Patent Application
20120260651
The present invention relates to a waste gate arrangement for a turbine, a turbine for an exhaust gas turbocharger, an exhaust gas turbocharger, a motor vehicle, and a method for operating such an exhaust gas turbocharger.
DE 10 2004 041 166 A1 describes the known construction of a turbocharger for a motor vehicle, which essentially comprises a radial turbine and a radial compressor, which is arranged in the intake section of the engine and is coupled to the turbine rotor of the radial turbine for conjoint rotation by a turbocharger shaft. During operation, the exhaust gas flow, which has a high kinetic and thermal energy, drives the turbine rotor, which imparts rotation to the compressor impeller through the coupling to the turbocharger shaft. The radial compressor draws in air and compresses it, with the result that there is a correspondingly larger mass of fresh air and hence more oxygen available in the intake section of the engine than with a conventional naturally aspirated engine. There is thus an increase in the mean engine pressure and hence in the engine torque, leading to a higher power output from the engine.
One of the ways of controlling the amount of exhaust gas flowing through the turbine is to insert a “waste gate valve” on the turbine side of the turbocharger. A waste gate valve is a controllable bypass valve. At a set boost pressure on the compressor side, this valve directs some of the hot exhaust gases produced past the turbine and directly into the exhaust. This makes it possible to prevent an excessive rotational speed of the turbocharger and an associated overload of the bearings thereof as well as overshooting of the mechanical and thermal limits of the internal combustion engine.
Control of the amount of exhaust gas flowing through the waste gate valve is accomplished by means of a waste gate flap, for example. The waste gate flap is arranged for conjoint rotation on a waste gate shaft, also referred to as a waste gate spindle, for example, which is rotatably mounted in the turbine housing. The waste gate flap is actuated by way of a linear motion at an actuating lever of the waste gate shaft by means of a pneumatic or electric actuator. This linear motion gives rise to a torque at the waste gate shaft, thereby enabling the waste gate valve to be opened and closed.
Owing to the high exhaust gas temperatures, the waste gate spindle in the turbine housing is typically provided with sliding support in a bushing. Since the bushing and the waste gate spindle have different coefficients of thermal expansion due to their different material properties and since, furthermore, a very wide temperature range has to be covered in the exhaust gas turbocharger, the sliding support between the bushing and the waste gate shaft is subject to play. As a result, there is only point contact between these friction partners, not surface contact. Essentially two bearing locations are formed. One at an end of the sliding contact bushing associated with the outside of the turbine housing and one at an end of the sliding contact bushing remote from the outside of the turbine housing.
Both during the opening and during the closing of the waste gate valve, normal forces resulting from an actuating force of the lever arm and an exhaust gas force acting on the waste gate flap act at these bearing locations. During the closing of the waste gate valve these normal forces are added and cause a relatively high resultant normal force in the sliding contact bushing, leading to very high friction torques in the bearing locations. During the opening of the waste gate valve, the actuator for actuating the lever arm must hold the waste gate valve closed with a certain force to ensure that the waste gate flap is just pushed open by the exhaust gas flowing through the waste gate valve. Although the force required for this is less than during the closing of the waste gate valve, the forces resulting from the actuating force and the exhaust gas force act in the same direction of action of force in the bearing locations and are added. Thus, a not inconsiderable friction torque arises in the bearing locations during the opening of the waste gate valve as well. Since the actuator for actuating the actuating lever must overcome these friction torques, the maximum friction torque to be overcome is critical for the design of the actuator.
In applications involving a pneumatically activated waste gate valve, this has hardly been allowed for hitherto, and the disadvantages, such as a high leakage mass flow owing to an inadequate closing force of the actuator and hence non-optimum operation of the turbocharger at full load in the low engine speed range of the internal combustion engine, have been consciously accepted. In initial production applications for electric actuators for activating the waste gate valve, a very powerful electric actuator has been used to overcome the high friction torques. However, this leads to very high forces when the actuator is cold, and this can therefore lead to damage to the turbocharger. Moreover, the use of a powerful and therefore also large actuating means leads to high costs and a high installation space requirement.
Naturally, the aim is to avoid this.
