DEVICE WITH CAMS USING INCOMPRESSIBLE FLUID AS STRUCTURAL ELEMENT TO BRING ABOUT THE DEFORMATION AND/OR DISPLACEMENT OF CAM PROFILES, IN ORDER TO VARY ENGINE VALVE TIMING

Abstract: The device comprises a type of cam with deformable and/or displaceable profile using an incompressible pressurized fluid (liquid) with calibrated channels and/or throttling passages, which allows the advance or delay in timing of the opening and/or closing of each of the valves of an internal combustion engine. The functioning of the device is based on the effect which a fluid under pressure, controlled by throttling passages and acting internally to a cam has on the overall structure of a cam or on elastic elements moving with said.

Description: "Device with cams using incompressible fluid as structural element to bring about the deformation and/or displacement of cam profiles, in order to vary engine valve timing". DESCRIPTION The invention concerns a fluid-mechanical device allowing a variation of the timing of the opening and/or closing of each of the valves of an internal combustion engine. Numerous systems are known for obtaining variable timing in internal combustion engines. The state of the art includes both mechanical systems and systems functioning with fluid under pressure; in both cases the solutions are often complex and unreliable in their construction. Those systems utilizing exclusively mechanical actuating mechanisms present the well-known disadvantages of complicated construction, rapid wear and low reliability (pats DE,A, 3 ,705 ,128 - DE,A, 3,720,947 - US,A, 3 , 14 ,099 ) . In fact, as is known, the fluid-mechanical systems used in the construction of machines in general have now almost completely taken the place of traditional exclusively mechanical systems since the latter provide only partial, unreliable and uneconomical solutions; in addition, the mechanical systems proposed in the cited patents have such a large number of components that the production of a reliable camshaft from the point of view of resistance to wear and operational life whilst keeping the dimension of the camshaft of the same order of magnitude as present ones, is impossible. It may be added that the purely mechanical systems used in the above cited patents are very costly because of the sophisticated micro-mechanical treatments that have to be given; fluid-mechanical systems would solve numerous technical as well as cost problems completely because of the inherent simplicity in the design of apparatus actuated by fluid pressure. The systems with fluid-mechanical actuation known through the patent literature have, however, an inherent instability in their functioning that renders their practical application impossible; the fluid in the cases cited cannot in fact guarantee the geometric stability of the cam profile in all intermediate positions that the latter can take up (Honda pat. appl. nr. 6042338 - 4/3/1985). This drawback has been brought to light by tests conducted on devices of the above-mentioned type. In particular there exists a patent application n. R 91 A 000572, assigned to the present assignees, in which a "cam device having deformable and/or displaceable profile, using fluid under pressure, to vary the timing of engine valves" is claimed. This device too, with fluid-mechanical actuation, suffers from the problems mentioned above, and does not guarantee stability and reliability in its functioning. Instead, the system proposed in the present application functions perfectly in that the incompressible fluid (liquid) has as its principle function to provide a support which is sufficiently rigid - and yet of variable volume depending on the type of profile required - placed underneath the deformable and/or displaceable profile. The system proposed overcomes in this way all the problems, whilst retaining a notable simplicity in its construction and guaranteeing stability and reliability in its functioning, combined with the achievement of lower operational costs. One's attention is drawn to the fact that the insistence on searching out an exclusively mechanical solution to the problem has been motivated by the obvious failure of the fluid-mechanical systems so far proposed: said systems, in fact, cannot work in that they use the fluid exclusively as means of actuation and not as a basically structural element, as proposed in the present application. The structural role is that of providing a support sufficiently rigid - and yet of variable volume depending on the type of profile required - placed underneath the deformable and/or displaceable profile; said function is guaranteed by the adoption of calibrated channels and/or throttling passages that enable the fluid to behave as and provide a rigid support of variable dimensions depending on characteristic in- and out-flow times. Using incompressible fluid, it is possible to deform a cam or parts of a cam so as to obtain a continuously variable profile depending on engine functioning parameters (e.g. engine revs and torque); by modifying the profile it is possible to vary the times of opening or closing of inlet and/or exhaust valves. The elastic deformation caused by the incompressible fluid acts on the whole cam or alternatively only on particular elastic elements placed so as to move with the cam profile or parts of same; in the first case the variation in profile occurs, to a greater or lesser extent, over the whole cam profile; in the second case, on the other hand, it occurs mostly over- the active parts of the cam, that is the opening or closing sections or just parts of these. To understand the inventive characteristics of the present application reference is made, purely by way of non-limitative examples, to the embodiments shown in figs. 1 and 2; each figure represents a cam sectioned along a plane perpendicular to the axis of rotation. The detailed description of the functioning is made referring to the constructional solution of fig. 1. Fig. 1 shows the fluid supply passage ( 1 ' ; ; appropriately-placed channels (2), suitably- calibrated or equipped with throttling passages, allow the fluid to fill cavity 3. The geometry of cavity 3 is calculated in order for the overall structure of the cam to have a graduated resistance to deformation; the pressurized fluid, impinging on the walls of the cavity 3, gives rise to a deformation of the yielding walls 4 and so to a variation of the profile of the cam, leading in this way to variation in valve timing. The variation of the profile depends on the volume of fluid present in the cavity 3. The yielding walls 4 pivot on the hinge F; along the sides opposite said hinge the elements 4 contact the structure 5 by means of the deformable elastic bodies K internal (or external) to the cam. The fluid, impinging on the walls of cavities 3, makes the elements 4 rotate about the hinge F; said elements, elastically deforming the bodies K , move gradually to the extreme position shown with a dotted line. The broken line 7 indicates the circumference, geometric position of the points of beginning of the opening phase and end of the closing phase of the valve; B and C represent the point of intersection between said circumference a d the external profile of elements 4 when these are in rest position. When the volume of the cavity 3 increases , said points gradually move -co the extreme position represented by- point A and D (maximurri volume of cavity 3); by acting on said volume the opening or the closing of the valve may be advanced or delayed in time. Said hinges F can take up any position (top, lateral, central, bottom, intermediate). The elements 4 (two or more) can take up the full extension of the cam or only a part of it. The calibrated channels 2 are dimensioned so as to allow the passage of fluid necessary for control of the device, that is, for adapting the geometry of the cam to the characteristics requested at any particular moment from the engine; the engine "requests" such variations in a characteristic time in excess of a second. The transit times of the yielding walls over the tappets are instead of the order of a hundredth of a second, that is two orders of magnitude less than the characteristic control time; the calibrated channels 2 therefore prevent the return of the fluid - which therefore behaves as a rigid support - during the transit times of the yielding walls 4 of the cam over the tappets, and in such a way at least that the passage of fluid necessary for the regulation of the variable profile i≤ allowed. In fact, the quantities of incompressible fluid occupying the cavities 3 enter and exit said cavities continually in accordance with variations in engine speed, that is to say with every acceleration or deceleration of the engine. So, for example, with reference to fig.l, in the extended-cam case passage of yielding walls 4 over the tappets would tend to force return of the fluid from cavities 3 to the central supply channel (1) because of the resulting displacement of the walls towards the center of the cam; said return flow is however prevented by the calibrated channels 2 which, during the time of passage of the yielding walls over the tappets , keep the volume of fluid necessary to obtain the desired cam profile in accordance with engine requirements inside the cavities 3. The maintenance of said volume of fluid is essential to ensure the stability of the cam profile during the passage of the yielding walls 4 over the tappets. Without calibrated channels 2, in fact, the tappets would be able to make the yielding walls move back to the center of the cam, causing the return flow of a certain volume of fluid from the cavities 3 towards the supply channel 1, causing in addition the undesirable extension of all other cams whose yielding walls, at this same moment, are not constrained by the tappets ; the profile of the cam would not be stable and the device could not work. A different embodiment compared to that illustrated in fig. 1 is shown in fig. 2, where the yielding structure of the cam comprises a resilient jacket which adheres to the internal structure of the cam itself. The incompressible fluid by filling the cavities 3 and acting on the resilient jacket 4 directly and/or through piston 6 , causes the deformation of said resilient jacket and thereby the variation in cam profile; for constructional reasons the resilient jacket can be of either constant or variable section. Referring to the different embodiments , such as in fig. 2, the jacket can be made in different ways depending on the degree of "deformability" required. To increase the degree of deformation possible, said jacket is given axial and/or oblique slits or alternatively is substituted, partially or totally, by an elastic element wrapped repeatedly around the cam profile. The variation of valve timing may also be obtained, apart from the ways described above, but still using . , variable quantities of incompressible fluid as in the present application, by moving the geometric axis of the base cylinder of the cam with respect to the axis of rotation of the camshaft; the degree of variation of valve timing depends on the extent of this axis displacement. The invention has been described and illustrated in a basic embodiment which is to be considered in no way limitative or restrictive as regards all possible detailed constructional solutions and all possible applications.

