Hydraulic driving device for work machine

Disclosed is a hydraulic drive system for a working machine, which enables to conduct forced regeneration continuously for a sufficient time. Based on an input of a lock detection signal S1 from a gate lock detection switch 40, a controller 50 detects that a gate lock lever 32 for controlling a gate lock on/off valve 33 is in a locked state, in other words, hydraulic actuators such as an arm cylinder 12 arranged on a hydraulic excavator 1 are all in non-operated states. Upon an input of a forced regeneration command signal So from a forced regeneration switch 53 in this detected state, control signals Cp,Cf are outputted to a boosting control valve 51 and regulator 52 to make a forced regeneration means (an arm cylinder control valve 27 and the regulator 52) conduct forced regeneration.

TECHNICAL FIELD

The present invention relates to a hydraulic drive system for a working machine such as a hydraulic cylinder. The hydraulic drive system can be adopted in the working machine, is provided with an exhaust gas purification device for capturing, by a filter, particulate matter in exhaust gas produced through incomplete combustion in an engine (prime mover), and burns particulate matter deposited on the filter to conduct its removal (so-called forced regeneration).

BACKGROUND ART

Conventionally, a hydraulic drive system for a working machine has been designed to permit detecting clogging of a filter in an exhaust gas purification device. When the working machine is in a non-operated state at the time of detection of clogging, the hydraulic drive system automatically performs both raising the delivery pressure of a hydraulic pump and increasing the delivery flow rate of the hydraulic pump in parallel, whereby an engine output is increased. This increase in engine output leads to a rise in the temperature of exhaust gas. When the temperature of the exhaust gas rises to a temperature needed for the burning of particulate matter, the particulate matter with which the filter is clogged burns off (see Patent Document 1).

PRIOR ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

Problem to Be Solved by the Invention

The above-mentioned, conventional hydraulic drive system automatically conducts forced regeneration in a non-operated state of the working machine, so that the continuation time of the forced regeneration depends on the length of the lasting time of the non-operated sate and the forced regeneration may not always be conducted continuously for a sufficient time. If forced regeneration of insufficient continuation time is repeated, particulate matter burns off in every forced regeneration in the filter at areas where the temperature is easy to rise, but at areas where the temperature is hard to rise, particulate matter does not sufficiently burn and remains and the deposit of particulate matter continues to proceed. Localized clogging of the filter as a result of such localized deposit of particulate matter as described above is more difficult to detect than overall clogging of the filter. Localized clogging of the filter, therefore, tends to be left uncleaned, thereby causing a reduction in engine output during operation of the working machine.

With the foregoing circumstances in view, the present invention has as an object thereof the provision of a hydraulic drive system for a working machine, which can conduct forced regeneration continuously for a sufficient time.

Means for Solving the Problem

To achieve the above-described object, the present invention is constituted as will be described next.[1] The present invention is characterized in that in a hydraulic drive system for a working machine, said hydraulic drive system being provided with plural hydraulic actuators for driving the working machine, a hydraulic pressure source for producing, by a hydraulic pump, pressure oil to be fed to the plural hydraulic actuators, control valves separately arranged for the plural hydraulic actuators, respectively, to control flows of pressure oil between the corresponding hydraulic actuators and the hydraulic pressure source, an engine as a drive source for the hydraulic pump, an exhaust gas purification device for capturing, by a filter, particulate matter in exhaust gas produced by the engine, a forced regeneration means for burning particulate matter deposited on the filter, and a control means for controlling the forced regeneration means, said forced regeneration means serving to raise a delivery pressure of the hydraulic pump to increase an engine output such that the exhaust gas is provided with heat needed to burn the particulate matter, valve positions of the control valves are set to change between initial positions, in which the flows of pressure oil from the hydraulic pressure source to the hydraulic actuators are cut off to guide the pressure oil to a hydraulic oil reservoir, and operating positions, in which the pressure oil from the hydraulic pressure source is guided to the corresponding hydraulic actuators; the forced regeneration means includes a specific one of the control valves as a means for raising the delivery pressure of the hydraulic pump; the hydraulic drive system is further provided with a forced regeneration command means for commanding conduct of forced regeneration when operated, and also with a non-operated state detecting means for detecting a non-operated state in which the valve positions of all the control valves are in states of the initial positions; and taking as a condition for the conduct of forced regeneration that a non-operated state has been detected by the non-operated state detecting means, the control means actuates the specific control valve to raise the delivery pressure of the hydraulic pump when the conduct of forced regeneration is commanded by the forced regeneration command means.

