Motor vehicles – Steering gear – With electric power assist
Reexamination Certificate
1997-08-14
2001-01-09
Hurley, Kevin (Department: 3619)
Motor vehicles
Steering gear
With electric power assist
C701S041000
Reexamination Certificate
active
06170600
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a vehicle steering system which combines a power steering system which assists the manual effort required by the vehicle operator to steer the vehicle and an automatic steering system which automatically steers the vehicle according to given road information.
BACKGROUND OF THE INVENTION
Various forms of automatic steering systems have recently been proposed which automatically steer the vehicle according to the configuration of the road. The road information can be derived from a GPS system incorporated with a map of the area, and/or from a television camera which may detect the position of a white line marked on the road or the shape of the road. It is also possible to use other guidance systems for guiding the vehicle along the road. According to such road information, a target value of a dynamic variable such as yaw rate, lateral acceleration, and steering angle is computed, and the vehicle steering system is controlled in such a manner that the deviation between the target value of the dynamic variable and the actual value of the dynamic variable is minimized.
It is now customary for a motor vehicle to be equipped with a power steering system which assists the manual steering input applied to a steering wheel by using a hydraulic cylinder or an electric motor.
FIG. 3
shows a typical electric power steering system. A steering wheel
21
is attached to an upper end of a steering shaft
22
, and a lower end of the steering shaft
22
is connected to a pinion
24
via a connecting shaft
23
which is provided with universal joints
23
a
and
23
b
at two ends thereof. The pinion
24
meshes with a rack
27
which extends laterally of the vehicle body and is guided to move along a longitudinal axial line thereof. The two ends of a rack shaft
28
carrying the rack
27
are connected to knuckle arms
26
of right and left front wheels W via tie rods
25
. To provide a power assist to this steering system, an electric motor
29
is coaxially combined with the rack
27
for axially actuating the rack
27
via a ball and nut mechanism
30
.
A steering torque sensor
31
is provided in an appropriate part of the steering system to detect the magnitude of the steering effort applied to the steering wheel
21
by the vehicle operator. The electric motor
29
is controlled by a controller
32
which receives an output signal from the steering torque sensor
31
so that a desired target steering torque may be produced.
The automatic steering system and the power steering system described above have various common components, and a significant reduction in size, cost, and complexity of the overall system can be achieved by sharing these common components by the two systems. The simplification of the overall system also contributes to an improvement in the reliability of the operation of these systems.
However, when these two systems are simply combined so as to share various component parts, certain inconveniences may arise. For instance, when both the automatic steering system and the power steering system are in operation, a manual effort to change the driving lane of the vehicle gives rise to an actual dynamic variable such as yaw rate, lateral acceleration, and steering angle which deviates from the target value of the dynamic variable, and the system tends to resist the manual effort.
To resolve such an inconvenience, it has been previously proposed in Japanese patent laid open publication No. 7-205831 to allow an automatic steering mode and a power steering mode to be selected in a mutually exclusive manner, and to provide a certain time lag in a switch-over between the two modes. However, according to this previous proposal, the time lag produces a blank period during which there is no steering control so that the transition from one mode to the other is not very smooth, and the vehicle operator may experience an undesirable sudden change in the handling of the vehicle.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide an automatic power steering system which allows an automatic steering system and a power steering system to share various components so as to simplify the structure.
A second object of the present inventions to provide an automatic power steering system which allows a smooth transition from one of the operation modes to the other without involving any absence of control.
According to the present invention, these and other objects can be accomplished by providing a steering control system for a vehicle, comprising: a steering mechanism; power steering means for applying an assist steering torque to the steering mechanism according a magnitude of manual steering effort; automatic steering means for applying an automatic steering torque to the steering mechanism according to road information; continuous switching means for continuously changing weights of the assist steering torque and the automatic steering torque in an overall steering torque according to the magnitude of the manual steering effort. Typically, the manual steering effort is given by an output of a steering torque sensor for measuring a steering torque applied to a steering wheel.
Thus, it is possible to avoid any interference between a power steering mode and an automatic steering mode, and to switch over between them without any discontinuity.
According to a preferred embodiment of the present invention, the power steering means comprises steering torque detecting means for detecting a manual steering torque applied to a steering wheel, an actuator for producing the assist steering torque, and first target drive torque determining means for determining the assist steering torque according to a magnitude of the manual steering torque. Additionally, the automatic steering means may comprise road configuration detecting means for detecting a configuration of a road on which the vehicle is traveling, target dynamic variable determining means for determining a target dynamic variable for the vehicle according to an output from the road configuration detecting means, and second target drive torque determining means for determining the automatic steering torque which is to be produced by the actuator according an output from the target dynamic variable determining means. Also, the continuous switching means may comprise actual dynamic variable detecting means for measuring an actual value of the dynamic variable, estimated dynamic variable computing means for computing a hypothetical dynamic variable which would be produced when the output of the second target drive torque determining means is applied to the steering mechanism, and dynamic variable weighting means for weighting an output of the estimated dynamic variable computing means and an output of the actual dynamic variable detecting means according to an output of the steering torque detecting means, an output of the dynamic variable weighting means being deducted from the output of the target dynamic variable determining means which is applied to the second target drive torque determining means.
Thus, the continuous switching means can identify the point of switching of switching from one steering mode to the other in an unambiguous manner. Also, a significant part of sensors and actuators can be shared by the automatic steering system and the power steering system so that a significant reduction in cost and size can be achieved with the added advantage of an improvement in reliability. Also, the vehicle operator can regain the manual override of the steering system whenever necessary. Therefore, the vehicle operator can take sudden and extreme steering actions when such a need arises. Conversely, when the vehicle operator wishes to return to the automatic steering mode, all he is required to do is to let go of the steering wheel, and the steering system takes over the control in a highly smooth manner.
The dynamic variable which is given as a variable for representing the navigational movement of the vehicle may cons
Allenby C. B.
Fischer Andrew J.
Honda Giken Kogyo Kabushiki Kaisha
Hurley Kevin
MacPherson Alan H.
LandOfFree
Automatic power steering system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automatic power steering system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automatic power steering system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2548552