Patent Publication Number: US-11035356-B2

Title: High pressure pump and method for compressing a fluid

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. § 119(a), this application claims priority to German Patent Application No. 102018217644.2, filed on Oct. 15, 2018, the contents of which is hereby incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     This application relates to a high pressure pump and a method for compressing a fluid to an injection system, in particular to a high pressure pump and a method for direct injection type of internal combustion engine. 
     BACKGROUND 
     For internal combustion engines of vehicles, high pressure pumps have been used to pressurize fuel up to 350 bar with a fuel flow of up to 100 liters per hour (L/h) for fuel injection systems. Such a fuel pump is called a plunger pump, and is driven by a camshaft. A feed pressure of about 3.5-5 bar is required to fill a compression chamber in the pump through a digital inlet valve, especially at high engine speed and therewith plunger speed. To increase feed pressure to the level from atmospheric pressure, an additional pump or a pre-supply pump has been used. 
       FIGS. 5A to 5C  show schemes of a prior art high pressure pump  200 . When a plunger or piston  220  moves down (suction stroke), it causes suction of a fluid  206  from an inlet  204  through a digital inlet valve  214  and filling a compression chamber  202 , as shown in  FIG. 5A . After reaching the bottom dead center, the plunger or piston  220  moves up (compression stroke) as shown in  FIG. 5B  and some fluid is forced through the digital inlet valve  214  against the feed pressure of about 5 bar, leading to supply flow pulsation. When the digital inlet valve  214  closes as shown in  FIG. 5C , the plunger or piston  220  compresses the remaining fluid  206  in the compression chamber  202  to a pressure slightly above a rail pressure in a common rail where the fluid  206  is stored for the injection system, and discharges the fluid  206  through an outlet check valve  210  to an outlet  208  until the plunger or piston  220  reaches the top dead center. 
     A periodic fuel flow created by plunger pumping strokes and an actuation of the digital inlet valve causes a periodic pressure pulsation. The periodic pressure pulsation influences a filling behavior of the compression chamber. Therefore, a damper membrane has previously been used to suppress the periodic pressure pulsation. 
     A spring has been used to keep the plunger in contact with a cam lobe even at high frequencies, however the constant and necessary spring preload causes cam drive load, friction, and wear, leading to an additional fuel consumption. 
     A plunger seal has been used to prevent the fuel from leaking to a cam side. However, the plunger seal causes friction and wear of the plunger, leading to fuel pollution or dilution by lubrication oil used in the cam side, which is responsible for engine wear and injector coking. 
     DE 20 2011 107 909 U1 describes a pistonless engine and variable combustion chamber geometry, characterized in that the engine has an elastic chamber jacket in which a bottom plate instead of a usual piston is firmly integrated whereby a friction-free volume change of a closed space is possible. 
     DE 695837 C describes a combustion pressure driven fuel pump comprising a large piston stage and an elastic spring piston. 
     It is an object of the disclosure to achieve an improved pump performance and efficiency in a cost-effective manner, in particular without using a plunger seal, a spring, and a damper membrane. 
     SUMMARY 
     One embodiment of the present disclosure is a combination of a compression chamber and a variable volume chamber in a high pressure pump. This combination allows for a stable supply of a fluid to the compression chamber, improved cam contact and sealing property to prevent fuel pollution or dilution, as well as reduction of feeding pressure for the high pressure pump. 
     According to an embodiment, the variable volume chamber comprises, or consists of a bellows. Thus the variable volume chamber may advantageously expand and shrink like a spring due to the flexibility of its structure. 
     According to an embodiment, the bellows comprises, or is made of, a metal or a plastic material. Metal is advantageous since it renders the bellows sturdy. Plastic is advantageous because it makes lightweight. 
     According to an embodiment, the manifold comprises a conduit, the conduit having a first end fluidically connected to the variable volume chamber and a second end fluidically connected between the inlet check valve and the digital inlet valve. This allows to connect the compression chamber and the variable volume chamber fluidically through the digital inlet valve. 
     According to an embodiment, the manifold comprises at least two separate conduits. This is advantageous for a smooth fluid exchange between the compression chamber and the variable volume chamber through the digital inlet valve. 
     According to an embodiment, the high pressure pump further comprises a safety valve between the compression chamber and the variable volume chamber or between the compression chamber and the manifold configured to control the pressure in the compression chamber to prevent overboost. Therefore, the reliability of the high pressure pump can be improved. 
     According to an embodiment, the high pressure pump further comprises a control unit to provide electrical control of the digital inlet valve. Therefore, one can control the digital inlet valve precisely. 
     According to an embodiment, a method of compressing a fluid is provided. The method comprises the steps of:
         connecting a fluid supply to a compression chamber, the compression chamber having an inlet, an outlet, an inlet check valve and a digital inlet valve, the compression chamber being connected to a variable volume chamber through a manifold and the digital inlet valve,   driving a plunger or piston in a reciprocating motion, and   compressing the fluid in the compression chamber and the variable volume chamber by the plunger or piston such that compressed fluid is discharged from the compression chamber through the outlet. This method allows supplying a fluid to the compression chamber stably, improved cam contact and sealing property, as well as reduction of the necessary feeding pressure for the high pressure pump.       

