Patent Publication Number: US-6991435-B2

Title: Variable displacement compressors which estimate an inclination angle of a plate of the compressor

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to variable displacement compressors. In particular, the present invention is directed towards compressors which estimate an inclination angle of a plate of the compressor to determine a driving torque of the compressor. 
   2. Description of Related Art 
   Known variable displacement compressors may be used in an air conditioning system of vehicle. Such known variable displacement compressors include a plate, e.g., a swash plate or a cam plate, and a piston which reciprocates within a cylinder bore. An inclination angle of the plate varies in response to an external signal, and the inclination angle determines a stroke length of the piston. Specifically, when the stroke length of the piston decreases, the amount of refrigerant which the piston compresses also decreases. Similarly, when the stroke length of the piston increases, the amount of refrigerant which the piston compresses also increases. Such known variable displacement compressors also determine a driving torque of a drive shaft of the compressor, and the external signal controls the inclination angle of the cam based on the determined driving torque. Such known compressors also use the determined driving torque to control the speed of an engine of the vehicle. 
   In a known variable displacement compressor described in Japanese Unexamined Patent Publication No. H05-164045, the driving torque is determined by using a magnetic film wrapped around the drive shaft, and a plurality of coils positioned adjacent to the magnetic film. When the drive shaft rotates, magnetostriction occurs in the magnetic film, which alters an output voltage of the coils. The driving torque of the drive shaft then is determined based on the output voltage of the coils. Nevertheless, in this known compressor, a torsional rigidity of the drive shaft is selected, such that the drive shaft readily may be twisted. The torsional rigidity of the drive shaft may be defined as the ratio of the torque applied about a centroidal axis of the drive shaft at a first end of the drive shaft to the resulting torsional angle, when a second end of the drive shaft is fixed. However, when the torsional rigidity of the drive shaft is selected, such that the drive shaft readily may be twisted, torsional vibration may occur. Torsional vibration may be defined as a periodic motion of the drive shaft in which the drive shaft is twisted about its axis first in first direction, and then in a second direction opposite to the first direction. This periodic motion may be superimposed on the rotational motion of the drive shaft. In addition, the drive shaft is subject to a bending force, and it is difficult to manufacture a drive shaft which is both readily twistable, and has a strength which is sufficient to retain its shape against the bending force. Moreover, the use of the coils increases the size and the cost of the compressor, and if the coils are not accurately positioned within the compressor, the determined driving torque may not be sufficiently accurate. 
   In another known variable displacement compressor described in Japanese Unexamined Patent Publication No. H05-99156, the driving torque is indirectly determined based on a pressure within the compressor, a temperature within the compressor, or a refrigerant flow-rate within the compressor, or combinations thereof. Nevertheless, the driving torque which is determined based on these measurements also may not be sufficiently accurate. 
   SUMMARY OF THE INVENTION 
   Therefore, a need has arisen for variable displacement compressors which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that the drive torque may be determined based on an estimation of the inclination angle of the plate of the compressor, and the determined drive torque may be more accurate than in the known compressors. 
   In an embodiment of the present invention, a variable displacement compressor comprises a plate having a variable inclination angle, and a piston engaging the plate. The piston reciprocates within a bore of the compressor in accordance with a rotation of the plate, and the piston has a stroke length which is determined by the inclination angle of the plate. The compressor also comprises a sensor positioned adjacent to the piston. The sensor generates an output signal when at least one predetermined portion of the piston is aligned with the sensor. The compressor also comprises a processing unit operationally coupled to the sensor. The processing unit estimates the inclination angle of the plate based on at least the output signal from the sensor. 
   In another embodiment of the present invention, a method for estimating a driving torque of a compressor is provided. The compressor comprises a plate having a variable inclination angle, and a piston engaging the plate. The piston reciprocates within a bore of the compressor in accordance with a rotation of the plate, and the piston has a stroke length which is determined by the inclination angle of the plate. The method comprises the steps of estimating the inclination angle of the plate, and estimating the driving torque based on at least the inclination angle. 
   Other objects, features, and advantage will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, the needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings. 
       FIG. 1  is a cross-sectional view of a variable displacement compressor according to an embodiment of the present invention. 
       FIG. 2  is a block diagram of a processing circuit and a control unit of the compressor of  FIG. 1 , according to an embodiment of the present invention. 
       FIG. 3  is a graph depicting data stored in a memory unit of the processing circuit of  FIG. 2 , according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention and their features and advantages may be understood by referring to  FIGS. 1–3 , like numerals being used for like corresponding parts in the various drawings. 
