Abstract:
A brake hydraulic pressure control unit is proposed. It includes housing, a pump mounted in the housing, a reservoir for hydraulic fluid, and hydraulic pressure control valves. The pump is adapted to draw hydraulic fluid in the reservoir and return the thus drawn fluid into a hydraulic circuit. The hydraulic pressure valves are adapted to selectively discharge fluid in the hydraulic circuit into the reservoir, thereby controlling brake hydraulic pressure. The control unit may further include a pulsation damper for muffling noise produced from the pump. The reservoir and the pulsation damper are both separate members from the housing and are mounted to the housing. Thus, the volume of the housing and the capacities of the reservoir and the pulsation damper can be determined independently of each other.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to a brake hydraulic pressure control unit for use in a vehicle for increasing and reducing brake hydraulic pressure using electric signals.  
         [0002]     A conventional such brake hydraulic control unit is disclosed in JP patent publication 8-502007.  
         [0003]     The brake hydraulic pressure control unit disclosed in this patent publication includes a housing in which is mounted a pump, a hydraulic fluid reservoir, hydraulic pressure control valves, and a motor for driving the pump. The pump draws hydraulic fluid in the reservoir and returns it to the brake line. The electronic control unit controls the brake pressure by selectively supplying hydraulic fluid into the hydraulic circuit (for pressure increase) and discharging hydraulic fluid into the reservoir (for pressure reduction) by opening and closing the hydraulic pressure control valves.  
         [0004]     The brake hydraulic pressure control unit disclosed in JP patent publication 8-502007 includes a pulsation damper disposed between the discharge port of the pump and the hydraulic circuit for muffling the pump operation noise.  
         [0005]     The reservoir and the pulsation damper are formed integrally with the housing. Specifically, as shown in  FIG. 10 , the reservoir comprises a bore  2  as a fluid chamber which is formed in the housing  1 , a reservoir piston  3  inserted in the bore  2 , a cover  4  coupled to the housing  1 , and a spring  5  disposed between the reservoir piston  3  and the cover  4  for biasing the reservoir piston  3  to move it in such a direction that the volume of the fluid chamber decreases.  
         [0006]     All the other conventional brake hydraulic pressure control units also have their reservoir formed as an integral part of the housing. Such an integral reservoir makes it difficult to reduce the size and cost of the entire unit for the following reasons.  
         [0007]     If a plurality of reservoirs of such brake hydraulic pressure control units have lengths substantially equal to one another, their capacities are proportional to the square of their diameters and proportional to their piston strokes. Thus, if the capacity of the reservoir is fixed, as such a reservoir, one having a greater diameter and a shorter length should be selected in order to reduce the size of the brake hydraulic pressure control unit to a minimum. But a reservoir having a large diameter increases the depth of the housing  11  (dimension shown by “S” in  FIGS. 10 and 11 ).  
         [0008]     Conversely, if a reservoir having a greater length and shorter diameter is used while keeping its capacity unchanged, the height H of the housing will increase. The numeral  7  in  FIGS. 10 and 11  indicates a pump-driving motor fastened to the housing.  
         [0009]     The width w of the housing  1  is determined by the pitch of pipe connections (not shown) provided on the top  1   a  of the housing  1 . Thus, if the depth s and/or height H is large, each side  1   b  naturally has a correspondingly large area. Such a housing is large in size.  
         [0010]     The minimum value of the capacity of the reservoir is determined by the structure of the vehicle on which the brake hydraulic pressure control unit is to be mounted. The minimum value of the capacity of the reservoir in turn determines the minimum size of the housing as described above. Thus, if it is desired to use a housing having the allowable minimum size for the vehicle on which the control unit is to be mounted, a large number of housings that are different in type and size from one another have to be prepared according to vehicle types. One way to avoid this problem is to use uniform housings which can accommodate the largest reservoir. But such housings are unnecessarily too large to accommodate smaller reservoirs. Preparing a large number of housings that are different in size from one another and preparing uniform but oversized housings are both economically unfavorable.  
         [0011]     For the pulsation damper, too, which is optionally provided as necessary, the greater its capacity, the more effectively it can damp pulsation. But if the damper, which is also an integral part of the housing as with the reservoir, is unnecessarily large in size, the size of the housing will also have to be unnecessarily increased, which pushes up the cost of the entire control unit.  
