Abstract:
A fuel supply system has a pump, a common rail, and injectors. Pressurized fuel is stored in the common rail. The common rail distributes the fuel to the injectors. A liquid fuel and a liquefied gas fuel such as dimethyl ether and a liquefied petroleum gas may be used as a fuel. In each injector, a valve element is actuated directly by an electromagnetic actuator. The injector has a low pressure chamber for decreasing a biasing force which acts on the valve element in a valve closing direction. The valve element can be divided for replacement. The injector has means for suppressing the bounce of the valve element. A hydraulic unit which utilizes the fuel suppresses the bounce of the valve element. The fuel supply system is connected to a refrigerating cycle. The fuel leaking from the fuel supply system is cooled and again liquefied by the refrigerating cycle.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based on Japanese Patent Applications No. 2001-307355 filed on Oct. 3, 2001, No. 2001-308495 filed on Oct. 4, 2001, No. 2001-317688 filed on Oct. 16, 2001, No. 2001-384772 filed on Dec. 18, 2001 and No. 2002-14338 filed on Jan. 23, 2002 the contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a fuel injection system and a fuel injector in an internal combustion engine (hereinafter referred to simply as engine).  
           [0004]    2. Related Art  
           [0005]    For example, in the case of a common rail type fuel injection system applied to a diesel engine, there usually is employed a fuel injector having a two- or three-way solenoid valve. In connection with such a fuel injector, for example the technique disclosed in JP-A-9-42106 is well known. According to this technique, fuel of a high pressure is introduced into a pressure control chamber provided on an opposite-to-nozzle holes side of a valve element, and the valve element is actuated by allowing the high-pressure fuel present in the pressure control chamber to leak to a low pressure side at every fuel injection. However, in the case of the fuel injector disclosed in the above publication, there occurs leakage of the high-pressure fuel from the pressure control chamber at every fuel injection. There also is a problem that the number of components increases and the structure becomes complicated.  
           [0006]    Recently there has been an increasing demand for reducing the cost of the fuel injector. To meet this demand, that is, for reducing the number of components which constitute the fuel injector, a study is being made about a direct-acting type fuel injector in which a valve element is actuated directly by an electromagnetic drive unit.  
           [0007]    On the other hand, as an alternative to gas oil and taking the volatilizability, ignitability and combustibility of fuel or emission into account, there recently has been studied the use of liquefied gas fuels such as dimethyl ether (DME) and liquefied petroleum gas (LPG) with a cetane number improving additive incorporated therein. LPG as referred to herein means a liquefied petroleum gas with a cetane number improver incorporated therein unless otherwise specified. In case of using a liquefied gas fuel, the fuel is apt to vaporize because of a low boiling point and the amount of fuel leaking from the fuel injector tends to increase. Therefore, it becomes necessary to provide a recovery system for recovering fuel leaking from the fuel injector. For example, as is disclosed in JP-A-11-22590, it is necessary to provide a purge tank for the recovery of vaporized liquefied gas fuel and a compression pump for compressing and liquefying a gaseous liquefied gas fuel recovered into the purge tank. As a result, there arises the problem that the cost of the fuel injection system concerned increases. To solve this problem, as noted above, it is proposed to use, for example, such a direct acting type fuel injector  100  as shown in FIG. 10 and thereby decrease the amount of fuel leaking from the fuel injector  100 .  
           [0008]    In the fuel injector  100  shown in FIG. 10, a valve element  101  extends vertically in the figure and an armature  102  is integrally provided at an upper end of the valve element  101  by laser welding for example. Holes  103   a  and  104   a  are formed in a casing  103  and a valve body  104 , respectively, and the valve element  101  is received into the holes  103   a  and  104   a.  A stator  105  is disposed in opposition to the armature  102 . When a coil  106  is energized and the armature  102  is thereby attracted to the stator  105 , the valve element  101  lifts upward in FIG. 10 against the biasing force of a spring  107 , whereby nozzle holes  108  are opened and high-pressure fuel fed from a common rail system is injected from the nozzle holes  108 . In such a fuel injector  100  as shown in FIG. 10, the number of components is small and hence it is possible to attain the reduction of cost. Moreover, in the fuel injector  100  shown in FIG. 10, it is possible to decrease the amount of leaking fuel and therefore it becomes unnecessary to use a purge tank for the recovery of leaking fuel and a compression pump.  
           [0009]    However, in the fuel injector  100  shown in FIG. 10, since the valve element  101  is actuated directly by an electromagnetic drive unit, it is necessary for the electromagnetic drive unit to actuate the valve member  101  against a force developed by an oil pressure acting on the valve element  101 . Accordingly, for enhancing the injection pressure of fuel injected from the fuel injector  100 , it is necessary to increase the size of the electromagnetic drive unit and thereby increase the driving force. However, the space ensured in an engine mounting portion is limited and therefore the size of the electromagnetic drive unit and that of the fuel injector  100  are limited. As a result, a maximum fuel injection pressure of about 30 MPa is a limit at present and a further increase of pressure is difficult.  
           [0010]    For example, in connection with a common rail type fuel injection system for a diesel engine, there is known such a fuel injector as is disclosed in JP-A-10-18934. On the other hand, as a direct-acting type fuel injector there is proposed one illustrated in FIG. 16. In the same figure, components equal to those illustrated in FIG. 10 are identified by like reference numerals.  
           [0011]    In an engine mounted on a vehicle, fuel injectors are replaced at every about 100,000 km running. In this case, for attaining the reduction of cost, it is proposed to remove a retaining nut  110  of a fuel injector  100  and replace only a nozzle portion  104  located at the tip of the injector. However, an armature  102  is fixed to a valve element  101  and the diameter of the armature  102  is usually larger than that of a hole  103   a.  This is for obtaining a satisfactory electromagnetic performance. Therefore, at the time of replacement of the nozzle portion  104 , not only the removal of the retaining nut  110 , but also a disassembling work for an electromagnetic solenoid portion  111  is required, resulting in that the maintainability is deteriorated. Thus, an improvement is desired.  
           [0012]    [0012]FIG. 28 shows a fuel injector  100  in the related art. When a valve element  101  is opened, the valve member moves until abutment against a valve opening stopper  112 . At this time, the valve element  101  bounces as a reaction of its abutment against the stopper  112 . In many cases, for example the layout of intake/exhaust valves in an engine head portion requires the valve element  101  to be long, with the result that the valve member becomes heavy. Particularly, in the case of such a liquefied gas fuel as DME, the bounce of the valve element  101  becomes large. Such a bounce of the valve element  101  obstructs an accurate adjustment of fuel quantity.  
           [0013]    In a fuel injector  100  shown in FIG. 33, when a valve element  101  opens, it strikes against a stopper  111  and bounces. Due to this bouncing during valve opening, an injection quantity Q becomes wavy relative to a pulse width T, thus making injection control difficult.  
           [0014]    Further, when a coil  106  is de-energized, with loss in attraction of an armature  102  by a stator  105 , and the valve element  101  closes with the biasing force of a spring  107 , the valve element  101  strikes against a sheet portion of a nozzle body  104  and causes bouncing. Due to this bouncing in valve closing, there occurs re-injection (secondary injection) after the end of injection, thus resulting in deterioration of the injection characteristic.  
           [0015]    On the other hand, in many cases, the valve element  101  is required to be long for example due to the layout of intake/exhaust valves in an engine head, resulting in that the valve element  101  becomes heavy and there occurs markedly such bouncing as referred to above.  
           [0016]    Particularly in the case of such liquefied gas fuels as LPG and DME, since their viscosities are low, not only the bouncing of the valve element  101  becomes large, but also the time taken until damping of the bounding becomes long and the aforesaid inconvenience occurs markedly.  
           [0017]    A leak fuel recovery system is disclosed, for example, in JP-A-11-22590. An outline thereof will now be given with reference to FIG. 35. In the same figure, fuel stored in a fuel tank  550  is discharged from a low pressure pump  551  and is compressed to a high pressure by means of a high pressure pump  552 , then is fed to a common rail  553 . Connected to the common rail  553  are fuel injectors  554  in a number corresponding to the number of engine cylinders.  
           [0018]    Fuel leaking from the high pressure pump  552  and fuel injectors  554  is once recovered into a fuel recovery tank (purge tank)  555 , then is liquefied by a fuel compressor  556  and is returned to the fuel tank  550 .  
           [0019]    In the construction of FIG. 35 it is necessary to provide a leak fuel recovery system comprising the fuel recovery tank  555  and the fuel compressor  556 , thus giving rise to the problem that the construction becomes complicated and the cost increases.  
         SUMMARY OF THE INVENTION  
         [0020]    It is an object of the present invention to provide an improved fuel injector.  
           [0021]    It is another object of the present invention to provide a fuel injector having a compact construction and capable of handling high pressure fuel.  
           [0022]    It is a further object of the present invention to provide a fuel injector improved in maintainability.  
           [0023]    It is a still further object of the present invention to provide a fuel injector wherein the bouncing of a valve member is suppressed.  
           [0024]    It is a still further object of the present invention to provide a liquefied gas fuel supply system having a high utility.  
           [0025]    In one aspect of the present invention there is provided a fuel injector which is provided with an oil pressure reducing means. The oil pressure reducing means reduces an oil pressure acting in a nozzle hole closing direction which oil pressure is included in an oil pressure acting on a valve element. Since the oil pressure acting on a valve element in the nozzle hole closing direction is reduced, the force required for an electromagnetic drive unit to actuate the valve element decreases. Consequently, even when the valve element is actuated directly by the electromagnetic drive unit, the pressure of fuel fed to the fuel injection system concerned can be increased while retaining the constitution of the electromagnetic drive unit for example. Thus, even when the valve element is actuated directly by the electromagnetic drive unit, the pressure of injected fuel can be further increased without an increase in size of the constitution.  
           [0026]    The above fuel injector according to the present invention is what is called an actuator direct acting type fuel injector wherein an armature is attracted to a stator upon energization of a coil and consequently a valve element integral with the armature moves to open the nozzle hole. In this construction, the valve element is provided in a divided manner into a rod portion and a valve portion, which are connected together through a connecting member. According to this construction, when the armature is attracted to the stator upon energization of the coil, the valve portion moves together with the rod portion to open or close the nozzle hole. With the rod portion, the valve portion and the connecting member connected to one another, the rod portion is accommodated in a first casing and the valve portion is accommodated in a second casing.  
           [0027]    According to the above construction, if the first and second casings are disassembled and the connecting member is disconnected, it becomes possible to remove only the valve portion exclusive of the rod portion. Therefore, when the valve portion is to be replaced after a long-term use of the fuel injector, the replacing work efficiency is improved. As a result, it is possible to realize a construction superior in maintainability of an actuator direct acting type fuel injector.  
