Automotive air conditioning system controlled by damped pressure switch

Description

[0001] To improve fuel economy automotive air conditioning systems control compressor operating to avoid unnecessary cooling and to avoid icing the evaporator. The clutch between the engine and the compressor is controlled by either a thermostatic switch or a pressure switch with the pressure switch having cost and installation advantages. Examples for such pressure responsive switches are described for instance in US-A-3 535 480, CH-A-471 458 and US-A-2 919 321. Use of the pressure switch has been confined to flooded evaporator type systems where the pressure changes slowly. In a finned coil evaporator, the pressure changes rapidly when the compressor starts and a pressure switch causes the clutch to cycle too fast. Therefore, finned coil systems have used the less desirable thermostatic switch.

[0002] In the known damped pressure responsive switch as shown in US-A-2 412 095 a restricted passage is provided between the inlet and the space immediately beneath the diaphragm, so that this switch will damp both kinds of pressure changes, the rapidly falling as well as the slowly rising pressure.

[0003] It is, therefore, an object of the present invention to provide a pressure responsive switch which is applicable in an automotive air conditioning system having a finned coil type of evaporator.

[0004] This task has been solved according to the present invention by the features of claim 1. By providing a pressure responsive switch with the claimed additional chamber which is able to act as a buffer and by connecting this chamber through the restriction to the suction line, it is possible to damp rapidly changing pressure only. According to the present invention a relatively large hole has to be drilled and a pin of known diameter has to be fixed in the hole so the clearance is the restricted passage. The pin can be made of wire. Wire diameter is quite exact. It is relatively easy to make a very restricted passage which can be "tuned" to the air conditioning system to give the desired lag when the compressor starts operating. The damped pressure switch does not slow down the response to rising pressure after the compressor stops since the system pressure rises slowly and the pressure in the damped chamber keeps up. Thus the trip point (when the compressor starts) can be sensed accurately...more accurately than with a thermostatic switch. In effect the pressure switch is damped only as the system pressure falls.

[0005] Claims 2 to 6 describe preferred embodiments of the invention.

[0006] Claims 7 and 8 describe a preferred use for the inventive pressure responsive switch in an automotive air conditioning system having a finned coil evaporator, because in such systems a very high damping rate is desired which requires such a small cross sectional area and such a length as to be virtually impossible to drill on a production basis.

[0007] An embodiment of the invention is shown in the attached drawings where:

Figure 1 is a vertical section through the damped pressure switch,

Figure 2 is a greatly enlarged section through the restrictor shown in the inlet in Figure 1, and

Figure 3 is a schematic showing of an automotive air conditioning system using the damped pressure switch.

[0008] The pressure switch housing has a lower portion 10 connected to the intermediate portion 12 by a clamp ring 14 and define, in cooperation with the intermediate portion, the damping chamber 16. Diaphragm 18 is clamped between the intermediate portion 12 and the partition housing portion 20 with diaphragm pad 22 resting on top of the diaphragm with an upwardly extending boss 24 slidably guided in the central bore of partition 20. The upper housing part 26 is mounted on top of the partition 20. The upper housing 26, the partition 20 and the intermediate housing 12 are connected together by a clamp ring 28. The space under the diaphragm 18 is sealed by O-ring 30 mounted in the groove in the partition and compressed against the rim of the diaphragm. The diaphragm is preferably a thin plastic film diaphragm.

[0009] The lower end of actuator 32 fits inside boss 24 and the tongue 34 of switch 36 engages the actuator between shoulders 38, 40 so that movement of the actuator will move the tongue. When the barrel spring 42 compressed between the end of tongue 34 and cross member 44 of the switch blade goes over center the contact carrying end 44 of the switch will snap-down to engage contact 46 which is supported by the terminal structure projecting through the upper housing part and terminating in connector 48. In the position shown in the drawing, the switch contact bears against a boss 50 molded in the upper housing part. The other end of the switch blade is connected to terminal arm 52 by rivet 54 and this terminal also projects through the upper housing to provide connector 56.

[0010] The actuator is biased downwardly by two springs designated a reset spring 58 and a trip spring 60. As the diaphragm rises with increasing pressure both springs become operative to oppose diaphragm movement before the switch snaps over center from the position shown in Figure 1 to make contact with the fixed contact 46 and thus complete the electric circuit between the connectors 48 and 56. On the return stroke as the pressure under the diaphragm decreases trip spring 60 becomes inoperative or ineffective before the switch snaps from fixed contact 46 back to the inert boss 50. Therefore, the trip force is determined by the force of both springs while the reset force is determined only by spring 58. It is emphasized that for the purpose of this invention any spring arrangement can be used although that just described briefly (and more fully described in the copending application) is deemed preferable.

