Electric Engine Coolant Heater

Abstract

A heater for warming coolant in a liquid-cooled engine, including a reservoir for coolant, the reservoir having an inlet and an outlet, a one-way inlet valve to permit coolant to enter the reservoir, a one-way outlet valve to permit coolant to leave the reservoir, a heating element in the reservoir, and a thermostat for controlling the heating element. The thermostat cuts out when the temperature of the coolant in the reservoir is above the boiling point of the coolant, so that the coolant is vaporized. After the heating element is turned off, the remaining vapor in the reservoir condenses, and the resulting partial vacuum draws in a fresh charge of coolant through the inlet, some of which proceeds immediately through the outlet to ram the heated coolant through the cooling system. The heating element is again energized and the cycle is repeated.

Description

This invention relates to a heater for prewarming the coolant of a liquid-coolant engine during cold weather when the engine is at rest.

Reliable starting of internal combustion engines (particularly automobile engines) in cold weather often requires the use of an auxiliary heater for warming the engine coolant. Such heaters employ electrical heating elements and they are energized by connecting them to the usual electrical mains. The heat provided by the auxiliary heater helps to lower the viscosity of the engine lubricant and to improve the vaporization of the fuel so that the engine is easier to crank and the fuel is easier to ignite. There are two types of such heaters which are in fairly general use: (1) the block heater, and (2) the tank heater. The block heater is designed to be inserted directly into the cooling system of the engine, for example through a frost plug. Although this type of heater is reasonably efficient, installation frequently poses difficulties even for mechanics having proper tools. Also, the block heater normally operates continuously, and frequently more power is consumed than actually is needed. The installation of tank heaters is relatively time consuming, particularly for the average car owner, and conventional tank heaters rely mainly on convection to heat the engine block. The resulting circulation of coolant does not always uniformly warm the engine.

The heater of the present invention is of the tank type. It is simple to install (the cooling system need not be drailed in most cases) and it provides a relatively strong flow of coolant to adequately heat the engine block. Furthermore, the supply of electricity to the heater is regulated so that only enough power is consumed to keep the engine coolant at a predetermined temperature.

A preferred form of the invention includes a reservoir having an inlet and an outlet, a one-way inlet valve to permit coolant to enter the reservoir, a one-way outlet valve to permit coolant to be expelled from the reservoir, a heating element in the reservoir and a thermostat electrically connected to the heating element. The thermostat has upper and lower temperature limits; at the upper limit the heating element is turned off, and at the lower limit the heating element is turned on. The upper limit is selected so that the coolant in the reservoir is vaporized, whereupon it is expelled forcibly through the outlet. The heating element turns off after much of the coolant in the reservoir has vaporized, and the remaining vapor in the reservoir condenses, creating a partial vacuum which draws in a fresh charge of coolant into the reservoir. The fresh charge enters the reservoir with considerable force, and a substantial portion of it passes through the outlet and tends to ram the heated coolant through the cooling system. When sufficient incoming coolant has entered the reservoir so that the temperature sensed by the thermostat has dropped to the lower limit, the heating element is again turned on and the cycle is repeated. An advantage of the present invention is that the reservoir can be connected in the cooling system of an automobile engine by simply cutting an existing hose leading from the interior heater and connecting the cut ends of the hose to the inlet and outlet of the reservoir. The time required for installation is comparatively short, and only simple tools are needed.

In the drawings which illustrate a preferred embodiment of the invention:

FIG. 1 is a perspective view, partly broken away, showing a heater;

FIG. 2 is a sectional view of a one-way outlet valve used in the heater of FIG. 1; and

FIG. 3 is an exploded view of an inlet valve used with the heater of FIG. 1 .

Referring to FIG. 1, a tank heater 10 is designed to be installed in the cooling system of a liquid-cooled internal combustion engine, particularly an automobile having an interior heater of the heat exchanger type. The interior heater is usually connected to the cooling system by a hose leading from the water pump of the engine. The heater 10 is conveniently installed by cutting said hose as near to the water pump as practicable and connecting the ends of the cut hose to the heater 10, as will be explained in more detail below.

