Abstract:
A motor is secured to a housing by securing bolts. These bolts are threaded into screw-threaded holes formed in the housing so as to be parallel to an axis of rotation of a motor driven shaft, which drives radially reciprocal plungers that are disposed in diametrically opposed pump bores located on either side of the shaft. The screw-threaded holes are arranged close to, but offset from, the pump bores so that extrapolations of the screw-threaded holes do not intersect the pump bores or cavities in which pressure pulsation dampers or reservoirs are defined, enabling the housing to be small and low in vibration and noise.

Description:
TECHNICAL FIELD 
     The present invention relates to a brake system which is applied to an anti-brake skid control (which will be hereinafter referred to as a “ABS control”), and is capable of controlling a traction of road wheels and a yawing rate of an automotive vehicle, and particularly to a brake system having a motor-driven pump. 
     BACKGROUND ART 
     Conventionally, it is well known that a brake system which performs an ABS control, is employed with a fluid-pressure control valve capable of reducing, holding, and building up the wheel-brake cylinder pressure, a pump provided for sucking brake fluid drained into the reservoir during the pressure-reduction operation of the fluid-pressure control valve and for discharging the sucked brake fluid toward the upstream side of the fluid-pressure control valve, a damper device provided for dampening pulsation in the brake fluid discharged from the pump, and a motor provided for driving the above-mentioned pump. 
     One such brake system has been disclosed in Japanese Patent Provisional Publication No. 2-231253. 
     In the conventional brake system, a plunger, constructing a pump, is slidably accommodated in the housing so that the plunger is arranged in a direction perpendicular to the rotational axis of the motor. A damper and a reservoir are disposed in the housing. A motor is mounted on one side wall of the housing. As regards the structure of installation of the motor on the housing, mounting bolts are arranged parallel to the rotational axis of the motor in the direction perpendicular to the axial direction of the plunger. These mounting bolts are screw-threaded into the corresponding female screw holes opening at the side wall of the housing. 
     Now then, in recent years, it is desired to small-size and to lighten an unit for an ABS control from the viewpoint of easy mounting of the system on the automotive vehicle. The small-sizing and lightening would be achieved by planning an optimal lay-out of a plunger pump, a damper, a reservoir, and a fluid-pressure control valve, all disposed in the housing of the ABS unit. 
     On the other hand, in designing for a damper and a reservoir, a volumetric capacity necessary for the damper and a volumetric capacity necessary for the reservoir must be selected, accounting for an enhanced dampening effect with respect to the brake fluid pressure and for an enhanced pressure-reduction effect with respect to the brake fluid pressure. Thus, as a matter of course, the degree of the small-sizing of the damper and the reservoir is limited. As a measure of small-sizing the damper and the reservoir, these elements are located closer to each other in the housing, to enable reduction in the total size of the housing. In this case, it is necessary to prevent the position of each of screw-threaded holes for mounting bolts which are used to mount the motor on the housing from overlapping the installation position of the damper and the installation position of the reservoir. On the other hand, it is also necessary to provide a totally-balanced fastening force at the respective fixed points by properly arranging each mounting device containing a bolt and the corresponding female screw-threaded portion. It is difficult to optimally form screw holes in the housing, while satisfying all of the previously-noted necessary conditions. 
     Additionally, when the pump motor is driven during the operation of the previously-described plunger pump, the reaction force to the fluid pressure acts in the axial direction of the pump (or the axial direction of the plunger) on the compression stroke of the plunger. Furthermore, the reaction force transmits from the plunger to the rotational axis of the motor and acts in the direction perpendicular to the rotational axis. As a result of this, the rotational axis of the motor oscillates. There is an increased tendency for the system to vibrate. This produces noise in the system. In such a case, the greater the perpendicular distance of the fixed point of the mounting bolt mounting the motor on the housing with respect to the axial line of the pump (the axial line of the plunger), the smaller the rigidity of supporting the motor. It is disadvantageous to noise and vibrations. 
     Assuming that the fixed point of the motor is aligned with the axial line of the plunger, the rigidity of supporting the motor can be enhanced. It is advantageous to reduction in noise and vibrations. However, the screw holes threadably receiving the mounting bolts and the cylindrical bore accommodating therein the plunger are arranged in the direction of the rotational axis of the motor. Therefore, it is necessary to provide a housing size enough to form the screw hole in a space between the side wall of the housing and the cylindrical bore accommodating therein the plunger. There is a problem that the housing is large-sized. 
