GB2435869A

GB2435869A - Driveline and control method for hybrid vehicle

Info

Publication number: GB2435869A
Application number: GB0703519A
Authority: GB
Inventors: Andrew Julian Burrows; Jan Pieter Prins; Paul Michael Bostock; Paul Adrian Beever; Robert Michael Barlow
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2006-02-25
Filing date: 2007-02-23
Publication date: 2007-09-12
Anticipated expiration: 2027-02-23
Also published as: GB0603849D0; GB0703519D0; GB2435869B

Abstract

A motor vehicle 11 has an engine 12 driving a transmission 13 which in turn drives a front final drive unit 14 connected to a pair of front wheels 15. The front final drive unit 14 also drives a rear drive take-off unit 17 which is connected to a rear final drive unit 18 by a propshaft 19. The rear final drive unit 18 houses an electric motor/generator 35 which can also drive the rear wheels through an epicyclic reduction gear 39, a pinion 31 and crown wheel 27. A clutch 33 controls the connection from the propshaft 19 to the pinion 31. The motor/generator 35 and an integrated starter generator 29 on the engine 12 are controlled by an electronic control unit (ECU) 51 for drawing power from or supplying power to a traction battery 61 and to an auxiliaries battery 62. The ECU 51 also controls the engine 12 and can also receive signals from a speed set control and ABS sensors associated with the wheels. For high torque off-road driving, the accelerator pedal (52 see fig 3) or speed set control (58 see fig 3) can set a ground speed which the ECU maintains by controlling the outputs of both the engine 12 and motor generator 35. The ECU response is improved by using current to or from the motor generator 35 to provide a motor speed signal which is a better indication of the speed of the rear wheels 21 than may be obtained from the ABS sensors at low vehicle speeds.

Description

Vehicle Dnveline The invention relates to hybrid electric motor

vehicles, particularly but not exclusively of the parallel hybrid kind where an internal combustion (IC) engine provides power to a four wheel drive transmission which has an electric motor/generator in the drive to one pair of wheels.

IC engines are capable of a wide range of speed and power outputs. However, the response to a sudden demand for a change in power output usually has to be modulated to ensure that exhaust emissions are within specified limits. This response may be inadequate in certain driving conditions, e.g. off-road when surges of power may be need to overcome obstacles or an instantaneous reduction in power is needed to prevent slip or maintain an acceptably low speed when crawling over rocks.

The present invention has an object of improving the response to sudden changes in the power required to be delivered to the wheels of the vehicle.

According to one aspect of the invention there is provided a hybrid electric motor vehicle having an internal combustion engine, a transmission to transmit power from the engine to a front pair of wheels and to a rear pair of wheels and an electric motor/generator arranged to drive one of said pairs of wheels through a reduction gear, the engine and the motor/generator being arranged to be controlled by an electronic control unit (ECU), wherein the motor/generator provides a motor speed signal to the ECU which is indicative of the speed of rotation of said one pair of wheels and the motor speed signal is used by the ECU to control the output of one or both of the engine and the motor/generator.

A control clutch may be provided between the engine and the motor/generator and the ECU is operable to disconnect the control clutch for a brief time while the motor speed signal is sensed, in which case the ECU may be arranged so that such disconnection only occurs when drive to the front wheels alone is sufficient to maintain the momentum of the vehicle.

The ECU may calculate a calculated ground speed based on the motor speed signal and I or signals of wheel speed provided by ABS sensors on the wheels, the vehicle also being provided with a signal from a global positioning system (GPS) arranged to provide an indication of the distance travelled by the vehicle in a given time and correct the calculated ground speed.

The vehicle may be provided with an ABS sensor on one of said one pair of wheels and arranged so that the motor speed signal is used in conjunction with a signal from the ABS sensor to infer the speed of the other of said one pair of wheels.

The invention also provides, according to another aspect thereof, a method of controlling a hybrid electric motor vehicle having an internal combustion engine, a transmission to transmit power from the engine to a front pair of wheels and to a rear pair of wheels and an electric motor/generator arranged to drive one of said pairs of wheels through a reduction gear, the engine and the motor/generator being arranged to be controlled by an electronic control unit (ECU), wherein the method includes providing a motor speed signal to the ECU from the motor/generator and which is indicative of the speed of rotation of said one pair of wheels and the ECU using the motor speed signal to control the output of one or both of the engine and the motor/generator.

