WO2010131942A1

WO2010131942A1 - Transmission system

Info

Publication number: WO2010131942A1
Application number: PCT/MY2010/000075
Authority: WO
Inventors: Fauzy Omar Basheer Osman @ Othman; Anuar Ahmad
Original assignee: Petroliam Nasional Berhad (Petronas)
Priority date: 2009-05-14
Filing date: 2010-05-13
Publication date: 2010-11-18
Also published as: CN102421619A; TWI527981B; CN102421619B; TW201100674A

Abstract

A transmission system having a first input shaft, a first centrifugal clutch having a first clutch drum being selectively driven by the first input shaft, a second input shaft, a second centrifugal clutch having a second clutch drum being selectively driven by the second input shaft. The first and second clutch drums are rotationally coupled by a fixed gear ratio. In one embodiment the first and second clutch drums are coaxial. A freewheeling clutch permits relative rotation between the second input shaft and the second clutch drum in a first direction but prevents relative rotation between the second input shaft and second clutch drum in a second direction. The transmission system may form part of a hybrid power unit. The hybrid power unit may form part of the vehicle including a first power unit in the form of an internal combustion engine and a second power unit in the form of an electric motor/generator. The internal combustion engine may drive the electric motor/generator in a generating mode via the freewheeling clutch to recharge an associated battery. The vehicle may be braked by driving the electric motor/generator in a generating mode via the freewheeling clutch. The electric motor/generator may drive the vehicle in reverse via the freewheeling clutch.

Description

TRANSMISSION SYSTEM

The present invention relates to a transmission system, in particular a transmission system for use with a hybrid vehicle.

Hybrid vehicles are known whereby a vehicle is provided with more than one prime mover. Typically one prime mover will be an internal combustion engine and another prime mover will be an electric motor. Depending upon the prevailing conditions, either the electric motor alone will operate to propel the vehicle, or the internal combustion engine alone will operate to propel the vehicle or the electric motor and the internal combustion engine will jointly propel the vehicle.

US5193634 shows just such a hybrid vehicle proportion system. In this case an internal combustion engine drives a continuously variable transmission (CVT) which is coupled to a centrifugal clutch which, when engaged, drives a wheel of the vehicle. In one embodiment an electric motor can drive the wheel via a freewheel clutch. In a second embodiment an electric motor can drive the wheel via a centrifugal clutch.

However, this system does not allow the internal combustion engine to drive the electric motor as a generator and hence recharge the associated batteries. Nor does it allow the wheel to drive the motor as a generator.

Thus, according to the present invention there is provided a transmission system having a first input shaft, a first centrifugal clutch having a first driving part mounted on said first input shaft and a first clutch drum being selectively driven by the first driving part, a second input shaft, a second centrifugal clutch having a second driving part mounted on said second input shaft and a second clutch drum being selectively driven by the second driving part, the first clutch drum being rotationally coupled to the second clutch drum and a freewheeling clutch permitting relative rotation between the second input shaft and the second clutch drum in a first direction but preventing relative rotation between the second input shaft and the second clutch drum in a second direction.

Advantageously, the freewheeling clutch allows a first and second clutch drums to drive the second input shaft. When the second input shaft is connected to an electric motor/generator, the electric motor/generator can operate as a motor to drive the second input shaft when required and can operate as a generator when required, being driven by the second input shaft. Furthermore, the second input shaft can be driven by the first input shaft. When such a system is provided in a vehicle, the second input shaft can be driven by the rear wheel and by using the electric motor/generator as a generator, braking of the vehicle can be affected whilst still recovering the braking energy and storing it in a battery.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a view of a vehicle according to the present invention including a hybrid power unit according to the present invention including a transmission system according to the present invention,

Figure 2 is a plan view of figure 1 ,

Figure 3 is a cross-section view of the transmission system of figure 1, and

Figure 4 is a view of part of figure 1 taken in the direction of arrow A.

With reference to figures 1 to 4 there is shown a vehicle 10, in this case a two wheeled moped. The moped includes a front wheel 11 and a rear wheel 12. A hybrid power unit 14 drives the vehicle. The hybrid power unit includes an engine 16 (in this case an internal combustion engine) and an electric motor/generator 18. A transmission system 20 is coupled to the rear wheel 12 via a drive arrangement, in this case in the form of a chain 22.

