Abstract:
The purpose of the present invention is to provide a DPF travel-time regeneration control system of stably raising the temperature even during travel and capable of decreasing the frequency of DPF regeneration when the vehicle is stopped. In this control system, if the DPF ( 5 ) needs to be regenerated, the vehicle is traveling on cruise control, and the exhaust temperature detected by an exhaust temperature sensor ( 11 ) is higher than a threshold value, then fuel is injected into the exhaust pipe by a fuel injection means ( 7 ), and if the exhaust temperature is lower than the threshold value, the exhaust temperature is raised by operating the exhaust brake without injecting fuel into the exhaust pipe.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to technology for regenerating a diesel particulate filter (OFF) by injecting fuel into an exhaust pipe in a diesel engine equipped vehicle during travel of the vehicle. 
       BACKGROUND ART 
       [0002]    As DPF regeneration technologies in a diesel engine equipped vehicle, technology for raising an exhaust temperature by post injection (fuel injection using a delayed injection timing for raising a exhaust temperature) into an engine cylinder using an injector and technology for raising a temperature by directly injecting fuel into an exhaust pipe are well known. 
         [0003]    However, the former (the post injection into the engine cylinder using the injector) has a problem of dilution of an engine lubricating oil (so-called “oil dilution.”) caused by injection of the fuel into the cylinder. 
         [0004]    On the other hand, the latter (direct injection of the fuel into the exhaust pipe) has a difficulty in stably increasing an exhaust temperature due to a fluctuation of a load during travel, and there is a problem that the OFF regeneration can be carried out only when a vehicle is stopped. 
         [0005]    As the prior art, technology concerning the DPF regeneration is also suggested (refer to Patent Literature 1 and Patent Literature 2), and technology for detecting stoppage of a vehicle and raising a temperature with the use of an exhaust brake is disclosed, for example (refer to Patent Literature 2). 
         [0006]    However, both the prior arts (Patent Literature 1 and Patent Literature 2) do not disclose DPF regeneration technology for stably raising an exhaust temperature during travel. 
       CITATION LIST 
     Patent Literatures 
       [0007]    Patent Literature 1: Japanese Patent Application Non-examined Publication Gazette No. 2011-111043 (JPA 2011-111040) 
         [0008]    Patent Literature 2: Japanese Patent Application Non-examined Publication Gazette No. 2005-282545 (JPA 2005-282545) 
       SUMMARY OF INVENTION 
     Problem be Solved by the Present Invention 
       [0009]    In view of the above-described problem of the prior arts, it is an object of the present invention to provide a DPF regeneration system, and a DPF regeneration method capable of stably raising an exhaust temperature and regenerating a DPF even during travel of a vehicle. 
       Solution to Problem 
       [0010]    There is provided a DPF regeneration system according to the present. invention, the (travel-time) DPF regeneration system based on in-exhaust-pipe fuel injection in a diesel engine equipped vehicle, comprising: 
         [0011]    an operation device (an auto cruise operation switch  13 ) that enables a vehicle to travel on cruise control, 
         [0012]    an exhaust brake ( 6 ) and a fuel injection means ( 7 ) being disposed to the exhaust pipe ( 3 ), 
         [0013]    a DPF ( 5 ) being disposed in a region on, the downstream side of the fuel injection means ( 7 ), 
         [0014]    an exhaust temperature sensor ( 11 ) being disposed in a region on the upstream side of the DPF ( 5 ), 
         [0015]    pressure sensors ( 12 ,  12 ) being disposed on the upstream side and the-downstream side of the DPF ( 5 ), and 
         [0016]    a control unit ( 10 ) that controls the exhaust brake ( 6 ) and the fuel injection means ( 7 ) in response to detection signals from the exhaust temperature sensor ( 11 ) and the pressure sensors ( 12 ) being provided, 
         [0017]    Wherein the control unit ( 10 ) has: 
         [0018]    a function to inject fuel into the exhaust pipe ( 3 ) by the fuel injection means ( 7 ) when a differential pressure between the upstream side and the downstream side of the DPF ( 5 ) measured by the pressure sensors ( 12 ,  12 ) is equal to or more than a threshold value, the vehicle is traveling on cruise control (the auto cruise operation. switch  13  is operated), and an exhaust temperature detected by the exhaust temperature sensor ( 11 ) is higher than a threshold value; and 
         [0019]    a function to operate (without injecting fuel into he exhaust pipe ( 3 )) the exhaust brake (to raise the exhaust temperature) when the differential pressure is equal to or more than the threshold value and die vehicle is traveling on cruise control but the exhaust temperature is lower than the threshold value. 
