CA1036903A

CA1036903A - Fluid pressure servocylinder

Info

Publication number: CA1036903A
Application number: CA234,310A
Authority: CA
Inventors: Ryuichi Sato
Original assignee: Nikkiso Co Ltd
Current assignee: Nikkiso Co Ltd
Priority date: 1975-04-12
Filing date: 1975-08-27
Publication date: 1978-08-22
Also published as: SE416994B; JPS5624121B2; JPS51119490A; DE2538203A1; NL7510790A; BR7507768A; CH596454A5; GB1519199A; DE2538203C2; SE7509950L; FR2307155A1; FR2307155B1

Abstract

A fluid pressure servocylinder which can be applied to a stroke length adjusting device for mechanism for converting a rotary motion into a reciprocating motion is disclosed. The servocylinder comprises a piston slidably arranged in a cylinder and including a bore extended therethrough, the piston being connected to a stroke length adjusting device, two pressure chambers arranged at each end of the piston in the cylinders and a variable needle communicated with one of the pressure cylinders. By adjusting a needle constituting the variable needle valve, it is possible to determine the position of the piston and hence adjust the stroke length of the reciprocating motion.

Description

- -This irrJention r~lates to a flu-id pressure servoc~llnder which rnakes use Or a flui~ ~,rec;sure so rls to set a position of a control system and which can be appli~YI to a stro~e length adjusting device for mechanisms for converting a rot ~J motlon into a reciprocating motion.
As a mes~Lrlism for con-~ertir~ a rotary motion into a reciprocating motion, various kinds of cranks have heretofore been proposed and carried out into effect. These cr~ ~s sre constructed so as to ad~ust a stroke length of the reciprocatir~ motion. In a conventional stroke ler~th adjustirlg device, a member for adjusting the stroke length is connected to a lead screw which is rotated so as to displace the adJusting member, thereby rectilinearly ad~ustirlg the stroke leng~th of the reciprocatir~ motion from 0 to 10~%.
The cbove mentionci stroke length ad~ustir~ devicc- which makes use of the lead screw, however, has such the disadvantage that the load of the aZ~usting merr.ber as a whole is subjected to the lead screw, and as a result, a considerably stror~ torque is required for operating the lead screw, that in the ease of rnaintainir~ a continuous motion with c desired stroke length, a reciprocatir~, mechanism such as a connecting rod and the like causes reciprccating shocks occurred in a repeated rnanner to apply stress to a joint between the lead screw and the ad~usting member, so that there is a risk of the joint being broken unless the lead screw is precisely worked so as to eliminate a loose engagement between the lead screw and the adjusting member whereby the lead screw becornes very expensive, and that a reaction force subjected to the lead sc~ew causes the lead screw to rotate and the adjusting set position becomes displaced~ thereby gradually ch~ulging the stroke length.
In addition~ the conventional stroke length adJusting device which rnakes use Or the lead screw rnakes its mechanism large in size and requires a considerably large ad~usting pc~wer. As a result, particularly in the case of constructlng the stroke length adjusting device so as to effect an

