The present invention is related to an apparatus for controlling the indexing of hydraulic stepping motor and in particular to a servo-valve for controlling the flow of htdraulic fluid thereto.
Hydraulic stepping motors are known which are constructed as a linear motor in form of a pressure fluid cylinder or in form of a hydraulic rotating motor. In either case it is known to combine such motors with a control or servo-valve comprising slide valve having a reciprocable linear shift member or with a member reciprocably rotatable about a central axis (see German Pat. No. OS 1,550,365). In connection with slide valves having a linear shiftable member it is possible and known to use also asymmetric pistons.
It is an object of the instant invention to provide improved apparatus for the control of hydraulic motors which may use any of these combinations. The apparatus may also be provided known intermediate amplifiers or gears altering the gear ratio between the hydraulic motor and the control valve.
It is the object of the instant invention to develop a hydraulic step motor of the type described in such a way as to render possible in a simple construction a high number of step positions and one having little leakage. In addition it is the object to provide a device having a very good dynamic performance, an insensitiveness against varying load moments, higher start-stop-frequencies and step losses.
According to the invention these tasks are solved by providing in conjunction with a hydraulic stepping motor a servo-control system comprising a slide valve comprising a housing and a slidable valve member arranged in, and coextensive with, the housing. The slidable valve member includes at least two fluid manifolds conjointly movable therewith and a plurality of primary positioning webs and secondary sealing webs alternately spaced from one another and uniformly distributed over its periphery. These projections define a plurality of intermediate gaps alternately connected with one or the other of the fluid manifolds. A plurality of uniformly distributed channels provided in the housing opens against these webs. The channels have a width identical with the peripheral width of the primary projections, but have mutual distances different from those existing between the primary projections and are fewer in number than these primary projections.
The main connecting conduits provide communication between the source of fluid under pressure and the fluid manifolds. A plurality of return conduits, each of which is connected to one of the channels, is coupled to a selector valve comprising a plurality of control valves each communicating with at least one of the return conduits. The control valves are actuable to couple a selected return conduit to a return duct outlet opening into a sump whereto the source of fluid under pressure is connected to receive therefrom the fluid it pressurizes.
In idle condition a uniform pressure exists as long as the valves in the selector are closed. In response to the opening of one of the valves, the corresponding intermediate gap discharges the fluid through its corresponding channel and the return fluid conduit, via the opened valve into the sump, thus a drop of pressure being provoked in the discharging gap and the step motor being caused to revolve in the decreased pressure direction. Then, one of the primary webs moves towards and covers the previously opened channel and finally blocks it. Therefore, the rotary valve member ceases to move and the fluid escape channel closure restores the pressure in the servo-valve, so that the rotation stops after a predetermined step only. Thus an effective control of step rotation is provided.
Preferably the servo-valve is of a rotary type including a rotatable cylindrical member housed in a cylindrical wall. The webs comprise radial projections. However, linear housing and slide members may be used since these too can be made with projecting webs and channels.
An advantage of the foregoing construction lies in the fact that by connecting the gaps between the webs, on the same facial sides, to a common manifold, indexing in opposite directions can be obtained in one or more steps.
It is particularly useful if in the preferable embodiment each separating web is broadened up to form a sealing member in such a way that in each position of the movable member at least some of the channels in the valve housing are covered by the sealing web.
The present invention results in a high number of indexing positions, together with a very small possibility of leakage. Due to this diminished leakage the dimensions of the slide valve may be significantly decreased in comparison with known systems having an equal number of positions. Furthermore, the number of control valves necessary in the selector valve device may be substantially decreased so that there is a remarkable decrease in constructive expenditure. The width of the separating webs, respectively, may in order to obtain a favorable behavior in operation, be chosen so that at both sides of each positioning web there remain gaps which are slit like ducts having a width corresponding to the width of the positioning web itself.
Preferably, the number of channels is nearly equal to the number of the positioning webs. Most favorably the number of the positioning webs and the number of the channels differ only to the extent of the valve 1.
Furthermore, it is useful if the conduits of two or more non-adjacent channels are connected to the return conduit via a single control valve of the selector valve device.
The invention will be described in more detail in the following with reference to the attached drawings showing two embodiments.