WO1982002498A1

WO1982002498A1 - A temperature compensated differential fluid pressure switch

Info

Publication number: WO1982002498A1
Application number: PCT/US1981/000108
Authority: WO
Inventors: Joe E Fuzzell
Original assignee: Joe E Fuzzell
Priority date: 1981-01-19
Filing date: 1981-01-19
Publication date: 1982-08-05

Abstract

A temperature compensated differential fluid pressure switch (16) includes a housing (22) having a fluid inlet (18) and outlet (20), an actuatable differential fluid pressure sensor (24) for sensing differential fluid pressure across the inlet (18) and outlet (20), a wax motor (54) and poppet valve (62) for controlling fluid communication between the fluid inlet (18) and fluid outlet (20) to inhibit actuation of the differential fluid pressure sensor (24) in response to the fluid being below a temperature threshold, and a magnetic device (74, 76) for generating a signal responsive to the differential fluid pressure. The temperature compensated differential pressure switch detects a plugged filter. Prior switches permit actuation of the differential pressure sensor during cold operating conditions and use a temperature sensor which is not highly accurate. The present invention uses a temperature sensor or wax motor that inhibits actuation of the differential pressure sensor during such conditions and is accurate to within a small percentage of the threshold temperature.

Description

A Temperature Compensated Differential Fluid Pressure Switch

Technical Field This invention relates generally to a temperature compensated differential pressure switch and more particularly to such a switch for detecting a clogged or plugged filter.

Background Art Fluidic systems such as lubricating oil or fuel systems use filters in a fluid line to remove contaminants carried by the fluid. A filter which becomes clogged or plugged by the contaminants will result in a decrease in the fluid flow. A loss of lubricant due to reduced oil flow or a loss of power due to reduced fuel flow will have obvious adverse consequences.

Temperature compensated differential pressure switches have been developed to warn of a plugged filter condition. Such switches include a differential pressure sensor which senses differential fluid pressure across the input and output of a filter. When the differential pressure exceeds a pressure threshold, indicating a plugged filter, a warning signal will be given, except as controlled by a temperature sensor of the switch.

During cold operating conditions, for example below 125ºF, the fluid viscosity is of a magnitude sufficient to produce a differential fluid pressure exceeding the pressure threshold even though the filter is not plugged. The temperature sensor, which senses the temperature of the fluid, controls the actuation of the warning signal. When the fluid temperature is below a temperature threshold of 125ºF, the temperature sensor prevents generation of the warning signal irrespective of the differential fluid pressure, whereas when the fluid temperature is above the temperature threshold, the temperature sensor does not inhibit the generation of the warning signal. Thus, when the fluid temperature exceeds the temperature threshold, and the differential fluid pressure exceeds the pressure threshold, the warning signal will be generated.

Two prior temperature compensated differential fluid pressure switches are disclosed in U.S. Patent No. 3,146,757, by B.R. Heymann et al, issued September 1, 1964, and U.S. Patent No. 4,029,042, by Charles Juhasz, issued June 14, 1977. Each of these patents uses a differential fluid pressure sensor which constitutes a piston that moves in response to the differential fluid pressure of the fluid. While each of these patents also has a fluid temperature sensor which functions in the manner indicated above, the piston can move not only during the warm operating conditions above 125ºF, but also during the cold operating conditions below this temperature.

One disadvantage with these prior switches is that during cold operating conditions, the pistons will move to sense the differential fluid pressure even though the temperature sensors will prevent any warning signal from being generated. In other words, the pistons are not inhibited from moving during cold operating conditions. This movement during cold operating conditions will increase piston wear and accumulation of dirt and thereby possibly reduce the life-time of the switches.

Furthermore, the accuracy of a temperature sensor in any temperature compensated differential fluid pressure switch is highly important to avoid false warning signals. U.S. Patent No. 3,146,757 uses a gimbal-like structure having a plurality of bimetallic bellow-shaped discs which are free to expand and contract with changes in the fluid temperature. U.S. Patent No. 4,029,042 uses a bimetallic ring that will expand and contract concentrically with changes in the fluid temperature. Neither of these bimetallic elements is highly accurate to within a very small percentage of the temperature threshold. Also, being metallic and subjected to expansion and contraction, these temperature sensors will become fatigued and thereby have a limited life.

