WO2004087453A1 - Rear-drive vehicle with an electronically controlled self-locking differential - Google Patents

Rear-drive vehicle with an electronically controlled self-locking differential Download PDF

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Publication number
WO2004087453A1
WO2004087453A1 PCT/EP2004/050434 EP2004050434W WO2004087453A1 WO 2004087453 A1 WO2004087453 A1 WO 2004087453A1 EP 2004050434 W EP2004050434 W EP 2004050434W WO 2004087453 A1 WO2004087453 A1 WO 2004087453A1
Authority
WO
WIPO (PCT)
Prior art keywords
vehicle
differential
value
control unit
central control
Prior art date
Application number
PCT/EP2004/050434
Other languages
French (fr)
Inventor
Franck Baldet
Original Assignee
Ferrari S.P.A.
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 Ferrari S.P.A. filed Critical Ferrari S.P.A.
Priority to US10/552,039 priority Critical patent/US7641585B2/en
Priority to DE602004010635T priority patent/DE602004010635T2/en
Priority to JP2006505519A priority patent/JP4819672B2/en
Priority to EP04741443A priority patent/EP1613499B1/en
Publication of WO2004087453A1 publication Critical patent/WO2004087453A1/en

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H48/00—Differential gearings
    • F16H48/20—Arrangements for suppressing or influencing the differential action, e.g. locking devices
    • F16H48/22—Arrangements for suppressing or influencing the differential action, e.g. locking devices using friction clutches or brakes
    • 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
    • B60K23/04—Arrangement or mounting of control devices for vehicle transmissions, or parts thereof, not otherwise provided for for differential gearing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H48/00—Differential gearings
    • F16H48/06—Differential gearings with gears having orbital motion
    • F16H48/08—Differential gearings with gears having orbital motion comprising bevel gears
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H48/00—Differential gearings
    • F16H48/20—Arrangements for suppressing or influencing the differential action, e.g. locking devices
    • F16H48/30—Arrangements for suppressing or influencing the differential action, e.g. locking devices using externally-actuatable means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16H—GEARING
    • F16H48/00—Differential gearings
    • F16H48/20—Arrangements for suppressing or influencing the differential action, e.g. locking devices
    • F16H2048/204—Control of arrangements for suppressing differential actions