A transmission system 20 can be selectively driven by the electric motor/generator 18. The transmission system 20 can also be selectively driven by the engine 16, in this case via a continuously variable transmission (CVT) 24. The CVT is known and includes a CVT drive pulley 26, a CVT belt 28 and a CVT driven pulley 30. Such CVT systems are well known on mopeds, and US2003/0092529 shows an example of such a CVT system. However, in summary the CVT driven pulley 30 has two flanges 3 IA, 3 IB (see figure 3) which are pressed together via a spring 32 causing the effective diameter of the pulley to expand. The CVT drive pulley 26 includes two flanges which can be pushed together by balls acting on ramps. As the speed of the engine increases the balls are centrifuged outwardly causing the two flanges of the CVT drive pulley 26 to be pressed together, thereby increasing the effective diameter of the drive pulley 26 and consequently decreasing the effective diameter of the driven pulley 30. Thus, when the engine 16 is running at a relatively low speed the effective diameter of the drive pulley 26 is relatively small compared to the effective diameter of the driven pulley 30. However when the engine is running at relatively high speed, the effective diameter of the drive pulley 26 increases and the effective diameter of the driven pulley 30 decreases. By way of example, in one embodiment the lowest ratio of the CVT 24 is 2.4, i.e. 2.4 rotations of the drive pulley 26 cause one rotation of the driven pulley 30. The high ratio is 0.8, i.e. 0.8 rotations of the drive pulley 26 cause one rotation of the driven pulley 30.

Figure 3 shows the transmission system 20 in more detail together with part of the CVT 24.

The transmission system 20 includes a first input shaft 40, a second input shaft 42, a first centrifugal (CF) clutch 44, a second centrifugal clutch 46 and a freewheeling clutch 48.

The CVT 24 includes a two piece housing 50 having a first half 5OA and a second half 50B. The first and second halves are secured together by bolts 51. The left hand end (when viewing figure 3) of the first input shaft 40 is secured in a bush 53 which in turn is mounted in a bearing 54 secured in a bearing housing of the first half 5OA. The first input shaft 40 is also mounted in a bearing 55 mounted in a bearing housing of the second half 50B. The driven pulley 30 is secured rotationally fast (i.e. rotationally fixed) to the first input shaft 40 so as to enable the CVT belt 28 to drive the first input shaft 40 when required.

The housing 50 is secured to the vehicle 10.

The second input shaft 42 includes a projection 60 received within recess 61 of the first input shaft 40. The recess 61 includes two needle roller bearings 56 which rotatably support projection 60 and hence the second input shaft 42 at its left hand end (when viewing figure 3). The right hand end of the second input shaft 42 is supported on bearing 62 which in turn is supported by vehicle 10 (shown schematically).

The first centrifugal clutch 44 includes a first clutch drum 64. The second centrifugal clutch 46 includes a second clutch drum 66. The first clutch drum 64 is secured to the second clutch drum 66 via bolts 68. The left hand side of the first clutch drum 64 is supported by bearings 65 which in turn is supported on the first input shaft 40. The right hand side of the second clutch drum 66 is supported by the freewheeling clutch 48 as will be further described below. The second clutch drum 66 includes an extension 70 upon which is mounted sprocket 71 which in turn drives chain 22.

Mounted on the right hand end of the first input shaft 40 is a first driving part 74 of the first centrifugal clutch 44. The first driving part 74 includes a plate 75A upon which is mounted a pin 76A. A clutch shoe 77A is pivotally mounted on the pin 76A. A spring (not shown) biases a working surface (not shown) of the shoe radially inwardly, away from an inner surface of the first clutch drum 64. As the speed of the first input shaft 40 increases, centrifugal forces tend to bias the working surface of the clutch shoe 77A radially outwardly until such time as it engages the inner surface of the first clutch drum 64 thereby engaging the first centrifugal clutch.

The second centrifugal clutch 46 also includes a driving part 79 which operate in a similar manner to the first driving part 74. Thus the driving part 79 includes a plate 75B upon which is mounted a pin 76B. A clutch shoe 77B is pivotally mounted on the pin 76B and a spring (not shown) biases a working surface of the clutch shoe 77B away from an inner surface of the second clutch drum 66. As the speed of the second input shaft 42 increases, centrifugal forces overcome the bias of the spring thereby allowing the working surface of the shoe 77B to engage the inner surface of the second clutch drum 66 thereby engaging the second centrifugal clutch.

