EP1457664A1 - Method and Apparatus to process Pressure Interactions between Succesive Injections in a Common Rail Fuel Injection System - Google Patents

Abstract

The process involves decreasing frequency of pressure wave by extending length of a supply pipe (40) connecting a common manifold (50) to every injector (60). The supply pipe is in spiral form and is effectuated by meshing on a bar or internal tube covered by an external tube by tight adjustment. An additional volume to attain a certain effect of emptiness is used for every supply pipe. An independent claim is also included for an injection system with a common manifold of fuel supply for motor vehicle.

Description

Field of the invention

The present invention relates to a process for treating pressure waves in a hydraulic line, as well as an injection device common rail for motor vehicle engine, implementing this process.

Prior art and problem posed

In so-called common injection systems rail ”or“ common rail ”(diesel, petrol or any other fuel), each injection generates, in the high pressure fuel system, waves from pressure responsible for interactions between successive injections. These interactions translate by poor control of the amount of fuel introduced into the cylinders, making it very difficult to tune the engines during development phases, and generating evolutions of their behavior over the life of the engine.

This problem is becoming more and more critical with the appearance of multiple injections authorized by new injection systems, consisting of cut an injection into several more injections small.

In current rail injection systems common, the flow of fuel injected is a function of the duration of piloting of the injector and the pressure in the high pressure hydraulic circuit. A mapping installed in the computer allows calculate the duration of piloting the injection on the base of the requested flow (acceleration sensor) and the applied pressure (pressure sensor on rail).

Currently, different solutions exist or are being considered to resolve the issues interactions between injections.

The interaction between two injections consecutive N and N + 1 to control the amount of fuel introduced during this injection, in taking into account the effect of injection N.

However, the second mapping cannot be filled once the parameters of injection N (the pressure disturbance is a function of these parameters). This solution is therefore, by construction, inactive during the development phase point. In addition, the only parameter that is taken into account account is the presence or not of an injection previous, but in no way other parameters influencing the injection (such as the amount of N injection, the time difference between N injections and N + 1, the presence of one or more injections before injection N, etc.).

Finally, it can only very difficult be used for more than two injections consecutive.

Another solution is a correction the activation time of the injectors, when (N + 1) th injection, using an algorithm estimating the variations in quantity injected due to N previous injections.

However, solutions of this type are very difficult to develop, given the number important parameters to take into account when writing the correction algorithm (geometric dimensions of the fuel system, injection pressure, temperature, quantities injected during previous injections (1 at N), quantity injected during the (N + 1) th injection, time intervals between injections 1 to N + 1, number of injections, etc.). In addition, they are very sensitive to industrial dispersions of manufacturing.

Insertion of one or more devices whose purpose is to create pressure drops on the hydraulic line supplying the injectors can be used, in order to reduce fluctuations in pressure following an injection (damping pressure waves by pressure drops). Through nature, this solution has the disadvantage of creating additional pressure losses on the line injectors, which are harmful to engine performance (loss of injection pressure effective, decrease in maximum quantities injected on the power point, etc.).

The present invention therefore proposes to limit the problems of interactions between injections, while avoiding problems and disadvantages mentioned above.

Summary of the invention

To this end, a first object of the invention is a method of processing interactions between successive injections into an injection system at common rail.

According to the invention, the frequency of the pressure wave by lengthening the length of the conduit supply connecting the ramp to each of the injectors.

The privileged implementation of such a process provides that the supply duct is put in spiral.

A second main object of the invention is a common rail injection system for a motor vehicle engine comprising a ramp and, for each engine cylinder, one injector and one supply duct connecting the ramp to the injector.

According to the invention, the supply duct has a length that is long enough to decrease the hydraulic line pressure wave frequency constituted by the supply duct.

Two locations of the conduits are considered. Indeed, a first consists of installing the supply pipes much of it in the ramp, while a second plans to install them off the ramp.

The preferred shape of the conduits power is the spiral. This saves lots of space while extending the length of these supply conduits.

In this case, a first realization preferential consists in carrying out the spiral in performing the equivalent of a thread on a bar covered with a first external tube by adjustment tight.

Another interesting achievement is to make another thread on the first outer tube which is itself covered with another second tube external.

Finally, a third achievement consists in tapping inside a tube in which one pushes a bar by tight adjustment.

A variant of the system according to the invention consists in adding, after each conduit power supply, an additional volume allowing to mitigate a certain draining effect.

List of Figures

• figure 1, un graphe représentant l'évolution de la pression dans un injecteur ;
• figure 2, en vue cavalière écorchée, une première réalisation de la partie importante du dispositif d'injection selon l'invention ;
• figure 3, en vue cavalière écorchée, une deuxième réalisation de la partie importante du dispositif selon l'invention ;
• figure 4, en vue cavalière écorchée, une troisième réalisation de la même partie importante du dispositif selon l'invention.
• figure 5, un schéma du système de la première réalisation du dispositif selon l'invention ;
• figure 6, un schéma de la deuxième réalisation du dispositif selon l'invention ;
• figure 7, un schéma de la troisième réalisation du dispositif selon l'invention.

