Patent Description:
A hydraulic excavator that is one of construction machines includes: a prime mover (particularly, for example, an engine or an electric motor); a hydraulic pump driven by the prime mover; a plurality of hydraulic actuators; a plurality of control valves that individually control the flow of hydraulic fluid from the hydraulic pump to the plurality of hydraulic actuators; and a plurality of operation devices that switch the plurality of control valves. In recent years, from the point of view of energy saving, noise reduction, and so forth, a hydraulic excavator is provided with an auto idle control function that decreases, when a no-operation state of the plurality of operation devices continues, the rotation speed of the prime mover from a standard rotation speed to an idle rotation speed (for example, refer to Patent Document <NUM>).

The hydraulic excavator of Patent Document <NUM> includes: a pilot pump driven by a prime mover; a hydraulic signal line that is connected between the discharge side of the pilot pump and a tank and in which a plurality of control valves described above are interposed such that the hydraulic signal line is interrupted when one of the plurality of control valves is switched from its neutral position; a pilot relief valve provided on the discharge side of the pilot pump; a fixed restrictor provided between the discharge side of the pilot pump and the plurality of control valves in the hydraulic signal line; a pressure sensor that detects the hydraulic pressure on the downstream side of the fixed restrictor (in other words, between the fixed restrictor and the control valves); and a controller that detects an operation state of the plurality of operation devices on the basis of a result of detection of the pressure sensor.

When one of the plurality of operation devices is operated (i.e., when one of the plurality of control valves is switched from its neutral position), since the hydraulic signal line is placed into an interrupted state, the hydraulic pressure detected by the pressure sensor increases to near relief pressure of the pilot relief valve. When none of the operation devices is operated (i.e., when all of the control valves are in their neutral position), the hydraulic signal line is placed into a communication state, and therefore, the hydraulic pressure detected by the pressure sensor drops. The controller decides whether or not any one of the operation devices is operated depending upon whether or not the hydraulic pressure detected by the pressure sensor exceeds a threshold value set in advance.

The controller decides that none of the operation devices is operated when the hydraulic pressure detected by the pressure sensor is equal to or lower than the threshold value. Then, when the state in which none of the operation devices is operated continues for a predetermined period of time, the controller decreases the rotation speed of the prime mover to the idle rotation speed. Further, the controller decides that any one of the operation devices is operated when the hydraulic pressure detected by the pressure sensor exceeds the threshold value. Then, the controller controls the prime mover to keep or return the rotation speed of the prime mover at or to the standard rotation speed.

In the prior art described above, the pressure sensor for detecting the hydraulic pressure on the downstream side of the fixed restrictor is provided, and the hydraulic pressure detected by the pressure sensor is compared with a threshold value to detect an operation state of operation devices. However, the prior art described above has such room for improvement as described below.

The threshold value described above is necessary to be set higher than a hydraulic pressure that is detected by the pressure sensor when the rotation speed of the prime mover is the standard rotation speed and the hydraulic signal line is in a communication state (particularly, the hydraulic pressure is a pressure that is the sum of the tank pressure and the pressure loss in an intermediate portion of the hydraulic signal line from the pressure sensor to the tank, and increases if the fluid temperature is low). Further, the threshold value is necessary to be set lower than a hydraulic pressure that is detected by the pressure sensor when the rotation speed of the prime mover is the idle rotation speed and the hydraulic signal line is in an interrupted state.

However, if the rotation speed of the prime mover decreases to the idle rotation speed, then the discharge flow rate of the pilot pump decreases. The pilot relief valve has an override characteristic that the relief pressure decreases in proportion to the decrease in the flow rate of the fluid. Therefore, there is the possibility that, if the idle rotation speed for the prime mover is excessively low, then the hydraulic pressure detected by the pressure sensor may not exceed the threshold value when the rotation speed of the prime mover is the idle rotation speed and the hydraulic signal line is in an interrupted state. In other words, there is the possibility that detection of an operation state of the operation devices may be disabled. Accordingly, it is difficult to set the idle rotation speed for the prime mover to a low value.

The present invention has been made in view of such a circumstance as described above, and it is an object of the present invention to provide a construction machine that is capable of detecting an operation state of an operation device even if the idle rotation speed for a prime mover is set to a low value and is capable of setting the idle rotation speed for the prime mover to a low value.

