Motor-pump System For Preventing A Vapor Lock

Abstract

The impeller of a pump is driven by the armature of a motor for pumping a liquid. In response to the onset of vapor bubble formation in the liquid, the impeller load decreases thereby decreasing the armature current and increasing the impeller speed to initiate the establishment of a vapor lock condition in the pump. A relay includes a winding responsive to the decrease in the armature current at the onset of vapor bubble formation in the liquid to open a set of contacts for switching a resistor in series with the motor armature. The resistor decreases the armature voltage thereby decreasing the impeller speed and increasing the impeller load to terminate the establishment of a vapor lock condition in the pump.

Description

DISCLOSURE

This invention relates to a motor-pump system for preventing the occurrence of a vapor lock condition in the pump.

According to one aspect of the invention, a pump includes a pump chamber having an inlet and an outlet. A pump impeller is rotatably mounted within the chamber for drawing liquid into the chamber through the inlet and for pumping liquid out of the chamber through the outlet. The load on the pump is directly related to the density of the liquid. In the absence of vapor bubble formation, the density of the liquid is substantially constant at a maximum level. However, at the onset of vapor bubble formation, the density of the liquid decreases thereby decreasing the load on the impeller. Where the liquid is a highly volatile petroleum fuel of the type used in the internal combustion engine of an automotive vehicle, vapor bubbles are readily formed as the temperature of the fuel increases.

In another aspect of the invention, a motor includes an armature shaft and an armature winding for rotatably driving the armature shaft. The operating characteristics of the motor are such that the current through the armature winding is directly related to the load on the armature shaft and the speed of the armature shaft is directly related to the voltage across the armature winding and is inversely related to the load on the armature shaft. Preferably, the motor is of the type having a permanent magnet field.

As contemplated by a further aspect of the invention, the armature shaft of the motor is coupled with the impeller of the pump for rotatably driving the impeller. When the load on the impeller is substantially constant at a maximum level in response to the absence of vapor bubble formation in the liquid, the load on the armature shaft is likewise at a maximum level to maintain the current through the armature winding at a maximum level and to maintain the speed of the armature shaft at a minimum level. However, when the load on the impeller decreases in response to the onset of vapor bubble formation in the liquid, the load on the armature shaft likewise decreases to decrease the current through the armature winding and to increase the speed of the armature shaft. In response to the increase in the speed of the armature shaft, the speed of the impeller increases to initiate a regenerative speed increase/load decrease reaction on the impeller which, if left to continue, would eventually develop a vapor lock condition about the inlet of the pump chamber thereby preventing the entry of fuel into the chamber. Where the pump is supplying fuel to the internal combustion engine of an automotive vehicle, a vapor lock condition would disable the vehicle by causing the engine to stall from a lack of fuel.

In yet another aspect of the invention, a relay includes a current sensor provided by a control winding which is connected in the series with the armature winding of the motor. Further, the relay includes a pair of contacts connected in parallel across a resistor which is also connected in series with the armature winding of the motor. When the current through the armature winding is at a maximum level in response to the absence of vapor bubble formation in the liquid, the current sensor closes the contacts so as to bypass the resistor thereby to maintain the voltage across the armature winding at a maximum level in response to the absence of vapor bubble formation in the liquid. COnversely, when the current through the armature winding decreases in response to the onset of vapor bubble formation in the liquid, the current sensor opens the contacts so as to not bypass the resistor thereby decreasing the voltage across the armature winding to decrease the speed of the armature shaft. In response to the decrease in the speed of the armature shaft, the speed of the impeller decreases to terminate the regenerative speed increase/load decrease reaction on the impeller so as to prevent the development of a vapor lock condition about the inlet of the pump chamber there-by permitting the entry of fuel into the chamber to increase the load on the impeller back to the maximum level.

These and other aspects and advantages of the invention will be best understood by reference to the following detailed description of a preferred embodiment when considered in conjunction with the accompanying drawing.

In the drawing, the sole FIGURE is a schematic diagram of a motor-pump system incorporating the principles of the invention for preventing the occurrence of a vapor lock condition in the pump.

Referring to the drawing, a pump 10 includes a housing which forms a pump chamber 12 having an inlet 14 and an outlet 16. A pump impeller 18 is rotatably mounted within the chamber 12 for drawing liquid into the chamber 12 through the inlet 14 and for pumping liquid out of the chamber 12 through the outlet 16 when the impeller 18 is rotatably driven in a clockwise direction. As an example, the pump 10 may be utilized to supply fuel to the internal combustion engine of an automotive vehicle. In such event, the inlet 14 would be immersed within the fuel stored in the fuel tank of the vehicle while the outlet 16 would be coupled to the vehicle engine.