In the present invention as described above in [1], the control means makes the forced regeneration means actuate the specific control valve to conduct forced regeneration when a non-operated state has been detected by the non-operated state detection means upon operation of the forced regeneration command means. In other words, an operator of the working machine can make the forced regeneration means initiate forced regeneration by operating the forced regeneration command means after the valve positions of all the control valves are brought into the states of initial positions, that is, into states that the working machine is inoperative. As a consequence, the operator can take time either before initiation of work or after completion of work by the working machine or periodically to purposefully conduct forced regeneration continuously for a sufficient time.[2] The present invention may also be characterized in that in the invention as described above in [1], working equipment of the working machine is provided with a boom and an arm pivotally connected to the boom; the plural hydraulic actuators include an arm cylinder; the specific control valve is an arm cylinder control valve for controlling a flow of pressure oil between the arm cylinder and the hydraulic pressure source; the hydraulic drive system is further provided with a stroke-end state detection means for detecting that the arm cylinder has been brought into a state of a stroke end on a side where a free end of the arm is brought close to the boom; and the control means controls the arm cylinder control valve such that the arm cylinder operates toward the stroke end, and based on detection results by the stroke-end state detection means, also controls the arm cylinder control valve such that the stroke-end state of the arm cylinder is maintained during the forced regeneration.

In the present invention as described above in [2], the arm and boom take an attitude as a whole during the forced regeneration that they are folded back toward a body of the working machine. As a consequence, the space occupied by the working machine in horizontal direction during the forced regeneration can be maintained small. Further, as the motion of the arm upon forced regeneration, the arm is actuated such that the free end of the arm comes closer to the boom. Compared with an actuation that moves the free end of the arm away from the boom, the potential problem that the working equipment may come into contact with an object around the working equipment can be made hardly occur accordingly.

Taking a hydraulic excavator as an example, a description will be made about the stroke-end state of the arm cylinder. Hydraulic excavators may be divided into two types, one being backhoe shovels and the other loading shovels. In a backhoe shovel, a stroke end on an extended side of an arm cylinder corresponds to a state of the arm cylinder that the free end of an arm is brought closest to a boom. In a loading shovel, on the other hand, a stroke end on a contracted side of an arm cylinder corresponds to a state of the arm cylinder that the free end of an arm is brought closest to a boom.[3] The present invention may also be characterized in that in the invention as described above in [1], working equipment of the working machine is provided with a boom, an arm pivotally connected to the boom, and a bucket or attachment pivotally connected to the arm; the plural hydraulic actuators include a bucket cylinder for pivoting the bucket or attachment connected to the arm; the specific control valve is a bucket cylinder control valve for controlling a flow of pressure oil between the bucket cylinder and the hydraulic pressure source; the hydraulic drive system is further provided with a stroke-end state detection means for detecting that the bucket cylinder has been brought into a state of a stroke end on an extended side or contracted side thereof; and the control means controls the bucket cylinder control valve such that the bucket cylinder operates toward the stroke end, and based on detection results by the stroke-end state detection means, also controls the bucket cylinder control valve such that the stroke-end state of the bucket cylinder is maintained during the forced regeneration.

In the present invention as described above in [3], a part of the working equipment, said part being to be actuated upon forced regeneration, is the bucket or attachment. Compared with the boom and arm, a change in the attitude of the working machine as a result of the actuation of such a part is limited smaller. Namely, in the present invention as described above in [3], the working equipment is actuated in association with forced regeneration but the forced regeneration can be conducted in a space smaller than that required for an actuation of the boom or arm out of the working equipment.[4] The present invention may also be characterized in that in the invention as described above in [2], the stroke-end state detection means detects the state of the stroke end of the arm cylinder based on an attitude of the arm relative to the boom.

Working machines include those which are each provided, at a joint where a boom and an arm are pivotally connected with each other, with an angle sensor for detecting an attitude, in other words, angle of the arm relative to the boom. The present invention as described above in [4] can detect the stroke-end state of the arm cylinder by making use of the angle sensor.[5] The present invention may also be characterized in that in the invention as described above in [3], the stroke-end state detection means detects the state of the stroke end of the bucket cylinder based on an attitude of the bucket or attachment relative to the arm.

Working machines include those which are each provided, at a joint where an arm and a bucket are pivotally connected with each other or at a link mechanism interposed between the arm and the bucket, with an angle sensor for detecting an attitude of the bucket relative to the arm, in other words, an angle of the bucket relative to the arm or an angle of the bucket relative to the link mechanism. The present invention as described above in [5] can detect the stroke-end state of the bucket cylinder by making use of the angle sensor.

Advantageous Effects of the Invention

According to the present invention, the operator can take time either before initiation of work or after completion of work by the working machine or periodically to purposefully conduct forced regeneration continuously for a sufficient time as mentioned above. The present invention can, therefore, contribute to the prevention of a reduction in engine output during operation of the working machine, which would otherwise be caused by leaving localized clogging of the filter uncleaned in the exhaust gas purification device.

MODES FOR CARRYING OUT THE INVENTION

A description will be made about the first and second embodiments of the present invention.

With reference toFIGS. 1,2-1and2-2, a description will be made about the first embodiment.FIG. 1is a left side view of a hydraulic excavator as a working machine according to the first embodiment of the present invention.FIG. 2-1is a hydraulic circuit diagram showing in a simplified form a hydraulic drive system arranged in the hydraulic excavator illustrated inFIG. 1.FIG. 2-2is a flow chart illustrating a flow of processing to be performed at a controller depicted inFIG. 2-1.