Definitions

  • the present invention relates to a rear-drive vehicle with a self-locking differential .
  • high-performance road sports cars are normally rear-drive, and have a self-locking differential for increasing the drive torque transmitted by the rear wheels to the road surface.
  • a rear-drive vehicle featuring a self-locking differential, as claimed in Claim 1.
  • Figure X shows a schematic plan view of a rear-drive vehicle in accordance with the present invention.
  • Figure 2 shows an operating diagram of a self- locking differential of the Figure 1 vehicle
  • Figure 3 shows a control method implemented by a central control unit of the Figure 1 vehicle
  • Figure 4 shows a further control method implemented by a central control unit of the Figure 1 vehicle.
  • Number 1 in Figure 1 indicates a vehicle having two front wheels 2 and two rear drive wheels 3, and comprising a front internal combustion engine 4 producing a drive torque T which is transmitted to rear drive wheels 3 by a power train 5.
  • Power train 5 comprises a clutch 6 housed in a casing integral with engine 4 and for connecting the drive shaft of engine 4 to a propeller shaft 7 terminating in a mechanical gearbox 8 at the rear; and a self-locking differential 9 is cascade- connected to gearbox 8, and from which extend two axle shafts 10, each integral with a respective rear drive wheel 3.
  • the passenger compartment 11 of vehicle 1 houses a steering wheel 12 for imparting a turning angle Dvol to front wheels 2; a brake pedal 13 controlling a braking system to generate a braking torque on wheels 2 and 3; and an accelerator pedal 14 for regulating the drive torque Tm generated by engine 4.
  • Vehicle 1 comprises a central control unit 15 connected to a number of sensors 16 distributed inside vehicle 1 to real-time detect respective parameters of vehicle 1, such as the travelling speed V of vehicle 1, the turning angle Dvol of vehicle 1, the yaw speed Psip of vehicle 1, the lateral acceleration Ay of vehicle 1, the longitudinal acceleration Ax of vehicle 1, the rotation speed WrearL, WrearR of each rear drive wheel 3, the position Pace of accelerator pedal 14, the position Pbra of brake pedal 13, and the drive torque Tm generated by engine 4.
  • Central control unit 15 may obviously be defined by a number of physically separate processing units connected to one another, for example, by a data BUS; and, as opposed to a physical sensor 16, an estimation algorithm may be implemented by central control unit 15 to determine one or more parameters of vehicle 1.
  • self-locking differential 9 comprises a box body 17; a bevel gear pair 18 housed inside box body 17, and which transmits drive torque Tm to the two rear drive wheels 3 via respective axle shafts 10; and a lock device 19 for partly locking one axle shaft 10 with respect to box body 17.
  • lock device 19 comprises a clutch 20 having a thrust chamber 21 filled with pressurized oil 22, and a number of disks 23 integral with one of axle shafts 10.
  • thrust chamber 21 is filled with pressurized oil 22
  • disks 23 are subjected to axial thrust substantially proportional to the pressure P of oil 22 inside thrust chamber 21.
  • Lock device 19 of differential 9 is connected to a regulating device 24 for regulating the lock percentage %L of differential 9 between zero and a maximum value (e.g. 50%) by regulating the pressure P of oil 22 inside thrust chamber 21.
  • central control unit 15 commands regulating device 24 to regulate the lock percentage %L of differential 9 as a function of the dynamic parameters of vehicle 1.
  • Regulating device 24 comprises a tank 25 of oil 22 at atmospheric pressure, from which extends a pipe 26 fitted with a pump 27 and a non-return valve 28 to feed pressurized oil 22 to a hydraulic accumulator 29; and hydraulic accumulator 29 communicates along a pipe 30 with an inlet of a proportional solenoid valve 31, from which extend a pipe 32 terminating inside thrust chamber 21, and a pipe 33 terminating in tank 25.
  • solenoid valve 31 keeps thrust chamber 21 isolated from tank 25 to maintain a constant pressure P of oil 22 inside thrust chamber 21, connects thrust chamber 21 to tank 25 to reduce the pressure P of oil 22 inside thrust chamber 21, and connects thrust chamber 21 to hydraulic accumulator 29 to increase the pressure P of oil 22 inside thrust chamber 21.
  • Solenoid valve 31 is driven by a power supply 34 controlled by central control unit 15 to supply a variable voltage to the terminals of a control coil 35 of solenoid valve 31 so that an electric current I circulates through control coil 35.
  • regulating device 24 comprises a sensor 36 for detecting the value of pressure P of oil 22 inside thrust chamber 21, and a sensor 37 for detecting the value of current I circulating through control coil 35 of solenoid valve 31.
  • central control unit 15 controls regulating device 24 by controlling power supply 34 to regulate the pressure P of oil 22 inside thrust chamber 21 as described above, and so regulate the axial thrust exerted on disks 23 of clutch 20 and, hence, the lock percentage %L of differential 9.
  • a target value %Lrif of the lock percentage of differential 9 is established in central control unit 15 as described later on, and is translated into an equivalent target value Prif of pressure P of oil 22 inside thrust chamber 21; target value Prif is compared with the actual value of pressure P, measured by sensor 36, to generate a pressure error E Pf from which a target value Irif of the current I circulating through coil 35 is determined by a PID regulator 38. Target value Irif is compared with the actual value of current I, measured by sensor 37, to generate a current error ⁇ , ⁇ which is used by a PID regulator 39 to control power supply 34.
  • central control unit 15 controls the value of pressure P of oil 22 inside thrust chamber 21 by means of a first control loop employing as a feedback variable the value of pressure P of oil 22 inside thrust chamber 21, and a second control loop within the first control loop and employing as a feedback variable the value of current I circulating through coil 35 of solenoid valve 31.
  • An alternative embodiment comprises two torque sensors 16, each connected to central control unit 15 and fitted to a respective axle shaft 10 to real-time detect the value of the torque transmitted by self-locking differential 9 to respective rear wheel 3 via relative axle shaft 10.
  • Each torque sensor 16 is preferably electromagnetic, and measures the torsional deformation of respective axle shaft 10 electromagnetically to determine the value of the torque transmitted by axle shaft 10 to relative rear wheel 3.
