Variable displacement piston machine with a sensor

A method of determining displacement of at least one main piston in at least one main cylinder of a piston machine in which tilting of a swash plate controls the displacement, and in which the swash plate is tilted by a plunger operating in an auxiliary cylinder, said method comprising the steps of:

• arranging an antenna in the auxiliary cylinder received within a bore provided in the plunger;
• transmitting an electromagnetic wave from the antenna and thereby inducing an electrical current in the plunger;
• analyzing the change of electrical parameters of the oscillating circuit based on the principles of a RF sensor employing an oscillator;
• determining from the analyzing, a displacement of the at least one main piston in the at least one main cylinder;
• and
• wherein the antenna senses movement of the plunger based on change of impedance by induction in the plunger and determines an angle of the swash plate based upon a functional dependency between the plunger and the antenna disposed linearly therein.

A variable displacement axial piston machine (1) comprising:

• a cylinder block (4), at least one main cylinder (5), at least one main piston (6), a swash plate (11), at least one plunger (12) arranged in a main housing (2);
• at least one auxiliary cylinder (13) fixed to the main housing (2) having a tubular wall (15) and a top section (16) formed in an auxiliary housing (3) and a sensor;
• wherein the main piston (6) is movable in the main cylinder (5) upon relative movement between the swash plate (11) and the main cylinder (5);
• wherein a stroke of the main piston (6) depends on a degree of tilting of the swash plate (11) relative to the main cylinder (5);
• wherein the plunger (12) can tilt the swash plate (11) relative to the main cylinder (5) and thereby control the stroke of the main piston (6) in the main cylinder (5),
• wherein the sensor comprises an antenna (17) which extends linearly from the top section (16) of the auxiliary cylinder (13) and is received within a bore (18) provided in the plunger (12) such that the antenna (17) senses movement of the plunger (12) and determines an angle of the swash plate (11) based upon a linear functional dependency between the plunger (12) and the antenna (17).