Patent Description:
One method of diagnosing the failure of a hydraulic pump is known from Patent Document <NUM>.

Patent Document <NUM> discloses a hydraulic pump failure diagnosing apparatus for a work machine. The work machine includes a plurality of variable displacement hydraulic pumps whose delivery rates are controlled by a regulator, a plurality of hydraulic actuators that are driven by a hydraulic fluid delivered by one or more of the variable displacement hydraulic pumps, a plurality of flow control valves that control the driving of the respective hydraulic actuators, and a line that connects one or more of the variable displacement hydraulic pumps to a tank through one or more of the flow control valves in a neutral position. The hydraulic pump failure diagnosing apparatus includes check valves associated with differential pressure sensors interposed individually between the variable displacement hydraulic pumps and the flow control valves, maximum delivery rate indicating means for indicating a maximum delivery rate of the variable displacement hydraulic pumps to the regulator while the variable displacement hydraulic pumps are being connected to the line, storage means for storing detected pressures from the check valves associated with differential pressure sensors with respect to the variable displacement hydraulic pumps that are delivering the maximum delivery rate indicated by the maximum delivery rate indicating means, and failure determining means for determining whether or not each of the variable displacement hydraulic pumps is favorable, on the basis of the detected pressures.

Patent Document <NUM> discloses a hydraulic drive unit which can measure a degree of damage to a variable capacity type hydraulic pump over the whole variable region of a pump tilting amount. Therein a hydraulic drive unit comprises a selector valve which is arranged at a pump discharge conduit for connecting the hydraulic pump and a control valve and opens/closes the pump discharge conduit, and a pressure detection device which is arranged on an upstream side rather than the selector valve of the pump discharge conduit and detects a discharge pressure of the hydraulic pump. A control device measures the discharge pressure of the hydraulic pump while changing a tilting amount of the hydraulic pump while maintaining a product of a rotation number of a prime motor and the pump tilting amount constant in a state that the selector valve is closed, and measures a degree of damage of the hydraulic pump on the basis of a measurement result.

Patent Document <NUM> discloses a device for diagnosing the failure of a variable displacement hydraulic pump and an electronically controlled control valve which are arranged in a hydraulic circuit, comprising a controller arranged to be changed to a normal control mode and a failure diagnostic mode.

The hydraulic pump failure diagnosing apparatus disclosed in Patent Document <NUM> incorporates the check valves associated with differential pressure sensors. However, the check valves associated with differential pressure sensors fail to provide sufficient accuracy in a small flow rate range for the following reasons.

A check valve allows a fluid to flow therethrough in a forward direction and prevents the fluid from flowing therethrough in a reverse direction. The check valve remains closed unless the differential pressure thereacross exceeds a predetermined pressure (cracking pressure). When the differential pressure exceeds the cracking pressure, the check valve is opened. As the differential pressure increases, the opening degree of the check valve increases, allowing the fluid to flow at a higher flow rate. Since the flow rate through the check valve varies largely depending on the differential pressure, it is difficult to determine the flow rate with high accuracy from the differential pressure. <FIG> (characteristic diagram of a conversion map of pressures and flow rates) of Patent Document <NUM> illustrates such a situation. According to <FIG>, inasmuch as the flow rate varies largely particularly in a range where the pressure (the differential pressure across the check valve) is low, the accuracy with which to convert and calculate a flow rate drops largely in a small flow rate range.

In order to increase the accuracy with which to convert and calculate a flow rate, it may be possible to reduce a change caused in the flow rate by the pressure, by reducing the amount of opening of the check valve. However, the check valve with the reduced amount of opening tends to cause a large pressure loss during normal operation other than diagnosis, resulting in an energy loss.

The present invention has been made in view of the above problems. It is an object of the present invention to provide a construction machine that is capable of measuring a minute leakage flow rate of a one-sided tilting variable displacement hydraulic pump.

In order to achieve the above object, according to the present invention, there is provided a construction machine including a prime mover, a tank that stores a hydraulic fluid, a one-sided tilting variable displacement first hydraulic pump that is driven by the prime mover and that delivers the hydraulic fluid drawn from the tank, a plurality of hydraulic actuators that are driven by the hydraulic fluid supplied from the first hydraulic pump, an operation device that gives an instruction for operations of the plurality of hydraulic actuators, and a controller that controls a revolution speed of the prime mover and tilting of the first hydraulic pump. The construction machine includes a first pressure sensor that detects a pressure of the first hydraulic pump, a first bleed-off adjusting device that is enabled to adjust a bleed-off flow rate of the first hydraulic pump, and an input device that gives an instruction for measurement of a leakage flow rate of the first hydraulic pump. The controller is connected to the operation device, the first pressure sensor, the first bleed-off adjusting device, and the input device, and is programmed to determine an operated state of the operation device on the basis of an input signal from the operation device, convert a detected signal from the first pressure sensor into a pressure value, and output a control signal based on a control command value to the first bleed-off adjusting device. The controller is configured to, in a case where the controller determines that the operation device is in a non-operated state and where a measuring command is inputted from the input device, measure the pressure of the first hydraulic pump while changing the control command value for the first bleed-off adjusting device in a state in which a flow rate of the first hydraulic pump is maintained, and calculate the leakage flow rate of the first hydraulic pump on the basis of the control command value for the first bleed-off adjusting device at the time that the pressure of the first hydraulic pump is stabilized at a predetermined pressure.