           [0028]    In the above construction, when the coil is energized, the armature is attracted to the stator against the biasing force of a spring and the valve element moves to its closing position. In this case, since an oil pressure damper chamber is provided between an end face of the armature and that of the stator, the bouncing of the armature and valve element is suppressed when the valve opens by virtue of a damper effect. Therefore, it is possible to keep the fuel injection quantity under control.  
           [0029]    According to the present invention, when an electric actuator (e.g., an electromagnetic solenoid or a piezo-electric actuator) causes an armature (driver) to displace in the valve opening direction, fuel having an accumulated pressure is injected from a nozzle. As a result of this injection, the pressure decreases on the nozzle side rather than in a throttle portion and the pressure in a second chamber becomes lower than that in a first chamber. Since the second chamber lower in pressure lies on the side (in the valve opening direction) opposite to the nozzle, a pressure receiving portion is urged to the opposite-to-nozzle side (in the valve opening direction) by virtue of a differential pressure. With this urging force based on the differential pressure, the bouncing of the valve element when opened is suppressed. When the electric actuator causes the armature to displace in the valve closing direction, the injection of fuel is stopped. Once the fuel injection is stopped, the flow of injected fuel is cut off suddenly, so that the pressure on the nozzle side rather than in the throttle portion increases to a higher level than the pressure of accumulated pressure fuel and the pressure in the second chamber becomes higher than that in the first chamber. At this time, the first chamber which is low in pressure lies on the nozzle side (in the valve closing direction), so that the pressure receiving portion is urged to the nozzle side (in the valve closing direction) by virtue of a differential pressure. With this urging force induced by the differential pressure, the bouncing of the valve element when closing is suppressed. Since the bouncing in valve opening and closing is thus suppressed, the injection characteristic is improved. Even in the case where the valve element is long and heavy, it is possible to improve the injection characteristic because the occurrence of bounce is suppressed by the differential pressure.  
           [0030]    Further, even where the fuel viscosity is low as in such a liquefied gas fuel as LPG or DME, since the occurrence of bounce is suppressed by the differential pressure, it is possible to improve the injection characteristic.  
           [0031]    According to a further feature of the present invention, fuel having an accumulated pressure is injected from the nozzle upon displacement of the armature in the valve opening direction by the electric actuator. With this fuel injection, the fuel flows from the first chamber to the second chamber formed on the side (in the valve opening direction) opposite to the nozzle through a passage formed along the side face of the armature. As a result of this fuel flow in the valve opening direction, the armature undergoes a force advancing toward the side (in the valve opening direction) opposite to the nozzle, whereby the bouncing of the valve body in valve opening is suppressed. When the electric actuator causes the armature to displace in the valve closing direction, the injection of fuel is stopped. Once the fuel injection is stopped, the flow of the injected fuel is cut off suddenly, so that the pressure on the nozzle side rather than in the throttle portion rises to a higher level than that of the accumulated pressure fuel which is fed and the pressure in the second chamber becomes higher than that in the first chamber. As a result, the fuel flows from the second chamber which is high in pressure to the first chamber located on the nozzle side (in the valve closing direction) through the passage formed along the side face of the armature. With this fuel flow in the valve closing direction, the armature undergoes a force advancing toward the nozzle side (in the valve closing direction), so that the bouncing of the valve element when closing is suppressed.  
           [0032]    In another aspect of the present invention there is provided a fuel supply system for the supply of a liquefied gas fuel, in which a liquefied gas fuel stored in a fuel tank is fed through fuel piping to a fuel injection system.  
           [0033]    In this system there is provided an air conditioner which is provided with at least an expansion valve, an evaporator, and a condenser, and a liquefied gas fuel stored in the fuel tank is fed as refrigerant to the air conditioner. Further, the liquefied gas fuel leaking from the fuel injection system is introduced into the air conditioner.  
           [0034]    The liquefied gas fuel introduced into the air conditioner is mixed as refrigerant into the liquefied gas fuel which is circulating through the air conditioner, then flows downstream.  
           [0035]    According to the above construction, the liquefied gas fuel leaking from, for example, a high pressure pump and a fuel injector both constituting the fuel injection system is subjected to a liquefying process in the air conditioner (condenser) and is returned to the fuel tank through the air conditioner. Thus, there is not required any additional construction as the fuel recovery system. Additionally, the condenser in the air conditioner plays the role of recovering the leak fuel in addition to its inherent role of liquefying the refrigerant (liquefied gas fuel) and thus the condenser can be used in common. As a result, it is possible to simplify the construction of the fuel supply system and reduce the cost thereof. 
       
    
    
     BREIF DESCRIPTION OF DRAWINGS  
       [0036]    Features and advantages of embodiments will be appreciated, as well as methods of operation and the function of the related parts, from a study of the following detailed description, the appended claims, and the drawings, all of which form a part of this application. In the drawings:  
         [0037]    [0037]FIG. 1 is a partial sectional view of an injector according to a first embodiment of the present invention;  
         [0038]    [0038]FIG. 2 is a block diagram of a fuel injection system according to the first embodiment of the present invention;  
         [0039]    [0039]FIG. 3 is a sectional view showing an assembled state of components which constitute the injector according to the first embodiment of the present invention;  
         [0040]    [0040]FIG. 4 is a partial sectional view of the injector according to the first embodiment of the present invention;  
         [0041]    [0041]FIG. 5 is a partial sectional view of an injector according to a third embodiment of the present invention;  
         [0042]    [0042]FIG. 6 is a sectional view of an injector according to a fourth embodiment of the present invention;  
         [0043]    [0043]FIG. 7 is a sectional view of an injector according to a fifth embodiment of the present invention;  
         [0044]    [0044]FIG. 8 is a partial sectional view of the injector according to the fifth embodiment of the present invention;  
         [0045]    [0045]FIG. 9 is a partial sectional view of the injector according to the fifth embodiment of the present invention;  
         [0046]    [0046]FIG. 10 is a sectional view of an injector according to a related art;  
         [0047]    [0047]FIG. 11 is a sectional view of an injector according to a sixth embodiment of the present invention;  
         [0048]    [0048]FIG. 12 is a perspective view of components of the injector according to the sixth embodiment of the present invention;  
         [0049]    [0049]FIG. 13 is a partial sectional view of the injector according to the sixth embodiment of the present invention;  
         [0050]    [0050]FIG. 14 is a partial sectional view of the injector according to the sixth embodiment of the present invention;  
         [0051]    [0051]FIG. 15 is a partial sectional view of the injector according to a seventh embodiment of the present invention;  
         [0052]    [0052]FIG. 16 is a sectional view of an injector according to a related art;  
         [0053]    [0053]FIG. 17 is a sectional view of an injector according to an eighth embodiment of the present invention;  
         [0054]    [0054]FIG. 18 is a partial sectional view of the injector according to the eighth embodiment of the present invention;  
         [0055]    [0055]FIG. 19 is a plan view of components of the injector according to the eighth embodiment of the present invention;  
         [0056]    [0056]FIG. 20 is a sectional view showing a disassembled state of components of the injector according to the eighth embodiment of the present invention;  
         [0057]    [0057]FIG. 21 is a partial sectional view of the injector according to the eighth embodiment of the present invention;  
         [0058]    [0058]FIG. 22 is a time chart showing the operation of the injector according to the eighth embodiment of the present invention;  
         [0059]    [0059]FIG. 23 is a graph showing an injection quantity characteristic of the injector according to the eighth embodiment of the present invention;  
         [0060]    [0060]FIG. 24 is a sectional view showing a disassembled state of the injector according to the eighth embodiment of the present invention;  
         [0061]    [0061]FIG. 25 is a sectional view showing a disassembled state of the injector according to the eighth embodiment of the present invention;  
         [0062]    [0062]FIG. 26 is a sectional view showing a disassembled state of an injector according to a ninth embodiment of the present invention;  
         [0063]    [0063]FIG. 27 is a sectional view showing a disassembled state of an injector according to a tenth embodiment of the present invention;  
         [0064]    [0064]FIG. 28 is a sectional view of an injector according to a related art;  
         [0065]    [0065]FIG. 29 is a sectional view of an injector according to an eleventh embodiment of the present invention;  
         [0066]    [0066]FIG. 30 is a time chart showing the operation of the injector according to the eleventh embodiment of the present invention;  
         [0067]    [0067]FIG. 31 is a graph showing an injection quantity characteristic of the injector according to the eleventh embodiment of the present invention;  
         [0068]    [0068]FIG. 32 is a sectional view of an injector according to a twelfth embodiment of the present invention;  
         [0069]    [0069]FIG. 33 is a sectional view of an injector according to a related art;  
         [0070]    [0070]FIG. 34 is a block diagram showing a fuel injection system and an air conditioner both according to a thirteenth embodiment of the present invention; and  
         [0071]    [0071]FIG. 35 is a block diagram of a system according to a related art. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0072]    Plural embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.  
         [0073]    [0073]FIG. 2 shows an outline of a fuel injection system according to a first embodiment of the present invention. The fuel injection system of this embodiment is a common rail type fuel injection system in a diesel engine which uses DME as fuel.  
         [0074]    DME stored in a fuel tank  1  is fed a high pressure pump  2  by means of a low pressure pump (not shown). The DME fed to the high pressure pump  2  is pressurized by the same pump and then is fed to a common rail  3 . In the common rail  3  is stored DME which has been accumulated at an injection pressure (50-80 MPa). Fuel injectors  10  in a number corresponding to the number of engine cylinders are connected to the common rail  3 . The fuel injectors  10  are operated in accordance with drive signals provided from an ECU  4 .  
         [0075]    The fuel injectors  10  are each provided with a casing  11  and a valve body  12 . The casing  11  and the valve body  12  are integrally clamped with a retaining nut  14  through a distance piece  13 . The casing  11  and the valve body  12  are formed with coaxial holes  11   a  and  12   a,  respectively, into which a valve element  20  is received. The valve element  20  is formed as an axially extending rod, having two slide portions  21  and  22 . Plural nozzle holes  15  are formed in a tip portion of the valve body  12 . A valve seat portion  16  is provided on an inlet side of the nozzle holes  15  of the valve body  12 . An abutment portion  23  capable of sitting on the valve seat portion  16  is provided at a tip of the valve element  20 . When the abutment portion  23  sits on the valve seat portion  16 , the flow of DME is shut off to stop the injection of fuel from the nozzle holes  15 . On the other hand, when the abutment portion  23  leaves the valve seat portion  16 , the flow of DME is allowed and is injected from the nozzle holes  15 .  
