In the typical automobile propelled by an internal combustion engine, there is placed in the engine compartment adjacent the engine a rechargeable storage battery. This battery supplies dc power for starting the car, for energizing the car lights and for powering other devices requiring dc power.
Because of the close proximity of the battery to the engine, it is exposed to heat at an elevated temperature emanating from the engine. When the engine has been operating for several hours, the heat of the engine developed during this period and transferred to the storage battery may impair its operation.
A conventional rechargeable storage battery for an automobile is identified as a lead-acid battery. The reason for this denomination is that the electrolyte of the battery is an acid and its plates are largely formed of a lead-based composition. The positive active electrode material of the battery is lead peroxide and the negative active electrode material is lead sponge.
When these electrodes are immersed in a sulfuric acid electrolyte (H2SO4—H2O), an electromotive force (EMF) is then developed between the electrodes. In an auto storage battery, each cell thereof produces a nominal voltage of 2 volts. Since the battery must provide a 12 volt output, it includes six 2 volt cells connected in a series. However, the voltage yielded by each storage battery cell is not exactly 2 volts but varies as a function of the concentration of the sulfuric acid electrolyte and its temperature.
As noted in the section “Storage Battery” in Vol. 17 page 443 of the McGraw-Hill Encyclopedia of Science and Technology, when the concentration of the storage battery electrolyte is 1200 spgr and the electrolyte temperature is at 25° C. (77° F.), then the cell voltage is 2.050V. But when at the same temperature, the acid concentration is 1300 spgr, then the output voltage of the cell increases to 2.148V.
Variations in the temperature of the electrolyte give rise to less dramatic changes in the cell voltage. Thus a small change in the temperature of the electrolyte produces only a slight change in cell output voltage in the millivolts range. However, should the electrolyte in a battery placed in the engine compartment of an automobile undergo a steep rise in temperature because of intense heat emanating from the engine, then the output of the battery cell may is fall below 2 volts. This results in a drop in the output voltage of the multi-cell battery so that it is then below its nominal 12 volt value. As a consequence, the battery in this overheated condition may be unable to carry out all of its assigned tasks.
One could try to prevent the electrolyte in a storage battery placed in an engine compartment from overheating by enveloping the battery in a thermal jacket composed of thermal insulation material. But in the environment of an auto engine compartment, a thermal jacket can only function to slow down the rate of heat transfer from the engine to the battery. It cannot prevent a gradual increase in electrolyte temperature resulting from prolonged operation of the engine in the course of which the battery is subjected to heat at high temperature levels.
In the context of a thermal jacket worn by an individual to keep his body warm in a cold environment, the jacket then functions to reduce the loss of heat from the body whose temperature is internally regulated so that it normally is at a temperature of about 37° C. But a storage battery is not internally heated nor cooled. If, therefore, one wishes to prevent a storage battery in the environment of an automobile engine compartment from overheating, it then becomes necessary to cool the battery.
It is known in the prior art to cool the battery of a vehicle to prevent it from overheating. Thus U.S. Pat. No. 5,937,664 to Takayoshi et al. (1998) discloses a battery cooling system for a vehicle whose passenger compartment is cooled by an air conditioner. The vehicle battery is placed in a separate chamber and there cooled by air drawn by a cooling fan from the air-conditioned passenger compartment and blown into the battery chamber.
The practical drawback to this arrangement is that it makes it necessary to create a special chamber for the battery as well to provide an air circulating system between this chamber and the passenger compartment.