In order to achieve the object described above, according to the present invention, there is provided a construction machine that includes: a prime mover; a hydraulic pump driven by the prime mover; a hydraulic actuator; a control valve that controls flow of hydraulic fluid from the hydraulic pump to the hydraulic actuator; an operation device that generates a pilot pressure corresponding to an operation amount of an operation lever and switches the control valve with the generated pilot pressure; and a controller that controls, when a no-operation state of the operation device continues, a rotation speed of the prime mover to an idle rotation speed set in advance, the construction machine including: a pilot pump that is driven by the prime mover and whose discharge pressure is used as a source pressure of the pilot pressure; a pilot relief valve provided on a discharge side of the pilot pump; a hydraulic pressure signal line that is connected between the discharge side of the pilot pump and a tank and in which the control valve is interposed such that the hydraulic pressure signal line is interrupted when the control valve is switched from a neutral position; a fixed restrictor provided between the discharge side of the pilot pump and the control valve in the hydraulic pressure signal line; a first pressure sensor that detects a hydraulic pressure on an upstream side of the fixed restrictor; and a second pressure sensor that detects a hydraulic pressure on a downstream side of the fixed restrictor, in which the controller is configured to detect an operation state of the operation device based on results of detection of the first pressure sensor and the second pressure sensor.

According to the present invention, it is possible to detect an operation state of the operation device even if the idle rotation speed for the prime mover is set to a low value, and to set the idle rotation speed for the prime mover to a low value.

In the following, an embodiment of the present invention is described with reference to the drawings taking a hydraulic excavator as an application target of the present invention.

<FIG> is a side elevational view depicting a structure of the hydraulic excavator according to the present embodiment, and <FIG> is a top plan view of the structure. It is to be noted that the front side (right side in <FIG> and <FIG>), the rear side (left side in <FIG> and <FIG>), the left side (back side facing the plane of <FIG> and upper side in <FIG>), and the right side (front side facing the plane of <FIG> and lower side in <FIG>) of an operator where the operator sits on an operator's seat when the hydraulic excavator is in such a state as depicted in <FIG> and <FIG> are hereinafter referred to merely as front side, rear side, left side, and right side, respectively.

The hydraulic excavator of the present embodiment includes a lower track structure <NUM> that can travel, an upper track structure <NUM> swingably provided on the upper side of the lower track structure <NUM>, and a work implement <NUM> coupled to the front side of the upper track structure <NUM>.

The lower track structure <NUM> includes a track frame <NUM> having an H shape as viewed from above. A driving wheel <NUM> and a driven wheel <NUM> are provided on the right side of the track frame <NUM>, and a right side crawler belt (crawler) 7A extends between and around the driving wheel <NUM> and the driven wheel <NUM>. The driving wheel <NUM> on the right side is rotated by driving of a right side travel motor <NUM>, and consequently, the right side crawler belt 7A is rotated. A driving wheel (not depicted) and a driven wheel (not depicted) are provided also on the left side of the track frame <NUM>, and a left side crawler belt 7B extends between and around them. The left side driving wheel is rotated by a left side travel motor (not depicted), and consequently, the left side crawler belt 7B is rotated.

On the front side of the track frame <NUM>, a blade <NUM> for earth removal is movably provided in the upward and downward direction. The blade <NUM> is moved upwardly and downwardly by driving of a blade cylinder (not depicted).

The work implement <NUM> includes: a swing post <NUM> pivotably coupled in the leftward and rightward direction to the front side of the upper track structure <NUM> (particularly, of a swing frame hereinafter described); a boom <NUM> pivotably coupled in the upward and downward direction to the swing post <NUM>; an arm <NUM> pivotably coupled in the upward and downward direction to the boom <NUM>; and a bucket <NUM> pivotably coupled in the upward and downward direction to the arm <NUM>. The swing post <NUM>, the boom <NUM>, the arm <NUM>, and the bucket <NUM> are pivoted by driving of a swing cylinder (not depicted), a boom cylinder <NUM>, an arm cylinder <NUM>, and a bucket cylinder <NUM>, respectively. It is to be noted that the bucket <NUM> is exchangeable for an attachment (not depicted) in which an optional hydraulic actuator is incorporated.

