Patent Publication Number: US-8974191-B2

Title: Air compressor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-078511 filed Mar. 31, 2011. The entire content of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an air compressor to supply compressed air to a power tool whose power source is compressed air. 
     BACKGROUND 
     There is a well known air compressor configured to supply compressed air to a pneumatically operated fastener driving tool in which compressed air is used as a power source. Such an air compressor includes a pair of air tanks, a motor, a fan, an air compression mechanism, and a control unit. The air compressor also includes a housing with which the motor and the air compression mechanism are covered. The compression mechanism includes a crank shaft, a cylinder, a piston, and a cylinder head. 
     In the air compressor, rotation of the motor is converted into a reciprocating movement of the piston in the cylinder via the crank shaft. In association with the reciprocating movement of the piston, air flows into the cylinder through an inlet port formed in a valve seat provided at a position between the cylinder and the cylinder head, so that the air is compressed in the cylinder. The compressed air flows out of the cylinder through an outlet port formed in the valve seat to flow into the pair of air tanks via a pipe. The compressed air is reserved in the pair of air tanks. 
     The pair of air tanks is arranged parallel to each other with respect to its axial direction. The control unit serving to control the motor to drive is disposed so as to be interposed between the pair of air tanks. Further, the motor is disposed above the pair of air tanks. The motor includes an output shaft that is arranged parallel to the axial direction of the pair of air tanks. The fan is rotatable coaxially and integrally with the output shaft of the motor. Further, the fan is disposed substantially above the pair of air tanks and closer to one end of the pair of air tanks in the axial direction than a remaining one end thereof. Rotation of the fan generates airflow in a gap formed between the pair of air tanks, thereby cooling down the control unit that generates heat when driving the motor. US patent application publication No. 2008/0112823 discloses such an air compressor. 
     SUMMARY 
     However, the above-described conventional air compressor is unable to sufficiently cool down a portion of the control unit that is positioned farther from the fan, while another portion of the control unit that is positioned closer to the fan can be sufficiently cooled down. 
     In view of the foregoing, it is an object of the present invention to provide an air compressor capable of sufficiently cooling a control unit. Further, it is another object of the present invention to provide an air compressor with a lightweight and downsized structure. 
     In order to attain the above and other objects, the present invention provides an air compressor including a housing, a motor, an air compression mechanism, a rotation shaft, a fan, a plurality of air tanks, and a control unit. The motor is disposed in the housing and has a rotor. The air compression mechanism is driven by the motor to generate compressed air. The rotation shaft is rotatable integrally with the rotor. The axial flow fan is disposed in the housing and rotatable integrally with the rotation shaft to generate airflow. The fan defines an outer circumference. The plurality of air tanks is juxtaposed with each other and arrayed in an array direction. Each of the plurality of air tanks has a hollow cylindrical configuration with an axis. Each of the plurality of air tanks is configured to reserve the compressed air generated by the air compression mechanism. The plurality of air tanks includes an endmost air tank and an adjacent air tank adjacent to the endmost air tank in the array direction. The control unit is configured to control the motor and disposed adjacent to and opposite to the adjacent air tank relative to the endmost air tank in the array direction. The control unit is disposed adjacent to and in confrontation with the outer circumference of the fan. 
     According to another aspect, the present invention provides an air compressor includes a housing, a motor, an air compression mechanism, a rotation shaft, a fan, an air tank, and a control unit. The motor is disposed in the housing and has a rotor. The air compression mechanism is driven by the motor to generate compressed air. The rotation shaft is rotatable integrally with the rotor. The fan is disposed in the housing and rotatable integrally with the rotation shaft to generate airflow. The fan defines an outer circumference. The air tank has a hollow cylindrical configuration with an axis. The air tank is configured to reserve the compressed air generated by the air compression mechanism. The control unit is configured to control the motor. The rotation shaft extends in a direction substantially perpendicular to the axis of the air tank. The control unit has an elongated configuration in a direction parallel to the axis of the air tank and is disposed adjacent to the air tank and the outer circumference of the fan. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a plan view of an air compressor provided with a fan according to one embodiment of the present invention; 
         FIG. 2  is a right side view of the air compressor according to the embodiment; and 
         FIG. 3  is a right side view of the air compressor according to the embodiment, in which airflow generated by the fan is indicated by arrows. 