         [0076]    The valve element  20  has a large-diameter portion  24  at a position corresponding to the distance piece  13  which is an intermediate portion. In the large-diameter portion  24  are disposed a spring retainer  25  and a shim  26 . A spring  27  is disposed between an inner wall of the casing  11  and the shim  26 , whereby the valve element  20  is urged downward in FIG. 2, i.e., in a nozzle hole closing direction.  
         [0077]    As shown in FIG. 3, the spring retainer  25  is constructed of two dividable pieces, while the shim  26  is formed by a ring-like plate. As shown in FIG. 4, the spring retainer  25  is mounted in a sandwich relation to the large-diameter portion  24  of the valve element  20 , followed by mounting of the shim  26 . As a result, the spring retainer  25  is clamped radially inwards by the shim  26  and is fixed to the valve element  20 . The shim  26  fulfills a spring force adjusting function. That is, the biasing force of the spring  27  can be adjusted by adjusting the plate thickness of the shim  26 .  
         [0078]    As shown in FIG. 2, an inlet port member  18  is attached to the casing  11  through a gasket  17 . The inlet port member  18  is connected to the common rail  3  and the high pressure DME is introduced from the common rail  3  into the holes  11   a  and  12   a  through the inlet port member  18 . A filter  19  for removing foreign matters contained in DME is press-fitted into the inlet port member  18 .  
         [0079]    An electromagnetic drive unit  30  is installed in the casing  11  on the side opposite to the valve body. The electromagnetic drive unit  30  has an armature  31 , a stator  32 , and a coil  33 . The armature  31  is fixed to an end portion of the valve element  20  on the side opposite to the nozzle holes integrally with the valve member. The stator  32  is disposed in opposition to the armature  31 . The coil  33  is disposed on an outer periphery side of the stator  32 . The coil  33 , when supplied with electric power from ECU  4 , generates a magnetic field. With the magnetic field generated by the coil  33 , a magnetic attraction is developed between the stator  32  and the armature  31 . In this embodiment, the valve element  20  is attracted in the nozzle hole opening direction by virtue of the magnetic attraction induced between the armature  31  and the stator  32  in the electromagnetic drive unit  30  and is actuated directly by the electromagnetic drive unit  30 . That is, the fuel injector  10  of this embodiment is a direct acting type fuel injector. A shim  34  is disposed between the stator  32  and the casing  11 . A cap housing  35  clamps and fixes the stator  32  to the casing  11  through the shim  34 . On an inner periphery side of the stator  32  is formed an armature chamber in which the armature  31  is accommodated movably.  
         [0080]    In mounting the electromagnetic drive unit  30  and the spring  27 , the valve element  20  and the armature  31  which are integral with each other are inserted into the holes  11   a  and  12   a  as deep as possible downward in FIG. 2. In this state, the shim  26  and the spring  27  are mounted to the valve element  20  and the bisplit spring retainer  25  mounted in a bisplit state to the large-diameter portion  24  of the valve element  20 . With the spring retainer  25  thus connected, the shim  26  is fitted thereon to fix the spring retainer. Thereafter, the distance piece  13  and the valve body  12  are fixed to the casing by means of the retaining nut  14 . Further, the stator  32  and the shim  34  are fixed to an end portion of the casing  11  on the side opposite to the valve body by means of the cap housing  35 , whereby the electromagnetic drive unit  30  is mounted to the casing  11 .  
         [0081]    In connection with mounting the electromagnetic drive unit  30  and spring  27  in accordance with the above procedure, an inside diameter d1 of the shim  26  is set larger than an outside diameter d2 of the large-diameter portion  24  of the valve element  20 , as shown in FIGS. 3 and 4. For example, d1 is 4.1 mm and d2 is 4.0 mm. Therefore, the shim  26  can be fitted onto the large-diameter portion  24  from the opposite-to-armature side of the valve element  20 . Further, in the armature chamber  36 , as shown in FIG. 2, a sufficient distance LZ is ensured between an end face of the armature  31  on the casing  11  side and an end face of the casing  11  on the armature  31  side is ensured, whereby the valve element  20  can be easily inserted downward in FIG. 2 and the spring  27  and other components can be mounted easily.  
         [0082]    The armature chamber  36  with the armature  31  received therein is in communication with the hole  11   a  through a passage  37 , whereby DME of a high pressure is introduced into the armature chamber  36  through the hole  11   a.  As shown in FIG. 1, a hole  20   a  is formed on the valve element  20  on the side opposite to the nozzle holes. A rod member  28  is provided on an inner periphery side of the hole  20   a  so as to be slidable with respect to an inner wall of the hole  20   a.  An oil pressure reducing means is constituted by both hole  20   a  and rod member  28 . A space formed between the hole  20   a  and the rod member  28 , i.e., a space formed in the hole  20   a  on the nozzle holes  15  side rather than on the rod member  28  side, serves as a low pressure chamber  29 . The rod member  28  is formed with a communication hole  281  and one end thereof is in communication with the low pressure chamber  29 , while the opposite end thereof is in communication with the fuel tank  1  shown in FIG. 2 which lies on the low pressure side.  
         [0083]    Therefore, the internal pressure of the low pressure chamber  29  is almost equal (about 0.6 MPa) to that of the fuel tank  1 . An O-ring  38  is installed between the rod member  28  and the stator  32  to prevent leakage of DME to the exterior from the armature chamber  36 .  
         [0084]    Since the inside diameter of the hole  20   a  and the outside diameter of the rod member  28  are almost equal to each other, the inner wall of the hole  20   a  and an outer wall of the rod member  28  slide with respect to each other. The rod member  28  is fixed to the stator  32  by press-fitting for example. Accordingly, when the armature  31  and the valve element  20  integral with each other reciprocate axially, the rod member  28 , as well as the armature  31  and the valve element  20 , reciprocate relatively with respect to each other, so that the volume of the low pressure chamber  29  changes.  
         [0085]    The inside diameter of the hole  20   a  and the outside diameter of the rod member  28  are assumed to be d3, while the outside diameter of the valve element  20  and the inside diameter of the valve seat portion  16  of the valve body  12  opposed to the abutment portion  23  are assumed to the d4. If d3 and d4 are set equal to each other like, for example, d3=1.8 mm and d4=1.8 mm, the oil pressure based on the high pressure DME acting on the valve element  20  becomes balanced. Further, the force induced by the oil pressure of DME acting on the valve element  20  decreases by an amount corresponding to the area of an end face  29   a  of the low pressure chamber  29  located on the nozzle holes  15  side. Thus, it is possible to improve the pressure of DME injected from the fuel injector  10 . For example, with d3=d4=1.8 mm, even when the pressure of DME is about 80 MPa,  
         [0086]    it is possible to actuate the valve element  20  without changing the constitution and output force of the electromagnetic drive unit  30  and the shapes of components.  
         [0087]    A small amount of DME present in the armature chamber  36  leaks out to the low pressure chamber  29  through the clearance between the hole  20   a  and the rod member  28 . However, the flow rate of DME leaking out to the low pressure chamber  29  in this embodiment is extremely small in comparison with that in the fuel injector disclosed for example in JP-A-9-42106 in which high pressure fuel present in the pressure control chamber is allowed to leak to the low pressure side at every fuel injection. Therefore, the DME leaking to the low pressure chamber  29  can be recovered directly into the fuel tank  1 .  
         [0088]    Next, the following description is provided about the operation of the fuel injector  10  according to the first embodiment.  
         [0089]    When electric power is fed from the ECU  4  to the coil  33 , a magnetic attraction is developed between the armature  31  and the stator  32  by a magnetic field created in the coil  33 . When the magnetic attraction developed between the armature  31  and the stator  32  becomes larger than the sum of both the biasing force of the spring  27  and the force based on the pressure in the holes  11   a  and  12   a  and acting on the valve element  20  in the nozzle holes closing direction, the armature  31  and the valve member  20  integral with the armature lift upward in FIG. 2. As a result, abutment portion leaves the valve seat portion  16  and the injection of fuel from the nozzle holes  15  is started.  
         [0090]    When the supply of electric power to the coil  33  is stopped, the magnetic attraction between the stator  32  and the armature  31  vanishes. Consequently, the valve element  20  move downward in FIG. 2 with both the biasing force of the spring  27  and the force based on the pressure of DME and acting on the valve element  20  in the nozzle holes closing direction. As a result, the abutment portion  23  sits on the valve seat portion  16  and the injection of fuel from the nozzles holes  15  is stopped.  
         [0091]    According to the fuel injector  10  of the first embodiment, as described above, the low pressure chamber  29  is formed in an end portion of the valve element  20  on the side opposite to the nozzle holes, whereby the force acting on the valve element  20  in the nozzle holes closing direction can be diminished. Further, by equalizing d3 to d4, it is possible to balance the pressure of DME acting on the valve element  20 , and hence it is possible to decrease the force for actuating the valve element  20  in the nozzle holes opening direction. Accordingly, the pressure of DME injected can be made high without an increase in drive force of the electromagnetic drive unit  30  and without an increase in size of the constitution of the same drive unit.  
         [0092]    In this first embodiment there is adopted a direct acting method wherein the valve element  20  is actuated directly by the electromagnetic drive unit  30 , for example in comparison with a fuel injector wherein a valve member is actuated by controlling the oil pressure in a pressure control chamber, it is possible to greatly diminish the amount of DME discharged from the fuel injector  10  to the low pressure side. The adoption of the direct acting method is further advantageous in that the leakage of fuel can be diminished even when a high pressure liquefied gas fuel, e.g., DME, is used as fuel as in this first embodiment.  
         [0093]    A description will be given below of a fuel injector according to a second embodiment of the present invention.  
         [0094]    This second embodiment is a modification of the first embodiment and the construction of a fuel injector  10  according to this second embodiment is the same as that in the first embodiment. In the second embodiment the relation between d3 and d4 is different from that in the first embodiment, which relation is set as d3&lt;d4. With d3&lt;d4, the force based on the pressure of DME and acting on the valve element  20  is imbalanced and becomes larger in the nozzle holes closing direction. More specifically, for d4=1.8 mm, d3 is set smaller in accordance with the maximum pressure of DME which is injected. By the setting, the period from the time when the supply of electric power to the coil  33  is stopped until the abutment portion  23  sits on the valve seat portion  16  is shortened and the response characteristic of the valve element  20  in valve closing is improved.  
         [0095]    The value of d3 can be calculated in accordance with both d4 and maximum injection pressure of DME. For example, if the maximum injection pressure of DME is 80 MPa, then for d4=1.8 mm, the value of d3 is set in the range from 1.4 to 1.6 mm. By the setting, when the pressure of DME fed to the fuel injector  10  is 80 MPa, the force based on the pressure of DME and acting on the valve member corresponds, for example in the conventional fuel injector  100  shown in FIG. 10, to the force which acts on the valve member  101  when the pressure of DME is in the range from about 15 to 30 MPa.  
