Patent Publication Number: US-6663356-B2

Title: Control valve for variable displacement type compressor

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a control valve used for a displacement variable compressor incorporated in a refrigerant circuit of an air-conditioning system for controlling the discharge displacement of the variable displacement type compressor, which can change the discharge displacement in accordance with the pressure in the crank chamber. 
     Japanese Unexamined Patent Publication No. 6-341378 discloses such a control. This control valve mechanically detects the pressure difference between two pressure monitoring points, which are located in a refrigerant circuit, and adjusts the pressure in a crank chamber by determining the position of a valve body in accordance with a force that acts on the spool, based on the pressure difference. 
     In the control valve, the spool is displaced by sliding along the inner wall of a pressure sensing chamber according to the fluctuations of the pressure difference. Therefore, the sliding resistance between the spool and the inner wall of the pressure sensing chamber or a foreign particle caught in the sliding portion hinders the smooth movement of the spool. Accordingly, the fluctuations of the pressure difference is not promptly reflected on the opening size of the valve and the discharge displacement of the compressor. As a result, the cooling performance of the associated air-conditioning system deteriorates. 
     Accordingly, it is required to perform surface treatment such as smooth grinding and to form a low-friction coating to reduce the sliding resistance between the spool and the inner wall of the pressure sensing chamber. Alternatively, a filter must be provided in the control valve to remove foreign particles. As a result, the cost of the control valve increases. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to provide an inexpensive control valve for a variable displacement type compressor that can promptly change the opening size of a valve according to the fluctuations of the pressure difference between two pressure monitoring points. 
     To achieve the foregoing objective, the present invention provides a control valve used for a variable displacement compressor installed in a refrigerant circuit of a vehicle air conditioner. The refrigerant circuit has a suction pressure zone. The compressor varies the displacement in accordance with the pressure in a crank chamber. The compressor has a bleed passage, which connects the crank chamber to the suction pressure zone. The control valve comprises a valve housing. A valve chamber is defined in the valve housing to form a part of the bleed passage. A valve body is accommodated in the valve chamber for adjusting the opening size of the bleed passage. A pressure sensing chamber is defined in the valve housing. A pressure sensing member separates the pressure sensing chamber into a first pressure chamber and a second pressure chamber. The pressure at a first pressure monitoring point located in the refrigerant circuit is applied to the first pressure chamber. The pressure at a second pressure monitoring point located in the refrigerant circuit is applied to the second pressure chamber. The pressure sensing member moves the valve body in accordance with the pressure difference between the first pressure chamber and the second pressure chamber such that the displacement of the compressor is varied to counter changes of the pressure difference. The pressure sensing member is a bellows or a diaphragm. 
     Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view of a swash plate type variable displacement compressor according to a first embodiment. 
     FIG. 2 is a cross-sectional view of the control valve provided in the compressor of FIG.  1 . 
     FIG. 3 is an enlarged partial cross-sectional view illustrating a control valve according to a second embodiment of the present invention. 
     FIG. 4 is an enlarged partial cross-sectional view illustrating a control valve according to a third embodiment of the present invention. 
     FIG. 5 is an enlarged partial cross-sectional view illustrating a control valve according to a fourth embodiment of the present invention. 
     FIG. 6 is an enlarged partial cross-sectional view illustrating a control valve according to a fifth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A control valve CV of a swash plate type variable displacement compressor that is provided in a vehicle air-conditioning system according to a first embodiment of the present invention will now be described with reference to FIGS. 1 and 2. 
     The compressor shown in FIG. 1 includes a cylinder block  1 , a front housing member  2  connected to the front end of the cylinder block  1 , and a rear housing member  4  connected to the rear end of the cylinder block  1 . A valve plate  3  is located between the rear housing member  4  and the cylinder block  1 . The front housing member  2 , the cylinder block  1  and the rear housing member  4  form a housing of the compressor. 
     A crank chamber  5  is defined between the cylinder block  1  and the front housing member  2 . A drive shaft  6  extends through the crank chamber  5 , rotatably supported. The drive shaft extends the swash plate  12  and supports the swash plate  12 . The drive shaft  6  is connected to an engine E of the vehicle. A lug plate  11  is fixed to the drive shaft  6  in the crank chamber  5  to rotate integrally with the drive shaft  6 . 
