FR2632062A1 - DEVICE FOR MEASURING GAS FLOWS - Google Patents

Abstract

In a device for measuring gas flow rates, in particular the air mass flow rate in the combustion engine of motor vehicles, comprising a gas flow resistance RL which, variable as a function of the temperature of the gas bathing it, is connected in series with a measuring resistor RM, and a power supply source 10 to bring the resistor RL to the operating temperature range, the voltage which the measuring resistor presents each time being representative of the gas flow, l The invention proposes, to accelerate the actuation of the measuring device, a heating means 10, 18 bringing the resistance RL very quickly to an initial temperature above the operating temperature range, and cooling, by the current of gas, resistance RL up to this temperature range.

Description

Device for measuring gas flows

  The present invention relates to a device for

  aimed at measuring gas flows, in particular mass flow

  air in the case of motor vehicles with

  internal bustion, and which includes resistance & flow

  ment of gas, in particular a hot film & probe, which, variable according to the temperature and bathed by the gas current, is connected in series with a measuring resistor, and a source of electric power intended for

  supply the assembly in series as well as wear the resistor

  gas flow tance at the operating temperature range, the voltage present each time the measuring resistance being treated as representative of the flow

gas.

  Such devices pose a problem of

  fact that after switching on the device the resistance

  this gas flow does not reach, for the operating mode-

  normal, that its temperature range is relatively late

  re regime and that it is therefore a highly delayed gas flow measurement. This drawback is felt in particular with regard to the measurement of the air mass flow rate in low-voltage motor vehicles of the on-board power supply network, since when the engine is started, no measurement and adjustment process can be used for determining the effective mass flow rate of the air is

still achievable.

  Consequently, the object of the present invention is to produce the device of the kind defined above, by

  simple measures, in such a way that it allows

  take a reliable measurement result much earlier with regard to the effective gas flow rate, so that, for example in the case of motor vehicles, the air mass flow rate can be reliably taken into account from the moment the internal combustion engine turns on

works by itself.

  This goal is achieved, for a measuring device

  gas flow rates, in particular to measure the flow

  air mass for motor vehicles with internal combustion engine, comprising a gas flow resistance, in particular a hot film probe, which, variable according to the temperature and bathed by the gas current, is connected in series with a measurement resistor, and a current supply source intended to supply the series connection as well as to bring the gas flow resistance to the operating temperature range, the voltage which the resistance of each measurement being treated as being representative of the gas flow rate, according to the invention by a rapid heating means which, in particular when the internal combustion engine does not

  does not turn on its own yet, carries the resistance to

  gas in a very short time at a set temperature

  part higher than the operating temperature range and the fact that the processing of the measurement data begins

  as soon as the gas flow resistance is cooled

  die, by the gas flow, up to the temperature interval

  dieting. While in the devices known up to now, the heating of the gas flow resistance takes place when the device is switched on exactly as in the normal operating state, the rapid heating provided upstream according to the invention and which goes beyond the operating temperature interval and the subsequent cooling, followed by the entry into action of the

  measurement data processing, allow a determination

  Significantly faster delivery of gas flow, especially air flow. It has been found for motor vehicles with internal combustion engines that the lapse of

  time elapsing between the start conditioned by the

  igniter and the autonomous starting of the combustion engine

  In general, this was sufficient to allow rapid heating of the gas flow resistance and the

  subsequent cooling down to the temperature interval

  diet. So the internal combustion engine can,

  as soon as it is switched on, be supplied with data

  due to correct gas flow or air mass flow.

  In a particularly preferred embodiment due to its simplicity the rapid heating means is of the direct heating type capable of carrying the gas flow resistance, preferably by means of

  the power source, at flow temperature.

  In this case, a switching device can be advantageously provided, in particular a transistorized switch, which short-circuits the measurement resistance during rapid heating and / or a switching device reducing the resistance to gas flow during rapid heating. and intended to temporarily connect parts of the gas flow resistor in parallel

  and / or a switching device capable of increasing the cost

  and / or the supply voltage of the power source

  tation during rapid heating. In this regard, the switching device short-circuits the measurement resistance and

  the switching device increasing the current and / or the voltage

  Power supply during rapid heating is used

  readable for any embodiment of resistance to

  gas flow, while the switching device reduces

  the resistance to gas flow during heating

  fast aging can only be used in the case where the gas flow resistance consists of several resistance forming parts, as is the case for example for hot film probes with shaped resistance tracks

  meanders and at least one median grip.

