Machine Drive Mechanism

Compressors with rack and pinion driving means between a power unit, such as an electric motor, and a compressor unit, such as a piston in a cylinder, are well known in the art. Some are illustrated in my U.S. Pat. No. 3,861,223.

This application is a continuation in part of my application Ser. No. 587,410 filed June 16, 1975, and is concerned with an improved machine drive mechanism, such as between the power unit and the compressor unit in the above mentioned patent, wherein a floating action arrangement is provided for a double rack in combination with a dual-function guide and seal connection between the double rack and an energy absorbing device or unit. The floating of the double rack between the gears, due to the rack's pivotal or flexible connection with a piston rod extending from the energy absorbing device, reduces the tendency of the rack's guide to vibrate and to bind and therefore keeps leakage and friction to a minimum. Also because of the floating gear structure, there is a reduction in the dynamic tooth stresses or an increase in the tooth load carrying capacity. The smaller the mass of the floating portion of the gear train, the greater the benefit of the floating arrangement, because the teeth can adjust to tooth errors faster. Sealing means between the guide and its supporting surface prevents oil or other contaminents from escaping from the power section into the energy absorbing device or vice versa especially because it does not vibrate.

FIG. 1 of the drawing is a fragmentary and schematic vertical sectional view of one embodiment of the invention in a compressor;

FIG. 2 is a similar plan view of the embodiment of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view of a modified form of a drive shaft between the units, providing transverse movement of the double rack and wherein transversely spaced racks merely serve as counter-balancing means;

FIG. 4 is a view similar to that of FIG. 3 of another modification of a floating double rack connected to only one of said units; and

FIG. 5 is another view, similar to FIG. 4, of a still further modification of the invention.

Suitable bearings are provided around piston rod 18a, on which pistons 13 and 16 are mounted, and piston rod 18b on which pistons 14 and 15 are mounted. In high pressure machines, which require very small clearances between the cylinders and pistons, most exact guiding of the pistons is required. Although the floating double rack already reduces vibration of shaft 18 to a minimum, when bearing wear and slack develops, it is possible that piston rods 18a and 18b could vibrate. In order to avoid this potential action of these piston rods, and to allow looser machining tolerances, yoke 17 connects the piston rods 18a and 18b to a piston rod 18, which is axially slidable in the compressor unit. The yoke has holes in the ends thereof which are larger than the diameter of the piston rods extending through the holes so as to allow transverse movement of the yoke with respect to rods 18a and 18b between spaced abutment shoulders on the rods. A bearing sleeve 19 in unit 12 slidably supports a piston-shaped guide or piston rod portion 20 therein. One end of the guide is suitably connected to rod 18 while the other end has a pivotal connection with one end of a double rack member 21 through a pivot pin 22. The guide preferably has sealing rings 23 in annular grooves therein but, for some applications, the guide may be non-grooved and sealing means provided in annular grooves in the bearing sleeve. It is thus seen that no transverse vibrations of either rod 18 or rods 18a and 18b will be transmitted therebetween.

The other end of member 21 has rack teeth 24 thereon which engage the teeth on pinion gears 25. The gears are mounted on fixed shafts 26 in a power unit housing 27. A crosshead 28 has a pair of spaced racks 29 at one end thereof which respectively engage one each of the pinion gears while the other end thereof slidably engages guide members 30 through bearing shoes 28a. The center portion of the crosshead at said other end is pivotally connected to one end of a connecting rod 31 by a pin 32. Slots 33 in the crosshead, through which pins 26 extend, enables the crosshead to move between the two positions shown.

The other end of connecting rod 31 is connected to a shaft 34 of a crank arm 35 which is part of a crankshaft 36. A belt pulley 37 is secured to the end of the crankshaft that projects out of housing 27. The pulley may be driven by any suitable power means, such as an electric motor (not shown).

In operation, as the pulley is rotated, the crank drives the racks back and forth. When racks 29 move to the left, rotating gears 25, the double rack floats between the gears and is driven by them to the right, and, vice versa, when racks 29 move to the right, the double rack moves to the left. The pivotal connection between the double rack and the compressor's piston rod as illustrated in FIGS. 1 and 2, permits this floating action and at the same time prevents vibration and binding action between the guide 20 and bearing sleeve 19. The movement of the piston rod back and forth causes the compressor pistons to function in a well known manner.

If desired, the drive mechanism may be reversed so that the rod 18 carries the spaced racks 29 and the guide 20 is connected to the connecting rod 31. Also, other arrangements may be provided to permit the double rack to float between the gears 25.

FIG. 3 illustrates a modification of the invention wherein a stem extension 121 has a rigid and prestressed threaded connection with a piston rod 118. A reduced diameter portion 121a has a tight fit in a stepped bore 118a, with a beveled end 121b pressing hard against the inner end of the bore. The prestressing distributes the loading on the threads over most of the threads rather than only the first few. The rod 118 extends through and is guided by a bearing seal 120 in unit 112. Stem extension 121 extends through double rack 124, and an internal flange 124a, on one end of the double rack is clamped against an annular shoulder 121c by a nut 138. The other end of the stem extension has a rigid and prestressed threaded connection with a crosshead 128 similar to the crosshead 28 of FIG. 1. A small space is provided between the inner surface of the double rack and the stem 121 so as to allow for some flexing of the free end of the rack with respect to the stem as well as flexing of the double rack with respect to the axis of the guide rod 118, which gives better gear teeth engagement. With this arrangement, a pair of spaced racks, (not shown) but similar to racks 29 are on a pair of rigid connecting plates separate from crosshead 28 and mainly serve as counterbalancing means.

The modification of FIG. 4 differs from that of FIG. 3 in that the end of guide rod 221 is connected to the adjacent end of double rack 224 rather than to the crosshead. An inwardly extending flange 224a is clamped between a shoulder 221a on stem 221 and a nut 238 on the threaded end of the stem.

The modification of FIG. 5 differs from that of FIG. 4 in that the flexible length of the stem 321 is positioned in slightly spaced relationship with the inside surface of an elongated stepped bore 318a in rod 318 rather than in the double rack 324.

The overall operation of the mechanism of FIGS. 3, 4 and 5 is generally the same as that of FIGS. 1 and 2. The main difference lies in having the double rack float between the gears 25 by the flexing of the stems connected to the double racks rather than by having the double rack pivot with respect to the piston rod. In the FIG. 3 and FIG. 4 modifications the double racks can also flex with respect to the stems.