US 4,542,652 AGranted

Method and apparatus for determining a relative distance in a cylinder and piston assembly

OwnerMartin Reuter, Johannes Koniginventors

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Abstract

In the method and installation for determining a relative distance between the front wall (22) of the cylinder and the piston (14), an ultrasonic converter (30) is used to which a plate (68) presenting a reflecting reference surface (66) for the formation of a reference path is secured. The group of reference oscillations (R) and the group of measurement oscillations (M) appearing in the output signal of the converter (30) after the emission of a group of transmitter oscillations (S) are detected by means of threshold switches (108, 120, 122). Thereby, a measurement signal and a reference signal are obtained, the latter being used for compensation by means of a processor (38) for the influence of the different propagation conditions affecting the measurement signal.

Claims11

Dependent claims

A method for determining the distance between a cylinder (12) and a piston (14) in a piston and cylinder assembly (10), which has a cylinder chamber (26) filled with a fluid medium and including end walls formed by the cylinder (12) and piston (14) comprising the steps of:

transmitting a group (S) of sequential ultrasonic oscillations from a first end wall (24) of the cylinder chamber (26) toward the second end wall (28) for reflection in the vicinity of the second end wall as a group (M) of measurement oscillations, the step of transmitting being performed by an ultrasonic converter supported at the first end wall (24) and including an incompressible carrier (44) having a flat surface (46), a plate-shaped piezoelectric oscillator (48) positioned parallel to the flat surface (46) and, in spaced relationship from the surface, a sound projecting surface (42) positioned parallel to the oscillator (48) and facing the second end wall, and means (50, 52, 54) for mismatching the characteristic impedance of the oscillator (48) and the carrier (44), and means (56, 58, 60, 62) for matching the impedance between the oscillator and the sound projecting surface (42);
receiving the group (M) of measurement oscillations at the first wall after reflection in the vicinity of the oppositely disposed second wall for measurement of the elapsed travel time of the oscillations between transmitting of the group (S) of ultrasonic oscillations and the receipt of the group (M) of measurement oscillations to establish a measure of the relative distance;
establishing a reference path (42, 66) of a prescribed length within the fluid medium of the cylinder chamber (26) with a reflection surface (66) at one end of the path;
transmitting a group of ultrasonic oscillations along the reference path from a first end for reflection at the surface (66) at the opposite second end;
receiving the oscillations reflected from the reference reflection surface (66) as a group (R) of reference oscillations at the first end;
measuring the elapsed travel time (T.sub.R) between the transmission and receipt of the ultrasonic oscillations along the reference path at the first end (42) and producing a reference signal proportional to the elapsed time;
and
establishing the relative distance between the cylinder and piston by modifying the measurement of the elapsed time of the group (M) of measurement oscillations in accordance with the reference signal as compensation for the influence of different propagation conditions within the cylinder chamber.

5 more elements

An apparatus for determining the relative distance between a cylinder (12) and a piston (14) of a piston and cylinder assembly (10) that defines a cylinder chamber (26) filled with a fluid medium, the end walls (24, 28) of the cylinder being formed by the cylinder head (12) and the piston (14) comprising:

electrical ultrasonic converter means (30) supported at the first end wall (24) of the cylinder chamber (26) for transmitting a group (S) of ultrasonic oscillations in the direction of the second wall (28) of the cylinder chamber (26) upon excitation by means of electrical excitation pulses (i.sub.1, i.sub.3), and also producing a corresponding electrical output signal upon impingement of ultrasonic oscillations, the converter including an incompressible carrier (44) having a flat surface (46), a plate-shaped piezoelectric oscillator (48) positioned parallel to the flat surface (46) of the carrier (44), and positioned in the cylinder chamber (26) in spaced relationship from the surface (46), a sound projecting surface (42) positioned parallel to the oscillator (48) and facing toward the second end wall (28) that is in contact with the fluid medium, the projecting surface preferably being formed from the same outer surface as one side of the oscillator (48), and means (50, 52, 54) for mismatching the characteristic impedance of the oscillator (48) and the carrier (44), and means (56, 58, 60, 62) for matching the impedance between the oscillator and the sound projecting surface (42),
electrical pulse generating means (94) coupled with the output of the converter means (30),
means defining a reference path (42, 66) extending through the fluid medium that is employed in the cylinder chamber (26), and including at a second end opposite the first end a reference wave reflecting surface (66) for reflecting ultrasonic oscillations;
means for transmitting a group (S) of ultrasonic oscillations from the one end of the reference path toward the reflecting surface at the second end;
and
detection circuit means (34) including means for measuring the travel time of the oscillations through the cylinder chamber between the leading edge of an excitation pulse (i.sub.1, i.sub.3) and the occurrence of a corresponding group (M) of measurement oscillations in an output signal of the converting means, and also for measuring the actual reference travel time (T.sub.R) of the ultrasonic oscillations transmitted and reflected along the reference path (42, 66), and further including calculating means (38) for modifying the measurement oscillation travel time in accordance with the departure of the actual reference travel time (T.sub.R) from a pre-established reference travel time to establish the true relative distance between the piston and cylinder.

3 more elements

Dependencies are inferred from the claim text.