According to the present invention configured as described above, it is possible to measure the pressure of the hydraulic pump while changing the operation amount of the bleed-off adjusting device in a state in which the flow rate of the hydraulic pump is maintained, and calculate the leakage flow rate of the hydraulic pump on the basis of the control command value for the bleed-off adjusting device at the time that the pressure of the hydraulic pump is stabilized at the predetermined pressure. It is thus possible to measure a minute leakage flow rate of the hydraulic pump.

The construction machine according to the present invention makes it possible to measure a minute leakage flow rate of the one-sided tilting variable displacement hydraulic pump.

As an example of a construction machine according to embodiments of the present invention, a hydraulic excavator will be described hereinbelow with reference to the drawings. Note that, in the drawings, identical components are denoted by identical reference characters, and their redundant description will appropriately be omitted below.

<FIG> is a side elevational view of a hydraulic excavator according to a first embodiment of the present invention.

In <FIG>, the hydraulic excavator, which is denoted by <NUM>, includes a track structure <NUM>, a swing structure <NUM> that is swingably mounted on the track structure <NUM>, and a work implement <NUM> that is mounted pivotably in a vertical direction on a front side of the swing structure <NUM>.

The work implement <NUM> includes a boom <NUM> that is mounted pivotably in a vertical direction on the front side of the swing structure <NUM>, an arm <NUM> that is mounted pivotably in a vertical or longitudinal direction on a distal end portion of the boom <NUM>, and a bucket <NUM> that is mounted pivotably in a vertical or longitudinal direction on a distal end portion of the arm <NUM>. The boom <NUM> is driven by boom cylinders <NUM> that are hydraulic actuators, the arm <NUM> is driven by an arm cylinder <NUM> that is a hydraulic actuator, and the bucket <NUM> is driven by a bucket cylinder <NUM> that is a hydraulic actuator. A cabin <NUM> to be occupied by the operator is mounted on the swing structure <NUM> at a front position thereon.

<FIG> schematically illustrates the configuration of a hydraulic drive system mounted on the hydraulic excavator <NUM>.

As illustrated in <FIG>, the hydraulic drive system, which is denoted by <NUM>, includes an engine <NUM> as a prime mover, a one-sided tilting variable displacement hydraulic pump <NUM> that is driven by the engine <NUM>, a hydraulic-pressure-pilot-type tilting control device <NUM> that controls a pump displacement volume (pump tilting) qp of the hydraulic pump <NUM>, a solenoid proportional valve <NUM> that applies, to the tilting control device <NUM>, a pilot pressure generated by reducing the primary pressure from a pilot hydraulic fluid source (not illustrated), the hydraulic actuators <NUM> to <NUM>, an operation device <NUM> that gives an instruction for operations of the hydraulic actuators <NUM> to <NUM>, a directional control valve unit <NUM>, a bleed-off valve <NUM>, a relief valve <NUM>, a pressure senor <NUM>, a monitor <NUM>, an input device <NUM> that gives an instruction for measurement of a leakage flow rate of the hydraulic pump <NUM>, and a controller <NUM> that controls the engine <NUM>, the solenoid proportional valve <NUM>, the bleed-off valve <NUM>, the monitor <NUM>, etc. The controller <NUM> has an input interface 40a that receives signals as input from the various components, a computing device 40b that includes, for example, a central processing unit (CPU) and peripheral circuits thereof and that performs various computing operations according to predetermined programs, a storage device 40c that stores the programs and various types of data, and an output interface 40d that outputs control signals to the components.

The directional control valve unit <NUM> is connected to a delivery line (pump delivery line) <NUM> connected to a delivery port of the hydraulic pump <NUM>, and controls the flows of a hydraulic fluid supplied from the hydraulic pump <NUM> to the hydraulic actuators <NUM> to <NUM>, according to operating actions on the operation device <NUM>.

The bleed-off valve <NUM> is disposed upstream of the directional control valve unit <NUM> with respect to the pump delivery line <NUM>, and is opened and closed according to a valve control signal from the controller <NUM> to establish and interrupt fluid communication through the pump delivery line <NUM>.

The relief valve <NUM> is a safety valve for limiting the pressure in the pump delivery line <NUM>, and is disposed upstream of the bleed-off valve <NUM> with respect to the pump delivery line <NUM>. When the pressure (= pump pressure Pp) in the pump delivery line <NUM> exceeds a predetermined pressure (relief setting pressure) Pr, the relief valve <NUM> is opened, discharging the hydraulic fluid from the pump delivery line <NUM> into a tank <NUM>.

The pressure sensor <NUM> is disposed upstream of the bleed-off valve <NUM> with respect to the pump delivery line <NUM>. The pressure sensor <NUM> converts the pressure (= pump pressure Pp) in the pump delivery line <NUM> into a pressure signal, and outputs the pressure signal to the controller <NUM>.

The controller <NUM> controls the bleed-off valve <NUM>, a revolution speed (engine speed) Neng of the engine <NUM>, and the pump tilting qp in response to a measuring command from the input device <NUM>. On the basis of the pump pressure Pp detected by the pressure sensor <NUM>, the controller <NUM> calculates a leakage flow rate Qleak of the hydraulic pump <NUM>, and stores the calculated leakage flow rate Qleak in the storage device 40c or outputs the calculated leakage flow rate Qleak to the monitor <NUM>, etc..

