Abstract:
A device for mixing a gaseous fuel into an oxygen-containing gas flow of a gas-powered internal combustion engine includes a housing component having an inlet that connects to a gaseous fuel supply conduit and a slit that opens into an intake pipe. The slit has a longitudinal extension that is oriented approximately perpendicular to the axial direction of the intake pipe. A valve body is movable relative to the housing component. An annular gap between the valve body and an outlet opening of the housing component has a cross-sectional area that varies in accordance with changes in the position of the valve body relative to the housing component. The annular gap determines the flow-through cross-section of a passageway between the inlet and the outlet. Furthermore, a gaseous fuel flow exiting from the slit is directed approximately perpendicular to the axial direction of the intake pipe.

Description:
CROSS-REFERENCE 
     This application is the U.S. National Stage of International Application No. PCT/EP2012/004953 filed on Nov. 30, 2012. 
     TECHNICAL FIELD 
     The invention relates to a gaseous fuel admixing device for a gas-powered internal combustion engine. 
     RELATED ART 
     For a fault-free and low-pollution combustion of gas-powered internal combustion engines, a precise admixing of the gaseous fuel into the air flowing through an intake pipe of the internal combustion engine is required. 
     A gas metering valve configured as a gaseous fuel injection value for the combustion chamber of a reciprocating gas engine is known from AT 502 512 A4 2007-04-15, the valve body of which is actuated by an electromagnet and has a contour such that the cross-sectional area of a gap formed between the valve body and an outlet opening varies linearly with movement of the valve body. 
     A flow valve for controlling the air mass flow-rate is known from DE 34 10 909 A1, the valve body of which has an outer surface or contour such that the cross-sectional area of a gap formed between the valve and an outlet opening progressively increases with movement of the valve body in an opening direction. 
     A gaseous fuel metering valve is described in U.S. Pat. No. 6,508,418 B1, the valve body of which ends in a spherical surface, which abuts on a conically-narrowing seat surface in the closed position. DE 600 25090 T2 describes a gas metering valve configured similar thereto. 
     U.S. Pat. No. 7,621,469 B2 describes a gas metering valve, in which the valve member is formed as a sphere and abuts on a valve seat, which narrows in a spherically-shaped manner, in the closed position. 
     U.S. Pat. No. 6,666,193 B2 describes a gas metering valve, the valve body of which ends in a spherical end surface, the radius of curvature of which is the same as the radius of curvature of an end portion of a seat surface. 
     SUMMARY 
     In one aspect of the present teachings, a gaseous fuel admixing device for a gas-powered internal combustion engine is provided that is capable of supplying a predetermined composition, which is as homogeneous as possible, of the gaseous fuel-air mixture to a combustion chamber of the internal combustion engine. 
     In another aspect of the present teachings, a gaseous fuel admixing device for a gas-powered internal combustion engine preferably includes a housing component that is connectable to an intake pipe of the internal combustion engine, the housing having an inlet for attachment to a gaseous fuel supply conduit and an outlet configured to open into the intake pipe. A valve body is movable relative to the housing component. An annular gap is formed between the valve body and an outlet opening of the housing component. The cross-sectional area of the annular gap preferably depends on (changes in accordance with) the position of the valve body relative to the outlet opening and the annular gap determines the flow-through cross-section of a connection from the inlet to the outlet. The gaseous fuel admixing device is preferably configured such that a gaseous fuel flow exiting from the outlet is directed (ejected or sprayed) approximately perpendicular to the axial direction of the intake pipe. 
     In the inventive gaseous fuel admixing device, since the gaseous fuel-flow flows into the air flow approximately perpendicular to the air flow directed through the intake pipe, a good mixture of the two flows is achieved. 
     According to another aspect of the present teachings, the valve body preferably is linearly and axially movable relative to the outlet opening and the outer contour of the valve body preferably is shaped such that the cross-sectional area of the annular gap formed between the outlet opening and the valve body changes in progressive dependence on the position of the valve body relative to the outlet opening. It is possible with such features of to mix the gaseous fuel, on a need-based manner, to maintain a predetermined mixture ratio, which is precise as possible and which can vary in dependence on (accordance with) the load of the internal combustion engine. 
