Abstract:
Provided is a construction machine configured so as to prevent wasteful fuel consumption by preventing an engine stall by means of the injection of an appropriate amount of fuel. A backhoe which is a construction machine in which a hydraulic pump is driven by power from an engine is configured so that the output torque characteristics of the engine is set on the basis of the atmospheric pressure detected by an atmospheric pressure sensor which is an atmospheric pressure detection means, and so that a rotational speed is set so that the maximum torque of the engine at a low idle rotational speed is greater than the maximum absorption torque of the hydraulic pump.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is the U.S. national stage of application No. PCT/JP2014/054453, filed on Feb. 25, 2014. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2013-113331, filed May 29, 2013, the disclosure of which is also incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a construction machine. 
       BACKGROUND ART 
       [0003]    Conventionally, when a construction machine is used in a high ground with low atmospheric pressure, an engine output is reduced following reduction of an air intake amount, whereby an absorbing torque of a hydraulic pump becomes larger than output torque of an engine and frequency of engine failure is increased. Then, the construction machine in which the absorbing torque of the hydraulic pump can be adjusted to an optional value is known. The construction machine has a control device of the hydraulic pump which prevents the engine failure by reducing the absorbing torque of the hydraulic pump following reduction of the engine output. For example, see the Patent Literature 1. 
         [0004]    In the construction machine described in the Patent Literature 1, the absorbing torque of the hydraulic pump is controlled so as to reduce load of the engine. Then, when the construction machine is used in the high ground with low atmospheric pressure or a fuel injection amount of the engine is suppressed for corresponding to recent regulation of exhaust gas in the high ground, the output torque of the engine may be reduced more than a reduction amount of the absorbing torque of the hydraulic pump so as to cause the engine failure. There is a problem in that an engine rotational speed is increased more than necessary for preventing the engine failure so as to cause useless consumption of fuel. 
       PRIOR ART REFERENCE 
     Patent Literature 
       [0005]    Patent Literature 1: the Japanese Patent Laid Open Gazette 2004-132195 
       DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
       [0006]    The purpose of the present invention is to provide a construction machine which can prevent the engine failure with suitable fuel injection amount so as to suppress useless consumption of fuel. 
       Means for Solving the Problems 
       [0007]    The problems to be solved by the present invention have been described above, and subsequently, the means of solving the problems will be described below. 
         [0008]    According to the present invention, in a construction machine in which a hydraulic pump is driven by power from an engine, an output torque characteristic of the engine is set based on an atmospheric pressure detected by an atmospheric pressure detection means, and a low idle rotational speed is set so that a maximum torque of the engine at the low idle rotational speed is larger than a maximum absorbing torque of the hydraulic pump. 
         [0009]    According to the present invention, the output torque characteristic is set based on an intake air temperature detected by an intake air temperature detection means and a fuel temperature detected by a fuel temperature detection means. 
         [0010]    According to the present invention, whether the low idle rotational speed is set based on the output torque characteristic and the maximum absorbing torque or not can be selected with a switching means. 
         [0011]    According to the present invention, when work with a hydraulic actuator is not performed, the low idle rotational speed is not set based on the output torque characteristic and the maximum absorbing torque. 
         [0012]    According to the present invention, when an absorbing torque of the hydraulic pump is not more than a predetermined value, the low idle rotational speed is not set based on the output torque characteristic and the maximum absorbing torque. 
       Effect of the Invention 
       [0013]    The present invention brings the following effects. 
         [0014]    According to the present invention, the low idle rotational speed is set corresponding to the work state. Accordingly, the engine failure can be prevented with suitable fuel injection amount so as to suppress useless consumption of fuel. 
         [0015]    According to the present invention, the low idle rotational speed is set more finely corresponding to the environment. Accordingly, the engine failure can be prevented with suitable fuel injection amount so as to suppress useless consumption of fuel. 
         [0016]    According to the present invention, the low idle rotational speed is switched corresponding to request of an operator. Accordingly, useless consumption of fuel can be suppressed without reducing work efficiency. 