         [0096]    According to this second embodiment, the force acting on the valve element  20  can be decreased even when the pressure of DME is improved. Besides, the spring  27  is disposed between the large-diameter portion  24  of the valve element  20  and an end face of the casing  11 , for example in comparison with the spring  107  in the conventional fuel injector  100  shown in FIG. 10, the spring  27  used in this embodiment is disposed apart from the stator  32 , thus permitting easy insertion of the rod member  28  into the stator  32 . Therefore, it is easy to change the inside diameter of the hole  20   a  and the outside diameter of the rod member  28  and hence the value of d3 can be changed easily.  
         [0097]    A fuel injector according to a third embodiment of the present invention is shown in FIG. 5, in which components substantially common to the first embodiment are identified by like reference numerals, and explanations thereof will here be omitted.  
         [0098]    In a fuel injector  40  according to this third embodiment, as shown in FIG. 5, a small-diameter portion  42  is formed at an end portion of a valve element  41  on the side opposite to nozzle holes. The small-diameter portion  42  is integral with the valve element  41  and extends to the opposite-to-nozzle-holes side of the valve element. A hole  43   a  is formed in a stator  43  and the small-diameter portion  42  can slide and reciprocate on an inner periphery side of the hole  43   a.  The hole  43   a  is in communication with a fuel tank  1  which corresponds to a low pressure side. According to this construction, a pressure equal to the internal pressure of the fuel tank  1  acts on an end face of the small-diameter portion  42  and also on the hole  43   a  as is the case with the low pressure chamber  29  in the first embodiment. An outside diameter of the small-diameter portion  42  and an inside diameter of the hole  43   a,  which are indicated at d5, are set so as to meet the relationship of d5≦d4 like d3 in the second embodiment. The amount of DME leaking out from the clearance between the small-diameter portion  42  and the hole  43   a  is very small, so that the leaking fuel is recovered directly into the fuel tank  1 .  
         [0099]    In this third embodiment, the pressure of DME acting on the valve element  41  in the valve closing direction can be reduced as in the first embodiment, thus making it possible to diminish the force required for actuating the valve element  41 .  
         [0100]    A fuel injector according to a fourth embodiment of the present invention is shown in FIG. 6, in which components substantially common to the first embodiment are identified by like reference numerals, and explanations thereof will here be omitted.  
         [0101]    In a fuel injector  50  according to this fourth embodiment, as shown in FIG. 6, an armature  52  fixed to an end portion of a valve element  51  on the side opposite to nozzle holes is formed in the shape of a flat plate. A stator  53  is provided in opposition to the armature  52 . A shim  54  is disposed between the stator  53  and a casing  11 . A cap housing  55  clamps and fixes the stator  53  to the casing  11  in a sandwiching relation to the shim  54 . The valve element  51  is provided with a slide portion  511 . The slide portion  511  is slidable with respect to an inner wall of a hole  12   a  formed in a valve body  12 .  
         [0102]    At an end portion of the valve element  51  on the side opposite to nozzle holes there is formed a small-diameter portion  512  integrally with the valve element  51 . The small-diameter portion  512  can slide and reciprocate along an inner periphery side of a hole  53   a  formed in the stator  53 . The hole  53   a  is in communication with a fuel tank  1  which corresponds to a low pressure side. According to this construction, a pressure equal to the internal pressure of the fuel tank  1  acts on the hole  53   a  and also on an end face of the small-diameter portion  512 . An inside diameter of the hole  53   a  and an outside diameter of the small-diameter portion  512 , which are indicated at d7, are set so as to meet the relationship of d 7 ≦d4 like d3 in the first or the second embodiment. The amount of fuel leaking out from the clearance between the small-diameter portion  512  and the hole  53   a  is very small, so that the leaking DME is recovered directly into the fuel tank  1 .  
         [0103]    In this fourth embodiment, the valve element  51  slides with respect to the valve body  12  or the stator  53  at two portions of slide portion  511  and small-diameter portion  512 . In comparison with the first embodiment wherein the valve member slides at three portions of slide portion  21 , slide portion  22 , and hole  20   a,  the management of coaxiality of components can be done easily in this fourth embodiment.  
         [0104]    A fifth embodiment of the present invention is shown in FIG. 7.  
         [0105]    In a fuel injector  60  according to this fifth embodiment, a valve element is constructed of a valve rod portion  71  and a valve needle portion  72 , which are connected together by a connecting portion  73 . The connecting portion  73  has a spherical ball  731  and a fixing member  732 . A valve body  62  is fixed to one end portion of a casing  61  and an electromagnetic unit  80  is fixed to an opposite end portion of the casing. A hole  62   a  is formed in the valve body  62  and a slide portion  74  and a slide portion  74  formed on the valve needle portion  72  is slidable with respect to an inner wall of the hole  62   a.  Plural nozzle holes  63  are formed in a tip end portion of the valve body  62 . A valve seat portion  64  is provided on an inlet side of the nozzle holes  63  of the valve body  62 . An abutment portion  75  capable of sitting on the valve seat portion  74  is provided at a tip of the valve needle portion  72 . When the abutment portion  75  sits on the valve seat portion  64 , the flow of DME is cut off to stop the injection of DME from the nozzle holes  63 . On the other hand, when the abutment portion  75  leaves the valve seat portion  64 , the flow of DME is started and DME is injected from the nozzle holes  63 .  
         [0106]    An electromagnetic drive unit  80  is installed on the casing on the side opposite to the valve body. The electromagnetic drive unit  80  has an armature  81 , a stator  82 , a coil  83 , and a cap housing  84 . The armature  81  is formed integrally with the valve rod portion  71  on the side opposite to the nozzle holes. The stator  82  is disposed in opposition to the armature  81 . The coil  83  is disposed on an outer periphery side of the stator  82 . The coil  83 , when supplied with electric power from ECU  4 , generates a magnetic field. With the magnetic field thus generated by the coil  83 , there occurs a magnetic attraction between the stator  82  and the armature  81 . By energizing the coil  83 , the valve rod portion  71  and the valve needle portion  72  as valve components are actuated directly by the electromagnetic drive unit  80 . A cap housing  84  is provided in a surrounding relation to an outer periphery side of the coil  83  and forms a magnetic circuit in cooperation with both armature  81  and stator  82 . The stator  82  and the casing  61  are fixed with a retaining nut  65  through a shim  85 .  
         [0107]    DME of a high pressure fed from a common rail  3  flows into an intake port  821  formed in the stator  82 . The DME having thus entered the intake port  821  then flows through flow passages  822  and  823  formed eccentrically with respect the central axis of the stator  82 , further through a flow passage  811  formed in the armature  81  and a flow passage  851  formed in the shim  85 , and is fed to the tip end portion of the valve body  62 .  
         [0108]    A small-diameter portion  76  is formed at an end of the valve rod portion  71  on the side opposite to nozzle holes.  
         [0109]    The small-diameter portion  76  is formed integrally with the valve rod portion  71  and extends to the side opposite to nozzle holes. A hole  82   a  is formed in the stator  82  and the small-diameter portion  76  can slide and reciprocate along an inner periphery side of the hole  82   a.  The hole  82   a  is in communication with a fuel tank  1  which corresponds to a low pressure side. According to this construction, a pressure equal to the internal pressure of the fuel tank  1  acts on the hole  82   a  and also on an end face  76   a  of the small-diameter portion  76 . If an outside diameter of the small-diameter portion  76  and an inside diameter of the hole  82   a  are assumed to be d9 and an inside diameter of the valve seat portion  64  in the valve body  62  and an outside diameter of the abutment portion  75  in the valve needle portion  72  are assumed to be d10, there exists a relationship of d9≦d10 as in the first and second embodiments. Since the amount of DME leaking out from the clearance between the small-diameter portion  76  and the hole  82   a  is very small, the leaking fuel is recovered directly into the fuel tank  1 .  
         [0110]    A detailed description will be given below about the valve element used in the fuel injector  60  of this embodiment.  
         [0111]    As shown in FIG. 8, the valve element has a valve rod portion  71  and a valve needle portion  72 , which are connected together by a connecting portion  73 . An end face of the valve rod portion  71  on the valve needle portion  72  side and an end face of the valve needle portion  72  on the valve rod portion  71  side are each formed in a centrally recessed conical shape and a ball  731  is held within the recessed space. The valve rod portion  71  and the valve needle portion  72  are formed with projecting portions  711  and  721 , respectively, which project radially outwards, and a fixing member  732  is engaged with the projecting portions  711  and  712 . At both axial ends of the fixing member  732  are formed a pair of retaining portions  732   a,  which are engaged with the projecting portions  711  and  712  of the valve rod portion  71  and the valve needle portion  72 , respectively.  
         [0112]    The fixing member  732  is formed of a metallic material such as steel and has a generally C-shaped section obtained by removing a part of a cylinder as shown in FIG. 9. The fixing member  732  can be fitted on the connection of the valve rod portion  71 , valve needle portion  72  and ball  731  radially from the outside and can be removed from the connection. Further, the fixing member  732  is formed with plural slits  732   b  to make the overall axial length changeable.  
         [0113]    The reason why the plural slits  732   b  are formed in the fixing member  732  and the fixing member  732  is made capable of expansion and contraction axially is as follows.  
         [0114]    The fuel injector  60  is usually replaced when a running distance of a vehicle with a diesel engine mounted thereon reaches a predetermined distance (about 100,000 km). Taking the cost of replacement of the fuel injector  60  into account, it is desirable to replace only the casing  61 , valve body  62  and valve needle portion  72  which are high in the frequency of wear or loss. In this embodiment wherein the valve rod portion  71  and the valve needle portion  72  are constituted as separate portions, there occur variations in size of both portions. Consequently, there is a fear that the lift quantity of the valve rod portion  71  and the valve needle portion  72  as constituents of the valve element, i.e., the spacing between the armature  81  and the stator  82 , may vary after the replacement of parts. Thus, it is necessary that the spacing between the armature  81  and the stator  82  be adjusted by changing the size of the ball  731 , and it is desirable that the fixing member  732  expand or contract according to the size of the ball  731 . For this reason the fixing member  732  is constituted so as to be capable of expansion and contraction.  
         [0115]    In this fifth embodiment the ball  731  is interposed between the valve rod portion  71  and the valve needle portion  72 , so even when the valve rod portion  71  or the valve needle portion  72  tilts due to a machining error for example, it is possible to connect the valve rod portion  71  and the valve needle portion  72  with each other while accepting the tilt by the ball  731 . Thus, a high machining accuracy is not required of the valve rod portion  71  or the valve needle portion  72  and hence it is possible to reduce the number of machining steps and the machining cost.  
