WO2004106101A1 - Control of the rear wheel drive assist in a front wheel drive vehicle - Google Patents

Control of the rear wheel drive assist in a front wheel drive vehicle Download PDF

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Publication number
WO2004106101A1
WO2004106101A1 PCT/GB2003/002324 GB0302324W WO2004106101A1 WO 2004106101 A1 WO2004106101 A1 WO 2004106101A1 GB 0302324 W GB0302324 W GB 0302324W WO 2004106101 A1 WO2004106101 A1 WO 2004106101A1
Authority
WO
WIPO (PCT)
Prior art keywords
vehicle
turn
electrical drive
torque
rear wheel
Prior art date
Application number
PCT/GB2003/002324
Other languages
French (fr)
Inventor
Adrian Tucker-Peake
Original Assignee
Gkn Technology Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Gkn Technology Limited filed Critical Gkn Technology Limited
Priority to AU2003227992A priority Critical patent/AU2003227992A1/en
Priority to PCT/GB2003/002324 priority patent/WO2004106101A1/en
Publication of WO2004106101A1 publication Critical patent/WO2004106101A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W10/00—Conjoint control of vehicle sub-units of different type or different function
    • B60W10/04—Conjoint control of vehicle sub-units of different type or different function including control of propulsion units
    • B60W10/08—Conjoint control of vehicle sub-units of different type or different function including control of propulsion units including control of electric propulsion units, e.g. motors or generators
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
    • B60K17/00—Arrangement or mounting of transmissions in vehicles
    • B60K17/34—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles
    • B60K17/356—Arrangement or mounting of transmissions in vehicles for driving both front and rear wheels, e.g. four wheel drive vehicles having fluid or electric motor, for driving one or more wheels
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
    • B60K23/00—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for
    • B60K23/08—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for for changing number of driven wheels, for switching from driving one axle to driving two or more axles
    • B60K23/0808—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for for changing number of driven wheels, for switching from driving one axle to driving two or more axles for varying torque distribution between driven axles, e.g. by transfer clutch
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60K—ARRANGEMENT OR MOUNTING OF PROPULSION UNITS OR OF TRANSMISSIONS IN VEHICLES; ARRANGEMENT OR MOUNTING OF PLURAL DIVERSE PRIME-MOVERS IN VEHICLES; AUXILIARY DRIVES FOR VEHICLES; INSTRUMENTATION OR DASHBOARDS FOR VEHICLES; ARRANGEMENTS IN CONNECTION WITH COOLING, AIR INTAKE, GAS EXHAUST OR FUEL SUPPLY OF PROPULSION UNITS IN VEHICLES
    • B60K6/00—Arrangement or mounting of plural diverse prime-movers for mutual or common propulsion, e.g. hybrid propulsion systems comprising electric motors and internal combustion engines ; Control systems therefor, i.e. systems controlling two or more prime movers, or controlling one of these prime movers and any of the transmission, drive or drive units Informative references: mechanical gearings with secondary electric drive F16H3/72; arrangements for handling mechanical energy structurally associated with the dynamo-electric machine H02K7/00; machines comprising structurally interrelated motor and generator parts H02K51/00; dynamo-electric machines not otherwise provided for in H02K see H02K99/00
    • B60K6/20—Arrangement or mounting of plural diverse prime-movers for mutual or common propulsion, e.g. hybrid propulsion systems comprising electric motors and internal combustion engines ; Control systems therefor, i.e. systems controlling two or more prime movers, or controlling one of these prime movers and any of the transmission, drive or drive units Informative references: mechanical gearings with secondary electric drive F16H3/72; arrangements for handling mechanical energy structurally associated with the dynamo-electric machine H02K7/00; machines comprising structurally interrelated motor and generator parts H02K51/00; dynamo-electric machines not otherwise provided for in H02K see H02K99/00 the prime-movers consisting of electric motors and internal combustion engines, e.g. HEVs
    • B60K6/50—Architecture of the driveline characterised by arrangement or kind of transmission units
    • B60K6/52—Driving a plurality of drive axles, e.g. four-wheel drive
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W10/00—Conjoint control of vehicle sub-units of different type or different function
    • B60W10/18—Conjoint control of vehicle sub-units of different type or different function including control of braking systems
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/02—Control of vehicle driving stability
    • B60W30/045—Improving turning performance
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W30/00—Purposes of road vehicle drive control systems not related to the control of a particular sub-unit, e.g. of systems using conjoint control of vehicle sub-units
    • B60W30/18—Propelling the vehicle
    • B60W30/18009—Propelling the vehicle related to particular drive situations
    • B60W30/18145—Cornering
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2520/00—Input parameters relating to overall vehicle dynamics
    • B60W2520/14—Yaw
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2540/00—Input parameters relating to occupants
    • B60W2540/18—Steering angle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60W—CONJOINT CONTROL OF VEHICLE SUB-UNITS OF DIFFERENT TYPE OR DIFFERENT FUNCTION; CONTROL SYSTEMS SPECIALLY ADAPTED FOR HYBRID VEHICLES; ROAD VEHICLE DRIVE CONTROL SYSTEMS FOR PURPOSES NOT RELATED TO THE CONTROL OF A PARTICULAR SUB-UNIT
    • B60W2720/00—Output or target parameters relating to overall vehicle dynamics
    • B60W2720/40—Torque distribution
    • B60W2720/406—Torque distribution between left and right wheel
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/62—Hybrid vehicles

