II. DISCUSSION In modern engine design, such as in a diesel fired engine, an engine is fitted with fuel injectors, which suppiy a predetermined flowrate of fuel into the combustion chamber of each cylinder of the engine. Typically, fuel is discharged at 20,000 PSI from the injectors into the combustion chamber at each engine cycle only for a very short period of time. This time frame usually ranges from 2 to 10 milliseconds depending on the engine speed and power load. Because of changing operating conditions of the engine, environmental factors and fuel efficiency requirements on engine manufacturers, precise regulation on the flowrate of these injectors has become increasingly important. Conventional fuel injector manufacturers monitor flowrate characteristics of a fuel injector, for quality control purposes, by using a flow meter to monitor flowrate of the fuel exiting the injector. Most flowmeters in use today employ mechanical moving parts which are slowly responsive to flow changes and generate electrical signals proportional to the flowrate of the fuel exiting the injector.

Fuel injector manufacturers typically analyze the flowrate characteristics of a fuel injector, for quality control purposes, by using a flowmeter to monitor the flowrate of the fuel exiting the injector. Most flowmeters in use today, employ mechanical moving parts which are slowly responsive to flow changes, and generate electrical signals proportional to the flowrate of fuel exiting the injector.

However, this type of flowmeter has certain perceived drawbacks.

Because the system is mechanical, it utilizes moving parts which have mass and thus inertia. Therefore, there is an inherent delay in the movement of these parts and thus in the response time of the system in reporting the flowrate. As a result, the response time of this type of flowmeter is generally in milliseconds. Because typical fuel injectors fire for a duration of 2 to 10 milliseconds, the mechanical system can only be used to successfully measure single pulse injector flow, by measuring the total flow of a substantial number of sequential injection samples, then dividing the total flow by the number of samples measured to obtain an average single pulse flowrate. This average single pulse flowrate is a numeric value, which does not provide detailed information, such as what would be provided by a graphical presentation of a true wave form.

Other known flowmeters measure the flowrate of fluid by measuring the pressure drop of the fluid as it passes through an orifice. The pressure of the fluid is measured at the entrance and the exit of the orifice and then converted into a corresponding flowrate by use of known fluid equations.

This type of flowmeter, however, if applied to the measurement of the flowrate of a fuel injector, has certain perceived drawbacks.

Fuel injector test machines of this sort require a flowmetering range of 100 to 1 or higher. Typical fluid flowrate ratios through orifices range from around 5 to 1. Because pressure drop is proportional to the square of the fluid velocity, this 5 to 1 flowrate ratio corresponds to a 25 to 1 pressure ratio, far beneath the required 100 to 1 flow ratio needed by injector test machines.

The present invention was developed in light of these drawbacks, among others.

SUMMARY OF THE INVENTION The present invention overcomes these drawbacks by providing a flowmeter which measures the flowrate of a fuel injector by monitoring the pressure drop across a variable orifice valve through the use of a fixed pressure sensor, having no moving mechanical parts. The present invention includes a fuel injector adapter for receiving the fuel injector, a flow measurement chamber which fluidly communicates with the injector through the fuel injector adapter, a pressure sensor for sensing the pressure of fuel inside the flow measurement chamber, and a variable orifice which regulates the pressure and thus the mesurable range of flowrate out of the flow measurement chamber. The variable orifice selectively adjusts the pressure drop for the flow rate exiting the flow measurement chamber, thereby selectively adjusting the flowrate and pressure ratios.

In another aspect of the present invention, the pressure sensor is a piezoelectric sensor. Because this type of sensor measures the force of the pressure against a piezoelectric element, it is fixed in position, i. e., it has no moving parts and there is no dampening caused by mechanical parts. Thus, rapidly fluctuating flowrates exiting the fuel injector may be measured.

According to another aspect of the present invention, the flow measurement chamber is evacuated to stiffen the spring rate of the fluid and help impede resonant frequencies, thus allowing a more accurate measurement of the true flowrate through the fuel injector. The present invention may also be fitted with a flow calibration device which calibrates the pressure sensor to a fixed or known flowrate value.

Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken into conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: Fig. 1 is a cross-sectional view of a flowmeter according to the present invention; and Fig. 2 is a graphical representation of the flowrate from a fuel injector as measured by a flowmeter according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, the present invention will now be described.

According to Fig. 1, the flowmeter 10, which is shown with a fuel injector 12 attached, generally comprises fuel injector adapter 14, flow calibrator 16, pressure sensor 18, variable orifice 20, and flow measurement chamber 22.

Engine fuel injector 12 has securing plate 24 which is attached to adapter 14 by fasteners 28 shown herein as bolts. Fuel injector 12 is seated in adapter 14 and is secured thereto by screwing bolts 28 through securing plate 24 and into the adapter 14. Flow calibrator 16 has piston 32 which is slidably engaged with seal area 34 and is insertable into cylinder 36. Piston 32 has threaded ball screw area 38 which engages with anti backlash ball nut 40. B Ball screw 38 is driven by stepping motor 44 through anti- backlash bellows coupling 42. Preferably, stepping motor 44 has a resolution of 200 steps per 1 revolution. Micro-stepping controller 46 operates stepping motor 44 and divides a two phase stepping motor drive signal into 16 parts, thereby increasing the stepping motor resolution to (16 times 200) 3,200 steps per revolution. It is noted that by increasing the effective resolution of stepping motor 44, greater precision of movement of piston 32 is obtained.

