FR3082695A1 - HEATING DEVICE COMPRISING AT LEAST TWO HEATING ELEMENTS - Google Patents

Abstract

The present invention relates to a heating device (20) comprising: - at least two heating elements (1, 2) configured to heat a fluid circulating in contact with the heating elements (1,2), - a control device (5) arranged to control each heating element (1,2) independently of the other heating element (2,1).

Description

Heating device comprising at least two heating elements

The present invention relates to an electric heating device for a motor vehicle, for heating a fluid. The heating device can be integrated into a thermal regulation system for the air blown into the passenger compartment of the vehicle. The invention also relates to a method for controlling the heating device.

The temperature and the quality of the air included in the passenger compartment of a motor vehicle is managed by a heating, ventilation and / or air conditioning system, usually designated by the acronym HVAC, meaning "Heating, ventilation and / or air conditioning ".

This heating installation includes a heat exchanger through which a heat transfer fluid is heated by the heat losses of the vehicle's heat engine. The air blown into the passenger compartment passes through this heat exchanger and can therefore be heated before arriving in the passenger compartment.

During the first minutes of operation of the vehicle, in cold ambient temperature, the heat engine is not hot enough to be able to provide the heat necessary to obtain the desired set temperature for the passenger compartment. The passenger compartment therefore remains at a cooler temperature than the setpoint for a period depending on the conditions of use of the vehicle. Passenger comfort is therefore degraded during this phase.

In order to accelerate the heating of the passenger compartment, it is known, in particular by the patent FR

042 854, to add an additional electric heater. This additional heating includes heating elements electrically powered by a vehicle battery when additional heating of the air is desired.

In a hybrid vehicle, such additional heating can be used not only during the first minutes of operation of the vehicle, but also during all the phases where the engine is not started. In a purely electric vehicle, such heating constitutes the main heating of the vehicle.

Additional heating includes a control device that allows or prohibits the flow of current through the heating elements. The control mode is generally the so-called pulse width modulation mode. By this is meant that the flow of current is successively activated and deactivated, with a given control frequency. The distribution between the fraction of time during which the heating element is supplied and the fraction of time during which the heating element is not supplied makes it possible to adjust the average thermal power dissipated. One or more transistors are used to successively ensure the phases of current flow and the phases of current interruption in each heating element. The control signal of the heating device therefore has a succession of transitions between a conducting state and a blocking state of the control transistor (s). Each transition generates an abrupt variation in the current in the vehicle's on-board network.

Furthermore, it is known to have several separate heating elements for heating different air flows. The different air flows can be directed towards different places in the passenger compartment, such as towards the windshield, towards the feet of the occupants of the front seats of the vehicle, or towards the rear seats of the vehicle. These different air flows pass through separate heating elements. The number of heating elements can therefore vary between applications, depending on the number of different zones to be heated.

In order to finely regulate the temperature of each of the different air flows, it is desirable to be able to control each of the heating elements independently. During each current control cycle, the duration of current flow can thus vary from one heating element to another.

In the case where the different heating elements are controlled simultaneously, the variations in the current in each of the heating elements are added, which can create a significant variation in the intensity of the current delivered by the vehicle battery. These variations tend to create disturbances in the operation of the control electronics of the heating device, as well as of the other electronic components of the vehicle. In addition, these variations in current also accelerate the aging of the battery for storing electrical energy.

In order to minimize the variations in intensity of the total current, it is better to avoid that the control transitions of the current passing through a heating element are synchronous with the control transitions of the current passing through another heating element.

The object of the invention is to provide a heating device in which each of the heating elements can be controlled independently of the other heating elements, while avoiding that the current control transitions take place synchronously, regardless of the variations. setpoint of the thermal power to be dissipated by each of the heating elements.

The invention also proposes a method for controlling a heating device making it possible to minimize instantaneous variations in the intensity of the supply current of the heating device, while allowing each of the heating elements to be heated in a differentiated manner.

To this end, the invention provides a heating device comprising:

- at least two heating elements configured to heat a fluid circulating in contact with the heating elements,

- A control device arranged to control each heating element independently of the other heating element.

Controlling each heating element independently optimizes the operation of the heating device. It is understood here that each heating element can be controlled with a setpoint of thermal power distinct from the setpoint of the other heating element. In addition, the activation phases of each heating element can also be triggered at times different from the activation phases of the other heating elements. Likewise, the deactivation phases of each heating element can also be triggered at times different from the deactivation phases of the other heating elements. The interactions between the different heating elements can thus be optimized.

According to a preferred embodiment, the heating device comprises at least three heating elements, each of the heating elements being controlled independently of each of the other heating elements.

The presence of three separate heating elements allows three air flows to be heated independently.

Advantageously, the heating device comprises a housing arranged to be traversed by a fluid, the heating elements being arranged in the housing.

Preferably, the housing is of parallelepiped shape.

The heating device thus has a compact shape.

The heating device comprises an electric power source arranged to electrically supply the heating elements in order to heat them.

