EP1486659A2

EP1486659A2 - A signal conditioning device and method, in particular for air flow rate measuring probes in internal combustion engines

Info

Publication number: EP1486659A2
Application number: EP20040013689
Authority: EP
Inventors: Marcello Malavasi
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-06-12
Filing date: 2004-06-10
Publication date: 2004-12-15
Also published as: ITPR20030044A1

Abstract

A signal conditioning device (1), in particular for probes (3) for measuring air flow rate in internal combustion engines, comprising means (2) for translating and/or amplifying a signal outputted by the measuring probe (3), before it reaches a unit (4) for controlling and managing the engine. A method for conditioning a signal coming from a worn but undamaged probe for measuring an air flow rate, in particular for internal combustion engines.

Description

The present invention relates to a signal conditioning device, in particular for air flow rate measuring probes in internal combustion engines, and related method.
It is well known that modem electronic injection engines, both petrol and
Diesel fuelled, are usually equipped with instruments for measuring the flow rate of the air that is aspirated by the engine.
Such measuring instruments, technically called debimetres, are usually positioned in the intake conduit of an engine and are tasked with communicating the quantity of air aspirated by the engine to an electronic unit.
Based on the information received from the debimetre, the unit is able to throttle the flow rate of fuel to be injected, in order to obtain a correct air/fuel mixture ratio.
In accordance with a first prior art, there are debimetres with swivelling plate or hinged flap, whose movement of rotation, proportional to the volumetric quantity of air that flows through the intake conduit, is contrasted by a torsional return spring. The displacement of the swivelling plate or of the flap is checked by a potentiometer (variable resistance) which translates into an electrical signal to be sent to the unit.
This type of debimetre is now obsolete and has been replaced by hot wire measuring devices.
These devices provide the measurement of the mass of air which is aspirated by the engine and not the measurement of the volumetric flow rate, as is the case in swivelling plate or flap debimetres.
This is extremely advantageous, because the quantity of the fuel to be injected depends on the aspirated mass of air and not on the volume.
The measurement is conducted by means of a membrane or a filament heated to a constant temperature, usually exceeding the temperature of the aspirated air by about 120°, which cools according to the mass of air that envelopes it.
To maintain constant the temperature of the membrane or of the filament, it is necessary to send a current of variable intensity as a function of the extent of the cooling (Venturi system). This current change is measured by the control unit to obtain, by means of a characteristic curve, the mass of air that flows through the intake conduit of the engine.
Normally, the current change is measured by means of a Wheatstone bridge circuit, whereof the measuring membrane or filament is a part.
Heated membrane or filament debimetres have the important drawback of getting very dirty, causing a significant drop in engine performance because of an erroneous measurement of the aspirated mass of air. Generally, the quantity of the mass flow rate measured by the debimetre is smaller than the quantity that actually does flow in the intake conduit.
Currently, the only way to overcome this drawback is to replace the debimetre.
Membrane or filament debimetres are generally made of platinum which, although it is a noble metal, after prolonged operating periods becomes impregnated with dust, lubricants and/or oily substances which inevitably penetrate inside intake conduits. This makes it impossible to clean the debimetre and, in view of the high price of platinum, it entails high costs for the replacement of the debimetre.
An object of the present invention is to propose a signal conditioning signal, in particular for air flow rate measuring probes in internal combustion engines, and a related method, which allow to avoid replacing the debimetre, whilst assuring that the control unit receives a measurement signal that reflects the actual operating parameters of the engine.
Another object of the present invention is to provide a device and a method able to influence the signal being outputted by the debimetre, in order the vary the operation of the engine in a manner that can also be different from one instant to the next.
A further object of the present invention is to achieve the above the aforesaid results within the context of a simple, rational and reliable constructive solution.
Said objects are fully achieved by the signal conditioning device, in particular for air flow rate measuring probes in internal combustion engines, and by the related method according to the present invention.
These and other objects shall become more readily apparent from the description that follows of a preferred embodiment illustrated, purely by way of non limiting example, in the accompanying drawing table, in which the sole figure shows a schematic view of a signal conditioning device, in particular for air flow rate probes in internal combustion engines.
The signal conditioning device is globally designated by the number 1 and originally comprises means 2 for translating and/or amplifying/attenuating (thereby meaning that amplification can be positive or negative) a signal outputted by an air flow measuring probe, preferably a debimetre 3 with heated filament, before the signal reaches an engine control and management unit 4.
The means 2 for translating and amplifying (positively and/or negatively) the signal outputted by the debimetre 3 comprise at least a device 5 for supplying electrical energy and at least one amplifier stage 6, to recover an loss of efficiency of the debimetre 3. In particular, said loss of efficiency occurs because of deposits of dirt onto the filament, such a dust, drops of oil or of other lubricants. In particular, the electrical energy power supply 5 is a regulator that stabilises to a predetermined value an electrical voltage coming from an external source of electrical energy, for example from the 12 Volt battery of the motor vehicle.
Alternatively, said regulator can receive currently directly from the debimetre 3, for example from a source of voltage or current associated to a Wheatstone bridge, which is known and commonly used in debimetres.
In the preferred embodiment, the regulator can receive current, both from an external source of electrical energy, and from the debimetre 3, thanks to the use of a switch 10, which can switch between two operative positions, respectively to a power supply by means of the external electrical source or by means of the debimetre itself.
In the preferred and illustrated embodiment, the means 2 for translating and/or amplifying positively and/or negatively the signal outputted by the debimetre 3 also comprise at least one amplifier stage 7 whose gain can be adjusted positively and/or negatively, functionally positioned upstream of the amplifier stage 6 with fixed gain (positive or negative).- The means 2 are provided with a plurality of filters 8, so-called EMI filters, to isolate the device 1 from any interference in the radio frequency band, coming from the outside environment.
The fixed and/or percent gain can also be adjusted by means of an electronic component.
According to a possible embodiment variant, not illustrated herein, the amplifier stage with fixed gain can be positioned upstream of the amplifier stage with adjustable gain.
In an alternative embodiment, not illustrated herein, the means 2 for translating and/or positively or negatively amplifying the signal of the probe are provided by at least one processor for receiving and processing, in a manner that is variable instant by instant, the signal outputted by the debimetre 3, in order to influence the performance of the engine.
In particular, the use of a processor allows to re-map the engine, allowing both to improve performance, if the signal of the debimetre 3 is conditions in such a way as to force the unit 4 to send a greater quantity of fuel to the engine, and a reduction in polluting emissions (for instance in case of except smokiness of the vehicle), if the signal of the debimetre 3 is conditioned in such a way as to force the unit 4 to send a smaller quantity of fuel. Specifically, to force the unit 4 to send a greater quantity of fuel, the output signal will have to be conditioned, in such a way that the unit detects an air flow rate that is greater than the actual one. Vice versa, to reduce the polluting emissions the signal will have to be conditioned in such a way that the unit 4 detects an air flow rate that is smaller than the one that actually flows through the engine intake conduits.
Even in the embodiment lacking a processor, the device 1 can nonetheless enable to improve engine performance and/or pollution emissions. It is sufficient for the means 2 to impose a greater or lesser translation and/or amplification of the signal outputted by the probe (with respect to the translation and/or amplification which would theoretically be sufficient to compensate for the loss of efficiency of the probe), to cause the unit to receive a further conditioned signal with respect to a value corresponding to the one that would be sensed by a fully efficient probe.
The device 1 is contained within a heat protecting shell 9, since it is usually positioned at a short distance from the engine.
The device 1 is interposed between the debimetre 3 and the unit 4, although in an alternative embodiment, not illustrated herein, it is incorporated directly in the debimetre, so that the latter can output a signal that has already been conditioned. In particular, in said embodiment, in the device 1 the means 2 for translating and/or positively and/or negatively amplifying the signal of the probe are preferably provided by at least one processor.
The method for conditioning a signal coming from a worn but undamaged probe for measuring an air flow rate, in particular for internal combustion engines, of the present invention, comprises the following steps:

