Method For Managing A Hybrid Compressor Of An Air-conditioning Circuit

Abstract

The invention relates to a method for managing a hybrid compressor (10) for an air-conditioning circuit of a motor vehicle having a heat engine, said hybrid compressor being suitable for being driven, on the one hand, by said heat engine and, on the other hand, by an electric motor (20) during phases in which the drive of the compressor (10) by means of the heat engine is interrupted. According to the invention, during a phase in which the drive is interrupted, said method comprises starting said electric motor (20) before said drive interruption begins. The invention can be used for air-conditioning motor vehicles having a heat engine and provided with an automatic stopping and restarting system.

Description

[0001] The present invention relates to a method for managing a hybrid compressor for an air-conditioning circuit of an engined motor vehicle.

[0002] The invention finds a particularly advantageous application in the field of the air-conditioning of engined motor vehicles equipped with an automatic stopping and restarting system, such as the systems able to implement the function known by the term "Stop and Start".

[0003] The "Stop and Start" function consists, under certain conditions, in automatically causing the complete stopping of the engine when the vehicle itself has stopped, and then in automatically restarting the engine following, for example, an action of the driver interpreted as a restart request.

[0004] A typical situation for implementing the "Stop and Start" function is that of stopping at a red light. When the vehicle stops at the light, the "Stop" mode of the "Stop and Start" function causes the automatic stopping of the engine, and the vehicle then enters the "Start" mode which allows the engine to restart automatically without it being necessary to use the means for initial starting of the motor, such as a contact key for example. When the light turns green, the "Start" mode automatically restarts the motor, especially by means of an alternator-starter, following the detection by the command system upon the starting of the vehicle of the depression by the driver of the clutch pedal, of the accelerator pedal, or else of any other action that can be interpreted as the driver's desire to restart his vehicle. The benefit of the "Stop and Start" function is understood in terms of energy saving and pollution reduction, particularly in urban surroundings.

[0005] Moreover, it is known that an air-conditioning circuit of an engined vehicle comprises a refrigerant fluid compressor which is driven by the shaft of the crankshaft of the engine by way of a belt and a pulley linked mechanically to the rod of the compressor. Stated otherwise, the air-conditioning circuit of the vehicle can only operate if the engine is driving the compressor. Consequently, during the vehicle stopping phases in the context of the "Stop and Start" function, the compressor is no longer driven by the engine and the air-conditioning ceases to operate. It follows from this that in the course of these stopping phases the setpoint temperature inside the cabin may not be maintained, and this can cause a feeling of discomfort for the passengers of the vehicle.

[0006] To ensure the maintaining of the temperature in the cabin during the phases of stopping of driving of the compressor by the engine, it is proposed to replace, for example, the usual compressor driven by the engine of the vehicle by a hybrid compressor consisting of two separate compression chambers, constituting, on the one hand, a so-called mechanical compressor whose rod is driven by the engine in the same manner as the usual compressor and, on the other hand, a so-called electric compressor whose rod is driven by an auxiliary electric motor. The rods of two compression chambers are independent.

[0007] When the engine is running, outside of the stopping phases determined by the "Stop and Start" function, the refrigerant fluid circulates in the air-conditioning circuit through the mechanical compressor driven by the shaft of the crankshaft of the engine, while the electric compressor is turned off. Conversely, during the phases of stopping of the "Stop and Start" function, the refrigerant fluid is directed toward the electric compressor, which is then driven by the electric motor. Thus, by virtue of the electric compressor, the continuity of operation of the air-conditioning circuit and the maintaining of the comfort temperature in the cabin are carried out when the engine has stopped.

[0008] It is necessary, however, to note that during the phases of stopping of the air-conditioning circuit, especially the engine stopping phases imposed by the "Stop and Start" function, the cabin is in general already conditioned in comfort conditions, so that the refrigerative power to be provided by the electric motor so as to maintain these conditions for a duration limited to a few tens of seconds is lower, at least by a factor of 2 to 3, than the power that must be provided by the engine. It is therefore possible to use for the electric compressor a compression chamber of reduced capacity driven by an electric motor of low power.

[0009] However, when the air-conditioning circuit is taken out of operation following an interruption of the driving of the mechanical compressor by the engine, rearrangements of pressure of the refrigerant fluid can occur along the air-conditioning circuit, which are liable to create a resistive torque which the electric motor must oppose at the moment at which it is harnessed to deputize for the stopping of the driving of the mechanical compressor by the engine. Under these conditions, however, the power necessary to overcome this resistive torque can become greater than the sufficient power that the electric motor must develop in order to maintain cabin comfort.

