GE IC3645SR3R404P2 - Proportional Operation for Dual Motor Vehicles; Creep Speed; Control Acceleration and 1 A Time; Current Limit

BASIC OPERATION AND FEATURES
SX TRANSISTOR CONTROL Page 6
July 1999
The oscillator section of the card has two adjustable
features, creep speed and minimum field current. With the
accelerator at maximum ohms or volts, the creep speed
can be adjusted by Function 2 of the Handset or a trimpot.
The field control section allows the adjustment of the field
weakening level in order to set the top speed of the motor.
This top speed function (Minimum Field Current) is enabled
when the armature current is less than the value set by
Function 24 and the accelerator input voltage is less than 1
volt. Top Speed can be adjusted by Function 7 of the
Handset or a trimpot.
The % ON-time has a range of approximately 0 to 100
percent. The SX controllers operate at a constant
frequency and the % ON-time is controlled by the pulse
width of the voltage/current applied to the motor circuits.
Section 2.1.1.b Proportional Operation for Dual Motor
Vehicles
A key performance advantage of this control is the ability to
achieve actual “proportioning” of motor speed. In a non-
proportioning, or single control, system, when the vehicle
starts to turn, the outside drive wheel turns in a larger
circle than the inside wheel. Depending on the geometry of
the vehicle, at some degree of turn angle, the inside wheel
must slow down to prevent scrubbing of the wheel. This is
accomplished on a single control system by disconnecting
the inside motor and letting the wheel “free wheel” or
“float” at whatever speed is dictated by the outside wheel
that is still under power. The main disadvantage of this
system is that no torque is available on that motor when the
inside wheel is in the “free wheel” mode, and the vehicle
performance in a turn is reduced. When the steer wheel
nears the 90
o
turn angle, the inside motor is re-connected in
the opposite direction of the outside wheel. At this point,
torque is returned to the inside wheel and the speed is the
same on both motors.
With two controls, the speed of each motor can be
regulated independently. The driver controls the speed of
the outside wheel with the accelerator input signal. The
inside wheel speed is controlled by the turn angle of the
steer wheel. A potentiometer is attached to the steer wheel
in order to communicate the steer angle to the controllers.
During vehicle manufacture, software selection identifies
each control for its application as a right or left control.
The controls are physically identical, and it is only software
that separates a right from a left control, or differentiates a
control for a dual motor application from one intended for a
single motor vehicle.
With this dual motor system, as the steer reaches some
pre-selected turn angel, approximately 15
o
, the speed of the
inside wheel decreases proportionally to the speed of the
outside wheel. This proportional decline will continue on a
tangential path, until the steer angle reaches another
predetermined angle of approximately 70
o
. At this point, the
inside wheel will stop. As the steer angle is increased
toward the 90
o
point, the inside wheel will reverse direction
and start to accelerate proportionally in speed. As the
steer angle reaches the 90
o
point, the inside wheel speed
will be the same as that of the outside wheel. During this
entire turn, except for several degrees when the motor was
stopped to reverse direction, torque was always present on
the inside wheel, providing a smoother ride throughout the
turning radius of the vehicle.
Details for the adjustment of the steer angle potentiometer
can be found in Section 7 of this manual.
0
O
10
O
10
O
20
O
20
O
30
O
30
O
40
O
40
O
50
O
50
O
60
O
60
O
70
O
70
O
80
O
80
O
90
O
100%
50%
50%
100%
90
O
100%
50%
50%
100%
RIGHT
MOTOR
LEFT
MOTOR
STEERING ANGLE
LEFT
TURN
RIGHT
TURN
LEFT
MOTOR
RIGHT
MOTOR
RIGHT
CONTROL
LEFT
CONTROL
0
O
90
O
90
O
REV - SPEED - FWD REV - SPEED - FWD
Section 2.1.1.c Creep Speed
With the accelerator at minimum speed, the creep speed
can be adjusted by Function 2 of the Handset. At creep
speed, the ON time can decreased to approximately 5%,
with the OFF time at approximately 95%. At full transistor
operation, this condition will be reversed (short OFF time,
long ON time). This variation of ON and OFF time of the
oscillator varies the voltage applied to the motor, thereby
varying the speed of the motor for a given load.
Section 2.1.1.d Control Acceleration
This feature allows for adjustment of the rate of time it
takes for the control to accelerate to 100% applied battery
voltage to the motor on hard acceleration. Armature C/A is
adjusted by Function 3 from 0.1 to 6 seconds.
Section 2.1.2 Current Limit
This circuit monitors motor current by utilizing sensors in
series with the armature and field windings. The
information detected by the sensor is fed back to the card
so that current may be limited to a preset value. If heavy
load currents are detected, this circuit overrides the
oscillator and limits the average current to a value set by
Function 4 and Function 8 of the Handset. The C/L setting is
based on the maximum thermal rating of the control.
Because of the flyback current through Q6, the motor
current is usually greater than battery current, except at
100% ON time.