The load on the impeller 18 of the pump 10 is directly related to the density of the liquid passing through the pump 10. In the absence of vapor bubble formation in the liquid, the density of the liquid is substantially constant at a maximum level so that the load on the pump is likewise substantially constant at a maximum level. However, at the onset of vapor bubble formation within the liquid, the density of the liquid decreases thereby decreasing the load on the impeller 18. Where the liquid is a petroleum fuel which the pump 10 is supplying to the internal combustion engine of an automotive vehicle, vapor bubbles or pockets are readily formed as the highly volatile fuel undergoes an increase in temperature.

An electric motor 20 includes an armature shaft 22 and an armature winding 24 connected between a pair of contact brushes 26 and 28 for rotatably driving the armature shaft 22 in a clockwise direction when energized from a voltage source 30 through a power switch 32. Where the pump 10 is installed within an automotive vehicle, the voltage source 30 may be provided by the vehicle storage battery and the power switch 32 may be provided by the vehicle ignition switch. The operating characteristics of the motor 20 are such that the current through the armature winding 24 is directly related to the load on the armature shaft 22 and the speed of the armature shaft 22 is directly related to the voltage across the armature winding 24 and is inversely related to the load on the armature shaft 22. Preferably, the field of the motor 20 is provided by a permanent magnet.

The armature shaft 22 of the motor 20 is coupled directly to the impeller 18 of the pump 10 for rotatably driving the impeller 18 from the armature shaft 22 such that the load on the impeller 18 is the load on the armature shaft 22. When the load on the impeller 18 is substantially constant at a maximum level in response to the absence of vapor bubble formation in the liquid, the load on the armature shaft 22 is likewise at a maximum level. Accordingly, due to the operating characteristics of the motor 20, the current through the armature winding 24 is at a maximum level while the speed of the armature shaft 22 is at a minimum level. Alternately, when the load on the impeller 18 decreases in response to the onset of vapor bubble formation in the liquid, the load on the armature shaft 22 likewise decreases. Again, due to the operating characteristics of the motor 20, the current through the armature winding 24 decreases while the speed of the armature shaft 22 increases thereby increasing the speed of the impeller 18.

As the speed of the impeller 18 increases, less liquid and more vapor is able to enter the pump chamber 12 through the inlet 14 because the vapor is more mobile than the liquid. Consequently, the load on the impeller 18 further decreases thereby increasing the speed of the impeller 18 to further decrease the liquid and increase the vapor entering the pump chamber 12. If allowed to continue, the eventual consequence of this regenerative speed increase/load decrease reaction is the development of a back pressure or vapor lock about the inlet 14 of the pump chamber 12 thereby preventing the entry of fuel into the chamber 12. Where the pump 10 is supplying fuel to the internal combustion engine of an automotive vehicle, the development of a vapor lock condition about the inlet 14 of the pump chamber 12 would disable the vehicle by causing the engine to stall from a lack of fuel.

In order to prevent the occurrence of a vapor lock condition in the pump 10, an anti-vapor lock arrangement is provided by a resistor 34 and a relay 36. The resistor 34 is connected in a series circuit with the armature winding 24 of the motor 20 for reducing the voltage across the armature winding 24 when the resistor 34 is not bypassed. Specifically, the voltage across the armature winding 24 is reduced by an amount equal to the voltage across the resistor 34.

The relay 36 includes a current sensor provided by a control winding 38 and a set of switching contacts provided by a pair of flexible and magnetizable reeds 40 and 42 which are electromagnetically coupled with the control winding 38. The contacts 40 and 42 are normally disposed in an opened position and are electromagnetically operable to a closed position against an inherent spring bias tending to return them to the opened position. In the usual manner, the reeds 40 and 42 are enclosed within an evacuated envelope 44 to ensure their sensitivity and durability. The control winding 38 is connected in series with the armature winding 24 of the motor 20. The switching contacts 40 and 42 are connected in parallel across the resistor 34.

When the current through the armature winding 24 of the motor 20 is at a maximum level in response to the absence of vapor bubble formation in the liquid, the electromagnetic field developed by the flow of the armature current through the control winding 38 is sufficient to overcome the spring bias of the switching contacts 40 and 42 which close so that the resistor 34 is bypassed. With the resistor 34 bypassed, the voltage across the armature winding 24 of the motor 20 is maintained at a maximum level thereby to maintain the speed of the armature shaft 22 and the speed of the impeller 18 at a maximum level.

When the current through the armature winding 24 of the motor 20 decreases in response to the initiation of vapor bubble formation in the liquid, the electromagnetic field developed by the flow of the armature current through the control winding 38 is insufficient to overcome the spring bias of the switching contacts which open so that the resistor 34 is not bypassed. With the resistor 34 not bypassed, the voltage across the armature winding 24 of the motor 20 is decreased to decrease the speed of the armature shaft 22 and the speed of the impeller 18. As the speed of the impeller 18 decreases, the regenerative speed increase/load decrease reaction on the impeller 18 is terminated to prevent the development of a vapor lock condition about the inlet 14 of the pump chamber 12.