  According to another characteristic of the invention, the

  rapid heating means to bring the resistance to

  Lement gas at the flow temperature is in the form of independent heating which can be for example heating with infrared rays, by induction or by means of a separate heating resistor, heated independently and thermally associated with the resistance to gas flow, in which latter case the heating resistance is advantageously in the form of a thin heating sheet deposited on the gas flow resistance by vaporization in order to obtain a

intimate thermal contact.

  The operating temperature range of the resistance

  gas flow rate must be greater than the temperature

  ture of the ambient environment. This is why it is preferred to a-

  adapt the heating process of the flow resistance

  gas at ambient conditions. In this regard it is recommended that the level of the flow temperature be variable depending on the temperature of the gas or air. Indeed, at high ambient temperatures it is advisable to choose a high flow temperature, then

  that at low or normal ambient temperatures a tem-

  lower starting temperature is sufficient and must be effective-

  be chosen so that the measurement process is more

quickly available.

  A characteristic of the device of the invention particularly suitable for simplifying the measurement process consists in that it includes a rapid heating means

  acting during a determined rapid heating time.

  In this case, however, it must be ensured that the determined rapid heating time is sufficient for all

  ambient temperatures, in order to be able to obtain a temperature

  sufficiently high starting point. In this regard, however, it is preferable that the rapid heating time be a function of the temperature of the gas or of the air since this is indirectly obtained a variation of the flow temperature as a function of the ambient temperature. According to another characteristic of the invention, the rapid heating time is approximately 100 ms at most. This duration proves to be sufficient and corresponds appreciably to the period of time elapsing between the starting process and the autonomous starting of the internal combustion engine. This time of

  rapid heating, followed by cooling down to the inter-

  operating temperature valle, is therefore practically im-

noticeable to the user.

  According to another characteristic of the device of the invention there is provided a recognition member which recognizes the switching on of the device and activates rapid heating, then locks until the deactivation

  device circuit, so that parasitic pulses

  your are deleted for sure and that no new heaters

  Fast aging cannot take place during the current operation.

  The device according to the invention comprises before-

  carefully a timer, to be started by switching on the device, having a temperature signal input for taking into account the temperature of the

  gas or ambient, and a response time, variable depending on

  tion of the latter, for the activation of the rapid heating means during the response time, that is to say the rapid heating time, which increases with the rise

  of the temperature. This embodiment is particularly

  very practical and simple since timers

  adjustable are commonly found commercially.

  It is inter alia in motor vehicles that it is necessary to measure the mass flow of gas or air, in order to obtain impeccable combustion and a favorable composition of the exhaust gases. To this end, measurement bridges are generally used comprising adjustment members in the supply branch of the bridge. In this respect it is advantageous that in a device according to the invention equipped with a measuring bridge and an adjusting member which, mounted in the supply branch of the measuring bridge, sets the latter to zero as a function of the differential voltage of the bridge, the regulating function of the regulating member is inactive during the operation of the rapid heating means, in which case the regulating member is preferably completely

  interconnected during rapid heating.

  According to another characteristic of the

  the invention a temperature measurement amplifier

  ends the gas or ambient temperature at a temperature compensation resistor located in the measuring bridge and is connected to a timer which, activated by switching on the device, has a time of

  temperature-dependent response, during which it

  fully connects the adjuster and closes an in-

  breaker ,. like for example a transistor switch

  se, mounted in parallel with the measuring resistor.

  This embodiment is particularly suitable in combination with a measuring bridge since it already has a temperature compensation resistance at which the ambient temperature, that is to say the

  gas or air stream temperature, can be determined

  born, in order to order according to the latter a

  timer suitable for rapid heating.

  The invention is explained in more detail below.

  with the aid of exemplary embodiments illustrated in the appended drawings in which: FIG. 1 represents, in diagram form, the principle of the present invention; FIG. 2 represents, in the form of a principle graph, the mode of operation of rapid heating; FIG. 3 schematically represents a hot film probe capable of serving as a gas flow resistance and comprising a resistance track in the form of meanders and a central tap;

  Figure 4 shows a measurement bridge with a mon-

  parallel tage of parts of the resistance & gas flow during rapid heating; and FIG. 5 represents a device equipped with a measurement bridge and a bypass used for rapid heating and making it possible to shunt the measurement resistance during a variable rapid heating time as a function of

temperature.