     According to another aspect of the present teachings, the outlet opening is preferably formed as a slit and the longitudinal extension (direction) of the slit is oriented approximately perpendicular to the axial direction of the intake pipe. With such features, it is achieved that the gaseous fuel flow entering into the intake pipe thoroughly infuses into the flow present in the intake pipe. 
     The invention will be explained in the following with the assistance of schematic drawings of an exemplary embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a section through an inventive gaseous fuel admixing device, cut in a longitudinally middle plane of the intake pipe, 
         FIG. 2  depicts a section through the gaseous fuel admixing device in the region of the inflow of the gaseous fuel into the intake pipe, cut perpendicular to the longitudinal axis of the intake pipe, 
         FIG. 3  depicts a perspective view of the inflow region of the gaseous fuel into the intake pipe in a cut-away intake pipe, 
         FIG. 4  depicts a perspective view of the valve body, and 
         FIG. 5  depicts an example for the dependence of the gaseous fuel flow-rate on the position of the valve body. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a sectional view of an inventive gaseous fuel admixing device, cut in a longitudinal middle plane of an intake pipe  10  of a not-depicted internal combustion engine. The intake pipe  10  can be an intake pipe that leads to a single cylinder of the internal combustion engine or can be an intake manifold, which is connected to plural cylinders. For example, a fresh air flow Φ 1  flows through the intake pipe  10 , which fresh air flow can be aspirated by the internal combustion engine or can be pressurized by a supercharger. The flow Φ 1  can contain only fresh air or can contain, for example, additional exhaust gas, which is fed back. 
     A housing  12  of the gaseous fuel admixing device, which is denoted with  14  as a whole, is affixed to the intake pipe  10 ; for example it is screw fastened to the intake pipe  10 . A guide component  16  is disposed in the housing; a valve body  18  is guided in the guide component  16  in a longitudinally-movable manner, in the depicted example in the vertical direction. A gaseous fuel supply conduit  20  leads into an inner chamber of the housing  12 . The guide component  16  ends in an outlet opening  22  formed in the bottom wall of the housing; a metering end portion  24  of the valve body  18  projects into the outlet opening  22  more or less deep in accordance with its position. According to  FIG. 1 , the outlet opening  22  is formed at the upper end of a flow guiding surface  26 , which connects the outlet opening  22  with an outlet  28  that opens into the intake pipe  10 . 
     An actuator  29 , e.g., a step motor, whose output shaft  30  is screw fastened to the valve body  18 , serves to move the valve body  18 , so that the valve body moves linearly with rotation of the output shaft. The rotational position of the output shaft  30  can be sensed by a rotary position encoder/sensor  32 . 
     Further, an electronic control apparatus  34  is accommodated in the housing  12 , and supplies signals via wires  36 ; such signals may include a load signal, which indicates the position of a not-depicted load controlling element for adjusting the load output) of the internal combustion engine, the output signal of the rotary position encoder  32 , the output signal of an oxygen sensor  38  disposed in the exhaust system, as well as optionally additional signals, such as the temperature of the internal combustion engine, the mass flow of the flow Φ 1  within the intake pipe  10 , the pressure in the intake pipe  10 , etc. The functions of the above-described functional groups are generally known and thus will not be described in further detail. The gaseous fuel supply conduit  20  is connected with a gaseous fuel source, which supplies gaseous fuel to the gaseous fuel supply conduit  20 , preferably at a constant pressure. This gaseous fuel is fed into the intake pipe flow Φ 1  in an amount, which is determined by the position of the valve body  18  relative to the outlet opening  22  and the pressure difference between the pressure in the intake pipe  10  and the pressure of the gaseous fuel. The gaseous fuel is exhausted through the outlet  28  as a gaseous fuel flow Φ 2  approximately perpendicular to the direction of the intake pipe flow Φ 1  and is redirected by the intake pipe flow Φ 1  while mixing therein, so that a mixture flow Φ 3  is supplied to the internal combustion engine. 
     Further details of the inventive gaseous fuel admixing device will be explained with the assistance of the following Figures. 