Accordingly, more fuel is permitted to enter the pump chamber 12 thereby increasing the load on the impeller 18 back toward a maximum level. As the load on the impeller 18 increases to a maximum level, the current through the armature winding 24 of the motor 20 likewise increases to a maximum level to reclose the contacts 40 and 42 through the electromagnetic action of the winding 38. With the contacts 40 and 42 closed, the resistor 34 is again bypassed.

It will now be appreciated that the foregoing description of a preferred embodiment of the invention is made for demonstrative purposes only and that various alterations and modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. In combination: a pump including a pump chamber having an inlet and an outlet and a pump impeller rotatably mounted within the chamber for drawing liquid into the chamber through the inlet and for pumping liquid out of the chamber through the outlet when the impeller is rotatably driven such that the load on the impeller is directly related to the density of the liquid which is substantially constant at a maximum level in response to the absence of vapor bubble formation and which decreases in response to the onset of vapor bubble formation thereby decreasing the load on the impeller; a motor including an armature shaft and an armature winding for rotatably driving the armature shaft such that the current through the armature winding is directly related to the load on the armature shaft and such that the speed of the armature shaft is directly related to the voltage across the armature winding and is inversely related to the load on the armature shaft, the armature shaft of the motor coupled with the impeller of the pump for rotatably driving the impeller such that when the load on the impeller is substantially constant at a maximum level in response to the absence of vapor bubble formation in the liquid the load on the armature shaft is likewise at a maximum level to maintain the current through the armature winding at a maximum level and to maintain the speed of the armature shaft at a minimum level and so that when the load on the impeller decreases in response to the onset of vapor bubble formation in the liquid the load on the armature shaft likewise decreases to decrease the current through the armature winding and to increase the speed of the armature shaft which in turn increases the speed of the impeller thereby initiating a regenerative speed increase/load decrease reaction on the impeller which if left to continue would lead to the development of a vapor lock condition about the inlet of the pump chamber so as to prevent the entry of fuel into the chamber; a resistor connected in series with the armature winding of the motor for reducing the voltage across the armature winding when the resistor is not bypassed; means responsive to the current through the armature winding of the motor for bypassing the resistor when the current through the armature winding is at a maximum level in response to the absence of vapor bubble formation in the liquid to maintain the voltage across the armature winding at a maximum level and for not bypassing the resistor when the current through the armature winding decreases due to the onset of vapor bubble formation in the liquid to increase the speed of the armature shaft which in turn decreases the speed of the impeller thereby terminating the regenerative speed increase/load decrease reaction on the impeller to prevent the development of a vapor lock condition about the inlet of the pump chamber so as to permit the entry of fuel into the chamber to increase the load on the impeller back to the maximum level.

2. In combination: a pump including a pump chamber having an inlet and an outlet and a pump impeller rotatably mounted within the chamber for drawing liquid into the chamber through the inlet and for pumping liquid out of the chamber through the outlet when the impeller is rotatably driven such that the load on the impeller is directly related to the density of the liquid which is substantially constant at a maximum level in response to the absence of vapor bubble formation and which decreases in response to the onset of vapor bubble formation thereby decreasing the load on the impeller; a motor including an armature shaft and an armature winding for rotatably driving the armature shaft such that the current through the armature winding is directly related to the load on the armature shaft and such that the speed of the armature shaft is directly related to the voltage across the armature winding and is inversely related to the load on the armature shaft, the armature shaft of the motor coupled with the impeller of the pump for rotatably driving the impeller such that when the load on the impeller is substantially constant at a maximum level in response to the absence of vapor bubble formation in the liquid the load on the armature shaft is likewise at a maximum level to maintain the current through the armature winding at a maximum level and to maintain the speed of the armature shaft at a minimum level and so that when the load on the impeller decreases in response to the onset of vapor bubble formation in the liquid the load on the armature shaft likewise decreases to decrease the current through the armature winding and to increase the speed of the armature shaft which in turn increases the speed of the impeller thereby initiating a regenerative speed increase/load decrease reaction on the impeller which if left to continue would lead to the development of a vapor lock condition about the inlet of the pump chamber so as to prevent the entry of fuel into the chamber; a resistor connected in series with the armature winding of the motor for reducing the voltage across the armature winding when the resistor is not bypassed; a relay including a pair of switching contacts connected across the resistor and a current sensor connected in series with the armature winding of the motor for closing the contacts so that the resistor is bypassed when the current through the armature winding is at a maximum level in response to the absence of vapor bubble formation in the liquid to maintain the voltage across the armature winding at a maximum level and for opening the contacts so that the resistor is not bypassed when the current through the armature winding decreases due to the onset of vapor bubble formation in the liquid to increase the speed of the armature shaft which in turn decreases the speed of the impeller thereby terminating the regenerative speed increase/load decrease reaction on the impeller to prevent the development of a vapor lock condition about the inlet of the pump chamber so as to permit the entry of fuel into the chamber to increase the load on the impeller back to the maximum level.