     It is, therefore, in view of the previously-described disadvantages of the prior art, an object of the present invention to provide a brake system which is capable of small-sizing the total size of the system and simultaneously reducing noise and vibrations, by disposing the fixed point of each of mounting bolts capable of mounting a motor on a housing at an optimal position, considering the lay-out of a damper and a reservoir arranged in the housing, in order to ensure a necessary volumetric capacity the damper and a necessary volumetric capacity of the reservoir. 
     DISCLOSURE OF THE INVENTION 
     The brake system of the present invention comprises a fluid-pressure generating means provided for generating a brake-fluid pressure depending on a driver&#39;s braking action, a brake actuating section connected through a brake circuit to the fluid-pressure generating means for applying a braking force to a road wheel, a fluid-pressure control means disposed in a middle of the brake circuit for reducing, holding, and building up the brake-fluid pressure of brake fluid in the braking-force actuating section, a reservoir disposed in a drain circuit into which the brake fluid is exhausted by the fluid-pressure control means during a pressure-reduction operating mode, a pump sucking the brake fluid in the reservoir and discharging the sucked brake fluid within toward the fluid-pressure generating means rather than the fluid-pressure control means of the brake circuit, a motor being a driving source of the pump, a motor shaft inserted into an inboard drive-shaft hole formed in a housing, and formed on an outer periphery thereof with a cam profile, pump bores constructing part of the pump and arranged symmetrically on a same axial line perpendicular to the motor shaft in a manner so as to sandwich the cam profile therebetween, plungers whose ends are in abutted-engagement with the cam profile, and the plungers respectively accommodated in the pump bores so that the plungers reciprocate according to rotation of the motor shaft, the motor being fixed to an end face of the housing by screwing mounting bolts into screw-threaded holes formed in the housing, and the screw-threaded holes being arranged substantially parrallelly in an axial direction of the motor shaft, and formed in a direction substantially perpendicular to an axis of the pump bore, wherein the screw-threaded holes are located at positions close to the pump bore to such an extent that the screw-threaded holes and the pump bore do not overlap each other when the pump bore is projected in axial directions of the screw-threaded holes. 
     Therefore, when the motor rotates, the plungers reciprocate in a direction perpendicular to the motor shaft, for sucking the brake fluid in the reservoir and for discharging the brake fluid into the brake circuit. At this time, reaction forces of the fluid pressure act on the plungers, such that the reaction forces are input in the direction perpendicular to the motor shaft. Then, the reaction forces input to the motor shaft are supported by means of the mounting bolts. Under this condition, since the mounting bolts and the screw-threaded holes are arranged to be sufficiently close to the pump bore to such an extent that the mounting bolts and the screw-threaded holes do not overlap with the pump bore in their projected directions, a high supporting rigidity can be obtained in comparison with a case where the mounting bolts and the screw-threaded holes are provided apart from the pump bore. 
     In addition, the screw-threaded holes are arranged at positions where the screw-threaded holes do not overlap with respect to the axis of the pump bore in the projected directions. Thus, in comparison with a case where the screw-threaded holes are arranged to overlap with the pump bore, the thickness measured from the end face of the housing to the pump bore can be reduced, thus small-sizing the dimension of the housing. 
