TOP SPEED ADJUSTMENT SYSTEM FOR A DC SERIES FIELD MOTOR

SYSTEME DE REGLAGE DU REGIME MAXIMAL POUR MOTEUR C.C. A CHAMP EN SERIE

English Abstract

A DC series field motor with a top speed adjustment system in accordance
with the present invention includes a motor field coil, a motor armature, a power
supply, and a variable resistor. The motor field coil and the motor armature arecoupled in series to the power supply and a variable resistor is coupled in parallel
with the motor field coil. The motor armature rotates at a first speed in response
to the first strength of the magnetic field generated by the motor field coil. When
the resistance of the variable resistor is adjusted, the first strength of the first
magnetic field is adjusted to a second strength and the motor armature rotates at a
second speed in response to the second strength.

French Abstract

Moteur série à courant continu avec un système de réglage de la vitesse de pointe comprenant une bobine d'excitation, une armature de moteur, une alimentation en énergie et une résistance variable. La bobine d'excitation et l'armature du moteur sont montées en série avec l'alimentation en énergie, et une résistance variable est montée en parallèle avec la bobine d'excitation. L'armature tourne à une première vitesse en réponse à la première intensité de champ magnétique générée par la bobine d'excitation. Lorsque la résistance de la résistance variable est réglée, la première intensité du premier champ magnétique est réglée à une deuxième intensité, et l'armature du moteur tourne à une deuxième vitesse en réponse à une deuxième intensité.

Claims

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CLAIMS

1. A DC series field motor with a top speed adjustment system
comprising:
a motor field coil which generates a magnetic field having a strength,
the coil having first and second terminals;
a motor armature coupled in series with said motor field coil, wherein
said motor field coil and said motor armature are coupled in series to a power
supply,
said motor armature rotating at a speed in response to said strength for said
magnetic
field; and
an adjustable variable resistor capable of providing any resistance value
within a range of resistances for adjusting the strength of said magnetic
field, said
variable resistor for adjusting coupled across the first and second terminals
in parallel
with said motor field coil, said motor armature speed dependent on the
magnetic field
strength.

2. The DC series field motor as set forth in Claim 1 wherein said
means for adjusting is a variable resistor.

3. The DC series field motor as set forth in Claim 2 wherein the
variable resistor has a resistance ranging from 6 milliohms to 12 milliohms.

4. The DC series field motor as set forth in Claim 2 further comprising
a switch coupled in series with said variable resistor, said switch being
normally open.

5. The DC series field motor as set forth in Claim 1 further comprising
a motor controller coupled in series with said power supply, said motor field
coil, and
said motor armature.


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6. An electric industrial vehicle with a top speed adjustment system
comprising:
a motor field coil generating a magnetic field having a strength, the coil
having first and second terminals;
a motor armature coupled in series with said motor field coil, wherein
said motor field coil and said motor armature are coupled in series to a power
supply;
a drive shaft for the electric industrial vehicle coupled to said motor
armature, said motor armature rotating said drive shaft as a speed in response
to said
strength of said magnetic field; and
an adjustable variable resistor capable of providing any resistance value
within a range of resistances coupled across the first and second terminals in
parallel
with said motor field coil, said variable resistor adjusting said strength of
said
magnetic field and said motor armature rotating said drive shaft at a speed in
response
to said strength for said magnetic field.

7. The electric industrial vehicle as set forth in Claim 6 wherein the
variable resistor has a resistance ranging from 6 milliohms to 12 milliohms.

8. The electric industrial vehicle as set forth in Claim 6 further
comprising a switch coupled in series with said variable resistor, said switch
being
normally open.

9. The electric industrial vehicle as set forth in Claim 6 further
comprising a motor controller coupled in series with said power supply, said
motor
field coil, and said motor armature.

