System for determining axial displacement of a rod, particularly the plunger of an electromagnetic fuel injector

Abstract: A system for determining axial displacement of a rod (1) forming part of a device comprising a member (2) in which are formed at least two chambers (4, 5) containing high-pressure fluid and each defined by a respective surface portion of the rod (1). The system consists in forming a sliding coupling between the rod portion (6) separating the two chambers (4, 5) and the seat (3) in which the rod (1) slides; in forming, on the aforementioned rod portion (6), a pair of annular grooves (7, 8) defining an annular surface portion (9); in forming at least a housing (10) on the aforementioned member (2); and in fitting inside the housing (10) a proximity transducer (10′) for determining displacement of the annular surface portion (9) parallel to the rod (1).

Description: The present invention relates to a system for determining axial displacement of a rod included in a device comprising also a member provided with at least two chambers for a high pressure fluid (up to 2000 bar), said member being provided with a seat for said rod, each said chamber being defined by a corresponding surface portion of said rod and said seat; which system is particularly suitable for determining the travel of a plunger on an electromagnetic fuel injector. In known devices of the aforementioned type, accurate measurements must be made of the travel of the plunger between the closed position, wherein it closes the injection orifice on the device, and the fully open position, bearing in mind that the plunger is housed inside a high-pressure chamber (as high as 2000 bar). By accurately determining the variation in travel as a function of time, it is possible to evaluate both injection advance and combustion inside the combustion chamber of the engine to which the device is fitted. It is known from the document GB-A-2 170 605 a system for determining the axial displacement of a valve plunger, wherein a rod is provided with a portion slidably coupled with a seat of a hollow member. The axial displacement of the rod is determined by a transducer located axially in one of the two chambers of the hollow member and including a permanent magnet adjacent a piezo-electric crystal to sense an element connected to the rod. Though the system proposed is particularly suitable for determining, to a high degree of accuracy, the displacement of a plunger on a device of the aforementioned type, it may also be employed for determining axial displacement of any type of rod forming part of other devices. According to the present invention, there is provided a system for determining axial displacement of a rod included in a device comprising also a member provided with at least two chambers for a high pressure fluid, said member being provided with a seat for said rod, each said chamber being defined by a corresponding surface portion of said rod and said seat, said chambers being in communication through said seat, a sliding coupling being provided for said rod between said seat and a portion of said rod separating said chambers; characterised by a pair of annular grooves provided on said portion of said rod and defining an annular surface portion; at least a housing provided in said member and communicating with said seat; and a proximity transducer provided inside said housing for determining displacement of said annular surface portion. The system according to the present invention will be described in detail and by way of example with reference to the accompanying drawing, which shows the body and plunger of an electromagnetic fuel injector, the displacement of which is determined using the system according to the present invention. Though, as already stated, the system according to the present invention is suitable for determining axial displacement of any type of rod forming part of any type of device, in the following description, the system will be described as employed for determining the displacement of plunger 1 inside body 2 of an electromagnetic fuel injector. Said plunger 1 slides inside a seat 3 substantially consisting of an axial hole formed inside body 2. As the bottom of plunger 1 (not shown) provides for closing one or more injection orifices in the injector nozzle, plunger 1 normally travels between a closed position, wherein said injection orifices are closed, and an open position, wherein fuel is allowed to flow through said orifices. The injector itself presents two chambers 4 and 5, the first extending between an outer surface portion of plunger 1 and the inner surface of seat 3, and the second formed above plunger 1 and coaxial with chamber 4. Chamber 4 normally contains pressurized fuel for injection through said injection orifices, whereas chamber 5 contains further pressurized fuel and acts as a control chamber on the injector. Plunger 1 is raised automatically in known manner when the pressure inside control chamber 5 is lowered by means of an electromagnetic valve, and the resulting pressure exerted on plunger 1 causes it to move upwards. For determining displacement of plunger 1 according to the present invention, a sliding coupling for plunger 1 is provided between portion 6 of the same and the surface of seat 3. Said portion 6 separates chambers 4 and 5, and the radial clearance of said sliding coupling is so selected as to enable plunger 1 to slide freely inside seat 3, while at the same time substantially preventing fuel leakage from chambers 4 and 5. According to the present invention, said portion 6 of plunger 1 presents two annular grooves 7 and 8 defining an annular surface portion 9, as shown clearly in the drawing. The system according to the present invention also consists in forming on body 2 at least a housing communicating with seat 3, and in providing inside said housing a proximity transducer 10' for determining displacement of said annular surface portion 9. Each housing 10 may consist simply of a hole having its axis perpendicular to that of seat 3. As shown in the accompanying drawing, a pair of housings 10 may conveniently be provided for respective proximity transducers 10' separated in the direction of the plunger axis. The distance between the axes of said holes is indicated "a" in the accompanying drawing. Alternatively, instead of one pair, provision may be made for two pairs of housings 10 for respective proximity transducers, the housings in each said pair being separated in the direction of the plunger axis. The annular cavities 11 formed between the surface of seat 3 and annular grooves 7 and 8 of portion 6 of plunger 1 communicate with each other and with a drain chamber 12 via a duct 13, so as to convey inside chamber 12 any fuel leaking from chambers 4 and 5 into grooves 11 through the radial clearance of the coupling between plunger portion 6 and seat 3. Proximity transducers 10' inside housings 10 may be of any known type, for determining displacement of annular surface portion 9, for example, as a function of a variation in capacity or magnetic flux. The signals produced by transducers 10' may be supplied to any type of device capable of processing said signals in any manner, e.g. for indicating displacement of plunger 1, or the manner in which said displacement varies as a function of time. The system according to the present invention therefore provides for determining displacement of the rod both quickly and easily, and requires only straightforward mechanical machining of the injector components for forming annular grooves 7 and 8 and holes 10. Moreover, said mechanical machining in no way affects the characteristics of the injector, which is in no way impaired by the rod displacement determining function, despite the rod operating in a high-pressure chamber of up to 2000 bar. In particular, should the system according to the present invention feature, not one, but two transducers 10' as shown in the accompanying drawing, these may be connected in the known so-called half inductive bridge configuration to obtain a highly reliable signal, especially as regards thermal drift. Should member 2 feature two pairs of transducers 10', with the transducers in each pair separated in the direction of the rod axis, said transducers may be connected in the known so-called full inductive bridge configuration.

