Patent Publication Number: US-7591636-B2

Title: Negative pressure supply apparatus

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a negative pressure supply apparatus for supplying a negative pressure to a pneumatic booster of an automotive brake system, for example. 
   In general, an automotive brake system is provided with a pneumatic booster to increase braking force. The pneumatic booster uses the engine intake (negative) pressure as a negative pressure source. That is, the engine intake (negative) pressure is introduced into a constant-pressure chamber (negative pressure chamber) to produce a differential pressure between the intake pressure and the atmospheric pressure, thereby generating thrust in a power piston to assist the brake system with operating force. 
   In recent years, automotive engines have been improved to reduce pumping loss in order to meet the demand for lower fuel consumption. Accordingly, the engine intake (negative) pressure is tending to decrease. Consequently, the negative pressure supplied to the pneumatic booster is likely to become insufficient. 
   In view of the above-described problem, a conventional technique uses an electrically-driven rotary vacuum pump as a negative pressure source of a pneumatic booster, so that a sufficient negative pressure can be supplied to the pneumatic booster irrespective of the engine running condition, as disclosed, for example, in Japanese Patent Application Unexamined Publication (KOKAI) No. 2002-195178. 
   However, the vacuum pump disclosed in the above-described publication suffers from the following problems. The conventional technique uses a vane pump as a vacuum pump. The vane pump has a complicated structure and a high production cost and is difficult to reduce in size. It is also conceivable to use a reciprocating piston type vacuum pump having a simple structure. In the reciprocating piston type vacuum pump, however, the atmospheric pressure acts on the piston as back pressure. Therefore, if the pump is used to obtain a high degree of vacuum required for the pneumatic booster, the load variation increases, and it becomes difficult to perform a smooth operation. 
   SUMMARY OF THE INVENTION 
   The present invention was made in view of the above-described circumstances. 
   An object of the present invention is to provide a negative pressure supply apparatus capable of supplying a negative pressure of high degree of vacuum with a simple structure. 
   The present invention provides a negative pressure supply apparatus including an ejector that has a nozzle and a diffuser disposed downstream of the nozzle. A vacuum port of the ejector opens between the nozzle and the diffuser. The negative pressure supply apparatus further includes a vacuum pump having a suction port connected to an outlet of the diffuser. A negative pressure is supplied from the vacuum port of the ejector. 
   In the negative pressure supply apparatus according to the present invention, suction by the vacuum pump causes air to flow from the nozzle to the diffuser in the ejector. Consequently, a fast jet is produced in a throat portion of the nozzle, and a negative pressure of higher degree of vacuum than that of the suction negative pressure of the vacuum pump is produced at the vacuum port of the ejector. Thus, it is possible to supply the negative pressure of high degree of vacuum. 
   The negative pressure supply apparatus according to the present invention may be arranged as follows. The vacuum port of the ejector and the suction port of the vacuum pump are connected to a negative pressure supply port through respective check valves. Either one of two negative pressures at the vacuum port and the suction port that is higher in the degree of vacuum than the other is supplied from the negative pressure supply port. 
   With the above-described arrangement, either the negative pressure at the vacuum port of the ejector or the negative pressure at the suction port of the vacuum pump that is higher in the degree of vacuum than the other negative pressure can be supplied through the associated check valve. Therefore, the negative pressure can be supplied efficiently. 
   The vacuum pump used in the negative pressure supply apparatus according to the present invention may be a reciprocation-type pump having a piston driven by a linear actuator. 
   With the above-described arrangement, the structure of the vacuum pump can be simplified, and it becomes possible to reduce the size and the production cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view of a negative pressure supply apparatus according to a first embodiment of the present invention. 
       FIG. 2  is a sectional view taken along the line A-A in  FIG. 1 . 
       FIG. 3  is a pneumatic pressure circuit diagram showing the arrangement of the apparatus shown in  FIG. 1 . 
       FIG. 4  is a longitudinal sectional view of a negative pressure supply apparatus according to a second embodiment of the present invention. 
       FIG. 5  is a pneumatic pressure circuit diagram showing the arrangement of the apparatus shown in  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will be described below with reference to the accompanying drawings. 
   A first embodiment of the present invention will be described with reference to  FIGS. 1 to 3 . As shown in  FIGS. 1 to 3 , a negative pressure supply apparatus  1  according to this embodiment has a vacuum pump unit  2  (vacuum pump) and an ejector unit  3 , which are joined to each other through a manifold unit  4 . 