Given this background, it is the underlying object of the present invention to provide an improved waste gate arrangement for a turbine.
According to the invention, this object is achieved by a waste gate arrangement having the features of patent claim 1 and/or by a turbine having the features of patent claim 10 and/or by an exhaust gas turbocharger having the features of patent claim 11 and/or by a motor vehicle having the features of patent claim 12 and/or by a method having the features of patent claim 13.
Accordingly, the following are provided: A waste gate arrangement for a turbine, particularly for an exhaust gas turbocharger, having a waste gate valve configured for directing exhaust gas past the turbine, having a waste gate shaft having a first bearing location and having a second bearing location, which are used to provide rotatable support for the waste gate shaft, having a lever arm mounted for conjoint rotation on the waste gate shaft and configured for imparting rotation to the waste gate shaft when a lever arm force is applied to the lever arm, and having a waste gate flap mounted for conjoint rotation on the waste gate shaft and controlling an amount of exhaust gas flowing through the waste gate valve and arranged relative to the first and the second bearing location in such a way that a lever arm normal force resulting from the lever arm force and an exhaust gas normal force resulting from an exhaust gas force acting on the waste gate flap have opposite directions of action of force in at least one of the bearing locations during opening and/or closing of the waste gate valve.
A turbine for an exhaust gas turbocharger, in particular for a motor vehicle, having a turbine housing, and having a waste gate arrangement according to the invention, wherein the waste gate valve, the first bearing location and the second bearing location are arranged in the turbine housing.
An exhaust gas turbocharger, in particular for a motor vehicle, having a turbine according to the invention, which has: a turbine rotor arranged in the turbine housing, a compressor having a compressor housing, a compressor impeller arranged in the compressor housing, and a turbocharger shaft, which connects the compressor impeller to the turbine rotor for conjoint rotation.
A motor vehicle having an exhaust gas turbocharger of this kind.
A method for operating an exhaust gas turbocharger which has a waste gate arrangement according to the invention, having a first operating mode, in which the waste gate flap is closed, wherein the lever arm normal force and the exhaust gas normal force at the first bearing location act in opposite directions of action of force and are approximately equal during the closing process, thereby producing a low bearing friction torque at the first bearing location.
The concept underlying the present invention consists then inter alia in that the waste gate shaft has two bearing locations and in that the waste gate flap is arranged on the waste gate shaft in such a way relative to the first and the second bearing location that the lever arm normal force and the corresponding exhaust gas normal force have opposite directions of action of force in at least one of the bearing locations during opening and/or closing of the waste gate valve. This makes it possible for the lever arm normal force and the exhaust gas normal force to cancel each other out at least partially in the bearing location concerned. The friction torque in the corresponding bearing location is thereby significantly reduced.
With the waste gate arrangement according to the invention, it is thus possible to ensure reliable opening and closing of the waste gate valve with an actuating means which is of smaller dimensions and is thus lighter and less costly. Advantageous embodiments and developments of the present invention will emerge from the dependent claims and from the description when taken in conjunction with the figures of the drawing.
In a preferred embodiment of the present invention, the lever arm is arranged at a first end of the waste gate shaft, the second bearing location is arranged at a second end of the waste gate shaft, the first bearing location is arranged between the lever arm and the second bearing location, and the waste gate flap is arranged on the waste gate shaft between the first bearing location and the second bearing location. This is an advantageous way of enabling the entire available length of the waste gate shaft to be used to achieve optimum lever ratios.
In a typical embodiment of the present invention, the waste gate shaft has a larger outside diameter at the first bearing location than at the second bearing location. As a result, the friction torques in the first bearing location are as large as possible during the opening of the waste gate valve. An increase in the friction effect during the opening of the waste gate valve has an advantageous effect on the decoupling of the actuating means from the pulsating gas forces of the exhaust gas. This significantly improves the control characteristic of the waste gate arrangement according to the invention and hence also the control characteristic of an exhaust gas turbocharger having a waste gate arrangement according to the invention.
