US 5,487,437 AGranted

Coupled differential turning control system for electric vehicle traction motors

OwnerIsaac Avitaninventor

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Abstract

A turning control system for an electric vehicle includes a differential filter which receives a signal indicative of a desired vehicle steer angle and generates a pair of signals representative of proportional speed and direction at a left and a right drive wheel of the vehicle. Speed limit factors generated by an angular speed limit filter and an operator set throttle control are applied to the signals indicative of proportional speeds to generate desired proportional speed signals. The desired proportional speed signals are applied to a motor coupling controller along with signals indicating the actual motor speeds. Error signals representative of the difference between the desired speed and the actual speed of each motor are scaled and integrated to generate lag signals (representative of accumulated error) and the lag signal of one motor is applied to the desired proportional speed signal of the other motor to generate coupled control signals which are applied to respective left and right motor control circuits.

Claims21

Dependent claims

A turning control system for an electric vehicle which traverses a support surface along a direction of travel, the vehicle having a left traction motor and a right traction motor, a left motor drive control circuit for controlling the operation of the left traction motor and a right motor drive control circuit for controlling the operation of the right traction motor, means drivingly coupling each traction motor with traction means for engaging and propelling the vehicle over a support surface, the traction means being laterally spaced from one another relative to the direction of travel of the vehicle, the turning control system comprising means for generating a signal representative of a desired vehicle steer angle, means receiving the desired vehicle steer angle signal and in response thereto, generating a left reference signal and a right reference signal, each reference signal being representative of the required speed and direction of the respective left and right traction motor for effecting a vehicle turn at the desired steer angle, the turning control system further including motor coupling means, the motor coupling means including means for receiving a signal representative of the instantaneous speed of the left traction motor, for receiving a signal representative of the instantaneous speed of the right traction motor and for receiving the reference signals and in response thereto, generating a signal representative of speed lag of the left traction motor and generating a signal representative of speed lag of the right traction motor, means for modifying the left reference signal as a function of the signal representative of the speed lag of the right traction motor to generate a left motor coupled control signal and means for modifying the right reference signal as a function of the signal representative of the speed lag of the left traction motor to generate a right motor coupled control signal, the turning control system further including means for applying the left motor coupled control signal to the left motor drive control circuit and means for applying the right motor coupled control signal to the right motor drive control circuit, whereby effective speed control is provided for each traction motor which compensates for speed lag in the respective opposite motor to avoid oversteering and understeering and to provide slip free engagement between the traction means and the support surface.

In an electric vehicle having a left drive wheel and a right drive wheel, the drive wheels being in contact with a support surface and being driven by a left traction motor and a right traction motor respectively, a left motor drive control circuit for controlling the operation of the left traction motor and a right motor drive control circuit for controlling the operation of the right traction motor, the drive wheels being laterally spaced about a fixed transverse axis, the vehicle having a pivotable steer wheel having a pivot axis positioned longitudinally from the fixed transverse axis a distance C and with the transverse distance between the pivot axis of the steer wheel and the left drive wheel being designated A and the transverse distance between the pivot axis of the steer wheel and the right drive wheel being designated B and with the steer wheel being oriented at a steer angle .alpha. relative to the fixed transverse axis, the improvement comprising a differential control system for providing proportional control of the left motor drive control circuit and the right motor drive control circuit to effect a vehicle turning maneuver, the control system including means for generating a desired speed reference signal, means for receiving a signal representative of the steer angle .alpha., and in response thereto generating a signal V.sub.l representative of the proportional required speed and direction of the left traction motor and generating a signal V.sub.r representative of the proportional required speed and direction of the right traction motor for effecting a vehicle turn at the steer angle .alpha. according to the following relationship:

V.sub.l =(sin .alpha.-(A/C) cos .alpha.)
V.sub.r =(sin .alpha.+(B/C) cos .alpha.)
the differential control system further including means for controlling maximum vehicle speed as a function of the steer angle .alpha. comprising means for receiving a signal representative of the steer angle .alpha. and in response thereto, generating an angular limit factor signal for progressively limiting vehicle speed as a function of decreasing vehicle radius of travel during a turning maneuver, means for receiving the desired speed reference signal and the angular limit factor signal and in response thereto, generating a limited desired speed signal, the differential control system further including means for generating a left motor reference signal which is a function of the signal V.sub.l and the limited desired speed signal, means for applying the left motor reference signal to the left motor drive control circuit and means for generating a right motor reference signal which is a function of the signal V.sub.r and the limited desired speed signal and means for applying the right motor reference signal to the right motor drive control circuit.