receiving an electrical signal coming from the worn probe;
replacing the worn probe with a new probe;
receiving an electrical signal coming from the new probe and obtained for equal engine operating parameters with respect to the measurement made by the worn probe;
comparing the received signals to measure the size of a drop in intensity of the signal coming from the worn probe;
removing the new probe;
reinstalling the worn probe;
amplifying and/or positively and/or negatively translating the signal outputted by the worn probe by a value equal to said previously measured intensity drop.

In particular, the amplification step takes place through the calculation of a microprocessor or micro-controller positively and/or negatively mixing the two regulating parameters, which are:

offset or amplification/attenuation;
percent gain or translation (positive or negative).

The method of the invention comprises an additional step of amplifying the signal coming from the worn probe, by means of an amplifier with adjustable gain, functionally positioned upstream of the amplifier with constant gain, and it further comprises a step of sending the conditioned signal to a unit for controlling and managing the operation of the engine.
In an alternative embodiment, the step of amplifying by means of a constant gain amplifier takes place before the step of amplifying by means of an amplifier with adjustable gain.
The method comprises a step of shielding the conditioned signal sent to the unit, to prevent any electromagnetic interference.
In accordance with a possible embodiment variant, the subject method comprises the following steps:

receiving an electrical signal coming from the probe;
amplifying/attenuating and/or translating the signal coming from the probe, in order to influence, in a manner which can vary instant by instant, the operating parameters of the engine;
sending the conditioned signal to a unit for controlling and managing the engine.

