FR2629706A1 - Liquid injection apparatus, in particular for use in dental care - Google Patents

Abstract

Apparatus for injecting liquid, in particular for use in dental care, by means of an adjustable pressurized jet, comprising a body in two parts and a movable assembly inside the body to create the jet. According to the invention, this apparatus is characterized in that the movable assembly mounted in the second part 203 of the body 201 comprises a working piston 233 subjected to the action of a control spring 241 progressively compressed by a thrust piece axial 276 joined by an elastic membrane 280 to the internal wall of a compression chamber 287 connected to a source of compressed air, and means for securing the working piston with a temporary immobilization member 269-270 provided in the body, coaxially with the piston, so that, beyond a determined stroke of the thrust piece, causing the progressive compression of the spring, the latter is suddenly released and determines the rapid displacement of the piston, by carrying out the expulsion from a metering chamber 243 of the liquid to be injected, communicating with a cartridge 235 forming a reserve of liquid.

Description

 The present invention relates to a liquid injection device, in particular for dental care, by means of a jet under adjustable pressure, suitable for penetrating directly into the gum of a patient.

 We have already described in patent application No. 87.07409 of May 26, 1987 on behalf of the applicants, an injection device of this kind, comprising an elongated body in two separable parts, placed end to end, of which the first known as medical, comprises at least one housing containing a sealed cartridge enclosing the liquid to be injected and having a movable bottom whose movement accompanies the sending of a given quantity of liquid from the cartridge to at least one metering chamber with variable volume also provided in said first part and conunicating at the end of the device with a nozzle fitted with an injector capable of forming a narrow jet of liquid following a sudden discharge of this liquid out of the metering chamber under the effect of a piston d expulsion moving in this chamber, and of which the second part called the motor, comprises a movable assembly with reciprocating movement and pneumatically controlled, adapted to cause the rapid displacement of the expulsion piston d in the metering chamber for the formation of the liquid jet through the nozzle.

 In this previous application, the mobile assembly comprises a working piston mounted in the second part of the body, cooperating with a propulsion spring progressively compressed under the effect of an appropriate air pressure controlled by the user of the device, noted by the practitioner who holds the body of it in dwarf shape and approaches the nozzle of the gum for the injection of the liquid jet, the slow compression of the spring being accompanied by the filling of the dosing chamber until the moment where the sudden release of pressure releases the spring which, in its rapid return, pushes the expulsion piston driving the liquid out of the chamber towards the injection nozzle.

 In the various embodiments more particularly envisaged in the aforementioned application, the control of the compressed air pressure and its abrupt release into the open air are carried out by means of a distributor, mounted coaxially with the working piston in the second part of the body of the device and moved by it over a short stroke at the end of movement of this piston in order to open at least one venting opening for the compression chamber, simultaneously stopping the air intake in the appliance.

 However, experience has shown that, in order to further improve the operational safety of the device, it may be preferable to place the dispenser outside the body, for example with direct control by the user, ci however having on the body of the device a manual unlocking member, arranged so that the implementation of the cycle and in particular the control of the expulsion piston can occur only when the practitioner has previously exactly positioned the nozzle relative to the gum, in particular. safely avoiding inadvertent triggering of the device which could be very dangerous since, in order to treat the oral cavity of a patient, the device must necessarily be approached by passing it near the eyes or others sensitive areas of the face.

 The invention therefore aims, while retaining the fundamental principles of the injection device already described and claimed in the aforementioned application, to provide even better job security, in particular in the implementation of the control and formation of the jet to be injected.

 It also aims to provide a simpler structure device and in particular easier to achieve industrially thanks to a structure of its various parts, both fixed and mobile, which is such that it essentially has a profile of revolution around the axis of the body.

 Another object of the invention is to provide an apparatus in which, depending on the case, the movable piston may or may not be part of an assembly which includes the cartridge itself, the latter therefore being immobilized in the body or, on the contrary, movable in the latter with the piston, the brutal expulsion of the liquid from the metering chamber towards the injection nozzle can be effected following a direct or indirect action of this piston.

