WO2008074201A1

WO2008074201A1 - Driving system for hybrid electric vehicle

Info

Publication number: WO2008074201A1
Application number: PCT/CN2007/001005
Authority: WO
Inventors: Chuanfu Wang; Hongbin Luo; Xiaoling Zhang; Youchuan Song; Yi Ren
Original assignee: Byd Company Limited
Priority date: 2006-12-19
Filing date: 2007-03-28
Publication date: 2008-06-26
Also published as: CN101204920A

Abstract

A driving system for a hybrid electric vehicle comprises an engine (1) and a motor (4) that provide power to a transmission device (5), a generator (2) that receives the power supply from the engine (1) to generate electric power, and a power supply unit (7) electrically connected between the generator (2) and the motor (4), a double-clutch unit (8) which is connected between the engine (1) and the generator (2) as well as between the engine (1) and the transmission device (5), and designed to transfer the power from the engine (1) to the generator (2) or the transmission unit selectively. When the vehicle runs at a low speed, the double-clutch unit (8) is controlled to transfer the power from the engine (1) to the generator (2) to generate electric power, and the motor (4) receives the electric power and outputs dynamic energy to the transmission device (5) to drive the vehicle running, so as to implement the series driving of the hybrid electric vehicle. When the vehicle runs at a high speed, the double-clutch unit (8) is controlled to transfer the power from the engine directly to the transmission device to drive the vehicle running.

Description

Driving System for Hybrid Electric Vehicle

TECHNICAL FIELD

The present invention relates to a driving system for hybrid electric vehicle.

BACKGROUND

Today, people face two major challenges: shortage of energy resources and deterioration of environment. Traditional vehicles are severely trapped in oil crisis increasingly; energy conservation and environmental protection has become a topic in development of the vehicle industry. In recent years, a hybrid electric vehicle (HEV) that utilizes two types of power sources and can reduce fuel consumption and exhaust emission were developed and applied, and put into commercial production and introduced to the market. Presently, the hybrid electric vehicle in mass production includes Toyota Prius, Toyota Crown, Honda Insight, and Honda Civic, etc. Existing driving systems for the hybrid electric vehicle can be roughly classified into the series, the parallel and the series/parallel forms (SHEV, PHEV and PSHEV), by the nature of electromechanical coupling.

The series power system comprises an engine, a generator, and a motor power assemblies, which are connected in series to form the power system; wherein, the engine drives the generator to generate electric power which is transferred via a controller to a battery or the motor; and the motor drives the vehicle to run via a transmission mechanism. Under a light load, the battery drives the motor to drive the wheels; under a heavy load, the engine drives the generator to generate electric power and thereby drive the motor. When the vehicle is under stop-start, acceleration, or climbing working condition, the engine-motor assembly and the battery together supply electric power to the motor; when the vehicle is at low speed, slide, or idle speed working condition, the battery drives the motor; when the battery is short of power, the engine-generator assembly charges the battery. The series structure is applicable to frequent stop-start and slow-speed running working condition in urban area. With the series structure, the engine can be adjusted to operate stably at the optimal condition-point, and the vehicle speed can be adjusted by adjusting the output of battery and motor. The series structure avoids the engine operating at idle speed or low speed, and thereby improves engine efficiency and reduces exhaust emission. However, it has the drawback that: the energy is converted several times, resulting in lower mechanical efficiency.

The parallel power system comprises the engine and the motor that drive the vehicle together; that is to say, the engine and the motor are in two systems, and can supply torque to the transmission device separately; on different roads, they can drive the vehicle together or separately. When the vehicle climbs, the motor and the engine can supply power to the transmission device; once the vehicle reaches to the cruising speed, the vehicle speed is maintained solely by the engine. The motor can serves as motor and generator, and therefore is also referred to as dynamotor. Since there is no separate generator, the engine can drive the wheels directly via the transmission device; this structure is more similar to the driving systems in conventional vehicles, and has a mechanical efficiency loss similar to those in ordinary vehicles.

The series and parallel power system combines the features of series system and parallel system. The power system comprises the engine, the generator, and the motor; it can be classified as engine-based system or motor-based system, depending on the booster mechanism. In an engine-based system, the engine serves as the primary power source, while the motor serves as the secondary power source; in a motor-based system, the engine serves as the secondary power source, while the motor serves as the primary power source. The advantage of such a structure is easy control, while the drawback is complex structure.

