Working machine

Abstract

A working machine includes a hydraulic control apparatus. In a straight travel valve of the hydraulic control apparatus, a communication path and a control valve that opens and closes the communication path are provided. During a combined operation of traveling operation and working operation, a working pressure and a traveling pressure are taken in as pilot pressures on either side. During a small traveling operation in which the traveling operation amount is small, the communication path is unconditionally closed. During a large traveling operation in which the traveling operation amount is large, if the working pressure is higher than the traveling pressure, the communication path is open, and if the working pressure is lower than the traveling pressure, the communication path is closed.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a working machine such as a hydraulic excavator having a hydraulic control apparatus.

2. Description of the Related Art

FIG. 6 shows a hydraulic control apparatus of a hydraulic excavator as an example of a working machine.

A straight travel valve 27 is a two-position four-port switching valve having a neutral position x, a straight travel position y, pump ports P1 and P2, and actuator ports A and B, and is switched and controlled by a secondary pressure of an electromagnetic proportional switching control valve 29 based on a command from a controller 28.

Operation signals according to the operation amounts of remote control valves 19 to 24 are input into the controller 28. During a single operation in which traveling operation and working operation (operation of working actuators 6, 7, 8, and 12) are performed separately, the straight travel valve 27 is at the neutral position x.

In this case, the discharged oil of a first pump 25 is supplied to a first group G1 via a path P1-B of the straight travel valve 27, and the discharged oil of the second pump 26 is directly supplied to a second group G2 (first pressurized oil supply state).

On the other hand, during a combined operation in which traveling operation and working operation are performed simultaneously, the straight travel valve 27 is switched from the neutral position x to the straight travel position y.

In this case, the discharged oil of the first pump 25 is supplied to hydraulic actuators 6, 7, 8, and 12 except for traveling motors 10 and 11 via a path P1-A of the straight travel valve 27 and a pressurized oil supply pipe L, and the discharged oil of the second pump 26 is distributed to both traveling motors 10 and 11 (second pressurized oil supply state).

In this second pressurized oil supply state, since both traveling motors 10 and 11 are driven by the common second pump 26, if the amounts of the right and left traveling operations are the same, both traveling motors 10 and 11 are supplied with the same amount of oil and rotate at the same speed. That is to say, straight travel is ensured.

In this case, since the amount of pressurized oil supplied to both traveling motors 10 and 11 is decreased by half compared with the first pressurized oil supply state, the speed is also decreased by half (sudden deceleration) and shock occurs.

As means for reducing the magnitude of this shock, a communication path 31 is provided in the straight travel valve 27. During the second pressurized oil supply state, the pump lines of both pumps 25 and 26 communicate with each other via the communication path 31, and part of the discharged oil of the first pump 25 is sent to the traveling side (see Japanese Unexamined Patent Application Publication No. 2000-17693).

However, the above-described configuration in which the communication path 31 is always open cannot meet the requirements of the following two cases.

(i) The case where working operation is performed during low-speed traveling (so-called “half-lever traveling” in which the operation amounts of the traveling remote control valves 19 and 22 are small)

If the actuating pressure of the working actuators 6, 7, 8, and 12 (working pressure) is higher than the pressure of the traveling motors 10 and 11 (traveling pressure), the discharged oil of the first pump 25 (the oil of the working side) flows into the traveling side, and the speed is increased despite the intention of the operator.

If the working pressure is lower than the traveling pressure, the discharged oil of the second pump 26 (the oil of the traveling side) flows into the working side, and traveling is further decelerated or even stopped.

Therefore, in such a situation, it is preferable that the communication path 31 be closed.

(ii) The case where working operation is performed during high-speed traveling (so-called “full-lever traveling” in which the operation amounts of the traveling remote control valves 19 and 22 are large)

In a situation where the working pressure is higher than the traveling pressure, part of the oil of the working side is supplied to the traveling side as intended, and therefore, sudden deceleration can be prevented. However, in a situation where the working pressure is lower than the traveling pressure, the oil of the traveling side flows into the working side, and the speed is decreased more sharply.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a working machine having a hydraulic control apparatus that can appropriately control (open or close) a communication path depending on the situation.