     According to another aspect of the invention, a brake system comprises a fluid-pressure generating means for generating a brake fluid pressure depending on a driver&#39;s braking action, a brake actuating section connected to the fluid-pressure generating means through a brake circuit, for applying a braking force to a road wheel, a fluid-pressure control means disposed in a middle of the brake circuit, for reducing, holding, and building up the brake-fluid pressure of brake fluid in the braking-force actuating section, a reservoir disposed in a drain circuit into which the brake fluid is exhausted by the fluid-pressure control means during a pressure-reduction operating mode, a pump sucking the brake fluid in the reservoir and discharging the sucked brake fluid within toward the fluid-pressure generating means rather than the fluid-pressure control means of the brake circuit, a motor being a driving source of the pump, a motor shaft inserted into an inboard drive-shaft hole formed in a housing, and formed on an outer periphery thereof with a cam profile, pump bores constructing part of the pump and arranged symmetrically on a same axial line perpendicular to the motor shaft in a manner so as to sandwich the cam profile therebetween, plungers whose ends are in abutted-engagement with the cam profile, and the plungers respectively accommodated in the pump bores so that the plungers reciprocate according to rotation of the motor shaft, the motor being fixed to an end face of the housing by screwing mounting bolts into screw-threaded holes formed in the housing, and the screw-threaded holes being arranged substantially parrallelly in an axial direction of said motor shaft, and formed in a direction substantially perpendicular to an axis of the pump bore, wherein the screw-threaded holes are located at positions close to a reservoir hole for the reservoir to such an extent that the screw-threaded holes and the reservoir hole do not overlap each other when the reservoir hole is projected in axial directions of the screw-threaded holes. 
     Therefore, this case just discussed above can produce the same operation and effects as the previously-described case where the pump bore is regarded as the object limiting the layout of the screw-threaded holes. Alternatively, the same effects can be obtained in case that, in addition to the pump bore and/or the reservoir hole, the damper hole may be regarded as the object limiting the layout of the screw-threaded screws. 
     Furthermore, the invention is characterized in that the mounting bolts are secured to two points being point-symmetrical with respect to a center of axis of rotation of the motor shaft, and the screw-threaded holes formed at the two points being point-symmetrical with respect to the center of axis of rotation, and that the screw-threaded holes are arranged so that a line connecting axes of the mounting bolts and a line connecting axes of the screw-threaded holes are inclined by a predetermined angle with respect to an axial line of the pump bore. 
     Since the mounting bolts and the screw-threaded holes are respectively arranged to be point-symmetrical with respect to the axis of the motor shaft, as set forth above, when the reaction force of the fluid pressure is input into the motor shaft in the direction perpendicular to the axis thereof, the moment about the fixed point is scarcely produced, and whereby a high supporting rigidity can be obtained. Also, the system of the invention is characterized in that the previously-noted predetermined angle is 20°. The mounting bolts and the screw-threaded holes are arranged so that an angle between the line connecting the mounting bolts or the screw-threaded holes and the axial line of the pump bore is 20°, and thus the moment about the fixed point is scarcely produced, thereby ensuring a high supporting rigidity. 
     Moreover, the invention is characterized in that the plungers comprise two plungers disposed in the housing and the pump bores comprise two pump bores disposed in the housing, and that a first reservoir and a first damper, both associated with a first plunger of the plungers, are provided in the housing, and a second reservoir and a second damper, both associated with a second plunger of the plungers, are provided in the housing, both of the reservoirs are disposed in first and second reservoir holes and both of the dampers are disposed in first and second damper holes, the first and second reservoir holes and the first and second damper holes being bored from a face perpendicular to all a face of the housing onto which the motor is fixedly connected and faces through which the pump bores open, and bored in a direction perpendicular to both the axis of the pump bore and the motor shaft, and that the two reservoir holes and the two damper holes are arranged so that a line connecting axes of the reservoir holes and a line connecting the damper holes do not overlap each other, and that one of the damper holes is arranged at a position where the one of the damper holes overlaps the pump bore when the pump bore is projected in an axial direction of the one of the damper holes, and that, when viewing the two screw-threaded holes from the face onto which the motor is mounted, one of the screw-threaded holes is arranged in the opposite side of the first damper hole overlapping the pump bore in a projected direction, while sandwiching the pump bore in cooperation with the one of the screw-threaded holes, whereas another screw-threaded hole of the two screw-threaded holes is disposed between the pump bore and the second damper hole, and that the diameters of openings of both of the damper holes are formed to be identical to each other, an axial dimension of the second damper hole is formed to be shorter than an axial dimension of the first damper hole, and that the second damper hole is formed, at a side wall thereof with an enlarged portion provided to enlarge a volumetric capacity of the second damper hole in a diametrical direction, so that the volumetric capacities of both of the damper holes are substantially identical to each other. 