   The vacuum pump unit  2  is a reciprocation-type pump having a piston driven by a moving magnet type linear motor. That is, a piston  6  serving also as a moving member is slidably fitted in a cylinder  5  serving also as a stator. The piston  6  is guided by a rod  7  secured in the cylinder  5 . The rod  7  extends along the center axis of the cylinder  5 . The cylinder  5  has a plurality of coils  8  installed on an outer peripheral portion thereof. The piston  6  has a magnetic path member  9  and a plurality of magnets  10  installed on an outer peripheral portion thereof. By energizing and thus exciting the coils  8  sequentially, the piston  6  can be moved to reciprocate in the cylinder  5 . An annular seal  6 A is provided on the center of the magnets  10  to divide the interior of the cylinder  5  into two chambers (described later). The annular seal  6 A is formed from a synthetic resin exhibiting excellent sliding performance. 
   The interior of the cylinder  5  is divided by the piston  6  into two chambers  5 A and  5 B (pump chambers). One chamber  5 A communicates with a first suction port  12  through a passage  11  and also communicates with a first discharge port  14  through a passage  13 . The passage  11  is provided with a check valve  15  that allows flow of air only in one direction from the first suction port  12  toward the chamber  5 A. The passage  13  is provided with a check valve  16  that allows flow of air only in one direction from the chamber  5 A toward the first discharge port  14 . The other chamber  5 B communicates with a second suction port  18  through a passage  17  and also communicates with a second discharge port  20  through a passage  19 . The passage  17  is provided with a check valve  22  that allows flow of air only in one direction from the second suction port  18  toward the chamber  5 B. The passage  19  is provided with a check valve  21  that allows flow of air only in one direction from the chamber  5 B toward the second discharge port  20 . The first and second suction ports  12  and  18  and the first and second discharge ports  14  and  20  are disposed to face the manifold unit  4 . 
   The ejector unit  3  is formed with an ejector  25 . As shown in  FIG. 2 , the ejector  25  has a nozzle  26  and a diffuser  27  disposed downstream of the nozzle  26  to form a Laval nozzle. Vacuum ports  29  are open in an area downstream of a throat portion  28  of the nozzle  26 . When a gas is supplied to flow from an inlet  30  of the nozzle  26  toward an outlet passage  31  (outlet) of the diffuser  27 , a fast jet reaching the velocity of sound is generated at the throat portion  28 . The fast jet sucks gas from the vacuum ports  29 . Thus, a negative pressure of higher degree of vacuum than that of the negative pressure in the outlet passage  31  of the diffuser  27  can be obtained from the vacuum ports  29 . The ejector  25  has a two-dimensional configuration formed from a planar recess provided on a joint surface of the ejector unit  3  at which it is joined to the manifold unit  4 . Thus, the ejector  25  having a complicated configuration can be formed easily with high accuracy. 
   The ejector unit  3  is provided with a negative pressure supply port  32  for connection with a negative pressure operated device (not shown) such as a pneumatic booster. The negative pressure supply port  32  communicates with the vacuum ports  29  and the outlet passage  31  via a passage  33  through respective check valves  34  and  35 . The check valve  34  allows flow of air only in one direction from the negative pressure supply port  32  toward hollow spaces communicated with the vacuum ports  29 . The check valve  35  allows flow of air only in one direction from the negative pressure supply port  32  toward the outlet passage  31 . 
   The manifold unit  4  is provided with a suction passage  36  for communication between the first and second suction ports  12  and  18  of the vacuum pump unit  2  and the outlet passage  31  of the ejector unit  3 . The manifold unit  4  is further provided with a discharge passage  37  for communication between the first and second discharge ports  14  and  20  of the vacuum pump unit  2  and the inlet  30  of the ejector unit  3 . The discharge passage  37  is open to the atmosphere through a check valve  38 . The check valve  38  allows flow of air only in one direction from the discharge passage  37  toward the atmosphere. 
   The operation of this embodiment, arranged as stated above, will be described below. 
   When the coils  8  of the vacuum pump unit  2  are excited by energization, the piston  6  in the cylinder  5  reciprocates by the action of magnetic fields from the coils  8 . Consequently, air is sucked in from the first and second suction ports  12  and  18  through the check valves  15  and  22 , and air is discharged from the first and second discharge ports  14  and  20  through the check valves  16  and  21 . Thus, air is sucked in from the outlet passage  31  of the ejector  25  through the suction passage  36  of the manifold unit  4 . The discharged air is supplied to the inlet  30  of the ejector  25  through the discharge passage  37 . At this time, the check valve  38  prevents the pressure in the discharge passage  37  from becoming a positive pressure. 
