U.S. patent application number 09/789012 was filed with the patent office on 2001-12-06 for control of incompatible torque requests in vehicle speed control.
Invention is credited to Inoue, Hideaki, Maruko, Naoki, Tamura, Minoru.
Application Number | 20010049578 09/789012 |
Document ID | / |
Family ID | 18566322 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010049578 |
Kind Code |
A1 |
Tamura, Minoru ; et
al. |
December 6, 2001 |
Control of incompatible torque requests in vehicle speed
control
Abstract
A system and method for controlling speed of a vehicle include
determining whether or not a stand-by braking torque is applied,
determining an actual distance from a preceding vehicle in front of
a vehicle, comparing the actual distance to a desired distance to
determine whether the actual distance is greater than the desired
distance, determining motor/engine torque to increase vehicle
speed, and applying the motor/engine torque when the actual
distance is greater than the desired distance. The system and
method terminates application of stand-by braking torque upon
receiving operator torque request.
Inventors: |
Tamura, Minoru; (Yokohama,
JP) ; Inoue, Hideaki; (Yokohama, JP) ; Maruko,
Naoki; (Kanagawa, JP) |
Correspondence
Address: |
Richard L. Schwaab
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W., Suite 500
Washington
DC
20007-5109
US
|
Family ID: |
18566322 |
Appl. No.: |
09/789012 |
Filed: |
February 21, 2001 |
Current U.S.
Class: |
701/96 ;
180/179 |
Current CPC
Class: |
B60K 31/0008
20130101 |
Class at
Publication: |
701/96 ;
180/179 |
International
Class: |
B60K 031/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2000 |
JP |
2000-043398 |
Claims
What is claimed is:
1. A system for controlling speed of a vehicle, comprising: a prime
mover coupled to at least one wheel of the vehicle for applying a
positive torque to the at least one wheel in response to an
accelerating signal; and a controller having a control logic for
determining an actual distance from a preceding vehicle in front,
comparing the actual distance to a set desired distance to
determine whether the actual distance is greater than the desired
distance, determining whether or not a stand-by braking torque is
applied to the at least one wheel, determining an additional torque
requested by an automatic distance regulation (ADR) to increase
vehicle speed when the actual distance is greater than the desired
distance and the stand-by braking torque is not applied, and
generating an accelerating signal for the prime mover to apply the
additional torque to the at least one wheel.
2. The system as claimed in claim 1, wherein the stand-by braking
torque is applied to the at least one wheel when there is a need
for operator braking action after determining whether or not there
is a need for operator braking action.
3. The system as claimed in claim 1, further comprising: a braking
device coupled to the at least one wheel for applying a braking
torque to the at least one wheel in response to a braking signal,
and a controller having a control logic for determining whether or
not there is a need for operator braking action, determining a
stand-by braking torque when there is a need for operator braking
action, and generating a braking signal for the braking device to
apply the stand-by braking torque to the at least one wheel.
4. The system as claimed in claim 3, wherein the control logic for
determining whether or not there is a need for operator braking
action includes: determining an actual distance from obstacle
located in the direction of the vehicle; determining an actual
vehicle speed; determining a brake pedal position; determining an
accelerator pedal position; and making the determination whether or
not there is a need for operator braking action based on the actual
distance, the actual vehicle speed, the brake pedal position, and
the accelerator pedal position.
5. The system as claimed in claim 4, wherein the control logic for
determining whether or not there is a need for operator braking
action includes: calculating a target deceleration based on the
actual vehicle speed, and the actual distance; comparing the target
deceleration to a predetermined deceleration value; comparing the
accelerator pedal position to a predetermined accelerator pedal
position value; and making the determination that there is a need
for braking when the target deceleration exceeds the predetermined
deceleration value, the brake pedal is released, and the
accelerator pedal position is less than the predetermined
accelerator pedal position value.
6. The system as claimed in claim 3, wherein the control logic for
determining the stand-by braking torque includes: determining a
first braking torque value as an initial value of the stand-by
braking torque when an initial vehicle speed upon initiation of
application of stand-by braking torque is less than a first vehicle
speed value; determining a second braking torque value, which is
greater than the first braking torque value, as an initial value of
the stand-by braking torque when the initial vehicle speed is
greater than a second vehicle speed value that is greater than said
first vehicle speed value; and determining one of intermediate
braking torque values, which fall between the first and second
braking torque values, as an initial value of the stand-by braking
torque when the initial vehicle speed is greater than the first
vehicle speed value but less than the second vehicle speed
value.
7. The system as claimed in claim 6, wherein the intermediate
braking torque values are represented by a linear function of the
vehicle speed.
8. The system as claimed in claim 7, wherein, at least over a range
of vehicle speed values that fall between the first and second
vehicle speed values, the heavier the weight of the vehicle, the
greater the initial value of the stand-by braking torque is.
9. The system as claimed in claim 3, wherein the stand-by braking
torque is invariable for a predetermined time.
10. The system as claimed in claim 3, wherein the stand-by braking
torque decreases at a predetermined rate since the determination
was made that there was a need for operator braking action.
11. The system as claimed in claim 3, wherein the stand-by braking
torque decreases at a first predetermined rate for the
predetermined time since the determination was made that there was
a need for operator braking action, and at a second predetermined
rate that is greater than the first predetermined rate after elapse
of the predetermined period of time.
12. A system for controlling speed of a vehicle, comprising: a
braking device coupled to the at least one wheel for applying a
braking torque to at least one wheel in response to a braking
signal, and a controller having a control logic for determining
whether or not there is a need for operator braking action,
determining a stand-by braking torque when there is a need for
operator braking action, determining whether or not there is
operator acceleration request, generating a braking signal for the
braking device to apply the stand-by braking torque to the at least
one wheel, and terminating application of the stand-by braking
torque when there is operator acceleration request.
13. The system as claimed in claim 12, wherein the step of
determining whether or not there is a need for operator braking
action includes: determining an actual distance from obstacle
located in the direction of the vehicle; determining an actual
vehicle speed; determining a brake pedal position; determining an
accelerator pedal position; and making the determination whether or
not there is a need for operator braking action based on the actual
distance, the actual vehicle speed, the brake pedal position, and
the accelerator pedal position.
14. The system as claimed in claim 13, wherein the step of
determining whether or not there is a need for operator braking
action includes: calculating a target deceleration based on the
actual vehicle speed, and the actual distance; comparing the target
deceleration to a predetermined deceleration value; comparing the
accelerator pedal position to a predetermined accelerator pedal
position value; and making the determination that there is a need
for braking when the target deceleration exceeds the predetermined
deceleration value, the brake pedal is released, and the
accelerator pedal position is less than the predetermined
accelerator pedal position value.