A working machine according to the present invention has the following basic configuration.

That is to say, a working machine includes a lower traveling body, an upper rotating body mounted on the lower traveling body, a working attachment attached to the upper rotating body, and hydraulic actuators including working actuators that actuate the working attachment, and right and left traveling motors. The hydraulic actuators is separated into a first group including one of the right and left traveling motors and a second group including the other traveling motor. The working machine further includes first and second pumps serving as hydraulic pressure sources, and a straight travel valve that switches the flow lines of discharged oils from the pumps. The straight travel valve is at a neutral position to supply the first and second groups with discharged oils of separate pumps during a single operation in which traveling operation and working operation are performed separately. In addition, the straight travel valve is switched to a straight travel position and supplies both traveling motors and the working actuators with discharged oils of separate pumps during a combined operation in which traveling operation and working operation are performed simultaneously. Moreover, the straight travel valve enables pump lines of both of the pumps to communicate with each other via a communication path in the process of switching of the straight travel valve from the neutral position to the straight travel position. The working machine further includes a control valve that opens and closes the communication path. During the combined operation, the control valve controls the communication path according to the position of the straight travel valve, a working pressure that is an actuating pressure of the working actuators, and a traveling pressure that is an actuating pressure of the traveling motors, in the following manners:

(I) during a small traveling operation in which the traveling operation amount is smaller than a predetermined value, the communication path is unconditionally closed; and

(II) during a large traveling operation in which the traveling operation amount is larger than the predetermined value, if the working pressure is higher than the traveling pressure, the communication path is open, and if the working pressure is lower than the traveling pressure, the communication path is closed.

According to the present invention, a working machine is provided with a control valve that opens and closes a communication path. During a small traveling operation in which the traveling operation amount is smaller than a predetermined value (half-lever traveling=low-speed traveling), the control valve unconditionally closes the communication path. During a large traveling operation in which the traveling operation amount is larger than the predetermined value (full-lever traveling=high-speed traveling), if the working pressure is higher than the traveling pressure, the control valve opens the communication path, and if the working pressure is lower than the traveling pressure, the control valve closes the communication path. Therefore, the following advantages can be obtained:

(1) The following adverse effects do not occur. During the half-lever traveling, the oil of the working side flows into the traveling side, and the speed is thereby increased, or the oil of the traveling side flows into the working side, and traveling is thereby further decelerated or even stopped.

(2) During the full-lever traveling, in a situation where the working pressure is higher than the traveling pressure, the oil of the working side is supplied to the traveling side as intended, and therefore, sudden deceleration can be prevented. On the other hand, in a situation where the working pressure is lower than the traveling pressure, since communication of oil between the traveling side and the working side is blocked, an adverse effect such that the speed is decreased more sharply can be prevented.

Thus, the communication path can be appropriately controlled (opened or closed) depending on the situation, and the operability of the combined operation can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the overall structure of a hydraulic control apparatus according to an embodiment of the present invention;

FIGS. 2A to 2D show the switching of the straight travel valve in the apparatus, using hydraulic symbols;

FIGS. 3A to 3D are half cross-sectional views showing the structure and the switching of the valve;

FIG. 4 is a half cross-sectional view showing the structure of a straight travel valve according to another embodiment of the present invention;

FIG. 5 is a schematic side view of a hydraulic excavator; and

FIG. 6 shows the overall structure of a hydraulic control apparatus of the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be described with reference to the drawings.

As an example of a working machine to which the present invention is applied, a hydraulic excavator will be described. As shown in FIG. 5, a hydraulic excavator includes a crawler-type lower traveling body 1, an upper rotating body 2 mounted on the lower traveling body 1 and rotatable around a vertical axis, and a working (excavating) attachment 9 attached to the upper rotating body 2. The working (excavating) attachment 9 includes a boom 3, an arm 4, a bucket 5, a cylinder 6 for raising and lowering the boom 3, a cylinder 7 for actuating the arm 4, and a cylinder 8 for actuating the bucket 5.