The invention and these various technical characteristics will be better understood on reading the following description, accompanied by a few figures representing respectively:

• FIG. 1, a graph representing the evolution of the pressure in an injector;
• Figure 2, in cutaway view, a first embodiment of the major part of the injection device according to the invention;
• Figure 3, in cutaway view, a second embodiment of the important part of the device according to the invention;
• Figure 4, in cutaway view, a third embodiment of the same important part of the device according to the invention.
• Figure 5, a diagram of the system of the first embodiment of the device according to the invention;
• Figure 6, a diagram of the second embodiment of the device according to the invention;
• Figure 7, a diagram of the third embodiment of the device according to the invention.

Detailed description of several realizations of the invention

Figure 1 shows two curves. The first one in a rather thin line represents the variations of pressure generated by an injection taking place with a device of the prior art. We realize that the pressure frequency is important and that pressure variations are just as much.

The strong line curve that affects the shape a single dome-shaped curve shows the variation pressure in the injection system according to the invention. We can see that the variations in pressures are much less intense and slower, the frequency being much lower.

In fact, the frequency is defined so that the "phasing" time, that is to say the time separating the end of a row N injection with the start of the next injection of rank N + 1 either lower or equal to the half-period of the pressure waves flowing in the hydraulic line connecting the injector to the common rail, and this throughout the field of engine operation.

Example

If the maximum phasing time between two consecutive injections is equal to x seconds, the half-period of the pressure waves circulating in the hydraulic line connecting the injector to the common rail must be greater than or equal to x seconds. In fact, the frequency of the hydraulic line must be less than or equal to 1 / (2.x) hertz, that is: f ≤ 1 / (2.x), f being the frequency in hertz of the pressure waves.

In addition, if we assimilate to a tube the entire hydraulic line between the nozzle of the injector and the common rail, the frequency of the first mode of the pressure wave of this hydraulic line can be estimated approximately by the following formula: f = c / (4.L), c the speed of sound in fuel in meters per second and L the length in meters of the equivalent hydraulic line between the nozzle of the injector and the common rail.

Knowing c, and f = 1 / (2.x), we can deduce the minimum value of L allowing to be in the case preferentially described above. We deduced from which the length of the extended tube object of the present invention to be introduced between the injector and the common rail so that the total length of this hydraulic line is greater than or equal to L.

For example if c = 1600 meters per second, x = 0.002 seconds, and the initial length of the _initial hydraulic line L = 0.4 meters, the length L = (2.xc / 4) -L _initial = 1.2 meters . The total length of the hydraulic line, _total L = 0.4 + 1.2 = 1.6 meters.

The drop in frequency of pressure waves created by a rank N injection therefore allows limit pressure fluctuations in the area of phasing corresponding to the consecutive row injection N + 1. This allows, among other things, to facilitate the engine tuning and processing interactions between the different injections by means of software correction, or other.

We specify that if the length added in the injection line is as described above, the magnitude of pressure fluctuations following the row N injection which is to be taken into account for its effect on the next injection of rank N + 1 is no longer the peak-to-peak amplitude, but the difference between the mean pressure value and its maximum value over the phasing time concerned.

However, as explained above, this increase in the injection line is theoretically relatively important, i.e. the order of the extra meter. This leads to a space under the engine hood, which can be unacceptable, knowing that a system of reduction of frequency is required for each injector.

Consequently, with reference to Figure 2, the main embodiment of the invention consists in make a spiral pipe. To this end, we form or machine a spiral groove 10 under the outer surface of a bar or inner tube 1. This the latter is placed inside an external tube 2 whose internal diameter corresponds to the external diameter of the inner tube 1. The fit should be tight or force so that there is no leakage from one turn to the other from the pipeline.

Referring to Figure 3, a second realization of the spiral pipe consists in forming a spiral groove 20 on the inner surface of a outer tube 22, like a thread, inside from which we introduce, by tight or force fit, an internal tube or bar 21.

A third, more complex achievement is to choose one of the two previous solutions and to realize it on several diameters. In others terms, in figure 4 we add a second tube internal 31B has on its external surface a first spiral groove 308. This second internal tube 31A is placed, by tight or force fit, to inside a first internal tube 31A, on the outer surface of which a spiral groove 30A is formed. The whole is placed inside a tube external 32, by tight or force fit. Moreover, by drilling holes in the first internal tube 31A, it is possible to connect the two grooves 30A and 30B at desired locations.

This doubles the length of the pipe, for the same length of added tube. In other words, this realization makes it possible to reduce the congestion due to the addition of pipes.