As illustrated inFIG. 1, the hydraulic excavator1is provided with a travel base2which runs by driving crawler tracks3, a revolving upperstructure4swingably connected to the travel base2, and working equipment7substantially centrally arranged on a front section of the revolving upperstructure4.

On a left front section of the revolving upperstructure4, an operator's cab5is mounted. Disposed behind the operator's cab5is an engine compartment6, in which a main pump22, engine23and the like of a hydraulic drive system20to be mentioned subsequently herein are accommodated. From a top part of the engine compartment6, an outlet pipe26extends to guide exhaust gas from the engine23outward of the hydraulic excavator1.

The working equipment7is provided with a boom8. The boom8of the working equipment7is pivotally connected at one end thereof to the revolving upperstructure4via a pin. To the opposite end of the boom8, an arm9is pivotally connected at one end thereof via a pin. To the opposite end of the arm9, a bucket10is pivotally connected at one end thereof via a pin. The boom8is drivable by a boom cylinder11. This boom cylinder11is pivotally connected at a bottom-side end of a cylinder tube11ato the revolving upperstructure4via a pin, and is also pivotally connected at an end of a rod11bto an intermediate part of the boom8via a pin. The arm9is drivable by an arm cylinder12. This arm cylinder12is pivotally connected at a bottom-side end of a cylinder tube12ato the boom8via a pin, and is also pivotally connected at an end of a rod12bto the one end of the arm9via a pin. The bucket10is arranged such that an extending/retracting motion of a bucket cylinder13is transmitted via a link mechanism13cto drive the bucket10. This bucket cylinder13is pivotally connected at a bottom-side end of a cylinder tube13ato the arm9via a pin, and is also pivotally connected at an end of a rod13bto the link mechanism13cvia a pin.

As depicted inFIG. 2-1, the hydraulic drive system20according to the first embodiment is provided, as plural hydraulic actuators making up a drive source for the hydraulic excavator1, with a left travel motor (not shown) and a right travel motor (not shown) as a drive source for the travel base2, a swing motor (not shown) as a drive source for the revolving upperstructure4, the boom cylinder11, the arm cylinder12, and the bucket cylinder13. (It is to be noted thatFIG. 2-1depicts only the arm cylinder12and the remaining hydraulic actuators are omitted.)

A hydraulic pressure source for a drive pressure to be fed to these plural hydraulic actuators is the main pump22(variable-displacement hydraulic pump). A drive source for this main pump22is the engine23(prime mover: diesel engine). An exhaust gas pipe24extends from the engine23, and this exhaust gas pipe24is provided with an exhaust gas purification device25. The exhaust gas purification device25serves to capture, by a filter, particulate matter in exhaust gas produced by incomplete combustion of fuel in the engine23. From the exhaust gas purification device25, the above-described outlet pipe26extends.

Between the main pump22and the respective hydraulic actuators, actuator control valves are interposed to control the directions and flows of pressure oil to be fed to the hydraulic actuators.FIG. 2-1depicts, as a representative of these actuator control valves, only an arm cylinder control valve27interposed between the main pump22and the arm cylinder12. This arm cylinder control valve27is a hydraulically-piloted, spring-centered, 3-position valve. The valve position of the arm cylinder control valve27is set such that it changes between an initial position27c(neutral position) and a first operating position27dor also between the initial position27cand a second operating position27e.The initial position27c(neutral position) is a valve position, in which a passage that guides pressure oil to a hydraulic oil reservoir21is formed while cutting off a flow of pressure oil from the main pump22to either a bottom chamber12a1or a rod chamber12a2of the arm cylinder12. The first operating position27dis a valve position on a side that the arm cylinder12is caused to extend, in which two passages are formed, one being a passage that guides pressure oil, which has been delivered from the main pump22, to the bottom chamber12a1of the arm cylinder12, and the other a passage that guides pressure oil, which is contained in the rod chamber12a2, to the hydraulic oil reservoir21. The second operating position27eis a valve position on a side that the arm cylinder12is caused to contract, in which two passages are formed, one being a passage that guides pressure oil, which has been delivered from the main pump22, to the rod chamber12a2of the arm cylinder12, and the other a passage that guides pressure oil, which is contained in the bottom chamber12a1, to the hydraulic oil reservoir21. A boom cylinder control valve, bucket cylinder control valve, left travel motor control valve, right travel motor control valve and swing motor control valve are also constructed like the arm cylinder control valve27.

A pilot pressure to be applied to the arm cylinder control valve27is produced by an arm control device29. This arm control device29has a pair of lever-operated pilot valves, and using a delivery pressure of a pilot pump28as a primary pressure, a pilot pressure is produced by one of these pilot valves. Similar control devices as the arm control device29are arranged for the boom cylinder control valve, bucket cylinder control valve, left travel motor control valve, right travel motor control valve and swing motor control valve, respectively.

A pilot line31extending from the pilot pump28, that is, a line that guides pressure oil, which is delivered from the pilot pump28and is distributed to all the control devices such as the arm control device29, is provided with a gate lock on/off valve33which can collectively cut off the primary pressure to all the control devices.

