US2265314A

US2265314A - Power transmission

Info

Publication number: US2265314A
Application number: US217395A
Authority: US
Inventors: Edwin L Rose
Original assignee: WATERBURY TOOL CO
Current assignee: WATERBURY TOOL CO
Priority date: 1936-07-15
Filing date: 1938-07-05
Publication date: 1941-12-09
Anticipated expiration: 1958-12-09

Description

Dec. 9, 1941; RQSE POWER TRANSMISSION 4 Sheets-Sheet 1 Original Filed July 15., 1936 ME ON.

lNVENTOR EDWIN L. ROSE ATTORNEY Dec. 9, 9 E. L.. ROSE 2,265,314

POWER TRANSMISSION Original Filed July 15, 1936 4 Sheets-Sheet 2 sos Dec. 9, 1941. 5L. ROSE POWER TRANSMISSION Originai Filed July 15, 1936 4 Sheets-Sheet 3 FIG. 4-

IBS

INVENTOR ED\N\N L. RO SE gg 2 WA ATTORNEY 1941- E. L. ROSE 2,265,314

POWER TRANSMISSION Original Filed July 15, 1936 4 Sheets-Sheet 4 FIG. 5

INVENTOR EDW \N L. ROSE ATTORNEY Patented Dec. 9, 1941 I rowan TRANSMISSION Edwin L. Rose, Waterbury, Conn., assignor to The Waterbury Tool Company, Waterbury, Conn., a corporation of Connecticut Original application July 15, 1936, Serial No.

1938, Serial No. 217,395

7 Claims.

This invention relates to power transmissions and particularly to transmissions of the hydraulic type comprising a fluid pump and fluid motor either or both of which may be provided with mechanism for varying its displacement in order to vary the speed ratio between the prime mover which operates the pump and the load device which the motor operates. This application is a division of my copending application, Serial No. 90,785, filed July 15, 1936, for Power transmission, now Patent No. 2,168,655. The invention is illustrated as adapted for use in a well drilling rig of well-known type in which 'a string of drill stem is caused to revolve by a rotary drilling head while a portion of the weight of the string rests upon the earth formation at the bottom of the hole being drilled, the remainder being suspended on a block and falls mounted in a drilling derrick and connected to a draw-works drum.

It is desirable in such drilling operations to maintain at a constant value that portion of the weight of drill string which rests upon the earth formation at the bottom of the hole and to be able to readily adjust such weight to different values as different formations are encountered. Various automatic control devices have been proposed for regulating the weight on the drill stem, many of which have been unsatisfactory, due to lack of sensitivity in their regulation. Some forms of automatic regulation utilize mechanism which is responsive to variations in tension in either the live or the dead end of the cable, which supports the drill string through the block and falls. Such devices may not be made sensitive to the degree required since the friction of the sheaves introduces a damping effect which in some instances may be as high as 25% of the suspended weight. Such a device therefore can respond only to changes in suspended weight which are greater in magnitude than the frictional damping effect between the drill string stem and the weight sensitive device.

In earth boring operations of this general class it is necessary from time to time as the work progresses to retract the drill stem from the hole for the purpose of replacing the cutting bit at the lower end of the drill stem. In so doing it is necessary to stop the rotational movement of the drill stem and hoistthe stem a suitable distance to near the top of the derrick, this distance usually being 90 feet, and to grip the stem at the rotary table and remove the section of the drill-stem projecting above the table. The hoisting apparatus is then lowered and connected to the remaining portion of the stem projecting Divided and this application July 5,

from the rotary table and hoisted another feet and the operation is repeated until the entire string is removed from the hole. After necessary repairs to the-bit are made, by reversing this process the bit may be again brought to working position at the bottom of the hole.

In many drilling operations of this'nature it is of prime importance that the hole be cut down to itsintended depth in the least possible total lapsed time. Inasmuch as normal. drilling operations are suspended while the drill string is being retracted and replaced for repair purposes, it is essential to keep the time consumed for this purpose to a minimum and it is customary to provide prime movers of several times the power output required for drilling operations so that the string may be retracted at a maximum speed and lost time reduced to a minimum. It will be seen that in retracting the string the weight of the string and the load to be lifted is progressively reduced as each section of drill stem is detached fromthe sections below it so that at each hoist of 90 feet the load to be hoisted is reduced by the weight'of one 90-foot section of drill stem.