 According to the invention, the apparatus considered is characterized in that the movable assembly mounted in the second part of the body comprises a working piston subjected to the action of a control spring progressively compressed by a piece of axial thrust joined together by an elastic membrane to the internal wall of a compression chamber connected to a source of compressed air, and means for securing the working piston with a temporary immobilization member provided in the body, coaxially with the piston, such so that, beyond a determined stroke of the thrust piece, causing the progressive compression of the spring, it is suddenly released and determines the rapid displacement of the piston, by carrying out the expulsion from a metering chamber liquid to be injected, communicating with a cartridge forming a reserve of liquid.

 Advantageously, the locking means consist of balls mounted in open housings provided in the external wall of the piston and held in position by a coaxial sleeve, sliding on this wall under the effect of the thrust piece, this sleeve comprising a profiled recess for escaping the balls and releasing the piston beyond a given stroke of the sleeve.

Other characteristics of an injection device established in accordance with the invention will become more apparent from the following description of several exemplary embodiments given by way of indication and without limitation, with reference to the appended drawings in which
- Figures la and lb are views of two consecutive parts of the apparatus according to the invention in a first alternative embodiment thereof.

 - Figure 2 is a cross-sectional view on a slightly larger scale, along the line Il-Il of Figure lb.

 - Figures 3 and 4 are views in partial longitudinal section on a larger scale of the organs for ensuring the blocking and then unblocking of the working piston of the device following the force exerted on it by the piece of thrust, itself actuated by a controlled pressure of compressed air.

 - Figure 5 is another partial sectional view of an alternative embodiment of the means for exercising on the liquid contained. in the cartridge of the device, the pressure necessary for the flow of this liquid towards the dosing chamber.

 - Figures 6 and 7 are views respectively in transverse and longitudinal sections, of an alternative embodiment of a device for immobilizing the working piston until the device has been properly put in position, before performing the injection of a liquid jet.

- Figure 8 illustrates a variant embodiment of the device
Figures 6 and 7.

 - Figures 9 and 10 on the one hand, 11 then 12 on the other hand, illustrate respectively and schematically three other alternative embodiments of the locking device associated with the device according to the invention.

 - Figures 13a and 13b show the two consecutive parts of the device according to another general variant thereof.

 In Figures la and lb which, placed end to end, illustrate a longitudinal section of the device considered, the reference 201 designates the body thereof, consisting of two coaxial parts, respectively 202 and 203, the first said medical part being capable of coupling to the second so-called engine by means of a quick connection system 204, of the quarter-turn or other type.

 At its end located on the left in the drawing, the part 202 comprises a thin and elongated end nozzle 205 comprising a supply channel 206 for a suitable injection liquid towards an end nozzle 207. Opposite this one ci, the spout 205 is fitted into a housing 208 provided at the end of a support 209 comprising an axial channel 210 disposed in the extension of the channel 206. This support 209 is itself mounted in the end 211 of an intermediate piece -212 on which it is screwed in 213 with the interposition of a seal 214. The channel 210 is in turn extended by a channel 215 in this intermediate piece 212 which also includes a thread 216 receiving a mandrel 217, - even axially pierced with a duct 218 in the axis of the channel 215 and connecting to the latter by means of a ball valve 219 subjected to the action of a spring 220 so that under the effect of this spring, a ball 221 normally closes the end of the conduit 218.

 The intermediate piece 212 is extended to the right in the drawing by an outer sleeve 222 surrounding the mandrel 217, this sleeve being secured to an end plug 223 screws at 224. The plug 223 has projecting ribs 225 suitable for cooperate with grooves of the same profile 226 to constitute, at the end of a sleeve of the same diameter 227 extending the sleeve 224, the quick connection system 204 between the two parts 202 and 203 of the body of the device.

 At its end opposite to the spout 205, the mandrel 217 comprises a closure end piece 228 allowing the mounting in the axis of the conduit 218 of a needle or trocar 229. This can be normally closed by a valve mounted in a cavity 230 of the mandrel and comprising a ball 231, suitable for closing off the corresponding end of the trocar.