Still further, in responding to differential fluid pressure, the prior switches, particularly the pistons, are subjected to droplets of fluid which have contaminants. These contaninants may be small metallic particles which have not been or cannot be separated by the filter. Greater amounts of contaminants will appear in the fluid during cold operating conditions when the fluid is viscous and the filter is not functioning adequately. These contaminants will cause abrasion and wear in the switch, primarily on the movable piston. In addition, both of the above-mentioned U.S. patents provide a warning signal in the form of an indicator button that moves upwardly when the fluid temperature and differential pressure are above the respective thresholds.. Therefore, these indicator buttons must be designed to overcome friction during this movement to properly warn of a plugged filter. Furthermore, vibration can cause these indicator buttons to move and give a false warning signal. This is particularly true if these prior switches are used in vehicles such as earthworking vehicles which are utilized in high vibration environments.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of The Invention

In one aspect of the present invention, a temperature compensated differential fluid pressure switch has means for sensing differential pressure of a fluid and means for generating a signal in response to the sensed differential fluid pressure exceeding a differential pressure threshold. Means is provided for sensing the temperature of the fluid and for inhibiting the differential pressure sensing means in response to the temperature being below a temperature threshold.

In prior temperature compensated differential fluid pressure switches, the piston of the differential fluid pressure sensor can move during both cold and warm operating conditions, causing piston wear. Also, the temperature sensors of the prior switches are not highly accurate, contaminants in the fluid can cause wear on such a piston, and vibration can produce a false warning of a plugged filter. The switch of the present invention uses a temperature sensor which inhibits movement of a piston of a differential fluid pressure sensor during cold operating conditions and includes a wax motor that is highly accurate to a very small percentage of the temperature threshold. The signal generating means of the present invention includes a magnet and a reed switch which are not highly perceptible to vibration and which also are used to filter contaminants from droplets of fluid entering the switch.

Brief Description of the Drawings

Fig. 1 is a block diagram of a fluid filtering circuit.

Fig. 2 is a cross-section of an embodiment of the temperature compensated differential fluid pressure switch of the present invention.

Best Mode For Carrying Out The Invention

Fig. 1 shows a fluid filter 10 having a fluid inlet 12 and a fluid outlet 14. The filter 10 can be part of a fluidic system and will remove contaminants from the fluid flowing from the inlet 12 to the outlet 14. The filter 10 eventually will become plugged with the contaminants, resulting in undesirable reduced fluid flow at the outlet 14 and the need to replace the filter 10. A temperature compensated differential fluid pressure switch 16 of the present invention is used to produce a warning signal when the filter 10 becomes plugged. The switch 16 has an Inlet 18 coupled to the filter inlet 12 and an outlet 20 coupled to the filter outlet 14 to sense differential fluid pressure across the filter 10, except during cold operating conditions as will be described. As the filter 10 becomes plugged, the fluid pressure at the fluid Inlet 12 will rise in relation to the fluid pressure at the outlet 14 to produce higher differential pressures. The switch 16 can be set to a differential fluid pressure threshold and when the differential fluid pressure exceeds the threshold, the warning signal can be generated indicating that the filter 10 is plugged.

During a cold operating condition, for example, below a temperature threshold of 125ºF for lubricating fluids such as oil, the viscosity of this fluid is such that the differential fluid pressure across the filter 10 can be above the pressure threshold, yet the filter 10 may not be plugged. To avoid producing a false warning signal of a plugged filter 10 during this cold operating condition, the switch 16 senses the temperature of the fluid and prevents or inhibits the sensing of the differential fluid pressure. At fluid temperatures above the temperature threshold of 125ºF the switch 16 allows the differential fluid pressure to be sensed to produce the warning signal if the filter 10 Is plugged. The switch 16, as shown in Fig. 2, includes a housing 22 supporting actuatable means 24 for sensing differential fluid pressure, means 26 for sensing the temperature of the fluid and for inhibiting actuation of the differential pressure sensing means 24 in response to the fluid temperature being below the temperature threshold and means 28 for generating a signal in response to the differential fluid pressure exceeding a differential pressure threshold.

The differential fluid pressure sensing means 24 includes an internal bore 30, an annular groove 32 and a stepped internal bore 34 which is coupled at one end to the fluid inlet 18 and closed at another end by a plug 36. A piston 38 is slidable within a bore 40 forming a fluid chamber 41. Piston 38 is loosely fitted within the bore 40 to permit fluid to flow from one side 42 to the other side 44 of the piston 38 between the outer diameter of the piston 38 and the bore 40. A spring 46 is disposed between the temperature sensing means 26 and the piston 38 to bias the latter to the left against a shoulder 48 of the housing 22. As will be shown, the piston 38 is movable along the bore 40 as a function of the differential fluid pressure across the filter 10.

