Electrical braking system for electric motor-driven vehicles

Claim 2

An electrical braking system for a vehicle driven by an electric motor having a field winding arranged so that said vehicle is driven in a direction in accordance with the direction of direct current flowing through said field winding, said system adapted to be carried by a said vehicle and comprising: a movable brake member adapted to be mounted to a said vehicle for movement between a normal first position and a second position; means for varying the amount of direct current applied to said field winding in dependence upon the relative position of said brake member between said first and second positions; means for sensing whether said vehicle is traveling either in first or second opposite directions; and, current direction control means controlling the direction of said direct current through said field winding so as to flow in a direction opposite to that for driving said vehicle in the sensed direction, whereby said electrical motor is electrically braked to retard motion of said vehicle in said sensed direction substantially in proportion to said relative position of said brake member.

Claim 3

An electrical braking system as set forth in claim 1, wherein said current varying means includes a potentiometer having a wiper arm mechanically coupled to said brake member for movement therewith.

Claim 4

An electrical braking system as set forth in claim 2, including: first actuatable switching means having a normal first condition wherein said potentiometer is deactivated and a second condition wherein said potentiometer is activated; and, switch control means for, upon energization, actuating said first actuatable switching means to said second condition.

Claim 5

An electrical braking system as set forth in claim 3, including limit switch means having a normal first condition and a second condition, when said brake member is moved from its normal first position toward said second position, for energizing said control means.

Claim 6

An electrical braking system as set forth in claim 1, including actuatable switching means having a normal first condition for activating said current direction control means and a second condition for deactivating said current direction control means; and, switch control means for, upon energization, actuating said actuatable switching means to said second condition.

Claim 7

An electrical braking system as set forth in claim 5, including circuit means for energizing said switch control means only upon the concurrent conditions that said vehicle is not moving and said brake member is displaced from its first position toward said second position, whereupon said current direction control means becomes deactivated.

Claim 8

An electrical braking system as set forth in claim 6, including mechanical brake control means for, upon energization of said switch control means, controlling mechanical braking means to mEchanically brake said vehicle.

Claim 9

An electrical braking system as set forth in claim 1, including switching means operated by said brake member for controlling mechanical braking means to mechanically brake said vehicle when said brake member is displaced to its second position.

Claim 10

An electrical braking system as set forth in claim 1, wherein said current direction control means includes a forward control circuit having first field current control means for, upon energization, controlling the direction of direct current flow in a forward direction through said field winding; and, a reverse control circuit having a second field current control means for, upon energization, controlling the direction of said current flow in a reverse direction through said field winding.

Claim 11

An electrical braking system as set forth in claim 9, wherein said forward control circuit includes first circuit means for energizing said first field current control means when said vehicle is traveling in said second direction and said reverse control circuit includes second circuit means for energizing said second field current control means when said vehicle is traveling in said first direction.

Claim 12

An electrical braking system for a vehicle driven by an electric motor having a field winding arranged so that said motor may be driven in one of two opposite directions in accordance with the direction of direct current pulses flowing through said winding and at a velocity substantially proportional to the frequency of said pulses applied to said winding under the control of a pulse control circuit for changing said pulse frequency in dependence upon the value of a resistor coupled to an input of said circuit, said braking system adapted to be carried by said vehicle and comprising: a variable resistor adapted to be coupled between a direct current voltage source and said circuit input for varying said pulse frequency; a movable brake member adapted to be mounted to said vehicle for movement between a normal first position and a second position, said brake member being coupled to said variable resistor for changing the resistance thereof in accordance with the relative position of said member as it is being displaced from said first position to said second position and thereby vary said pulse frequency; means for sensing whether said vehicle is traveling in either first or second opposite directions; and, current direction control means controlled by said sensing means for controlling the direction of said current pulses through said field winding so as to flow in a direction opposite to that for driving said vehicle in said sensed direction, whereby said electric motor is electrically braked to retard motion of said vehicle in said sensed direction in accordance with said relative position of said brake member.