Freewheeling clutch (also known as an overrunning clutch or a one way clutch) 48 is known per se. The principle of operation of a freewheeling clutch is that it permits an outer part to rotate freely relative to an inner part in one direction but prevents rotation of the outer part relative to the inner part in the opposite direction. Freewheeling clutch 48 has an outer part 80 and an inner part 81. Figure 4 shows a view of vehicle 10 taken in the direction of arrow A (see figure 1 and figure 3). The freewheeling clutch 48 is configured so as to allow the inner part 81 to rotate clockwise relative to the outer part 80 but prevent anticlockwise rotation of the inner part 81 relative to the outer part 80. Thus, when the vehicle 10 is moving a forwards direction B because the one way clutch prevents anticlockwise movement of the inner part 81 relative to the outer part 80, then the inner part 81 will also be rotating in a clockwise direction. In other words, when the vehicle 10 is moving in a forwards direction, the inner part 81 must be rotating in a clockwise direction at least as fast as the outer part 80.

The electric motor/generator includes a power shaft 19 which is directly coupled to the right hand end of the second input shaft 42 (see figure 3). The electric motor is electrically coupled to an electrical energy storage device, in this case a battery 17.

Operation of the transmission system 20 is as follows:-

With the electric motor/generator stationary and with the engine running at an idle speed the CVT gear ratio will be 2.4 : 1 and hence the input shaft will be turning slower than the engine. At this speed the first centrifugal clutch 44 will not be engaged and hence engine power will not be transmitted to the rear wheel. Thus, with the engine idling the first input shaft 40 will be rotating. However, the first clutch drum 64, the second clutch drum 66 and the second input shaft 42 will all be stationary. As engine speed is increased the first input shaft speed will increase, firstly because of the increase in engine speed and secondly because of the change in gear ratio of the CVT. Thus, the clutch shoe 77A will be caused to spin and centrifuge radially outwardly so as to engage and rotate the first clutch drum 64 thereby causing the second clutch drum to rotate which in turn rotates the sprocket 71 and hence drives the rear wheel. Note that as the second clutch drum 66 is caused to rotate it will in turn rotate the outer part 80 of the freewheeling clutch and, as mentioned above, since the freewheeling clutch is configured so that the inner part 81 rotates at least as fast as the outer part 80 (when rotating clockwise when viewing figure 4) then the freewheeling clutch 48 will cause the second input shaft to rotate at the same speed as the first input shaft. As mentioned above, the electric motor/generator power shaft 19 is directly coupled to the second input shaft 42, and hence, under these circumstances the motor rotor will be rotating. However, under these circumstances the motor is not acting as a generator, and hence is not absorbing power, nor is it acting as a motor, and hence is not delivering power. Under these circumstances the vehicle is solely being propelled by the engine in spite of the fact that the motor rotor is rotating (but see below when the electric motor/generator is acting as a generator to recharge the battery).

The vehicle can alternatively be propelled by the electric motor/generator alone. Thus, under these circumstances the electric motor/generator directly turns the second input shaft 42 in a clockwise direction when viewing figure 4. When the second input shaft 42 is rotating at a low speed the second centrifugal clutch will be disengaged. Furthermore the freewheeling clutch will be operating in a freewheeling mode, i.e. when viewing figure 4 the inner part 81 will be rotating at the same speed as the electric motor/generator whereas the outer part will be stationary. As the speed of the electric motor/generator increases the clutch shoe 77B of the second centrifugal clutch will be centrifuged outwardly and engage the inner surface of the second clutch drum 66 causing the second centrifugal clutch to engage thereby propelling the vehicle. Under these circumstances the engine, the CVT and first input shaft will all be stationary and the first centrifugal clutch will be disengaged.

When it is required to slow the vehicle, the electric motor/generator can be driven by the rear wheel 12. Thus, when the vehicle 10 is travelling at a steady speed in a forwards direction B the engine 16 may be stationary and the electric motor/generator is operating as a motor to drive the vehicle. When braking is required the electric motor/generator can be switched to a generating mode which causes the second input shaft 42 to be braked. However, the inertia of the vehicle will continue to cause the rear wheel 12 to rotate in a clockwise direction when viewing figure 4 thereby causing the outer part 80 to also rotate in a clockwise direction. The freewheeling clutch is configured such that rotation of the outer part 80 causes clockwise rotation of the inner part 81 thereby driving the electric motor/generator in its generating mode and allowing the kinetic energy of the vehicle to be converted into electrical energy which is then stored in the battery 17.

The transmission system also allows for a reverse. Thus, with the engine stationary and the vehicle stationary the electric motor/generator can be powered in a reverse direction which will cause the freewheel clutch to engage. Reverse on a two wheeled vehicle is useful, for example when reversing out of a parking slot.

As mentioned above, it is possible to operate the vehicle using engine power alone, or using electric power alone, or using a combination of both. However, table 1 shows typical operating modes of the vehicle.

