Abstract:
The invention relates to a valve-type device including a housing having a fluid access ( 7 ) which is shut off by a shutter ( 9 ) secured to an actuator ( 10 ) as a function of the temperature of the fluid passing through the device. The device also includes an expanding-material safety thermostatic element ( 22 ) located in the stream of fluid passing through the housing. The element  22  actuates the shutter ( 9 ) when, as a result of defective operation of the actuator ( 10 ) or of its control equipment, the shutter has not been moved by the actuator. The actuator also consists of an expanding-material thermostatic element containing a heating means ( 13 ) connected to control equipment.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a valve type of thermostatic device with a proportional-control actuator. The actuator includes a thermostatic element, such as a conventional expanding-wax thermostatic element, to give the device a back-up mode of operation if the actuator or its control gear should prove defective. 
     Thermostatic devices of the valve type are used, for example, in internal combustion engine cooling circuits for regulating the temperature of the cooling liquid (generally an aqueous mixture known as “coolant”) introduced into the engine in order to optimize its operation. These devices act on a flow of “hot” liquid coming from the vehicle engine and/or a flow of “cold” liquid coming from a cooling radiator, and these flows are mixed to form a “warm” cooling liquid which is reintroduced into the engine. 
     It should be noted that the words “hot”, “cold” and “warm” are used with a view to simplifying the vocabulary to indicate relative temperature levels of the three streams of liquid when the device is operating in steady state. However, the respective temperatures of these three streams may be very similar, and may even be identical when the thermostatic device is still closed. 
     Thermostatic devices motorized by means of an electric motor comprising a back-up thermostatic element are already known. These devices may, for example make it possible, inside a chamber of the device, to mix a stream of cold liquid with the stream of hot liquid even when the engine or its control gear are defective, if the temperature of the liquid in which the thermostatic element is immersed exceeds a desired value. One particular example of this type of device is known from the French patent published under the number 2 703 730. 
     The thermostatic device in that document 2 703 730 is motorized by means of an electric motor comprising a rotary output shaft actuating the moving shutter of the thermostatic device by means of a conventional screw-nut coupling system that converts the rotary movement of the shaft into a translational movement. This moving shutter, such as a spool or “plug,” gradually uncovers a cold liquid inlet access of this device at the same time as it gradually shuts off a hot liquid inlet access, and vice versa. The back-up thermostatic element is aligned with the screw of the screw-nut system. When its temperature rises, its piston exerts a force on them plug, if the latter has not been moved or has not been moved far enough by the screw-nut system, and the force is oriented in the direction to uncover the cold liquid inlet access and to shut off the hot liquid inlet access so that under the thrust of the piston of the thermostatic element, the spool can actually move in that direction. The screw-nut system coupling is telescopic and, more specifically, mounted so that it can slide on the shaft of the motor, urged by a spring towards the plug in the direction to uncover the hot liquid inlet access and to shut the cold liquid inlet access. Thus, when the thermostatic element exerts a force on the plug in the opposite direction which is higher than that of the spring, in order to shut off the hot liquid inlet access and uncover the cold liquid inlet access, the spring is compressed by the retraction of the screw-nut system and there is then nothing to prevent this respective shutting-off and uncovering. 
     Because this device is of the plug valve type, it has a configuration which is sometimes difficult to tailor to certain engine and cooling circuit structures. Another disadvantage of this device is that when the temperature of the liquid in which the thermostatic element is immersed decreases, the screw-nut system accompanies the retracting movement of the thermostatic element which, because the electric motor or its control gear is defective, leads to a further rise in temperature, a further elongation of the thermostatic element, and an operation which tends towards instability with “warm” liquid at a temperature appreciably higher than the desired temperature. In addition, the thermostatic element has to be relatively powerful in order to overcome the resistive force of the spring, and the screw-nut system with its telescopic spring-loaded mounting is relatively bulky, which means that the dimensions of the thermostatic device cannot be reduced as far as might be necessary. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to overcome these drawback. The invention therefore relates to a thermostatic device comprising a housing including fluid accesses so that it is possible for at least one fluid access to be shut off by a shutter. A metering actuator fixed to the housing and equipped with an output stem that can move in translation and is mechanically connected to the shutter in order to actuate this shutter in terms of translation selectively in a direction in which it gradually shuts off the access that can be shut off and in a direction in which it gradually, as a function of at least one engine operating parameter detected by at least one sensor, uncovers the access. A safety thermostatic element is situated at least partially in the stream of fluid and includes a part designed to actuate the shutter in translation when, as a result of defective operation, the latter has not been actuated by the metering actuator and the temperature of the stream of fluid exceeds, by a predetermined value, the temperature which should have given rise to such actuation by this actuator. The metering actuator is a proportional-control actuator consisting of an expanding-material thermostatic element also containing a heating means associated with the means for connecting the heating means to control gear involving a computer connected to the sensor, by which the metering actuator is driven through the connecting means. 
