A FLUID LEVEL SENSOR AND A METHOD THEREOF FIELD OF INVENTION

The present invention relates in general to fuel level sensors of the type in which a fluid- responsive float arm moves a contact wiper over a variable resistance conductive path on a thick film resistor card. The position of the contact wiper on the card corresponds to the level of fuel in the tank as measured by the float. As the wiper moves along the surface of the card, the difference in resistance is measured in an electric circuit indicates the level of liquid fuel in the tank.

BACKGROUND OF THE INVENTION

Variable resistance fuel level sensors are known in the art for indicating the level of liquid fuel in a vehicle fuel tank. Such fuel sensors typically comprise a housing mounted in the interior of the fuel tank, a resistor card mounted on the housing, a float arm assembly pivotally connected to the housing, and a conductive wiper connected to and operated by the float arm. The conductive wiper has a sliding contact, which moves along the resistive path of the card, and a ground contact to a ground terminal. A positive terminal on the housing supplies electric current to the card with suitable connections from a remote power source.

The resistive path on the card is often accurate, comprising a plurality of conductive pads with varying resistance along the length of the arc. The float arm pivots on an axis approximately coincident with the center of the arc. The float arm assembly includes a bent thin strip float arm with a float mounted at its free end and a pivot pin extending through a hole in the housing.

A plastic support arm on the cover provides stop surfaces, which interact with stops on the housing to define the limit of travel of the float arm and wiper.

A main concern with these types of fuel senders is the need for uniformity, stability and consistency in the fit and operation of the moving parts over the lifetime of the unit. Relaxation of spring tension, unbalanced moment forces, and inherently weak or unstable mounting and support arrangements can all affect the reliability and repeatability of the

readings from the fuel sender unit. Some of the areas particularly critical to reliable and consistent functioning are the sliding wiper interfaces, the spring rates and contact forces of the conductive wiper and the pivot support of the float arm assembly. Reducing the amount of variation, imbalance and loose fit in these areas of the fuel sender greatly increases the unit's reliability and calibration accuracy. None of the prior art to date has adequately and systematically addressed the above-listed factors in a comprehensive manner.

OBJECTS OF THE INVENTION

One of the principle objects of the invention is to develop a fluid level sensor, a method to detect fluid level and a method of assembling the fluid level sensor.

STATEMENT OF INVENTION

Accordingly the present invention provides a fluid level sensor, comprising a housing (114) having a snap fit (112) onto which a thick film resistor card (109) is fixed, a shaft

(106) with one side of the shaft (106) passing through a wiper arm (107), at least one washer (108) and a spring (110) to mate with the housing (114), a housing cover (103) to cover the housing (114) wherein other side of the shaft (106) mates with the cover, and a float arm (105) fixed to the shaft (106) which moves the wiper arm (107) when the fluid level varies, wherein the wiper arm (107) makes contact with the thick film resistor card (109) to indicate the fluid level; the present invention also provides a method to detect fluid level, said method comprises acts of: mounting a thick resistor card (109) onto a housing (114) by a snap fit (112), placing a shaft (106) such that one side of the shaft (106) passes through a wiper arm (107), washers (108) and a spring (110) so as to mate with the housing (114), locking a housing cover (103) with the housing (114) wherein the other side of the shaft (106) mates with the housing cover (103), and fixing a float arm (105) to the shaft (106) to move the wiper arm (107) when the fluid level varies wherein the wiper arm

(107) makes contact with the thick film resistor card (109) to indicate the fluid level; the present invention also provides a method of assembling a fluid level sensor comprising steps of: mounting a thick resistor card (109) onto a housing (114) by a snap fit (112),

placing a shaft (106) such that one side of the shaft (106) passes through a wiper arm (107), washers (108) and a spring (110) so as to mate with the housing (114), locking a housing cover (103) with the housing (114) wherein the other side of the shaft (106) mates with the housing cover (103), and fixing a float arm (105) to the shaft (106) to move the wiper arm (107) when the fluid level varies wherein the wiper arm (107) makes contact with the thick film resistor card (109) to indicate the fluid level.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 : shows thick film resistor

Figure 2: shows Assembly view of the instant invention

Figure 3: shows Exploded view of instant invention

Figure 4: shows the sub-assembly view of the instant invention

DETAILED DESCRIPTION OF INVENTION

The primary embodiment of the present is a fluid level sensor, comprising: a housing (114) having a snap fit (112) onto which a thick film resistor card (109) is fixed, a shaft (106) with one side of the shaft (106) passing through a wiper arm (107), at least one washer

(108) and a spring (110) to mate with the housing (114), a housing cover (103) to cover the housing (114) wherein other side of the shaft (106) mates with the cover (103), and a float arm (105) fixed Io the shaft (106) which moves the wiper arm (107) when the fluid level varies wherein the wiper arm (107) makes contact with the thick film resistor card

(109) to indicate the fluid level.

In yet another embodiment the shaft (106) mates with the housing (114) through a bush (111) onto which the spring (110) is placed.

