Integrated control for electric lift trucks

• US 6,226,582 B1
• Filed: 07/21/1998
• Issued: 05/01/2001
• Est. Priority Date: 07/21/1997
• Status: Expired due to Fees

• Current Assignee: SRE Controls Inc. (Tersus Energy Ltd.)
• Original Assignee: SRE Controls Inc. (Tersus Energy Ltd.)
• Inventors: Gadbois, Pierre C., Adsett, Robert T.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): MANCHO, RONNIE M
• Application Number:
  US09/120,079
• Time in Patent Office: 1,015 Days
• Field of Search: 414/694, 414/685, 180/68.5, 180/333, 180/65.8, 180/286, 180/315, 180/321, 180/324, 180/53.2, 37/397, 37/379, 318/67, 318/799, 318/700, 318/802, 323/222, 323/326, 363/21, 701/50, 701/22, 701/24
• US Class Current: 701/50
• CPC Class Codes: B66F 9/20 Means for actuating or controlling masts, platforms, or forks power take-off from vehicle transmissions, combined with vehicle propulsion systems B60K

Abstract

A control system for an electric lift truck that controls a traction motor and a hydraulic pump motor is disclosed. The speed of rotation of both motors is controlled by a pulse width modulated current supplied from a battery source by the controller in direct response to a demand communicated to the controller through an interface manipulated by an operator. A pump driven by the pump motor supplies pressurized hydraulic fluid to a lift mechanism and a power assisted steering unit. A joystick with function switches mounted thereto is provided so that the operator steers with one hand while controlling truck propulsion and all functions of the lift mechanism with the other hand. The direct control of the pump motor speed enables a fully proportional control of the hydraulic system. The control system is a compact structure that requires minimal cabling and ensures that the hydraulic system operates with energy efficiency and minimal wear.

Claims

1. A control system for an electric lift truck, the electric lift truck including a first electric motor for truck propulsion and a second electric motor connected to a hydraulic pump for supplying pressurized hydraulic fluid through a hydraulic circuit to a hydraulic lift mechanism, comprising:

an interface for providing an integrated drive and hydraulic control system to permit an operator to control the propulsion of the electric lift truck and a plurality of functions of the hydraulic lift mechanism, the interface generating a plurality of electronic control signals in response to inputs through the interface by the operator;

an electronic controller connected to the interface and the first and second electric motors for receiving the electronic control signals from the interface, and controlling a speed and a direction of revolution of the first electric motor, and a speed of revolution of the second electric motor in direct relation to the electronic control signals so that hydraulic functions are controlled by direct control of the second motor as well as incremental opening of control valves in response to the electronic control signals.

2. A control system as claimed in claim 1 wherein the controller is a pulse-width modulation controller and the first and second electric motors are DC or AC motors.

3. A control system as claimed in claim 1 wherein the hydraulic circuit further comprises a power assisted steering system to which a hydraulic fluid is supplied with high priority from the pump.

4. A control system as claimed in claim 3 further comprising an on-demand pressure switch that is connected to the hydraulic circuit between the hydraulic pump and the power assisted steering system so that the on-demand pressure switch is triggered by a pressure rise in a supply of hydraulic fluid for the power assisted steering system, the on-demand pressure switch generating an electric signal to prompt the controller to change a speed of revolution of the second electric motor from a first speed to a second speed which is faster than the first speed.

5. A control system as claimed in claim 4 wherein the controller executes an algorithm for measuring electric signals from the on-demand pressure switch and the interface respectively, and controls the speed of revolution of the second electric motor in response to the signals so that the hydraulic pump meets a demand of both of the power assisted steering system and the hydraulic lift mechanism.

6. A control system as claimed in claim 5 wherein the controller controls the second electric motor to operate at an idle when no hydraulic fluid pressure is required for the hydraulic functions of the lift mechanism or the power assisted steering system.

7. A control system as claimed in claim 6 wherein the functions of the hydraulic lift mechanism are enabled by:

a lift cylinder for lifting and lowering the lift mechanism;

a tilt cylinder for tilting the lift mechanism;

a reach cylinder for moving the lift mechanism toward and away from a front of the lift truck;

a side-shift cylinder for moving the lift mechanism left and right with respect to the front of the lift truck; and

a solenoid-valve block for selectively communicating the fluid pressure from the pump to the lift, tilt, reach or side-shift cylinder.

