A position sensor, which has the capability of outputting an electrical signal according to a change in impedance of a tubular detection coil caused by a physical displacement of a magnetic core in the detection coil, has been utilized for measurement and control in many technical fields such as internal combustion and electric power facility. In this kind of position sensor, it is not difficult to imagine that a change in impedance of the detection coil resulting from an external factor other than the displacement of the magnetic core becomes a cause of deteriorating the detection accuracy. For example, during the displacement of the magnetic core made of a magnetic metal material such as ferrite in the detection coil, when the magnetic core comes into contact with an inner peripheral surface of the detection coil, and receives an external force such as stress or strain, a change in magnetic permeability of the magnetic core occurs. This phenomenon is generally known as the Villari effect. Since such a change in magnetic permeability leads to variations in detection accuracy, a countermeasure for preventing that the magnetic core receives the stress or strain is important to ensure the operation reliability of the position sensor.
For example, in a differential transformer position sensor disclosed in Japanese Patent Early publication No. 2002-90106, it is proposed that a magnetic core is coaxially disposed in a metal cylinder formed by a stainless steel pipe, and a resin material is filled as a buffer member in a clearance between an outer peripheral surface of the magnetic core and the metal cylinder. In this case, the strength of the magnetic core as a whole can be increased by the presence of the metal cylinder between the magnetic core and the detection coil. However, as the distance between the inner peripheral surface of the detection coil and the magnetic core increases, a ratio of magnetic fluxes reaching the magnetic core relative to the magnetic fluxes generated from the detection coil decreases, so that a deterioration in sensitivity of the position senor may occur. In addition, since the diameter size of the magnetic core increases, it is needed to make a suitable design change to the magnetic coil. Furthermore, there is another problem of reducing a rising amount of output sensitivity relative to an insertion amount of the magnetic core into the detection coil.