[0011] The lower housing 10 is provided with an inlet 62 which is connected to the suction line 74 leading from the outlet of the finned tube evaporator 76 in the automotive air conditioning system shown in Figure 3. Inlet 62 leads to damping chamber 16 and the damping chamber is connected to the space (100) under the diaphragm by passage 64. As previously indicated, in a finned tube evaporator coil type of automotive air conditioning system the pressure of the evaporator outlet drops quite rapidly when the compressor operates and the air conditioning load on the system is light. Normally, the sequence is as follows. When the compressor does not operate, the pressure in the system at the evaporator outlet will rise to the point where the diaphragm actuates the switch to go over center and complete the electric circuit. This engages clutch 78 in the automotive air conditioning system to cause the compressor 80 to operate. Under light load conditions the compressor has excess capacity and therefore the pressure draws down very rapidly at the evaporator outlet. If the pressure switch has fast response to the rapid drop, the switch would go over center (to shut off the compressor) in a short period of time and the pressure switch would soon thereafter sense a high pressure. As a result the clutch would be cycled quite frequently. This is undesirable. Generally, under light load conditions the clutch should not desirably cycle more than four times a minute. The pressure drop is fast and if the switching is delayed no harm is done. When the clutch is disengaged, the pressure will rise but the rise is much slower than the drop.

[0012] To slow down or damp the response of the pressure switch a restriction is put in the inlet 62 leading to the damping chamber 16. Restriction takes the form of a metal insert 66 through which hole 68 is drilled. It is virtually impossible to drill a small enough hole to achieve an adequate restriction leading to the damping chamber 16. Therefore, the hole is made of a size which can be drilled easily and then a pin 70 made from wire is mounted in the hole by bending the ends to prevent the pin from dropping out of the hole. Wire sizes are very accurately dimensioned. Therefore, the wire diameter can be selective relative to the diameter of the hole so that the clearance between the wire and the hole will determine the restriction. The effective restriction is also affected by the length of the restriction. The amount of restriction required to achieve the desired maximum of four cycles per minute of the switch or clutch in the air conditioning system is also affected by the volume of the damping chamber. If the volume is small the restriction has to be greater. Tests demonstrate that a damping chamber 9.34 cm³ (0.57 cu. ins.) volume in combination with a restricted orifice (hole) of 0.0813 cm (0.032 inches) diameter by approximately 0.635 cm (0.25 inches) long with a pin of 0.0737 cm (0.029 inches) diameter gave a satisfactory cycling frequency at low air conditioning load conditions. Tests also indicate that the performance is improved if with the same orifice and pin arrangement the chamber volume is increased to 16.39 cm³ (1.0 cu. in.). Thus, with the test conditions chamber volume to effective orifice area (area of the hole minus area of the pin) can range between 10000 to 18000 when calculated in cm³ and cm² (or 3000 and 7000 when calculated in cu. in. and sq. in.). The ratio of the length of the restricted passage to its area is about 600 when calculated in cm and cm² (or 1700 when calculated in inch and sq. inch). If a longer orifice or restrictive passage is used, the chamber volume can be reduced. The insert 66 is machined to provide three fins or ribs 72 to secure a better seal of the insert 66 to the plastic housing 10. The housing is moulded onto the insert 66. The insert is made of metal to insure accurate dimensioning of the hole. The requisite accuracy can't be obtained on a reliable basis by trying to machine or mold a hole in a plastic part. Thus, with an accurate hole drilled in a metal insert 66 and an accurately sized pin mounted in the hole the clearance or restricted passage will be very accurate and repeatable. The length of the insert 66 and hence the length of the hole is another easily maintained dimension.

[0013] The pressure switch controls the electrically operated clutch between the input 82 and the compressor 80. The input 82 is driven by V-belts from the engine (not shown). The compressor discharge line 84 leads to the condenser coil 86 which discharges through conduit 88 leading to the dehydrator/receiver 90. Flow from the receiver through conduit 92 to the evaporator 76 is controlled by thermostatic expansion valve 94 which regulates flow to the evaporator in accordance with the temperature at the evaporator outlet as sensed by the feeler bulb 96 strapped on the suction line. The pressure switch when closed completes the circuit to the clutch from battery 98. With the damped pressure switch controlling the clutch (and therefore the compressor operation) the system operates as well or better than one with a thermostatic switch. Under light conditions when the pressure causes the switch to close the pressure in the suction line 74 drops very rapidly but the pressure switch does not respond rapidly due to the damped response. When the switch finally opens the pressure in the suction line rises slowly and the pressure change in the damping chamber 16 keeps pace. In effect the pressure switch damps response to the fast drop-it does not damp the response to the slow rise. And the pressure switch in effect has a normal response to the pressure changes in normal load operation of the system. In effect, the pressure switch delays response only under the conditions where delay is desired.