The gate lock on/off valve33is a lever-operated, spring return valve, and is operated by a gate lock lever32. In this gate lock on/off valve33, the initial position corresponds to an open position33a,and the operating position corresponds to a closed position33b.The closed position33bis a valve position, in which the pilot line31is closed and the primary pressure to all the control devices such as the arm control device29is collectively cut off. The gate lock lever32can be selectively held by an unillustrated construction in a locked position corresponding to the valve position of the gate lock on/off valve33or in a canceled position corresponding to the open position33aof the gate lock on/off valve33.

Attached to the gate lock lever32is a lock detection switch40, which detects that the gate lock lever32is in a locked position, in other words, in a locked state, and outputs a lock detection signal S1(electrical signal).

On the pin joint that pivotally connects the boom and the revolving upperstructure4with each other, a boom angle sensor43is arranged to output an angle of the boom8relative to the revolving upperstructure4by converting it into a boom angle detection signal Sbm (electrical signal). On the pin joint that pivotally connects the arm9and boom8with each other, an arm angle sensor41is arranged to output an angle of the arm9relative to the boom8by converting it into an arm angle detection signal Sa (electrical signal). On the pin joint that pivotally connects the arm9and bucket10with each other, a bucket angle sensor42is arranged to output an angle of the bucket10relative to the arm9by converting it into a bucket angle detection signal Sbt (electrical signal).

In a main line30, a delivery pressure sensor44is arranged on a side upstream of all the actuator control valves such as the arm cylinder control valve27to output a delivery pressure of the main pump22by converting it into a delivery pressure detection signal Sp (electrical signal).

The arm cylinder control valve27has a pair of hydraulic pilot ports27a,27b,and these hydraulic pilot ports27a,27bare both connected to the arm control device29. Further, only the hydraulic pilot port27ais connected to a boosting control valve51in addition to the arm control device29. When a pilot pressure is applied to the hydraulic pilot port27a,a spool of the arm cylinder control valve27is moved to a side where the arm cylinder12brings the free end of the arm9closer to the boom8, in other words, to the side of the first operating position which is the valve position on a side where the arm cylinder12is caused to extend. The boosting control valve51is interposed between an upstream side of the gate lock on/off valve33in the pilot line31and the hydraulic pilot port27a.This boosting control valve51is a spring-return, proportional solenoid valve, and is actuated upon application of a control signal Cp (electrical signal). An initial position51ais a valve position in which a passage is formed to bring the hydraulic pilot port27ainto communication with the hydraulic oil reservoir21. An operating position51bis a valve position in which a passage is formed to bring the hydraulic pilot port27ainto communication with the pilot pump28. A pilot pressure to be applied to the hydraulic pilot port27achanges steplessly depending on changes in the valve position of the boosting control valve51, and becomes higher as the valve position comes closer to the operating position51b.

The delivery flow rate of the main pump22is controlled by a regulator52. This regulator52is electrically operated, and upon receipt of a control signal Cf (electrical signal), is actuated in a direction that the delivery flow rate of the main pump22is increased.

The engine23is controlled to obtain an engine output corresponding to every variation in the load on the main pump22. The engine output, therefore, increases when the delivery flow rate of the main pump22increases and the delivery pressure of the main pump22rises. When the temperature of exhaust gas rises as a result of an increase in engine output and this temperature reaches a value needed for the burning of particulate matter, forced regeneration is conducted to burn off the particulate matter deposited on the filter of the exhaust gas purification device25. The hydraulic drive system20is designed to permit conducting this forced regeneration. Upon forced regeneration, a means for increasing the delivery flow rate of the main pump22is the regulator52, and as a means for raising the delivery pressure of the main pump22, a specific one of all the actuator control valves, for example, the arm cylinder control valve27is used. Therefore, the arm cylinder control valve27and regulator52make up a forced regeneration means for increasing the engine output to provide the exhaust gas with heat needed to burn the particulate matter deposited on the filter of the exhaust gas purification device25.

As a forced regeneration command means for commanding the conduct of forced regeneration when operated by a part of the body, a forced regeneration switch53is arranged. This forced regeneration switch53is a spring-return, push-button switch, and in its ON state, outputs a forced regeneration command signal So (electrical signal) as a command for conducting forced regeneration.

The lock detection signal S1outputted from the lock detection switch40, the boom angle detection signal Sbm outputted from the boom angle sensor43, the arm angle detection signal Sa outputted from the arm angle sensor41, the bucket angle detection signal Sbt outputted from the bucket angle sensor42, the delivery pressure detection signal Sp outputted from the delivery pressure sensor44and the forced regeneration command signal So outputted from the forced regeneration switch53are inputted to the controller50.

The controller50is a unit, which is provided with

CPU, ROM, RAM and the like and is operated in accordance with a computer program. This controller50is set to determine whether or not the lock detection signal S1has been applied from the lock detection switch40. When the lock detection switch40is in a state of outputting a lock detection signal, the gate lock on/off valve33is in an operating state. As the pilot line31is cut off in this state, no pilot pressure is applied to any of the hydraulic pilot ports of all the actuator control valves such as the arm cylinder control valve27(the left travel motor control valve, right travel motor control valve, boom cylinder control valve, arm cylinder control valve27, bucket cylinder control valve, and swing motor control valve), and therefore, all the actuator control valves assume the initial positions (neutral positions), respectively. By determining whether or not the lock detection signal S1has been applied from the lock detection switch40, the controller50hence functions as a non-operated state detection means for detecting a non-operated state in which all the actuator control valves assume the initial positions, respectively.