15. The system as claimed in claim 12, wherein the step of
determining the stand-by braking torque includes: determining a
minimum braking torque value as an initial value of the stand-by
braking torque when a measure of the vehicle speed at moment upon
determination that there is a need for operator braking action is
less than a first vehicle speed value; determining a maximum
braking torque value, which is greater than the first braking
torque value, as an initial value of the stand-by braking torque
when the measure of the vehicle speed at moment upon determination
that there is a need for operator braking action is greater than a
second vehicle speed value that is greater than said first vehicle
speed value; and determining one of intermediate braking torque
values, which fall between the minimum and maximum braking torque
values, as an initial value of the stand-by braking torque when the
measure of the vehicle speed at moment upon determination that
there is a need for operator braking action is greater than said
first vehicle speed value but less than said second vehicle speed
value.
16. The system as claimed in claim 15, wherein the intermediate
braking torque values are represented by a linear function of the
vehicle speed.
17. The system as claimed in claim 16, wherein, at least over a
range of vehicle speed values that fall between the first and
second vehicle speed values, the heavier the weight of the vehicle,
the greater the initial value of the stand-by braking torque
is.
18. The system as claimed in claim 12, wherein the stand-by braking
torque is invariable for a predetermined time.
19. The system as claimed in claim 12, wherein the stand-by braking
torque decreases at a predetermined rate since the determination
was made that there was a need for operator braking action.
20. The system as claimed in claim 12, wherein the stand-by braking
torque decreases at a first predetermined rate for the
predetermined time since the determination was made that there was
a need for operator braking action, and at a second predetermined
rate that is greater than the first predetermined rate after elapse
of the predetermined period of time.
21. A computer readable storage medium having stored data
representing instructions readable by a computer to control speed
of a vehicle, the computer readable storage medium comprising:
instructions for determining an actual distance from a preceding
vehicle in front; instructions for comparing the actual distance to
a set desired distance to determine whether the actual distance is
greater than the desired distance; instructions for determining
whether or not a stand-by braking torque is applied to the at least
one wheel; instructions for determining an additional torque
requested by an automatic distance regulation (ADR) to increase
vehicle speed when the actual distance is greater than the desired
distance and the stand-by braking torque is not applied; and
instructions for applying the additional torque to at least one
wheel of the vehicle.
22. A computer readable storage medium having stored data
representing instructions readable by a computer to control speed
of a vehicle, the computer readable storage medium comprising:
instructions for determining whether or not there is a need for
operator braking action; instructions for determining a stand-by
braking torque when there is a need for operator braking action;
instructions for determining whether or not there is operator
acceleration request; instructions for applying the stand-by
braking torque to at least one wheel of the vehicle; and
instructions for terminating application of the stand-by braking
torque when there is operator acceleration request.
23. A method for controlling speed of a vehicle, comprising:
determining whether or not there is a need for operator braking
action; determining whether or not there is operator acceleration
request; determining a stand-by braking torque when there is a need
for operator braking action; applying the stand-by braking torque
to at least one wheel of the vehicle to reduce vehicle speed of the
vehicle; terminating application of the stand-by braking torque
when there is operator acceleration request; determining an actual
distance from a preceding vehicle in front; comparing the actual
distance to a set desired distance to determine whether the actual
distance is greater than the desired distance; determining whether
or not a stand-by braking torque is applied to the at least one
wheel; determining an additional torque requested by an automatic
distance regulation (ADR) to increase vehicle speed when the actual
distance is greater than the desired distance and the stand-by
braking torque is not applied; and applying the additional torque
to the at least one wheel to increase vehicle speed of the
vehicle.
24. A system for controlling speed of a vehicle, comprising: a
detection system to detect environmental data in front of the
vehicle; operator demand sensors to detect vehicle operator
request; a prime mover coupled to at least one wheel of the vehicle
for applying a positive torque to the at least one wheel in
response to an accelerating signal; a braking device coupled to the
at least one wheel for applying a braking torque to at least one
wheel in response to a braking signal; and controller means having
a control logic for determining whether or not there is a need for
operator braking action; determining whether or not there is
operator acceleration request; determining a stand-by braking
torque when there is a need for operator braking action; generating
a braking signal for the braking device to apply the stand-by
braking torque to the at least one wheel of the vehicle to reduce
vehicle speed of the vehicle; terminating application of the
stand-by braking torque when there is operator acceleration
request; determining an actual distance from a preceding vehicle in
front; comparing the actual distance to a set desired distance to
determine whether the actual distance is greater than the desired
distance; determining whether or not a stand-by braking torque is
applied to the at least one wheel; determining an additional torque
requested by an automatic distance regulation (ADR) to increase
vehicle speed when the actual distance is greater than the desired
distance and the stand-by braking torque is not applied; and
generating an acceleration signal for the primer mover to apply the
additional torque to the at least one wheel to increase speed of
the vehicle.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a system and method for
controlling speed of a vehicle.
[0002] To enhance safety of a car and passengers in present-day
road traffics, efforts are being made to support the operator in
routine driving operations.
[0003] In this direction, antilock braking systems (ABS) have been
proposed and adopted to enhance longitudinal vehicle stability in
dynamically critical conditions in braking process.
[0004] "Automatic distance regulation" (ADR) systems have been
proposed that are intended to detect and carry out a controlled
braking action to control the distance of a vehicle from other
vehicles and/or stationary objects in the direction of vehicle
motion. JP-A 7-144588 discloses a system whereby traveling speed
and deceleration of a vehicle in front are determined using a
Doppler sensor and a vehicle speed sensor, which are on a vehicle
to be controlled, and a desired distance from the vehicle in front
is determined in response comparison of the traveling speed of the
vehicle in front with a predetermined value of 15 km/h. In this
system, a driver is warned and an automatic braking action is
initiated if the distance from the vehicle in front becomes less
than the desired distance. JP-A 10-114237 discloses a technique to
release ADR in response to operator acceleration request for
passing a preceding vehicle in front without relying on detection
of accelerator pedal position. Using a predetermined characteristic
curve, a throttle position is estimated from a present position of
the throttle actuator. The operator acceleration request is
detected after comparison of a deviation of the actual throttle
position from the estimated throttle position with a threshold
value. The deviation becomes zero when the accelerator pedal is
released, but the deviation exceeds the threshold value when the
accelerator pedal is depressed.