The heating elements can thus supply heat independently of the temperature of the heat-transfer fluid making it possible to heat the heating installation in which the heating device can be integrated.

According to one embodiment, the voltage of the electrical power source is greater than 300 V.

This voltage range is adapted to the batteries of vehicles with electric propulsion and makes it possible to minimize losses by the Joule effect.

Advantageously, the heating elements are heating resistors of the type with a positive temperature coefficient.

This type of heating element provides heating power adapted to needs while being compact and inexpensive.

According to a preferred embodiment, the heating elements comprise a set of heating resistors of the type with a positive temperature coefficient, the heating resistors being juxtaposed.

The juxtaposition of several heating resistors makes it possible to constitute a heating element providing the desired thermal power.

According to one embodiment, the control device comprises at least two transistors, each transistor being configured to circulate an electric current in a heating element when the transistor is in a conducting state and to interrupt the circulation of current in the heating element when the transistor is in a blocking state, the transition between the on state and the blocking state defining a falling edge of the command and the transition between the blocking state and the on state defining a rising edge of the command.

In other words, each heating element is controlled in all or nothing. The electronic circuit of the control device is thus simple. The distribution between the time during which a heating element is activated and the time during which the heating element is deactivated makes it possible to control the dissipated thermal power.

According to one embodiment, the control device is configured to independently control each transistor.

Each heating element can thus be activated or deactivated independently of the other heating elements, since each transistor is controlled independently.

According to a preferred embodiment, the control device is configured so that when the heating elements are ordered, all the rising edges and all the falling edges of the control are time-shifted by a duration greater than or equal to a first predetermined duration. .

The variations over time in the intensity of the current consumed by the heating device are thus minimized. Disturbances transmitted to other equipment on the electrical network are also minimized. In addition, the battery for storing electrical energy is less stressed, which improves its lifespan.

Advantageously, the first predetermined duration is equal to 0.2 ms.

This value allows sufficient separation of the rising control edges, as well as the falling control edges, while allowing a sufficiently high control frequency. The variations in the intensity of the current thus generate a low level of disturbance.

According to one embodiment, the control device is configured to control each transistor according to a pulse width modulation mode.

Piloting in pulse width modulation allows precise control of the thermal power supplied and with a short response time. The control software is also not very complex.

Advantageously, the control device is configured to control each transistor with a single control period.

The control software is thus not very complex.

According to a preferred embodiment, the control device is configured so that the rising control edges of each transistor are temporally offset by a duration equal to the control period divided by the number of transistors.

The rising edges are thus distributed over time at regular intervals. The disturbances caused by the establishment of the electric current in each heating element are minimized.

According to a variant implementation of the invention, the control device is configured so that the falling control edges of each transistor are temporally offset by a duration equal to the control period divided by the number of transistors.

In this case, the control falling edges are thus distributed in time at regular intervals. It is the disturbances caused by the interruption of the electric current in each heating element which are minimized.

Preferably, the heating device comprises a circuit for deactivation of the control device, the deactivation circuit being placed in series between the electric power source and the control circuit.

The deactivation circuit makes it possible to protect the heating device against a possible failure of the control circuit, such as for example a short circuit causing permanent activation of one or more heating elements. The risks associated with overheating caused by a fault in the control circuit are eliminated.

Advantageously, the heating elements extend along parallel axes.

Advantageously also, the heating elements are coplanar.

The same incident air flow can thus be easily distributed between the different heating elements of the heating device.

According to a preferred example of implementation of the invention, the heating device comprises a housing arranged to be traversed by a fluid,

- three heating elements arranged in the housing and configured to heat the fluid,

- a control device arranged to control each heating element independently of the other heating elements.

The heater can thus independently heat three different air flows. Three distinct zones, each with temperature requirements or different thermal power, can thus be treated.

The invention also relates to a heating, ventilation and / or air conditioning installation of a motor vehicle comprising a heating device as described above.

The heating device according to the invention thus makes it possible to optimize the operation of the heating installation in which it is integrated.

Preferably, the heating, ventilation and / or air conditioning installation is configured to blow air to at least two separate zones, each air flow being in contact with a heating element separate from the heating device and being heated. independently of other air flows.

The thermal requirements of different zones can thus be treated.

The invention also relates to a method for controlling a heating device, the heating device comprising:

- at least two heating elements configured to heat a fluid circulating in contact with the heating elements,

a control device arranged to control the heating elements, the control method comprising the step:

- control each heating element independently of the other heating element.

According to a preferred embodiment of the control method, each heating element is controlled according to a pulse width modulation mode.

Advantageously, the control method includes the step:

- Obtain a thermal power setpoint to be dissipated by each of the heating elements of the heating device (step 60),

- Determine a control duration for each heating element from the thermal power setpoint (step 61).

The maximum thermal power of the heating device is determined by construction, depending on the number of integrated heating elements and their individual thermal power. The thermal power setpoint to be dissipated by each of the heating elements is determined by the control system of the heating installation. The duration of control of each heating element is obtained from the setpoint power, the maximum power and the control frequency.

