Patent Application
20050226733
The present invention relates to a position sensor applicable to a linear compressor and used for detecting the position of the compressor actuator, as well as to a linear compressor provided with a position sensor.
A linear compressor basically comprises an actuator or piston that is axially displaced inside a cylinder bore and that has the function of compressing the gas during the cooling cycle. In order to allow this gas to go in and out,the compressor is further provided with a head comprising a suction valve and a discharge valve. This head is located at the end of the actuator stroke.
The actuator, together with a magnetic component and a resonant spring, forms a resonant assembly that is driven by a linear motor. This resonant assembly develops a linear movement, and the axial displacement of the actuator provides the necessary compression of the gas.
If there are variations in operation or variations in the feed voltage of the compressor, the resonant assembly comes out of its normal course of movement and is displaced beyond the permitted limit, causing the actuator to collide with the compressor head. This abnormality causes noises and damage to the compressor, especially to the valve head.
One can try to solve this problem by controlling the voltage levels applied to the motor or by controlling the displacement of the actuator in the bored-through body, in order for the latter not to damage the head.
This control over the displacement of the actuator may also be effected by positioning the sensor on the head, so that it will signal or interrupt the energy supply upon detection of the beginning of collisions of the actuator against the head. Although this solution stops the collision of the activator, it does not avoid it from damaging the head, mainly if a sensor failure happens.
Another solution foreseen for controlling the course of displacement of the actuator inside the cylinder bore consists in using a position sensor, usually inductive transducers that detect the passage of the actuator by a determined control point. The disadvantage of this solution lies in the high cost of the device used and the difficulty in installing and maintaining it, which causes the final cost of the compressor to rise.
PI 0001404-4 relates to a position sensor placed close to the compressor head and capable of signaling the passage of the actuator by a maximum recommendable point, in order to prevent it from bumping against the head at the moments of variations in its operation. This sensor is made of an electrically conductor material, which upon receiving contact of the actuator emits an electric signal to a control circuit, which prevents the actuator from continuing its advance towards the valve head.
However, in order for this solution to be possible, the sensor has to be insulated from the rest of the compressor, as for instance, from the cylinder bore and from the head, so that the circuit can remain open until the actuator leans against the sensor. In the embodiment to which PI 0001404-4 refers, this insulation may be effected by means of joints made of a sealing material and electrically inert, placed at the portion in which the sensor is in contact with the compressor or all over the head. In this regard, the sensor is manufactured from a blade that constitutes the valve and that is positioned on the head.
The use of sealing joints requires an adequate adjustment in the positioning of the valve blade that has the sensor, of the head and of the cylinder bore.
As described in PI 0101976-7, another proposed solution consists in using a sensor plate independent of the suction valve, but with the same external profile, the electric insulation of this plate being effected by depositing upon it a painting layer of the epoxy or varnish type, or another type having electric resistance characteristics. The main disadvantages of this solution lie in the need for electric insulation throughout the sensor place and to the possibility of escape of current due to the area of the sensor plate.
The objective of the present invention is to provide a sensor capable of detecting and controlling the position of the actuator close to the head and to the compressor valves, in order to prevent the actuator from bumping against the head during a failure in its functioning, without this raising the costs of manufacturing the compressor.
The objective of this invention is achieved by means of a sensor, particularly useable in detecting the position of an actuator of a compressor in which the actuator is axially displaceable inside a cylinder bore, the sensor comprising a probe and a hermetic terminal to be arranged in a head of the cylinder, the probe being positioned inside the cylinder bore, the probe and the hermetic terminal being associable with each other by means of the contact of the actuator with the probe, the hermetic terminal being connected to a control circuit.
The objectives of this invention are also achieved by means of a linear compressor provided with an actuator, a cylinder bore and a head, the actuator being axially displaceable inside the cylinder bore, the linear compressor comprising a position sensor comprising a probe and a hermetic terminal, the hermetic terminal being arranged in the head and the probe being positioned inside the cylinder bore, tho probe and the hermetic terminal being associable with each other by means of the contact of the actuator with the probe, the hermetic terminal being connected to a control circuit.