     Therefore, in this invention, in forming one of the two screw-threaded holes between the pump bore and the second damper hole, and in ensuring a space necessary to form this screw-threaded hole, the axial dimension of the second damper hole is shortened and additionally diametrically-enlarged portions are formed in the second damper hole so that the volumetric capacity of the second damper hole is substantially identical to the volumetric capacity of the first damper hole, and whereby the damper performance can be ensured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view illustrating a first embodiment of a brake unit employed in a brake system made according to the present invention. 
     FIG. 2 is a side view illustrating the previously-noted brake unit. 
     FIG. 3 is a plan view illustrating the previously-noted brake unit. 
     FIG. 4 is a cross-sectional view taken along the line S 4 -S 4  shown in FIG.  2 . 
     FIG. 5 is a general view corresponding to a block system diagram showing the brake system of the embodiment. 
     FIG. 6 is a front view illustrating a second embodiment of a brake unit employed in a brake system made according to the invention. 
     FIG. 7 is a side view illustrating the previously-noted brake unit. 
     FIG. 8 is a bottom view illustrating the previously-noted brake unit. 
     FIG. 9 is a cross-sectional view taken along the line S 9 —S 9  shown in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereunder, the embodiments made according to the invention is described in detail by reference to the attached drawings. 
     First Embodiment 
     FIGS. 1 through 5 show the brake system of the first embodiment. FIG. 1 shows the front view of the brake unit, FIG. 2 shows the side view of the brake unit, FIG. 3 shows the plan view of the brake unit, FIG. 4 shows the cross section of the brake unit (the cross-sectional view taken along the line S 4 —S 4  of FIG.  2 ), and FIG. 5 shows the circuit diagram of the hydraulic brake system. 
     First of all, the whole construction of the brake system is hereunder described in brief by reference to FIG.  5 . The brake system is designed to be executable a skid control or an ABS control. Reference sign  1  shown in the drawing denotes a master cylinder capable of generating a brake fluid pressure when depressing a brake pedal  2  by a driver. The master cylinder  1  is connected through a brake circuit  3  to wheel cylinders  4 .  4  serving as a brake actuating section (in the drawing, only two wheel-brake cylinders are shown, and the other two wheel-brake cylinder, connected to the brake circuit  3 , are omitted for the purpose of illustrative simplicity). Additionally, fluid-pressure control valves  5  are disposed in the middle of the brake/circuit  3 , for reducing, holding, and building-up the brake fluid pressure of the brake fluid in the wheel-brake cylinder  4 . A drain circuit  7  is connected to each of the fluid-pressure control valves  5 , for exhausting the brake fluid into a reservoir  6  during the pressure-reduction operating mode. A suction circuit  9  for a pump  8  is connected to the reservoir  6 , whereas a discharge circuit  10  for the pump  8  is connected to a line closer to the master cylinder side (which will be hereinafter referred to as an “upstream side”) rather than the fluid-pressure control valve  5  of the brake circuit  3 . When the pump  8  is driven according to rotation of a motor  11 , the brake fluid in the reservoir  6  is returned to the brake circuit  3 . 
     The discharge circuit  10  is employed with a damper  12  for absorbing pulsation of the fluid discharged from the pump  8 . A suction valve  9   a  and a discharge valve  10   a  are respectively disposed in the suction circuit  9  and the discharge circuit  10  for the purpose of prevention of back flow. 
     A normally-open type gate valve  13  is also disposed upstream of a connected point of the discharge circuit  10  to the brake circuit  3 , so that the gate valve is closed during the operation of the ABS. 
     In the shown embodiment, the master cylinder  1  is exemplified as the fluid-pressure generating means. In short, the fluid-pressure generating means corresponds to a means for generating a brake-fluid pressure depending on the braking action of the driver. Alternatively, the braking action may be electrically detected. The fluid-pressure generating means may be replaced by a means producing the fluid pressure created by the fluid-pressure source, on the basis of the detected value, by way of electronic control. 
     In the system block diagram shown in FIG. 5, the block surrounded by the one-dotted line A 1  is included in a brake unit of the brake system to which the concept of the present invention shown in FIGS. 1 though  4  is applied. 