Axial piston type hydraulic pumps are widely used on construction machines, and their variable displacement mechanisms include a bent axis type and a swash plate type. Both types achieve variable displacement by changing piston strokes to change the displacement volume.

<FIG> illustrates the structure of a variable displacement bent-axis hydraulic pump as an example of the one-sided tilting variable displacement hydraulic pump <NUM>.

As illustrated in <FIG>, a tubular casing <NUM> includes a substantially hollow cylindrical casing body 1A having a bearing portion on one end and a head casing 1B closing the other end of the casing body 1A.

A rotational shaft <NUM> is rotatably mounted in the casing body 1A. A cylinder block <NUM> is positioned within the casing body 1A and corotates with the rotational shaft <NUM>. The cylinder block <NUM> has a plurality of cylinders <NUM> defined therein along axial directions thereof. Pistons <NUM> are slidably housed in the respective cylinders <NUM>. Connecting rods <NUM> are attached to the respective pistons <NUM>.

Spherical portions 6A are mounted on the respective distal ends of the connecting rods <NUM> and are swingably supported on a drive disk <NUM> mounted on the distal end of the rotational shaft <NUM>. The cylinder block <NUM>, together with a valve plate <NUM> to be described later, are disposed at a tilting angle θ as a tilting amount with respect to the rotational shaft <NUM>. A pump displacement volume is determined depending on the tilting angle θ.

The cylinder block <NUM> is held in sliding contact with one side end face of the valve plate <NUM>, and the other side end face of the valve plate <NUM> is held in sliding contact with a tilting slide surface <NUM> that is curved in a recessed manner and that is formed on the head casing 1B.

The valve plate <NUM> has a through hole 8A defined centrally therein, and the distal ends of a central shaft <NUM> and a swing pin <NUM>, which are to be described later, are inserted into the through hole 8A from the respective sides of the valve plate <NUM>. The valve plate <NUM> also has a pair of supply and discharge ports (not illustrated) that are intermittently brought into fluid communication with the cylinders <NUM> when the cylinder block <NUM> is rotated. The head casing 1B has a pair of supply and discharge passages (not illustrated) that are defined therein and that are opened at the tilting slide surface <NUM>. The supply and discharge passages are kept in fluid communication with the supply and discharge ports regardless of the tilting position (tilting angle <NUM>) of the valve plate <NUM>.

The central shaft <NUM> supports the cylinder block <NUM> thereon between the drive disk <NUM> and the valve plate <NUM>. A spherical portion 10A is mounted on an end of the central shaft <NUM> and is swingably supported on the drive disk <NUM> at a central axial position thereon. The opposite end of the central shaft <NUM> protrudes centrally through the cylinder block <NUM> and is slidably inserted into the through hole 8A in the valve plate <NUM> to center the cylinder block <NUM> with respect to the valve plate <NUM>.

A tilting mechanism <NUM> tilts the valve plate <NUM> along the tilting slide surface <NUM>. The tilting mechanism <NUM> includes a cylinder chamber <NUM> that is defined in the head casing 1B and that has fluid passage holes 12A and 12B defined at axially opposite ends of the cylinder chamber <NUM>, a servo piston <NUM> that is slidably fitted in the cylinder chamber <NUM> and that defines fluid pressure compartments 13A and 13B in the cylinder chamber <NUM>, and a swing pin <NUM> that has a proximal end portion fixed to the servo piston <NUM> and a distal end portion including a spherical distal end 15A which is swingably inserted through the through hole 8A in the valve plate <NUM>.

A control unit <NUM> controls the tilting mechanism <NUM> to tilt the valve plate <NUM>. The control unit <NUM> is disposed outside of the head casing 1B and includes a restriction control valve (not illustrated) for performing feedback control on the amount of a hydraulic fluid (pilot pressure) supplied from and discharged to a pilot pump (not illustrated). The restriction control valve includes a sleeve (not illustrated) integrally coupled to the servo piston <NUM> by a feedback pin <NUM> inserted through an oblong hole 1C defined in the head casing 1B.

When the restriction control valve of the control unit <NUM> is controlled by the operation lever <NUM> or the like, a hydraulic fluid (pilot pressure) depending on the degree to which the operation device <NUM> is operated is supplied from the pilot pump to, and discharged to the pilot pump from, the fluid pressure compartments 13A and 13B in the tilting mechanism <NUM> through the fluid passage holes 12A and 12B, slidingly displacing the servo piston <NUM> under the pressure difference between the fluid pressure compartments 13A and 13B. The servo piston <NUM> thus slidingly displaced in the cylinder chamber <NUM> causes the swing pin <NUM> to tilt the valve plate <NUM> and the cylinder block <NUM> in one of the directions indicated by an arrow A, by the tilting angle θ. The sleeve of the restriction control valve is displaced in unison with the servo piston <NUM>, performing feedback control on the amount of the hydraulic fluid from the pilot pump to keep the servo piston <NUM> displaced to a state corresponding to the degree to which the restriction control valve is controlled.

The axial piston type variable displacement hydraulic pump thus constructed is capable of varying the flow rate of the hydraulic fluid delivered therefrom, by changing the angle to which the bent axis is tilted or by changing the tilting amount (tilting) of the swash plate when a swash-plate pump is used, thereby changing the displacement volume of the piston per revolution thereof.

