Machine element or mechanism – Gearing – With fluid drive
Patent
1991-10-09
1992-11-24
Wright, Dirk
Machine element or mechanism
Gearing
With fluid drive
125 14, F16H 4700
Patent
active
051652854
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention is related to a driving device according to the preamble of claim 1. The driving device is preferably intended to put a saw blade connected to the axle in rotation. Furthermore, it is preferred that the rotatable members form parts of a hydraulic motor in that they are capable of being put into rotation by actuation by means of a hydraulic fluid. The rotatable members preferably form gears in engagement with each other A device of the nature defined in the introduction is disclosed in the Swedish patent 8700255-6. In this prior device, one of the gears is always rotationally fixedly connected to the axle so that one single transmission ratio is possible.
In sawing machines of the nature discussed, there is a need for using sawing blades having different diameters in dependence upon the saw cut depth aimed at. Sawing blades having a large diameter require a lower number of revolutions than sawing blades having a small diameter. One must therefore in the known device adjust the hydraulic fluid flow when changing between saw blades having different diameters. In other known machines designs have been chosen so that in such cases an exchange of hydraulic motor occurs instead. The latter is laborious as well as time and cost consuming.
Gear hydraulic motors according to the Swedish patent 8700255-6 have a very favourable relation power/weight as long as the number of revolutions is relatively high, in practice above about 1000 revolutions/minute. However, the efficiency decreases markedly with reduced number of revolutions. Saw blade speeds as low as 400-1000 revolutions/minute may come in question with saw blades having a large diameter. This means a very unfavorable efficiency compared with the number of revolutions of over 1000 revolutions/minute which with the same gear motors may be used for saw blades having a small diameter. It follows from this that it is not suitable to carry out variation of the number of revolutions by adjusting the hydraulic fluid flow. There are, however, other hydraulic motor types having a high efficiency also with low numbers of revolutions but the weight of these motors is discouragingly high.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a driving device, the design of which should be such that it enables driving of the axle with at least two different transmission ratios. A specific aim is to design the device so that it obtains a possibility for these two different transmission ratios without the device becoming heavy or bulky in an inconvenient degree.
This object it primarily obtained according to the invention by providing the device with the features first of all defined in the characterizing portion of claim 1. Preferable developments of the device according to the invention, in particular concerning the means for making the device operate according to either of at least two operational states, are defined in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
With reference to the enclosed drawings a more close description of an embodiment example of the invention will follow hereinafter. In the drawings:
FIG. 1 is a side view of a sawing machine comprising the driving device, according to the invention;
FIG. 2 is a cross section through the sawing machine illustrated in FIG. 1;
FIG. 3 is an enlarged view illustrating a portion of the sawing machine according to FIG. 2 in section, and
FIG. 4 is a diagrammatical section through a rotatable arm of the sawing machine, the section extending perpendicularly to the plane of the drawing according to FIG. 2 and parallel to the plane of rotation of the arm.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The sawing machine illustrated in the drawings comprises a body 1 and an arm 3 rotatable in relation to the body about an axis 2. An axle 4 in the form of a saw shaft is arranged on the arm 4, said saw shaft being rotatably supported about an axis spaced from the axis 2 of rotation of the arm 3 and generally parallel thereto. At one end of the shaft
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patent: 4797025 (1989-01-01), Kennedy
patent: 4836494 (1989-06-01), Johnsen et al.
patent: 4848845 (1989-07-01), Kennedy
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