US 3735741 A
A piston engine of the type in which opposed pistons drivingly engage a shaft between the pistons by engagement with cam parts fixed on the shaft. A return spring compressible in a direction parallel to the axis of the pistons is spaced laterally from this axis. Pivotally mounted levers engage the spring ends and the pistons to urge the latter against the cam parts. Cups may cover the spring ends, the outside of these cups facing a common scavenging chamber such that inward and outward movement of the cups under the action of the springs and the levers pump air into and out of this scavenging chamber.
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Description (OCR text may contain errors)
llnited States Patent [191 Hatz [ PISTON ENGINE  Inventor: Ernst Hatz, Alte, Germany  Assignee: Motorenfabrik Hartz KG., Ruhstorf,
Germany  Filed: Aug. 16, 1971  AppLNol: 172,056
 Foreign Application Priority Data Aug. 27, 1970 Germany ..P 20 42 632.8
 US. Cl ..l23/56 C, 74/55, 92/72, 123/43, 123/197 Int. Cl ..]F02b 75/24 Field of Search ..l23/56 BC, 56 B, 123/56 C, 55 AA; 417/534; 92/129  References Cited 1 UNITED STATES PATENTS 2,407,343 9/1946 Pyne ..4l7/2l4 [451 May 29, 1973 FOREIGN PATENTS OR APPLICATIONS 603,720 6/1948 Great Britain ..l23/56 C Primary ExaminerClarence R. Gordon Attorney-Larson, Taylor & Hinds [5 7] ABSTRACT A piston engine of the type in which opposed pistons action of the springs and the levers pump air into and out of this scavenging chamber.
7 Claims, 2 Drawing Figures PISTON ENGINE RELATED APPLICATION This application is an improvement on my previous Application Ser. No. 851,944, filed Aug. 21, 1969 now US. Pat. No. 3,604,402.
BACKGROUND OF THE INVENTION This invention relates to to piston engines and in particular it relates to piston engines of the type in which pistons engage a driven shaft directly through cam parts rather than through a crank mechanism.
Engines of this general type are known, as shown for example in my previous patent application Ser. No. 851,944, filed Aug. 21, 1969 as well as in the references cited therein. In this type of mechanism, since the pistons and the driven shaft are not positively connected in the same manner as with a crank drive, means such as springs must be provided to urge the parts against each other to assure proper positioning of the cam parts relative to the pistons, especially during the power stroke of the latter to assure maximum power transmission.
However, problems are encountered in providing springs of sufficient force within the minimal space requirements of such engines, nd to this end, there exists a need for continuing improvements.
SUMMARY OF THE INVENTION Thus, it is a purpose of this invention to provide a new and improved arrangement for urging the pistons and the cam parts together in a piston engine of the present type.
Specifically, it is a purpose of the present invention to provide a piston return arrangement in a piston engine of the present type which utilizes return springs of sufficient power for all speeds but which requires a minimum of space within the piston engine housing and which is equipped with simple and economically made elements and which can be used both for internal combustion engines of two-stroke or four-stroke type engines as well as other piston engines.
This object is met in the present invention by the fact that at least one return spring is disposed laterally of and parallel to the axis of the pistons and is arranged between two spring cups which are mounted for guided movement, and that there is associated with each piston at least one restoring lever mounted in the engine housing and bearing on the one hand of said spring cups and on the other hand against the piston.
An advantageous construction of the elements which is very suited to mass production is obtained by arranginga transverse pin, fastened in the piston, and a restoring lever in the form of a flat part having one arm bearing against this pin.
In the case of piston engines in which each piston has i a roller cooperating with cam parts of the driven shaft,
it is of advantage, in accordance with another form of the invention, to provide two similar parallel compression springs, both spaced laterally from the axis of the pistons, and two restoring levers associated with each spring, these levers being disposed in mirror image fashion about a plane perpendicular to the axis of the pistons and passing centrally between the two pistons, the two restoring levers associated with each spring engaging a different one of said pistons.
