Measuring and testing – Simulating operating condition – Marine
Reexamination Certificate
2000-08-17
2003-01-14
McCall, Eric S. (Department: 2855)
Measuring and testing
Simulating operating condition
Marine
Reexamination Certificate
active
06505505
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method and a device for determining the ambient pressure for an internal combustion engine and to an air mass meter for the device.
The ambient air pressure is evaluated by a number of control systems involved in controlling operation of an internal combustion engine. In view of this fact, there is often provided a corresponding ambient pressure sensor in a control unit.
The ambient pressure can be used, for example, to determine the degree of loading of an air filter that is connected upstream of the intake tract of the internal combustion engine. If the absolute pressure in the intake pipe downstream of the air filter is measured in front of a throttle valve, it is possible, if the pressure difference between this absolute pressure and the ambient pressure exceeds a threshold which is dependent on operating parameters, to conclude that the pressure drop at the air filter is excessive.
The ambient pressure may also be taken into account when determining the injection times.
According to the prior art, an ambient pressure pick-up is indispensable for measuring the ambient pressure. For example, German published patent application DE 44 26 272 A1 provides a pressure gauge in the intake tract and a separate ambient pressure pick-up. Both feed their measured values to a control unit which in addition is connected to a temperature sensor disposed in the intake tract.
German published patent application DE 39 14 784 A1 dispenses with the option of constant measurement and uses an absolute pressure pick-up downstream of a throttle valve in the intake tract, the value from which pick-up is read only above a minimum opening angle of the throttle valve.
SUMMARY OF THE INVENTION
The object of the invention is to provide a method and device for determining the ambient pressure at an internal combustion engine and an air mass meter therefor which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind.
With the above and other objects in view there is provided, in accordance with the invention, a method of determining an ambient pressure for an internal combustion engine, with an air mass meter in. the intake tract. The method comprises the following steps: measuring a starting or initial value for an ambient pressure, an air mass flow rate, an air temperature, and an absolute pressure in an intake tract of an internal combustion engine upstream of a throttle member in an intake air flow direction; and determining an ambient pressure prevailing outside the intake tract from the starting value for the ambient pressure, the air mass flow rate, the air temperature, and the absolute pressure.
The method according to the invention is based on the recognition that the pressure drop between an air filter and a throttle member in the intake tract of the internal combustion engine is a function of the pressure loss coefficient in the intake tract and of the air mass flow rate, the air temperature and the ambient pressure. Adding the pressure drop to the absolute pressure in the intake tract gives the ambient pressure. Therefore, there are two recommended variants for determining the ambient pressure.
Firstly, the equation which can be derived from this addition can be suitably rearranged so that the ambient pressure results as a function of the air mass flow rate, the air temperature and the pressure loss coefficient in the intake tract and of the absolute pressure in the intake tract. Secondly, it is possible to use a recursive method, in which, working on the basis of a starting value for the ambient pressure, firstly the pressure drop is calculated and from this, together with the absolute pressure in the intake tract, a new value is obtained for the ambient pressure. It is thus possible to determine the ambient pressure by recursion. The starting value may, for example, be produced by measuring the absolute pressure in the intake tract when the internal combustion engine is stationary or idling, since in these situations the absolute pressure in the intake tract substantially equates to the ambient pressure.
In accordance with an added feature of the invention, a pressure loss coefficient is taken into account, and the pressure loss coefficient is chosen in dependence on a cross-sectional area of the intake tract in a region of the air mass measurement and/or a pressure loss factor representing a flow condition in the intake tract.
In accordance with an additional feature of the invention, a pressure drop between an air filter and the throttle member in the intake tract is determined in dependence on the air mass flow rate, the air temperature, the pressure loss coefficient, and the starting value for the ambient pressure; and a new value for the ambient pressure is calculated by adding the absolute pressure in the intake tract and the pressure drop. The absolute pressure is preferably determined with the internal combustion engine at standstill or in idling.
In accordance with another feature of the invention, the pressure loss coefficient is calculated from the pressure drop, using the ambient pressure, the air mass flow rate and the air temperature, and, if a threshold is exceeded, a signal is emitted indicating a necessity to exchange the air filter upstream of the intake tract in the intake air flow direction.
In accordance with a further feature of the invention, the pressure drop is defined as a difference between ambient pressure and absolute pressure in the intake tract. In the alternative, the pressure drop is directly present.
In accordance with again an added feature of the invention, the pressure loss coefficient is calculated with the equation
C
b
=
Δ
p
·
p
u
Q
2
T
,
where C
b
is the pressure loss coefficient, p
u
is the ambient pressure, &Dgr;p is a pressure drop, Q is the air mass flow, and T is the air temperature.
In accordance with again an additional feature of the invention, the starting value is the absolute pressure in the intake tract, which equates to the ambient pressure;
the absolute pressure is continuously recorded during a subsequent start-up; and
the pressure loss coefficient is calculated with the equation
C
b
=
(
p
u
-
p
s
)
·
p
u
Q
2
T
,
where C
b
is the pressure loss coefficient, p
u
is the ambient pressure, p
s
is the absolute pressure, Q is the air mass flow rate, and T is the air temperature in the intake tract;
the pressure loss coefficient C
b
is stored in a characteristic diagram as a function at least of the air mass flow rate Q, which represents an operating parameter of the internal combustion engine; and
during further determination of the ambient pressure p
u
, values of the characteristic diagram as a function of operating parameters are taken into account for the pressure loss coefficient C
b
.
With the above and other objects in view there is also provided, in accordance with the invention, a device for determining an ambient pressure for an internal combustion engine with an intake tract, comprising:
an air mass meter in an intake tract of an internal combustion engine;
an absolute pressure pick-up connected to the air mass meter;
a temperature sensor;
a control unit connected to the air mass meter, to the absolute pressure pick-up, and to the temperature sensor, the control unit being configured to determine an ambient pressure p
u
in accordance with the method according to claim 1, without an ambient pressure pick-up.
There is also provided, in accordance with the invention, an air mass meter for the above-outlined device. The novel air mass meter comprises:
a housing attached to the intake tract of the internal combustion engine and communicating therewith through a passage connecting the housing to the intake tract for pressure compensation purposes;
an air mass sensor mounted at the housing and projecting into the intake tract; and
an absolute pressure sensor.
In accordance with yet another feature of the invention, the housing has an electrics
Henzinger Ronald
Leiderer Harald
Leiderer Hermann
Wildgen Andreas
Greenberg Laurence A.
Mayback Gregory L.
McCall Eric S.
Stemer Werner H.
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