Table 1

With the vehicle stationary, the battery is neither being charged nor discharged.

With the vehicle moving away from stationary using electric power as the second input shaft progressively increases in speed, the second centrifugal clutch will progressively engage thereby turning the second clutch drum at the same speed as the second input shaft. Under these circumstances the outer part 80 will be rotating at the same speed as the inner part 81 though the freewheel clutch will not be transmitting any power.

Typically, where circumstances allow, with a vehicle speed between 0 km/h and 50 km/h the vehicle will be powered by the motor alone.

Above a vehicle speed of 50 km/h the engine will be used. If above this speed the battery requires recharging then the motor/generator can be switched to generating mode. However, if the battery is fully charged then whilst the second input shaft will be rotating at the same speed as the first input shaft, the motor/generator will be switched such that no power is absorbed.

For maximum power both the engine can be used to propel the vehicle and the motor/generator can be used to propel the vehicle.

At vehicle speeds below 50 km/h when the battery is low on power the engine can be turned on so as to both propel the vehicle and drive the motor/generator in a generating mode to recharge the battery.

During braking (with the engine on or off) the motor/generator can be switched to a generating mode thereby converting kinetic energy of the vehicle into stored electrical energy in the battery.

Since reversing generally occurs at low speed, the second input shaft will only be driven in a reverse direction at low speed and hence the second centrifugal clutch will not become engaged.

As described above, the drive arrangement connecting the transmission system to the rear wheel is chain 22. In further embodiments alternative drive arrangements could be used, such as a drive belt, or a drive shaft.

The physical position of various components relative to each other provide for a compact arrangement. Thus, as shown in figure 1, the engine is positioned in front of the transmission system 20 and in particular the CVT drive pulley 26 is positioned in front of the CVT driven pulley 30. The electric motor/generator 18, transmission system 20, and CVT driven pulley 30 are all positioned between the driven wheel 12 and the engine 16. When considering figure 2 the chain 22 is positioned on the right hand side of a plane defined by the centre of the rear wheel 12 and the CVT 24 is positioned to the left of the plane. When considering figure 3 the drive arrangement (chain 22) is positioned between the electric motor/generator on the right hand side of the chain and the first clutch drum 64, second clutch drum 66 and freewheeling clutch 48 all on the left hand side of the chain 22.

A suitable control system is provided to control the engine and the electric motor/generator. The control unit will control the mode of operation of the engine in conjunction with the mode of operation of the electric motor/generator especially as shown in the various operating modes of table 1. The controller will monitor or estimate battery power and set the operating mode of the electric motor/generator to motor mode or generator mode as required. The controller can also drive the electric motor in reverse direction when required.

Figure 3 shows a variant of the transmission system 20 which additionally includes a clutch 90 (shown schematically). In this case the clutch 90 is a friction clutch having friction plates biased together by a spring means, such as belleville washers. One side of the clutch is connected to the first input shaft 40 and the other side of the clutch is connected to the second input shaft 42. Depending upon the relative speed of the first input shaft 40 and second input shaft 42, the clutch 90 is designed to be able to slip. Thus, when the engine is stationary and the vehicle is being driven by the electric motor/generator the clutch 90 will slip. When the vehicle is being driven by the engine, as described above, the second input shaft 42 will be rotating at the same speed as the first input shaft 40 due to the operation of the freewheeling clutch being engaged and hence no slip of clutch 90 will occur. The advantage of clutch 90 is that it allows the engine to power the electric motor/generator in generating mode whilst the vehicle is stationary. Thus, with the engine at idle and the vehicle stationary the CVT driven pulley 30 would rotate one rev for every 2.4 revs of the engine. At this speed, the first centrifugal clutch 44 is not engaged. However, the clutch 90 can transmit sufficient torque to rotate the second input shaft 42 and with the electric motor/generator in generating mode the battery can be recharged. Under these circumstances the second input shaft 42 will rotate at the same speed as the first input shaft 40 and this is at a speed where the second centrifugal clutch 46 will not engage.

As described above, the first and second clutch drums are secured together via bolts 68, i.e. they are secured together by a fixed gear ratio, in this example one to one. In further embodiments the first and second clutches could be coupled by a gear ratio other than a one to one gear ratio. In particular the first and second clutches could be coupled by a variable gear ratio.

As described above the electrical energy storage device is a battery, though in further embodiments alternative forms of electrical energy storage device could be used, such as capacitors.