     In FIGS. 1 through 4, reference sign  21  denotes a housing. Two pump bores  22 ,  22  are bored, on the same axial line, in the housing  21 , so that ends of the pump bores open the respective side walls  21   b ,  21   b  (see FIG.  4 ). In the drawing, reference sign  22   a  denotes the pump axis corresponding to the axial line of the pump bore. A cylinder  23  and a cap  24  are inserted into each of the pump bores  22 , in that order. In addition, The above-mentioned cap  24  and the cylinder  23  are fixed in place by screwing the nut  25  into the opening end of the pump bore  22 . 
     A plunger  26  is accommodated in the above-mentioned cylinder  23 . The plunger  26  is urged by means of a spring  27  in a direction that the plunger is projected from the cylinder  23 . The tip end of each of the plungers  26  is brought into abutted-engagement with the cam profile  28 . Therefore, each of the plungers  26  reciprocates along the axial line of the pump axis  22   a  in accordance with rotation of the cam profile  28 , for sucking the brake fluid into a pressure chamber  29 , and then discharging the pressurized brake fluid. 
     The previously-noted cam profile  28  is formed on the outer periphery of a motor shaft  30  corresponding to a rotational shaft of the motor  11 . That is to say, the above-mentioned motor shaft  30  is inserted into an inboard drive-shaft hole  31  which is located between the two pump bores  22  and bored in the housing  11  in a direction perpendicular to the two pump bores  22 . In the drawing, reference sign  30   a  denotes the center of axis of rotation corresponding to the center of axis of the motor shaft. 
     Furthermore, two flanged portions  11   b,    11   b  are formed at the end of the cover  11   a  of the motor  11  in such a manner as to be point-symmetrical with respect to the center of the axis of rotation. Mounting bolts  32  are penetrated through the flanged portions  11   b,  and then screwed into the respective screw-threaded hole  33  which open at one side face (which will be hereinafter referred to as a “front face  21   a ”) of the housing  21  and are threadably formed in the housing  21 , with the result that the motor  11  is located at and fixed to the front face  21   a  of the housing  21 . The previously-noted screw-threaded hole  33  is arranged substantially parallel to the center of axis of rotation, and located at a position close to the pump bore  22 , but not overlapped with the pump bore under a condition where the screw-threaded hole is projected in the axial direction. As seen in FIG. 1, the two mounting bolts  32  are located to be point-symmetrical with respect to the center  30   a  of axis of rotation, and also the two screw-threaded holes  33  are located to be point-symmetrical with respect to the center of axis of rotation. And yet, the line a passing through both the center-of-axis  33   a  of the screw-threaded hole is provided on a line (θ=20°) inclined by an inclined angle of 20° from the pump axis  22   a.  As shown in FIG. 2, the depth of the screw-threaded hole  33  is formed into such a depth that the bottom end of the screw-threaded hole may reach the pump bore  22  if the screw-threaded hole  33  is provided on the pump axis  22   a.    
     In the drawing, reference signs  34 ,  34  denote mount insulators required for mounting the housing  21  on the vehicle body, when installing the housing on the vehicle body. 
     Hereunder described is the operation of the system of the embodiment. 
     When the motor  11  is driven and the motor shaft  30  rotates, the reciprocating motion of each of the plungers  26 ,  26  take place, and whereby the sucking and discharging operation of the brake fluid are made. At this time, the reaction forces F 1 , F 2  (see FIG. 4) to the fluid pressure, act against the plungers  26 ,  26  in the axial direction. Additionally, the reaction forces F 1 , F 2  are transmitted from the plungers  26  into the motor shaft  30  in the direction perpendicular to the motor shaft. The, the reaction forces F 1 , F 2  input into the motor shaft  30  are supported finally by means of the mounting bolts  32 ,  32 . 
     As previously-discussed, in the first embodiment, the mounting bolts  32  and the screw-threaded holes  33  are both are arranged to be point-symmetrical with respect to the center  30   a  of axis of rotation, and also the center-of-axis  33   a  is arranged in such a manner as to be inclined by only 20° with respect to the pump axis  22   a.  The screw-threaded hole  33  is thus located to be close to the pump bore  22  in the projected direction of the screw-threaded hole. This assures a high rigidity of supporting the motor. 