Definitions

  • This invention relates to the controlling of a front wheel drive vehicle with rear wheel drive assist.
  • ESPs Electronic Stability Programmes
  • slippery roads usually on occasions when a vehicle is substantially or completely out of a driver's control and combine engine power reduction with individual wheel brake application to produce a path correction yaw moment, which restores or attempts to restore the sliding vehicle to the driver's chosen path.
  • the electrically driven 'hang-on' system may include an electric motor in driving relation with the rear axle of the vehicle to drive both wheels thereof by way of a differential gearing device, or separate electric motors in driving relation with each wheel of the rear axle.
  • 'Hang-on' systems were introduced to provide increased traction between the vehicle and a road surface to aid the driver in adverse weather conditions, such as ice and snow.
  • a method of controlling a front wheel drive vehicle which additionally has an electrical drive for the rear wheels of the vehicle, comprising detecting at least one cornering parameter and applying an unequal torque to the rear wheels by the electrical drive in response to the detected cornering parameter.
  • the rate of turn of the vehicle can be increased or decreased.
  • the electrical drive applies an unequal torque to the rear wheels and increases or decreases the yaw moment of the vehicle. This assists the vehicle in manoeuvring around the corner and/or returning the vehicle to the driver's control.
  • the at least one cornering parameter may include a desired rate of turn that the driver wishes the vehicle to complete, indicated, for example, by the rotation which the driver inputs on the steering wheel.
  • This desired rate of turn of the vehicle may then be compared with the actual rate of turn of the vehicle, for example, measured by a rate of turn sensor.
  • the electrical drive may apply an equal torque, or zero torque, to the rear wheels of the vehicle.
  • the electrical drive may apply a higher torque to the outermost rear wheel of the vehicle, with respect to the cornering direction, thus applying a corrective yaw moment to the vehicle.
  • a braking force may be applied to the innermost wheel of the vehicle at the same time as the higher torque is applied to the outermost wheel of the vehicle.
  • the electrical drive may increase the torque applied to the outermost rear wheel until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
  • the braking force applied to the innermost rear wheel may, at the same time as the electrical drive is increased to the outermost rear wheel or independently thereof, be increased until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
  • the electrical drive may apply a higher torque to the innermost rear wheel of the vehicle, with respect to the cornering direction, thus applying a corrective yaw moment to the vehicle.
  • a braking force may be applied to the outermost rear wheel of the vehicle at the same time as the higher torque is applied to the innermost wheel of the vehicle.
  • the electrical drive may increase the torque applied to the innermost rear wheel until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
  • the braking force applied to the outermost rear wheel may, at the same time as the electrical drive is increased to the innermost rear wheel or independently thereof, be increased until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
  • a front wheel drive vehicle which additionally has an electrical drive for the rear wheels, including means for detecting at least one cornering parameter and for causing the electrical drive to apply an unequal torque to the rear wheels in response to the detected cornering parameter.
  • the electrical drive may be a 'hang on' electrical drive system and may be in the form of two electric motors, each motor in driving relation with a respective rear wheel of the vehicle. In this way each motor can apply torque independently of the other motor and hence apply an unequal torque to the rear wheels.
  • the electrical drive may comprise a single electrical drive to the rear axle of the vehicle and differential means adapted to apply an unequal torque to the rear wheels of the vehicle, for example a torque distributing differential.
  • Figure 1 shows diagrammatically the effect of the present invention on a vehicle which is cornering; and Figure 2 shows a flow diagram of the method in accordance with the present invention.
  • FIG. 1 there is shown a front wheel drive vehicle 10 with front wheels 12a, b and rear wheels 14a, b.
  • the suffixes 'a' and 'b' correspond to the left and right-hand side of the vehicle 10 respectively, with reference to the eye view of a driver of the vehicle 10.
  • the front wheels 12a, b are driven by a conventional internal combustion engine and drive train, whereas the rear wheels 14a, b are driven by an electric 'hang-on' system comprising one or more electric motors 15 (not shown) in driving relation with the rear wheels 14a, b.
