Patent Publication Number: US-2004052648-A1

Title: Compressor

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to a compressor achieving a structure for preventing pressure waves generated during suction, compression and discharge phases of the compression mechanism.  
       BACKGROUND ART  
       [0002] Examples of compressors in the related art include the compressor disclosed in Japanese Unexamined Patent Publication No. H 11-351142, comprising at least an air inlet port through which a coolant gas from an evaporator is taken in, a suction chamber for containing the coolant gas having flowed in through the air inlet port, a cam plate that is slidably and tiltably mounted at a rotating shaft and is made to rotate with the rotating shaft, a piston that engages in a reciprocal movement as the cam plate oscillates and a cylinder having the piston slidably inserted therein that is allowed to communicate with the suction chamber or a discharge chamber as necessary, which translates the rotation of the rotating shaft to a reciprocal movement of the piston via the cam plate, takes in and compresses the coolant gas from the suction chamber as the piston reciprocates inside the cylinder and thus changes the volumetric capacity of the cylinder and discharges the compressed coolant gas into the discharge chamber.  
       [0003] In addition, this compressor includes a clutchless mechanism that sets the discharge capacity to the lowest level by raising the pressure in a crank case and thus minimizing the tilt of the cam plate and, at the same time, stops the coolant gas intake by closing the inlet port so as to circulate the coolant gas inside the compressor to prevent the evaporator from becoming frozen when the load is at the smallest level.  
       [0004] In a so-called piston reciprocating compressor such as that described above, the piston engages in a reciprocal movement as the cam plate rotates and a suction valve and a discharge valve open/close as the pressure in the compression space fluctuates to repeat suction, compression and discharge. Since delays in opening/closing the valves and tramping of the valves themselves are bound to occur during this process, pressure waves are released into the suction chamber or the discharge chamber provided between the suction port and the compression space, which may induce a resonance frequency in the chamber to develop into an extremely intense pulsating wave.  
       [0005] Particularly problematic is a pulsating wave occurring on the suction chamber side having a frequency within a specific range of 400 Hz˜1,000 Hz, which, together with the inherent value (the resonance frequency) of the evaporator, causes a vibration of the evaporator main unit that, in turn, is communicated into the vehicle cabin as unpleasant noise. In addition, while a damping muffler is provided on a piping to damp the suction pulsation or the suction path of the compressor is constricted as a solution to the problem discussed above in the related art, these measures are bound to increase the production cost and to lower the performance of the compressor. Furthermore, in an air-conditioning system which utilizes a condenser instead of a heater core, the condenser needs to be installed inside the cabin, which gives a rise to an added problem of noise occurring as a result of a vibration of the condenser caused by the discharge pulsation at the compressor.  
       [0006] Accordingly, an object of the present invention is to provide a compressor capable of damping a suction pulsation or a discharge pulsation of the compressor by adopting a simple structure.  
       DISCLOSURE OF THE INVENTION  
       [0007] In order to achieve the object described above, in the compressor according to the present invention having at least a housing constituted of a front head, a cylinder block and a rear head, a compression mechanism that is driven in response to a rotation of a drive shaft passing through the front head, a suction chamber formed at the rear head, at which an inlet port of the compression mechanism opens and a discharge chamber formed at the rear head at which an outlet of the compression mechanism opens, either the suction chamber or the discharge chamber is formed toward the center of the rear head with the other chamber formed further outward relative to the chamber at the center, a tunnel-shaped communication path passing through the suction chamber or the discharge chamber formed toward the center of the rear head and the other chamber formed further outward at the rear head, which communicates the chamber with corresponding port is formed and a muffler space is formed between the communication path and a pipe connection part at which the port is mounted.  
       [0008] Thus, according to the present invention, in which the suction chamber or the discharge chamber formed toward the center of the rear head is made to communicate with the corresponding port via the tunnel-shaped communication path and a muffler space is formed between the tunnel-shaped communication path and the pipe connection part at which the port is mounted, the suction pulsation can be suppressed if the suction chamber and the pipe connection part at which the suction port is mounted are made to communicate with each other via the communication path and the discharge pulsation can be prevented if the discharge chamber and the pipe connection part at which the discharge port is mounted are made to communicate with each other via the communication path.  
       [0009] In addition, according to the present invention, it is desirable that the muffler space communicate with the outer end of the communication path.  
       [0010] The tunnel portion defining the communication path may be formed as an integrated part of the rear head, or a separate pipe member may be inserted at the rear head to form the tunnel.  
       [0011] Furthermore, the compression mechanism should include at least a plurality of cylinders formed at the cylinder block, each having an inlet to communicate with the suction chamber and an outlet to communicate with the discharge chamber, pistons each slidably inserted at one of the cylinders so as to freely move reciprocally a rotary cam plate that rotates together with the drive shaft to cause a reciprocal movement of the pistons and a volumetric capacity varying mechanism capable of changing the angle of the rotary cam plate.  
       [0012] It is also desirable that the communication path be a suction path that communicates between the suction chamber and the corresponding suction port. Since this prevents the pulsating wave on the intake chamber side from resonating with the inherent value (resonance frequency) of the evaporator, a vibration of the evaporator installed in the cabin can be particularly effectively suppressed or prevented.  