[0005] Other systems have been proposed that are intended to
initiate braking action before the operator of a vehicle initiates
braking action. JP-A 6-24302 discloses a system whereby, when a
foot of the operator leaves an accelerator pedal, two micro
switches are both closed to energize a solenoid for activating a
brake pedal. Energizing the solenoid pulls the brake pedal to
partially activate a braking system before the foot of the operator
is stepped on the brake pedal.
SUMMARY OF THE INVENTION
[0006] Commonly assigned co-pending U.S. patent application Ser.
No. 09/640,792 filed on Aug. 18, 2000 discloses a preview brake
control system for assisting vehicle operator braking action. For
assisting vehicle operator braking action, a detection sub-system
on a vehicle to be controlled detects obstacles, which are in or
near the direction of motion of the vehicle, and provides
corresponding environmental data to a brake controller. In
addition, the vehicle has vehicle condition sensors for detecting
parameters indicative of the condition or state of motion of the
vehicle and transmitting corresponding data to the controller, and
vehicle operator demand sensors for detecting parameters indicative
of power or brake demand of the operator and transmitting
corresponding data to the controller. From the data reported
concerning the obstacles, the vehicle condition parameters and the
operator demand parameters, the controller ascertains whether or
not there is a need for operator braking action. The controller
determines a stand-by braking torque in terms of a brake pressure
and generates a braking signal for a braking sub-system or braking
device to apply the stand-by braking torque to at least one or
wheels of the vehicle. As sensors for detection of the obstacles
located in or near the direction of motion of the vehicle,
conventional radar sensors employing laser, whose application is
familiar to those skilled in the art, are used. However, any other
types of sensors that permit an adequate preview of the range of
motion of the vehicle and which are suitable for service under
rough vehicle condition may be used. For full description of the
preview brake control system, U.S. patent application Ser. No.
09/640,792, which has its corresponding European Patent Application
No. 00307108.1 filed on Aug. 18, 2000, has been hereby incorporated
by reference in its entirety.
[0007] If both the preview brake control system and an ADR system
are installed in a vehicle, there would be a need to avoid
application of an additional torque (positive torque) to a wheel or
wheels of a vehicle when a stand-by braking torque (negative
torque) is applied to the wheels. Application of the stand-by
braking torque continues for a predetermined time since
determination of a need for operator braking action. Let us
consider the case where immediately after the vehicle has
approached a preceding vehicle, the stand-by braking torque is
applied corresponding to a need for vehicle operator braking
action. Under this condition, the ADR system is put into operation
before the preceding vehicle shifts to the next lane. Then, the ADR
system requests an additional torque to increase speed of the
vehicle toward a set cruising speed because the lane has been
cleared. If the additional torque is applied immediately to wheel
or wheels of the vehicle against the stand-by braking torque, there
may occur shocks when the stand-by braking torque disappears upon
elapse of the predetermined time. Such shocks are objectionable to
the operator.
[0008] There would be another need to terminate application of a
stand-by braking torque in response to vehicle operator
acceleration request for passing a preceding vehicle by shifting to
the next lane after having approached to the preceding vehicle
quickly enough to initiate application of the stand-by braking
torque.
[0009] It is an object of the present invention to provide a system
and method for controlling speed of a vehicle, which has met at
least one of the above-mentioned needs.
[0010] In carrying out the above object and other objects,
advantages, and features of the present invention, a system for
controlling speed of a vehicle is provided, which comprises a prime
mover coupled to at least one wheel of the vehicle for applying a
positive torque to the at least one wheel in response to an
accelerating signal; and a controller having a control logic for
determining an actual distance from a preceding vehicle in front,
comparing the actual distance to a set desired distance to
determine whether the actual distance is greater than the desired
distance, determining whether or not a stand-by braking torque is
applied to the at least one wheel, determining an additional torque
requested by an automatic distance regulation (ADR) to increase
vehicle speed when the actual distance is greater than the desired
distance and the stand-by braking torque is not applied, and
generating an accelerating signal for the prime mover to apply the
additional torque to the at least one wheel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Further objects and advantages of the invention will be
apparent from reading of the following description in conjunction
with the accompanying drawings.
[0012] FIG. 1 is a block diagram illustrating a system or method
for controlling incompatible torque requests, one for braking
torque (negative torque) and the other for additional torque
(positive torque), according to the present invention.
[0013] FIG. 2 is a flowchart illustrating control logic for one
embodiment of the present invention in a vehicle.
[0014] FIG. 3 is a flowchart illustrating control logic for another
embodiment of the present invention in a vehicle.
[0015] FIGS. 4A, 4B, and 4C, when combined, provide a timing
diagram illustrating operation to control the two incompatible
torque requests.
[0016] FIG. 5 is a block diagram illustrating a system or method
for applying a transition braking torque to at least one wheel of a
vehicle that uses a solenoid operated brake booster as a brake
actuator.
[0017] FIG. 6 is a schematic sectional view of the brake booster
shown in FIG. 5.
[0018] FIG. 7 is a flowchart illustrating operation of a system and
method according to the present invention.
[0019] FIG. 8 graphically represents variation characteristic of
initial values of braking torque upon determination of a need for
operator braking action against vehicle speeds and weights.
[0020] FIG. 9 graphically represents two different manners of
gradual reduction of stand-by braking torque after initial
determination of a need for operator braking action.
BEST MODES FOR CARRYING OUT THE INVENTION
[0021] Referring now to FIG. 1, a block diagram illustrating
operation of a system or method for controlling speed of a vehicle
according to the present invention is shown. System 10 preferably
includes a first controller 12, such as a brake controller, in
communication with a second controller 14 via an appropriate
communication link 16. Second controller 14 is preferably an engine
controller, Communication link 16 preferably conforms to an
intra-controller bus standard, but is at least capable of
exchanging information and commands relative to present operating
conditions and control of the vehicle. Depending upon the
particular application, second controller 14 may be either an
engine controller, such as used for internal combustion engines, or
a motor controller, such as used for electric or fuel cell
vehicles. Similarly, controller 14 may be used to control a hybrid
system which utilizes one or more types of prime movers to power
the drive train of a vehicle.
[0022] In one preferred embodiment of the present invention,
controllers 12 and 14 comprise microprocessor-based controllers
with associated microprocessors, represented by reference numerals
18 and 20, respectively. Microprocessors 18 and 20 communicate with
associated computer-readable storage media 22 and 24, respectively.