  • each rear wheel 14a, b is driven by a respective electric motor 15a, b, although a single electric motor in geared relation to the rear axle may be used together with means for applying an unequal torque to the wheels 14a, b, such as, for example, a torque distributing differential.
  • the vehicle 10 is shown firstly travelling along a road surface 18 in a straight line and about to negotiate a bend in the road, to the right. On the bend there is a region 20 of the road, having a lower coefficient of friction than the road surface 18.
  • the region 20 may be, for examples, water or an oil spillage. Due to the lower coefficient of friction, it is more difficult for the wheels 12, 14 of the vehicle 10 to grip the region 20 of the road surface 18.
  • a fixed obstruction in the form of a tree 30 is also shown.
  • the tree 30 is in line with the path along which the vehicle 10 is initially travelling.
  • each position shows the position in which the vehicle 10 would have finished after encountering the region 20 of the road surface 18.
  • the position of the vehicle 10 shown generally at 'A' indicates the position where the vehicle could finish if on commencing to negotiate the bend the driver finds that the slippery road surface causes the vehicle not to turn to the extent the driver expects.
  • the driver had applied a braking force to both the front and rear wheels 12, 14 and has also applied a greater steering angle to the front wheels 12.
  • Position 'B' shows a position in which the vehicle could finish if the vehicle were provided with a known ESP system which has caused a braking force to be applied to the rear wheel on the inside of the vehicle, with respective to the direction in which the vehicle 10 is turning.
  • the ESP system applies a braking force to the rear wheel 14b (shown by arrow 17).
  • the braking force 17 is applied to the wheel 14b, drive to the front wheels 12 (shown by arrows 19) is not necessarily reduced, thereby assisting the vehicle in avoiding the tree 30 by eliminating or substantially reducing under-steer.
  • position 'C shows the position in which the vehicle 10 would finish if the method in accordance with the present invention had been used.
  • a higher torque shown by the arrow 22
  • the higher torque 22 is applied to the rear wheel 14a, in this example, by the motor 15a of the hang-on system.
  • the hang-on system need not be engaged prior to the vehicle 10 encountering the region 20. If the hang-on system is not engaged torque need only be applied to the wheel 14a, however if the hang-on system is engaged prior to the vehicle 10 encountering the region 20 an increased torque can be applied to the wheel 14a.
  • the torque applied to the wheel 14b can be reduced to cause the same effect as braking of the wheel 14b.
  • the increased torque 22, together with the braking force 17, or the reduction of torque, applied to the wheel 14b further increases the yaw moment of the vehicle, than that of the vehicle 10 shown in position 'B' and hence the path along which the vehicle 10 travels manoeuvres the vehicle more sharply away from the tree 30.
  • the magnitude of the braking force 17 applied to the wheel 14b in positions 'B' and 'C and the magnitude of torque 22 applied to the wheel 14a are calculated in response to the a cornering parameter by a computer program using, for example, a flow diagram similar to that shown in figure 2.
  • the computer program compares the speed of the vehicle, the actual rate of turn of the vehicle and the desired rate of turn of the vehicle which the driver inputs through the steering wheel of the vehicle 10 and calculates the magnitudes of the torque 22 and the braking force 17 which are required to equate the actual rate of turn of the vehicle 10 to the desired rate of turn of the vehicle 10.
  • the computer program first ascertains whether the ESP is operating, then compares the steering wheel angle with a predetermined value (shown in figure 2 as HWkp 0 ) and then ascertains whether the driver has applied a braking force to the wheels of the vehicle. Using the above information the computer program decides whether to adopt the method in accordance with the present invention.
  • the invention is primarily concerned with correcting the rate of turn of a vehicle which is under-steering, it could also be applied to a vehicle which over-steers.
  • the braking force 17 and torque 22 are applied to the rear wheels 14a and 14b respectively (i.e. opposite to that of an under-steering vehicle).
  • the computer program in this case also calculates the magnitude of braking force 17 and torque 22 needed to equate the actual rate of turn of the vehicle with the desired rate of turn the driver inputs to the vehicle 10.
  • braking forces 16, 17 applied to the rear wheels 14 could be applied in the conventional manner by disc or drum brakes, however the same result could also be achieved by apply a negative torque to one or both rear wheels 14 by the motor(s) 15 or a similar electric hang-on system.