  • Central control unit 15 controls regulating device 24 to regulate the lock percentage %L of differential 9 as a function of the value of the torque transmitted by self-locking differential 9 to each rear wheel 3. More specifically, central control unit 15 predicts time changes in the angular rotation speed of each rear wheel 3, using the value of the torque transmitted by respective axle shaft 10, and controls regulating device 24 to regulate the lock percentage %L of differential 9 as a function of future time changes in the angular rotation speed of each rear wheel 3.
  • Central control unit 15 has the advantage of estimating a target value of the lock percentage %L of differential 9 as a function of the dynamic parameters of vehicle 1, of estimating a target value of the torque transmitted by each axle shaft 10 as a function of the target value of lock percentage %L of differential 9, and of controlling regulating device 24 by means of a feedback control loop employing as a feedback variable the value of the torque transmitted to each rear wheel 3.
  • the control loop of the torque value may contain a control loop of the value of pressure P of oil 22 inside thrust chamber 21 and/or a control loop of the value of current I circulating through coil 35.
  • the target value %Lrif of the lock percentage of differential 9 is established in central control unit 15 as described later on, and is compared with the actual value of lock percentage %L of differential 9, measured by torque sensors 16 fitted to axle shafts 10, to generate an error E % ⁇ of lock percentage.
  • a control signal S is obtained from lock percentage error E %L by a PID regulator 40, and is supplied to a control block 41 to determine a corresponding target value Irif of the current I circulating through coil 35.
  • Target value Irif is compared with the actual value of current I, measured by sensor 37, to generate a current error Ei which is used by PID regulator 39 to control power supply 34.
  • control signal S supplied by PID regulator 40 is added a further contribution, which depends directly on target value %Lrif of the lock percentage of differential 9, and is supplied by a computing block 42 implementing an inverse model.
  • the signal supplied to control block 41 depends on both the error in the value of lock percentage %L of differential 9 (closed-loop feedback control) and on the target value %Lrif of the lock percentage of differential 9 (direct open-loop control) .
  • This solution is employed to increase overall control response speed.
  • central control unit 15 controls the lock percentage %L of differential 9 by means of a first control loop employing the value of lock percentage %L of differential 9 as a feedback variable, and a second control loop within the first control loop and employing as a feedback variable the value of current I circulating through coil 35 of solenoid valve 31.
  • central control unit 15 determines the target value of the lock percentage %L of differential 9 as a function of the dynamic parameters of vehicle 1, the position Pace of accelerator pedal 14, the position Pbra of brake pedal 13, the drive torque Tm, the gear engaged, and intervention of any other electronic devices on vehicle 1 (e.g. ABS, ASR and ESP) .
  • the dynamic parameters of vehicle 1 employed by central control unit 15 to determine the target value of the lock percentage %L of differential 9 may be; the travelling speed V of vehicle 1, the turning angle Dvol of vehicle 1, the yaw speed Psip of vehicle 1, lateral acceleration Ay of vehicle 1, longitudinal acceleration Ax of vehicle 1, and the rotation speed WrearL, WrearR of each rear drive wheel 3.
  • central control unit 15 may also take into account the driving mode (normal, sport, low-grip) selected by the driver of vehicle 1.
  • central control unit 15 When driving along a substantially straight route, central control unit 15 zeroes the lock percentage %L of differential 9 in normal driving mode, and gradually increases the lock percentage %L of differential 9 in sport mode.
  • the discriminating factor between normal and sport mode may be defined by the position Pace of accelerator pedal 14, the longitudinal acceleration Ax value of vehicle 1, and/or the speed V value of vehicle 1.
  • central control unit 15 When cornering, central control unit 15 gradually increases the lock percentage %L of differential 9 if accelerator pedal 14 is released, to stabilize vehicle 1. When cornering, central control unit 15 gradually reduces the lock percentage %L of differential 9 if accelerator pedal 14 is pressed (sharply) , to maximize both stability and cornering acceleration performance of vehicle 1. More specifically, the reduction in the lock percentage %L of differential 9 is proportional to the lateral acceleration Ay of vehicle 1, the speed V of vehicle 1, the drive torque Tm of engine 4, and/or the gear engaged. In this condition, central control unit 15 may also reduce the drive torque Tm of engine 4 to limit the power oversteering effect.
  • central control unit 15 estimates the road grip of wheels 2, 3, and accordingly zeroes the lock percentage %L of differential 9 when the road grip of wheels 2, 3 is far from the grip limit, gradually increases the lock percentage %L of differential 9 when the road grip of wheels 2, 3 nears the grip limit, and reduces the lock percentage %L of differential 9 to zero when the road grip of wheels 2, 3 is almost at the grip limit.
  • central control unit 15 preferably increases the lock percentage %L of differential 9 gradually in proportion to the value of lateral acceleration Ay of vehicle 1 and the value of speed V of vehicle 1.
  • the road grip of wheels 2, 3 is estimated as a function of the value of turning angle Dvol of vehicle 1 and the value of lateral acceleration Ay of vehicle 1. More specifically, central control unit 15 zeroes the lock percentage %L of differential 9 when the value of turning angle Dvol of vehicle 1 is substantially directly proportional to the value of lateral acceleration Ay of vehicle 1, and gradually increases the lock percentage %L of differential 9 when no substantially direct proportion relationship exists between the value of turning angle Dvol of vehicle 1 and the value of lateral acceleration Ay of vehicle 1.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Transportation (AREA)
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  • Arrangement And Driving Of Transmission Devices (AREA)