Next, a pump delivery leakage will be described below.

As described above, major movable and slidable parts of the hydraulic pump include sliding surfaces of the bearings, sliding surfaces of the pistons <NUM> and the cylinders <NUM>, sliding surfaces of the cylinder block <NUM> and the valve plate <NUM>, sliding surfaces of the valve plate <NUM> and the head casing 1B, etc. The hydraulic fluid to be delivered from the hydraulic pump flows from the cylinder block <NUM> through the valve plate <NUM> to a delivery port (not illustrated). If the sliding surfaces are not well lubricated, they wear when sliding, tending to increase the gaps between the tilting slide surfaces. When the gaps are increased until the clearance between the movable and slidable components exceeds a predetermined normal clearance level, the hydraulic fluid to be delivered from the hydraulic pump flows (leaks) from the gaps into lower-pressure regions. As a result, the flow rate of the hydraulic fluid delivered from the hydraulic pump becomes smaller than a normal delivery flow rate by the flow rate of the leaking hydraulic fluid.

The relation between a theoretical pump flow rate, a pump leakage flow rate, and a pump pressure will be described below. The theoretical pump flow rate represents a pump flow rate based on the assumption that the pump leakage flow rate is zero.

The relation between various flow rates in the hydraulic drive system <NUM> and the pump pressure Pp is expressed by the following equation. <NUM>] <MAT>.

Note that the theoretical pump flow rate Qpref is expressed by the following equation. <NUM>] <MAT>.

According to the present embodiment, since the pump pressure Pp is kept constant under the control of the bleed-off valve <NUM>, the following equation is obtained from the equation (<NUM>). <NUM>] <MAT>.

Further, as the pump leakage flow rate Qleak is measured while the relief valve <NUM> is closed (i.e., while the relief flow rate Qrelief is zero), the following equation is obtained from the equation (<NUM>). <NUM>] <MAT>.

By applying the equation of the orifice to the central bypass flow rate Qcb in the equation (<NUM>), the following equation is obtained. <NUM>] <MAT>.

In the equation (<NUM>), the pressure difference ΔP across the bleed-off valve is constant, and the working oil density ρ remains essentially unchanged. Therefore, the equation (<NUM>) may be simplified as follows. <NUM>] <MAT>.

According to the equation (<NUM>), it will be seen that the leakage flow rate Qleak of the hydraulic pump <NUM> can be calculated from the theoretical pump flow rate Qpref and the opening area Acb of the bleed-off valve <NUM>. Further, by grasping a change in the opening area Acb while the theoretical pump flow rate Qpref is constant, it is possible to grasp a change in the leakage flow rate Qleak. Note that, as the storage device 40c of the controller <NUM> stores opening area characteristic data with respect to a control command value for the bleed-off valve <NUM>, the opening area Acb can easily be determined from the control command value for the bleed-off valve <NUM>. Moreover, since the leakage flow rate Qleak becomes a function of only the opening area Acb by making the theoretical pump flow rate Qpref constant, it is possible to calculate the leakage flow rate Qleak easily and accurately from the control command value for the bleed-off valve <NUM>.

<FIG> illustrates functional blocks of the controller <NUM>. Note that, in <FIG>, only a configuration for measuring the leakage flow rate across the hydraulic pump <NUM> is illustrated, and a configuration for driving the actuators <NUM> to <NUM> is omitted from illustration.

In <FIG>, the controller <NUM> includes a measurement control section <NUM>, a pump pressure measuring section <NUM>, an engine speed control section <NUM>, a pump tilting control section <NUM>, a valve control section <NUM>, and a leakage flow rate calculating section <NUM>.

The measurement control section <NUM> controls the engine speed control section <NUM>, the pump tilting control section <NUM>, and the valve control section <NUM> in response to a measuring command for starting measuring the leakage flow rate Qleak and a lever neutral signal. The measuring command may be generated by operating the input device such as a switch <NUM> that is disposed in the cabin <NUM>, or may automatically be generated immediately after the engine <NUM> of the hydraulic excavator <NUM> is started to power up the controller <NUM>. In such a case, an electric power signal that is inputted from the power supply device (not illustrated) of the controller <NUM> corresponds to the measuring command. The lever neutral signal represents a signal generated when the actuators <NUM> to <NUM> are not operated, and is generated according to input signals from the operation lever <NUM> of the actuators <NUM> to <NUM>.

The pump pressure measuring section <NUM> converts a pressure signal from the pressure sensor <NUM> into a pump pressure Pp of the hydraulic pump <NUM>, and outputs the pump pressure Pp to the valve control section <NUM> and the leakage flow rate calculating section <NUM>.

The engine speed control section <NUM> controls the engine <NUM> to make the engine speed Neng equal to a predetermined revolution speed (prescribed revolution speed), in response to a command from the measurement control section <NUM>.

The pump tilting control section <NUM> adjusts the opening degree of the solenoid proportional valve <NUM> and drives the tilting control device <NUM> to make the tilting qp of the hydraulic pump <NUM> equal to a desired value, in response to a command from the measurement control section <NUM>.