The heater 10 includes a two-piece housing 12, a one-way inlet valve 14, a one-way outlet valve 16, a heating element 18, and a thermostat 20.

The housing 12 is of noncorrosive material, such as zinc or aluminum and it comprises a cylindrical shell 22 having an end wall 24 in which an outlet opening is formed, and an end member 26 which can be secured to the shell 22 by any conventional means (not shown) to provide a liquidtight seal. The shell 22 and the end member 26 when joined together form a reservoir into which coolant is drawn, heated until it vaporizes and then expelled, as discussed below. The end wall 24 of the shell 22 is formed with a generally cylindrical, tubular, open-ended boss 28 which extends both inwardly and outwardly of the end wall 24. The boss 28 constitutes an outlet for the tank 10. The outer end of the boss 28 is internally threaded to receive an adapter 30 for accommodating hoses which will not fit onto the boss 28 directly. The boss 28 and the adapter 30 are respectively provided with grooves 32, 34 in their outer surfaces to facilitate the attachment of a hose with a conventional hose clip. The inner end of the boss 28 is shaped to receive the valve 12, as shown in FIG. 2, and explained more fully below.

The end member 26 of the housing 12 has an outwardly projecting, cylindrical, tubular, open-ended boss 36 the axis of which is preferably in line with the axis of the boss 28. The boss 36 constitutes an inlet for the tank 10. The outer end of the boss 36 is provided with internal threads for receiving an adapter 38 that is similar to the adapter 34, and likewise grooves 40, 42 are respectively provided in the outer surfaces of the boss 36 and the adapter 38 to facilitate attachment of a hose by means of conventional hose clamps. The inner end of the boss 36 is formed to receive the valve 14, as shown in FIG. 3 and explained more fully below.

The end member 26 includes an outwardly projecting generally semicylindrical portion 44 that is integral with an end wall 46. The portion 44 of the end member 26 opens outwardly, but it is closed by a removable cover plate 48 which can be held in place by screws or other conventional means. The cover plate 48 has a central opening through which an electrical cable (not shown) can be inserted. The inlet valve 14 includes a generally circular disc 50 the center of which is slightly dished, and which is preferably of aluminum or cadmium plated steel. The disc 50 is formed with two opposed, outwardly projecting tabs 52 (FIG. 3), and the inner end of the boss 36 is formed with recesses 54 for receiving the tabs 52 so that the disc 50 can hang downwardly with the tabs 52 in the recesses 54. The inner end of the boss 36 is further formed with a circular recess 56 that is slightly larger in diameter than the diameter of the disc 50, and the recess 56 terminates at its inner end in a shoulder 58 against which the disc 50 is seated when it is in its closed position. The disc 50 is held in place by a washer 60 (also preferably of aluminum or cadmium plated steel) that is frictionally engaged in a circular recess 62 formed in the outer end of the boss 36, and the internal diameter of the washer 60 is larger than the diameter of the disc 50 so that the disc 50 can freely swing upwardly through the washer 60 to an open position, where there is relatively little restriction to the flow of incoming coolant. The disc 50 fits rather loosely in place, but when the pressure in the reservoir builds up the disc 50 is pressed firmly against the shoulder 58 to thereby prevent any vapor from being expelled through the inlet of the heater 10.

The outlet valve 16 is very similar to the inlet valve 14, except that it is arranged so that the fluid is permitted to flow only out of the heater 10 and not into it. The valve 14 includes a disc 64 that is identical to the disc 50, and it hangs inside a recess formed in the boss 28 in a manner similar to the disc 50. In its open position, as shown in FIG. 2, the disc 64 can swing upwardly in the same direction as the disc 50. The disc 64 is held in place by a washer 66, but in this case the washer 66 has an internal diameter that is smaller than the diameter of the disc 64 so that the washer 66 constitutes a valve seat for the disc 64. In its closed position, as shown in solid lines in FIG. 2, the disc 64 is pressed against the outer surface of the washer 66.

