Wheel substitutes for land vehicles – With means for tensioning track by moving at least one endwheel – Condition responsive
Patent
1995-09-20
1998-04-14
Mitchell, David M.
Wheel substitutes for land vehicles
With means for tensioning track by moving at least one endwheel
Condition responsive
305149, B62D 55112
Patent
active
057384215
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase of PCT/EP94/00727 filed 26 Sep. 1995 and based upon German national application P43 09 746.4 of 26 Mar. 1993 under the International Convention.
FIELD OF THE INVENTION
The invention relates to a hydraulic chain tensioner for the automatic tensioning of the crawler chains of crawler vehicles having two-, four- or eight-wheel articulated suspensions. More particularly, the invention relates to a chain tensioner which comprises essentially two tensioning cylinders and a plurality of valves, the two tensioning cylinders being interconnected by ducts and being connected by further ducts of the valves, the tensioning cylinders being fitted to the chassis of the crawler vehicle and the leading wheels of the crawler vehicle bearing against the piston rods of the tensioning cylinder.
BACKGROUND OF THE INVENTION
The loop lengths of the crawler chains of crawler vehicles are subject to changes when riding over an uneven terrain and when negotiating an obstacle. In the case of crawler vehicles having supporting rolls the required chain extension is made possible by a chain slack in the upper run of the chain.
In known hydraulic chain tensioning units piston and diaphragm-type accumulators are used or set into operation for spring deflection only when the chains are subjected to large forces. For spring deflections at low chain forces the known chain tensioning units are combined with a mechanical spring equipped with a stop member.
Because in the case of transport crawler chains, due to the low construction height, the accumulator action of chain slack in the upper run is absent, the required chain extension for the lower run cannot be provided by a chain slack in the upper run. Accordingly, particularly in the event of hard, uneven terrains high tensile forces arises in the chains with resultant increased chain wear-and-tear.
OBJECTS OF THE INVENTION
An object of the invention is to provide in a crawler vehicle, an improved chain tensioner to substantially increase the life expectancy of the chains by reducing the chain tension peaks which arise.
SUMMARY OF THE INVENTION
This object is attained in that, parallel to the tensioning cylinders, a soft spring is connected so that at the start of a load being applied to the chain tensioning means only a small pressure increase arises in the tensioning cylinders or, put differently, only a minor increase in the chain tension occurs.
Advantageously the soft spring takes the form of a hydro-pneumatic spring fitted between the tensioning cylinders and the valves and connected by way of a third duct to the duct which connects the tensioning cylinders to the valves and the gas space of which is only under slight precompression.
In the chain tensioning unit according to the invention, the soft spring or hydro-pneumatic spring permits activation of the tensioning cylinders even under minor chain forces. If the chain tensioning means is loaded by external forces applied to the chain, for example by ground unevenness, the tensioning cylinders retract against the initially low pretensioning pressure of the gas space of the hydro-pneumatic spring, such that initially only a minor pressure increase occurs in the chain tensioning cylinders and accordingly only a minor increase in the tensile forces of the chain as compared with a nonsprung tensioning means. As a result, the chain is effectively protected against straining in the frequently occurring tension range exceeding the pretensioning.
Since on the one hand--with a view to reduced wear-and-tear --the pretensioning of the gas space of the hydro-pneumatic spring is to be as low as possible but on the other hand, if the pretensioning is too low there occurs a distinct deterioration of the riding performance of the transport crawler pretensioning in the gas space of the hydro-pneumatic spring according to a further feature of the invention amounts to 2 to 10%, preferably 3 to 6.3% of the maximum tensioning pressure at the cylinders.
In an advanta
REFERENCES:
patent: 4874052 (1989-10-01), Purcell et al.
patent: 4893883 (1990-01-01), Satzler
patent: 5334106 (1994-08-01), Purcell
patent: 5452949 (1995-09-01), Kelderman
Neymans Helmut
Schmitz Michael
Dubno Herbert
Krupp Fordertechnik GmbH
Mitchell David M.
Yun Jonathan J.
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