In still another embodiment the wiper (107) sweep angle is ranging from about 60° to about 110°.

In still another embodiment the wiper arm (107) is in sliding contact with the thick film resister whose resistance variation is equivalent to the fluid level.

In still another embodiment the float arm (105) includes a bent strip with a float mounted at its free end which varies with the fluid level.

In still another embodiment the housing cover (103) locks with the housing (114) by snap fit (115).

In still another embodiment the housing cover (103) provides for stoppers (104) to control the wiper arm (107) sweep angle.

Another embodiment of the present invention is a method to detect fluid level, said method comprises acts of: mounting a thick resistor card (109) onto a housing (114) by a snap fit (112), placing a shaft ( 106) such that one side of the shaft (106) passes through a wiper arm (107), washers (108) and a spring (110) so as to mate with the housing (114), locking a housing cover (103) with the housing (114) wherein the other side of the shaft (106) mates with the housing cover (103), and fixing a float arm (105) to the shaft (106) to move the wiper arm (107) when the fluid level varies wherein the wiper aπn (107) makes contact with the thick film resistor card (109) to indicate the fluid level.

In yet another embodiment variation in the wiper arm (107) movement moves its contact with the thick film resistance to vary its resistance.

Another embodiment of the present invention is a method of assembling a fluid level sensor comprising steps of: mounting a thick resistor card (109) onto a housing (114) by a snap fit (112), placing a shaft (106) such that one side of the shaft (106) passes through a wiper arm (107), washers (108) and a spring (110) so as to mate with the housing (114), locking a housing cover (103) with the housing (114) wherein the other side of the shaft (106) mates with the housing cover (103), and fixing a float arm (105) to the shaft (106) to

move the wiper arm (107) when the fluid level varies wherein the wiper arm (107) makes contact with the thick film resistor card (109) to indicate the fluid level.

In yet another embodiment the shaft (106) mates with the housing (114) through a bush (111) on which the spring (110) is placed.

In still another embodiment the wiper arm (107) is in sliding contact with the thick film resister whose resistance variation is equivalent to the fuel level.

In still another embodiment the housing cover (103) is fixed onto the housing (114) by a snap fit (115).

The fluids used by the instant invention comprises of water, fuels, chemical solvents or reagents and liquefied gases. However, the fluids does not limit to the above mentioned list.

Instant invention is related to fluid level sensor, comprising: a housing (114), a thick film resistor card (109) fixed within the housing (114), a shaft (106) with one side of the shaft (106) passing through a wiper arm (107), atleast one washer (108) and a spring (110) to fix with the housing (114) and other side of the shaft (106) mates with an housing cover (103), where the housing cover (103) covers the housing (114), a float arm (105) is fixed to the shaft (106) which carries a float at its free end which varies with the fluid level variation and moves the wiper arm (107) as shown in the figure 3. The wiper arm (107) is in contact with the thick resistor card (109).

The thick film resistor card (109) is of inverted type as shown in the figure I ₃ by means of which a junction region providing a conductive path from the resistive film to the resistor contact and lead, the junction region being defined by a region surrounding the interface between the contact wiper arm (107) and resistive film, and the resistance varies along the length of the arc for any resistant value as per the requirement of the end user.

As shown in the figures 3 and 4, the sub assembly 1 consists of the housing (114) wherein the bush (111) in mounted onto a hole (113) of the housing (114) upon which a spring (110) is placed. The thick film resistor card (109) is fixed onto the snap fit (112) of the housing in inverted position. The sub assembly 2 consists of a shaft (106) as a pivot with one side passing through a wiper arm (107) and washers (108). A float arm (105) is fixed on to the shaft (106). This sub assembly 2 is mounted onto the sub assembly 1 such that the shaft (106) is mounted onto the bush (111), spring (110) arrangement. The sub assembly 3 consists of housing cover (103) which locks with the housing (114) by the snap fit (115) and a bush (101).

In sub assembly 2 of figure 2, the mentioned float arm (105) includes a bent strip with a float mounted at its free end which varies with the fuel level. With the movement of float arm (105) the shaft (106) move which causes the wiper arm (107) to move. Thus, the wiper arm (107) which is in sliding contact with the thick resistor card (109) varies the resistance of the card (109) proportionately with fuel level variation. The figure.2 shows the complete assembly of the fluid level sensor.

The housing (114) arrangement is made stable with the help of spring (110) arrangement. The spring (110) is used to prevent wiper arm (107) from permanent deflection due to slashing or vibration. The fuel level sensors cover (103) absorbs the load due to vibration and positioning itself by moving back and forth in longitudinal direction by means of spring (110). The spring (110) locks the wiper (107) with the shaft (106) and washers (108) so that there is no motion of wiper (107) due to slashing or vibrations. The wiper (107) sweep angle is ranging from about 60° to about 110°. The stoppers (104) on the housing cover (103) control the wiper (107) sweep angle.