For a given maximum horsepower of the prime mover and a given weight of drill string there is only one speed ratio between the prime-mover and the draw-works drum which will permit the string to be retracted at aspeed which utilizes the full power of the prime mover. It is obviously impractical to provide direct mechanical gearing between the prime mover and the draw-works drum with sufficient speed ratios to permit full power hoisting of the stem at each 90-foot hoist. In drilling rigs in general use heretofore variable speed chains and sprockets or spur gearing have been provided with usually 4 or 6 available speed ratios and the operator has selected the highest drive ratio which will permit the prime mover to hoist the stem without stalling. With this construction it is necessary to use one speed ratio for a considerable number of consecutive hoists of the drill stem before the drill stem weight is reduced sufficiently to enable the operator to shift to the next higher ratio. It will be seen that with this method of operation the speed of hoisting is the same for several consecutive hoists of the drill stem and inasmuch as the weight of theure 2.

which operates with a high degreeof sensitivity to small changes in the suspended weight.

I matic feed control for maintaining constant weight on the bit at the bottom-oi. the hole, which is responsive directly to the suspended weightand A further object is to provide a power trans.

mission suitable for use as a draw-works drive for a well drilling rig whereby the ratio of power transmission between the prime mover and the draw-works drum may be adjusted to the value necessary to utilize the full power outputof the wherein the Kelly a ball ,60 from the travelling- -block,; not shown,

a hydraulic cylinder assembly 6'4 being secured to the Kelly. A. suitable swivelling connection at 66 is provided for permitting circulation of the 1 Y =mud laden cutting fluid to the, interior of the";

tool string. The power transmission and control "system therefor includesa stroke varying hyprime mover at each hoist of the drillstem. j v A further object is to provide a pow'er transmission of such character wherein ar r.- operatorcontrolled member may be'moved tbcause the draw-works drum to rotate in hoisting 'dlrection and wherein automatic means beyond the control of the operator acts to select the proper ratio of power transmission necessary to utilize the full power output of the prime mover for any givenweight of drill stem. 1 v I It is also an object to provide a power trans- I mission for a well drilling apparatus incorporat- Further objects and advantages of the presen invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a cross sectional view of a power transmission incorporating a preferred form of the present invention.

Figure 2 is a diagrammatic view of the hydraulic circuits employed in the invention.

Figure 3 is afragmentary side view of a hydraulic power transmission forming part of the invention.

Figure 4 is a cross section on line 4-4 of Figure 3. I

Figure 5 is a vertical sectional view of a weight sensitive control element forming part of the present invention.

Figure 6 is a cross section on line 6'-6 of Fig- Figure 7 is a fragmentaryv sectionalview on line 'II of Figure 2. a

The transmission illustrated in Figure 1 consists of a variable displacement 'fluid motor 26 and a variable displacement fluid pump 32.

output shaft of the motor may be connected by suitable driving connections, shown morefully in. my copending application, to a draw-works drumwhile the input shaft 34 of the .pump may be connected by other driving connections to a' suitable prime mover such as a Diesel engine.

;j The details of the drilling rig being of no con- 'cemin the present invention, they are not illustrated herein. Normally such a rig comprises a draw-worksxor winch by which the tool string may be raised-or lowered in the hole together with suitable rotary driving means wheredraulic motor 62 for the variable displacement pump 32 and a stroke varyinghydraulic motor 94 for the variable displacement motor 26. The

- ;motor 26 and pump 32 are illustrated as of the Waterbury construction comprising revolving cylinder'barrels 96 within which-pistons 96 are 'recipro'cated. by the motionoffsocket rings I00 which revolve in' tilting boxSQIM and I04.

The tiltingbox I02 carries a stud 'I06'having. a

pivoting and sliding connection witha differen.

tialpiston- I06 mounted in cylinder bores I I0 and -I I2 of the hydraulic motor 62. The bore H2 is subjected to a constant. fluid pressure from an- I auxiliary pump 4, througha conduit 6 while} g the bore H0 is subjected-either to pressure from the pump H4 or to exhaust sidepressure in accordance with the movement of certain control .valves laterto be described.