- 2 - ~ -~

103'6903 ~utomatic adJustment, addition~1 installations such as a servomotor and the like become large in size and eYpensive inl~mufacturing cost. In addition, slch ~utomatlc stroke len~th a-l~ustlru~ device provides a material increase in consumed electric power or amount of air and air pressure for a pneumatic type device and hence the device is noc economical. In addition, such auto~atic stroke length adjuctingr device requires a lor~r servotime and its response becomes degraded.
The inventors have found out by their er.thusiastic study that by connecting a piston to one end Or an operating shart~ by forming pressure chambers at both ends of the piston~ by con~unicating these pressure chambers with each other throuF,h a bore formed in the piston, by provlding a variable throttle valve in one of the pressure chc~bers while providing a stationary throttle opening in another pressure chamber and by supplyir~
pressure fluid from one of the pressure chambers to another pressure chamber, it is possible to displace the piston in response to a set position of the variable throttle valve so as to bring the two pressure chambers in a balanced condition, thereby setting the operatin~ shaft to any desired position.
An object of the irrlention, therefore~ is to provide a fluid pressure servocylinder which can adJust a variable throttle valve provided for a pressure chamber so as to set an operating shaft to any desired position.
A feature of the invention is the provision of a fluid pressure servocylinder comprising an operating shaft~ a piston slidably arranged in a cylircler and connected to one end of the operating shaft and including a bore extruded therethrou~h, a pressure chamber at each en~ of the piston, the pressure chambers be~n& communicated with each other by said bore, a variable throttle valve opposed to an end opening of the bore communicated with one of the pressure chambers~ and a stationary throttle openin2 provided for another pressure chamber.
The inventors have found out by their further study that by 103~ii903 secur~ir~ the fl~Aid pr~e,,sure serJocylinder tG one en~ of a stroke length adjusting shar oi~ a mecr~mi~m fGr converting a rotary motion into a reciprocatin~ motion ~nd by a~tJus~ing a ~ria~le throttle Yalve provided for one of pressure ch~mbers of ~he fluird pressure se~locylinder, it is possible to set the stroke le~th ad~usting shaf`t to any desired position and adjust the stroke length of the reciprocating motion in an easy marmer.
Ar,other feature of the invention, therefore, is the provision of a fluid pressure servocylinder ln whlch the above mentioned operating shaft is connected to one end of a stroke ]ength ad~usting shaft of a mechanism for converting a rotary motion into a reciprocating rnotion, the displacement of the piston permittir~ the converting mechanism to ad~ust a stroke ler~th of the reciprocatir~ motion.
In the present invention~ it is the most preferable to use an oil pressure as the fluid pressure, but any other liquid pressure or gas pressure may also be used In addition~ various kinds of mechanisrns which are capable of ad~usting a stroke length to be described later may be used as a mechanism for converting a rotary motion into a reciprocating motion.
Other ob~ects and advantages of the present invention will become apparent as the detailed description thereof proceeds.
The invention will r.ow be described in greater detail with reference to the accompanying dra~n~gs, wnerein:
Fig. 1 is a lor~itudin~l sectional view of one embodiment of a fluid pressure servocylinder according to the invention and Figs. 2 to 5 are longitudinal sectional views of various embodiments thereof applied to various kinds of mechanisms each converting a rotary motion in~o a reciprocating motion~ respectively.
Referring to Figo 1~ reference llumeral 10 designates a pistor cornected at its one er~d to an operating shaft 12 and slidably enclosed

3~ in a cylinder 14. The cylinder 14 is closed at each end thereof to form _ 4 _ ~031~03 pressure chambers 16, 18. To one of the pressure chambers 16 is connected a fluid pressure conduit 20 connected to a f luid pressure source such as a fluid pressure pump 22 and the like.
The piston 10 has extended through it a bore 24 to communicate the two pressure chambers 16, 18 with each other. In one of the pressure chambers 16, provision is made of a needle 28 opposed to an end opening 26 of the bore 24 and threadedly engaged with one end of the cylinder 14 to constitute a variable throttle valve which permits the needle 28 to move in its axial , 10 direction. In addition, the cylinder l4 is provided at that end thereof which constitutes another pressure chamber 18 with .~
a stationary throttle opening 30.
Let the inner diameter of one of the pressure cham-bers 16 be D, and the inner diameter of another pressure chamber 18 be D2, it is preferable to define Dl D2.
In this manner, by setting the needle 28 arranged in the pressure chamber 16, it is possible to supply the operating fluid in the pressure chamber 16 through the bore 24 in the piston 10 to the pressure chamber 18 so as to increase the fluid pressure in the pressure chamber 18, thereby moving the piston 10 toward the pressure chamber 16. Such movement of the piston 10 causes the end 26 of the bore 24 to move toward the front end of the needle 28. As a result, the open end 26 ' of the bore 24 acts as a throttle valve with respect to the operating fluid flowing from the pressure chamber 16 into the bore 24 so as to produce a constant pressure difference between the pressure chamber 16 and the pressure chamber 18. In this manner, if the pressure difference between the pressure chamber 16 and the pressure chamber 18 becomes constant, the piston 10 is stopped. Since the pressure chamber 18 is provided with the stationary throttle opening 30, if the pressure in the pressure chamber 16 is in balance with the pressure in the ~ _ 5 _ k 103~903 pressure chamber 18, the operating fluid always flows from the pressure chamber 16 through the bore 24, pressure chamber 18 and J stationary throttle opening 30 into the outside of the cylinder 14.

