A diesel engine used in a construction machine is required to satisfy various regulations and standards. One of the standards requires contaminants such as nitrogen oxides (NOx) and particulate matters (PM) contained in exhaust gas to be reduced, and this standard may be a major environmental standard together with a regulation in respect to noise when using the construction machine.
In order to satisfy the environmental standard, for example, the Tier-4i exhaust regulation, the present applicant uses a diesel engine to which various means such as an exhaust gas recirculation (EGR) apparatus, and a diesel particulate filter (DPF) apparatus are applied.
Here, the diesel particulate filter (DPF) indicates a filter, which is disposed on a path through which exhaust gas discharged from the diesel engine is discharged, and may trap and filter particulates (soot) that are particulate matters including, for example, soot in a muffler, and when an amount of trapped particulates becomes a predetermined level or more, there are problems in that back pressure becomes higher, and performance of the filter deteriorates.
Therefore, this filter needs a process of arbitrarily removing particulates trapped in the filter periodically or in accordance with the trapped amount, and this is typically referred to as a ‘DPF regeneration’ or ‘combustion removal’.
The regeneration may be classified into passive regeneration and active regeneration in accordance with an implementation method thereof. Particularly, the active regeneration of the DPF refers to a manner in which an operator forcibly drives an engine of the construction machine to discharge high-temperature exhaust gas without substantially performing work, and a small amount of fuel, which is supplied to an exhaust path, causes an exothermic reaction with a diesel oxidation catalyst (DOC), which is also disposed on the exhaust path in advance, based on the temperature of the exhaust gas so as to raise the temperature of the exhaust gas to a higher temperature that is required to combust (regenerate) particulates, thereby combusting particulates trapped in the filter.
Typically, the engine discharges the exhaust gas having a higher temperature when the engine is driven by receiving a load rather than when the engine is in an idle drive state. However, unlike the passive regeneration, in a case of the active regeneration, because the engine is driven in a substantial non-load state (idle state) in a state in which the construction machine is stopped, a considerably long period of time is required to raise a temperature of the exhaust gas up to a predetermined temperature that is needed to enable the exothermic reaction of the DOC. Therefore, for example, a procedure of forcibly controlling a pump needs to be performed so as for the pump to discharge the working fluid so as to produce so-called a ‘non-work load’ in order to apply a load to the engine without performing work.
Meanwhile, recently, a construction machine is being developed which includes an electro-hydraulic pump that is driven by receiving an electronic control signal instead of the existing hydraulic signal. For example, FIG. 1 illustrates an example of a hydraulic circuit diagram of a structure including the electro-hydraulic pump. For reference, in a hydraulic system of FIG. 1, details in respect to elements such as a pilot line through which an operation of an operator is transmitted, a working machine which performs actual work, and the like are omitted.
Referring to FIG. 1, the construction machine includes electro-hydraulic pumps 10a and 10b that are driven by a diesel engine 20, a discharge flow rate of the electro-hydraulic pumps 10a and 10b may be adjusted by receiving an electronic control signal (for example, current signal) that is transmitted from a controller 50, for example, through adjustors 12a and 12b such as an electromagnetic proportional control valve (EPPR). In addition, the working fluid discharged from the electro-hydraulic pumps 10a and 10b is supplied to a plurality of working machines (not illustrated) and the like through a plurality of main control valves (MCV) 30 to drive the working machines. In addition, the diesel engine 20 is controlled by an engine control unit (ECU) 22.
Recently, as illustrated in FIG. 1, in order to improve fuel efficiency and work efficiency, development on a construction machine including a hydraulic circuit having a hermetic structure is being actively conducted. For example, the hydraulic circuit having the hermetic structure includes center bypass cut valves 40a and 40b that correspond to the respective electro-hydraulic pumps 10a and 10b, and a center bypass cut solenoid valve 42 that controls operations of the center bypass cut valves 40a and 40b, and the hydraulic circuit is maintained in a hermetic state in a state in which the center bypass cut valves 40a and 40b are closed.
As such, in a case of the construction machine configured as the hermetic system, because only torque (a function of pressure and a flow rate in the hydraulic pump), which is required by a user, is basically produced, torque generated in the diesel engine in an idle state is theoretically close to “0”.
Therefore, in spite of the hermetic system, in order to perform active regeneration of the DPF in a case of the construction machine having the electro-hydraulic pump, means need to be sought which may produce so-called a non-work load by discharging the working fluid while the electro-hydraulic pump does not drive the working machine.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.