A particularly simple manufacture and assembly of the elements is achieved in accordance with a further feature of the invention inasmuch that the two spring cups associated with each return spring are guided in a cylindrical sleeve fixed in the housing, the return spring being arranged in the interior of this sleeve.
Where the invention is applied to a two-stroke internal combustion engine with scavenging of the cylinder through a common scavenging chamber, a preferred embodiment of the invention is to be found in circumstances where the outer side of each outer cup of each pair of spring cups faces towards the scavenging chamber so that the two spring cups associated with a return spring constitute a scavenging pump.
In accordance with a further advantageous feature of the invention the return spring has a peripheral depression at its central area and it bears loosely at this part on a pin, fixed in the housing, under the action of the return spring.
Thus, is is a purpose of the present invention to provide a new an improved piston engine of the present type comprising a cam driving engagement between the pistons and the driven shaft.
It is another object of the present invention to provide, in a piston engine of the present type, a return spring for urging the pistons against the driven shaft, which spring is sufficiently powerful to be useful at all speeds and which requires a minimum of space within the engine housing.
It is another object of the present invention to provide, in a piston engine of the type described, a simple and economical piston return mechanism.
It is another object of the present invention to provide, in a piston engine of the type describe, a spring piston return mechanism which is also operative as a scavenging pump.
Other objects and the advantages of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS There follows a detailed description of a preferred embodiment of the present invention to be read together with the accompanying drawings.
FIG. I is a longitudinal section view of a piston engine constructed in accordance with the present invention.
F IG. 2 is a cross-sectional view taken along line II-II of FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the figures, like elements are represented by like numerals throughout the two views.
The embodiment illustrated is a piston engine comprising a two-cylinder two stroke internal combustion engine of known general performance. Two diametrically-opposite cylindrical bores Ila, llb are machined in a cylinder block 1, and an internal chamber lc is provided between them. A driven shaft 2 is mounted in bearings (not shown) in an axially central position and is adapted to drive a required unit (not shown). Sealing means of known form are provided to hermetically seal the inner chamber llc from the exterior. Cooling fins are arranged in known fashion around the periphery of the cylinder while a cylinder head 7a, 7b is secured at each end to the block 1. Mounted in each cylinder head is a spark plug 8a, 8b of normal commercial type. A cover 11 carrying the carburetor 9 and the suction valve is secured by screws to the narrow side of block 1. The rotary part of an electromagnetic ignition distributor of a type known per se and not here shown is also'driven by the driven shaft 2. The periphery of this distributor is also formed to constitute a number of conductor blades which act as a cooling air blower to cool the cylinders.
Additionally provided in the cylinder block 1 in the area of cylinders la, 1b, are scavenging ports lsa, lsb which conduct the scavenging gas through the cylinder in the usual way. Arranged in each cylinder is a piston 14a, 14b which is reciprocable in the direction of the central axis of the cylinder. The coupling between pistons l4 and the driven shaft 2 is, however, obtained here not through the agency of a connecting rod but as follows.
Transversely mounted in each piston 14a, 14b is a roller bolt a, 15b on which rotates a roller 16a, 16b through interposed needle bearings (not shown). Engaged with each of these rollers is a cam having cam parts 2na, 2nb on shaft 2. These cam parts are of the same shape and may be integral with the shaft or be made separately and rigidly connected thereto. Cam parts 2na, 2nb are disposed diametrically opposite to one another so that they cooperate alternately with the rollers 16a, 16b of the pistons during the rotation of shaft 2. This arrangement is shown in greater detail in my application Ser. No. 851,944, filed Aug. 21, 1969.
A return spring arrangement is provided to guarantee application of cams 2na, 2nb against pistons 14a, 14b, and this is constituted as follows.