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3 3o A - 5a -I,et tht inr.fr dl3rlete of sne Or the pressure chambers 16 be Dl3 tne ir~ler di~eter of ~;o~her Irle;sure c~lmbeI 18 be ~ and ~1 < D2 the balarLced cor.diti~r, in ~Ihich the ~lif`~erencc bet,leen the pressure Pl inthe pressure ch~her 16 Ird the rprecsllre P~ in th~ pre;cure ch~mber 18 is cor.stant is ~rlJen by the followir~ ~orrnula Pl x ~D, = P2 x ~4~ 2 , ., ~, . q . . ( 1 ) The pressure P] is determined by a de,~ree of opening of the variable throttle valve and the piston 10 :is held at a posltion determ ned by this degree of opening of the variable throttle valve.
From this balarlc2d condition, if the needle 28 is moved upwardly, for ex~mple, the va~iable throttle valve becomes open, so th~t the reduced pressure ~Pl becomes substantially negligibly small~ thereby making the pressure in the pressure chamber 16 substanti&lly equal to the pressure in the pressure chamber 18.
Since Dl c D2, the force subjected to each end of the piston 10 is given by P x IrD2 c p x lrD2 As a result, the piston 10 is pushed upwardly ar.d then stopped at a position where the above formula (1) is satisfied under a se~ closed condition of the varlable throttle valve.
Fron the balanced condition, if the needle 28 is moved downwardly, the variable throttle valve becomes closed, so that substantially no fluid flows through the bore 24 into the pressure chamber 18. As a result, the pressure in the pressure ch~mber 18 becomes substantially zero. Then, the pressure in the pressure chamber 16 only causes the piston 10 to move downwardly until the pressure in the pressure chamber 16 beccnes in balance with the pressure in the pressure charnber 18. In this case, it is preferable to make the diameter of the open end 26 of the bore 24 larger than the diameter of the needle 28, but such is not always a cond tion necessary for the operation of the throttle valve per se.

- In this manner, an a ~ Qstroent ln position of the needle 1 28 opposed to the open end 26 of the bore 24 of the pi~ton 10 ensures, an easy and rapid displacernent of the piston 10 and provides a fluid pressure servocylinder 32 which is capable of adjusting the position of the operating shaft 12 connected to the piston 10 in a simple and convenient manner.
In the present embodiment, the fluid pressure servo-cylinder 32 is provided between the plston 10 and that wall surface of the cylinder 14 which is adjacent to the pressure cham-1 10 ber 16 with a hollow space 34. The hollow space 34 is provided 3 at that wall surface portion of the cylinder 14 which is opposed to the piston 10 with a drain hole 36 open to the outside of the ; cylinder 14 for the purpose of smoothly operating the piston 10.
The fluid pressure servocylinder 32 shown in Fig. 1 is capable of determining the position of the piston 10 by adjusting ~ the needle 28 constituting the variable needle valve arranged in _ one of the pressure chambers 16, so that use may be made of a manually operating knob 38 associated with an indicator 40. As a result, it is possible to determine the position of the piston 10 in an easy manner. In addition, the needle 28 can easily be ad-justed with the aid of an extremely small power, so that an auto-matic adjustment of the needle 28 may be effected by means of a - servomotor and the like which is extremely small in size.
The fluid pressure servocylinder 32 constructed as above described according to the invention and applied to a mechanism for converting a rotary motion to a reciprocating motion for the purpose of adjusting a stroke length of the reciprocating motion will now be described with reference to embodiments thereof.
In Fig. 2 is shown one embodiment according to the invention, in which a mechanism for converting a rotary motion into a reciprocating motion is constituted by two rotary bodies 42, 44 opposed with each other, lQ369~3 a crank 48 composed of an inclined shaft portion 46 and a cam 50 engaged with the inclined shaft portion 46. To the cam 50 is connected to a connectiny rod 52 connected with a plunger and the like which performs, for example, a pump operation.
The rotary body 54 is surrounded by a stationary sleeve 42, while the rotary body 44 is surrounded by a rotary sleeve 56.
The rotary sleeve 56 is provided at its outer periphery with a worm wheel 58 threadedly engaged with a worm shaft 50 connected to ' a driving device (not shown). If the rotary sleeve 56 is rotated, ¦ 10 the rotary bodies 42, 44 together with tne inclined shaft portion 46 are rotated to effect an eccentric motion of the cam 60, thereby reciprocatively moving the connecting rod 52.
To the outer end of one of the ro-tary bodies 42 of the ! crank 48 constructed as above described is connected an operating shaft 62 having one end connected to the piston lU of the fluid pressure servocylinder 32 constructed as above described.
In the present embodiment, by setting the needle 28 constituting the variable throttIe valve arranged in one of the j pressure chambers 16 of the fluid pressure servocylinder 32 to a desired position, it is possible to displace the crank 48 and to displace the cam 5U engagement with the inclined shaft portion 46 i of the crank 48 thereby to change the center of rotation of the cam 50 in relation to the center of rotation of the crank 48 (eccentricity) so that the stroke length of the connecting rod 52 connected to the cam 50 may be adjusted.
In Fig. 3 is shown another embodiment of the invention in which a mechanism for converting a rotary motion into a recipro-cating motion is constituted by two rotary bodies 64, 66 opposed with each other, a crank 70 arranged between the two rotary bodies 64, 66 and including an inclined shaft portion 68 having a groove and an eccentric wheel 72 slidably engaged with the inclined A