Abstract

A rear-drive vehicle (1) having a self-locking differential (9); a regulating device (24)for regulating the lock percentage (%L) of the differential (9); a number of sensors (16) for real-time detecting dynamic parameters of the vehicle (1); and a central control unit (15) for controlling the regulating device (24) to regulate the lock percentage (%L) of the differential (9) as a function of the dynamic parameters of the vehicle (1).

Description

REAR-DRIVE VEHICLE WITH AN ELECTRONICALLY CONTROLLED SELF-LOCKING DIFFERENTIAL
TECHNICAL FIELD
The present invention relates to a rear-drive vehicle with a self-locking differential .
BACKGROUND ART
At present, high-performance road sports cars are normally rear-drive, and have a self-locking differential for increasing the drive torque transmitted by the rear wheels to the road surface.
Tests have shown, however, that currently marketed self-locking differentials do not always succeed in maximizing the drive torque transmitted by the rear wheels to the road surface. What is more, the presence of the self-locking differential makes the vehicle harder and less safe to drive, in that, should one of the rear wheels temporarily lose grip, the self-locking differential almost immediately transfers part of the drive torque to the other rear wheel, thus possibly resulting in rear-end swerving of the vehicle, which must be skilfully counteracted by the driver acting promptly on the vehicle controls to prevent the vehicle spinning.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a rear-drive vehicle featuring a self-locking differential, being cheap and easy to produce, and, at the same time, eliminating the aforementioned drawbacks.
According to the present invention, there is provided a rear-drive vehicle featuring a self-locking differential, as claimed in Claim 1. BRIEF DESCRIPTION OF THE DRAWINGS
A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:
Figure X shows a schematic plan view of a rear-drive vehicle in accordance with the present invention;
Figure 2 shows an operating diagram of a self- locking differential of the Figure 1 vehicle;
Figure 3 shows a control method implemented by a central control unit of the Figure 1 vehicle; Figure 4 shows a further control method implemented by a central control unit of the Figure 1 vehicle.
BEST MODE FOR CARRYING OUT THE INVENTION
Number 1 in Figure 1 indicates a vehicle having two front wheels 2 and two rear drive wheels 3, and comprising a front internal combustion engine 4 producing a drive torque T which is transmitted to rear drive wheels 3 by a power train 5. Power train 5 comprises a clutch 6 housed in a casing integral with engine 4 and for connecting the drive shaft of engine 4 to a propeller shaft 7 terminating in a mechanical gearbox 8 at the rear; and a self-locking differential 9 is cascade- connected to gearbox 8, and from which extend two axle shafts 10, each integral with a respective rear drive wheel 3.
The passenger compartment 11 of vehicle 1 houses a steering wheel 12 for imparting a turning angle Dvol to front wheels 2; a brake pedal 13 controlling a braking system to generate a braking torque on wheels 2 and 3; and an accelerator pedal 14 for regulating the drive torque Tm generated by engine 4.
Vehicle 1 comprises a central control unit 15 connected to a number of sensors 16 distributed inside vehicle 1 to real-time detect respective parameters of vehicle 1, such as the travelling speed V of vehicle 1, the turning angle Dvol of vehicle 1, the yaw speed Psip of vehicle 1, the lateral acceleration Ay of vehicle 1, the longitudinal acceleration Ax of vehicle 1, the rotation speed WrearL, WrearR of each rear drive wheel 3, the position Pace of accelerator pedal 14, the position Pbra of brake pedal 13, and the drive torque Tm generated by engine 4. Central control unit 15 may obviously be defined by a number of physically separate processing units connected to one another, for example, by a data BUS; and, as opposed to a physical sensor 16, an estimation algorithm may be implemented by central control unit 15 to determine one or more parameters of vehicle 1.
As shown in Figure 2, self-locking differential 9 comprises a box body 17; a bevel gear pair 18 housed inside box body 17, and which transmits drive torque Tm to the two rear drive wheels 3 via respective axle shafts 10; and a lock device 19 for partly locking one axle shaft 10 with respect to box body 17. More specifically, lock device 19 comprises a clutch 20 having a thrust chamber 21 filled with pressurized oil 22, and a number of disks 23 integral with one of axle shafts 10. When thrust chamber 21 is filled with pressurized oil 22, disks 23 are subjected to axial thrust substantially proportional to the pressure P of oil 22 inside thrust chamber 21. Lock device 19 of differential 9 is connected to a regulating device 24 for regulating the lock percentage %L of differential 9 between zero and a maximum value (e.g. 50%) by regulating the pressure P of oil 22 inside thrust chamber 21. In actual use, central control unit 15 commands regulating device 24 to regulate the lock percentage %L of differential 9 as a function of the dynamic parameters of vehicle 1.
Regulating device 24 comprises a tank 25 of oil 22 at atmospheric pressure, from which extends a pipe 26 fitted with a pump 27 and a non-return valve 28 to feed pressurized oil 22 to a hydraulic accumulator 29; and hydraulic accumulator 29 communicates along a pipe 30 with an inlet of a proportional solenoid valve 31, from which extend a pipe 32 terminating inside thrust chamber 21, and a pipe 33 terminating in tank 25. In actual use, solenoid valve 31 keeps thrust chamber 21 isolated from tank 25 to maintain a constant pressure P of oil 22 inside thrust chamber 21, connects thrust chamber 21 to tank 25 to reduce the pressure P of oil 22 inside thrust chamber 21, and connects thrust chamber 21 to hydraulic accumulator 29 to increase the pressure P of oil 22 inside thrust chamber 21. Solenoid valve 31 is driven by a power supply 34 controlled by central control unit 15 to supply a variable voltage to the terminals of a control coil 35 of solenoid valve 31 so that an electric current I circulates through control coil 35. To ensure solenoid valve 31 is activated correctly, regulating device 24 comprises a sensor 36 for detecting the value of pressure P of oil 22 inside thrust chamber 21, and a sensor 37 for detecting the value of current I circulating through control coil 35 of solenoid valve 31. In actual use, central control unit 15 controls regulating device 24 by controlling power supply 34 to regulate the pressure P of oil 22 inside thrust chamber 21 as described above, and so regulate the axial thrust exerted on disks 23 of clutch 20 and, hence, the lock percentage %L of differential 9. As shown in Figure 3, a target value %Lrif of the lock percentage of differential 9 is established in central control unit 15 as described later on, and is translated into an equivalent target value Prif of pressure P of oil 22 inside thrust chamber 21; target value Prif is compared with the actual value of pressure P, measured by sensor 36, to generate a pressure error EPf from which a target value Irif of the current I circulating through coil 35 is determined by a PID regulator 38. Target value Irif is compared with the actual value of current I, measured by sensor 37, to generate a current error Ε,χ which is used by a PID regulator 39 to control power supply 34. In other words, central control unit 15 controls the value of pressure P of oil 22 inside thrust chamber 21 by means of a first control loop employing as a feedback variable the value of pressure P of oil 22 inside thrust chamber 21, and a second control loop within the first control loop and employing as a feedback variable the value of current I circulating through coil 35 of solenoid valve 31.