In particular, said step of amplifying/attenuating and/or translating the signal outputted by the probe preferably takes place with the use of a processor.
The invention achieves important advantages.
First of all, a device and a method in accordance with the present invention allow to avoid replacing the debimetre, whilst assuring to the unit the reception of a measurement signal that reflects the actual operating parameters of the engine.
Secondly, the subject device, especially in the embodiment providing for the use of a processor, is able to influence the signal outputted by the debimetre, in order to vary, also in a different manner instant by instant, the operation of the engine. In particular, it is possible to condition the signal outputted by the debimetre, both to enhance the performance of the engine, and to reduce its polluting emissions.
Thirdly, the electronic component can be made to intervene to make it change the degree of intervention based on the wear of the debimetre after several km of application.
Advantageously, the subject device is simple and economical and the method is easy to implement.

Claims

A signal conditioning device (1), in particular for air flow rate measuring probes (3) in internal combustion engines, characterised in that it comprises means (2) for translating and/or amplifying positively and/or negatively a signal outputted by the measuring probe (3), before the signal reaches an engine control and management unit (4).
Device as claimed in claim 1, characterised in that the means (2) for translating and/or amplifying the signal of the probe (3) comprise:

at least a device (5) for supplying electrical energy;

at least an amplifier/attenuator (6) with fixed gain to recover any loss of efficiency of the probe (3).
Device as claimed in claim 2, characterised in that the means (2) for translating and/or amplifying the signal of the probe (3) further comprise:

at least one amplifier stage (7) with adjustable or percent gain, functionally positioned upstream of the amplifier stage (6) with fixed gain;

a plurality of filters (8), so-called EMI filters, to isolate the device (1) from any interference in the radio frequency band, coming from the outside environment.
Device as claimed in claim 2, characterised in that the means (2) for translating and/or amplifying the signal of the probe (3) further comprise:

at least one amplifier stage (7) with constant gain, functionally positioned upstream of the amplifier stage (6) with adjustable gain;

a plurality of filters (8), so-called EMI filters, to isolate the device (1) from any interference in the radio frequency band, coming from the outside environment.
Device as claimed in claim 1, characterised in that the means (2) for translating and/or amplifying the signal of the probe (3) comprising at least one processor for receiving and processing, in a manner that is variable instant by instant, the signal outputted by the probe (3), to influence engine performance and a processor that adjusts the offset intervention (amplification/attenuation) and percent gain (translation) in positive and/or in negative and varies the mixing of the parameters even in the presence of wear in the debimetre.
A device as claimed in claim 1, characterised in that it is contained within a heat-protective shell.
A device as claimed in claim 1, characterised in that it is directly incorporated in a probe for measuring air flow rate in internal combustion engines (debimetre).
A method for conditioning a signal coming from a worn but undamaged probe for measuring an air flow rate, in particular for internal combustion engines, characterised in that it comprises the following steps:

receiving an electrical signal coming from the worn probe;

replacing the worn probe with a new probe;

receiving an electrical signal coming from the new probe and obtained for equal engine operating parameters with respect to the measurement made by the worn probe;

comparing the received signals to measure the size of a drop in intensity of the signal coming from the worn probe;

removing the new probe;

reinstalling the worn probe;

amplifying and/or positively and/or negatively translating the signal outputted by the worn probe by a value equal to said previously measured intensity drop.
Method as claimed in claim 8, characterised in that the amplification step takes place first by means of at least one amplifier with adjustable gain and then by means of at least one amplifier with constant gain.
Method as claimed in claim 8, characterised in that the amplification step takes place first by means of at least one amplifier with constant gain and then by means of at least one amplifier with adjustable gain.
Method as claimed in claim 8, characterised in that it comprises a step of sending the conditioned signal to a unit for controlling and managing the operation of the engine.
Method as claimed in claim 11, characterised in that it comprises a step of shielding the conditioned signal sent to the unit, to prevent any electromagnetic interference.
A method for conditioning a signal coming from a probe for measuring an air flow rate, in particular for internal combustion engines, characterised in that it comprises the following steps:

receiving an electrical signal coming from the probe;

amplifying/attenuating and/or translating the signal coming from the probe, in order to influence, in a manner which can vary instant by instant, the operating parameters of the engine;

sending the conditioned signal to a unit for controlling and managing the engine.
A probe for measuring an air flow rate in internal combustion engines, characterised in that it is associated to a device (1) as claimed in any of the previous claims from 1 through 5.