         [0020]    Further, there is provided. a DPF regeneration method according to the present invention, the DPF regeneration method being based on in-exhaust-pipe fuel. injection in a diesel engine equipped vehicle in which an exhaust brake ( 6 ) and a fuel injection means ( 7 ) are disposed to the exhaust pipe ( 3 ), a DPF ( 5 ) is disposed in a region on the downstream side of the fuel injection means ( 7 ), an exhaust temperature sensor ( 11 ) is disposed in a region on the upstream side of the DPF ( 5 ), and pressure sensors ( 12 ,  12 ) are disposed on the upstream side and the downstream side of the DPF ( 5 ), the method comprising: 
         [0021]    a step (a step S 1 ) of comparing a differential pressure between the upstream side and the downstream side of the DPF ( 5 ) obtained by the pressure sensors ( 12 ,  12 ) with a threshold value and determining whether regeneration of the DPF ( 5 ) is required or not; 
         [0022]    a step (a step S 2 ) of determining whether a vehicle is traveling on cruise control or not (an auto cruise operation switch  13  is operated) from an operation state of an. operation device (the auto cruise operation switch  13 ) that enables the vehicle to travel on cruise control; 
         [0023]    a step (a step S 3 ) of comparing an exhaust temperature detected by the exhaust temperature sensor ( 11 ) with a threshold value; 
         [0024]    a step (a step S 4 ) of injecting the fuel, into the exhaust pipe ( 3 ) by the fuel injection means ( 7 ) when the DPF ( 5 ) must be regenerated (YES at the step S 1 ), the vehicle is traveling on cruise control (the auto cruise operation switch  13  is operated) (YES at the step S 2 ), and the exhaust temperature detected by the exhaust temperature sensor ( 11 ) is higher than a threshold value (YES at the step S 3 ); and 
         [0025]    a step (a step S 5 ) of operating an exhaust brake when the DPF ( 5 ) must be regenerated (YES at the step S 1 ) and the vehicle is traveling on cruise control (YES at the step S 2 ) but the exhaust temperature is lower than the threshold value (NO at the step S 3 ). 
       Advantageous Effects of invention 
       [0026]    As described above, in the prior art, since an engine load of a vehicle is not fixed during travel of the vehicle according to the technology for raising an exhaust temperature to regenerate a OFF by injecting the fuel into the exhaust pipe ( 3 ), stably raising the exhaust temperature is difficult. 
         [0027]    On the other hand, according to the present invention, the fuel is injected into the exhaust pipe by the fuel injection means ( 7 ) only when the vehicle is traveling on cruise control (the auto cruise operation switch  13  is operated). Here, since travel is carried out at a constant speed on cruise control irrespective of a driver&#39; s pedal operation, a load variation in the vehicle engine is small, stable combustion is enabled, and hence the exhaust temperature is kept constant in the exhaust pipe. Therefore, as different from the technology for injecting the fuel into the exhaust pipe to regenerate the DPF, by detecting auto cruise travel during travel of the vehicle, the engine load of the vehicle is fixed even during travel of the vehicle, and the exhaust temperature can be stably raised. Thus, the DPF can be regenerated during travel of the vehicle (traveling on cruise control) as well as stoppage of the vehicle. 
         [0028]    Moreover, according to the present invention, if the exhaust temperature is lower than a threshold value even though the vehicle is traveling on cruise control, the exhaust brake is operated to raise the exhaust temperature (without injecting the fuel, into the exhaust pipe). As a result, the exhaust temperature can be raised to a level that enables regeneration of the DPF. 
         [0029]    Consequently, when the exhaust temperature is raised. and regeneration of the DPF is required even during travel of the vehicle, the DPF can be stably regenerated. As a result, the DPF does not have to be frequently regenerated when the vehicle is stopped. Additionally, the exhaust brake can be automatically operated in tandem with determination on whether regeneration of the DPF is necessary or not, and a driver&#39;s operation is not required. That is, the DPF regeneration enables preventing the driver&#39; s fatigue from increasing without unnecessary operations of the driver. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  is a block diagram of an embodiment according to the present invention; 
           [0031]      FIG. 2  is a block diagram of a control unit according to the embodiment; and 
           [0032]      FIG. 3  is a flowchart showing control according to the embodiment. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    An embodiment according to the present invention will, now be described with reference to the accompanying drawings hereinafter. 
