Method for Supplying an Internal Combustion Engine With Fuel and a Fuel Supply System for Performing the Method

This application discloses subject matter generally related to the subject matter disclosed in my co-pending application Ser. No. 420,972, filed Sept. 21, 1982, both applications being commonly assigned.

The present invention relates to a method for supplying an internal combustion engine with liquefied petroleum gas (LPG) as fuel, and to a fuel supply system for an internal combustion engine which supplies the LPG to the engine.

A fuel supply system for blowing in LPG is already known, in which a metering of the vaporized LPG is effected in accordance with the air throughput in the intake manifold by means of a pressure measurement in a venturi. The pressure in the venturi varies with the square of the flow velocity, so that a desired metering of a quantity of LPG which is at a linear ratio with the aspirated air quantity cannot be made. Also, only a rough adaptation of the LPG-air mixture to the various operating states of the internal combustion engine can be made with the known apparatus, resulting in an increased consumption of LPG, reduced output and unfavorable exhaust gases. In metering the vaporized LPG, the danger also exists that oily components dissolved in the liquid LPG may be deposited as oily residues on the metering valve after the LPG has evaporated and cause errors in metering.

It is an object of the present invention to provide a method for supplying an internal combustion engine with LPG according to which the LPG is itself used for cooling purposes, and to a corresponding fuel supply system that is not subject to the disadvantages noted above.

According to the method aspect of the present invention, the pressure of the LPG is maintained above its vapor pressure and is cooled by means of metered LPG. The fuel supply system for achieving the above includes a metering valve, a heat exchanger and a pressure generating assembly. The pressure generating assembly maintains the LPG at a pressure above its vapor pressure upstream of the metering valve. The LPG metered is at least partially evaporated and within the heat exchanger serves to cool the LPG flowing to the upstream side of the metering valve. The two flows are therefore directed in opposition within the heat exchanger.

The method and apparatus according to the present invention have the advantage over the prior art that without first forming vapor bubbles, precise metering of the quantity of LPG is effected in accordance with operating characteristics of the engine, so that with the lowest possible LPG consumption and low toxic emissions, the greatest possible output is attained. It is additionally advantageous that because of the vaporization of the LPG effected in the intake manifold, the aspirated air is cooled; the result is that the cylinders are filled to a greater extent and the mixture has a higher octane value, producing an improvement in output and a reduction in the tendency to knocking.

The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawing.

The single FIGURE of the drawing shows an exemplary embodiment of the invention in simplified form, and the invention is described in greater detail below.

In the fuel supply system for LPG shown in the drawing, the air required for combustion flows downstream of an air filter (not shown) in the direction of the arrow via an intake manifold section 1 into a conical section 2, in which an air flow rate meter 3 is disposed, and further through an elastically deformable section 4 and a section 5 via a throttle valve 6 to an intake manifold section 7. From the intake manifold section 7, the air flows to one or more cylinders 8 of an internal combustion engine, for example a mixture-compressing internal combustion engine, either with externally supplied ignition or with self-ignition. The air flow rate meter 3 is, for example, a baffle valve 3 disposed transversely with respect to the flow direction, which moves within the conical section 2 of the intake manifold in accordance with an approximately linear function, for example, of the quantity of air flowing through the intake manifold. By means of a constant restoring force engaging the air flow rate meter 3 and a constant air pressure prevailing upstream of the air flow rate meter, the pressure prevailing between the air flow rate meter 3 and the throttle valve 6 likewise remains constant. The air flow rate meter 3 controls a metering valve 10. A pivot lever 11 connected with the air flow rate meter transmits the adjusting movement of the air flow rate meter 3. The pivot lever 11 is supported in common with a correction lever 12 on a pivot pin 13, and upon its pivoting movement it actuates a movable valve element, embodied as a metering piston 14, of the metering valve 10. The desired fuel-air mixture can be corrected by a mixture regulating screw 17 disposed between the pivot lever 11 and the correction lever 12.

The metering piston 14 is slidably disposed in a guide bore 25 of the metering valve housing 26 and is provided with an annular groove 27. Remote from the pivot lever 11, the annular groove 27 is limited by an axial limiting surface 28 acting as a control surface, which upon an axial movement of the metering piston 14 opens a metering opening 29 to a greater or lesser extent toward the annular groove 27. The metering opening 29 is embodied in the wall of the guide bore 25, for instance in the form of a slit.

The supply of LPG fuel is effected from an LPG tank 35, which is embodied as a specially constructed pressure container and which, when filled, contains LPG at a pressure of approximately 10 to 15 bar.