     According to an embodiment, the method of compressing a fluid further comprises the following steps: providing a safety valve between the compression chamber and the variable volume chamber or between the compression chamber and the manifold, and releasing an overboost into the variable volume chamber or the manifold by the safety valve if the overboost occurs. This allows for preventing an overboost in the compression chamber. 
     According to an embodiment, the method of compressing a fluid further comprises the following step: controlling the digital inlet valve electrically. This allows controlling the digital inlet valve. 
     According to an embodiment, feeding pressure of the fluid supply is less than 1 bar. This allows reducing the power consumption of an additional pump or the pre-supply pump to feed the fluid into the high pressure pump, leading to a reduction of fuel consumption. 
     According to an embodiment of the method of compressing a fluid, the flow rate of the fluid from the supply is less than 100 L/h. This also allows reducing the power consumption of the additional pump or the pre-supply pump to feed the fluid into the high pressure pump, lowering the fuel consumption. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Exemplary aspects are illustrated in the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
         FIGS. 1A, 1B, 1C, 1D, 1E, and 1F  are schematic drawings of one embodiment of a high pressure pump in accordance with an embodiment; 
         FIG. 2  is a schematic drawing of a high pressure pump comprising a safety valve in accordance with an embodiment; 
         FIG. 3  is a schematic drawing of a high pressure pump comprising a control unit in accordance with an embodiment; 
         FIG. 4  is a schematic flow diagram illustrating step of compressing a fluid in accordance with an embodiment; and 
         FIGS. 5A, 5B and 5C  are schematic drawings of a prior art high pressure pump. 
     
    
    
