US1640896A - Air spring - Google Patents

Description

Ann. 30 1927.

* I B. B. HOLMES AIR SPRING Filed Nov. 25, 1922 xii 3 run 114 oz Patented Aug. 30, 1927.

BRADFORD B. HOLMES, OF NEW YORK, N. Y.

AIR SPRING.

Application filed November 23, 1922.

The invention relates to pneumatic cushioning devices and more particularly to that type of pneumatic cushioning device which automatically adjusts itself to the sustained load.

Pneumatic cushioning devices of this type comprise two telescoping members which form a variable volume chamber adapted to contain air under pressure. The chamber is divided into two spaces, one of which serves as a main or primary cushion and the other of which serves as a reservoir and may also serve as an auxiliary cushion. The main or primary cushion contains air normally at low pressure and the reservoir or auxiliary cushion contains air normally at relatively high pressure. When the low pressure cushion is abnormally compressed there is a flow of air into the reservoir or high pres sure cushion. The back flow of air to the low pressure cushion is regulated by the relative posit-ions of the parts. Pneumatic cushioning devices of the above type are particularly adapted for application to vehicles, such as automobiles and form the subjectmatter of copending applications, which, since the present application was filed, have resulted in Letters Patent as follows: No. 1.437.894 issued Dec. 5. 1922; No. 1,438,527 issued Dec. 12, 1922; No. 1,439,417 issued Dec. 19. 1922. The present invention is more particularly an improvement on the structure disclosed in my last named Patent No. 1,439,4 17. I

A desirable feature of a pneumatic cushioning device is such an arrangement of the parts to permit the use of a thin. free flowing liquid as a lubricant and liquid seal for the various parts. Such a liquid is not seriously affected by seasonal changes in the Weather. whereas the relatively heavy and viscous oils heretofore used are. and for that reason seriously impair the function of the device in winter. Hence it has heretofore commonly been the practice to use oils of different body and viscosity in Winter and summer. A serious difliculty sometimes encountered in the use of thin liquids is the fact that such liquids are readily churned into a spray during the vibration of the parts and have a tendency to accumulate in the lOWGI parts of the device and interfere with the functioning thereof. One object of Serial No. 602,824.

parts of the device and to provide means whereby the liquid is conveyed to the moving parts and any excess returned to the reservoir. This mode of operation assures a sufficient amount of liquid between the moving parts to enable them to have a proper dash pot action, but prevents the liquid from accumulating to such an extent as to interfere with the cushioning function of the device.

Another object of the invention is to simplify and improve the construction of pneumatic cushioning devices of this type, rearranging the parts so as to reduce their number. Incidentally this reduction in the number of the parts results in greater durability and smoothness of action and also in a lessened cost of manufacture. This object is accomplished by a radical change in the construction and arrangement of the check valve which. permits the flow of air from the low pressure cushion during abnormal compression thereof into the reservoir or high pressure cushion: in the construction and arran gement of the bleed valve by which there is a back fiOW of air from the reservoir or high pressure cushion to the low pressure cushion: and in the construction and arrangement of the partition which divides the variable volume chamber as a whole into the low pressure cushion and the reservoir .or high cushion. It will be understood in this connect-ion that although the high pressure cushion functions as a cushion in conjunction with. the low pressure cushion, its chief function is to serve as a reservoir to receive air from the low pressure cushion when the latter is abnormally compressed and to feed back this air to the low pressure cushion to restore the parts to normal riding condition. Hence it will be understood that the reservoir may or may not act as a'cushion. In 1 the air therein, whereas in the high pressure cushion or reservoir the ratio of" the total volume to total variatlon of volume is relatively high. Hence it will be seen that the cushion function of the reservoir may be regarded as incidental until the ratio of total volume to total variation of volume is reduced substantially.

A further object of the invention is the provision of means for preventing any leakage of liquid from pneumatic cushioning devices. The jointbetween the relatively moving telescopic members of a pneumatic cushioning device is commonly sealed by a leather packing. When a heavy or viscous oil is used it is difficult to arrange the packing so that it will wipe the joint clean at each relative movement of the parts. After the leather has passed over the adjacent surface a thin coat or film of oil is left on it. This in time results in a creeping or seepage of the oil along the sliding joint and the eventual waste of the oil. By using a thin, free flowing liquid the leather packing wipes the joint clean at each relative movement of the parts. Hence there can be substantially no leakage. A thin, free flowing liquid, however, is readily thrown from the packing it is intended to cover during the vibration of-the parts while the device is in use. The present invention provides means for keeping the leather packing sealing the oint between the telescopic members constantly submerged undcr a bath of liquid, thus enabling a thin, free flowing liquid to be used. These and other features of the invention are more fully described hereinafter and particularly pointed out in the appended claims.