         [0012]     If the size of the housing is reduced to a minimum, it will be difficult to increase the capacities of the reservoir and the pulsation damper even slightly.  
         [0013]     An object of this invention is to provide a low-cost, compact brake hydraulic pressure control unit comprising a housing and a reservoir and optionally a pulsation damper in which the size of the housing can be determined irrespective of the capacities of the reservoir and the pulsation damper.  
       SUMMARY OF THE INVENTION  
       [0014]     According to this invention, there is provided a brake hydraulic pressure control unit comprising a housing, a pump mounted in the housing, a reservoir for hydraulic fluid, and hydraulic pressure control valves, the pump being operated to draw hydraulic fluid in the reservoir and return the thus drawn fluid into a hydraulic circuit, the hydraulic pressure valves being adapted to selectively discharge fluid in the hydraulic circuit into the reservoir, thereby controlling brake hydraulic pressure, the reservoir being a separate member from the housing and mounted to the housing.  
         [0015]     Preferably: 
    {circle over ( 1 )} the reservoir is selected from among a plurality of reservoirs having different capacities from one another;     {circle over ( 2 )} the reservoir mounted to the housing and the other reservoirs not selected have common connecting portions at which they can be connected to the housing;     {circle over ( 3 )} each reservoir includes a piston having a diameter and a connecting portion at which the reservoir is connected to the housing, the connecting portion having a diameter smaller than the diameter of the piston;     {circle over ( 4 )} each reservoir includes a casing manufactured by non-cutting method; and/or     {circle over ( 5 )} each reservoir includes a casing formed of a corrosion-resistant metal or resin.    
 
         [0021]     This brake hydraulic pressure control unit may further comprise a pulsation damper mounted to the housing between a discharge port of the pump and the hydraulic circuit, the pulsation damper being a separate member from the housing.  
         [0022]     Preferably: 
    {circle over ( 1 )} the pulsation damper is a volume damper in the shape of a container;     {circle over ( 2 )} the pulsation damper is selected from among a plurality of pulsation dampers having different capacities from one another;     {circle over ( 3 )} the plurality of pulsation dampers have common connecting portions at which any of them can be connected to the housing;     {circle over ( 4 )} each pulsation damper comprises a body having an external diameter and a connecting portion at which the damper is connected to the housing, the connecting portion having a diameter smaller than the external diameter of the body of the first pulsation damper;     {circle over ( 5 )} each pulsation damper includes a casing manufactured by non-cutting method;     {circle over ( 6 )} each pulsation damper includes a casing formed of a corrosion-resistant metal or resin; and/or     {circle over ( 7 )} each pulsation damper is a one-piece damper consisting of a casing.    
 
         [0030]     Further preferably, the reservoir and the pulsation damper are mounted to the housing so as to be virtually unseparable from the housing or separable only with extreme efforts.  
         [0031]     By forming the reservoir and the housing separately from each other, it is possible to select the reservoir from among a plurality of reservoirs having different capacities according to the type of vehicle on which the control unit of the invention is to be mounted, without changing the size of the housing. Thus, housings of the same type and size can be used for a variety of different vehicle types.  
         [0032]     The volume of the housing has no influence on the capacity of the reservoir, and vice versa. Thus, any of a plurality of reservoirs having different capacities can be mounted to a single, common housing having a necessary minimum volume and size. The capacity of the reservoir is restricted only by the type of vehicle on which the control unit is to be mounted, and not by the size of the housing.  
         [0033]     This is also true with the relation between the housing and the pulsation damper of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]     Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:  
         [0035]      FIG. 1  is a schematic side view of a brake hydraulic pressure control unit embodying this invention;  
         [0036]      FIG. 2  is a basic circuit diagram of a hydraulic brake system of a vehicle which includes a brake hydraulic control unit such as the one according to the present invention;  
         [0037]      FIG. 3  is a sectional view of a reservoir as mounted to the housing of the control unit of  FIG. 1 ;  
         [0038]      FIG. 4  is a sectional view of a different reservoir as mounted to the housing;  
         [0039]      FIG. 5  is a sectional view of a still another reservoir as mounted to the housing;  
         [0040]      FIG. 6  is a sectional view of a yet another reservoir as mounted to the housing;  
         [0041]      FIG. 7  is a sectional view of a further different reservoir as mounted to the housing;  
         [0042]      FIG. 8  is a sectional view of another reservoir as mounted to the housing;  
         [0043]      FIG. 9  is a sectional view of a pulsation damper to be mounted to the housing;  
         [0044]      FIG. 10  is a sectional view of a reservoir of the brake hydraulic pressure control unit disclosed in Japanese patent publication 8-502007, which is a one-piece member of the housing; and  
         [0045]      FIG. 11  is a view for explaining the dimensions of the housing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0046]     Now referring to the drawings, the embodiment of the present invention will be described.  