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Automation & Control Theory (AREA)
  • Electric Propulsion And Braking For Vehicles (AREA)
  • Arrangement And Driving Of Transmission Devices (AREA)

Abstract

A method of controlling a front wheel drive vehicle, which additionally has an electrical drive for the rear wheels of a vehicle, comprising detecting at least one cornering parameter and applying an unequal torque to the rear wheels by the electrical drive in response to the detected cornering parameter.

Description

CONTROL OF HE REAR HEEL DRIVE ASSIST IN A FRONT HEEL DRIVE VEHICLE
Title: Controlling A Front Wheel Drive Vehicle With Rear Wheel Drive Assist.
Description of Invention
This invention relates to the controlling of a front wheel drive vehicle with rear wheel drive assist.
One known method of controlling vehicles to assist in the stability thereof is by the use of what are generally referred to as Electronic Stability Programmes (ESPs). These use hardware, some of which is already in place on the vehicle. ESPs mainly operate on slippery (low friction) roads usually on occasions when a vehicle is substantially or completely out of a driver's control and combine engine power reduction with individual wheel brake application to produce a path correction yaw moment, which restores or attempts to restore the sliding vehicle to the driver's chosen path. Although such methods can accomplish the main goal of restoring the vehicle to the driver's chosen path, they give rise to a number of performance problems and disadvantages, such as:- repeated application of individual wheel brakes on low friction surfaces can lead to overheating of the brakes; individual wheel brake application may not generate a sufficient corrective yaw moment on low friction surfaces to correct the path of the vehicle; repetitive individual wheel brake application can give rise to excessive Noise Vibration Harshness (TSTVH); and path correction is achieved inefficiently through individual wheel brake application, which is less pleasing to the driver;
Also the driver's first reaction, when losing control of the vehicle, is to decelerate, i.e. lift off of the accelerator, which can further aggravate control problems. Mechanical four-wheel drive systems increase the stability of a vehicle by sharing drive and cornering roles between the four wheels of the vehicle. However, such systems do not actively steer the vehicle and as both axles of the vehicle are mechanically connected to one another, the drive to one or both axles must be disengaged prior to the ESP intervening.
It is known to provide the rear (free) axle of a front wheel drive motor vehicle with an electrical drive, which drives the rear axle of the vehicle, when required, to convert, in effect, a two-wheel drive vehicle into a four-wheel drive vehicle. Such an electric drive is known as a 'hang on' system. The electrically driven 'hang-on' system may include an electric motor in driving relation with the rear axle of the vehicle to drive both wheels thereof by way of a differential gearing device, or separate electric motors in driving relation with each wheel of the rear axle. 'Hang-on' systems were introduced to provide increased traction between the vehicle and a road surface to aid the driver in adverse weather conditions, such as ice and snow.
It is the broad object of the present invention to provide an improved method of controlling of a front wheel drive vehicle with rear wheel drive assist.
According to a first aspect of the invention there is provided a method of controlling a front wheel drive vehicle, which additionally has an electrical drive for the rear wheels of the vehicle, comprising detecting at least one cornering parameter and applying an unequal torque to the rear wheels by the electrical drive in response to the detected cornering parameter.
By applying an unequal torque to the rear wheels of the vehicle the rate of turn of the vehicle can be increased or decreased. Thus, if a driver loses control of the vehicle, or tries to manoeuvre the vehicle around a corner which is too sharp for the speed with which the vehicle is travelling, the electrical drive applies an unequal torque to the rear wheels and increases or decreases the yaw moment of the vehicle. This assists the vehicle in manoeuvring around the corner and/or returning the vehicle to the driver's control.