In another preferred embodiment of the present invention, the waste gate shaft has two individual shafts, which can be inserted axially one inside the other, wherein the first bearing location is arranged on a first individual shaft designed as a hollow shaft, and wherein the second bearing location is arranged on a second individual shaft designed as a solid shaft. This significantly simplifies the production and also the mounting of the waste gate shaft, thereby markedly reducing production costs for the waste gate arrangement according to the invention.
In a particularly preferred embodiment of the present invention, the first and the second bearing location and the waste gate flap are arranged spaced apart in a longitudinal direction of the waste gate shaft. This makes it possible to set advantageous lever ratios, which can be set in such a way that the normal forces resulting from the lever force and the exhaust gas force have opposite directions of action of force and cancel each other out at least partially in at least one bearing location.
In another preferred embodiment of the present invention, the first bearing location, the second bearing location and the waste gate flap are spaced apart in such a way in the longitudinal direction of the waste gate shaft that the lever arm normal force and the exhaust gas normal force cancel each other out at a closing point of the waste gate valve, in which the waste gate valve is completely closed. This advantageously allows the required retention force of the actuating means to be markedly reduced at the closing point of the waste gate valve. As a result, the energy consumption of the actuating means is significantly reduced, thereby increasing the efficiency of an exhaust gas turbocharger having a waste gate arrangement according to the invention.
In an equally preferred embodiment of the present invention, the waste gate flap is coupled to the waste gate shaft by means of an arc-shaped intermediate piece. It is thereby advantageously possible to connect a valve element of the waste gate flap to the intermediate piece without play in a conventional manner by means of a rivet washer from the rear side of the arc-shaped intermediate piece. This makes it possible to manufacture the waste gate arrangement according to the invention in a production unit for known waste gate arrangements without increased outlay in terms of adaptation and costs. As a result, the production costs for the waste gate arrangement according to the invention are reduced.
In an equally preferred embodiment of the present invention, the waste gate flap has a rounded valve element. This ensures reliable sealing of the waste gate valve, thereby reliably preventing leaks of exhaust gas. This increases the efficiency of an exhaust gas turbocharger having a waste gate arrangement according to the invention since the entire amount of exhaust gas is passed through the turbine of the exhaust gas turbocharger when an internal combustion engine is operating at full load at high engine speed.
In a typical embodiment of the present invention, an actuating means, by means of which the lever arm force can be applied to the lever arm, is provided. The actuating means ensures reliable positioning of the waste gate valve in the desired position, and it is thereby possible to set the desired degree of opening of the waste gate valve and hence to ensure the functionality of an exhaust gas turbocharger having a waste gate arrangement according to the invention.
In a preferred embodiment of the present invention, a second operating mode is provided, in which the waste gate flap is completely closed, wherein a closing point of the waste gate flap is chosen in such a way that the lever arm normal force and the exhaust gas normal force cancel each other out in the first bearing location. As a result, it is advantageously possible to reduce the dimensions of the actuating means. The weight, installation space and production costs for the waste gate arrangement according to the invention are thereby reduced.
In another preferred embodiment of the present invention, a third operating mode is provided, in which the waste gate flap is opened, wherein the lever arm normal force and the exhaust gas normal force at the first bearing location during the opening process act in opposite directions of action of force and the exhaust gas normal force is greater than the lever arm normal force, thereby producing a high bearing friction torque at the first bearing location. Decoupling of the actuating means from the pulsating exhaust gas normal forces is advantageously possible by means of a high bearing friction torque during the opening of the waste gate valve. This significantly improves the control characteristic of an exhaust gas turbocharger having a waste gate arrangement according to the invention.
The above embodiments can be combined in any desired manner insofar as this is reasonable.
The present invention is explained in greater detail below with reference to the illustrative embodiments given in the schematic figures of the drawing, in which:
Unless otherwise stated, identical components, elements and features have been provided with the same reference signs in the figures of the drawing.
The operation of the waste gate arrangement 1 according to the invention during closing S of the waste gate valve is explained below.