8. A control system as claimed in claim 1 wherein the power assisted steering system comprises:

a torque generator;

a priority valve with a low priority to the hydraulic lift mechanism to ensure that an operative volume of hydraulic fluid is delivered to the torque generator at all times.

9. A control system as claimed in claim 1 wherein the interface comprises a joystick enabled to generate signals simultaneously representative of movement with respect to a first axis and a second axis so that the speed and direction of revolution of the first electric motor is controlled by the signals representing movement with respect to the first axis and the functions of the hydraulic lift mechanism are simultaneously controlled by the signals representing movement with respect to the second axis.

10. A control system as claimed in claim 9 wherein the joystick further comprises a plurality of buttons for selecting hydraulic function options so that a control function of the joystick is selectable.

11. A control system as claimed in claim 10 wherein the plurality of buttons comprise a first, a second and a third button connected to the controller and the buttons are mapped to lift functions so that a tilt cylinder, a reach cylinder, a side-shift cylinder or a lift cylinder is controlled when the signals representative of movement with respect to the second axis are detected by the controller, the cylinder being controlled depending on lift function mapping and button selection.

12. A control system as claimed in claim 11 further comprising a proportional valve and a solenoid check valve connected in series between the lift cylinder and a tank for the hydraulic fluid, the solenoid check valve and proportional valve being controlled by an electric current switched by the controller so that when the signals representative of movement with respect to the second axis instruct the controller to lower the lift mechanism, a lowering speed of the lift mechanism is controlled.

13. A control system as claimed in claim 11 wherein the plurality of buttons further include an additional button connected to the controller, and the controller switches battery current to energize a horn relay to sound a horn when the additional button is pressed.

14. A control system as claimed in claim 12 wherein the controller responds to the joystick so that the speed of revolution of the first and the second electric motors increases when the signals representative of movement with respect to the first and the second axes respectively are detected by the controller, except in a lift mechanism lowering operation, and the direction of revolution of the first electric motor is changed when the top end of the joystick is tilted from a vertical orientation in opposite directions along the first axis and the direction of a movement of a lift mechanism function is changed when the signals representing movement in opposite directions with respect to the second axis.

15. A control system as claimed in claim 7 further comprising a check valve between the solenoid-valve block and the lift cylinder to prevent the lift mechanism from falling if a supply of hydraulic fluid is interrupted.

16. A control system as claimed in claim 1 wherein the control system includes a first controller and a second controller, the first controller controlling the first motor and the second controller controlling the second motor and lift functions of the electric lift truck.

17. A control system as claimed in claim 16 wherein the interface comprises a joystick enabled to generate signals simultaneously representative of movement with respect to a first and a second axis, the joystick being connected to the first and second controllers so that the speed and direction of the first electric motor is controlled in response to the signals representative of movement with respect to the first axis, and the functions of the hydraulic lift mechanism are controlled by signals representative of movement with respect to the second axis.

18. A control system as claimed in claim 16 wherein the interface comprises a joystick having a top end movable along the first axis and a thumb wheel rotatably mounted to a top end of the joystick and rotatable with respect to the second axis, the joystick being connected to the first and second controllers so that the speed and direction of the first electric motor is controlled when the top end of the joystick is moved along the first axis, and the functions of the hydraulic lift mechanism are controlled by a rotation of the thumb wheel with respect to the second axis.

19. A control system as claimed in claim 18 wherein the joystick further comprises a plurality of buttons for hydraulic function options so that a control function of the joystick is user selectable and the controller executes the control function when the thumb wheel is rotated and the function changes when one of the buttons is pressed.

20. An electronically controlled hydraulic system for a lift truck having a power assisted steering and a hydraulic lift mechanism, comprising:

a pump driven by an electric motor for supplying pressurized hydraulic fluid to a torque generator for the power assisted steering and to the hydraulic lift mechanism;

a hydraulic circuit including a reservoir for the hydraulic fluid and a priority valve, the hydraulic circuit being in fluid communication with the pump and torque generator as well as the hydraulic lift mechanism, the priority valve distributing a fluid flow to the torque generator with a high priority so that a required supply of the pressurized fluid to the torque generator is ensured;

an on-demand pressure switch connected to the hydraulic circuit, the on-demand pressure switch being triggered and generating an electric signal when the torque generator causes a rise in the hydraulic fluid pressure;

an interface for an operator to control a plurality of functions of the hydraulic lift mechanism, the interface generating a plurality of control signals in response to manipulation of the interface by the operator;

a controller for controlling the motor, the controller being connected to the on-demand pressure switch and the interface so that when the controller receives a signal from the on-demand pressure switch or a signal from the interface, the controller changes a speed of revolution of the motor, but the controller operates the motor at an idle speed when the power assisted steering and the lift mechanism are each in a standby state and a supply of pressurized hydraulic fluid is not required.