 Around the mandrel 217 is slidably mounted the tubular end 232 of a hollow sleeve 233, internally defining a housing 234 inside which is mounted a cartridge 235 whose end directed towards the tank 205, includes a plug 236. That -This is prior to the use of the device pierced by the end of the trocar 229 in order to allow, under conditions which will be specified below, the flow of a liquid contained in this cartridge through the trocar 229 then beyond this, in the duct 218 provided that the ball 231 frees the passage necessary for this flow.

 On the tubular end 232 of the sleeve 233 is mounted a movable and hollow piston 237, suitable for sliding on the mandrel 217, annular seals 238 and 239 mounted inside the piston ensuring the seal. The piston 237 has a transverse bearing surface 240 for a control spring 241 bearing opposite to a stop face 242 provided on the intermediate piece 212. The movable piston 237 thus defines with the fixed mandrel 217 an annular chamber 243 constituting the metering chamber for the product withdrawn from the cartridge 235 and brought into this chamber by at least one transverse passage 244 provided in the mandrel.

 On the outer sleeve 222 is attached and fixed an outer cover 245 on which is articulated around an axis 246 a lever 247, provided at one end with a heel 248 suitable for locking in position the movable piston 237 by engagement in a housing open 249 of this piston. Opposite the heel 248, the lever 247 includes a control imprint 250 for the user's finger making it possible to tilt the lever around its axis against a spring 251 mounted in a housing 252 of the intermediate piece 212, this tilting thus making the heel 248 escape from the housing 249.

 The sleeve 227 includes a light 253 making it possible to directly visualize the cartridge 235, through the body of the device, and in particular when the latter is made of a transparent plastic material, to follow the evolution of the level of the liquid which it contains, as and when injections of successive doses, the evacuation of the liquid accompanied by the displacement of a sliding bottom 254, opposite the plug 236, this bottom 254 being subjected to the action of the head 255 of a piston rod 256, slidably mounted through a guide support 257, being subjected to the permanent action of a spring 258.

 Between the hollow sleeve 233 and the outer sleeves 222 and 227 is mounted a guide tube 259, delimiting with the sleeve 227 a space 260 in which springs 261 are mounted, regularly distributed around the axis of this sleeve and fixed to their ends respectively at 262 on the sleeve 227 and at 263 on a cylindrical washer 264, made integral by a transverse screw 265 of the guide support 257 through a slot 266, formed laterally in the sleeve 233 and the tube 259 (Figure 2).

 At its upper part, the sleeve 233 comprises an end piece 267, extended axially by an end part 268, provided with open grooves 269 suitable for receiving a plurality of balls 270 mounted in this groove in order to block this part 268 vis-à-vis screw of a coaxial tube 271. The guide tube 259 also has an extension 272, coming to cap the tube 271 from the outside, immobilizing the balls 270. The extension 272 has a bearing inclined inwards 273 and at exterior a shoulder 274 for a return spring 275, bearing opposite to a flange 276 extending transversely to the end of the coaxial tube 271. Another spring 277 is mounted outside the tube 259 and s also presses against the rim 276, the latter being stopped opposite by a washer 278 blocked by screws 279 against the internal surface of the sleeve 227.

 The rim 276 is associated with a sealing membrane 280 immobilized against the upper face of the rim by a support plate 281, this membrane being terminated by a bead 282, trapped between the bottom 283 of a terminal plug 284 provided in end of the device and a clamping piece 285 provided with a tubular extension 286 making it possible to introduce into the body of the device behind the membrane 280, a suitable pressure of compressed air in a chamber 287, thus delimited. The end plug 284 is immobilized on the tubular extension 286 by means of a nut 288 and is also held by a ring 289 secured to the sleeve 227 into which the plug 284 is screwed thanks to an internal thread 290.

 Figures 3 and 4 allow, in conjunction with Figures la and lb, to better illustrate the way in which the apparatus is implemented in the embodiment described above, where the assembly constituted by the parts 237, 233 , 267, 268 in particular constitutes the working piston, the rim 276, the tube 271 and the membrane 280, constituting the thrust piece.