         [0116]    In the above plural embodiments DME is used as fuel introduced into the respective fuel injectors. In the present invention, however, there also may be used as fuel another liquefied gas fuel such as LPG or an ordinary liquid fuel such as gas oil or gasoline. Also as to the fuel injection system, it is not limited to the common rail type.  
         [0117]    Next, a sixth embodiment of the present invention will be described. In this embodiment the present invention is applied to a fuel injector for a vehicular diesel engine wherein a liquefied gas such as DME or LPG is used as fuel.  
         [0118]    The fuel injector according to this embodiment is what is called a direct acting type fuel injector wherein a valve element is directly operated by means of an electromagnetic solenoid (actuator).  
         [0119]    [0119]FIG. 11 illustrates a sectional structure of the fuel injector and a construction around the same injector. The fuel injector, indicated at  230 , is actuated in accordance with a drive signal provided from ECU  4 .  
         [0120]    The construction of the fuel injector  230  will now be described in detail. A casing  231  and a valve body  232  constitute a first casing member and a second casing member respectively, which are rendered integral with each other by tightening a retaining nut  233 . Coaxial holes  231   a  and  232   a  are formed in the casing  231  and  232 , respectively, and a rod (rod portion)  234  and a valve (valve portion)  235 , which constitute a valve element, are received into the holes  231   a  and  232   a.  A slide portion  234   a  of the rod  234  is in contact with an inner wall of the hole  231   a,  while a slide portion  235   a  of the valve  235  is in contact with an inner wall of the hole  232   a,  the rod  234  and the valve  235  being slidable vertically in the figure. A space adjusting shim (shim member)  236  is interposed between the rod  234  and the valve  235 , and in this state these components are connected together by means of a fixing member  237  which serves as a connecting member. The valve member construction comprising the rod  234 , valve  235 , shim  236 , and fixing member  237  is a characteristic portion of this embodiment and the details thereof will be described later.  
         [0121]    Plural nozzle holes  232   b  are formed in a tip portion of the valve  232 . The nozzle holes  232   b  close when a tip of the valve  235  comes into abutment against the valve body  232  and open when the tip of the valve  235  leaves the valve body  232 .  
         [0122]    In an electromagnetic solenoid section, an armature  239  is fixed to an upper end in the figure of the rod  234  and a first stator  240  is provided in opposition to the armature  239 . A second stator  242  is attached to the first stator  240  through an insert member  241  which is formed of a non-magnetic material such as SUS304. These components are rendered integral in an oil-tight manner by such means as laser welding. A coil  243  is mounted on an outer periphery of the first stator  240 . Further, a spring  244  is received in the first stator  240  and the valve element comprising the rod  234  and the valve  235  is urged to the valve closing side (lower side in the figure).  
         [0123]    A plate  245  is disposed between the second stator  242  and the casing  231  and in this state a cap housing  246  is mounted to the casing  231 . The plate  45  also functions as a valve stopper and the lift quantity of the rod  234  (valve  235 ) is restricted by abutment of an upper surface of the slide portion  234   a  of the rod  234  against the plate  245 .  
         [0124]    An inlet port member  248  is attached to the casing  231  in a sandwiching relation to a gasket  247 . Fuel of a high pressure is introduced from a common rail into the holes  231   a  and  232   a  through the inlet port member  248 . A bar filter  249  for preventing the entry of foreign matters is press-fitted and fixed into the inlet port member  248 .  
         [0125]    The hole  231   a  is in communication with an armature chamber  251  through a communication passage  250 . Therefore, the high pressure fuel acts on the rod  234  and the valve  235  at any position and it is possible to prevent the leakage of fuel from high to low position in the associated slide portion.  
         [0126]    In the fuel injector  230  of the above construction, when the coil  243  is de-energized, the valve element (rod  234  and valve  235 ) is held in its closed position with the biasing force of the spring  244 . At this time, the nozzles holes  232   b  close and the fuel injection by the fuel injector  230  is stopped. When the coil  243  is energized, the armature  239  is attracted to the first stator  240  and the valve element (rod  234  and valve  235 ) moves to the valve opening side (upward in the figure) against the biasing force of the spring  244 , whereby the nozzle holes  232   b  are opened to effect fuel injection.  
         [0127]    A detailed description will be given below about a characteristic construction of the valve element. FIG. 12 is a sectional view showing the connection between the rod  234  and the valve  235  on a larger scale and FIG. 13 is a perspective view showing the construction of the fixing member  237 .  
         [0128]    As shown in FIG. 12, a lower end face of the rod  234  and an upper end face of the valve  235  are both flat faces and the shim  236 , which is in the shape of a flat plate, is interposed between both flat end faces. The rod  234  and the valve  235  are formed with outwardly projecting flange portions  234   b  and  235   b,  respectively, and the fixing member  237  is mounted so as to engage the flange portions  234   b  and  235   b.  That is, the fixing member  237  as a pair of upper and lower engaging portions  237   a.    
         [0129]    As shown in FIG. 13, the fixing member  237  is formed of a metallic material such as iron or steel and is in a C-shape in plan obtained by removing a part of a cylinder. The fixing member  237  can be fitted on the connection of the rod  234 , valve  235  and shim  236  from the outside and can be removed. In the fixing member  237  are formed plural slits (expanding/contracting portions)  237   b  so as to make the axial length of the fixing member changeable.  
         [0130]    The reason why the fixing member  237  is given the expanding/contracting function by the slits  237   b  will be set forth below.  
         [0131]    Generally, the fuel injector  230  is replaced at every predetermined running distance of the vehicle concerned (at every about 100,000 km), and from the standpoint of cost it is only the nozzle portion (valve body  232  and valve  235 ) that is replaced. In this case, according to the above construction wherein the valve element is divided into rod  234  and valve  235 , there occur variations in size of those components and this is presumed to be a cause of a change in valve lift quantity (an air gap quantity between the armature and the stator) after the replacement of parts. Thus, there arises the necessity of changing the thickness of the shim  236  to adjust the spacing, and the fixing member  237  is given a function of expansion and contraction so that it can cope with a change in thickness of the shim  236 .  
         [0132]    More specifically, in FIG. 14 which shows the connection of rod  234  and valve  235  in a disassembled manner, if the distance between an lower end face of the casing  231  and that of the rod  234  is assumed to be L1 and the distance between an upper end face of the valve body  232  and that of the valve  235  is assumed to be L2, the distance L1 is measured in an abutted state of the rod  234  against the plate  245 . Likewise, for (new) valve body  232  and valve  235  after replacement, the distance L2 is measured in an abutted state of the tip of the valve  235  against the sheet portion of the valve body  232 . Then, a required thickness of the shim  236  is determined from the distances L1 and L2.  
         [0133]    In replacing the nozzle portion (valve body  232  and valve  235 ), the retaining nut  233  is released and the valve body  232  is removed. Further, the fixing member  237  is removed and the valve  235  is removed from the rod  234 . Now, the removal of the used nozzle portion (valve body  232  and valve  235 ) is completed. Then, the distances L1 and L2 shown in FIG. 14 are measured in the manner described above and a shim  236  matching the measured values is provided, thereafter, a new nozzle portion (valve body  232  and valve  235 ) is mounted. The mounting may be done in reverse procedure from the dismounting procedure.  
         [0134]    According to this embodiment described above in detail there are obtained the following effects.  
         [0135]    When the valve portion is to be replaced after a long-term use of the fuel injector  230 , the efficiency of the replacing work is improved. As a result, in the actuator direct acting type fuel injector  230 , there can be realized a construction superior in maintainability.  
         [0136]    Since the shim  236  is interposed between the rod  234  and the valve  235  and these components are interconnected by the fixing member  237  having an expanding/contracting function, even if the thickness of the shim  236  is changed, it is possible to cope with the change.  
         [0137]    Since the rod  234 , valve  235  and shim  236  are abutted and connected together at respective flat faces, even if the central axes of the rod  234  and valve  235  are slightly deviated due to a machining error for example, the rod  234  and the valve  235  can be connected together while accepting (absorbing) the deviation.  
         [0138]    Since the fuel injector  230  described above is of an actuator direct acting type construction, there is little leakage of fuel and the fuel injector can be embodied suitably as a fuel injector for a liquefied gas fuel.  
         [0139]    A seventh embodiment of the present invention will now be described. FIG. 15 is a sectional view showing a connection between a rod  234  and a valve  235  on a larger scale. In the construction illustrated in FIG. 15, a lower end face of the rod  234  and an upper end face of the valve  235  are in the shape of a centrally recessed cone, with a spherical ball  261  as a shim being interposed therebetween. By changing the size (diameter) of the ball  261  there is adjusted a valve lift quantity (air gap quantity between an armature and a stator). In this case, even if the connection between the rod  234  and the valve  235  tilts slightly due to a machining error for example, the rod  234  and the valve  235  can be connected together while accepting the tilt.  
         [0140]    Although in the above embodiments the present invention is embodied as fuel injectors for the injection of a liquefied gas fuel such as DME or LPG, the present invention may also be applied to fuel injectors which inject other fuels. For example, the invention may be embodied as a fuel injector for the injection of gas oil or gasoline. Also in this case it is possible to realize a construction superior in maintainability.  
         [0141]    Next, an eighth embodiment will now be described. FIG. 17 illustrates a sectional structure of a fuel injector according to this embodiment and a construction around the fuel injector.  
         [0142]    A detailed description will now be given about the construction of the fuel injector. A casing  331  and a valve body  332  constitute a dividable casing member. Both are rendered integral with each other by tightening a retaining nut  333 . A part (a lower end portion in the figure) of the casing  331  is constituted in a divided form as a distance piece  334 . Coaxial holes  331   a  and  332   a  are formed in the casing  331  and the valve body  332 , respectively, and an elongated valve element  335  is received therein. The valve element  335  has slide portions  335   a  and  335   b  at two upper and lower positions in the figure. Plural nozzle holes  332   b  are formed in a tip portion of the valve body  332 . When a tip of the valve element  335  comes into abutment against the valve body  332 , the nozzle holes  332   b  close, while when the tip of the valve element  335  leaves the valve body  332 , the nozzle holes  332   b  open.  
         [0143]    A large-diameter portion  335   c  is formed at an intermediate position of the valve element  335  (a position corresponding to the distance piece  334 ) and a spring retainer  336  and a shim (shim member)  337  are disposed so as to be put on the large-diameter portion  335   c.  A spring  338  is provided between an inner wall of the casing  331  and the shim  337  and the valve element  335  is urged to the valve closing side (downward in the figure) constantly by the spring  338 .  