     A drive plate, which is a swash plate  12  in this embodiment, is accommodated in the crank chamber  5 . The swash plate  12  slides along the drive shaft  6  and inclines with respect to the axis of the drive shaft  6 . A hinge mechanism  13  is provided between the lug plate  11  and the swash plate  12 . The swash plate  12  is coupled to the lug plate  11  and the drive shaft  6  through the hinge mechanism  13 . The swash plate  12  rotates synchronously with the lug plate  11  and the drive shaft  6 . 
     Formed in the cylinder block  1  are cylinder bores  1   a  (only one is shown in FIG. 1) at constant angular intervals around the drive shaft  6 . Each cylinder bore  1   a  accommodates a single headed piston  20  such that the piston can reciprocate in the bore  1   a . In each bore  1   a  is defined a compression chamber, the volume of which varies in accordance with the reciprocation of the piston  20 . The front end of each piston  20  is connected to the periphery of the swash plate  12  through a pair of shoes  19 . As a result, the rotation of the swash plate  12  is converted into reciprocation of the pistons  20 , and the strokes of the pistons  20  depend on the inclination angle of the swash plate  12 . 
     The valve plate  3  and the rear housing member  4  define, between them, a suction chamber  21  and a discharge chamber  22 , which surrounds the suction chamber  21 . The valve plate  3  forms, for each cylinder bore  1   a , a suction port  23 , a suction valve  24  for opening and closing the suction port  23 , a discharge port  25 , and a discharge valve  26  for opening and closing the discharge port  25 . The suction chamber  21  communicates with each cylinder bore  1   a  through the corresponding suction port  23 , and each cylinder bore  1   a  communicates with the discharge chamber  22  through the corresponding discharge port  25 . 
     When the piston  20  in a cylinder bore  1   a  moves from its top dead center position to its bottom dead center position, the refrigerant gas in the suction chamber  21  flows into the cylinder bore  1   a  through the corresponding suction port  23  and the corresponding suction valve  24 . When the piston  20  moves from its bottom dead center position toward its top dead center position, the refrigerant gas in the cylinder bore  1   a  is compressed to a predetermined pressure, and it forces the corresponding discharge valve  26  to open. The refrigerant gas is then discharged through the corresponding discharge port  25  and the corresponding discharge valve  26  into the discharge chamber  22 . 
     A mechanism for controlling the pressure of the crank chamber  5  (a crank chamber pressure Pc) includes a bleed passage  27 , a supply passage  28  and the control valve CV as shown in FIGS. 1 and 2. The passages  27 ,  28  are formed in the housing. The bleed passage  27  connects the suction chamber  21  as a suction pressure zone with the crank chamber  5 . The control valve CV is located in the bleed passage  27 . The supply passage  28  connects the discharge chamber  22  as a discharge pressure zone with the crank chamber  5 . A fixed restrictor  28   a  is located in the supply passage  28 . 
     The control valve CV changes the opening size of the bleed passage  27  to adjust the flow rate of refrigerant gas from the crank chamber  5  to the suction chamber  21 . The crank pressure Pc is changed in accordance with the relationship between the flow rate of refrigerant gas from the discharge chamber  22  to the crank chamber  5  and the flow rate of refrigerant gas flowing out from the crank chamber  5  to the suction chamber  21  through the bleed passage  27 . The difference between the crank chamber pressure Pc and the pressure in the cylinder bores  1   a  is changed in accordance with the crank chamber pressure Pc, which varies the inclination angle of the swash plate  12 . This alters the stroke of each piston  20  and the compressor displacement. 
     FIG. 1 illustrates a refrigerant circuit of the vehicle air-conditioning system. The refrigerant circuit has a swash plate type variable displacement compressor and an external refrigerant circuit  30 . The external refrigerant circuit  30  connects the discharge chamber  22  to the suction chamber  21 . The external refrigerant circuit  30  includes, for example, a condenser  31 , an expansion valve  32  and an evaporator  33 . The opening of the expansion valve  32  is feedback-controlled based on the temperature detected by a heat sensitive tube  34  at the outlet of the evaporator  33  and the evaporating pressure. The expansion valve  32  supplies refrigerant, the amount of which corresponds to the thermal load, to the evaporator  33  to regulate the flow rate. 
