DE10062616A1 - Device for measuring the amount of a medium dispensed by a system - Google Patents

Abstract

A device (10) is used to measure the amount of a medium (18) delivered by a system (20, 16a-16d). The device (10) is used in particular for measuring the injection quantity of injection systems (16a-16d, 20) of internal combustion engines. The device (10) comprises a connecting device, by means of which at least one delivery system (16a-16d) can be connected to a measuring space (12) in a pressure-tight manner. A piston (14) is held displaceably in a guide (44) of the device (10). The piston (14) limits the measuring space (12) in some areas. A device (40) is also provided which detects a displacement of the piston (14). In order to minimize vibrations and thereby increase the measuring accuracy of the device (10), the piston (14) is made in a lightweight construction.

Description

State of the art

The present invention relates to a device for Measure the amount of one delivered by a system Medium, in particular for measuring the injection quantity of Injection systems of internal combustion engines, with one Connection device through which at least one Dispensing system can be connected to a measuring space in a pressure-tight manner, a piston slidably held in a guide, the limited the measuring area in some areas, and one Displacement of the piston detecting device.

Such a device is known from the market. at it is a continuous flow rate- Measuring device (also called KFMG). The KFMG includes one Flow meter showing the sum of all during one injected single injection quantities with a certain time measures great accuracy. The KFMG also includes one So-called scatter indicator, which shows the individual deviation of the individual injections from which results from the sum measurement resulting average of all individual injections.  

From the mean measured by the flow meter and the measured by the scatter indicator with high resolution Individual values can be used to calculate all quantities of interest be such. B. the individual injection quantities, the scatter from one injection to another, etc. With the Scatter indicator is one in a tour slidably held piston, which is a measuring chamber, in the the injections take place, limited in some areas. The Movement of the piston is caused by high resolution inductive displacement sensor measured. From the postponement of the Piston and piston diameter can be the volume of a corresponding single injection can be determined.

The known device already works with very high Accuracy. In certain cases, for example injections in close succession smallest injection quantity, but can be an even higher one Accuracy may be desirable.

The present invention therefore has the task of a device of the beginning mentioned type so that it can be used for a measurement even the smallest single injections with high accuracy is possible. The device is said to be relatively inexpensive and be simple.

This task is the beginning of a device mentioned type in that the piston in Lightweight construction is made.

Advantages of the invention

In the known device, the piston was made of steel manufactured. Such a steel piston is very stable, however, due to its high weight, it tends to one Single injection to a low frequency vibration,  which only subsides slowly However, the piston will like this is proposed according to the invention, in a lightweight construction manufactured and so the mass of the vibrating system is reduced, on the one hand, the frequency of the vibrations of the Piston after a single injection and higher others decay the vibration faster, because with one high frequency the damping is greater. Furthermore, can the actual movement of the piston from the high frequency Vibrations through a simple low pass filter reliable way to be separated.

The device according to the invention thus enables the Measure the amount of a single injection very reliably, without complex and maintenance-intensive Damping devices for the piston are required. This also reduces the manufacturing costs for the device according to the invention reduced. Be careful noted that such a piston is lightweight not only with a continuous flow meter (KFMG) can be used, but also e.g. B. at one Injection quantity indicator (EMI).

Advantageous developments of the invention are in Subclaims specified.

In a first further training it is proposed that the Pistons made of aluminum and / or at least in some areas a fiber composite material is produced. With aluminum on the one hand it is an extremely stable and on the other hand, a very light material that so far excellent for the formation of the piston in Lightweight construction is suitable. In addition, aluminum is very corrosion-resistant compared to the usual one such device used medium. At a  Device which is used to measure the injection quantity of Injection systems of internal combustion engines is used the medium is generally one Substance, the physical properties of which Get the properties of fuel as close as possible. Also a fiber composite material, e.g. B. carbon fiber reinforced Plastic (CFRP) or carbon fiber reinforced carbon (CFC) can be used to manufacture the piston according to the invention be used. Such a piston can still have lower weight.

It is also possible and particularly preferred that the leadership of the piston is at least partially made of aluminum. Such an aluminum guide reduces especially in The sliding friction associated with an aluminum piston between the piston and the guide, causing the piston even better on the smallest single injections responds. As a result, the measurement accuracy and the Measuring range of the device according to the invention again improved or expanded.