         [0017]    According to the present invention, the low idle rotational speed is set corresponding to the work state. Accordingly, the engine failure can be prevented with suitable fuel injection amount so as to suppress useless consumption of fuel. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a left side view of an entire configuration of a construction machine according to an embodiment of the present invention. 
           [0019]      FIG. 2  is a schematic drawing of a hydraulic circuit of the construction machine according to the embodiment of the present invention. 
           [0020]      FIG. 3A  is a graph of relation between an output torque characteristic of an engine and a low idle rotational speed.  FIG. 3B  is a graph of relation between low idle rotational speeds. 
           [0021]      FIG. 4  is a flow chart of a control mode for setting the low idle rotational speed of the construction machine according to the embodiment of the present invention. 
           [0022]      FIG. 5  is a flow chart of a control mode of low idle control of the construction machine according to the embodiment of the present invention. 
           [0023]      FIG. 6  is a flow chart of a control mode of automatic deceleration control of the construction machine according to the embodiment of the present invention. 
           [0024]      FIG. 7  is a flow chart of a control mode for setting the low idle rotational speed of the construction machine according to another embodiment of the present invention. 
           [0025]      FIG. 8  is a flow chart of a control mode of automatic deceleration control of the construction machine according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Firstly, a backhoe  1  which is an embodiment of a construction machine according to the present invention is explained referring to  FIG. 1 . In below explanation, a direction of an arrow A is regarded as a front direction of the backhoe  1  and a direction of an arrow U is regarded as an upward direction of the backhoe  1  so as to specify longitudinal, lateral and vertical directions. Though the backhoe  1  is explained as an embodiment of the construction machine in this embodiment, the construction machine is not limited thereto. 
         [0027]    As shown in  FIG. 1 , the backhoe  1  mainly has a traveling device  2 , a revolving device  3  and a working device  4 . 
         [0028]    The traveling device  2  mainly has a pair of left and right crawlers  5 , a left traveling hydraulic motor  5 L and a right traveling hydraulic motor  5 R. By driving the left crawler  5  by the left traveling hydraulic motor  5 L and driving the right crawler  5  by the right traveling hydraulic motor  5 R, the traveling device  2  can make the backhoe  1  travel forward and rearward and turn. 
         [0029]    The revolving device  3  mainly has a revolving base  6 , a revolving motor  7 , an operation part  8  and an engine  9 . The revolving base  6  is a main structure of the revolving device  3 . The revolving base  6  is arranged above the traveling device  2  and supported rotatably by the traveling device  2 . In the revolving device  3 , by driving the revolving motor  7 , the revolving base  6  can be revolved with respect to the traveling device  2 . On the revolving base  6 , the working device  4 , the operation part  8  and the engine  9  which is a power source are arranged. 
         [0030]    The operation part  8  has various operation instruments and can operate the backhoe  1 . The operation part  8  is provided in a left front part of the revolving base  6 . In the operation part  8 , a seat  11  is arranged at a substantially center of a cabin  10 , and an operation lever device  26  (see  FIG. 2 ) is arranged at left and right sides of the seat  11 . The operation lever device  26  can operate the working device  4  and the revolving base  6 . 
         [0031]    The operation part  8  has an accelerator  27  for changing a throttle opening degree of the engine  9  and a switch  28  which is a switching means (see  FIG. 2 ). By operating the accelerator  27 , an operator can change an output of the engine  9  (rotational speed of the engine  9 ). 
         [0032]    The switch  28  selects alternatively whether later-discussed low idle control is confirmed or not, whether automatic deceleration control is confirmed or not, or whether both the low idle control and the automatic deceleration control are confirmed or not. By operating the switch  28 , an operator can select whether the low idle control and the automatic deceleration control are confirmed or not respectively. 
         [0033]    The working device  4  mainly has a boom  12 , an arm  13 , a bucket  14  which is a kind of an attachment, a boom cylinder  15 , an arm cylinder  16 , and an attachment cylinder  17 . 
         [0034]    One of ends of the boom  12  is supported rotatably on a front part of the revolving base  6 . The boom  12  is rotated centering on the one of the ends by the boom cylinder  15  which is driven telescopically. 