The controller50are set to control the boosting control valve51and regulator52by outputting the control signals Cp,Cf. The controller50and boosting control valve51make up a control means for controlling the forced regeneration means which is made up from the regulator52and arm cylinder control valve27.

The controller50is set to determine, based on the boom angle detection signal Sbm from the boom angle sensor43, the arm angle detection signal Sa from the arm angle sensor41and the bucket angle detection signal Sbt from the bucket angle sensor42, whether or not the working equipment7is in a proper attitude. The proper attitude is a state in which as illustrated inFIG. 1, the bucket10is folded and carried over the arm9, the arm9is folded and carried under the boom8, and the boom8has descended with the end of the arm9(the link mechanism13c) being in contact with a reference ground level G.

The controller50is set to operate according to steps S1to S6illustrated inFIG. 2-2. The controller50is actuated in association with a stat-up of the engine23. When the forced regeneration command signal So is inputted from the forced regeneration switch53after the start-up (YES in step51), the controller50determines whether or not the input of the lock detection signal S1from the lock detection switch40is continuing, namely, whether or not the gate lock lever32is in a locked state (step S2). In parallel with this determination, the controller50also determines, based on the boom angle detection signal Sbm from the boom angle sensor43, the arm angle detection signal Sa from the arm angle sensor41and the bucket angle detection signal Sbt from the bucket angle sensor42, whether or not the working equipment7is in a proper attitude (step S2).

When the locked state of the gate lock lever32and the proper attitude are both detected by the determinations in step S2(YES in step S2), the controller50makes the forced regeneration means (the arm cylinder control valve27and regulator52) initiate forced regeneration (step S3). In other words, control signals Cp,Cf which correspond to preset control values are outputted to the boosting control valve51and regulator52, respectively. No forced regeneration is initiated unless the locked state of the gate lock lever32and the proper attitude have been both detected (NO in step S2).

The boosting control valve51to which the control signal Cp has been applied produces a pilot pressure, and this pilot pressure is applied to the hydraulic pilot port27aof the arm cylinder control valve27. The valve position of the arm cylinder control valve27, therefore, changes from the initial position27cto the side of the first operating position27d.As a result, the arm cylinder12extends, and in addition, the delivery pressure of the main pump22rises. On the other hand, the regulator52to which the control signal Cf has been applied increases the delivery flow rate of the main pump22.

While the gate lock lever32is in the locked state, the engine23is controlled in an idling state for energy saving and noise reduction. In association with an increase in the delivery flow rate of the main pump22and a rise in its delivery pressure, however, the engine23is controlled to increase its output. When the engine output increases, the temperature of exhaust gas rises so that particulate matter burns with the heat of the exhaust gas, in other words, forced regeneration is conducted. During the forced regeneration, the controller50performs adjustments of the control signal Cp based on the delivery pressure detection signal Sp from the delivery pressure sensor44to maintain the delivery pressure of the main pump22at a predetermined pressure needed for the forced regeneration or higher.

From the time point of the initiation of the output of the control signal Cp to the boosting control valve51, the controller50also determines, based on the arm angle detection signal Sa from the arm angle sensor41, whether or not the arm cylinder12is in a stroke-end state on the extended side. Namely, the controller50functions as a stroke-end state detection means for detecting that the arm cylinder12is in the stroke-end state on the side where the free end of the arm9is brought closer to the boom8, that is, on the extended side. Based on the results of the determination, the controller50applies the control signal Cp to the arm cylinder control valve27such that the stroke-end state of the arm cylinder12is maintained.

The controller50counts an elapsed time from the time point of the initiation of the output of the control signals Cp,Cf in step S3, and continues the output of the control signals Cp,Cf until elapse of a predetermined time as long as the detection of the locked state of the gate lock lever32continues. When the continuous output time of the control signals Cp,Cf has passed the predetermined time (YES in step S4), the output of these control signals Cp,Cf is stopped to end the forced regeneration (step S5). It is to be noted that the predetermined time is set as a time sufficient to remove particulate matter from the filter of the exhaust gas purification device25.

When the locked state of the gate lock lever32has become no longer detected before the elapse of the predetermined time (NO in step S4), on the other hand, the controller50stops the output of the control signals Cp,Cf at this time point, and stops the forced regeneration (step S6).

According to the hydraulic drive system20of the first embodiment, the following advantageous effects can be brought about.

