DRIVING CONTROL DEVICE FOR CONSTRUCTION MACHINE [Technical field]

[l] The present invention relates to a technical field of a driving control device for construction machines such as a hydraulic shovel.

[Background]

[2] In general, some construction machines such as crawler hydraulic shovels include driving sections provided on right and left sides thereof respectively driven by right- or left-side driving motor, and are configured such that forward and backward driving motions of the right- and left- side driving sections are performed according to operation of right- or left- side driving operating devices (such as driving operating pedals or driving operating lever). In such a configuration, driving the construction machine straightly in a forward or backward direction requires that the right- and left-side driving operating devices be operated in the same amounts throughout the driving. However, driving the machine straightly for a long time gives a significant burden on an operator, who should carefully operate the right- and left- side driving operating devices in the same amounts throughout the driving.

[3] Conventionally, for such a problem, such a technique has been known that a changing-over switch for switching to constant-speed driving is provided, so that the machine can move straightly at a constant speed in the forward or backward direction automatically simply by switching operation of the changing-over switch (for example, see Patent Literature l). As an additional configuration thereto, such a technique has been disclosed that, to steer (change a direction of) the machine during the constant-speed straight- direction driving, at least one of the right- or left-side driving operating devices is operated to cancel the straight- direction driving and cause the right- and left- side driving sections to drive respectively at speeds corresponding to operating amounts of the right- and left-side driving operating devices, so that the machine can be steered rightward or leftward by operating the right- and left- side driving operating devices even during the constant-speed straight- direction driving.

[Citation List] Referential Literature

Patent Literature 1

Japanese Patent Application Publication, Tokukaihei, No. 11-131530 [Summary of the Invention]

[4] However, according to the Patent Literature 1, when at least one of the right- or the left- side driving operating devices is operated to steer the machine rightward or leftward during the constant- speed straight- direction driving by the switch operation, the driving speed is suddenly changed over from the speed of the constant- speed straight- direction driving to the speeds corresponding to the operating amount of the right- and the left- side driving operating devices. Consequently, it may cause a significant change in driving speed depending on the operating amounts of the driving operating devices. Furthermore, According to the Patent Literature 1, it is configured that, during the constant-speed straight- direction driving by the switching operation, pressure applied from a pilot hydraulic pressure source serves as a commanding signal supplied to a driving direction switching valve. Thus, the direction switching valve is changed over by full stroke and a maximum flow is applied to the driving motors. That is, the machine is moving at a highest speed during the constant-speed straight- direction driving by the switching operation and when the driving operating devices are operated in such a state, the speeds are suddenly changed to the speeds corresponding to the operating amounts of the driving operating devices. The driving operating devices are in a neutral position because they have not been operated during the constant- speed straight- direction driving, but are now moved from the neutral position in order to steer the machine. When the steering operation is started, the speed would be suddenly decelerated, which would result in instable driving. This is a problem to be solved by the present invention.

[5] In view of these circumstances, the present invention was made in order to solve these problems. The invention of Claim 1 is a driving control device for a construction machine including right- and left-side driving motors for driving right- and left-side driving sections, respectively, right- and left-side motor driving means for driving the right- and left-side driving motors, and right- and left-side driving operating devices for operating the right- and left- side driving sections to drive, the driving control device including: a straight- direction driving operating device configured to be operated to operate straight- direction driving of the construction machine! a steering operating device configured to be operated to steer rightward and leftward the construction machine during the straight- direction driving operated by the straight- direction driving operating device! and a control device for receiving operation signals from the right- and left-side driving operating devices, the straight- direction driving operating device, and the steering operating device, the control device being configured to perform mode setting for setting a straight- direction driving control mode according to the operation signal from the straight- direction driving operating device, normal driving control for driving, when the straight- direction driving control mode is not set, the right- and left- side driving motors at speeds corresponding to operating amounts of the right- and left-side driving operating devices, respectively, constant-speed straight- direction driving control for driving the right- and left-side driving motors at a constant speed when the straight- direction driving control mode is set, and steering control under straight- direction driving control mode for a case where the steering operating device is operated while the constant- speed straight- direction driving control is being carried out, the steering control under straight- direction driving control mode being such that one of the driving motors is caused to reduce its speed according to the operating amount of the steering operating device, wherein the one of driving motor is associated with the steering direction in which the steering operating device is operated, and the other one of the driving motors, which is associated with a steering-opposite direction, is caused to maintain the constant speed. [6] The invention of Claim 2 is a driving control device according to claim 1, wherein the right- and left-side driving motors are configured to be supplied with oil pressure from an oil pressure pump driven by an engine controlled by an engine control section configured to perform engine speed lowering control for lowering engine speed while the control device is carrying out the steering control under straight- direction driving control mode. [7] The invention of Claim 3 is a driving control device according to claim 1 or 2, comprising straight- direction speed setting means for allowing to variably set a driving speed of the constant- speed straight- direction driving control. [8] The invention of Claim 4 is a driving control device according to any one of claims 1 to 3, wherein the right- and left- side driving operating devices are configured to be usable as the steering operating devices when the straight- direction driving control mode is set.