The invention will now be described by way of example and with reference to the accompanying drawings, in which:-Fig.1 is a schematic diagram of a motor vehicle according to the invention; Fig.2 is a schematic diagram of a final drive unit shown in Fig.1; and Fig. 3 is block diagram illustrating a control system of the vehicle shown in Fig.1.

Referring to Figs. I and 2, a motor vehicle 11 has an transverse mounted IC engine 12 driving a transmission 13 (which may be a manual gearbox, or any type of automatic transmission) which in turn drives a front final drive unit 14 connected to a pair of front wheels 15 by front driveshafts 16. The front final drive unit 14 also drives a rear drive take-off unit 17 which is connected to a rear final drive unit 18 by a longitudinal propshaft 19.

The rear final drive unit 18 is connected to a pair of rear wheels 21 by rear driveshafts 22.

The rear final drive unit 18 has a casing 23 which comprises a rear casing part 24 and a front casing part 25, the casing parts being connected at a flange face 26. The rear casing part 24 carries the inboard ends of the rear dnveshafts 22 and a crownwheel 27 which drives the rear driveshafts 22 through a differential 28. The front casing part 25 carries a pinion 31 which meshes with the crownwheel 27 and is part of a pinion shaft 32 which is joumalled in the front casing part 25. The rear end of the propshaft 19 is also joumalled in the front casing part 25 and carries a control clutch 33 which controllably couples the propshaft 19 to the pinion shaft 32.

As described so far, the vehicle 11 is of a generally known type. In the present invention, the front casing part 25 also houses the stator 34 of an electric motor/generator whose rotor 36 is rotatable on the pinion shaft 32. The rotor 36 is fast with a sun gear 37 which meshes with planet gears 38 of an epicyclic reduction gear 39. The planet gears 28 are each rotatable on a carrier 41 which is rotatable on the pinion shaft 32 and is selectably coupled to the pinion shaft 32 by a disconnect clutch 42. The planet gears 28 also mesh with a ring gear 43 fast with the front casing part 25. The epicyclic reduction gear 39 provides a reduction gear ratio between the speed of the rotor 36 and that of the pinion shaft 32, this ratio being between 2.5:1 and 5:1 depending on the detail design (i.e. the number of teeth of the sun gear 37, the planet gears 28 and the ring gear 43).

The rear casing part 24 carrying the inboard ends of the rear driveshafts 22 and the crownwheel 27 can be the same as would be provided for a conventional non-hybrid motor vehicle with the same general power train layout as is shown in Fig.1 while the front casing part 25 can be interchangeable with a similar unit which simply carries a pinion 31 to mesh with the crownwheel 27 and a control clutch 33 to connect the pinion shaft 32 to the propshaft 19. Either there is an appropriate adjustment to the length of the propshaft 19 or the overall length is kept the same.

The motor/generator 35 is controlled by an electronic control unit (ECU) 51. Power is generated by the motor/generator 35 and by another motor/generator, conveniently referred to as the integrated starter generator 29, driven by (or driving) the engine 12. Both the motor/generator 35 and the integrated starter generator 29 draw current from or supply current to a traction battery 61 and to an auxiliaries battery 62. The traction battery 61 would ordinarily be a high voltage unit while the auxiliaries battery 62 would be 12V for the supply & control of the normal vehicle electrical systems.

The control system shown in Fig. 3 includes the ECU 51 which in this example also controls the engine 12, the motor/generator 35 and the control clutch 33. Additionally, the ECU 51 also controls the disconnect clutch 42 and, where appropriate, the transmission 13. The ECU 51 is a conventional power train controller with the usual inputs of a driver demand, in this case from an accelerator pedal 52, air mass flow, temperatures etc. Also received are signals of front wheel speed 53 derived from ABS sensors on the front wheels 15, signals of rear wheel speed 54 derived from ABS sensors on the rear wheels 21, motor current 55 as sensed by the current supplied to or from the motor/generator 35, an inclinometer 56 and a global positioning system (GPS) 57. The ECU 51 can also receive signals from a speed set control 58 which is shown here as having + and -buttons but which in practice may be cruise control set speed buttons.