A cushion embodying the preferred form of the present invention is illustrated in the accompanying drawings in which Fig. 1 is a view, chiefly in vertical axial section, showing one of the cushions mounted upon an automobile. I

Fig. 2 is a section on the line 22 of Fig. 1.

Fig. 3 is a section on the line 3-3 of F 1.

The improved pneumatic cushioning device of the present invention as illustrated in the drawings, comprises an outer and an inner telescoping member. The outer telescoping member is a vertically arranged cylinder 9 threaded into a base 6 held by a bolt 7 to the end of the spring horn 8 of the vehicle body. The upper end of the cylinder is closed by a cap 10. A piston 27 is mounted to slide in the lower open end of the cylinder to form a variable volume chamber adapted to contain a body of air under pres sure. The lower side of the piston or plunger 27 is provided with lugs or ears 29 to receive a pin 30 on which the upper end of a strut link 31 is pivoted. The lower end of the strut link is pivotally connected by the bolt 32 with the outer end of a leaf spring 33 which forms part of the running gear of the vehicle.

The piston or plunger 27 is provided with a tubular extension 26 which projects upwardly within the cylinder 9 and is in sliding contact therewith. The variable volume chamber thus formed is divided into a low pressure cushion space A and a high pressure cushion space composed of the parts B and C which are always in free communication with each other. The chamber is divided into the low and high pressure cushion spaces by means of a plate or partition 21 screwed on the lower end of a hollow stem or tube 11, the upper end of which is screwed into a threaded hole in the cap 10, the shoulder 12 on the stem seating tightly against the cap. Resting on the partition plate 21 with its rim or flange projecting upwardly into the high pressure cushion is a cup leather or packing 23 which normally seals the low pressure cushion A from the high pressure cushion B and C. The cup leather is held in place between the plate 21 and a washer 22 which seats against a shoulder 20 formed on the lower end of the stem 11. l/Vhen the cushion A is abnormally compressed during the oscillation either of the partition 21 or the piston 27 due to load shocks or road irregularities, the cup leather 2S performs a valvular function as a check-valve, which permits a flow ofabno 'mally compressed air from the low pressure cushion A into the high pressure cushion B and C. Thus the cup leather or valvular packing 23 performs the double function of normallysealing the low pressure cushion from the high pressure cushion and acting as a check-valve. The lower side of the partition plate 21 is provided with a depending skirt or flange 2 1 which forms a dash pot plunger and cooperates with a recess 28 in the piston 27 to constitute a compression dash pot to check extreme compressive movements of the cushioning device.

The expulsion of the air from the low pressure cushion results in a lowered riding position of the vehicle body and the parts of the cushioning device connected therewith. In this condition of the parts, the cushions are brought into communication to permit a back flow of air from the high pressure cusl1- ion into the low pressure cushion to restore the parts to normal riding position. The bleed valve construction of the present invention comprises a series of ports arranged as vertical grooves 36 extending upwardly from the piston 27 in the interior surface of the piston extension 26. There may be any preferred number of grooves, 4 being shown in the drawings. The length of these grooves in relation to the upper margin of the cup leather 23 defines the riding position of the parts of the cushioning device. Vfher-e it is desired that the piston shall have a relatively short stroke, as in the, cushioning devices located at the front of length of the groove is, a detail which is variable according to the desired characteristics of the cushion.

When the parts are in normal riding position, the cup leather or valvular packing 23 seals the upper ends of the bleed valve grooves 36. When, however, the parts are in lowered position due to the abnormal compression of the low pressure cushion, the

upper ends of the grooves extend beyond the upper margin of the cup leather and there is a back flow of air from the high pressure cushion into the low pressure cushion until the parts are restored to normal riding position. It has been found that the cup leather 23 is not injuriously affected by contact with the grooves 36, probably for the reason that its normal position is above the grooves and that when the cushion A is abnormally compressed due to load shocks and road irregularities and the cup leather is substantially below the upper ends of the grooves, the cup leather is forced inward y out of contact with the interior wall of the piston extension 26 as an incident to the valve function of the cup leather.