The heating element 18 is conventional, and it may be in the form of a loop of one or more turns, which preferably is positioned near the bottom of the housing 12. The heating element 18 is provided with ends 68, 70 that are engaged in openings formed in the end member 26 of the housing 12, and the ends 68, 70 can be retained in place by swagging the surrounding metal of the end member 26 to provide a firm and leak proof seal. Electrical terminals 72, 74 respectively protrude from the ends 68, 70 of the heating element 18, and they are of course electrically insulated from the housing 12. The heating element 18 can be designed to operate at the usual main voltages (e.g. 110 or 220 volts AC).

The thermostat 20 is rigidly attached to the end wall 46 of the end member 26, between the ends 68, 70 of the heating element. The inner surface of the end wall 46 directly opposite the thermostat 20 is formed with a recess 75 which receives a portion of the heating element 18, so that there is reasonably good thermal contact between the outer surface of the heating element 18 and the thermostat 20. The thermostat 20 has two terminals 76, 78 and is connected in series with the heating element 18 by a lead (not shown) so that the heating element is controlled by the thermostat 20. The thermostat 20 has an upper limit at which the thermostat turns off the heating element 18 and a lower limit at which the heating element is turned on. The upper limit is such that coolant in the reservoir is vaporized before the heating element 18 is turned off; the lower limit determines the average temperature of the coolant in the cooling system. In a prototype of the heater 10, an upper limit of 250.degree. F. and a lower limit of 170.degree. F. was used; these limits were found to be satisfactory in a six cylinder engine with a 50 percent glycol antifreeze mixture, which was kept at an average temperature of 70.degree. F.

The heater 10 is most conveniently installed in a horizontal position, as this position usually involves little or no sharp bends in the connecting hoses. In addition, the heater 10 should be installed at about the upper level of the coolant in the engine block. If the heater 10 is installed too low, the coolant tends to circulate continuously by convection and the desired vaporization does not take place to the same extent. It is conceivable that the heater 10 could be installed vertically, with the inlet at the top, but this is not as desirable as the horizontal position in most automobile installations because the heater hose to which connection is made is most frequently horizontally disposed In most cases the installation of the heater 10 simply entails cutting the hose leading from the water pump to the interior heater and attaching the cut ends of the hose to the respective bosses 28 and 36, with the hose leading from the water pump connected to the outlet of the heater 10. The hose should be raised to at least the level of the top of the radiator to avoid loss of coolant. Hose clamps can then be installed to secure the hoses on the bosses 28 and 36. The engine should then be idled for several minutes to fill the heater 10 with coolant. Alternatively, the heater 10 could be filled with antifreeze before installation.

In operation, the heater 10 is connected with a suitable source of electrical power. When the temperature of the coolant in the reservoir of the housing 12 falls below the low limit of the thermostat 20, the heating element 18 is energized and it remains energized until most of the coolant in the reservoir is vaporized. The hot vapor is expelled through the outlet valve 16, and eventually condenses and mixes with the coolant downstream from the heater 10. When the high temperature limit of the thermostat 20 has been reached, the heating element is disconnected from the power source and remains disconnected until the temperature has again dropped to the low temperature limit. The remaining vapor in the reservoir condenses and the resulting partial vacuum draws in a fresh charge of coolant through the inlet valve 14. The fresh charge of coolant enters the reservoir with considerable force, and a considerable portion of it continues directly through the reservoir and the outlet valve. As explained above this action tends to ram the heated coolant through the cooling system. When the temperature drops to the low limit of the thermostat 20, the heating element again is energized and the cycle is repeated. It will thus be noted that the operation of the heating element 18 is not continuous, but instead is periodic. The average amount of power consumed depends on the ambient temperature, wind, etc., for example it was determined in a prototype heater that power consumption varies from about 850 watts at -20.degree. F. to 180 watts at +32.degree. F., to maintain an engine temperature of about 50.degree. F.

In a prototype of the heater, the separation between the valves was about 2 three-quarter inches, the diameter of the discs 50 and 64 was about one-half inch. The heating element 18 was rated at 850 watts.