Two like return springs 3a, 3b in the form of helical compression springs are provided and are disposed axially parallel to one another and to the axis of the pistons. The ends of each spring 3a and3b are disposed on support cups 4a, 5a, and 4b, 5b respectively which slide in fixed guide sleeves 6a and 6b respectively in the housing 1. Actually, the numeral 4b does not appear in the figures. It is the upper cup of the lower of the two springs shown in FIG. 2 and it is similar in construction to element 4a. However, it is convenient to refer to this element as 4b in this description of the preferred embodiments. Bearing on each cup 4a, 5a or 4b, 5b is one arm 12a or 12b ofa restoring lever 120 or 12b which is pivoted on a fixed axis pivot pin 13a or 13b in the housing 1. The other arm 12a" or 12b" bears on a transverse pin 17a or 17b which is fixed in the associated piston 14a or 14b. Thus two like restoring levers 12a and 12b are associated with each piston 14a or 14b, and each of these levers cooperates with the corresponding spring 3a or 317. Thus there are in toto four like restoring levers for the two pistons illustrated and two return springs of equal strength, these being arranged in the manner illustrated.
The area surrounding the guide sleeves 6a, 612 (including the spring cups which are guided therein) communicates with the scavenging chamber lc.
By virtue of the arrangement of the two springs 3a, 3b described above, during the outward movement of pistons 14, that is to say to the outer dead center position, these springs are compressed by the arms 12a or 12b of their respective restoring levers and the four spring cups 4a, 5a and 4b, 5b act as suction pumps in the scavenging chamber 1c, so that the valve 10 is opened because of the suction effect thereby created.
During the initial movement of the pistons, that is to say to the inner dead center position, the axial ends of the return springs, because of the spring rcsilicncc, press the spring cups apart again, so that because of the super atmospheric pressure which is thereby created in the scavenging chamber 1c the valve 10 is re-closed in this phase. This movement of the spring cups 4a, 5a and 4b, 5b in rhythm with the movement of the pistons is thus used to provide a pumping effect so that these parts act as a charging arrangement or a super charger. This suction and scavenging air in chamber 1c undergoes a useful pre-compression.
The operation of the arrangement described may be likened to that of known two-stroke engines with spark ignition, so that it is unnecessary to go further in explaining the operation of the two working cycles here concerned. What is different is the fact that the two pis tons work at the same stroke concurrently, that is, the two of them move together either to the outer dead center position or to the inner dead center position. What is also different is the fact that in the present arrangement the movement of pistons 14a, 14b to the outer dead center position is produced only by the action of cams 2na, 2nb while the rotation of shaft 2 is produced during the movement of these pistons to the inner dead center position, again from the pistons through the same cams. Thus the non-positive engagement between the elements 14a, 14b on the one hand and the elements 2na and 2nb on the other hand is ensured at every instant during the two strokes (up to a specific rate of rotation), namely by the pressure or counter pressure acting on each piston from the cam or from the associated combustion chamber.
A trouble-free operation is thereby ensured if the inertial forces acting on the pistons are equal to or less that the pressure in the combustion chamber acting on these pistons. In the example illustrated it has been assumed that the piston lift curve which is calculated from the diameter of the roller, the cam circle and the curvature of the approach and run-off flanks, and the base circle of the cam, is a true sine curve. Thus a trouble-free operation is ensured, so long as the equation P nw r(a) is adhered to, where P the pressure on the piston.
n twice the rate of rotation of the driven shaft.
w twice the angular rate of the driven shaft.
r half the height of the cam, and
a twice the rotary angle of the driven shaft.
During the outward stroke (from inner to outer dead center) the pistons 14a, 14b accelerate up to half the length of stroke, that is, at least until the scavenging ports lsa, lsb are closed. Immediately after these ports are passed by the piston, a counter pressure builds up in each of the cylinders 1a and 1b which increases the pressure applied by the piston 14a, 14b, or its roller 16a, 16b on the corresponding cam 2na, 2nb. As soon as the half stroke is exceeded the piston rate is slowed down considerably but the counter pressure at this point is already more than the decelerating forces so that even at this phase of the outward movement, the non-positive engagement is maintained. The maximum deceleration forces act on the piston at the outer dead center position. At this point of time, however, the counter forces acting on the cylinder are a maximum. For the inward movement of the piston (from outer to inner dead center) the same thing applies analogously as was applied above to the outward movement. Thus the non-positive coupling between the piston and cam is also maintained during the inward stroke.
