Electronically controlled hydraulic system for lowering a boom in an emergency

• US 6,647,718 B2
• Filed: 10/04/2001
• Issued: 11/18/2003
• Est. Priority Date: 10/04/2001
• Status: Expired due to Fees

• Current Assignee: Husco International Incorporated
• Original Assignee: Husco International Incorporated
• Inventors: Stephenson, Dwight B.
• Primary Examiner(s): Lopez, F. Daniel
• Application Number:
  US09/970,761
• Publication Number:
  US 20030066417A1
• Time in Patent Office: 775 Days
• Field of Search: 604/03, 604/05, 915/15, 414/700, 414/708
• US Class Current: 60/403
• CPC Class Codes: B66C 23/88 Safety gear for cranes in general B66C15/00; for rope, cable, or chain winding mechanisms B66D1/54
• CPC Class Codes: B66F 17/006 for working platforms
• CPC Class Codes: E02F 9/226 Safety arrangements, e.g. hydraulic driven fans, preventing cavitation, leakage, overheating
• CPC Class Codes: F15B 11/20 controlling several interacting or sequentially-operating members
• CPC Class Codes: F15B 20/004 Fluid pressure supply failure
• CPC Class Codes: F15B 21/08 Servomotor systems incorporating electrically operated control means F15B21/02, F15B21/065 take precedence

Abstract

An industrial lift truck has a boom that is raised and lowered by a first hydraulic actuator and a load carrier that is pivoted with respect to the boom by a second hydraulic actuator. In the event that the supply of hydraulic fluid for powering the actuators fails, the boom may be lowered by gravity by draining fluid from the first hydraulic actuator. To prevent a load from sliding off the load carrier as the boom descends, the load carrier is pivoted to maintain a substantially constant angular relationship to the ground. This is accomplished by selectively conveying fluid drained under pressure from the first hydraulic actuator into the second hydraulic actuator. Changes in the position of the boom are sensed and, in response, the flow of fluid into the second hydraulic actuator is controlled to produce corresponding changes in the load carrier position.

Claims

1. In a machine having a boom, that is moved by a first hydraulic actuator, and a load carrier, that is coupled to the boom and moved with respect thereto by a second hydraulic actuator;

a method for moving the boom when pressurized fluid from a source is not available, said method comprising;

sensing a first position of the boom;

draining hydraulic fluid under pressure from the first hydraulic actuator without applying pressurized fluid from the source to the first hydraulic actuator;

conveying the hydraulic fluid from the first hydraulic actuator to the second hydraulic actuator without employing pressurized fluid from the source; and

controlling flow of the hydraulic fluid into the second hydraulic actuator in response to the first position of the boom to produce movement of the load carrier with respect to the boom, wherein as the boom moves, an angular relationship of the load carrier with respect to a surface on which the machine is supported is maintained substantially constant.

2. The method as recited in claim 1 wherein controlling flow of the hydraulic fluid comprises:

sensing a first pressure of the fluid draining from the first hydraulic actuator;

sensing a second pressure of fluid in the second hydraulic actuator; and

enabling the hydraulic fluid to enter the second hydraulic actuator in response to the first pressure being greater than the second pressure.

3. The method as recited in claim 1 wherein controlling flow of the hydraulic fluid comprises:

measuring a first angle representing the first position of the boom;

measuring a second angle between the load carrier and the boom;

calculating a sum of the first angle and the second angle; and

as the first angle changes when the boom descends, controlling the flow of the hydraulic fluid to move the load carrier and vary the second angle to maintain the sum of the first angle and the second angle substantially constant.

4. The method as recited in claim 1 wherein controlling flow of the hydraulic fluid comprises:

measuring a first angle representing the first position of the boom;

measuring a second angle representing a position of the load carrier with respect to the boom; and

regulating the flow of the hydraulic fluid to move the load carrier so that the second angle changes by an amount that is substantially equivalent to an amount the first angle changes.

5. The method as recited in claim 1 further comprising:

deriving, from the first position, a desired position for the load carrier; and

the flow of the hydraulic fluid is controlled to place the load carrier into the desired position.

6. The method as recited in claim 1 further comprising:

sensing a second position of the load carrier;

deriving from the first position a desired position for the load carrier; and

wherein controlling flow of the hydraulic fluid comprises terminating that flow when the second position corresponds to the desired position.