The sliding joint between the tubular piston extension 26 and the interior surface of the cylinder 9 is sealed by a packing 42 in the form of a cup leather whose rim ex-. tends in an upward direction. The upper end of the piston extension 26 is beveled and the packing 42 is held thereagainst by means of an annular rib or flange 41 extending outwardly from a reservoir 40 threaded into the upper open end of the piston extension and whose function will be presently described. The upper free end of the cup leather is held in snug contact with the in: terior surface of the cylinder by means of a spring ring 43 which may be an ordinary metal piston ring. t is essential for the proper functioning of the device that the packing 42 be kept covered by a bath of liquid and for this purpose a baffie44 is provided which is formed as an upwardly and outwardly extending flange of the reservoir 40. The baffle 44 projects into close proximity with the interior surface of the cylinder 9 but avoids contact therewith, and it is separated from the top ofthe packing 42 a substantial distance to provide an annular space to contain the liquid which covers the packing. The baffle 44 functions vto confine the liquid above the packing 42 even when the parts are in rapid vibration.

The sliding joint between the piston or plunger 27 and the interior surface of the cylinder is sealed by a ring 35 mounted in a groove in the piston. The ring 35, which may be an ordinary one-piece metal piston ring, is chiefly for the purpose of removing dust from the cylinder and preventing it from working upward. The ring may, however, perform a scaling function.

The reservoir 40 is adapted to hold a supply of liquid above the working parts of the cushioning device and means are provided for feeding the liquid from the reservoir to the working parts and for returning the excess liquid to the reservoir, enough liquid being left betweentlie parts so that they will have a dash pot action at the extreme ends of the strokes in both directions. From the bottom 46 of the reservoir 40, which is cup-like in its general form, rises a central hub 45 in snug sliding contact with the stem 11. The upper end of the hub 45 extends a substantial distance above the baffle 44 so that the normal level ofv the liquid in the reservoir, which is clearly indicated in Fig. 1, is a substantial distance above the baffle. Thus the packing 42 is kept constantly moist by a sealing bath of oil or other lu bricating and sealing liquid. The reservoir 40 is provided with an annular bottom 46 which serves as a. dash pot plunger designed to enter the cup leather 23 near the limit of extension of the device and form therewith an extension dash pot to check extreme extension movements of the device. I

The annular bottom 46 of the reservoir 40 subdivides the high pressure cushion or reservoir into the lower space E and upper space C, which are kept in free open communication with each other, through the port holes 18 in the upper part of the stem 11 and the port holes 19 in the lower part of the stem. When the vehicle is running over arough road, the piston and the parts connected with it will be in more or less rapid vibration and therefore there will be fluctuations of air through the ports 18 and hollow stem 11 and the ports 19. Some of the liquid in the reservoir will be quickly churned into a spray which will be carried back and forth through the stem 11. For mechanical convenience the stem 11 which supports the partition plate 21 is made hollow and utilized as a duct for the transference of liquid from and back to the reservoir. It is obvious that a duct separate from the stem 11 and otherwise arranged may be. employed for this purpose.

The ports 19 are so positioned that the surging of the air through them and up and down the stem '11 will keep the desired quantity of sealingliquid and no more in the cup leather 23. Any excess quantity of s aling liquid will be in'nnedia tely blown up through the stem 11 and into the space above the reservoir 40. The bleed valve grooves 36 provide channels through which liquid spray from the cushion B finds its wayinto cushion fraud into the dash pot recess 28. If any excess liquid should tend to accumulate in the recess 28 it would, on the first extreme compressive movement of the cushioning device, be forced up around the cup leather 23, thereby increasing the quantity of li( uid in the can leather and resultin in the immediate transfer of such li'quid up through the stem 11 and into the space above the reservoir. Thus it is seen that the surges of air through the duct in the stem 11 serve alternately to feed liquid to the lower part of the device and then return the excess liquid into the reservoir.

The base (5 being connected to the spring horn by a single bolt 7 must be held in its upright position by other means. 9* split clamp 50, which has an arm 51 terminating in a round face 52, is used for this purpose. The split clamp 50 is clamped around the cylinder 9 by means of the nuts 53 on the tierod and hence may be loosened and adjusted vertically to bring the rounded end 52 into contact with the upper surface of the spring horn. When the clamp is adjusted, the nuts 53 are tightened and the arm 51 is connected to the spring horn by the bolt 55. The tie-rod El extends from side to side of the car, its opposite ends being connected by thenuts 53 to the clamps 50 on the cushioning devices on opposite sides of the car. 1t will be understood that a cushioning device is used on each side of the front of the car and on each side at the rear. This means of mounting the cushioning devices on the vehicle forms the subject-matter of my copending application, Serial No. 602,823, filed Nov. 23, 1922, and not specifically claimed in the present application.

