DE19938899B4 - Method and device for determining the ambient pressure in an internal combustion engine - Google Patents

Abstract

Method for determining the ambient pressure p _u in an internal combustion engine with an air mass meter in the intake tract, in which method a starting value for the ambient pressure p _u , the air mass flow Q, the air temperature T and the absolute pressure p _s in the intake tract upstream of a throttle element are measured and that outside the Intake tract prevailing ambient pressure p _{u is determined} from the starting value, the air mass flow Q, the air temperature T and the absolute pressure p _s .

Description

The invention relates to a method and a device for determining the ambient pressure at a Internal combustion engine, the device being an air mass meter having.

When controlling the operation of an internal combustion engine some control systems evaluate the ambient air pressure. For this purpose, a corresponding ambient pressure sensor is often located in a control unit.

The ambient pressure can do this, for example be used, the degree of loading of the intake tract of the internal combustion engine determine upstream air filter. If you measure the absolute pressure in the Intake pipe downstream of the air filter in front of a throttle valve, so can one if the pressure difference between this absolute pressure and the ambient pressure an operating parameter dependent Threshold exceeds conclude that there is an excessive pressure drop at the air filter.

The ambient pressure can also take into account the determination of the injection times.

According to the state of the art, an ambient pressure sensor is required to measure the ambient pressure constantly. For example, the DE 44 26 272 A1 a load cell in the intake tract and a separate ambient pressure transducer, both of which deliver their measured values to a control unit, which additionally also to a temperature sensor located in the intake tract. connected.

The DE 39 14 789 A1 dispenses with the possibility of constant measurement and uses an absolute pressure transducer downstream of a throttle valve in the intake tract, the value of which is only read out above a minimum opening angle of the throttle valve.

The invention is based on the object Method and a device for determining the ambient pressure to provide an internal combustion engine so that a constant Measurement without an ambient pressure sensor is possible.

This task is carried out in the claims 1 and 8 defined invention solved.

The method according to the invention is based on knowledge from that the Pressure drop between an air filter and a throttle element in the Intake tract of an internal combustion engine is a function of the pressure loss coefficient in the intake tract as well as the air mass flow, the air temperature and of the ambient pressure. Addition of the pressure drop to the absolute pressure in the intake tract provides the ambient pressure. Therefore, they offer two variants to determine the ambient pressure.

For one, you can get those out of this Addition derivable equation to transform it appropriately so that the ambient pressure itself as a function of air mass flow, air temperature and the pressure loss coefficient in the intake tract and the absolute pressure in the Intake tract results. Second, you can use a recursive procedure apply, starting from a starting value for the ambient pressure first the pressure drop is calculated and from this together with the absolute pressure in the intake tract a new value for the Ambient pressure is obtained. So you can recursively measure the ambient pressure determine. The starting value can be measured, for example, by measuring the absolute pressure in the intake tract with the internal combustion engine stopped or in idle mode generated because in these cases the absolute pressure in the intake tract is essentially the ambient pressure like.

The device according to the invention sees one Air mass meter between an air filter and a throttle element in the intake tract with an absolute pressure transducer inside and an air temperature sensor in the intake tract, which are connected to a control unit that at Implementation of the inventive method no recourse must take on an ambient pressure signal to increase the ambient pressure determine.

A possible air mass meter for this device points in a housing the air mass sensor and an absolute pressure sensor so that the essential Components of the device in a compact, simple and inexpensive to manufacture Component are realized. This air mass meter also has still the advantage of wiring and connectors, which are relatively expensive components, simplified are.

The pressure loss coefficient in the intake tract is decisively shaped by the pressure drop across the air filter. For the pressure drop is essentially responsible for loading the air filter. This loading changes but only slowly towards each other the ambient pressure. About that in addition, the degree of loading of the air filter has no influence on the Air pressure present in the intake tract if none or as good as no air mass flow is sucked in. This is the at standstill Internal combustion engine or idling the case.

Thus, the pressure loss coefficient, the used in the calculation of the pressure value according to the first variant by means of an absolute pressure measurement in the intake tract at standstill or calibrate or determine idle speed of the internal combustion engine. This determined value is then used for the further implementation of the Procedure used.

One can conclude that the air filter is too heavily loaded, ie causing an excessive pressure drop, if the pressure loss coefficient exceeds a predetermined threshold.

The invention thus has the advantage that to determine of the ambient pressure on a separate ambient pressure sensor can be dispensed with. It is also possible to determine the degree of loading of the air filter to determine and thus determine its need for replacement.

Advantageous embodiments of the Invention are in the subclaims characterized.

