Patent Application
20140033704
The present invention relates to a construction vehicle, in particular, a landfill compactor (landfill construction), also known as refuse compactor, or a road milling machine (road construction), having a main drive comprising at least one internal combustion engine by means of which at least part of the operating power needed to run the construction vehicle is provided.
Such construction vehicles typically always comprise an engine, in particular, an internal combustion engine, for traction and also for driving working implements such as milling drums, conveyors, hydraulic pumps, compactors, etc., mounted on the construction vehicle. The internal combustion engine produces off gas, resulting from the fuel combustion process, and emits this into the environment. To this end, an exhaust system is provided for the purpose of conducting the off gases generated during the combustion process from the internal combustion engine to the outside environment. As a rule, this off gas has a high temperature when it leaves the construction vehicle or the engine. Energy in the form of heat energy is thus discharged into the environment. As a rule, the energy present in the off gas is not utilized. In modern construction vehicles powered by internal combustion engines, approximately 30% or more of the energy supplied escapes unused in the form of hot off gases.
For economic as well as environmental reasons, this release of unused energy in the form of waste heat into the environment is not ideal. Furthermore, the requirements regarding CO2 emissions and the fuel consumption of construction vehicles are becoming increasingly stricter.
It is an object of the present invention to provide a construction vehicle showing improvements in terms of fuel consumption, in which the waste heat from driving engines, in particular, internal combustion engines, can be recycled into the power flow of the construction vehicle.
One aspect of the present invention involves a construction vehicle having an energy converter specifically designed to convert off gas heat energy coming from the internal combustion engine into mechanical kinetic energy. The heat energy contained in the off gases can thus be utilized as energy for powering the construction vehicle itself and/or the working implements of the construction vehicle. This improves the efficiency of the construction vehicle and is conducive to a reduction in power consumption. Another aspect is that, according to one embodiment of the present invention, this principle is to be applied only to a certain type of construction machines, especially those which are typically operated with high engine loads or with a high share of high load or full load intervals of the internal combustion engine. This particularly refers to construction machines which are continuously operated in relatively high load ranges and are accordingly designed for long operation intervals in high load ranges, as is the case especially for construction machines for ground processing such as landfill compactors or road milling machines. High load range particularly refers to the range in which at least 50% of the maximum available motor performance is used for operating the construction machine.
The fundamental principle of a currently relevant energy converter resides in its capacity to capture heat energy from the off gases and then recycle it in a utilizable form as mechanical energy. To this end, the energy converter comprises, in a thermal circuit in which a heat transfer fluid such as water is passed through a circuit having a high pressure side and a low pressure side, a heat exchanger, by means of which heat from the off gas of the internal combustion engine can be transferred to a heat transfer fluid. The heat exchanger is integrated in the exhaust line or exhaust system of the internal combustion engine, wherein use can be made of a number of different configuration principles. For instance, parts of the heat exchanger can be installed directly in the stream of off gas for achieving the most directly possible transfer of heat from the off gas to the heat exchanger. Particularly, as regards retrofitting, however, it has been found to be advantageous when the heat exchanger is installed in the construction vehicle such that it surrounds or at least partially surrounds off gas conducting elements, ideally in direct contact therewith. It has been shown that when the heat exchanger is disposed in a region of the exhaust line in which the off gas conducted therethrough during normal operation and, in particular, during operation of the internal combustion engine at the rated power has an off gas temperature of at least 250° C. and, more particularly, of at least 300° C. The term “exhaust line” is used to designate the means employed for conducting the off gases generated by fuel combustion from the internal combustion engine or from the engine block per se to the environment of the construction vehicle by means of, say, suitable pipelines. The heat exchanger comprises a fluid inlet and a fluid outlet, and the fluid passing through the heat exchanger vaporizes in the heat exchanger due to the heat energy uptake.
Another component of the energy converter is an expansion machine which communicates with the heat exchanger for fluid transportation and by means of which mechanical energy can be generated from the heat energy as the heat transfer medium expands and cools. Such an expansion machine can comprise expansion chambers such as are found in piston/cylinder combinations, in which the expansion of the heat transfer fluid in the piston/cylinder chamber ultimately gives rise to mechanical movement of the piston, as is the case, for example, with a piston expander. Instead of such a displacement machine, the expansion machine may alternatively be a fluid flow engine, in particular, a turbine, for example.
In order to achieve a directional fluid circuit within the energy converter, a pump is provided for the purpose of conveying the heat transfer medium from the heat exchanger to the expansion machine. In principle, the pump can be disposed at virtually any point in the fluid circuit, but it has been found to be particularly preferable to position it immediately upstream of the heat exchanger, as regarded in the direction of flow of the fluid.
