Abstract:
A pressure regulator can be used particularly in a CNG-operated motor vehicle as an electronically controlled pressure reducer for maintaining the gas pressure constant on the injection valve used for filling the respective cylinder. The pressure regulator is composed of a control unit ( 1 ), a pressure reducer ( 3 ) that is controlled by the control unit ( 1 ), and a throttle ( 2 ) which connects the gas outlets ( 20, 40 ) of the working chamber ( 17 ) of the control unit ( 1 ) and the pressure reducer ( 3 ). A piezoelectric actuator ( 11 ) which affects the valve ( 21, 22 ) of an overflow device ( 14 ) makes it possible to specifically modify the gas pressure (P 2 ) in the working chamber ( 17 ) of the control unit ( 1 ) and simultaneously influence the position of the valve ( 38, 39 ) of the overflow device ( 33 ) of the pressure reducer ( 3 ), thus allowing the output pressure (Pout) of the pressure reducer ( 3 ) to be adjusted to a predefined desired value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2007/053373 filed Apr. 5, 2007, which designates the United States of America, and claims priority to German Application No. 10 2006 019 404.7 filed Apr. 24, 2006, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention concerns a pressure regulator for gaseous media. 
       BACKGROUND 
       [0003]    Natural gas in particular comes into consideration as an environmentally acceptable and affordable alternative to diesel or gasoline fuel. In order to be able to carry the natural gas serving as fuel in sufficient quantity in a motor vehicle, the gas is compressed to approximately 10-200 bar, depending on gas quantity and temperature, and stored in a pressurized tank. The storage pressure is thus considerably higher than the operating pressure of the injection valves filling each of the cylinders of the engine. The fuel supply of a motor vehicle powered by Compressed Natural Gas (CNG) is therefore equipped with a pressure reducer or pressure regulator, as known for example from DE 195 24 413, U.S. Pat. No. 5,771,857 or U.S. Pat. No. 6,003,543, which is disposed between the gas reservoir and the injection valve and which lowers the storage pressure amounting to up to 200 bar to a preset value of typically 8 bar. 
         [0004]    If a very great amount of natural gas flows into the cylinders of the combustion engine due to an abrupt change in load, the pressure in the supply line supplying the injection valve with natural gas temporarily drops below the desired setpoint pressure, since the pressure regulator reacts to this drop in pressure only after a time delay. This response has a disadvantageous effect on the desired driving dynamics of the motor vehicle. Efforts are therefore made to keep the location of the gas line between the pressure reducer/regulator and the assigned injection valve as small as possible. In practice, however, this can only be realized to a limited extent since the installation of the pressure reducer/regulator in proximity to the injection valve poses considerable design engineering problems. In addition, the squeezing together of the two components leads to a corresponding lengthening of the storage-side, high-pressure-resistant and consequently comparatively expensive gas line. 
       SUMMARY 
       [0005]    A pressure regulator for gaseous media can be provided whose output-side pressure level can be varied comparatively quickly over a wide range or can be set to a predefined value. 
         [0006]    According to an embodiment, a pressure regulator for gaseous media may comprise a control unit and a pressure reducer controlled by the control unit, a first housing chamber of the control unit which is connected to a storage unit and to a second housing chamber of the control unit via a first overflow device with a variable cross-section, the storage unit containing a pressurized gaseous medium, —a first housing chamber of the pressure reducer connected to the storage unit and a second overflow device with a variable cross-section connected to a second housing chamber of the pressure reducer,—a gas outlet of the second housing chamber of the pressure reducer leading indirectly or directly into a gas line,—a third housing chamber of the pressure reducer fluidically connected to a gas outlet of the second housing chamber of the control unit, and a throttle unit connected to the gas outlet of the second housing chamber of the control unit on the gas inlet side and to the gas line on the gas outlet side. 
         [0007]    According to a further embodiment, the housing chambers of the control unit may have a common first partition provided with a first gas through-opening and a first closing element sealing off the first gas through-opening in a non-operated position is guided in a displaceable manner relative to the first gas through-opening. According to a further embodiment, the first closing element may be secured to an outer wall of the second housing chamber of the control unit, and the outer wall may be guided in an axially displaceable manner. According to a further embodiment, the pressure regulator may comprise an electromechanical transducer displacing the first closing element or the outer wall of the second housing chamber in the axial direction. According to a further embodiment, the pressure regulator may comprise a piezoelectric, magnetorestrictive or electrostrictive transducer. According to a further embodiment, the first and second housing chambers of the pressure reducer may have a common second partition provided with a second gas through-opening and that a second closing element sealing off the second gas through-opening in a non-operated position is guided in a displaceable manner relative to the second gas through-opening. According to a further embodiment, the second closing element may be secured to a partition which is common to the second and third housing chambers of the pressure reducer and may be guided in an axially displaceable manner. According to a further embodiment, the housing chambers of at least one of the control unit and the pressure reducer may be in each case embodied cylindrically and the outer wall of the second housing chamber of at least one of the control unit and the common partition of the second and third housing chambers of the pressure reducer have the form of a piston. 