21. An electronically controlled hydraulic system as claimed in claim 20 wherein the controller is pulse-width modulation controller and the motor is a DC or AC motor.

22. An electronically controlled hydraulic system as claimed in claim 21 wherein the hydraulic circuit comprises:

a lift cylinder for lifting and lowering the lift mechanism;

a tilt cylinder for tilting the lift mechanism;

a reach cylinder for moving the lift mechanism toward and away from a front of the lift truck;

a side-shift cylinder for moving the lift mechanism left and right with respect to the front of the lift truck; and

a solenoid-valve block for selectively directing the pressurized fluid from the pump to a one of the lift, tilt, reach and side-shift cylinders.

23. An electrically controlled hydraulic system as claimed in claim 22 wherein the hydraulic circuit further comprises a proportional valve and a solenoid check valve connected in series between the lift cylinder and the tank, the solenoid check valve and proportional valve being controlled by the controller so that a lowering speed of the lift mechanism is controlled.

24. An electrically controlled hydraulic system as claimed in claim 23 wherein the hydraulic circuit further comprises a check valve connected between the solenoid-valve block and the lift cylinder for preventing the lift mechanism from falling in case of an interruption in the supply of pressurized hydraulic fluid.

25. An operator interface for providing an integrated drive and hydraulic control system to permit the operator to control an electric lift truck, the electric lift truck including a first electric motor for truck propulsion and a second electric motor connected in driving relation to a hydraulic pump, comprising:

a joystick enabled to generate electric signals simultaneously representative of movement with respect to a first and second axis;

an electric controller for controlling a speed and direction of revolution of the first electric motor and a speed of revolution of the second electric motor respectively, the controller receiving the electric signals generated by the joystick when the operator manipulates the joystick to generate electric signals representative of movement along the first and second axes, and controls a speed and a direction of revolution of the first electric motor in response to electric signals representative of movement with respect to the first axis and controls a speed of revolution of the second electric motor in response to electric signals representative of movement with respect to the second axis so that hydraulic functions are controlled by direct control of the second motor as well as incremental opening of control valves in response to the electronic control signals.

26. An operator interface as claimed in claim 25 wherein the first axis and second axes are at right angles to each other, and the joystick is tiltable along the first and second axes by the operator of the lift truck.

27. An operator interface as claimed in claim 25 wherein a thumb wheel is mounted to a top end of the joystick, the thumb wheel being rotatable with respect to the second axis and the joystick is tiltable along the fist axis.

28. An operator interface as claimed in claim 26 wherein the direction of revolution of the first electric motor is changed when the joystick is tilted along the first axis and past a vertical orientation and a direction of a movement of a lift mechanism is changed when the joystick is moved along the second axis and past the vertical orientation.

29. An operator interface as claimed in claim 25 wherein the joystick further comprises a plurality of buttons which may be pressed to control a plurality of functions of the hydraulic lift mechanism, in addition to a default function which is operative when none of the buttons are pressed.

30. An operator interface as claimed in claim 29 wherein the signals representing movement of the joystick with respect to the second axis causes the controller to actuate a solenoid check valve and a proportional valve in a hydraulic circuit to lower an hydraulic lift mechanism of the electric lift truck when a lowering option is selected.

31. An operator interface as claimed in claim 29 wherein the plurality of buttons are mapped to control a tilt option, a reach option, a side-shift option, and a horn.

32. An operator interface as claimed in claim 25 wherein the lift truck is equipped with power steering and the controller generates a signal to cause the second electric motor to operate at an idle speed when the joystick is in a vertical orientation or the joystick is manipulated to generate signals for selecting a function for lowering the hydraulic lift mechanism.

33. An operator interface as claimed in claim 26 wherein threshold areas are mapped on each side of the first axis and signals generated by the joystick when the joystick is tilted along the second axis within the threshold areas are ignored by the controller so that the slight tilting of the joystick to one side as the joystick is tilted along the first axis to control a lift truck propulsion does not activate a lift function.

34. An operator interface as claimed in claim 33 wherein a width of the threshold areas are proportional to the tilt of the joystick along the first axis so that the width of the threshold areas increases as a speed of the vehicle increases.