Brake mechanism

Abstract: A brake mechanism for a wheeled unit comprises a brake rod (13) moveable longitudinally in a wheel mounting (14) and a brake handle mounting (15) one end (16) of which brake rod (13) is adapted to engage the periphery of the wheel (17) and a brake handle (18) adapted to move between a release position and a braked position, a first compression spring (25) between the brake handle (18) and a first abutment (26) on the brake rod (13) , whereby initial movement of the brake handle (18) from the release position moves the brake rod (13) into engagement with the wheel (17), whilst continued movement of the brake handle towards the braked position compresses the first compression spring (25) to load the brake rod (13) against the wheel (17), means on the brake handle mounting for releasably retaining the brake handle (18) in the braked position, and a second compression spring (27) between the wheel mounting and a second abutment (28) on the brake rod (13) and having a lesser rating than the first compression spring (25), whereby the brake rod (13) is moved out of engagement with the wheel (17) when the brake handle (18) is released from the braked position and is moved back into the release position.

Description: This invention relates to brake mechanisms for wheeled units, such a trollies, rollpallets and the like, and particularly but not exclusively to parking brakes for such units. Parking brakes are required to restrain units during loading or unloading or whilst the unit is parked, i.e., within a vehicle. Previously braking has been achieved by fitting foot operated brakes to swivel castors or by incorporating a mechanism into the structure of the wheeled unit to provide brake operation by means of a hand brake. Frequent adjustment of these systems is necessary to allow for tyre wear or brake pad wear which is often difficult and/or costly to effect. In many instances the responsibility is on the operator of the wheeled unit to identify that the brakes are ineffective and notify maintenance engineers, but in practice, wheeled units continue to be used with ineffective brakes increasing the risk of serious accidents. GB-A-1 382 806 discloses a brake mechanism for a wheeled unit comprising a brake rod movable longitudinally in a wheel mounting and a brake handle mounting, one end of which brake rod is adapted to engage the periphery of the wheel; a brake handle adapted to move between a release position and a braked position; and means on the brake handle mounting for releasably retaining the brake handle in the braked position; the mechanism being further provided with a compression spring between the brake handle and an abutment on the brake rod, whereby initial movement of the brake handle from the release position moves the brake rod into engagement with the wheel. The wheel in GB-A-1 382 806 is provided with an axially directed flange having a series of radially directed holes into any one of which the end of the brake rod may enter, to stop rotation of the wheel, when the compression spring urges the end of the brake rod towards the flange upon movement of the brake handle from the release position. WO-A-84/03073 discloses a braking mechanism that operates on the principle of applying a brake shoe, in the form of a disc, against the periphery of a wheel. The wheels, in order to be durable, have been made of relatively hard materials, such as nylon or polyurethane, and the forces on the brake shoe need to be high to ensure effective braking. Thus, mechanisms to apply these forces are therefore complex or resultant wear either in the mechanism or in the tyre or brake pad can render the brake ineffective. In fact quite a low degree of wear will result in considerable loss of brake power. Recently wheels have been provided with tyres of a new high performance resilient rubber which whilst softer than conventional tyres are tougher and very durable. Consequently the softness of the tyre permits much lower brake forces. According to the present invention, a brake mechanism for a wheeled unit comprises a brake rod movable longitudinally in a wheel mounting and a brake handle mounting, one end of which brake rod is adapted to engage the periphery of the wheel; a brake handle adapted to move between a release position and a braked position; and means on the brake handle mounting for releasably retaining the brake handle in the braked position; the mechanism being further provided with a compression spring between the brake handle and a abutment on the brake rod, whereby initial movement of the brake handle from the release position moves the brake rod into engagement with the wheel; characterised in that continued movement of the brake handle towards the braked position compresses the compression spring to load the brake rod against the wheel; and in that a second compression spring is provided between the wheel mounting and a second abutment on the brake rod and having a lesser rating than the first compression spring, whereby the brake rod is moved out of engagement with the wheel when the brake handle is released from the braked position and is moved back into the release position. The invention further includes a wheeled unit according to claim 6. The retaining means on the brake handle mounting may be provided by means of a block having a longitudinal slot therein, into which the brake handle projects, the slot, defining the movement of the handle between the release position and the braked position, being provided at one end with a lateral recess to hold the brake handle in the locked position. A further lateral recess is preferably provided at the other end of the slot to hold the brake handle in the release position. The block is conveniently provided with a guide bore intersecting the slot substantially at right angles to that portion of the brake handle which projects into the slot, said bore slidably receiving a sleeve that is slidable on the brake rod between the first compression spring and the brake handle. The abutments on the brake rod are conveniently provided by washers welded in the rod. It can be seen that the invention ensures that the braking forces are applied via the compression springs and that there is no rigid direct linkage between the handle and the wheel. It is a further advantage that wear on the wheels does not diminish the effectiveness of the brake. Conveniently on a wheeled unit a pair of brake mechanisms are provided one on each of a pair of wheels, which mechanisms are preferably connected by a common handle. The brake handle may act upon the brake rod directly, or through the sleeve, but preferably is connected by means of a linkage to a brake bar which acts upon the brake rod or sleeve. The invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is a perspective of a wheeled unit having a pair of brake mechanisms in accordance with the invention; Figure 2 is an exploded perspective of one brake mechanism in its release position in accordance with the invention; Figure 3 corresponds to Figure 2 but shows the other brake mechanism of Figure 1 in partial engagement; Figure 4 is a fragmentary side elevation of the brake mechanism of Figure 2 in its release position; Figure 5 corresponds to Figure 4 but shows the brake mechanism in its braked position; Figure 6 is a sectional side elevation of the linkage between the handle and the brake rod, of Figure 1, in its release position; Figure 7 corresponds to Figure 6 but shows the handle intermediate its release and braking position; and Figure 8 corresponds to Figure 6 but shows the handle in its braking position. In Figure 1 a wheeled unit (10) is provided with a pair of brake mechanisms (11) and (12) each comprising a brake rod (13) movable longitudinally in a wheel mounting (14) and a brake-handle mounting (15), one end (16) of the brake rod (13) being adapted to engage the periphery of a wheel (17). Referring to Figures 2 to 5 a brake handle (18) projects into a slot (19) in a block (20), the slot having an upper lateral recess (21) to hold the handle in its released position (see particularly figures 2 and 4) and a lower lateral recess (22) to hold the handle in its braked position (see particularly Figures 3 and 5), the block has a guide bore (23) intersecting the slot (19) and slidably receives a sleeve (24) slidable on the brake rod (13) between a first compression spring (25) and the handle, which spring abuts a first abutment (26) on the brake rod (13) whereby initial movement of the brake handle (18) from the release position moves the brake rod (13) into engagement with the wheel, whilst continued movement of the brake handle (18) towards the braked position compresses the first compression spring (25) to load the brake rod (13) against the wheel. A second compression spring (27) is provided between the wheel mounting (14) and a second abutment (28) on the rod (13) whereby the brake rod is moved out of engagement with the wheel (17) when the brake handle is released from the braked position and is moved back into the release position. Thus, in Figures 2 to 5 it can be seen that by releasing the handle (18) from the upper lateral recess (21) and urging it down onto the sleeve (24) against the first spring (25) forces the brake rod (13) onto the wheel (17) thereby creating effective braking of the unit. During use the wheel may become greatly worn but the mechanism remains effective even after the wheel (17) is worn to the level shown by the line (29) in Figure 5. In Figures 6 to 8 the handle (18X) is connected by means of a linkage (30) to a brake bar (31) which acts upon the sleeve (24) to activate the brake. Detent means (32) are provided to lock the brake on, as an alternative, or in addition to the recesses in the block.