[0010] Hence, an aim of the invention is to propose a method for managing a hybrid compressor for an air-conditioning circuit of an engined motor vehicle, said hybrid compressor being able to be driven, on the one hand, by said engine, and, on the other hand, by an electric motor during phases of interruption of driving of the compressor by the engine, which would make it possible to circumvent the difficulty represented by the use of an electric motor of too low power in regard to the resistive torque induced by the variations in refrigerant fluid pressure during the stoppage of the air-conditioning circuit.

[0011] This aim is achieved, in accordance with the invention, because said method consists, during a driving interruption phase, in starting said electric motor before the commencement of said driving interruption.

[0012] Thus, the electric motor is set into operation by anticipation, before the engine stops driving the compressor and therefore before the air-conditioning circuit ceases to operate. The electric motor does not therefore have to overcome the diverse variations in refrigerant fluid pressure which appear in the air-conditioning circuit following the complete stopping of the air-conditioning circuit. It is then possible, without any drawback, to use an electric motor of low power.

[0013] According to a first embodiment of the invention, in which said hybrid compressor comprising a first refrigerant fluid compression chamber comprising a first compression rod able to be driven by said engine and a second refrigerant fluid compression chamber comprising a second compression rod able to be driven by said electric motor, said method comprises steps consisting in detecting by anticipation a phase of interruption of driving of the first compression rod by the engine, in switching the refrigerant fluid from the first to the second compression chamber, and in starting the electric motor before the commencement of the interruption of driving of the first compression rod by the engine.

[0014] This first embodiment is implemented especially when said driving interruption is a stopping of the engine, and, more specially, when said stopping of the engine is an automatic stopping determined by a function for automatic stopping and restarting of the engine of the vehicle, such as the "Stop and Start" function.

[0015] According to a second embodiment of the invention in which said hybrid compressor comprising a variable-capacity refrigerant fluid compression chamber comprising a single compression rod able to be driven by the engine in a higher interval of capacities and by the electric motor in a lower interval of capacities, said method comprises steps consisting in detecting by anticipation a phase of interruption of driving of the compression rod by the engine, in switching the capacity of the compression chamber from the higher interval to the lower interval of capacities, and in starting the electric motor before the commencement of the interruption of driving of the compression rod by the engine.

[0016] The invention provides, generally, that said driving interruption is a decoupling of the engine from a compression rod of the hybrid compressor, and, more specially, that the decoupling of the engine is determined by a function for automatic stopping and restarting of the engine of the vehicle, such as the "Stop and Start" function, or by a vehicle acceleration request.

[0017] In the case of a hybrid compressor with two separate compression chambers, the decoupling is performed between the engine and the first compression rod, while in the case of a hybrid compressor with a variable-capacity compression chamber, the decoupling is performed between the engine and the single compression rod of the chamber.

[0018] In practice, the starting of the electric motor before the commencement of the interruption of driving of the hybrid compressor by the engine is carried out by means for detecting stopping of the engine of a function for automatic stopping and restarting of the engine of the vehicle, or by means for detecting a vehicle acceleration request.

[0019] Within the framework of the "Stop and Start" function, these detection means may be extremely varied and depend generally on the strategy chosen by constructors. It is possible to cite for example the detection of an action on the brake pedal when the speed of the vehicle goes below a given threshold.

[0020] The description which follows with regard to the appended drawings, which are given by way of nonlimiting examples, will elucidate the invention and the manner in which it may be embodied.

[0021] FIG. 1 is a diagram of an air-conditioning circuit comprising a hybrid compressor of a first type.

[0022] FIG. 2 is a diagram of an air-conditioning circuit comprising a hybrid compressor of a second type.

[0023] FIG. 3 is a chart illustrating the operation of the hybrid compressors of FIGS. 1 and 2 for various life situations of a motor vehicle equipped with the "Stop and Start" function.

[0024] FIG. 4 is a chart illustrating the operating chronology of the engine and electric motor of the hybrid compressors of FIGS. 1 and 2 during automatic stopping of the engine by the "Stop and Start" function,

[0025] In FIG. 1 is represented a conventional air-conditioning circuit of an engined motor vehicle, comprising a compressor 10 of a refrigerant fluid which may be an organic, inorganic or eutectic fluid. It is possible to cite as nonlimiting examples supercritical carbon dioxide CO2, the refrigerants known by the references R134A, 1234yf or else GAR ("Global Alternative Refrigerant"). Downstream of the compressor 10, the pressurized refrigerant fluid passes through a heat exchanger 11 called a "gas cooler" for carbon dioxide or a "condenser" for R134A since, in this case, the refrigerant initially in the gas phase exits the condenser in liquid form.

