Heating device for vehicle using the coolant fluid circuit

In the heating mode, the fluid in the air conditioning circuit flows in a bypass branch avoiding the condenser. The evaporator then receives the fluid in the gaseous state and acts as a heat exchanger for dissipating the heat produced in the compressor. The heat dissipated by the evaporator can be used for heating the cabin when that which is produced by the propulsion engine of the vehicle is insufficient. In addition, the fluid pressure at the inlet of the evaporator, and therefor the calorific power produced by the latter, is adjusted by a pressure regulator disposed in the bypass branch.

CROSS-REFERENCE TO RELATED APPLICATIONS 
The present application claims the benefit of previously filed French 
patent application 96.01164 filed in France on Jan. 31, 1996 and PCT 
international application FR97/00083 filed on Jan. 17, 1997 to which the 
instant application corresponds. 
FIELD OF THE INVENTION 
This invention relates to a method for modifying the temperature of a 
stream of air to be delivered into the cabin of a vehicle, by heat 
exchange with an evaporator in which there flows a fluid which also passes 
through a compressor and through an expansion device, the said method 
including a cooling mode for cooling the stream of air, in which the said 
fluid is caused to flow through, in succession, the evaporator, the 
compressor, a condenser in which it yields heat to another medium, and an 
expansion device. 
BACKGROUND OF THE INVENTION 
Such a method is conventionally used for the air conditioning of the cabin 
of the vehicle, especially a vehicle having a heat engine or an electric 
motor. When heating of the air to be passed into the cabin is required, 
the heat produced by the engine is commonly used, for example by causing 
the stream of air in contact with a heating radiator through which a 
coolant fluid for the engine passes. 
When the engine is cold, it is not possible to draw heat from it for 
heating the cabin, and this delays the achievement of the desired 
temperature in the latter and is therefore detrimental to the comfort of 
the occupants. In some cases, the coolant liquid never does reach a high 
enough temperature during the journey to give a comfortable temperature in 
the cabin. 
In order to get the cabin up to temperature more quickly, recourse can be 
had to additional devices, in particular those comprising burners or 
electric radiators, which involve high costs. 
FR-A-2 717 126, on the other hand, proposes modification of the process by 
a heating mode for the stream of air, in which the fluid leaving the 
compressor is passed to the evaporator without passing through a 
condenser. 
The heating mode that can be used for heating the cabin, especially when 
the engine is cold, thus depends on the existing air conditioning 
installation with minor modifications. 
However, the calorific power generated in the heating mode is determined by 
the mass flow produced by the compressor, which is itself a function of 
the speed at which it is driven, and consequently a function of the 
running mode of the engine. This power can be either greater or less than 
that necessary for the heating of the cabin. In particular, in the event 
of starting at low temperature, the initial density of the fluid in the 
air conditioning circuit, and consequently the mass flow produced by the 
compressor, is insufficient to give satisfactory heating. 
BRIEF SUMMARY OF THE INVENTION 
The object of the invention is to adapt the calorific power produced by the 
evaporator to the heating demand of the vehicle, for all circumstances. 
The invention is directed in particular to a method of the kind defined in 
the introduction hereof, and provides that, in the heating mode, the 
pressure of the fluid at the inlet of the evaporator is so controlled as 
to regulate the calorific power produced, and, when the mass of fluid 
flowing in the evaporator is insufficient to provide the required 
pressure, fluid is transferred from the condenser into the evaporator. 
The invention firstly enables the calorific power to be adjusted up or down 
by virtue of the fluid pressure, and secondly it enables the reserve of 
fluid in the liquid state contained in the condenser to be used for 
augmenting the quantity of fluid flowing in the heating mode, in such a 
way as to augment the mass flow and the calorific power at a given speed 
of the compressor. 
Optional features of the invention, complementary or alternative, are set 
forth below: 
the fluid is expanded by an expansion device in the cooling mode and by a 
controlled pressure regulator, implementing the control of the pressure of 
the fluid at the inlet of the evaporator, in the heating mode. 
the evaporator acts as an evaporator in the cooling mode and acts only as a 
heat exchanger in the heating mode. 
the vehicle has a propulsion engine which releases heat in operation, and 
the heating mode is used for heating the cabin in those periods in which 
the heat released by the engine is insufficient for that purpose. 
The invention also provides an air conditioning installation for the cabin 
of a motor vehicle, comprising a fluid circuit having a first branch 
containing an evaporator followed by a compressor, a second branch 
containing a condenser, and a third branch containing no condenser, the 
second and third branches being in parallel with each other so as 
respectively to constitute, with the first branch, a cooling loop which 
also contains an expansion device interposed between the condenser and the 
evaporator, and a heating loop, together with flow diverting means for 
controlling the flow of fluid either into the cooling loop or into the 
heating loop, the installation further including means for delivering into 
the cabin air which has undergone heat exchange with the evaporator, 
characterized in that the heating loop contains a controlled pressure 
regulator adapted to enable the pressure of the fluid delivered into the 
evaporator to be fixed at a selected value, and in that fluid transfer 
means are provided for transferring into the heating loop, when the latter 
is established by the flow diverting means, some of the fluid contained in 
the second branch. 
The installation according to the invention may; include at least some of 
the following features: 
the expansion device and the pressure regulator are placed in the second 
branch and in the third branch respectively. 
the fluid transfer means comprise a fourth branch joining the second branch 
to a junction point located on the first branch between the outlet of the 
evaporator and the inlet of the compressor, and being adapted to enable 
fluid to flow exclusively from the second branch towards the said junction 
point, and a stop valve, which is interposed in the first branch between 
the evaporator and the junction point and which is controlled in such a 
way as to interrupt the flow of fluid exclusively when the heating loop is 
established by the flow diverting means, and for a limited period. 
the flow diverting means comprise a four-way valve connected to the 
downstream ends of the first and fourth branches and to the upstream ends 
of the second and third branches, being adapted to assume a first position 
in which it puts the first and second branches into mutual relationship so 
as to establish the cooling loop, and a second position in which it puts 
into relationship with each other, firstly the first and third branches so 
as to establish the heating loop, and secondly the second and fourth 
branches so as to activate the transfer means when the stop valve is 
closed. 
the four-way valve, in its first position, also puts into relationship with 
each other the third and fourth branches, and unidirectional flow means 
are provided for preventing flow of the fluid in the third branch towards 
the four-way valve. 
unidirectional flow means are provided for permitting flow of the fluid in 
the second branch, downstream of the condenser, only towards the 
evaporator and only at a given differential pressure. 
The features and advantages of the invention will be explained in greater 
detail in the following description, with reference to the attached 
drawings.

