Abstract:
A detection switch is mounted on an input shaft through a clevis for detecting the operation of an automatic brake unit without the depression of a brake pedal. The detection switch may also be mounted on the brake pedal. The clevis and the brake pedal are connected together in a manner to permit a relative displacement therebetween through an operating stroke of the detection switch. When the brake pedal is depressed, the brake pedal is maintained at an advanced position relative to the input shaft, and the detection switch detects a retracting movement of the brake pedal with respect to the input shaft from the advanced position during an automatic brake operation. The arrangements allow the detection switch to be mounted on either the input shaft or the brake pedal, does not require design of a small size and facilitates the mounting of the detection switch.

Description:
FIELD OF THE INVENTION 
     The invention relates to an automatic brake unit capable of operating a brake booster without the depression of a brake pedal, and more particularly, to an automatic operation detector which detects an operation of an automatic brake unit. 
     DESCRIPTION OF THE PRIOR ART 
     An automatic brake unit is known in the art which comprises a brake booster, a brake pedal which, when depressed, drives an input shaft of the brake booster to operate it, an automatic brake operating mechanism which operates the brake booster without the depression of the brake pedal, and a detection switch for detecting the operation of the brake booster without the depression of the brake pedal (Japanese Laid-Open Patent Application No. 86395/1997 and 127947/2000). 
     The detection switch is contained in a valve body of the brake booster. However, in order to allow the detection switch to be contained in the valve body, a redesign of passages and/or a change in the configuration of adjacent parts is required, presenting a difficulty in securing a space to contain the switch. 
     If a space can be secured to contain the detection switch, the space is very limited and thus requires a special design of a small size for the detection switch, resulting in an increased cost and an assembly which is less than desired. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide an automatic operation detector for an automatic brake unit which avoids a need for a special design of a small size for a detection switch and which allows a mounting space for the switch to be easily secured. 
     Specifically, in accordance with the present invention, there is provided an automatic brake unit comprising a brake booster, a brake pedal which, when depressed, drives an input shaft of the brake booster to operate it, an automatic brake operating mechanism which operates the brake booster without the depression of the brake pedal, and a detection switch for detecting the operation of the brake booster without the depression of the brake pedal; 
     the arrangement being such that the input shaft and the brake pedal are connected together in a manner to permit a relative displacement therebetween through at least an operating stroke of the detection switch, the detection switch being mounted on either the input shaft or the brake pedal so that when the brake pedal is depressed, the brake pedal is maintained at an advanced position with respect to the input shaft while the detection switch detects a retracting movement of the brake pedal with respect to the input shaft from the advanced position during an automatic brake operation. 
     With the described arrangement, the input shaft and the brake pedal are displaceable relative to each other through at least an operating stroke of the detection switch, which can then detect a retracting movement of the brake pedal with respect to the input shaft from the advanced position during an automatic brake operation. 
     On the other hand, during a normal brake operation, as the brake pedal is depressed, the brake pedal drives the input shaft forward. At this time, the brake pedal drives the input shaft forward while it is maintained at an advanced position with respect to the input shaft. Accordingly, this condition is not detected by the detection switch as an automatic brake operation. 
     Rather than containing the detection switch in a valve body of the brake booster, it can be mounted on either the input shaft or the brake pedal. Thus, a mounting space for the detection switch can be easily secured and no special design of a small size is required therefor, thus facilitating the mounting of the detection switch. 
     Above and other objects, features and advantages of the invention will become apparent from the following description of several embodiments thereof with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross section of a first embodiment of the invention; 
     FIG. 2 is a cross section taken along the line II—II shown in FIG. 1; 
     FIG. 3 is a cross section illustrating a phase of operation which is different from that shown in FIG. 2; 
     FIG. 4 is a fragmentary cross section of an essential part of a second embodiment of the invention; and 
     FIG. 5 is a cross section taken along the line V—V shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Several embodiments of the invention will now be described with reference to the drawings. Referring to FIG. 1, a tandem brake booster  1  includes a shell  2 , the interior of which is partitioned by a center plate  3  into a forwardly located front chamber  4  and a rearwardly located rear chamber  5 . A substantially tubular valve body  6  is slidably fitted through the axial portion of the center plate  3 . 