During the closing of the waste gate valve, the lever arm force 9 is applied to the lever arm, thereby imparting rotation to the waste gate shaft 5. During the closing of the waste gate valve, the exhaust gas flowing through the waste gate valve presses against the valve element 19 and tends to force it out of the valve seat of the waste gate valve. The exhaust gas force 12 thus causes a torque which acts on the waste gate shaft 5 in the opposite direction to a torque resulting from the lever arm force 9. A lever arm normal force 11 resulting from the lever arm force 9 and an exhaust gas normal force 13 resulting from the exhaust gas force 12 and acting counter to the lever arm normal force 11 acts in the first bearing location 6. A lever arm normal force 27 resulting from the lever arm force 9 and an exhaust gas normal force 28 resulting from the exhaust gas force 12 acts in the second bearing location 7. The lever arm normal force 27 and the exhaust gas normal force 28 have the same direction of action of force, for example.
The waste gate flap 10 is arranged on the waste gate shaft 5 between the first and the second bearing location 6, 7 in the longitudinal direction 1 in such a way that the lever arm normal force 11 and the exhaust gas normal force 13 preferably have opposite directions of action of force in the first bearing location 6 and cancel each other out at least partially. The lever arm normal force 11 and the exhaust gas normal force 13 preferably cancel each other out completely at a closing point of the waste gate valve, at which the waste gate valve is completely sealed by means of the valve element 19. By virtue of the fact that the lever arm normal force 11 and the exhaust gas normal force 13 cancel each other out at least partially at the first bearing location 6, the friction torques in the first bearing location 6 resulting from a bearing normal force representing a resultant of forces 11 and 13 is small. As a result, an actuating means for adjusting the waste gate shaft 5 can be given smaller dimensions.
The lever arm force 9 can be applied to the lever arm 8 by the actuating means 20 via the coupling 31. The application of the lever arm force 9 to the lever arm 8 imparts rotation to the waste gate shaft 5. In this way, the waste gate valve can be closed or opened. The engine controller 30 transmits the control command for opening or closing the waste gate valve to the actuating means 20 via the data line 29, depending on the operating state of the internal combustion engine.
The operation of the waste gate arrangement 1 according to the invention during opening O of the waste gate valve is explained below.
During the opening O of the waste gate valve, the exhaust gas force 12 presses against the waste gate flap 10 in such a way that the waste gate flap 10 is just pushed open. This means that the actuating means must apply a lever arm force 9 via the lever arm which just allows the exhaust gas to push open the waste gate flap 10. As a result, the lever arm normal forces 11 and 27 at the first and the second bearing location, respectively, are smaller than the exhaust gas normal forces 13 and 28 in the first and the second bearing location, respectively. At the first bearing location, the lever arm normal force 11 and the exhaust gas normal force 13 act in opposite directions and cancel each other out at least partially. Owing to the fact that the lever arm normal force 11 and the exhaust gas normal force 13 do not cancel each other out completely during opening O, a higher friction torque is produced in the first bearing location in comparison with the closing of the waste gate valve. As a result, the actuating means is advantageously decoupled from the generally pulsating exhaust gas force 12, resulting in a significant improvement in the control characteristic of a turbine of an exhaust gas turbocharger having a waste gate arrangement according to the invention.
Since there are virtually no bearing normal forces acting at the first bearing location 6 during the closing of the waste gate valve as described above because the lever arm normal force and the exhaust gas normal force in the first bearing location cancel each other out almost completely, the large diameter D of the first bearing location 6 has virtually no effect on the friction torques which arise during closing, which the actuating means would have to overcome in addition to the torque resulting from the exhaust gas force.
In the second bearing location 7, the effect of friction is minimized by means of a shaft diameter d which is as small as possible.
If, on the other hand, the waste gate valve is opened, the bearing normal force in the first bearing location 6 rises and generates a large friction torque owing to the large shaft diameter D. As a result, the actuating means is advantageously decoupled from the generally pulsating exhaust gas force during the opening of the waste gate valve, thereby allowing a significant improvement in the control characteristic of a waste gate arrangement 1 of this kind.
where:
ΣMzBΣMzB is the sum of the torques about the z axis around point B,
Fbar is the lever arm force, 9, and
Fgas is the exhaust gas force, 12.
where:
ΣMzAΣMzA the sum of the torques about the z axis around point A,
Fbar is the lever arm force, 9, and Fgas is the exhaust gas force, 12.