An alternative embodiment comprises two torque sensors 16, each connected to central control unit 15 and fitted to a respective axle shaft 10 to real-time detect the value of the torque transmitted by self-locking differential 9 to respective rear wheel 3 via relative axle shaft 10. Each torque sensor 16 is preferably electromagnetic, and measures the torsional deformation of respective axle shaft 10 electromagnetically to determine the value of the torque transmitted by axle shaft 10 to relative rear wheel 3.
Central control unit 15 controls regulating device 24 to regulate the lock percentage %L of differential 9 as a function of the value of the torque transmitted by self-locking differential 9 to each rear wheel 3. More specifically, central control unit 15 predicts time changes in the angular rotation speed of each rear wheel 3, using the value of the torque transmitted by respective axle shaft 10, and controls regulating device 24 to regulate the lock percentage %L of differential 9 as a function of future time changes in the angular rotation speed of each rear wheel 3. Central control unit 15 has the advantage of estimating a target value of the lock percentage %L of differential 9 as a function of the dynamic parameters of vehicle 1, of estimating a target value of the torque transmitted by each axle shaft 10 as a function of the target value of lock percentage %L of differential 9, and of controlling regulating device 24 by means of a feedback control loop employing as a feedback variable the value of the torque transmitted to each rear wheel 3. Obviously, the control loop of the torque value may contain a control loop of the value of pressure P of oil 22 inside thrust chamber 21 and/or a control loop of the value of current I circulating through coil 35.
More specifically, as shown in Figure 4, the target value %Lrif of the lock percentage of differential 9 is established in central control unit 15 as described later on, and is compared with the actual value of lock percentage %L of differential 9, measured by torque sensors 16 fitted to axle shafts 10, to generate an error E%ι of lock percentage. A control signal S is obtained from lock percentage error E%L by a PID regulator 40, and is supplied to a control block 41 to determine a corresponding target value Irif of the current I circulating through coil 35. Target value Irif is compared with the actual value of current I, measured by sensor 37, to generate a current error Ei which is used by PID regulator 39 to control power supply 34. In a preferred embodiment, to the control signal S supplied by PID regulator 40 is added a further contribution, which depends directly on target value %Lrif of the lock percentage of differential 9, and is supplied by a computing block 42 implementing an inverse model. In other words, the signal supplied to control block 41 depends on both the error in the value of lock percentage %L of differential 9 (closed-loop feedback control) and on the target value %Lrif of the lock percentage of differential 9 (direct open-loop control) . This solution is employed to increase overall control response speed. In other words, central control unit 15 controls the lock percentage %L of differential 9 by means of a first control loop employing the value of lock percentage %L of differential 9 as a feedback variable, and a second control loop within the first control loop and employing as a feedback variable the value of current I circulating through coil 35 of solenoid valve 31.
As vehicle 1 is running, central control unit 15 determines the target value of the lock percentage %L of differential 9 as a function of the dynamic parameters of vehicle 1, the position Pace of accelerator pedal 14, the position Pbra of brake pedal 13, the drive torque Tm, the gear engaged, and intervention of any other electronic devices on vehicle 1 (e.g. ABS, ASR and ESP) . For example, the dynamic parameters of vehicle 1 employed by central control unit 15 to determine the target value of the lock percentage %L of differential 9 may be; the travelling speed V of vehicle 1, the turning angle Dvol of vehicle 1, the yaw speed Psip of vehicle 1, lateral acceleration Ay of vehicle 1, longitudinal acceleration Ax of vehicle 1, and the rotation speed WrearL, WrearR of each rear drive wheel 3. To determine the target value of the lock percentage %L of differential 9, central control unit 15 may also take into account the driving mode (normal, sport, low-grip) selected by the driver of vehicle 1.
When driving along a substantially straight route, central control unit 15 zeroes the lock percentage %L of differential 9 in normal driving mode, and gradually increases the lock percentage %L of differential 9 in sport mode. In addition to the mode settings made by the driver, the discriminating factor between normal and sport mode may be defined by the position Pace of accelerator pedal 14, the longitudinal acceleration Ax value of vehicle 1, and/or the speed V value of vehicle 1.
When cornering, central control unit 15 gradually increases the lock percentage %L of differential 9 if accelerator pedal 14 is released, to stabilize vehicle 1. When cornering, central control unit 15 gradually reduces the lock percentage %L of differential 9 if accelerator pedal 14 is pressed (sharply) , to maximize both stability and cornering acceleration performance of vehicle 1. More specifically, the reduction in the lock percentage %L of differential 9 is proportional to the lateral acceleration Ay of vehicle 1, the speed V of vehicle 1, the drive torque Tm of engine 4, and/or the gear engaged. In this condition, central control unit 15 may also reduce the drive torque Tm of engine 4 to limit the power oversteering effect.
When cornering at substantially steady speed, central control unit 15 estimates the road grip of wheels 2, 3, and accordingly zeroes the lock percentage %L of differential 9 when the road grip of wheels 2, 3 is far from the grip limit, gradually increases the lock percentage %L of differential 9 when the road grip of wheels 2, 3 nears the grip limit, and reduces the lock percentage %L of differential 9 to zero when the road grip of wheels 2, 3 is almost at the grip limit. As the road grip of wheels 2, 3 nears the grip limit, central control unit 15 preferably increases the lock percentage %L of differential 9 gradually in proportion to the value of lateral acceleration Ay of vehicle 1 and the value of speed V of vehicle 1.
The road grip of wheels 2, 3 is estimated as a function of the value of turning angle Dvol of vehicle 1 and the value of lateral acceleration Ay of vehicle 1. More specifically, central control unit 15 zeroes the lock percentage %L of differential 9 when the value of turning angle Dvol of vehicle 1 is substantially directly proportional to the value of lateral acceleration Ay of vehicle 1, and gradually increases the lock percentage %L of differential 9 when no substantially direct proportion relationship exists between the value of turning angle Dvol of vehicle 1 and the value of lateral acceleration Ay of vehicle 1.
Operating as described above when cornering at substantially steady speed, understeering of vehicle 1 is eliminated when the road grip of wheels 2, 3 is far from the grip limit (linear relationship between turning angle Dvol and lateral acceleration Ay) , vehicle 1 is slightly oversteered when the road grip of wheels 2, 3 nears the grip limit, and vehicle 1 is understeered (i.e. performs more safely and predictably) when the road grip of wheels 2, 3 is almost at the grip limit.
Tests have shown that regulating device 24, as described above, for regulating the lock percentage %L of differential 9 provides for improving performance, directional stability, active safety (even at the grip limit), and driving pleasure.