     A front power piston  7  is connected around the outer periphery of the valve body  6  which is located within the front chamber  4  while a rear power piston  8  is connected around the outer periphery of the valve body  6  which is located within the rear chamber  5 . 
     A front diaphragm  11  is applied to the back surface of the front power piston  7  to divide the interior of the front chamber  4  into a forwardly located constant pressure chamber A and a rearwardly located variable pressure chamber B. A rear diaphragm  12  is applied to the back surface of the rear power piston  8  to divide the interior of the rear chamber  5  into a forwardly located constant pressure chamber C and a rearwardly located variable pressure chamber D. 
     The constant pressure chambers A and C communicate with each other through a constant pressure passage  13  formed in the valve body  6 , thus normally introducing a negative pressure into the constant pressure chambers A and C. On the other hand, the variable pressure chambers B and D communicate with each other through a variable pressure passage  14  formed in the valve body  6 . 
     A valve mechanism  15 , which is known in itself, for switching a communication between the constant pressure chambers A and C and the variable pressure chambers B and D is mounted inside the valve body  6  at a rear portion thereof. 
     Specifically, the valve mechanism  15  comprises a vacuum valve  16  and an atmosphere valve  17 , and in the inoperative condition shown where a brake pedal  18  is not depressed, the vacuum valve  16  is open while the atmosphere valve  17  is closed. Thus, in the inoperative condition, the constant pressure chambers A and C and the variable pressure chambers B and D communicate with each other, and a negative pressure is introduced into these chambers. 
     A solenoid  19  is disposed inside the valve body  6  and has lead wires  21 , which are applied to the front internal peripheral surface of the valve body  6  to extend axially forward, whereupon they cross the constant pressure chamber A to be passed through a grommet  22 , which is fitted into a through-opening  2 A in the shell  2  so as to maintain a hermetic seal, to be connected to a power supply which is located outside the shell  2 . In this manner, the solenoid  19  is electrically connected to the power supply, not shown, through the lead wires  21 . 
     The solenoid  19  has an axial through-opening  19 A in alignment with the axis thereof, into which the outer periphery of a front portion of a valve plunger  23 , which forms part of the valve mechanism  15 , is slidably fitted. The valve plunger  23  is normally urged rearward by a valve return spring  24 , and accordingly, under the condition that the solenoid  19  is not energized, the atmosphere valve  17  is closed while the vacuum valve  16  is open. 
     If the brake pedal  18  is depressed in the inoperative condition shown where the solenoid  19  is not energized, an input shaft  25  and its connected valve plunger  23  are driven forward or to the left, whereby the vacuum valve  16  is closed while the atmosphere valve  17  is opened. 
     This interrupts the communication between the constant pressure chambers A and C and the variable pressure chambers B and D, and the atmosphere is introduced into the variable pressure chambers B and D. Accordingly, the pressure differential between the negative pressure within the constant pressure chambers A and C and the atmosphere within the variable pressure chambers B and D causes the valve body  6  and an output shaft  27  mounted thereon to be driven forward against the resilience of a return spring  26 . In this manner, the tandem brake booster  1  is operated. 
     If the brake pedal  18  is released under the operated condition, the valve return spring  24  urges the valve plunger  23  backward, whereby the atmosphere valve  17  is closed while the vacuum valve  16  is opened. This establishes the communication between the constant pressure chambers A and C and the variable pressure chambers B and D again, and these chambers assume an equal pressure. Accordingly, the valve body  6  and the output  27  return to their inoperative positions shown under the resilience of the return spring  26 . 