     
    
    
     DETAILED DESCRIPTION 
     An air compressor according to one embodiment of the present invention will be described while referring to  FIGS. 1 to 3  wherein like parts and components are designated by the same reference numerals to avoid duplicating description. 
     The portable type air compressor  1  serves to supply compressed air to a pneumatic tool such as a pneumatically operated fastener driving tool. The total weight of the air compressor  1  is approximately 12.9 kg. The air compressor  1  is capable of supplying one hundred and ten (110) liters per minute of compressed air with a maximum pressure of 4.5 MPa. As shown in  FIG. 1 , the air compressor  1  includes a housing  10 , a motor  20 , an axial flow fan,  25 , an air compression mechanism  30 , a compressed air take off unit  40 , a tank unit  50 , and a control unit  70 . 
     In the following description, the terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “beneath”, “right”, “left”, “front”, “rear” and the like will be used assuming that the air compressor  1  is disposed in an orientation in which it is intended to be used. More specifically, left, right, top, and bottom sides in  FIG. 1  are left, right, rear, and front sides of the air compressor  1 . 
     As shown in  FIG. 1 , the tank unit  50  includes a pair of air tanks  51  and  52 , a frame  53 , and a communication pipe  54  ( FIG. 2 ). The pair of air tanks  51  and  52  serves to reserve compressed air supplied from the air compression mechanism  30 . Each of the air tanks  51  and  52  has a hollow cylindrical configuration having each closed end, and has an axis extending in a left-to-right direction (axial direction). The pair of air tanks  51  and  52  is disposed such that the axis thereof is arranged parallel to each other. That is, the pair of air tanks  51  and  52  is juxtaposed with each other in a front-to-rear direction (array direction). The air tank  52  is adjacent to the endmost air tank  51  in array direction. Further, the one end (left end) of the air tank  51  is arranged in alignment with the one end (left end) of the air tank  52  in the front-to-rear direction, and the remaining one end (right end) of the air tank  51  is also arranged in alignment with the remaining one end (right end) of the air tank  52  in the front-to-rear direction. The pair of air tanks  51  and  52  is supported to the frame  53  fixed to the housing  10  so that the air tanks  51  and  52  are spaced apart from each other at a regular interval in the front-to-rear direction. In other words, the pair of air tanks  51  and  52  is not in contact with each other in the front-to-rear direction, and a gap is formed therebetween ( FIG. 2 ). The interior of the air tank  51  is in communication with the interior of the air tank  52  via the communication pipe  54 . The air tank  51  is positioned downstream of the air tank  52  in a direction that compressed air flows. Accordingly, the air tank  51  and the air tank  52  are also respectively referred to as a downstream air tank  51  and an upstream air tank  52 . The total weight of the pair of air tanks  51  and  52  and the frame  53  is approximately 3.3 kg. The total volume of the pair of air tanks  51  and  52  is approximately eight (8) liters. 
     As shown in  FIG. 2 , the housing  10  covers the motor  20 , the axial flow fan  25 , the air compression mechanism  30 , a major part of the pair of air tanks  51  and  52 , and the control unit  70 . For the sake of simplicity,  FIGS. 1 to 3  are illustrated as if the housing  10  were was transparent. However, in fact, the housing  10  is non-transparent. The housing  10  is made of resin in black. The housing  10  has an upper housing  11  and a lower housing  12 . The total weight of the housing  10  including the upper housing  11  and the lower housing  12  is approximately 0.6 kg to 0.7 kg. The upper housing  11  covers a major part of an upper portion of the air tank  52 , and a major part of an upper rear portion of the air tank  51 . The upper housing  11  has a lower rear edge that is connected to the lower housing  12 . The lower housing  12  is positioned so as to confront a lower rear portion of the air tank  51 . The lower housing  12  covers the control unit  70  and the lower rear portion of the air tank  51 . 