[9] The invention of Claim 5 is a driving control device according to any one of claims 1 to 4, wherein the straight- direction driving operating device or the right- and left- side driving operating devices are usable as an operating device for stopping the driving of the construction machine when the constant- speed straight- direction driving control or the steering control under straight- direction driving control mode is being carried out. [10] The invention of Claim 1 makes it possible to smoothly steer rightward and leftward without significantly changing the driving speed even during the constant- speed straight- direction driving control in which the right- and left- side driving motors are driven at a constant speed, thereby achieving stable steering operation during constant-speed straight-direction driving. [ll] The invention of Claim 2 makes it possible to reduce the driving speed during steering control under the straight- direction driving control mode than during the constant-speed straight- direction driving control, thereby achieving more stable steering.

[12] The invention of Claim 3 makes it possible to arbitrarily set the driving speed of the constant- speed straight- direction driving according to the operator or situation of a workplace etc.

[13] The invention of Claim 4 makes it possible to eliminate the need of additionally proving a steering operating device, thereby facilitating dual-use of components. [14] The invention of Claim 5 makes it possible to eliminate the need of additionally providing an operating device for stopping the driving while the constant-speed straight- direction driving control and the steering control under straight- direction driving control mode are being carried out, thereby facilitating dual-use of components.

[Brief Description of Drawings]

[15] Fig. 1 is a perspective view of a hydraulic shovel.

[16] Fig. 2 is a perspective view illustrating inside of an operator room. [17] Fig. 3 is a view illustrating an input and output of a control device and a hydraulic circuit of a driving motor.

[18] Fig. 4 is a flow chart illustrating a procedure of control of the control device.

[19] Fig. 5 is a view illustrating operation signals of right- and left-side driving operating devices and operation pilot pressures of right- and left-side electromagnetic proportional valves for forward driving during constant- speed straight- direction driving control.

[20] Fig. 6 is a view illustrating an operating amount of a slide switch for steering and the output pilot pressures of the right- and left- side forward electromagnetic proportional valves for forward driving during steering control under straight- direction driving control mode, where (A) indicates a case of steering leftward and (B) indicates a case of steering rightward.

[21] Fig. 7 is a view illustrating operating signals of right- and left-side driving operating devices and the output pilot pressures of the right- and left- side forward electromagnetic proportional valves for forward driving during steering control under straight- direction driving control mode according to second embodiment, where (A) indicates a case of steering rightward and (B) indicates a case of steering leftward. [Description of Embodiments] [22] In the following, embodiments of the present invention will be explained referring to drawings. In the drawings, the reference numeral 1 indicates a hydraulic shovel, which is an illustrative example of construction machines. The hydraulic shovel 1 has a basic configuration similar to a conventional one, such as including various sections such as a lower driving portion 2, an upper rotating portion 3 rotatably provided on the lower driving portion 2, and a working device 4 mounted on the upper rotating portion 3.

[23] The lower driving portion 2 includes a pair of right- and left- side crawler driving sections 5L and 5R configured to drive forward and backward and stop as driven by right- and left- side driving motors 6L and 6R respectively provided for the driving sections 5L and 5R.

[24] On the other hand, the reference numeral 7 indicates an operation room provided on the upper rotating portion 3. The operation room 7 includes, but not limited to, an operator seat 8, various operating devices such as right- and left-side working operating levers 9L and 9R of a joy stick type provided on right- and left sides of the operator seat 8, and right- and left- side driving operating devices 10L and 10R provided in front of the operator seat 8, and a monitor device 11 for displaying a machine status and a camera-captured image and for performing various setting. Furthermore, the right- and left- side driving operating devices 10L and 10R include right- and left-side driving operating levers lOaL and lOaR, and right- and left-side driving operating pedals lObL and lObR, so that the operator can optionally select either the levers to operate by hand or the pedals to operate by leg corresponding to driving situation, or the like. [25] The right- and left- side working operating levers 9L and 9R are configured to be operated by swinging for rotating the upper rotating portion 3 and driving the working device 4. Any one of right- and left- side working operating levers 9L or 9R(here, right-side working operating lever) 9R is provided with, at a grip section thereof, a forward button 12, a backward button 13, and a steering slide switch 14 (later described), which can be operated by a thumb gripping the grip section. In this embodiment, the forward button 12 and the backward button 13 are push button switches of a self-return type, and correspond to straight- direction driving operating devices of the present invention. The steering slide switch 14 is a slide switch to be operated by sliding rightward and leftward from a neutral position, and corresponds to a steering operating device of the present invention.

[26] The right- and left-side driving operating devices 10L and 10R

(right- and left- side driving operating levers lOaL and lObR, and right- and left- side driving operating pedals lObL and lObR), and right- and left-side working operating levers 9L and 9R are electric types configured to supply their operation signals (representative of operating directions and operating amounts) in the form of electric signals to a control device 15 later described. Furthermore, the forward button 12, the backward button 13, and the steering slide switch 14 provided on the grip section of the working operating lever 9R are also configured to supply their operation signals to the control device 15. The control device 15 and the monitor device 11 are connected with each other interactively.