         [0034]      FIG. 1  shows a configuration of a DPF regeneration control system according to the present invention. It is to be noted that a vehicle having this system mounted therein is equipped with an auto cruise (constant-speed travel) control device, but the illustration of the auto cruise control device is omitted in  FIG. 1 . 
         [0035]    In  FIG. 1 , an exhaust pipe  3  extends from an engine  1  through a turbo charger  2 . 
         [0036]    In the exhaust pipe  3 , an exhaust brake  6  is disposed in a region on a downstream side (a right-hand side in  FIG. 1 ) of the turbo charger  2 , and an oxidation catalyst  4  and a DPF  5  are integrally disposed on the downstream side of the exhaust brake  6 . Further, in the an pipe  3 , a fuel injection means  7  (a device that injects fuel into the exhaust pipe  3 : e.g., a nozzle) is disposed in a region on the downstream side of the exhaust brake  6 . It is to be noted that a relative positional relationship between the fuel injection means  7  and the exhaust brake  6  is not restricted to the conformation shown in  FIG. 1 . 
         [0037]    In the exhaust pipe  3 , exhaust temperature sensors  11 ,  11  are disposed in a region between the oxidation catalyst  4  and the DPF  5  (a region on an upstream side of the DPF  5 ) and a region on the downstream side of the DPF  5 , respectively. Although not shown, the exhaust temperature sensor  11  may be disposed in the region between the oxidation catalyst  4  and the DPF  5  alone (the region on the upstream side of the DPF  5 ). 
         [0038]    Pressure sensors  12 ,  12  are disposed on the upstream side and the downstream side of the DPF  5 , respectively. It is possible to detect a pressure difference between the upstream side and the downstream side of the DPF  5  based on a difference between a measurement value of the pressure sensor  12  on the upstream side of the DPF  5  and a measurement value of the pressure sensor  12  on the downstream side of the DPF  5 . 
         [0039]    The exhaust temperature sensors  11 ,  11  and the pressure sensors  12 ,  12  are connected to a control unit  10  through signal transmission lines, and respective detection signals are input to the control unit  10 . 
         [0040]    The control unit  10  is also connected to an auto cruise operation switch  13  (an operation device that enables a vehicle to travel on cruise control) and information showing whether the vehicle is traveling on cruise control or not is input to the control unit  10 . 
         [0041]    The control unit  10  is connected to control devices of the fuel injection means and the exhaust brake  6  through the signal transmission lines and has a function for outputting control signals to the respective devices. 
         [0042]    In  FIG. 2 , particulars of the control unit  10  are shown as a functional block diagram. 
         [0043]    The auto cruise operation switch  13  is connected to an auto cruise determination unit  10 A in the control. unit  10  through the signal transmission line. The auto cruise determination. unit  10 A outputs a signal concerning whether the vehicle is traveling on cruise control or not (an auto cruise operation signal) to an exhaust brake operation determination unit  10 C in response to a signal from the auto cruise operation switch  13  (a signal indicating whether the vehicle is traveling on cruise control or not). 
         [0044]    Furthermore, the pressure sensors  12 ,  12  are connected to a DPF regeneration determination unit  10 B through signal transmission lines. The DPF regeneration determination unit  10 B has a function to calculate a pressure difference between the upstream side and the downstream side of the DPF  5  based on a difference between measurement values of the pressure sensors  12 ,  12  and determine whether the DPF must be regenerated or not based on the calculated pressure difference. Moreover, the DPF regeneration determination unit  10 B outputs a determination result representing whether the DPF must be regenerated or not (a regeneration determination signal) to the exhaust brake operation determination unit  10 C. 
         [0045]    Each exhaust temperature sensor  11  is connected to the exhaust brake operation determination unit  10 C through the signal transmission line. The exhaust brake operation determination unit  10 C receives an exhaust temperature measured by the exhaust temperature sensor  11 , an operation signal from the auto cruise determination unit  10 A, and a regeneration determination signal from the DPF regeneration determination unit  10 B and outputs a control signal to a fuel injection means control unit  10 D or an exhaust brake control unit  10 E. 