     The upper housing  11  has a single handle  11 A ( FIG. 2 ). The handle  11 A protrudes upward from an upper surface of the upper housing  11  and extends in the left-to-right direction. More specifically, the handle  11 A is positioned above a center portion of the air tank  51  in the axial direction of the air tank  51  and also above a crank casing  31  (described later). The handle  11 A is provided at a position just above the center of gravity of the air compressor  1 . The handle  11 A is also provided at a position offset from an intermediate position between the axes of the pair of air tanks  51  and  52  in the front-to-rear direction toward the control unit  70  (described later). 
     The upper housing  11  has a front end portion confronting the crank casing  31 , and the front end portion is formed with a plurality of through holes (not shown) for providing communication between the interior and exterior of the upper housing  11 . Further, the upper housing  11  has a rear end portion confronting the axial flow fan  25  (described later), and the rear end portion is formed with a plurality of through holes (not shown) for providing communication between the interior and exterior of the upper housing  11 . The lower housing  12  has a lower front edge that is spaced apart from the lower rear portion of the air tank  51 . More specifically, a gap is formed between the lower front edge of the lower housing  12  and the lower rear portion of the air tank  51 , thereby defining an air passage between the interior and exterior of the upper housing  11 . Further, the gap formed between the pair of air tanks  51  and  52  also defines an air passage between the interior and exterior of the upper housing  11 . 
     On the upper surface of the upper housing  11 , a main power switch (not shown) and an operation panel (not shown) are provided. The air compressor  1  is turned on or off through the main power switch. When the air compressor  1  is turned on, a commercial three-phase AC power supply provides an electrical power with the control unit  70 , the motor  20  and the like to drive the same. The operation panel serves to display internal pressure values of the air tanks  51  and  52  and warning signs such as overload. 
     The motor  20  and the air compression mechanism  30  are disposed inside the upper housing  11 , and are positioned above the air tank  51  and in substantially the axial center thereof. The total weight of the motor  20  and the air compression mechanism  30  is approximately 5.7 kg to 5.9 kg. In the present embodiment, a three-phase AC brushless motor is employed as the motor  20 . As shown in  FIG. 1 , the motor  20  includes a stator  21 , a rotor  22 , and an output shaft  23  that is rotatable integrally with the rotor  22 . The motor  20  is disposed such that the output shaft  23  is arranged perpendicular to the axial direction of the air tank  51 . The output shaft  23  has a front end portion that extends through the crank casing  31  (described later). 
     As shown in  FIG. 1 , the axial flow fan  25  is disposed inside the upper housing  11  at a position rearward of the air tank  51  in the front-to-rear direction. The axial flow fan  25  is provided with a rotation shaft  24  that is also disposed inside the upper housing  11 . The rotation shaft  24  is fixed to the output shaft  23  at a rear end portion of the output shaft  23 , and is arranged to be coaxial with the output shaft  23 . In other words, the rotation shaft  24  extends in a direction parallel to the array direction in which the air tanks  51  and  52  are arrayed. The axial flow fan  25  is fixed to the rotation shaft  24  and rotatable coaxially and integrally with the rotation shaft  24 . 
