Driving force control system for front-and-rear wheel drive vehicles

• US 6,528,959 B2
• Filed: 07/17/2001
• Issued: 03/04/2003
• Est. Priority Date: 07/19/2000
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Kitano, Kazuhiko, Uchiyama, Naoki, Fukuda, Toshihiko, Nakasako, Tooru, Honda, Kenji, Yonekura, Takahiro
• Primary Examiner(s): Leykin, Rita
• Application Number:
  US09/906,054
• Publication Number:
  US 20020041167A1
• Time in Patent Office: 595 Days
• Field of Search: 318/52, 318/55, 318/58, 318/64, 180/65.1
• US Class Current: 318/55
• CPC Class Codes: B60K 28/16 responsive to, or preventing, skidding of wheels brake control systems for vehicle drive stability B60T8/1755; arrangements responsive to a speed condition for adjusting wheel braking force B60T8/32; control of vehicle driving stability otherwise than by controlling the propulsion unit only B60W30/02; preventing wheel slippage by reducing power in rail vehicles B61C15/00
• CPC Class Codes: B60K 6/48 Parallel type
• CPC Class Codes: B60K 6/52 Driving a plurality of drive axles, e.g. four-wheel drive
• CPC Class Codes: B60L 2240/486 Operating parameters
• CPC Class Codes: B60T 2201/04 Hill descent control
• CPC Class Codes: B60T 2270/602 ABS features related thereto
• CPC Class Codes: B60T 8/1769 specially adapted for vehicles having more than one driven axle, e.g. four-wheel drive vehicles
• CPC Class Codes: B60T 8/48 connecting the brake actuator to an alternative or additional source of fluid pressure , e.g. traction control systems
• CPC Class Codes: B60W 10/06 including control of combustion engines
• CPC Class Codes: B60W 10/08 including control of electric propulsion units, e.g. motors or generators
• CPC Class Codes: B60W 20/00 Control systems specially adapted for hybrid vehicles hybrid vehicle design, B60K6/00; electric vehicles B60L
• CPC Class Codes: B60W 20/10 Controlling the power contribution of each of the prime movers to meet required power demand
• CPC Class Codes: B60W 2520/10 Longitudinal speed
• CPC Class Codes: B60W 2530/00 Input parameters relating to vehicle conditions or values, not covered by groups B60W2510/00 or B60W2520/00
• CPC Class Codes: B60W 2540/10 Accelerator pedal position
• CPC Class Codes: B60W 2540/18 Steering angle
• CPC Class Codes: B60W 2552/15 Road slope, i.e. the inclination of a road segment in the longitudinal direction
• CPC Class Codes: B60W 2710/0666 Engine torque
• CPC Class Codes: B60W 2710/1061 Output power
• CPC Class Codes: B60W 2720/106 Longitudinal acceleration
• CPC Class Codes: Y02T 10/62 : Hybrid vehicles
• CPC Class Codes: Y10S 903/916 : with plurality of drive axles

Abstract

There is provided a driving force control system for a front-and-rear wheel drive vehicle, which is capable maintaining an optimum slip condition of the drive wheels even on a low-friction road surface, ensuring a proper grip of rear wheels even on a low-friction road surface or a downhill slope, even when the driver operates the steering wheel while the vehicle is performing decelerating travel on such a road, and smoothly performing the assistance of an electric motor when the vehicle is accelerated without developing a torque step, thereby ensuring stable traveling and excellent acceleration and drivability. The front-and-rear wheel drive vehicle drives the front wheels by an engine, and rear wheels by an electric motor via an electromagnetic clutch. The target driving force for driving the vehicle is calculated based on at least a vehicle speed and an accelerator pedal opening. The present traveling condition of the vehicle is determined. The driving force for driving the vehicle is controlled based on the calculated target driving force in dependence on the determined traveling condition of the vehicle.