With the hydraulic drive system20, the operator of the hydraulic excavator1can make the forced regeneration means (the arm cylinder control valve27and regulator52) initiate forced regeneration by operating the forced regeneration switch53after bringing the valve positions of all the actuator control valves such as the arm cylinder control valve27into the states of initial positions, that is, into states, where the hydraulic excavator1is inoperative, by bringing the gate lock lever32into the locked state. As a consequence, the operator can take time either before initiation of work or after completion of work by the hydraulic excavator1or periodically to purposefully conduct forced regeneration continuously for a sufficient time. The hydraulic drive system20can, therefore, contribute to the prevention of a reduction in engine output during operation of the hydraulic excavator1, which would otherwise be caused by leaving localized clogging of the filter uncleaned in the exhaust gas purification device25.

In the hydraulic drive system20, the arm9and boom8take an attitude as a whole during forced regeneration that they are folded back toward the revolving upperstructure4of the hydraulic excavator1. As a consequence, the space occupied by the hydraulic excavator1in horizontal direction during the forced regeneration can be maintained small. Further, as the motion of the arm9upon forced regeneration, the arm9is actuated such that its free end comes closer to the boom8. Compared with an actuation that moves the free end of the arm9away from the boom8, the potential problem that the working equipment7may come into contact with an object around the working equipment7can be made hardly occur accordingly.

In the hydraulic drive system20, the stroke-end sate of the arm cylinder12is detected based on the angle of the arm9relative to the boom8, in other words, the attitude of the arm9relative to the boom8. As the hydraulic excavator1, there is one having an arm angle sensor41arranged irrelevant to forced regeneration. Using this arm angle sensor, the hydraulic drive system20can detect the stroke-end state of the arm cylinder.

It is to be noted that, although the above-described hydraulic drive system20according to the first embodiment is adopted in the backhoe shovel, the present invention is not limited to one adopted in such a backhoe shovel but may be adopted in a loading shovel. In a backhoe shovel, however, the stroke end on the extended side of an arm cylinder corresponds to the state of the arm cylinder that the free end of the arm is brought closest to the boom. In a loading shovel, on the other hand, the stroke end on the contracted side of the arm cylinder corresponds to the state of the arm cylinder that the free end of the arm is brought closest to the boom. It is, therefore, necessary to actuate the cylinder control valve to a side, where the arm cylinder is contracted, when the actuation of the arm upon force regeneration is set as an actuation that brings the free end of the arm closer to the boom.

In the hydraulic drive system20, the arm cylinder control valve27is used as a specific actuator control valve. However, the specific control valve in the present invention may be the bucket cylinder control valve. According to this construction, a part of the working equipment, said part being to be actuated upon forced regeneration, is the bucket or an attachment. Compared with the boom and arm, a change in the attitude of the working machine as a result of the actuation of such a part is limited smaller. Namely, the forced regeneration can be conducted in a space smaller than that required for an actuation of the boom or arm out of the working equipment. As a hydraulic excavator, there is one provided with an angle sensor arranged irrelevant to forced regeneration at a pin joint, which pivotally connects the arm and bucket with each other, or at a link mechanism interposed between the arm and the bucket. When the bucket cylinder control valve is the specific control valve, the stroke-end state of the bucket cylinder can be detected by using the angle sensor.

The hydraulic drive system20has been described above by citing as an illustrative proper attitude the state that as illustrated inFIG. 1, the bucket10is folded and carried above the arm9, the arm9is folded and carried under the boom8, and the boom8has descended with the free end of the arm9(the link mechanism13c) being in contact with the referenced ground level G. The proper attitude may, however, be other than the illustrated state. The proper attitude may be a state that only the arm is folded and carried under the boom, a state that only the bucket is folded and carried above the arm, or a state that only the arm and bucket are both folded under the boom. In other words, it is possible to adopt as a proper attitude insofar as at least one of the boom, arm and bucket is in such a state that it has been driven to a movable limit angle.

Second Embodiment

With reference toFIGS. 3-1and3-2, a description will be made about the second embodiment of the present invention.FIG. 3-1is a hydraulic circuit diagram showing in a simplified form a hydraulic drive system according to the second embodiment of the present invention.FIG. 3-2is a flow chart illustrating a flow of processing to be performed at a controller depicted inFIG. 3-1. Among elements and signals illustrated inFIG. 3-1, like elements and signals to the corresponding ones illustrated inFIG. 2-1are designated using like reference signs.

In the hydraulic drive system60according to the second embodiment, the actuator control valves such as the arm cylinder control valve27are constructed such that they can be electrically controlled. Taking the arm cylinder control valve27as an example, a description will be made. The hydraulic pilot port27aof the arm cylinder control valve27is provided with a proportional solenoid valve62as an accessory. The hydraulic pilot port27bof the arm cylinder control valve27is provided with a proportional solenoid valve63as an accessory. The proportional solenoid valve62produces a pilot pressure, which is to be applied to the hydraulic pilot port27a,by using the delivery pressure of the pilot pump28as a primary pressure. The proportional solenoid valve63produces a pilot pressure, which is to be applied to the hydraulic pilot port27b,by using the delivery pressure of the pilot pump28as a primary pressure. A control signal Ce to be applied to a solenoid of the proportional solenoid valve62and a control signal Cc to be applied to a solenoid of the proportional solenoid valve63are both outputted from a controller64.

