Pressure regulator for gaseous media

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 (P2) 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.

CROSS-REFERENCE TO RELATED APPLICATIONS

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

The present invention concerns a pressure regulator for gaseous media.

BACKGROUND

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.

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

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.

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.

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. 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.

DETAILED DESCRIPTION

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.

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

The control unit1of the pressure regulator, depicted merely schematically inFIG. 1, for a CNG-powered combustion engine is equipped with an electromechanical transducer11controlled by the engine controller (not shown) as its final control element. A piezoelectric actuator in particular proves suitable as an electromechanical transducer11since its length can be very quickly changed in a defined and reproducible manner by application of an electric voltage. The electromechanical transducer11acts on a piston13which is mounted so as to be axially displaceable in a cylindrical housing12and which simultaneously closes off the housing12of the control unit1in a gas-tight manner on the transducer side. A partition15which is provided with an in particular circular through-opening14subdivides the housing12of the control unit1into two cylindrical chambers16/17, with the storage pressure Pin=200-250 bar prevailing in the lower chamber16connected via a high-pressure-resistant supply line18to the natural gas reservoir19, while a lower pressure P2≦Pinis present at the gas outlet20of the upper housing chamber17.

In the non-operated state (piezoelectric actuator11discharged or not activated) the tapered, cone- or disk-shaped head21, serving as a valve, of the tappet22connected to the piston13closes the through-opening14, embodied as a seal seat, of the partition15, with the result that no natural gas can flow from the lower housing chamber16into the upper housing chamber17, which is designated in the following as the working chamber. The tappet head21serving as a valve remains in this position even if the piezoelectric actuator11fails 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.

In the state shown inFIG. 1, the force Fp=Pin×A2+P2×(A1−A2) is exerted onto the piston13and hence also onto the piezoelectric actuator11, where Pinand P2designate the aforementioned chamber pressures, A1the tappet-side surface of the piston13, and A2the surface of the tappet head21on which the pressure is effective. Thus, the tappet head21lifts off from its seal seat and reveals the through-opening14only when the piezoelectric body's change in length enforced by active charging of the piezoelectric actuator11exerts a force satisfying one of the conditions Fpiezo>Fpon the piston13and the piston13and the tappet22fixed thereto move downward in the axial direction.

The cylindrical housing31of the pressure reducer3controlled by the control unit1is subdivided into three chambers35-37by means of a piston32that is guided in a displaceable manner in the axial direction (valve-side surface A3) and a partition34that is again provided with, for example, a circular through-opening33. Depending on the position within the housing31of the piston32closing off the upper chamber35in a gas-tight manner, the tapered, cone- or disk-shaped head38serving as a valve (pressure-effective surface A4) of the tappet39connected to the piston32reveals the through-opening33of the partition34to a greater or lesser degree or completely seals it off. Because the upper housing chamber35of the pressure reducer3is fluidically connected via a supply line40to the working chamber17of the control unit1, the pressure P2also obtains there. The lower housing chamber37of the pressure reducer3is filled with natural gas by the storage unit19via a branch18′ of the supply line18and the chamber pressure is in this way maintained constant at Pin.

A gas pressure Poutestablishes itself in the middle housing chamber36. Said pressure Poutalso obtains in the gas line41which is connected to the gas outlet40of the middle housing chamber36and which is directly connected to the respective injection valve or leads into what is termed a gas manifold.

A throttle2(cross-sectional area D2) connects the working chamber17of the control unit1to the middle housing chamber36of the pressure reducer3or gas line41.

The two sensors42/43measure the storage pressure Pinand the pressure P2at the gas outlet40of the middle housing chamber36and report the respective measured values to the engine controller so that the latter can control the piezoelectric actuator accordingly and adjust the pressure P2or set it to a predefined setpoint value.

The Mode of Operation of the Pressure Regulator

As a result of being charged the piezoelectric actuator11stretches and causes the piston13in the housing12of the control unit1to be moved downward. This movement is followed by the tappet22which is mechanically rigidly connected to the piston13, such that the tappet's head21embodied as a valve lifts off from the seal seat and reveals the through-opening14. Natural gas can now flow from the lower housing chamber16into the working chamber17, with the result that the gas pressure P2increases both in the working chamber17and in the upper housing chamber35of the pressure reducer3connected to the working chamber17. If the gas pressure P2in the housing chamber35exceeds a threshold value that is dependent on the storage pressure Pinand the surfaces A3and A4of the piston32or the tappet head38, the piston32and the tappet39mechanically rigidly connected thereto, together with valve38, move downward. Natural gas can accordingly flow into the middle housing chamber36and via its outlet40into the gas line41. Said gas flow is further reinforced by a configuration-induced smaller gas flow which discharges from the working chamber17of the control unit1via the throttle2. The injection process starts when the pressure Poutdependent on the surfaces A1, A2, D2, A3and A4reaches the setpoint value and the engine controller opens the injection valve.

When the piezoelectric actuator11is discharged, the piston13of the control unit1is pushed upward back into its starting position due to the pressure conditions then obtaining, with the result that the valve21prevents the natural gas from overflowing from the lower housing chamber16into the working chamber17. The dynamics of this closing operation are in this case dependent on the size of the throttle diameter D2. Along with the pressure P2in the working chamber17, the pressure in the upper housing chamber35of the pressure reducer3also drops correspondingly and the valve38closes. The injection process is thus terminated.

The Gas Supply of the Combustion Engine

As shown schematically inFIG. 2, the gas supply of each of the cylinders of the combustion engine50consists for example of a pressure regulator52according toFIG. 1that is fed from the CNG storage tank51and an electromagnetically actuated injection valve53. Additionally required isolation valves and temperature and pressure sensors are not shown. In addition to the various engine components, an engine controller54controls both the injection valve53and the pressure regulator52or its piezoelectric actuator. Since the engine controller54knows 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 valve53assigned to the respective cylinder during a change in load and compensate by means of prior (time T′:=T−dT) adjustment of the gas pressure P2at the engine-side output of the pressure reducer52.

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 inFIG. 3, only a single metering unit60is now used, said metering unit60consisting 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 controller54and supplied to the engine via a throttle55.