  According to FIG. 1, a power source 10, preferably an adjustable direct current source, can

  by means of a switch S supply a mount

  ge in series composed of a measurement resistance RM and a gas flow resistance RL variable according to the temperature and bathed by the gas current. Depending on the operating conditions of the device, the voltage of

  UA output which at the RM measurement resistance decreases

  naked during operation is each time represented

  tive gas flow since the gas current bathing the resistance & gas flow RL subtracts from it more or less heat energy. Preferably, the gas flow resistance RL as well as the measurement resistance RM are mounted in a measurement bridge 12 together with a resistance of

  RT temperature compensation and fixed RF resistance.

  The temperature compensation resistor RT detects the temperature of the gas stream without the gas stream

  bathing takes from it energy. Differential voltage

  it bridge in the zero branch of the measurement bridge 12 is supplied to a differential amplifier 20 whose output signal controls or regulates the power source 10 so that the differential voltage of the bridge becomes zero. After balancing the bridge, the output voltage UA is representative of the gas or air mass flow. The fact that a measuring bridge constitutes a variant which can replace a simple series connection is elucidated in FIG. 1 by a dotted representation of the other

various components.

  According to FIG. 1, a circuit recognition device 14 detects the process of circuiting the device and this, in this case, by recognizing the process of closing the switch S. Instead, however, it could also be brought to the organ of

  recognition of switching on 14 another mid signal

  turns on. As the point representation shows

  tilled in Figure 1, the circuit recognition device 14 then ensures that at least one of three rapid heating measurements indicated for the resistance & gas flow RL is taken for a short period of time. A first possibility is that during

  rapid heating the RM measurement resistance is simple-

  ment short-circuited, that is to say shunted, by a switching means presented in the form of a switch 16, so that all the voltage of the power source 10 is available to heat the flow resistance of RL gas (in the case of a measuring bridge 12 the process of setting the zero voltage of the bridge must obviously be

  interrupted during this rapid heating). A second possibility

  Bility is to adjust the power level of the power source 10 upward so that more heat output becomes available for heating the gas flow resistor RL. Instead of these two direct heating measures it can also

  be provided with independent heating by means of a resistor

  separate heating element which thermally differs

  directly associated with the gas flow resistance RL.

  These and other rapid heating measures can be taken individually or alternatively

  various combinations can be chosen.

  In order to elucidate rapid heating, the variation of the temperature T of the gas flow resistance RL as a function of time t is shown in FIG. 2. At time tl the gas flow resistance RL present

  ambient temperature, i.e. that of the environment

  surprising, since no heating has yet taken place. Thanks to

  one or more of the rapid heating measurements men-

  until then t2, rapid heating takes place until a flow temperature TA which is higher than the operating temperature or at the operating temperature interval TB is reached. Then there occurs until time t3 a cooling conditioned by the current

  gas, which cooling lasts until the temperature

  operating temperature or the operating temperature range TB is reached. Then the gas flow resistance is conventionally supplied as well as heated from the power source 10 and cooled by the gas stream, which can cause its temperature to oscillate at

  within the operating temperature range TB.

  Such an oscillation also occurs in the case of a measuring bridge 12 when the temperature of the gas stream oscillates or when there is an abrupt variation in the gas mass flow with a subsequent adjustment to zero of the bridge. It is therefore important that the flow temperature TA be greater than the operating temperature range. Such rapid heating, including the subsequent cooling phase, can be carried out in a very short period of time, for example in a time of up to about 100 ms. These rapid heating measurements allow the operating temperature range to be reached at least much more quickly than without rapid heating; the duration of

  switching on can for example be divided by 20.

  Figure 3 shows a special type of gas flow resistor 22 in the form

  a hot film probe comprising resistance tracks

  ce 24, 26 in the form of meanders. In this case the resistance

  Gas flow tance has on each side a terminal or external socket and a central socket 28. By means of appropriate wiring, the resistance tracks 24 and 26 can be mounted in series or in parallel. In case of

  parallel mounting of the corresponding resistance tracks

  tes 24, 26 the total resistance is reduced by me-

  so that when supplied with a constant voltage

  stante the total current and the heating power are found

  wind doubled. Therefore parallel mounting is suitable

  for the rapid heating process.