     The evaporator  33 , the suction chamber  21 , the cylinder bores  1   a , the discharge chamber  22 , and the condenser  31  form the main circuit of the refrigerant circuit. A section of the refrigerant circuit for controlling displacement, that is, the discharge chamber  22 , the supply passage  28 , the crank chamber  5 , the bleed passage  27 , and the suction chamber  21 , forms the sub-circuit of the refrigerant circuit. 
     As shown in FIG. 2, the control valve CV includes a bleed side valve portion and a solenoid portion  60 . The bleed side valve portion controls the opening size of the bleed passage  27  connecting the suction chamber  21  with the crank chamber  5 . The solenoid portion  60  as an external controlling means serves as an electromagnetic actuator for controlling an operation rod  40  provided in the control valve CV based on the level of an externally supplied current. The operation rod  40  has a valve body portion  43  at its one end, a guide portion  44  at its the other end, and a connecting portion  42 , which join the valve body portion  43  with the guide portion  44 . 
     A valve housing  45  of the control valve CV includes a cap  45   a , an upper-half body  45   b , and a lower-half body  45   c . A valve chamber  46  and a communication passage  47  are defined in the upper-half body  45   b . A pressure sensing chamber  48  is defined between the upper-half body  45   b  and the cap  45   a . The valve chamber  46  and the communication passage  47  are connected through a valve hole  49 . The cross-sectional area of the valve hole  49  is smaller than that of the communication passage  47 . 
     The operation rod  40  is located in the valve chamber  46 , the valve hole  49  and the communication passage  47  such that the operation rod  40  moves in the axial direction of the control valve CV (vertical direction in FIG.  2 ). The valve chamber  46  communicates with the communication passage  47  selectively in accordance with the position of the operation rod  40 . The communication passage  47  is isolated from the pressure sensing chamber  48  by the valve body portion  43  of the operation rod  40 . 
     The upper end face of a fixed iron core  62  serves as the bottom wall of the valve chamber  46 . A port  51 , which extends radially from the valve chamber  46 , connects the valve chamber  46  with the suction chamber  21  through a downstream part of the bleed passage  27 . A port  52  extending radially from the communication passage  47  connects the communication passage  47  with the crank chamber  5  through an upstream part of the bleed passage  27 . Thus, the port  51 , the valve chamber  46  the valve hole  49 , the communication passage  47 , and the port  52  serve as part of the bleed passage  27 , which connects the suction chamber  21  with the crank chamber  5  and serves as the control passage. 
     The valve body portion  43  of the operation rod  40  is located in the communication passage  47 . A step between the communication passage  47  and the valve hole  49  functions as a valve seat  53 . In the position shown in FIG. 2 (the lowest position), the valve body portion  43  contacts the valve seat  53  so that the valve hole  49  is closed. When the operation rod  40  moves upward from the lowest position, the valve hole  49  opens and the valve chamber  46  and the communication passage  47  are connected. The valve body portion  43  of the operation rod  40  functions as a bleed side valve body, which selectively adjusts the opening size of the bleed passage  27 . 
     A tubular pressure sensing member  54 , which has a closed end, is accommodated in the pressure sensing chamber  48 . The pressure sensing member  54  is a bellows in this embodiment. The pressure sensing member  54  is made of metal material such as copper. The upper end portion of the pressure sensing member  54  is secured to the cap  45   a  of the valve housing  45  by, for example, welding. The pressure sensing member  54  defines a first pressure chamber  55  and a second pressure chamber  56  in the pressure sensing chamber  48 . 
     An accommodating portion  54   a  is formed at the bottom wall portion of the pressure sensing member  54 . The distal end of the valve body portion  43  of the operation rod  40  is inserted in the accommodating portion  54   a . The pressure sensing member  54  is elastically deformed during its installation. The pressure sensing member  54  is pressed against the valve body portion  43  through the accommodating portion  54   a  by a force based on elasticity. The amount of initial elastic deformation of the pressure sensing member  54  during the installation can be changed according to the degree of press fitting of the cap  45   a  in the upper-half body  45   b.    
