Fluid level switch

A fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes a mounting plate, a float housing, and a float assembly positioned within the float housing. The mounting plate retains first and second contacts. The float housing is configured to receive fluid from the fluid reservoir and the float assembly is movable in response to the level of fluid in the float housing. The float assembly includes a contact member electrically connecting the first and second contacts when the level of the fluid is below the acceptable level. The contact member is coupled to the float for movement with the float and for movement relative to the float.

BACKGROUND

The present invention relates to fluid level sensors, and more specifically to low oil sensors for engines.

Fluid level sensors are generally used to determine the level of fluid retained within an enclosure. Some fluid level sensors activate an indicator when the fluid level decreases below a desired fluid level while others automatically shut off the system using the fluid.

In operation, fluid level sensors are positioned directly in a fluid reservoir, or within a smaller enclosure in fluid communication with the fluid reservoir. The enclosure maintains a fluid level proportional to the amount of fluid in the reservoir. One example of an application of a fluid level sensor is a sensor for the oil level within the crankcase of an internal combustion engine. The engine requires a desired amount of oil within the crankcase to properly lubricate the engine during operation. If the oil level is too low, the engine can be damaged due to improper lubrication. A fluid level sensor can be used to determine when the oil level within the crankcase is below a desired level.

Prior art systems often employ the use of a float within a housing to move with the level of fluid as the level of fluid changes. A sensor or an electrical contact can be positioned in the vicinity of the float and can be used to detect when the level of fluid is not within a desired range. The sensor or contact can communicate the condition of the fluid level through a indicator such as a warning light or by automatically shutting off the device that is using the fluid to operate. For example, the float can complete an electrical connection between a ground and an ignition contact to shut off the engine when the float is in a position indicative of low fluid or complete an electrical circuit for an audible indicator or visual indicator.

The use of such a system is generally reliable in shutting off the engine when a low amount of fluid is present. However, signaling a low fluid condition can be inconsistent due to the effect of the vibrations caused by moving parts of the engine, for example. This causes the fluid to move and splash around in the reservoir, thereby causing movement of the float and an unstable contact between the ground and ignition contact. This movement has the potential to prevent the float from grounding the ignition long enough to completely shut down the engine.

SUMMARY

In some embodiments, the present invention is directed to a low fluid sensor that can be mounted to an engine or other machine to accurately detect a condition of low fluid. The apparatus can include a float contact that compensates for the movement of a float due to splashing of fluid in a reservoir for a system that has moving parts.

Using a float contact that is movable relative to the float allows the low fluid sensor to more accurately determine a low fluid condition and limit the incidence of intermittent grounding of the ignition. A movable float contact allows for tolerance or dimensional variations of the contacts. In the case that the contacts are not exactly the same size or height, the moveable plate is still capable of touching all of the contacts simultaneously. Additionally, a movable float contact can remain in contact with the ground and ignition contact even while the float is moving in response to vibrations, because the float contact is weighted and loosely coupled to the float so that the float contact does not move with every slight dip and peak of the float. Instead, the plate will continue to contact the electrical contacts and therefore allow the low fluid indicator to remain in a “shut-off” state until more fluid is added to the system.

One embodiment of the present invention is directed to a fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes a mounting plate, a float housing, and a float assembly positioned within the float housing. The mounting plate retains first and second contacts. The float housing is configured to receive fluid from the fluid reservoir and the float assembly is movable in response to the level of fluid in the float housing. The float assembly includes a contact member electrically connecting the contacts when the level of the fluid is below the acceptable level. The contact member is coupled to the float for movement with the float and for movement relative to the float.

Another embodiment of the invention is directed to a fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes first and second contacts, and a float assembly adapted to be in fluid communication with the fluid reservoir. The float assembly includes a float and a contact member. The float is movable between a raised position when the fluid is at an acceptable level and a lowered position when the fluid is below the acceptable level. The contact member is coupled to the float about at least a portion of the periphery of the contact member. The contact member electrically connects the first and second contacts when the fluid is below the acceptable level.

Another embodiment of the invention is directed to a fluid level switch for a machine having a fluid reservoir adapted to contain a fluid at an acceptable level. The fluid level switch includes a float housing, first and second contacts, and a float assembly. The float housing is configured to receive fluid from the fluid reservoir, and the first and second contacts are positioned on a same side of the float housing. The float assembly is positioned within the float housing and includes a float and a contact member. The float is movable between a raised position when the fluid is at an acceptable level and a lowered position when the fluid is below the acceptable level. The contact member is coupled to the float for movement with the float between raised and lowered positions and for movement relative to the float. The contact member electrically connects the first and second contacts in at least one of the raised and lowered condition.

DETAILED DESCRIPTION

A fluid level switch10of a first embodiment of the present invention is illustrated inFIG. 1. The fluid level switch10includes a mounting plate12fastened to a vertical wall14of an engine by mounting screws16. Any conventional fastener can be employed to secure the mounting plate12to the vertical wall14as just described, such as screws, nails, rivets, pins, posts, clips, clamps, inter-engaging elements, and any combination of such fasteners. The mounting plate12is L-shaped to include a support portion18. As shown inFIG. 2, the support portion18includes three apertures20, however, the number of apertures20can vary.