The valve control section <NUM> adjusts the amount of opening (degree of opening) of the bleed-off valve <NUM> to bring the pump pressure Pp into conformity with a predetermined target pressure and outputs the opening degree of the valve to the leakage flow rate calculating section <NUM>, in response to a command from the measurement control section <NUM>. The target pressure referred to herein is set to such a pressure that is relatively high (e.g., <NUM> MPa) but that is lower than the relief setting pressure Pr (e.g., <NUM> MPa).

The leakage flow rate calculating section <NUM> calculates the leakage flow rate Qleak on the basis of the opening degree of the valve at the time that the pump pressure Pp is in conformity with the target pressure, and outputs the calculated leakage flow rate Qleak to the monitor <NUM>, etc., located in the cabin <NUM>. Note that the leakage flow rate calculating section <NUM> may be arranged to indicate the leakage flow rate Qleak not only to the operator in the cabin <NUM>, but also to a vehicle administrator, a service department, or the like.

<FIG> is a flowchart of a sequence of measurement of a pump leakage flow rate that is carried out by the controller <NUM>. In response to a command for measuring a pump leakage flow rate based on a request from the operator, the administrator, the service personnel, or the like, the controller <NUM> interrupts a normal control sequence (not illustrated) and changes to the measuring sequence. The steps of the measuring sequence will successively be described hereinbelow.

The controller <NUM> first determines whether or not the operation lever <NUM> is neutral (non-operated or not) (step S1).

If the controller <NUM> determines Yes (the operation lever <NUM> is neutral) in step S1, then the controller <NUM> sets the engine speed to the prescribed revolution speed and sets the delivery flow rate (pump flow rate) of the hydraulic pump 21a to a predetermined flow rate (prescribed flow rate).

After step S2, the controller <NUM> measures a pump pressure Pp (step S3).

After step S3, the controller <NUM> determines whether or not the pump pressure Pp is equal to a target pressure (step S4).

If the controller <NUM> determines No (the pump pressure Pp is not equal to the target pressure) in step S4, then the controller <NUM> adjusts the opening degree of the bleed-off valve <NUM> (step S5), and returns to step S3. Specifically, if the pump pressure Pp is lower than the target pressure, then the controller <NUM> corrects the degree of opening in a valve closing direction, and if the pump pressure Pp is higher than the target pressure, then the controller <NUM> corrects the degree of opening in a valve opening direction.

If the controller <NUM> determines Yes (the pump pressure Pp is equal to the target pressure) in step S4, then the controller <NUM> acquires data on the opening degree of the bleed-off valve (step S6).

After step S6, the controller <NUM> determines whether or not data for a prescribed number of times has been obtained (step S7). This is to secure a number of pieces of data enough to perform a subsequent leveling process such as a moving average process or a filtering process, in view of data variations, etc., and the prescribed number of times is established depending on the contents of the processing and the data acquisition rate.

If the controller <NUM> determines No (data for the prescribed number of times has not been obtained) in step S7, then the controller <NUM> returns to step S3.

If the controller <NUM> determines Yes (data for the prescribed number of times has been obtained) in step S7, then the controller <NUM> performs the leveling process on the latest data for the prescribed number of times (step S8).

After step S8, the controller <NUM> restores the opening degree Acb of the bleed-off valve, the pump tilting qp, and the engine speed Neng to their values prior to the start of the measuring sequence (step S9).

After step S9, the controller <NUM> calculates a pump leakage flow rate Qleak on the basis of the opening amount Acb of the bleed-off valve that is calculated in step S9 (step <NUM>). Then, the measuring sequence is ended (the normal control sequence is reinstated).

According to the present embodiment, the construction machine <NUM> includes the prime mover <NUM>, the tank <NUM> that stores the hydraulic fluid, the one-sided tilting variable displacement hydraulic pump <NUM> that is driven by the prime mover <NUM> and that delivers the hydraulic fluid drawn from the tank <NUM>, the hydraulic actuators <NUM> to <NUM> that are driven by the hydraulic fluid supplied from the hydraulic pump <NUM>, the operation device <NUM> that gives an instruction for operations of the hydraulic actuators <NUM> to <NUM>, and the controller <NUM> that controls the engine speed Neng of the prime mover <NUM> and the tilt qp of the hydraulic pump <NUM>. The construction machine <NUM> further includes the pressure sensor <NUM> that detects a pressure Pp of the hydraulic pump <NUM>, the bleed-off adjusting device <NUM> that can adjust a bleed-off flow rate Qcb of the hydraulic pump <NUM>, and the input device <NUM> that gives an instruction for measurement of the leakage flow rate Qleak of the hydraulic pump <NUM>. The controller <NUM> is connected to the operation device <NUM>, the pressure sensor <NUM>, the bleed-off adjusting device <NUM>, and the input device <NUM>, and is programmed to determine an operated state of the operation device <NUM> on the basis of an input signal from the operation device <NUM>, convert a detected signal from the pressure sensor <NUM> into a pressure value, and output a control signal based on a control command value to the bleed-off adjusting device <NUM>. When the controller <NUM> determines that the operation device <NUM> is in a non-operated state and when a measuring command is inputted from the input device <NUM>, the controller <NUM> measures a pressure Pp of the hydraulic pump <NUM> while changing the control command value for the bleed-off adjusting device <NUM> with the flow rate Qpref of the hydraulic pump <NUM> being maintained, and calculates a leakage flow rate Qleak of the hydraulic pump <NUM> on the basis of the control command value for the bleed-off adjusting device <NUM> at the time that the pressure Pp of the hydraulic pump <NUM> is stabilized at a predetermined pressure.

