Abstract
Measurements of the underlap for four-way valves gave results that the underlap was not only uneven but also geometrically asymmetric for some four-way valves. Both the unevenness and the asymmetricity have considerable influence on the characteristics of the valve-controlled cylinder.
In addition to the unevennesses i=(Δ1/Δ)- 1, i= (Δ'1/Δ')-1, the asymmetricity η=Δ'1/Δ is introduced for a valve, where Δ, Δ' are the mean underlaps of the left side and the right side three-way valves and Δ1, Δ'1 are the underlaps on the supply sides. represents the right side.
Considering i, η and Δ of a valve, the frequency response of a valve-controlled cylinder with viscous friction, Coulomb friction and mass load was theoretically analyzed where the flow versus pressure characteristic curves were approximated partially as polynomials of degree 3 of the pressure.
The tendency shown by the theoretical results agreed fairly well with that of the experimental results. The frequency characteristics of (piston velocity)/(spool displacement) = V(jω)/ Y(jω)show the same tendency for an asymmetric valve as that for a symmetric valve. But, for the case where an asymmetric valve is used, there is null shift of the valve ( δο) for avoiding the piston drift. δο changes in proportion to i, and |δο| becomes larger according to the increase in η (for η>1) or 1/η (for η <1).δο changes little for the changes in Δ and frequency ω.