The temperature sensing means 26 has a hollow housing 50 which is screwed into the housing 22 by threads 52 and against which the spring 46 is disposed. A wax motor 54 has a housing 56 that is retained in the housing 50 by a snap ring 58 and has a piston 60 that is movable in and out of the housing 56 depending on the temperature of the fluid. A small clearance exists between the outer diameter of housing 56 and the adjacent inner diameter of housing 50 to permit fluid to flow between these housings to the fluid outlet 20. As will become apparent, the differential fluid pressure threshold can be preset with the sensor means 24 by screwing the housing 50 in or out to increase or decrease the bias of spring 46.

A valve means 62 has a poppet valve 63 which is disposed on a seat 64 of the housing 50, and has a movable plug 66 into which the poppet valve 63 is screwed. An extension spring 68 is disposed between the housing 56 and the movable plug 66 to bias the piston 60 into contact with the plug 66. as shown.

An O-ring seal 70 Is positioned about the housing 50 to seal the chamber 41, thereby allowing fluid to flow only from chamber 41, through the valve seat 64, hollow housing 50 and around the wax motor housing 56 to the outlet 20. An O-ring seal 72 can be used to seal the Inlet 18 from the outlet 20 to accurately sense the differential fluid pressure across filter 10.

When the fluid temperature is below the temperature threshold, the piston 60 is partially drawn into the housing 56 and the extension spring 68 becomes unextended to move the plug 66 closer to the housing 56, thereby, maintaining the poppet valve 63 on the seat 64. This Is the position shown in Fig. 2. With this closing of the seat 64, fluid pressure in the chamber 41 will rise. When the fluid temperature exceeds the temperature threshold, the piston 60 of the wax motor 54 will extend from the housing 56 to move the plug 66 against the bias of the extension spring 68 and move the valve 63 off the seat 64. Consequently, fluid can flow from the chamber 41 through the seat 64 and about the housing 56 to the outlet 20, thereby reducing the fluid pressure in chamber 41.

The signal generating means 28 includes a magnet 74, having north and south poles as shown, that is connected to the piston 38 and Is movable with this piston 38. A normally open reed switch 76 is disposed In a bore 78 of the housing 22 and has an electrical connection 79 which can lead to an alarm such as a light (not shown). As shown in Pig. 2, the magnet 74 is in a position to close the reed switch 76 to prevent generating any alarm signal. Should the differential fluid pressure across filter 10, as sensed by sensing means 24, be greater than the pressure threshold during warm operating conditions, the piston 38 will move sufficiently to the right and displace the magnet 74 so that the reed switch 76 will open to produce an electrical signal to turn on the alarm. The internal bore 34 has threads 80. The magnetic lines of force from the magnet 74 extend into the bore 34. As the fluid flows through the bore 34, ferrous metallic particles or contaminants in this fluid will be attracted by the magnet 74 towards the threads 80 which act as a sump for these contaminants, thereby filtering the fluid before it reaches the piston 38. Industrial Applicability

The filter 10 and temperature compensated differential fluid pressure switch 16 can be used in, for example, a lubricating fluidic system of a vehicle such as an earth-working vehicle. Three vehicle operating conditions will be discussed to explain the invention, including a cold fluid operating condition, a warm fluid operating condition in which the filter 10 Is not plugged and a warm fluid operating condition in which the filter 10 is plugged.