Fig.1 shows the structure of a typical driving system for a hybrid electric vehicle in prior art. As shown in Fig.l, the power output shaft of engine 1 is connected to the planet carrier of a planetary gear mechanism 3; therefore, partial power is transferred via the ring gear in the planetary gear mechanism 3 to the transmission device 5 and drives the wheels 6 to rotate; the rest power drives generator 2 via the sun gear to generate electric power and transfer the electric power to the battery 7; then, the battery 7 supplies power to the motor 4 to drive the motor 4 to transfer power to the transmission device 5, so as to drive wheels 6 to rotate. In addition, a gearbox or transmission can be mounted on the transmission device 5, as required. In that structure, the planetary gear mechanism 3 serves as a power distribution mechanism. In some cases, a power combination mechanism, such as a planetary gear mechanism, can be used to combine the power output from engine 1 and the power output from motor 4, and then transfer the combined power to wheels 6.

Those driving systems for hybrid electric vehicle have been described in a number of patent documents (e.g., CN1413855A), and have been widely applied in the field.

However, there is no such a driving system for hybrid electric vehicle in prior art that can choose series power drive mode when the vehicle runs at low speed, and choose parallel power drive mode when the vehicle runs at high speed, and thereby meet the demand for high torque when the vehicle runs at low speed and meet the demand for high power when the vehicle runs at high speed.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a driving system for hybrid electric vehicle, which can choose series power drive mode when the vehicle runs at low speed and choose parallel power drive mode when the vehicle runs at high speed, and thereby meets the demand for high torque at low speed and meet the demand for high power at high speed. The driving system for hybrid electric vehicle provided in the present invention comprises an engine and a motor that provide power to a transmission device, a generator that receives power supply from the engine to generate electric power, and a power supply unit electrically connected between the generator and the motor; wherein, the system further comprises a double-clutch unit which is connected between the engine and the generator as well as between the engine and the transmission device, and designed to transfer the engine power to the generator or the transmission device selectively.

When the vehicle runs at low speed (e.g., below 50KnVh), the first clutch in the double-clutch unit disengages and the second clutch engages, so that the engine power is transferred via the engaged second clutch to the generator to generate electric power and store the electric power to the power supply unit; then, the power supply unit supplies power to the motor, which transfers mechanical energy to the transmission device and drives the vehicle to run, and thereby implement the series drive mode for the hybrid electric vehicle. In that case, the engine operates under an economic working condition; therefore, the economical efficiency of fuel is improved, and the exhaust emission is reduced. In addition, since the rotate speed of the motor is low, the torque is high, and the working efficiency is high. Furthermore, as the self-regulating rotate speed feature of the motor, indefinite ratios control can be implemented simply. When the vehicle runs at high speed (e.g., >50Km/h), the first clutch in the double-clutch unit engages, and the second clutch disengages, so that the engine power is transferred via the engaged first clutch to the transmission device directly and drive the vehicle to run, i.e., it implements the engine power drive mode simply, so as to meet the demand for high power at high speed. When the vehicle requires higher power (e.g., when it accelerates or climbs), the motor can be put into operation, with power supply from the power supply unit; in that case, the power from the engine and the power from the motor are both transferred to the transmission device simultaneously to drive the vehicle to run, so as to implement the parallel drive mode. In a preferred embodiment of the present invention, the system further comprises a planetary gear mechanism, which comprises the first to the third rotating components connected to the driven part of the first clutch, the driven part of the second clutch, and the transmission device, respectively. In a more preferred embodiment, the planetary gear mechanism 3 comprises a planet carrier connected to the driven part of the first clutch, a sun gear connected to the driven part of the second clutch, and a ring gear connected to the transmission device.

In above preferred embodiments, since a planetary gear mechanism is utilized, when the vehicle requires higher power (e.g., when it accelerates or climbs), the engine power can be distributed via the planetary gear mechanism, so that partial power is transferred to the transmission device, while the rest power is transferred the generator to generate electric power and store the electric power to the power supply unit; then, the power supply unit supplies power to the motor, so that the motor transfers mechanical energy to the transmission device. In that case, the hybrid drive mode for the vehicle is implemented simply.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1 is a schematic view showing the structure of a typical driving system for hybrid electric vehicle in the prior art;

Fig.2 is a schematic view showing the structure of the driving system for hybrid electric vehicle in an embodiment of the present invention;

Fig.3 is a schematic view showing the structure of the driving system for hybrid electric vehicle in another embodiment of the present invention.

DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS

Hereunder the present invention will be described in embodiments, with reference to the accompanying drawings.

Fig.2 is a schematic view showing the structure of the driving system for hybrid electric vehicle in an embodiment of the present invention.