     By virtue of the fact that the proportional-control metering actuator is a thermostatic element designed to be heated at the command of a computer, rather than an electric motor such as a stepping motor, the cost price of the thermostatic device is appreciably lowered. 
     Conventional devices with two thermostatic elements have a metering thermostatic element, the expanding material of which is heated only by the fluid passing through the housing, and also have a thermostatic element for adjusting the threshold at which regulation began, and could be heated or not at the command of a computer. Thus a comparison between the conventional device and the present invention will clearly demonstrate that the device according to the present invention makes it possible to obtain a vehicle engine operating temperature which is always optimum from two points of view, including fuel consumption and pollutant emissions, irrespective of the load on this engine. 
     The thermostatic device may also exhibit one or more of the following features. 
     The heating means may comprise a resistive electrical component, and the connecting means may be electrical conductors designed to connect the resistive component to the control gear comprising the vehicle on-board computer. 
     The safety thermostatic element may be set to actuate the shutter in the opening direction at a fluid temperature a few degrees higher than the temperature at which the metering actuator is set to actuate the shutter in that direction. 
     The metering thermostatic element may be arranged in the housing downstream of the access that can be shut off by a shutter. 
     The metering thermostatic element may be carried by a support extending into a duct belonging to the housing. 
     The metering thermostatic element and the safety thermostatic element may be arranged one on each side of the access that can be shut off, and the metering thermostatic element may have an output stem which can move in terms of translation and which projects towards the shutter. The safety thermostatic element may have a piston, also projecting towards the shutter and facing the output stem, and the piston may be fixed to the output stem. 
     The safety thermostatic element may have a collar housed at least partially in skirt of the shutter. 
     The device may comprise a return spring resting against the shutter to exert a force on it that tends to return it in the direction of closing. 
     Finally, the output stem and the piston are secured together with the interposition of a thrust washer designed to be able to rest selectively, at the end of travel, against the free end of a ring of the metering element and against the free end of a ring of the back-up element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent from the description which will follow of one embodiment of the invention illustrated by the appended drawings in which: 
     FIG. 1 is a diagrammatic section view of a thermostatic device according to the invention in a condition in which the moving shutter of the device is subjected to the action of the metering actuator when the latter and/or its control gear is or are not defective; and 
     FIG. 2 is a diagrammatic section view of a thermostatic device according to the invention in a condition in which, as the actuator and/or its control gear is or are defective, the back-up thermostatic element has taken over to actuate the moving shutter. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order not to overload the drawing, a certain number of components and lines relating to components which are behind the section planes have not been depicted in the figures, but the arrangement of the device according to the invention will be made easier to understand by the description which will follow. 
     The thermostatic device depicted comprises, in the known way, various members housed in a housing. The housing is generally made of synthetic material, formed of a duct or pipe  1 , and may be straight or may be elbowed. Fingers  2 , housed in a body  3  consisting of a region of a vehicle engine surrounding a passage  4  through which the engine cooling liquid passes are carried on pipe  1 . The passage is hollowed out in this region and one or more conduits for the circulation of fluid, such as a cooling liquid, terminate therein. The pipe  1  is externally equipped with a fixing flange  5  via which it is fixed to the body, for example by screws. The region of its free end opposite to its end region which has the fingers  2  is designed for another duct such as a hose to be attached to it. 
     In this case, the pipe  1  and the passage  4  have an axisymmetric overall shape with a cross section at right angles to the axis which is approximately circular, and the axes run, in alignment, along one and the same central longitudinal axis, in a first direction. 
     The region of the housing running into the passage  4  has at least one first access (fluid inlet)  6  for fluid coming from the engine, and a second access (fluid outlet)  7  for transmitting in the downstream direction some of the fluid which is intended to be recirculated, generally by means of a water pump. 
     The first access  6  lies near the free end of the fingers  2 , and the second access  7  is delimited by the end region of the duct  1 , to which the fingers are connected. At this second access  7 , the interior surface of the pipe  1  has a frustoconical shape widening towards the first access to form a seat  8  for a shutter which here consists of a shutter element  9  for metering the fluid allowed to flow through the passage  4  to the pipe  1 . The region of the housing that runs between the first access  6  and the seat  8  will hereafter be referred to as the “upstream region” of the housing, while the region which runs beyond the seat  8  into the pipe  1  towards the free end thereof will be termed the “downstream region” of the housing. 