Claims: A system for determining axial displacement of a rod (1) included in a device comprising also a member (2) provided with at least two chambers (4, 5) for a high pressure fluid, said member (2) being provided with a seat (3) for said rod (1), each said chamber (4, 5) being defined by a corresponding surface portion of said rod (1) and said seat (3), said chambers (4, 5) being in communication through said seat (3), a sliding coupling being provided for said rod (1) between said seat (3) and a portion (6) of said rod (1) separating said chambers (4, 5); characterised by a pair of annular grooves (7, 8) provided on said portion (6) of said rod (1) and defining an annular surface portion (9); at least a housing (10) provided in said member (2) and communicating with said seat (3); and a proximity transducer (10') provided inside said housing (10) for determining displacement of said annular surface portion (9). A system as claimed in Claim 1, characterised in that a pair of said housings (10) are provided in said member (2) for housing respective proximity transducers (10') separated in the direction of said rod axis and connected in a "half inductive bridge" configuration. A system as claimed in Claim 1, characterised in that two pairs of said housings (10) are provided in said member (2) for housing respective proximity transducers (10'), the housings in each said pair being separated in the direction of said rod axis and connected in a "full inductive bridge" configuration. A system as claimed in one of the foregoing Claims, characterised in that an annular cavity (11) between said annular grooves (7, 8) of said rod (1) and said seat (3) communicates via a duct (13) with a drain chamber (12) for collecting any fluid leaking between the mating surfaces of said portion (6) and said seat (3). A system as claimed in one of the foregoing Claims, characterised in that said seat (3) for said rod (1) consists of an axial hole formed in said member (2), and each said housing (10) consists of a hole having its axis perpendicular to that of said axial hole forming said seat (3) and terminating inside said axial hole forming said seat (3). A system as claimed in Claim 5, characterised in that one of said chambers (4) is formed between said rod (1) and the surface of said hole forming said seat (3), while the other said chamber (5) consists of a cavity coaxial with said seat (3) and located above said rod (1). A system as claimed in one of the foregoing Claims, characterised in that said member (2) consists of the body of an electromagnetic fuel injection valve, and said rod (1) consists of a valve plunger.

Inventors: DAMIANI VINCENZO, PICCIALLO MICHELE, RICCO MARIO, DAMIANI, VINCENZO, PICCIALLO, MICHELE, RICCO, MARIO
Applicants: ELASIS SISTEMA RICERCA FIAT, ELASIS SISTEMA RICERCA FIAT NEL MEZZOGIORNO SOCIETA CONSORTILE PER AZIONI
Application year: 1990
Main classification: G01M15
IPC codes: F02M51, F02M47, G01B21, F02M65