Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
1998-09-23
2001-05-22
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S050000, C701S065000, C701S066000, C701S071000, C701S072000, C701S001000
Reexamination Certificate
active
06236927
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to materials handling vehicles and, more particularly, to methods and apparatus for braking such vehicles. While the present invention is generally applicable to materials handling vehicles, it will be described herein with reference to a rider reach fork lift truck for which it is particularly applicable and for which it is initially being utilized.
Braking of fork lift trucks may be accomplished through the use of a mechanical brake, such as disclosed in U.S. Pat. No. 5,057,728, which is incorporated herein by reference, or by using the dynamic braking characteristics of the electric traction motor, such as disclosed in U.S. Pat. No. 5,340,202, which is incorporated herein by reference.
The brake shown in the '728 patent is a three-step brake; that is, the brake is capable of providing three levels of braking force, depending upon braking requirements. Of course, mechanical brakes are subject to wear; therefore, to reduce wear, and since regenerative braking using the traction motor conserves battery charge, it is desirable to use the electric motor for as much of the braking requirements as possible. On a rider reach fork lift truck, a single, electrically powered and steerable drive wheel is mounted on one corner of the power unit of the truck, and a caster wheel is mounted on the other corner. For some trucks, the caster wheel is also provided with a brake or a caster brake.
Thus, while motor braking and mechanical braking of the drive wheel and, in some applications also mechanical braking of the caster wheel, are known for materials handling vehicles, there is an ongoing need to improve the methods and apparatus which operate and coordinate these braking systems for improved braking performance. Such improvements would better adapt braking performance for known operating conditions of travel direction and allowable travel speed/fork height, distribute braking requirements between mechanical braking and regenerative braking associated with the steerable drive wheel, use regenerative braking as much as possible, and engage the brake on the caster wheel in proper proportion to the brake on the drive wheel. Preferably, the improved braking control would be computer controlled and hence be easily adaptable in the field and also enable simplified manufacturing of materials handling vehicles utilizing the improved braking control.
SUMMARY OF THE INVENTION
This need is met by the invention of the present application wherein a computer controlled braking system utilizes the gross vehicle weight of a materials handling vehicle and maximum allowable speeds of the vehicle to calculate braking force for the vehicle. The maximum allowable speed is determined based on the direction of travel of the vehicle: forward, i.e., forks forward; and, reverse, i.e., power unit forward, and the height of load carrying forks of the vehicle. For vehicles equipped with a caster brake, the calculated braking force is proportionally and programmably distributed between a drive brake and the caster brake. The drive brake includes a mechanical brake, which is used for braking the vehicle when moving and also holding the vehicle when parked, and motor braking which is performed by a traction motor which drives the drive wheel. The drive brake force, either the total calculated braking force or the drive brake portion of the calculated braking force if a caster brake is provided, is divided between the mechanical brake and the motor braking so that the motor provides as much braking as is possible to reduce wear on the mechanical brake and also to conserve battery power.
For vehicles equipped with a caster brake, the caster brake portion of the calculated braking force is determined as a percentage or proportion of the total braking force. The percentage is programmable and can differ dependent upon the direction of travel of the vehicle. The caster brake portion is reduced to zero or clipped and reverts to the drive brake if it is below a minimum caster brake force. In a similar manner, if the caster brake force is calculated to be greater than a maximum caster brake force, the caster brake force in excess of the maximum caster brake force is clipped and reverts to the drive brake. A maximum caster brake current can be set to accommodate different brake hardware. A user of the vehicle can select adjustments to the calculated drive brake force and, if provided, can also select independent adjustments to the calculated caster brake force.
In accordance with one aspect of the present invention, a method for braking a materials handling vehicle comprises setting a gross vehicle weight for the vehicle, determining a maximum allowable speed for the vehicle, detecting a service brake request and, upon receiving a service brake request, calculating braking force for the vehicle in response to the gross vehicle weight and the maximum allowable speed. The calculated braking force may then be converted into braking control actions. The step of determining a maximum allowable speed for the materials handling vehicle may comprise the steps of determining a height of materials handling forks of the vehicle, and correlating a maximum allowable vehicle speed with the height of materials handling forks of the vehicle. The step of determining a maximum allowable speed for the materials handling vehicle may further comprise determining a direction of travel of the materials handling vehicle, and correlating the maximum allowable vehicle speed with the direction of travel of the vehicle.
The step of calculating braking force may comprise the steps of setting braking force for a materials handling vehicle equal to the gross vehicle weight multiplied by 0.03 times the maximum allowable speed for the materials handling vehicle, and solving the resulting equation. To optimize brake performance for the particular floor conditions, the method may further comprise determining a user adjustment setting for the braking force, and adjusting the braking force with the user adjustment setting.
Preferably, the materials handling vehicle has a drive wheel driven by a traction motor and a mechanical brake associated with the drive wheel, and the braking force is then divided between the two by determining a portion of the braking force to be performed by the mechanical brake, and a portion of the braking force to be performed by operation of the traction motor. The step of determining a portion of the braking force to be performed by operation of the traction motor may comprise subtracting the portion of the braking force to be performed by the mechanical brake and a rolling resistance of the vehicle from the braking force. In that event, if the result of subtracting the braking force to be performed by the mechanical brake and the rolling resistance of the vehicle from the braking force is less than zero, the portion of the braking force to be performed by operation of the traction motor is set to zero.
If the vehicle has a caster brake in addition to a drive brake, the method may comprise determining a caster brake portion of the braking force, and a drive brake portion of the braking force. The step of determining a caster brake portion of the braking force preferably comprises taking a percentage of the braking force as the caster brake portion of the braking force. The method may further comprise taking a first percentage of the braking force as the caster brake portion for vehicle travel in a first direction, and taking a second percentage of the braking force as the caster brake portion for vehicle travel in a second direction opposite to the first direction. The method may further comprise determining a user adjustment setting for the caster brake portion, and adjusting the caster brake portion in accordance with the user adjustment setting. Also, the method may further comprise determining a user adjustment setting for the drive brake portion, and adjusting the drive brake portion in accordance with the user adjustment setting. Preferably, separate and in
Crown Equipment Corporation
Cuchlinski Jr. William A.
King and Schickli PLLC
Mancho Ronnie
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