     That is to say, as the fixed points of the mounting bolts  32  and the screw-threaded holes  33  are gradually shifted apart from the pump axis  22   a , the moment created by the reaction forces F 1 , F 2  acting on the previously-noted plungers  26  becomes greater. Assuming that the fixed points are arranged in such a manner as not to be point-symmetrical with respect to the center  30   a  of axis of rotation, the moment acting on the fixed points owing to the input force to the motor shaft  30 , tends to become greater. In the present embodiment, the fixed points are symmetrical each other with respect to the center  30   a  of axis of rotation, and additionally located at the location sufficiently close to the pump axis  22   a , thus ensuring a high rigidity of support. 
     Also, in the first embodiment, as discussed above, in order to enhance the rigidity of support, the screw-threaded holes  33  are arranged close to the pump bore  22  in their projected positions, so that the screw-threaded holes do not overlap with the pump axis  22   a  and the pump bore  22  in the projected positions. It is possible to reduce the thickness of the housing  21  (to reduce the dimension B shown in FIG.  2 ), in comparison with a case where the screw-threaded hole  33  is located in a manner so as to overlap with the pump axis  22   a.  This allows the housing  21  to form more compactly. That is to say, assuming that the thickness of the housing  21  retained at the same dimension as that of the first embodiment in the case that the screw-threaded hole  33  is located to overlap with the pump bore  22 , the screw-threaded hole  33  may penetrate through the pump bore  22 . In this case, there is the need for locating the pump bore  22  considerably apart from the front face  21   a  of the housing  21  (that is, the need for increasing the dimension B shown in FIG.  2 ). This increases the thickness of the housing  21 , thus large-sizing the housing  21 . 
     As explained above, the system of the first embodiment has an effect that it is possible to reconcile the enhanced rigidity of supporting the motor  11  against the reaction forces F 1 , F 2  to the fluid pressure acting on the plungers  26 , and the compactly-sized system arisen from the thin-walled housing  21 . 
     Second Embodiment 
     Hereinafter described is the brake system of the second embodiment. In explaining the second embodiment, for the purpose of simplification of the disclosure, the same reference signs used to designate elements in the first embodiment will be applied to the corresponding elements used in the second embodiment, while detailed description of the same reference signs will be omitted because the above description thereon seems to be self-explanatory. 
     In the system block diagram shown in FIG. 5, the component parts surrounded by the one-dotted line A 2  are employed in a brake unit of the second embodiment shown in FIGS. 6 through 9. In the second embodiment, the reservoir  6  and the damper  12  are further added to the construction of the first embodiment. That is to say, a first group of a first reservoir  61  and a first damper  121 , and a second group of a second reservoir  62  and a second damper  122  are provided in the housing  21  of the second embodiment, so that the first and second groups are respectively associated with the two plungers  26  (not shown in FIGS.  6 - 9 )(the two reservoirs are the two dampers are elements different from that of the first embodiment, and thus reference signs different from FIG. 5 are used to indicate these different elements). Both the dampers  121  and  122  and the reservoirs  61  and  62  are disposed in the damper holes  121   a  and  122   a  and the reservoir holes (not shown) respectively opening in the bottom face  21   c  of the housing  21 . Additionally, as seen in FIG. 8, the line  12   a  passing through both the center of axis of the damper  121  and the center of axis of the damper  122  and the line  6   b  passing through both the center of axis of the reservoir  61  and the center of axis of the reservoir  62  are arranged to be slightly offset from each other in the direction of the center  30   a  of axis of rotation of the motor  11 . Thus, the thickness of the housing  21  (the dimension in the direction of the center-of-axis  30   a  of rotation) can be reduced. 
     Also in the second embodiment, the machined positions of the screw-threaded holes  33  and the mounting bolts  32  are designed to be equal to those of the first embodiment. 
     Then, in the second embodiment, the shape of the damper hole  121   a  associated with the first damper  121  is different from the shape of the damper hole  122   a  of the second damper  122 . That is to say, the opening ends of both the damper holes  121   a  and  122   a  are formed into the same diameter. Assuming that the damper holes  121   a  and  122   a  are formed into the same diameter over their entire length in order to ensure the required volumetric capacity, the entire axial length of both damper holes becomes equal to the axial dimension of the damper hole  121   a  of the first damper  121 . However, if the damper hole  122   a  of the second damper  122  is formed into the same shape of that of the first damper  121 , there is no space necessary to form the screw-threaded hole  33  shown in the right-hand of FIG. 6, that is, the screw-threaded hole  33  being located in a manner so as to be sandwiched between the pump axis  22   a  and the second damper  122 . 