 In order to be able in particular to inject a given dose of liquid through the nozzle 207 previously positioned in the vicinity of the place where this injection is to be carried out, the user firstly releases the lever 247, the piston 237, by releasing the heel 248 from # this lever with respect to the housing 249. At this instant and by an appropriate command, for example at the foot, it introduces by the tubular extension 286, a suitable compressed air pressure in the compression chamber 287. Under the effect of the latter, the assembly formed by the flange 276 and the tube 271 moves by driving sinultaneous x nt by the end portion 268 the fanchon 233 itself causing the displacement of the piston 237 against spring 241.

 In this movement, the metering chamber 243 is gradually filled with liquid sucked out of the cartridge 235 through the trocar 229, the conduit 218 and the transverse passages 244, the flow of the liquid being authorized by the displacement of the ball 231 in the housing 230 which releases the open end of the trocar.

 This movement continues in particular until the balls 270, which join the tube 271 of the end fitting 268 of the driving piston, come before the inclined bearing 273 of the extension 272, then allowing the escape of these balls from their housing 269. At this instant, the working piston is suddenly released, the spring 241 brutally pushing the mobile seat in the opposite direction. Simultaneously, the liquid contained in the metering chamber 243 is expelled from it by the passages 244 and the conduit 218 under the effect of the pressure, the ball 221 normally closing the conduit 218 being pushed back against its spring 219, allowing the liquid to escape to the successive conduits 215, 210 and 206 Clearance than the injection nozzle 207. At the same time, the ball 231 returns to close the end of the trocar 229, avoiding the backflow of the liquid towards the carpule.

 In the terminal phase of the movement, the springs 274 and 277 return the flange 276 to the initial position with return of the balls 270 in their housing 269 to once again secure the tube 271 and the terminal part 268, the apparatus being ready for a new cycle. Operating.

 Figure 5 illustrates an alternative embodiment of the apparatus shown in Figures la and lb, with regard to the means for exerting on the bottom 254 of the cartridge 235 a suitable pressure, regardless of the degree of re-tightening of this cartridge as and when the operating cycles of the device, with fornation with each shot through the injector 207, a jet of fine liquid and under pressure.

 In this variant, the extension 268 of the hollow fanchon 233 which slides in the tube 271 delimits on the side of the cartridge a sealed chamber 291, joined by an axial duct 292 passing through the extension 268 to the opposite part of the tube 271, itself in unification by the tubular extension 286 with the external source of compressed air causing, as described above, the displacement of the thrust piece. An annular seal 294 is carried by the extension 268 and is in contact with the internal surface of the extension 271. In the chamber 291 is mounted a piston 295, itself carrying an annular seal 296 in contact with the internal surface of the hollow sleeve 233, 268, this piston 295 being connected by an axis 297 to the bottom 254 of the cartridge. In this variant, it is therefore directly the pressure of the air in the chamber 291, acting on the piston 295 which is permanently transmitted to the bottom 254, by transmitting to the liquid of the carpule a thrust which remains constant to itself each time the control air pressure is admitted into the apparatus. This device is thus equivalent to that described in relation to Figures la and lb, involving the springs 261 and the guide support 257.

 In the first embodiment envisaged above, the device can only be implemented insofar as the user has previously tilted the locking lever 247, by exerting on the control imprint 250 a limited effort. against the spring 252, thereby releasing the heel 248 from the lever and releasing the hollow sleeve 233.

 Figures 6 and 7 illustrate another alternative embodiment which, without aiming to block this time the hollow sleeve, nevertheless prevents the escape of the liquid out of the annular chamber 243, thus not allowing again but in another form, the creation of the jet at the outlet of the injector that once the device previously and properly positioned, the user then only authorizing the implementation of the operating cycle.

 In this variant, the device for temporarily prohibiting operation consists of a button 298, normally pushed upward relative to the body 222 by means of a spring 299, this button comprising a rod 300 secured to a transverse plate 301 and provided a central hole 302.

The plate is mounted to slide vertically under the effect of the button 298 inside a housing 303 provided in the intermediate piece 212. Coite we can easily see it in the view of Figures 6 and 7, when the button 398 is in relaxed position, the transverse plate 301 closes the connection between the two parts 304 and 305, respectively located on either side of the duct 218, seals 306 and 307 being advantageously provided on each side in recesses 308 and 309 receiving them opposite the plate in the housing 303. On the other hand, if the user exerts on the button 298 a force directed downwards against the spring 299, he brings the hole 302 in coincidence with the two parts 304 and 305, thereby ensuring the continuity of the conduit 218 with flow of the liquid withdrawn from the chamber 243 and delivery under pressure of the latter to the injector 207.

