1. Technical Field
The field of the invention relates to engine systems using pressure sensors. In particular, the field of the invention relates to systems that use a determination of barometric pressure.
2. Background of the Invention
In engine control systems, it is advantageous to provide an estimate of atmospheric (barometric) pressure. Barometric pressure (BP) affects engine exhaust backpressure, which affects the residual burnt exhaust gas remaining in the cylinder at the close of the exhaust valve. Further, barometric pressure affects available manifold vacuum for operating various accessories.
The inventors herein have recognized that it is possible to provide an accurate barometric pressure value utilizing an exhaust gas recirculation (EGR) system. In one specific example, the EGR system has an upstream valve and a downstream orifice, with a gauge pressure sensor upstream of the orifice and an absolute pressure sensor downstream of the orifice. In such an approach, whenever EGR flow is substantially zero, barometric pressure can be calculated utilizing the gauge and absolute pressure sensor readings together.
However, the inventors herein have also recognized that further improvements can be obtained with such a system configuration by utilizing a new method for measuring EGR flow.
In one example, the above advantages over prior approaches are provided by a method for measuring flow through an orifice having a gauge pressure sensor coupled upstream of the orifice and an absolute pressure sensor coupled downstream of the orifice. The method comprises calculating an estimate of atmospheric pressure; and determining the flow based on a gauge pressure sensor reading, an absolute pressure sensor reading, and said estimate of atmospheric pressure.
By using a gauge pressure sensor reading, an absolute pressure sensor reading, and an estimate of atmospheric pressure, it is possible to obtain accurate EGR flow measurements. In one specific example, the gauge pressure value is coupled with the calculated barometric pressure to determine an upstream absolute pressure value. Then, this can be utilized with the downstream absolute pressure to calculate flow, i.e., rather than using one gauge value and one absolute, effectively two absolute pressure are provided. Note that this is just one example.
Alternatively, the downstream gauge value can be utilized with the calculated barometric pressure to determine a downstream gage value that can be compared with the upstream gauge value, i.e., rather than using one gauge value and one absolute, effectively two gauge pressure are provided. Various other schemes can be employed to harmonize an upstream gauge pressure reading and a downstream absolute pressure reading.
An advantage of the above aspect of the invention is improved engine control, thus giving reduced emissions.