     The air compression mechanism  30  is connected to the motor  20  and disposed in front of the motor  20 . The air compression mechanism  30  is driven by the motor  20  to generate compressed air. As shown in  FIG. 1 , the air compression mechanism  30  includes the crank casing  31 , a first compressor  32 , and a second compressor  33 . The crank casing  31  is provided with a crank shaft (not shown). The first compressor  32  includes a first cylinder (not shown), a first cylinder head (not shown), and a first piston (not shown) disposed in the first cylinder. The second compressor  33  includes a second cylinder (not shown), a second cylinder head (not shown), and a second piston (not shown) disposed in the second cylinder. The crank shaft provided in the crank casing  31  is configured so as to be rotatable integrally with the output shaft  23  of the motor  20 . The crank shaft is drivingly connected to the first and second pistons of the first and second compressors  32  and  33 , thereby converting the drive force of the motor  20  to reciprocating movements of the first and second pistons via the crank shaft. The first compressor  32  is provided with a first valve seat (not shown) at a position between the first cylinder head and the first cylinder. The first valve seat is formed with a first inlet port (not shown) and a first outlet port (not shown). The second compressor  33  is provided with a second valve seat (not shown) at a position between the second cylinder head and the second cylinder. The second valve seat is formed with a second inlet port (not shown) and a second outlet port (not shown). The first outlet port is connected to the second inlet port through a tubular member  55 . The second outlet port is connected to the air tank  52  through a tubular member  56 . 
     The crank casing  31  has a front portion in which an air intake port  31   a  ( FIG. 2 ) is formed. The air intake port  31   a  provides communication between the interior and exterior of the crank casing  31 . The air intake port  31   a  is provided at a position opposing the axial flow fan  25  relative to the motor  20  and the crank casing  31 . In other words, the air intake port  31   a  is not in direct confrontation with the axial flow fan  25 . Accordingly, airflow generated by the axial flow fan  25  does not directly impinge on the front portion of the crank casing  31  in which the air intake port  31   a  is formed. 
     As shown in  FIG. 2 , the air compressor  1  further includes a drain discharging device  57 . More specifically, the drain discharging device  57  is disposed above the right end portion of the air tank  51 . The drain discharging device  57  is provided with a drain cock  57 A and a drain discharge port  57   a . A user manually operates the drain cock  57 A to selectively open and close the drain cock  57 A. The drain discharging device  57  is configured such that when the drain cock  57 A is opened, drain and compressed air reserved in the air tanks  51  and  52  can be simultaneously discharged from the drain discharge port  57   a  through the communication pipe  54  and a flow passage formed in the drain discharging device  57 . 
     The compressed air take off unit  40  includes decompression valves  58 A and  58 B, pressure gauges  59 A and  59 B, compressed air take off ports (couplers)  60 A and  60 B, pressure regulation handles  61 A and  61 B for regulating a pressure of compressed air to be taken off, and socket holders  62 A and  62 B. More specifically, as shown in  FIG. 1 , the decompression valve  58 A, the pressure gauge  59 A, the compressed air take off ports  60 A, the pressure regulation handle  61 A, and the socket holder  62 A are disposed above a left portion of the air tank  52 , and the decompression valve  58 B, the pressure gauge  59 B, the compressed air take off ports  60 B, the pressure regulation handle  61 B, and the socket holder  62 B are disposed above a right portion of the air tank  52 . 
     The decompression valve  58 A is connected to the downstream air tank  51  via a tubular member (not shown). The pressure regulation handle  61 A is attached to and disposed above the decompression valve  58 A. The socket holder  62 A is threadingly engaged with the decompression valve  58 A. The pressure gauge  59 A is threadingly engaged with an upper edge of the socket holder  62 A. The compressed air take off port  60 A is threadingly engaged with a left edge of the socket holder  62 A. The compressed air take off port  60 A is connectable to a pneumatic tool such as a pneumatically operated fastener driving tool via a hose to supply compressed air to the pneumatic tool. 
     Likewise, the decompression valve  58 B is connected to the downstream air tank  51  via a tubular member (not shown). The pressure regulation handle  61 B is attached to and disposed above the decompression valve  58 B. The socket holder  62 B is threadingly engaged with the decompression valve  58 B. The pressure gauge  59 B is threadingly engaged with an upper end portion of the socket holder  62 B. The compressed air take off port  60 B is threadingly engaged with a right end portion of the socket holder  62 B. The compressed air take off port  60 B is connectable to a pneumatic tool via a hose to supply compressed air reserved in the air tanks  51  and  52  to the pneumatic tool. 
