the drive shaft (5), and the second rotary member (7b) is connected to the motor (2); wherein the clutch (7) is brought into engagement by rotating the second rotary member (7b) at a speed higher than a predetermined speed so that the second rotary member (7b) comes into engagement with the first rotary member (7a); and the hybrid vehicle (Ve) further comprises a one-way clutch (6) that is disposed in parallel to the clutch (7) to unilaterally transmit torque of the prime mover to the drive shaft (5).

[Claim 3]

The hybrid vehicle (Ve) as claimed in claim 1 or 2, wherein a rotational speed of the engine (1) is increased by bringing the clutch (7) into engagement so that torque of the motor (2) is applied thereto in a same rotational direction.

[Claim 4]

The hybrid vehicle (Ve) as claimed in any of claims 1 to 3, further comprising: a controller (15) configured to carry out a motoring of the engine (1) by increasing a rotational speed of the clutch (7) by the motor (2) to bring the clutch (7) into engagement, when the engine (1) is required to be started during propelling the vehicle (Ve) by the torque of the motor (2, 3) while stopping the engine (1).

[Claim 5]

The hybrid vehicle (Ve) as claimed in claim 4, wherein the controller (15) is further configured to maintain the clutch (7) in partial engagement while establishing a predetermined torque transmitting capacity, by increasing a rotational speed of the motor (2, 3, 20) to be higher than a threshold value (a) and maintaining thereto.

[Claim 6]

The hybrid vehicle (Ve) as claimed in claim 4 or 5, wherein the controller (15) is further configured to increase an output torque of the motor (2, 3, 20) to cancel an inertia torque of the engine (1) when the clutch (7) starts to be brought into engagement to start the engine (1).

[Claim 7]

The hybrid vehicle (Ve) as claimed in any of claims 4 to 6, wherein the controller (15) is further configured to increase a rotational speed of the engine (1) after starting the engine (1), so as to rotate a rotary member of the one-way clutch (6) of the prime mover side at a speed higher than that of a rotary member of the one-way clutch (6) of the drive shaft (5) side.

[Claim 8]

The hybrid vehicle (Ve) as claimed in any of claims 4 to 7, wherein the controller (15) is further configured to control a rotational speed of the motor (2, 3, 20) after starting the engine (1), so as to rotate the rotary member of the one-way clutch (6) of the prime mover side at a speed higher than that of the rotary member of the one-way clutch (6) of the drive shaft (5) side.

[Claim 9]

The hybrid vehicle (Ve) as claimed in any of claims 1 to 8,

wherein the motor includes at least a first motor (2) and a second motor (3) delivering torque to the output shaft (5); and

the hybrid vehicle (Ve) further comprises a power distribution device (4) that is interposed between the engine (1) and the first motor (2) to deliver torques of the engine (1) and the first motor (2) to the drive shaft (5) while synthesizing or splitting those torques.

[Claim 10]

The hybrid vehicle (Ve) as claimed in claim 9, wherein the controller (15) is configured to carry out a motoring of the engine (1) by increasing a rotational speed of the clutch (7) by the first motor (2) to bring the clutch (7) into engagement, when the engine (1) is required to be started during propelling the vehicle (Ve) by the torque of the second motor (3) while stopping the engine (1).

[Claim 11]

The hybrid vehicle (Ve) as claimed in claim 10, wherein the controller (15) is further configured to increase an output torque of the second motor (3) to cancel an inertia torque of the engine (1) when the clutch (7) starts to be brought into engagement to start the engine (1).