The present invention relates to a waste heat utilization system for an internal combustion engine, in particular in a motor vehicle. The invention also relates to a method for operating a waste heat utilization system of this kind.
A waste heat utilization system, which has a waste heat utilization circuit in which a working medium circulates and which contains in succession in the flow direction of the working medium a pumping device for driving the liquid working medium, a vaporizer for vaporizing the working medium, an expansion machine for depressurizing the gaseous working medium and a condenser for condensing the working medium, is disclosed in DE 10 2009 050 068 A1. A pressure reservoir, which contains a balancing volume filled with liquid working medium and which is fluidically connected to the waste heat utilization circuit between the condenser and the pumping device, is also provided. At the same time, the balancing volume is actively adjustable, that is to say adjustable dependent on the current operating state of the waste heat utilization system, by means of an adjusting device. In the known waste heat utilization system, the adjusting device is designed as a pressure regulating device.
A further waste heat utilization system, which is fitted with an active pressure reservoir which can be actuated with the help of a control device, is disclosed in DE 10 2010 054 733 A1.
A further waste heat utilization system with pressure reservoir is disclosed in DE 10 2011 122 436 A1.
In order to improve a waste heat utilization system with regard to the energy yield, with a hermetically sealed working medium, such as with an organic working medium for example, it is necessary to be able to adapt the pressure in the working medium, for example, by means of an active or controllable pressure reservoir, during the operation of the waste heat utilization system. For example, this enables undesirable reduced pressures within the waste heat utilization circuit to be avoided.
The present invention is concerned with the problem of specifying, for a waste heat utilization system of this kind, an improved or at least an alternative embodiment which is distinguished in particular by an active or controllable pressure reservoir, with the help of which the pressure in the working medium can be varied particularly easily.
The invention is based on the general idea of equipping the pressure reservoir with a cylinder which encloses the balancing volume, wherein an adjusting piston, which can be adjusted in its stroke by an actuator, is arranged in the cylinder. As a result of this measure, the pressure reservoir has a comparatively simple construction. Furthermore, adjustable stroke pistons are technically comparatively easy to manage, as a result of which a reliably operating active or controllable pressure reservoir can be provided.
In a waste heat utilization system of this kind, it can further be provided that the pressure reservoir is either fluidically connected to the waste heat utilization circuit between the condenser and the pumping device, or is arranged in the condenser and therefore fluidically connected to the waste heat utilization circuit within the condenser. The latter leads to an extremely compact arrangement.
A development, in which a separating piston, which separates the balancing volume from a gas volume in the cylinder, is arranged in the cylinder in a stroke-adjustable manner, wherein the adjusting piston axially constrains the gas volume, is particularly advantageous. The separating piston and the adjusting piston therefore lie axially opposite one another in the cylinder, wherein between them they axially constrain the gas volume. With this design, a stroke adjustment of the adjusting piston leads directly to a change in the gas volume. As a result, the pressure in the gas volume is changed accordingly, which then leads to a stroke adjustment of the separating piston. The stroke adjustment of the separating piston then leads to a change in the balancing volume and to a change in the pressure in the working medium. In this way, the pressure in the working medium can be changed indirectly by a stroke adjustment of the adjusting piston. As a result of this design, it is possible to significantly reduce the risk of leakages into the environment, as only the gas volume has to be sealed with respect to the environment.
In an advantageous development, the adjusting piston can contain at least one throttle point, through which gas can transfer from the gas volume into a back volume, which is located on a side of the adjusting piston which faces away from the balancing volume. This enables a vaporization function to be integrated into the adjusting piston in order to be able to damp pressure surges.
A method according to the invention for operating a waste heat utilization system of this kind is characterized in that the balancing volume is adjusted depending on the current operating state of the waste heat utilization system. In particular, the operating method can be designed to the effect that reduced pressures in the waste heat utilization circuit are prevented by adjusting the balancing volume. Furthermore, the operating method can preferably be designed to the effect that the expansion capacity of the expansion machine is optimized in order to maximize the energy yield or waste heat recovery.
According to another advantageous embodiment of the waste heat utilization system, this can be equipped with a control device which is electrically coupled to the adjusting device and which is designed or programmed such that it is capable of executing the above-mentioned operating method.
According to an advantageous embodiment, a vaporizer of the waste heat utilization circuit can be designed as a main vaporizer which is coupled to an exhaust gas system of the internal combustion engine in a heat-transferring manner. For example, this main vaporizer can be arranged in the exhaust gas system downstream of a turbine of an exhaust gas turbocharger and/or downstream of an oxidation catalytic converter.
In addition or alternatively, a vaporizer of the waste heat utilization circuit can be designed as an additional vaporizer which is coupled to an exhaust gas recirculation system of the internal combustion engine in a heat-transferring manner. In the case of an additional vaporizer of this kind, an exhaust gas recirculation cooler within the exhaust gas recirculation system can possibly be dispensed with. An exhaust gas recirculation system of this kind enables exhaust gas to be recirculated from an exhaust gas system of the internal combustion engine to a fresh air system of the internal combustion engine. Expediently, in doing so, this exhaust gas recirculation is arranged on the high-pressure side, that is to say downstream of a compressor of the exhaust gas turbocharger and upstream of the turbine of the exhaust gas turbocharger.
Particularly advantageous is an embodiment of the waste heat utilization system in which a recuperation heat exchanger is provided, which serves to pre-heat the liquid high-pressure working medium, that is to say upstream of the vaporizer, and to pre-cool the gaseous low-pressure working medium, that is to say upstream of the condenser. The energetic efficiency of the waste heat utilization system can be improved with the help of a recuperation heat exchanger of this kind.
Further important characteristics and advantages of the invention can be seen from the drawings and from the associated description of the figures based on the drawings.
It is understood that the characteristics stated above and still to be described below can be used not only in the specified combination in each case, but also in other combinations or in their own right without departing from the scope of the present invention.
Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein the same references refer to the same or similar or functionally identical components.
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The internal combustion engine 1 shown here is also equipped with an exhaust gas recirculation system 15 which feeds back exhaust gas from the exhaust gas system 6 to the fresh air system 5. In doing so, the exhaust gas recirculation system 15 is arranged on the high-pressure side. An extraction point 16 of the exhaust gas recirculation system 15 is therefore connected upstream of the turbine 9 and, in the example of
The internal combustion engine 1 is also equipped with a waste heat utilization system 18. This includes a waste heat utilization circuit 19 in which a working medium 20, preferably an organic working medium 20, circulates. In a flow direction 21, indicated by arrows, of the working medium 20 in the waste heat utilization circuit 19, the waste heat utilization system 18 contains in succession in the waste heat utilization circuit 19 a pumping device 22 for driving the liquid working medium. In the example of
Main branch 24 and supplementary branch 25 are brought together at a combining point 29 downstream of the vaporizer 26. This is followed in the flow direction 21 by an expansion machine 30, in which the now gaseous and expediently superheated working medium can be depressurized. In doing so, the expansion machine 30 converts energy of the working medium, in particular enthalpy, into mechanical work, which can then be used further in the form of mechanical work or which can be converted into electrical energy in a generator, for example. A condenser 31, in which the working medium is condensed before it passes to the pumping device 22 once more, is arranged downstream of the expansion machine 30 in the waste heat utilization circuit 19.
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Finally, the waste heat utilization system 18 shown here is equipped with a pressure reservoir 33 which contains a balancing volume 34. The balancing volume 34 is filled with liquid working medium 20. In the example of
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Number | Date | Country | Kind |
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10 2013 021 578.1 | Dec 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/003156 | 11/26/2014 | WO | 00 |