   Thus, air flows from the inlet  30  of the nozzle  26  toward the outlet passage  31  of the diffuser  27 . Consequently, a fast jet reaching the velocity of sound occurs by the action of the combination of the nozzle  26  and the diffuser  27 , which form a Laval nozzle, and a negative pressure of higher degree of vacuum than that of the suction negative pressure of the vacuum pump unit  2  is produced at the vacuum ports  29 . The negative pressure of high degree of vacuum is supplied from the negative pressure supply port  32  to a negative pressure operated device, e.g. a pneumatic booster, through the check valve  34 . 
   In this way, the negative pressure produced in the vacuum pump unit  2  can be boosted by the ejector  25 , and it is possible to supply a negative pressure of high degree of vacuum that is required for a negative pressure operated device, e.g. a pneumatic booster, while reducing the load on the vacuum pump unit  2 . At this time, if a negative pressure of the order of from −250 mmHg to −300 mmHg is produced by the vacuum pump unit  2 , a negative pressure of the order of −500 mmHg can be supplied. As a result, the load on the vacuum pump unit  2  can be reduced. Therefore, it becomes possible to make the vacuum pump compact in size. Further, because the load variation due to suction and discharge is reduced, it becomes possible to attain smooth operation of the vacuum pump. 
   In a case where the negative pressure supply apparatus  1  is used for a pneumatic booster of an automotive brake system, for example, the negative pressure in the pneumatic booster may be extremely reduced by continuous operation of the brake. In such a case, the check valve  35  opens to suck in air directly from the negative pressure supply port  32  through the first and second suction ports  12  and  18  of the vacuum pump unit  2 , thereby increasing the suction flow rate. Thus, the negative pressure in the pneumatic booster can be recovered rapidly. 
   Next, a second embodiment of the present invention will be described with reference to  FIGS. 4 and 5 . 
   It should be noted that, in the following description, members or portions corresponding to those in the foregoing first embodiment are denoted by the same reference numerals, and only portions in which the second embodiment differs from the first embodiment will be explained in detail. 
   As shown in  FIGS. 4 and 5 , in a negative pressure supply apparatus  39  according to this embodiment, the manifold unit  4  in the first embodiment is omitted, and the vacuum pump unit  2  and the ejector unit  3  are joined directly to each other. The first and second suction ports  12  and  18  of the vacuum pump unit  2  communicate with each other through a passage  40  in a hollow rod  7  and thus communicate directly with the outlet passage  31  of the ejector unit  3 . The first and second discharge ports  14  and  20  are open directly to the atmosphere. The inlet  30  of the ejector unit  3  communicates with the first discharge port  14  and hence opens to the atmosphere. 
   In the vacuum pump unit  2  in this embodiment, the piston  6  has a larger diameter and a shorter stroke than in the first embodiment. Consequently, only two coils  8  are provided in the vacuum pump unit  2  in the second embodiment. In addition, by making use of an extra space resulting from the increase in diameter of the piston  6 , the suction-side check valves  15  and  22  and the discharge-side check valves  16  and  21  are disposed along the diametrical direction of the piston  6 . Thus, the suction-side check valves  15  and  22  and the discharge-side check valves  16  and  21  are allowed to use identical components to form these different check valves. That is, in the embodiment shown in  FIG. 1 , the suction-side check valves  15  and  22  and the discharge-side check valves  16  and  21  are provided in concentric relation to each other. Therefore, the check valves  16  and  21  unavoidably become larger in radial dimensions than the check valves  15  and  22 . In the embodiment shown in  FIG. 4 , the end faces of the vacuum pump unit  2  have an increased area. Therefore, two check valves of the same configuration can be installed on each end face in opposite orientations so as to be used for the suction and discharge purposes, respectively. 
   With the above-described arrangement, the negative pressure produced in the vacuum pump unit  2  can be boosted by the ejector  25 , and it is possible to supply a negative pressure of high degree of vacuum that is required for a negative pressure operated device, e.g. a pneumatic booster, while reducing the load on the vacuum pump unit  2 , as in the case of the first embodiment. It should be noted that in the second embodiment the inlet  30  of the ejector  25  is supplied with air at the atmospheric pressure. 
   In addition, the manifold unit  4  in the first embodiment is omitted, and component sharing between the check valves  15 ,  16 ,  21  and  22  is allowed. Further, the number of coils  8  is reduced to only two. Therefore, it is possible to simplify the structure and to reduce the production cost in comparison to the first embodiment. 
   Although the first and second embodiments use a reciprocating piston type pump as a vacuum pump, it is also possible to use a different type of pump, e.g. an axial piston pump, a vane pump, or a scroll pump. As a drive source of the pump, it is possible to use not only a moving magnet type linear motor but also a different type of linear motor, e.g. a linear SRM (Switched Reluctance Motor), which requires no magnet. When a rotary pump is used, a rotary motor is also usable.