shaft portion 68. In the present embodlment, the rotary body 66 is surrounded by a rotary sleeve 74 so as to be driven in the same manner as in the embodiment shown ln Fiy. ~. l'o the s t ,, .

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- 8a -outer end of another rotary body 64 is connected an operating shaft 76 which is provided at its one end with the piston 10 of the fluid pressure servocylinder 32.
Also, in the present embodiment, by setting the needle 28 for constituting the variable throttle valve arranged in one of the pressure chambers 16 of the fluid pressure servocylinder 32 to a desired position, it is possible to displace the crank 70 and adjust a stroke length of the reciprocatiny motion in the same manner as in the previous embodiments.
In Fig. 4 is shown a further embodiment of the invention in which the mechanism for converting a rotary motion into a re-ciprocating motion is constituted by two rotary bodies 80, 82 opposed with each other, a crank 86 arranged between the two rotary bodies 80, 82 and including an eccentric screw threaded shaft portion 84 and a cam 88 threadedly engaged with the eccentric screw threaded shaft portion 84. In the present embodiment, the rotary body 80 is surrounded by a stationary sleeve 90, while the rotary body 82 is surrounded by a rotary sleeve 92 constructed to be driven as in the embodiment shown in Fig. 2. The rotary body 80 is rotatable and axially movable in the stationary sleeve 90 whereas the rotary body 82 is axially movable in the rotary sleeve 92 and also rotatable therewith. To the outer end of one of the rotary bodies 80 is connected an operating shaft 94 which is pro-vided at its one end with the piston 10 of the fluid pressure servocylinder 32.
In the present embodiment constructed as above described, by the upward and downward movements of the crank 86, the cam means 88 threadedly engaged with the eccentric threaded shaft 84 rotates eccentrically around the threaded shaft 84 with variation of the center of the rotation of the cam in relation to the center of the rotation of the rotary sleeve 92 (eccentricity), so as to effect a suitable stroke length adjustment in the same manner as ~ .
_~ _ A

