IMPROVEMENTS IN OR RELATING TO GRIP WHEELS COMPRISING STRAKES

Abstract: A grip wheel (1) comprising a frame, (6), a plurality of strakes (11) and means for selectively extending and with­ drawing said strakes (11) relative to the edge of the grip wheel frame (6). The means for selectively extending and withdrawing said strakes (11) comprises a central member (13) to which the strakes (11) are rotatably connected. The central member (13) is movable relative to the centre of rotation of the grip wheel frame (6) to provide a centre of rotation of the strakes (11) which is offset from the centre of rotation of the grip wheel frame (6).

Description: IMPROVEMENTS IN OR RELATING TO GRIP WHEELS COMPRISING STRAKES The present invention relates to grip wheels and in particular to grip wheels each comprising a frame, a plurality of strakes and - means for selectively extendSng-or withdrawing said strakes relative to'the edge of the/wneelffiame.. Where vehicles, such as farm tractors, JCB's etc. have to travel over soft slippery surfaces, such as mud, a great deal of the motive power can be lost as a result of slipping of the vehicle drive wheels on the slippery surface. In order to overcome this problem it is known to attach to the vehicle drive wheels grip wheels comprising a plurality of strakes which are disposed around the circumference of the grip wheels and which extend past the outer edge of the vehicle wheels to engage in the soft slippery surface over which the vehicle is travelling, thus increasing the traction of the vehicle over the slippery surface. In its simplest form the grip wheel comprises a plurality of strakes which are rigidly fixed around a wheel which can be attached to the drive wheel of a vehicle. This arrangement has, however, a number of disadvantages, the most significant of which is that the grip wheels must be removed from the vehicle wheels before the vehicle can drive off the soft slippery surface onto a hard surface, like, for example, a road. This obviously wastes a lot of time and means that vehicle downtime can be significant In order to overcome the aforementioned problem of the above type of grip wheel it is known to provide grip wheels in which the strakes cm be withdrawn past the outside edge of the vehicle wheel. The strakes on these grip wheels are pivotally secured to the edge of a circular central member and are extended or withdrawn by inanually rotating the circular member about its centre in one direction or the other. However, the driver still has to leave his cab to adjust the strake positions,thus still wasting time. It is an object of the present invention to provide a grip wheel comprising a plurality of strakes in which the above mentioned problems are obviated or mitigated. According to the present invention there is provided a grip wheel comprising, a frame, a plurality of strakes, means for selectively extending and withdrawing said strakes relative to the edge of the grip wheel frame and means for connecting the grip wheel to a vehicle such that the centre of rotation of the grip wheel frame lies over the centre of rotation of a vehicle axle, charcterised in that said means for selectively extending and withdrawing said strakes comprises a central member to which the strakes are rotatably connected, which central member is movable relative to the centre of rotation of the grip wheel frame to provide a centre of rotation of the strakes which is offset from the centre of rotation of the grip wheel frame. Preferably means are provided for securing the grip wheel to either the wheel or the axle of the vehicle. Preferably where the grip wheel is secured to the wheel of a vehicle the central member is movable in a vertical plane between the top and the bottom of the grip wheel frame, the central member being moved towards the bottom of the grip wheel frame to extend the strakes at least beyond the edge of the vehicle wheel at the bottom there of and moved towards the bp of the grip wheel frame to withdraw the strakes at the bottom thereof to at least the edge of the vehicle wheel. Preferably, where the grip wheel is secured directly to an axle of the vehicle the central member is movable is a vertical plane between the top and bottom of the grip wheel frame the central member being moved towards the bottom of the grip wheel frame to extend the strakes at least beyond the edge of the grip wheel/at the bottom thereof and moved towards the top of the grip wheel frame to withdraw the strakes at the bottom thereof to at least the edge of the grip wheel frame. Preferably where the vehicle runs on the grip wheel the grip wheel frame is provided with a tyre to provide resistance to shock. The central member may be moved by means of a hydraulic piston, a pneumatic piston, an electric motor or any other suitable motive means Preferably means are provided whereby the said motive means is fixed in position relative to the grip wheel frame, for example by a tie rod secured to a stationary tart of the vehicle to which the grip wheel is attached. Preferably the motive means a connected to a motive means operating supply external to the grip wheel by connecting means which connecting means is provided with a swiveling connection mounted at the centre of the grip