As better illustrated inFIG. 2, the support portion18comprises two electrical contacts22,24. The first electrical contact, such as a ground contact22, is made from a piece of the support portion18that has been bent upwardly a distance from the surface of the support portion18, thereby forming an aperture23. The second electrical contact is an ignition contact24that is made up of a conductive material and that extends through an aperture26in the support portion18. Although the second contact of the illustrated embodiment is described as being an ignition contact, the second contact in other embodiments can alternatively be any live or hot contact not necessarily electrically connected to the ignition. In the illustrated embodiment, an insulator28supports the ignition contact24and is press-fit into an aperture29of the support portion18. However, the insulator28can be coupled to the support portion18in various ways such as the use of fasteners or molding. The insulator28acts to prevent electrical contact between the ground contact22and the ignition contact24.

The fluid level switch10also includes a cylindrical float housing30with protrusions32that line up with the apertures20for coupling the float housing30to the support portion18. The float housing30has an open end34where the protrusions32are located and a closed end36having a centrally located aperture38. In other embodiments, the aperture38could be located anywhere on the closed end to vent for air. A gap or cutout40in the float housing30provides clearance for the insulator28when the float housing30is coupled to the support portion18and allows for a snap-fit assembly. The insulator28is partially located within the float housing30to reduce the size of the fluid level switch10. The location of the insulator28can vary and is not limited to the placement shown inFIG. 2. Specifically, the insulator28does not have to be located partially within the float housing30.

A cylindrical float42made of a buoyant material is shown inFIGS. 2 and 3. The float42is held in a retaining member44having a cage structure. Both a bottom portion46and a top portion48of the retaining member44are open. The retaining member44has a plurality of tabs50on the top portion48that can retain the float42within the retaining member44. The float42rests on a first lip52that includes an outer diameter54equal to the upper portion48of the retaining member44and an inner diameter55smaller than that of the float42. The first lip52thereby supports the bottom57of the float42. A plate56can be positioned between the float42and the bottom portion46of the retaining member44. The plate56sits on a second lip58on the bottom portion46of the retaining member44. The second lip58is spaced from the first lip52a distance D to allow movement of the plate56(having a thickness T) relative to the float42within the retaining member44. The plate56is disc-shaped and has apertures60for weight adjustment. A centrally located, raised portion61of the plate56helps to prevent the plate56from becoming stuck to the float42due to viscous properties of the fluid. The raised portion allows only a small portion of the plate56to contact the float42. The plate56, also referred to as a contact plate, is not limited to the illustrated shape, but can take on a plurality of shapes and sizes such that it can provide electrical communication between two contacts. It is preferable that the plate56be more dense than the fluid, however it is not required. In the preferred embodiment, gravity pulls the plate56down on the contacts22,24.

FIG. 3illustrates the internal structure of the fluid level switch10. The plate56rests upon the second lip58of the retaining member44. Between the top of the plate56and the bottom57of the float42is a space62. The space62allows linear and angular motion of the plate56to help improve switching characteristics. The bottom57of the float42rests upon the first lip52of the retaining member44, and is held at the top portion58of the retaining member44by the tabs50. In combination, the float42, plate56, and retaining member44define a float assembly64(FIG. 2). The float assembly64fits within the cylindrical float housing30. As shown inFIGS. 1 and 2, the protrusions32of the float housing30engage the apertures20to cover contacts22,24. The gap40in the float housing30prevents interference from the insulator28when the float housing30is coupled to the support portion18.

A first side of the float housing30is defined below the float42, and everything located below reference line63is considered to be below the float42. A second side of the float housing30is defined above the float42, and everything located above reference line65is considered to be above the float42. As illustrated inFIG. 3, both contacts22,24are below the float42and on the first side of the housing30.

One embodiment of the present invention can be located in the crankcase of an engine. The crankcase is a relatively turbulent environment and the level of fluid, such as oil, may fluctuate greatly depending on a number of factors, such as slight tilting or changes to the orientation of the engine and the crankshaft or other moving parts splashing the oil. Other embodiments could be used on pumps, transmissions, or any other machine with moving parts and a fluid reservoir.

As illustrated inFIGS. 1 and 2, the fluid level switch10allows oil to flow into and out of the float housing30through the apertures23,26,38. The protrusions32of the float housing30may have apertures66as well to allow for fluid flow into the float housing30. Since the float42is made of a buoyant material, the float42will cause the float assembly64to rise and fall with the oil level. When oil is added to the engine, the float assembly64will rise with the level of the oil. As oil is used in the system, the float assembly64will lower with the oil level.

As the level of oil nears an undesired low level, the float assembly64and hence the plate56move increasingly closer to the contacts22,24, as shown inFIG. 3. When the oil reaches a predetermined level that would be considered a “low oil” condition, the plate56touches the contacts22,24. Because the plate56is more dense than the fluid being monitored, the plate56will tend to stay in relatively the same position although the plate56, in most situations, is submerged in fluid. As shown inFIG. 4, the space62between the plate56and the float42is intended to be large enough to allow the plate56to remain in contact with electrical contacts22,24even while the float42and retaining member44move and tilt inside the cylindrical float housing30caused by misaligned contacts22,24or agitated fluid from normal engine vibration or operation.