DETAILED DESCRIPTION OF THE INVENTION 
There flows in this circuit a fluid which passes from the liquid state to a 
gaseous state by absorbing heat, and from the gaseous state to the liquid 
state by yielding heat, as is normally the case in vehicle air 
conditioning installations. The components of the circuit are also 
normally found in these air conditioning installations. 
The circuit shown comprises three branches 1, 2 and 3 which are joined 
together at two junction points A and B. The branch 1 contains a 
compressor 4, which drives the fluid in it from the point A towards the 
point B, and an evaporator which is connected upstream of the compressor. 
The branch 2 contains, going from the point B towards the point A, a 
condenser 6, a bottle 7, a non-return valve 8 with integral differential 
pressure regulation, and an expansion device 10. A fluid accumulator 11 
and a stop valve 12 are interposed, in that order, in the branch 1 between 
the evaporator 5 and the compressor 4. In the branch 3, going from the 
point B towards the point A, there are connected a fluid reservoir 13, a 
non-return valve 14 and a pressure regulator 15, which is associated with 
a control unit 16. 
A fourth branch 17 of the circuit connects the point B to a point C in the 
branch 1 between the valve 12 and the compressor 4, and contains a 
non-return valve 18 which permits flow of the fluid only from the point B 
towards the point C. A four-way electromechanical valve 19 is located at 
the junction point B, so that its four ports 19-1, 19-2, 19-3 and 19-4 are 
connected respectively to the downstream end of the first branch, that is 
to say to the outlet of the compressor 4, to the upstream end of the 
second branch, that is to say to the inlet of the condenser 6, and to the 
upstream ends of the third and fourth branches. 
The electromechanical valve 19 is so controlled as to adopt two positions 
corresponding respectively to the two Figures. In that of FIG. 1, the 
valve puts into communication with each other, firstly its ports denoted 
19-1 and 19-2, and secondly its ports denoted 19-3 and 19-4. The fluid 
then flows in a closed loop constituted by the branches 1 and 2, with the 
non-return valves 14 and 18 preventing any flow between the other two 
branches. This loop, works as a conventional air conditioning circuit, 
with the fluid passing from the liquid state to the gaseous state in the 
evaporator 5 by absorbing heat, and from the gaseous state to the liquid 
state in the condenser 6 by yielding heat. The heat absorbed in the 
evaporator 5 can be taken, directly or indirectly, into a stream of air to 
be delivered into the cabin of the vehicle. 
In the configuration of FIG. 2, the valve 19 puts into communication with 
each other, firstly its ports 19-1 and 19-3, and secondly its ports 19-2 
and 19-4. The fluid therefore flows, when the valve 12 is open, in a 
closed loop constituted by the branches 1 and 3. The fluid then passes 
through the compressor 4, the pressure regulator 15 which provides 
pressure reduction, and the evaporator 5. The non-return valve 8 prevents 
it from reaching the condenser from the point A. Since it no longer passes 
through the condenser, the fluid remains permanently in the gaseous state. 
The evaporator 5 no longer works as an evaporator, but it does continue to 
act as a heat exchanger, enabling much of the heat produced by the 
compression of the fluid in the compressor 4 to be dissipated, and this 
heat can be used for heating the cabin when the heat engine of the vehicle 
is cold. In particular, since the fluid in circulation is at a temperature 
which is greater than ambient temperature, a stream of air to be delivered 
into the cabin can be heated by direct contact with the evaporator. 
The unit 16 controls the pressure regulator 15, in such a way as to obtain 
a desired fluid pressure at the outlet of the latter, and consequently at 
the inlet of the evaporator 5. In this connection, it is the pressure of 
the fluid entering the evaporator that determines the calorific power 
produced by the latter. The pressure setting is for example calculated 
from the temperature of the outside atmosphere and the temperature within 
the cabin. If the pressure at the outlet of the regulator 15 remains lower 
than the set value, the unit 16 causes the valve 12 to close momentarily. 
The fluid aspired by the compressor 4 then necessarily comes from the 
condenser 6 through the branch 17, and augments the mass of fluid 
contained in the loop 1, 3. The valve 12 is once again opened, for example 
at the end of a fixed closure time, or after the compressor has performed 
a fixed number of rotations since it was closed. The fluid pressure at the 
outlet of the valve 12 is now again higher than in the branch 17, and the 
flow in the latter is again interrupted. Circulation in the closed loop 1, 
3 is repeated with an increased mass of fluid, thus giving a corresponding 
increase, both in the pressure at the outlet of the regulator 15 and in 
the heat output from the evaporator 5.