The upper track structure <NUM> includes a swing frame <NUM> that serves as a basic structure, an operation room <NUM> of the canopy type provided on the left side of a front portion of the swing frame <NUM>, and a counterweight <NUM> provided at a rear end of the swing frame <NUM>. The swing frame <NUM> of the upper track structure <NUM> is coupled to the upper side of the track frame <NUM> of the lower track structure <NUM> through a swing wheel <NUM>. The upper track structure <NUM> swings by driving of a swing motor (not depicted).

At the doorway of the operation room <NUM>, a gate lock lever (not depicted) is provided which can be operated between a raised position (getting on/off permission position) and a lowered position (getting on/off restriction position). In the inside of the operation room <NUM>, an operator's seat <NUM> on which an operator is to sit, a plurality of operation lever devices (details are hereinafter described) capable of being operated by the operator, and a rotation speed indicator <NUM> (refer to <FIG> hereinafter described) are provided.

The hydraulic excavator includes a hydraulic drive system that drives a plurality of hydraulic actuators (particularly, the right side travel motor <NUM>, left side travel motor, blade cylinder, swing cylinder, boom cylinder <NUM>, arm cylinder <NUM>, bucket cylinder <NUM>, optional hydraulic actuator, and swing motor described hereinabove) according to the operation of the plurality of operation lever devices. The configuration of the hydraulic drive system is described with reference to <FIG>.

<FIG> is a diagram depicting the configuration of the hydraulic drive system in the present embodiment. It is to be noted that <FIG> depicts a configuration relating to the right side travel motor <NUM> and the boom cylinder <NUM> as representatives.

The hydraulic drive system of the present embodiment includes an electric motor <NUM> (prime mover), a battery <NUM> that serves as an electric power supply to the electric motor <NUM>, an inverter <NUM> that controls the rotation speed of the electric motor <NUM>, a hydraulic pump <NUM> and a pilot pump <NUM> that are driven by the electric motor <NUM>, a right side travel control valve <NUM> that controls the flow of hydraulic fluid from the hydraulic pump <NUM> to the right side travel motor <NUM>, a boom control valve <NUM> that controls the flow of hydraulic fluid from the hydraulic pump <NUM> to the boom cylinder <NUM>, an operation lever device <NUM> that switches the right side travel control valve <NUM>, an operation lever device <NUM> that switches the boom control valve <NUM>, and a controller <NUM>.

The operation lever device <NUM> includes, though not depicted, a travel operation lever capable of being operated by an operator, a first pressure reducing valve that operates in response to a front side operation of the traveling operation lever, and a second pressure reducing valve that operates in response to a rear side operation of the traveling operation lever. The first pressure reducing valve generates a pilot pressure corresponding to a front side operation amount of the travel operation lever by using the discharge pressure of the pilot pump <NUM> as source pressure, and outputs the generated pilot pressure to a pressure reception portion on one side of the right side travel control valve <NUM>. Consequently, the right side travel control valve <NUM> is switched from a neutral position to a switched position on one side thereof such that the travel motor <NUM> is rotated in one direction. The second pressure reducing valve generates a pilot pressure corresponding to a rear side operation amount of the travel operation lever by using discharge pressure of the pilot pump <NUM> as source pressure and outputs the generated pilot pressure to a pressure reception portion on the other side of the right side travel control valve <NUM>. Consequently, the right side travel control valve <NUM> is switched from a neutral position to a switched position on the other side thereof such that the right side travel motor <NUM> is rotated in the opposite direction.

The operation lever device <NUM> includes, though not depicted, a work operation lever capable of being operated by an operator, a third pressure reducing valve that operates in response to a front side operation of the work operation lever, and a fourth pressure reducing valve that operates in response to a rear side operation of the working operation lever. The third pressure reducing valve generates a pilot pressure corresponding to a front side operation amount of the work operation lever by using the discharge pressure of the pilot pump <NUM> as source pressure, and outputs the generated pilot pressure to a pressure reception portion on one side of the boom control valve <NUM>. Consequently, the boom control valve <NUM> is switched from a neutral position to a switched position on one side thereof such that the boom cylinder <NUM> is contracted. The fourth pressure reducing valve generates a pilot pressure corresponding to a rear side operation amount of the working operation lever by using discharge pressure of the pilot pump <NUM> as source pressure and outputs the generated pilot pressure to a pressure reception portion on the other side of the boom control valve <NUM>. Consequently, the boom control valve <NUM> is switched from the neutral position to a switched position on the other side thereof such that the boom control valve <NUM> is stretched.