For these three different achievements, the outside diameters of tubes or bars, inner and outer diameters of the tubes, the thread characteristics, i.e. pitch, width and depth of the grooves, their shape, etc., and the materials used are preferably determined so that the fluid cannot pass from the row of row M to the row of row M + 1 of the same thread, that following the groove making the threading and not passing in a possible game that can exist between the bar or the inner tube and the tube in which it is inserted.

On the other hand, the presence of a pipeline or of a very long conduit between the ramp of common distribution and injectors tend to increase the draining effect of the hydraulic line between the common rail and the injectors. In consequence, during an injection, the nose of the injector is not replenished as quickly and it a loss of injection pressure ensues additional, therefore a possible degradation of the engine response. To limit this effect, characteristics of pipe and rod threads are chosen so as to reduce the pressure losses in long tubes. The higher the cross section of the the larger the thread, i.e. the greater the thread wide and deep, the lower the pressure drop. The higher the surface condition of the materials at the level of threads and bars is of good quality, that is to say smooth, the lower the pressure drop.

Another method to mitigate the effect of draining consists in adding one or more volumes between each injector and the conduits or pipes long. Indeed, with reference to Figure 5, a first complete injection system according to the invention includes a fuel rail, itself supplied by a supply pipe 51 fitted with a pump 52 and coming from a tank of fuel 53. The distribution ramp 50 supplies four injectors 60 through four supply conduits placed in an external tube 40. Now, the latter has a slightly larger total volume, as shown in Figure 6. Indeed, each tube external 40 has an additional internal volume 41, which therefore reduces the draining effect.

With reference to Figure 7, another realization consists in installing the conduits additional inside the ramp distribution 70. Indeed, each conduit can be made by a thread groove 71 made on the tube or the central bar 72 of the ramp distribution 70. Taking into account the fact that each conduit has a significant volume of fuel, the sum of the volumes of the four supply conduits 71 may possibly be equivalent to the volume contained in the usual common rail. So we choose the dimensions of the thread grooves constituting the supply conduits 71 for this purpose. So the central bar 71 can be machined with N threads for N injector 60. You can also machine a single thread on the central bar 72 whose length corresponds to the total length of the conduits supply for the N injectors 60. In this case, we use N-1 separations to share the thread in N supply lines 71.

The central bar 72 is preferably pierced in its center by a central pipe 75 which connects the outlet of a high pressure pump 73 to the start of each supply conduit 71 by holes drilled radially 76. The N injectors 60 can thus be supplied each by a supply tube 77 connected to the output each of a conduit supply 71.

We can also consider a combination of this achievement with that of the achievements previous, in particular achievements represented in Figures 3 and 4. Such an injection system can also be used to decrease the frequency of hydraulic line located upstream of the ramp injection, downstream of the high pressure pump. Such frequency reducer system is then placed between the high pressure pump and the common rail.

It is also possible to use, by example in the case of a six-cylinder V engine, two common distribution ramps equipped with injection system according to the invention for three cylinders.

Thanks to its compactness, the system the invention makes it possible to house a large duct length in a small footprint.

Such a system can also be used in all cases where we wish to make an agreement acoustics by adapting the length of the lines hydraulics used.

Claims (10)

Method for treating the interactions between successive injections in a common rail fuel injection system, characterized in that it consists in reducing the frequency of the pressure wave by lengthening the length of the supply duct (40, 71) connecting the ramp (50, 70) to each of the injectors (60). Method according to claim 1, characterized in that it consists in placing each supply conduit (40, 71) in a spiral. Common rail fuel injection system for a motor vehicle engine comprising at least one fuel rail (50, 70) and, for each cylinder of the engine: an injector (60); a supply conduit (40, 71) connecting the common rail (50, 70) to each of the injectors (60); characterized in that the supply duct (40, 71) is of a length sufficiently extended to decrease the frequency of the pressure wave of the hydraulic line formed by the supply duct (40, 71). System according to claim 3, characterized in that the supply conduits (71) are largely in the common supply rail (70). System according to claim 3, characterized in that the supply conduits (40) are outside the supply ramp (50). System according to any one of Claims 3 to 5, characterized in that each supply duct (40, 71) has a spiral shape. System according to claim 6, characterized in that the supply duct is produced by performing a thread (10) on a bar or an internal tube (1) covered with a first external tube (2, 31A) by tight adjustment. System according to claim 7, characterized in that the first external tube (31B) covering the internal tube (31A) is itself covered with another external tube (32) by tight fitting. System according to claim 7, characterized in that each supply duct produced by a thread (20) on the internal surface of an external tube (22) in which an internal bar (21) is pressed by tight fitting. System according to any one of claims 3 to 9, characterized in that one uses, for each injector (60) an additional volume (41) for each supply conduit (40).

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