As will be appreciable by one of ordinary skill in the art,
computer-readable storage media may include various devices for
storing data representing instructions executable to control
braking, engine, or motor systems. For example, computer-readable
storage medium 22 may include a random access memory (RAM) 26, a
read-only memory 28, and/or a keep-alive memory (KAM) 30.
[0023] Computer-readable storage medium 24 may include a random
access memory (RAM) 32, a read-only memory (ROM) 34, and/or
keep-alive memory (KAM) 36. These functions may be carried out
through any of a number of known physical devices including EPROM,
EEPROM, flash memory, and the like. The present invention is not
limited to a particular type of computer-readable storage medium,
examples of which are provided for convenience of description
only.
[0024] Controllers 12 and 14 also include appropriate electronic
circuitry, integrated circuits, and the like to effect control of
the braking, engine, or motor systems. As such, controllers 12 and
14 are used to effect control logic implemented in terms of
software (instructions) and/or hardware components, depending upon
the particular application. Details of control logic implemented by
controllers 12 and 14 are provided with reference to FIGS. 2, 3,
and 8.
[0025] Controller 14 receives various signals from sensors to
monitor present operating conditions of the vehicle. For example,
signals may include cruise control signals, indicated generally by
reference numeral 38, an accelerator pedal position signal 40, a
gear selector signal 42, and a vehicle speed signal 44. The cruise
control signals represent a set cruise speed, a set desired
vehicle-to-vehicle distance, and an ON/OFF position of an automatic
distance regulation (ADR) switch. Depending upon the particular
application, additional signals may be provided, such as battery
limit signal 46. Controller 14 may be in direct communication with
associated sensors, switches, and other input devices or may
receive information relative to sensed parameters via another
controller, such as controller 12. Controller 14 receives
environmental data in front of the vehicle from controller 12.
Controller 14 may be in direct communication with a detection
system or unit to receive such environmental data. In operation of
automatic distance regulation (ADR) initiated by turning on ADR
switch, signals representing the environmental data are processed
by controller 14 to determine an actual distance from a preceding
vehicle in front for comparison with a set desired distance.
Controller 14 compares the actual distance to the set desired
distance. If the actual distance is greater than the set desired
distance, additional engine/motor torque is determined or
requested. The additional torque is then applied to the associated
wheel or wheels of the vehicle. For internal combustion engine
applications, additional torque is typically provided by
controlling the quantity of fuel delivered to an engine 47 or
controlling the opening of the engine throttle. For electric
vehicles, additional torque may be provided by increasing the
energy available to a motor/generator 47. Of course, for hybrid
vehicles, additional torque may be provided by an internal
combustion engine in combination with an associated traction motor.
When actual distance becomes less than the set desired distance, a
negative or braking torque is required to reduce speed of the
vehicle to maintain the set desired distance. Controller 14
attempts to reduce the vehicle speed by reducing the corresponding
torque provided by the motor and/or engine 47 of the vehicle. When
the engine and/or motor torque has been reduced to its minimum
level, controller 14 determines whether additional braking torque
is required. If additional braking torque is required, controller
14 determines a braking torque and generates a braking torque
request to brake controller 12. If no preceding vehicle is
available, controller 14 compares an actual vehicle speed to a set
cruise vehicle speed and controls application of positive or
negative torque to at least one wheel of the vehicle.
[0026] In one embodiment of the present invention, controller 12 is
in direct communication with the detection system to receive
environmental data, indicated generally by reference numeral 48, in
front of the vehicle. Signals 48 are processed by controller 12 to
determine an actual distance from obstacle located in the direction
of the vehicle.
[0027] Brake controller 12 preferably receives inputs from a
braking system or brake actuator 50 indicative of present operating
conditions of the braking system. For example, controller 12 may
receive brake system pressures 52 indicative of a pneumatic or
hydraulic pressure for operating one or more braking devices, which
may include any device that applies a negative torque to wheels 54,
56, 58, and 60. A braking device includes various types of friction
brakes, such as disk brakes 62, 64, 66, and 68 or drum brakes.
Controller 12 receives a signal indicative of brake pedal position
as represented by reference numeral 70. Alternatively, brake pedal
position signal 70 may be provided directly from a sensor
associated with a brake pedal or may be provided indirectly through
brake actuator 50. For conventional hydraulic or pneumatic braking
systems, a brake pedal input 72 provides a fluid coupling between
the associated brake pedal and brake actuator 50. This fluid signal
may be converted to an appropriate electrical signal to provide the
brake pedal position signal 70.
[0028] Brake controller 12 processes the signals received from
various sensors and messages from controller 14, which include a
braking torque request from controller 14. Controller 12 generates
braking commands or signals for application of at least one of
friction brakes 62, 64, 66, and 68.
[0029] In operation, system 10 receives the environmental data from
the detection system, vehicle speed signal 44, brake pedal position
signal 70, accelerator pedal position signal 40 to determine
whether or not there is a need for operator braking action. Brake
controller 12 may make this determination. When there is a need for
operator braking action, controller 12 determines a stand-by
braking torque. Various manners of determining whether or not there
is a need for operator braking action are disclosed in the
incorporated U.S. patent application Ser. No. 09/640,792 as well as
several variations in determining a stand-by braking torque.
[0030] Referring now to FIG. 2, a flowchart illustrating control
logic of one embodiment of the present invention is shown. As will
be appreciated by one of ordinary skill in the art, the flowcharts
illustrated in FIGS. 2, 3, and 7 may represent any of a number of
processing strategies which may include event-driven,
interrupt-driven, multi-tasking, multi-threading, and the like. As
such, various steps or functions illustrated may be performed in
the sequence shown, in parallel, or in some cases omitted.
Likewise, the order of processing is not necessarily required to
achieve the objects, features, and advantages of the present
invention, but is provided for ease of illustration and description
only. Preferably, the control logic illustrated in FIGS. 2, 3, and
7 is implemented primarily in software, which is executed by one or
more microprocessor-based controllers. Of course, the control logic
may be implemented in software, hardware, or a combination of
software and hardware, depending upon the particular
application.
[0031] The flowchart of FIG. 2 illustrates control logic for one
embodiment of the present invention in a vehicle having a
conventional friction braking system that is directly controlled by
the vehicle operator via an associated brake pedal. A target or
desired so-called "vehicle-to-vehicle" distance is determined as
represented by block 80 as well as a target or desired so-called
cruising vehicle speed. The desired distance and cruising vehicle
speed may be indicated by the vehicle operator via an appropriate
switch, such as an ADR switch or a cruise control set speed and
distance switch.