in the previous embodiments.
In Fig. 5 is shown a stil:L further embodiment of the invention in which the mechanism ~or converting the rotary motion into the reciprocating motion is constituted by a rotary shaft 96, an eccentric wheel 98 secured to the rotary shaft 96, and a swing-ing crank 100 pivotally mounted on the eccentric wheel 98 and j provided with a crank pin 102 slidably mounted thereon. The crank pin 102 is connected to an adjustinc; shaft 104. To the outer end ' of the adjusting shaft 104 is connected an ' ,1 - 9a -~036~03 operatiN~ .r,a.t lC~ rjroJi(i~fl -~. it; onl~ f-~nd with thf piston ln of the fluid pr ess~e Sf r~ocylinder 32.
Also~ in the present c~TI~ocli~rnt bJ/ ~ftti~r the needle ~8 constituting the v~ri~ble throttle ~ lv* arrar~r~d in one of 'he pre.isure chambers 16 of the rluid pressllr~-: sc-rT~rocylin~fr ~2 tc a de~irf-(i position, it is possible to adjust the position of thf crar~ pin 102 and e~fect a suitab].e stroke length ad~ustm,ent in thf~ s~ne manner as in the previoll.. eTnbod:irnents In the stroke ler~,th adjustinF, device provided ~ith the fluid pressure servocylinde~r according to the inventlon, by using an oil pressure as the fluid pressurf3 ~!erti.cally arranging the mecharJi.sm for convertir~ therotar~y motion into the reciprocating motlon in an oll tank, lubricating the ~,echanism parts with the oil and cyclically suppiying the oil in the oil tanh- to an oil pressure pump9 it is possible to make the installation small in size and economical.
In additiong the oil pressure pump may be of an independently driven type, but it may be arran~ed at the end of a driving worm shaft of a main ~ump. In this manner, the oil pressure pl)mp may be driven by the driving force for operating the rnain pump~
It will be understood that while 'che invention has been described with reference to preferred eTnbodiments thereof, the fluid pres~lre servo-cylinder according to the invention may widely be applied to various kinds of mechanisms for displacir~ the reciprocating motion as their position deter~lning mechanisrn. Particularly, by applying the fluid pressure servocylinder accordir~ to the invention to a stroke length ad~usting device f a mechanisTn for drivîng a reciprocating pump5 it is pc3sible to effect a correct and srnooth stroke length adjustment in a simple r~nner.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fluid pressure servocylinder mechanism comprising an operating shaft, a piston slidably arranged in a cylinder and including a bore extended therethrough, the piston connected to one end of said operating shaft, a pressure chamber provided at each end of the piston, each said pressure chamber having comm-unication with the other through the bore, one of said pressure chambers having a pressure fluid inlet, a needle confronted coaxially of the piston to an end opening of the bore in said one of the pressure chambers having a pressure fluid inlet, means for adjusting said needle along an axial direction of the piston to obtain a variable throttling function, and a fixed throttling means arranged in the other of said pressure chambers leading to a pressure fluid outlet outside the pressure chamber.

2. A mechanism as claimed in claim 1, including means for converting rotary motion into adjustable-stroke-length reciprocating motion, said operating shaft having connection with said means for converting for adjusting stroke length in response to slidable motion of said piston.

3. A mechanism as claimed in claim 2, wherein the means for converting rotary motion into reciprocating motion comprises: a crank including an inclined shaft portion between confronting first and second rotary bodies, the first rotary body having connection with said operating shaft, a cam having axially movable engagement with the inclined shaft portion, the first rotary body enclosed by a stationary sleeve, the second rotary body enclosed by a rotary sleeve, and a connecting rod having connection with the cam; whereby rotation of the rotary sleeve turns the crank, moves the cam eccentrically and reciprocates said connecting rod.

4. A mechanism as claimed in claim 3, wherein the means for converting rotary motion into reciprocating motion comprises a crank including a grooved inclined-shaft portion between confronting first and second rotary bodies an an eccen-tric wheel having axially movable engagement with said inclined shaft portion, the first rotary body having engagement with said operating shaft, a connecting rod having connection with the eccentric wheel, and a rotary sleeve enclosing one of said rotary bodies and upon rotation turning the crank and through eccentric motion of the eccentric wheel permitting reciprocating motion of said connecting rod.

5. A mechanism as recited in claim 2, wherein the means for converting rotary motion into reciprocating motion com-prises a crank including a threaded eccentric shaft connected between first and second rotary bodies, the first rotary body having engagement with said operating shaft, cam means threadedly engaging the threaded eccentric shaft, a connecting rod engaging the cam means, a stationary sleeve enclosing the first rotary body, a rotary sleeve eccentrically enclosing the second rotary body whereby rotation of the rotary sleeve reciprocates the connecting rod through a stroke length determined by the position of said operating shaft.

6. A mechanism as claimed in claim 2, wherein the means for converting rotary motion to reciprocating motion com-prises a rotary shaft, an eccentric wheel having engagement with the rotary shaft, a swinging crank having pivotal connection to the eccentric wheel, a crank pin having sliding connection with the swinging crank, means connecting said crank pin with said operating shaft, and a connecting rod having connection with a portion of the swinging crank, whereby rotation of the rotary shaft reciprocates the connecting rod through a stroke-length determined by the position of said operating shaft.