Description

CA 02185474 1998-10-27
- -1-
TOP SPEED ADJUSTMENT SYSTEM FOR A
D.C. SERIES FIELD MOTOR
FIELD OF THE INVENTION
This invention relates generally to speed adjustment system and more
particularly to a system for adjusting a top speed of an electric industrial
vehicle with
a DC series field motor and an open loop speed control system to an upper
limit.
BACKGROUND OF THE INVENTION
A problem in the manufacture of electric industrial vehicles with open
loop speed control systems is that the top speed of different electric
industrial vehicles
which are the same model type can vary. Controlling the top speed of the
electric
industrial vehicle is important for both safety and marketing reasons. If the
top speed
of an electric industrial vehicle is too high (e.g. above the top recommend
speed for
the lift truck), then the electric industrial vehicle may tip over when the
vehicle
reaches the top speed. Additionally, consumers prefer to have a consistent top
speed
for the same model of electric industrial vehicle. Moreover, government
regulations
often require that the speed of certain electric industrial vehicles not
exceed a top set
speed.
SUMMARY OF INVENTION
In accordance with one aspect of the present invention there is provided
a DC series field motor with a top speed adjustment system comprising: a motor
field
coil which generates a magnetic field having a strength, the coil having first
and
second terminals; a motor armature coupled in series with said motor field
coil,

CA 02185474 1998-10-27
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wherein said motor field coil and said motor armature are coupled in series to
a power
supply, said motor armature rotating at a speed in response to said strength
for said
magnetic field; and an adjustable variable resistor capable of providing any
resistance
value within a range of resistances for adjusting the strength of said
magnetic field,
said variable resistor for adjusting coupled across the first and second
terminals in
parallel with said motor field coil, said motor armature speed dependent on
the
magnetic field strength.
In accordance with another aspect of the present invention there is
provided an electric industrial vehicle with a top speed adjustment system
comprising:
a motor field coil generating a magnetic field having a strength, the coil
having first
and second terminals; a motor armature coupled in series with said motor field
coil,
wherein said motor field coil and said motor armature are coupled in series to
a power
supply; a drive shaft for the electric industrial vehicle coupled to said
motor armature,
said motor armature rotating said drive shaft as a speed in response to said
strength of
said magnetic field; and an adjustable variable resistor capable of providing
any
resistance value within a range of resistances coupled across the first and
second
terminals in parallel with said motor field coil, said variable resistor
adjusting said
strength of said magnetic field and said motor armature rotating said drive
shaft at a
speed in response to said strength for said magnetic field.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of a top speed adjustment system for an
electric industrial vehicle with a DC series field motor in accordance with
the present
invention; and
FIG. 2 is an enlarged view of the variable resistor shown in FIG. 1.

CA 02185474 1998-10-27
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DETAILED DESCRIPTION
A top speed adjustment system 10 for an electric industrial
vehicle 12 with a DC series field motor in accordance with the present
invention is
illustrated in FIG. 1. Electric industrial vehicle 12 includes a motor field
coil 14,
a motor armature 16, a variable resistor 18, and a battery 20. With system 10,
every
electric industrial vehicle 12 of a particular model can be easily adjusted to
have the
same upper limit for the top speed.
Referring more specifically to FIG. 1, motor 11 comprises motor field
coil 14 and motor armature 16. One terminal from motor field coil 14 is
coupled in
series to one terminal of motor armature 16. The other terminal of motor
armature 16
is coupled in series to one terminal of a motor controller 22. The other
terminal of
motor controller 22 is coupled to ground and to a negative terminal for
battery 20.
Motor controller 22 is part of an open loop speed control system (not shown)
in
electric industrial vehicle 12. A positive terminal for