[0026] In the example of FIG. 1, the exchanger 11 may be a water-type exchanger, or an air-type exchanger cooled directly by the outside air.

[0027] The refrigerant fluid is thereafter conducted toward a relief valve 12 so that it is cooled before entering the evaporator 13 where heat exchange then occurs between the cooled refrigerant and air blown toward the cabin of the vehicle.

[0028] The refrigerant fluid, reheated on output from the evaporator 13, is then returned to the compressor 10 to perform a new thermal cycle.

[0029] As may be seen in FIG. 1, the compressor 10 of FIG. 1 is a hybrid compressor of the type with two separate compression chambers, namely, on the one hand, a first chamber 101 comprising a first compression rod 111 able to be driven by the shaft of the crankshaft of the engine (not represented) of the vehicle via a belt and a pulley 30 linked mechanically to the rod 111 by way of a clutch 31, and, on the other hand, a second chamber 102 comprising a second compression rod 112, independent of the first rod 111, able to be driven by an electric motor 20.

[0030] During nominal operation of the air-conditioning circuit, the rod 111 of the first compression chamber 101 is driven by the engine, the pulley 30 being coupled to the rod 111 by the clutch 31. The refrigerant fluid then circulates through the first chamber 101 whose capacity, of the order of 100 cm.sup.3, is chosen so as to allow the hybrid compressor 10 to ensure an optimal comfort level inside the cabin of the vehicle, whatever the outside temperature, the sunshine and the degree of relative humidity.

[0031] However, it can happen, in certain circumstances, that the air-conditioning compressor 10 is no longer driven by the engine of the vehicle and that, consequently, the air-conditioning circuit ceases to operate and can no longer guarantee the maintaining of the comfort temperature inside the cabin. Such is the case especially during the engine stopping phases determined by a system for automatic stopping and restarting of the engine able to implement the "Stop and Start" function of the vehicles equipped with this function.

[0032] In order to ensure continuity of air-conditioning in the cabin, the circulation of refrigerant fluid is switched from the first chamber 101 to the second chamber 102 by a valves device internal to the hybrid compressor 10, and then the electric motor 20 is started so as to drive the second compression rod 112 and maintain the air-conditioning circuit in operation during these stopping phases.

[0033] When the electric motor 20 takes over from the then stopped engine, the cabin of the vehicle is in principle already at the comfort temperature, so that, having regard to the fact that the duration of the stopping phases is generally limited to a few tens of seconds, the refrigerative power to be provided by the electric motor 20 is relatively low. By way of example, in a conventional manner, a refrigerative power of 6 kW is necessary in order to guarantee comfort in the cabin of a vehicle exposed to a high temperature of 25 to 45.degree. C. under sunshine of 1000 W.m.sup.2 and relative humidity of 50 and 60%. However, when the vehicle is already conditioned to the comfort temperature, the refrigerative power to be provided lies between 1 kW and 3 kW depending on the segment of the vehicle.

[0034] Consequently, the capacity of the second compression chamber 102 can be limited, with respect to the capacity of the first chamber 101, to values of about 20 cm.sup.3 for example.

[0035] In the chart of FIG. 3 have been represented the operating states of the engine and of the electric motor 20 for driving the hybrid compressor 10 of a motor vehicle equipped with the "Stop and Start" function, the value 0 corresponding to the stopping of the motor and the value 1 to its operation.

[0036] As may be seen in this figure, when the first compression rod 111 is no longer driven by the engine because the latter is stopped automatically in accordance with the "Stop and Start" function, the electric motor 20 is set into operation so as to drive the rod 112 of the second compression chamber 102 and thus ensure maintenance of the comfort in the cabin during the engine stopping phase.

[0037] However, it is necessary to emphasize that, under these conditions, the electric motor 20 must provide, on starting, sufficient torque to overcome the resistive torque induced by the rearrangements of refrigerant fluid pressure which occur in the air-conditioning circuit at the moment of the stopping of the engine. The torque to be provided by the electric motor 20 then becomes very significant and demands higher powers than those which are strictly necessary to ensure the maintaining of the air-conditioning.