Preferably, the control device comprises at least two transistors, each transistor being configured to circulate an electric current in a heating element when the transistor is in a conducting state and to interrupt the circulation of current in the heating element when the transistor is in a blocking state, the transition between the passing state and the blocking state defining a falling edge of the command and the transition between the blocking state and the passing state defining a rising edge of the command, the control method comprising step:

- control each transistor in turn during the control duration determined for each heating element, the rising control edge of one transistor being offset from the rising control edge of another transistor by a duration equal to the period control divided by the number of control transistors, each transistor being controlled only once during a control period (step 62).

The control device control law triggers the activation of each transistor in turn, in a time-distributed manner. The time intervals between the control of each of the transistors are equal, except for the uncertainty linked to the sampling and to the discretization of the signals. The current draw phases are thus always separated, and cannot occur simultaneously. The phases of increasing the intensity of the current are thus smoothed over time, that is to say that their instantaneous temporal variations are minimized.

According to one embodiment, the control method comprises the steps:

- For each heating element, determine the instant corresponding to the falling control front of the transistor from the value of the instant corresponding to the rising control front and the determined control duration (step 63),

If the determined control duration of the second transistor is increasing and if the difference between the determined instant of the falling control edge of the second transistor and the instant corresponding to the falling control edge of the first transistor is less than a first predetermined duration, maintaining the second transistor in the on state for a predetermined additional duration in order to ensure a minimum time difference between the instants of passage in the deactivation state of the first heating element and of the second heating element (step 64).

As the instants corresponding to the rising edges are offset, and the control durations of each of the transistors are independent, it can occur in theory that the instants corresponding to the falling edges are very close or coincide. The method according to the invention makes it possible to avoid this undesirable event, by monitoring before cutting the current in a transistor designated by second transistor if the temporal separation between the falling edges of the commands of the various transistors is sufficient. When the duration of control of the second transistor is increasing over time, this transistor is controlled for a period longer than the value calculated to ensure the set thermal power, in order to avoid cutting the current almost simultaneously in several transistors. In other words, the instant of interruption of the current is delayed.

According to a preferred embodiment, the control method comprises the steps:

- For each heating element, determine the instant corresponding to the falling control front of the transistor from the value of the instant corresponding to the rising control front and the determined control duration (step 63),

- If the determined control duration of the second transistor is decreasing and if the difference between the determined instant of the falling control edge of the second transistor and the instant of the falling control edge of the first transistor is less than a first predetermined duration, shorten the duration of holding the second transistor in the passing state by a predetermined duration in order to ensure a minimum time difference between the instants of passage in the deactivation state of the first heating element and of the second heating element (step 65).

When the duration of control of the second transistor is decreasing over time, the control method corrects the control time so that this transistor is controlled for a period shorter than the value calculated to provide the set thermal power. Thus, a power cut almost simultaneously in several transistors is avoided. In other words, the instant of power cut is anticipated.

Advantageously, the predetermined additional duration is equal to 0.5 ms.

This value makes it possible to ensure a sufficient separation of the instants of interruption of the current, while allowing a control frequency in pulse width modulation sufficiently rapid. For example, a control frequency of 100 hertz can be used.

Advantageously, the predetermined duration for shortening the duration for which the second transistor is kept in the on state is equal to 0.5 ms.

As before, this value makes it possible to ensure a sufficient separation of the instants of interruption of the current, while allowing a control frequency in pulse width modulation sufficiently rapid.

Other characteristics and advantages of the invention will appear on reading the detailed description of the embodiments given by way of nonlimiting examples, accompanied by the figures below:

FIG. 1 is a schematic sectional view of a heating, ventilation and / or air conditioning installation comprising a heating device according to the invention,

FIG. 2 is a schematic side and partial view of a heating device,

FIG. 3 is a schematic top view of the heating device of FIG. 2 integrated in a heating, ventilation and / or air conditioning installation,

FIG. 4 is a perspective view of a heating device,

FIG. 5 is a curve illustrating the evolution as a function of time of the control signals applied to the heating device,

FIG. 6 is a curve illustrating the evolution of the control signals applied to two elements of the heating device,

FIG. 7 is a block diagram of the method according to the invention,

FIG. 8 is a curve illustrating the evolution over time of the control signals applied to two elements of the heating device during the implementation of the method,

Figures 9 and 10 are curves illustrating the evolution of the control time of two heating elements of the heating device as a function of time during the implementation of the method.

In order to facilitate the reading of the figures, the various elements are not necessarily shown to scale.

FIG. 1 shows a heating, ventilation and / or air conditioning installation 50 of a motor vehicle comprising a heating device 20 according to the invention.

In this heating installation 50, the air outside the vehicle is blown into the interior of the vehicle interior by a blower 18. The flow of forced air passes through a heat exchanger 19, the heat exchanger 19 being traversed by the coolant of the vehicle's engine. In stabilized operating conditions, the air passing through the exchanger 19 is heated by the engine coolant.