The upper end of the hollow stem 11 is internally threaded to receive a threaded valve fitting 13 which formed with a hexagonal flange let. by which it is screwed to place, the flange l l seating against a gasket 15. it will be observed that this gasket 15 seals the threaded joint between the cap 10 and the stem ii and also the joint between the stem i1 and the fitting 13. The valve fitting 13 is formed with an axial port Within which is mounted an inwardly opening check-valve, preferably of the so-called universal type, commonly used in pneumatic tires, Valves of this general type are familiar to those skilled in the art and it is therefore unnecessary to more fully illustrate or describe the valve. The valve fitting 18 serves merely as a convenient con nection through which air may be pumped into the cushioning device, and normally the valve is closed by a sealing cap 16. All these parts are enclosed in a dust cap 17 threaded onto the cover 10.

tition.

lVhen the pneumatic cushioning device has been applied to the automobile and before it is inflated, the valve fitting 13 is unscrewed and a suitable thin lubricant and sealing liquid is then poured in until it overflows. The quantity so introduced is approximately sufficient to fill the space above the reservoir 4-0 up to the top of the central hub and the cup leather 23 up to the top of the ports 19. The quantity of liquid introduced is thus only suflicient to fill the reservoir with a small surplus for the dash pots. t is not necessary to introduce the liquid directly to the other parts'of the device, because it is rapidly distributed in the operation thereof. When the liquid has been thus introduced and the valve fitting is replaced, air is pumped in until a pressure is created within the device somewhat more than suiiicient to sustain the maximum load to be borne. The parts Will then extend until the valvular packing 23 blanks the ends of the ports 36. 'lVhen the air is first pumped in the surplus liquid above the rim of the cup leather 23 is forced down the grooves 36 into the dash pot recess 28 in the piston 27.

As described above, the partition 21 acts with the recess 28 in piston 27 to form a compression dash pot and with the plunger 46 to form an extension dash pot. I dash pots come into action only on the last quarter inch or so of extreme compression and extension strokes. This permits the free action of the cushioning device on air alone except at the extreme limits of the strokes, when the dash pots prevent the striking of the piston and the reservoir against the par- In order that the dash pots shall work under all conditions, it is essential that they shall be fill-ed, but not to excess, with liquid. The movementsof the piston cause the interior of the cushioning device to be filled with spray. The spray is carried from space G into space B by way of the duct in the stem 11, and from space Binto space A by way of the grooves 36. This spray tends to settle out, filling the dash pots with liquid. i urplus liquid in dash pot 28 is transferred from space A into space B on extreme compression movements of the parts, and from space B into space G on all extension move ments of the parts. It is evident therefore that the movements of the parts act to supply the dash pots with liquid and also to remove excess liquid from the dash pots and return it to the reservoir.

The self-regulative function of the cushioning device is secured in a manner substantially similar to that of the structures disclosed in the above applications. The cup check valve and the grooves or ports 36 and the cup leather serve asthe return or bleed valve. Sudden compressive movements of the device due to sudden and heavy load These till) leather or valvularpacking 25 serves as a V Cir shocks result in sharp rises of pressure in the low pressure cushion A so that air is displaced upward past the cup leather 23. The transfer of pressure fluid from the low pressure cushion to the high pressure cushion reduces the load sustaining action of the device and results in a lowered riding position of the parts. If this lowered riding position brings the upper ends of the grooves 36 above the upper margin of the cup leather 23, in the intervals between load or road shocks, back flow of air will occur from the high pressure cushion to the low pressure cushion and the parts of the device will be thereby restored to normal riding position with the cup leather 23 slightly overlapping the ends of the ports 36. Hence the cushion ing device automatically adjusts itself to the imposed load. 1

Having thus described the invention what I claim as new is 1. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having a tubular extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, a reservoiri'or holding a supply of liquid, a partition supported by the cylinder across the interior of the piston and adaptedto form a compression dash pot with the piston and an extension dash pot with the reser voir to check extreme movement of the parts of the device in either direction, and means operable by movements of the piston for transferring liquid from the reservoir to fill the dash pots and for returning surplus liquid to the reservoir.

2. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having a tubular extension arranged to slide in the open end of thevcylinder to form a variable volumei chamber adapted to contain air under pressure, said piston including a dash pot plunger and a partition supported from the cylinder across the interior of the piston extension and adapted to form an extension dash pot with the dash pot plunger of the piston and a compression in the piston.

3. A pneumatic cushioning device for vehicles having in combination, a vertical cylinder closed at its upper end, a piston having a tubular extension arranged to slide in the lower open end of the cylinder to form a variable volume chamber adapted to contain .air under pressure, a partition arranged across the piston extension and supported from a stem extending downwardly from the top of the cylinder, and a dash pot plunger supported from the top of the piston extension and surrounding the stem, the piston having a dash pot recess therein, the partition being adapted to form an extendash pot with a recess formed sion dash pot with the plunger and a compression dash pot with the recess in the piston.

4:. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having a tubular extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, a partition supported by the cylinder across the interior of the piston extension, a reservoir supported from the piston extension above the partition and the piston for containing a supply of liquid, the partition being arranged to form a dash pot with the bottom of the reservoir and with the piston, and means for supplying liquid from the reservoir to the dash pots and for returning excess liquid from the dash pots to the reservoir.

5. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having "a tubular extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, said piston extension including a dash pot plunger, a partition supported by the cylinder across the interior of the piston extension and arranged to form an extension dash pot with the dash pot plunger of the piston extension and a compression dash pot with a dash pot recess in the piston, a reservoir for containing a supply of liquid supported above the dash pots, and means for transferring liquid from the reservoir to the dash pots and for returning excess liquid from the dash pots to the reservoir.

6. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having a tubular extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, a partition carried by the cylinder, fitting in the tubular extension of the piston and dividing the chamber into a low pressure cushion and a high pressure cushion, means for controlling the flow of air from one cushion to the other and back again, a reservoir supported above the partition and the piston, and means for distributing liquid from the reservoir to the working parts of the device and for returning excess liquid to the reservoir. i

7. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having a tubular extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to the other and back again, a reservoir supported on the open end of the piston extension, a stem connecting the partition with the cylinder, and a duct to convey liquid from the reservoir to the working parts of the device and excess liquid back to the reservoir.

8. A pneumatic cushioning device having in combination, a vertically arranged cylinder closed at its upper end, a piston arranged to slide in the lower open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, said piston having a tubular extension sliding within the cylinder, a leather packing seal ing the joint between the piston extension and the cylinder, a partition across the interior of the piston extension dividing the chamber into a low pressure cushion and a high pressure cushion, means for control-' ling the flow of air from one cushion to the other and back again, a reservoir mounted on the upper open end oi the piston extension adapted to contain liquid normally at a higher level than the working parts of the device, and a hollow stein supporting the partition from the cylinder and having vents above and below the liquid reservoir, where by liquid is conveyed to the top of the partition and excess liquid is returned to the reservoir.

9. A pneumatic cushioning device for vehicles comprising a cylinder closed at one end connected with the vehicle body, a piston connected with the vehicle running geararranged to slide in the open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, a par tition dividing the chamber into a low pressure cushion and a high pressure cushion, means for controlling the flow of air from one cushion to the other and back again, a hollow stem supporting the partition from the cylinder,

mally at a higher level than the working parts of the device, said hollow stem having a vent above the reservoir and another vent below the reservoir, whereby the liquid is conveyed from the reservoir to points below it and excess liquid is returned to the reser- 'voir during abnormal compressive movements of the parts of the device.

10. A pneumatic cushioning device having .7

sealing the joint between the piston and the cylinder, a reservoir mountedon the open end of the piston extension adapted to con-,

tain liquid normally at a level above the end of the piston extension to keep the packa reservoir supporter above the partition adapted to contain liquid iior-' from being thrown out of the liquid containing space during the relative movements of the parts of the device.

11. A pneumatic cushioning device having in combination, a cylinder closed at one end,

a piston, having a tubular extension arranged to slide in the open end of thecylinder to form a variable volume' chamber adapted to contain air under pressure, a partition-supported by thecylinder across the interior of the piston extension dividing the chamber into a low pressure cushion and a high pressure cushion, and a cup leather supported on the partition and'serving as a chec c-valve toperinit air to flow from the low pressure cushion during abnormal co1iipression thereof into the high" pressure cushion, said piston extension having grooves which establish communication 'between the two cushions when the low pressure cushion is abnormally compressed.