As shown in Fig.2, the driving system for hybrid electric vehicle provided in the present invention comprises an engine 1 and a motor 4 that supply power to a transmission device 5, a generator 2 designed to receive power from engine 1 to generate electric power, and a power supply unit 7 electrically connected between the generator 2 and the motor 4; wherein, the system further comprises a double-clutch unit 8 which is connected between the engine 1 and the generator 2 as well as between the engine 1 and the transmission device 5, and designed to transfer the power from the engine 1 to the generator 2 or transmission device 5 selectively. Double clutch units are usually used on a transmission, to form a double-clutch transmission (DCT) to implement stepless gearshift operation. DCT not. only ensures dynamic property and economical efficiency of the vehicle, but also greatly improves comfort of the vehicle. DCT technique employs two clutches on the basis of AMT technique, to control odd gear positions and even gear positions separately; during the gear shift process, another gear is already in engaged state before a gear disengages; in that way, DCT solves the problem of power interruption during gear shift. DCT can employ dry clutches or wet clutches, which are significantly different in working characteristics. Dry clutch can absorb a large quantity of heat by means of the disks and flywheels, and thereby is insensitive to the heat generation rate of sliding friction; however, due to the poor heat dissipation nature of air, the heat can't be dissipated in a short time; consequently, dry clutch is restricted by the total heat generated from sliding friction. Dry clutch is suitable for engaging for a short duration, therefore the heat generated is low in short sliding friction duration. Wet clutch employ oil-cooled friction disks, and thereby is restricted by heat generation rate instead of total heat generated; therefore, wet clutch is suitable for the case in which the pressure rises up gradually and the heat generation rate is low during the clutch engaging process. A smaller clutch margin factor can be chosen in the design, and the oil pressure increasing rate of the pressure cylinder can be controlled, to control the friction torque to increase gradually. DCT is developed on the basis of parallel manual transmission. It inherits the advantages of manual transmission, including high transmission efficiency, compact mounting space, light weight, and low cost. Furthermore, like AMT, DCT can protect the investment in existing production equipment for manual transmission units as far as possible. In addition, DCT implements power-based gear shift and avoid power interruption during the gear shift process, which means it absorbs the advantage of AT in gear shift performance. Some structures of DCT are essential components in driving systems for hybrid electric vehicle that are studied in major projects domestically and abroad.

CN 2587699Y has disclosed a DCT mechanism, comprising a transmission control unit (TCU) linked to clutches and gear-shift synchronizer, and a five gear position transmission unit; wherein, two wet clutches Cl and C2 are mounted on the power input shaft, the drive gears of the transmission unit are connected to clutches Cl and C2 against odd and even gear positions, and the clutches Cl and C2 transfer power in alternate to implement gear shift. That mechanism can effectively solve the problem of power interruption during the gear-shift process of existing electrically controlled mechanical automatic transmission units in vehicles and improve comfort during the vehicle runs. Above DCT can be used in the present invention.

In addition, double-clutch units are also disclosed in several patent documents, such as CN 1621715 A and CN 1523253 A, and have been widely applied. All above double-clutch units and other appropriate double-clutch units in prior art can be used for the double clutch unit 8 described in the present invention. The structure of double-clutch will not be described in detail hereunder in the present invention.

As a typical embodiment, as shown in Fig. 2, the double-clutch unit 8 in the present invention comprises the first clutch Cl and the second clutch C2; wherein, the driven part 81 of the first clutch Cl is connected to the transmission device 5, and the driven part 82 of the second clutch C2 is connected to the generator 2; the driving part 83 of the double-clutch unit 8 is connected to the output shaft 11 of the engine 1.

The first clutch Cl and the second clutch C2 can be existing dry clutches or wet clutches, and they can be controlled to engage or disengage with an existing transmission control unit (TCU). The TCU can be a mechanical one, hydraulic one, or electronic one.

When the vehicle runs at low speed, (for example, the vehicle runs at a speed lower than a specific speed (e.g., 50Km/h) on a urban road), the first clutch Cl disengages and the second clutch C2 engages, under the control of the existing TCU, so that the power from engine 1 is transferred in sequence via the output shaft 11 of engine 1, the driving part 83 of double-clutch unit 8, and the driven part 82 of the second clutch C2, to generator 2, to drive the rotator of generator 2 to rotate and generate electric power, and transfer the electric power to the power supply unit 7. Then, the power supply unit 7 supplies power to motor 4, so that motor 4 transfers power to the transmission device and drives the vehicle to run at low speed. In that case, engine 1 operates under an economic working condition; therefore, the economical efficiency of fuel oil is improved, and the exhaust emission is reduced. In addition, since the speed of motor 4 is low, the torque is high, and the working efficiency is high. Furthermore, as the self-regulating rotate speed feature of motor 4, indefinite ratios control can be implemented simply.