Claims

1. A transmission system having a first input shaft, a first centrifugal clutch having a first driving part mounted on said first input shaft and a first clutch drum being selectively driven by the first driving part, a second input shaft, a second centrifugal clutch having a second driving part mounted on said second input shaft and a second clutch drum being selectively driven by the second driving part, the first clutch drum being rotationally coupled to the second clutch drum and a freewheeling clutch permitting relative rotation between the second input shaft and the second clutch drum in a first direction but preventing relative rotation between the second input shaft and the second clutch drum in a second direction.

2. A transmission system as defined in claim 1 in which the first input shaft is concentric with the second input shaft.

3. A transmission system as defined in claim 2 including a bearing in a recess of one of the first and second input shafts which receives a projection on the other of the first and second input shafts.

4. A transmission system as defined in any preceding claim in which the first clutch drum is rotationally coupled by a fixed gear ratio to the second clutch drum, preferably the fixed gear ratio is one to one.

5. A transmission system as defined in any preceding claim in which the first clutch drum is concentric with the second clutch drum.

6. A transmission system as defined in any preceding claim in which the first clutch drum is rotationally fast with the second clutch drum.

7. A transmission system as defined in any preceding claim in which the freewheeling clutch is concentric with the second clutch drum and the second input shaft.

8. A transmission system as defined in claim 7 when dependent upon claim 2 in which said second clutch drum is positioned axially between said first clutch drum and said freewheeling clutch.

9. A transmission system as defined in any preceding claim including a further clutch operable to transmit torque directly between the first input shaft and the second input shaft.

10. A transmission system as defined in claim 9 in which the further clutch is a friction clutch.

11. A transmission system as defined in claim 9 or 10 in which the further clutch is concentric with the first input shaft.

12. A transmission system as defined in claim 9, 10 or 11, in which the further clutch is concentric with the second input shaft.

13. A hybrid power unit including a transmission system as defined in any preceding claim including a first power unit operably coupled to the first input shaft and an electric motor/generator operably coupled to the second input shaft.

14. A hybrid power unit as defined in claim 13 in which the electric motor/generator includes an output shaft concentric with the second input shaft.

15. A hybrid power unit as defined in claim 13 or 14 in which the first power unit is an internal combustion engine.

16. A hybrid power unit as defined in claim 15 in which the first power unit is coupled to the first input shaft by a continuously variable transmission.

17. A hybrid power unit as defined in claim 16 in which the continuously variable transmission has a first variable pulley coupled to a second variable pulley via a belt and the first variable pulley is concentric with an output shaft of the first power unit and/or the second variable pulley is concentric with the first input shaft.

18. A vehicle including a hybrid power unit as defined in any one of claims 13 to 17 including a driven wheel driven by at least one of the first and second clutch drums.

19. A vehicle as defined in claim 18 when dependent upon claim 17 in which the second variable pulley is positioned between the first power unit and the driven wheel.

20. A vehicle as defined in claim 18 or 19 in which said at least one of said first and second clutch drums drives the driven wheel via a drive arrangement positioned on one side of a plane defined by the driven wheel and the continuously variable transmission is positioned on the other side of the plane.

21. A vehicle as defined in any one of claims 18 or 19 in which said at least one of the first and second clutch drums drives the driven wheel via a drive arrangement positioned between the electric motor/generator and at least one of the first clutch drum, second clutch drum and freewheeling clutch, preferably the drive arrangement is positioned between the electric motor/generator and at least two of the first clutch drum, second clutch drum and freewheeling clutch, more preferably the drive arrangement is positioned between the electric motor/generator and three of the first clutch drum, second clutch drum and freewheeling clutch.

22. A method of operating a vehicle as defined in any one of claims 18 to 21 including operating the electric motor/generator in a generating mode and driving the electric motor/generator by the first power unit via the freewheeling clutch.

23. A method of braking a vehicle as defined in any one of claims 18 to 21 including the step of driving the vehicle at a speed, braking the vehicle by operating the electric motor/generator in a generating mode and driving the electric motor/generator by the driven wheel via the freewheeling clutch to slow the vehicle.

24. A method of driving a vehicle as defined in any one of claims 18 to 21 including the step of driving the vehicle in a forwards direction and including the step of reversing the vehicle by operating the electric motor/generator in a reverse direction to drive the driven wheel in a reverse direction via the freewheeling clutch.

25. A method of operating the vehicle as defined in any one of claims 18 to 21 including the step of providing a further clutch operable to drive the second input shaft from the first input shaft, the method including operating the electric motor/generator in a generating mode and driving the electric motor/generator by the first power unit via the further clutch.

26. A method as defined in claim 25 including the step of ensuring the driven wheel is stationary.