[0032] The actual distance from a preceding vehicle is then
determined as represented by block 82. The actual distance may be
determined by an associated detection system employing a laser
radar. The actual distance is compared to the desired distance to
generate a corresponding distance error as represented by block 84.
If the distance error falls within predetermined limits, a torque
correction or adjustment is not required and control returns back
to block 82. If the actual distance is greater than the desired
distance, it is determined whether or not stand-by braking torque
is applied to associated wheel or wheels of the vehicle as
represented by block 86. The application of stand-by braking torque
may be determined by communicating with the brake controller 12. If
the stand-by braking torque is being applied, control returns back
to block 82. If no stand-by braking torque is applied, additional
engine/motor torque is requested at indicated by block 88. The
additional torque is then applied to associated wheel or wheels as
indicated by block 90. For internal combustion engine applications,
controlling the quantity of fuel delivered to the engine typically
provides additional torque. For electric or hybrid fuel vehicles,
increasing the energy available to the motor/generator may provide
additional torque. Of course, in combination with an associated
traction motor, an internal combustion engine may provide
additional torque.
[0033] At block 84, when actual distance becomes less than the
desired distance by a predetermined amount, a negative or braking
torque is required to maintain or control speed of the vehicle.
Block 92 attempts to reduce the vehicle speed by reducing the
corresponding torque provided by the motor and/or engine of the
vehicle. When the engine and/or motor torque has been reduced to
its minimum level, which may correspond to idling or fuel cutoff of
an internal combustion engine, block 94 determines whether
additional braking torque is required. If no additional braking
torque is necessary to maintain the desired distance, then control
returns to block 82.
[0034] If additional braking torque is required as indicated by
block 94, block 96 determines a braking torque and generates an
appropriate command or braking signal to a braking actuator that
controls actual application of braking torque to associated wheel
or wheels of the vehicle as represented by block 98. Control then
returns back to block 82.
[0035] As will be appreciated by one of ordinary skill in the art,
the control functions or steps illustrated with respect to FIGS. 2,
3, and 7 are preferably repeated at predetermined time intervals of
10 milliseconds or based upon a predetermined event.
[0036] Referring now to FIG. 3, a flowchart illustrating another
embodiment of the present invention is shown. Block 100 represents
determination whether or not there is a need for operator braking
action. This determination may be made as taught by the
incorporated U.S. patent application Ser. No. 09/640,792. If there
is a need for operator braking action, block 102 determines a
stand-by braking torque as a function of the present vehicle speed,
which will be later discussed in connection with FIGS. 8 and 9. As
represented by block 104, the stand-by braking torque is held for a
predetermined period of time Ts, which may be set around 1 second.
If, within the predetermined time Ts, there is no operator
acceleration request as represented by blocks 106 and 108, an
appropriate command or braking signal is kept generated to a
braking actuator to apply the stand-by braking torque to associated
wheel or wheels of the vehicle as represented by block 110. Then,
immediately after elapse of the predetermined time Ts, the stand-by
braking torque is reset to zero as represented by block 112. Then,
the stand-by braking torque that has been applied disappears.
[0037] If the vehicle operator requests acceleration within the
predetermined time Ts as represented by block 108, application of
stand-by braking torque is terminated as represented by blocks 112
and 110
[0038] Referring to FIGS. 4A, 4B, and 4C, a timing diagram
illustrates operation of a system and method according to the
present invention, which has been illustrated by the flowchart of
FIG. 2.
[0039] At moment t1, a need for operator braking action arises, and
a stand-by braking torque is applied as illustrated in FIG. 4A. It
is assumed that automatic distance regulation (ADR) is put into
operation immediately after moment t1. Subsequently, at moment t2
within the predetermined time Ts, a preceding vehicle in front
shifts to the next lane and the ADR system requests an additional
torque to increase the vehicle speed toward the cruising speed as
illustrated in FIG. 4B. However, the additional quantity of fuel or
throttle angle corresponding to the additional torque requested by
the ADR system is prohibited until elapse of the predetermined time
Ts because the stand-by braking torque is applied. At moment t3
upon or immediately after disappearance of the stand-by braking
torque, the additional quantity of fuel is delivered to apply the
additional torque to wheel or wheels of the vehicle.
[0040] In one embodiment, the stand-by braking torque is invariable
over the predetermined time Ts. FIG. 9 provides two different
manners of time dependent reduction of level of stand-by braking
torque. As illustrated by the fully drawn line in FIG. 9, a
stand-by braking torque may be reduced from an initial level or
value to zero level at a gradual rate over the predetermined period
of time Ts and the extended period of time. Alternatively, as
indicated by the one-dot chain line, a stand-by braking torque may
be reduced at a first rate over the predetermined period of time Ts
and at a second greater rate over the extended period of time.
These time dependent variations of stand-by braking torque are
advantageous in minimizing shocks upon termination of application
of stand-by braking torque.
[0041] Referring to FIGS. 5, 6, and 7, FIG. 7 is a flowchart, and
FIGS. 5 and 6 illustrate hardware.
[0042] Referring to FIG. 5, the reference numeral 200 designates
controller(s), which correspond to portion in FIG. 1 enclosed by
the phantom rectangle. The flowchart of FIG. 7 illustrates control
logic in a vehicle having an internal combustion engine with a
throttle 202 whose opening angle is adjusted by an actuator 204.
The vehicle has a conventional braking system 50 including a master
brake cylinder 206 with a brake booster 208 and a brake pedal 210.
A brake pressure sensor 212 is provided to detect brake pressure
delivered from master cylinder 206 to friction brakes 62 and 64 for
front wheels 54 and 56.
[0043] Vehicle speed sensor 214 is provided to detect speed Vm of
vehicle. A brake switch 216 and an accelerator stroke sensor 218
are provided to sense operator demand. Brake switch 216 is
operatively connected to brake pedal 210. Specifically, brake
switch 216 is connected to a rod-shaped actuator 220 of brake
booster 208. The setting is such that brake switch 216 has an
off-state when brake pedal 210 is released and has an on-state when
brake pedal 210 is depressed. Accelerator stroke sensor 28 detects
instantaneous stroke of an accelerator pedal 222 and generates an
accelerator stroke or pedal position signal SA. A detection system
224 includes a distance detection sensor for detecting a distance L
from an obstacle, including a preceding vehicle, in front and
generates a distance signal. Detection system 224 includes a laser
radar or a millimeter wave radar. An ADR switch 226 is provided.
