EP0080741A1 - Aerodynamic pressure wave machine with exhaust by-pass - Google Patents

Abstract

In a gas-dynamic pressure wave machine with an exhaust gas bypass (so-called waste gate), a flap (12) is provided in the bypass (11), which opens to limit the peak pressure in the internal combustion engine (9) at higher engine speeds. A flap control by means of a pressure cell (14) is provided with a process pressure, for example exhaust gas pressure, as a control variable. For height compensation and temperature compensation, the process pressure is coupled with a constant pressure (vacuum or overpressure) in such a way that the process pressure must be increased by the same amount as the atmospheric pressure decreases. For this purpose, the pressure cell (14) is divided into two chambers (16, 17) separated by a membrane (15), one of which is subjected to the process pressure and the other is kept under constant pressure. The membrane (15) acts on the flap (12) via a linkage (19-23).

Description

The invention relates to a gas dynamic pressure wave machine for charging an internal combustion engine, in which an exhaust gas bypass in the gas housing with a medium-controlled flap connects the high-pressure gas inflow channel to the low-pressure gas outflow channel.

The use of an exhaust gas bypass in small engines for passenger cars charged by means of pressure wave machines - in which the peak pressure is limited and which have a wide speed range - can be quite interesting. Since such engines have an elastic torque, which is imparted by the flat pressure curve over the entire engine speed range, less exhaust gas has to be blown into the exhaust pipe compared to exhaust gas turbocharging and, on the other hand, only has to be blown off at higher engine speeds. As a result, the poorer specific fuel consumption caused by the unused blow-off occurs only in a narrow range, which experience has shown to be rare in passenger cars.

Regulation of the charge air pressure by targeted blowing in a pressure wave machine mentioned at the outset is known from GB-PS 775,271. If the exhaust gas pressure exceeds a predetermined value, a spring-loaded flap arranged in a bypass between the high-pressure gas inflow channel and the low-pressure gas outflow channel opens. Part of the exhaust gas goes through this bypass directly into the exhaust without going through the pressure wave process.

Since this well-known blow-off control only ever works with a fixed overpressure when driving uphill, the bypass opens too early under these conditions, so that the final pressure required for acceleration processes is not reached due to the decreasing air density with increasing altitude.

The invention defined in the characterizing part of claim 1 is therefore based on the object of creating a boost pressure limiting device which is independent of the atmospheric pressure.

The use of a pressure can known per se, the membrane of which is mechanically coupled to the flap to be actuated, is to be regarded as a particularly simple and inexpensive solution.

Similar pressure cans for actuating a bypass valve are known in exhaust gas turbochargers (DE-AS 28 22 207). The fact that the decisive control pressure is present in one chamber on the occasion of the valve stroke, but an atmospheric pressure prevails in the other chamber, makes this arrangement unsuitable for making a height correction.

In order to at least partially recuperate the energy of the bypass flow, pressure wave machines which ensure the low-pressure flushing can postpone a time lag have the gas pocket arranged in the gas housing in the high-pressure gas inflow opening (publication No. CH-T 123 143 of the applicant), this gas pocket is connected to the bypass. This connection is conveniently made behind the flap. If it is designed as a wall hole extending into the gas pocket, the static pressure of the bypass flow is applied to the gas pocket when the flap is open. Greater recovery is achieved in that the connection is designed as an open sampling tube directed into the core flow in the manner of a flow-through probe.

In the drawing, an embodiment of the invention is shown schematically. The single figure shows a development of a cylindrical section halfway up the cells through the rotor and through the adjoining parts of the side parts of the housing.

The basic structure of a pressure wave machine and its exact structure can be found in the already mentioned document CH-T 123 143. For the sake of simplicity, the pressure wave machine shown is shown as a single-cycle machine, which is expressed in that the gas housing 2 and the air housing 3 are provided with only one high-pressure and one low-pressure opening on their sides facing the rotor 1. In order to explain the function of the system more clearly, the flow directions of the working media and the direction of rotation of the pressure wave machine are indicated by arrows.

