TRACK TENSIONING MEANS FOR TRACKED VEHICLES

Abstract: Tensioning means for the tracks of a tracked vehicle comprise a pair of hydraulically-operated, double-acting rams (6) connected one to the idler wheel (2) of each track (4) in such a manner that extension and/or retraction of the rams effects movement of the associated idler wheels (2), and a hydraulic circuit (14 to 24) for controlling the movement of said rams (6), and therefore of the idler wheels (2), actuation of the hydraulic circuit being effected from within the personel compartment of the vehicle.

Description: This invention relates to tensioning means for the tracks of tracked vehicles. Tracked vehicles, be they for military purposes such as tanks or for civil purposes such as construction site equipment, periodically require the tension in the tracks thereof to be adjusted, for example to compensate for track wear or to vary the ride height attitude dependent upon loading of the vehicle. Conventional tracks of such vehicles include an idler wheel adjacent the front regions thereof, (although said idler wheels can be elsewhere within the track) and adjust­ ment of the track is commonly achieved by bodily movement of the idler wheel to a position taking up any slack and providing the required tension. In the case of military vehicles such as battle tanks, adjustment of the locations of the idler wheels is commonly achieved by manual rotation of an adjustment nut using an associated spanner. Clearly this is a laborious task requiring the use of extraneous equipment and requiring the presence of personel outside the vehicle at the idler wheels. In the case of civil construction equipment, it is standard practice for movement of the idler wheels to be effected by means of single-acting grease-filled rams reacting on the idler wheels, it being necessary to pump up these rams with grease guns until the required tension is reached. This can again be a tedious operation and suffers from the further disadvantage of being messy, part­ icularly on retraction of the rams. It would be desirable to be able to provide means for tensioning and detensioning the tracks of tracked vehicles the operation of which was more convenient and less prone to mess than the aforementioned arrangements. According to the present invention there is provided track tensioning means for a tracked vehicle, the vehicle including a personel compartment and a pair of tracks each incorporating an adjustable idler wheel, the tension­ ing means comprising, for each track, an hydraulically-­ operated, double-acting ram interconnected with, and adapted to effect movement of, the associated idler wheel, and a hydraulic control circuit for said rams actuation of which is effected from within the personel compartment of the vehicle. It will be appreciated that, with such an arrangement, adjustment of the tension in the tracks can be achieved from within the personel compartment by appropriate control of hydraulic fluid supply to the means, thus obviating the necessity for outside personal attendance at the idler wheel, while the hydraulic rams, being double-acting, permit powered retraction thereof as well as powered extension. In preferred tensioning means, the hydraulic rams are each mounted on associated mounting members, for example trunnions, which members are themselves mounted in, to be pivotal relative to, the body of the vehicle whereby the hydraulic rams are movable bodily with said mounting members about axes extending substantially transversely of the vehicle. Conveniently the hydraulic circuit includes, for each double-acting hydraulic ram, a one-way check valve mounted on the associated mounting member to be movable with said member, the check valves preferably being mounted on that part of the associated mounting member located within the vehicle, although said valves could be mounted outside the vehicle. The hydraulic control circuit includes a control pump which may be either manually operated or electrically operated, said pump conveniently incorporating a low pressure relief valve adjustable to determine the hydraulic pressure in the rams and therefore the tension applied to the tracks. The control circuit preferably further includes, for each hydraulic ram, a pressure relief valve adapted to relieve pressure within the associated ram when said pressure exceeds a predetermined maximum value. Conven­ iently the pressure relief valves are mounted on, to be movable with, the mounting members of the associated rams. Each hydraulic ram may include means permitting attachment thereto of a jacking screw to permit mechanical movement of the piston thereof in the event of hydraulic failure at the ram. By way of example only, an embodiment of the invent­ ion will now be described in greater detail with reference to the accompany drawings of which: Fig. 1 is a schematic layout of tensioning means according to the invention, and Fig. 2 is a hydraulic circuit diagram of the tension­ ing means of Fig. 1. Referring to the drawings, the tracked vehicle includes a pair of idler wheels 2, one associated with each track indicated schematically at 4, the positions of which wheels 2 are to be adjusted by the tensioning means of the invention. The tensioning means include a pair of double-acting hydraulic rams 6, one for each idler wheel 2, the piston rods 8 of which are attached to, to effect linear movement of, the associated idler wheels 2. The cylinders 10 of the rams 6 are mounted on, to be movable with, associated trunnions 12 themselves mounted in, to be pivotal relative to, the sidewalls of the vehicle hull, the trunnions 12 projecting through the hull sidewalls into the interior of the vehicle. The hydraulic control circuit for the rams 6 is located within the vehicle and includes an oil reservoir 14 and a two-speed manually-operated pump 16. A pair of directional control valves 18 permit supply of hydraulic fluid under pressure to either ram 6 on appropriate actuation of said valves 18, while an adjustable low pressure relief valve 20 within the pump 16 determines the pressure of fluid at the rams 6 and therefore the tension in the associated tracks. The pump 16 has a first mode - low pressure high displacement - for initial extension of the rams 6, and a second mode - high pressure low displacement - for final setting of the rams 6 at the desired pressure. A pair of pilot-operated check valves 22, one for each ram 6, are mounted within the vehicle on the ram trunnions 12 to be movable with said trunnions 12 whereby no flexible connections between said valves 22 and the rams 6 are required, the check valves protecting the rams 6 from hydraulic collapse in the event of a downstream pressure system reduction or leakage by holding the system pressure in the ram cylinders 10. Also mounted within the vehicle on the trunnions 12, one for each ram 6, are a pair of overload relief valves 24 to protect the system from pressure spikes induced by external forces, these overload valves 24 being set to relieve pressure progressively within the rams 6 at a combination of a predetermined maximum idler wheel load plus track tension. Again the mounting of the relief valves 24 on the trunnions 12 obviates the requirement for any flexible connection to the high pressure, ram side of these valves 24. The hydraulic connections between the rams 6 and the valves 22,24 is conveniently fed through the centre of the mounting trunnions 12 into the vehicle compartment. Thus it will be appreciated that the high pressure part of the hydraulic circuit is in effect locked at the trunnions 12 and is movable therewith, the only flexible connections required in the circuit being located within the vehicle to take up the small oscillations of the trunnions 12 and in that part of the circuit not under pressure. Such an arrangement thus maximises reliability and safety of the hydraulic circuitry by eliminating any flexible connect­ ions under high fluid pressure. In the unlikely event of hydraulic failure within the high pressure part of the circuit due, for example, to physical failure of the metal of the rams, failure of the seals within the rams 6 or failure of the check valves 22 or pressure relief valves 24, pressure on the piston rods of the rams 6 can be maintained mechanically by providing threaded jacking screw holes 26 in the rear ends of the rams 6 whereby mechanical jacks can be screwed into the cylinders 10 of the rams 6 to abut the pistons of the rams 6 and to maintain them in their operative positions within the cylinders 10. The rams 6 are double-acting whereby constant lubri­ cation is provided at the piston rods 8 and at the oil seals thus increasing the life of the rams 6. Further, any leakage of oil from the ram 6 indicates that the piston rod seal has gone and this can therefore be replaced before the main piston seal goes. A double-acting ram has the advantage of acting as its own oil reservoir because of the constant volume of oil within the ram regardless of its operative position, and consequently there is little displacement of oil in the main reservoir 14 of the hydraulic circuit. Further, double-acting rams enable retraction under power as well as powered extension of the piston rods 8, thus providing quick and efficient tensioning and equally quick and efficient de-tensioning to allow for adjustment of the track quickly for such activities as link renewal, routine maintenance, bridge launch and recovery and fascine laying. The described system can thus be operated by one man from within the personel compartment of the vehicle, eliminating the disadvantages mentioned above of the known arrangements, the hydraulic circuitry including a high pressure section concentrated at and adjacent the rams and incorporating a hydraulic lock to prevent the loss of track tension and overload protection to avoid damage to the system.