       [0013] It is also desirable that a small hole to communicate with the suction path be formed at the furthest end of the muffler space so as to allow the oil remaining in the muffler space to return to the suction path. Since a specific effective volumetric capacity and a specific effective length are assured with regard to the muffler space as a result, the capability of the muffler space can be maintained at a desirable level.  
       [0014] Moreover, it is desirable that a valve mechanism capable of opening/closing of the suction path in response to an external signal be provided at the suction path. Since the suction path is shut off even when the pistons are moving over a very small stroke in this structure, the evaporator does not freeze, and a so-called clutchless structure is achieved.  
       [0015] It is desirable that the small hole mentioned earlier be formed so as to open toward the upstream side of the valve mechanism. In this case, no bypass passage bypassing the valve mechanism is formed and the clutchless structure can be utilized effectively. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016]FIG. 1 is a sectional view of the compressor achieved in an embodiment of the present invention; and  
     [0017]FIG. 2 illustrates the communication path and the muffler space. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
     [0018] The following is an explanation of an embodiment of the present invention, given in reference to the drawings.  
     [0019] A compressor  1  in FIG. 1 includes a housing  5  constituted of a front head  2 , a cylinder block  3  and a rear head  4 . A rotating shaft  6  passes through the front head  2  and is rotatably supported at the front head  2  and the cylinder block  3 . A crank case  7  is formed inside the front head  2 , and an opening of the crank case  7  is blocked by the cylinder block  3 . A valve plate  8  is clamped and locked between the cylinder block  3  and the rear head  4 .  
     [0020] A plurality of cylinders  9  extending along the axis of the rotating shaft  6  are formed around the rotating shaft  6  at the cylinder block  3 , and an intake  10  and an outlet  11  formed at the valve plate  8  are made to open at each of the cylinders  9 . The inlet  10  and the outlet  11  are opened/closed by valve elements. A piston  12  is slidably inserted at each cylinder  9 , the end of the piston  12  toward the crank case slidably interlocks with a rotary cam plate  13  and the rotary cam plate  13  is caused to rotate by a rotating plate  14  secured the rotating shaft  6  via a linking mechanism  30 . In addition, the rotary cam plate  13  is attached to the rotating shaft  6  so that its angle relative to the rotating shaft  6  can be freely adjusted. A baffle plate  31  and a cover  32  are provided on the outside of the cylinder block  3 , with a discharge path  15  to communicate with a discharge port (not shown) formed at the cover  32 . at the baffle plate  31 , discharge gas path holes  33   a  are formed to reduce the extent of the discharge pulsation.  
     [0021] In the compressor  1  achieved in the embodiment, a discharge chamber  16  that communicates with the outlet  11  formed at the valve plate  8  is formed ofurther outward at the rear head  4  and a suction chamber  17  to communicate with the suction chamber  10  is formed at the center of the rear head  4 . In addition, the discharge chamber  16  communicates with the crank case  7  via a pressure control valve  18  mounted at the rear head  4 . It is to be noted that the pressure control valve  18  is controlled with an external control signal, that the power supply to the pressure control valve  18  is stopped if the freezing capability is judged to be unnecessary and that the level of the electrical current that is supplied rises as the heat load rises.  
     [0022] In addition, a suction port  20 , at which a suction-side connector  19  connected with the piping and extending from the evaporator (not shown) is mounted, is formed at an external circumferential side surface of the rear head  4 . The suction port  20  is made to communicate with the suction chamber  17  via a communication path  21  defined by a tunnel portion  25  which is formed as an integrated part of the rear head  4 . A cutoff valve  22  that opens/closes the communication path  21  is provided on the communication path  21  and the communication path  21  is blocked by the cutoff valve  22  when the freezing operation is judged to be unnecessary so as to ensure that no coolant gas is taken in from the evaporator.  
     [0023] Furthermore, a muffler space  23  is formed around the tunnel portion  25  defining the communication path  21 , as shown in FIGS. 1 and 2. One end of the muffler space  23  opens at the suction port  20  and a small hole  24  which communicates with the upstream side of the cutoff valve  22  at the communication path  21  is formed at the other end (the furthest end). It is desirable that the muffler space  23  be formed over a length of approximately 30 mm along the communication path  21  around the tunnel portion  25 . By forming the muffler space  23  over the length of approximately 30 mm, a damping peak frequency of approximately 800 Hz is achieved. Under normal circumstances, it is desirable to estimate the damping frequency relative to the length of the muffler space  23  through the finite element method and to set the length of the muffler space  23  in correspondence to the desired damping frequency band.  
