Patent Publication Number: US-2018038751-A1

Title: Compressor unit

Description:
TECHNICAL FIELD 
     The present invention relates to a compressor unit suitable for a tire puncture repair kit. 
     BACKGROUND ART 
     Japanese Patent Application Publication No. 2015-157458 (Patent Document 1) discloses a tire puncture repair kit comprising a compressor and a pressure meter. The pressure meter has the function of a relief valve, and can control the pressure of compressed air supplied from the compressor to a pneumatic tire. Thus, it is not necessary to employ a relief valve, and the tire puncture repair kit can be reduced in the size and production cost. 
     The pressure meter disclosed in Patent Document 1 comprises a tubular body communicating with a surge chamber of the compressor, a piston disposed in the tubular body movably by the compressed air from the surge chamber, a spring for biasing the piston toward the front end of the tubular body, and an indicator for the displacement of the piston. The peripheral wall of the tubular body is provided with an exhaust hole. When the compressed air is increased and reaches to a specified pressure, an O-ring of the piston is moved beyond the exhaust hole to discharge the compressed air, thereby, overpressure is released from the exhaust hole. 
     In such pressure meter, the opening area of the exhaust hole is small, and the exhaust hole is gradually opened as the O-ring is passing over the exhaust hole. Thus, it is difficult to release the overpressure instantaneously when the compressed air reaches to the specified pressure. Therefore, there is room for improvement in the functions as of a relief valve such as quick response capability and pressure control accuracy. 
     SUMMARY OF THE INVENTION 
     It is therefore, an object of the present invention to provide a compressor unit comprising a pressure meter which is capable of controlling the pressure of compressed air supplied to an object to be supplied with the compressed air without using a relief valve, and which is improved in the quick response capability and pressure control accuracy. 
     According to the present invention, a compressor unit comprises: 
     a compressor comprising a cylinder comprising a pump chamber portion for compressing air, and a surge chamber portion communicating with the pump chamber portion to receive the compressed air from the pump chamber portion, and 
     a pressure meter for measuring the pressure of the compressed air in the surge chamber, 
     wherein 
     the pressure meter comprises 
     a tubular body having a front end which is provided with a through hole communicating with the surge chamber, and a rear end to which a cap is attached, and
 
a meter-piston provided with a seal ring, and disposed in the tubular body movably in the longitudinal direction thereof by the compressed air from the through hole, and
 
a spring disposed in the tubular body between the piston and the cap, and biasing the piston toward the front end of the tubular body so that the meter-piston can be moved according to the change in the pressure of the compressed air, and
 
an indicator for the displacement of the meter-piston, and
 
     the tubular body comprises 
     a small diameter portion in which the seal ring of the meter-piston contacts with the inner circumferential surface thereof so that the seal ring seals between the inner circumferential surface and the piston, and
 
a large diameter portion which has an inside diameter larger than that of the small diameter portion so that a gap is formed between the inner circumferential surface thereof and the seal ring, and which is connected to the small diameter portion via a step at which the insider diameter of the tubular body is changed,
 
whereby when the compressed air reaches to a specified pressure and the seal ring of the piston is moved from the small diameter portion to the large diameter portion beyond the step, the compressed air is discharged through the gap.
 
