GB2125156A

GB2125156A - Heat storage in motor vehicles

Info

Publication number: GB2125156A
Application number: GB08223249A
Authority: GB
Inventors: E M Rowbotham
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1982-08-12
Filing date: 1982-08-12
Publication date: 1984-02-29

Abstract

The invention relates to the use in a motor vehicle of a phase change material as a heat storage medium. The phase change material is one which can exist in two phases and which the reaction to change from one phase to another is reversible and exothermic in one direction. The phase change material can be employed to heat the manifold, battery, coolant, lubricant, fuel or passenger compartment when the vehicle is started from cold so as to improve the overall efficiency.

Description

SPECIFICATION Heat storage in motor vehicles The present invention relates to heat storage in motor vehicles.

Motor vehicle engines generate heat during operation and a substantial amount of this energy is wasted. Indeed special steps have to be taken to dissipate the heat to prevent the engine from over heating. However, there are also several instances in a motor vehicle where energy is expended in order to generate heat or else the engine runs inefficiently through lack of heat.

The present invention in its broadest aspect proposes the use in a motor vehicle of a phase change material as a heat storage medium.

The term phase change material is used here to describe a material which can exist in two phases and in which the reaction to change from one phase to another is reversible and is exothermic.

Examples of such phase changes are the freezing of a super-cooled liquid and the crystallisation of a super-saturated salt solution. In the latter case, the phase is not purely a physical one but a chemical one with the salt changing its degree of hydration. To store energy, the phase change material is heated so as to cause a change of phase and to release the stored energy when required the material is triggered to return to its original phase.

A first example of energy being wasted on starting is the inefficient use of fuel due to insufficient vapourisation of the fuel in the inlet manifold. During cold start, because of such inefficient vapourisation and combustion, it is usual to enrich the mixture by the use of a choke which results in increased fuel consumption.

In accordance with a second aspect of the present invention, an inlet manifold for a motor vehicle is provided with a jacket containing a phase change material operative to undergo a phase change during cold starting to heat the inlet manifold.

The use of a phase change material offers several important advantages in the context of a motor vehicle. First, the heat is not stored by merely raising the temperature of a storage medium and is not therefore lost if the vehicle should be allowed to remain standing for any length of time. Secondly, the release of the stored energy can be controlled by triggering the phase change reaction, so that a substantial amount of heat can be made available quickly whenever desired. Furthermore, the temperature after triggering may also be controlled by the choice of phase change material.

The phase change can be triggered by any convenient form of nucleation of the freezing or the crystallisation of the liquid. For example, a seed may be introduced into the liquid and withdrawn electromagnetically to initiate the reaction. Alternatively, it is believed that it may be possible to commence the phase change by radiation to form a nucleation site. This may be achieved electronically by means of high frequency radiation or possibly ultrasonic radiation.

As an example of a suitable phase change material, one can use sodium acetate trihydrate in super saturated solution. There are however numerous salts from which to choose and the optimum choice in each case depends upon the temperature which one wishes to generate, sodium acetate being appropriate for an inlet manifold.

In a motor vehicle, a substantial current is required on starting from cold but a low temperature reduces the output of the battery.

In accordance with a second aspect of the present invention, there is provided a battery for use in a motor vehicle having a compartment or a jacket filled with a phase change material.

The phase change material used in a battery will typically be designed to raise the temperature of the battery to normal ambient temperature. The phase change material may be in the form of sealed bags placed in the electrolyte or may even be contained in the separater plates. It is merely important that the phase change material should be in intimate thermal contact with the electrolyte and that the phase change material should be heated to revert to its metastabie state after a period of normal use.

According to a further aspect of the present invention, there is provided an engine incorporating a phase change material for raising the temperature of the coolant or the lubricant during cold starting.

To raise the temperature of the lubricant, a matrix containing the phase change material may be disposed within the sump of an engine or the oil may be circulated through such a matrix after it has been triggered to raise its temperature.

Raising the temperature of the oil reduces its viscosity and once again improves the efficiency of the engine on cold starting.

The same method when used to heat the coolant, that is to say the water, can assist the operation of the thermostat to raise the temperature of the engine block so as to reduce the time taken to reach normal operating temperatures.

As so far described, the invention has proposed various utilisations of a phase change material to increase overall efficiency and reduced petrol consumption especially during cold starting.

Phase change materials can however have further uses in motor vehicles in particular to improve the comfort in the passenger compartment during cold start. Thus a heat exchanger filled with a phase change material may be used in conjunction with the blower to provide hot air in the passenger compartment during cold starting before the temperature of the water has reached a sufficient level to enable the heater to function properly.

This can also assist and improve demisting and defrosting during cold starting.

A still further possible utilisation of a phase change material in a motor vehicle is for raising the temperature of the windscreen washing fluid.

Furthermore, in extremely cold climates a phase change material may be employed in the fuel tank to prevent freezing of the fuel.

Claims

1. A motor vehicle comprising a phase change material arranged to be heated under normal engine operating conditions and means for triggering an exothermic phase change in the phase change material to release heat when required.

2. A motor vehicle as claimed in Claim 1, wherein the phase change material is arranged in thermal contact with the inlet manifold and is operative to heat the inlet manifold to vaporise fuel when the engine is started from cold.

3. A motor vehicle as claimed in claim 2, wherein the phase change material is arranged in a jacket surrounding the inlet manifold.

4. A motor vehicle as claimed in Claim 1, wherein the phase change material is arranged in thermal contact with the battery to heat the battery cells when starting from cold.

5. A motor vehicle as claimed in claim 4, wherein the phase change material is arranged within a battery compartment.

6. A motor vehicle as claimed in Claim 1, wherein the phase change material is provided for raising the temperature of the engine coolant or the lubricant during cold starting.

7. A motor vehicle as claimed in Claim 1, wherein the phase change material is provided for heating the passenger compartment during starting from cold.

8. A motor vehicle as claimed in Claim 1, wherein the phase change material is arranged in thermal contact with a fluid employed in the motor vehicle to prevent freezing of the fluid or to melt the fluid if frozen.

9. A motor vehicle as claimed in any preceding claim, wherein the means for triggering a phase change reaction comprises means for introducing a seed into the material.

10. A motor vehicle as claimed in any of claims 1 to 8, wherein the means for triggering a phase change reaction comprises means for exposing the material to an energy beam.