Claims

1. A driving force control system for a front-and-rear wheel drive vehicle that drives one pair of respective pairs of front drive wheels and rear drive wheels by an engine, and another pair of the respective pairs by an electric motor,

the driving force control system comprising:

vehicle speed-detecting means for detecting a vehicle speed of the vehicle;

driving force demand degree-detecting means for detecting a degree of demand for a driving force for driving the vehicle;

target driving force-calculating means for calculating a target driving force for driving the vehicle, based on at least the vehicle speed and the degree of demand for the driving force;

traveling condition-determining means for determining a present traveling condition of the vehicle; and

driving force control means for controlling a driving force of the engine and a driving force of the motor based on the calculated target driving force, in dependence on the traveling condition of the vehicle determined by said traveling condition-determining means.

2. A driving force control system according to claim 1, wherein said driving force demand degree-detecting means comprises accelerator opening-detecting means for detecting an accelerator opening,

wherein said traveling condition-determining means includes differential rotational speed-detecting means for detecting a differential rotational speed between a rotational speed of the front drive wheels and a rotational speed of the rear drive wheels based on a parameter indicative of the traveling condition of the vehicle, target differential rotational speed-setting means for setting a target differential rotational speed based on the parameter indicative of the traveling condition of the vehicle, and slip determination means for determining a slip condition of the one pair driven by the engine, based on the detected differential rotational speed and the target differential rotational speed, and

wherein said driving force control means includes target motor driving force-calculating means for calculating a target motor driving force of the electric motor based on the target driving force, target engine driving force-calculating means for calculating a target engine driving force of the engine based on the target driving force and the target motor driving force, motor drive control means for controlling driving of the electric motor based on the target motor driving force, engine drive control means for controlling driving of the engine based on the target engine driving force, and engine driving force-correcting means for decreasing the target engine driving force such that the differential rotational speed is held at the target differential rotational speed, when it is determined by said slip determination means that the one pair driven by the engine are slipping.

3. A driving force control system according to claim 2, wherein said driving force control means further includes motor driving force-correcting means for increasing the target motor driving force when said slip determination means determines that the one pair driven by the engine are slipping.

4. A driving force control system according to claim 2, wherein said traveling condition-determining means further includes differential rotational speed change amount-detecting means for detecting an amount of change in the differential rotational speed, and

wherein said engine driving force-correcting means decreases the target engine driving force according to the detected amount of change in the differential rotational speed.

5. A driving force control system according to claim 2, wherein the parameter indicative of the traveling condition of the vehicle includes at least one of a degree of a slope of a road, a steering angle, the vehicle speed, and the accelerator opening.

6. A driving force control system according to claim 1, wherein the vehicle includes an accelerator pedal, and a steering wheel,

wherein said driving force demand degree-detecting means includes accelerator condition-detecting means for detecting whether or not the accelerator pedal is in a released condition,

wherein said traveling condition-determining means includes downhill traveling-determining means for determining whether or not the vehicle is traveling downhill, and steering angle-detecting means for detecting an steering angle of the steering wheel, and

wherein said driving force control means includes target deceleration-setting means for setting a target deceleration based on the detected steering angle when said accelerator condition-detecting means detects that the accelerator pedal is in the released condition and at the same time said downhill traveling-determining means determines that the vehicle is traveling downhill, engine braking force-calculating means for calculating an engine braking force according to the detected vehicle speed when said accelerator condition-detecting means detects that the accelerator pedal is in the released condition, target braking force-setting means for setting a target braking force of the electric motor for braking the rear wheels, based on the set target deceleration and the calculated engine braking force, and drive control means for controlling driving of the electric motor based on the set target driving force.

7. A driving force control system according to claim 6, wherein the vehicle includes a brake,

wherein said traveling condition-determining means includes brake operation-detecting means for detecting whether or not the brake is being operated,

wherein said driving force control means further includes target deceleration-increasing means for correcting the set target deceleration such that the set target deceleration is increased to a larger value than assumed when the brake is not being operated, when said brake operation-detecting means detects that the brake is being operated.