The tilting box I04 carries a stud II6 having a pivoting andsliding connection with a differential piston I20 reciprocable in bores I22 and I24 of the fluid motor 64. The bore I24 is subjected to constant pressure from the pump II4 through a conduit I21 while the bore I22 is subjected either to auxiliary pump pressure or to atmospheric pressure in accordance with the movements of a pressure responsive pilot valve I26 at certain times, and at other times is sub-' jected constantly to auxiliary pump pressure.

A movable valve member I26 of the pilot valve I26'is mounted in a bore I30 of the pilot valve I26 and has a reduced diameter stem I32 projecting through the bottom wall of the bore I30 and carries two piston heads I34 and I36. The lower end of the bore is in communication through a conduit I36 with the working circuit of the hydraulic transmission preferably through a shuttle'valve I40 as indicated in Figure 2 where by the side of the working circuit-which is of higher pressure at any instant is placed in communication with the lower end of the bore I30. An adjustable spring I42 urges the valve member I26 downwardly against the pressure exerted in the lower end of the bore I30. A conduit I44 is normally closed by the piston I36 and is opened to the exhaust side pressure at the interior of the case of the motor 26 through a passage I46 when-valve member I26 moves downwardly'while communication is established betweenconduit I44. and the auxiliary pump 4 through a conduit I46 when the valve member The plunger I62 is formed with a groove I56 comby .the"Kelly or squared section at the top end of-the string may be rotated. The tool string is suspended-from a block and falls in the derrick by means of a swivel connection which is, in the present invention, modifled to function as a part of the transmission controlling mechanism. This part of themechanism is -illustrated in Figure 5 I26 is moved upwardly.

The fluid motor 62 is under the control of a manually operable follow-up valve I which comprises a plunger I62 slidable in a bore I54 formed in the small end of the piston I06. The bore I64 is-in communication with the interior of the case of the pump 32 through a passage I66.

municating with the bore I64 by a passage I66 and a groove I62 communicating with the cylinder bore 2 through a e I64. The piston I66 is formed with a bore I66 leadingfrom the cylinder III to a groove I66 (seeFIgure 6) which connects a radialbore I16 with adiametrically opposite bore I'|2.' I-Qngitudinalmovement ofthe plunger I62 in either direction from the 'I6 is by meansof I position illustrated thus opens a connection either from the cylinder bore H2 or from thebore I54 to the bore'I88, leading to the cylinder H and thus causes movement of the piston I08 in a manner to follow up the movements of the plunger I52. The plunger I52 is controlled manually through a collar I41 and a fork I49 (Figure '1) which may be connected to a suitable control handle, not shown, adjacent the drillers station.

Plunger I52 is adapted to be rotated angularly about its axis in order to move grooves I58 and I82 out of register with the radial bores I10 and I12 as illustrated in Figure 6. For this purpose, a sleeve I14 is mounted adjacent theend ofthe cylinder I I2, and is connected to the plunger I52 by a sliding key I18. An arm I18 on the sleeve I14 may be moved to rotate the sleeve I14 and plunger I52 as desired without affecting the longitudinal position of the plunger I52.

For the purpose of automatically controlling the tilting box I02 to maintain the horsepower delivered by the transmission at a constant maximum, certain valves are provided capable of predominating over the control exercised by the plunger I52. Referring now to Figure 2, a speed governor operated valve I80 is provided, having a movable member, I82 provided with a piston head I84 for controlling the passage of fluid between a conduit I88 and the interior of the casing of the pump 32. The member I82 is operated by means of an arm I88 which is controlled by a speed governor I90 responsive to the speed of the shaft 34 of the pump 32. The arm lies in a downward position, illustrated, at normal pump speeds and moves upwardly Whenever the pump speed falls below normal, to connect conduit I88 with the interior of the casing through a conduit I85. A pressure responsive valve I92 is also adapted to control communication between the cylinder H0 and the interior of the casing of the pump 32. This valve comprises a movable member I94 having a piston head I98 adapted to control communication between a conduit I98 and'the interior of the casing of the pump 32. A piston head 200 is subjected to pressure from the shuttle valve I40 through a conduit 202 which is counteracted by an adjustable spring 204 so that when the pressure in either side of the working circuit rises beyond a predetermined safe value the valve member I94 rises to connect the conduit I98 with the interior of the casing of the pump 32 through a conduit 208.