wheel, to enable the motive means to rotate wit the grip wheel frame in the event of it becoming ed, without damaging the said connecting means. Preferably the tie rod comprises a tube through which the supply ine to the motive means is carrie. Preferably the motive means and the central member are secured to a multi-armed member, the arms of which engage with the grip wheel frame, through rollers, to enable the grip wheel frame to move relative thereto, but to maintain the motive means fixed in position relative to the grip wheel frame. Preferably each strake is connected to a linking member which is rotatably connected to the central member, a knuckle joint being provided between each strake and its respective linking member. Preferably each knuckle joint comprises a shear pin to protect the grip wheel against excessive forces on the strake. Preferably the means for securing the grip wheel to the vehicle wheel or axle comprises a bolt assembly. Preferably each strake is carried in a channel member of the grip wheel frame, in which channel member, it is movable in and out. Preferably means are provided for transmitting torque forces on the strakes away from the central member to the means for connecting the grip wheel to the vehicle wheel. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing in which Fig. 1 shows a front view of a grip wheel embodying the present invention attached to a vehicle wheel; and Fig. 2 shows a section of the grip wheel of Fig. 1 along lines I-I. Referring to Figs. 1 and 2 the grip wheel 1 is attached to the wheel 2 of a vehicle (not shown) by means of bolt assemblies 3. Each bolt assembly 3 comprises a screw shackle 4, into one end of which a bolt 5 engages to secure the said end of the screw shackle 4 to the grip wheel frame 6, and into the other end of which the end 7 of a bolt 8 engages. Before engaging in the screw shackle 4 the bolt 8 passes through a lug on the wheel rim and through the wheel dish which are both secured onto the bolt 8 by means of a nut (not shown). Thus, the grip wheel is attached to the vehicle wheel. To prevent movement of the grip wheel 1 on the ends of the bolts 8 a tensioning plate 9 is provided between the rim 10 of the vehicle wheel hub and the bolt 8. As the screw shackle 4 is screwed onto the bolt 8 the tensioning plate 9 is tightened between the slightly sloping rim 10 and the bolt 8, thus ensuring that forces on the grip wheel 1 are transmitted to the vehicle wheel hub and not to the bolts 8. The bolt assembly 3 provides a particularly advantageous means of securing the grip wheel 1 to the vehicle wheel 2. The length of the end 7 of bolt 8 engaging in the screw shackle 4 can be adjusted according to the different wheel rim widths which my be chosen. This enables different wheel rim widths to be coped with easily, which is of particular importance in agricultural vehicles where the wheel rim width varies for particular types of crops. In addition the grip wheel can easily be secured to existing parts of the vehicles wheel. In the prior art specially provided lugs have to be welded to the vehicle wheel to enable the grip wheel to be attached. Where the distance between the grip wheel and the wheel dish is very great the nut securing the wheel rim and dish together can be replaced by an eye-nut into which a hook at the end of a threaded rod engaging in the screw shackle is hooked. The bolt 8 is replaced by a short bolt which only engages in the eye nut to secure the rim and dish together. This arrangement provides 2 greater degree of movement of the threaded portions engaging in the screw shackle, than in the previous arrangement, thus making alignment of the screw shackles with the threaded portions easier. As an alternative to the bolt assembly 3, a more simple arrangement of a single bolt engaging with the grip wheel and the vehicle wheel to secure one to the other may be provided. So that the distance between the grip wheel and the vehicle wheel can be adjusted to allow for different wheel rim widths spacers can be proved on the bolt between the grip wheel and the vehicle wheel. In addition, a tensioning plate can be tightened into position against the rim of the vehicle wheel by the bolts to ensure that forces on the bolts are transmitted to the vehicle wheel. The grip wheel 1 comprises a plurality of strakes 11 which are equidistantly spaced around the circumference of the grip wheel frame 6. Each strake 11 is connected through a linkage member 12 to a central bearing 13. Each linkage member 12 is connected to the central bearing 13 through respective rotatable members 14. In turn the central bearing 13 is connected to the piston rod 15 of a hydraulic piston 16, which is connected to a hydraulic supply (not shown) by means of a pipe 17. The hydraulic piston 15 is secured to a star shaped member 18, the points 19 of which, engage through rollers 20 with the inside ring 21 of the grip wheel frame 6. A bar 19a, secured to a fixed part of the body of the vehicle, for example the mudguard, fixes the star shaped member 18 in position, whilst the rollers 20 enable the grip wheel frame 6 to move relative to the fixed star shaped member 18. In this way the positions of the hydraulic piston 16 and of the central bearing 15 are fixed