Braking system for a lift truck

• US 20060273656A1
• Filed: 03/07/2006
• Published: 12/07/2006
• Est. Priority Date: 03/07/2005
• Status: Active Grant

• Current Assignee: Crown Equipment Corporation
• Original Assignee: Crown Equipment Corporation
• Inventors: Sherman, Daniel L., Hammer, Joe K.
• Granted Patent: US 7,681,963 B2
• Time in Patent Office: Days
• US Class Current: 303/89
• CPC Class Codes: B60T 13/04 by spring or weight fluid released B60T13/10
• CPC Class Codes: B60T 13/662 characterised by specified functions of the control system components
• CPC Class Codes: B60T 13/74 with electrical assistance or drive
• CPC Class Codes: B60T 13/746 and mechanical transmission of the braking action
• CPC Class Codes: B66F 9/07509 Braking

Abstract

A braking system for a lift truck performs all service braking using truck traction drive motors. Mechanical, spring applied, electrically released brakes are coupled to wheels on opposite sides of the truck with the mechanical brakes applying unequal braking forces to the wheels. The mechanical brakes perform park braking and, in the event an electrical system problem arises, backup braking as well that can be modulated by an operator of the truck regardless of the operating condition of the truck.

Claims

1. A lift truck comprising:

a first wheel located on a first side of said truck;

a second wheel located on a second side of said truck opposite from said first side;

a first brake associated with said first wheel;

a second brake associated with said second wheel;

wherein said first brake applies a first braking force to immobilize said truck; and

said second brake applies a second braking force to immobilize said truck, said first braking force and said second braking force being unequal to one another.

2. A lift truck as claimed in claim 1 further comprising an operator controlled service brake request device for controlling said first and second brakes in the event of a failure in a control system for said first and second brakes

3. A lift truck as claimed in claim 1 wherein said unequal first and second braking forces are divided in accordance with vehicle geometry to reduce truck skewing.

4. A lift truck as claimed in claim 3 wherein said unequal first and second braking forces are divided so that the braking force applied to one side of the truck is equal to X% of the total combined braking force of the first and second brakes and the braking force applied to the other side of the truck is equal to Y% of the total combined braking force of the first and second brakes so that X%+Y%=100%.

5. A lift truck as claimed in claim 3 wherein said braking forces are fractionally divided so that the braking force applied to one side of the truck is equal to a fraction X of the total combined braking force of the first and second brakes and the braking force applied to the other side of the truck is equal to a fraction Y of the total combined braking force of the first and second brakes so that X+Y=1.

6. A lift truck as claimed in claim 3 wherein said braking forces are fractionally divided so that braking forces applied to one side of the truck is equal to ⅓

of the total combined braking force of the first and second brakes and the braking force applied to the other side of the truck is equal to ⅔

of the total combined braking force of the first and second brakes.

7. A lift truck as claimed in claim 1 further comprising:

at least one drive motor for driving said first wheel and said second wheel;

at least one traction motor controller connected for controlling said at least one drive motor for both moving said truck and for braking said truck, said traction motor controller controlling said at least one drive motor to provide service braking for said truck;

said first brake comprising a first mechanical brake coupled to said first wheel to provide a first fractional portion of mechanical braking for park braking said truck;

said second brake comprising a second mechanical brake coupled to said second wheel to provide a second fractional portion of mechanical braking for park braking said truck, said first and second fractional portions complementing each other to provide total park braking for said truck; and

a brake logic control module for controlling said first and second mechanical brakes regardless of the operating status of said truck.

8. A lift truck as claimed in claim 7 further comprising:

a first drive motor for driving said first wheel;

a second drive motor for driving said second wheel; and

wherein said at least one traction motor controller is connected for controlling said first and second drive motors for both moving said truck and for braking said truck, said at least one traction motor controller controlling said first and second drive motors to provide service braking for said truck.

9. A lift truck as claimed in claim 7 wherein said brake logic control module operates said first mechanical brake upon failure to receive a traction control brake release enable signal.