  In the device partially shown in FIG. 4, the measurement bridge 12 consists, on the one hand, of two partial resistances & gas flow RL1 and RL2 in series with the measurement resistance RM and, on the other hand, of the temperature compensation resistance RT in series with the fixed resistance RF. The differential amplifier 20

  detects the differential voltage of the bridge to be able to e-

  carry out as in the case of FIG. 1, an adjustment of a power source (not shown) so as to obtain a zero voltage of the bridge. The partial gas flow resistances RL1 and RL2 correspond to the tracks of

  resistance 24 and 26 of the hot film probe 22 of the fig-

  re 3. The circuit recognition device 14, which

  corresponds in principle to that of Figure 1,

  requires the switching equipment 30 comprising three elements

  individual switches 32, 34 and 36 which are shown in Figure 4 in the rapid heating position. In this state, the switches 32 and 34 respectively bypass the partial resistors RL1 and RL2, the mutual connection of which, that is to say the series connection, is interrupted by the switch 36. Thus the partial resistors are

  are mounted in parallel, which leads to a

  increased heating power and a more rapid heating phase

  pide of gas flow resistance. At the end of

  fast heating time switches 32, 34 open

  switch and the switch 36 closes so that the resistors

  partial RL1 and RL2 are connected in se-

  laughs for normal operating condition. This embodiment of Figure 4 is only suitable when the gas flow resistance is achieved, or can be

split into at least two parts.

  In the embodiment of Figure 5 the measuring bridge 12 consists of the series connection of any resistance to gas flow RL as well as

  the measurement resistance RM and the compensation resistance

  RT temperature as well as RF fixed resistance.

  The differential amplifier 20 makes it possible to obtain the balance

  bridge breaking by appropriately influencing an organ-

  adjustment 42 in the bridge supply branch of the power source 10. If, for example, in the normal operating state the gas flow increases, then the

  gas flow resistance RL is more strongly re-

  cooled to then be due to the zero adjustment process of the bridge, as a result of the influence still exerted on the adjustment member 42, heated more strongly until the bridge is balanced. The increased heating current produces, at the measurement resistance RM, an increased output voltage Ua which is treated as

  representative of the gas mass flow.

  According to FIG. 5, the switching-on recognition member 14 detects the switching-on process, for example the jump in switching-on voltage of the power source 10, to thus start a

  timer 40, for example a mono-relaxation stage

  stable, which in turn delivers a switching impulse

  switch 16 bypassing the RM resistance

  and at the same time fully interconnects the re-

  setting 42 by interrupting the adjustment process. The impulse

  switching on length has a length of, for example, up to about 100 ms, period of time during which

  rapid heating of the flow resistance

  gas RL, since the latter is connected directly to the power source 10. When the starting temperature TA (see FIG. 2) is reached, in this case at the end of the activation pulse circuit, the switch 16 opens again and the regulating member 42 is brought

  by the differential amplifier 20 to resume the process

above normal setting.

  In the embodiment of Figure 5 the im-

  switching-on pulse delivered by the timer 40 has a duration which is a function of the temperature of the gas or of the air. To this end, the temperature of the gas or air stream is detected by means of a

  temperature measurement 38 connected to the resistance

  RT temperature thinking and is brought to timer 40. Thus the length of the switching pulse can be adapted each time to the gas temperature, so as to be able to thus obtain a rapid heating time also

  short as possible. In this context, it should be remembered

  1st that the flow temperature TA must be higher than the operating temperature range TB, without however

  greatly exceed it. Given the cooling,

  summed by the gas flow, from TA to TB and the duration of this cooling, TA should not be significantly

greater than TB.

  It is also important that the recognition body

  this circuit 14 is automatically locked after a first circuit detection, until the device is switched off. This prevents parasitic pulses from intervening and triggering

  inadvertently a new rapid heating.

  The devices shown and described are particularly suitable for motor vehicles with motor &

  internal combustion and low-voltage supply network

  on-board station. They are however also suitable for other applications where it is a question, after switching on a device, of quickly determining flow rates or

gas flow rates.