The vehicle operator manipulates ADR switch 226 to initiate
automatic distance regulation (ADR). The weight M of the vehicle is
provided to controller 200 via an appropriate input device as
represented by a block 228. The vehicle weight M may be determined
by a load sensor utilizing a load sensing valve to measure load on
front wheels and load on rear wheels of the vehicle.
[0044] Referring to FIG. 6, brake booster 208 includes an
electro-magnetically operable control valve arrangement 240.
Controller 200 provides braking command or signal to control valve
arrangement 240 for adjustment of brake pressure to any desired
pressure level. Brake booster 208 comprises an essentially rotation
symmetrical housing 242, in which a rear chamber 244 and a front
chamber 246 are arranged and separated from each other by a movable
wall 248. Control valve arrangement 240 is coupled with movable
wall 248 for a common relative movement with respect to housing
242. The front end of rod-shaped actuation member 220, which is
coupled with brake pedal 210, acts on control valve arrangement
240.
[0045] Within brake booster 208, a power output member 250 is
arranged which bears against control valve arrangement 240. Power
output member 250 is provided for activation of master brake
cylinder 206.
[0046] Control valve arrangement 240 comprises an essentially
tubular valve housing 252. The front end of valve housing 252 is
coupled to movable wall 248. A return spring 254 arranged within
brake booster 208 resiliently biases the control valve arrangement
240 rearwardly. Within valve housing 252, an electromagnetic
actuator 300 is arranged which includes a solenoid coil 300a and a
plunger 300b. Arranged within plunger 300b is an operating rod 302.
The front end of operating rod 302 bears against power output
member 250. A return spring 304 located within plunger 300b has one
end bearing against a retainer (no numeral) fixedly connected to
plunger 300b and opposite end bearing against the rear end of
operating rod 302. The front ball end of rod-shaped actuator 220 is
fixedly inserted into socket recessed inwardly from the rear end of
operating rod 302. A return spring 306 located within valve housing
308 has one end bearing against a shoulder of valve housing 308 and
opposite end bearing against a shoulder of rod-shaped actuator
220.
[0047] Valve housing 308 is formed with a passage 310 through which
fluid communication between rear and front chambers 244 and 246 is
established. The front end of passage 310 is always open to front
chamber 246, while the rear end of passage 310 is located within a
valve seat 312. Valve seat 312 is located within an annular space
defined between plunger 300b and valve housing 308 and faces a
valve member 314 that forms an upper portion of a slide. The slide
is located between plunger 300b and valve housing 308. A return
spring 316 has one end bearing against an integral abutment 318 of
plunger 300b and opposite end bearing against the slide. An air
admission port 320 is formed through a lower portion of the slide.
This lower portion of the slide serves as a valve seat 322. Port
320 is provided to admit ambient air into rear chamber 244. Valve
seat 322 formed with port 320 faces a valve member 324 integral
with plunger 300b. Valve seat 312 and valve member 314 cooperate
with each other to form an interruption or vacuum valve. Valve seat
322 and valve member 324 cooperate with each other to form an
ambient air admission valve.
[0048] In the rest position shown in FIG. 6 with the vacuum source
disconnected, atmospheric pressure prevails in both chambers 244
and 246. With the vacuum source connected, i.e., with the engine
running, a vacuum is built up in front chamber 246 so that movable
wall 248 together with the control valve arrangement 240 is
slightly displaced in a forward direction.
[0049] Accordingly, a new pressure balance is achieved between two
chambers 244 and 246. From this position, a lost travel free
activation of the brake booster 208 is ensured.
[0050] Under a normal brake actuation by the vehicle operator, the
brake booster 208 operates in a usual manner by interrupting the
connection between two chambers 244 and 246 via the interruption
valve (312, 314) and admitting ambient air into rear chamber 244
via the ambient air admission valve (324, 322).
[0051] Electromagnetic actuator 300 can actuate control valve
arrangement 240. For this purpose, current through solenoid 300a is
regulated in response to braking command furnished by controller
200. This command causes a displacement of control valve
arrangement 240 so that ambient air can flow into rear chamber
244.
[0052] Referring to FIG. 7, a flowchart illustrates operation of a
system and method according to the present invention.
[0053] In one embodiment, the flowchart of FIG. 7 is repeated at
predetermined intervals of 10 milliseconds.
[0054] Blocks 400, 401, 402, 404, and 406 represent input of
vehicle speed Vm, vehicle weight M, accelerator pedal stroke
S.sub.A, brake switch output, and actual distance L from obstacle
or preceding vehicle in front, respectively.
[0055] Time derivative dL/dt of actual distance L is calculated as
represented by block 408. The time derivative dL/dt may be
approximated by a difference between the present and previous
values of L.
[0056] At block 410, using vehicle speed Vm and the time derivative
dL/dt, a target deceleration G.sub.B is determined by calculating
the equation as follows:
G.sub.B={Vm.sup.2-(Vm-dL/dt).sup.2}/2L.
[0057] Block 412 represents determination whether or not timer
count T.sub.P is cleared. If T.sub.P=0, control goes to block 414.
At block 414, G.sub.B is compared with a predetermined deceleration
value G.sub.BS in the neighborhood of 6.0 m/sec.sup.2 to determine
whether G.sub.B exceeds G.sub.BS. If G.sub.B.ltoreq.G.sub.BS and
thus there is no need for operator braking action, control goes to
block 416. At block 416, stand-by brake pressure P.sub.PB is reset
equal to 0 (zero) before control goes to ADR control beginning with
block 434. If G.sub.B>G.sub.BS and thus there is a need for
operator braking action, control goes to block 418.
[0058] Block 418 represents determination whether or not there is
an operator acceleration request. This determination is made by
comparing accelerator pedal stroke S.sub.A to a predetermined
stroke value S.sub.AS. If S.sub.A>S.sub.AS and thus there is an
operator acceleration request, control goes to block 416 because
the operator acceleration request clearly indicates that the
operator has no intention to carry out braking action. If
S.sub.A.ltoreq.S.sub.AS and thus there is no operator acceleration
request, control goes to block 420.
[0059] At block 420, the present vehicle speed Vm is set as a
stand-by braking process initial vehicle speed V0 and determines an
initial value of stand-by brake pressure P.sub.PB by performing a
table look-up operation of maps illustrated in FIG. 8 using vehicle
weight M and initial vehicle speed V0. The next block 422
represents increment of timer count T.sub.P by a predetermined unit
of 1 (one) before control goes to block 434.