A selector valve 208 is provided for manually transferring control between the automatic constant horsepower control used during hoisting of the drill stem from the well and the automatic constant weight control used while drilling. For this purpose the valve 208 is provided with a movable member 2I0 having pistons 2| 2, 2I4, 2I8, and 2I8. A conduit 220 leads to the body of the valve 208 between the pistons 2I4 and 2I8 and is connected to the outlet line 222 of the auxiliary pump II4. A conduit 223 connects to the body of the valve 208 between the pistons 2I4 and 2I8 and leads to the cylinder I22 of the,

motor 94. Between the-piston heads 2I8 and 2I8 the conduit I 44 connects to the body of the valve 208. Between the piston heads 2I2 and 2I4, a conduit 224 connects to the body of the valve'208 and leads to a pilot control valve 228, later to be described. Between the heads '2I2 and 2 I4 a conduit 228 connects to the valve body and leads to the cylinder IIO of the motor 92. To the left of the piston 2I2 a conduit 230 connects to the body of the valve 208 and leads to the conduits I88 and I98. A bore, not shown, is provided longitudinally through the center of the member2l0 for connecting the extreme end spaces of the valve body together.

In the position of the valve illustrated in Figure 2, which is the position for constant weight control, the cylinder I22 is subjected to the outlet pressure of the pump I I4 through the

conduits

222, 220, and 223 and is cut of! from the conduit I44 which is controlled by valve I 28 by the piston head 2I0. The cylinder H0 is subjected to controlby the pilot valve 228 through the conduits 228 and 224 while it is cut off from control by the speed responsive valve I80. and pressure responsive valve I92 by the piston head 2I2. The valve 208 is controlled from a stem 232 which is connected to a suitable control handle, not shown, adjacent the drillers station. A control rod 238 is also connected to the same handle and operates a bell crank 240 which is connected by means of a link 242 to the arm I18 of the sleeve I14 so that when the valve 208 is moved into drilling position the sleeve I14 is turned to move the grooves I58 and I82 out of register with the bores I10 and I12. The passages I80 and I84 are somewhat smaller than the passages between cylinder IIO and the exhaust side of the system through valves I80 and I92 so that during constant horsepower operation, the valves I80 and I92 may predominate over the follow-up valve I50.

Referring to Figure 5 which shows the mechanism for controlling the weight on the drilling bit, the cylinder 84, which is mounted at the top of the Kelly 18, includes a cover 244-having a central bore through which a circular stem 248 may slide, which bore is sealed with a packing member 248. The stem 248 carries the bail 80 at its upper end and is provided with a piston 250 at its lower end having a fluid tight sliding fit in the interior bore of the cylinder 84. Piston 250 carries a valve 252 adapted to control the passage of fluid from the top to the bottom of the piston 250. For this purpose the piston is provided with a bore 254 having an enlarged portion 258, the bore 254 being adapted to receive a piston member 258 of the valve'2 52. Passages 280 extend from the bore 254 to the lower side of the piston 250. The valve 252 is controlled in accordance with the position of the piston 250 relative to the cylinder 84 by means of a lever 282 pivoted at 284 and having a heel 288 adapted to rest on the bottom surface of the cylinder 84. A spring 281 constantly urges the valve 252 down-- wardly and holds the heel 288 against the bottom of the cylinder 84.

A conduit 288 is formed in the stem 248 to communicate with the space above the piston 250 and terminates in a pipe 280a which is connected by a flexible hose, not shown, to the transmission control mechanism. A conduit 210 extends from the lower face of the piston 250 through the stem 246 and terminates in a pipe 210a which is connected by a flexible hose, not

shown, to the transmission control mechanism. The conduit 288 is connected to the outlet of a second auxiliary pump 212 and to a port 214 in the pilot valve 228. The conduit 210 is connected to the inlet of auxiliary pump 212 and to a port extends through the movable member 218 to connect the bores :90 and 292. An adjustable between the port 298 and a port 300 which is connected to a conduit 306 leading from the dis-- charge conduit 222 of the auxiliarypump II4. When the valve member 218 is moved to the left communication is established between the port 298 and a; port 304 communicating with a conduit 306 which leads tothe return conduit 308 for the auxiliary pump H4. ,The conduit 308 is in communication with the usual expansion tank 3I0'which is also connected by conduits, not shown, with the interior of the casings of th motor 28 and the pump 32.