     When the solenoid  19  is energized under the inoperative condition shown in FIG. 1, the magnetic force from the solenoid  19  moves the valve plunger  23  forward relative to the valve body  6 , thus allowing the atmosphere valve  17  to be opened and the vacuum valve  16  to be closed without the depression of the brake pedal  18 . In this manner, the tandem brake booster  1  can be operated as an automatic brake. At this time, the input shaft  25  and the brake pedal  18  are driven integrally forward as the tandem brake booster  1  is operated. 
     The arrangement described above remains substantially unchanged from the known arrangement. In the present embodiment, the solenoid  19 , the lead wires  21  and the power supply, not shown, constitute together an automatic brake operating mechanism. However, any arrangement may be used as such an automatic brake operating mechanism which is capable of operating the brake booster  1  without the depression of the brake pedal  18 . 
     An automatic operation detector which detects the operation of the brake booster  1  without the depression of the brake pedal  18  is constructed as follows: 
     Specifically, a clevis  31  is connected to the rear end of the input shaft  25 , and the input shaft  25  is coupled to the brake pedal  18  through the clevis  31 . At its upper end, the brake pedal  18  is connected in a rockable manner to a car body  33  through a pin  32 . 
     As shown in FIGS. 1 and 2, the clevis  31  is formed with an opening  31   a  which is elongate in a direction in which the brake pedal  18  rocks, and a pin  18   a  projecting from the brake pedal  18  is engaged with the elongate opening  31   a,  thus permitting the input shaft  25  and the brake pedal  18  to be connected together while allowing a relative displacement therebetween through a travel of the pin  18   a  within the elongate opening  31   a.    
     The rear end of the clevis  31  is bent into an L-configuration, and a detection switch  34  is mounted thereon. The detection switch  34  has a probe  34   a  which is disposed in abutment against the pin  18   a  of the brake pedal  18  from the rear side. The probe  34   a  projects from the detection switch  34  to turn it off when the pin  18   a  of the brake pedal  18  is located forwardly within the elongate opening  31   a,  but is urged into the detection switch  34  to turn it on when the pin  18   a  of the brake pedal  18  moves rearward within the elongate opening  31   a.  In this manner, the input shaft  25  and the brake pedal  18  are displaceable relative to each other through at least an operating stroke of the detection switch  34 . 
     A spring  35  is disposed between the pin  31   b  projecting from the clevis  31  and the pin  18   a  from the brake pedal  18 , and the resilience of the spring  35  urges the pin  31   b  of the clevis  31  forward relative to the pin  18   a  of the brake pedal  18 . The resilience of the spring  35  is chosen to be less than the resilience of the valve return spring  24  which is disposed within the valve body  6 . 
     It is to be noted that the brake pedal  18  is not associated with a pedal return spring which is usually provided in order to maintain the brake pedal  18  at its inoperative position, but is adapted to maintain the input shaft  15  and the brake pedal  18  in their inoperative positions shown in FIG. 1 under the resilience of the valve return spring  24  disposed within the valve body  6 . 
     Under this condition, the brake pedal  18  is maintained in its inoperative position in which it abuts against a stop lamp switch  36  mounted on the car body  33 , and assumes an advanced position relative to the clevis  31  and the input shaft  25 , and accordingly, the pin  18 a from the brake pedal  18  is located forwardly within the elongate opening  31   a  in the clevis  31  against the resilience of the spring  35 , whereby the detection switch  34  remains to be off. 
     In the described arrangement, if the brake pedal  18  is depressed under the inoperative condition shown, the force of depression applied to the brake pedal  18  is transmitted through the pin  18   a  of the brake pedal  18  to the clevis  31  and the input shaft  25 , whereby the brake pedal  18  is maintained at its advanced position relative to the clevis  31  and the input shaft  25 , maintaining the detection switch  34  off. 
     Accordingly, the brake booster  1  is operated as the brake pedal  18  and the input shaft  25  are driven forward, but the detection switch  34  remains off, and this condition of operation cannot be detected as an automatic brake condition. 