Claims

1. A pressure switch having a diaphragm (18) mounted in a housing (10, 12, 20, 26) for movement in response to pressure changes in a space (100) beneath said diaphragm (18), said space (100) communicating with an inlet (62) by way of a passage (64), the movement of the diaphragm (18) being operative to actuate the switch, characterised by a chamber (16) arranged between said passage (64) and said inlet (62), a partition (66) between the inlet (62) and the chamber (16), a hole (68) in the partition (66), and a pin (70) mounted in the hole (68), with clearance between the pin (70) and the hole (68), the clearance being a restricted passage retarding pressure change in the chamber (16) when pressure at the inlet (62) changes rapidly.

2. A pressure switch according to claim 1, in which the partition (66) is made of metal and the housing (10) is moulded onto the partition (66).

3. A pressure switch according to claims 1 or 2, in which the pin (70) projects through the partition (66) and the ends of the pin (70) are bent to prevent the pin (70) from falling out of the hole (68).

4. A pressure switch according to any of claims 1 to 3, in which the ratio of chamber (16) volume to the area of the restricted passage (68, 70) is between approximately 10000 and 18000 when calculated in cm³ and cm² (or approximately 3000 and 7000 when calculated in cu. in. and sq. in.).

5. A pressure switch according to any of claims 1 to 4, in which the ratio of the length to the area of the restricted passage (68, 70) is. about 600 when calculated in cm and cm² (or about 1700 when calculated in inch and sq. inch).

6. A pressure switch according to any of claims 1 to 5, in which the chamber (16) volume and the length and area of the restricted passage (68, 70)-. are selected so the switch will not cycle more than four times per minute when the inlet (62) is connected to the evaporator outlet in an automotive air conditioning system.

7. An automotive air conditioning system of the type having a compressor (80) driven by the engine through an electrically operated clutch (78), the compressor (80) operating to deliver refrigerant to a condenser (86), the refrigerant leaving the condenser (86) flowing to finned coil type of evaporator (76), the evaporator outlet being connected to the compressor inlet by a suction line (74), and means being provided for controlling the operation of the clutch (78) and the compressor (80), said means including a switch controlling engagement of the clutch (78), characterised in that said switch is a pressure switch according to any of claims 1 to 6.

8. The automotive air conditioning system of claim 7, in which the restriction (68, 70) and the chamber (16) are sized so that the clutch (78) will not cycle more than four times per minute under light air conditioning loads.

Ansprüche

1. Druckschalter mit einem Diaphragma (18), das in einem Gehäuse (10, 12, 20, 26) unter dem Einfluß von Druckänderungen in einem Raum (100) unter dem Diaphragma (18) bewegbar angeordnet ist, wobei der Raum (100) mit einem Einlaß (62) über eine Passage (64) in Verbindung steht, und wobei der Schalter durch die Bewegung des Diaphragmas betätigt wird, gekennzeichnet durch eine zwischen der Passage (64) und dem Einlaß (62) angeordnete Kammer (16), einer Trennwand (66) zwischen dem Einlaß (62) und der Kammer, eine Öffnung (68) in der Trennwand (66) und einen Stift (70) der in der Öffnung (68) mit einem Spielraum zwischen dem Stift (70) und der Öffnung (68) angeordnet ist, wobei der Spielraum eine gedrosselte Durchströmungsöffnung bildet, die eine Druckänderung in der Kammer (16) verzögert, wenn sich der Druck am Einlaß (62) schnell verändert.

2. Druckschalter nach Anspruch 1, wobei die Trennwand (66) aus Metall besteht und das Gehäuse (10) an die Trennwand (66) angegossen ist.

3. Druckschalter nach Anspruch 1 oder 2, wobei sich der Stift (70) durch die Trennwand (66) erstreckt und wobei die Enden des Stiftes (70) gebogen sind, um den Stift (70) gegen das Herausfallen aus der Öffnung (68) zu sichern.

4. Druckschalter nach einem der Ansprüche 1 bis 3, wobei das Verhältnis des Volumens der Kammer (16) zur Fläsche der gedrosselten Durchtrittsöffnung (68, 70) zwischen etwa 10.000 und 18.000 bei Bemessung in cm³ oder cm² (oder etwa 3.000 bis 7.000 bei Berechnung in cu. in. und sq. in.) beträgt.

5. Druckschalter nach einem der Ansprüche 1 bis 4, wobei das Verhältnis der Länge zur Fläche der gedrosselten Durchtrittsöffnung (68, 70) etwa 600 bei Bemessung in cm oder cm² (oder etwa 1.700 bei Bemessung in inch und sq. in.) beträgt.