12. A pneumatic cushioning device having in combination, a cylinder closed at one end, a piston having a tubular extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to contain air under pressure, a cup leather supported across the interior of the piston extension dividing the chamber into a low pressure load sustaining cushion and a high pressure load, sustaining cushion, said cup leather serving as a check-valve to permit flow 01" air from the low pressure cushion during abnormal compressionthereof into the high pressure cishion, and means for 13. A pneumatic cushioning device for vehicles having in combination, a vertically arranged cylinder closed at its upper end supported fromthe body of the vehicle,- a piston connected with the running gear of the vehicle and ha "ing a tubular extension arranged to slide in-the open end of the cylinder to form a' variable volume chamber adapted to contain airunder pressure, a stem extending downwardly into. the chamber from the cylinder, a cup leather supported from the stem across the chamber dividing it into a low pressure cushion and ahigh pressure cushion, said cup leather serving as a check-valve to permit flow of air from the low pressure cushion when it is abnormally compressed intothe high pressure cushion, said piston extension having grooves ext-ending upwardly from. the piston, theupper ends of the grooves being normallyfsealed by the cup leather, said grooves serving to permit back flow of air from the'high pressure cushion to the low pressure cushion.

14. A pneumatic cushioning device having in combination, two telescoping members forming a variable volume chamber adapted to contain air under pressure, a partition supported from one of said members dividing the chamber into a low pressure cushion and a high pressure cushion, a

cup leather supported from said partitionand normally sealing the two cushions from each other, said cup leather acting as a check-valve to permit flow of air from the low pressure cushion into the high pressure cushion when the low pressure cushion is abnormally compressed, the interior wall of one of said members being provided with ports adjacent the partition and normally sealed by the cup leather, said ports serving during sustained abnormal compression of the members to permit back flow of air from the high pressure cushion into the low pressure cushion.

15. A pneumatic cushioning device for vehicles having in combination, a vertical cylinder closed at its upper end connected with the body part of the vehicle, a piston connected with the running gear of the vehicle and having a tubular" extension arranged to slide in the open end of the cylinder to form a variable volume chamber adapted to con tain air under pressure, a hollow stem extending into the chamber from the top of the cylinder, a valvular packing supported from the lower end of the stem dividing the chamber into a low pressure cushion and a high pressure cushion, said valvular packing permitting flow of air from the low pressure cushion into the high pressure cushion when the low pressure cushion is abnormally compressed, ports in the piston extension normally closed by the valvular packing and serving when the parts of the device are in low riding position to permit back flow of air from the high pressure cushion into the low pressure cushion, a packing carried by the upper end of the piston extension sealing the joint between the extension and the cylinder, and a reservoir mounted on the upper end of the piston extension adapted to contain liquid normally at a level above the working parts of the device, the hollow stem having vents into the high pressure cushion above and below the reservoir, the vibration of the parts serving to transfer liquid from the reservoir through the stem to the parts below the reservoir and to trans fer excess liquid though the stem back into the reservoir.

16. A pneumatic cushioning device for vehicles having in combination, a vertical cylinder closed at its upper end connected with the body part of the vehicle, a piston connected with the running gear of the vehicle and having a tubular extension arranged to slide in the open end 015 the cylinder to form a variable volume chamber adaptedto contain air under pressure, a hollow stem extending into the chamber from the top of the cylinder, a valvular packing supported from the lower end of the stem dividing the chamber into a low pressure cushion and a high pressure cushion, said valvular packing permitting flow of air from the low pressure cushion into the high pressure cushion when the low pressure cushion is abnormally compressed, ports in the piston extension nor mally closed by the valvular packing and serving when the parts of the device are in low riding position to permit back flow of airfrom the high pressure cushion into the low pressure cushion, a packing carried by the upper end of the piston extension sealing the joint between the extension and the cylinder, and a reservoir mounted on the upper end of the piston extension adapted to contain liquid normally at a level above the working parts of the device, said reservoir being provided with a baflie extending over the packing between the extension and the cylinder to keep said packing covered with liquid, the vibration of the parts serving to transfer liquid from the reservoir through the stem to the parts below the reservoir and to transfer excess liquid through the stem back into the reservoir.

In testimony whereof I have signed my name to this specification.

BRADFORD B. HOLMES.

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