The at least one cornering parameter may include a desired rate of turn that the driver wishes the vehicle to complete, indicated, for example, by the rotation which the driver inputs on the steering wheel.
This desired rate of turn of the vehicle may then be compared with the actual rate of turn of the vehicle, for example, measured by a rate of turn sensor.
If the desired rate of turn that the driver wishes the vehicle to complete and the actual rate of turn of the vehicle are equal then the electrical drive may apply an equal torque, or zero torque, to the rear wheels of the vehicle.
If the desired rate of turn that the driver wishes the vehicle to complete is greater than the actual rate of turn of the vehicle, for example when the vehicle is under-steering, the electrical drive may apply a higher torque to the outermost rear wheel of the vehicle, with respect to the cornering direction, thus applying a corrective yaw moment to the vehicle.
To further increase the corrective yaw moment applied to the vehicle, a braking force may be applied to the innermost wheel of the vehicle at the same time as the higher torque is applied to the outermost wheel of the vehicle.
The electrical drive may increase the torque applied to the outermost rear wheel until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
Similarly, the braking force applied to the innermost rear wheel may, at the same time as the electrical drive is increased to the outermost rear wheel or independently thereof, be increased until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
If the actual rate of turn of the vehicle is greater than the desired rate of turn that the driver wishes the vehicle to complete, for example when the vehicle is over-steering, the electrical drive may apply a higher torque to the innermost rear wheel of the vehicle, with respect to the cornering direction, thus applying a corrective yaw moment to the vehicle.
To further increase the corrective yaw moment applied to the vehicle, a braking force may be applied to the outermost rear wheel of the vehicle at the same time as the higher torque is applied to the innermost wheel of the vehicle.
The electrical drive may increase the torque applied to the innermost rear wheel until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
Similarly, the braking force applied to the outermost rear wheel may, at the same time as the electrical drive is increased to the innermost rear wheel or independently thereof, be increased until the actual rate of turn of the vehicle is equal to the desired rate of turn that the driver wishes the vehicle to complete.
According to a second aspect of the invention there is provided a front wheel drive vehicle, which additionally has an electrical drive for the rear wheels, including means for detecting at least one cornering parameter and for causing the electrical drive to apply an unequal torque to the rear wheels in response to the detected cornering parameter.
The electrical drive may be a 'hang on' electrical drive system and may be in the form of two electric motors, each motor in driving relation with a respective rear wheel of the vehicle. In this way each motor can apply torque independently of the other motor and hence apply an unequal torque to the rear wheels.
The electrical drive may comprise a single electrical drive to the rear axle of the vehicle and differential means adapted to apply an unequal torque to the rear wheels of the vehicle, for example a torque distributing differential.
The invention will now be described with reference to the accompanying drawings, in which
Figure 1 shows diagrammatically the effect of the present invention on a vehicle which is cornering; and Figure 2 shows a flow diagram of the method in accordance with the present invention.
