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Claims  |
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That which is claimed is:
1. A drive train for an electric vehicle, said drive train comprising:
an electric motor for driving one or more wheels of the vehicle and being
rotatable in opposite directions corresponding to respective opposite
directions of actual vehicle movement, said electric motor having a
controllable torque output magnitude;
sensing means associated with said electric motor for sensing rotational
speed and direction thereof;
selector means for permitting driver selection of a direction of intended
vehicle movement; and
rollback detection and compensation means connected to said electric motor,
and responsive to said sensing means and said selector means, for
determining vehicle rollback defined by a sensed direction of actual
vehicle movement opposite to a selected direction of intended vehicle
movement and for controlling the output torque magnitude of said electric
motor responsive to sensed rotational speed of said electric motor and as
a predetermined function thereof to counteract the vehicle rollback.
2. A drive train according to claim 1 wherein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor as a nonconstant function of rotational
speed of said electric motor during vehicle rollback.
3. A drive train according to claim 1 wherein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor as a linear function of rotational speed
of said electric motor during vehicle rollback.
4. A drive train according to claim 1 wherein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor as a function of rotational speed squared
of said electric motor during vehicle rollback.
5. A drive train according to claim 1 wherein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor at a predetermined constant value
responsive to a rotational speed of said electric motor being above a
predetermined value.
6. A drive train according to claim 1 further comprising a traction battery
connected to said electric motor.
7. A drive train for an electric vehicle, said drive train comprising:
a traction battery;
an electric motor connected to said traction battery for driving one or
more wheels of the vehicle, said electric motor being rotatable in
opposite directions corresponding to respective opposite directions of
actual vehicle movement, said electric motor having a controllable torque
output magnitude;
sensing means associated with said electric motor for sensing rotational
speed and direction thereof;
selector means for permitting driver selection of a direction of intended
vehicle movement; and
rollback detection and compensation means connected to said electric motor,
and responsive to said sensing means and said selector means, for
determining vehicle rollback defined by a sensed direction of actual
vehicle movement opposite to a selected direction of intended vehicle
movement and for controlling the output torque magnitude of said electric
motor responsive to sensed rotational speed of said electric motor and as
a nonconstant function thereof to counteract the vehicle rollback.
8. A drive train according to claim 7 wherein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor as a linear function of rotational speed
of said electric motor during vehicle rollback.
9. A drive train according to claim 8 herein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor as a function of rotational speed squared
of said electric motor during vehicle rollback.
10. A drive train according to claim 9 wherein said rollback detection and
compensation means includes means for controlling the output torque
magnitude of said electric motor at a predetermined constant value
responsive to a rotational speed of said electric motor being above a
predetermined value.
11. A drive train for an electric vehicle, said drive train comprising:
an electric motor for driving one or more of wheels of the vehicle and
being rotatable in opposite rotational directions corresponding to
opposite directions of vehicle movement, said electric motor having a
controllable torque magnitude;
sensing means associated with said electric motor for sensing rotational
speed and direction thereof;
selector means for permitting driver selection of a direction of intended
vehicle movement;
driver input means for permitting driver selection of vehicle braking or
vehicle acceleration; and
control means connected to said electric motor for controlling the output
torque magnitude and rotational direction thereof in response to said
driver input means, said control means further comprising rollback
detection and compensation means responsive to said sensing means and said
selector means for determining vehicle rollback defined by a sensed
direction of actual vehicle movement opposite to a selected direction of
intended vehicle movement and for controlling the output torque magnitude
of said electric motor responsive to sensed rotational speed of said
electric motor and as a nonconstant function thereof to thereby counteract
the vehicle rollback even in an absence of driver selection of one of
vehicle braking and vehicle acceleration.
12. A drive train according to claim 11 wherein said rollback detection and
compensation means comprises means for generating a first torque request
value as a nonconstant function of rotational speed of said electric motor
during vehicle rollback, wherein said control means comprises means for
generating a second torque request value responsive to said driver input
means during vehicle rollback, and wherein said control means further
comprises means for adding the first and second torque request values for
controlling the output torque magnitude of said electric motor.
