Motor drive vacuum pump
This application is a Continuation-in-Part application Ser. No. 906,617, filed on Sept. 10, 1986, now abandoned, which is a Continuation of application Ser. No. 535,328, filed Sept. 23, 1983, now abandoned. 
    
    
     The present invention relates to a motor drive vacuum pump. More particularly, it relates to a motor drive vacuum pump having an improved discharging passage. 
     BACKGROUND OF THE INVENTION 
     As this kind of the motor drive vacuum pump, there has been known one as shown in FIG. 1 of the accompanying drawing. In FIG. 1, the reference numeral 1 designates a motor which comprises a stator 1a consisting of magnetic poles each of which holds a field winding, a rotor 1b rotatably supported with respect to the stator 1a leaving a small air gap 1c therebetween, and a housing 1d holding the stator 1a and the rotor 1b therein. A vacuum pump 3 is attached to the motor 1 and is driven by a motor shaft 2. The references 4 and 5 respectively designate an intake port and a discharge port connected to the vacuum pump 3. The intake port 4 is connected to the vacuum tank 6. The reference 7 designates a check valve connected between the intake port 4 and the vacuum tank 6. The numeral 8 designates a drain hole formed in the housing 1d of the motor 1. 
     The operation of the device described above will be explained. 
     Actuation of the motor 1 causes revolution of the shaft 2 to drive the vacuum pump 3 with the result that air in the vacuum tank 6 is sucked through the check valve 7 and the intake port 4 and is sent pressurized to the discharge port 5 to be discharged in the atmosphere. The check 7 valve is to prevent air from reversely flowing into the vacuum tank 6 when the vacuum pump 3 is stopped, which keeps the vacuum tank 6 in an evacuated state. 
     In the conventional device having the construction described above, there has been a problem of noise generated from the discharge port 5. Especially, in a vane type vacuum pump which is so constructed that air sucked from the intake port 4 is compressed on the way to the discharge port 5 before discharged, the compressed air causes a great noise when it is discharged from the discharge port 5. Further, when vacuum (mmHg) in the vacuum tank 6 increases and there is a small amount of air to be sucked, there disadvantageously occurs noise due to sliding movement of the vanes. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide a motor drive vacuum pump suppressing generation of noise from a discharge port and being reliable in operation by connecting the discharge port of a vacuum pump to the motor interior to discharge air from the vacuum pump to the atmosphere through the motor interior via a drain hole wherein a discharge valve is provided in a part of a discharging passage. 
     It is another object of the present invention to provide a motor drive vacuum pump capable of deadening noise in an economical manner by connecting a discharge port of a vacuum pump to the motor interior and by discharging air through a discharge valve which serves as a drain hole of the motor. 
     It is still another object of the present invention to provide a motor drive vacuum pump capable of deadening noise and incrasing the quality of a motor by introducing air from a vacuum pump into the motor interior through a discharge valve and discharging the air to the atmosphere through a drain hole of the motor. 
     SUMMARY OF THE INVENTION 
     The foregoing and the other objects of the present invention have been attained by providing a motor drive vacuum pump comprising a motor provided with a rotor, a stator and a housing holding the rotor and the stator therein; a vacuum pump which is attached on the side surface of the motor housing and is driven by the motor to forcibly feed air from an intake port to a discharge port to thereby generate vacuum; a discharging passage means comprising a discharging hole for introducing the air to be discharged through the discharge port of the vacuum pump into the motor interior and a through hole formed in a part of the housing to discharge the air introduced into the motor interior to the atmosphere; and a discharge valve provided in a part of the discharging passage means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing objects, and as well as specific construction and operations of the motor drive vacuum pump according to the present invention will become apparent and understandable from the following detailed description thereof when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a side view, partly in cross-section, of a conventional motor drive vacuum pump; 
     FIG. 2 is a side view, partly in cross-section, of an embodiment of the motor drive vacuum pump of the present invention; 
     FIG. 3 is a side view similar to FIG. 2 of another embodiment of the present invention; and 
     FIG. 4a and 4b are respectively cross sectional views in the closing and opening states of a discharge valve and FIG. 4c is a bottom view of the discharge valve used in the motor drive vacuum pump of the present invention; and 
     FIG. 5 is a diagram illustrating comparative tests of the efficiency of the embodiment shown in FIG. 3 with and without the umbrella type discharge valve 10a in place. 
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described with reference to FIGS. 2-4. The same reference numerals designate the same or corresponding parts. 
     FIG. 2 shows a first embodiment of the present invention in which a motor 1 comprises a stator 1a composed of magnetic poles on which field windings are wound, a rotor 1b rotatably supported leaving a small air gap 1c between the outer peripheral surface of the rotor and the inner peripheral surface of the stator, and a housing 1d for holding the stator 1a and the rotor 1b therein. The housing 1d composed of a front bracket 1d-1 and a rear bracket 1d-3 which rotatably support the rotor 1b and a frame 1d-2 for supporting the stator 1a. The front and rear brackets 1d-1 and 1d-3 are of a closed type without any opening communicating the motor interior with the atmosphere. A drain hole 8 is formed in the frame 1d-2 to drain water. A vacuum pump 3 is attached to the motor 1 and is driven by a rotary shaft 2. 