2185474.
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battery 20 is coupled to the other terminal of motor field coil 14. Although a
battery 20 is shown as the power source, other sources of power can be used if
desired.
A drive shaft 24 for electric industrial vehicle 12 is coupled to motor
armature 16. When motor 11 is turned on, motor armature 16 rotates drive
shaft 24 to drive the wheels (not shown) of lift truck 12 in a manner well
known in
the art and thus not described in detail here. Motor armature 16 can rotate
drive
shaft 24 up to a top speed. Since electric industrial vehicle 12 has an open
loop
speed control system (not shown), the top speed between different electric
industrial vehicles of the same model type can vary. With top speed adjustment
system 10, the top speed for every electric industrial vehicle of the same
model
type can be set to substantially the same upper limit.
Top speed adjustment system 10 comprises a switch 26 and variable
resistor 18. An enlarged view of variable resistor with terminals 21 and 23 is
shown in FIG. 2. A solder bead 25 is located adjacent terminal 23 and sets the
minimum resistance point for variable resistor 18. As shown in FIG. 1, switch
26
is coupled in series with variable resistor 18 and both switch 26 and variable
resistor 18 are coupled in parallel with motor field coil 14. Switch 26 is
normally
open and is closed if the speed of electric industrial vehicle 12 must be
adjusted.
In this particular embodiment, variable resistor 18 has a resistance ranging
from 6
milliohms to 12 milliohms, although the range of resistance can vary depending
upon the particular application. As explained in greater detail below, the
resistance
of variable resistor 18 is adjusted to set or calibrate the top speed of
electric
industrial vehicle 12 to an upper limit.
When motor controller 22 is turned on, current from battery 20
flows through motor field coil 14, motor armature 16, and motor controller 22.
Current flowing through motor 11 generates a magnetic field which causes motor
armature 16 to rotate. As the flow of current increases, the strength of the



2185414
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magnetic field increases until the motor 11 reaches top speed. This speed is
dependent upon the load on motor 11. Motor controller 22 controls the flow
current and thus the speed at which drive shaft 24 is rotated and electric
industrial
vehicle 12 moves. Since motor controller 22 is part of an open loop control
system
(not shown) in electric industrial vehicle 12, the top speed for electric
industrial
vehicle 12 will be different for each vehicle depending upon the vehicle's
mechanical rolling resistance.
To further increase the speed of vehicle 12, switch 26 is closed to
couple variable resistor 18 in parallel with motor field coil 14. Coupling
variable
resistor 18 in parallel with motor field coil 14 weakens the magnetic field of
field
coil 14 and thus increases the speed at which motor armature 16 rotates drive
shaft 24. Again assuming a constant voltage and a constant load, increasing
the
resistance of variable resistor 18 increases the flow of current through motor
field
coil 14, thus increasing the magnetic field which reduces the speed at which
motor
armature 16 rotates drive shaft 24. Therefore, decreasing the resistance of
variable
resistor 18 decreases the flow of current through motor field coil 14, thus
decreasing the magnetic field of the field coil 14 which increases the speed
at
which motor armature 16 rotates drive shaft 24.
To set the top speed of electric industrial vehicle 12 to an upper
limit, top speed of electric industrial vehicle 12 is measured and compared
against
the upper limit. If there is a difference, then switch 26 is closed to couple
variable
resistor 18 in parallel with motor field coil 14. As discussed above, when
variable
resistor 18 is coupled in parallel with motor field coil 14 the magnetic field
can be
altered and thus the speed at which motor armature 16 rotates drive shaft 24
can be
adjusted. Increasing the resistance of variable resistor 18 reduces the speed
at
which motor armature 16 rotates drive shaft 24 and decreasing the resistance
of
variable resistor 18 increases the speed at which motor armature 16 rotates
drive
shaft 24. Accordingly, the resistance of variable resistor 18 is adjusted and
the
speed of electric industrial vehicle 12 is measured until the top speed of
electric



21854?4
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industrial vehicle 12 substantially matches the set upper speed limit.
Adjusting the
top speed by weakening the magnetic field of motor field coil 14 does result
in a
reduction in torque, but since a electric industrial vehicle 12 will only be
allowed
to reach the top speed at a light or no load condition, the reduction in
torque to
increase speed is an acceptable trade off. As described above, top speed
adjustment
system 10 is easy to install and is easy to use.
Having thus described the basic concept of the invention, it will be
readily apparent to those skilled in the art that the foregoing detailed
disclosure is
intended to be presented by way of example only, and is not limiting. Various
alterations, improvements, and modifications will occur and are intended to
those
skilled in the art, but not expressly stated herein. These modifications,
alterations
and improvements are intended to be suggested hereby, and within the spirit
and
scope of the invention. Accordingly, the invention is limited only by the
following
claims and equivalents thereto.

Representative Drawing