         [0047]     As shown in  FIG. 1 , the brake hydraulic pressure control unit according to this invention, generally designated by  10 , comprises a housing  11  in which is mounted a pump  12 , a reservoir  13  in which is stored hydraulic fluid discharged from a hydraulic circuit, a pulsation damper  14  for muffling noise originating from the pump  12 , a motor  15  for driving the pump  12 , and an electronic control unit  16 . The motor  15  and the electronic control unit  16  are fastened to one side and the other side of the housing  11 , respectively. The reservoir  13  and the pulsation damper  14  are mounted to the bottom of the housing  11 .  
         [0048]     The reservoir  13  and the pulsation damper  14  are manufactured separately from each other and from the housing  11 , and are mounted to the housing  11 . Thus, the housing  11  itself is compact in size and can be mounted on a variety of different vehicles without changing its design or size at all.  
         [0049]     The reservoir  13  and the pulsation damper  14  are selected from among a plurality of reservoirs and dampers having different capacities, respectively. Similarly, the motor  15  is selected from among a plurality of motors having different outputs, and the electronic control unit  16  can be selected from among a plurality of different control units and combined with the housing  11 .  
         [0050]      FIG. 2  shows the basic circuit structure of a hydraulic brake system for a vehicle which is provided with the brake hydraulic pressure control unit  10  according to this invention, which includes, as described above, the pump  12 , reservoir  13 , pulsation damper  14 , and motor  15 , and further includes a pressure increase valve  17  and a pressure reduction valve  18  (see  FIG. 1 ). Besides the control unit  10 , this brake system includes a brake pedal  19 , a tandem master cylinder  20  and wheel cylinders  21 . In the drawings and the description, only one of the two hydraulic circuits is shown and described.  
         [0051]     In  FIG. 2 , the lines enclosed in one-dot line are formed in the housing  11 . The pump  12  is mounted in the housing  11  as described above. The pump  12  may be a double action piston pump. Since such a pump is well-known in the art, its detailed structure is neither described nor shown here.  
         [0052]     The pressure increase valve  17 , which opens and closes a line for increasing pressure, and the pressure reduction valve  18 , which opens and closes a line for reducing pressure, are mounted in the housing  11 . One or some elements (e.g. coils  17   a  and  18   a ) of the pressure increase valve  17  and pressure reduction valve  18  are integral parts of the electronic control unit  16 . When the electronic control unit  16  is fastened to the housing  11 , such elements are coupled or joined to the remaining mechanical elements of the valves  17  and  18 , which are mounted in the housing  11 .  
         [0053]     As described above, the reservoir  13  and the pulsation damper  14  are manufactured separately from the housing  11  and mounted to the housing as shown in  FIG. 1 .  
         [0054]      FIGS. 3-8  show how different reservoirs  13  are mounted to the housing  11  in several examples.  
         [0055]     As shown in  FIGS. 3 and 4 , the reservoir  13  comprises a casing  13   a  defining a fluid storage chamber  13   b , a reservoir piston  13   c  that changes the volume of the chamber  13   b  by moving axially of the casing, and a spring  13   d  biasing the reservoir piston  13   c  in such a direction that the volume of the fluid storage chamber  13   b  decreases. The reservoir  13  is selected from among a plurality of reservoirs having different capacities and having connecting portions  13   e  that are identical in shape and size.  
         [0056]     In the arrangement of  FIG. 3 , the connecting portion  13   e  has a threaded outer surface  22  which is threadedly engaged in a threaded hole formed in the housing  11  to mount the reservoir  13  to the housing  11 . But in order to positively prevent the reservoir from being inadvertently disconnected from the housing  11 , the reservoir  13  should rather be connected to the housing  11  in such a way that once they are joined together, they are practically unseparable or separable only with extreme efforts.  