         [0035]    One of ends of the arm  13  is supported rotatably on the other end of the boom  12 . The arm  13  is rotated centering on the one of the ends at by the arm cylinder  16  which is driven telescopically. 
         [0036]    One of ends of the bucket  14  which is the kind of the attachment is supported rotatably on the other end of the arm  13 . The bucket  14  is rotated centering on the one of the ends by the attachment cylinder  17  which is driven telescopically. 
         [0037]    As the above, in the working device  4 , an articulated structure which digs soil with the bucket  14  is configured. In the working device  4 , hydraulic piping (not shown) is provided for supplying pressure oil to the boom cylinder  15 , the arm cylinder  16 , and the attachment cylinder  17 . Though the working device  4  which has the bucket  14  and performs digging work is provided in the backhoe  1  according to this embodiment, the working device is not limited thereto and a working device  4  which has a hydraulic breaker instead of the bucket  14  and performs crush work may alternatively be provided. 
         [0038]    Next, a hydraulic circuit  18  provided in the backhoe  1  is explained referring to  FIG. 2 . 
         [0039]    As shown in  FIG. 2 , the hydraulic circuit  18  has a revolving motor direction switching valve  19 , a boom cylinder direction switching valve  20 , an arm cylinder direction switching valve  21 , an attachment direction switching valve  22 , a traveling motor direction switching valve  23 , a hydraulic pump  24 , and a control device  25 . 
         [0040]    The revolving motor direction switching valve  19 , the boom cylinder direction switching valve  20 , the arm cylinder direction switching valve  21  and the attachment direction switching valve  22  are pilot type direction switching valves which change flows of pressure oil supplied to the revolving motor  7 , the boom cylinder  15 , the arm cylinder  16 , and the attachment cylinder  17  by sliding spools by pilot pressure. 
         [0041]    The revolving motor direction switching valve  19  switches direction of pressure oil supplied to the revolving motor  7 . When the revolving motor direction switching valve  19  is at one of positions, the revolving motor  7  is driven rotatively along one direction by the pressure oil. When the revolving motor direction switching valve  19  is at the other position, the revolving motor  7  is driven rotatively along the other direction by the pressure oil. 
         [0042]    The boom cylinder direction switching valve  20  switches direction of pressure oil supplied to the boom cylinder  15 . The boom cylinder  15  is extended and contracted by operation of the boom cylinder direction switching valve  20  so that the boom  10  is swung upward or downward. 
         [0043]    The arm cylinder direction switching valve  21  switches direction of pressure oil supplied to the arm cylinder  16 . The arm cylinder  16  is extended and contracted by operation of the arm cylinder direction switching valve  21  so that the arm  13  is swung toward a crowd side or a dump side. 
         [0044]    The traveling motor direction switching valve  23  switches direction of pressure oil supplied to the left traveling hydraulic motor  5 L and the right traveling hydraulic motor  5 R (hereinafter, simply referred to as “traveling motors  5 L and  5 R). When the traveling motor direction switching valve  23  is at one of positions, the traveling motors  5 L and  5 R are driven rotatively along one direction by the pressure oil. When the traveling motor direction switching valve  23  is at the other position, the traveling motors  5 L and  5 R are driven rotatively along the other direction by the pressure oil. 
         [0045]    The attachment direction switching valve  22  switches direction of pressure oil supplied to the attachment cylinder  17 . The attachment cylinder  17  is extended and contracted by operation of the attachment direction switching valve  22  so that the bucket  14  is swung toward a crowd side or a dump side. 
         [0046]    The revolving motor direction switching valve  19 , the boom cylinder direction switching valve  20 , the arm cylinder direction switching valve  21 , the attachment direction switching valve  22  and the traveling motor direction switching valve  23  are configured so that directions of flows of pressure oil supplied to the direction switching valves can be changed by pilot pressure based on operation of the operation lever device  26 . 
         [0047]    The hydraulic pump  24  is driven by the engine  9  and discharges pressure oil. The hydraulic pump  24  is a variable capacity type pump whose discharge amount can be changed by changing a slant angle of a movable swash plate (not shown). The pressure oil discharged from the hydraulic pump  24  is supplied to the direction switching valves. 