Claims

What we claim as our invention is:

1. A heater for warming liquid coolant in a cooling system of an engine and for forcing said coolant through the cooling system without creating any appreciable convection current in said heater, said heater comprising:

a. an enclosed reservoir for containing liquid coolant, said reservoir having a fluid inlet and a fluid outlet to permit said reservoir to be connected in said cooling system with said coolant substantially filling said reservoir;

b. a one-way inlet valve in communication with said fluid inlet to permit coolant to flow into said reservoir and to prevent coolant from leaving said reservoir through said fluid inlet;

c. a one-way outlet valve in communication with said fluid outlet to permit heated coolant to leave said reservoir and to prevent coolant from entering said reservoir through said fluid outlet;

d. an electrical heating element coupled to said reservoir for heating said coolant; and

e. a thermostat having an upper limit and a lower limit, said thermostat being electrically connected to said heating element to control the supply of electricity to said heating element, said thermostat being positioned so that it is in thermal contact with the contents of said reservoir and is responsive to the temperature of said coolant in said reservoir in both its liquid and vapor states, the supply of electricity to said heating element being interrupted when the temperature sensed by the thermostat reaches said upper limit, and being resumed when said temperature falls to said lower limit, said upper limit being such that at least a portion of the liquid coolant in said reservoir is vaporized when said heating element is energized and heated coolant is expelled through said outlet, the heating element being disconnected from its supply of electricity by said thermostat when said upper limit has been reached, whereupon the temperature in said reservoir falls so that the vapor pressure in said reservoir drops substantially thereby drawing a fresh charge of liquid coolant into said reservoir through said fluid inlet.

2. A heater as claimed in claim 1 wherein said fluid inlet and said fluid outlet are substantially in alignment and said heating element is in said reservoir.

3. A heater as claimed in claim 2 wherein said inlet valve comprises a first disclike member positioned at the inner end of said fluid inlet against an end wall of said reservoir, said first disclike member being pivotally mounted and the inner end of said fluid inlet being shaped to provide a seat for said first disclike member when said first disclike member is pressed against said fluid inlet inner end.

4. A heater as claimed in claim 3 wherein said outlet valve comprises a second disclike member positioned at the inner end of said fluid outlet against an opposite end wall of said reservoir, said second disclike member being pivotally mounted, and a washer secured to said opposite end wall and positioned inwardly of said second disclike member to provide a seat for the same.

5. A heater as claimed in claim 2 wherein a portion of said heating element is adjacent to an inner surface of a wall of said reservoir, and said thermostat is in contact with an outer surface of said wall opposite said portion of said heating element, said wall being thermally conductive.

6. In combination with an engine cooling system containing liquid coolant, a heater for warming the liquid coolant and for forcing said coolant through the cooling system, the heater being positioned at about the upper level of coolant in the system so that the heater is substantially full of coolant; the heater comprising an enclosed reservoir for containing liquid coolant, said reservoir having a fluid inlet and a fluid outlet to permit said reservoir to be connected in said cooling system with said coolant substantially filling said reservoir; a one-way inlet valve in communication with said fluid inlet to permit coolant to flow into said reservoir and to prevent coolant from leaving said reservoir through said fluid inlet; a one-way outlet valve in communication with said fluid outlet to permit heated coolant to leave said reservoir and to prevent coolant from entering said reservoir through said fluid outlet; an electrical heating element coupled to said reservoir for heating said coolant; and a thermostat having an upper limit and a lower limit, said thermostat being electrically connected to said heating element to control the supply of electricity to said heating element, said thermostat being positioned so that it is in thermal contact with the contents of said reservoir and is responsive to the temperature of said coolant in said reservoir in both its liquid and vapor states, the supply of electricity to said heating element being interrupted when the temperature sensed by the thermostat reaches said upper limit, and being resumed when said temperature falls to said lower limit, said upper limit being such that at least a portion of the liquid coolant in said reservoir is vaporized when said heating element is energized and heated coolant is expelled through said outlet, the heating element being disconnected from its supply of electricity by said thermostat when said upper limit has been reached whereupon the temperature in said reservoir falls so that the vapor pressure in said reservoir drops substantially thereby drawing a fresh charge of liquid coolant into said reservoir through said fluid inlet.

7. Apparatus as claimed in claim 6 wherein said fluid inlet and said fluid outlet are substantially in alignment.