EP2527653A1

EP2527653A1 - A free piston type compressor

Info

Publication number: EP2527653A1
Application number: EP11167100A
Authority: EP
Inventors: Edo B. Wissink
Original assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Current assignee: Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek TNO
Priority date: 2011-05-23
Filing date: 2011-05-23
Publication date: 2012-11-28
Also published as: US20140099216A1; WO2012161575A1; EP2718567B1; EP2718567A1

Abstract

The invention relates to a free piston type compressor 10 comprising a first piston 2a and a second piston 2b interconnected with a torsion body 3a, 3b and driven by a first motor 4a and a second motor 4b, said first piston and second piston being conceived to displace along a displacement direction wherein the said motors are adapted to drive the first piston and the second piston in a direction transversal to the displacement direction D.

Description

FIELD OF THE INVENTION

The invention relates to a free piston type compressor.
The invention further relates to an air conditioning system.

BACKGROUND OF THE INVENTION

An embodiment of a free piston type compressor is known from US 5, 275, 542 . In the known compressor the piston and a driving linear electromotor are connected by a shaft.
The known free piston type compressor has the following disadvantages:

piston movement is not controlled mechanically;
speed of the electromotor is limited to the speed of the compression piston. Accordingly, a relative large and thus expensive motor is required to deliver a sufficient force to the piston;
motor and compression piston move simultaneously in the same direction which may induce considerable vibration.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved free piston compressor. In particular, it is an object of the invention to provide a free piston compressor which is substantially vibration free.
To this end the free piston type compressor according to the invention comprises a first piston and a second piston interconnected with a torsion body and driven by a first motor and a second motor, said first piston and second piston being conceived to displace along a displacement direction wherein the said motors are adapted to drive the first piston and the second piston in a direction transversal to the displacement direction.
It is found that when the free piston is driven by a torsion body the resulting construction is substantially vibration-free due to the fact that the compressor according to the invention comprises two opposite moving pistons which are adapted to move with substantially the same speed.
In addition, it is found that the stroke of the compressor may be mechanically controlled, which is advantageous. More in particular, it is found that the speed of rotation of the compressor according to the invention is much higher that the speed of translation. Accordingly, a relatively small motor may be used. This may substantially reduce the manufacturing costs of the compressor according to the invention.
More in particular, the torsion based compressor may have the following additional advantages:

the motor power may be completely independent from the compression control; the energy delivered by the motor is used to control the amplitude of the torsional vibration. Increasing the amplitude gives an increased compressor power. Stroke of the piston increases, while the top dead centre remains unchanged;
the rotor of the electromotor may be integrated in the piston.