[27] Next, Fig. 3 illustrates a hydraulic circuits of the right- and left- side driving motors 6L and 6R. In Fig. 3, the reference numeral 16 indicates hydraulic pumps serving as hydraulic sources for the right- and left-side driving motors 6L and 6R, the reference numeral 17 indicates pilot pumps serving as hydraulic sources for pilot pressure. The hydraulic pumps 16 and pilot pumps 17 are configured to be driven by an engine (not illustrated) mounted on the upper rotating portion 3. The reference numeral 18 is a fuel tank.

[28] Furthermore, in Fig. 3, the reference numerals 19L and 19R are right- and left- side driving control valves for fuel supply controls for the right- and left- side driving motors 6L and 6R, respectively. The right- and left- side driving control valves 19L and 19R are provided with pilot ports 19aL, 19bL, 19aR, and 19bR for forward and backward driving. When no pilot pressure is supplied to the pilot ports 19aL, 19bL, 19R, 19bR for forward and backward driving, the right- and left- side driving control valves 19L and 19R are in a neutral position N at which the fuel is not supplied to the right- and left- side driving motors 6L and 6R. But when the pilot ports 19aL and 19aR for forward driving are supplied with the pilot pressure, the right- and left-side driving control valves 19L and 19R are changed over to a forward movement position X, at which the fuel supply control for driving the driving motors 6L and 6R forward is performed. When the pilot ports 19bL and 19bR for backward driving are supplied with the pilot pressure, the right- and left-side driving control valves 19L and 19R are changed over to a backward movement position Y, at which the fuel supply control for driving the driving motors 6L and 6R backward is performed. In this case, spool movement amounts of the right- and left- side driving control valves 19L and 19R in the forward movement position X and the backward movement position Y are adjusted according to how much pilot pressure is supplied to the forward pilot ports 19aL and 19aR and the backward pilot ports 19bL and 19bR. By this, the supply flow rate into the right- and left-side driving motors 6L and 6R is increased or decreased according to the increase or decrease of the spool movement amounts, and by this, driving speeds of the right- and left- side driving motors 6L and 6R are controlled to increase or decrease. When the forward driving speeds of the right- and left- side driving motors 6L and 6R are equal, the machine moves straightly in the forward direction. When the backward driving speeds of the right- and left- side driving motors 6L and 6R are equal, the machine moves straightly in the backward direction. On the other hand, if the forward or backward driving speeds of the right- and left-side driving motors 6L and 6R are different, the machine moves forward or backward with steering rightward or leftward. In such a case, if the driving speed of the left-side driving motor 6L is faster than the right-side driving motor 6R, the machine steers rightward. If the driving speed of the right-side driving motor 6R is faster than the left ^¬ side driving motor 6L, the machine steers leftward. The steering will be to steer at a sharp angle when the difference between the driving speeds of the right- and left- side driving motors 6L and 6R is greater.

[29] Moreover, in Fig. 3, the reference numerals 20FL, 20BL, 20FR, and 20BR are right- and left- side forward and backward electromagnetic proportional valves for forward and backward driving. These electromagnetic proportional valves 20FL, 20BL, 20FR, and 20BR are configured to output, according to control commands from the control device 15, pilot pressures respectively to the forward and backward pilot ports 19aL, 19bL, 19aR, and 19bR of the right- and left- side driving control valves 19L and 19R. By controlling the pilot pressures output respectively from the right- and left-side forward and backward electromagnetic proportional valves 20FL, 20BL, 20FR, and 20BR, the driving of the right- and left-side driving motors 6L and 6R can be controlled. The right- and left-side driving control valves 19L and 19R and the right- and left- side electromagnetic proportional valves 20FL, 20BL, 20FR, and 20BR correspond to the right- and left-side motor driving means of the present invention.

[30] On the other hand, as illustrated in Fig. 3, the control device 15 is configured to receive the operation signals from the right- and left- side driving operating devices 10L and 10R (right- and left-side driving operating levers lOaL and lOaR and right- and left-side driving operating pedals lObL and lObR), the forward button 12, the backward button 13, and the steering slide switch 14, and the signals from the monitor device 11, and to output, based on these signals thus received, the control commands to the right- and left-side forward and backward electromagnetic proportional valves 20FL, 20BL, 20FR, and 20BR.

[31] Here, the present embodiment is configured such that the operator can use to monitor device 11 to select whether to validate or invalidate setting of later-described "straight-direction driving control mode" and to set a driving speed in "constant-speed straight- direction driving control". The driving speed in "constant-speed straight- direction driving control" can be set in a range of 80% to 100% arbitrarily where 100% is the maximum driving speed. However, in the present embodiment, the explanation is made based on the premises that the driving speed in the "constant-speed straight- direction driving control" is set to 100%, that is, to the maximum driving speed. The monitor device 11 corresponds to the straight- direction driving speed setting means of the present invention.