The hydraulic excavator further includes left and right traveling motors 10 and 11 that cause the lower traveling body 1 to travel and a rotating motor 12 that causes the upper rotating body 2 to rotate.

FIG. 1 shows the overall structure of a hydraulic control apparatus.

The hydraulic actuators are separated into two groups: a first group G1 including the right traveling motor 11, the bucket cylinder 8, and the boom cylinder 6; and a second group G2 including the left traveling motor 10, the rotating motor 12, and the arm cylinder 7.

The hydraulic actuators of the group G1 are connected in tandem by a center bypass line C1 with the traveling motor 11 most upstream. The hydraulic actuators of the group G2 are connected in tandem by a center bypass line C2 with the traveling motor 10 most upstream. On the other hand, the hydraulic actuators except for the traveling motors (working actuators) 6, 7, 8, and 12 are connected in parallel to a pressurized oil supply line L provided separately from the center bypass lines C1 and C2. Reference character T denotes a tank.

In addition, each hydraulic actuator is provided with a hydraulic pilot control valve 13, 14, 15, 16, 17, or 18 that controls its operation, and a remote control valve 19, 20, 21, 22, 23, or 24 that serves as operating means for switching the hydraulic pilot control valve.

As pressurized oil supply sources for the hydraulic actuators, first and second pumps 25 and 26 are provided. The discharged oils of both pumps 25 and 26 are supplied to the groups G1 and G2 via a hydraulic pilot straight travel valve 32.

In the present embodiment, the straight travel valve 32 is a four-position four-port switching valve having four switch positions: a neutral position a at the left end in the figure, a straight travel position 6 at the right end in the figure, and first and second middle positions β and γ, and four ports: two pump ports P1 and P2, and two actuator ports A and B. This straight travel valve 32 is switched and controlled by a secondary pressure of an electromagnetic proportional switching control valve 29 in response to a command from a controller 33 based on operation signals (for example, signals from pressure sensors that detect the remote control valve pilot pressures).

That is to say, the straight travel valve 32 is set to the neutral position α during the single operation of traveling or working. This state is called “first pressurized oil supply state.”

In this first pressurized oil supply state, as in the neutral position x of the straight travel valve 27 in FIG. 6, the discharged oil of the first pump 25 is supplied to the first group G1 via a path P1-B of the straight travel valve 32, and the discharged oil of the second pump 26 is directly supplied to the second group G2.

If an independent travel switch 34 is operated, the straight travel valve 32 is switched to the straight travel position 6. This state is called “second pressurized oil supply state.”

In this second pressurized oil supply state, the discharged oil of the first pump 25 is supplied to the working actuators 6, 7, 8, and 12 via a path P1-A of the straight travel valve 32 and a pressurized oil supply line L, and the discharged oil of the second pump 26 is distributed to both traveling motors 10 and 11 so as to ensure straight traveling.

In addition, the traveling system is completely separated from the working system, and an independent traveling state is thereby obtained. Therefore, for example, when the working machine travels, hanging a load, the load can be prevented from swinging.

In this case, if switching from the first pressurized oil supply state to the second pressurized oil supply state is suddenly performed, the amount of the pressurized oil supplied to both traveling motors 10 and 11 sharply decreases, the speed is thereby sharply decreased, and shock occurs.

As a measure against this problem, the straight travel valve 32 is provided with a communication path 35 for supplying part of the discharged oil of the first pump 25 to the traveling side, as in the straight travel valve 27 of the related art.

However, if the communication path 35 is always open, unfavorable situations can occur during the half-lever traveling and the full-lever traveling depending on the relationship between the working pressure and the traveling pressure as described above.

To solve this problem, a control valve 36 for opening and closing the communication path 35 is incorporated into the straight travel valve 32.

FIGS. 2A to 2D are enlarged views showing the configurations of the straight travel valve 32 having the control valve 36 at the positions a to 6, respectively, using hydraulic symbols.

FIGS. 3A to 3D show the specific valve structure (half cross-section) of the straight travel valve 32. As shown in the figures, a sub-spool 38 is provided in a main spool 37 that is a spool of the straight travel valve 32. The sub-spool 38 can stroke in the horizontal direction in the figures.

