Theoretical Analysis and Design of a Variable Delivery External Gear Pump for Low and Medium Pressure Applications

This paper describes a unique design concept that is capable of electronically controlling the flow delivered by an external gear pump (EGP). The principle used for varying the flow relies on the variable timing concept which has been previously demonstrated by the author's research team for EGP's operating at high pressures (HPs) (p > 100 bar). This principle permits to vary the flow within a certain range, without introducing additional sources of power loss. In this paper, the above concept has been applied to formulate a design for a variable delivery EGP for low pressure (LP) applications (p < 30 bar), suitable for direct electric actuation. Specific design principles for the gear and the flow variation mechanisms are introduced to limit the force required by the electric actuation, and for maximizing the flow variation range. Also, the low target pressure allows the variable timing principle to be realized with an asymmetric solution, with only one variable timing element present at one side of the gears. A detailed analysis concerning the relationship between the electrically commanded position of the flow varying element and the theoretical flow delivered by the pump is also presented. This analysis is used to formulate analytical expressions for the instantaneous flow rate and the flow nonuniformity of the pump. The paper details the design principle of the proposed variable flow pump and describes the multi-objective optimization approach used for sizing the gears and flow variation mechanism. The paper also discusses the experimental activity performed on a prototype of the proposed unit, able to achieve a flow variation of 31%.

Modeling and Design Enhancement of Differential-Frequency Microgyroscopes Made of Nanocrystalline Material

The performance of a microgyroscope consisting of a microbeam made of nanocrystalline silicon connected to a rigid proof mass and subjected to electric actuation is numerically investigated. The operating principle is based on the transfer of mechanical energy among two vibration modes (drive and sense) via the Coriolis effect. The onset of the base rotation is observed to split the common natural frequency of the two bending modes along drive and sense directions into a pair of closely-spaced natural frequencies. The difference between this pair of frequencies is considered as the output parameter detecting the rotation rate. We follow an analytical approach to obtain closed-form solutions of the static and dynamic responses of the microsystem. Furthermore, we perform a sensitivity analysis of the output parameter of the present microgyroscope to the rotation rate when varying the material properties of the microbeam and the electric actuation.