A high heat transfer efficiency can be achieved when a condenser is interposed between the expansion machine and the heat exchanger, more particularly between the expansion machine and the pump, in the direction of fluid flow through the thermal circuit. The purpose of the condenser is to liquefy the gaseous heat transfer medium down-stream of the expansion machine. Use can be made of a number of various arrangements for cooling the condenser. Preference is given to the integration of the condenser in an engine coolant circuit, by way of example. The temperature thereof typically ranges from a minimum of 85° C. to a maximum of 110° C. The advantage of this arrangement is that the condenser in the energy converter can be included in a cooling circuit that is generally already present in construction vehicles, which results in a very cost-effective implementation of the present invention. In order to improve the heat energy transfer a step further, it is preferred, in an alternative embodiment, to integrate the condenser in a separate cooling circuit comprising, in particular, a pipe system, a pump, and heat sink elements. In particular, a low-temperature cooling circuit has been found to be ideal. The feature that particularly distinguishes a low-temperature cooling circuit is that it is cooled down to a level in the order of 10 K above the ambient temperature, in other words to 55° C. in the case of an ambient temperature of 45° C. Particular preference is given to an extended utilization of the cooling circuit, more particularly, the low-temperature cooling circuit, for cooling the charge air for the internal combustion engine, by which means the cooling circuit in this embodiment assumes a dual function consisting of “condenser cooling” and “charge air cooling”.
The focus of the present invention is therefore on the use of a thermodynamic cycle in which energy can be drawn from the exhaust line of the construction vehicle and fed back to the construction vehicle elsewhere as mechanical energy. Particularly good results are obtained when the energy converter operates according to the Rankine cycle principle. For an explanation of the fundamentals of this thermodynamic cycle, reference is made to pages D22 and D23 of the 21st edition of DUBBEL, Handbuch fur den Maschinenbau (DUBBEL, Manual of Mechanical Engineering). Essential components are a fluid vaporizer, an expansion machine such as, for example, a fluid flow engine, especially a turbine, or a displacement machine, especially a piston expander, a condenser and a pump, which are connected in a fluid circuit. According to the method of operation, in a first step fluid is vaporized and superheated in the heat exchanger by the supply of off gas heat from the internal combustion engine. The subsequent conversion into mechanical energy is achieved through subsequent expansion of the fluid in the expansion machine, for example, a turbine or a piston expander. The fluid is then condensed and finally pumped through the circuit back to the heat exchanger.
According to the present invention, the construction machine has an internal combustion engine with a motor power rating of more than 200 kW. This performance class of internal combustion engines provides optimal results in terms of economic efficiency and utilization of the energy recovery process. The motor power rating is determined in accordance with ISO 3046-1, which is, in its entirety, incorporated herein by reference.
Preferred aspects of the present invention relate, in particular, to the specific integration of the energy converter in the construction vehicle. For example, coupling of a power take-off of the internal combustion engine to the expansion machine has been found to be advantageous. A drive torque provided by the expansion machine can thus be coupled into the power take-off and utilized. The internal combustion engine and the expansion machine are thus more or less connected in parallel as a drive train. The drive energy of the expansion machine is thus readily implemented without having to configure an additional drive train for the expansion machine. Additionally, a supplementary transmission can be interposed between the expansion machine and the power take-off in order to adapt the output speed of the expansion machine to the speed of the power take-off.
In addition, there are other possible variants regarding the connection of the pump of the energy converter. In order to provide pumping power, a pump drive is required. Preference is given to an arrangement of the pump such that it can be driven by the power take-off. This is achieved, for example, directly via the output shaft of the power take-off or via the supplementary transmission. With this arrangement, a separate drive for the pump is not required. A less complex and therefore more reliable construction vehicle can thus be produced. Furthermore, a more compact arrangement arises, whereby the dimensions of the construction vehicle can be reduced or space for additional working implements be provided.
To operate, for example, onboard monitoring and control systems, lighting equipment, and electric motors for traction and/or for driving working implements, modern construction vehicles, such as, in particular, road milling machines and landfill compactors, frequently show a high consumption of electrical energy. Hence it is advantageous when the energy recovered by the energy converter is available to the construction vehicle as electrical energy. This is preferably achieved by an aspect of the present invention in which the expansion machine is drive-coupled to a generator and drives the latter for the purpose of generating electrical energy.
The electrical energy generated by the generator can also be used, for example, to power the construction vehicle. Specifically for such embodiments, it is ideal when the construction vehicle comprises an electric motor coupled to the internal combustion engine via a power take-off thereof, the electric motor being drivable with the energy generated by the generator. For example, the electric motor is rotatably coupled via its output shaft to the power take-off and thereby applies its drive energy to the power take-off. The energy generated by the expansion machine can thus be simply decoupled, spatially, from the energy input into the power take-off by arranging the generator and the electric motor so as to be disposed spatially apart from each another. Furthermore, extended possibilities in terms of control technology arise, for example, for the purpose of controlling the speed of the electric motor without the use of an additional transmission mechanism.