As shown, the diameter of the middle portion of the sub-spool 38 is smaller than the diameter of the right and left end portions thereof (the right and left end portions in FIGS. 3A to 3D. The words “right” and “left” will hereinafter designate directions in FIGS. 3A to 3D). Between the middle portion of the sub-spool 38 and the inner surface of the main spool 37, a communication path 35 is formed. Reference numerals 39 and 40 denote communicating ports for causing the communication path 35 to communicate with the pump ports P1 and P2.

On the right side of the sub-spool 38, a working side pilot chamber 41 is provided. On the left side of the sub-spool 38, a traveling side pilot chamber 42 is provided. The main spool 37 is provided with working side pilot ports 43 and 44 and a traveling side pilot port 45. The working side pilot ports 43 and 44 introduce the working pressure (the pressure of the first pump 25) into the working side pilot chamber 41. The traveling side pilot port 45 introduces the traveling pressure (the pressure of the second pump 26) into the traveling side pilot chamber 42. In FIGS. 3A to 3D, reference character Tp denotes a tank port, and reference character Dr denotes a drain port.

The two working side pilot ports 43 and 44 are provided for the purpose of causing the working side pilot chamber 41 to communicate with the tank port Tp or the drain port Dr in the neutral state of the straight travel valve shown in FIGS. 2A and 3A and in the half-lever traveling operation state during the combined operation shown in FIGS. 2B and 3B, and for the purpose of causing the working side pilot chamber 41 to communicate with the pump port P1 in the full-lever traveling operation state shown in FIGS. 2C and 3C.

Reference numeral 46 denotes a spring provided in the traveling side pilot chamber 42. The sub-spool 38 is pressed by a resultant force of the force of the spring 46 and the traveling pressure introduced into the traveling side pilot chamber 42, rightward in FIGS. 3A to 3D (so as to close the communication path 35), and is pressed by the working pressure introduced into the working side pilot chamber 41, leftward (so as to open the communication path 35).

Thus, the sub-spool 38, the pilot chambers 41 and 42 on either side, the pilot ports 43 to 45, the spring 46, and so on constitute the control valve 36. By means of this control valve 36, the communication path 35 is opened or closed depending on the position of the straight travel valve 32, the working pressure, and the traveling pressure as follows.

When the straight travel valve 32 is at the neutral position α, as shown in FIG. 3A, the working side pilot chamber 41 communicates with the tank port Tp and the drain port Dr, and the traveling side pilot chamber 42 communicates with the pump port P2 via the traveling side pilot port 45.

Therefore, the pressure (the traveling pressure) is introduced only into the traveling side pilot chamber 42. Consequently, the sub-spool 38 is pressed rightward to close the communication path 35 (control valve 36). As a result, communication between the pump ports P1 and P2 is blocked, and the first pressurized oil supply state is caused, that is to say, the discharged oil of the first pump 25 and the discharged oil of the second pump 26 are separately supplied to the first group G1 and the second group G2, respectively.

If the combined operation is performed from this state, transition is made to the state of FIG. 3B or FIG. 3C depending on the traveling operation amount.

First, in a half-lever traveling stage in which the traveling operation amount is small, as shown in FIG. 3B, the working side pilot chamber 41 communicates with the drain port Dr, and the traveling side pilot chamber 42 continues communicating with the pump port P2 via the traveling side pilot port 45. Therefore, the communication path 35 remains closed.

That is to say, during the half-lever traveling, the communication path 35 is unconditionally closed regardless of the working pressure and the traveling pressure.

Therefore, the following unfavorable situations can be prevented from occurring. When the working pressure is higher than the traveling pressure, the discharged oil of the first pump 25 flows into the traveling side, and the speed is increased despite the intention of the operator who wants to travel at low speed. When the traveling pressure is higher than the working pressure, the discharged oil of the second pump 26 (the oil of the traveling side) flows into the working side, and traveling is further decelerated or even stopped.