     In order to selectively actuate the shutter element  9  in translation in a direction in which it gradually shuts off the fluid outlet access  7  and in a direction in which it progressively (particularly as a function of the temperature of the stream of cooling fluid passing through the thermostatic device detected by a sensor CT 1  immersed in this stream approximately at the first access  6 ) opens the access  7 , the device comprises a metering actuator  10  fixed to the housing and equipped with an output stem  11  mechanically connected to the shutter element  9 . 
     More specifically, the metering actuator  10  is a linear motor consisting of a thermostatic element including an expanding material  12 , such as expanding wax, and also including a means for heating this material, such as a resistive electrical component  13 . Connecting means  14  connects the heating means to control equipment (i.e., a controller) designed to cause the thermostatic element to operate as a proportional-control linear motor. More specifically, in this case, the electrical power supplied to the thermostatic element  10  (and the travel of the stem  11 ) is proportional to the difference between the measured temperature of the fluid and a programmed-in reference temperature. Control may also be integral (proportional action at the “surface” of the difference) and/or derivative (partial compensation for dead times), and it is also possible to use “fuzzy logic.” 
     The resistive electrical component  13  may be a simple electrical resistor, a helix-wound resistor known commercially by the name of THERMOCOAX, a resistor printed onto an insulating wafer, a resistive rod, or a thermistor known in the art by the name C.T.P. The connecting means  14  is an electrical conductor connected to the resistive component  13 . 
     The thermostatic element constituting the metering actuator  10  is carried by an elbowed tubular support  15  integrally connected to the housing and running inside the housing in its downstream region. The tubular support  15  opens to the outside of the pipe  1  via an orifice pierced in the side wall of pipe  1 , and opens to the inside of the pipe via a circular orifice centered on the central longitudinal axis common to the pipe  1  and to the passage  4  and opening towards the seat  8 . The support  15  thus has a first portion running in the first direction defined above as being that of the aforementioned longitudinal axis of the device, in which the envelope  16  of the thermostatic element is fixed, and a second portion running in a second direction at right angles to the first direction in the particular instance in which the pipe  1  is not elbowed, and in which in this instance a grommet  17  is fixed for the passage of the electrical conductors which constitute the connecting means  14 . As an alternative, the second portion may be used for fixing an electrical connector to which the conductors  14  are connected. 
     The resistive component  13  is fixed at one of its ends into an end region of the envelope  16  which is inserted into the first portion of the support  15 , and the greater part of the length of resistive component  13  runs into the mass of expanding material  12 . The opposite end region of the envelope  16 , the greater part of the length of which extends into the pipe  1  outside the support  15 , comprises a collar  18  in which is crimped a ring  19  forming a guide support for the output stem  11  which passes slidingly through the ring  19  and to which is fixed a deformable tubular cap  20  lodged in the mass of expanding material contained in the envelope  16 . The region of the output stem  11  that runs inside the envelope  16  is inserted into the cap  20 . By contrast, it is the region of the output stem  11  which projects out of the envelope  16  and out of the ring  19  towards the shutter element  9  which is connected mechanically to the shutter element  9  in order to actuate it in translation. 
     The operation of the metering actuator  10  is controlled by equipment (controller) comprising a computer  21  which may be the vehicle on-board computer or may be a separate computer. The computer  21  receives information about the temperature T 1  of the cooling fluid, transmitted to it by the sensor CT 1  immersed in the stream of fluid upstream of the seat  8  for the shutter element, and possibly also receives information about the air temperature T 2  at the engine inlet, information about the vehicle speed, information about the engine load, and/or information about the external temperature, which items of information are transmitted to it by appropriate sensors. In order to slave or at least drive the metering actuator  10  using the computer control equipment, the computer  21  is connected to the actuator  10  directly by the connecting conductors  14  or through any conductor that might be fixed into the support  15 . 
     The thermostatic device according to the invention further comprises a safety thermostatic element  22  also containing an expanding material  23  which is an expanding wax, but without internal heating means. An envelope  24  of the element  22  is immersed in the cooling fluid passing through the upstream region of the housing. This safety element  22  is arranged in line with the metering actuator  10  by being centered on the central longitudinal axis of the pipe  1  and of the passage  4 , but in opposition to the metering element. The closed end of envelope  24  is approximately in line with the free end of the fingers  2 , and ring  25  forms a guiding support for piston  26  and is approximately level with the shutter element  9 . 
     More specifically, the end region of the envelope  24  near the bottom thereof is centered between the fingers  2  by being mounted to slide in a hole in the central part of a bridge element  27  carried by the fingers  2  and running in the upstream region of the housing. For this purpose, the bridge element  27  has branches projecting radially towards the fingers  2 , and the free ends of the branches are housed in respective notches  28  of the fingers near the free end of the fingers and are in abutment against bottom surfaces of these notches, which run at right angles to the longitudinal axis of the housing, due to the action of a helical spring  29 . This spring, surrounding the safety element  22 , has one of its ends resting against the branches of the bridge element and has the opposite end resting against the shutter element  9 . 