     The first pressure chamber  55  is connected to the discharge chamber  22 , in which a first pressure monitoring point P 1  is located, through a first port  57  formed in the cap  45   a  and a first pressure detecting passage  37 . The second pressure chamber  56  is connected to a crank chamber  5 , which is a second pressure monitoring point P 2 , through a second port  58 , which extends through the upper-half body  45   b , and a second pressure detecting passage  38 . The pressure of the first pressure monitoring point P 1 , which is the discharge pressure Pd, is applied to the first pressure chamber  55 . The pressure of the second pressure monitoring point P 2 , which is the crank chamber pressure Pc, is applied to the second pressure chamber  56 . 
     The solenoid portion  60  includes an accommodating cylinder  61  having a closed end. A fixed iron core  62  is fitted in the accommodating cylinder  61 . A solenoid chamber  63  is defined in the accommodating cylinder  61 . A movable iron core  64  is located in the solenoid chamber  63  to be movable in the axial direction. A guide hole  65 , which extends in the axial direction, is formed at the center of the fixed iron core  62 . The guide portion  44  of the operation rod  40  is located in the guide hole  65  to be movable in the axial direction. The bottom end of the guide portion  44  is secured to the movable iron core  64  in the solenoid chamber  63 . Therefore, the movable iron core  64  and the operation rod  40  move vertically as a unit. 
     A return spring  66 , which is formed of a coil spring, is accommodated between the fixed iron core  62  and the movable iron core  64  in the solenoid chamber  63 . The return spring  66  urges the operation rod  40  downward in FIG. 2 such that the movable iron core  64  is separated from the fixed iron core  62 . 
     A coil  67  is wound around the fixed iron core  62  and the movable iron core  64 . A drive signal is supplied to the coil  67  from a drive circuit  71 . The drive signal is supplied based on a command from a controller  70  in accordance with the external information from the external information detector  72 . The external information includes the temperature of the passenger compartment of the vehicle and a target temperature. The coil  67  generates the electromagnetic force between the movable iron core  64  and the fixed iron core  62  corresponding to the level of supplied current. The current value that is supplied to the coil  67  is controlled by adjusting the applied voltage to the coil  67 . The duty control is used for adjusting the applied voltage in this embodiment. 
     The opening size of the control valve CV of the first embodiment is determined by the position of the operation rod  40 . 
     When no current is supplied to the coil  67 , or when duty ratio is zero percent, the downward force of the pressure sensing member  54  and the return spring  66  position the rod  40  at the lowest position shown in FIG.  2 . Thus, the valve body portion  43  closes the valve hole  49 . Therefore, the crank chamber pressure Pc is the maximum, which increases the difference between the crank chamber pressure Pc and the pressure in the cylinder bore  1   a . Accordingly, the inclination angle of the swash plate  12  is the minimum, which minimizes the discharge displacement of the compressor. 
     When a current having the minimum duty ratio is supplied to the coil  67  (the minimum duty ratio is greater than zero percent), the upward electromagnetic force exceeds the downward force of the pressure sensing member  54  and the return spring  66 . Thus, the operation rod  40  moves upward. The upward electromagnetic force, which is directed oppositely to the downward force of the return spring  66 , counters the downward force of the pressure difference between the two pressure monitoring points P 1  and P 2  (pressure difference ΔP=Pd−Pc) In this case, the downward force of the pressure difference acts in the same direction as the downward force of the pressure sensing member  54 . The valve body portion  43  of the operation rod  40  is positioned with respect to the valve seat  53  such that the upward force and the downward force are balanced. 