         [0000]    According to a further embodiment, at least one of the first and second gas through-opening can be embodied as a seal seat and that at least one of the first and second closing element may have a disk-shaped, cone-shaped or tapered valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]    The invention is explained in more detail with reference to drawings, in which: 
           [0009]      FIG. 1  shows the schematic structure of a pressure regulator according to an embodiment for a CNG-powered combustion engine, and 
           [0010]      FIGS. 2 and 3 : show two variants of the gas supply for a CNG-powered combustion engine. 
       
    
    
     DETAILED DESCRIPTION  
       [0011]    The pressure regulator according to various embodiments can be used in particular in a CNG-powered vehicle as an electronically controllable pressure reducer for maintaining the system pressure at the injection valve constant or, in conjunction with a motor-actuated nozzle or injection valve, be used as an electronically controlled metering unit for gaseous media. It is therefore possible to realize the function of the pressure regulator and that of the injection valve in a single, compactly designed unit controlled by the engine controller. 
         [0012]    According to various embodiments, the pressure at the output of the pressure reducer or, as the case may be, a mass flow can be controllably varied since the control unit effecting the change in state contains, as its final control element, an electromechanical transducer that responds very quickly to electrical signals and is controlled for example by an engine controller. 
       The Structure of the Pressure Regulator 
       [0013]    The control unit  1  of the pressure regulator, depicted merely schematically in  FIG. 1 , for a CNG-powered combustion engine is equipped with an electromechanical transducer  11  controlled by the engine controller (not shown) as its final control element. A piezoelectric actuator in particular proves suitable as an electromechanical transducer  11  since its length can be very quickly changed in a defined and reproducible manner by application of an electric voltage. The electromechanical transducer  11  acts on a piston  13  which is mounted so as to be axially displaceable in a cylindrical housing  12  and which simultaneously closes off the housing  12  of the control unit  1  in a gas-tight manner on the transducer side. A partition  15  which is provided with an in particular circular through-opening  14  subdivides the housing  12  of the control unit  1  into two cylindrical chambers  16 / 17 , with the storage pressure P in =200-250 bar prevailing in the lower chamber  16  connected via a high-pressure-resistant supply line  18  to the natural gas reservoir  19 , while a lower pressure P 2 &lt;P in  is present at the gas outlet  20  of the upper housing chamber  17 . 
         [0014]    In the non-operated state (piezoelectric actuator  11  discharged or not activated) the tapered, cone- or disk-shaped head  21 , serving as a valve, of the tappet  22  connected to the piston  13  closes the through-opening  14 , embodied as a seal seat, of the partition  15 , with the result that no natural gas can flow from the lower housing chamber  16  into the upper housing chamber  17 , which is designated in the following as the working chamber. The tappet head  21  serving as a valve remains in this position even if the piezoelectric actuator  11  fails due to a fault or if it should no longer be controllable for other reasons. This behavior ensures that the pressure regulator remains closed (“normally off”) for safety reasons in the event of a malfunction. 
         [0015]    In the state shown in  FIG. 1 , the force F p =P in ×A2+P2×(A 1 -A 2 ) is exerted onto the piston  13  and hence also onto the piezoelectric actuator  11 , where P in  and P 2  designate the aforementioned chamber pressures, A 1  the tappet-side surface of the piston  13 , and A 2  the surface of the tappet head  21  on which the pressure is effective. Thus, the tappet head  21  lifts off from its seal seat and reveals the through-opening  14  only when the piezoelectric body&#39;s change in length enforced by active charging of the piezoelectric actuator  11  exerts a force satisfying one of the conditions F piezo &gt;F p  on the piston  13  and the piston  13  and the tappet  22  fixed thereto move downward in the axial direction. 
         [0016]    The cylindrical housing  31  of the pressure reducer  3  controlled by the control unit  1  is subdivided into three chambers  35 - 37  by means of a piston  32  that is guided in a displaceable manner in the axial direction (valve-side surface A 3 ) and a partition  34  that is again provided with, for example, a circular through-opening  33 . Depending on the position within the housing  31  of the piston  32  closing off the upper chamber  35  in a gas-tight manner, the tapered, cone- or disk-shaped head  38  serving as a valve (pressure-effective surface A 4 ) of the tappet  39  connected to the piston  32  reveals the through-opening  33  of the partition  34  to a greater or lesser degree or completely seals it off. Because the upper housing chamber  35  of the pressure reducer  3  is fluidically connected via a supply line  40  to the working chamber  17  of the control unit  1 , the pressure P 2  also obtains there. The lower housing chamber  37  of the pressure reducer  3  is filled with natural gas by the storage unit  19  via a branch  18 ′ of the supply line  18  and the chamber pressure is in this way maintained constant at P in . 