         [0046]    As will be described later in detail with reference to  FIG. 3 , when the exhaust brake operation determination unit  10 C receives an auto cruise operation signal indicating that the vehicle is traveling on cruise control and also receives a regeneration determination signal indicating the need for regenerating the DPF  5  and the exhaust temperature measured by the exhaust temperature sensor  11  is a high temperature (higher than a threshold value), the exhaust brake operation determination unit  10 C outputs a control signal for injecting fuel into the exhaust pipe  3  by the fuel injection. means  7  to the fuel injection means control unit  10 D. In such a case, the control signal is not output to the exhaust brake control unit  10 E. 
         [0047]    On the other hand, when the exhaust brake operation determination unit  10 C receives the auto cruise operation signal indicating that the vehicle is traveling on cruise control and also receives the regeneration determination signal indicating the need for regenerating the DPF but the exhaust temperature measured by the exhaust temperature sensor  11  is a low temperature (lower than the threshold value), the exhaust brake operation determination unit  10 C outputs a control signal for operating the exhaust brake  6  to the exhaust. brake control. unit  10 E. In such a case, the control signal is not output to the fuel injection means control unit  10 D. 
         [0048]    The control in the illustrated embodiment will now be described with reference to  FIG. 3 . 
         [0049]    At a step S 1  in  FIG. 3 , whether regeneration of the DPF  5  is required or not is determined based on a differential pressure between the upstream and downstream sides of the DPF in the DPF regeneration determination unit  10 B. For example, when a pressure difference between the upstream side and the downstream side of the DPF  5  is calculated from measurement values of the pressure sensors  12 ,  12 , the calculated pressure difference is compared with a threshold value, and the pressure difference is higher than the threshold value, it is determined that the DPF  5  must be regenerated (Y at the step S 1 ), and the processing advances to a step S 2 . 
         [0050]    On the other hand, when the pressure difference is equal to or less than the threshold value, it is determined that the DPF  5  does not have to be regenerated (N at the step S 1 ), and the processing advances to a step S 6 . 
         [0051]    Here, the threshold value is set in accordance with specifications of the non-illustrated vehicle, characteristics of the DPF  5 , traveling conditions, and others on a case-by-case basis. 
         [0052]    At the step S 2  (when it was determined that “the DPF must be regenerated” at the step S 1 ), the auto cruise determination unit  10 A (refer to  FIG. 2 ) determines whether the vehicle is traveling on cruise control, or not. That is, whether the vehicle is traveling on cruise control or not is determined based on a signal from the auto cruise operation switch  13  (the signal indicating whether the vehicle is traveling on cruise control or not). 
         [0053]    When the auto cruise operation switch  13  is operated (the auto cruise operation switch  13  is ON), it is determined that the vehicle is traveling on cruise control (Y at the step S 2 ) and the processing advances to a step S 3 . 
         [0054]    On the other hand, when the auto cruise operation switch  13  is not operated (the auto cruise operation switch  13  is OFF), it is determined that the vehicle is not traveling on cruise control (N at the step S 2 ), and the processing advances to a step S 6 . Since an engine load of the vehicle is not constant when the vehicle is not traveling on cruise control, the fuel is not injected into the exhaust pipe  3  in order to avoid a situation where the exhaust temperature is not increased even though the fuel is injected into the exhaust pipe  3  or that the exhaust temperature is excessively increased. 
         [0055]    At the step S 3  (when it was determined that the vehicle is traveling on cruise control), whether the exhaust temperature detected by the exhaust temperature sensor  11  is higher than a threshold value or not is determined. 
         [0056]    If the exhaust temperature is higher than the threshold value (Y et the step S 3 ), the processing advances to a step S 4 . At the step S 4 , since the vehicle is traveling on cruise control (Y at the step S 1 ), regeneration of the DPF  5  is determined to be needed (Y at the step S 2 ), the exhaust temperature measured by the exhaust temperature sensor  11  is a high temperature (Y at the step S 3 ), and hence it is determined that regeneration of the DPF  5  is enabled by injecting the fuel into the exhaust pipe  3 . Further, the exhaust brake operation determination unit  10 C ( FIG. 2 ) outputs the control signal to the fuel injection means control unit  10 D ( FIG. 2 ) and injects the fuel into the exhaust pipe  3  by the fuel injection means  7  (in-exhaust-pipe fuel injection is carried out). In this case, the control signal is not output to the exhaust brake control unit  10 E, and the exhaust brake  6  is not operated (the exhaust brake OFF). 