Referring to figure 1 there is shown a front wheel drive vehicle 10 with front wheels 12a, b and rear wheels 14a, b. The suffixes 'a' and 'b' correspond to the left and right-hand side of the vehicle 10 respectively, with reference to the eye view of a driver of the vehicle 10. The front wheels 12a, b are driven by a conventional internal combustion engine and drive train, whereas the rear wheels 14a, b are driven by an electric 'hang-on' system comprising one or more electric motors 15 (not shown) in driving relation with the rear wheels 14a, b. In this example, each rear wheel 14a, b is driven by a respective electric motor 15a, b, although a single electric motor in geared relation to the rear axle may be used together with means for applying an unequal torque to the wheels 14a, b, such as, for example, a torque distributing differential.
The vehicle 10 is shown firstly travelling along a road surface 18 in a straight line and about to negotiate a bend in the road, to the right. On the bend there is a region 20 of the road, having a lower coefficient of friction than the road surface 18. The region 20 may be, for examples, water or an oil spillage. Due to the lower coefficient of friction, it is more difficult for the wheels 12, 14 of the vehicle 10 to grip the region 20 of the road surface 18.
On the outside of the bend a fixed obstruction in the form of a tree 30 is also shown. The tree 30 is in line with the path along which the vehicle 10 is initially travelling.
Three final positions of the vehicle 10 are shown, each position shows the position in which the vehicle 10 would have finished after encountering the region 20 of the road surface 18. The position of the vehicle 10 shown generally at 'A' indicates the position where the vehicle could finish if on commencing to negotiate the bend the driver finds that the slippery road surface causes the vehicle not to turn to the extent the driver expects. The driver had applied a braking force to both the front and rear wheels 12, 14 and has also applied a greater steering angle to the front wheels 12.
An instinctive reaction of a driver, when trying to avoid an obstacle, is to apply a braking force (shown by arrows 16) to the rear and front wheels 12, 14 and to steer away from the obstruction, i.e. the tree 30. However, this is not always the best course of action as it can lead to under-steer of the vehicle and hence in position 'A' the vehicle has crashed into the tree 30.
Position 'B' shows a position in which the vehicle could finish if the vehicle were provided with a known ESP system which has caused a braking force to be applied to the rear wheel on the inside of the vehicle, with respective to the direction in which the vehicle 10 is turning. Instead of permitting the driver to brake both front and rear wheels 12, 14, the ESP system applies a braking force to the rear wheel 14b (shown by arrow 17). Also, at the same time the braking force 17 is applied to the wheel 14b, drive to the front wheels 12 (shown by arrows 19) is not necessarily reduced, thereby assisting the vehicle in avoiding the tree 30 by eliminating or substantially reducing under-steer. By applying a braking force 17 to the rear wheel 14b, the yaw moment of the vehicle is increased and hence the path along which the vehicle travels, shown by the dashed line 24, avoids the tree 30.
Finally, position 'C shows the position in which the vehicle 10 would finish if the method in accordance with the present invention had been used. Together with the braking force 17 applied by the ESP (shown in position 'B'), a higher torque (shown by the arrow 22) is applied to the wheel 14a. The higher torque 22 is applied to the rear wheel 14a, in this example, by the motor 15a of the hang-on system. The hang-on system need not be engaged prior to the vehicle 10 encountering the region 20. If the hang-on system is not engaged torque need only be applied to the wheel 14a, however if the hang-on system is engaged prior to the vehicle 10 encountering the region 20 an increased torque can be applied to the wheel 14a. Together with the increased torque is applied to the wheel 14a, or independently thereof, the torque applied to the wheel 14b can be reduced to cause the same effect as braking of the wheel 14b. The increased torque 22, together with the braking force 17, or the reduction of torque, applied to the wheel 14b, further increases the yaw moment of the vehicle, than that of the vehicle 10 shown in position 'B' and hence the path along which the vehicle 10 travels manoeuvres the vehicle more sharply away from the tree 30.