Claims: 1. Track tensioning means for a tracked vehicle, the vehicle including a personel compartment and a pair of tracks (4) each incorporating an adjustable idler wheel (2), the tensioning means being characterised by, for each track (4), an hydraulically-operated, double-acting ram (6) interconnected with, and adapted to effect movement of, the associated idler wheel (4), and a hydraulic control circuit (14 to 24) for said rams (6) actuation of which is effected from within the personel compartment of the vehicle. 2. Track tensioning means as claimed in claim 1 in which the hydraulic rams (6) are mounted on associated mounting members (12), which members (12) are themselves mounted in, to be pivotal relative to, the body of the vehicle whereby the hydraulic rams(6) are movable bodily with said mounting members (12) about axes extending substantially transversely of the vehicle. 3. Track tensioning means as claimed in claim 2 in which the mounting members each comprises a trunnion (12). 4. Track tensioning means as claimed in claim 2 or claim 3 in which the hydraulic circuit includes, for each double-acting hydraulic ram (6), a one-way check valve (22) mounted on the associated mounting member (12) to be movable with said member (12). 5. Track tensioning means as claimed in claim 4 in which the check valves (22) are mounted on that part of the mounting member (12) located within the vehicle. 6. Track tensioning means as claimed in claim 4 or claim 5 in which the hydraulic circuit includes a control pump (16) incorporating a low pressure relief valve (20) adjustable to determine the hydraulic pressure in the rams (6) and therefore the tension applied to the tracks (4). 7. Track tensioning means as claimed in any one of claims 4 to 6 in which the hydraulic control circuit includes, for each hydraulic ram (6), a pressure relief valve (24) adapted to relieve pressure within the assoc­ iated ram (6) when said pressure exceeds a predetermined maximum value. 8. Track tensioning means as claimed in claim 7 in which the pressure relief valves (24) are mounted on, to be movable with, the mounting members (12) of the associated rams (6). 9. Track tensioning means as claimed in any one of claims 1 to 8 in which each hydraulic ram includes means (26) permitting attachment thereto of a jacking screw to permit mechanical movement of the piston thereof in the event of mechanical failure at the ram (6).

Inventors: ARMSTRONG, ROBERT, BROWN, JAMES WILLIAM 8 VICTORIA TERRACE
Applicants: VICKERS PLC
Application year: 1988
Main classification: B62D55
IPC codes: B62D55