relative to the centre of rotation of the grip wheel frame 5 and are prevented from being twisted out of position by forces transmitted from the strakes 11 to the central bearing 13. A slot 22 is provided in the star shaped member 18 through which the central bearing 13 connects to the piston rod 15 of the hydraulic piston 16. In order to prevent excessive forces being absorbed solely in the piston rod 15 the hydraulic piston 16 is pivotable about a pivot 22a. This enables the connecting member between the central bearing 13 and the piston rod 15 to come in contact with the sides of the slot 22 when there is twisting force on the piston rod 15. The twisting forces are thus absorbed in the star shaped member 18. It will be appreciated that the bar 19a may be replaced by a hollow tube through which the hydraulic supply pipe 17 is run for protection. It will further be appreciated that in order to protect the supply pipe 17, to the hydraulic piston 16, from being damaged in the event that the star shaped member 18 jams in the grip wheel frame 6 the supply pipe 17 may be provided with a swivel connection mounted at the centre of rotation of the grip wheel frame 6. In the event that the star shaped member 18 jams in the grip wheel frame 6, the connection to the hydraulic piston 16, carried by the star shaped member 18, will simply rotate about the swivel connection. So that the star shaped member 18 can rotate with the grip wheel frame 6 a shear pin is preferably provided to secure the bar 19a to, for example, the mudguard. 1when the star shaped member 18 jams the shear pin will shear, thus Dreventing the bar 19a from being damaged. By operating the hydraulic piston 16 the central bearing 13 can be moved up and dozen in the slot 22 provided in the star shaped member 18 to occupy positions between the top and bottom of the centre of rotation of the grip wheel frame 6. As previously mentioned each strake 11 is connected to the central bearing 13 through a linkage member 12. Between each strake 11 and its linkage member 12 is provided a knuckle joint 23 which allows the central bearing 13 and the linkage members 12 to move relative to the strakes 11. Each knuckle joint 23 comprises a shear pin which shears in the event of its respective strake 11 hitting a hard object in the ground thus preventing damage to the grip wheel 1 as a whole. The strakes 11, linkage member 12 and knuckle joints 23 are all identical individual components, however each component may be connected to the next in one of two ways by rotating it through 1800 to the component it is to be connected to. In addition each linkage member 12 can be connected to its respective rotatable member 14 on the central bearing 13 in one of two possible positions. In this way it is possible to derive sixteen different positions at which each linkage member 12 can be connected to the central bearing 13. Each strake 11 is movable in and out of a channel 24 provided in grip wheel frame members 25 connected between the middle and outer rings 26 and 27 respectively of the grip wheel frame. Strictly speaking the strakes need only be secured in position relative to the edge of the grip wheel frame, but the arrangement of rings 26 and 27 and the frame members 25 ensures that torque forces on the strake when it is engaged in the ground are largely distributed away from the central bearing 13 to the bolt assemblies 3 through frame members 28. It will be appreciated that when the hydraulic piston 16 is operated, the central bearing 13 is moved downwards in the slot 22. Since the central bearing 13 represents the centre of rotation of the strakes 11 the distance by which the central bearing 13 is moved is the distance by which the strakes 11 are withdrawn at the top of the grip wheel frame 6 and extended at the bottom of the grip wheel frame 6. From this it will be realised that as the central bearing 13 is moved further downwards in the slot 22 the strakes 11 can be made to extend progressively further from the bottom of the grip wheel frame 6 and become further withdrawn into the channels 24 at the top of the grip wheel frame 6. Further, since the central bearing 13 represents the centre of rotation of the strakes 11 those strakes 11 rotated to the bottom of the grip wheel 1 are extended beyond the edge of the grip wheel frame 6, whilst those strakes 11 rotated to the top of the grip wheel 1 are withdrawn into the channels 24 of the grip wheel frame members 25. Those strakes 11 in between top and bottom positions of the grip wheel 1 are in progressively decreasing or increasing stages of extension as they approach the bottom of the grip wheel 1 depending upon whether the central bearing 13 is above or below the centre of rotation of the grip wheel frame 6. When the hydraulic piston 16 is switched off, springs 29 withdraw the piston rod 15 into the hydraulic cylinder 16 causing the central bearing 13 to be moved above the centre of rotat of the grip wheel frame 6. As a result the strakes 11 become progressively extended as they rotate from the bottom of the grip wheel 1 to the top. By suitable adjustment of the positions to which the central bearing 13 is moved about the centre of rotation of the grip wheel frame 6, it can be ensured that the strakes 11 only