In normal on-road use of the vehicle 11 the engine 12 can drive the front wheels 15 through the transmission 13, the front final drive unit 14 and the front driveshafts 16 while also driving the rear wheels 21 through the rear take-off unit 17, the propshaft 19, the rear final drive unit 18 and the rear dnveshafts 22. The rear take-off unit 17 is driven in a direct ratio of the drive to the front wheels 15, the control clutch 33 allowing drive torque to the rear wheels 21 as required to maintain an appropriate torque split between the front and rear wheels. Under gentle low speed driving conditions, the electric motor generator 35 can be used to drive the vehicle with the engine 12 stopped, in which case the control clutch 33 would disconnect and drive would be to the rear wheels 21 only through the epicyclic reduction gear 39. For higher road speeds, particularly out of town driving, the engine 12 would drive as described above with the integrated starter generator 29 and, where needed, the electric motor generator 35 supplying current to the batteries 61 and 62.

Under more severe low speed driving conditions, the motor generator 35 can be used to supplement the power supplied by the engine 12.

For off-road driving, the engine 12 would be kept running and the power provided by the engine and/ or the motor generator 35 as required. For conditions requiring a large torque to the wheels 15, 21, e.g. when travelling through sand or up very steep inclines, the engine 12 and the motor generator 35 would both supply power.

Frequently, particularly when driving off-road, there is a requirement to rapidly switch from providing a high torque to the wheels to providing no torque at all or indeed a reverse torque (i.e. braking). This can arise particularly when traversing over large boulders or when the friction between the wheels and the ground suddenly changes as can occur when driving through sand. Under such conditions it is usually preferable to include an element of speed governing, either by setting a target speed by using the speed set control 58 or by maintaining a set position of the accelerator pedal 52. In a conventional vehicle driven by an internal combustion engine, the response of the engine is compromised by the inertia of the air mass in the inlet & exhaust tracts and by emissions constraints. While the ECU 51 can reduce or increase the output of the engine 12 as rapidly as possible, there is usually a reduction in the optimum traction which may detract from the overall control of the vehicle.

However, in the arrangement shown, the motor generator 35 can be used to rapidly supply additional torque, either positive or negative, to allow for any deficiency or excess of torque from the engine 12, as is well known in the operation of parallel hybrid vehicles (see e.g. US3732751 and US3791473).

The speed set control 58 can be used to set a ground speed in a manner similar to that described in EP0983894 for downhill travel where individual wheel speeds are monitored. In practice this uses the speed sensors which are used for the ABS system.

However, at very low wheel speeds the level and frequency of the signal from such sensors can be unreliably low, particularly when traversing large boulders. To overcome this problem, the ECU 51 can also use the current to or from the motor generator 35 to provide a motor speed signal 55 which is a better indication of the speed of the rear wheels 21 than is usually obtained from the rear ABS sensors at 54 in a manner analogous to that described for a series hybrid vehicle in GB2334496. The front ABS sensors at 53 can still provide an indication of the ground speed. The motor speed signal 55 is better than that from the ABS sensors at 54 because the motor generator 35 can have several poles and the sensitivity is enhanced by the gear ratio provided by the epicyclic reduction gear 39 and by the crownwheel 27 and pinion 31, i.e. because the motor generator 35 rotates much faster than the rear wheels 21. The motor speed signal 55 may result from a minimal drive output torque or retardation torque from the motor generator 35. Indeed an adequate level of the motor speed signal 55 may be obtainable when the motor generator 35 is open circuit when residual magnetism may be enough to provide sufficient output.

The ECU 51 can use the motor speed signal 55 as an input for the control of the engine 12 as well as that of the motor generator 35 itself and thereby improve the response of the engine which would ordinarily rely on the signal from its own speed sensor to govern its speed.

In a modification, the ECU disconnects the control clutch 33 momentarily (i.e. for a very brief period of time) while the speed of the motor generator 35 is sensed. This can give a more accurate indication of ground speed since slippage of the wheels would then be minimal. The ECU can be programmed to ensure that such disconnection only occurs when drive to the front wheels alone is sufficient to maintain the momentum of the vehicle.

The GPS 57 provides a further check of road speed or ground speed. Because the road speed has to be inferred from the wheel speed there is a danger when in very slippery conditions that the wheel speeds differ from the road speed by so much and for so long that the road speed estimation is wrong. The GPS can correct this by giving an accurate estimation of the distance travelled in a given time. A similar correction may be provided by using radar or ultrasound. The inclinometer 56 can improve response by enabling an estimation of the degree of acceleration or deceleration of the vehicle for a given torque at the wheels.