Claims

1) A rear-drive vehicle (1) comprising a self- locking differential (9) , and a number of sensors (16) for real-time detecting respective dynamic parameters of the vehicle (1); the vehicle (1) being characterized by comprising a regulating device (24) for regulating the lock percentage (%L) of the differential (9) , and a central control unit (15) for controlling the regulating device (24) to regulate the lock percentage (%L) of the differential (9) as a function of the dynamic parameters of the vehicle (1) .
2) A vehicle (1) as claimed in Claim 1, wherein the self-locking differential (9) comprises a box body (17); a bevel gear pair (18) housed in the box body (17) , and which transmits the drive torque (Tm) to the two rear drive wheels (3) by means of respective axle shafts (10) ; and a lock device (19) for partly locking one axle shaft (10) with respect to the box body (17); the lock device (19) comprising a clutch (20) in turn having a number of disks (23) integral with one of the axle shafts (10) , and a thrust chamber (21) filled with a fluid (22) under pressure (P) to exert variable axial thrust on the disks (23) . 3) A vehicle (1) as claimed in Claim 2, wherein the regulating device (24) regulates the pressure (P) of the fluid (22) inside the thrust chamber (21) .
4) A vehicle (1) as claimed in Claim 3, wherein the regulating device (24) comprises a solenoid valve (31) for selectively connecting the thrust chamber (21) to a tank (25) into which the fluid (22) is drained, or to a tank (29) for supplying the fluid (22) under pressure (P) .
5) A vehicle (1) as claimed in Claim 4, wherein the central control unit (15) estimates a target value of the lock percentage (%L) of the differential (9) as a function of the dynamic parameters of the vehicle (1) , estimates a target value (Prif) of the pressure (P) of the fluid (22) inside the thrust chamber (21) as a function of the target value of the lock percentage (%L) of the differential (9) , and controls the solenoid valve (31) to apply inside the thrust chamber (21) the target value (Prif) of the pressure (P) of the fluid (22) .
6) A vehicle (1) as claimed in Claim 5, wherein the regulating device (24) comprises a first sensor (36) for detecting the value of the pressure (P) of the fluid (22) inside the thrust chamber (21) , and a second sensor (37) for detecting the value of the current (I) circulating through the solenoid valve (31) ; the central control unit (15) controlling the value of the pressure (P) of the fluid (22) inside the thrust chamber (21) by means of a first control loop employing as a feedback variable the value of the pressure (P) of the fluid (22) inside the thrust chamber (21) , and a second control loop within the first control loop and employing as a feedback variable the value of the current (I) circulating through the solenoid valve (31) .
7) A vehicle (1) as claimed in one of Claims 1 to 6, and comprising an engine (4) producing a drive torque (Tm) which is transmitted to the rear drive wheels (3) by the self-locking differential (9) ; an accelerator pedal (14) which modulates the drive torque (Tm) generated by the engine (4); and a brake pedal (13) which modulates a brake torque acting on the vehicle (1) .
8) A vehicle (1) as claimed in Claim 7, wherein the central control unit (15) controls the regulating device
(24) to regulate the lock percentage (%L) of the differential (9) as a function of the travelling speed
(V) of the vehicle (1), the turning angle (Dvol) of the vehicle (1), the yaw speed (Psip) of the vehicle (1), the lateral acceleration (Ay) of the vehicle (1) , the longitudinal acceleration (Ax) of the vehicle (1) , the rotation speed (WrearL, WrearR) of each rear drive wheel
(3) , the position (Pace) of the accelerator pedal (14) , the position (Pbra) of the brake pedal (13) , and the drive torque (Tm) .
9) A vehicle (1) as claimed in Claim 7 or 8, wherein, when cornering, the central control unit (15) increases the lock percentage (%L) of the differential (9) when the accelerator pedal (14) is released. 10) A vehicle (1) as claimed in Claim 7, 8 or 9, wherein, when cornering, the central control unit (15) reduces the lock percentage (%L) of the differential (9) when the accelerator pedal (14) is pressed. 11) A vehicle (1) as claimed in Claim 10, wherein the reduction in the lock percentage (%L) of the differential (9) is proportional to the lateral acceleration (Ay) of the vehicle (1) , the speed (V) of the vehicle (1) , and the drive torque (Tm) of the engine (4) .
12) A vehicle (1) as claimed in Claim 10 or 11, wherein the central control unit (15) reduces the drive torque (Tm) of the engine (4) to limit the power oversteering effect.
13) A vehicle (1) as claimed in one of Claims 7 to 12, wherein, when cornering at substantially steady speed, the central control unit (15) estimates the road grip of the wheels (2, 3), zeroes the lock percentage (%L) of the differential (9) when the road grip of the wheels (2, 3) is far from the grip limit, and gradually increases the lock percentage (%L) of the differential (9) when the road grip of the wheels (2, 3) nears the grip limit . 14) A vehicle (1) as claimed in Claim 13, wherein the central control unit (15) reduces the lock percentage (%L) of the differential (9) to zero when the road grip of the wheels (2, 3) is almost at the grip limit.
15) A vehicle (1) as claimed in Claim 13 or 14, wherein, as the road grip of the wheels (2, 3) nears the grip limit, the central control unit (15) gradually increases the lock percentage (%L) of the differential
(9) in proportion to the value of the lateral acceleration (Ay) of the vehicle (1) and the value of the speed (V) of the vehicle (1) .
16) A vehicle (1) as claimed in Claim 13, 14 or 15, wherein the central control unit (15) zeroes the lock