The controller64is a unit, which has CPU, ROM, RAM and the like and is operated in accordance with a computer program. Inputted to the controller64are the boom angle detection signal Sbm outputted from the boom angle sensor43, the arm angle detection signal Sa outputted from the arm angle sensor41, the bucket angle detection signal Sbt outputted from the bucket angle sensor42, the delivery pressure detection signal Sp outputted from the delivery pressure sensor44, and the forced regeneration command signal So outputted from the forced regeneration switch53.

To the controller64, an actuation command signal Ea (electrical signal) which corresponds to a command value for the actuation of the arm cylinder12is inputted from an arm control device29. The arm control device29has a lever-operated variable resistor, and outputs the control direction and control quantity of the control lever by converting them into the actuation command signal as an electrical signal. The controller64is set to compute control values for the proportional solenoid valves62,63based on the actuation command signal and to output control signals Ce,Cc corresponding to the control values. The proportional solenoid valves62,63are spring-return control valves. In the proportional solenoid valve62, an initial position62ais a valve position in which a passage is formed to bring the hydraulic pilot port27ainto communication with the hydraulic oil reservoir21, while an operating position62bis a valve position in which a passage is formed to bring the hydraulic pilot port27ainto communication with the pilot pump28. A pilot pressure to be applied to the hydraulic pilot port27achanges steplessly depending on changes in the valve position of the proportional solenoid valve62, and becomes higher as the valve position comes closer to the operating position62b.The proportional solenoid valve63is also constructed like the proportional solenoid valve62.

The actuator control valves other than the arm cylinder control valve27, that is, the boom cylinder control valve, bucket cylinder control valve, left travel motor control valve, right travel motor control valve and swing motor control valve are also provided with proportional solenoid valves as accessories, which are similar to the proportional solenoid valves62,63for the arm cylinder control valve27. Like the arm control device29for the arm cylinder control valve27, the boom cylinder control valve, bucket cylinder control valve, left travel motor control valve, right travel motor control valve and swing motor control valve are also provided with control devices, respectively. By these control devices, actuation command signals (electrical signals) corresponding to command values for the actuation of the boom cylinder, arm cylinder, left travel motor, right travel motor and swing motor are inputted to the controller64. Based on actuation command signals from the respective control devices other than the arm control device29, the controller64computes, in a similar manner as for the actuation command signal Ea from the arm control device, control values for the proportional solenoid valves arranged as accessories for the actuator control valves corresponding to the actuation command signals, and outputs control signals corresponding to the control values.

The controller64is set to determine whether or not an actuation command signal has not been outputted from any of all the control devices such as the arm control device61. In a state that no actuation command signal has been outputted from any of all the control devices, the controller64does not give a control signal to any of the proportional solenoid valves arranged as accessories for all the actuator control valves (the left travel motor control valve, right travel motor control valve, boom cylinder control valve, arm cylinder control valve27, bucket cylinder control valve, swivel motor control valve). Accordingly, no pilot pressure is applied to any of the hydraulic pilot ports of all the actuator control valves such as the arm cylinder control valve27, whereby all the actuator control valves assume the initial positions (neutral positions). Namely, the controller64functions as a non-operated state detection means for detecting a non-operated state, in which all the actuator control valves assume the initial positions, by determining whether or not the hydraulic drive system is in a state in which no actuation command signal has been outputted from any of all the control devices such as the arm control device61.

Similar to the controller50in the first embodiment, the controller64is also set to determine, based on the boom angle detection signal Sbm from the boom angle sensor43, the arm angle detection signal Sa from the arm angle sensor41and the bucket angle detection signal Sbt from the bucket angle sensor42, whether or not the working equipment7is in a proper attitude.

In the second embodiment, the regulator52and arm cylinder control valve27make up a forced regeneration means as in the first embodiment. Different from the first embodiment, however, a control means for this forced regeneration means is made up from the controller64and proportional solenoid valve62.

The controller64is set to operate according to steps S11to S16illustrated inFIG. 3-2. The controller64is actuated in association with a stat-up of the engine23. When the forced regeneration command signal So is inputted from the forced regeneration switch53after the start-up (YES in step S11), the controller64determines whether or not no actuation command signal has been inputted from any of all the control devices such as the arm control device61, namely, whether or not there is no actuation command (step S12). In parallel with this determination, the controller64also determines, based on the boom angle detection signal Sbm from the boom angle sensor43, the arm angle detection signal Sa from the arm angle sensor41and the bucket angle detection signal Sbt from the bucket angle sensor42, whether or not the working equipment7is in a proper attitude (step S12).

When the state of no actuation command from any control device and the proper attitude are both detected by the determinations in step S12(YES in step S12), the controller64makes the forced regeneration means (the arm cylinder control valve27and regulator52) initiate forced regeneration (step S13). In other words, control signals Ce,Cf which correspond to preset control values are outputted to the proportional solenoid valve62and regulator52, respectively. No forced regeneration is initiated unless the state of no actuation command from any control device and the proper attitude have been both detected (NO in step S2).