The air flow then passes through the heating device 20. The heating device 20 comprises heating elements which can be electrically controlled. Thus, the heating device 20 can supplement or replace the heating provided by the heat exchanger 19.

For example, in the first minutes of vehicle operation, the engine is not hot enough to be able to provide the heat necessary to obtain the desired set temperature for the passenger compartment. The heating device 20 thus makes it possible to accelerate the rise in temperature of the passenger compartment by providing additional heat in addition to that provided by the heat exchanger 19.

In the case of a hybrid vehicle, the heat engine may not be in operation and may not provide heat during certain driving phases. The heat supplied by the heating device 20 then replaces the heat usually supplied by the heat exchanger 19.

The air flow is then directed by flaps 24, 25 towards ventilation outlets 26 and 27.

A first outlet from the heating installation 50 may for example correspond to the windshield of the vehicle, a second outlet at the feet of the front passengers and a third outlet to the rest of the passenger compartment. To simplify, only two outputs 26 and 27 have been shown in FIG. 1.

Preferably, the heating, ventilation and / or air conditioning installation 50 is configured to blow air to at least two separate zones, each air flow being in contact with a heating element separate from the heating device and being heated independently of other air flows.

According to one embodiment, the heating device 20 according to the invention comprises:

- at least two heating elements 1, 2 configured to heat a fluid circulating in contact with the heating elements 1,2,

- A control device 5 arranged to control each heating element 1,2 independently of the other heating element 2,1.

By "controlling independently" is meant that each heating element can be controlled with a setpoint of thermal power distinct from the setpoint of the other heating element. In addition, the activation phases of each heating element can also be triggered at times different from the activation phases of the other heating elements. Likewise, the deactivation phases of each heating element can also be triggered at times different from the deactivation phases of the other heating elements.

According to a variant implementation of the invention, the heating device 20 comprises at least three heating elements 1,2,3, each of the heating elements 1,2,3 being controlled independently of each of the other heating elements 3,2 1.

In the example illustrated here, the heating device 20 comprises a housing 6 arranged to be traversed by a fluid,

- three heating elements 1,2,3 arranged in the housing 6 and configured to heat the fluid,

- A control device 5 arranged to control each heating element 1,2,3 independently of the other heating elements 3,2,1.

The heating device 20 can thus independently heat three different air flows.

Figures 3 and 4 schematically describe the passage of the different air flows. In FIG. 3, each heating element 1, 2, 3 faces a separate duct 21, 22, 23 of the heating installation 50. The ducts 21, 22, 23 are delimited by walls separation 28 and 29. Each duct 21, 22, 23 can be traversed by a flow of air heated by a separate heating element 1, 2, 3.

Three distinct zones, each with different temperature or thermal power requirements, can thus be treated. It is thus possible to heat the air flow sent to the windshield in a different manner in order to defrost / disambiguate it, that sent to the feet of the occupants and that sent to the rest of the passenger compartment. The three separate air flows are shown diagrammatically by the arrows F1, F2, F3 in FIGS. 3 and 4.

FIG. 4 details the construction of a heating device 20.

The heating device 20 comprises a housing 6 arranged to be traversed by a fluid, the heating elements 1, 2, 3 being arranged in the housing 6.

The housing 6 provides mechanical maintenance of the heating elements. The housing 6 comprises a frame into which the heating elements are inserted, as well as ribs connecting the opposite sides of the frame in order to stiffen it.

In the example shown, the housing 6 is of parallelepiped shape.

The heating elements 1,2,3 extend along parallel axes A1, A2, A3. The heating elements 1,2,3 are coplanar.

In the example shown, the fluid passing through the housing 6 is the air blown towards the passenger compartment.

As shown diagrammatically in FIG. 3, the heating device comprises an electric power source 7 arranged to supply electrically the heating elements 1,2,3 in order to heat them.

According to one embodiment, the voltage of the electric power source 7 is greater than 300 V. This voltage range corresponds to the batteries of vehicles with exclusive electric propulsion. The voltage can be 400 V. It can also be 800 V. According to other embodiments, corresponding to use on hybrid vehicles, the voltage of the electric power source 7 can be 48 V, or another 12 V.

The electrical connector 12 makes it possible to connect the heating device 20 to the electrical power source 7. The connector 15, shown diagrammatically in FIG. 2, allows the heating device 20 to exchange information with the electronic system controlling the entire heating installation 50. This connector thus allows the heating device 20 to receive instructions for the heating power to be provided. The electronic system controlling the entire heating installation 50 has not been shown.

The heating elements 1, 2, 3 are here heating resistors of the type with a positive temperature coefficient. By this term is meant that the resistance of the heating element increases when its temperature increases.

According to an embodiment not shown, each heating element 1, 2, 3 comprises a single heating resistor of the type with a positive temperature coefficient.

According to the embodiment illustrated here, the heating elements 1, 2, 3 comprise a set of heating resistors 4 of the type with a positive temperature coefficient, the heating resistors 4 being juxtaposed.