[32] Next, the control performed by the control device 15 is described.

The control device 15 performs "normal driving control" when the later- described "straight- direction driving control mode" is not set. In the "normal driving control", in order to control the right- and left- side driving motors 6L and 6R based on the operation signals (operation direction and operating amount) from the right- and left-side driving operating devices 10L and 10R (right- and left-side driving operating levers lOaL and lOaR, and the right- and left-side driving operating pedals lObL and 10bR),the control commands are output to the right- and left-side forward and backward electromagnetic proportional valves 20FL, 20BL, 20FR, and 20BR. That is, when the left-side driving operating device lOL is operated for forward driving, a control command of pilot pressure output is output to the left- side forward electromagnetic proportional valve 20FL in order to drive the left-side driving motor 6L to drive forward. When the left-side driving operating device 10L is operated for backward driving, a control command of pilot pressure output is output to the left-side backward electromagnetic proportional valve 20BL in order to drive the left- side driving motor 6L to drive backward. Moreover, when the right- side driving operating device 10R is operated for forward driving, a control command of pilot pressure output is output to the right-side forward electromagnetic proportional valve 20FR in order to drive the right-side driving motor 6R to drive forward. When the right-side driving operating device 10R is operated for backward driving, a control command of pilot pressure output is output to the right-side backward electromagnetic proportional valve 20BR in order to drive the right-side driving motor 6R to drive backward. In this case, the driving speeds of the right- and left- side driving motors 6L and 6R are adjusted according to the operating amounts of the right- and left-side driving operating devices 10L and 10R (the greater the operating amounts of the driving operating devices 10L and 10R, the faster the driving speeds of the driving motors 6L and 6R). In the "normal driving control", the right- and left ^¬ side driving motors 6L and 6R are independently driven forward or backward according to the operating direction of the right- and left-side driving operating devices 10L and 10R and at a speed corresponding to the operating amount of the right- and left-side driving operating devices 10L and 10R.

[33] Furthermore, the control device 15 is configured to perform the setting of the "straight- direction driving control mode", "constant-speed straight- direction driving control", and "steering control under straight- direction driving control mode" based on the operation of the forward button 12, the backward button 13, and the steering slide switch 14. These controls are explained referring to the flowchart of Fig. 4. To begin with, the control device 15 judges whether the setting of the "straight- direction driving control mode" is valid or not (Step Si). [34] The judgement at Step Si is made according to the input signal from the monitor signal 11. That is, as described above, it is configured such that the operator can use the monitor device 11 to select whether to validate or invalidate the setting of the "straight- direction driving control mode". If the operator selects to validate the setting of the "straight-direction driving control mode", a signal indicative of validating the setting is input to the control device 15. Then, if the control device 15 receives the signal indicative of validating the setting, the control device 15 judges as "Yes" at the Step 1, that is judges that the setting of the "straight-direction driving control mode" is valid, and then the process proceeds to the next step. If the control device 15 judges as "No" at Step Si, that is, judges that the setting of "straight- direction driving mode" is invalid, the process will not proceed to the next step but returns to the judging at Step Si.

[35] If the control device 15 judges as "Yes", at the Step 1, then the control device 15 judges whether or not the forward button 12 is operated (Step S2). If the control device 15 judges as "Yes" at the Step S2, that is, judges that the forward button 12 is operated, the control device 15 turns ON a preparation flag (Step S3). If the control device 15 judges as "No" at Step S2, that is, judges that the forward button 12 is not operated, the process will not proceed to the next step but returns to the judging at Step S2.

[36] After the preparation flag is turned ON at the Step S3, then the control device 15 judges whether a predetermined setting time (for example, 5 sec to 10 sec) has elapsed since the preparation flag is turned ON (Step S4). If the control device 15 judges as "No" at the Step S4, that is, judges that the setting time has not elapsed, the judging whether or not the forward button 12 is operated is carried out again (Step S5).

[37] If the control device 15 judges as "Yes" at the Step S5, that is, judges that the forward button 12 is operated, the control device 15 sets the "straight- direction driving control mode" (Step S6) and turns off the preparation flag (Step S7). That is, the "straight-direction driving control mode is set when it is judged at the Step Si that the "straight- direction driving mode" is validly set and it is judged through the Steps S2, S4 and S5 that the forward button 12 is operated twice within the setting time.