13. A drive train according to claim 11 wherein said control means includes
means for controlling the output torque magnitude of said electric motor
as a linear function of rotational speed of said electric motor during
vehicle rollback.
14. A drive train according to claim 11 wherein said control means includes
means for controlling the output torque magnitude of said electric motor
as a function of rotational speed squared of said electric motor during
vehicle rollback.
15. A drive train according to claim 11 wherein said control means includes
means for controlling the output torque magnitude of said electric motor
at a predetermined constant value responsive to a rotational speed of said
electric motor being above a predetermined value.
16. A drive train according to claim 11 further comprising a traction
battery connected to said electric motor.
17. An electric vehicle comprising:
a frame;
one or more vehicle wheels rotatably mounted on said frame;
a traction battery carried by said frame;
an electric motor connected to said traction battery for driving one or
more wheels of the vehicle, said electric motor being rotatable in
opposite directions corresponding to respective opposite directions of
actual vehicle movement, said electric motor having a controllable torque
output magnitude;
sensing means associated with said electric motor for sensing rotational
speed and direction thereof;
selector means for permitting driver selection of a direction of intended
vehicle movement;
driver input means for permitting driver selection of vehicle braking or
vehicle acceleration; and
control means connected to said electric motor for controlling the output
torque magnitude and rotational direction thereof in response to said
driver input means, said control means further comprising rollback
detection and compensation means responsive to said sensing means and said
selector means for determining vehicle rollback defined by a sensed
direction of actual vehicle movement opposite to a selected direction of
intended vehicle movement and for controlling the output torque magnitude
of said electric motor responsive to sensed rotational speed of said
electric motor and as a nonconstant function thereof to thereby counteract
the vehicle rollback even in an absence of driver selection of one of
vehicle braking and vehicle acceleration.
18. A drive train according to claim 17 wherein said rollback detection and
compensation means comprises means for generating a first torque request
value as a function of rotational speed of said electric motor during
vehicle rollback, wherein said control means comprises means for
generating a second torque request value responsive to said driver input
means during vehicle rollback, and wherein said control means further
comprises means for adding the first and second torque request values for
controlling the output torque magnitude of said electric motor.
19. A drive train according to claim 17 wherein said control means includes
means for controlling the output torque magnitude of said electric motor
as a linear function of rotational speed of said electric motor during
vehicle rollback.
20. A drive train according to claim 17 wherein said control means includes
means for controlling the output torque magnitude of said electric motor
as a function of rotational speed squared of said electric motor during
vehicle rollback.
21. A drive train according to claim 17 wherein said control means includes
means for controlling the output torque magnitude of said electric motor
at a predetermined constant value responsive to a rotational speed of said
electric motor being above a predetermined value.
22. A method for operating an electric vehicle including an electric motor
for driving one or more wheels of the vehicle and being rotatable in
opposite directions corresponding to respective opposite directions of
actual vehicle movement, and a selector for permitting driver selection of
a direction of intended vehicle movement, said method comprising the steps
of:
sensing a rotational direction of the electric motor corresponding to a
respective direction of actual vehicle moment;
determining vehicle rollback defined by the sensed direction of actual
vehicle movement being opposite the intended direction of vehicle
movement;
sensing a rotational speed of the electric motor corresponding to a
respective speed of actual vehicle movement; and
controlling an output torque magnitude of the electric motor responsive to
the sensed rotational speed of the electric motor and as a predetermined
function thereof to counteract the vehicle rollback.
23. A method according to claim 22 wherein the step of controlling the
electric motor to counteract the vehicle rollback comprises controlling
the electric motor at an output torque magnitude as a nonconstant function
of sensed rotational speed of the electric motor.
24. A method according to claim 23 wherein the step of controlling the
electric motor at an output torque magnitude comprises controlling the
electric motor at an output torque as a linear function of sensed
rotational speed of the electric motor.
25. A method according to claim 23 wherein the step of controlling the
electric motor at an output torque magnitude comprises controlling the
electric motor at an output torque as a function of sensed rotational
speed squared of the electric motor.