     When the rotational speed of the engine E decreases, which decreases the discharge displacement of the compressor per unit of time, the discharge pressure Pd drops, which causes the downward force based on the pressure difference ΔP to decrease. Accordingly, the forces applied to the operation rod  40  are not balanced. Therefore, the operation rod  40  moves upward, thus compressing the pressure sensing member  54  and the return spring  66 . The valve body portion  43  of the operation rod  40  is positioned such that the resulting increase in the downward forces of the pressure sensing member  54  and the spring  66  compensates for the reduction in the downward force based on the lower pressure difference ΔP. As a result, the opening size of the valve hole  49 , that is, the opening size of the control valve CV, increases, which decreases the crank chamber pressure Pc. Accordingly, the difference between the crank chamber pressure Pc and the pressure in each cylinder bore  1   a  decreases. Thus, the inclination angle of the swash plate  12  increases, which increases the discharge displacement of the compressor. When the discharge displacement of the compressor increases, the discharge pressure Pd increases, which increases the pressure difference ΔP. 
     On the other hand, when the rotational speed of the engine E increases, which increases the discharge displacement per unit of time of the compressor, the discharge pressure Pd increases, which increases the downward force based on the pressure difference ΔP. Accordingly, the forces applied to the operation rod  40  are not balanced. Therefore, the operation rod  40  moves downward, and the pressure sensing member  54  and the return spring  66  expand. The valve body portion  43  of the operation rod  40  is positioned such that the resulting decrease in the downward forces of the pressure sensing member  54  and the return spring  66  compensates for the increase in the downward force based on the greater pressure difference ΔP. As a result, the opening size of the valve hole  49  decreases, which increases the crank chamber pressure Pc. Accordingly, the difference between the crank chamber pressure Pc and the pressure in each cylinder bore  1   a  increases. Thus, the inclination angle of the swash plate  12  decreases, which decreases the discharge displacement of the compressor. When the discharge displacement of the compressor decreases, the discharge pressure Pd decreases, which decreases the pressure difference ΔP. 
     When the duty ratio of the current that is supplied to the coil  67  increases, which increases the electromagnetic force, balance of the various forces is not achieved by the pressure difference ΔP. Therefore, the operation rod  40  moves upward so that the pressure sensing member  54  and the return spring  66  are compressed. The valve body portion  43  is positioned such that the resulting increase in the downward forces of the pressure sensing member  54  and the spring  66  compensates for the increase in the upward electromagnetic force. Therefore, the opening size of the valve hole  49  is increased, which increases the discharge displacement of the compressor. As a result, the discharge pressure Pd increases, which also increases the pressure difference ΔP. 
     When the duty ratio of the current that is supplied to the coil  67  decreases, which decreases the electromagnetic force, balance of the various forces is not achieved by the pressure difference ΔP at the time. Therefore, the operation rod  40  moves downward, and the pressure sensing member  54  and the return spring  66  expand. The valve body portion  43  is positioned such that the decrease in the downward force of the pressure sensing member  54  and the spring  66  compensates for the decrease in the upward electromagnetic force. Therefore, the opening size of the valve hole  49  is decreased, which decreases the discharge displacement of the compressor. As a result, the discharge pressure Pd decreases, which also decreases the pressure difference ΔP. 
     As described above, the control valve CV of this embodiment positions the operation rod  40  according to the fluctuations of the pressure difference ΔP at the time. The control valve CV maintains the target value of the pressure difference ΔP, which is determined by the duty ratio of the current that is supplied to the coil  67 . The target value of the pressure difference ΔP is changed by adjusting the duty ratio of the current that is supplied to the coil  67 . The pressure difference ΔP fluctuates if the crank chamber pressure Pc varies even when the discharge pressure Pd is constant. However, the crank chamber pressure Pc is far smaller than the discharge pressure Pd. Thus, the crank chamber pressure Pc is deemed to be substantially constant. 
     The first embodiment provides the following advantages. 
     The pressure sensing member  54  is displaced according to the fluctuations of the pressure difference ΔP without sliding along the inner wall of the pressure sensing chamber  48 . Therefore, the operation rod  40  is displaced promptly and accurately in accordance with the fluctuations of the pressure difference ΔP. Accordingly, there is no need to perform surface treatment, as in the prior art, to reduce the sliding resistance between a spool and the inner wall of the pressure sensing chamber  48 . It is also not necessary to provide a filter on each pressure detecting passage  37  and  38  to remove foreign particles. Thus, the cost of the control valve CV is reduced. 