         [0057]    When the fuel is injected into the exhaust pipe  3  by the fuel injection means  7 , the exhaust temperature in the exhaust pipe  3  increases by the injected fuel, and the DPF  5  is regenerated (DPF is regenerated by the increase in exhaust temperature). Furthermore, the processing returns to the step S 1 . 
         [0058]    On the other hand, if the exhaust temperature is a low temperature equal to or less than the threshold value (N at the step S 3 ), the processing advances to a step S 5 . At the step S 5 , although the vehicle is traveling on cruise control (Y at the step S 1 ) and regeneration of the DPF  5  is determined to be needed (Y at the step S 2 ), the exhaust temperature measured by the exhaust temperature sensor  11  is a low temperature, and regeneration of the DPF  5  is impossible, and hence it is determined that the exhaust temperature must be raised. Therefore, the exhaust brake operation determination unit  10 C ( FIG. 2 ) outputs a control signal for operating the exhaust brake  6  to the exhaust brake control unit  10 E, but the control signal is not output to the fuel injection device control unit  10 D, and the fuel is not injected into the exhaust pipe  3 . 
         [0059]    Operating the exhaust brake  6  enables increasing the engine load of the vehicle to boost an amount of fuel supply to the engine and raising the exhaust temperature. Moreover, the processing returns to the step S 1 . 
         [0060]    The threshold, value of the exhaust temperature should be set in accordance with specifications of the vehicle, characteristics of the DPF  5 , and others on a case-by-case basis. 
         [0061]    It is to be noted that, when the exhaust temperature increases to be higher than the threshold value as a result of operating the exhaust brake (Y at the step S 3 ), the exhaust brake  6  enters a non-operating state, and the fuel is injected into the exhaust pipe  3  (the step S 4 ). 
         [0062]    If regeneration of the DPF is determined to be unnecessary at the step S 1  (N at the step S 1 ) or if the vehicle is not traveling on cruise control. at the step S 2  (N at the step S 2 ), regeneration of the DPF  5  is not performed, and both the fuel injection  7  and the exhaust brake  6  do not operate (the step S 6 ). Additionally, the processing returns to the step S 1 . 
         [0063]    According to the illustrated embodiment, when the auto cruise operation switch  13  is operated (the auto cruise operation switch  13  is ON), a relatively stable traveling state of the vehicle is detected (Y at the step S 2 ), and the exhaust temperature is high (Y at the step S 3 ), the fuel is injected into the exhaust pipe  3  to regenerate the DPF  5 . Therefore, even if the vehicle is traveling, the DPF  5  can be regenerated by injecting the fuel into the exhaust pipe  3 . 
         [0064]    Here, if the exhaust temperature is low (N at the step S 3 ), the engine load is increased, by operating the exhaust brake  6 , and the exhaust temperature is thereby raised. Further, when the exhaust temperature is raised to a level that is sufficient for regeneration of the DPF  5  (a temperature higher than the threshold value), the fuel is injected into the exhaust pipe  3  to regenerate the DPF  5 . 
         [0065]    Therefore, even though the DPF  5  is regenerated by injecting the fuel into the exhaust pipe  3 , it is possible to execute the DPF regenerating operation during travel of the vehicle. 
         [0066]    It is stated that the illustrated embodiment is just an illustrative example and it is not a description that is intended to restrict the technical scope of the present invention. 
       EXPLANATIONS OF LETTERS OR NUMERALS 
       [0067]      1  . . . engine 
         [0068]      2  . . . turbo charger 
         [0069]      3  . . . exhaust pipe 
         [0070]      4  . . . oxidation catalyst 
         [0071]      5  . . . diesel particulate filter (DPF) 
         [0072]      6  . . . exhaust brake 
         [0073]      7  . . . fuel injection means 
         [0074]      10  . . . control unit 
         [0075]      11  . . . exhaust temperature sensor 
         [0076]      12  . . . pressure sensor 
         [0077]      13  . . . auto cruise operation switch