The hot exhaust gases of the internal combustion engine 9 enter through the high-pressure gas inflow channel 4 into the rotor 1, which is provided with axially straight cells 5 that are open on both sides, expand therein and leave it via the low-pressure gas outflow channel 6 into the exhaust, not shown. Atmospheric fresh air is drawn in on the air side and overflows the low-pressure air inlet duct 7 axially into the rotor 1, is compressed therein and leaves it as charge air via the high-pressure air outlet duct 8 to the motor 9.

To understand the actual, extremely complex gas dynamic pressure wave process, which is not the subject of the invention, reference is made to the already mentioned document CH-T 123 143. The process sequence necessary for understanding the invention is briefly explained below: The cell band consisting of the cells 5 is the development of a cylindrical section of the rotor 1, which moves downward in the direction of the arrow when the latter rotates. The pressure wave processes take place inside the rotor and essentially cause a gas-filled space and an air-filled space to form. In the former, the exhaust gas relaxes and then escapes into the low-pressure gas outflow duct 6, while in the second part of the fresh air drawn in is compressed and pushed out into the high-pressure air outlet duct 8. The remaining fresh air portion is flushed through the rotor into the low-pressure gas discharge channel 6 and thus causes the exhaust gases to exit completely. This rinsing is essential for the process flow and must be maintained under all circumstances. In any case, it must be avoided that exhaust gas remains in the rotor 1 and is supplied to the engine 9 with the charge air in a subsequent cycle. In addition, the purge air cools the cell walls, which are heated up by the hot exhaust gases.

A bypass 11 with a medium-controlled flap 12 is arranged in the web 10 between the high-pressure gas inflow channel 4 and the low-pressure gas outflow channel 6, as is known from GB-PS 775,271. In the present case, this flap 12 is pivotally mounted within the bypass 11 in a pivot point, not specified. As control means for di _P flap actuation, high pressure gas is stoomized via a line 13 removed from the pressure wave process and thus applied to a pressure can 14.

This pressure cell is divided into two chambers 16, 17 by a membrane 15. The membrane 15 cooperates with a compression spring 18 and is connected to the flap 12 via a linkage 19, 20. These elements are only shown schematically. The configuration shown and described below is of course not the simplest and most effective. It was only chosen to clearly explain the principle of the invention.

In the starting position there is a constant pressure in chamber 17, which can be either a partial vacuum, full vacuum or an overpressure. In the equilibrium position of the membrane 15, i.e. if there is only atmospheric pressure in the chamber 16, the bypass flap 12 is closed. During engine operation in the plane, for example at sea level, the membrane 15 is moved to the right against the spring action with increasing exhaust pressure. A very soft spring 18 and only a slight back pressure in the chamber 17 are assumed here, so that the diaphragm movement starts early. Above a certain gas pressure, the so-called response pressure, the driver surface 22 of the sleeve 21 arranged on the connecting rod 19 bears against the end surface 23 of the connecting rod 20 leading to the flap 12. If the exhaust gas pressure is increased further by increasing the engine speed and the diaphragm is moved further to the right, the bypass flap 12 opens.

At high altitudes, for example when driving on mountain pass roads, the performance of the engine decreases due to the low air density. Exhaust gas temperature and smoke, on the other hand, increase. About this rising exhaust gas temperature, which improves the pressure wave process is compensated hhhenbedingte the power loss to a large, but unzureirhend ^p n part.

The use of a bypass adjustment device depending on the ambient pressure without height correction, as is known from DE-AS 28 22 207, would now have a disadvantageous effect. In this known pressure cell, the force in the valve closing direction is lower due to the low external pressure, as a result of which the bypass opens at an even lower control pressure than when operating at sea level. This would result in a lower boost pressure and a drop in performance as with a naturally aspirated engine.

The use of a pressure can according to the invention remedies this, which is first explained in a phase with a closed bypass. The low external pressure at altitude creates a new state of equilibrium by expanding the chamber 17 and thus a membrane movement to the left. As a result, the connecting rod 19 is shifted to the left. In order to permit this movement with the flap 15 closed anyway, the sleeve 21 of the membrane connecting rod 19 slides over the end face 23 of the flap connecting rod 20 without exerting any force.

