Electricity: motive power systems – Battery-fed motor systems
Reexamination Certificate
2001-08-22
2002-11-26
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Battery-fed motor systems
C318S376000, C318S434000
Reexamination Certificate
active
06486626
ABSTRACT:
The present invention relates to control apparatus for electric vehicles, and in particular to error or fault detection in control apparatus arranged to drive the vehicle.
Electric vehicles are well-known and an example
200
is shown in FIG.
1
. The electric vehicle
200
comprises input means
1
which is operable by a user or driver to indicate a desired motion of the vehicle. In the case of electric wheelchairs, the input means is typically a joystick to facilitate control. The joystick generates an X signal indicative of the component of a joystick deflection along a nominal X axis and a Y signal indicative of the component of the deflection along a nominal Y axis. Usually the Y axis is aligned with the forward-reverse axis of the vehicle and movement of the joystick in the X direction corresponds to left-right movement. Thus, the Y signal is indicative of a desired forward-reverse motion of the vehicle and the X signal is indicative of a desired turning motion of the vehicle. The X and Y signals generated by the joystick are usually analogue signals and are transmitted to a controller
3
where they are converted into digital signals X
D
and Y
D
by an analogue to digital converter (ADC)
31
. The digital signals are processed by a microprocessor or microchip
32
which outputs a control signal
91
used to control the speed of a motor
2
arranged to drive a wheel
10
of the vehicle. In
FIG. 1
, only one motor
2
and one wheel
10
are shown. Typically however, the vehicle will comprise two driven wheels and two corresponding driving motors. Turning motion is achieved by driving the wheels at different respective angular velocities and forward-reverse motion is achieved by driving the two wheels at a common angular velocity.
In general, the control signal
91
is a function of (i.e. it is determined by or calculated from) both the X and Y inputs.
The control signal
91
is used to control circuitry
33
which regulates the supply of power from a battery
4
to the motor
2
. The circuitry
33
outputs a further control signal
92
, which is a voltage signal applied to the motor.
A problem with the arrangement shown in
FIG. 1
is that a fault in the input means, controller hardware or software may affect the motor control signal
92
and may result in the wheel being driven at an inappropriate speed, i.e. the user may lose control. Clearly this is undesirable and may be dangerous.
So-called dual decode joysticks are known which, in addition to generating X and Y signals, also produce nominal inverse outputs X
i
and Y
i
. X and X
i
are independently indicative of the X position of the joystick, and similarly Y and Y
i
are independently indicative of its Y position. Thus, for a given joystick deflection, a dual decode joystick produces two independent signals indicative of the X component of that deflection, and two independent signals indicative of the Y component of the deflection. The “normal” and “inverse” signals are usually generated in physically separate output circuits. Thus, malfunctions or faults with the joystick hardware can be detected by comparing X with X
i
and Y with Y
i
.
Electric vehicles employing dual decode joysticks are known, and an example is shown in FIG.
2
. Normal and inverse X and Y signals are transmitted to the controller
3
where they are converted into corresponding digital signals by the ADC
31
. The digital signals then pass to a processor
32
. Three nominal processing operations are performed, represented schematically by regions
321
,
322
and
323
in the figure. In the first processing operation
322
the normal and inverse X signals X
D
and X
Di
are compared. If the signals differ by more than a predetermined value (an error threshold) then an error signal is generated. Similarly in the second processing operation
323
the normal and inverse Y signals are compared and an error signal may be generated. It will be apparent that the apparatus may be designed to respond to an error signal (fault indication) in a number of different ways. For example, the vehicle may be brought to a rest by interrupting the power supply from the battery, by applying a brake, by appropriate control of the circuitry
33
, or by other means. the controller may also provide an indication to the user or a service engineer that a joystick fault has developed.
Alternatively, if the normal and inverse signals are within the predetermined range or threshold then the normal X and Y signals are passed to the third processing operation
321
by which the control signal
91
is generated.
Although the use of a dual decode joystick represents an improvement on previous arrangements, there are still problems associated with the control apparatus of FIG.
2
. In particular, only faults in the joystick and ADC hardware will be detected. Faults associated with the controller hardware and software still, in general, remain undetected and may result in the incorrect control signal being applied to the motor.
It is therefore desirable to address the problems associated with the prior art.
According to a first aspect of the present invention there is provided control apparatus for an electric vehicle, the apparatus comprising:
input means operable to generate a first signal indicative of a component of a desired motion of the vehicle and a second signal independently indicative of said component;
an electric motor arranged to drive a wheel of the vehicle;
a controller arranged to control the motor according to said first signal; and
means for generating a signal indicative of a voltage across windings of the motor,
the controller further including:
means for calculating a quantity indicative of a nominal expected voltage across said windings according to said second signal;
means for comparing said voltage with said expected voltage; and
means for generating an error signal in response to said voltage and expected voltage differing by more than a predetermined amount.
The means for generating a signal indicative of a voltage across windings of the motor may comprise a voltage dividing circuit and/or a filter circuit and the signal may be proportional to an average voltage developed across the windings. The controller may include a microprocessor which may calculate the expected average voltage (or a quantity proportional to it) from the second signal and, for example, from a preprogrammed quantity indicative of the supply voltage from a battery.
Advantageously, the error or fault signal may be generated in response to any error or fault resulting in a sufficiently large difference between the actual and expected (predicted) voltages developed or seen across the motor windings. Thus, this aspect of the present invention provides an error check on all of the control apparatus, including the input means (eg. a joystick), the controller circuitry and any software, and the motor windings themselves.
As such, it represents a considerable improvement in error detection and safety over the prior art. Errors or faults not affecting the voltage developed across the motor windings are, by definition, less serious from a control/safety point of view.
The input means may be further operable to generate third and fourth signals independently indicative of another component of a desired motion of the vehicle, the controller may be arranged to control the motor (ie its speed and direction of rotation) according to the first and third signals, and the calculating means may calculate the quantity indicative of the expected voltage according to the second and fourth signals.
The motor may be brushless and comprise three phase windings.
According to a second aspect of the present invention there is provided, control apparatus for an electric vehicle the apparatus comprising:
input means operable to generate a first signal indicative of a component of a desired motion of the vehicle and a second signal independently indicative of said component;
an electric motor arranged to drive a wheel of the vehicle; and
a controller responsive to said first signal to control the motor, the
Dang Khanh
Elliott Industries Limited
Westerman, Champlin & Kelly, P.A.
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