When the vehicle runs at high speed, (for example, the vehicle runs at a speed higher than a specific speed (e.g., 50KnVh) on a highway), the first clutch Cl engages and the second clutch C2 disengages, under the control of the existing TCU, so that the power from engine 1 is transferred in sequence via the output shaft 11 of engine 1, the driving part 83 of double-clutch unit 8, and the driven part 81 of the first clutch Cl, to the transmission device, to drive the vehicle to run, i.e., engine power drive mode is implemented simply and the demand for high power at high speed is met.

When the vehicle requires higher power (e.g., it accelerates or climbs), motor 4 can be started as an assistance to engine power drive; in that state, motor 4 is powered by power supply unit 7. In that case, the power from engine 1 and the power from motor 4 are transferred to the transmission device 5 to drive the vehicle; in that way, parallel drive mode is implemented simply. In addition, in that case, an existing power combination mechanism (e.g., a planetary gear mechanism) can be used to combine the power from engine 1 and the power from motor 4 and transfer the combined power to transmission device 5 to drive the vehicle.

When the vehicle brakes or slows down, motor 4 can serve as a generator to absorb energy, i.e., it transforms the mechanical energy from transmission device 5 into electric energy and stores the electric energy into power supply unit 7. Once the vehicle slows down from high speed to the preset low speed, the second clutch

C2 engages and the first clutch Cl disengages gradually, so that the vehicle enters into the series drive mode at low speed.

Furthermore, the transmission device 5 usually comprises a drive shaft, a reducer, a differential gear, axle shaft, and drive wheels, etc. A transmission can be incorporated into the transmission device 5 as required (e.g., the transmission device disclosed in CN 1413855A), so as to implement speed control with the transmission when the vehicle runs, especially in engine drive mode or parallel drive mode. Fig. 3 is a schematic view showing the structure of the driving system for hybrid electric vehicle in another embodiment of the present invention. Different from the embodiment described above, this embodiment is provided with a planetary gear mechanism 3. With the planetary gear mechanism 3, parallel and series drive mode (PSHEV) can be implemented for the vehicle. As shown in Fig.3, the driving system further comprises a planetary gear mechanism 3, which comprises the first to the third rotating components 31, 32, and 33, connected to the driven part 81 of the first clutch Cl, the driven part 82 of the second clutch C2, and the transmission device 5 respectively. The planetary gear mechanism 3 is well-known in the field, and usually comprises a sun gear, a pinion gear (connected to the planet carrier), and a ring gear. The planetary gear mechanism can further comprise a brake or a controller, to fix or restrict any one of the three rotating components selectively.

Preferably, the planetary gear mechanism 3 comprises a planet carrier 31 connected to the driven part 81 of the first clutch Cl, a sun gear 32 connected to the driven part 82 of the second clutch C2, and a ring gear 33 connected to the transmission device 5. However, those skilled in the art can understand that the present invention is not limited to that preferred structure and a variety of modifications can be made to it. For example, the driven part 81 of the first clutch Cl can be connected to the ring gear 33, the driven part 82 of the second clutch C2 can be connected to the sun gear 32, and the transmission device 5 can be connected to the planet carrier 31. In the above embodiment, when the vehicle runs at low speed, (for example, the vehicle runs at a speed lower than a specific speed (e.g., 50Km/h) on a urban road), the first clutch Cl disengages and the second clutch C2 engages, under the control of the existing TCU, so that the power from engine 1 is transferred in sequence via the output shaft 11 of engine 1, the driving part 83 of double-clutch unit 8, and the driven part 82 of the second clutch C2, to generator 2, to drive the rotator of generator 2 to rotate and generate electric power, and transfer the electric power to the power supply unit 7. Then, the power supply unit 7 supplies power to motor 4, so that the motor 4 transfers power to the gear system and drives the vehicle to run a low speed. In that case, engine 1 operates under an economic working condition; therefore, the economical efficiency of fuel oil is improved, and the exhaust emission is reduced. In addition, since the speed of motor 4 is low, the torque is high, and the working efficiency is high. Furthermore, thanks to the self-regulating feature of motor 4, indefinite ratios control can be implemented simply. In that case, since the driven part 82 of the second clutch C2 is also connected to the sun gear 32, the sun gear 32 will rotate synchronously with the driven part 82 of the second clutch C2 and the rotator of generator 2. In addition, since the transmission device 5 is connected to the ring gear 33, the ring gear 33 will also rotate.