In other words, one or more of the heating elements 1, 2, 3 are formed by several heating elements 4 of the resistance type with a positive temperature coefficient, mechanically juxtaposed and electrically connected. The type of resistance used in each heating element as well as their number makes it possible to constitute a heating element providing the thermal power desired for the intended application. Ceramic type heating elements are preferred.

The maximum heating power is between 2 kW and 6 kW depending on the voltage of the electrical power source as well as the type and number of heating elements used.

The control device 5 comprises at least two transistors 8.9, each transistor 8.9 being configured to circulate an electric current in a heating element 1.2 when the transistor 8.9 is in a conducting state and interrupt the circulation of the current in the heating element 1.2 when the transistor 8.9 is in a blocking state, the transition between the on state and the blocking state defining a falling edge Fdl, Fd2 of the control and the transition between the state blocking and the passing state defining a rising edge Fml, Fm2 of the command.

In other words, each heating element is controlled in all or nothing. The electronic circuit of the control device 5 is thus simple. The distribution between the time during which a heating element is activated and the time during which the heating element is deactivated makes it possible to control the dissipated thermal power.

The control device 5 is configured to independently control each transistor 8, 9.

Each heating element can thus be activated or deactivated independently of the other heating elements, since each transistor is controlled independently.

As shown diagrammatically in FIG. 2, the transistors 8, 9, 10 are arranged on a printed circuit board 14 of the control device 5. The control device 5 comprises a microcontroller, not shown.

The transistors 8, 9, 10 can be of the IGBT type (for English “Insulated Gate Bipolar Transistor”) The transistors can also be of the Mosfet type. (for the English "Metal Oxide Semiconductor Field Effect Transistor".)

The control device 5 is configured to control each transistor 8, 9, 10 according to a pulse width modulation mode. This type of control, well known to those skilled in the art, is also commonly designated by the term "PWM", from the acronym "pulse width modulation".

The power dissipated by each heating element can be adjusted by varying the command duty cycle, i.e. the fraction of the command period during which the command is activated.

The heating device 20 also includes a deactivation circuit 11 of the control device 5, the deactivation circuit 11 being placed in series between the electric power source 7 and the control circuit 5.

The deactivation circuit 11 thus makes it possible to protect the heating device 20 as well as its environment against a possible failure of the control circuit 5. The failure can be for example a short circuit causing permanent activation of one or more heating elements. A diagnosis of the order is carried out in real time. The deactivation circuit 11 can be part of the control circuit 5. The deactivation circuit 11 can also be a separate circuit.

FIG. 5 schematically represents the evolution over time of the control signal of each of the heating elements 1, 2, 3. Curve 41 represents the control of the first transistor 8, making it possible to activate and deactivate the first element heating 1. The curve 42 represents the control of the second transistor 9, making it possible to control the second heating element 2, and the curve 43 represents the control of the third transistor 10, making it possible to control the third heating element 3.

In chronological order, the second transistor is controlled after the first transistor, and the third transistor is controlled after the second transistor. The three transistors play the same role and the designation first, second, third transistor is therefore arbitrary.

In the example shown in FIG. 5, the control device 5 is configured to control each transistor 8,9,10 with a single control period Te. The order period Te is here is 10 milliseconds. In other words, the control frequency here is 100 Hertz.

In FIG. 5, the control duty cycle (or PWM) of the transistor 8 is equal to the control duration Tl divided by the control period Te. Similarly, the duty cycle of the transistor 9 is equal to the control time T2 divided by the control period Te, and that of the transistor 10 is equal to T3 divided by Te.

The control device 5 is here configured so that the rising edges Fml, Fm2, Fm3 for controlling each transistor 8, 9, 10 are time-shifted by a duration Doff equal to the control period Te divided by the number of transistors 8 , 9.10.

In other words, in the example shown in FIG. 5, the rising control edges of the three transistors 8, 9, 10 are phase-shifted in time by a duration Doff equal to one third of the control period Te.

The rising fronts of control Fml, Fm2, Fm3 of the transistors 8, 9, 10 are thus distributed in time at regular intervals. The amplitude of instantaneous variations in the intensity of the electric current is minimized. The disturbances generated by the establishment of the electric current in each heating element 1, 2, 3 are minimized.

As shown diagrammatically in FIG. 5, the second transistor 9 is controlled on curve 42 for a shorter duration T2 than the control duration T1 of the first transistor 8, curve 41.

For certain values of the difference in control duration between these two transistors, it is possible that the instants corresponding to the falling control edges coincide. In other words, the power failure can occur simultaneously in the two transistors. This case should be avoided in order to minimize variations in the intensity of the current. In addition, even if there is no strict coincidence, it is desirable to avoid that the falling control edges are too close in time.

In the same way, the end of control of the third transistor can coincide with that of the second transistor, as well as with the end of control of the first transistor.