     With this configuration, the pressure gauges  59 A and  59 B can monitor pressures of compressed air around the compressed air take off ports  60 A and  60 B, respectively. Further, regardless of intensity of the pressure of compressed air introduced into the air tanks  51  and  52 , the pressures of compressed air at the compressed air take off ports  60 A and  60 B can be respectively regulated at fixed pressure values by the pressure regulation handles  61 A and  61 B so that the fixed pressure values are less than or equal to the maximum pressure value. As a result, compressed air with a pressure value less than or equal to the maximum pressure value can be obtained from the compressed air take off ports  60 A and  60 B. 
     The control unit  70  is configured to control the motor  20  to start or to stop (turn on or turn off). As shown in  FIG. 2 , the control unit  70  is disposed inside a rear portion of the upper housing  11  and inside the lower housing  12 . The control unit  70  is provided at a position opposite the air tank  52  relative to the air tank  51 . More specifically, the control unit  70  is positioned adjacent to the air tank  51  and spaced apart from the rear end portion of the air tank  51  in the front-to-rear direction. A distance between the control unit  70  and the rear end portion of the air tank  51  is approximately 4 mm. Further, the control unit  70  is positioned in direct confrontation with and adjacent to a lower end of an outer circumferential portion of the axial flow fan  25 . The control unit  70  is spaced apart from the lower end of the outer circumferential portion of the axial flow fan  25  at a distance of approximately 15 mm in a vertical direction (top-to-bottom direction). The weight of the control unit  70  is approximately 0.9 kg. The control unit  70  has an elongated configuration in a direction parallel to the axis of the air tank  51 . 
     Next, an air compressing operation of the air compressor  1  with the above-described configuration will be described. When the air compressor  1  is in operation, air flows into the upper housing  11  through the plurality of through holes formed in the upper housing  11 . Then, the air flows into the crank casing  31  through the air intake port  31   a  in association with the reciprocating movement of the first piston in the first cylinder provided in the first compressor  32 . Subsequently, the air flows into the first cylinder through the first inlet port formed in the first valve seat of the first compressor  32 . The air is compressed in the first cylinder so as to have a pressure value of 0.7 to 0.8 MPa. The compressed air is taken off from the first outlet port formed in the first valve seat of the first compressor  32  to flow into the second cylinder provided in the second compressor  33  through the second inlet port formed in the second valve seat of the second compressor  33  via the tubular member  55 . The compressed air is further compressed in the second cylinder so as to have a pressure value of 3.0 to 4.5 MPa, the allowable maximum pressure value. The further compressed air is taken off from the second outlet port formed in the second valve seat of the second compressor  33  to flow into the air tank  52  through the tubular member  56 . The compressed air introduced into the air tank  52  partly flows into the air tank  51  via the communication pipe  54 . Hence, the compressed air is reserved both in the air tank  51  and in the air tank  52  at the same pressure. 
     As shown in  FIG. 3 , when the air compressor  1  operates to compress air, air introduced into the upper housing  11  through the plurality of through holes formed in the rear end portion of the upper housing  11  passes over the control unit  70  to impinge upon the upper rear portion of the air tank  51  due to air entrainment in association with the rotation of the axial flow fan  25 . A part of the airflow moves downward along the rear portion of the air tank  51  to cool down the control unit  70 . Further, airflow generated by the axial flow fan  25  and flowing in the axial direction of the axial flow fan  25  cools down the motor  20  and the air compression mechanism  30 . 