26. A method according to claim 22 wherein the step of controlling the
electric motor to counteract the vehicle rollback comprises controlling
the electric motor even in an absence of driver selection of one of
vehicle braking and vehicle acceleration.
27. A method according to claim 26 further comprising the steps of
generating a first torque request value as a nonconstant function of
rotational speed of said electric motor during vehicle rollback, and
generating a second torque request value responsive to driver input for
either of braking or acceleration of the vehicle; and wherein the step of
operating the electric motor comprises adding the first and second torque
request values for operating the electric motor. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates to the field of electric vehicles, and more
particularly, to a drive train for an electric vehicle including control
of electric motor torque output.
BACKGROUND OF THE INVENTION
Electric vehicles are receiving considerable attention as a substitute for
present gasoline-fueled vehicles. This interest is based primarily on zero
atmospheric emissions obtainable from an all-electric vehicle. Several
states are considering stricter emissions regulations for vehicles, and
California has adopted regulations that will require zero emissions for a
percentage of vehicles in certain urban areas. Electric vehicles also
offer other advantages including reducing dependency on imported oil,
since utilities in the United States generate a large portion of their
energy demands using coal, gas, nuclear, and hydroelectric sources.
Even hybrid electric vehicles, such as those incorporating a small gasoline
engine running at a constant speed to recharge an electric traction
battery, offer anticipated lower emissions. See, for example, U.S. Pat.
No. 4,351,405 to Fields et al. which discloses a hybrid vehicle including
a gasoline engine for driving the front wheels during high speed and long
distance driving, while the rear wheels are connected to electric motors
for low speed and stop and go driving.
To obtain widespread acceptance as a suitable substitute for conventional
gasoline-fueled vehicles, an electric vehicle should desirably mimic the
operation of such a conventional gasoline vehicle, especially the drive
train including a conventional automatic transmission. Functions such as
braking and acceleration are readily controlled in an electric vehicle
through a conventional brake pedal and accelerator pedal. The selection of
drive, reverse, park, and neutral positions are also imitated on an
electric vehicle. However, in a conventional gasoline vehicle, the engine
always rotates in a same direction and the vehicle includes a clutch or
fluid coupling to transmit torque to the vehicle wheels. In other words, a
conventional automatic transmission will tend to start the vehicle moving
forward, or creep, on a level surface once the driver releases the brake
with the engine idling.
Moreover, starts upward on an incline are readily accommodated in a
gasoline vehicle because the creep of the automatic transmission
compensates for vehicle rollback during the time from when the driver
releases the brake until the driver can depress the accelerator. In
addition, even a conventional vehicle with a standard transmission
includes numerous contributors of rolling friction which have a tendency
to reduce the speed of rollback when starting upward on an incline.
An electric vehicle may have one or more electric motors directly driving
the wheels as disclosed in U.S. Pat. No. 4,913,258 to Sakuri et al.
Alternately, an electric vehicle may have an electric motor driving a set
of wheels through a gearbox and differential. Since the electric motor
does not typically "idle" as a conventional gasoline engine, a typical
electric vehicle has a tendency to first roll backwards when starting
upward on an incline. This rollback is particularly troublesome in traffic
where the vehicle may roll backwards into the vehicle behind. In addition,
when an electric vehicle rolls backward on a grade, the motor is rotating
in a direction opposite to the desired direction of travel, and gear lash
and drive shaft spring must first be taken up from the drive train before
the vehicle may begin to move forward.
Current battery technology limits the driving range of an electric vehicle
to be considerably less than a gasoline vehicle. Accordingly, much
development has gone into reducing rolling friction of the tires and
various mechanical train drive components of an electric vehicle to
thereby improve efficiency and increase the driving range. Unfortunately,
the reduced rolling friction exacerbates the problem of starting upward on
an incline, since the electric vehicle has a tendency to roll back even
faster.
Battery powered vehicles, such as automobiles, forklifts, and other utility
vehicles, typically include some form of motor control logic that may
assist in starting the vehicle when the vehicle is positioned on a grade.