Claims: CLAIMS 1. Device with cams to vary engine valve timing, using incompressible fluid as a structural element to produce the deformation and/or displacement of cam profiles, characterized by the fact that: - functioning of the device is guaranteed by the presence of appropriatel -dimensioned calibrated channels and/or throttling passages which are placed upstream from each and every deformable and/or displaceable part-profile; said calibrated channels and/or throttling passages allow the passage of the incompressible fluid, and therefore the variation in volume of the cavities 3 , in a characteristic time comparable to characteristic times of variation of engine speed; said calibrated channels and/or throttling passages prevent the return of fluid from the cavities underneath the portions of profile which are deformable and/or displaceable towards the center of the camshaft during transit of the deformable and/or displaceable walls over the tappets; - the volumes of incompressible fluid occupying the cavities 3 enter and exit continually said cavities in accordance with any change in engine speed, that is with every acceleration and deceleration of the engine. 2. Device with cams, according to claim 1, characterized by the fact that the displacements of the yielding walls depend on the volume of fluid present in cavities 3. 3. Device with cams, according to claim 1, characterized by the fact that variation in valve timing is obtainable by displacing, solely through use of quantities of incompressible fluid, the geometric axis of the base cylinder of the cam with respect to the axis of rotation of the camshaft.

Inventors: DI FRANCESCO GIULIO, GIGANTINO ANNA, DI FRANCESCO, GIULIO, GIGANTINO, ANNA
Applicants: FRANCESCO GIULIO DI, GIGANTINO ANNA, DI FRANCESCO, GIULIO, GIGANTINO, ANNA
Application year: 1993
Main classification: F01L13
IPC codes: F01L13, F16H53