A relief valve 3| 2 connects by conduits 3I4 and 3I6 with the outlet and the inlet of the pump II4 for the purpose of limiting the pressure developed in the conduit'222. A- relief valve3I8 is interposedin a conduit'320f leadin from the conduit 306 to the conduit 210 for the purpose of replenishing fluid in the system fed-bythe the well the speed of hoisting is determined solely by the speed responsive valve I 80. As soon as the tilting box I02 begins to'move into stroke,

pressure is created in the high pressure valve port of the hydraulic transmission which is transmitted through conduit I38 to the valve I26. As.

. soon as this pressure reaches a predetermined I22, thus'moving the piston I to the left and placing the tilting box I04 in full stroke position. As the'piston I 08 continues to move to the right ,a point is reached where the speed of hoisting is such that the maximum horsepower of the prime mover is utilized. Any' movement of thetilting box I02 beyond this point causes the prime mover auxiliary pump 212. The valve 3I8 maybe set so that a predetermined drop in pressure in the low pressure conduit 210 permits fluid to pass from the'conduit 302 to the conduit 210 until the pressure in the latter rises to normal operat-. ing value. A relief valve 322 is also provided in a conduit 324 leading between theconduit 210 and the return conduit 308 for the auxiliary pump I I4. The valve 322 is preferably set to open at a predetermined pressure rise above normal in the low pressure conduit 210. Conveniently the conduit 210 may be maintainedat a range of pressures between atmospheric and 25 lbs. per sq. in. thereabove. Thus the valve 322 would be set to relieve at 25 lbs. per sq. in. while the valve 3L8 would be set to relieve at the samevalue at which thevalve 3I2 isset The auxiliary pumps '4 and 212 may be driven from the shaft 34 by a belt drive 326' while a belt drive 328 operates the speed governor I90.

In operation of the device when it is desired to hoist the drill'stem, the selector valve 208 is moved to the left hand position, in Figure 2, in which sleeve I14 holds the grooves I58 and I62 in register with the bores I10 and I12, and the speed of hoisting may be controlled by shifting the plunger I52.. Thus if the plunger I52 is moved to the right, Figures 1 and 2, fluid will be adto fall off in speed which accordingly operates the speed governor I90 to lift the valve I80. As soon as valve I80 lifts the cylinder H0 is opened tothe exhaust side of the system through conduits 228, valve 208, conduits 23.0 and I86.'valve I80 and conduit I85. Movement of the tilting box I02 is therefore prevented beyond a position at which the speed of hoisting is such as to-use the full horsepower of the prime mover; f

As. the weight of the drilling stem is gradually decreased by' progressive removal of sections thereof,thetilting box I02 moves further toward full stroke "position at each time the plunger I52 is operated to hoist. When the weight of the stem decreases sumciently so that the tilting box I02 can move into full stroke position without slowing down the prime mover, the transmission operates at one to one ratio until a further decrease in the weight of the stem permits the valve I26 to drop thus opening the cylinder' l22 to the exhaust side of the system through conduit 223-, valve 208, conduit I44, valve I26 and conduit I46. The piston I20 thereby moves to the right until the stroke of the motor 28 has decreased sufliciently to maintainthe pressure at which the valve I26 is set. The hoisting speed is thereby increased to the point where the full power of the prime'mover is utilized. As the weight of the stem further decreases, the stroke of the motor 28 is correspondingly decreased until the minimum stroke is reached at the point where the last strand of drill stem is removed from The drill string may be fed into the hole again as sections are added thereto by permitting the drill string to fall of its ownweight in the usual manner. When the drill string has been completely fed into the hole, drilling may be resumed mitted to' the cylinder I I0 from pump I I4 through the conduits 222, and H6, cylinder 2, conduit. I64, groove.l62, bore I12, groove I68 and bore I66.- The piston I88 will thereby move to the right by the same distance that the plunger I52 was'moved to the right and the tilting box I02 will be moved into strokoin a direction causing I the hoist drum is to wind cable thereon and 1m -.the drill string; Conveniently the plunger I52 maybe thrownto its limit so that the tilting e box l02will be;moved' into iullystrokeii' the weight of the drili string is such as to permit hoisting'at this speed. 'Considering the operaby operating the handle to shift the selector valve 208 and the sleeve I14 into drilling position.