[38] On the other hand, if the control device 15 judges as "Yes" at the Step S4, that is judges that the setting time has elapsed since the preparation flag is turned ON, the control device 15 turns OFF the preparation flag (Step S9), and the process returns to the judging at Step S2. Moreover, if the control device 15 judges as "No" at the Step S5, that is, judges that the forward button 12 has not been operated twice, then the control device 15 judges whether or not the backward button 13 is operated (Step S8). If the control device 15 judges as "Yes" at the Step S8, that is, judges that the forward button 13 is operated, the control device 15 turns OFF the preparation flag (Step S9), and the process returns to the judging at the Step S2. On the other hand, if the control device 15 judges "No" at Step S8, that is, judges that the backward button 13 is not operated, the process returns to the judging at Step S4. It is configured that the "straight-direction driving control mode" is not set if it is judged through Steps S2, S4, and S5 that the forward button 12 is not operated again within the setting time since the first operation of the forward button 12, and that the backward button 13 is operated within the setting time since the first operation of the forward button 12. Furthermore, the "straight-direction driving control mode" is not set also if it is judged at Step Si that the setting of the "straight-direction driving control mode" is invalid. With this configuration, it is possible to prevent such a case that the "straight- direction driving control mode is erroneously set by unintended operation etc. by the operator.

[39] On the other hand, if the process at Step S6 sets the "straight- direction driving control mode", the control device 15 carries out the "constant- speed straight- direction driving control" (Step S10). In the "constant- speed straight- direction driving control", in order to cause the machine to move straightly in the forward direction at a constant speed, the control device 15 outputs a control command to instruct the right- and left- side forward electromagnetic proportional valves 20FL and 20FR to output equal pilot pressures. As a result of this, the right- and left-side driving control valves 19L and 19R are switched over to the forward movement position X with the equal spool movement amounts, so that the right- and left- side driving motors 6R and 6L are driven forward at the equal speed. As a result, the machine moves forward straightly at a constant speed. That is, in the "constant-speed straight- direction driving control", as illustrated in Fig. 5, Even if the right- and left-side driving operating devices 10L and 10R are not operated and the operation signal from the driving operating devices 10L and 10R are of 0%, the control device 15 outputs a control command to instruct the right- and left- side forward electromagnetic proportional valves 20FL and 20FR to output the pilot pressures of 100%, thereby driving the driving motors 6R and 6L forward at the maximum speed. Note that the % of the operation signal in Fig. 5 is such that 0% indicates that the driving operating devices 10L and 10R are not operated, and 100% indicates that the driving operating devices 10L and 10R are fully operated, while % of the output pilot pressure is such that 0% indicates that the pilot pressures are not output from the forward electromagnetic proportional valves 20FL and 20FR, and 100% indicates that the output pilot pressures are maximum. In the present embodiment, as described above, the driving speed under the "constant-speed straight- direction driving control" is set to 100% (maximum driving speed) via the monitor device 11, and thus the control device 15 outputs the control command to instruct the output of the 100% pilot pressure. However, if the driving speed is set to less than 100%, the control device 15 controls the forward electromagnetic proportional valves 20FL and 20FR to output pilot pressures for the driving speed as set.

[40] Furthermore, when the "constant-speed straight- direction driving control" is being performed, the control device 15 judges whether or not stopping operation is performed (Step Sll). In the present embodiment, the stopping operation is the operation of the forward button 12, the operation of the backward button 13, or the backward operation of at least one of the right- and left-side driving operating devices 10L and 10R. When any of these operations is carried out, the control device 15 judges that stopping operation is carried out.

[41] If the control device 15 judges as "Yes" at the Step Sll, that is, judges that any stopping operation (the operation of the forward button 12, the operation of the backward button 13, or the backward operation of at least one of right- and left-side driving operating devices 10L and 10R) is carried out, the control device 15 outputs a control command to instruct the right- and left- side forward electromagnetic proportional valves 20FL and 20FR to stop the output of the pilot pressure (Step S12), and cancels the "straight- direction driving control mode" (Step Si 3). By this, the right- and left- side driving control valves 9L and 9R are switched over to the neutral position N so as to stop the fuel supply to the driving motors 6L and 6R, thereby stopping the machine and ending the "constant-speed straight- direction driving control".

[42] On the other hand, if the control device 15 judges as "No" at the

Step Sll, that is, judges that the stopping operation is not performed, then the control device 15 judges whether or not the steering slide switch 14 is operated (Step SI 4).

[43] If the control device 15 judges as "No" at the Step Si 4, that is, judges that the steering slide switch 14 is not operated, the process returns to the control at Step S10. That is, if both the stopping operation and the operation of the steering slide switch 14 are not performed during the "constant- speed straight- direction driving control", the "constant-speed straight- direction driving control" is continued.