     According to the air compressor  1  in the above-described embodiment, the air compressor  1  includes the control unit  70 . The control unit  70  is disposed adjacent to and spaced apart from the air tank  51  at a prescribed distance in the front-to-rear direction. Further, the control unit  70  is provided at a position opposite the air tank  52  relative to the air tank  51  that is disposed juxtaposed with the air tank  52 . Further, the control unit  70  is disposed in direct confrontation with and adjacent to the outer circumferential portion of the axial flow fan  25  in the vertical direction. Despite the position of the control unit  70  such that the control unit  70  is disposed so as not to confront the axial flow fan  25  in the axial direction of the axial flow fan  25 , air entrainment in association with the rotation of the axial flow fan  25  generates airflow toward the control unit  70 . As a result, the control unit  70  can be efficiently cooled. 
     Further, it is not necessary to dispose the control unit  70  between the air tanks  51  and  52 . Accordingly, the degree of freedom in design of the air compressor  1  can be enhanced. Therefore, reduction in size and weight of the air compressor  1  can be easily attained. 
     The rotation shaft  24  is oriented (extends) in a direction that the pair of air tanks  51  and  52  is juxtaposed (i.e. front-to-rear direction). Further, the axial flow fan  25  is provided at a position opposite the air tank  52  relative to the air tank  51  in the direction. Hence, the axial flow fan  25  and the control unit  70  are disposed not above the pair of air tanks  51  and  52  but offset from the same in the direction. Therefore, the degree of freedom in design of the air compressor  1  can be enhanced. Hence, reduction in size and weight of the air compressor  1  can be easily attained. 
     The tank unit  50  includes the two air tanks  51  and  52 . Compared with a case that more than two air tanks are provided, the total weight of the air tanks  51  and  52  can be reduced. The total volume of the air tanks  51  and  52  can also be reduced but made greater than that of a single air tank. 
     Further, the tank unit  50  includes the upstream air tank  52  and the downstream air tank  51 . The upstream air tank  52  is connected to the air compression mechanism  30 , so that compressed air directly flows into the upstream air tank  52 . The downstream air tank  51  is connected to the upstream air tank  52 , and a part of compressed air introduced into the upstream air tank  52  flows into the downstream air tank  51 . With this configuration, the temperature of compressed air reserved in the downstream air tank  51  can be reduced to lower than the temperature of compressed air reserved in the upstream air tank  52 . As a result, the control unit  70  that is disposed closer to the downstream air tank  51  than to the upstream air tank  52  can be efficiently cooled. 
     Further, the housing  10  is provided with the single handle  11 A. The handle  11 A is provided at a position offset from the intermediate position between the axes of the air tanks  51  and  52  in the front-to-rear direction (i.e. direction that the air tanks  51  and  52  are juxtaposed) toward the control unit  70 . Hence, the handle  11 A is disposed above the center of gravity of the air compressor  1 . Accordingly, portability of the air compressor  1  can be improved, and a user can easily carry the air compressor  1  with one hand. 
     Further, the air intake port  31   a  is formed in the air compression mechanism  30  to allow air to flow into the crank casing  31 . The air intake port  31   a  is provided at a position such that airflow generated by the axial flow fan  25  does not directly impinge upon the air intake port  31   a . Therefore, the degree of freedom in design of the air compressor  1  can be enhanced. Hence, reduction in size and weight of the air compressor  1  can be easily attained. 
     The air compressor  1  according to the present invention is useful in the field of portable type air compressors that supply compressed air to pneumatic tools whose power source is compressed air and that are easy to carry. 
     While the present invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the present invention. For example, while the three-phase AC power brushless motor is used as the motor  20  in the above-described embodiment, other types of motor may be used. 
     In the above-described embodiment, the tank unit  50  includes the two air tanks  51  and  52 . However, the number of air tanks provided in the tank unit  50  is not limited to two. The tank unit  50  may include a plurality of air tanks more than two. 
     In the above-described embodiment, the rotation shaft  24  is coaxially fixed to the output shaft  23  of the motor  20  at the rear end portion of the output shaft  23 . Further, the axial flow fan  25  is coaxially fixed to the rotation shaft  24  and rotatable integrally with the rotation shaft  24 . However, the axial flow fan  25  may be coaxially fixed to the output shaft  23  of the motor  20  and rotatable integrally with the output shaft  23 .