5 percentage (%L) of the differential (9) when the value of the turning angle (Dvol) of the vehicle (1) is substantially directly proportional to the value of the lateral acceleration (Ay) of the vehicle (1) , and gradually increases the lock percentage (%L) of the 10 differential (9) when no substantially direct proportion relationship exists between the value of the turning angle (Dvol) of the vehicle (1) and the value of the lateral acceleration (Ay) of the vehicle (1) .
17) A vehicle (1) as claimed in one of Claims 13 to 15 16, wherein the central control unit (15) estimates the road grip of the wheels (2, 3) by estimating the value of the lateral acceleration (Ay) of the vehicle (1) .
18) A vehicle (1) as claimed in one of Claims 13 to 16, wherein the central control unit (15) estimates the
20 road grip of the wheels (2, 3) by estimating the value of the turning angle (Dvol) of the vehicle (1) and value of the lateral acceleration (Ay) of the vehicle (1) .
19) A vehicle (1) as claimed in one of Claims 7 to 18, wherein, when driving along a substantially straight
25 route, the central control unit (15) zeroes the lock percentage (%L) of the differential (9) in normal driving mode, and gradually increases the lock percentage (%L) of the differential (9) in sport driving mode. 20) A vehicle (1) as claimed in one of Claims 1 to 19, and comprising two axle shafts (10) , each connecting the self-locking differential (9) mechanically to a respective rear wheel (3) ; and two torque sensors (16) , each of which is connected to the central control unit (15), is fitted to a respective axle shaft (10), and real-time detects the value of the torque transmitted by the self-locking differential (9) to the respective rear wheel (3) via the relative axle shaft (10) ; the central control unit (15) controlling the regulating device (24) to regulate the lock percentage (%L) of the differential (9) as a function of the value of the torque transmitted by the self-locking differential (9) to each rear wheel (3). 21) A vehicle (1) as claimed in Claim 20, wherein each torque sensor (16) is electromagnetic, and measures electromagnetically the torsional deformation of the respective axle shaft (10) to determine the value of the torque transmitted by the axle shaft (10) to the relative rear wheel (3) .
22) A vehicle (1) as claimed in Claim 20 or 21, wherein the central control unit (15) predicts time changes in the angular rotation speed of each rear wheel (3) , using the value of the torque transmitted by respective axle shaft (10) , and controls the regulating device (24) to regulate the lock percentage (%L) of the differential (9) as a function of future time changes in the angular rotation speed of each rear wheel (3) . 23) A vehicle (1) as claimed in Claim 20, 21 or 22, wherein the central control unit (15) estimates a target value of the lock percentage (%L) of the differential (9) as a function of the dynamic parameters of the vehicle (1) , and controls the regulating device (24) by means of a feedback control loop employing as a feedback variable the value of the lock percentage (%L) of the differential (9).
24) A vehicle (1) as claimed in Claim 23, wherein the regulating device (24) comprises a solenoid valve
(31) controlled to vary the lock percentage (%L) of the differential (9), and a second sensor (37) for detecting the value of the current (I) circulating through the solenoid valve (31) ; the central control unit (15) controlling the regulating device (24) by means of a first control loop employing the value of the lock percentage (%L) of the differential (9) as a feedback variable, and a second control loop within the first control loop and employing as a feedback variable the value of the current (I) circulating through the solenoid valve (31) .
25) A vehicle (1) as claimed in Claim 20, 21 or 22, wherein the central control unit (15) estimates a target value of the lock percentage (%L) of the differential (9) as a function of the dynamic parameters of the vehicle (1) , and controls the regulating device (24) by adding a feedback control loop employing the value of the lock percentage (%L) of the differential (9) as a feedback variable, and a direct open control loop employing the target value of the lock percentage (%L) of the differential (9) as a control variable.
26) A vehicle (1) as claimed in Claim 25, wherein the regulating device (24) comprises a solenoid valve (31) controlled to vary the lock percentage (%L) of the differential (9), and a second sensor (37) for detecting the value of the current (I) circulating through the solenoid valve (31) ; the central control unit (15) controlling the regulating device (24) by means of a first control loop employing the value of the lock percentage (%L) of the differential (9) as a feedback variable, and a second control loop within the first control loop and employing as a feedback variable the value of the current (I) circulating through the solenoid valve (31) .
PCT/EP2004/050434 2003-04-04 2004-04-02 Rear-drive vehicle with an electronically controlled self-locking differential WO2004087453A1 (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US10/552,039 US7641585B2 (en) 2003-04-04 2004-04-02 Rear-drive vehicle with an electronically controlled self-locking differential
DE602004010635T DE602004010635T2 (en) 2003-04-04 2004-04-02 VEHICLE WITH REAR AXLE DRIVE WITH AN ELECTRONICALLY CONTROLLED SELF-LOCKING DIFFERENTIAL
JP2006505519A JP4819672B2 (en) 2003-04-04 2004-04-02 Rear-wheel drive vehicle with electronically controllable self-locking differential
EP04741443A EP1613499B1 (en) 2003-04-04 2004-04-02 Rear-drive vehicle with an electronically controlled self-locking differential