       FIGS. 2 to 4  show structural details: 
       FIG. 2  shows an enlarged sectional view of the metering end portion  24  of the valve body  18  ( FIG. 1 ) in a sectional view similar to  FIG. 1 , but cut perpendicular to the longitudinal axis of the intake pipe  10 . The metering end portion  24  projects in a vertically movable manner into the outlet opening  22 , which is formed directly in a bottom wall  40  of the housing  12  in the depicted example. The outlet opening  22  has a segment with a circular cylindrical cross-section that transitions via the flow guiding surface  26  into the outlet  28 , which opens into the intake pipe  10 . Depending on the position of the metering end portion  24  relative to the outlet opening  22 , an annular gap  42  having a variable width b indicated by the double arrows is formed, through which the gaseous fuel flows into the intake pipe  10 . The cross-sectional shape of the flow guiding surface  26 , which widens in a funnel-shaped manner in the illustration of  FIG. 2 , transitions from a circular-shaped cross-section (cut perpendicular to the direction of movement of the valve body) into a slit-shaped cross-section in the region of the outlet  28 .  FIG. 3  depicts a perspective view towards the outlet  28  in a cut-away intake pipe  10 , and shows the slit-shaped outlet  28 , as viewed through a hole  44  in the wall of the intake pipe  10 . The longitudinal direction of the slit  28  is perpendicular to the axial direction of the intake pipe  10 , so that gaseous fuel flows into the intake pipe flow Φ 1  ( FIG. 1 ) in the shape of a fan or a flat-spray due to the flow guiding surface  26 , which widens in a plane perpendicular to the axial direction of the intake pipe, wherein substantially the entire cross-section of the intake pipe  10  is encompassed by the gaseous fuel flow Φ 2  and a thoroughly-homogenously mixed mixture flow Φ 3  results, which arrives in the combustion chamber of the not-depicted internal combustion engine. The slit-shaped outlet  28 , together with the flow guiding surface  26 , forms a flat-spray nozzle. 
     The contour or outer surface of the metering end portion  24  of the valve body  18 , which is illustrated in an exemplary manner in  FIG. 4 , is such that the through-flow cross-section formed by the annular gap  42  for the gaseous fuel increases progressively, preferably exponentially, starting from a minimal value in a lower end position of the valve body according to  FIG. 2  to a maximal value, which is defined by the cross-sectional area of the outlet opening  22 . 
       FIG. 5  shows the ratios in an exemplary manner. On the abscissa, the number A of steps is depicted, by which the actuator  29  configured as a stepper motor is actuated, wherein in each step the metering end portion  24  is moved upward in accordance with  FIG. 2  from a lowermost end position. Thus, A indicates the position of the valve body  18  relative to the outlet opening  22  in the axial direction of the outlet opening. The total amount of travel amounts, e.g., to approximately 8 mm. The ordinate indicates the mass flow M of the gaseous fuel flow Φ 2  in kg/s. The mass flow M is proportional to the width b of the annular gap  42 . It is assumed that the mass flow M reaches a maximal value after 1,500 steps. In the embodiment according to  FIG. 5 , the mass flow after 1,000 steps amounts to 43% of the maximal value and after 500 steps 17% of the maximal value. As is apparent, the mass flow M progressively increases with increasing displacement of the valve body, namely during the first 500 steps from a minimal value to 17% of the maximal value, after 500 additional steps by an additional 25% to 43% of the maximal value and after 500 additional steps by 57% to the maximal value. 
     During the controlling or regulation of the admixing of the gaseous fuel flow into the intake pipe flow, the following criteria are to be fulfilled: 
     1. For a precise lambda regulation, i.e. control of the ratio of the mass flow of the intake pipe flow Φ 1  to the mass flow of the gaseous fuel flow Φ 2  such that a predetermined value, which can depend on the operational parameters of the internal combustion engine, is maintained, a high level of control quality, i.e. a small step width, is required. 
     2. The mixture flow Φ 3  or the total mass flow must instantaneously follow as much as possible the load requirements on the internal combustion engine, i.e. the position of the load controlling element, such as a throttle valve disposed in the intake pipe  10  upstream of the outlet  28 , i.e. it must be changeable within a short time between a minimal valve and a maximal value. The gaseous fuel mass flow must follow this total mass flow, i.e. it also must be changeable within a short time from a minimal value to a maximal value. 