         [0048]    Next, the control device  25  and an ECU  29  provided in the backhoe  1  are explained. 
         [0049]    The control device  25  transmits a control signal to the ECU  29 . Substantially, the control device  25  may be configured by connecting a CPU, a ROM, a RAM, a HDD and the like with a bus, or may alternatively be a one-chip LSI or the like. Various programs for controlling the ECU  29  are stored in the control device  25 . 
         [0050]    The control device  25  is connected to the operation lever device  26  and can obtain an operation signal from the operation lever device  26 . 
         [0051]    The control device  25  is connected to the accelerator  27  and can obtain an operation signal from the accelerator  27 . 
         [0052]    The control device  25  is connected to the switch  28  and can obtain an operation signal from the switch  28  (operation signal whether the low idle control and/or the automatic deceleration control are performed or not). 
         [0053]    The ECU  29  controls the engine  9  and the like. Substantially, the ECU  29  may be configured by connecting a CPU, a ROM, a RAM, a HDD and the like with a bus, or may alternatively be a one-chip LSI or the like. Various programs for controlling the engine  9  and the like are stored in the ECU  29 . 
         [0054]    The ECU  29  memorizes an output torque characteristic map M 1  for calculating an output torque characteristic Tp (Tp 0 , Tp 1 , . . . ) of the engine  9  from an atmospheric pressure P (atmospheric pressures P 0 , P 1 , . . . ) so as to satisfy an emission control value, a low idle rotational speed map M 2  for calculating a low idle rotational speed Vlb of the engine  9  from the calculated output torque characteristic Tp of the engine  9 , and the like. 
         [0055]    In this embodiment, the output torque characteristic Tp is an output-permissible range at each engine rotational speed in the state in which the engine  9  satisfies the emission control value (hereinafter, simply referred to as “rotational speed”), that is, a maximum output torque at each rotational speed under the atmospheric pressure P. 
         [0056]    In this embodiment, a rotational speed Vla indicates a rotational speed calculated based on the operation of the accelerator  27 . The rotational speed Vlb indicates a rotational speed calculated based on the output torque characteristic Tp of the engine  9  so as to make the maximum output torque of the engine  9  at this rotational speed larger than a maximum absorbing torque Th of the hydraulic pump  24 . A rotational speed Vlc indicates an original low idle rotational speed of the engine  9 . 
         [0057]    Concretely, an output torque characteristic Tp 1  which indicates maximum output torque of the engine  9  at each rotational speed is calculated based on an atmospheric pressure P 1  from the output torque characteristic map M 1  (see  FIG. 3A ). The rotational speed Vlb can be calculated based on the calculated output torque characteristic Tp 1  from the low idle rotational speed map M 2  so as to make a maximum output torque Tb 1  at the rotational speed Vlb larger than the maximum absorbing torque Th of the hydraulic pump  24  (see  FIG. 3A ). 
         [0058]    In this embodiment, setting of the calculated rotational speed Vlb as the low idle rotational speed of the engine  9  is regarded as the low idle control. Setting of the rotational speed Vlc as the low idle rotational speed of the engine  9  at the time at which work with a hydraulic apparatus is not performed is regarded as the automatic deceleration control. 
         [0059]    The ECU  29  is connected to various sensors and a fuel injection device (not shown) provided in the engine  9  and can control an injection amount of fuel injected by the fuel injection device and the like. 
         [0060]    The ECU  29  is connected to an atmospheric pressure sensor  30  and can obtain an atmospheric pressure P detected by the atmospheric pressure sensor  30 . 
         [0061]    The ECU  29  is connected to a fuel temperature sensor  31  and can obtain a fuel temperature Tf in a fuel injection pump (not shown) detected by the fuel temperature sensor  31 . 
         [0062]    The ECU  29  is connected to an intake air temperature sensor  32  and can obtain an intake air temperature Ti of the engine  9  detected by the intake air temperature sensor  32 . 