Claim 13

An electrical braking system for a vehicle driven by an electric motor having a field winding arranged so that said motor may be driven in one of two opposite directions in accordance with the direction of direct current pulses flowing through said winding and at a velocity substantially proportional to the frequency of said pulses applied to said winding under the control of a pulse control circuit for changing said pulse frequency in dependence upon the value of a resistor coupled to an input of said circuit, said braking system adapted to be carried by said vehicle and comprising: a variable resistor adapted to be coupled between a direct current voltage source and said circuit input for varying said pulse frequency; a movable brake member adapted to be mounted to said vehicle for movement between a normal first position and a second position, said brake member being coupled to said variable resistor for changing the resistance thereof in accordance with the relative position of said member as it is being displaced from said first position to said second position and thereby vary said pulse frequency; means for sensing whether said vehicle is traveling in either first or second opposite directions; and, current direction control means controlled by said sensing means for controlling the direction of said current pulses through said field winding so as to flow in a direction opposite to that for driving said vehicle in said sensed direction, whereby said electric motor is electrically braked to retard motion of said vehicle in said sensed direction in accordance with said relative position of said brake member.

Claim 14

An electrical braking system as set forth in claim 11, including pulse stretcher means for increasing the pulse width of said current pulses applied to said field winding to obtain greater electrical braking forces for a given pulse frequency.

Claim 15

An electrical braking system as set forth in claim 12, including actuatable switching means having a normal first condition wherein said pulse stretcher means is deactivated and a second condition wherein said pulse stretcher means is activated; and switch control means for, upon energization, actuating said actuatable switching means to said second condition.

Claim 16

An electrical braking system as set forth in claim 13, including limit switch means having a normal first condition and a second condition, when said brake member is moved from its normal first position toward said second position, for energizing said switch control means and, hence, activating said pulse stretcher means.

Claim 17

An electrical braking system as set forth in claim 11, wherein said variable resistor has a wiper arm coupled to said brake member for movement therewith to vary the resistance of said variable resistor.

Claim 18

In an order picker vehicle driven by a direct current operated electric motor having a field winding, said vehicle having a lift vertically movable between lower and upper positions, said lift having means for supporting an operator together with manually operable controls for controlling lift height and vehicle speed, the improvement for electrically braking said vehicle comprising: a manually movable brake member mounted to said lift for movement relative to said lift between a normal first position and a second position; means for varying the amount of direct current applied to said field winding in dependence upon the relative position of said brake member between said first and second positions; vehicle direction sensing means for sensing whether said vehicle is traveling in a forward or reverse direction; and, motor current control circuit means controlled by said direction sensing means for reversing the direction of direct current flowing through said field winding to dynamically brake said motor and thereby retard motion of said vehicle in said sensed direction with a braking force dependent on the relative position of said brake member between its said first and second positions.

Claim 19

In an order picker vehicle driven by a direct current operated electric motor having a field winding, said vehicle having a lift vertically movable between lower and upper positions, said lift having means for supporting an operator together with manually operable controls for controlling lift height and vehicle speed, the improvement for electrically braking said vehicle comprising: a manually movable brake member mounted to said lift for movement relative to said lift between a normal first position and a second position; means for varying the amount of direct current applied to said field winding in dependence upon the relative position of said brake member between said first and second positions; vehicle direction sensing means for sensing whether said vehicle is traveling in a forward or reverse direction; and, motor current control circuit means controlled by said direction sensing means for reversing the direction of direct current flowing through said field winding to dynamically brake said motor and thereby retard motion of said vehicle in said sensed direction with a braking force dependent on the relative position of said brake member between its said first and second positions.

Claim 20

In an order picker vehicle as set forth in claim 16, wherein said current varying means includes a variable resistor having a wiper arm coupled to said brake member for movement therewith.

Claim 21

In an order picker vehicle as set forth in claim 16, including first limit switch means mounted to said lift so as to be actuated by said brake member only when said brake member is displaced from its first position toward said second position, and circuit control means for deactivating said motor current control circuit means only upon the concurrent conditions that said first limit switch means is actuated and said vehicle is stationary.

Claim 22

In an order picker vehicle as set forth in claim 16, wherein said vehicle has actuatable mechanical braking means and said improvement further includes: second limit switch means mounted to said lift so as to be actuated when said brake member is displaced to its second position for, in turn, actuating said mechanical braking means.