Claims (16)

  1 - Device intended to measure gas flow rates, in particular the air mass flow rate for motor vehicles with internal combustion engine, and comprising a gas flow resistance (RL), in particular a   hot film probe, which, variable depending on the temperature   crossed out and bathed in the gas stream, is connected in series with a measurement resistor (RM), and a power supply source (10) to supply the series connection as well as to bring the gas flow resistance to the operating temperature interval, the voltage that   each time has the measurement resistance being processed   representative of the gas flow, characteristic   dried by a rapid heating means (10, 16, 18, 30) which, when the device is switched on, in particular when the internal combustion engine is not yet running by itself, heats the gas flow resistance (RL) for a short time so as to bring it to a flow temperature (TA) higher than the operating temperature range (TB), and by entering the action of   processing of measurement data as soon as after cooling   as a result of the gas flow, the temperature of the gas flow resistance is reduced to   the operating temperature range.   2 - Device according to claim 1, character-   risé by a rapid heating means (10, 16, 30) of the type allowing to heat the gas flow resistance   directly, preferably by means of the power source   tation (10), so as to bring it to the temperature of share (TA).   3 - Device according to claim 2, character-   controlled by a switching means (16), in particular a   transistorized switch, which short-circuits the resistance   this measurement (RM) during rapid heating.   4 - Device according to claim 2 or 3, ca-   activated by switching equipment (30) reducing the gas flow resistance (RL) during rapid heating and intended for temporary connection in parallel   parts (RLl, RL2; 24, 26) of the flow resistance gas (RL).   - Device according to any one of the claims   cations 2 & 4, characterized by a switching means   able to temporarily increase the supply current and / or supply voltage to the power source (10) during rapid heating.   6 - Device according to claim 1, character-   rised by a rapid heating means (18) presented under the   form of independent heating capable of carrying the re-   gas flow resistance (RL) at flow temperature share (TA).   7 - Device according to claim 6, character-   risé by an independent heating means to the rays rays frarouges.   8 - Device according to claim 6, character-   rised by independent means of induction heating.   9 - Device according to claim 6, character-   by a separate heating resistor (18) capable of being heated independently and associated thermally &   gas flow resistance (RL).   - Device according to claim 9, character-   rised by a heating resistor (18) presented in the form of a thin heating sheet capable of being independently heated and deposited by vaporization on the   gas flow resistance (RL).   11 - Device according to any one of the claims   previous cations, characterized in that the level of the flow temperature (TA) is variable depending on the gas or air temperature.   12 - Device according to any one of the claims   previous cations, characterized by heating means   fast acting during a fast heating time deter- mined (4 t).   13 - Device according to claim 12, character-   that the rapid heating time (Zbt) is functional   gas or air temperature.   14 - Device according to claim 12 or 13, characterized in that the rapid heating time (, t) can go up to around 100 ms.   - Device according to any one of the claims   previous cations, characterized by a recon-   birth of circuit (14) which detects the circuiting of the device and activates rapid heating to   then lock until the device is switched off sitive.   16 - Device according to any one of the claims   previous cations, characterized by a timer (40) to be started by switching on the device and which has a temperature signal input in order to take into account the gas or ambient temperature, and a response time, or switching delay, dependent on this temperature, to activate the rapid heating means during the switching delay, that is to say the rapid heating duration, which is all the longer as the temperature is high.   17 - Device according to any one of the claims   previous cations, equipped with a measuring bridge (12) and an adjustment member (42) mounted in the supply branch of the measuring bridge and which sets the measuring bridge to zero as a function of the voltage differential of the bridge, characterized in that the regulatory function of the organ   (42) is inactive during operation fast heating means.   18 - Device according to claim 17, character-   in that the adjusting member (42) is completely   terconnected during rapid heating.   19 - Device according to claim 17 or 18,   characterized in that a temperature measuring amplifier   ture (38) detects the gas or ambient temperature at a temperature compensation resistor (RT) located in the measurement bridge (12) and is connected to a timer (40) which, activated by switching on circuit of   device, has a response time, or delay   mutation, variable as a function of temperature and during which it interconnects the regulating member (42) completely   and closes a switch (16), such as an inter-   solid state breaker, mounted in parallel with the resistor ce of measurement (RM).