In a further modification, the motor speed signal 55 is used in conjunction with a signal from one of the rear ABS sensors. This may allow the other rear ABS sensor to be omitted so that the speed of the associated wheel can be inferred from the speed of the other rear wheel as sensed by its associated ABS sensor and the input speed to the axle as sensed by the motor generator 35. Such an arrangement may be used for the vehicle's ABS and I or traction control systems. Alternatively, the motor speed signal 55 can be used as descnbed above in the event that the signal from one of the rear ABS sensors is lost.

While a single ECU is described, it will be appreciated that the engine 12 and the motor generator 35 can be under the control of separate ECUs which communicate with each other, e.g. via a CAN bus. Furthermore, the rear drive take-off unit 17 may incorporate a centre differential, preferably with a lock-up clutch. However, in place of the transverse mounted IC engine 12, transmission 13, front final drive unit 14 and rear drive take-off unit 17 there may be a longitudinally mounted IC engine and transmission with a conventional transfer case, either of the type which provides a direct drive to the rear axle or one which incorporates a centre differential, preferably with a lock-up clutch. Although a front engine arrangement is described, the invention is also applicable to a rear or mid engine arrangement.

Claims

CLAIMS

A hybrid electric motor vehicle having an internal combustion engine, a transmission to transmit power from the engine to a front pair of wheels and to a rear pair of wheels and an electric motor/generator arranged to drive one of said pairs of wheels through a reduction gear, the engine and the motor/generator being arranged to be controlled by an electronic control unit (ECU), wherein the motor/generator provides a motor speed signal to the ECU which is indicative of the speed of rotation of said one pair of wheels and the motor speed signal is used by the ECU to control the output of one or both of the engine and the motor/generator.

2. A vehicle according to claim I wherein a control clutch is provided between the engine and the motor/generator and the ECU is operable to disconnect the control clutch for a brief time while the motor speed signal is sensed.

3. A vehicle according to claim 2 wherein the ECU is arranged so that such disconnection only occurs when drive to the front wheels alone is sufficient to maintain the momentum of the vehicle.

4. A vehicle according to any preceding claim wherein the ECU calculates a calculated ground speed based on the motor speed signal and / or signals of wheel speed provided by ABS sensors on the wheels, the vehicle also being provided with a signal from a global positioning system (GPS) arranged to provide an indication of the distance travelled by the vehicle in a given time and correct the calculated ground speed.

5. A vehicle according to any preceding claim and provided with an ABS sensor on one of said one pair of wheels and arranged so that the motor speed signal is used in conjunction with a signal from the ABS sensor to infer the speed of the other of said one pair of wheels.

-10 - 6 A method of controlling a hybnd electric motor vehicle having an internal combustion engine, a transmission to transmit power from the engine to a front pair of wheels and to a rear pair of wheels and an electric motor/generator arranged to drive one of said pairs of wheels through a reduction gear, the engine and the motor/generator being arranged to be controlled by an electronic control unit (ECU), wherein the method includes providing a motor speed signal to the ECU from the motor/generator and which is indicative of the speed of rotation of said one pair of wheels and the ECU using the motor speed signal to control the output of one or both of the engine and the motor/generator.

7. A method according to claim 6 wherein a control clutch is provided between the engine and the motor/generator and the ECU operates to disconnect the control clutch for a brief time while the motor speed signal is sensed.

8. A method according to claim 7 wherein such disconnection only occurs when drive to the front wheels alone is sufficient to maintain the momentum of the vehicle.

9. A method according to any of claims 6 to 8 wherein the ECU produces a calculated ground speed based on the motor speed signal and / or signals of wheel speed provided by ABS sensors on the wheels, the vehicle also being provided with a signal from a global positioning system (GPS) which provides an indication of the distance travelled by the vehicle in a given time and corrects the calculated ground speed.

10. A method according to any of claims 6 to 9 when the vehicle is provided with an ABS sensor on one of said one pair of wheels, the motor speed signal being used in conjunction with a signal from the ABS sensor to infer the speed of the other of said one pair of wheels.

11. A hybrid electric motor vehicle substantially as described herein with reference to the accompanying drawings. -11 -

12. A method of controlling a hybrid electric motor vehicle substantially as described herein with reference to the accompanying drawings.