Further, when the controller <NUM> according to the present embodiment determines that the operation device <NUM> is in the non-operated state, on the basis of an input signal from the operation device <NUM>, and when the measuring command is inputted from the input device <NUM>, the controller <NUM> adjusts the flow rate of the hydraulic pump <NUM> to a predetermined flow rate, measures the pressure Pp of the hydraulic pump <NUM> while changing the control command value for the bleed-off adjusting device <NUM> with the flow rate of the hydraulic pump <NUM> being maintained at the predetermined flow rate, and calculates the leakage flow rate Qleak of the hydraulic pump <NUM> on the basis of the control command value for the bleed-off adjusting device <NUM> at the time that the pressure Pp of the hydraulic pump <NUM> is stabilized at the predetermined pressure.

According to the present embodiment as configured as described above, the pressure Pp of the hydraulic pump <NUM> can be measured while changing the control command value for the bleed-off adjusting device <NUM> with the leakage flow rate Qleak of the hydraulic pump <NUM> being maintained, and the leakage flow rate of the hydraulic pump <NUM> can be calculated on the basis of the control command value for the bleed-off adjusting device <NUM> at the time that the pressure Pp of the hydraulic pump <NUM> is stabilized at the predetermined pressure. Consequently, a minute leakage flow rate Qleak of the hydraulic pump <NUM> can be measured.

In addition, when the controller <NUM> according to the present embodiment determines that the operation device <NUM> is in the non-operated state, on the basis of an input signal from the operation device <NUM>, and when the measuring command is inputted from the input device <NUM>, the controller <NUM> may measure the pressure Pp of the hydraulic pump <NUM> while adjusting the control command value for the bleed-off adjusting device <NUM> with the present flow rate Qpref of the hydraulic pump <NUM> being maintained, and store the control command value for the bleed-off adjusting device <NUM> at the time that the pressure Pp of the hydraulic pump <NUM> is in conformity with the target pressure, in association with the pressure Pp and the present flow rate Qpref of the hydraulic pump <NUM>. In this case, though the flow rate Qpref of the hydraulic pump <NUM> varies each time a leakage flow rate is measured, it is possible to grasp a change in the leakage flow rate Qleak by confirming a transition of the control command value for the bleed-off adjusting device <NUM> that is stored in association with the pressure Pp and the flow rate Qpref which are identical to each other or which are in the same range. Moreover, since the flow rate Qpref of the hydraulic pump <NUM> does not change before and after the leakage flow rate Qleak is measured, it is possible to reduce adverse effects on the operability after the measurement is finished.

Furthermore, the controller <NUM> according to the present embodiment performs a leveling process on the control command value for the bleed-off adjusting device <NUM> before calculating the leakage flow rate Qleak. As the leveling process removes the effect of noise, etc., from the control command value for the bleed-off adjusting device <NUM>, it is possible to increase the accuracy with which to measure the leakage flow rate Qleak.

An additional control process for controlling the pump pressure Pp by using the bleed-off valve <NUM> will be described below with reference to <FIG>. While the present control process is being carried out, a target pressure is inputted as a command to the controller <NUM>. The controller <NUM> calculates a pump pressure Pp from a pressure signal from the pressure sensor <NUM>, calculates a control command value for the bleed-off valve <NUM> for making the pump pressure Pp equal to the target pressure, and outputs a valve control signal based on the control command value to the bleed-off valve <NUM>. While the present control process is not being carried out, the controller <NUM> outputs an operation command for fully opening the bleed-off valve <NUM>.

According to the present embodiment, the configuration for calculating the pump leakage flow rate Qleak on the construction machine side has been described above. Time information and the feature quantities (the control command value for the bleed-off valve <NUM>, the pump leakage flow rate Qleak, etc.,) that are indicative of the degree of damage of the hydraulic pump <NUM> may be transferred to an analyzing server located in another site through communication means using satellite communications, and the analyzing server may perform a diagnostic process.

<FIG> illustrates a configurational example in which an analyzing server performs a diagnostic process. In this example, a threshold value for determining a fault may easily be changed by the analyzing server. Moreover, as not only data on one machine but also data on a number of machines to be compared (machines of the same kind, class, etc.,) can be collected, a determining threshold value may be decided by comparing relative values representing deviations or departures from a population. In such a case, simpler designs can be achieved because a determining threshold value does not need to be decided in advance but is decided through its adjustment while in operation.

Inasmuch as symptoms of a fault of the pump can be diagnosed on the basis of the determining threshold value that has been defined on the basis of the feature quantities and time information and its tendency over time, the symptoms of the fault of the pump can be grasped outside the construction machine.

A second embodiment of the present invention will be described below mainly with respect to its features where it is different from the first embodiment.

According to the first embodiment, since the bleed-off valve <NUM> is positioned immediately downstream of the hydraulic pump <NUM>, a leakage flow rate of the hydraulic pump <NUM> can be measured without being adversely affected by the directional control valve unit <NUM>, etc. However, with the construction machine <NUM> whose actuators <NUM> to <NUM> are driven by the hydraulic fluid delivered from the hydraulic pump <NUM>, there is a situation where it is preferable to evaluate a leakage across not only the hydraulic pump <NUM> but also the directional control valve unit <NUM>, because not only the hydraulic pump <NUM> but also the directional control valve unit <NUM> are largely involved in supplying the hydraulic fluid to the hydraulic actuators <NUM> to <NUM>.