         [0144]    As shown in FIG. 20, the spring retainer  336  is constituted by bisectable halves (pieces) and the shim  337  is constituted by a ring plate. As shown in FIG. 21, the spring retainer  336  is mounted to the large-diameter portion  335   c  in a sandwiching relation to the valve element  335 , followed by further mounting of the shim  337  to fix the spring retainer  336 . The shim  337  fulfills a spring force adjusting function. That is, the biasing force of the spring  338  is adjusted by changing the plate thickness of the shim  337 .  
         [0145]    Referring back to FIG. 17, an inlet port member  348  is attached to the casing  331  in a sandwiching relation to a gasket  347  and fuel of a high pressure is introduced from a common rail into the holes  331   a  and  332   a  through the inlet port member  348 . A bar filter for preventing the entry of foreign matters is press-fitted and fixed into the inlet port member  348 .  
         [0146]    On the other hand, according to the construction of an electromagnetic solenoid section, an armature  339  is fixed to an upper end in the figure of the valve element  335  and a stator  340  is provided in opposition to the armature  339 .  
         [0147]    A coil  341  is disposed on an outer periphery of the stator  340 . A shim  342  is disposed between the stator  340  and the casing  331  and in this state a cap housing  343  is mounted to the casing  331 .  
         [0148]    An armature chamber  351  for receiving the armature  339  therein is in communication with the hole  331   a  through a communication passage  350  and a liquefied gas fuel of a high pressure is introduced into the armature chamber  351 . Therefore, the high pressure fuel acts on the valve element  335  at any position and thus it is possible to eliminate the leakage of fuel such that the fuel leaks out from high to low pressure position in the slide portion of the valve element.  
         [0149]    The space between the armature  339  and the stator  340  serves as an oil pressure damper chamber  344 , the construction of which will now be described with reference to FIG. 18. In the same figure, out of an end face of the stator  340  and that of the armature  339 , the former is formed flat. On the other hand, on an outer edge portion of the end face of the armature  339  is formed annular protuberance  339   a,  which corresponds to a stepped portion, with a recess being defined so as to be surrounded by the protuberance  339   a.  The protuberance  339   a  also plays the role of a stopper when the armature moves. When the valve element  335  opens, an open position thereof is defined by the position at which the protuberance  339   a  of the armature  339  abuts the stator  340 . FIG. 19 is a plan view of the armature  339  as seen from above. As shown in the same figure, cutout portions are formed in the protuberance  339   a  at one or more positions (two positions in the figure).  
         [0150]    The larger the volume change rate of the oil pressure damper chamber  344  relative to the valve lift quantity (stroke), the more outstanding the effect as an oil pressure damper. In other words, in the construction of FIG. 18, the smaller the height LX of the protuberance  339   a,  the more outstanding the effect as an oil pressure damper. However, if the height LX of the protuberance  339   a  is too small, it is difficult to attain a high machining accuracy.  
         [0151]    In this embodiment the height LX is set at 0.1-0.3 mm as an example. A lift quantity (distance LY in the figure) of the valve element  335  is adjusted by the shim  342  disposed between the stator  340  and the casing  331 .  
         [0152]    In the fuel injector  330  of the above construction, when the coil  341  is de-energized, the valve element  335  is held in its closed position with the biasing force of the spring  338 . At this time, the nozzle holes  332   b  are closed to stop the injection of fuel by the fuel injector  330 . When the coil  341  is energized, the armature  339  is attracted to the stator  340  and the valve element  335  moves to its open side (upper side in the figure) against the biasing force of the spring  338 . The valve element  335  lifts until abutment of the protuberance  339   a  of the armature  339  against the stator  340 , so that the nozzle holes  332   b  open to effect the injection of fuel.  
         [0153]    With lift of the valve element  335 , the spacing (distance LY) between the protuberance  339   a  of the armature  339  and the stator  340  becomes shorter and the volume of the oil pressure damper chamber  344  becomes smaller. The fuel present within the oil pressure damper chamber  344  flows out through the spacing (distance LY) between the protuberance  339   a  and the stator  340 , which spacing, however, becomes narrower with lift of the valve element  335  and acts as an oil pressure damper. When the valve opening of the fuel injector  330  is completed, the oil pressure chamber  344  is shut off from the exterior by contact of the protuberance  339   a  with the stator  340 .  
         [0154]    When the fuel injector  330  closes, the valve element  335  returns to its closed position with the biasing force of the spring  338  upon de-energization of the coil  341 . At this time, the liquefied gas fuel is introduced between the armature  339  and the stator  340  through the cutout portions  339   b,  whereby the disengagement between the armature  339  and the stator  340  is done quickly. Consequently, the closing motion of the valve element  335  is assisted and the valve element  335  closes quickly.  
         [0155]    [0155]FIG. 22 is a time chart showing a lift behavior of the valve element relative to a drive signal for the fuel injector  30  and FIG. 23 illustrates an injection quantity characteristic of the fuel injector  330 . In both figures, the related art is indicated with dotted lines for comparison purpose.  
         [0156]    In FIG. 22, after turning ON of a drive signal which is inputted to the fuel injector  330  from ECU  4 , the lift of the valve element  335  is started and the valve opening motion is ended upon abutment of the protuberance  339   a  of the armature  339  against the stator  340 . Thereafter, the fuel injector  330  is held in its open condition. In this case, the bouncing of the valve element  335  upon arrival of the valve element  335  at its opening position (upon abutment of the protuberance  339   a  against the stator  340 ) is diminished. After opening of the valve element  335  and upon turning OFF of a drive signal, the fuel injector  330  closes.  
         [0157]    In FIG. 23, the pulse width plotted along the axis of abscissa represents an elapsed time from the start of valve opening. In this embodiment, unlike the related art, there is obtained a characteristic such that the injection quantity increases monotonously with an increase of the pulse width. Thus, it is seen that a satisfactory injection characteristic (metering characteristic) can be achieved.  
         [0158]    Next, a description will be given of a mounting procedure for the fuel injector  330 , especially a mounting procedure for the spring  338 , with reference to FIGS. 24 and 25. First, the electromagnetic solenoid section and the inlet port member  348  are mounted to the casing  331 .  
         [0159]    The valve element  335  integral with the armature is also mounted.  
         [0160]    As shown in FIG. 24, an integral combination of the valve element  335  and the armature  339  is brought down insofar as possible and in this state the spring  338  and the shim  337  are fitted on the valve element  335 , then two bisplit spring retainer halves  336  are mounted on the large-diameter portion  335   c.  Then, as shown in FIG. 25, with the two spring retainer halves  336  coupled together, the shim  337  is fitted to fix the spring retainer  336 . Thereafter, the distance piece  334  and the valve body  332  are fixed with the retaining nut  333 , whereby the mounting of the fuel injector  330  is completed.  
         [0161]    In the above mounting work, the diameter d1 of the shim  337  is set larger than the outside diameter d2 of the large-diameter-portion  335   c  of the valve element  335 . For example, d1 is 4.1 m and d2 is 4.0 mm. Therefore, the shim  337  can be inserted from the lower side of the valve element  335 . Further, as shown in FIG. 17, the distance LZ (armature moving space) between a lower end face of the armature  339  and the casing  331  in the armature chamber  351  is ensured sufficiently, whereby the valve element  335  can be brought down as shown in the figure, thus permitting easy mounting of the spring  338 , etc.  
         [0162]    According to this embodiment described above in detail there are obtained the following effects.  
         [0163]    Since the oil pressure damper chamber  344  is provided between the armature  339  and the stator  340 , the bouncing of the valve element  335  and that of the armature  339  in valve opening are suppressed by virtue of a damper effect. Consequently, the fuel injection quantity can be kept under control.  
         [0164]    Since the cutout portions  339   b  are formed in the protuberance  339   a  of the armature  339 , disengagement between the armature  339  and the stator  340  is done quickly when the valve element  335  returns to its closed position after valve opening. Accordingly, the fuel injector  330  operates in a satisfactory manner.  
         [0165]    Since the spring  338  is disposed at an intermediate position of the valve element  335 , it is not necessary for the spring to be interposed between the armature and the stator as in the construction of FIG. 28. Consequently, it is possible to realize an advantageous construction including the oil pressure damper chamber  344 . As to the construction of the spring retainer portion, since the spring retainer  336  comprising plural split pieces is used, it is easy to effect mounting of the spring retainer  336 . Further, the spring force can be adjusted by adjusting the thickness of the shim  337 .  
         [0166]    Since the fuel injector  330  described above adopts an actuator direct acting type construction, the leakage of fuel is diminished and the fuel injector thus embodied is suitable as a fuel injector for a liquefied gas fuel. Further, since a liquefied gas fuel is low in viscosity, the use thereof causes a serious problem of valve element bouncing, but this problem can be solved by the above construction of the fuel injector  330 .  
         [0167]    A ninth embodiment will now be described. In this ninth embodiment, as shown in FIG. 26, an end face of an armature  339  is formed flat and an annular protuberance  361  is formed on an end face of a stator  340 . In this case, the protuberance  361  corresponds to a stepped portion and an oil pressure damper chamber  344  is formed by a recess which is surrounded with the protuberance  361 .  
         [0168]    Next, a tenth embodiment will be described. In this tenth embodiment, as shown in FIG. 27, a stator  340  is provided with a stepped portion  362  instead of protuberance  361 . In FIG. 27 the machining of the stator  340  for forming an oil pressure damper chamber  344  is easier than in FIG. 26. At a position near the protuberance  361  or near the stepped portion  362  the stator  340  may be divided in two vertically in the figure. In this case, the machining of the protuberance  361  or the stepped portion  362  becomes still easier. Stepped portions (or protuberances) may be formed at end faces of both armature and stator to define an oil pressure damper chamber.  
         [0169]    When the valve element  335  opens in the construction of FIGS. 26 and 27, its open position is defined by the position at which an end face of the armature  339  abuts the protuberance  361  or the stepped portion  362 . In this case, it is preferable that a cutout portion be formed in at least one position of the protuberance  361  or the stepped portion  362 .  
         [0170]    Although in the above embodiments the protuberance  339   a  of the armature  339  or the protuberance  361  or the stepped portion  362  of the stator  340  functions as a stopper, there may be provided a separate stopper member. That is, it is not always necessary to adopt the construction wherein the armature  339  side and the stator  340  side are in contact with each other. There may be adopted another construction insofar as there is obtained an oil pressure damping function during movement of the valve element  335 .  