In a particularly preferred development of device according to the invention have the piston and / or the leadership at least on the facing each other Surfaces a hard coating, which preferably is applied by electrolytic oxidation. The Abrasion resistance of such a hard coating is still better than that of steel, what the life of the Improved device according to the invention. Furthermore the sliding friction between the piston and the Leadership diminishes.

An embodiment in which the piston is hollow and preferably inside  is closed and its coat is preferably thin-walled and has molded reinforcements. This can Weight of the piston can be reduced again at the same time high stability of this way manufactured piston.

In another training, it is proposed that the diameter of the piston compared to its length is small. Such a piston moves at one Injection a greater distance than using a piston larger diameter. This means that the resolution of the device according to the invention is improved. The Possibility to design a piston in this way arises only because of the low Weight of the piston according to the invention the vibrations a single injection low or high frequency are.

A device in which the piston is designed so that its on a Total volume related mass and the specific density of the medium to be measured are approximately the same. In this case the piston floats or "floats" in the one to be measured Medium, causing leakage through the gap between the Piston and its guidance minimized or even entirely can be excluded. Beyond that too this reduces the vibrations of the piston.

Overall, it is for the measurement accuracy of the Favorable device according to the invention, if this at a Injection relatively quickly into a thermal Balance comes. This is also due to the fact that it with an injection and "braking" of the injected medium to a temperature increase in the  Measuring room is coming. Therefore, it is beneficial if the piston is off made of a material with high thermal conductivity is.

It is also advantageous if the end face (s) of the piston, which immerses or immerses in the medium, a has circumferential slope. Through this conical Chamfer the piston side immersed in the medium pressure vibrations are also alleviated.

drawing

The following are two exemplary embodiments of the invention with reference to the accompanying drawing in detail explained. The drawing shows:

Figure 1 is a schematic representation of a first embodiment of an apparatus for measuring the amount of a medium dispensed by a system.

FIG. 2 shows a partially sectioned illustration of a region of a second exemplary embodiment of a device for measuring the quantity of a medium released by a system; FIG. and

Fig. 3 is a diagram showing the movement of a piston of the device of Fig. 1 or 2 and the corresponding injection pulses.

Description of the embodiments

In Fig. 1, an apparatus transmits for measuring the injection quantity of an injection system of an internal combustion engine identified overall by reference numeral 10. It comprises a measuring chamber 12 which is delimited at the top by a displaceable, hollow piston 14 which is made of lightweight construction, in the present case made of aluminum. A total of four injection nozzles 16 a- 16 d are arranged on the lower boundary wall of the measuring space 12 , which, for. B. are connected to the measuring chamber 12 in a pressure-tight manner via suitable seals (not shown). The injection nozzles 16 a- 16 d, a medium able to inject 18 in the measurement space 12, which is fed to them in the present embodiment of an injection pump 20th The injection pump 20 is driven by an engine 22 . It is connected to a control and processing device 26 via a status sensor 24 .

It goes without saying that the device shown in FIG. 1 could also be used for measuring the injection quantity from other injection systems. So it would be z. B. conceivable that instead of the injection nozzles 16 a- 16 d, a high-pressure injection valve is connected to the measuring chamber 12 , which is used in internal combustion engines with direct injection and is connected to a high-pressure medium supply ("common rail principle"). Furthermore, the piston could also be made of a fiber composite material, for example CFRP or CFC.

The injection pump 20 receives the medium 18 from a reservoir 28 . This in turn is via a flow measuring device 30 , for example a PLU gear pump flow meter, and an adjustable throttle, for. B. a slot throttle 32 , fluidly connected to the measuring chamber 12 . The slot throttle 32 is adjusted by a servomotor 34 , which in turn is controlled by the control and processing device 26 .

A counter-pressure chamber 36 is formed above the piston 14 . The top of the piston 14 is also connected to a piston rod 38 which cooperates with an inductive displacement sensor 40 in a manner not shown in the figure. This in turn provides the control and processing device 26 with corresponding measurement signals. The back pressure chamber 36 can also be connected to a compressed air source 42 via a valve (not shown in the figure). The piston 14 is held displaceably in a guide 44 only indicated schematically in FIG. 1. Guide 44 and piston 14 have a hard coating on the mutually facing surfaces, which was applied by electrolytic oxidation. The measurement results are displayed on a monitor 46 , and the control and processing device 26 is programmed using a keyboard 48 .