Claims: A brake mechanism for a wheeled unit comprising: a brake rod (13) moveable longitudinally in a wheel mounting (14) and a brake handle mounting (15), one end (16) of which brake rod (13) is adapted to engage the periphery of the wheel; (17) a brake handle (18) adapted to move between a release position and a braked position; and means on the brake handle mounting for releasably retaining the brake handle (18) in the braked position; the mechanism being further provided with a compression spring (25) between the brake handle (18) and an abutment (26) on the brake rod (13), whereby initial movement of the brake handle (18) from the release position moves the brake rod (13) into engagement with the wheel (17), characterised in that continued movement of the brake handle towards the braked position compresses the compression spring (25) to load the brake rod (13) against the wheel (17), and in that a second compression spring (27) is provided between the wheel mounting and a second abutment (28) on the brake rod (13) having a lesser rating than the first compression spring (25), whereby the brake rod (13) is moved out of engagement with the wheel (17) when the brake handle (18) is released from the braked position and is moved back into the release position. A brake mechanism for a wheeled unit as claimed in Claim 1, characterised in that the retaining means on the brake handle mounting is provided by a block (20) having a longitudinal slot (19) therein, into which the brake handle projects, the slot, defining the movement of the handle between the release position and the braked position, being provided at one end with a lateral recess (21) to hold the brake handle in the locked position. A brake mechanism for a wheeled unit as claimed in Claim 2, characterised in that a further lateral recess (22) is provided at the other end of the slot (19) to hold the brake handle in the release position. A brake mechanism for a wheeled unit as claimed in either of Claims 2 or 3, characterised in that the block is provided with a guide bore (23) intersecting the slot (19) substantially at right angles to that portion of the brake handle which projects into the slot, said bore slidably receiving a sleeve (24) that is slidable on the brake rod between the first compression spring and the brake handle. A brake mechanism for a wheeled unit as claimed in any preceding Claim, characterised in that the abutments (26, 28) on the brake rod (13) are provided by washers welded on the rod. A wheeled unit having at least one brake mechanism comprising: a brake rod (13) moveable longitudinally in a wheel mounting (14) and a brake handle mounting (15), one end (16) of which brake rod (13) is adapted to engage the periphery of the wheel; (17) a brake handle (18) adapted to move between a release position and a braked position; and means on the brake handle mounting for releasably retaining the brake handle (18) in the braked position; the mechanism being further provided with a compression spring (25) between the brake handle (18) and an abutment (26) on the brake rod (13), whereby initial movement of the brake handle (18) from the release position moves the brake rod (13) into engagement with the wheel (17), characterised in that continued movement of the brake handle towards the braked position compresses the compression spring (25) to load the brake rod (13) against the wheel (17), and in that a second compression spring (27) is provided between the wheel mounting and a second abutment (28) on the brake rod (13) having a lesser rating than the first compression spring (25), whereby the brake rod (13) is moved out of engagement with the wheel (17) when the brake handle (18) is released from the braked position and is moved back into the release position. A wheeled unit as claimed in Claim 6, characterised by being provided with a pair of brake mechanisms, one on each of a pair of wheels (17). A wheeled unit as claimed in Claim 7, characterised in that the mechanisms are activated by a common handle (18) acting upon the brake rods (13). A wheeled unit as claimed in Claim 8, characterised in that the handle (18) is connected by means of a linkage (30) to a brake bar (31) which acts upon the brake rods (13).

Inventors: BROWN BARRY, BROWN, BARRY
Applicants: TWIL HANDLING & DISPLAY LTD, TWIL HANDLING & DISPLAY LIMITED
Application year: 1992
Main classification: B62B5
IPC codes: B62B5