According to the invention, the control device 5 is configured so that when the heating elements 1,2,3 are ordered, all the rising edges Fm and all the falling edges Fd of the control are time-shifted by a greater duration or equal to a first predetermined duration dl.

The variations over time in the intensity of the electric current consumed by the heating device 20 are thus minimized. Disturbances transmitted to other equipment on the electrical network are thus minimized.

The first predetermined duration dl is equal to 0.2 ms.

This value allows sufficient separation of the rising control edges, as well as the falling control edges, while allowing a high control frequency. The aim is that variations in the intensity of the current thus generate a low level of disturbance.

This object is achieved by the control method which will now be described.

Thus, the invention also relates to a method for controlling a heating device, the heating device comprising:

- at least two heating elements 1,2 configured to heat a fluid circulating in contact with the heating elements 1,2,

a control device 5 arranged to control the heating elements 1, 2, the control method comprising the step:

- control each heating element 1,2 independently of the other heating element 2,1.

In the method according to the invention, each heating element 1, 2 is controlled in a pulse width modulation mode.

The ordering process includes the step:

- Obtain a setpoint P1, P2 of thermal power to be dissipated by each of the heating elements 1, 2 of the heating device (step 60),

- Determine a control duration Tl, T2 of each heating element 1,2 from the setpoint P of thermal power (step 61).

The maximum thermal power of the heating device is determined by construction, depending on the number of integrated heating elements and their individual thermal power.

The thermal power setpoint to be dissipated by each of the heating elements is determined by the control system of the heating installation, from the actual thermal conditions prevailing in the passenger compartment, from the external conditions and from the settings desired by the driver.

The duration of control of each heating element is obtained from the setpoint power, the maximum power and the control frequency. The fraction of time during which a heating element is controlled is substantially equal to the fraction of the maximum heating power to be supplied by the heating element considered.

The control device 5 comprises at least two transistors 8.9, each transistor 8.9 being configured to circulate an electric current in a heating element 1.2 when the transistor 8.9 is in a conducting state and interrupt the circulation of the current in the heating element 8.9 when the transistor 8.9 is in a blocking state, the transition between the on state and the blocking state defining a falling edge Fdl, Fd2 of the control and the transition between the state blocking and the on state defining a rising edge Fml, Fm2 of the command, the command method comprises the step:

- control each transistor 8.9 in turn during the control period T1, T2 determined for each heating element 1.2, the rising edge Fml, Fm2 for controlling a transistor 8.9 being offset from the rising edge for controlling another transistor 9.8 with a duration equal to the control period Te divided by the number of control transistors 8.9, each transistor 8.9 being controlled only once during a control period Te ( step 62).

As illustrated in FIG. 5, the method of controlling the heating device triggers the activation of each transistor in turn, in a time-distributed manner. The time intervals between the control of each of the transistors are equal, except for the uncertainty linked to the sampling and to the discretization of the signals. The current draw phases are thus always separated, and cannot occur simultaneously. The phases of increasing the intensity of the current are thus smoothed over time, that is to say that their instantaneous temporal variations are minimized.

The ordering process includes the steps:

- For each heating element 1,2, determine the instant corresponding to the falling edge Fdl, Fd2 for controlling the transistor 8,9 from the value of the instant corresponding to the rising edge Fml, Fm2 for controlling and the duration of command T1, T2 determined (step 63),

- If the determined control duration T2 of the second transistor 9 is increasing and if the difference between the determined instant of the falling edge Fd2 of control of the second transistor 9 and the instant corresponding to the falling edge Fdl of control of the first transistor 8 is less at a first predetermined duration dl, maintaining the second transistor 9 in the on state for an additional predetermined duration adl in order to ensure a minimum time offset between the instants of passage in the deactivation state of the first heating element 1 and of the second heating element 2 (step 64).

In the example shown where the heating device comprises three heating elements and three control transistors, the controls are phase shifted by a third of the period. Consequently, in the case where the control durations of two transistors differ by an amount equal to a third of period, with the duration of the transistor controlled chronologically in second shorter than that of the transistor controlled first, the falling edges of control are synchronized. This situation should be avoided.

Figure 6 illustrates the acceptable boundary cases. Curve 41 represents the control of the first transistor 8. Curves 42a and 42b represent the control of the second transistor 9 in two different cases. Curve 42a illustrates the case where the falling control edges are separated by the minimum acceptable duration dl, the falling control edge Fd2 of the second transistor occurring before the falling control edge Fdl of the first transistor. The curve 42b illustrates the case where the falling control edges are also separated from the minimum acceptable duration dl, this time the falling control edge Fd2 of the second transistor occurring after the falling control edge Fdl of the first transistor.

The control process modifies the duration of the control initially planned in order to prevent the falling edges from coinciding or being very close to each other.

First, the direction of variation of the control time of the second transistor 9 is determined.

In cases where the duration of control of the second transistor 9 is increasing over time, the control of the second transistor 9 is maintained for a duration greater than the duration initially determined, in order to ensure sufficient temporal separation between the falling edges.

In other words, the instant of interruption of the current is delayed.