6. Druckschalter nach einem der Ansprüche 1 bis 5, wobei das Volumen der Kammer (16) und. die Länge und Fläche der gedrosselten Durchtrittsöffnung (68, 70) derart ausgewählt sind, daß der Schalter nicht mehr als viermal pro Minute schaltet, wenn der Einlaß (62) an den Auslaß eines Verdampfers in einem Airconditioning. - System eines Kraftfahrzeuges angeschlossen ist.

7. Airconditioning-System für ein Kraftfahrzeug mit einem Kompressor (80), der vom Motor über eine elektrisch betätigbare Kupplung (78) antreibbar ist, wobei der Kompressor (80) Kühlmittel zu einem Kühler (86) fördert, das den Kühler (86) verlassende Kühlmittel zu einem mit einer gerippten Rohrschlange versehenen Verdampfer (76) fließt, der Auslaß des Verdampfers mit dem Kompressoreinlaß durch eine Saugleitung (74) verbunden ist und eine Einrichtung vorgesehen ist, um die Wirkungsweise der Kupplung (78) und den Kompressor (80) zu steuern, wobei die Einrichtung die Kupplung (78) über einen Schalter kontrolliert, dadurch gekennzeichnet, daß der Schalter ein Druckschalter nach einem der Ansprüche 1 bis 6 ist.

8. Airconditioning-System für Kraftfahrzeuge nach Anspruch 7, wobei die Durchtrittsöffnung (68, 70) und die Kammer (16) derart bemessen sind, daß die Kupplung (78) nicht mehr als viermal pro Minute unter leichter Airconditioning - Belastung schaltet.

Revendications

1. Manocontact présentant une membrane (18) montée dans un boîtier (10, 12, 20, 26) en vue d'un mouvement en réponse à des variations de pression dans un espace (100) situé au-dessous de ladite membrane (18), ledit espace (100) communiquant avec une entrée (62) par l'intermédiaire d'un passage (64), le mouvement de la membrane (18) agissant de façon à manoeuvrer le manocontact, caractérisé par une chambre (16) disposée entre ledit passage (64) et ladite entrée (62), une cloison (66) entre l'entrée (62) et la chambre (16), un perçage (68) dans ladite cloison (66), et une tige (70) montée dans le perçage (68), avec un jeu entre la tige (70) et le perçage (68), le jeu constituant un passage étranglé retardant une variation de pression dans la chambre (16) lorsque la pression régnant à l'entrée (62) varie rapidement.

2. Manocontact selon la revendication 1, dans lequel la cloison (66) est réalisée en métal et le boîtier (10) est moulé par par-dessus la cloison (66).

3. Manocontact selon les revendications 1 ou 2, dans lequel la tige (70) s'étend à travers la cloison (66) et les extrémités de la tige (70) sont pliées afin d'empêcher la tige (70) de tomber hours du perçage (68).

4. Manocontact selon l'une quelconque des revendications 1 à 3, dans lequel le rapport du volume de la chambre (16) à la section du passage étranglé (68, 70) est comprise entre approximativement 10.000 et 18.000 lorsqu'on calcule en cm³ et cm² (ou approximativement 3.000 et 7.000 lorsqu'on calcule en pouce cube et pouce carré).

5. Manocontact selon l'une quelconque des revendications 1 à 4, dans lequel le rapport de la longueuer à la section du passage étranglé (68, 70) est d'environ 600 lorsqu'on calcule en cm et cm² (ou d'environ 1.700 lorsqu'on calcule en pouce et pource carré).

6. Manocontact selon l'une quelconque des revendications 1 à 5, dans lequel le volume de la chambre (16) et la longueur et la section du passage étranglé (68, 70) sont choisis de façon que le manocontact ne décrive pas un cycle plus de quatre fois par minute lorsque l'entrée (62) est reliée à la sortie d'évaporateur d'un système de conditionnement d'air d'automobile.

7. Système de conditionnement d'air pour automobile, du type présentant un compresseur (80) entraîné par le moteur par l'intermédiaire d'un embrayage à commande électrique (78), le compresseur (80) fonctionnant pour délivrer de réfrigérant à un condenseur (86), le réfrigérant quittant le condenseur (86) s'écoulant vers un type d'évaporateur (76) à serpentin à ailettes, la sortie d'évaporateur étant reliée à l'entrée de compresseur par une conduite d'aspiration (74), et des moyens étant prévus pour commander le fonctionnement de l'embrayage (78) et du compresseur (80), lesdits moyens comprenant un .interrupteur commandant la venue en prise de l'embrayage (78), caractérisé en ce que ledit interrupteur est un manocontact selon l'une quelconque des revendications 1 à 6...

8. Système de conditionnement d'air pour automobile de la revendication 7, dans lequel l'étranglement (68, 70) et la chambre (16) sont dimensionnés de façon que l'embrayage (78) ne décrive pas un cycle plus de quatre fois par minute sous de faibles charges de conditionnement d'air.

Drawing