Measuring and testing – Internal combustion engine or related engine system or... – Compression
Patent
1989-12-06
1991-06-04
Myracle, Jerry W.
Measuring and testing
Internal combustion engine or related engine system or...
Compression
123465, G01M 1500
Patent
active
050203630
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining atmospheric air pressure in pressure-controlled fuel injection systems.
In vehicle engines having pressure-controlled fuel injection systems, i.e. systems in which the basic measured variable of the system is the intake manifold pressure, the exhaust back-pressure, which is dependent upon the prevailing atmospheric air pressure, influence the residual quantity of gas remaining in the engine cylinders during the exhaust cycle and hence the volume of fresh gas that can enter the cylinder on the next induction stroke. This has the result that, as the atmospheric air pressure decreases, the mixture in the cylinders of the engine becomes leaner. For example, when the engine is idling, the mixture becomes leaner, typically by approximately 4.5% per 1,000 m. altitude. In order for this error to be corrected, it is necessary to provide some means of determining the prevailing atmospheric air pressure.
A measure of the prevailing atmospheric air pressure can be obtained using the pressure value measured by the conventional intake manifold pressure sensor when the engine speed is still zero or extremely low, e.g. cranking speed. However, since the atmospheric pressure changes with the altitude at which the vehicle is operating, a measure of atmospheric pressure made initially by measuring the intake manifold pressure at start up of the engine requires correction to take account of a changing altitude of operation of the vehicle.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for obtaining a value for the atmospheric air pressure, based on the measured intake manifold pressure but measured during running, non-idling conditions.
In accordance with the present invention, there is provided a method of determining the prevailing atmospheric air pressure in a pressure-controlled injection system, the method comprising detecting when the engine is operating at or above a predetermined load condition, measuring the prevailing intake manifold pressure (Ps) at that condition, and multiplying the measured intake manifold pressure (Ps) by a predetermined numerical factor (K) to provide a pressure value (Po) representative of the atmospheric air pressure.
By arranging for the predetermined load condition to correspond to the pre-established condition that the measured manifold pressure is a predetermined percentage of the actual atmospheric pressure, a value corresponding to the actual atmospheric pressure can be obtained for any given measured intake manifold pressure, if said pre-established condition has been reached.
In order to establish whether said predetermined load condition has been reached and/or exceeded, the ratio of measured throttle valve angle and engine speed can be monitored and compared with stored values.
Preferably, there is pre-established a characteristic engine-specific curve of the respective throttle valve opening angle .alpha. necessary to achieve at a plurality of given engine speeds (N) the condition that the measured manifold pressure is a predetermined fixed percentage (Q) of the actual atmospheric pressure, the existence of said predetermined load condition being established when the curve is exceeded during vehicle operation and the then prevailing intake manifold pressure (Ps) being multiplied by said factor K(=100/Q) to produce a pressure value (Po) representative of the prevailing atmospheric air pressure.
In a more sophisticated embodiment, there is pre-established a plurality of characteristic engine-specific curves, each of which corresponds to the respective throttle valve opening angle (.alpha.) necessary to achieve at a plurality of given engine speeds (N) the condition that the measured manifold pressure is a respective fixed percentage (Q) of the actual atmospheric pressure, each curve being based on a different percentage (Q), and wherein, in operation of the vehicle, the atmospheric pressure is determined by multiplying the measured intake manifold pressure
REFERENCES:
patent: 4590563 (1986-05-01), Matsumura et al.
patent: 4600993 (1986-07-01), Pauwels et al.
patent: 4926335 (1990-05-01), Flowers et al.
Hirschmann Klaus
Junginger Erich
Schnaibel Eberhard
Myracle Jerry W.
Robert & Bosch GmbH
Striker Michael J.
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