[44] On the other hand, if the control device 15 judges as "Yes" at the Step Si 4, that is, judges that the steering slide switch 14 is operated, the control device 15 performs "steering control under straight- direction driving control mode" (Step S15). The "steering control under straight- direction driving control mode" is such control that is for steering the machine rightward or leftward when steering operation is carried out while the "straight-direction driving control mode" is being carried out, and that when the steering slide switch 14 is slid leftward from the neutral position in order to steer the machine leftward, the control device 15 outputs a control command to instruct the left ^¬ side forward electromagnetic proportional valve 20FL to reduce the pilot pressure according to the operating amount (slide amount) of the steering slide switch 14 from the pilot pressure output during the "constant- speed straight- direction driving control" (the pressure is reduced more as the operating amount is greater). Meanwhile, the control device 15 outputs a control command to instruct the right-side forward electromagnetic proportional valve 20FR to maintain the pilot pressure output during the "constant- speed straight- direction driving control". As a result of this, the left- side driving motor 6L reduces its speed according to the operating amount of the steering slide switch 14 from the driving speed during the "constant-speed straight- direction driving control" (the driving speed is reduced more as the operating amount is greater), while the right-side driving motor 6R drives at the same speed as the right-side driving motor 6R has driven during the "constant-speed straight- direction driving control". As a result, the machine steers leftward smoothly without changing the driving speed significantly from the speed at which the machine has driven during the "constant-speed straight- direction driving control". In this case, because the left- side driving motor 6L reduces its speed according to the operating amount of the steering slide switch 14, the left-side driving motor 6L reduces its speed gradually if the steering slide switch 14 is slowly slid to gradually increase the operating amount. Furtherore, also when the steering slide switch 14 is slid rightward from the neutral position in order to steer the machine rightward, an operation similar to the above except that the right and the left are exchanged is carried out, that is, the right-side driving motor 6R reduces its speed according to the operating amount of the steering slide switch 14 from the driving speed at which the right-side driving motor 6R drives during the "constant-speed straight- direction driving control" (the driving speed is reduced more as the operating amount is greater), while the left-side driving motor 6L drives at the same speed as the left- side driving motor 6L has driven during the "constant-speed straight- direction driving control". As a result, the machine steers rightward smoothly without changing the driving speed significantly from the speed at which the machine has driven during the "constant-speed straight-direction driving control". Note that, in the case of steering leftward, the left- side driving motor 6L corresponds to a steering- direction associated driving motor of the present invention, and the right-side driving motor 6R corresponds to a steering-opposite direction associated driving motor of the present invention. Similarly, in the case of steering rightward, the right-side driving motor 6R corresponds to the steering- direction associated driving motor of the present invention, and the left- side driving motor 6L corresponds to the steering-opposite direction associated driving motor of the present invention. Moreover, Fig. 6(A) illustrates the operating amount (slide amount) in operating the steering slide switch 14 leftward, and the output pilot pressures from the left- side forward electromagnetic proportional valves 20FL and the right-side forward electrostatic proportional valves 20FR. Fig. 6(B) illustrates the operating amount (slide amount) in operating the steering slide switch 14 rightward, and the output pilot pressures from the left- side forward electromagnetic proportional valves 20FL and the right-side forward electrostatic proportional valves 20FR. Note that the % of the operating amount in Figs. 6(A) and 6(B) is such that 0% indicates that the steering slide switch 14 is not operated (in the neutral position), and 100% indicates that the steering slide switch 14 is fully operated, while % of the output pilot pressure is such that 0% indicates that the pilot pressures are not output from the forward electromagnetic proportional valves 20FL and 20FR, and 100% indicates that the output pilot pressures are of the "constant-speed straight- direction driving control" (the maximum pilot pressure in the present embodiment).

[45] Furthermore, even in the "steering control under straight- direction driving mode", the control device 15 performs the judging of Step Sll, that is, performs the judging whether or not any stopping operation (the operation of the forward button 12, the operation of the backward button 13, or the backward operation of at least one of right- and left- side driving operating devices 10L and 10R) is carried out. If the control device 15 judges that any stopping operation is carried out, the control device 15 performs the process of Steps S12 and S13 described above, thereby stopping the machine and ending the "steering control under straight- direction driving mode". On the other hand, if the control device 15 judges at Step Sll that any stopping operation is not carried out in the "steering control under straight- direction driving mode", the "steering control under straight- direction driving mode" is continued. [46] Note that the setting of the "straight-direction driving control mode" and the controlling of the "constant- speed straight- direction driving control" and the "steering control under straight- direction driving control mode" described above are controlling for driving the machine forward. In case of driving the machine backward, the backward switch 14 is operated instead of the forward switch 12, and the control device 15 outputs a control command to the right- and left- side backward electromagnetic proportional valves 20BL and 20BR instead of the right- and left-side forward electromagnetic proportional valves 20FL and 20FR. The operation for the backward driving is carried out in a procedure similar to that for the operation for the forward driving, and thus its explanation is omitted here.