If the engine is now loaded, the diaphragm 15 and the sleeve 21 are moved to the right with increasing exhaust gas pressure without being in engagement with the flap connecting rod 20. Even the exhaust gas pressure that opens the flap at sea level is not sufficient for this. Only when the engine speed increases further, and thus the boost pressure or exhaust gas pressure increases, does the driving surface 22 stop at the end surface 23. With the stroke of the connecting rod 20 then set in, the flap is actuated in the opening direction.

All the elements involved are dimensioned such that only real height compensation is carried out. The order of magnitude of the displacements is chosen so that the flap 12 always has the same absolute response pressure begins to open. Starting from sea level, this means that the relevant control pressure in the chamber 16 must be increased by the same amount by which the atmospheric pressure decreases with increasing altitude in order to move the membrane 15 into the flap response position.

An advantageous development of the invention is the connection of the bypass 11 to a gas pocket 24, which is also arranged in the web 10 between the high-pressure gas inflow channel 4 and the low-pressure gas outflow channel 6 and is open to the rotor 1. Depending on the machine design, such a gas bag is essential in order to maintain the purging - i.e. the full expulsion of the expanded gases into the exhaust - in the low pressure zone in every operating state. When operating with the bypass closed, this gas pocket draws high-pressure exhaust gas energy through the opening 25 in the web 10. This supply of energy can shift the characteristic diagram of the pressure wave machine and change the swallowing capacity. In the case of bypass operation, it can happen that the supply of the gas pocket with high-pressure exhaust gas is insufficient, which impairs the absolutely necessary low-pressure purging.

This is where the invention comes in, when an appropriately dimensioned proportion of the bypass flow flows into a probe-like sampling tube 26 and is fed into the gas pocket 24 when the flap 12 is open. From there, the energy-rich contents of the pocket reach the already relaxed gas in cells 5 and perform its own function there.

Of course, the invention is not limited to what is shown and described. In deviation from this, the charge air pressure or any other process pressure could be used as a control variable instead of the exhaust gas pressure. Furthermore, the pressure cell could be an actual pressure cylinder in which the described Membrane is replaced by a reciprocating piston. Furthermore, when using a membrane, this could also be designed as a spring. A rubber bladder would also be conceivable as a container for the constant pressure to be stored. The constant pressure can of course also be varied for adaptation purposes, for which purpose the corresponding chamber can be provided with a valve, for example a ball check valve.

In general, there are two basic options when choosing constant pressure. If a high overpressure in the chamber 17 and a very soft spring 18 are used for this, a progressive control pressure / lifting function which is interesting for the flap control is obtained. Other considerations are based on the use of vacuum as a constant pressure and hard spring 18. Here the spring characteristic is of crucial importance. A vacuum can is advantageous in that temperature influences are switched off, which can occur depending on the arrangement of the pressure can in the hot engine compartment. In the case of overpressure cans, these temperatures influence the pressure in the chamber 17, which must be kept constant.

Finally, the bypass 11 does not necessarily have to be arranged in the web 10 of the gas housing 2. It could just as well be accommodated outside of the pressure wave machine in the lines leading to and from the high-pressure gas inflow channel 4, respectively. Guide low pressure gas discharge channel 6.

Claims (3)

1. Gas-dynamic pressure wave machine for charging an internal combustion engine, in which an exhaust gas bypass with a medium-controlled flap connects the high-pressure gas inflow channel to the low-pressure gas outflow channel in the gas housing, characterized in that a pressure socket (14) known per se is provided for actuating the bypass flap (12) which is divided by a movable membrane (15) connected to the flap (12) into two chambers (16, 17), one chamber (16) of which is subjected to a control pressure, and that in the second chamber (17th ) there is a constant pressure which is either higher or lower than the atmospheric pressure. 2. Gas-dynamic pressure wave machine according to claim 1, in which a gas pocket (24) open to the rotor is arranged in the gas housing (2) between high-pressure gas inflow channel (4) and low-pressure gas outflow channel (6), characterized in that the exhaust gas bypass (11) downstream of the flap (12) is connected to the gas pocket (24). 3. Gas dynamic pressure wave machine according to claim 2, characterized in that the gas pocket (24) is connected to the bypass (11) via a removal tube (26) directed into the core flow of the bypass (11).

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