         [0063]    The ECU  29  can calculate the output torque characteristic Tp of the engine  9  based on the obtained atmospheric pressure P from the output torque characteristic map M 1 . 
         [0064]    The ECU  29  can calculate the rotational speed Vlb based on the calculated output torque characteristic Tp of the engine  9  from the low idle rotational speed map M 2 . 
         [0065]    The ECU  29  is connected to the control device  25  and can obtain operation signals from the operation lever device  26 , the accelerator  27  and the switch  28  obtained by the control device  25 , an operation signal whether the low idle control is performed or not, and an operation signal whether the automatic deceleration control is performed or not. 
         [0066]    Next, referring to  FIGS. 3 to 6 , a control mode for setting the low idle rotational speed of the engine  9  in the ECU  29  of the backhoe  1  configured as the above is explained. In this embodiment, isochronous control that a fixed engine rotational speed is maintained with respect to variation of load is performed concerning the engine  9  by the ECU  29 . 
         [0067]    As shown in  FIG. 3A , the engine  9  of the backhoe  1  is set by the ECU  29  so that the output torque characteristic is Tp 0  when the atmospheric pressure is P 0  and the output torque characteristic is Tp 1  when the atmospheric pressure is P 1 . Namely, the engine  9  is controlled so that the output up to a maximum output torque Tc 0  is permitted at the rotational speed Vlc which is the low idle rotational speed when the atmospheric pressure is P 0  and the output up to a maximum output torque Tc 1  is permitted at the rotational speed Vlc which is the low idle rotational speed when the atmospheric pressure is P 1 . Therefore, in the engine  9 , the maximum output torque Tc 1  at the rotational speed Vlc is smaller than the maximum absorbing torque Th of the hydraulic pump  24  according to the output torque characteristic. 
         [0068]    As shown in  FIG. 3B , the ECU  29  sets the rotational speed of in the engine  9  to be the rotational speed Vla based on an operation amount of the accelerator  27  when the control signal which confirms the low idle control is not obtained from the control device  25 . The ECU  29  sets the low idle rotational speed of in the engine  9  to be the rotational speed Vlb when the control signal which confirms the low idle control is obtained from the control device  25 . The ECU  29  sets the low idle rotational speed of in the engine  9  to be the low idle rotational speed Vlc until the operation signal of the operation lever device  26  is obtained from the control device  25  when the control signal which confirms the automatic deceleration control is obtained. 
         [0069]    A control mode of the ECU  29  for setting the low idle rotational speed of the engine  9  is explained concretely. 
         [0070]    As shown in  FIG. 4 , at a step S 110 , the ECU  29  obtains the atmospheric pressure P 1  detected by the atmospheric pressure sensor  30  and shifts to a step S 120 . The ECU  29  can obtain the fuel temperature Tf 1  in a fuel tank (not shown) detected by the fuel temperature sensor  31  and the intake air temperature Ti 1  of the engine  9  detected by the intake air temperature sensor  32 . 
         [0071]    At the step S 120 , the ECU  29  obtains the operation signal from the accelerator  27 , calculates the rotational speed Vla based on the operation amount of the accelerator  27 , and shifts to a step S 130 . 
         [0072]    At the step S 130 , the ECU  29  calculates the output torque characteristic Tp 1  based on the obtained atmospheric pressure P 1  from the output torque characteristic map M 1 , sets the calculated output torque characteristic Tp 1  as the output torque characteristic of the engine at the atmospheric pressure P 1 , and shifts to a step S 140 . The ECU  29  can calculate the output torque characteristic Tp 1  based on the fuel temperature Tf 1  and the intake air temperature Ti 1  obtained further from the output torque characteristic map M 1 . 
         [0073]    At the step S 140 , the ECU  29  calculates the rotational speed Vlb based on the set output torque characteristic Tp 1  from the low idle rotational speed map M 2 , and shifts to a step S 150 . 
         [0074]    At the step S 150 , the ECU  29  judges whether the calculated rotational speed Vlb is larger than the calculated rotational speed Vla or not. 
         [0075]    As a result, when the rotational speed Vlb is judged to be larger than the rotational speed Vla, the ECU  29  shifts to a step S 160  (see  FIG. 3B ). 