Accordingly, the motors of the compressor according to the invention may be adapted to deliver a substantially limited force or energy for compensating for the energy loss of the compression process. Accordingly, the efficiency of the compressor of the invention is increased.
An embodiment of the invention with an integrated motor will be discussed in more detail with reference to Figure 2 and Figure 3. In this embodiment the compressor comprises two opposite interconnected pistons, where each piston is also part of the electromotor, the rotor. A first connection element is a torsion body provided in the centre to control the torsion stiffness. An exemplar embodiment is given in Figure 2. A second connection element may comprise a set of flexible rods, required to control the movement of the pistons. An exemplary embodiment is discussed with reference to Figure 3. Flexible rods may be provided to transform the rotation to a controlled translation in accordance with the invention.
It is found to be advantageous to implement the torsion body because the motion is not directly dependent on the characteristics of the electromotor.
During operation of the compressor according to the invention, the first motor and the second motor are adapted to rotate with a substantially the same frequency having the opposite phases.
This technical measure is based on the insight that when the first motor and the second motor are adapted to rotate with the same frequency having the opposite phases for both translation and rotation, the overall vibration of the compressor is very small.
The vibration can be further decreased in the embodiment of the invention given in Figure 1. This embodiment has no integrated motor. This gives the possibility to split the rotor of the motor symmetrically, so it is possible to build a completely balanced compressor.
The air conditioning system according to the invention comprises a free piston type compressor according to any one of the preceding claims.
These and other aspects of the invention will be discussed with reference to drawings wherein like reference signs correspond to like elements. It will be appreciated that the drawings are presented for illustrative purposes only and may not be used for limiting the scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 presents in a schematic way an embodiment of the compressor according to the invention, having a completely balanced design.
Figure 2 presents in a schematic way an embodiment of the compressor with integrated motors, showing the torsion body.
Figure 3 presents in a schematic way an embodiment of the compressor with integrated motors, showing the movement of the piston controlled by a set of flexible rods.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 presents in a schematic way an embodiment of the compressor according to the invention in a completely balanced design. The compressor 10 according to the invention comprises a first free piston 2a and a second free piston 2b interconnected by a torsion body having torsion rods 3a, 3b, said torsion rods being driven by a first electromotor 4a and a second electromotor 4b. The electromotors 4a, 4b, may have a suitable set of coils 5a, 5b for enabling application of a suitable driving force to the rods 3a, 3b. In accordance with the invention the driving force is applied transversely to the direction of the expected displacement D of the first free piston and the second free piston. The free pistons 2a, 2b will experience a substantially translational displacement with substantially no rotation, while the motor sections 4a, 4b having an opposite to and fro rotation.
The capacity of such compressor may easily be adjusted by adjusting the vibration amplitude, by changing driving power.
The movement of the pistons 2a, 2b in the direction D is enabled by opposite driving directions of the motors applied to the torsion rods. In a particular embodiment, the first motor 4a and the second motor 4b may rotate with a substantially the same frequency having the opposite phases. The motors thus couple the driving force to the pistons via the torsion rods 3a, 3b. Because the torsion rods are driven in the opposite directions the free pistons will be alternatively attracted to each other and recoil back to the original position. The torsion rods are implemented from a material which undergoes elastic deformation when driven by the motors. The symmetrical spitted electromotor in three sections, enables a fully balanced design. However, it will be appreciated that an alternative embodiment may be used, wherein the driving motor having two halves is used. A motor with two sections simplifies the design, but the compressor will not be fully balanced any more.
Figure 2 and 3 present in a schematic way an embodiment of the compressor having integrated electro motors. The pistons are part of the electromotor, the rotors. The pistons are connected by a torsion bar in the center, see 23, which may be encircled by a set of elastic rods 33 required to control the displacement of both pistons 21, 22 in Figure 2 or 31a, 31b in Figure 3, respectively.
In a particular embodiment of Figure 2 depicting the compressor 20 according to the invention, the first free piston 21 and the second free piston 22 are interconnected by a torsion body 23, which may be implemented as an elastic torsion spring. It will be appreciated that other per se known embodiments of an elastic spring may be used. For the clarity reasons the complete motors driving the torsion body are not depicted.
In accordance with the invention when the alternating driving force is applied to the torsion body 23 the free pistons 21, 22 will rotate to and fro and translate back and forth along the translation direction D which is substantially parallel to the longitudinal axis L of the compressor 20.
Figure 3 shows the sets of elastic rods controlling the movement of the pistons. In view 30a a shortening of the compressor is illustrated upon the elastic bending of the rods 33 driven by the torsion force by the electromotor on the pistons. The free pistons will rotate and translate in the opposite directions as is depicted by the respective arrows.
In view 30b the compressor returns to its original (rest) state when no driving force is applied. The pistons are now in their top dead centre position, approaching the valve plates 24A and 24B.
In view 30c a second shortened condition of the compressor is shown when the free pistons 31a, 31b are driven by the torsion force of the electro motors in opposite direction with respect to the direction shown in view 30a.
By suitably alternating the driving directions for the free pistons 31a, 31b a pulse-like translational movement of the compressor may be obtained. It will be appreciated that Figure 2 and Figure 3 depict an embodiment of the invention wherein a centrally positioned integrated motor having a first motor section and a second motor section is provided, wherein each motor section may be provided with its own set of torsion bars connected to the pistons.
It is found that the compressor according to the invention has the following additional advantages:

well vibration balanced of construction;
high speed of the electromotor is easy transfer to a high driving force of the free pistons;
a continuous adjustment of the capacity is possible by varying the amplitude of the torsion movement;
oil-free application is possible, which makes the compressor according to the invention particularly versatile in use;
high motor speed enables the use of small and cheap motors.

While specific embodiments have been described above, it will be appreciated that the invention may be practiced otherwise than as described. Moreover, specific items discussed with reference to any of the isolated drawings may freely be inter-changed supplementing each outer in any particular way. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described in the foregoing without departing from the scope of the claims set out below.

Claims

A free piston type compressor comprising a first piston and a second piston interconnected with a torsion body and driven by a first motor and a second motor, said first piston and second piston being conceived to displace along a displacement direction wherein the said motors are adapted to drive the first piston and the second piston in a direction transversal to the displacement direction.
The compressor according to claim 1, having an integrated motor, where the torsion body comprises a central torsion rod encircled by a set of elastic rods for controlling the displacement.
The compressor according to claim 1, with a centrally positioned integrated motor having a first motor section and a second motor section, wherein each motor section is provided with its own set of torsion bars connected to the pistons.
The compressor according to any one of the preceding claims, wherein the first motor and the second motor are adapted to rotate with a substantially the same frequency having the opposite phases.
The compressor according to any one of the preceding claims, wherein the rotors of the respective motors are integrated with the respective free pistons.
The compressor according to any one of the preceding claims, wherein the torsion body is adapted to undergo an elastic deformation.
An air conditioning system comprising a free piston type compressor according to any one of the preceding claims.