[47] As the stopping operation during the setting of the "straight- direction driving control mode" in the present embodiment, as described above in case where the machine is moving forward, the operation of the forward button 12, the operation of the backward button 13, or the backward operation of at least one of right- and left-side driving operating devices 10L and 10R is set,, but in case where the machine is moving backward, the operation of the forward button 12, the operation of the backward button 13, or the forward operation of at least one of right- and left- side driving operating devices 10L and 10R is set. [48] In the present embodiment configured as above, the hydraulic shovel 1 includes the right- and left- side driving section 5L and 5R, the right- and left- side driving motors 6L and 6R for driving the right- and left- side driving sections 5L and 5R, respectively, the right- and left-side motor driving means (the right- and left- side driving control valves 19L and 19R, the right- and left- side forward and backward electromagnetic proportional valves 20FL, 20BR, 20FR, and 20BR) for driving the right- and left- side driving motors 6L and 6R, and the right- and left-side driving operating devices 10L and 10R configured to be operated to control the respective driving of the right- and left- side driving sections 5L and 5R. However, in addition of these, the hydraulic shovel 1 further includes the straight- direction driving operating devices (the forward button 12, and the backward button 13) and the steering operating device (the steering slide switch 14) configured to be operated to steer the machine during the straight- direction driving performed according to the operation of the forward button 12 and backward button 13, and the control device 15 for receiving the operation signals from the right- and left- side driving operating devices 10L and 10R, the forward button 12 and the backward button 13, and the steering slide switch 14. The control device 15 is configured to perform the mode setting for setting the "straight-direction driving control mode" according to the operation signal of the forward button 12 and the backward button 13, the "normal driving control" for driving, when the "straight- direction driving mode" is not set, the right- and left-side driving motors 6L and 6R respectively at the speeds corresponding to the operating amounts of the right- and left-side driving operating devices 10L and 10R the "constant-speed straight- direction driving control" for driving the right- and left-side driving motors 6L and 6R when the "straight-direction driving control mode" is set, and the "steering control under straight- direction driving control mode" for a case where the steering slide switch 14 is operated while the "constant-speed straight- direction driving control" is being carried out, the "steering control under straight- direction driving control mode" being such that one of the driving motors 6L and 6R is caused to reduce its speed according to the operating amount of the steering slide switch 14, wherein the one of the driving motors 6L and 6R is associated with the steering direction in which the steering slide switch 14 is operated, and the other one of the driving motors 6L and 6R is caused to maintain the constant speed. [49] As such, in the present embodiment, the "straight- direction driving control mode" is set according to the operation of the forward button 12 and the backward button 13, and when the "straight- direction driving control mode" is set, the "constant-speed straight- direction driving control" for driving the right- and left- side driving motors 6L and 6R at a constant speed is carried out, whereby the machine can move straightly at an harmonious speeds according to the operation of the forward button 12 and the backward button 13, so that the operator does not need to carefully operate the right- and left ^¬ side driving operating devices 10L and 10R always in the same operating amounts during the straight- direction driving, thereby significantly reducing the burden of the operator. Furthermore, in this configuration, to steer the machine rightward or leftward while the "constant-speed straight- direction driving control" is being carried out, the steering slide switch 14 is operated to performed the "steering control under straight- direction driving control mode" in which one of the driving motors 6L and 6R is caused to reduce its speed from the speed of the constant-speed straight- direction driving according to the operating amount of the steering slide switch 14, wherein the one of the driving motors 6L and 6R is associated with the steering direction in which the steering slide switch 14 is operated, and the other one of the driving motors 6L and 6R is caused to maintain the speed of the constant-speed straight- direction driving. As a result, the rightward or leftward steering can be carried out smoothly without significantly changing the driving speed, thereby achieving stable steering from the constant- speed straight- direction driving.

[50] Furthermore, in this configuration, the driving speed in the "constant-speed straight- direction driving control" can be variably set via the monitor device 11. By this, the driving speed of the constant- speed straight- direction driving of the machine can be arbitrarily set according to the operator, situation of the work place, or the like. Even though the present embodiment uses the monitor device 11 as the straight- direction driving speed setting means, the present invention is not limited to this and an operating device such as dials can be additionally provided as the straight- direction driving speed setting means.

[51] Furthermore, in the present embodiment, the straight- direction driving operating devices (the forward switch 12 and the backward switch 13) or the right- and left-side driving operating devices 10L and 10R are used as the operating devices for stopping the driving under the "straight- direction driving control mode". This eliminates the need of additionally providing an operating device for stopping the driving, thereby facilitating dual-use of the components. Furthermore, in the present embodiment, as the operating devices for stopping the driving, the right- and left-side driving operating devices 10L and 10R are configured such that the driving is stopped by the backward operation of the driving operating devices 10L and 10R in case the machine is moving forward, and the driving is stopped by the forward operation of the driving operating devices 10L and 10R in case the machine is moving backward. Thus, even though the right- and left-driving operating device s 10L and 10R are used differently from the "normal driving control", the operator can comfortably use the right- and left-driving operating devices 10L and 10R as the operating device for stopping the driving. [52] It should be noted that the present invention is not limited to the embodiments described above. The present invention is not limited to the above-described embodiment where the grip section of the working operating lever is provided with the straight- direction driving operating devices (the forward switch 12 and the backward switch 13), and the steering operating device (steering slide switch 14). The straight- direction driving operating devices and the steering operating device may be provided at any suitable positions inside the operator rooms.

