Abstract:
A brake fluid reservoir ( 10 ) for a motor vehicle having at least one impervious and flexible wall ( 12 ) whose capacity is adjusted to the volume of brake fluid contained therein to avoid placing the reservoir at a depression with a drop in the level of brake fluid. The flexible wall ( 12 ) forms a pouch containing brake fluid and has an outlet arrangement ( 16 ) that is initially closed by an impervious membrane ( 32 ) that is punctured to supply brake fluid to a second reservoir ( 20 ) connected to a brake system.

Description:
The invention relates to a brake fluid reservoir, particularly for a motor vehicle. 
     BACKGROUND OF THE INVENTION 
     Known brake fluid reservoirs are made of rigid material and are generally arranged above the master cylinders of the braking circuits to which they are connected, so that the brake fluid can flow under gravity from the reservoirs to the master cylinders. 
     In order to avoid the possibility of a depression, which would carry the risk of preventing the fluid from flowing, being created in a brake fluid reservoir, the interior of the reservoir is connected to the surrounding atmosphere via a vent orifice, so as to maintain atmospheric pressure within the reservoir. However, because brake fluid is very sensitive to moisture, because water vapor dissolves in the brake fluid and lowers its boiling point, with a risk of the formation of vapor lock in the braking circuits, and because it is also very inflammable, it is necessary to avoid letting this fluid come into contact with the air or allowing it to escape to the open air, and systems of baffles have to be mounted for this purpose in the reservoir vent holes. 
     Furthermore, it is commonplace for level detection means to be mounted in these reservoirs, which means are generally enclosed in glass ampoules the fragility of which makes them fairly tricky to handle and to fit, with the inevitable risk of breaking these ampoules.  
     SUMMARY OF THE INVENTION 
     It is a particular purpose of the invention to afford a simple, effective and economic solution to these problems. 
     The subject of the invention is a brake fluid reservoir which can be isolated from the ambient surroundings while at the same time avoiding the risks of the formation of a depression within the reservoir. 
     The invention proposes to this end a brake fluid reservoir, particularly for a motor vehicle, at least part of this reservoir containing brake fluid, characterized in that this part is sealed with respect to the surrounding atmosphere and comprises at least one impervious and flexible wall allowing its capacity to be adjusted to the volume of brake fluid and/or air it contains, so as to avoid placing the reservoir in depression when the volume of brake fluid in the reservoir drops. 
     The flexible wall present in the reservoir according to the invention can accompany a drop in level of the fluid in the reservoir and vary the internal volume of the reservoir without that leading to a change in pressure in the reservoir, which means that the latter can be completely isolated from the surrounding atmosphere without the risk of internal depression. This isolation avoids any contact between the brake fluid and water vapor in the reservoir and also prevents the brake fluid from escaping from the reservoir. 
     In a first embodiment of the invention, the flexible wall sealingly connects two rigid parts of the reservoir, that are mounted so as to be able to move one relative to the other.  
     As a preference, these two parts of the reservoir comprise an upper part and a lower part, the upper part being able to move in translation on the lower part. 
     In another embodiment of the invention, the flexible wall forms an upper part of the reservoir, the lower part of which is rigid. 
     In a preferred embodiment of the invention, the flexible wall forms a pouch inside the reservoir and is initially filled with brake fluid. It advantageously comprises, at the lower part, fluid outlet means sealingly connected to a second reservoir placed at a level below that of the first mentioned reservoir and comprising means of connection to a braking circuit. 
     In one particularly advantageous embodiment of the invention, the outlet means of the pouch are initially closed off by a sealed membrane and the means of connection to the second reservoir comprise means of puncturing this membrane. 
     As an alternative, the reservoir according to the invention may comprise two aforesaid pouches initially filled with brake fluid and each of which is connected to one compartment of the second reservoir, each compartment of this second reservoir being connected to a braking circuit. 
     The invention will be better understood, and other features, details and advantages thereof will become more clearly apparent, from reading the description which follows, given by way of example with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view in vertical section of a brake fluid reservoir according to the invention, connected to a braking circuit;and  
         FIGS. 2 and 3  are schematic views in vertical section of alternative forms of embodiment of the reservoir according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , the reference  10  denotes a first reservoir or upper reservoir containing a pouch  12  of flexible material impervious to brake fluid, made for example of an appropriate plastic chemically resistant to brake fluid and possibly having an outer coating for sealing, such as a thin layer of aluminum or similar for example. In this case, the upper part of the pouch  12  advantageously comprises a transparent window  14  allowing visual observation of the inside of this pouch. 
     The lower part of the pouch  12  is connected with sealing to a tube  16  which extends through an orifice  18  in the lower wall of the reservoir  10  toward a second reservoir  20  placed at a level lower than that of the first reservoir  10  and comprising two compartments  22 ,  24  each connected by a pipe,  26 ,  28  respectively, to a double braking circuit  30  of a conventional type. 
     The lower end of the tube  16  is initially closed by an impervious membrane  32  which is automatically perforated when the lower end of the tube  16  is fixed to the upper end of a pipe  34  feeding the second reservoir  20 . 