The magnitude of the braking force 17 applied to the wheel 14b in positions 'B' and 'C and the magnitude of torque 22 applied to the wheel 14a are calculated in response to the a cornering parameter by a computer program using, for example, a flow diagram similar to that shown in figure 2. The computer program compares the speed of the vehicle, the actual rate of turn of the vehicle and the desired rate of turn of the vehicle which the driver inputs through the steering wheel of the vehicle 10 and calculates the magnitudes of the torque 22 and the braking force 17 which are required to equate the actual rate of turn of the vehicle 10 to the desired rate of turn of the vehicle 10. As shown in the example in figure 2, the computer program first ascertains whether the ESP is operating, then compares the steering wheel angle with a predetermined value (shown in figure 2 as HWkp0) and then ascertains whether the driver has applied a braking force to the wheels of the vehicle. Using the above information the computer program decides whether to adopt the method in accordance with the present invention.
Although the invention is primarily concerned with correcting the rate of turn of a vehicle which is under-steering, it could also be applied to a vehicle which over-steers. In such a situation, the braking force 17 and torque 22 are applied to the rear wheels 14a and 14b respectively (i.e. opposite to that of an under-steering vehicle). The computer program in this case also calculates the magnitude of braking force 17 and torque 22 needed to equate the actual rate of turn of the vehicle with the desired rate of turn the driver inputs to the vehicle 10.
It must be understood that the braking forces 16, 17 applied to the rear wheels 14 could be applied in the conventional manner by disc or drum brakes, however the same result could also be achieved by apply a negative torque to one or both rear wheels 14 by the motor(s) 15 or a similar electric hang-on system.
In the present specification "comprises" means "includes or consists of and "comprising" means "including or consisting of.
The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A method of controlling a front wheel drive vehicle, which additionally has an electrical drive for the rear wheels of a vehicle, comprising detecting at least one cornering parameter and applying an unequal torque to the rear wheels by the electrical drive in response to the detected cornering parameter.
2. A method according to claim 1 wherein the at least one cornering parameter includes a desired rate of turn that the driver wishes the vehicle to complete.
3. A method according to claim 2 wherein the desired rate of turn of the vehicle is compared with the actual rate of turn of the vehicle.
4. A method according to claim 3 wherein if the desired rate of turn and the actual rate of turn of a vehicle are equal the electrical drive applies an equal torque, or zero torque, to the rear wheels of the vehicle.
5. A method according to claim 3 wherein if the desired rate of turn is greater than the actual rate of turn of the vehicle the electrical drive applies a higher torque to the outermost rear wheel of the vehicle, with respect of the cornering direction.
6. A method according to claim 5 wherein a braking force is applied to the innermost rear wheel of the vehicle at the same time as the higher torque is applied to the outermost rear wheel of the vehicle.
7. A method according to claim 5 or claim 6 wherein the electrical drive increases the torque applied to the outermost rear wheel of the vehicle until the actual rate of turn of the vehicle is equal to the desired rate of turn of the vehicle.
8. A method according to claim 6 or claim 7 wherein the braking force applied to the innermost rear wheel is, at the same time as the electrical drive is increased to the outermost rear wheel or independently thereof, increased until the actual rate of turn of the vehicle is equal to the desired rate of turn of the vehicle.