   Referring to  FIG. 1 , a variable displacement compressor  100  according to an embodiment of the present invention is depicted. Compressor  100  may comprise a cylinder block  2  and a crankcase  4  fixed to a first end of cylinder block  2 . Crankcase  4  may define a crank chamber  3 . Cylinder block  2  and crankcase  4  may support a shaft  6 , e.g., a drive shaft. Shaft  6  extends in an axial direction within compressor  100 , and one end of shaft  6  penetrates crankcase  4  and is operationally coupled to a pulley  7 . Pulley  7  transmits a rotational force from a driving source, e.g. an engine of a vehicle, to shaft  6 . 
   Cylinder block  2  may have a plurality of cylinder bores  1  formed therein, and cylinder bores  1  may extend in an axial direction toward crank chamber  3 . Compressor  100  also may comprise a plurality of pistons  11 , and each piston  11  may be positioned within a corresponding one of cylinder bores  1 , such that each piston  11  reciprocates independently within their corresponding cylinder bore  1 . Each piston  11  may comprise a tail portion  11   a  and a head portion  11   b , and each piston  11  may be manufactured from an aluminum alloy. Moreover, a valve plate (not numbered) may be fixed to cylinder block  2  to enclose each piston  11  within their corresponding cylinder bore  1 . The valve plate may have a suction port (not numbered) and a discharge port (not numbered) formed therethrough, and a cylinder block  5  may be fixed to the valve plate. A suction chamber (not shown) and a discharge chamber (not shown) may be formed within cylinder head  5 , and the suction chamber and the discharge chamber may be in refrigerant communication with cylinder bores  1  via a suction port (not numbered) and a discharge port (not numbered), respectively. 
   Compressor  100  also may comprise a plate  8 , e.g., a cam plate or a swash plate, operationally coupled to shaft  6  via a hinge mechanism  9 , such that an inclination angle of plate  8  may be varied. Compressor  100  also may comprise a plurality of shoe pairs  10 , and a peripheral portion of plate  8  may be positioned between a first and a second shoe of shoe pair  10 . Shoes pairs  10  may be supported by shoe supporters (not numbered) which are formed integrally with tail portion  11   a , and each shoe  10  may slide on an inner surface of a corresponding one of the shoe supporters. Thus, plate  8  may be coupled to pistons  11  via shoes pairs  10 . When shaft  6  rotates, plate  8  also rotates. Moreover, plate  8  slides between shoe pairs  10 , and pistons  11  reciprocate within their corresponding cylinder bore  1 . When pistons  11  move away from the suction chamber, pistons  11  draw a refrigerant, e.g., a liquid refrigerant or a refrigerant gas, from the suction chamber into the corresponding cylinder bore  1 . Similarly, when pistons  11  move toward the suction chamber, piston  11  compresses the refrigerant within the corresponding cylinder bore  1 , and discharge the compressed refrigerant into the discharge chamber. Moreover, the inclination angle of plate  8  determines a stroke length of pistons  11 , and the stroke length of pistons  11  determines a discharge volume V of compressor  100 . Specifically, when the stroke length of pistons  11  decreases, discharge volume V of compressor  100  also decreases. Similarly, when the stroke length of pistons  11  increases, discharge volume V of compressor  100  also increases. 
   In an embodiment of the present invention, compressor  100  also may comprise at least one sensor  14 , e.g., at least one proximity sensor, positioned adjacent to at least one of pistons  11 . For example, the at least one proximity sensor may be an edy-current type proximity sensor. The at least one piston  11  which sensor  14  is positioned adjacent to hereinafter is referred to as “selected piston  11 .” Tail portion  11   a  of selected piston  11  may comprise a first recess  11   c  and a second recess  11   d  formed therein. The distance between second recess  11   d  and piston head  11   b  may be less than the distance between first recess  11   c  and piston head  11   b . Tail portion  11   a  of selected piston  11  also may comprise a first protrusion  11   e  and a second protrusion  11   f . First protrusion  11   e  is formed between first recess  11   c  and a terminal end of tail portion  11   a , and second protrusion  11   f  is formed between first recess  11   c  and second recess  11   d . In an embodiment, sensor  14  may be positioned, such that first protrusion lie, first recess  11   c , second protrusion  11   f , second recess  11   d , and piston head  11   b  are successively aligned with sensor  14  when the stroke length of piston  11  increases from a minimum stroke length to a maximum stroke length. Moreover, sensor  14  may be configured to discriminate first recess  11   c  and second recess  11   d  from first protrusion  11   e , second protrusion  11   f , and piston head  11   b . For example, sensor  14  may generate an output signal when sensor  14  is aligned with from first protrusion  11   e , second protrusion  11   f , or piston head  11   b , and sensor  14  may not generate an output signal when sensor  14  is aligned with first recess  11   c  or second recess  11   d . In another example, sensor  14  may not generate an output signal when sensor  14  is aligned with from first protrusion  11   e , second protrusion  11   f , or piston head  11   b , and sensor  14  may generate an output signal when sensor  14  is aligned with first recess  11   c  or second recess  11   d . As such, when the stroke length of piston  11  increases from the minimum stroke length to the maximum stroke length, the output signal from sensor  14  may be a pulsed output signal, e.g., a substantially rectangular-shaped, pulsed output signal. 