With the torque equilibrium about the z axis ΣMzAΣMzA and the torque equilibrium about the z axis ΣMzBΣMzB, the optimum lever ratio is obtained, at which the normal the resulting in the first bearing location 6 from the lever arm force 9 and the exhaust gas force 12 cancel each other out completely, and the resultant bearing normal force 34 is thus equal to zero:
With this lever ratio, a minimum friction torque is produced in the first bearing location 6 during the closing of the waste gate valve.
Owing to a reduction in the friction effect during the closing of the waste gate flap, it is possible to select a smaller and hence less costly actuating means since the maximum torque required to close the waste gate flap falls.
Increasing the friction effect during the opening of the waste gate valve has an advantageous effect on the decoupling of the actuating means from the generally pulsating forces of the exhaust gas. During the opening of the waste gate valve, the waste gate flap is just pushed open by the exhaust gas. The actuating means therefore does not have to supply a high torque during opening.
Through appropriate support for the waste gate shaft and appropriate lever ratios and shaft diameters in the first and the second bearing location, the waste gate arrangement according to the invention can thus be modified in such a way that the friction torques during the closing of the waste gate valve are as far as possible equally small and are as large as possible during the opening of the waste gate valve. This enables the actuating means to be given smaller dimensions, resulting in a fall in the procurement costs thereof, the required installation space and the energy consumption.
An internal combustion engine 39 having a plurality of cylinders 40 is coupled in terms of fluid flow by an exhaust line 41 to a turbine rotor 22 of a turbine 2, said rotor being arranged in a turbine housing 21. The waste gate valve 4 having the waste gate flap 10 forms a bypass around the turbine 2 for the exhaust gas. The turbine rotor 22 is connected to a compressor impeller 25 for conjoint rotation by a turbocharger shaft 26. The compressor impeller 25 is arranged in a compressor housing 24 of a compressor 23 of an exhaust gas turbocharger 3. The compressor impeller 25 is coupled to the internal combustion engine 39 in terms of fluid flow by an intake section 38.
During the operation of the internal combustion engine 39 with the exhaust gas turbocharger 3, the internal combustion engine 39 supplies the turbine rotor 22 with exhaust gas via the exhaust line 41. The turbine rotor 22 lowers the enthalpy of the exhaust gas, and the kinetic and thermal energy of the exhaust gas is converted into rotational energy.
The rotational energy is transmitted to the compressor impeller 25 by the turbocharger shaft 26. The compressor impeller 25 draws in fresh air, compresses it and feeds the compressed fresh air to the internal combustion engine 39 via the intake section 38.
By virtue of the fact that there is more oxygen in the compressed air volume per unit volume, more fuel can be burnt in the internal combustion engine 39 per unit of air volume, thereby increasing the power output of the internal combustion engine 39. Depending on the operating state of the internal combustion engine 39, exhaust gas can be directed past the turbine 2 by means of the waste gate valve 4, e.g. at a constant high speed of a motor vehicle having an internal combustion engine 39 with an exhaust gas turbocharger 3 at full load and high engine speeds. Directing some of the exhaust gas past the turbine 2 reliably prevents overloading of the internal combustion engine 39. By virtue of the fact that the exhaust gas turbocharger 3 has a waste gate arrangement according to the invention, the dimensions of the actuating means required for the adjustment of the waste gate flap 10 can be reduced, as described above. The weight, installation space, production costs and energy consumption of an internal combustion engine 39 having an exhaust gas turbocharger 3 with a waste gate arrangement according to the invention are thereby reduced.
The materials, numerical data and dimensions presented are to be taken as illustrative and serve merely to explain the embodiments and developments of the present invention.
The indicated waste gate arrangement for a turbine, the turbine for an exhaust gas turbocharger and the exhaust gas turbocharger having a turbine can be used to particular advantage in the motor vehicle sector and, in this sector, can preferably be used for passenger vehicles, e.g. with diesel or spark ignition engines, but can also be used in any other turbocharger applications, if required.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 048 125.7 | Oct 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/064069 | 9/23/2010 | WO | 00 | 6/26/2012 |