Creep, as in a gasoline vehicle, has been simulated in an electric
forklift for operation on a level surface as shown in the graph of vehicle
speed versus motor torque of FIG. 1, wherein a forward direction of
intended movement is selected. The forklift control computer applies power
to the motor to generate a predetermined constant output torque indicated
by Point A on the graph, irrespective of the vehicle speed.
It has also been common in electric vehicles to limit the rate at which
torque output can be increased from the electric motor to provide for a
smooth and jerk-free start. In other words, to compensate for the lack of
a clutch or fluid coupling, such as a torque converter in a conventional
gasoline-fueled vehicle, a timed ramp on either the motor terminal voltage
or armature current has been used to regulate the rate of torque increase
from the motor of an electric vehicle.
Unfortunately, the timed ramp function is undesirable for starting on a
grade. For example, in order to limit the jerkiness when starting on a
level surface, the timed ramp is set to a relatively slow initial setting
so that torque does not build up too quickly; however, with this same
setting, substantial rollback may still occur on a grade because of the
slowness of increasing torque.
SUMMARY OF THE INVENTION
It is therefore object of the present invention to provide an electric
vehicle drive train and associated method for counteracting rollback of
the vehicle as when starting the vehicle upward on a grade.
It is another object of the present invention to provide a drive train and
associated method for permitting smooth starting upward on a grade.
These and other objects, features and advantages of the invention are
provided by an electric vehicle drive train including an electric motor
being rotatable in opposite directions corresponding to respective
opposite directions of actual vehicle movement, sensing means associated
with electric motor for sensing its rotational direction, selector means
for permitting driver selection of a direction of intended vehicle
movement, and rollback detection and compensation means responsive to the
sensing means and the selector means for determining vehicle rollback and
for operating the electric motor to counteract the vehicle rollback.
Vehicle rollback is defined by a sensed direction of actual vehicle
movement opposite to a selected direction of intended vehicle movement.
The direction of actual vehicle movement corresponds to a respective
sensed rotational direction of the electric motor.
As would be readily understood by those skilled in the art, the drive train
preferably counteracts "backward" rollback when the forward or "D"
direction is selected and the vehicle is facing upward on an incline.
Similarly, the drive train counteracts "forward" rollback when the "R"
direction is selected and the vehicle is facing backwards up an incline.
As would also be readily appreciated by those skilled in the art, the
drive train may also advantageously provide a smooth transition when the
vehicle is accidentally or inadvertently shifted into reverse, for
example, while moving in a forward direction. The present invention also
takes up gear lash and any spring in the drive shaft(s) to thereby provide
smoother starting.
The sensing means associated with the motor preferably includes means for
sensing a rotational speed of the motor which corresponds to the speed of
the vehicle, since the motor is typically coupled to the vehicle wheels
through a gear reduction transmission. Accordingly, the rollback detection
and compensation means includes means for controlling the output torque
magnitude of the electric motor as a nonconstant function of rotational
speed of the motor during vehicle rollback. In one embodiment, the output
torque magnitude is controlled as a linear function of rotational speed of
the electric motor. In another embodiment, the output torque magnitude is
controlled as a function of the square of the sensed rotational speed of
the motor. Other nonconstant functions of torque control based upon speed
are also contemplated by the present invention. The output torque
magnitude of the electric motor is also preferably set at a predetermined
constant value responsive to a rotational speed of the electric motor
being above a predetermined value.
The electric motor is preferably an induction motor utilizing a form of
vector control, such as achieved using a universal field orientation
controller, while those skilled in the art will recognize that other types
of electric motor drives having a controllable output torque magnitude may
also be used. The drive train according to the invention also preferably
includes a traction battery carried by the vehicle frame. The traction
battery is also connected to the induction motor, such as through a
suitable power control circuit including a DC-to-AC inverter.