         [0171]    Although in the above embodiments a sufficient distance LZ (armature moving space) between the lower end face of the armature  339  and the casing  331  is ensured so that the valve element  335  can be brought down in the armature chamber  351 , this point is not essential to accomplishing the present invention. There may be adopted a construction wherein the distance LZ (armature moving space) is small. In this case, however, for improving the mountability of the spring  338  disposed at an intermediate position of the valve element  335 , it is preferable to for example shallow the spring receiving portion of the casing  331  which portion is for receiving the spring  338  therein (extend the length of the distance piece  334  upward in FIG. 17).  
         [0172]    Although in the above embodiments the present invention is embodied as fuel injectors for the injection of liquefied gas fuels such as DME and LPG, the invention may be embodied as a fuel injector for the injection of any other fuel, e.g., gas oil or gasoline. Also in this case it is possible to keep the fuel injection quantity under control.  
         [0173]    Next, an eleventh embodiment will be described. In this embodiment, a nozzle side (valve closing direction) and an opposite-to-nozzle side (valve opening direction) are assumed to be a lower side and an upper side, respectively, but these are for the convenience of explanation and are different from those in actual mounting.  
         [0174]    [0174]FIG. 29 illustrates a sectional structure of a fuel injector  401  and a construction around the fuel injector.  
         [0175]    The construction of the fuel injector  401  will be described below in detail.  
         [0176]    A casing of the fuel injector  401  is constituted by a coupled combination of a body  406  and a nozzle body  407 , which are rendered integral with each other by tightening a retaining nut  408 . Coaxial through holes  409  and  410  are formed in the body  406  and the nozzle body  407 , respectively, with an elongated valve element  411  being received into the through holes  409  and  410 .  
         [0177]    The valve element  411  is adapted to slide vertically through the through holes  409  and  410  and has slide portions  412  and  413  at two upper and lower positions respectively. Plural nozzle holes  414  are formed at a tip portion of the nozzle body  407 . When a tip of the valve element  411  comes into abutment against (sits on) the nozzle body  407 , the nozzle holes  414  close, while when the tip of the valve element  411  leaves (disengages from) the nozzle body  407 , the nozzle holes  414  open.  
         [0178]    A compression coil spring  415  is disposed at an upper end portion of the valve element  411 . The valve element  411  is urged downward constantly with a restoring force of the spring  415 .  
         [0179]    A fuel hole  416  is formed on an upper side of the valve element  411  and fuel fed from an inlet  417  flows through a passage formed within the body  416 , a first chamber  420  formed just under an armature  418 , a throttle portion  421  defined by a clearance between the armature  418  and a surrounding component, further through a second chamber  422  formed just above the armature  418 , and is introduced into the fuel hole  416  located centrally of the armature  418 .  
         [0180]    The throttle portion  421  is defined by a clearance between a side face of the armature  418  and a lower inner core  434  which constitutes a lower portion of a stator  423 . The clearance is set at a value in the range from 60 to 300 μm in terms of a radial size.  
         [0181]    In an intermediate position of the valve element  411  is formed a branch hole  426  for conducting fuel conducted from the fuel hole  416  into a fuel passage  425  which is formed between the through hole  409  of the body  406  and the valve element  411 . The fuel thus introduced into the fuel passage  425  is then conducted to the nozzle holes  414  side through a nozzle chamber  427  formed between the through hole  410  of the nozzle body  407  and the valve element  411 .  
         [0182]    Next, the inlet  417  will be described below.  
         [0183]    The inlet  417  is mounted to the body  406  in a sandwiching relation to a gasket  430  and serves as an inlet for a common rail  3 . A bar filter  431  for preventing the entry of foreign matters is press-fitted and fixed into the inlet  417 .  
         [0184]    Next, reference will be made below to an electromagnetic solenoid valve  432 .  
         [0185]    An armature  418  in the electromagnetic solenoid  432  is fixed to the upper portion of the valve element  411  by press-fitting for example, and a stator  423  is disposed in opposition to the armature  418 . Thus, there is constituted what is called a plunger type solenoid.  
         [0186]    The stator  423  is made up of an upper inner core  433  having an attraction face, a lower inner core  434  located sideways of the armature  418  and having a pole face, and a ring-like middle inner core  435  sandwiched between the upper inner core  433  and the lower inner core  434 .  
         [0187]    The upper inner core  433  and the lower inner core  434  are formed of a soft magnetic material because they serve as magnetic paths of the electromagnetic solenoid  432 . On the other hand, the middle inner core  435  is formed of a non-magnetic material to block the passage of a magnetic flux.  
         [0188]    The upper inner core  433 , the lower inner core  434 , and the middle inner core  435  are stacked and in this stacked state they are integrally fixed by a bonding means such as laser welding to constitute the stator  423 .  
         [0189]    A coil  436  for generating a magnetic force to let the armature  418  be attracted to the stator  423  is disposed on an outer periphery of the stator  423  and is fixedly molded with resin together with connecting terminals  438  within a solenoid housing  437 .  
         [0190]    A stopper  440  is disposed between the stator  423  and the body  406 . The stopper  440  not only functions to determine a fully open position of the valve element  411  but also functions as a shim for adjusting the spacing (i.e., a final gap) between the armature  418  and the stator  423 .  
         [0191]    The following description is now provided about the operation and effect of the fuel injector  401  in this embodiment.  
         [0192]    [0192]FIG. 30 is a time chart showing pressure behaviors of the lower first chamber  420  and the upper second chamber  422 . In the same figure, valve lift and injection rate in this embodiment are indicated with solid lines and those in the related art are indicated with broken lines.  
         [0193]    [0193]FIG. 31 is a T-Q characteristic diagram showing an injection quantity (Q) relative to pulse width T.  
         [0194]    Upon turning ON of a drive signal provided from ECU  4  to energize the coil  436 , the armature  418  is attracted to the stator  423  and the valve element  418  lifts upward against the biasing force of the spring  415 . When the valve element  411  abuts the stopper  440 , the valve opening motion is over and subsequently the valve element is held in the open condition. As the valve element  411  rises, its tip leaves (disengages from) the nozzle body  407  and the nozzle holes  414  open, allowing liquid fuel to be injected through the nozzle holes.  
         [0195]    In the fuel injector  100  of the related art shown in FIG. 33, the valve element  101  and the stopper  111  strike against each other at the time of valve opening, resulting in that there occurs bouncing of the valve element  101  several times as indicated with broken lines in FIG. 30. The injection rate is influenced by the bouncing and deteriorates. Further, as indicated with a broken line in FIG. 31, the injection rate Q is wavy relative to the pulse width T and thus it is impossible to effect a stable injection control.  
         [0196]    In the fuel injector  401  of this embodiment, as compared with the above related art, when the injection of fuel is started, the internal pressure of the nozzle chamber  427  and that of the second chamber  422  (an upper surface of the armature  418 ) which is in communication with the nozzle chamber  427  decrease. At this time, the internal pressure of the first chamber  420  (a lower surface of the armature  418 ) changes little because the propagation thereof is prevented by the throttle portion  421  formed sideways of the armature  418 . Consequently, an oil pressure difference acts up and down of the armature  418  and the armature (corresponding to the pressure receiving portion) is urged upward (in the valve opening direction) due to the oil pressure difference. With the urging force induced by the pressure difference, the bounce of the valve element  411  in valve opening is suppressed.  
         [0197]    At the time of fuel injection, the fuel flows out of the first chamber  420  (below the armature  418 ), then flows through the passage (throttle portion  421 ) formed sideways of the armature  418 , and further flows toward the overlying second chamber  422  (above the armature  418 ). With this upward flow of the fuel, the armature  418  is given an upward force (in the valve opening direction). Also by this action the bounce of the valve element  411  is prevented.  
         [0198]    Upon turning OFF of the drive signal provided from ECU  4  to de-energize the coil  436 , there no longer is any attractive force for the armature  418  by the stator  423  and the valve element  411  is displaced downward with the biasing force of the spring  415 . When the valve element  411  abuts the sheet of the valve body  407 , the valve closing operation is over and thereafter the closed state of the valve is maintained. When the valve element  411  moves down and the tip thereof comes into abutment against (sits on) the nozzle body  407 , the nozzle holes  414  close to stop the injection of fuel.  
         [0199]    In the conventional fuel injector  100  shown in FIG. 33, due to collision of the valve element  101  with the nozzle body  104  at the time of valve opening there occurs bouncing of the valve element  101  several times as indicated with a broken line in FIG. 30. As a result, there occurs a secondary injection after closing of the valve.  
         [0200]    In the fuel injector  401  of this embodiment, as compared with the above related art, when the injection of fuel is stopped, the flow of injected fuel is cut off suddenly, so that the internal pressure of the nozzle chamber  427  and that of the second chamber  422  (the upper surface of the armature  418 ) which is in communication with the nozzle chamber  427  increase. At this time, the internal pressure of the first chamber  420  (the lower surface of the armature  418 ) changes little because the propagation thereof is prevented by the throttle portion  412  formed sideways of the armature  418 . Consequently, an oil pressure difference acts up and down of the armature  418  and the armature is urged downward (in the valve closing direction) due to the oil pressure difference. With the urging force induced by the pressure difference, the bounce of the valve element  411  in valve closing is suppressed.  
         [0201]    When the nozzle holes  414  are cut off and the internal pressure of the second chamber  422  rises, fuel flows out of the second chamber  422  (above the armature  418 ), then flow through the passage (throttle portion  421 ) formed sideways of the armature  418 , and further flows toward the first chamber  420  (below the armature  418 ). With this downward flow of the fuel, the armature  418  is given a downward force (in the valve closing direction). Thus, also by this action the bounce of the valve element  411  in valve closing is suppressed.  
         [0202]    On the other hand, since the fuel injector  401  described above adopts a direct acting type construction wherein the valve element  411  is actuated directly with the electromagnetic solenoid  432 , there is little leakage of fuel and thus the fuel injector  401  is suitable as a fuel injector for a liquefied gas fuel.  
         [0203]    Besides, even when the valve element  411  is long and heavy as in this embodiment, it is possible to improve the injection characteristic because the occurrence of bouncing of the valve element  411  is suppressed.  
         [0204]    Further, in the case where the viscosity of fuel is low like such a liquefied gas fuel as LPG or DME, there arises a serious problem caused by bouncing of the valve element  411 , but according to this embodiment it is possible to suppress the bounce of the valve element even in case of a low fuel viscosity.  
         [0205]    A fuel injector  451  according to a twelfth embodiment of the present invention will now be described with reference to FIG. 32 which illustrates a sectional structure of the fuel injector  451 . A description will be given below about a principal portion different from the previous eleventh embodiment. In this twelfth embodiment the same reference numerals as in the eleventh embodiment represent the same functional components as in the eleventh embodiment.  