During cold fluid operating conditions when the lubricating fluid is viscous, the piston 60 of the wax motor 54 will be partially withdrawn into the housing 56, whereby the valve 62 will close on the seat 64. The cold fluid in the Inlet 18 will flow through the bore 30, groove 32, bore 34 and Into the bore 40 at side 42 of the piston 38. This fluid also will flow around the piston 38 to the chamber 41 where it will be trapped due to the closure or the valve 62. Consequently, the fluid pressure in chamber 44, together with the bias of the spring 46, will hold the piston 38 against the shoulder 48, as shown in Fig. 2, irrespective of the differential pressure across the filter 10. That is, by this closure of the valve 62, the temperature sensing means 26 will inhibit the movement of the piston 38 and, hence, the actuation of the differential fluid pressure sensing means 24. Under this cold operating condition, the magnet 74 will be in a position to close the normally open reed switch 76 to prevent generation of a false warning signal. Such a warning signal otherwise could be generated because the viscosity of the fluid in line 12 could result in a differential fluid pressure across the filter 10 that is greater than the pressure threshold. In the warm operating condition in which the filter 10 is not plugged, i.e. above the temperature threshold of, for example, 125ºF, the wax motor 54 will sense this temperature so that the piston 60 will be extended to open the valve seat 64 by moving the valve 62 to the left, as shown in Fig. 2. Consequently, fluid will flow from the inlet 18 through the bore 30, annular groove 32, bore 34, and against side 42 of piston 38, and will flow from chamber 41, through seat 64, around the wax motor 54 and out the outlet 20. Thus, fluid pressure will act against side 42 and side 44 of piston 38, with a differential fluid pressure across these sides being a function of the differential fluid pressure across the filter 10. As the fluid pressure acting on side 42 rises in relation to the fluid pressure acting on side 44, the piston will move to the right against the bias of spring 46. Therefore, above this temperature threshold, the temperature sensor means 26 does not inhibit actuation of the differential pressure sensing means 24. On the assumption that the filter 10 Is not presently plugged, the differential fluid pressure threshold will not be exceeded. Therefore, the piston 38 will not move too far to the right so that the magnet 74 will continue to maintain the reed switch 76 closed. Assume now that In the warm operating condition, the filter 10 is plugged to a degree such that the differential fluid pressure across filter 10 is greater than the pressure threshold. Under this condition, the fluid pressure acting on the side 42 will be so much greater than the pressure acting on side 44 and the bias of spring 46 as to move the piston 38 further to the right. In this position the magnet 74 will be moved out of operative relationship with the reed switch 76. The switch 76 thereby will open to generate a signal that can activate the alarm (not shown).

In summary, the temperature sensor means 26 functions not only to prevent a false warning of a plugged filter 10 during a cold operating condition but actually inhibits actuation of the differential pressure sensor means 24 during this condition. Thus, the lifetime of the differential pressure sensor means 24 is improved by limiting the wear on the piston 38. Furthermore, the wax motor 54 is highly accurate to about + or - 1% of the temperature threshold for which it is designed. Thus, within this range, the wax motor 54 can sense the temperature of the fluid to inhibit or permit actuation of the differential pressure sensor means 24.

Also, with respect to the signal generating means 28, because of the north-south orientation of the magnet 74 in relation to the reed switch 76, vibration, which might move the piston 38 a short distance along the bore 40 from the Fig. 2 position, normally will not move the magnet 74 so far as to cause the switch 76 to open and produce a false warning signal. In addition, in all the operating conditions the magnet 74, together with the threads 80, function to filter ferrous metallic contaminants in the fluid flowing in the bore 34, thereby again reducing the likelihood of wear of the piston 38. Also, due to the use of the magnetically operated reed switch 76, neither the connection 79 nor the switch 76 need penetrate the housing 22 where the fluid flows, thereby minimizing the chances for leakage.

Furthermore, with the reed switch 76 being normally open, at which position the warning signal is generated, a fail-safe circuit is provided. For example, with the magnet 74 in the position shown and the switch 76 closed, a loose connection 79 will open the circuit to actuate the alarm, though this would not be due to a plugged filter 10. Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

1. In a temperature compensated differential fluid pressure switch (16) having actuatable means (24) for sensing differential pressure of a fluid and means (28) for generating a signal in response to the sensed differential fluid pressure exceeding a differential pressure threshold, the improvement comprising: means (26) for sensing the temperature of the fluid and for inhibiting actuation of said actuatable differential pressure sensing means (24) in response to the fluid temperature being below a temperature threshold.

2. In a temperature compensated differential fluid pressure switch (16) according to claim 1 wherein said temperature sensing means (26) includes: a) a wax motor (54); and b) valve means (62) for passing the fluid therethrough and being openable and closeable by said wax motor (54).

3. In a temperature compensated differential fluid pressure switch (16) according to claim 1, wherein said means (28) for generating includes a magnet (74) and a magnetic switch (76) being controlled by said magnet (74).

4. In a temperature compensated differential fluid pressure switch (16) according to claim 3 wherein said magnetic switch (76) is a normally open reed switch.

