GB2155321A - Improvements in and relating to castors - Google Patents

Abstract

A castor having an auxiliary brake member (14) mounted on a swivelling part (1) of the castor, a main brake (13) and the auxiliary brake member (14) being arranged to engage the peripheral surface of the tyre (15) of the castor wheel (9) when a brake pedal (6) is actuated both said brakes (13,14) thereby maintaining engagement with the tyre (15) to resist the rolling rotation of the castor wheel (9) in either direction. The auxiliary brake member may be a sprag (14). <IMAGE>

Description

SPECIFICATION Improvements in and relating to castors The present invention relates to castors of the type in which the wheel is mounted for swivelling movement about an axis normal to but laterally offset from the axis of rolling rotation, and wherein a main brake mounted on a swivelling part of the castor is applied as a result of movement of a wheel carrier part of the castor serving as a pedal, the carrier part and the swivelling part being pivotally connected to one another and the tyre of the wheel and the main brake being maintained in engagement with one another as a direct result of the over centre action of the pivoting wheel carrier thereby restraining rolling rotation of the wheel. In this type of castor the geometry of the castor in the braked position eliminates (1) the offset of the wheel relative to the vertical axis (2) any bending stress and (3) horizontal movement.

According to the present invention there is provided a castor of the type set forth wherein an auxiliary brake member is mounted on the swivelling part of the castor, the said brake and the auxiliary brake member being arranged to engage the peripheral surface of the tyre of the wheel when the brake pedal is actuated both said brakes thereby maintaining engagement with the tyre to resist the rolling rotation of the wheel in either direction.

The invention will now be described by way of example only with reference to the figures of the accompanying drawings in which: Figure 1 is a side elevation partly in section of a castor of the invention with the brake pedal down and the wheel braked; Figure 2 is a side elevation of the castor of Figure 1 with the pedal up and the brake removed; Figures 3A 3B & 3C respectively are a section on section station AA, a part section on section station BB of Figure 1 and a scrap plan.

The wheeled castor comprises a swivelling fork shown generally at 1 of inverted U-shape having legs 2122 depending from a connecting bridge 3. A bearing assembly shown generally at 4 in the form of a double ball race is located on the said bridge 3 to permit swivelling rotation of the fork 1 about the vertical axis Vj Vii of a stem 5 with a detent pin 52.

A wheel carrier shown generally at 6 serves also as a brake pedal, it comprises a pair of spaced legs 6 62 mounted on a main axle 8 in a sleeve 82 of a castor wheel 9, that rotates about said axle 8 on axis A1A2 and between the legs 2 and 22, that are coupled together at the ends remote from the axle 8 by a cross member 10 in the form of a pin to be engaged by the foot of a user to apply the said brake and put the castor (Figure 1) into the braked condition. A securing nut 83 is on a threaded one end of axle 8 as shown in Figure 3A.The wheel carrier brake pedal 6 is pivotably connected to swivelling fork 1 by means of the legs 2122 and a two part pivot pin 121 122 such that the wheel carrier 6 and fork 1 can pivot relatively to one another about an axis B1 B2 parallel to the axis A1 A2 of axis 8, i.e. the rolling axis A1 A2 of the wheel 9 of the castor.

A braking rod 13 constitutes the brake of the castor and it extends between the depending legs 2, 22 of fork 1, the braking rod 13 being parallel to the axle 8 and being located above the outer peripheral surface of the wheel 9. The braking rod 13 is the main brake and is provided with a central knurled portion 132 serving as a frictional braking surface. An auxiliary brake member in the form of a sprag 14 (Figure 3B) is rigidly mounted on the braking rod 13 adjacent the inner surface of one of the depending legs 21 of fork 1. The sprag 14 is rigidly trapped between a shoulder of the braking rod 13 and the inside surface of one of the legs 21 the sprag 14 having a curved portion 142 extending inwardly to a free edge 143 arranged to contact the tyre 15 of the wheel 9 at an acute angle of incidence a see Figure 3C; the tyre 15 being of resilient material, e.,g. polyurethane elastomer.

A locking plate 161 is provided to hold the wheel axle 8 in the 'brake on' position relative to the fork 1. This plate 16 is riveted to the leg 22 of fork 1 and is provided with an aperture 162 to receive the pivot pin 122. The locking plate 16 is of shallow dish formation the outline of which is clearly seen in Figure 1 it has a frusto-conical recess 163 resiliently to engage the domed head 84 of the wheel axle 8 which frusto-conical recess 163 is on the line Vi Vii.

In the normal rolling position of the castor, the axle 8 is offset (distance e1) from the swivelling axis Vi Vii of the stem 5 and the wheel 9 is out of contact with both braking elements viz the brake 13 and sprag 14 and a stop 63 abuts with the leg 2, as shown in Figure 2.

On depression of the wheel carrier brake pedal 6, wheel axel 8 is moved clockwise in the sense illustrated in Figure 1 so that the offset e, between the swivel Vi Vlj and rolling axis AlA2 is substantially eliminated and the swivelling axis Vi V, substantially aligns with point AX on the rolling axis A,A2.

During this pedal depression, the wheel tyre 15 progressively approaches and makes contact with the knurled portion 133 of the main braking element 13 and finally bears against it at some 15 short of the vertical. At this position, the outer edge 143 of the sprag 14 presses into the periphery of the tyre 15 and the domed head 82 of axle 8 snap engages in the frusto-conical recess 163 formed in the locking plate 16, so that the wheel 9 is located in the correct braking position relative to the fork 1 and the two braking elements the main 13 and the auxiliary 14 cannot now accidentally be dislodged therefrom without positive upward movement of the wheel carrier brake pedal 6.The locking plate 16 is of spring steel or other material having similar properties to ensure it can snap on to the domed head 82 of axle 8 thereby retaining it in the correct braking position, and also allowing it to be disengaged when required by the application of firm pressure to the brake pedal 6.

It should be noted that the rolling rotation of the castor which involves clockwise rotation of the wheel 9, tends to increase the braking force of the wheel 9 against the braking surface 132 of the brak ing rod 13. However, counter clockwise rotation under certain circumstances can tend to decrease the braking force attributed to the said brake by moving the wheel 9 away from the braking surface and in order to enhance the overall braking effect the edge 142 of the sprag 14 digs into the outer peripheral side surface of the tyre 15 of the wheel 9, thereby ensuring that the wheel is effectively braked under all circumstances when required by virtue of the auxiliary brake member viz the sprag 14.

Claims (4)

1. A castor of the type set forth wherein an auxiliary brake member is mounted on the swivelling part of the castor, the said brake and the auxiliary brake member being arranged to engage the peripheral surface of the tyre of the wheel when the brake pedal is actuated both said brakes thereby maintaining engagement with the tyre to resist the rolling rotation of the wheel in either direction.

2. The castor as claimed in Claim 1 wherein the auxiliary brake member is a sprag.

3. The castor as claimed in Claim 2 wherein the sprag is arranged to contact the tyre at an acute angle of incidence.

4. A castor constructed and arranged substantially as hereinbefore described and as shown in the figures of the accompanying drawings.