extend beyond the outer edge of the vehicle wheel 2 at the top or bottom of the grip wheel 1. It will be appreciated that in the embodiment of the present invention of Figs. 1 and 2 where the central bearing is moved between positions above and below the centre of rotation of the grip wheel frame 6 the extension and withdrawal of each strake 11, out of and into channels 24, as the grip wheel 1 rotates acts to clean each strake 11 of mud which might adhere to it as it leaves the ground. The efficiency of te grip wheel 1 in inaintaining traction of the vehicle is thus not decreased by a build up of mud on the strakes 11. In addition, because each strake only extends fully beyond the edge of the vehicle wheel at the top or bottom positions there is no interference caused by the strakes to accessories towed behind the vehicle or to the driver when moving about in front of the vehicle wheel. It will also be appreciated that the strakes may be extended whilst the vehicle is moving because of the hydraulically operated system. Further, because the strakes extend fully into the ground gradually the amount of rolling resistance and shock to the vehicle is considerably reduced compared to the prior art. The distance by which the strakes extend beyond the edge of the grip wheel frame is determined by the distance through which the central bearing 13 is moved and the length of the strakes 11. In view of this it will be appreciated that where desired the central bearing 13 need only be moved through the distance which the strakes 11 extend past the edge of the vehicle wheel to ensure that the strakes 11 do not engage with the ground. It will be appreciated that where a four wheel drive vehicle is used grip wheels are attached to each of the four drive wheels. Where this is the case chains may be connected between the star shaped member 18 of each wheel thereby keeping the hydraulic piston 16 stationary and replacing the bar 19a. It will further be appreciated that the hydraulic piston for moving the central bearing may be replaced by a pneumatic piston, an electrical motor or any other convenient means. It will still further be appreciated that whilst in the drawings the ends of the strakes are shown secured in the base of the knuckle joints, preferably the strakes are secured against the knuckle joints so that in the event of an excessive force being received by a strake the shear pin therein can easily shear. This may be achieved by securing the strake to the opposite side of the knuckle joint as viewed in Fig. 1. Finally it will be appreciated that the grip wheel of the present invention is not limited to being attached to the wheel of a vehicle. The grip wheel may in fact be secured directly to the axle of the vehicle. An example of an arrangement where this is appropriate is the case of a seed or tuber drilling trailer. In such trailers the rate at which the wheels go round determines the rate at which seeds are dispensed from the drilling trailer. Where these trailers are used in wet conditions the wheels can slip which results in uneven distribution of seeds. By providing appropriate means for securing the grip wheel to the axle of the trailer the grip wheel forms an ideal replacement to the ordinary wheel of the trailer.

Claims: CLAIMS: 1. A grip wheel (1) comprising a frame (6), a plurality of strakes (11), means for selectivelt extending and withdrawing said strakes (11) relative to the edge of the grip wheel frame (6), and means (3) for connecting the grip wheel (1) to a vehicle such that the centre of rotation of the grip wheel frame (6) lies over the centre of rotation of a vehicle axle, characterised in that said means for selectively extending and withdrawing said strakes (11) comprises a central member (13) to which the strakes (11) are rotatably connected, which central member (13) is movable relative to the centre of rotation of the grip wheel frame (6) to provide a centre of rotation of the strakes (11) which is offset from the centre of rotation of the grip wheel frame (6). 2. A grip wheel according to claim 1, charact ear'wised in that means (3) are provided for securing the grip wheel (1) to a wheel secured to the axle of the vehicle. 3. A grip wheel according to claim 2, characterised in that the central member (13) is movable in a vertical plane between the top and the bottom of the grip wheel frame (6), the central member (13) being moved towards the bottom of the least grip wheel frame (6) to extend the strakes (11) at beyond the edge of the vehicle wheel at the bottom thereof and moved towards the top of the grip wheel frame (6) to withdraw the strakes (11) at the bottom thereof to at least the edge of the vehicle wheel. 4. A grip wheel according to claim 3, characterised in that the central member (13) is moved towards the top of the grip wheel frame (6) from the bottom through a distance sufficient to withdraw the strakes (11) at the bottom of the grip wheel frame to the edge thereof. 5. A grip wheel according to claim 2, 3 or 4, characterised in that the means (3) for securing the grip wheel to the vehicle wheel comprises a bolt assembly (4,5, 8 and 9). 