     For the reasons set forth above, the entire length of the second damper  122  is designed so that the damper hole  122   a  does not reach the screw-threaded hole  33 . As seen in FIGS. 6,  8  and  9  (corresponding to the cross section taken along the line S 9 —S 9  of FIG.  7 ), enlarged portions  122   b  are provided at two places in the side wall of the damper hole  122   a , so that the whole volumetric capacity of the damper hole of the second damper is identical to that of the damper hole  121   a  of the first damper  121 . 
     Since the system of the second embodiment is constructed as described above, the second embodiment produces the following effects in addition to the effects of the first embodiment. 
     In the second embodiment, the screw-threaded holes  33  into which the mounting bolts  33  necessary to mount the cover  11   a  of the motor  11  are screwed, are arranged to be point-symmetrical with respect to the center-of-axis  30   a  of rotation. In ensuring the space enough to form the screw-threaded hole between the pump bore  22  of the housing  21  and the second damper  122   a  in order to produce a high rigidity of supporting the motor when the reaction force to fluid pressure is input from the plungers  26  to the motor shaft  30 , it is possible to assure the same volumetric capacity of the first damper  121  having a relatively long entire length by providing the enlarged portions  122   b  enlarged in the diametrical direction, while suppressing the entire length of the damper hole  122   a  of the second damper  122  to a shorter value. Therefore, the second embodiment can produce an effect that it is possible to provide the desired damper performance while compactly small-sizing the housing  21  by reducing the up-and-down dimension thereof in FIG.  6 . 
     Additionally, in the second embodiment, since the line  6   b  connecting both the reservoirs  61  and  62  and the line  12   a  connecting both the dampers  121  and  122  are arranged to be offset from each other. This reduces the dimension of the housing  21  in the direction-of-axis  30   a  of rotation, thus producing the effect of compactly-sized housing. It will be understood that the invention is not limited to the particular embodiments shown and described herein. But, although the pump bore is exemplified as the object limiting the layout of the screw-threaded hole  33  of the first embodiment, in lieu thereof, the reservoir hole and/or the damper hole may be regarded as the object. Alternatively, all of the pump bore, the reservoir hole, and the damper hole may be regarded as the object. 
     As explained above, the brake system of the invention is designed or constructed so that the screw-threaded hole overlap with the pump bore to such an extent that the screw-threaded hole does not overlap with the center of axis of the pump bore when the screw-threaded hole is projected in the direction of the center-of-axis, or so that the screw-threaded hole is located at a position close to the pump bore, thus reconciling the supporting of the motor with a high rigidity when the reaction forces to the fluid pressure acting on the plungers are transmitted to the motor, and the provision of the compactly-sized system arisen from the housing small-sized by reducing the thickness measured from the end face of the housing to the pump bore. 
     Furthermore, the mounting bolts and the screw-threaded holes are arranged with respect to the center of axis of rotation of the motor, and thus the moment about the fixed point of the motor is scarcely produced. This ensures a more enhanced rigidity of supporting. 
     Moreover, the line connecting the axes of the mounting bolts or the screw-threaded holes and the axial line are arranged to be angularly offset from each other by 20°. Thus, the moment created at the fixed point of the motor is scarcely produced, thus ensuring a more enhanced rigidity at a supporting point. 
     In forming one of the two screw-threaded holes midway between the pump bore and the second damper hole, and in ensuring a space enough to form the screw-threaded hole, the small-sizing of the housing can be attained by shortening the axial dimension of the second damper hole, and additionally the damper performance can be ensured by forming the volumetric capacity of the second damper hole into substantially the same volumetric capacity as the first damper hole by way of the provision of the enlarged portions in the second damper hole in its diametrical direction. Thereby, the system can be small-sized without lowering the damper performance. 
     In addition to the ABS control unit, the invention is widely applicable to a brake system such as a traction control unit by means of which wheel-slip can be controlled during rapid acceleration, a control unit that can control a yawing rate, or the like.