     For example, the sealed joint between the tube  16  and the pipe  34  is produced by screwing on a threaded ring  36  which, in succession, tightens the end flanges of the tube  16  and of the pipe  34  together with sealing, then causes the membrane  32  to be perforated by a pointed element  38  mounted fixedly inside the pipe  34 , in the upper part thereof.  
     The two compartments  22 ,  24  of the lower reservoir  20  are separated from one another in the lower part and communicate in the upper part, making it possible to maintain a minimum level of fluid in one of the compartments if fluid in the braking circuits fed by the other compartment should leak. 
     A safety valve  40  is also provided on the second reservoir  20 , this safety valve allowing escape to the outside in the event of an overpressure within the reservoirs  10 ,  20 , to prevent them bursting. 
     A level detector  42  of a conventional type is also mounted inside the second reservoir  20  and is connected to an external circuit that warns of a lack of brake fluid. 
     Initially, the pouch  12  is filled entirely with brake fluid isolated from the surrounding atmosphere by the impervious membrane  32  closing the outlet tube  16  of the pouch  12 . 
     The upper reservoir  10  advantageously comprises a removable lid  44  which is not airtight and is preferably transparent, allowing a pouch  12  filled with brake fluid to be placed without difficulty inside this reservoir and its outlet tube  16  passed through the orifice  18  of the reservoir. Screwing the threaded ring  36  onto the lower end of the tube  16  allows this tube to be connected with sealing to the pipe  34  of the lower reservoir  20  and allows the membrane  32  to be punctured. The tubes of the braking circuit  30  have been filled with brake fluid beforehand, and connecting the pouch  12  to the lower reservoir  20  allows the topping-up of this reservoir. The flexibility of the pouch  12  allows it to collapse down into the upper reservoir  10  as brake fluid flows into the lower reservoir  20 . This flow  does not cause any air to enter the pouch  12  nor does it cause any relative depression. The brake fluid is thus well protected from any contact with the ambient atmosphere and from the water vapor it may contain. If the detector  42  signals that the brake fluid level has dropped below a minimum level, all that is required is for the ring  36  to be unscrewed and the pouch  12  contained in the upper reservoir  10  changed. 
     To improve safety, two pouches  12  filled with brake fluid may be placed side by side in the upper reservoir  10 , and one of these pouches connected to one compartment  22  of the lower reservoir  20  and the other pouch to the other compartment  24  of this lower reservoir. In this case, the two compartments  22 ,  24  can be completely separate of each other. 
     In the alternative form of the embodiment depicted schematically in  FIG. 2 , the brake fluid reservoir  50  comprises a rigid lower part  52  of cylindrical or parallelepipedal shape, comprising two compartments  54 ,  56 , each formed with an outlet pipe  58 ,  60 , respectively connected to a braking circuit, and a rigid upper part  62 , also of cylindrical or parallelepipedal shape, comprising an upper wall  64  and a peripheral wall or side walls  66  that are connected to the corresponding peripheral wall or corresponding side walls of the lower part  52  by a flexible wall  68  made of a material impervious and resistant to brake fluid. 
     In this embodiment, the brake fluid entirely fills the reservoir  50 , the upper part  62  of which is borne by the brake fluid. The flexible wall  68  allows this upper part  62  to slide or move in translation downward on the lower part  52  when the brake fluid level in the reservoir  50  drops.  
     A safety valve  40  may be mounted on the upper wall  64  of the upper part  62  of the reservoir, and a level detector  42  may be mounted in the lower part  52  of the reservoir. 
     The upper wall  64  of the upper part  62  of the reservoir may also comprise a filling orifice  70 , sealed by a screw cap  72  or bayonet-type plug. 
     As a preference, the upper part  62  of the reservoir  50 , borne by the brake fluid contained in the reservoir, is made of a lightweight material capable of floating on the brake fluid, so as not to impede the filling of the reservoir  50  at atmospheric pressure. 
     The flexible wall  68  forms a skirt the upper and lower peripheries of which are sealed to the lower edge of the upper part  62  and to the upper edge of the lower part  52  of the reservoir. 
     In the alternative form of the embodiment of  FIG. 3 , the reservoir is made essentially of rigid material, except for its upper wall  74  which is made of flexible material, impervious and resistant to brake fluid, this flexible wall  74  being fixed at its periphery with sealing along the upper edge of the side walls or peripheral walls  76  of the reservoir. 
     A removable lid  78  may be mounted in the upper edge of the reservoir to protect the flexible wall  74 . This lid has dimensions greater than the internal transverse dimensions of the reservoir so that by deformation, but without stretching and therefore without a return force, it can accompany a drop in level of the brake fluid in the reservoir. 
     In this form of embodiment, the reservoir comprises a filling pipe  80  that can be sealed off using a plug  82 , this pipe  80  running from the top of  the reservoir and opening into this reservoir under the flexible wall  74 . A safety valve  40  is also mounted on the peripheral wall of the reservoir under the flexible wall  74 . A level detector  42  may also be mounted in the reservoir, under this flexible wall, as depicted. 
     For the remainder, the lower part of the reservoir may comprise two compartments  84 ,  86  each connected by a pipe  88 ,  90 , respectively, to a braking circuit, these two compartments communicating with one another at the upper part, as already described.