     The rotary shaft 2 of the motor 1 extends into the pump chamber of the vacuum pump 3. The vacuum pump 3 is provided with a side plate 3a attached to the front bracket 1d-1 of the motor 1 and a casing 3b defining the pump chamber. The vacuum pump 3 is a well known vane type vacuum pump comprising a rotor fixed to the rotor shaft 2 which extends into the pump chamber in an eccentric manner and a plurality of vanes which are held in the rotor so as to be radially extendable and are in slide-contact with the inner peripheral portion of the pump chamber. The vacuum pump 3 is provided with an intake port 4 and a discharge port 5, and the intake port 4 is connected to a vacuum tank 6 through a check valve 7. 
     The reference numeral 9 designates a discharging hole perforated through the side plate 3a and the front bracket 1d-1 to communicate the discharge chamber of the vacuum pump 3 with the motor interior, and the numeral 10 designates a discharge valve fitted to the drain hole 8 to drain water condensed in the motor 1. The discharge valve 10 (shown in FIG. 4) comprises an umbrella type valve 10a made of a flexible material and having a plurality of air vent holes 10b opened and closed by the umbrella type valve 10a. The discharging hole 9, the drain hole 8, and the inner space of the motor 1 constitute a discharging passage means. 
     In the construction described above, when the motor 1 is actuated, air in the vacuum tank 6 is sucked through the intake port 4; is fed through the discharge port 5 of the vacuum pump 5 via the discharging hole 9 into the inner space of the motor 1; is then passed through the air gap 1c and a small space formed by the umbrella type valve 10a and the air vent holes 10b of the discharge valve 10; and is finally discharged to the atmosphere. Thus, the construction that air from the vacuum pump 3 is introduced into the motor interior before it is discharged suppresses variation of pressure, and noise generated from the discharge port can be minimized. Further, the suppressing of noise is further increased by passing air through small spaces between the vent holes 10b and the umbrella type valve 10a. 
     Water condensed or entering in the motor interior is discharged with the air through the discharge valve 10, which also serves as a drain hole. 
     FIG. 3 shows another embodiment of the present invention. The same reference numerals designate the same parts. In FIG. 3, the reference numeral 9a designates a first discharging hole perforated through the side plate 3a of the vacuum pump 3, and the numeral 9b designates a second discharging hole perforated through the front bracket 1d-1 so as to be communicated with the first discharging hole 9a. The second discharging hole 9b has a cross-sectional area larger than that of the first discharging hole 9a. The numeral 10 designates a discharge valve provided in the second discharging hole 9b and composed of an umbrella type valve 10a and a plurality of air vent holes 10b. 
     In the second embodiment having the construction described above, when the motor 1 is actuated, air in the vacuum tank 6 is sucked through the intake port 4, and is passed through the first discharging hole 9a,--the air gap formed by the umbrella type valve 10a and the air vent holes 10b provided in the second discharging hole 9b, and the inner space of the motor 1, and is finally discharged through the drain hole 8 to the atmosphere. The motor drive vacuum pump shown in FIG. 3 can also be minimize noise as in FIG. 2. 
     As described above, in accordance with the present invention constructed in such a manner that the discharge port of a vacuum pump is connected to the inner space of a motor so that air from the vacuum pump is discharged through the inner space and a drain of the motor and a discharge valve is provided at a part of the discharging passage, the following excellent effects are obtainable. 
     (a) Noise of the vacuum pump is reduced in an economical manner. 
     (b) The discharge valve increases discharge resistance, to thereby further reducing the discharge noise. 
     (c) Entrance of water, dust, etc. into the vacuum pump is avoided, whereby reliability of the vacuum pump increases. 
     (d) The cooling effect to the motor is improved and reduction in the properties of the motor is prevented because air is passed through the inner space of the motor. 
     FIG. 5 is a diagram illustrating comparative tests of the efficiency of the embodiment shown in FIG. 3 with and without the umbrella type discharge valve 10a in place. As is apparent from this diagram, the pump characteristics (i.e., the achievable degree of vacuum) were notably improved with use of the umbrella type discharge valve 10a. Specifically, with the umbrella type discharge valve 10a in place, a vacuum of 620 mm Hg was obtained, whereas without the umbrella type discharge valve 10a in place, a vacuum of only 480 mm mercury could be obtained. This is an improvement of 29% with the umbrella type discharge valve 10a in place. 
     When the pump of the present invention is used as a negative pressure source for a brake booster installed in a vehicle, the foregoing means that a larger braking force can be obtained with the use of a smaller foot force. This is a very significant effect both safety-wise and economically. 
     The present invention is also applicable to a vacuum pump not only for use with the vehicle, but also for other usage. In such cases, improvements of 20 to 30% are obtainable. 
     The exact degree of vacuum achievable is, of course, dependent on the parts clearances. However, the diagram shown in FIG. 5 is believed to be a fair representation of the order of magnitude improvement achievable with this invention.