Next, from this half-lever traveling state, if the operator performs the full-lever traveling operation with the intention of traveling at high speed, as shown in FIG. 3C, the traveling pressure is introduced into the traveling side pilot chamber 42. On the other hand, the working pressure is introduced into the working side pilot chamber 41 via the pump port P1 and the working side pilot port 43. The position of the sub-spool 38 is determined by the pressures of the pilot chambers 41 and 42 on either side.

That is to say, if the traveling pressure is higher than the working pressure, the sub-spool 38 is pressed rightward, and if the traveling pressure is lower than the working pressure, the sub-spool 38 is pressed leftward. Therefore, when the traveling pressure is higher than the working pressure, the communication path 35 is closed, and when the traveling pressure is lower than the working pressure, the communication path 35 is open.

Since the communication path 35 is open in a situation where the traveling pressure is lower than the working pressure, part of the oil of the working side is supplied to the traveling side as intended, thereby preventing sudden deceleration of traveling.

On the other hand, since the communication path 35 is closed in a situation where the traveling pressure is higher than the working pressure, an adverse effect such that the oil of the traveling side flows into the working side and the speed is thereby decreased more sharply is prevented.

By means of the ON operation (switching to ON) of the independent travel switch 34 shown in FIG. 1, the straight travel valve 32 is switched to the straight travel position 6. In this case, as shown in FIG. 3D, flow paths of the discharged oils of the pumps are switched to P1-A and P2-B, the communication path 35 is blocked, and the above-described straight traveling state (independent traveling state) is caused.

That is to say, when the straight travel valve 32 is switched to the straight travel position 6, the communication path 35 is unconditionally closed. In this case, at the straight travel position 6, an independent traveling function such that traveling operation is completely independent from working operation can be obtained. Therefore, for example, when the working machine travels, hanging a load, the load can be prevented from swinging.

As described above, by opening or closing the communication path 35 with the control valve 36 depending on the situation (whether the half-lever traveling or the full-lever traveling is selected, and the working pressure and the traveling pressure during the full-lever traveling), the flow of oil during the combined operation can be made desirable and the operability of the combined operation can be improved.

In addition, the control valve 36 is incorporated into the straight travel valve 32, that is to say, the communication path 35 and the sub-spool 38 for opening and closing the communication path 35 are provided in the main spool 37 that is a spool of the straight travel valve 32, and the sub-spool 38 is actuated by the working pressure and the traveling pressure. Therefore, it is not necessary to provide a space for the control valve, and a control circuit. As a result, it is easy to mount the control valve 36, and the cost can be reduced.

In the present embodiment, the control valve 36 is a hydraulic pilot valve, the working pressure is introduced into one of the pilot chambers of the control valve 36, and the traveling pressure is introduced into the other pilot chamber.

In this configuration, the communication path 35 and the sub-spool 38 are provided in the main spool 37 that is a spool of the straight travel valve 32, the pilot chambers are formed on either side of the sub-spool 38, the working side pilot ports that introduce the working pressure into one of the pilot chambers and the traveling side pilot port that introduces the traveling pressure into the other pilot chamber are provided in the main spool 37, and the communication path 35, the sub-spool 38, the pilot chambers, the working side pilot ports, and the traveling side pilot port constitute the control valve 36.

According to this configuration, the control valve 36 is a hydraulic pilot valve, the working pressure is introduced into one of the pilot chambers of the control valve 36, and the traveling pressure is introduced into the other pilot chamber. Therefore, opening or closing of the control valve during the full-lever traveling can be performed automatically and accurately depending on the working pressure and the traveling pressure.

As a method to realize this configuration, it is possible to take the communication path 35 out of the straight travel valve 32, to provide a control valve, and to cause the control valve to operate outside as described above.

However, this external control valve method has the following problems. For example, the cost is substantially increased because it is necessary to newly install a control valve outside in addition to the providing of a control circuit therefor. Moreover, it is necessary to create a space for the control valve in a limited space.