         [0057]     Such joint arrangements, i.e. unseparable joint arrangements are shown in  FIGS. 4-8 . In the arrangement of  FIG. 4 , the connecting portion  13   e  has a large-diameter portion  23  (or a flange instead) which is engaged in a recess formed in the housing  11  by plastically deforming a portion  25  of the housing  11 . The connecting portion  13   e  of  FIG. 5  has a recess  2  in which a rib  25  is engaged by plastically deforming the rib  25 . In  FIG. 6 , the connecting portion  13   e  is pressed into the housing  11 . In  FIG. 7 , the connecting portion  13   e  is fastened to the housing  11  by a pin or pins  26  that are driven into the housing  11  so as to be received partly in a groove formed in the inner surface of a hole of the housing  11  into which the connecting portion  13   e  of the reservoir  13  is inserted, and partly in a groove formed in the outer surface of the connecting portion  13   e  so as to radially oppose the former groove. In the arrangement of  FIG. 8 , the connecting portion  13   e  of the reservoir  13  and the housing  11  are joined together by plastic injection. Specifically, molten resin is poured into opposed grooves formed in the inner surface of a hole of the housing  11  into which the connecting portion  13   e  of the reservoir  13  is inserted and in the outer surface of the connecting portion  13   e , respectively, from outside of the housing. In order to join the housing  11  and the reservoir  13  together in such a way that they are unseparable or separable only with extreme efforts, two or more of the arrangements of  FIGS. 3-8  may be combined.  
         [0058]     Preferably, as shown in  FIG. 3 , the connecting portion  13   e  has a diameter d that is smaller than the diameter D of the reservoir piston  13   c  so that the diameter of the reservoir  13  can be freely decided irrespective of the size of the housing  11 , or the size of the housing  11  can be reduced irrespective of the diameter of the reservoir  13 .  
         [0059]     Preferably, the casing  13   a  of the reservoir  13  is manufactured by non-cutting method for higher productivity. For example, the casing  13   a  of  FIG. 4  comprises two separate parts, i.e. a body portion having the connecting portion  13   e , which is, in this arrangement, formed by drawing, and a bottom cover formed by pressing. These two parts are joined together by caulking.  
         [0060]     For improved corrosion resistance, the housing  13   a  of the reservoir  13  is preferably formed of aluminum, stainless steel or a resin.  
         [0061]     Preferably, the pulsation damper  14  is also mounted to the housing  11  in the same manner as the reservoir  13  is mounted to the housing  11 . Specifically, they are joined together using one or a combination of the joint arrangements shown in  FIGS. 3-8 .  
         [0062]     Preferably, a connecting portion  14   a  of the pulsation damper  14  has a diameter that is smaller than the external diameter D of the body of the pulsation damper  14  so that the diameter of the body of the damper  14  can be freely designed irrespective of the size of the housing  11 , or the size of the housing  11  can be reduced irrespective of the diameter of the body of the damper  14 .  
         [0063]     For the same reasons as set forth above with respect to the reservoir, the pulsation damper  14  is preferably manufactured by non-cutting method, and is formed of aluminum, stainless steel or a resin.  
         [0064]     The pulsation damper  14  is preferably a one-piece member as shown in  FIG. 9  because it is simple in structure and inexpensive.  
         [0065]     Unlike conventional reservoir and damper, which are actually integral parts of the housing, the reservoir and the damper of the brake hydraulic pressure control unit according to the present invention are manufactured separately from the housing and joined to the housing. Thus, the reservoir and the damper can be selected from among a plurality of reservoirs and dampers having different capacities according to the type of vehicle on which the brake hydraulic control unit according to the present invention is to be mounted, and then can be joined to the housing. The same housing can thus be used for a variety of different vehicles. Such housings can be mass-produced at a low cost because they may be identical to each other in spite of the fact that they can be mounted on different types of vehicles.  
         [0066]     Another advantage of this invention is that the housing can be designed more freely than conventional such housings. Thus, it is possible to reduce the size of the housing and the material cost of the housing. Since the housing can be designed more freely, the manufacturer can more easily answer customers&#39; requirements.  
         [0067]     Both the reservoir and the pulsation damper are small in the pressure-bearing surface and simple in structure. This also contributes to reduction in cost and size.  
         [0068]     Overall, the brake hydraulic pressure control unit according to this invention can be designed with greater freedom, and manufactured at a low cost with a reduced size.