The invention is described below Reference to the drawing explained in exemplary embodiments. In the drawing shows:

1 1 shows a schematic representation of an internal combustion engine with a device for determining the ambient pressure,

2 is a schematic sectional view through an air mass meter and

3 and 4 Flow diagrams for two different methods for determining the ambient pressure.

1 schematically shows an internal combustion engine with a device for determining the ambient pressure. Only the components essential for understanding the invention are shown. The internal combustion engine 1 has an intake tract 2, which is an air filter 3 is connected upstream. In the intake tract 2 there is a temperature sensor 4 which measures the temperature of the intake air. The temperature sensor 4 delivers its signal to a control unit via a line, not specified 5 which, for example, the entire operation of the internal combustion engine 1 can control. Alternatively, the temperature sensor 4 also the air outside the intake tract 2 measure, then it must be ensured that the internal combustion engine heats up during operation 1 no falsified measurement. Next is in the intake tract 4 an air mass meter 10 arranged, both the intake air mass flow Q and the absolute pressure p _s in the intake tract 2 detected. The air mass meter delivers via lines not specified 10 its measured values to the control unit 5 , Alternatively, the temperature sensor 4 also in the air mass meter 10 be integrated.

The control unit carries out or initiates the procedures to be described.

The air mass meter 10 is in a preferred training in 2 shown in more detail in a schematic sectional view. The air mass meter 10 has a pipe section 14 that in the intake tract 2 is used. In the pipe section 14 there is an air mass sensor 11 , This can be a hot wire or hot foil sensor, for example. On the pipe section 14 is an electrical housing attached, which consists of a lower housing part 15 with housing cover 16 consists. The air mass sensor 11 is on the lower part of the housing 15 appropriate. Through a channel 18 , which can be designed as a bore, for example, is the inside of the electrical housing with the inside of the pipe piece 14 connected. In the lower part of the housing 15 there is a circuit board 13 to which the air mass sensor 11 connected. On the board 13 is the circuit for controlling and reading the air mass sensor 11 , Next is on the board 13 an absolute pressure sensor 12 as well as the necessary circuit. The circuit board 13 is on a plug 17 connected via which the lines to the control unit 5 to run. The circuit board 13 with the absolute pressure sensor 12 is from one layer 20 covered, which is, for example, silica gel. The layer 20 is applied in liquid form and then hardened. So that layer 20 not through the channel 18 can occur is a suitable nozzle 19 on the channel 18 intended. The layer 20 serves the board 13 and the absolute pressure sensor 12 as well as the lines to the plug 17 against harmful influences caused by the pipe section 14 to protect flowing intake air. At the same time is the layer 20 Trained so that the pressure inside the electrical housing that over the channel 18 to the pressure of the pipe section 14 is coupled, transmits. Because the absolute pressure sensor 12 under the layer 20 directly, ie without membrane or similar, to that in the intake tract 2 built-in pipe section 14 the absolute pressure sensor can be connected 12 exactly the absolute air pressure in the intake tract 4 to capture. Of course there is also a known membrane in the channel 18 possible. Leaked or condensed liquids from the housing 15 . 16 is the air mass meter 10 installed in a suitable location. This is compared to the representation of the 2 rotated 90 ° to the right.

Downstream of the air mass meter 10 is in the intake tract 2 the internal combustion engine 1 a (in 1 throttle element (not shown). Depending on the position of this throttle element, this can be, for example, a throttle valve, but adjustment via a variable intake valve stroke of the internal combustion engine is also required 1 possible, - a differently sized air mass flow Q flows through the air mass meter 10 , In an internal combustion engine without throttling, for example in a direct-injection lean-burn internal combustion engine, the air mass flow Q is determined by the operating parameters of the internal combustion engine 1 certainly. The type of throttling does not matter.

Which is in the intake tract 2 Setting pressure drop can be determined using the following equation: dp = C F · Rho / (2v 2 ) (1)

Here dp is the pressure drop, C _{F is} a pressure loss factor that represents the intake tract geometry, rho the density of the intake air and v its flow velocity. The density rho can can be replaced by the following equation: rho = p u / (R · T) (2)

R is the general gas constant (287 J / kgK), T is the air temperature and p _{u is} the ambient pressure. Furthermore, the velocity v is given by the air mass flow as follows: v = Q / (rhoA) (3)

Q is the air mass flow and A the cross-sectional area of the air mass meter 10 , Substituting equations (3) and (2) in equation (1), we get with C _b = C _F · R / (2 · A ² ): dp = C b · T · Q 2 / p u (4)

From this drop in pressure, the absolute pressure p _s in the intake tract can be used 2 determine by adding the ambient pressure p _u : p u = p s + dp (5)

This equation now offers two variants for determining the ambient pressure, which are now based on the flow diagrams of the 3 and 4 are explained.