[53] Furthermore, the above- described embodiment is provided with the steering slide switch 14 as the steering operating device for steering the machine rightward or leftward during the "constant- speed straight- direction driving control". However, the right- and left- side driving operating devices 10L and 10R (the right- and left-side driving operating lever lOaL and lOaR, and the right- and left-side driving operating pedals lObL and lObR) may be configure to be usable as the steering operating devices. In this case, the left- side driving operating device 10L is set to be used as the steering operating device for the rightward steering and the right-side driving operating device 10R is set to be used as the steering operating device for the leftward steering, and the control device 15 is configured to perform the "steering control under straight- direction driving control mode" when any of the right- and left- side driving operating devices 10L and 10R is operated while the "constant-speed straight- direction driving control". A "steering control under straight- direction driving control mode" in this case is illustrated in Fig 7 as a Second embodiment. The control illustrated in Fig. 7(A) is a case where the left- side driving operating device 10L is operated, that is, the machine is steered rightward when the machine is moving forward straightly at a constant speed. In this case, the control device 15 receives an operation signal corresponding to the operating amount of the left- side driving operating device 10L (an operation signal increased as the operating amount is greater) from the left- side driving operating device 10L, while the left-side driving operating device 10L supplies 0% operation signal. The control device 15 receives the operation signal from the left- side driving operating device 10L, and then outputs a control command to instruct the left- side forward electromagnetic proportional valve 20FL to maintain the output pilot pressure output during the "constant- speed straight- direction driving control" and a control command to instruct the right-side forward electromagnetic proportional valve 20FL to reduce the output pilot pressure according to the operating amount of the left- side driving operating device 10L (to be a lower pressure as the operating amount is greater) from the one output during the "constant- speed straight- direction driving control". As a result of this, the left-side driving motor 6L (driving motor associated with the steering-opposite direction) is driven at the same speed as in the "constant- speed straight- direction driving control", while the right-side driving motor 6R (driving motor associated with the steering direction) reduces its speed according to the operating amount of the left- side driving operating 10L from the driving speed of the "constant-speed straight- direction driving control" (to be a lower speed as the operating amount is greater), thereby steering the machine rightward smoothly without significantly changing the driving speed from the "constant-speed straight- direction driving control". The control illustrated in Fig. 7(B) is a case where the right-side driving operating device 10R is operated, that is, the machine is steered leftward when the machine is moving straightly at a constant speed. In this case, the control similar to the rightward steering except that the right and left are exchanged is carried out. The right-side driving motor 6R (driving motor associated with the steering- opposite direction) is driven at the same speed as in the "constant-speed straight- direction driving control", while the left-side driving motor 6L (driving motor associated with the steering direction) reduces its speed according to the operating amount of the right-side driving operating 10R from the driving speed of the "constant-speed straight- direction driving control" (to be a lower speed as the operating amount is greater), thereby steering the machine leftward smoothly without significantly changing the driving speed from the "constant- speed straight- direction driving control". Thus, the present invention can be put into practice with the configuration as in the second embodiment where the right- and left-side driving operating devices 10L and 10R (the right- and left ^¬ side driving operating levers lOaL and lOaR, and the right- and left- side driving operating pedals lObL and lObR) are used as the steering operating devices. In this case, there is no need to additionally provide the steering operating devices, thereby facilitating the dual-use of components. In the second embodiment, the left- side driving operating device 10L is used as the steering operating device for the rightward steering and the right-side driving operating device 10R is used as the steering operating device for the leftward steering. This configuration is configured similarly to the "normal driving control" in which the rightward steering is carried out by operating the left-side driving operating device 10L in a greater operating amount than that of the right-side driving operating device 10R, and the leftward steering is carried out by operating the right-side driving operating device 10R in a greater operating amount than that of the left- side driving operating device 10L. This configuration allows the operator to use the right- and left- side driving operating devices 10L and 10R as the steering operating devices comfortably.

[54] The right- and left- side working operating levers may be configured to be usable as the steering operating devices. In this case, the right- and left-side working operating levers are used as the steering operating devices but not as the operating devices for the rotation of the upper rotating portion 3 and the driving of the working device 4 during the "constant-speed straight- direction driving control" and the "steering control under the straight- direction driving mode". [55] Furthermore, the control device may be connected to an engine control section for controlling the engine and be configured that when the control device performs the "steering control under straight- direction driving control mode" the control derive outputs a control command to the engine control section in order to cause it to perform engine speed lowering control for lowering engine speed than in the "constant-speed straight- direction driving control". This configuration decelerates the driving speed in the "steering control under straight- direction driving control mode" than in the "constant- speed straight- direction driving control", thereby allowing more stable steering.

[Industrial applicability]

[56] The present invention is applicable to driving control devices of construction machines, such as hydraulic shovels, provided with right- and left ^¬ side driving sections.

[Reference Sign List]

5L, 5R: Right- and left- side driving sections

6L, 6R: Right- and left- side driving motors

10L, 10R: Right- and left-side driving operating device

11: Monitor device

12 ^' · Forward button

13: Backward button

14 ^' · Steering slide switch

15: Control device

16 ^: Hydraulic pump

19L, 19R: Right- and left-side driving control valves

20FL, 20BL, 20FR, 20BR: Right- and left-side forward and backward electromagnetic proportional valves