   Compressor  100  also may comprise a processing circuit  200  operationally coupled to sensor  14 , and a rotational speed detection circuit  21  for detecting the rotational speed of shaft  6 . The rotational speed of shaft  6  may be equal to the rotational speed of plate  8 , e.g., rotational speed detection circuit  21  may indirectly detect the rotational speed of plate  8 , and processing circuit  200  may estimate the inclination angle of plate  8  based on the output signal from sensor  14  and the rotational speed of shaft  6 . Processing circuit  200  then may transmit an inclination angle signal to a control unit  22 , and the inclination angle signal is based on the estimated inclination angle of plate  8 . Moreover, control unit  22  may control the stroke length of pistons  11  and the speed of the engine of the vehicle based on the inclination angle signal. 
   Referring to  FIG. 3 , while not willing to bound by a theory, it is believed that there is a relationship between an average voltage of the output signal from sensor  14 , a pulse count during a single rotation of shaft  6 , and the inclination angle of plate  8 , and this relationship may be determined empirically. This relationship between the average voltage and the inclination angle of plate  8  during each pulse count may be stored as data in a memory unit  31  of processing circuit  200 . Moreover, the inclination angle of plate  8  may be estimated by comparing the average voltage and the pulse count with the data stored in memory unit  31 . For example, when the average voltage is about 2.6 Volts and the pulse count is three pulses, then the inclination angle may be about 10°. The pulse count may be the number of pulses in the output signal during a single rotation of shaft  6 . Because the rotational speed of shaft  6  may be equal to the rotational speed of plate  8 , the pulse count also may be the number of pulses in the output signal during a single rotation of plate  8 . 
   Referring to  FIG. 2 , a block diagram of processing circuit  200  and control unit  22  according to an exemplary embodiment of the present invention are depicted. Processing circuit  200  may comprise an amplifying circuit  32  operationally e.g., mechanically, electrically, or electromechanically, coupled to sensor  14  for amplifying the output signal from sensor  14 . Processing circuit also may comprise a cycle calculating circuit  33  operationally coupled to rotational speed detecting circuit  21  for calculating a rotational cycle of shaft  6 . Moreover, processing circuit  200  may comprise a counter circuit  34  operationally coupled to amplifying circuit  32  and cycle calculating circuit  33  for generating the pulse count during the rotational cycle of shaft  6 . Processing circuit  200  further may comprise voltage smoothing circuit  35  operationally coupled to amplifying circuit  32  for averaging the voltage of the output signal of sensor  14  to generate the average voltage. Processing circuit  200  also may comprise an inclination angle estimating circuit  36  operationally coupled to memory unit  31 , counter circuit  34 , and voltage smoothing circuit  35 . Inclination angle estimating circuit  36  may estimate the inclination angle of plate  8  based on the average voltage, the pulse count, and the data stored in memory unit  31 . The inclination angle estimating circuit  36  then transmits the inclination angle signal to control unit  22 . 
   In an embodiment of the present invention, control unit  22  may comprise a volume calculating circuit  37  operationally coupled to processing circuit  200 . Control unit  22  also may comprise a torque estimating circuit  38  operationally coupled to volume calculating circuit  37 . Volume calculating circuit  37  may calculate a discharge volume V of compressor  100  per rotation of shaft  6 , e.g., based on the formula V=S·L·n, where S is the cross-sectional area of piston  11 ; L is the stroke length of piston  11 , which is estimated based on the inclination angle of plate  8 ; and n is the number of cylinder bores  1 . Volume calculating circuit  37  then may transmit a discharge volume signal to torque estimating circuit  38 . Torque estimating circuit  38  also may receive a signal indicating the discharge pressure P d  within compressor  100 , and a signal indicating the suction pressure P s  within compressor  100 . Moreover, torque estimating circuit  38  may estimate the driving torque T based on discharge pressure P d , suction pressure P s , and discharge volume V, e.g., based on the formula T=K·P s ·[(P d /P s ) m −1]·V, where K and m are constants. 
   While the invention has been described in connection with preferred embodiments, it will be understood by those skilled in the art that variations and modifications of the preferred embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or from a practice of the invention disclosed herein. It is intended that the specification and the described examples are consider exemplary only, with the true scope of the invention indicated by the following claims.