The proportional solenoid valve62to which the control signal Ce has been applied produces a pilot pressure, and this pilot pressure is applied to the hydraulic pilot port27aof the arm cylinder control valve27. The valve position of the arm cylinder control valve27, therefore, changes from the initial position27cto the side of the first operating position27d.As a result, the arm cylinder12extends, and in addition, the delivery pressure of the main pump22rises. On the other hand, the regulator52to which the control signal Cf has been applied increases the delivery flow rate of the main pump22.

While all the actuators are in non-operated states, the engine23is controlled in an idling state for energy saving and noise reduction. In association with an increase in the delivery flow rate of the main pump22and a rise in its delivery pressure, however, the engine23is controlled to increase its output. When the engine output increases, the temperature of exhaust gas rises so that particulate matter burns with the heat of the exhaust gas, in other words, forced regeneration is conducted. During the forced regeneration, the controller64performs adjustments of the control signal Ce based on the delivery pressure detection signal Sp from the delivery pressure sensor44to maintain the delivery pressure of the main pump22at a predetermined pressure needed for the forced regeneration or higher.

From the time point of the initiation of the output of the control signal Ce to the proportional solenoid valve62in step S13, the controller64also determines, based on the arm angle detection signal Sa from the arm angle sensor41, whether or not the arm cylinder12is in the stroke-end state on the extended side. Namely, the controller64functions as a stroke-end state detection means for detecting that the arm cylinder12is in the stroke-end state on the side where the free end of the arm9is brought closer to the boom8, that is, on the extended side. Based on the results of the determination, the controller64applies the control signal Ce to the proportional solenoid valve62such that the stroke-end state of the arm cylinder12is maintained.

The controller64counts an elapsed time from the time point of the initiation of the output of the control signals Ce,Cf, and continues the output of the control signals Ce,Cf until elapse of a predetermined time as long as the detection of the state of no actuation command from any control device continues. When the continuous output time of the control signals Ce,Cf has passed the predetermined time (YES in step S14), the output of these control signals Ce,Cf is stopped to end the forced regeneration (step S15). It is to be noted that the predetermined time is set as a time sufficient to remove particulate matter from the filter of the exhaust gas purification device25.

When the state of no actuation command from any control device has become no longer detected before the elapse of the predetermined time (NO in step S14), on the other hand, the controller64stops the output of the control signals Ce,Cf at this time point, and stops the forced regeneration (step S16).

According to the hydraulic drive system60of the second embodiment, the following advantageous effects can be brought about.

With the hydraulic drive system60, the operator of the hydraulic excavator1can make the forced regeneration means (the arm cylinder control valve27and regulator52) initiate forced regeneration by operating the forced regeneration switch53after bringing the valve positions of all the actuator control valves such as the arm cylinder control valve27into the states of initial positions, that is, into states, where the hydraulic excavator1is inoperative, by stopping operation of all the control devices such as the arm control device29. As a consequence, the operator can take time either before initiation of work or after completion of work by the hydraulic excavator1or periodically to purposefully conduct forced regeneration continuously for a sufficient time. The hydraulic drive system60can, therefore, contribute to the prevention of a reduction in engine output during operation of the hydraulic excavator1, which would otherwise be caused by leaving localized clogging of the filter uncleaned in the exhaust gas purification device25.

In the hydraulic drive system60, the arm9and boom8take, as in the hydraulic drive system20according to the first embodiment, an attitude as a whole during forced regeneration that they are folded back toward the revolving upperstructure4of the hydraulic excavator1. As a consequence, the space occupied by the hydraulic excavator1in horizontal direction during the forced regeneration can be maintained small. Further, as the motion of the arm9upon forced regeneration, the arm9is actuated such that its free end comes closer to the boom8. Compared with an actuation that moves the free end of the arm9away from the boom8, the potential problem that the working equipment7may come into contact with an object around the working equipment7can be made hardly occur accordingly.

In the hydraulic drive system60, the stroke-end sate of the arm cylinder12is also detected, as in the hydraulic drive system20according to the first embodiment, based on the angle of the arm9relative to the boom8, in other words, the attitude of the arm9relative to the boom8. As the hydraulic excavator1, there is one having an arm angle sensor41arranged irrelevant to forced regeneration. Using this arm angle sensor, the hydraulic drive system20can detect the stroke-end state of the arm cylinder.

In the above-described hydraulic drive system60according to the second embodiment, the non-operated state detection means relies upon determining whether or not no actuation command signal has been outputted to the controller64from any of all the control devices. However, the non-operated state detection mean is not limited to such a means, but can be a similar non-operated state detection means as in the hydraulic drive system according to the first embodiment, specifically one capable of detecting a non-operated state by determining whether or not the gate lock lever32is in the locked state based on whether or not a lock detection signal has been outputted from the lock detection switch40.

Similar to the above-described hydraulic drive system20according to the first embodiment, the hydraulic drive system60is also adopted in the backhoe shovel. However, the present invention is not limited to one adopted in such a backhoe shovel but may be adopted in a loading shovel.

In the hydraulic drive system60, the arm cylinder control valve27is also used as a specific actuator control valve as in the hydraulic drive system20according to the first embodiment. However, the specific control valve in the present invention may be the bucket cylinder control valve.

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