     During this normal operation, the pin  18 a of the brake pedal  18  directly urges against the clevis  31 , thus avoiding any degradation in the feeling during the normal brake operation which might otherwise be caused by a rattling or a lost motion caused by the elongate opening  36   a  provided corresponding to the stroke of the detection switch  34 . 
     By contrast, when the solenoid  19  is energized by the automatic brake operating mechanism mentioned above, the magnetic force from the solenoid  19  moves the valve plunger  23  forward relative to the valve body  6  as mentioned previously, thus opening the atmosphere valve  17  and closing the vacuum valve  16  without the depression of the brake pedal  18 . As the input shaft  25  and the clevis  31  are driven forward, the resilience of the spring  35  causes the pin  18   a  of the brake pedal  18  to move rearward within the elongate slot  31   a,  whereupon the detection switch  34  is turned on to indicate the automatic brake operation (see FIG.  3 ). 
     After the pin  18   a  of the brake pedal  18  has moved to the rear end of the elongate opening  31   a,  the brake pedal  18  is driven forward integrally while maintaining its retracted position with respect to the clevis  31  and the input shaft  25 . 
     As shown in the embodiment illustrated, it is not necessary that the detection switch  34  be contained within the valve body  6  of the brake booster  1 , but may be mounted on the clevis  31  associated with the input shaft  25 , and accordingly, there is no need for a special design of a small size for the detection switch, which can be easily mounted in a space which can be easily secured. 
     FIGS. 4 and 5 show a second embodiment of the invention. In the first embodiment mentioned above, the brake pedal  18  is integrally formed with the pin  18   a,  but in the second embodiment, a pin  141  is separate from a brake pedal  118 . The pin  141  includes a shank  141   a  which extends from one side of a clevis  131  sequentially through an elongate opening  131   a  formed in one side of the clevis  131 , a through-opening  118   b  formed in a brake pedal  118  and an elongate opening  131   a  formed in the other side of the clevis  131 . The pin  141  has a head  141   b,  and a washer  142   a  is mounted on the shank  141   a  to cooperate with the head  141   b  to prevent the pin  141  from being withdrawn from the clevis  131  and the brake pedal  118 . 
     The rear end of the clevis  131  is bent into an L-configuration, on which a detection switch  134  is mounted. The detection switch  134  has a probe  134   a  which is disposed in abutment against the shank  141   a  of the pin  141  integrally mounted on the brake pedal  118  from the rear side. 
     A channel-shaped bracket  143  is mounted on the side of the clevis  131 , and a pusher pin  144  slidably extends through the opposite ends of the bracket  143 . The pusher pin  144  is slidable axially of an input shaft  125 , and has a step on which a retainer  145  is mounted. A spring  135  is disposed between the retainer  145  and the bracket  143  to urge the pin  144  rearward until the rear end of the pin  144  resiliently abuts against the pin  141 . 
     Thus, the spring  135  acts through the pin  144  to urge the pin  141  and the brake pedal  118  rearward or in a direction in which the detection switch  134  can be turned on. However, the resilience of the spring  135  is chosen to be less than the resilience of a valve return spring  124  which is disposed within a valve body  106 , whereby the detection switch  134  remains off in an inoperative condition in which the brake pedal  118  abuts against a stop lamp switch  136  mounted on a car body  133 . It will be apparent that the second embodiment is capable of achieving equivalent function and effect as achieved by the first embodiment. 
     In the both embodiments mentioned above, the detection switch  34  or  134  is mounted on the input shaft  25  or  125  through the interposition of the clevis  31  or  131 . However, it should be understood that the detection switch may also be mounted on the brake pedal, and since such an arrangement would be obvious to one skilled in the art, it will not be specifically illustrated. 
     While the invention has been described above in connection with several embodiments thereof, it should be understood that a number of changes, modifications and substitutions therein are possible in light of the above disclosure without departing from the spirit and the scope of the invention defined by the appended claims.