The operation lever device <NUM> or <NUM> configures an operation device that generates a pilot pressure corresponding to the operation amount of an operation lever and switches the control valve with the generated pilot valve. It is to be noted that, though not depicted, the foregoing similarly applies also to the configuration relating to the left side travel motor, blade cylinder, swing cylinder, arm cylinder <NUM>, bucket cylinder <NUM>, optional hydraulic actuator, and swing motor.

A pilot relief valve <NUM> and a lock valve <NUM> are provided on the discharge side of the pilot pump <NUM>. The pilot relief valve <NUM> exhibits an open state when the discharge pressure of the pilot pump <NUM> is equal to or higher than relief pressure, and returns part of hydraulic pressure discharged from the pilot pump <NUM> to the tank. Consequently, the discharge pressure of the pilot pump <NUM> is kept at the relief pressure.

The lock valve <NUM> is switched in response to an operation of the gate lock lever described hereinabove. In particular, a lock switch is provided which has a closed state when the gate lock lever is in its lowered position and has an open state when the gate lock lever is in its raised position. Then, if the lock switch is placed into the closed state, then the solenoid part of the lock valve <NUM> is energized through the lock switch to switch the lock valve <NUM> from its neutral position to a switched position. Consequently, the discharge line of the pilot pump <NUM> is placed into communication to introduce the discharge pressure of the pilot pump <NUM> into the operation lever devices <NUM> and <NUM> and so forth. On the other hand, if the lock switch is placed into the open state, then the solenoid part of the lock valve <NUM> is not energized, and the lock valve <NUM> is placed into its neutral position by biasing force of a spring. Consequently, the discharge line of the pilot pump <NUM> is interrupted. As a result, even if the operation lever device <NUM> or <NUM> or the like is operated, no pilot pressure is generated and any of the plurality of hydraulic actuators does not operate.

A hydraulic signal line <NUM> is connected to the discharge side of the pilot pump <NUM>. The hydraulic signal line <NUM> is connected between the discharge side of the pilot pump <NUM> and a tank <NUM> and has a plurality of control valves (including, more particularly, not only the right side travel control valve <NUM> and the boom control valve <NUM> described hereinabove, but also a left side travel control valve, a blade control valve, a swing post control valve, an arm control valve, a bucket control valve, an optional control valve, and a swing control valve) interposed therein. The hydraulic signal line <NUM> becomes a communication state when all control valves are in their neutral position and becomes an interrupted state when any of the control valves is switched from its neutral position.

A fixed restrictor <NUM> is provided between the discharge side of the pilot pump <NUM> and the plurality of control valves in the hydraulic signal line <NUM>. Further, a pressure sensor <NUM> (first pressure sensor) for detecting the hydraulic pressure on the upstream side of the fixed restrictor <NUM> and another pressure sensor <NUM> (second pressure sensor) for detecting the hydraulic pressure on the downstream side of the fixed restrictor <NUM> (in other words, between the fixed restrictor <NUM> and the control valves) are provided.

The rotation speed indicator <NUM> is capable of indicating a standard rotation speed for the electric motor <NUM> within a predetermined range (particularly, for example, <NUM> to <NUM> rpm) depending upon the rotational operation position of a dial and outputs a signal corresponding to this, for example. The controller <NUM> sets the standard rotation speed for the electric motor <NUM> in response to the signal from the rotation speed indicator <NUM> and controls the inverter <NUM> such that the rotation speed of the electric motor <NUM> becomes the standard rotation speed.

Further, the controller <NUM> controls, when a state in which none of the operation devices is operated continues for a predetermined period of time, the inverter <NUM> such that the rotation speed of the electric motor <NUM> becomes an idle rotation speed (particularly, a low rotation speed set in advance so as to be lower than the standard rotation speed described above) (auto idle control). Here, as the most significant feature of the present embodiment, the controller <NUM> detects an operation state of the plurality of operation devices on the basis of results of detection of the pressure sensors <NUM> and <NUM>. Describing more particularly, the controller <NUM> detects an operation state of the plurality of operation devices on the basis of the differential pressure between the hydraulic pressure detected by the pressure sensor <NUM> and the hydraulic pressure detected by the pressure sensor <NUM> (hereinafter referred to as differential pressure across the fixed restrictor <NUM>).