Pressure sensor 18 is a piezoelectric sensor with a rated response time of 1 micro second. Pressure sensor 18 outputs a pressure signal to injector test machine computer 48 which is representative of the pressure within flow measurement chamber 22.

Variable orifice 20 has needle valve 52 slidably engaged to seal area 54 and insertable into needle valve seat 56. Needle valve 52 has threaded

ball screw area 58 which engages ball nut 60. Needle valve 52 is driven by stepping motor 64 through anti-backlash bellows coupling 62. Like stepping motor 44, stepping motor 64 is driven by a micro-stepping controller 47 which provides a total resolution of approximately 3,200 steps per revolution.

Variable orifice 20 also has fuel outlet 66.

Flow measurement chamber 22 is a cubical enclosure which preferably is less than about 1 cubic centimeter in volume and preferably is evacuated.

This evacuation is formed by providing a continuously ascending discharge path from the tip of fuel injector 12 to flow measurement chamber 22. It is noted, however, that a vacuum pump may also be used to evacuate flow measurement chamber 22.

The general operation of the present invention will now be described with further reference to Fig. 1. Fuel injector 12 is first secured to adapter 14 by bolting securing plate 24 around the periphery of fuel injector 12 with bolts 28. Next, flowmeter 10 is calibrated by filling flow measurement chamber 22 with fuel supplied by fuel inlet 35. Micro-stepping controller 46 next instructs stepping motor 44 to drive piston 32 into cylinder 36 at a predetermined rate.

This movement of piston 32 into cylinder 36 causes the fuel within flow measurement chamber 22 to flow through variable orifice 20 at a predetermined flowrate which corresponds to a predetermined pressure within the flow measurement chamber 22. Pressure sensor 18 reads this pressure and provides a pressure signal to injector test machine computer 48. Injector test machine computer 48 then compares this measured pressure with a stored pressure which is equal to the predetermined pressure. By comparing

the sensed pressure to the predetermined pressure, injector tester computer 48 then calibrates the pressure signal generated from pressure sensor 18.

Thus it should be understood by those skilled in the art that the flowmeter of the present invention is self-calibrating.

When the flowrate from fuel injector 12 is to be determined, fuel injector 12 is instructed to fire fuel into flow measurement chamber 22. This fuel flows from flow measurement chamber 22, through variable orifice 20 and out fuel outlet 66. Because of the position of needle valve 52 within orifice 56, a pressure drop is created between flow measurement chamber 22 and fuel outlet 66. This pressure drop corresponds to the flowrate through variable orifice 20 by the equation Q=K times the square root of Delta P.

Here, Q equals the mass flowrate of fluid, K is a constant which represents the geometry of variable orifice 20 and the position of needle valve 52 in orifice 56, and Delta P is equivalent to the difference in pressure (divided by the mass density of the fuel) between the pressure sensed within flow measurement chamber 22 and ambient pressure. Pressure sensor 18 senses the fuel pressure within flow measurement chamber 22 and provides a corresponding pressure signal to injector test machine computer 48. By knowing the position of needle valve 52 within orifice 56, and ambient pressure and sensed pressure within flow measurement chamber 22, injector test machine computer 48 calculates the mass flowrate through variable orifice 20 by use of the above discussed equation. Due to the conservation of mass and energy, as is known, It is noted that the mass flowrate through variable orifice 20 is equivalent to the mass flowrate through fuel injector 12.

Injector tester computer 48 typically requires a flowmetering range of at least 100 to 1. As shown in the above discussed equation, the sensed pressure is proportional to the square of the fluid velocity. This means that a 5 to 1 flow ratio is equivalent to a 25 to 1 pressure ratio. Because of this insufficient flowmetering range, the accuracy of the flowmeter 10 may be severely restricted. To compensate for this insufficiency, micro-stepping controller 47 may be used to instruct stepping motor 64 to reposition needle valve 52 within orifice 56. This repositioning is then communicated to injector <BR> <BR> <BR> <BR> test machine controller 48 which recalculates a corresponding K value (which is representative of the geometry of variable orifice 20) for the above discussed equation. By changing this K value, the relation between the flow ratio and the pressure ratio as discussed above may be magnified or reduced depending on the requirements of injector test machine controller 48.

Needle valves 32 and 52 may be positioned all the way closed within orifices 36 and 56 respectively to provide a complete shutoff condition used for leak testing of fuel injector 12.

Likewise, needle valve 52 may be moved to a fully open position to allow maximum flowrate through fuel injector 12 for flushing purposes.

With reference to Fig. 2, the accuracy and response time of the present invention is illustrated. In Fig. 2, the event time in micro-seconds (representative of the time from initial firing of fuel injector 12) is shown on a X axis while the nozzled back pressure sensed by pressure sensor 18 is shown on a Y axis. Here, two flow curves have been generated by the same fuel injector. With respect to the closed rack, the flowrate of fuel injector 12

begins at approximately zero, peaks at approximately at 2,100 micro- seconds, and terminates at approximately 4,500 micro-seconds. Likewise, with respect to the wide open rack condition, fuel injector 12 starts with a flowrate of zero at zero micro-seconds, peaks at approximately 5,100 micro- seconds at a corresponding pressure of 1,400 psig, and terminates at approximately 8,700 micro-seconds.

While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation, and alteration without deviating from the scope and fair meaning of the subadjoined claims.