5. In a temperature compensated differential fluid pressure switch (16) according to claim 1 wherein said actuatable differential pressure sensing means 24 includes: a) a fluid chamber (41); b) a piston (38) having first (42) and second (44) sides and being slidable in said fluid chamber (41); and c) fluid inlet passage means (30, 32, 34) for communicating fluid to said first (42) and second (44) sides of said piston (38).

6. In a temperature compensated differential fluid pressure switch (16) according to claim 5 wherein said signal generating means (28) includes: a) a magnet (74) being connected to said piston (38); and b) a magnetic switch (76) being controlled by said magnet (74).

7. In a temperature compensated differential fluid pressure switch (16) according to claim 1 wherein said differential pressure sensing means (24) has a settable differential pressure threshold, and said temperature sensing means (26) includes means (50, 52) for presetting said differential pressure sensing means (24) to said differential pressure threshold.

8. In a temperature compensated differential fluid pressure switch (16) according to claim 1 wherein said differential pressure sensing means (24) includes means (34) for receiving fluid, and said signal generating means (28) includes means (74) for filtering the fluid in said receiving means (34).

9. In a temperature compensated differential fluid pressure switch (16) according to claim 8 wherein said receiving means (34) includes a bore having threads (80), and said filtering means (74) includes a magnet (74) being adapted to attract the contaminants into said threads (80).

10. A temperature compensated differential fluid pressure switch (16), comprising: a) a housing (22) having a fluid inlet (18) and a fluid outlet (20); b) actuatable means (24) for sensing differential fluid pressure across said fluid inlet (18) and said fluid outlet (20); c) wax motor means (54, 62) for controlling fluid communication between said fluid inlet (18) and said fluid outlet (20) to inhibit actuation of said differential fluid pressure sensing means (24) in response to the fluid being below a temperature threshold; and d) magnetic means (74, 76) for generating a signal in response to the differential fluid pressure exceeding a differential pressure threshold.

11. A temperature compensated differential fluid pressure switch (16) according to claim 10 wherein said wax motor means (54, 62) includes: a) an openable and closeable poppet valve (63, 66) being adapted to pass fluid therethrough; and b) a wax motor (56, 60) being coupled to said poppet valve (63, 66).

12. A temperature compensated differential fluid pressure switch (16) according to claim 10 wherein said magnetic signal generating means (74, 76) includes: a) a magnet (74) being movable to different positions in response to changes in the differential fluid pressure; and b) a fixed magnetic switch (76) being controlled by said magnet.

13. A temperature compensated differential fluid pressure switch (16) according to claim 11 wherein said actuatable differential fluid pressure sensing means (24) includes: a) a fluid chamber (41) being adapted to receive fluid from said fluid inlet (18); and b) a piston (38) having first (42) and second (44) sides and being movable in said fluid chamber (41) In response to fluid pressure at said first (42) and second (44) sides, said magnet (74) being coupled to said piston (38).

14. A temperature compensated differential fluid pressure switch (16), comprising: a) a first housing (22) having a fluid inlet (18) and a bore (40); b) actuatable means (24) for sensing differential fluid pressure across said fluid inlet (18) and a fluid outlet (20), including i) a piston (38) having a first side (42) and a second side (44) and being slidable in said bore (40), said first side (42) being in fluid communication with said fluid inlet (18) and said piston (38) being adapted to permit fluid to flow from said first side (42) to said second side (44); and ii) a piston biasing spring

(46); c) means (26) for sensing the temperature of the fluid and for inhibiting actuation of said actuatable differential pressure sensing means (24) in response to fluid temperature being below a temperature threshold, including i) a second hollow housing (50) having said fluid outlet (20) and a valve seat (64) at said second side (44) of said piston (38) and being coupled in said bore (40), said spring (46) being disposed between said hollow housing (50) and said second side (44); ii) a poppet valve (62) being removably seated on said seat (64) and being disposed in said hollow housing (50); and Claim 14 - continued -

iii) a wax motor (54) being coupled to said poppet valve (62) and being disposed in said hollow housing (50) to permit fluid to flow to said outlet (20); and d) means (28) for generating a signal in response to the sensed differential fluid pressure exceeding a differential pressure threshold, Including i) a magnet (74) being coupled to said piston (38); and ii) a reed switch (76) being disposed in said first housing (22) and outside said bore (40).