When none of the operation devices is operated (i.e., when all of the control valves are in the neutral position), since the hydraulic signal line <NUM> is placed in a communication state, the differential pressure across the fixed restrictor <NUM> is great. On the other hand, if any one of the operation devices is operated (i.e., when any one of the control valves is switched from its neutral position), since the hydraulic signal line <NUM> is placed into an interrupted state, the differential pressure across the fixed restrictor <NUM> decreases to a level near to zero. The controller <NUM> decides that none of the operation devices is operated when the differential pressure across the fixed restrictor <NUM> is equal to or higher than a threshold value set in advance. Then, when the state in which none of the operation devices is operated continues for a predetermined period of time, the controller <NUM> decreases the rotation speed of the electric motor <NUM> to the idle rotation speed. Further, the controller <NUM> decides that one of the operation devices is operated when the differential pressure across the fixed restrictor <NUM> is lower than the threshold value. Then, the electric motor <NUM> keeps or returns the rotation speed of the electric motor <NUM> at or to the standard rotation speed.

Now, a processing procedure of the controller of the present embodiment is described. <FIG> is a flow chart depicting the processing procedure of the controller in the present embodiment. It is to be noted that the process depicted in <FIG> is executed periodically.

In step S1, the controller <NUM> calculates the differential pressure across the fixed restrictor <NUM> on the basis of results of detection of the pressure sensors <NUM> and <NUM>. Then, the processing advances to step S2, at which the controller <NUM> decides whether or not the differential pressure across the fixed restrictor <NUM> is equal to or higher than a threshold value. When the differential pressure across the fixed restrictor <NUM> is equal to or higher than the threshold value (i.e., when none of the operation devices is operated), the processing advances to step S3.

In step S3, the controller <NUM> decides whether or not the rotation speed of the electric motor <NUM> is controlled to the idle rotation speed (in other words, whether or not the electric motor <NUM> is in the idle state). When the rotation speed of the electric motor <NUM> is not controlled to the idle rotation speed (in other words, when the electric motor <NUM> is not in the idle state), the processing advances to step S4.

In step S4, the controller <NUM> counts up a no-operation duration. Then, the processing advances to step S5, in which the controller <NUM> decides whether or not the no-operation duration reaches a predetermined time period.

When the no-operation duration does not reach the predetermined time period in step S5, the processing advances to step S6. In step S6, the controller <NUM> controls the electric motor <NUM> to be driven at its standard rotation speed. On the other hand, when the no-operation duration reaches the predetermined time period, the processing advances to step S7. In step S7, the controller <NUM> controls the electric motor <NUM> to be driven at the idle rotation speed. It is to be noted that, when the rotation speed of the electric motor <NUM> is controlled to the idle rotation speed (in other words, when the electric motor <NUM> is in the idle state) in step S3, the processing advances to step S7 bypassing the steps S4 and S5 described above.

When the differential pressure across the fixed restrictor <NUM> is lower than the threshold value (i.e., when any one of the control valves is operated) in step S2, the processing advances to step S6 described hereinabove through step S8. In step S8, the controller <NUM> clears the count of the no-operation duration.

In this manner, in the present embodiment, the controller <NUM> calculates the differential pressure across the fixed restrictor <NUM> on the basis of results of detection of the pressure sensors <NUM> and <NUM> and detects an operation state of the plurality of operation devices on the basis of the differential pressure. The differentia pressure of the fixed restrictor <NUM> used in the present embodiment can suppress the influence of the rotation speed of the electric motor <NUM> and so forth in comparison with the hydraulic pressure on the downstream side of the fixed restrictor <NUM> used in the prior art. Describing more particularly, even in a case where the rotation speed of the electric motor <NUM> is low and consequently the hydraulic pressure on the upstream side of the fixed restrictor <NUM> is low or in a case where the pressure loss in a portion of the hydraulic signal line <NUM> from the fixed restrictor <NUM> to the tank <NUM> is high and consequently the hydraulic pressure on the downstream side of the fixed restrictor <NUM> is high, the differential pressure across the fixed restrictor <NUM> when any one of the operation devices is operated goes down to near zero, and the differential pressure across the fixed restrictor <NUM> when none of the operation devices is operated becomes great. Therefore, the threshold value for deciding an operation state of the plurality of operation devices can be set easily. Further, even if the idle rotation speed for the electric motor <NUM> is set low, an operation state of the operation devices can be detected. Accordingly, the idle rotation speed for the electric motor <NUM> can be set low.