By means of a pressure generating assembly in the form of a pump 36, which is preferably disposed in the LPG tank 35, the LPG is pumped via a filter 37 and a blocking valve 38 into a supply line 39. The blocking valve 38 and the filter 37 may likewise be advantageously disposed within the LPG tank 35. The blocking valve 38 interrupts the supply line 39 when the system is shut off. The pump 36 pumps the LPG into the supply line 39 at a pressure, for example, 5 bar above the vapor pressure of the LPG. A pressure regulating assembly 40 in the supply line 39, for example, a pressure regulator of known design, regulates a predetermined pressure in the supply line 39 which, for example, is 4 bar above the vapor pressure. The pressure regulator 40 may be disposed outside the LPG tank 35 or, as indicated by dashed lines at 40', inside the LPG tank 35. The LPG in the supply line 39 is carried upstream of the metering valve 10 and into a heat exchanger 42, through which it flows countercurrent to the LPG metered at the metering valve 10 and is thus cooled by the metered LPG which is at least partially evaporating.

By means of the pressure regulation above the vapor pressure and the additional cooling in the heat exchanger 42, it is assured that the LPG at the metering valve 10 will remain in the liquid state, even at a higher ambient temperature, and pressure changes caused by changes in speed will not occur in the system caused by changes in speed until the desired evaporation takes place, such pressure differences would otherwise cause an unstable formation of vapor bubbles. The LPG traveling through the supply line 39 into the annular groove 27 of the metering piston 14 is capable of flowing to a greater or lesser extent, depending upon the axial position of the control face 28, via the metering opening 29 into an injection chamber 44 of a regulating valve 45. In this injection chamber 44, a valve seat 47 cooperating with a regulating valve diaphragm 46 and a regulating valve spring 48 urging the regulating valve diaphragm 46 in the opening direction of the regulating valve 45 are disposed. The regulating valve diaphragm 46 divides the injection chamber 44 from a control chamber 49, which communicates with the supply line 39, for example, via the annular groove 27 of the metering piston 14. By means of the regulating valve 45, a constant pressure difference is maintained at the metering opening 29, regardless of the quantity of LPG metered at the metering valve 29. The metered LPG flowing out via the valve seat 47 of the regulating valve 45 passes by way of a connecting line 51 into the heat exchanger 42, where it can flow via an evaporation nozzle 52 into an injection line 53, with at least partial evaporation and simultaneous cooling of the LPG flowing via the supply line 39. By means of the injection line 53, the LPG is carried for example to the intake manifold section 5 and then blown into the intake manifold section 5 via one or more nozzles 54 upstream of the throttle valve 6.

The annular groove 27 of the metering piston 14, remote from the control surface 28, is limited by a limiting surface 56. A compensation step 57 is embodied on the metering piston 14 oriented toward the air flow rate meter 3, and the size of the annular surface of the compensation step 57 is equal to that of the limiting surface 56. The annular surface of the compensation step 57 on one end defines a compensation chamber 58 embodied within the guide bore 25. The chamber 58 communicates via an intersecting line 59 with a return flow line 60 leading to the LPG tank 35. As a result, the vapor pressure of the LPG, which varies with the ambient temperature, is prevented from influencing the position of the metering piston 14.

In order to generate the restoring force exerted on the metering piston 14, and thus on the air flow rate meter 3, LPG is again used. To this end, a control pressure line 63 branches off from the supply line 39 via an uncoupling throttle 62. A pressure chamber 65 communicates via a damping throttle 64 with the control pressure line 63, the pressure chamber being embodied in the guide bore 25 of the metering piston 14, and the metering piston 14 protrudes into this pressure chamber 65 with its end surface 66 remote from the air flow rate meter 3. In order to adapt the LPG-air mixture to operating characteristics of the engine, the pressure in the control pressure line 63 and thus the restoring force exerted on the metering piston 14 and the air flow rate meter 3 are variable. To this end, a pressure control valve 68 is disposed in the control pressure line 63, being triggerable by operating characteristics such as temperature, rpm, throttle valve position, exhaust gas composition, and others and influencing the pressure in the control pressure line 63 in order to adapt the mixture. The pressure control valve 68 may be electromagnetically actuable, or it may be embodied as described by way of example below and shown in the drawing. The pressure control valve 68 is embodied as a flat seat valve, having a fixed valve seat 69 which protrudes into a return flow chamber 70 and by way of which the control pressure line 63 discharges into the return flow chamber 70. A valve diaphragm 71, which separates the return flow chamber 70 from a vacuum chamber 72, cooperates with the fixed valve seat 69 and communicates with a vacuum line 73 leading to the intake manifold section 7 downstream of the throttle valve 6. The valve diaphragm 71 is connected via a coupling member 74 with a compensating diaphragm 75, which divides the vacuum chamber 72 from a compensating chamber 76. Both the return flow chamber 70 and the compensating chamber 76 communicate with the return flow line 60 leading to the LPG tank 35. The compensating diaphragm 75 serves to compensate for influence of the LPG vapor pressure on the valve diaphragm 71. To this end, it is necessary for the valve surface of the valve diaphragm 71 oriented toward the return flow chamber 70 to be of equal size with the face of the compensating diaphragm 75 oriented toward the compensating chamber 76; the diaphragm surfaces oriented toward the vacuum chamber 72 should likewise be of equal size. In a closing direction of the pressure control valve 68 a valve spring 80 communicates with the valve membrane 71 via a spring disk 78, a valve pin 79 and the coupling element 74. The valve spring 80 is displaced between the spring disc 78 and means supported by a fixed housing element 81.

