METHOD FOR CONSTRUCTING A MATHEMATICAL MODEL OF A PETROL FUEL INJECTOR OF A BI-FUEL SUPPLY PLANT OF A MOTOR FOR A MOTOR VEHICLE AND ELECTRONIC CONTROL BOARD OF THE GAS INJECTORS USABLE IN A BI-FUEL SUPPLY PLANT OF A MOTOR FOR A MOTOR VEHICLE

Technical Field

The present invention relates to a method for constructing a mathematical model of a petrol fuel injector of a bi-fuel supply plant of a motor for a motor vehicle, and an electronic control board of the gas injectors usable in a bi-fuel supply plant of a motor for a motor vehicle.

The present invention has been developed for general use and, in particular, for use in the motor vehicle after-sales sector (known as the "aftermarket").

Prior Art

As is known, in a bi-fuel supply plant two control boards are present: one for the "petrol side" and the other for the "gas side".

In particular, the "petrol side" control board has a master function, so that in response to input motoring parameters, calculates the injection times and commands the corresponding petrol injectors for supplying the motor with a quantity of petrol such that the air-petrol mixture combustion ratio in the cylinders assumes a predetermined value, for example stoichiometric. On the other hand, the "gas side" (slave) control board drives the gas injectors with the aim of supplying the motor with a quantity of gas that is energetically equivalent.

The plant is retro-activated due to the presence of a lambda probe, for the control of the air/fuel ratio.

Given the intrinsic differences between the petrol injectors and the gas injectors, the energetic equivalence is established by means of appropriate correctors organised in "maps". The installer traditionally sets the various motoring parameters and compiles the carburetion maps for the various functioning points of the motor. This is a long and laborious operation.

Further, as these operations are not always carried out on the motor bench, not all the working points of the motor can be tried out (both due to physical difficulties and for reasons of time), so that the maps present various boxes that are empty or completed by interpolation algorithms.

Aim of the invention

In this context, the technical task objective at the base of the present invention relates to a method for constructing a mathematical model of a petrol fuel injector of a bi-fuel supply plant of a motor for a motor vehicle, and an electronic control board of the gas injectors usable in a bi-fuel supply plant of a motor for a motor vehicle, which obviate the drawbacks in the above-mentioned prior art.

In particular, an aim of the present invention is to provide a method for constructing a mathematical model of a petrol fuel injector of a bi-fuel supply plant of a motor for a motor vehicle, which is more rapid, precise and reliable than known methods.

A further aim of the present invention relates to a method for constructing a mathematical model of a petrol fuel injector of a bi-fuel supply plant of a motor for a motor vehicle, and an electronic control board of the gas injectors usable in a bi-fuel supply plant of a motor for a motor vehicle, usable in motor vehicle after-sales.

Brief description of the drawings

Additional features and advantages of the present invention will become more apparent from the indicative and thus non-limiting description of a preferred but not exclusive embodiment of a method for constructing a mathematical model of a petrol fuel injector of a bi-fuel supply plant of a motor for a motor vehicle and an electronic control board of the gas injectors in a bi-fuel supply plant of a motor for a motor vehicle, as illustrated in the appended drawings, in which: - figure 1 illustrates the simplified diagram of a bi-fuel supply plant of a motor for a motor vehicle;

- figure 2 illustrates characteristic curves of the flow rate of the gas as a function of the injection duration of the gas;

- figure 3 illustrates a characteristic curve of the flow rate of the petrol as a function of the injection duration of the petrol.

Detailed description of preferred embodiments of the invention

With reference to the figures, reference numeral 1 denotes a bi-fuel supply plant for a motor M for a motor vehicle.

The bi-fuel supply plant is in itself of known type.

In this context, for simplicity of description reference is made to a bi-fuel supply plant 1 comprising the following essential elements:

- a plurality of petrol injectors IB;

- a control board CB of the petrol injectors IB;

- a plurality of gas injectors IG;

- a control board CG of the gas injectors IG;

- a switching unit S comprising a switch for switching supply to the cylinders of the motor M from petrol to gas and vice versa.

In particular, the control board CG of the gas injectors IG receives in inlet at least a first signal RPM representing the rotation and phase of the motor M and a second signal MAP representing the load of the motor M (detected by an appropriate sensor, not illustrated).

Each gas injector IG is characterised, for a predetermined pair of pressure p and temperature T values, by a curve of the flow rate QG as a function of the injection duration tG.

For example, in figure 2 two curves of the flow rate QG are illustrated as a function of the injection duration tG, for two different pairs of pressure p, p' and temperature T, T values.

In this context, it is assumed that the characteristic curve of the gas injectors IG is known. Likewise, the petrol injector IB is characterisable by means of a flow rate curve QB as a function of the injection duration te, having a progression as illustrated in figure 3.

In particular, the flow rate QB of the petrol is linked to the injection duration te by the following formul

where K is a coefficient representing the geometry of said petrol injector IB, PB is an injection pressure of the petrol and toFF is the intercept at the origin.

In this context, pe is taken to be the injection pressure value of the petrol from which the pressure value PMAP has already been subtracted, i.e. the absolute pressure value present in the aspirating manifold of the motor M. In this context, for the petrol injector IB the coefficient K representing the geometry and the intercept at the origin toFF. are not known.

The method for constructing a mathematical model of a petrol injector IB, i.e the method for determining the curve ΟΒ(ΪΒ) for the petrol injector IB, is described in the following.