The device 10 operates as follows: In operation, the injection pump 20 draws a test medium (such as fuel or a fuel similar fluid) from the reservoir 28 and injected this sequentially via the injection nozzles 16 a- 16 d in the measurement chamber 12 of the device 10 a. The sequential injection of the test medium into the measuring space 12 is also clear from the upper part of FIG. 3, in which the injection pulses 50a-50d, which are spaced apart from one another, are shown over time.

In order to enable continuous operation, in which test medium is continuously injected into the measuring space 12 , and in order nevertheless to be able to use a displacement sensor with a small measuring range and therefore high resolution, the test medium 18 is continuously removed from the via the slotted throttle 32 and the flow measuring device 30 Measuring room 12 is returned to the storage container 28 . The flow rate is set via the slit throttle 32 and the servomotor 34 by the control and processing device 26 such that the piston 14 remains in an overall central position.

The control characteristic of the control and processing means 26 is designed to sufficiently slow that no attempt is made by that to steer the short-term deflections of the piston 14 injections single a- through the injectors 16 due to the 16 d. In this regulated state, assuming constant pumping power of the injection pump 20 , a constant amount of test medium 18 flows from the measuring space 12 via the slit throttle 32 and the flow measuring device 30 into the reservoir 28 and from there again via the injection pump 20 and the injection nozzles 16 a- 16 d back into the measuring room 12 .

However, not only the total flow rate for the assessment of the of the injection nozzles 16 a- 16 d and consisting of the injection pump 20 injection important, which is detected by the flow measuring unit 30, but also the 16 d a- from the individual injectors 16 at each Injection pulse 50 a- 50 d ( FIG. 3) injected quantities Q ₁ -Q ₄ of test medium 18 . These can vary from one injection nozzle 16 to another due to manufacturing tolerances in the injection pump 20 and in the injection nozzles 16 a- 16 d, which is evident from the upper diagram of FIG. 3 by the different duration of the injection pulses 50 a- 50 d. The corresponding movement of the piston 14 is shown by the lower diagram in FIG. 3. The individual injection quantities Q ₁ -Q _{4 of} the injection nozzles 16a-16d are now calculated as follows:
The quantity or volume of test medium 18 injected during a series of pulses consisting of four individual injections 50 a- 50 d

4 Q _a = Q ₁ + Q ₂ + Q ₃ + Q ₄ .

Under the influence of the different injection pulses 50 a- 50 d and the constant discharge rate 4 Q _a , the piston 14 makes a movement x, as shown in FIG. 3. If one detects the position x of the piston 14 via the inductive displacement sensor 40 in the pauses between the individual injection pulses 50 a- 50 d and at exactly the same time intervals t / 4, the amount Q _i of test medium 18 has been injected between two detection times and the amount Q _a flowed off. The piston is then around the volume

A (X _{n + 1} - X _n ) = Q _{n + 1} -Q _a

has been displaced, where A represents the cross-sectional area of the piston 14 . By measuring X _{n + 1} and X _n by the inductive displacement sensor 40 and measuring Q _a by the flow measuring device 30 , Q _{n + 1} can be calculated as

Q _{n + 1} = Q _a + A (X _{n + 1} - X _n )

It is understood that the determination of d injected from the injection nozzles 16 a-16 in an individual injection pulse injection amount Q _i of the test medium 18 is accurate to, may be the movement x of the piston 14 from the inductive displacement sensor 40 detects more accurately. Vibrations of the piston 14 after a single injection of 50 a- 50 d through an injection nozzle 16a-16d would greatly distort the measurement result. In the device 10 shown in FIG. 1, however, the piston 14 is made of aluminum and is hollow. The piston 14 therefore has a very small mass and can therefore follow the volume change of the test medium 18 in the measuring space 12 very easily and spontaneously.

Because of the low mass of the piston 14, it vibrates, if at all, with a relatively small amplitude and high frequency, which can be filtered out by a suitable low-pass filter in the control and processing device 26 without falsifying the actual measurement result. The guide 44 of the piston 14 is also made of aluminum, and the mutually facing surfaces (without reference number) of the piston 14 on the one hand and the guide 44 on the other hand are provided with a hard coating, which is preferably applied by electrolytic oxidation. As a result, the friction between piston 14 and guide 44 is minimal, which further favors the fact that piston 14 can react spontaneously to changes in volume of test medium 18 in measuring chamber 12 .