     In the compressor unit according to the present invention, it is preferable that the indicator is attached to the tubular body, and 
     the indicator comprises a scale panel which is marked with a scale for showing the displacement of the piston, and located in an upper surface of the compressor unit. 
     In the compressor unit according to the present invention, it is preferable that the indicator comprises a pointer plate which is provided with a pointer for pointing the scale of the scale panel, and disposed along the lower surface of the scale panel, and 
     the pointer plate is fixed to the piston via a connecting portion protruding from the outer circumferential surface of the piston so that the pointer plate is moved together with the piston. 
     In the compressor unit according to the present invention, it is preferable that the large diameter portion is provided with a slot which extends in the longitudinal direction of the tubular body, and penetrates through the peripheral wall of the large diameter portion, and 
     the connecting portion which connects between the pointer plate and the piston, passes through the slot. 
     In the compressor unit according to the present invention, it is preferable that the scale panel is provided with a guide for guiding the pointer plate in the longitudinal direction of the tubular body. 
     Therefore, in the compressor unit according to the present invention, the gap is formed over the entire circumference of the piston to ensure a large opening area. Moreover, when the seal ring is moved beyond the step, the gap having the large opening area is instantly formed, and the overpressure is instantaneously released. Therefore, it is possible to improve the quick response capability and pressure control accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a compressor unit as an embodiment of the present invention. 
         FIG. 2  is a plan view showing the internal configuration of the compressor unit. 
         FIG. 3  is a perspective view of the pressure meter of the compressor unit. 
         FIG. 4  is a cross-sectional side view of the pressure meter. 
         FIG. 5  is a cross-sectional view taken along line A-A of  FIG. 4 . 
         FIG. 6  is an exploded cross-sectional side view of the pressure meter. 
         FIG. 7  is an enlarged cross-sectional view showing the gap between the seal ring and the inner circumferential surface of the large diameter portion of the tubular body. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail in conjunction with accompanying drawings. 
     As shown in  FIGS. 1 and 2 , a compressor unit  1  according to the present invention comprises a housing case  4 , a compressor  5  for generating compressed air disposed in the housing case  4 , and a pressure meter  6  for measuring the pressure of the compressed air disposed in the housing case  4 . 
     The compressor  5  comprises a cylinder  9 , a piston  8  disposed in the cylinder  9 , and a motor M connected to the piston  8  via a crank mechanism  7  to reciprocate the piston  8  in the cylinder  9 . 
     The motor M is a DC motor which can be operated by a 12V DC power supply of the car. The power cord of the motor M is connected to a power plug which can be connected to a cigarette lighter socket of the car, and between the motor M and the power plug, the power cord is provided with a power switch Sw attached to a top plate portion  4 A of the housing case  4 . 
     The cylinder  9  comprises a pump chamber portion  9 A and a surge chamber portion  9 B. 
     In the pump chamber portion  9 A, the piston  8  is disposed so that the piston can reciprocate. The pump chamber portion  9 A forms a pump chamber  12 A for compressing the air together with the piston  8 . 
     The surge chamber portion  9 B communicates with the pump chamber portion  9 A via a one-way valve (not shown), and forms a surge chamber  12 B for receiving the air compressed in the pump chamber portion. The surge chamber  12 B stabilizes the pulsative pressure of the compressed air supplied from the pump chamber  12 A. 
     The surge chamber portion  9 B is provided with two tubular coupling portions  15  and  16  which project therefrom. The pressure meter  6  is connected to the tubular coupling portion  15 . 
     A hose  17  to be connected to an object to be supplied with the compressed air (for example, a pneumatic tire, a puncture repair kit, etc.) is connected to the connection tubular part  16 . 
     As shown in  FIGS. 3 and 4 , the pressure meter  6  comprises a tubular body  18 , a meter-piston  19 , a spring  20  and an indicator  21 . 
     The tubular body  18  has a front end provided with a through hole  22  communicating with the surge chamber  12 B, and a rear end to which a cap  23  is attached to close the opening. More specifically, a tubular connector portion  24  having a small diameter is concentrically and continuously formed at the front end of the tubular body  18  having a larger diameter, and a center bore of the connector portion  24  forms the through hole  22 . The connector portion  24  is connected to the above-mentioned tubular coupling portion  15  airtightly owing to a seal ring  24 A such as an O-ring attached to the outer circumferential surface of the connector portion  24 . 
     The tubular body  18  is composed of a small diameter portion  18 F formed on the front end side and having a smaller inside diameter, and a large diameter portion  18 R on the rear end side having a larger inside diameter and connected to the small diameter portion  18 F via a step K at which the inside diameter of the tubular body  18  is abruptly changed. A cap  23  is screwed to a threaded rear end part of the large diameter portion  18 R. 
     The meter-piston  19  comprises 
     a cylindrical piston main body  19 A loosely inserted into the tubular body  18  and for example, made of a synthetic resin, and
 
a seal ring  25  such as an O-ring attached to the outer circumferential surface of the piston main body  19 A.
 