In particular, it is preferred to interpose a storage unit for electrical energy between the generator and the electric motor. The storage unit comprises, for example, a rectifier and a battery. The energy generated by the generator can thus be stored temporarily and used when needed by the electric motor.
In principle, the basic energy conditions for operating the embodiment of the present invention involving an energy converter can vary over a wide spectrum, wherein optimum energy recovery results are achieved by preferentially operating within specific operating parameters. Preference is given to operation of the energy converter within a range in which an off gas stream of at least 25% of the off gas stream available at the rated output of the internal combustion engine is available. In this context, the off gas stream indicates the mass of off gas of the combustion engine to be discharged or being discharged within a determined period of time measured in mass per time. For example, in a development, provision can be made for the construction vehicle to have a control mechanism that controls the operating performance of the internal combustion engine in such a way that the latter is operated as far as possible within a range that is also optimal for energy recovery. To this end, said control mechanism can monitor certain parameters such as the off gas temperature and/or the operating performance of the internal combustion engine, in particular, and it can regulate, for example, the operation of the internal combustion engine and/or of the energy converter. The control mechanism is ideally part of an energy management system of the construction vehicle, which in addition to energy recovery, monitors and regulates other optimization strategies for reducing the energy requirement of the construction vehicle.
Optimum results with the use of the present energy recovery system are achieved, in particular, with such construction vehicles that provide ideal basic energy conditions for the operation of the energy converter. Thus the construction vehicle is preferably a landfill compactor, a ground milling machine, in particular, a road milling machine, a recycler, a stabilizer or surface miner, or a road paver. In the context of the present invention, preference is therefore given to utilization of the energy recovery system disclosed herein particularly for these types of construction vehicle. Generic examples are the landfill compactors having the type designations BC 672 RB-3 and BC 772 RB-3, which are offered and distributed by the applicant. Self-propelled landfill compactors of this type are characterized by padfoot drums and a clearing shield for processing waste placed on the ground. Generic road milling machines are, for example, offered and distributed by the applicant under type designations BM 1000/30-2, BM 1200/30-2 and BM 2000/30-2. For an example of the fundamental structure and functioning of such road milling machines, reference is made to WO 2013072066 A1. With respect to their respective drive device, landfill compactors and road milling machines are configured for high shares of high load up to full load operation. In this context, full load operation means the maximum performance of the internal combustion engine running at the corresponding speed.
The present invention will be explained in more detail below with reference to exemplary embodiments and to the appending drawings, in which:
Like components shown in the figures are designated by like reference signs. Not each instance of a component is specifically denoted in all figures.
The expansion machine 11, which, in particular, can be a turbine or a piston expander, is part of the energy converter 13, which converts heat energy from the off gases of the internal combustion engine 3 to mechanical energy and utilizes it, via the power take-off 9, on the working implements of the construction vehicle 1, e.g., the traction drive and/or the milling drum 8. On the exhaust line 7 there is provided a heat exchanger 15, which is helically wound around a region of the exhaust line 7 near the engine in which the off gas temperature under the aforementioned conditions is at least 250° C. The purpose of the heat exchanger 15 is to transfer heat energy from the off gases of the internal combustion engine 1 to a heat transfer fluid (e.g., water), which is fed through a circuit within the energy converter 13 in the fluid flow direction “b”. A pump 17 inserted in the fluid circuit 20 forces the heat exchanger fluid via a conduit system of the fluid circuit 20 to the heat exchanger 15 so that the heat exchanger fluid can absorb heat energy from the off gases in the exhaust line and is thus heated and, depending on the embodiment, vaporized and superheated. This side of the fluid circuit between the pump 17 and the expansion machine 11 is the high pressure side of the fluid circuit. The heat transfer fluid coming from the heat exchanger 15 is conducted to the expansion machine 11. The expansion machine 11 operates with, for example, turbine elements, which enable the energy of the compressed heated heat transfer medium expanding in the expansion machine 11 to be converted to mechanical kinetic energy. Recirculation of the heat transfer fluid cooled in the expansion machine 11 back to the pump 17 takes place on the low pressure side via a condenser 19, which is integrated in, for example, a cooling package of the construction vehicle 1, as illustrated in more detail in
In the embodiments shown in
Finally,
Finally, the purpose of
While the present invention has been illustrated by description of various embodiments and while those embodiments have been described in considerable detail, it is not the intention of Applicant to restrict or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of Applicants' invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 015 267.1 | Jul 2012 | DE | national |
The present application claims priority under 35 U.S.C. §119 of German Patent Application No. 10 2012 015 267.1, filed Jul. 31, 2012, the disclosure of which is hereby incorporated herein by reference in its entirety.