At temperatures below an engine operating temperature of approximately 80.degree. C., the closing force transmitted onto the pressure control valve 68 by the valve pin 79 can act counter to an element which functions in accordance with temperature and takes the form of a bimetallic spring 82, one end of which rests on the spring disk 78 during the warmup phase of the engine, and the other end of which is secured to a bolt 83 pressed into the housing of the pressure control valve 68. An electrical heating element 84 may be mounted on the bimetallic spring 82 and supplied with current beginning with engine ignition. The pressure control valve 68 furthermore has a control diaphragm 85, which separates the vacuum chamber 72 from an atmospheric chamber 86 in which atmospheric pressure prevails. The control diaphragm 85 is engaged by a spring plate 87 on which one end of a control spring 88 is supported. The other end of the control spring 88 engages the spring plate 78. The control spring 88 extends parallel to and is coaxial with the valve spring 80. Movement of the control diaphragm 85 is limitable in that the spring plate 87 can come to rest on contact 81 in one movement direction and on a stop 89 in the opposite movement direction.

The mode of operation of the system is as follows:

Upon starting of the engine, the blocking valve 38 is opened and the LPG is pumped to the metering valve 10 by means of the pump 36 by way of the supply line 39 and the heat exchanger 42. Upon starting, the engine aspirates air via the intake manifold 1, by means of which the air flow rate meter 3 undergoes a certain deflection out of its position of rest. In accordance with the deflection of the air flow rate meter 3, the metering piston 14 is displaced as well via the lever 11. The control surface 28 of the metering piston 4 opens the metering opening 29 to a greater or lesser extent toward the annular groove 27 in accordance with the position of the metering piston 14, so that an LPG quantity is metered at the metering valve in accordance with the aspirated air quantity ascertained by the air flow meter 3, and this quantity of LPG is carried by means of the injection line 53, for example to intake manifold section 5, and is blown into the intake manifold section 5 by way of one or more nozzles 54 upstream of the throttle valve 6. In order to control a larger quantity of mixture during engine warmup, a bypass 91 which bypasses the throttle valve 6 is provided at the intake manifold sections 5, 7; the cross section of the bypass 91 is controlled in accordance with temperature in a known manner by a supplementary mixture valve 92 during the warmup phase of the engine.

The direct connection between the air flow rate meter 3 and the metering piston 14 effects a predetermined ratio between the aspirated quantity and the metered LPG quantity. In order to attain a further enrichment of the mixture supplied to the engine during the warmup phase of the engine, a lesser pressure can be controlled by the pressure control valve 68 in the pressure chamber 65, so that the restoring force exerted on the air flow rate meter 3 and the metering piston 14 is reduced, and a larger quantity of LPG is metered and blown into the intake manifold by way of the nozzle 54. To this end, the spring plate 78 of the pressure control valve 68 is engaged by the bimetallic spring 82 during the warmup phase of the engine such that the valve spring 80 and the control spring 88 are relieved, and the valve diaphragm 71 lifts to a greater extent from the valve seat 69. As a result the pressure in the control pressure line 63 and in the pressure chamber 65 decreases.

After the warmup phase of the engine has elapsed, that is, after the bimetallic spring 82 has been heated by the electrical heating element 84, the bimetallic spring 82 bends away from the spring plate 78 and is disengaged from the spring plate 78 so that the spring forces of the valve spring 80 and the control spring 88 become fully effective, and a higher pressure results in the control pressure line 63. This causes a leaning down of the mixture supplied to the engine. A leaning of the mixture of this kind is desirable when the engine is being operated in the partial-load range. In the partial-load range of the engine, the vacuum in the intake tube section 7 and thus, via the vacuum line 73 in the vacuum chamber 72 of the pressure control valve 68 is so great that the pressure force of the atmospheric air in the atmospheric chamber 86 is sufficient to cause the control diaphragm 85 to come to rest on the fixed housing element 81, counter to the force of the control spring 88. Now if at full load the vacuum drops or the absolute pressure in the intake manifold 7 downstream of the throttle valve 6 increases, then an increased absolute pressure also becomes effective in the vacuum chamber 72 via the vacuum line 73. This greater absolute pressure, engaging the control diaphragm 85, moves the diaphragm 85 toward the stop 89, thus relieving the control spring 88, and the valve diaphragm 71 opens the valve seat 69 to a greater extent so that the pressure in the control pressure line 63 and in the pressure chamber 65 is reduced. This causes an enrichment of the mixture by way of an increased metered quantity of LPG. In the same manner, if there is a sudden acceleration of the engine, the sudden opening of the throttle valve 6 effects a pressure increase in the vacuum line 73, which causes an enrichment of the mixture just as is the case at full load.

The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other embodiments and variants thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.