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The hot-wire(H/W) element of an air flow sensor has a tendency to indicate lower than actual flow rate when subjected to large-amplitude oscillatory flow. First, the causes for this measurement error is investigated and a new dynamic model for H/W is proposed. The dynamic model is a combination of the static non-linearity output characteristic of the H/W element and the dynamic response of the H/W element. Second, a signal processing method is developed to correct the measurement error of the H/W by inversing the proposed H/W dynamic model. The result shows that by using this signal processing method, the measurement error of the H/W is reduced.

This paper describes an advanced bypass flow passage configuration for a thermal air flow sensor which increases the dynamic flow-rate range, and describes its basic fluid mechanic relations in terms of Bernoulli' s principle. This configuration consists of a main flow path and two bypasses located inside the main flow path. Thermal and temperature compensation probes are installed only in the primary bypass. The secondary bypass connects with the primary bypass downstream of the probes. The flow velocity, and consequently the pressure, in the primary bypass is affected by this conflux. The conflux loss coefficient increases as the flow rate in the secondary bypass increases. As a result, the flow velocity in the primary bypass decreases as the total air flow rate increases. In tests, the dynamic range is shown to be increased by about 30% for flow velocities in the primary bypass of between 0.5 m/s and 50 m/s.

A fuel injector adapter which can divide the fuel spray into two streams and produce fine fuel atomization is being developed to improve fuel economy and transient performance in four-valve gasoline engines. The adapter has the shape of a pair of spectacles and is attached to the orifice outlet of the injector. The optimum shape of the adaptor is investigated by 3-D viscous flow analysis by FEM and experiment. A 17% improvement in transient performance over the conventional Hitachi injector is confirmed by engine tests in a passenger car.

This report introduces an advanced flow passage design for bypass type of hot-wire air flow meter. The design was employed in an air flow meter integrated into a throttle body i.e. an integral type air flow meter. Features of the design are (1) configuration integrated on a single piece die-cast body employing a two dimensional L-shaped bypass passage and (2) a wide bypass inlet with oval profile. This design yields better performance and is more economical. This paper describes the features of this new flow passage configuration with respect to measurement accuracy and signal noise. That is, it deals with relations between the passage configuration and the signal output deflections due to throttle valve position or distortion on inlet airflow. It also deals with the effects on signal noise caused by turbulence in upstream flow and by fluctuation in bypass air due to flow confluence at the bypass outlet.

A new type hot wire probe has been developed for measurement of intake mass air flow rate in electronic fuel injection systems. The probe was composed of a coiled platinum wire covered with a glass-ceramic composite material. Improvement in response time has been achieved through the reduction of heat transfer from the hot wire probe to the leading wires, resulting from low thermal conductivity of the covering material. The decrease of the longitudinal heat flow rate has been revealed by the measurement of temperature distribution in the probe.

This report outlines the developmental status of the Hitachi hot wire air flow meter. It describes the newly developed hot wire probe and the air flow meter body to realize an improved cost performance ratio. In addition, it covers approaches to improve response time when the air flow rate is changed and to avoid deterioration in measurement accuracy caused by dirt deposits on the hot wire probe.