In an electric vehicle having a left drive wheel and a right drive wheel, the drive wheels being in contact with a support surface and being driven by a left traction motor and a right traction motor respectively, a left motor drive control circuit for controlling the operation of the left traction motor and a right motor drive control circuit for controlling the operation of the right traction motor, the drive wheels being laterally spaced about a fixed transverse axis, the vehicle having a pivotable steer wheel having a pivot axis positioned longitudinally from the fixed transverse axis a distance C and with the transverse distance between the pivot axis of the steer wheel and the left drive wheel being designated A and the distance between the longitudinal axis of the steer wheel and the right drive wheel being designated B and with the steer wheel being oriented at a steer angle .alpha. relative to the fixed axis, the improvement comprising a differential control system for providing proportional control of the left motor drive control circuit and the right motor drive control circuit to effect a vehicle turning maneuver, the control system including means for receiving a signal representative of the steer angle .alpha., and in response thereto generating a signal V.sub.l representative of the proportional required speed and direction of the left traction motor and generating a signal V.sub.r representative of the proportional required speed and direction of the right traction motor for effecting a vehicle turn at the steer angle .alpha. according to the following relationship:

V.sub.l =(sin .alpha.-(A/C) cos .alpha.)
V.sub.r =(sin .alpha.+(B/C) cos .alpha.)
the differential control system further including means for generating a left motor reference signal which is a function of the signal V.sub.l and means for applying the left motor reference signal to the left motor drive control circuit and means for generating a right motor reference signal which is a function of the signal V.sub.r and means for applying the right motor reference signal to the right motor drive control circuit, the means for generating the signals V.sub.l and V.sub.r representative of the proportional required speed and direction of the left and right traction motors comprising motor coupling means, the motor coupling means including means for receiving signals representative of the instantaneous speed of the left traction motor and the instantaneous speed of the right traction motor and for determining the speed lag of the left traction motor and the speed lag of the right traction motor and for generating the left motor reference signal as a function of signal V.sub.l and the speed lag of the right traction motor and for generating the right traction motor reference signal as a function of the signal V.sub.r and the speed lag of the left traction motor.

A method of controlling an electric vehicle which traverses a support surface along a direction of travel during a turning maneuver, the vehicle having a left traction motor and a right traction motor, a left motor drive control circuit for controlling the operation of the left traction motor and a right motor drive control circuit for controlling the operation of the right traction motor and means drivingly coupling each traction motor with traction means for engaging and propelling the vehicle over a support surface, the method comprising the steps of:

(a) generating a signal representative of a desired steer angle for the turning maneuver;
(b) employing the signal representative of the desired steer angle to generate a left traction motor reference signal and a right traction motor reference signal, the reference signals being proportional to the required speeds of the left and right traction motors for effecting the turning maneuver at the desired steer angle;
(c) generating a signal representative of the actual motor speed of the left traction motor and generating a signal representative of the actual speed of the right traction motor;
(d) generating a left motor speed lag signal as a function of the left traction motor reference signal and the actual speed of the left motor and generating a right motor speed lag signal as a function of the right motor reference speed signal and the actual speed of the right motor;
(e) employing the left motor reference speed signal and the right motor speed lag signal to generate a left motor coupled control signal and employing the right motor reference speed signal and the left motor speed lag signal to generate a right motor coupled control signal;
and
(f) applying the left motor coupled control signal to the left motor drive control circuit and the right motor coupled control signal to the right motor drive control circuit.

4 more elements

Dependencies are inferred from the claim text.