     The seal ring  25  can closely contact with the inner circumferential surface of the small diameter portion  18 F to seal between the inner circumferential surface and the piston main body  19 A. Thus, by the compressed air supplied through the through hole  22 , the meter-piston  19  is moved in the tubular body  18  in the longitudinal direction thereof. 
     When the seal ring  25  is moved to the large diameter portion  18 R together with the piston main body  19 A, as shown in  FIG. 7 , a gap D is formed between the large diameter portion  18 R and the seal ring  25 . Accordingly, when the compressed air reaches to a specified pressure, and the seal ring  25  is moved beyond the step K, the compressed air is discharged through the gap D. 
     Since the gap D is formed over the entire circumference of the piston, it is possible to secure a large opening area as compared with the exhaust hole of the Patent Document 1. Therefore, the overpressure can be released instantaneously, and it is possible to improve the quick response capability and pressure control accuracy. 
     The spring  20  is disposed between the meter-piston  19  and the cap  23  in order to bias the meter-piston  19  toward the front end. The spring  20  in this example is a compression coil spring, and the displacement (in this example, the amount of compression) of the spring  20  varies according to the magnitude of the pressure of the compressed air. 
     The cap  23  in this example is provided with a tubular holding portion  23 A. The tubular holding portion  23 A protrudes toward the inside of the tubular body  18  and is inserted into the coil spring  20  to concentrically hold the spring  20 . 
     The tubular holding portion  23 A also functions as a guide  26  for guiding the meter-piston  19  concentrically. 
     More specifically, the meter-piston  19  in this example is provided with a guide shaft  19 B disposed radially inside the piston main body  19 A concentrically, and 
     the guide shaft  19 B is slidably inserted into the center bore of the tubular holding portion  23 A. Thereby, the movement of the meter-piston  19  in the longitudinal direction of the tubular body is guided. 
     The indicator  21  indicates the displacement of the meter-piston  19 . 
     The indicator  21  in this example comprises a scale panel  30  appearing in the upper surface S of the compressor unit  1 , and a pointer plate  31  disposed along the lower surface of the scale panel  30 . 
     The scale panel  30  is a plate made of a synthetic resin or the like. 
     The outer or inner surface of the scale panel  30  is marked with a scale  32  for showing the displacement of the meter-piston  19  by using an appropriate technique, e.g. printing, engraving, molding and the like. 
     The scale panel  30  is attached to the tubular body  18  through leg portions  33 . 
     In this example, the scale panel  30 , the leg portions  33  and the tubular body  18  are integrally molded. 
     The pointer plate  31  is a plate made of a synthetic resin or the like. The pointer plate  31  is disposed along the lower surface of the scale panel  30 . The upper or outer surface of the pointer plate  31  is marked with a pointer  34  for pointing the scale  32  by using an appropriate technique, e.g. printing, engraving, molding and the like. The pointer plate  31  is fixed to the meter-piston  19  through a connecting portion  35  so that the pointer plate  31  is moved together with the meter-piston  19 . The connecting portion  35  projects from the outer circumferential surface of the meter-piston  19  (piston main body  19 A). 
     In this example, the pointer plate  31 , the connecting portion  35  and the meter-piston  19  is integrally molded. 
     The scale panel  30  is transparent at least in a portion in which the scale  32  is marked so that the pointer  34  is visible through the transparent portion. Thus, the pointer  34  indicates the displacement of the meter-piston  19 , i.e. the pressure of the compressed air. 
     The scale panel  30  in this example is provided with a guide portion  38  for guiding the pointer plate  31  in the longitudinal direction. 
     The guide portion  38  is formed by a pair of ribs which protrude from the lower surface of the scale panel  30  and extend in the longitudinal direction along the side edges  31 E of the pointer plate  31 . 
     The above-mentioned large diameter portion  18 R in this example is provided with a slot  36  which penetrates through the peripheral wall of the large diameter portion, and extends in the longitudinal direction of the tubular body  18 . 
     The large diameter portion  18 R is provided with reinforcing ribs  37  which extend along the respective edges of the slot  36  and protrude from the outer circumferential surface of the large diameter portion  18 R by a small height. 
     The above-mentioned connecting portion  35  which extends from the meter-piston  19 , passes through the slot  36  and is united with the pointer plate  31  at the upper end. 
     Thus, when the compressed air reaches to a specified pressure, the compressed air flowing out through the gap D is discharged toward the outside of the pressure meter  6  through the slot  36 . 
     Such indicator  21  can increase the display size of the scale and the pointer in order to improve the visibility. 
     While detailed description has been made of a preferable embodiment of the present invention, the present invention can be embodied in various forms without being limited to the illustrated embodiment. 
     DESCRIPTION OF THE REFERENCE SIGNS 
     
         
           1  compressor unit 
           5  compressor 
           6  pressure meter 
           9  cylinder 
           9 A pump chamber portion 
           9 B surge chamber portion 
           12 A pump chamber 
           12 B surge chamber 
           18  tubular body 
           18 F small diameter portion 
           18 R large diameter portion 
           19  meter-piston 
           20  spring 
           21  indicator 
           22  through hole 
           23 A tubular holding portion 
           23  cap 
           25  sealing ring 
           30  scale panel 
           31  pointer plate 
           32  scale 
           34  pointer 
           35  connecting portion 
           36  slot 
           38  guide portion 
         D gap 
         K step