8. A driving force control system according to claim 7, wherein the vehicle includes clutch means for disconnecting and connecting between the rear wheels and the electric motor,

wherein said driving force control means includes clutch driving means for disconnecting the clutch means when the vehicle speed is higher than a predetermined vehicle speed, and disconnecting the clutch means when the vehicle speed is equal to or lower than the predetermined vehicle speed, and target deceleration-decreasing means for correcting the set target deceleration such that the set target deceleration is decreased to a smaller value than the target deceleration increased by said target deceleration-increasing means.

9. A driving force control system according to claim 1, wherein the vehicle include an accelerator pedal and a steering wheel,

wherein said driving force demand degree-detecting means includes accelerator condition-detecting means for detecting whether or not the accelerator pedal is in a released condition,

wherein said traveling condition-determining means includes steering angle-detecting means for detecting a steering angle of the steering wheel, and

wherein said driving force control means includes engine braking force-calculating means for calculating an engine braking force of the engine according to the detected vehicle speed when said accelerator condition-detecting means detects that the accelerator pedal is in the released condition, target braking force-setting means for setting a target braking force of the electric motor for braking the rear wheels to a value corresponding to the calculated engine braking force, target braking force-correcting means for correcting the set target braking force according to the detected steering angle, and drive control means for controlling driving of the electric motor based on the corrected target braking force.

10. A driving force control system according to claim 1, wherein the vehicle includes a torque converter, and is driven while switching between a four-wheel drive mode in which the one pair are driven by the engine via the torque converter and at the same time the another pair are driven by the electric motor and a two-wheel drive mode in which the driving of the another pair by the electric motor is inhibited,

wherein said driving force demand degree-detecting means includes accelerator opening-detecting means for detecting an accelerator opening,

wherein said traveling condition-determining means includes speed ratio-detecting means for detecting a speed ratio of the torque converter, reference speed ratio-storing means for storing a predetermined reference speed ratio, and speed ratio-determining means for determining whether or not the detected speed ratio is smaller than the predetermined reference speed ratio, and

wherein said driving force control means includes target motor driving force-calculating means for calculating a target motor driving force of the electric motor based on the target driving force, target engine driving force-calculating means for calculating a target engine driving force of the engine based on the target driving force and the target motor driving force, motor drive means for driving the electric motor based on the target motor driving force, and motor drive-permitting means for permitting the driving of the electric motor by said motor drive means when an amount of change in the target driving force is equal to or larger than a predetermined value, and when the amount of change in the target driving force is smaller than the predetermined value, permits the driving of the electric motor on condition that the speed ratio-determining means determines that the detected speed ratio is smaller than the predetermined reference speed ratio.

11. A driving force control system according to claim 1, wherein the vehicle includes a torque converter, and is driven while switching between a four-wheel drive mode in which the one pair are driven by the engine via the torque converter and at the same time the another pair are driven by the electric motor and a two-wheel drive mode in which the driving of the another pair by the electric motor is inhibited,

wherein said driving force demand degree-detecting means includes an accelerator opening-detecting means for detecting an accelerator opening,

wherein said traveling condition-determining means includes speed ratio-detecting means for detecting a speed ratio of the torque converter, reference speed ratio-storing means for storing a predetermined reference speed ratio, speed ratio-determining means for determining whether or not the detected speed ratio is larger than the predetermined reference speed ratio, and stepping operation-detecting means for detecting whether or not the accelerator pedal in the released condition is stepped on, during the traveling of the vehicle, and

wherein said driving force control means includes target motor driving force-calculating means for calculating a target motor driving force of the electric motor, motor drive means for driving the electric motor based on the calculated target motor driving force, and motor drive-permitting means for permitting the driving of the electric motor by said motor drive means when said stepping operation-detecting means detects that the accelerator pedal is stepped on, and when said stepping operation-detecting means does not detect that the accelerator pedal is stepped on, inhibits the driving of the electric motor on condition that the speed ratio-determining means determines that the detected speed ratio is smaller than the predetermined reference speed ratio.