6. A grip wheel according to claim 5, charact erised in the the bolt assembly comprises a screw shackle (4) into one end of which a bolt (5) engages to secure the grip wheel frame (6) thereto and into the other end of which the threaded portion of a rod engaging with the vehicle wheel hub engages to secure the grip wheel frame to the vehicle wheel. 7. A grip wheel according to claim 6, charac terised in thatih e amount of the threaded portion of the said rot t80gaging in the screw shackle (4) is adjustable to enable the distance between the grip wheel (1) and the wheel hub to be adjusted to different wheel rim widths. 8. A grip wheel according to claim 6 or 7, characterised in that a tensioning plate (9) is tightened into position between the said rod (8) and the rim (10) of the vehicle wheel to transmit forces in the grip wheel (1) to the vehicle wheel. 9. A grip wheel according to claim 5 characterised in that the bolt assembly (4,5,8 and 9) comprises a bolt which engages with the vehicle wheel hub and the grip wheel frame (6) to secure one to the other, and that spacers are provided along the length of the bolt to enable the distance between the grip wheel and the wheel hub to be adjusted to different wheel rim widths. 10. A grip wheel according to claim 9 characterised in that a tensioning plate (9) is tightened into position against the rim (10) of the vehicle wheel by the bolts to transmit forces in the bolts to the vehicle wheel. 11. A grip wheel according to claim 1, characterised in that, means for securing the grip wheel (1) to the axle of the vehicle are provided. 12. A grip wheel according to claim 11, characterised in that the vehicle runs on the frame (6) of the grip wheel (1). 13. A grip wheel according to claim 11 or 12, characterised in that the central member (13) is movable in a vertical plane between the top and bottom of the grip wheel frame (6), the central member (13) being moved towards the bottom of the grip wheel frame (6) to extend the strakes (11) at least beyond the edge of the grip wheel fame (6) at the bottom thereof and moved towards the top of the grip wheel frame (6) to withdraw the strakes (11) at the bottom thereof to at least the edge of the grip wheel frame (6). 14. A grip wheel according to any of claims ii, 12 or 13 characterised in that the grip wheel frame (6) is provided with a tyre to provide resistance to shock. 15. A grip wheel according to any preceding claim, characterised in that the grip wheel frame (6) comprises means (25, 26 and 27) for transmitting torque forces on the strakes (11) away from the central bearing (13) to the means (3) for connecting the grip wheel (1) to the vehicle. 16. A grip wheel according to any preceding claim, characterised in that the motive means (16) is fixed in position relative to the grip wheel frame (6). 17. A grip wheel according to claim 16, characterised in that the motive means (16) and the central bearing (13) are secured to a multi-armed member (18), the arms (19) of which engage with the grip wheel frame (6) through rollers (20) to enable the grip wheel frame (6) to move relative thereto, but to maintain the motive means (16) fixed in position relative to the grip wheel frame (6). 18. A grip wheel according to claim 17, characterised in that the multi-armed member (18) is prevented from rotating with the grip wheel frame (6) by means of a tie rod (19a)attached between the multi-armed member (18) and to a stationary part of the vehicle. 19. A grip wheel according to claim 18, characterised in that a shear pin connects the tie rod (19a) to the stationary part of the vehicle or to the multi-armed member, which shear pin can shear in the event of the multi-armed member becoming jammed and thus forced to move with the grip wheel frame. 20. A grip wheel according to claim 19, characterised in that the motive means (16) is connected to a motive iflaans operating supply external to the grip wheel ( by connecting means, which connecting means is provided with a swiveling connection mounted at the centre of the grip wheel (1), to enable the motive means to rotate with the grip wheel frame (6) in the event of it becoming Jammed, without damaging the said connecting means. 21. A grip wheel according to claim 18, 19 or 20, characterised in that the connecting means comprises a tube through which the supply line to the motive means is carried. 22. A grip wheel according to any preceding claim, characterised in that each strake (11) is connected to a linking member (12), which is rotatably connected to the central member (13), a knuckle joint (23) being provided between each strake (11) and its respective linking member (12). 23. A grip wheel according to claim 22, characterised in that each knuckle Joint (23) comprises a shear pin to protect the grip wheel (1) against excessive forces onte strake (11). 24. A grip wheel according to any preceding claim, characterised in that each strake ( is carried in a channel member (24) of the grip wheel frame (6) in which channel member (24) it is movable ki and out. 25. A grip wheel according to any preceding claim, characterised in that the central member (13) is moved by means of a hydraluic piston (16). 26. A grip wheel substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: GETHING, ROBERT
Applicants: GRIPWHWEEL LIMITED
Application year: 1983
Main classification: B60B15
IPC codes: B60B15