9. A method according to claim 1, 2 or 3 wherein if the actual rate of turn of the vehicle is greater than the desired rate of turn of the vehicle, the electrical drive applies a higher torque to the innermost rear wheel of the vehicle, with respect to the cornering direction.
10. A method according to claim 9 wherein a braking force is applied to the outermost rear wheel of the vehicle at the same time as the higher torque is applied to the innermost rear wheel of the vehicle.
11. A method according to claim 9 or claim 10 wherein the electrical drive increases the torque applied to the innermost rear wheel of the vehicle until the actual rate of turn of the vehicle is equal to the desired rate of turn of the vehicle.
12. A method according to claim 10 or claim 11 wherein the braking force applied to the outermost rear wheel is, at the same time as the electrical drive is increased to the innermost rear wheel of the vehicle or independently thereof, increased until the actual rate of turn of the vehicle is equal to the desired rate of turn of the vehicle.
13. A front wheel drive vehicle, which additionally has an electrical drive for the rear wheels, including means for detecting at least one cornering parameter and for causing the electrical drive to apply an unequal torque to the rear wheels in response to the detected cornering parameter.
14. A front wheel drive vehicle according to claim 13 wherein the electrical drive is a 'hang on' electrical drive system.
15. A front wheel drive vehicle according to claim 14 wherein the 'hang on' electrical drive system is in the form of two electric motors, each motor in driving relation with a respective rear wheel of the vehicle.
16. A front wheel drive vehicle according to claim 13 wherein the electrical drive comprises a single electrical drive to the rear axle of the vehicle and a differential means adapted to apply an unequal torque to the rear wheels of the vehicle.
17. A front wheel drive vehicle according to claim 16 wherein the differential means is provided by a torque distributing differential.
18. A front wheel drive vehicle according to any one of claims 13 to 17 wherein the cornering parameter includes at least one of a desired rate of turn that a driver wishes the vehicle to complete and the actual rate of turn of the vehicle.
19. A front wheel drive vehicle according to claim 18 wherein the desired rate of turn of the vehicle is determined by at least the angle inputted by the user to the steering wheel.
20. A method according to claim 19 wherein the desired rate of turn of the vehicle is also determined by the speed of the vehicle.
21. A method of controlling a front wheel drive vehicle substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
22. Any novel feature or novel combination of features described herein and/or in the accompanying drawings.
PCT/GB2003/002324 2003-05-29 2003-05-29 Control of the rear wheel drive assist in a front wheel drive vehicle WO2004106101A1 (en)

Priority Applications (2)

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AU2003227992A AU2003227992A1 (en) 2003-05-29 2003-05-29 Control of the rear wheel drive assist in a front wheel drive vehicle
PCT/GB2003/002324 WO2004106101A1 (en) 2003-05-29 2003-05-29 Control of the rear wheel drive assist in a front wheel drive vehicle

Applications Claiming Priority (1)

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PCT/GB2003/002324 WO2004106101A1 (en) 2003-05-29 2003-05-29 Control of the rear wheel drive assist in a front wheel drive vehicle

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US9719585B2 (en) 2010-07-14 2017-08-01 E-Aam Driveline Systems Ab Axle assembly with torque distribution drive mechanism
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WO2014146806A1 (en) * 2013-03-22 2014-09-25 Jaguar Land Rover Limited Improvements in vehicle steering
CN113272202A (en) * 2018-11-13 2021-08-17 瑞维安知识产权控股有限责任公司 System and method for providing a forward lean mode to a vehicle
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CN113272202B (en) * 2018-11-13 2024-02-13 瑞维安知识产权控股有限责任公司 System and method for providing a forward leaning mode to a vehicle

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