 Figures 8 to 12 illustrate other variants of the means suitable for carrying out, in other forms, the provisional prohibition of the operation of the apparatus, as long as the latter is not brought into a suitable position, with the injector 207 in close proximity to where the jet of liquid is to be carried out.

 In the example illustrated in Figure 8, the intermediate piece 212 has a transverse hole 310 for mounting radial pins 311, each subjected to the action of a spring 312 bearing against an overhanging head 313 and tending to push these pins towards the outside of the slot, by disengaging the heel 314 of a plunger 315 suni from a seal 316 in its external surface and slidably mounted in a housing 317 of the intermediate piece 212. The plunger 315 comprises a end stud 318 suitable for locking the ball 221 of the valve in the closed position, thereby closing the end of the conduit 218. This same plunger is subjected to the action of a spring 319 bearing on a fixed plate 320 mounted in the opposite part of the end piece 211 with the interposition of a seal 321.

 In the variant considered, the intermediate piece 212 is associated with a sliding wheel 322, comprising an external imprint 328 allowing the user to make it slide freely on the external surface of the piece by bringing opposite the heads 313 of the pins 311 a annular recess 324 thus allowing these pins to escape towards the outside, releasing the heel 314 and consequently the plunger 315 and the ball 221. The sliding wheel 322 is permanently returned to the locking position of the pins 311 thanks to a spring 325 mounted in a housing 326 between the outer sleeve 222 and a bearing surface of this wheel so that if the operator releases its force against this spring, the latter returns the wheel to the position where the heads of the pins 311 are returned towards the inside by again blocking the plunger 315.

 In the variant illustrated in Figures 9 and 10, a substantially equivalent but simpler mounting is shown, the intermediate piece 212 having an external shoulder 327 forming a stop for the esterity of a spring leaf 328, secured by a rivet 329 on a sliding wheel 330. This wheel 330 has an internal recess 331 in which, depending on the axial position of the wheel on the external sleeve 222, a stud 332 provided at the end of the blade 328 can be struggled. A spring 333 is mounted behind the wheel to ensure the recall in position thereof.

 In FIG. 9, the thumbwheel 330 is such that the narrow part of the housing 331 pushes the stud 332 inwards, the blade 328 blocking under these conditions the intermediate piece 212 and consequently all the elements which constitute the piece of thrust of the device, due to the support of the shoulder 327 on the blade 328.

 In the position illustrated in FIG. 10, the thumbwheel 330 is pushed back against the spring 333, allowing the pins 332 to escape into the wider part of the recess 331, the leaf spring 328 coming out of the shoulder 327 thereby freeing the part 212.

 In FIG. 11, the variant illustrated is equivalent to that envisaged above, the stud 332 here being replaced by a ball 334, facilitating the movement of the wheel by driving back into the housing 331.

 Finally, in FIG. 12, a similar arrangement has been used, but in which the ball 334 can be erased in a recess 335 in the wheel 330 which has a profile opposite to that provided in the previous examples, the spring leaf 336 being this once fixed by a rivet 338 on the intermediate piece 212, this blade being shaped so that its free end 337 is bent to abut against a bearing 339, provided in the outer sleeve 222.

 Figures 13a and 13b illustrate another alternative embodiment of the apparatus according to the invention, arranged so that, unlike the first variant where the liquid is withdrawn from the cartridge in the annular metering chamber when the part thrust returns to the rear position, this withdrawal takes place here during the retraction of the mandrel 426 by means of the return spring 421, before the thrust part is suddenly released to produce, through the end injector , the desired throw.

 In this variant, the device previously comprises a body 401 formed by two coaxial parts, respectively 402 and 403. The internal part 402 comprises a terminal nozzle 404 supporting the injector (not shown) and end with an internal conduit 405. It is connected to an end part 406 by an appropriate connection means 407. In this part 406 is provided a conduit 408, provided with a ball valve 409 mounted in a support part 410. The part 406 is joined by a thread 411 with the end 412 of an intermediate piece 413. In contrast, the latter is provided with a quick coupling member 414 with a connector 415 provided at the end of a tube 416 itself doubled by an external sleeve 417. A side window 418 is provided in this sleeve in a manner analogous to the arrangements already envisaged in the first variant.