The present invention will now be described in greater detail with reference to an embodiment represented in the drawings. The figure shows:
According to a preferred embodiment and as can be seen In
The position sensor comprises a probe 4, positioned inside the cylinder bore 3, and a hermetic terminal 7, connected to a control circuit 8.
The probe 4 is thin and flexible and may be constituted by a metallic blade, which may be replaced by a cylindrical, massive or hollow piece, or else may have another appropriate shape. This probe 4 comprises a first end 11, a contact projection 10, a contact region 9 and a second end 12. The first end 11 is fixed between the aid 5 and the cylinder bore 3, while the second end 12 is free from engagement.
In a variation of fixation of this probe 4, it is fixed on the actuator 2 itself, the first end 11 being fixed on the face of the actuator 2, while the second end 12 remains free from fixation or engagement.
The contact projection 10 is formed from a bending of the body of the probe 4. This projection 10 is arranged between the first end 11 and the second end 12, so as to remain aligned with the hermetic terminal 7.
The contact region 9 is arranged at the second end 12 and has a substantially curved profile reducing the friction during the contact of the actuator 2 with this region 9.
The contact projection 10 and the contact region 9 are arranged on different planes. With respect to the head 5, the contact projection 10 has a null spacing since it is permanently in contact with the head 5, as shown in detail A, while the contact region 9 has a spacing h, as can be seen in detail B of
The hermetic terminal 7 will be positioned in an insulated cavity 15, filled with an insulating material 16 and arranged on the head 5 of the compressor.
According to detail A of
In addition, the hermetic terminal 7 is connected to the control circuit 8, formed by an electric circuit comprising a source of electric voltage 21, preferably of direct current, and a resistor 22, both connected in series with the hermetic terminal 7 and the head 5, as illustrated in detail C of
When the actuator 22, in its axial displacement, reaches a determined distance from the head 6, that is to say, a first control point 6, the actuator 2 contacts the contact region 9 of the probe 4, displacing it as far as the second control point 6′ arranged at a displacement distance H from the first control point 6.
When the contact region 9 reaches the second control point 6′, the contact projection 10 is physically in contact with the hermetic terminal 7, forming an electric contact with the control circuit 8. In this way, the Contact of the actuator 2 with the contact region 9 is substantially simultaneous with the contact of the contact projection 10 with the hermetic terminal 7.
Said electric contact formed with the control circuit 8, that is, the indication that the actuator 2 has reached the first control point 6 and the second control point 6′ causes, the voltage level measured at the terminals. (not shown) close to the resistor 22 to pass from the logical level “0” to the logical level “1”. This variation is read by the control circuit 8, which may further include an electronic circuit capable of interpreting this signaling, which corrects the path of the actuator 2, thus preventing it from bumping against the head 5, that is to say, it causes the maximum displacement of the actuator 2 toward the head 5 to return to below the first control point 6.
Once this excess in displacement of the actuator 2 is corrected, the contact region 9 is again positioned at the same level as the first control point 6. For this purpose, the probe 4 should preferably be made from a material having an elastic deformation zone that embraces the amplitude of this deformation which the probe 4 undergoes during this displacement of the region 9 from the first control point 6 to the second control point 6′. This is because, after the efforts have ceased, the region 9 should necessarily return to its initial position, that is to say, coinciding with the first control point 6.
Thus, the material employed in constructing this probe 4, independently of its shape and profile, should be little susceptible to hysteresis, that is to say, to the residual deformations along the time of use of the sensor.
The present invention has the advantage of meeting the need for painting the sensor plate in an attempt to insulate it from the rest of the components of the compressor, thus increasing the reliability of the insulation of the probe 4 and providing a more precise control over the position of the actuator 2.
Another advantage of the present invention lies in the low cost of the hermetic terminal 7 and in its great availability on the market. For this reason, the applied modifications do not render the final compressor assembly expensive.
A preferred embodiment having been described, one should understand that the scope of the present invention embraces other possible variations, being limited only by the contents of the accompanying claims, which include the possible equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| PI 0200898-0 | Mar 2002 | BR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/BR02/00184 | 12/13/2002 | WO | 4/26/2005 |