As can be seen from Fig. 1, the piston 14 is hollow inside and its jacket is extremely thin-walled. The stability of the jacket (without reference number) of the piston 14 is ensured by reinforcements which are not visible in the figure. The overall design of the piston 14 is selected such that its total mass, based on its total volume, is approximately equal to the specific density of the test medium 18 located in the measuring chamber 12 and in the back pressure chamber 36 . This means that the piston 14 floats "weightlessly" within the test medium 18, so to speak. In this way, leakages between the measuring chamber 12 and the counter-pressure chamber 36 are minimized or completely eliminated by the gap between the piston 14 and the guide 44 . Due to the injection of the test medium 18 by the injectors 16 a- 16 d in the measurement space 12 there is a heating of the test medium 18 in the measuring space 12th Because the piston 14 is made of aluminum, which has excellent thermal conductivity, the piston 14 also very quickly assumes a corresponding temperature, which is also favorable for the measurement accuracy during a measurement campaign.

In the exemplary embodiment of a device 10 shown in FIG. 2, those parts which have functions equivalent to parts of the first exemplary embodiment shown in FIG. 1 have the same reference numerals. They are not explained in detail again below. Instead, only the special features of the piston 14 shown in FIG. 2 are discussed below:
As can be seen from Fig. 2, the diameter of the piston 14 is relatively small compared to its length. This means that the piston 14 shown in FIG. 2 is displaced by a greater distance during an injection through the injection nozzle 16 than the piston 14 shown in FIG. 1 with an equivalent injection. This improves the resolution of the device 10 .

However, the possibility of being able to use a piston designed in this way presupposes that the piston 14 executes no or only slight vibrations during an injection through the injection nozzle 16 . This can only be achieved in that the piston 14 in the exemplary embodiment shown in FIG. 2 is made in a lightweight construction, in the present case from fiber composite material. It is possible, for. B. the production of carbon fiber reinforced plastic or carbon fiber reinforced carbon. As can also be seen from FIG. 2, the piston 14 has a conical bevel 52 and 54 on its underside as well as on its top. Such a conical bevel 52 or 54 further reduces pressure vibrations in the test medium 18 and thus also vibrations of the piston 14 .

Claims (9)

1. Device for measuring the amount of a medium ( 18 ) delivered by a system, in particular for measuring the injection amount of injection systems ( 16 , 20 ) of internal combustion engines, with a connecting device through which at least one delivery system ( 16 ) with a measuring space ( 12 ) can be connected in a pressure-tight manner, a piston ( 14 ) which is displaceably held in a guide ( 44 ) and which limits the measuring space in some areas, and a device ( 40 ) which detects a displacement of the piston, characterized in that the piston ( 14 ) is manufactured in a lightweight construction. 2. Device according to claim 1, characterized in that the piston ( 14 ) is made at least in regions of aluminum and / or titanium and / or a fiber composite material. 3. Device according to one of the preceding claims, characterized in that the guide ( 44 ) of the piston ( 14 ) is at least partially made of aluminum. 4. Device according to one of the preceding claims, characterized in that the piston ( 14 ) and / or the guide ( 44 ) at least on the mutually facing surfaces have a hard coating, which is preferably applied by electrolytic oxidation. 5. Device according to one of the preceding claims, characterized in that the piston ( 14 ) is hollow and preferably closed in its inner and its jacket is preferably thin-walled and has integrally formed reinforcements. 6. Device according to one of the preceding claims, characterized in that the diameter of the piston ( 14 ) is small compared to its length. 7. Device according to one of the preceding claims, characterized in that the piston ( 14 ) is designed so that its mass based on its total volume and the specific density of the medium ( 18 ) to be measured are approximately the same. 8. Device according to one of the preceding claims, characterized in that the piston ( 14 ) is made of a material with high thermal conductivity. 9. Device according to one of the preceding claims, characterized in that the end face (s) of the piston ( 14 ) which immerses or immerses in the medium ( 18 ) has or have a circumferential bevel ( 52 , 54 ).