     The pressure difference, which is the base for the adjusting operation of the opening size of the control valve CV, can be adjusted by changing the duty ratio of the current that is supplied to the coil  67 . Therefore, compared with a control valve that has no electromagnetic structure (an external control means) or a control valve that only allows a single target pressure difference, the control valve CV of the present invention can be more finely controlled. 
     The control valve CV adjusts the pressure in the crank chamber  5  by regulating the bleed passage  27 . The control valve CV changes the opening size of the bleed passage  27 . Therefore, the amount of refrigerant gas that is supplied to the crank chamber  5  from the discharge chamber  22  can always be minimized by the fixed restrictor  28   a  in the supply passage  28 . In other words, the amount of compressed refrigerant gas that leaks into the crank chamber  5  can be minimized. Compared with a control valve that regulates the supply passage  28 , the invention reduces the deterioration of the efficiency of the refrigerant cycle caused by re-expansion of the compressed refrigerant gas in the compressor. This leads to low fuel consumption of the engine E. 
     The control valve CV does not directly receive the discharge pressure Pd for adjusting the pressure in the crank chamber  5 . Therefore, the pressure-resistant structures and the sealing structures at the passages  52 ,  47 ,  49 ,  46 , and  51  in the housing  45  of the control valve CV are simplified. 
     The present invention may be modified as follows. 
     According to a second embodiment as shown in FIG. 3, a diaphragm may be used as the pressure sensing member  54 . In the second embodiment, the pressure sensing member  54  and a separate spring  81 , which function as the pressure sensing member  54  in FIG. 2, are located between the cap  45   a  and the pressure sensing member  54 . 
     According to a third embodiment shown in FIG. 4, a ball  82  may be provided in the accommodating portion  54   a  of the pressure sensing member  54  in the embodiments shown in FIG. 2 or  3 . In this case, the pressure sensing member  54  and the valve body portion  43  of the operation rod  40  contact each other through the ball  82 . Even when the pressure sensing member  54  is tilted with respect to the axial direction of the operation rod  40 , the ball  82  aligns the load to be transmitted in the axial direction of the operation rod  40  from the pressure sensing member  54  to the operation rod  40 . Thus, the invention prevents the opening size of the control valve CV from being different from the desired value due to tilting of the valve body portion  43  of the operation rod  40 . 
     According to a fourth embodiment shown in FIG. 5, the first pressure monitoring point P 1  may be located in the discharge pressure zone (the discharge chamber  22  in FIG. 5) between the discharge chamber  22  and the condenser  31  of the refrigerant circuit. The second pressure monitoring point P 2  may be located in the suction pressure zone (the suction chamber  21  in FIG. 5) between the evaporator  33  and the suction chamber  21  of the refrigerant circuit. 
     According to a fifth embodiment shown in FIG. 6, the first pressure monitoring point P 1  may be located in the crank chamber  5 . The second pressure monitoring point P 2  may be located in the suction pressure zone (the suction chamber  21  in FIG. 6) between the evaporator  33  and the suction chamber  21  of the refrigerant circuit. In the fifth embodiment, the internal space of the pressure sensing member  54  is equivalent to the second pressure chamber  56 . The space between the inner wall of the pressure sensing chamber  48  and the pressure sensing member  54  is equivalent to the first pressure chamber  55 . Therefore, in the fifth embodiment, the operating direction of the force based on the pressure difference ΔP is reversed compared with the embodiments shown in FIGS. 1 to  5 . For example, the increased duty ratio (electromagnetic force) of the current that is supplied to the coil  67  decreases the target pressure difference. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms. 
     The first pressure monitoring point P 1  may be located in the discharge pressure zone between the discharge chamber  22  and the condenser  31  of the refrigerant circuit. The second pressure monitoring point P 2  may be located downstream of the first pressure monitoring point P 1  at the same discharge pressure zone. 
     The first monitoring point P 1  may be located in the suction pressure zone between the evaporator  33  and the suction chamber  21 . The second pressure monitoring point P 2  may be located downstream of the first pressure monitoring point P 1  at the same suction pressure zone. 
     The present invention may be embodied in an air-conditioning system that has a wobble plate type variable discharge compressor. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.