As has also been pointed out the forces and counter forces which act on each piston in the embodiment illustrated are so related to one another as to ensure by this means along a continuous non-positive engagement between piston and cam up to a critical speed of rotation. The return springs 3a and 3b are thus not per se required during the running of the engine. They serve only to assist in starting a stationary internal combustion engine in instances where both pistons may have remained inadvertently in the outer dead center position. In such instances, the springs must move the two pistons towards the inner dead center position during movement of the cams on starting ,to ensure engagement between the parts. The springs are only required to overcome the friction between piston and cylinder and the relatively small scavenging pressure in the chamber 1c, and possibly the intrinsic weight of the piston (if the internal combustion engine is of a type in which the axis of the pistons is vertical). The spring power which is necessary for this purpose is however very small, so that the return springs need only be of weak gauge.
The return spring arrangement illustrated is eminently suitable for pistons with rollers. In the case of pistons without these rollers one return lever only need be associated with each piston, which in turn would mean a single, correspondingly powerful, return spring for the two pistons. Additionally it is pointed out that for example in engine types having four pistons (with two piston pairs) the return spring system illustrated would be associated with .each pair of pistons.
Although the invention has been described in considerable detail with respect to preferred embodiments thereof, it will be apparent that the invention is capable of numerous modifications and variations apparent to those skilled in the art without departing from the spirit and scope of the invention.
I claim: I
1. A piston engine comprising at least one pair of axially aligned opposed cylinders, a reciprocating piston in each cylinder, a driven shaft located between the pistons, and driving means for placing said pistons and said shaft into driving relationship with each other, said driving means comprising at least one pair of cam parts mounted on the shaft on diametrically opposite sides of its axis for rotation with the shaft, said cam parts being engageable with said pistons such that the driving force between the pistonsv and the shaft is transmitted through contact between said cam parts and said pistons in a direction generally parallel to the axis of the pistons, a return means for urging the pistons against the cam parts, said return means comprising at least one return spring disposed laterally of the axis of the pistons, and resiliently deformable in a direction generally parallel to the axis of the pistons, a cup at each end of said spring, and at least one restoring lever associated with each piston, each said restoring lever being pivotable about a pivot axis in the housing and bearing against the cup of said return spring and the piston on opposite sides of its pivot axis, respectively, the two said cups associated with the return spring being guided in a cylindrical sleeve fixed in the housing, the spring being arranged in the interior of this sleeve, such that the restoring force of the spring acts through the restor} ing lever, causing the restoring lever to urge its respective piston against the cam parts.
2. A piston engine according to claim 1, said pistons being in the form of a two-stroke internal combustion engine having a common cylindrical scavenging chamber, the outer side of each cup facing towards this scavenging chamber so that the two said cups associated with the return spring constitute a scavenging pump which draws air into the scavenging chamber and then therefrom into the cylinders as the said cups are moved towards and away from each other under the action of said spring and said restoring levers.
3. A piston engine according to claim 1, including a pair of springs located side by side in the housing each spring having associated therewith a pair of said restoring levers, one for each piston.
4. A piston engine according to claim 3, wherein each return spring is a helical spring compressible in a direction generally parallel to the axis of the pistons, each spring having a cup over each of its axial ends, wherein two levers bear against first adjacent axial ends of the two springs to urge one piston against the cam parts and the other two levers bear against the opposite axial ends of the two springs to urge the other piston against the cam parts.
5. A piston engine according to claim 3, in which each piston carries a roller cooperating with the cam parts of the driven shaft, wherein the two springs are parallel compression springs, and wherein the two restoring levers associated with each spring are disposed in mirror image fashion about a plane perpendicular to the axis of the pistons and passing centrally between the two pistons, the two restoring levers associated with each spring engaging a different one of said pistons.
6. A piston engine according to claim 1, wherein a transverse pin is fastened in each piston and each restoring lever is formed with a flat part on the portion of the arm thereof bearing against this pin.
7. A piston engine according to claim ll, in which the return spring has a peripheral depression at its central area and it bears loosely at this part on a pin, fixed in the housing, under the action of the return spring.