As an option, a clutch 9 can be provided between the generator 2 and the sun gear 32. When the clutch 9 disengages, the driven part 82 of the second clutch C2 or the rotator of generator 2 will not transfer power to the sun gear 32. In addition, a clutch 10 can be provided between the ring gear 33 and the transmission device 5; when the clutch 10 disengages, ring gear 33 will not rotate together with the transmission device 5. By providing clutch 9 and clutch 10 and making them disengage, the three rotating components 31, 32 and 33 are kept in still state. For the convenience of automatic control, the clutch 9 and clutch 10 are preferably electrically controlled clutches.

When the vehicle runs at high speed, (for example, the vehicle runs at a speed higher than a specific speed (e.g., 50Km/h) on a highway), the first clutch Cl engages and the second clutch C2 disengages, under the control of the existing TCU, so that the power from engine 1 is transferred in sequence via the output shaft 11 of engine 1, the driving part 83 of double-clutch unit 8, the driven part 81 of the first clutch Cl, and the planet carrier 31 and ring gear 33 in planetary gear mechanism 3, to the gear system, to drive the vehicle to run, i.e., engine power drive mode can be implemented simply and the demand for high power at high speed is met. In that case, the sun gear 32 can be fixed with the brake in planetary gear mechanism 3, so that the sun gear 32 outputs power to the transmission device 5 via the ring gear 33. Or, if no brake is used, the rotator of generator 2 can be controlled with a controller, so as to control the state of the sun gear 32 connected to the rotator of generator 2.

When the vehicle requires higher power (e.g., when it accelerates or climbs), motor 4 can be started as an assistance to the engine power drive; in that state, motor 4 is powered by power supply unit 7. In that case, the power from engine 1 and the power from motor 4 are transferred to the gear system 5 to drive the vehicle; in that way, parallel drive mode can be implemented simply. If the power supply unit 7 is short of power and has to be charged, the braking or restriction to the sun gear 32 in the planetary gear mechanism 3 can be released, so that partial power from engine 1 is transferred via the sun gear 32 to generator 2, to drive generator 2 to generate electric power and store the electric power to power supply unit 7; then, the power supply unit 7 will supply power to motor 4, to drive motor 4 to transfer power to transmission device 5.

When the vehicle brakes or slows down, motor 4 can serve as generator to absorb energy, i.e., it transforms the mechanical energy from gear system 5 into electric energy and stores the electric energy to power supply unit 7. Once the vehicle slows down from high speed to the preset low speed, the second clutch C2 engages and the first clutch Cl disengages gradually, so that the vehicle enters into the series drive mode at low speed. That case is identical to the case in the first embodiment.

In addition, similar to the first embodiment, the second embodiment can also be provided with a transmission unit in transmission device 5, so as to implement speed control with the transmission unit when the vehicle runs.

Claims

1. A driving system for a hybrid electric vehicle, comprising an engine (1) and a motor (4) that supply power to a transmission device (5), a generator (2) designed to receive the power from the engine (1) to generate electric power, and a power supply unit (7) electrically connected between the generator (2) and the motor (4); wherein, the system further comprises a double-clutch unit (8) which is connected between the engine (1) and the generator (2) as well as between the engine (1) and the transmission device (5), and designed to transfer the power from the engine (1) to the generator (2) or the transmission device (5) selectively.

2. The driving system as in claim 1, wherein, the double-clutch unit (8) comprises a first clutch (Cl) and a second clutch (C2), the driven part (81) of the first clutch (Cl) is connected to the transmission device (5), the driven part (82) of the second clutch (C2) is connected to the generator (2), and the driving part (83) of the double-clutch unit (8) is connected to the output shaft (11) of the engine (1).

3. The driving system as in claim 2, further comprising a planetary gear mechanism (3) which comprises the first to the third rotating components (31, 32, and 33) connected to the driven part (81) of the first clutch (Cl), the driven part (82) of the second clutch (C2), and the transmission device (5), respectively.

4. The driving system as in claim 2, further comprising a planetary gear mechanism (3) which comprises a planet carrier (31) connected to the driven part (81) of the first clutch (Cl), a sun gear (32) connected to the driven part (82) of the second clutch (C2), and a ring gear (33) connected to the transmission device (5).

5. The driving system as in claim 4, further comprising a clutch (9) connected between the generator (2) and the sun gear (32).

6. The driving system as in claim 4 or 5, further comprising a clutch (10) connected between the ring gear (33) and the transmission device (5).

7. The driving system as in claim 6, wherein, the clutches (9 and 10) are electrically controlled clutches.

8. The driving system as in claim 1, wherein, the transmission device (5) has a transmission.