     The shutter element  9  includes a bearing annulus  30  made of synthetic material which, facing the seat  8 , has an approximately frustoconical surface with a diameter that increases towards the fluid inlet access  6 . The bearing annulus  30  is designed to rest against the seat  8  when the shutter element is in the closed position. The element  9  also includes a metallic reinforcement  31  in the form of a dish with a circular periphery, and the peripheral region of the reinforcement  31  is inserted in the interior surface of the bearing annulus  30 . The central regions of the bridge element  27  and of the metallic reinforcement  31  surrounding the envelope  24  of the safety element  22  comprise, facing each other, respective approximately cylindrical skirts for centering the helical spring  29  around the envelope  24 . 
     At the end opposite to its bottom near the free end of the fingers  2 , the envelope  24  has a collar  32  in which is crimped the ring  25  through which the rod of the piston  26  passes. The rod is mounted to slide in the ring and is also fixed to a deformable tubular cap  33  housed in the mass of expanding material contained in the envelope  24 . The region of the rod of the piston  26  extending into the envelope is inserted into cap  33 . The collar  32  is housed at least partially in the skirt  34  of the metallic reinforcement  31 , and the surface of its shoulder connects to the cylindrical part of the envelope containing the expanding material, extends in a plane perpendicular to the longitudinal axis of the housing, and rests against the bottom of the skirt of the metallic reinforcement  31 . 
     The mechanical connection between the metering actuator  10  and the safety element  22  with the shutter element  9  allows, in normal operation, proportional actuation of the shutter element by the metering element under the control of the gear involving the computer. In the event of defective operation of the metering actuator  10  and/or its control equipment, the connection also allows actuation of the shutter element by the safety element. 
     This mechanical connection is extremely simple because all that is required is for the output stem  11  of the metering element and the piston  26  of the safety element to be fixed together with the interposition of a thrust washer  35  projecting annularly with respect to the stem  11  and the piston  26 . The washer  35  is arranged at the end of travel, to rest selectively against the free end of the ring  19  of the metering actuator and against the free end of the ring  25  of the back-up element. For example, the stem  11  at its free end has a threaded finger and the piston  26  at its free end has a tapped hole into which this threaded finger, around which the thrust washer  35  is slipped, is screwed. 
     Thus, the flow of the cooling liquid can be regulated according to the temperature of the water circuit, the air inlet temperature, the vehicle speed, the engine load and the external temperature, by moving the shutter element  9  away from the seat at will. The flow and the temperature in the water circuit can be set to the optimum value for obtaining maximum consumption saving and minimum pollution for each phase in the operation of the engine regardless of the load thereon. More specifically, the thermostatic device according to the invention and its control gear can be set so that, when the gearbox is in a given gear, the voltage applied to the metering actuator  10  follows the variations in vehicle speed and maintains a cooling fluid temperature at the outlet of the engine which is approximately constant, for example within a 4° C. range. When the cooling fluid temperature sensor detects that the amount by which optimum temperature is exceeded is greater than a predetermined value, suggesting defective operation of the metering actuator  10  or of its control equipment, the safety element  22  positioned upstream of the shutter element  9  moves the shutter element  9  to a distance which is itself predetermined according to an algorithm in the computer which takes account of the information delivered by the other sensors. The value of the threshold at which the safety element  22  comes into operation can be chosen, for example, in a range from 2° C. to 5° C. higher than the ideal set temperature for high temperatures. For example, in the case of an ideal temperature of 100° C. to 102° C., it may be possible to choose a temperature of 104° C. for the temperature at which the safety element begins to open, and a temperature of 110° C. at which it is wide open. 
     Alarm equipment may be connected to the computer to let the driver of the vehicle know if it becomes impossible to set to the ideal temperature, in which case the vehicle will have to be taken to a workshop where the cooling circuit can be checked out, adjusted and, if necessary, repaired. 
     By virtue of the fact that the metering actuator  10  is downstream of the shutter element  9 , the reaction time for opening the shutter element when the shutter is first opened in operation, is shortened. 
     By virtue of the fact that this element is a thermostatic element heated under the control of a computer, operation similar to that of a thermostatic device with a stepping motor and reversible screw is obtained. Hence, an appreciably less complex set-up is achieved at an appreciably lower cost. 
     Of course, the invention is not restricted to the form of the embodiment described hereinabove and depicted, and others may be envisaged without departing from its scope.