First of all, the engine (M) is supplied with petrol.

The motor M is taken into a first stable working condition to which corresponds a first value of a ratio Λ characteristic of carburetion.

In particular, the ratio Λ characteristic of the carburetion is the ratio between the air quantity actually requested for combustion with respect to the theoretical air requirement.

In the first working condition the motor M is preferably at a minimum working regime without loads.

In the first working condition, the injection pressure pei is detected as well as and the injection duration tei of the petrol injector IB.

While maintaining the first working condition, the supply is switched from petrol to gas.

This determines an imbalance in carburetion. To return to the balanced condition, the injection duration tG of said gas injector IG is varied up to reaching a first injection duration .GI such that the characteristic ratio Λ of the carburetion newly assumes the first value.

On reaching the first value for the ratio Λ, a situation is thus reached in which it is not required for the rapid correctors to intervene.

By knowing the characteristic curve of the gas injector IG, the flow rate of dispensed gas QGI corresponding to the first injection duration tGi is determined.

It is therefore possible to calculate the flow rate of petrol QBI relative to the first working condition as a function of the energetic equivalence of the flow rate of dispensed gas QGI at the first injection duration tGi of the gas injector IG.

Thus a first point Pi of the characteristic curve of the flow rate QB of the petrol injector IB has been obtained, the x-axis whereof is represented by the injection duration tei previously detected and the y-axis whereof is represented by the flow rate of petrol QBI just calculated.

With the first point Pi defined, the gas supply is newly switched from gas to petrol.

The motor M is taken into a second stable working condition to which corresponds a second value of the ratio Λ characteristic of carburetion. In the second working condition the motor M is preferably working at a minimum working regime with a plurality of active loads (for example, air- conditioning, headlights, fans, windscreen wipers, etc.).

Alternatively, in the second working condition the motor M is in a loaded condition due to the movement of the motor vehicle.

In the second working condition, the injection pressure pB2 is detected as well as and the injection duration tB2 of the petrol injector IB.

Maintaining the second working condition of the motor, the gas supply is newly switched from petrol to gas.

This determines an imbalance in carburetion. To return to the balanced condition, the injection duration tG of said gas injector IG is varied up to reaching a first injection duration tG2 such that the characteristic ratio Λ of the carburetion newly assumes the second value.

On reaching the second value for the ratio Λ, a situation is thus reached in which the rapid correctors do not intervene.

By knowing the characteristic curve of the gas injector IG, the flow rate value of dispensed gas QG2 corresponding to the second injection duration tG2 is determined.

It is therefore possible to calculate the flow rate QB2 of the second working condition as a function of the energetic equivalence of the flow rate of dispensed gas QG2 at the second injection duration tG2 of the gas injector IG.

Thus a second point P2 of the characteristic curve of the flow rate QB of the petrol injector IB has been obtained, the x-axis whereof is represented by the injection duration tB2 previously detected and the y-axis whereof is represented by the flow rate of petrol QB2 just calculated.

With two points Pi , P2 of the characteristic curve of the flow rate QB of the petrol injector I B known, the two unknown factors can be calculated, i.e. the coefficient K representing the geometry and the intercept at the origin tOFF.

The distance between the first point Pi and the second point P2 should preferably be the same as or greater than a minimum value. Vice versa, should the distance be less than a minimum value, the second working condition is modified up to reaching (or exceeding) the minimum distance value between the two points Pi , P2.

In particular, after having detected the injection duration tB2 of said petrol injector IB in the second working condition, the relative interval AtB between the injection duration tB2 in the second condition and the injection duration tBi in the first working condition is calculated.

As long as the relative interval ts is lower than a predefined threshold AtBmin, the following steps are cyclically carried out in chronological order: - modifying the second working condition of the motor M;

- detecting the injection duration tB2 of the petrol injector I B in the second working condition of the motor M;

- calculating the relative interval ts between the injection duration tB2 in the second condition and the injection duration tei in the first working condition.

Two points are sufficient for the characterisation of the petrol injector. Should it be desired to improve the precision of the model it is possible to identify two further points.

The control board CG of the gas injectors IG is configured for determining the characteristic curve of the flow rate QB of a petrol injector IB using the above-described method.

After having characterised the petrol injector I B, the control board CG of the gas injectors IG is able to determine the gas flow rate QG to be supplied to the motor M.

In particular, during the functioning of the motor M with gas supply, the injection duration (te) of the petrol injectors IB is detected.

With the duration known, the petrol flow rate QB and therefore, as a function of the energy equivalence, the gas flow rate QB to be dispensed are calculated.

Once the petrol fuel injector IB has been characterised, the initial self- calibration of the plant 1 can be proceeded. It is further possible to include a periodic calibration during the driving of the vehicle.

From the description provided the characteristics of a method for constructing a mathematical model of a petrol fuel injector of a bi-fuel supply plant of a motor for a motor vehicle emerge clearly, as well as those of an electronic control board of the gas injectors usable in a bi-fuel supply plant of a motor for a motor vehicle, according to the present invention, as are the resulting advantages thereof.

In particular, in order to construct the mathematical model of the petrol fuel injector it is sufficient to set two stable working conditions of the motor. The method is therefore simple, reliable, rapid and can easily be used in any workshop (after-market applications). Further, should it be desired to improve the precision of the characteristic curve of the petrol injectors, it is possible to set further stable working conditions of the motor.