[0038] Hence, to avoid a superfluous over-rating of the electric motor 20, the invention proposes a method for managing the hybrid compressor 10 comprising the steps consisting in detecting by anticipation a phase of interruption of driving of the first compression rod 111 by the engine, in switching the refrigerant fluid from the first 101 to the second 102 compression chamber, and in starting the electric motor 20 before the commencement of the interruption of driving of the first compression rod 111 by the engine. In this way, the electric motor 20 is set into operation before the stopping of the air-conditioning circuit and therefore before the occurrence of any pressure rearrangements in the air-conditioning circuit. The power of the electric motor 20 can therefore be rated accordingly.

[0039] To carry out the anticipation of the starting of the electric motor 20, it is possible to use the means implemented by the "Stop and Start" function to detect whether the engine stopping conditions are satisfied and impose a stopping of the engine if these conditions are satisfied.

[0040] This is what is represented by FIG. 4 in which it is seen that as soon as conditions of automatic stopping of the engine are detected by the "Stop and Start" function, a signal of anticipation of starting of the electric motor 20, generated for example by the onboard computer, is dispatched before the actual stopping of the engine toward the control circuit of the electric motor through the vehicle's CAN ("Car Area Network") network. The conditions of automatic stopping of the engine depend on the strategy adopted by the vehicle constructor. It is possible to cite, inter alia, an action on the brake pedal when the vehicle is traveling at low speed, less than 5 km/hour for example.

[0041] FIG. 4 shows another circumstance in which the electric motor 20 may be set into operation so as to guarantee the continuity of the comfort temperature during a stoppage of the air-conditioning circuit. This situation is that of an acceleration of the vehicle when requiring the best response to the acceleration request by applying a maximum torque to the shaft of the crankshaft, obtained by recovering the resistive torque due to the driving of the compressor. In this circumstance, the interruption of the driving of the first compression chamber 101 is not related to a stopping of the engine, but to the decoupling of the pulley 30 for driving the compression rod 111 of the chamber.

[0042] In this case, the electric motor 20 is started as soon as the acceleration request is detected by usual detection means and before the engine is actually decoupled from the compression rod 111.

[0043] In FIG. 2 is represented a hybrid compressor 10' of the type comprising a variable-capacity compression chamber 100 whose rod 110 may be driven, either by the electric motor 20, or by the shaft of the crankshaft of the engine (not represented) of the vehicle via a belt and the pulley 30 able to be linked mechanically to the rod 110 by way of the clutch 31.

[0044] It is necessary to emphasize here that this architecture of hybrid air-conditioning compressor is distinguished from the compressor of FIG. 1 by the fact that it implements only a single compression chamber and a single rod that can equally well be driven by the engine or by the electric motor, instead of two separate compression chambers of independent rods.

[0045] During nominal operation, the rod 110 of the compression chamber 100 is driven by the engine, the pulley 30 being coupled to the rod 110 by the clutch 31. The capacity of the compression chamber is then chosen in a higher interval of values close to the maximum capacity, of the order of 100 cm.sup.3 for example. Under these conditions, the hybrid compressor 10' is capable of ensuring an optimal comfort level inside the cabin of the vehicle, whatever the outside temperature, the sunshine and the degree of relative humidity.

[0046] However, it can happen, just as for the hybrid compressor 10 with two chambers of FIG. 1, that the air-conditioning compressor 10' is no longer driven by the engine of the vehicle and that, consequently, the air-conditioning circuit ceases to operate and no longer ensures maintenance of the comfort temperature inside the cabin. Such is the case, as seen above, during the engine stopping phases determined by a function for automatic stopping and restarting of the "Stop and Start" type, or during the vehicle acceleration request phases.

[0047] In order to ensure continuity of air-conditioning in these circumstances, the electric motor 20 is set into operation during the phases of stopping of driving of the compressor 10' by the engine. Stated otherwise, it may be considered that the electric motor 20 then substitutes itself for the engine in its function of driving the compression chamber 100. Of course, the engine is, preferably, disengaged from the compression rod 110.

[0048] It was already mentioned above that the refrigerative power to be provided by the electric motor 20 during operation is relatively low.

[0049] Consequently, the capacity of the compression chamber 100 may be reduced, with respect to the nominal operating conditions, to values lying in a lower interval of capacities of about the minimum capacity of 20 cm.sup.3 for example.