         [0206]    In this twelfth embodiment, disc  441  (corresponding to the pressure receiving portion) which undergoes a differential pressure is provided at an upper end of a valve element  411  which extends upward beyond the armature  418 , and a first chamber  420  is formed below the disc  441 , while a second chamber  422  is formed above the disc  441 . Further, a throttle portion  421  is defined by a clearance between the disc  441  and a component (body  406 ).  
         [0207]    Also with this arrangement it is possible to obtain the same effects as in the eleventh embodiment. The disc  441  which undergoes a differential pressure need not be positioned above the armature  418 , nor need be the disc  441  in the shape of a disc.  
         [0208]    Although the fuel injectors  401  and  451  of the above eleventh and twelfth embodiments are for the injection of a liquefied fuel such as DME or LPG, the present invention is also applicable to fuel injectors which inject other fuels. For example, the present invention may be applied to a fuel injector for the injection of gas oil or gasoline while preventing the occurrence of bouncing of a valve element used therein.  
         [0209]    Although in the above embodiments there is used the electromagnetic solenoid  432  as an example of an electric actuator, there may be used another electric actuator such as a piezoelectric actuator comprising a large number of stacked piezoelectric elements.  
         [0210]    Further, a passage resistance means for increasing the passage resistance of fuel may be provided in the throttle portion  421  so that the force of fuel flowing through the throttle portion  421  is greatly exerted on the valve element  411 .  
         [0211]    A thirteenth embodiment of the present invention will now be described. In this embodiment there are provided a fuel supply system for the injection and supply of a liquefied gas fuel such as DME or LPG to a diesel engine and also provided an air conditioner.  
         [0212]    In FIG. 34, a liquefied gas fuel such as DME or LPG is stored in a liquid state within a fuel tank  510 . The internal pressure of the fuel tank  510  is equal to a saturated vapor pressure of the liquefied gas fuel. In case of using DME as a liquefied gas fuel, a saturated vapor pressure of DME is about 0.6 MPa at room temperature, for example, 25° C. A low pressure pump  511  is disposed within the fuel tank  510 . With the low pressure pump  511 , the liquefied gas fuel is fed in a pressurized state to a predetermined feed pressure (3 MPa or so) to a high pressure pump  513  through a pipe  512 .  
         [0213]    The internal pressure of the fuel tank  510  is equal to a saturated vapor pressure of the liquefied gas fuel, and when the temperature of the liquefied gas fuel locally rises only slightly or the pressure thereof locally drops only slightly within the fuel tank  510 , there occur bubbles (vapor). In such a case, by disposing the low pressure pump  511  within the fuel tank  510 , the formation of bubbles caused by a pressure drop in a path extending from the fuel tank  510  to the low pressure pump  511  and a deficient suction of the low pressure pump  511  are prevented. At the same time, a temperature difference between the fuel tank  510  and the low pressure pump  511  becomes smaller, whereby the formation of bubbles caused by the temperature difference and the resulting deficient suction of the low pressure pump  511  are prevented.  
         [0214]    The high pressure pump  513  compresses the liquefied gas fuel to a high pressure (35 MPa or so) corresponding to the injection pressure and feeds the thus-compressed high pressure fuel to a common rail  515  through a pipe  514 . The liquefied gas fuel leaking from a slide portion or a seal portion of the high pressure pump  513  passes through a pipe  516  and is recovered into a fuel recovery tank  517 . The common rail  515  and the fuel recovery tank  517  are connected together through a pipe  518 , with a pressure limiting valve  519  being disposed at an intermediate position of the pipe  518 . In this case, surplus fuel is recovered into the fuel recovery tank  517  through the pressure limiting valve  519  lest the fuel pressure within the common rail  515  should exceed a predetermined level (35 MPa or so).  
         [0215]    Fuel injectors  520  in a number corresponding to the number of engine cylinders are connected to the common rail  514 , and as the fuel injectors  520  are actuated, the high pressure fuel stored in the common rail  515  is fed by injection to the diesel engine. The fuel injectors  520  are each constructed of an electromagnetic control valve  520   a  which intermits the supply of the high pressure fuel from the common rail  515  and an injection nozzle  520   b  which causes a valve element to move with operation of the electromagnetic control valve  520   a  and allows the fuel to be injected from a nozzle tip. The operation of each fuel injector is controlled by means of a microcomputer (not shown). The liquefied gas fuel leaking for example from a valve element slide portion of each fuel injector  520  passes through a pipe  521  and is recovered into the fuel recovery tank  517 .  
         [0216]    The following description is now provided about the air conditioner. The fuel which has been pressurized to about 3 MPa into a liquefied state by means of the low pressure pump  511  passes through a pipe  531  and is fed to an expansion valve  532 . An air conditioner control valve  533  is installed at an intermediate position of the pipe  531 , whereby the air conditioner is controlled ON and OFF. For example, when an air conditioner switch is turned ON by a vehicle occupant, the air conditioner control valve  533  is opened to permit the passage of the liquefied gas fuel flowing from the fuel tank  510  toward the expansion valve  532 . Upon turning OFF of the air conditioner switch, the air conditioner control valve  533  is closed to inhibit the passage of the liquefied gas fuel flowing from the fuel tank  510  toward the expansion valve  532 .  
         [0217]    In the expansion valve  532 , the liquefied gas fuel which is in a liquefied state is expanded rapidly into mist of a low temperature and low pressure and the misty fuel flows to an evaporator  535  through a pipe  534 . In the evaporator  535 , a latent heat necessary for evaporation is removed from the ambient air through evaporator fins, whereby the ambient air is cooled. At this time, a blower motor  536  is operated and the air present within the vehicle compartment is cooled thereby. The liquefied gas fuel evaporated in the evaporator  535  passes through a pipe  537  and is fed to the fuel recovery tank  517 .  
         [0218]    A pressure bulb  538  is attached to the pipe  537  and the degree of opening of the expansion valve  532  is adjusted in accordance with the fuel temperature detected by the pressure bulb  538 . More specifically, the degree of opening of the expansion valve  532  becomes large when the fuel temperature is high, while it becomes small when the fuel temperature is low.  
         [0219]    The liquefied gas fuel which has been recovered in a gaseous state into the fuel recovery tank  517  flows through a pipe  539  into a compressor  540 , in which it is sucked and compressed. The liquefied gas fuel having been increased in both temperature and pressure in the compressor  540  passes through a pipe  541  and flows into a condenser  542 . Then, in the condenser  542 , the liquefied gas fuel is cooled with an engine cleaning fan and is liquefied while being removed its condensation latent heat. The fuel thus liquefied flows into a receiver tank  544 , in which it is separated into gas and liquid. Then, only the liquid passes through a pipe  545  and is fed into the fuel tank  510 .  
         [0220]    At an intermediate position of the pipe  545  is provided a check valve  546 , which permits only the flow of fuel advancing from the receiver tank  544  (condenser  542  side) toward the fuel tank  510 . Therefore, for example when the engine is OFF, a reverse flow of the liquefied gas fuel from the interior of the fuel tank  510  to the receiver tank  544  is prevented.  
         [0221]    According to the above construction shown in FIG. 34, in the common rail type fuel injection system, the liquefied gas fuel leaking from the high pressure pump  513 , common rail  515  and fuel injectors  520  is once recovered into the fuel recovery tank  517  and is thereafter liquefied by means of the compressor  540  and the condenser  542 , then is returned to the fuel tank  510 . In this case, the compressor  540  and the condenser  542  not only plays its inherent role of liquefying the refrigerant (liquefied gas fuel) but also fulfills the role of recovering the leakage fuel. Thus, the sharing of the compressor  540  and the condenser  542  can be achieved.  
         [0222]    Since in this embodiment the fuel injection system and the air conditioner share the compressor  540 , the operation of the compressor  540  is kept ON during operation of the engine, but the operation of the air conditioner is turned ON or OFF arbitrarily by the air conditioner control valve  533 . At this time, also in the case where the air conditioner control valve  533  is closed to turn OFF the air conditioner, the foregoing leakage fuel is separately liquefied by the compressor  540  and the condenser  542 .  
         [0223]    According to this embodiment described above in detail there are obtained the following effects.  
         [0224]    Unlike the related art, since the compressor  540  and the condenser  542  are shared by the common rail type fuel injection system and the air conditioner, it is not necessary to use a fuel compressor dedicated to the recovery of fuel. As a result, it is possible to simplify the construction as a fuel supply system and reduce the cost. Of course, also as to the vehicle which carries this system thereon, the cost thereof can be reduced.  
         [0225]    Since there is adopted a construction wherein a liquefied gas fuel is stored in a liquid state within the fuel tank  510  and is fed in the liquid state to the expansion valve  532  in the air conditioner, it is possible to feed the liquefied gas fuel in the liquid state to the expansion valve  532  from just after the start of the engine. That is, although the refrigerant (liquefied gas fuel) usually vaporizes while the engine is OFF, it is no longer required to wait for liquefaction of the refrigerant just after the start of the engine. Consequently, a vehicle compartment cooling effect can be obtained so much earlier.  
         [0226]    Further, since the low pressure pump  511  is disposed within the fuel tank  510 , a pressure drop in the path from the fuel tank  510  to the low pressure pump  511 , the formation of bubbles due to a temperature difference between the fuel tank  510  and the low pressure pump  511 , and a consequent deficiency in suction of the low pressure pump  511 , can be prevented.  
         [0227]    The position for the discharge of leakage fuel from the fuel injection system to the air conditioner side is not limited to the position between the evaporator  535  and the compressor  540 . It may be changed as desired if it is possible to carry out the liquefying process for the leakage fuel and if the construction adopted permits the leakage fuel to be discharged upstream of the condenser  542 .  
         [0228]    Although in this embodiment the compressor  540  is essential to the air conditioner, it is also possible to accomplish the air conditioner without using the compressor  540 . Particularly, in case of using a liquefied gas fuel as refrigerant, the liquefaction of the liquefied gas fuel can be done by only cooling and condensation in the condenser  542  and thus an air conditioner is constituted.  
         [0229]    It is also possible to embody this system without using the fuel recovery tank  517 . In this case, the fuel leaking from the fuel injection system may be discharged directly into a pipe (e.g., the pipe  539 ) laid within the air conditioner.  
         [0230]    Although the fuel injection system in this embodiment is a common rail type fuel injection system, there may be used another type of a fuel injection system. For example, there may be adopted a construction wherein the liquefied gas fuel is pressurized high and is then fed to each fuel injector, using a distribution type fuel injection pump, without using a common rail.  
         [0231]    Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined in the appended claims.