• 1. Before starting a recursion 3 a starting value for the ambient pressure p _{u is} calculated in step S1. This starting value can be obtained, for example, by having the absolute pressure p _s in the intake tract when the internal combustion engine is at a standstill or idling 2 detected. Due to the vanishing or very low air mass flow Q, it can be seen directly from equation (5) or (4) that the absolute pressure in the intake tract p _{s is} then essentially equal to the ambient pressure p _u . The air mass flow Q and the air temperature T are measured in step S2. In step S3, the pressure drop dp is calculated in accordance with equation (4), the starting value for the ambient pressure obtained from step S1 being included in the calculation. A value stored in a memory of the control device can be used for the pressure loss coefficient Cb. The pressure loss coefficient Cb will be discussed in more detail later. In step S4, the absolute pressure p _s in the intake tract 4 measured. In step S5, a new value for the ambient pressure p _{u is} calculated from the pressure drop dp and the absolute pressure p _s according to equation (5). This value is used for the next recursion step, for which the process jumps back to step S2. This variant of the ambient pressure determination has the advantage that only simple arithmetic operations (additions, multiplications and divisions) have to be carried out.
• 2. Instead of the recursive method above, the ambient pressure can also be determined by the in the block diagram of the 4 reproduced procedures can be determined. For this purpose, the pressure loss coefficient Cb is first removed from the memory in step S6. The pressure loss coefficient Cb will be discussed in more detail later. Next, the air mass flow Q and the air temperature T and the absolute pressure p _s in the intake tract are measured in step S7. Then the ambient pressure p _u is calculated in step S8 according to a transformed version of the equation (5):
  

In both variants of the determination of the ambient pressure p _u , the pressure loss coefficient Cb is included in the equation used. Since the pressure loss coefficient Cb is essentially due to the pressure loss at the air filter 3 it is determined which of the slowly changing degree of loading of the air filter 3 depends, it can be assumed that the pressure loss coefficient Cb will change very slowly compared to the ambient pressure p _u . In order to be able to determine the current pressure loss coefficient Cb, the ambient pressure p _{u is} determined while idling or when the internal combustion engine is at a standstill, since then the absolute pressure p _s in the intake tract 2 is substantially equal to the ambient pressure p _u . The current value for the pressure loss coefficient Cb can then be determined by comparing the calculated with the measured ambient pressure p _u .

If this value exceeds a threshold, you can use an excessively dirty air filter 3 conclude.

Theoretically, the pressure loss coefficient Cb is independent of the operating parameters of the internal combustion engine 1 , If such dependencies cannot be ruled out in practice, for example due to transitions between laminar and turbulent flow processes, you can do this before starting the internal combustion engine 1 the absolute pressure p _s equal to the ambient pressure p _u in the intake tract 2 measure up. When the internal combustion engine starts immediately afterwards 1 can then be determined with p _u - p _a = dp and equation (4) Cb as a function of operating parameters, for example the air mass flow Q, by continuous measurement of p _s and stored in a map. These map values for Cb can then be used when determining the ambient pressure p _u according to one of the above variants.

Finally, by means of the value for Cb thus obtained or from the value for p _u measured before the start, the pressure loss dp during idling can also be determined exactly, so that a change in the pressure loss coefficient Cb during idling phases can thus be detected.

The air temperature T is also included in all calculations. It is therefore necessary that the air temperature T can be measured with the same dynamics as the air mass flow Q. However, this is not possible with some common temperature sensors. The method for determining the ambient pressure should therefore preferably be briefly suspended in those operating phases in which experience has shown a rapid temperature change. This is the case, for example, when starting again after a hot idle run, if the internal combustion engine has been operated for a while with low cooling (standstill of a motor vehicle) after periods of high load and then the cooling capacity rises again (motor vehicle is started again). In addition, due to the slowly changing air filter loading, a certain filtering is possible to the extent that sudden changes in the pressure loss coefficient Cb can be rejected. In general, a time constant of several days is sufficient for the determination. Such abrupt changes in the pressure loss coefficient Cb can occur, for example, when an internal combustion engine driving a motor vehicle is in operation 1 under heavy rain if, for example, the air filter gets wet while driving, which greatly increases the pressure drop it causes. Such changes should be discarded in the filtering.