The illustrated embodiment uses an “engine shutdown” method by grounding the primary ignition current when the plate56is touching both contacts22,24. For example, the operator of a lawnmower or snow blower can be alerted of such a situation through the engine being shut-off during operation. Upon the operator adding enough oil to the system whereby the plate is not touching either electrical contact22,24, the engine can be restarted and regular operation can resume.

An alternate design for the fluid level switch10uses an “indicator method” to alert an operator of the low oil situation. When the plate56touches both contacts22,24, an electrical circuit can be completed to alert the operator of a low oil situation through an indicator such as a “low oil” light or a “low oil” alarm or buzzer. When the “low oil” indicator is activated, the operator knows that a low oil situation is occurring. In that case, the operator can choose to continue operating the machine while in a state of low oil and risk damaging the engine, or can add oil until the plate56is no longer touching the contacts22,24.

In the engine shutdown method, a latching module68(illustrated inFIG. 4) can be used to prevent intermittent or false shutdown due to switch bouncing caused by engine vibration and turbulence of the fluid surrounding the float assembly64. False shutdown occurs when vibration and turbulence of the engine and fluid do not allow the float to ground the ignition long enough to completely shut down the engine. The latching module68operates to ground the ignition even after the plate56bounces out of contact with the first and second contacts22,24. In one embodiment, the latching module68includes a capacitor and a silicon controlled rectifier (“SCR”) electrically connected to the capacitor. When the plate56electrically connects the first and second contacts (i.e., when the fuel level switch closes), the ignition pulse from the engine's ignition system charges the capacitor. When the charge of the capacitor reaches a voltage value that is sufficiently high to switch the SCR “on”, the primary winding current is shunted through the SCR to ground, thereby shutting down the engine. The SCR remains “on”, using the energy stored in the capacitor as the engine rotates during coastdown. As long as the SCR is “on”, the primary winding current will remain shunted through the SCR regardless of whether the fluid level switch re-opens due to vibrations.

A fluid level switch110according to an alternate embodiment of the present invention is illustrated inFIG. 5. The fluid level switch110is adapted for mounting to a horizontal surface114using mounting fasteners116. A mounting plate112can be fastened to the horizontal surface114in the same manner that the first embodiment of the mounting plate12can be fastened to a vertical surface14. Mounting plate112is similar to the support portion18as shown inFIG. 1and the fluid level switch110operates similar to fluid level switch10.

Another embodiment of a mounting plate212is illustrated inFIG. 6. The mounting plate212is adapted to be fastened to a vertical surface14similar to the mounting plate12illustrated inFIG. 1. The mounting plate212has a support portion218that comprises three electrical contacts222,268,24(shown inFIG. 2). The electrical contacts, such as ground contacts222,268, are made from pieces of the support portion218that have been bent upwardly a distance from the surface of the support portion218thereby forming apertures223,270. The electrical contact24is made of conductive material and extends through an aperture226in the support portion218. The mounting plate212used with the float assembly64is similar to the mounting plates12,112illustrated inFIGS. 1-5. In other embodiments, the mounting plate212can be reconfigured to be fastened to a horizontal surface114similar to the mounting plate112illustrated inFIG. 5.

A fluid level switch310of another embodiment of the present invention is illustrated inFIG. 7. The fluid level switch310includes a mounting plate312that can fastened to a wall of an engine by inserting fasteners through apertures316. The mounting plate312includes a support portion318that has two electrical contacts322,368. The electrical contacts322,368can be ground contacts and are made from pieces of the support portion318that have been bent upwardly a distance from the surface of the support portion318thereby forming apertures323,370.

The fluid level switch310also includes an electrical contact324that extends through an aperture326in the support portion318. The electrical contact324can be an ignition contact and is made from a conductive material. The ignition contact extends through the aperture326in the support portion318such that the ignition contact does not contact the mounting plate312.

In the illustrated embodiment, a shield328supports the ignition contact324and is coupled to the mounting plate312by the protrusions332of the float housing330. Specifically, the protrusions332of the float housing330extend through the apertures320of the mounting plate312and into apertures334of the shield328to couple the mounting plate312between the float housing330and the shield328. The shield328reduces the effect of oil turbulence within the oil reservoir on the operation of the fuel level switch310. Specifically, the shield328resists the flow of oil through apertures323,370making the operation of the plate56and float42less affected by the turbulence outside the float housing330. The shield328is made of an insulating material. In addition, the shield328replaces the insulator28,128of the previous embodiments (FIGS. 1-6) to support the ignition contact324and to prevent electrical contact between the ignition contact324and the ground contacts322,368and between the ignition contact324and the mounting plate312.

The fluid level switch310also includes a float assembly364similar to the float assembly64of the first embodiment as illustrated inFIG. 2except that the protrusions332of the float housing330are slightly extended to capture the shield328. The reference numbers used to describe the float assembly64ofFIG. 2are used to describe the corresponding components of the float assembly364inFIG. 7.