10. A lift truck as claimed in claim 1 further comprising a mast assembly along which forks are raised and lowered, a mast height sensor and a brake control which releases said first and second brakes in response to first and second brake release signals, respectively, said brake control operating said first brake if either one of said first and second brake release signals is not received and said mast assembly is not above a staging height.

11. A lift truck as claimed in claim 10 further comprising an operator service braking control, said brake control also operating said second brake upon any request for service braking.

12. A lift truck as claimed in claim 11 wherein said brake control does not operate either of said first and second brakes if said mast assembly is above staging height.

13. A lift truck as claimed in claim 1 wherein said lift truck further comprises a mast assembly along which forks are raised and lowered, a mast height sensor, and a brake control which operates both said first and second brakes after expiration of a predetermined time period after either one of first and second brake release signals is not received and said mast assembly is not above a staging height.

14. A lift truck as claimed in claim 13 wherein said brake control does not operate either of said first and second brakes if said mast assembly is above staging height.

15. A lift truck as claimed in claim 1 wherein said lift truck further comprises an operator controlled service brake request device, a mast assembly along which forks are raised and lowered, a mast height sensor, and a brake control which applies said first and second brakes if truck deceleration is below a given percentage of a requested deceleration rate, said mast assembly is not above a staging height and said service brake request device is activated to a predefined percentage of maximum braking.

16. A lift truck as claimed in claim 1 wherein said lift truck further comprises an operator controlled accelerator which can be used to command acceleration and inversion service braking, a mast assembly along which forks are raised and lowered, a mast height sensor, and a brake control which applies said first and second brakes if truck deceleration is below a given percentage of a requested deceleration rate, said mast assembly is not above a staging height and said accelerator is activated to command maximum inversion braking.

17. A lift truck as claimed in claim 1 wherein said lift truck further comprises means for monitoring truck speed, a mast assembly along which forks are raised and lowered, a mast height sensor, and a brake control which applies at least said first brake if truck speed is above a requested speed by a predetermined amount, said mast assembly is not above a staging height and a service brake request device is activated to a predefined percentage of maximum braking.

18. A method for operating a lift truck having first and second wheels located on first and second sides of said truck, respectively, a first brake associated with said first wheel, a second brake associated with said second wheel, an operator controlled service brake request device, a mast assembly along which forks are raised and lowered, and a mast height sensor, said method comprising:

applying a first braking force with said first brake to immobilize said truck; and

applying a second braking force with said second brake to immobilize said truck, said first braking force being unequal to said second braking force.

19. A method as claimed in claim 18 further comprising generating first and second brake release signals to release said first and second brakes, respectively, when said truck is to be operated.

20. A method as claimed in claim 19 further comprising:

monitoring said first and second brake release signals; and

reapplying said first braking force in response to failure to receive either said first or said second brake release signals and said mast assembly being below a staging height.

21. A method as claimed in claim 20 further comprising:

monitoring said service brake request device; and

reapplying said second braking force in response to a request for service braking.

22. A method as claimed in claim 21 further comprising:

timing a period from initial failure to receive either said first or said second brake release signals; and

maintaining application of said first brake and applying said second brake upon expiration of a predefined period of time from failure to receive either said first or said second brake release signals.

23. A method as claimed in claim 22 comprising:

setting said first braking force to ⅓

of the total braking force applied by said first and second brakes; and

setting said second braking force to ⅔

of the total braking force applied by said first and second brakes.

24. A method as claimed in claim 19 further comprising:

applying said first and second brakes if truck deceleration is below a given percentage of a requested deceleration rate, said mast assembly is not above a staging height and said service brake request device is activated to a predefined percentage of maximum braking.

25. A method as claimed in claim 19 wherein said lift truck further comprises an operator controlled accelerator which can be used to command acceleration and inversion service braking, said method further comprising:

applying said first and second brakes if truck deceleration is below a given percentage of a requested deceleration rate, said mast assembly is not above a staging height and said accelerator is activated to command maximum inversion braking.

26. A method as claimed in claim 19 wherein said lift truck further comprises means for monitoring truck speed, said method further comprising:

applying at least said first brake if truck speed is above a requested speed by a predetermined amount, said mast assembly is not above a staging height and said service brake request device is activated to a predefined percentage of maximum braking.