[0050] Of course, the higher and lower intervals of capacities may be reduced simply to the maximum and minimum capacities alone. The compression chamber 110 then switches in a binary manner between these two capacities depending on whether the motive drive for the rod of the chamber is the engine or the electric motor.

[0051] Having regard to the fact that the power requested of the electric motor 20 is relatively low, it is possible to envisage the use of an electric motor, with or without brushes, supplied by a low-voltage direct current provided, in particular, by the 12 V network of the vehicle, it being possible for the electric current source to be a battery 40 or an extra unit furnished or not with a storage capacitor.

[0052] In a practical manner, the variable-capacity compression chamber 100 may be embodied by a conventional compression chamber with vanes whose intake volume, corresponding to the capacity, can be adjusted between the minimum value of 20 cm.sup.3, for example, and the maximum value of 100 cm.sup.3, for example, by varying the position of the intake orifice in the chamber.

[0053] Just as for the hybrid compressor 10 of FIG. 1, it is possible to avoid the electric motor 20 having to provide a torque increased by the resistive torque resulting from the rearrangements of refrigerant fluid pressure upon the stopping of the air-conditioning circuit by the implementation of a method for managing the hybrid compressor 10' comprising steps consisting in detecting by anticipation a phase of interruption of driving of the compression rod 110 by the engine, in switching the capacity of the compression chamber 100 from the higher interval to the lower interval of capacities, and in starting the electric motor 20 before the commencement of the interruption of driving of the compression rod 110 by the engine.

[0054] Whether the interruption of driving of the compressor 10' by the engine is due to an automatic stopping determined by the "Stop and Start" function or to an acceleration request, the transition between the driving of the compression rod 110 by the engine and driving by the electric motor 20 is performed by decoupling the pulley 30 from the compression rod 110 by means of the clutch 31.

[0055] The sought-after anticipation for setting the electric motor 20 into operation is obtained, in accordance with FIG. 4, by starting the electric motor before the actual decoupling of the engine from the compression rod 110.

[0056] The means for detecting a stopping of the engine or an acceleration request are the same as those used for the compressor 10 of FIG. 1, as is the control of the electric motor 20 by a starting anticipation signal.

Claims

1. A method for managing a hybrid compressor for an air-conditioning circuit of an engine motor vehicle, the hybrid compressor being able to be driven by said engine and by an electric motor during phases of interruption of driving of the compressor by the engine, the method comprising: during a driving interruption phase, starting said electric motor before commencement of said driving interruption.

2. The method as claimed in claim 1, wherein the hybrid compressor comprises: a first refrigerant fluid compression chamber comprising a first compression rod able to be driven by said engine, and a second refrigerant fluid compression chamber comprising a second compression rod able to be driven by said electric motor, wherein the method further comprises: detecting by anticipation a phase of interruption of driving of the first compression rod by the engine, switching the refrigerant fluid from the first to the second compression chamber, and starting the electric motor before commencement of the interruption of driving of the first compression rod by the engine.

3. The method as claimed in claim 1, wherein the hybrid compressor comprises: a variable-capacity refrigerant fluid compression chamber comprising a single compression rod able to be driven by the engine in a higher interval of capacities and by the electric motor in a lower interval of capacities, wherein the method further comprises: detecting by anticipation a phase of interruption of driving of the compression rod by the engine, switching the capacity of the compressing chamber from the higher interval to the lower interval of capacities, and starting the electric motor before commencement of the interruption of driving of the compression rod by the engine.

4. The method as claimed in claim 2, wherein said driving interruption is a stopping of the engine.

5. The method as claimed in claim 4, wherein said stopping of the engine is an automatic stopping determined by a function for automatic stopping and restarting of the engine of the vehicle ("Stop and Start").

6. The method as claimed in claim 2, wherein said driving interruption is a decoupling of the engine from a compression rod of the hybrid compressor.

7. The method as claimed in claim 6, wherein the decoupling of the engine is determined by a function for automatic stopping and restarting of the engine of the vehicle ("Stop and Start").

8. The method as claimed in claim 6, wherein the decoupling of the engine is determined by a vehicle acceleration request.

9. The method as claimed in claim 1, wherein the starting of the electric motor before the commencement of the interruption of driving of the hybrid compressor by the engine is carried out by means for detecting stopping of the engine of a function for automatic stopping and restarting of the engine of the vehicle ("Stop and Start").

10. The method as claimed in claim 8, wherein the starting of the electric motor before the commencement of the interruption of driving of the hybrid compressor by the engine is carried out by means for detecting a vehicle acceleration request.