According to the present embodiment, the communication path 35 and the sub-spool 38 are provided in the main spool 37 that is a spool of the straight travel valve 32, and the working pressure and the traveling pressure are introduced into the pilot chambers on either side of the sub-spool 38, that is to say, the control valve 36 is incorporated into the straight travel valve 32. Therefore, it is not necessary to provide a space for the control valve, and a control circuit. As a result, it is easy to mount the control valve, and the cost can be reduced. Another Embodiment As shown in FIG. 4, the pilot ports 43 and 45 that cause the pilot chambers 41 and 42, respectively, to communicate with the pump ports P1 and P2, respectively, in the full-lever traveling state during the combined operation, may be provided with a throttle. In addition, pilot ports 47 and 48 having a throttle and communicating with the tank port Tp may be added to the working side and the traveling side, respectively.

In both the working side and the traveling side, the pressures generated in the pilot chambers 41 and 42 can be variously set by the sizes of the throttles of the two pilot ports 43 and 47 and the sizes of the throttles of the two pilot ports 45 and 48, respectively. Therefore, the present embodiment has the following advantages. For example, freedom of choice expands with respect to the size of the spring 46 of the traveling side. In addition, the pilot pressures on either side can be stabilized.

The above-described double throttle pilot structure may be provided in only one of the working side and the traveling side.

Although the invention has been described with reference to the preferred embodiments in the attached figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.

Claims

1. A working machine comprising: a lower traveling body; an upper rotating body mounted on the lower traveling body; a working attachment attached to the upper rotating body; hydraulic actuators including working actuators that actuate the working attachment, and right and left traveling motors, the hydraulic actuators being separated into a first group including one of the right and left traveling motors and a second group including the other traveling motor; first and second pumps serving as hydraulic pressure sources; a straight travel valve adapted to switch the flow lines of discharged oils from the pumps, the straight travel valve being at a neutral position to supply the first and second groups with discharged oils of separate pumps during a single operation in which traveling operation and working operation are performed separately, being switched to a straight travel position to supply both traveling motors and the working actuators with discharged oils of separate pumps during a combined operation in which traveling operation and working operation are performed simultaneously, and enabling pump lines of both of the pumps to communicate with each other via a communication path in the process of switching of the straight travel valve from the neutral position to the straight travel position; and a control valve adapted to open and close the communication path, wherein, during the combined operation, the control valve controls the communication path according to the position of the straight travel valve, a working pressure that is an actuating pressure of the working actuators, and a traveling pressure that is an actuating pressure of the traveling motors, in the following manners: (I) during a small traveling operation in which the traveling operation amount is smaller than a predetermined value, the communication path is unconditionally closed; and (II) during a large traveling operation in which the traveling operation amount is larger than the predetermined value, if the working pressure is higher than the traveling pressure, the communication path is open, and if the working pressure is lower than the traveling pressure, the communication path is closed.

2. The working machine according to claim 1, wherein, when the straight travel valve is switched to the straight travel position, the communication path is unconditionally closed.

3. The working machine according to claim 1, wherein the control valve is a hydraulic pilot valve, the working pressure is introduced into a first pilot chamber of the control valve, and the traveling pressure is introduced into a second pilot chamber.

4. The working machine according to claim 2, wherein the control valve is a hydraulic pilot valve, the working pressure is introduced into a first pilot chamber of the control valve, and the traveling pressure is introduced into a second pilot chamber.

5. The working machine according to claim 3, wherein the communication path and a sub-spool are provided in a main spool that is a spool of the straight travel valve, the first pilot chamber and the second pilot chamber are formed on either side of the sub-spool, a working side pilot port that introduces the working pressure into the first pilot chamber and a traveling side pilot port that introduces the traveling pressure into the second pilot chamber are provided in the main spool, and the communication path, the sub-spool, the first pilot chamber, the second pilot chamber, the working side pilot port, and the traveling side pilot port constitute the control valve.

6. The working machine according to claim 4, wherein the communication path and a sub-spool are provided in a main spool that is a spool of the straight travel valve, the first pilot chamber and the second pilot chamber are formed on either side of the sub-spool, a working side pilot port that introduces the working pressure into the first pilot chamber and a traveling side pilot port that introduces the traveling pressure into the second pilot chamber are provided in the main spool, and the communication path, the sub-spool, the first pilot chamber, the second pilot chamber, the working side pilot port, and the traveling side pilot port constitute the control valve.