 Inside the tube 416 is mounted a hollow sleeve 419, terminated at its end directed towards the spout 404, of a piston 420. A return spring 421 is provided between this piston 420 and a bearing surface 422 provided in the intermediate piece 413. Inside the piston 420 is formed a conduit 423, extended on one side by a needle or trocar 424 and closed on the other hand a ball valve 425, provided opposite a mandrel 426 comprising an axial duct 428, this mandrel being able to move in contact with a seal 429 mounted in the internal surface of a housing 430 provided in the part 413.

 The needle 424 perforates the end plug of a cartridge 431 mounted in the internal region 432 delimited between the hollow sleeve 419 and the piston 420.

 At its opposite end, the cartridge 431 is closed by a movable bottom 433, permanently subjected to the thrust of a piston 434 secured to an axial rod 435, a spring 436 being mounted between the piston 434 and a bearing surface 437 and the cylindrical extension 438 of a tube 439.

 This tube 439 has a shoulder 440 mounted movable S inside the hollow sleeve 419 and capable of coming to bear against an internal rim 441 provided in an end piece 442 formed at the end of this sleeve. The end piece 42 has a shoulder 443 forming a bearing surface for a strong spring 444, itself applied at its opposite end to a flange 445 immobilized on the extension 438 of the tube 439 by a ring 446, the latter being screwed on a thread 147 in the external surface of the extension 438. An elastic membrane 448 is mobilized between the flange 445 and the ring 446, this membrane having an end bead 449 held between a flange 450 and a cover 451.

The latter is finally immobilized with respect to the sleeve 417 by a ring 452 screwed at 453.

 In FIG. 13b, there is shown at 454 the arrival of compressed air in the apparatus, the latter being able to pass through the cover 451 through passage orifices 455 to come to exert on the flange 445 an appropriate force.

The seal during the movement of the thrust piece of the device is produced by the membrane 448. The flange 445 is extended by a tubular piece 456, movable coaxially in the outer sleeve 417. This piece 456 has in its internal surface an inclined bearing 457 and a cylindrical extension 458, sliding in contact with the external surface of the hollow sleeve 416 in contact with locking balls 459 trapped in housings 460 provided in the end piece 442 of the sleeve 419. A spring 461 is mounted between a fixed bearing surface 462 of the tube 416 and a shoulder 463 of the tubular part 456.

 In this variant embodiment, the operation of the apparatus is as follows: when the user has brought the apparatus to the precise vicinity of the place where an injection of liquid is to be carried out, the apparatus being provided with a unlocking similar to one of those described previously in any one of FIGS. 1 to 12 but not shown here), it controls by a foot switch for example, the air intake which by the orifices 455 exerts on the rim 445 forming the piston a corresponding thrust, first compressing the control spring 444. In this movement, the tube 439 moves with the rim, exerting a force on the piston 434 and the bottom 433 of the cartridge 431 by the spring 436. The corresponding pressure releases the ball 425 from the conduit 423 and allows the liquid from the cartridge to come fill the housing 430 forming metering chamber, the mandrel 426 remaining in a fixed position due to the thrust in the opposite direction of the spring. ort 421.

 Simultaneously, the tubular part 456 moves with the flange 445 by compressing the spring 461.

 At the end of the race, the tubular part 456 has its inclined bearing 457 opposite the balls 456 and allows the latter to escape towards the outside, between the end piece 442 and the tubular part. The end piece 442 and consequently the hollow sleeve 419 of which it is integral are suddenly released, the spring 444 previously compressed by the movement of the rim 445 suddenly relaxes by pushing this sleeve 419 and with it the piston 420 and the mandrel 426 The valve 425 closes while the valve 409 opens allowing the liquid accumulated in the housing 430 to be completely and suddenly expelled through the conduits 408 and 405 to the injector provided at the end of the spout. 404.