[0060] FIG. 8 graphically represents the initial values of stand-by
braking torque in terms of brake pressure P.sub.PB against the
initial vehicle speed V0. With the same brake pressure P.sub.PB,
the higher the initial vehicle speed V0, the less the vehicle
operator perceives deceleration. The lower the initial vehicle
speed V0, the more the vehicle operator perceives deceleration.
Taking these into account, when the initial vehicle speed V0 falls
in a lower range B1 and thus is less than a first vehicle speed
value, a predetermined lower braking torque value expressed in
terms of a predetermined lower brake pressure Pmin is set as an
initial value of the stand-by braking torque. When the initial
vehicle speed V0 falls in a higher range B3 and thus is greater
than a second vehicle speed value, a predetermined higher braking
torque value expressed in terms of a predetermined higher brake
Pmax is set as an initial value of the stand-by braking torque. The
second vehicle speed value is greater than the first vehicle speed
value. The predetermined higher brake pressure Pmax is greater than
the predetermined lower brake pressure Pmin. When the initial
vehicle speed value V0 falls in an intermediate vehicle speed range
B2 limited by the first and second vehicle speed values, one of
intermediate braking torque values, which fall between the
predetermined lower and higher braking torque values, as an initial
value of the stand-by braking torque. As shown in FIG. 8, the
intermediate braking torque values are represented by a linear
function of the initial vehicle speed values V0. At least over a
range of initial vehicle speed values that fall between the first
and second vehicle speed values (intermediate vehicle speed range
B2), the heavier the vehicle weight M, the greater the initial
value of the stand-by braking torque is. With the same braking
torque, the heavier the vehicle weight M, the less the vehicle
operator perceives deceleration.
[0061] Turning back to the flowchart of FIG. 7, subsequently after
timer count T.sub.P has been incremented at block 422, control goes
from block 412 to block 424. Block 424 represents determination
whether or not brake pedal 210 is depressed by checking for the
output of brake switch 216. If brake pedal 210 is depressed,
control goes to block 426. At block 426, timer count T.sub.P is
cleared before control goes to block 416. If brake pedal 210 is not
depressed or released, control goes to block 428.
[0062] Block 428 represents determination whether or not there is
an operator acceleration request by comparing accelerator pedal
stroke S.sub.A to predetermined value S.sub.AS. If accelerator
pedal 222 is depressed indicating the presence of operator
acceleration request, control goes to block 426. This is the case
where stand-by braking torque is not needed. If accelerator pedal
222 is not depressed or released, control goes to block 430.
[0063] Block 430 represents determination whether or not timer
count T.sub.P has reached a predetermined value Ts in the
neighborhood of 1 second. If T.sub.P<Ts, control goes to block
422 where timer count T.sub.P is increased by 1 (one) before
control goes to block 434. If T.sub.P.gtoreq.Ts, control goes to
block 426 and then to block 414 before control goes to block
434.
[0064] Block 434 represents determination whether or not ADR switch
226 is turned on. Turning on ADR switch 226 initiates ADR control.
If ADR switch 226 assumes OFF state, control goes to block 436. At
block 436, a present ADR brake pressure P.sub.BC(n) is reset equal
to 0 (zero) and an additional throttle command .theta. is reset
equal to 0 (zero) before control goes to block 456. Block 456
represents selection of higher one of P.sub.BC(n) and P.sub.PB
before control goes to block 458. Block 456 represents output of
the selected higher one of P.sub.BC(n) and PPB, and an additional
throttle command .theta. before control goes to 460. At block 460,
the present value P.sub.BC(n) is stored as the previous value
P.sub.BC(n-1) before control returns to start point of the
flowchart.
[0065] If, at block 434, ADR switch 226 is in ON state, control
goes to block 433. Block 433 represents determination whether or
not there is an operator acceleration request by comparing
accelerator pedal stroke S.sub.A to S.sub.AS. If accelerator pedal
222 is depressed, control goes to block 435. Block 435 represents
release of ADR control by turning off ADR switch and resetting
P.sub.BC(n) and .theta. before control goes to blocks 456, 458 and
460. If accelerator pedal 222 is not depressed or released, control
goes from block 433 to block 438.
[0066] At block 438, it is determined whether actual distance L is
less than L1 (L<L1), L is not less than L1 and not greater than
L2 (L1.ltoreq.L.ltoreq.L2), or L is greater than L2. If
L1.ltoreq.L.ltoreq.L2, it is determined that actual distance L from
a preceding vehicle in front falls in the neighborhood of a desired
distance, and control goes to block 436. If L<L1, it is
determined that actual distance from the preceding vehicle is too
short and control goes to block 440. At block 440, the previous ADR
brake pressure P.sub.BC(n-1) is increased by a predetermined value
.DELTA.P.sub.BC to give the result as present ADR brake pressure
P.sub.BC(n), and additional throttle command .theta. is reset equal
to 0 (zero). If L>L2, it is determined that actual distance L
from the preceding vehicle is too long, and control goes to block
442.
[0067] At block 442, present ADR brake pressure P.sub.BC(n) is
reset equal to 0 (zero) before control goes to block 444. Block 444
represents determination whether or not stand-by brake pressure
P.sub.PB is 0 (zero). If P.sub.PB>0, control goes to block 456.
If P.sub.PB=0, control goes to block 446.
[0068] At block 446, additional throttle command .theta. is
increased by a predetermined value .DELTA..theta. before control
goes to block 456.
[0069] Assuming now that ADR switch 226 is turned off so that ADR
control is not in progress, control always goes from block 434 to
block 436. Under this condition, the preview brake control only is
carried out by pefforming functions of blocks 400-430, which are
disposed upstream of block 434. Assuming also that timer count
T.sub.P is cleared (T.sub.P=0), the target deceleration G.sub.B,
calculated at block 410, becomes zero or in the neighborhood of
zero in any one of the following cases: 1) there is no preceding
vehicle in front; 2) distance from a preceding vehicle is
sufficiently great; and 3) a distance from a preceding vehicle is
invariable and the preceding vehicle runs at the same speed. Under
this condition, control goes from block 414 to block 416 where
P.sub.PB is reset before control goes to block 434. Since ADR
switch 226 is turned off, control goes from block 434 50 block 436
where P.sub.BC(n) and .theta. are reset. Thus, the throttle 202 is
adjusted to a position corresponding to the accelerator pedal
position set by the vehicle operator.