         [0017]    A gas pressure P out  establishes itself in the middle housing chamber  36 . Said pressure P out  also obtains in the gas line  41  which is connected to the gas outlet  40  of the middle housing chamber  36  and which is directly connected to the respective injection valve or leads into what is termed a gas manifold. 
         [0018]    A throttle  2  (cross-sectional area D 2 ) connects the working chamber  17  of the control unit  1  to the middle housing chamber  36  of the pressure reducer  3  or gas line  41 . 
         [0019]    The two sensors  42 / 43  measure the storage pressure P in  and the pressure P 2  at the gas outlet  40  of the middle housing chamber  36  and report the respective measured values to the engine controller so that the latter can control the piezoelectric actuator accordingly and adjust the pressure P 2  or set it to a predefined setpoint value. 
       The Mode of Operation of the Pressure Regulator 
       [0020]    As a result of being charged the piezoelectric actuator  11  stretches and causes the piston  13  in the housing  12  of the control unit  1  to be moved downward. This movement is followed by the tappet  22  which is mechanically rigidly connected to the piston  13 , such that the tappet&#39;s head  21  embodied as a valve lifts off from the seal seat and reveals the through-opening  14 . Natural gas can now flow from the lower housing chamber  16  into the working chamber  17 , with the result that the gas pressure P 2  increases both in the working chamber  17  and in the upper housing chamber  35  of the pressure reducer  3  connected to the working chamber  17 . If the gas pressure P 2  in the housing chamber  35  exceeds a threshold value that is dependent on the storage pressure P in  and the surfaces A 3  and A 4  of the piston  32  or the tappet head  38 , the piston  32  and the tappet  39  mechanically rigidly connected thereto, together with valve  38 , move downward. Natural gas can accordingly flow into the middle housing chamber  36  and via its outlet  40  into the gas line  41 . Said gas flow is further reinforced by a configuration-induced smaller gas flow which discharges from the working chamber  17  of the control unit  1  via the throttle  2 . The injection process starts when the pressure P out  dependent on the surfaces A 1 , A 2 , D 2 , A 3  and A 4  reaches the setpoint value and the engine controller opens the injection valve. 
         [0021]    When the piezoelectric actuator  11  is discharged, the piston  13  of the control unit  1  is pushed upward back into its starting position due to the pressure conditions then obtaining, with the result that the valve  21  prevents the natural gas from overflowing from the lower housing chamber  16  into the working chamber  17 . The dynamics of this closing operation are in this case dependent on the size of the throttle diameter D 2 . Along with the pressure P 2  in the working chamber  17 , the pressure in the upper housing chamber  35  of the pressure reducer  3  also drops correspondingly and the valve  38  closes. The injection process is thus terminated. 
       The Gas Supply of the Combustion Engine 
       [0022]    As shown schematically in  FIG. 2 , the gas supply of each of the cylinders of the combustion engine  50  consists for example of a pressure regulator  52  according to  FIG. 1  that is fed from the CNG storage tank  51  and an electromagnetically actuated injection valve  53 . 
         [0000]    Additionally required isolation valves and temperature and pressure sensors are not shown. In addition to the various engine components, an engine controller  54  controls both the injection valve  53  and the pressure regulator  52  or its piezoelectric actuator. Since the engine controller  54  knows all the parameters determining the engine power and hence also the injection process, it is also able to calculate in advance (time T) the pressure changes occurring at the injection valve  53  assigned to the respective cylinder during a change in load and compensate by means of prior (time T′:=T-dT) adjustment of the gas pressure P 2  at the engine-side output of the pressure reducer  52 . 
         [0023]    The gas supply of the combustion engine can be considerably simplified by dispensing with the separate filling of the individual cylinders. The natural gas is therefore no longer injected into the intake pipe of the respective cylinder, in other words injected separately, but is admixed with the aspirated air already in the plenum of the intake manifold. In a system of this kind, as shown schematically in  FIG. 3 , only a single metering unit  60  is now used, said metering unit  60  consisting of the above-described pressure regulator and a nozzle fed by the pressure regulator and actuated by means of stepper or servo motors. By means of this unit which combines the functions of the pressure regulator and those of the injection valve, a controllable mass flow can be generated under the control of the engine controller  54  and supplied to the engine via a throttle  55 .