 In the following phase, the air pressure being released, the springs 421 and 461 bring all the moving parts back to the initial position, the stop of the flange U5 against the flange 450 allowing the end piece 442 to move alone at the end stroke, until the balls 459 are brought back opposite their housings 460 in which they are then pushed back, again locking the end piece and the tube 416 until a new operating cycle is engaged.

Claims (11)

 1 - Apparatus for injecting liquid, in particular for dental care, by means of an adjustable pressure jet, comprising a body in two parts and a movable assembly inside the body to create the jet, characterized in that that the movable assembly mounted in the second part (203) of the body (201) comprises a working piston (237) subjected to the action of a control spring (241) progressively compressed by an axial thrust piece (276 ) joined by an elastic membrane (280) to the internal wall of a compression chamber (287) connected to a source of compressed air, and means for securing the working piston with a temporary immobilization member (269270) provided in the body, coaxially with the piston, so that, beyond a determined stroke of the thrust piece, causing the progressive compression of the spring, the latter is suddenly released and determines the rapid displacement of the piston, carrying out the expulsion from a metering chamber (243) d u liquid to be injected, communicating with a cartridge (235) forming a liquid reserve.  2 - Injection device according to claim l, characterized in that the blocking means consist of balls (270) mounted in open housings (269) provided in the external wall of the piston (237) and held in position by a coaxial sleeve (272), sliding on this wall under the effect of the thrust piece, this sleeve comprising a profiled recess (273) for the escape of the balls and the release of the piston beyond a given stroke of the muff.  3 - Injection device according to one of claims 1 or 2, characterized in that the working piston (237) comprises a coaxial sleeve (233) and is slidably mounted relative to an axial mandrel (217) fixed, delimiting an annular chamber (243) for metering the liquid between the mandrel and the sleeve, this chamber communicating with an axial channel (218) provided in the mandrel in the extension of a spout (205) provided at the end with a liquid injector (207) forming a narrow jet under the effect of the pressure created by the movement of the working piston (237).  4 - Injection device according to claim 3, characterized in that the axial channel comprises a ball valve (231) provided opposite a trocar (229) communicating with the interior of the cartridge (235) to allow the admission of the liquid into the metering chamber (243) by radial conduits (244) formed in the mandrel (217), said valve closing the communication with the cartridge during the displacement of the working piston (237) under the effect of control spring (241).  5 - Injection device according to any one of claims 1 to 4, characterized in that the sleeve (233) coaxial with the working piston cooperates with a locking lever (247) with manual control articulated around an axis ( 246) on the body (201), this lever comprising a heel (248) suitable for engaging in an open housing (249) of the sleeve (233) to prevent it from sliding relative to the fixed mandrel (217).  6 - Injection device according to any one of claims 1 to 5, characterized in that the cartridge has a movable bottom (254) under the effect of a support piston (255) permanently subjected to the action of springs (260) mounted around an outer hollow sleeve (259) in which the working piston slides, these springs being secured at the end of a crosspiece (257) moving in a lumen (266) of the sleeve .  7 - Injection device according to claim 2, characterized in that the working piston (237) has a tubular extension (268) movable axially in the sleeve (272).  8 - Injection device according to claim 3, characterized in that the body (201) has a slot (303) for the movement of a transverse plate (300) actuated by a push button (298), this plate comprising a central passage (302) allowing the continuity of the channel (218) to escape the liquid coming from the metering chamber towards the injector, only when the push button is pressed inside the slot of the body.  9 - Injection device according to claim 1, characterized in that the temporary immobilization member of the working piston comprises a sliding wheel on the outer surface of the body (201) to immobilize or release the heads (313) of pins radial (311-) relative to a recess (324) in the wheel, these pins blocking or releasing in turn a plunger (315) blocking or releasing a ball valve (221) provided on the axial channel (218).  10 - Injection device as claimed in # 9 ation, characterized in that the sliding wheel cooperates with at least one pin (332) or a ball (334) and a spring leaf (328) whose end immobilizes the piston of work (237).  11 - Injection device according to claim 1, characterized in that the working piston itself has the shape of a hollow sleeve and has a tubular extension directly subjected to the action of the control spring.