     So that the second-mentioned criterion is fulfilled, the step motor can be controlled by the electronic control apparatus  34  with a corresponding rapid change of the load requirement, e.g., within 50 ms it can be moved by 1,500 steps, so that a rapid tuning of the gaseous fuel flow Φ 1  to the intake pipe flow Φ 2 , e.g., the fresh air flow, controlled by the load controlling element, is possible. The changing of the gaseous fuel flow in dependence on the intake pipe flow takes place in a controlled manner, preferably by storing in the electronic control apparatus  34  the dependence of the position of the valve body  18  on the load controlling element or on the output signal of a mass flow measuring apparatus disposed in the intake pipe upstream of the outlet  28 . The actuator  29 , which is preferably configured as a stepper motor, displaces the valve body in accordance with this feed forward control (driver control), wherein the position of the valve body is sensed by the rotary position encoder  32 . Superimposed onto the feed forward control (driver control) of the gaseous fuel flow, a controlling of the position of the valve body  18  preferably takes place in the control apparatus  34  with the assistance of the output signal of the oxygen sensor  38 . If the output signal of the lambda sensor  38  deviates from a target value, which is accessible in the electronic control apparatus  34 , a stepwise adjustment of the valve body  18  takes place such that the deviation returns to zero as much as possible. So that a high level of control quality is achieved, the step width of the stepper motor or actuator  29  during a control operation decreases in the range of larger gaseous fuel mass flows. As is apparent from  FIG. 5 , a constant step width in the range of larger gaseous fuel flows leads to a larger change of the gaseous fuel flow than during small gaseous fuel flows. Therefore, as soon as the gaseous fuel flow Φ 2  amounts to more than 15% of the maximal gaseous fuel flow, the mode of the stepper motor is switched, e.g., from a whole step mode to a half step mode by halving the step width of the stepper motor. In the range of higher gaseous fuel mass flows, e.g., at gaseous fuel mass flows greater than 50% of the maximal flow, it can be switched to a quarter mode by decreasing the step width to a quarter of the step width in the normal mode. In this way, a high level of control quality can be achieved during the control operation. 
     The invention, which was described above in an exemplary manner, can be modified in various ways: 
     The non-linear dependence of the cross-section of the annular gap  42  can also be achieved by the position of the valve body  18  such that the valve body or its metering end portion  24  has a constant cross-section and the outlet opening  22  is formed with a varying cross-section in the axial direction. The flow guiding surface  26  need not be formed directly in the bottom wall  40  of the housing  12 , but rather can be formed by a separate flow guiding part, which ends in the outlet  28 . 
     To actuate the valve body  18 , various actuators could be provided, e.g., pneumatic or hydraulic actuators, which preferably do not necessarily have to operate as stepper actuators. 
     The gaseous fuel admixing device is preferably entirely accommodated in the housing  12  so that it can be mounted on any existing intake pipe, wherein the intake pipe need only be furnished with a hole. The intake pipe need not necessarily have a circular cross-section. 
     The slit forming the outlet need not necessarily be formed on a flow guiding surface that leads from the outlet opening to the slit. 
     With the inventive gaseous fuel admixing device, the following advantages, among others, are achieved: 
     The gaseous fuel can be changed between idling and full throttle with a high dynamic of displacement. 
     Lambda regulation can take place at every operational point with high precision. 
     The combustible gas mixture supplied to the internal combustion engine exhibits a good homogeneity. 
     The device is applicable to various engines in a simple manner, because the adaptation can take place merely by software changes. 
     The device combines, preferably in a simple compact form, the functionalities, gas admixing, gas metering to the fresh air and the gas-/air mixture formation in only one component. 
     REFERENCE NUMBER LIST 
     
         
           10  Intake pipe 
           12  Housing 
           14  Gaseous fuel admixing device 
           16  Guide component 
           18  Valve body 
           20  Gaseous fuel supply conduit 
           22  Outlet opening 
           24  Metering end portion 
           26  Flow guiding surface 
           28  Outlet 
           29  Actuator 
           30  Output shaft 
           32  Rotary position encoder 
           34  Electronic control apparatus 
           36  Wires 
           38  Oxygen sensor 
           40  Bottom wall 
           42  Annular gap 
           44  Hole 
           46  Fan 
         Φ 1  Intake pipe flow 
         Φ 2  Gaseous fuel flow 
         Φ 3  Total flow