         [0076]    On the other hand, when the rotational speed Vlb is judged not to be larger than the rotational speed Vla, the ECU  29  shifts to a step S 260 . 
         [0077]    At the step S 160 , the ECU  29  obtains the operation signal of the switch  28  from the control device  25 , and judges whether the low idle control is confirmed or not based on the obtained operation signal. 
         [0078]    As a result, when the low idle control is judged to be confirmed, the ECU  29  shifts to a step S 170 . 
         [0079]    On the other hand, when the low idle control is judged not to be confirmed, the ECU  29  shifts to a step S 370 . 
         [0080]    At the step S 170 , the ECU  29  starts the low idle control A, and shifts to a step S 171  (see  FIG. 5 ). When the low idle control A is finished, the ECU  29  returns to the step S 110 . 
         [0081]    At the step S 260 , the ECU  29  obtains the operation signal of the switch  28  from the control device  25 , and judges whether the automatic deceleration control is confirmed or not based on the obtained operation signal. 
         [0082]    As a result, when the automatic deceleration control is judged to be confirmed, the ECU  29  shifts to a step S 270 . 
         [0083]    On the other hand, when the automatic deceleration control is judged not to be confirmed, the ECU  29  shifts to the step S 370 . 
         [0084]    At the step S 270 , the ECU  29  starts the automatic deceleration control B, and shifts to a step  5271  (see  FIG. 6 ). When the automatic deceleration control B is finished, the ECU  29  returns to the step S 110 . 
         [0085]    At the step S 370 , the ECU  29  sets the low idle rotational speed to be the rotational speed Vlb, and returns to the step S 110 . 
         [0086]    As shown in  FIG. 5 , at the step S 171  of the low idle control A, the ECU  29  obtains the operation signal of the switch  28  from the control device  25 , and judges whether the automatic deceleration control is confirmed or not based on the obtained operation signal. 
         [0087]    As a result, when the automatic deceleration control is judged to be confirmed, the ECU  29  shifts to a step S 172 . 
         [0088]    On the other hand, when the automatic deceleration control is judged not to be confirmed, the ECU  29  shifts to the step S 183 . 
         [0089]    At the step S 172 , the ECU  29  judges whether the operation signal of the operation lever device  26  is obtained from the control device  25  or not. 
         [0090]    As a result, when the operation signal of the operation lever device  26  is judged not to be obtained, the ECU  29  shifts to a step S 173 . 
         [0091]    On the other hand, when the operation signal of the operation lever device  26  is judged to be obtained, the ECU  29  shifts to the step S 183 . 
         [0092]    At the step S 173 , the ECU  29  sets the low idle rotational speed to be the rotational speed Vlc, and finishes the low idle control A and returns to the step S 110 . 
         [0093]    At the step S 183 , the ECU  29  sets the low idle rotational speed to be the rotational speed Vlb, and finishes the low idle control A and returns to the step S 110 . 
         [0094]    As shown in  FIG. 6 , at the step S 271  of the automatic deceleration control B, the ECU  29  judges whether the operation signal of the operation lever device  26  is obtained from the control device  25  or not. 
         [0095]    As a result, when the operation signal of the operation lever device  26  is judged not to be obtained, the ECU  29  shifts to a step S 272 . 
         [0096]    On the other hand, when the operation signal of the operation lever device  26  is judged to be obtained, the ECU  29  shifts to the step S 282 . 
         [0097]    At the step S 272 , the ECU  29  sets the low idle rotational speed to be the rotational speed Vlc, and finishes the automatic deceleration control B and returns to the step S 110 . 
         [0098]    At the step S 282 , the ECU  29  sets the rotational speed to be the rotational speed Vla, and finishes the automatic deceleration control B and returns to the step S 110 . 