As illustrated in <FIG>, the hydraulic drive system <NUM> includes variable displacement first and second hydraulic pumps 21a and 21b that are driven by the engine (prime mover) <NUM>, a first directional control valve unit 24a that includes a plurality of directional control valves 24a1 parallel-connected to a pump delivery line 28a of the first hydraulic pump 21a, and a second directional control valve unit 24b that includes a plurality of directional control valves 24b1 parallel-connected to a pump delivery line 28b of the second hydraulic pump 21b.

The directional control valves 24a1 of the first directional control valve unit 24a and the directional control valves 24b1 of the second directional control valve unit 24b are each connected to any one of the hydraulic actuators <NUM> to <NUM> and hydraulic actuators <NUM>, 120R, and <NUM>. Each of the directional control valves 24a1 and the directional control valves 24b1 has its spool shiftable by a pilot pressure (hydraulic or electromagnetic) controlled by the operation lever <NUM> located in the cabin <NUM> or the operation device <NUM> such as an operating pedal. First and second bleed-off valves 25a and 25b are connected respectively to bypass lines 60a and 60b that allow the hydraulic fluid from the first and second hydraulic pumps 21a and 21b to flow into the tank <NUM>. The first and second bleed-off valves 25a and 25b control flow rates (bleed-off flow rates) of the hydraulic fluid flowing from the first and second hydraulic pumps 21a and 21b into the tank <NUM>, according to commands from the controller <NUM> (illustrated <FIG>).

The hydraulic actuators mounted on the hydraulic excavator <NUM> include left and right track motors 120R and <NUM> and a swing motor <NUM>, each including a hydraulic motor, the boom cylinders <NUM> for driving the boom <NUM>, the arm cylinder <NUM> for driving the arm <NUM>, and the bucket cylinder <NUM> for driving the bucket <NUM>. Of these hydraulic actuators, the boom cylinders <NUM> and the arm cylinder <NUM> are supplied with the combined hydraulic fluid from the first and second hydraulic pumps 21a and 21b. Note that, though the hydraulic drive system <NUM> according to the present embodiment has the two hydraulic pumps 21a and 21b, the number of hydraulic pumps used may be varied, if necessary, depending on the work load, etc..

The relief valve <NUM> that restricts the maximum pressure of a hydraulic circuit is disposed between the first and second hydraulic pumps 21a and 21b and the tank <NUM>, and thus, protection of the respective components included in the hydraulic circuit is achieved.

The present embodiment is different from the first embodiment in that it includes the bleed-off valves 25a and 25b disposed downstream of the directional control valve units 24a and 24b, instead of the bleed-off valve <NUM> (illustrated in <FIG>) disposed upstream of the directional control valve unit <NUM>. As illustrated in <FIG>, the directional control valves 24a1 and 24b1 for controlling the flow of the hydraulic fluid supplied to the actuators are connected parallel to the supply ports of the pumps, and leakages of the hydraulic fluid from the directional control valves 24a1 and 24b1, as well as leakages from the pumps, adversely affect the driving of the actuators.

Moreover, since the pump leakage flow rate Qleak is measured in a state in which the pump pressure Pp is kept constant under the control of the bleed-off valve <NUM> and in which the relief valve <NUM> is closed (i.e., the relief flow rate Qrelief is zero), the following equation is obtained from the equation (<NUM>). <NUM>] <MAT>.

According to the equation (<NUM>), since the sum of the pump leakage flow rate Qleak and the directional control valve leakage flow rate Qcv is calculated, it is possible to measure a leakage flow rate of the entire hydraulic fluid supply system including the hydraulic pumps 21a and 21b and the directional control valve units 24a and 24b.

Operation of the hydraulic drive system at the time of measuring a pump leakage flow rate is the same as that according to the first embodiment, and will be omitted from description. As the hydraulic drive system operates as described above, the leakage flow rate of the entire hydraulic fluid supply system can be measured from a minute leakage flow rate range, and can be measured highly accurately through the theoretical pump flow rate Qpref at the time that the pump pressure Pp gradually exceeds the target pressure (e.g., <NUM> MPa) in a state in which the bleed-off flow rate Qcb is zero and in which the relief flow rate Qrelief is zero. It is thus possible to evaluate the degree of damage of the supply source of the hydraulic fluid of the construction machine.

The bleed-off adjusting devices 25a and 25b according to the present embodiment are the bleed-off valves 25a and 25b that are connected respectively to the bypass lines 60a and 60b interconnecting the directional control valve units 24a and 24b and the tank <NUM> and that can be opened and closed according to valve control signals from the controller <NUM>.

According to the present embodiment configured as described above, it is possible to measure a minute leakage flow rate of the entire hydraulic fluid supply system including the hydraulic pumps 21a and 21b and the directional control valve units 24a and 24b.

A third embodiment of the present invention will be described below mainly with respect to its features where it is different from the first embodiment.