7. The method as recited in claim 1 wherein controlling flow of the hydraulic fluid comprises:

measuring a positional change of the boom with respect to a reference point on the machine; and

controlling the flow of the hydraulic fluid in response to the positional change of the boom to produce a corresponding change in the position of the load carrier with respect to the boom.

8. The method as recited in claim 1 wherein controlling flow of the hydraulic fluid comprises:

sensing inclination of the load carrier with respect to a given axis; and

as the boom descends, controlling the flow of the hydraulic fluid to move the load carrier to maintain the inclination of the load carrier with respect to the given axis substantially constant.

9. In a machine having a pump, a boom, and a load carrier coupled to the boom, wherein the boom is moved by a first hydraulic actuator that has first and second chambers and the load carrier is moved with respect to the boom by a second hydraulic actuator that has third and fourth chambers, a method for lowering the boom during an abnormal operating condition comprising:

coupling the first hydraulic actuator to a supply line and a tank return line by a first valve assembly, wherein the supply line receives pressurized fluid from the pump under normal operating conditions;

coupling the second hydraulic actuator to the supply line and the tank return line by a second valve assembly;

when pressurized fluid is unavailable from the pump, activating the first valve assembly to drain hydraulic fluid under pressure from the first chamber of the first hydraulic actuator into the supply line, which results in the boom lowering; and

when pressurized fluid is unavailable from the pump, selectively activating the second valve assembly to cause hydraulic fluid to flow from the supply line into the third chamber of the second hydraulic actuator, wherein as the boom lowers, an angular relationship of the load carrier with respect to a surface on which the machine is supported is maintained substantially constant.

10. The method as recited in claim 9 further comprising:

sensing a first pressure of the fluid draining from the first hydraulic actuator;

sensing a second pressure of fluid in the third chamber of the second hydraulic actuator; and

wherein the second valve assembly is selectively activated in response to the first pressure being greater than the second pressure.

11. The method as recited in claim 9 wherein selectively activating the second valve assembly comprises:

measuring a first angle representing a position of the boom;

measuring a second angle representing a position of the load carrier with respect to the boom; and

activating the second valve assembly to apply hydraulic fluid to the second hydraulic actuator so that the second angle changes by an amount which is substantially equivalent to an amount that the first angle changes.

12. The method as recited in claim 11:

further comprising calculating a sum of the first angle and the second angle; and

controlling the second valve assembly; and

wherein activating the second valve assembly controls flow of the hydraulic fluid to vary the second angle so that the sum of the first angle and the second angle is maintained substantially constant.

13. The method as recited in claim 9 further comprising:

sensing a first position of the boom;

deriving, from the first position, a desired position for the load carrier; and

the flow of the hydraulic fluid is controlled to place the load carrier into the desired position.

14. The method as recited in claim 9 further comprising activating the first valve assembly to cause hydraulic fluid to flow into the second chamber of the first hydraulic actuator from the supply line.

15. The method as recited in claim 9 further comprising activating the second valve assembly to cause hydraulic fluid to drain from the fourth chamber of the second hydraulic actuator into the tank return line.

16. The method as recited in claim 9 further comprising conveying an amount of hydraulic fluid, that is drained from the first hydraulic actuator, into the tank return line.

17. In a machine having a boom, that is moved by a first hydraulic actuator, and a load carrier, that is coupled to the boom and moved with respect thereto by a second hydraulic actuator;

a method for moving the boom comprising;

when pressurized fluid from a source is not available draining hydraulic fluid under pressure from the first hydraulic actuator;

when pressurized fluid from the source is not available, conveying the hydraulic fluid from the first hydraulic actuator to the second hydraulic actuator;

sensing inclination of the load carrier with respect to a given axis; and

controlling flow of the hydraulic fluid into the second hydraulic actuator to produce movement of the load carrier which maintains the inclination of the load carrier with respect to the given axis substantially constant.

18. The method as recited in claim 17 wherein controlling flow of the hydraulic fluid comprises:

sensing a first pressure of the fluid draining from the first hydraulic actuator;

sensing a second pressure of fluid in the second hydraulic actuator; and

enabling the hydraulic fluid to enter the second hydraulic actuator further in response to the first pressure being greater than the second pressure.