[0070] If distance L from a preceding vehicle becomes short to an
extent that G.sub.B exceeds G.sub.BS, control goes from block 414
to block 418. If, under this condition, the vehicle operator
depresses accelerator pedal 222, control goes from block 418 to
block 416, and stand-by braking torque is not applied. This is the
case where the vehicle operator has intention to continue the
present running state.
[0071] If, under the condition where G.sub.B exceeds G.sub.BS, the
vehicle operator releases accelerator pedal 222, control goes from
block 418 to block 420. This is the case where vehicle operator
braking action is imminent so that stand-by braking torque is
needed to assist the braking action. At block 420, an appropriate
stand-by brake pressure P.sub.PB is determined corresponding to
initial vehicle speed VO and vehicle weight M. Since ADR switch 226
is in OFF state, the stand-by brake pressure P.sub.PB is selected
at block 456 and output at block 458. Current corresponding to the
brake pressure P.sub.PB flows through solenoid 300a (see FIG. 6),
causing application stand-by braking torque to wheels 54-60 of the
vehicle prior to the vehicle operator braking action.
[0072] Stand-by brake pressure P.sub.PB is variable corresponding
to vehicle speed V0 and vehicle weight M. The less the initial
vehicle speed V0, the less stand-by brake pressure P.sub.PB is. The
greater the vehicle weight M, the greater stand-by brake pressure
P.sub.PB. Accordingly, the magnitude of stand-by braking torque
applied to the vehicle wheels corresponds to vehicle speed and
weight, providing any objectionable feel to the vehicle
operator.
[0073] If the vehicle operator does not depress brake pedal 210
after releasing accelerator pedal 222 due to acceleration of the
preceding vehicle or moving off thereof, the application of
stand-by braking torque disappears immediately after timer count
T.sub.P exceeds Ts. In this regard, it is noted that control goes
from block 430 to blocks 426 and 416 to reset timer count T.sub.P
and stand-by brake pressure P.sub.PB upon elapse of predetermined
time Ts.
[0074] If, within the predetermined time Ts, the vehicle operator
depresses brake pedal 210, the brake switch 216 is turned on.
[0075] Then, control goes from block 424 to blocks 426 and 416,
terminating the preview braking, making a swift shift to ordinary
braking.
[0076] Referring also to FIGS. 4A, 4B, and 4C, at moment t1, the
preview brake control where stand-by brake pressure P.sub.PB is
applied begins. With brake and accelerator pedals 210 and 222 held
released, the vehicle operator turns on ADR switch 226 immediately
before moment t2. Then, control goes from block 434 to block 433.
Since accelerator pedal 222 is released, control goes from block
433 to block 438.
[0077] If, under this condition, the preceding vehicle shifts to
the next lane or the vehicle operator shifts to the next lane to
pass the preceding vehicle, the actual distance L suddenly becomes
greater than L2. Since stand-by brake pressure P.sub.PB remains
till elapse of the predetermined time Ts, control goes along blocks
438, 442, 444, and 456. Although potential additional torque
request appears at moment t2, the stand-by brake pressure P.sub.PB
remains and no additional torque corresponding to the potential
additional torque request is applied to the vehicle wheels until
elapse of the predetermined time Ts.
[0078] Immediately after moment t3 upon elapse of the predetermined
time Ts, control goes from block 430 to blocks 426 and 416,
terminating preview brake control. Then, control goes from block
444 to block 446, generating additional torque corresponding to the
additional torque request. Thus, as illustrated in FIG. 4C, the
throttle angle is increased to increase the vehicle speed toward
the set cruising speed. In this manner, without any objectionable
shocks to the vehicle operator, a shift from the preview brake
control to ADR control can be made.
[0079] If there is an operator acceleration request by depressing
the accelerator pedal, control goes from block 428 to blocks 426
and 416, terminating application of stand-by braking torque
immediately. Thus, quick acceleration performance is provided in
response to the vehicle operator acceleration request.
[0080] In the embodiment, the system keeps the stand-by brake
pressure P.sub.PB invariable over the predetermined period of time
Ts.
[0081] If desired, the system may vary the stand-by brake pressure
P.sub.PB in a manner as illustrated by the fully drawn line in FIG.
9 or by the one-dot chain line in FIG. 9. Alternatively, the system
may vary the stand-by brake pressure PPB at continuously changing
rates.
[0082] In the embodiment, brake switch 216 is provided to detect
operator effort to manipulate brake pedal 210. If desired, stroke
of the brake pedal may be relied on to detect the initiation of
operator braking effort.
[0083] In the embodiment, description has been made with reference
to a preceding vehicle in front. The present invention is
applicable to the situation where the detection system 224 detects
obstacles in the direction of the vehicle.
[0084] In the embodiment, relative speed between vehicles is
determined by calculating the derivative of distance L with respect
to time. If a detection system is capable of detecting the relative
speed, the detected relative speed may be used.
[0085] In the embodiment, the brake booster 208 employing solenoid
coil 300a is used to generate brake pressure corresponding to
P.sub.PB or P.sub.BC(n). Brake actuator is not limited to such
brake booster and may take any other form in implementing the
present invention. For example, brake pressure corresponding to
P.sub.PB or P.sub.BC(n) may be produced by regulating a system
hydraulic pressure discharged by a pump.
[0086] In the embodiment, the hydraulic braking system
communicating with friction brakes is used as braking devices. If
desired, a braking device may be implemented by a traction
motor/generator, represented generally by reference numeral 47 in
FIG. 1, which applies a negative, or retarding torque when used as
a braking device. The braking device may be directly coupled to one
or more wheels 54-60 via an appropriate mechanical or hydraulic
linkage.
[0087] In the embodiment, the automatic distance regulation (ADR)
is carried out to bring the distance L into a target window
expressed by L1.ltoreq.L.ltoreq.L2. The present invention is not
limited to this. If desired, a target vehicle-to-vehicle distance
L* is determined by calculating a product of vehicle speed Vm and
time that is required to reduce a distance from a preceding
vehicle. Using the distance L* as a target, ADR may be carried out
to reduce a deviation of an actual distance L from L* toward
zero.
[0088] While the present invention has been particularly described,
in conjunction with preferred embodiments, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art in light of the foregoing description. It
is therefore contemplated that the appended claims will embrace any
such alternatives, modifications and variations as falling within
the true scope and spirit of the present invention.
[0089] This application claims the priority of Japanese Patent
Application No. 2000-043398, filed Feb. 21, 2000, the disclosure of
which is hereby incorporated by reference in its entirety
* * * * *