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITBO2003A000199 2003-04-04
IT000199A ITBO20030199A1 (en) 2003-04-04 2003-04-04 REAR DRIVE VEHICLE EQUIPPED WITH DIFFERENTIAL

Publications (1)

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WO2004087453A1 true WO2004087453A1 (en) 2004-10-14

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US (1) US7641585B2 (en)
EP (1) EP1613499B1 (en)
JP (2) JP4819672B2 (en)
DE (1) DE602004010635T2 (en)
IT (1) ITBO20030199A1 (en)
WO (1) WO2004087453A1 (en)

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EP3100893A1 (en) 2015-06-04 2016-12-07 FERRARI S.p.A. Method to control a road vehicle with an electronically controlled self-locking differential when driving along a curve
IT202100015206A1 (en) 2021-06-10 2022-12-10 Ferrari Spa METHOD OF CONTROLLING A ROAD VEHICLE WITH INDEPENDENT ENGINES ACTING ON WHEELS ON THE SAME AXLE AND RELATED ROAD VEHICLE
IT202100021065A1 (en) 2021-08-04 2023-02-04 Ferrari Spa METHOD FOR DETERMINING AN OPTIMIZED TORQUE DISTRIBUTION AT THE DRIVE WHEELS OF A ROAD VEHICLE AND RELATED ROAD VEHICLE

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WO2008008705A3 (en) * 2006-07-14 2008-03-06 Borgwarner Inc Limited slip differential
EP3100893A1 (en) 2015-06-04 2016-12-07 FERRARI S.p.A. Method to control a road vehicle with an electronically controlled self-locking differential when driving along a curve
IT202100015206A1 (en) 2021-06-10 2022-12-10 Ferrari Spa METHOD OF CONTROLLING A ROAD VEHICLE WITH INDEPENDENT ENGINES ACTING ON WHEELS ON THE SAME AXLE AND RELATED ROAD VEHICLE
EP4101682A1 (en) 2021-06-10 2022-12-14 FERRARI S.p.A. Control method for a road vehicle with independent engines acting on the wheels of the same axle and relative road vehicle
IT202100021065A1 (en) 2021-08-04 2023-02-04 Ferrari Spa METHOD FOR DETERMINING AN OPTIMIZED TORQUE DISTRIBUTION AT THE DRIVE WHEELS OF A ROAD VEHICLE AND RELATED ROAD VEHICLE
EP4129785A1 (en) 2021-08-04 2023-02-08 FERRARI S.p.A. Method for determining an optimized torque distribution to the drive wheels of a road vehicle and relative road vehicle

Also Published As

Publication number Publication date
JP4819672B2 (en) 2011-11-24
JP2011137549A (en) 2011-07-14
DE602004010635T2 (en) 2008-12-11
EP1613499A1 (en) 2006-01-11
US7641585B2 (en) 2010-01-05
JP2006522287A (en) 2006-09-28
DE602004010635D1 (en) 2008-01-24
ITBO20030199A1 (en) 2004-10-05
EP1613499B1 (en) 2007-12-12
US20070158126A1 (en) 2007-07-12

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