Under these conditions the auxiliary pump 212 delivers fluid through the conduit 268 through theupper chamber of the cylinder 84. The pressure maintained in this chamber is'determined by the setting of the spring 296 which may be ad-' justed to maintain any desired proportion of the total weight of the drill stem suspended from the traveling block. As drilling proceeds the. drill stemis fed downwardly as required to maintain the weight on the drilling bit constant. Thus as the drill makes hole the resulting small increase in the weight suspended on the traveling block tends to pull the cylinder 84 downwardlythus tending to'close' the valve 252 and increase" the pressure above the piston 250. The valve memher 218 is thereby moved to the left permitting fluid to fiow from the cylinder I IO through conduit 228, valve 208, conduit 224, port 298, port 304, conduit 306 and conduit 308 to the exhaust tilting box I02 in a slight stroke in the lowering direction such that the drill -is fed downwardly at the same rate at which the bit makes hole. Should the drill be fed downwardly too rapidly the cylinder 84 will tend to rise, thus opening the valve 252 wider and permitting valve member 218 to move to the right. Fluid from the auxiliary pump H4 is thus permitted to pass through the conduits 222 and 302, port 300, port 298, conduit 224, valve 208 and conduit 228 to the cylinder I ID. The rate of feed is thus adjusted to correspond to the rate at which the bit makes hole" and the weight supported from the travelling block is thus maintained constant.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

, 1. A control system for a variable displacement fluid pressure energy translating device comprising' in combination, a control member movable to vary the displacement of the device, a manually operable member, means for moving the control member in accordance with movements of the manually operable member, and means for moving the control member in response to predetermined operating conditions at said translating device regardless of the position of the manually operable member, and without exerting appreciable force on the manually operable member.

2. A control system for a variable displacement fluid pressure energy translating device comprising in combination, a control member movable to vary the displacement of the device, a manually operable member, means for moving the control member in accordance with movements of the manually operable control member, means for moving the control member in response to predetermined operating conditions at said translating device regardless of the position of the manually operable member, additional means for moving the control member, and manually shiftable means for selectively rendering the control member responsive either to the first mentioned means or to the last mentioned means.

3-. A fluid pressure operated control device comprising in combination a follow-up servo motor including a fluidoperated piston, a pilot controlling member, valve means responsive to the differential position of the piston and the pilot member for controlling the flow of fluid to operate the piston, and additional valve means for controlling the flow of fluid to the piston in opposition to, and predominant over, the fiow directed by the first mentioned valve means.

4. A fluid pressure operated control device comprising in combination a follow-up servo motor including a; fluid operated piston; a pilot controlling member, valve means responsive to the differential position of the piston and the pilot member for controlling the flow of fluid to operate the piston, and'means for at times causing said piston to move in opposition to the movement thereof which is otherwise dictated by said valve means, said last means comprising a valve operable to direct the flow of fluid to operate the piston at a greater rate of flow thanthat controlled by the first mentioned valve means.

5. A fluid pressure operated control device comprising in combination a follow-up servo motor including a fluid operated piston, a pilot controlling member, valve means responsive to the differential position of the piston and the ,pilot member for controlling the flow of fluid to operate the piston, additional valve means for controlling the flow of fluid to the pistonjin opposition to, and predominant over, the fiow directed by theflrst mentioned valve means, and pressure responsive means for operating the last mentioned valve means.

6. A fluid pressure operated control device comprising in combination a follow-up servo. motor including a fluid operatedpiston, a pilot controlling member, valve means responsive to the differential position of the piston and the pilot member forcontrolling the flow of fluid to operate the piston, additional valve means for controlling the flow of .fluid to the piston in opposition to, and predominant over, the flow directed by the first mentioned valve means, and speed responsive means for operating the last mentioned valve means.

'7. A fluid pressure operated control device comprising in combination a follow-up servo motor including a fluid operated piston, a pilot controllingmember, valve means responsive to the differential position of the piston and the pilot member for controlling the flow of fluid to operate the piston, means for at times causing said piston to move in opposition to the movement thereof which is otherwise dictated by said valve means, and speed responsive means for operating the last mentioned means.

EDWIN L. ROSE.