     DETAILED DESCRIPTION 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. Generally, this application is intended to cover any adaptations or variations of the specific embodiments discussed herein. 
     According to a first embodiment, as illustrated in  FIGS. 1A to 1F , a high pressure pump  100  comprises a compression chamber  102  having an inlet  104  for connecting to a fluid supply to intake a fluid  106 , and an outlet  108 , an inlet check valve  112  between the compression chamber  102  and the inlet  104 , a digital inlet valve  114  between the compression chamber  102  and the inlet check valve  112 , a variable volume chamber  116  connected to the compression chamber  102  through a manifold  118  and the digital inlet valve  114 , and a plunger or piston  120  configured to compress the fluid  106  in the compression chamber  102  and the variable volume chamber  116 . 
     The fluid  106  may be a liquid, in particular, a fuel, such as diesel or gasoline or the like. 
       FIG. 1A  shows that opening the digital inlet valve  114 , when the plunger or piston  120  moves down (suction stroke) to the bottom dead center, it causes suction of the fluid  106  through the inlet check valve  112 . 
     As shown in  FIGS. 1B and 1C , when the plunger or piston  120  moves up (compression stroke), the inlet check valve  112  closes and the pressure in the compression chamber  102 , manifold  118  and variable volume chamber  116  increases. Therefore, supply flow pulsation due to a back flow against the feed flow ( FIG. 4B ) can be avoided. 
     When the digital inlet valve  114  closes as shown in  FIG. 1D , the pressure in the manifold  118  and variable volume chamber  116  reaches about 5 bar, for example, and the pressure in the compression chamber  102  reaches slightly above a rail pressure level in the injection system and discharges the fluid  106  through the outlet check valve  110  to the outlet  108  until the plunger or piston  120  reaches the top dead center. 
     When the plunger or piston  120  moves down (suction stroke), the outlet check valve  110  closes and the digital inlet valve  114  opens and about 5 bar, for example, pressurized fluid fills the compression chamber  102 , as shown in  FIG. 1E . Then the suction process begins again to refill the manifold  118  and the variable volume chamber  116  and the compression chamber  102 , as shown in  FIG. 1F . After this, the process of  FIGS. 1B to 1F  as described above is repeated. In this way, reduction of a necessary feeding pressure for the high pressure pump  100  can be achieved. That is, an additional pump or a pre-supply pump to feed the fluid  106  into the high pressure pump  100  may be omitted or the power consumption of the additional pump or the pre-supply pump can be reduced. 
     Advantageously, the bottom part of the plunger or piston  120  may be integrated into the bottom part of the variable volume chamber  116 . This allows for preventing the fluid from leaking to a cam side and/or lubricant from leaking from the cam side into the fluid. 
     In addition, the variable volume chamber  116  allows for improvement of contacting the cam with the bottom part of the variable volume chamber  116 , since the variable volume chamber  116  acts like a spring. Therefore, a spring for the plunger or piston  120  may be omitted. 
     Furthermore, since the variable volume chamber  116  functions as a spring, a periodic pressure pulsation can be suppressed and stabilized. The pulsation is caused by a periodic fluid flow created by plunger or piston  120  pumping strokes and an actuation of the digital inlet valve  114 . Therefore, a damper membrane may be omitted. 
     The variable volume chamber  116  advantageously comprises, or consists of a bellows. In that case, the variable volume chamber  116  expands or shrinks flexibly in accordance with the movement of the plunger or piston  120 . The bellows is made preferably of a metal such as a steel or the like, or a plastic material such as an Aramide, in particular PPTA or the like. This may be advantageous since the bellow can be light in weight. 
     As shown in  FIGS. 1A to 1F , the manifold  118  comprises a conduit  122 , the conduit  122  having a first end  124  fluidically connected to the variable volume chamber  116  and a second end  126  fluidically connected between the inlet check valve  112  and the digital inlet valve  114 . Therefore the compression chamber  102  and the variable volume chamber  116  are fluidically connected through the digital inlet valve  114 . 
     The manifold  118  may comprise at least two separate conduits  122 . This is advantageous for a smooth fluid exchange between the compression chamber  102  and the variable volume chamber  116  through the digital inlet valve  114 . 
     As shown in  FIG. 2 , the pump  100  may further comprise a safety valve  128  preferably between the compression chamber  102  and the variable volume chamber  116 . Alternatively, the safety valve  128  may be connected between the compression chamber  102  and any other part of the low pressure side, e.g. the manifold  118 . If an overboost occurs in the compression chamber  102 , the overboost can be released into the variable volume chamber  116  and the pressure in the compression chamber  102  can be kept within desired pressure levels. Because the variable volume chamber  116  has low pressure of up to 5 bar and spring and/or cushion like features, it may absorb the shock caused by sudden pressure changes. 
     As shown in  FIG. 3 , the pump  100  further comprises a control unit  130  to provide electrical control of the digital inlet valve  114 . This control unit  130  may be an engine control unit. 
       FIG. 4  shows a flow diagram illustrating a method of compressing a fluid  106 , the method comprising connecting S 10  a fluid supply to a compression chamber  102 , the compression chamber  102  having an inlet  104 , an outlet  108 , an inlet check valve  112  and a digital inlet valve  114 . The compression chamber  102  is connected to a variable volume chamber  116  through a manifold  118  and the digital inlet valve  114 . The method further includes driving S 20  a plunger or piston  120  in a reciprocating motion, e.g. into and out of the compression chamber  102 , and compressing S 30  the fluid  106  in the compression chamber  102  and the variable volume chamber  116  by the plunger or piston  120  such that compressed fluid  106  is discharged from the compression chamber  102  through the outlet  108 . The variable volume chamber  116  acts like a low pressure pump by changing the volume in accordance with the movement of the plunger or piston  120 . 
     The method of compressing a fluid  106  may further include providing a safety valve  128  between the compression chamber  102  and the variable volume chamber  116  or between the compression chamber  102  and the manifold  118 , and releasing an overboost into the variable volume chamber  116  or the manifold  118  by the safety valve  128  if the overboost occurs. Therefore overboost in the compression chamber  102  can be prevented and the reliability of the high pressure pump  100  can be improved using the safety valve  128 . 
     The method of compressing a fluid  106  may also include controlling the digital inlet valve  114  electrically. The digital inlet valve  114  may be solenoid valve. 
     In the method of compressing a fluid  106 , feeding pressure of the fluid supply is preferably less than 1 bar. As explained using  FIGS. 1A to 1F , the variable volume chamber  116  needs only low pressure feed. Thus an additional pump or a pre-supply pump to feed the fluid into the high pressure pump  100  can be omitted or the power consumption of the additional pump or the pre-supply pump can be reduced. 
     In the method of compressing a fluid  106 , the flow rate of the fluid from the supply may be less than 100 liters per hour (L/h). The variable volume chamber  116  needs only low pressure feed with low flow rate. Therefore an additional pump or a pre-supply pump to feed the fluid into the high pressure pump  100  may be omitted or the power consumption of the additional pump or the pre-supply pump can be reduced. 
     While a number of exemplary aspects have been discussed above, those of skill in the art will recognize that still further modifications, permutations, additions and sub-combinations thereof of the disclosed features are still possible. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.