The predetermined additional duration adl is equal to 0.5 ms. This value corresponds to 5% of the value of the opening duty cycle for a command period of 10 milliseconds, i.e. a command frequency of 100 Hz.

This scenario is illustrated in FIG. 9. Curve 51 shows the evolution of the control time applied to the first transistor. Curve 52 shows the evolution of the control time actually applied to the second transistor. Curve 52 ′ shows the change in control time which would be applied to the second transistor if the control method did not act.

The sign E corresponds to a shift in order time equal to a third of the period. In this case, the falling control edges of the first and second transistor would be in phase, which is to be avoided.

At time tl, the difference between the duration of control of the second transistor 9 and the duration of control of the first transistor becomes equal to one third of the control period Te minus the minimum acceptable value dl. As the order time is increasing, the offset would become less than the acceptable limit without the intervention of the order process. In order to ensure a minimum offset of the control edges of the transistors, the control time of the second transistor is increased by the value Adl, in order to ensure a sufficient offset.

The application of an offset to the command time actually applied lasts until time t2. At time t2, the command time 52 ′ for controlling the second transistor ceases to be too close to the minimum acceptable offset d1. The control time actually applied then joins, between times t2 and t3, the setpoint calculated to ensure the desired thermal power. The slope of the curve 52, that is to say the speed of convergence towards the setpoint can be adjusted.

FIG. 8 illustrates the control signal of the transistor when the control time is increased. Curve 42 'in solid lines shows the command actually applied, curve 42 in dotted lines showing the command which would be applied without the intervention of the method according to the invention.

According to a preferred embodiment, the control method comprises the steps:

- For each heating element 1,2, determine the instant corresponding to the falling edge Fdl, Fd2 for controlling the transistor 8,9 from the value of the instant corresponding to the rising edge Fml, Fm2 for controlling and the duration Tl , T2 of determined command (step 63),

- If the determined control duration T2 of the second transistor is decreasing and if the difference between the determined instant of the falling edge Fd2 of control of the second transistor 9 and the instant of the falling edge Fdl of control of the first transistor 8 is less than one first predetermined duration dl, shorten the duration of holding the second transistor 9 in the passing state by a predetermined duration ral in order to ensure a minimum time offset between the instants of passage into the deactivation state of the first heating element 1 and of the second heating element 2 (step 65).

For the cases where the duration of control of the second transistor is decreasing in time, the time of control of the second transistor is shortened compared to the duration initially determined, in order to ensure a sufficient temporal separation between the falling edges. In other words, the instant corresponding to the power cut is anticipated relative to the value calculated for the purpose of ensuring the set thermal power of the heating element.

The predetermined duration ral of shortening the duration of holding the second transistor in the on state is equal to 0.5 ms.

As before, this value makes it possible to ensure a sufficient separation of the instants of interruption of the current, while allowing a control frequency in pulse width modulation sufficiently rapid.

This case is illustrated in FIG. 10. The curve 71 shows the evolution of the control time applied to the first transistor 8. The curve 72 shows the evolution of the control time actually applied to the second transistor 9. The curve 72 ' shows the evolution of control time which would be applied to the second transistor 9 if the control method according to the invention did not act.

The sign E corresponds to an order time difference equal to a third of the period. In this case, the falling control edges of the first transistor 8 and of the second transistor 9 would be in phase, which is to be avoided.

At time t4, the difference between the control duration of the second transistor and the control duration of the first transistor 8 becomes equal to one third of the control period Te minus the minimum acceptable value dl. As the control time is decreasing, from time t4 the offset would become less than the acceptable limit without the intervention of the control process. In order to ensure a minimum offset of the control edges of the transistors, the control time of the second transistor is reduced by the value Ral, in order to ensure a sufficient offset, that is to say at least equal to Adl. In the example shown, Ral is 0.5 ms and dl is 0.2 ms.

The shift in control time actually applied lasts until time t5. At time t5, the command time setpoint of the second transistor ceases to be too close to the minimum acceptable offset dl. The control time actually applied then joins the calculated setpoint to ensure the desired thermal power. As before, the slope of the curve 72, that is to say the speed of convergence towards the setpoint can be adjusted.

The cases where the control duration of the second transistor is stable over time is already dealt with by the previous cases where this duration is either increasing or decreasing. Indeed, a phase of stability of the control time is necessarily preceded by a phase either of growth or of decrease. Consequently, the steps already described also ensure minimum temporal separation of the control edges in steady state.

FIG. 8 illustrates the control signal of the transistor when the control time is reduced. Curve 42 ”in solid lines shows the command actually applied, curve 42 in dotted lines showing the command which would be applied without the intervention of the method according to the invention.

According to embodiments not shown, the heating device 20, the heating installation 50 as well as the associated control method can also include one or more of the characteristics below, considered individually or combined with each other:

The heating device can include any number of heating elements and associated control transistors, this number being greater than or equal to two. The control method can be applied in the same way.