     [0024] As the main drive engine (not shown) rotates, causing rotation of the rotating shaft  6  in the compressor  1  structured as described above, the rotating plate  14  fixed to the rotating shaft  6  also rotates, which, in turn, causes the rotary cam plate  13  to rotate and oscillate via the linking mechanism  30 . Then, as the rotary cam plate  13  rotates and oscillates, with the pistons  12  each having one end thereof slidably fixed to the rotary cam plate  13  make reciprocal movement relative to the cylinders  9 , thereby changing the volumetric capacity of the compression space defined by the pistons  12  and the cylinders  9 . As the volumetric capacity of the compression space changes as described above, the coolant gas is taken in from the suction chamber  17 , becomes compressed and is discharged into the discharge chamber  16 . Through this process, the coolant gas having been evaporated at the evaporator is taken into the suction chamber  17  from the suction port  20  via the communication path  21 , becomes compressed and is then let out from the discharge chamber  16  through the discharge path  15  to the next process, e.g., to the condenser.  
     [0025] When the heat load is significant, the high-level pressure supplied to the crank case  7  is reduced through the pressure control valve  18  to lower the pressure in the crank case and thus, the back pressure at the pistons  12  is lowered. As a result, the stroke of the pistons  12  becomes larger to increase the quantity of the discharge from the compressor  1 . When it is decided that the freezing operation is not necessary, the high-level pressure is supplied to the crank case  7  through the pressure control valve  18 , thereby raising the back pressure of the pistons  12  and, as a result, the stroke of the pistons  12  becomes smaller to reduce the quantity of the discharge from the compressor  1 . In addition, when the heat load is at the lowest level, the communication path  21  is blocked with the cutoff valve  22 , and thus, the coolant gas supply to the suction chamber  17  stops. In this case, the coolant gas is made to circulate inside the compressor  1  with the compressor  1  discharging no coolant gas, thereby achieving a clutchless compressor.  
     [0026] While the coolant gas is taken in, compressed and discharged through the suction, compression and discharge phases at the compressor  1 , as described above, the individual phases, e.g., the suction phase, are executed intermittently with the plurality of pistons  12  and, as a result, a pressure fluctuation occurs, for instance, in the suction chamber  17 , which is then transmitted toward the evaporator as a pulsating wave. Since the evaporator is normally installed in the cabin, this pulsating wave would be communicated as unpleasant noise if its frequency matched the resonance frequency of the evaporator (which varies depending upon the model but is normally within a range of 300 Hz˜1,000 Hz). However, according to the present invention in which the muffler space  23  is provided near the communication path  21 , the pulsating wave can be damped in the frequency band.  
     [0027] While a more significant pulsating wave is observed on the high pressure side than on the low pressure side in the compressor under normal circumstances, the high pressure side is usually located in the engine compartment and the evaporator on the low pressure side is installed in the cabin. For this reason, the resonance occurring at the evaporator is a problem to be addressed. However, in an air-conditioning system which utilizes a high pressure side condenser in place of a heater core, the problem of resonance at the condenser manifesting as noise must be addressed. Accordingly, in an air-conditioning system in which the condenser set on the high pressure side of the freezing cycle is installed inside the cabin, a communication path that communicates between a discharge chamber and a discharge port may be provided by forming the discharge chamber toward the center of the rear head  4  and forming a suction chamber around the discharge chamber and a muffler space to communicate with this communication path may be formed around the communication path. By adopting the structure, the pulsating wave propagating from the discharge chamber toward the condenser can be damped to prevent resonance from occurring at the condenser.  
     [0028] In addition, the small hole  24  which communicates between the muffler space  23  and the upstream side of the cutoff valve  22  at the communication path  21  is formed at the furthest end of the muffler space  23  so as to prevent stagnation of the oil in the muffler space  23 . The damping effect achieved by providing the muffler space  23  normally corresponds to the length (depth) of the muffler space  23 . For this reason, the small hole  24  is formed to prevent any stagnation of the oil so as to ensure that the damping target frequency band does not change due to a change in the depth of the muffler space  23  caused by remaining oil in the muffler space  23 .  
     [0029] It is desirable to set the diameter of the small hole  24  to approximately 1 mm, since the damping target frequency band would change if the diameter was larger than approximately 1 mm and the oil discharge efficiency would be lowered if the diameter was smaller than approximately 1 mm. However, the diameter of the small hole  24  may be varied to achieve an intentional change in the damping frequency band. Moreover, as the small hole  24  opens at the upstream side of the cutoff valve  22 , the suction chamber  17  and the suction port  20  are not allowed to communicate with age other via the small hole  24  when the communication path  21  is blocked by the cutoff valve  22  and, as a result, the communication path  21  is blocked with a high degree of reliability.  
     INDUSTRIAL APPLICABILITY  
     [0030] As explained above, according to the present invention in which a muffler space is provided at a communication path between the suction side or the discharge side and the corresponding port, the pulsating wave generated at the suction side or the discharge side can be damped to prevent unpleasant noise in the cabin.  
     [0031] In addition, since the muffler space is formed at the external circumference of the tunnel portion which defines the communication path at the rear head and thus the communication path can be formed as an integrated part of the rear head, the production cost does not go up. Even when the communication path is formed by using a separate part, the communication path can be formed with ease by forming spaces to constitute the communication path and the muffler space in advance at the rear head and then mounting a pipe for defining the communication path subsequently. Thus, an increase in the production cost can be minimized.  
     [0032] Moreover, since the small hole through which the oil is discharged is formed at the muffler space, the damping characteristics achieved in the muffler are stabilized to achieve reliable noise prevention.