         [0099]    According to the configuration, an operator does not need to set the low idle rotational speed sensuously corresponding to work state. Namely, the backhoe  1  according to the present invention is set to the rotational speed Vla calculated based on the accelerator  27 , the rotational speed Vlb calculated based on the output torque characteristic Tp 1  of the engine  9 , or the rotational speed Vlc which is the original low idle rotational speed of the engine  9  corresponding to the work state and drive state of the engine  9 . Furthermore, in the backhoe  1  according to the present invention, an operator determines whether the low idle control and the automatic deceleration control are confirmed or not corresponding to the work state. Accordingly, an engine failure can be prevented with suitable fuel injection amount without reducing work efficiency so as to suppress useless consumption of fuel. 
         [0100]    By considering not only the atmospheric pressure P 1  detected by the atmospheric pressure sensor  30  but also the fuel temperature Tf 1  detected by the fuel temperature sensor  31  and the intake air temperature Ti 1  detected by the intake air temperature sensor  32 , the low idle rotational speed is set more finely in accordance with environment. Accordingly, the engine failure can be prevented with suitable fuel injection amount so as to suppress useless consumption of fuel. 
         [0101]    Next, the backhoe  1  which is another embodiment of the construction machine according to the present invention is explained referring to  FIGS. 7 and 8 . In below explanation, a control mode of the ECU  29  for setting the low idle rotational speed of the engine  9  is explained concretely. A concrete explanation of parts similar to the embodiment explained already is omitted, and parts different to the embodiment explained already is explained mainly. 
         [0102]    The switch  28  selects alternatively whether the automatic deceleration control is confirmed or not. Namely, the backhoe  1  of this embodiment is configured so that the low idle control is confirmed always. By operating the switch  28 , an operator can select whether the automatic deceleration control is confirmed or not. 
         [0103]    A control mode of the ECU  29  for setting the low idle rotational speed of the engine  9  is explained concretely. 
         [0104]    As shown in  FIG. 7 , at the step S 150 , the ECU  29  judges whether the calculated rotational speed Vlb is larger than the calculated rotational speed Vla or not. 
         [0105]    As a result, when the rotational speed Vlb is judged to be larger than the rotational speed Vla, the ECU  29  shifts to a step S 170  (see  FIG. 3B ). 
         [0106]    On the other hand, when the rotational speed Vlb is judged not to be larger than the rotational speed Vla, the ECU  29  shifts to a step S 260 . 
         [0107]    At the step S 170 , the ECU  29  starts the low idle control A, and shifts to a step S 171  (see  FIG. 5 ). When the low idle control A is finished, the ECU  29  returns to the step S 110 . 
         [0108]    According to the configuration, the backhoe  1  according to the present invention is set to the suitable low idle rotational speed certainly corresponding to the work state and drive state of the engine. Accordingly, the engine failure can be prevented with suitable fuel injection amount so as to suppress useless consumption of fuel. 
         [0109]    Furthermore, as shown in  FIG. 8 , in the automatic deceleration control B, when an absorbing torque of the hydraulic pump  24  is not more than a predetermined value, the rotational speed may be set to Vlc. 
         [0110]    Concretely, at a step S 471  of the automatic deceleration control B, the ECU  29  judges whether the absorbing torque of the hydraulic pump  24  is not more than the predetermined value or not. 
         [0111]    As a result, when the absorbing torque of the hydraulic pump  24  is judged not to be more than the predetermined value, the ECU  29  shifts to the step S 272 . 
         [0112]    On the other hand, when the absorbing torque of the hydraulic pump  24  is judged to be more than the predetermined value, the ECU  29  shifts to a step S 282 . 
         [0113]    According to the configuration, in a work state with low load in which possibility of the engine failure is low, the backhoe  1  according to the present invention is set to the rotational speed Vlc with low fuel consumption. Accordingly, the engine failure can be prevented with suitable fuel injection amount so as to suppress useless consumption of fuel. 
       INDUSTRIAL APPLICABILITY 
       [0114]    The present invention can be used for an art of a construction machine. 
       DESCRIPTION OF NOTATIONS 
       [0000]    
       
           1  backhoe 
           9  engine 
           24  hydraulic pump 
           30  atmospheric pressure sensor 
         P 1  atmospheric pressure 
         Tp 1  output torque characteristic 
         Th maximum absorbing torque 
         Vlb rotational speed