The control device can be configured so that the falling edges Fdl, Fd2 for controlling each transistor 8, 9 are time-shifted by a duration equal to the control period divided by the number of transistors.

In this case, the control falling edges are thus distributed in time at regular intervals. The triggering time of the rising edges is determined from the control time and the value of the time corresponding to the falling control edge.

The principle already explained for ensuring a temporal separation of the falling control edges is applied in a similar manner in order to ensure a satisfactory separation of the rising control edges.

- The fluid passing through the housing 6 can be a heat transfer liquid such as the coolant of the heat engine. The heating device 20 can thus heat the liquid passing through a heat exchanger, which itself heats the air blown into the passenger compartment. In other words, the heating elements of the heating device heat the air in the passenger compartment indirectly.

- More generally, the fluid passing through the housing 6 can be any liquid or gas having to be heated during its use.

- The principle of the invention is applicable outside the automotive field described here, as long as the heating elements are controlled by transistors activated in turn.

Of course, other modifications and variations suggest themselves to those skilled in the art, after thinking about the different embodiments illustrated.

The invention is in no way limited to the embodiments described and illustrated in this application, which are given by way of examples and are not intended to limit the scope of the invention.

Claims (12)

1. Heating device (20) comprising: - at least two heating elements (1, 2) configured to heat a fluid circulating in contact with the heating elements (1,2), - a control device (5) arranged to control each heating element (1,2) independently of the other heating element (2,1). 2. Heating device (20) according to the preceding claim, comprising an electrical power source (7) arranged to electrically supply the heating elements (1,2) in order to heat them. 3. Heating device (20) according to the preceding claim, wherein the voltage of the electric power source (7) is greater than 300 V. 4. Heating device (20) according to one of the preceding claims, in which the heating elements (1,2) are heating resistors of the positive temperature coefficient type. 5. Heating device (20) according to one of the preceding claims, in which the control device (5) comprises at least two transistors (8,9), each transistor (8,9) being configured to circulate a current electric in a heating element (1,2) when the transistor (8,9) is in a conducting state and interrupt the flow of current in the heating element (1,2) when the transistor (8,9) is in a blocking state, the transition between the passing state and the blocking state defining a falling edge (Fdl, Fd2) of the control and the transition between the blocking state and the passing state defining a rising edge (Fml, Fm2) of the command. 6. Heating device (20) according to the preceding claim, wherein the control device (5) is configured so that when controlling the heating elements (1,2) all rising edges (Fm) and all edges descendants (Fd) of the command are time-shifted by a duration greater than or equal to a first predetermined duration (dl). 7. Heating device (20) according to the preceding claim, wherein the first predetermined duration (dl) is equal to 0.2 ms. 8. Heating device (20) according to one of claims 5 to 7, in which the control device (5) is configured to control each transistor (8,9) in a pulse width modulation mode, with a single control period (Te), and in which the control device (5) is configured so that the rising edges (Fml, Fm2) of control of each transistor (8,9) are time-shifted by a duration (Doff ) equal to the control period (Te) divided by the number of transistors (8,9). 9. Installation for heating, ventilation and / or air conditioning (50) of a motor vehicle comprising a heating device (20) according to one of the preceding claims. 10. A method of controlling a heating device, the heating device comprising: - at least two heating elements (1,2) configured to heat a fluid circulating in contact with the heating elements (1,2), - a control device (5) arranged to control the heating elements (1,2), the control method comprising the step: - control each heating element (1,2) independently of the other heating element (2,1). 11. Control method according to the preceding claim, comprising the steps: - For each heating element (1,2), determine the instant corresponding to the falling edge (Fdl, Fd2) for controlling the transistor (8,9) from the value of the instant corresponding to the rising edge (Fml, Fm2 ) of command and of a determined command duration (T1, T2) (step 63), - If the determined control duration (T2) of the second transistor (9) is increasing and if the difference between the determined instant of the falling edge (Fd2) of control of the second transistor (9) and the instant corresponding to the falling edge ( Fdl) control of the first transistor (8) is less than a first predetermined duration (dl), maintain the second transistor (9) in the on state for a predetermined additional duration (adl) in order to ensure a minimum time offset between the instants of passage into the deactivation state of the first heating element (1) and of the second heating element (2) (step 64). 12. Control method according to claim 10 or 11, comprising the steps: - For each heating element (1,2), determine the instant corresponding to the falling edge (Fdl, Fd2) for controlling the transistor (8,9) from the value of the instant corresponding to the rising edge (Fml, Fm2 ) of command and of the duration (T1, T2) of command determined (step 63), 5 - If the determined control duration (T2) of the second transistor is decreasing and if the difference between the determined instant of the falling edge (Fd2) of control of the second transistor (9) and the instant of the falling edge (Fdl) of control of the first transistor (8) is less than a first predetermined duration (dl), shortening the duration of holding the second transistor (9) in the on state by a predetermined duration 10 (ral) in order to ensure a minimum time difference between the instants of passage into the deactivation state of the first heating element (1) and the second heating element (2) (step 65).