Claims (12)

Method for determining the ambient pressure p _u in an internal combustion engine with an air mass meter in the intake tract, in which method a starting value for the ambient pressure p _u , the air mass flow Q, the air temperature T and the absolute pressure p _s in the intake tract upstream of a throttle element are measured and that outside the Intake tract prevailing ambient pressure p _{u is determined} from the starting value, the air mass flow Q, the air temperature T and the absolute pressure p _s . Method according to Claim 1, characterized in that a pressure loss coefficient Cb is further taken into account in the determination, which is derived from the cross-sectional area A of the intake tract in the area of the air mass measurement and / or one of the flow conditions in the intake tract ( 2 ) reproducing pressure loss factor C _{f is selected} depending. Method according to Claim 2, characterized in that a) a pressure drop dp between an air filter and the throttle element in the intake tract is dependent on the air mass flow Q; Air temperature T, pressure loss coefficient Cb and the starting value for the ambient pressure p _{u is} determined and b) a new value for the ambient pressure p _{u is} determined by adding the absolute pressure p _s in the intake tract and the pressure drop d _P. Method according to Claim 1, characterized in that the starting value is obtained by measuring the absolute pressure p _s with the internal combustion engine stopped or idling. Method according to one of the preceding claims, characterized in that from the given in a method according to claim 1 with claim 2 as the difference between ambient pressure p _u and absolute pressure p _s in the intake tract or directly present in a method according to claim 3 or claim 4, the pressure drop dp Pressure loss coefficient Cb is determined using the ambient pressure p _u , the air mass flow Q and the air temperature T, and if a threshold value is exceeded, a replacement requirement for an air filter upstream of the intake tract is signaled. Method according to claim 5, characterized in that the pressure loss coefficient Cb is calculated by the following equation: Cb = dp · p u / (Q 2 T). Method according to one of the preceding claims, characterized in that - the starting value is measured as the absolute pressure p _s in the intake tract equal to the ambient pressure p _u before starting the internal combustion engine, - the absolute pressure p _{s is} continuously recorded during the subsequent start and - a pressure loss coefficient Cb is obtained The following equation is calculated: Cb = (p _u - p _s ) · p _u / (Q ² T), where Q is the air mass flow and T is the air temperature in the intake tract ", - Cb as a function of at least the air mass flow Q in representing an operating parameter of the internal combustion engine is stored in a map and - when determining the ambient pressure p _u depending on the operating parameters, values taken from this map for the pressure loss coefficient Cb are taken into account. Device for determining the ambient pressure p _u in an internal combustion engine ( 1 ) with an intake tract ( 2 ) with: a) an air mass meter ( 10 ) in the intake tract ( 2 ), b) an associated absolute pressure sensor ( 12 ) and c) a temperature sensor ( 4 ), d) all connected to one control unit ( 5 ) are connected without a connection to an ambient pressure sensor according to one of the preceding method claims 1 7 determines the ambient pressure p _u . Apparatus according to claim 8, characterized in that an air mass meter is provided with one in an intake tract ( 2 ) an internal combustion engine ( 1 ) outstanding air mass sensor ( 11 ) on one of the intake tract ( 2 ) attachable housing ( 14-16 ) in which an absolute pressure sensor ( 12 ), one channel ( 18 ) the housing ( 14-16 ) with the intake tract ( 2 ) for pressure equalization. Device according to claim 9, characterized in that the housing ( 14-16 ) of the air mass meter an electrical housing ( 15 . 16 ) in which the absolute pressure sensor ( 12 ) is arranged and on which a plug ( 17 ) is attached; via which both the air mass sensor ( 11 ) as well as the absolute pressure sensor ( 12 ) are electrically contactable. Apparatus according to claim 10, characterized in that the housing is a piece of pipe ( 14 ) that enters the intake tract ( 2 ) can be used in which the air mass sensor ( 11 ) is arranged, and that with the electrical housing ( 15 . 16 ) is connected, the channel ( 18 ) the electrical housing ( 15 . 16 ) with the pipe section ( 14 ) connects. Device according to claim 10 or 11, characterized in that the absolute pressure sensor ( 12 ) on a board ( 13 ) to which the air mass sensor ( 11 ) is connected to a floor ( 17 ) of the electrical housing ( 15 . 16 ) is arranged and that a liquid applied and hardened layer ( 20 ) for pressure transmission and protection of circuit board ( 13 ), Absolute pressure sensor ( 12 ) and connecting wires over the board ( 13 ) and the absolute pressure sensor ( 12 ) is arranged, with a nozzle ( 19 ) on the canal ( 18 ) prevents the layer ( 20 ) before curing in the channel ( 18 ) can reach.