It is to be noted that, although, in the foregoing description of the embodiment, a case is described as an example where the controller <NUM> calculates the differential pressure across the fixed restrictor <NUM> (particularly, differential pressure between the hydraulic pressure detected by the pressure sensor <NUM> and the hydraulic pressure detected by the pressure sensor <NUM>), and compares this differential pressure and a threshold value with each other to decide an operation state of a plurality of operation devices, this is not restrictive. Alternatively, the controller may add a predetermined differential pressure to a hydraulic pressure detected by the pressure sensor <NUM> to set a threshold value and compare the hydraulic pressures detected by the pressure sensor <NUM> and the threshold value with each other to decide an operation state of the plurality of operation devices. Also in such a modification as just described, advantages similar to those described above can be achieved.

Further, although, in the foregoing description of the embodiment, a case is described as an example where the operation lever device includes a pressure reducing valve that generates a pilot pressure corresponding to an operation amount of an operation lever by using the discharge pressure of the pilot pump <NUM> as source pressure and outputs the generated pilot pressure to the pressure reception portion of the control valve (in other words, the operation device that switches the control valve is configured only from the operation lever device), this is not restrictive. The operation lever device may include, for example, a potentiometer that detects an operation amount of the operation lever and outputs a corresponding electric operation signal. Then, the controller generates instruction current in response to the electric operation signal from the operation lever device and outputs the instruction current to a solenoid proportional valve. The solenoid proportional valve generates a pilot pressure corresponding to the instruction current from the controller by using the discharge pressure of the pilot pump <NUM> as source pressure and outputs the generated pilot pressure to the pressure reception portion of the control valve. In other words, the operation device that switches the control valve may be configured from the operation level device, controller, and solenoid proportional valve. Also in such a modification as just described, advantages similar to those described above can be achieved.

Further, although, in the foregoing description of the embodiment, a case is described as an example where the hydraulic excavator includes the electric motor <NUM> as the prime mover, this is not restrictive, and alternatively, an engine may be provided as the prime mover.

Claim 1:
A construction machine that includes a prime mover (<NUM>), a hydraulic pump (<NUM>) driven by the prime mover (<NUM>), a hydraulic actuator (<NUM>), a control valve (<NUM>) that controls flow of hydraulic fluid from the hydraulic pump (<NUM>) to the hydraulic actuator (<NUM>), an operation device (<NUM>) that generates a pilot pressure corresponding to an operation amount of an operation lever and switches the control valve (<NUM>) with the generated pilot pressure, and a controller (<NUM>) that controls, when a no-operation state of the operation device continues, a rotation speed of the prime mover (<NUM>) to an idle rotation speed set in advance, the construction machine comprising:
a pilot pump (<NUM>) that is driven by the prime mover (<NUM>) and whose discharge pressure is used as a source pressure of the pilot pressure;
a pilot relief valve (<NUM>) provided on a discharge side of the pilot pump (<NUM>);
a hydraulic pressure signal line (<NUM>) that is connected between the discharge side of the pilot pump (<NUM>) and a tank (<NUM>) and in which the control valve (<NUM>) is interposed such that the hydraulic pressure signal line (<NUM>) is interrupted when the control valve (<NUM>) is switched from a neutral position;
a fixed restrictor (<NUM>) provided between the discharge side of the pilot pump (<NUM>) and the control valve (<NUM>) in the hydraulic pressure signal line (<NUM>);
a first pressure sensor (<NUM>) that detects a hydraulic pressure on an upstream side of the fixed restrictor (<NUM>); and
a second pressure sensor (<NUM>) that detects a hydraulic pressure on a downstream side of the fixed restrictor (<NUM>), wherein
the controller (<NUM>) is configured to detect an operation state of the operation device (<NUM>) based on results of detection of the first pressure sensor (<NUM>) and the second pressure sensor (<NUM>).