The drive train preferably also includes driver input means for permitting
driver selection of one of vehicle braking or vehicle acceleration. The
driver input means also preferably includes conventional brake and
accelerator pedals. Control means is preferably connected to the electric
motor for controlling the output torque magnitude and rotational direction
thereof in response to the accelerator and brake pedals during normal
driving of the vehicle. The rollback detection and compensation means
cooperates with the control means to counteract vehicle rollback even in
an absence of driver selection of one of vehicle braking or acceleration,
as when the driver is moving his foot from the brake pedal to the
accelerator pedal. In other words, the drive train of the present
invention will closely mimic the operation of a conventional
gasoline-fueled vehicle having an automatic transmission, by preventing
substantial rollback when starting upward on a hill. Rollback in an
electric vehicle may be even more severe than may occur with a
conventional vehicle, because rolling resistance is minimized in an
electric vehicle to provide greater range for a given battery capacity.
Another aspect of the invention is that the rollback detection and
compensation means includes means for generating a first torque request
value as a function of rotational speed of the electric motor during
vehicle rollback. The control means further includes means for generating
a second torque request value responsive to the driver's selection of
acceleration, for example, as when starting upward on an incline.
Accordingly, the rollback detection and compensation means includes means
for adding the first and second torque request values together to control
the magnitude of the torque output of the electric motor. Thus, smoother
acceleration from a rollback condition is also provided by the invention.
A method according to the invention for operating an electric vehicle
includes the steps of sensing a rotational direction of the electric motor
corresponding to a respective direction of actual vehicle movement,
determining vehicle rollback defined by the sensed direction of actual
vehicle movement being opposite the intended direction of vehicle
movement, and operating the electric motor to counteract the vehicle
rollback. The method further preferably includes the step of sensing the
rotational speed of the electric motor. Accordingly, the step of operating
the electric motor to counteract the vehicle rollback includes the step of
operating the electric motor at an output torque magnitude as a
nonconstant function of sensed rotational speed of the electric motor.
This function may be either linear, or based upon the square of speed, or
based upon another nonconstant function of speed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph of a motor torque and speed illustrating a constant
torque independent of speed for providing creep in an electric forklift as
in the prior art.
FIG. 2 is a perspective schematic fragmentary view of an electric vehicle
according to the present invention.
FIG. 3 is a schematic block diagram of an electric vehicle drive train
according to the invention.
FIG. 4 is a graph of vehicle speed versus motor torque illustrating a
linear function of torque output versus speed according to one embodiment
of the present invention.
FIG. 5 is a graph of vehicle speed versus motor torque illustrating torque
output as a function of the speed squared according to another embodiment
of the present invention.
FIG. 6 is a flow chart block diagram illustrating operation of the drive
train for an electric vehicle according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described more fully hereinafter with
reference to the accompanying drawings, in which a preferred embodiment of
the invention are shown. This invention may, however, be embodied in many
different forms and should not be construed as limited to the embodiments
set forth herein. Rather, applicant provides these embodiments so that
this disclosure will be thorough and complete, and will fully convey the
scope of the invention to those skilled in the art. Like numbers refer to
like elements throughout.
Referring first to FIG. 2 the drive train and its associated components are
illustrated installed in an electric vehicle 10 according to the
invention. The vehicle 10 includes a body 11 that may be carried by a
separate supporting frame, or the vehicle may be of unibody construction
thereby having a body with an integral frame, as would be readily
understood by those skilled in the art. The vehicle's wheels 12 are
rotatably mounted to the frame. As would also be readily understood by
those skilled in the art, in addition to applicability to an all-electric
vehicle 10 as described herein, the drive train according to the present
invention may also have applicability to hybrid types of electric vehicles
which include an additional power source, such as an internal combustion
engine.
A traction battery 13 is carried by the frame of the vehicle 10 in a lower
medial and rearward portion to thus provide a lower center of gravity and
more even weight distribution between the front and rear wheels. As would
be readily appreciated by those skilled in the art, the traction battery
13 preferably comprises a plurality of rechargeable interconnected battery
cells.
The vehicle 10 preferably includes a Vehicle Control Unit (VCU) 14 which,
among other tasks, determines and sends a desired torque request signal to
a control computer for a DC-to-AC inverter, both of which are enclosed
within a protective housing 15 under the hood of the vehicle. The desired
torque request signal is processed by the control computer f | | |