The present embodiment has, as its object, the provision of a method of evaluating and diagnosing a leakage flow rate when the evaluation and comparison of measurement results is inappropriate in situations that are widely different from normal measuring environments. In a specific example, the hydraulic fluid may have an extremely low temperature of -<NUM> in a diagnosis carried out in a severely cold situation in a highly cold climate. In this case, since a leakage flow rate through an annular gap in a pump is generally affected by the viscosity of the hydraulic fluid, it is expected that the temperature environment will affect the way in which the hydraulic fluid leaks. In situations where the hydraulic fluid has different temperatures depending on whether or not it is warmed up, it is not suitable to quantitatively evaluate a leakage flow rate calculated according to the first embodiment. According to the present embodiment, there will be described a method of calculating a leakage flow rate suitable for evaluation in widely different measuring environments.

As indicated by the hydraulic circuit arrangement illustrated in <FIG>, since the construction machine such as a hydraulic excavator has the left and right track motors <NUM> and 120R, it is normal for the construction machine to have two hydraulic pumps of the same specifications in order to obtain equivalence between the left and right systems. Providing the two hydraulic pumps 21a and 21b are free of damage and have similar leakage flow rate characteristics, the two hydraulic pumps 21a and 21b should have equal leakage flow rates even if an environment such as temperature is widely different from its normal level. Conversely, if the leakage flow rates of the two hydraulic pumps 21a and 21b are widely different from each other, then the hydraulic pump with the larger leakage flow rate can be recognized as being more damaged than the other hydraulic pump.

Therefore, when a temperature environment is widely different from its normal level, the effect of the change in the temperature environment on each of the leakage flow rates can be reduced for a more appropriate leakage diagnosis, by adding the effect of deviations of the leakage flow rates of the two hydraulic pumps in calculating the leakage flow rates of the two hydraulic pumps.

<FIG> illustrates the general configuration of a hydraulic drive system <NUM> according to the present embodiment, and <FIG> illustrates a process for correcting leakage flow rates Qleak1 and Qleak2 of the hydraulic pumps 21a and 21b according to the present embodiment. Note that the process of calculating the leakage flow rates Qleak1 and Qleak2 of the hydraulic pumps 21a and 21b has been described in the first embodiment.

In the example illustrated in <FIG>, a weighted mean of the leakage flow rate Qleak1 and the absolute value of the deviation (= Qleak1 - Qleak2) between the leakage flow rates Qleak1 and Qleak2 is calculated as a corrected leakage flow rate Qleak1, and a weighted mean of the leakage flow rate Qleak2 and the absolute value of the difference (= Qleak2 - Qleak1) between the leakage flow rates Qleak2 and Qleak1 is calculated as a corrected leakage flow rate Qleak2 of the hydraulic pump 21a.

A coefficient K1 for determining the specific weights of the leakage flow rates Qleak1 and Qleak2 and a coefficient K2 for determining the specific weight of the absolute value of the deviation between the leakage flow rates Qleak1 and Qleak2 are established in such a manner that the condition of K1 + K2 = <NUM> is satisfied, that the coefficient K1 is dominant (e.g., <NUM>) at a standard temperature TN, and that the coefficient K2 becomes more dominant (e.g., <NUM>) as the temperature drops.

The hydraulic excavator <NUM> according to the present embodiment further includes a one-sided tilting variable displacement second hydraulic pump 21b that is driven by the prime mover <NUM> and that delivers the hydraulic fluid drawn from the tank <NUM>, a second pressure sensor 27b that detects a pressure Pp2 of the second hydraulic pump 21b, a second bleed-off adjusting device 25b that is capable of adjusting a bleed-off flow rate Qcb2 of the second hydraulic pump 21b, and a temperature sensor <NUM> that detects the temperature of the hydraulic fluid. The hydraulic actuators <NUM> to <NUM> can be driven by the hydraulic fluid supplied from the second hydraulic pump 21b. The controller <NUM> is connected to the second pressure sensor 27b, the second bleed-off adjusting device 25b, and the temperature sensor <NUM>. The controller <NUM> is programmed to convert a detected signal from the second pressure sensor 27b into a pressure value, output a control signal based on a control command value to the second bleed-off adjusting device 25b, and convert a detected signal from the temperature sensor <NUM> into a temperature value. When the controller <NUM> determines that the operation device <NUM> is in a non-operated state and when a measuring command is inputted from the input device <NUM>, the controller <NUM> measures a pressure Pp2 of the second hydraulic pump 21b while changing the control command value for the second bleed-off adjusting device 25b with the flow rate of the second hydraulic pump 21b being maintained, calculates the leakage flow rate Qleak2 of the second hydraulic pump 21b on the basis of the control command value for the second bleed-off adjusting device 25b at the time that the pressure Pp2 of the second hydraulic pump 21b is stabilized at a predetermined pressure, and corrects the leakage flow rate Qleak1 of the first hydraulic pump 21a and the leakage flow rate Qleak2 of the second hydraulic pump 21b depending on the temperature of the hydraulic fluid.

Claim 1:
A construction machine comprising:
a prime mover (<NUM>);
a tank (<NUM>) that stores a hydraulic fluid;
a one-sided tilting variable displacement first hydraulic pump (<NUM>, 21a) that is driven by the prime mover (<NUM>) and that delivers the hydraulic fluid drawn from the tank (<NUM>);
a plurality of hydraulic actuators (<NUM> to <NUM>) that are driven by the hydraulic fluid supplied from the first hydraulic pump (<NUM>, 21a);
an operation device (<NUM>) that gives an instruction for operations of the plurality of hydraulic actuators (<NUM> to <NUM>); and
a controller (<NUM>) that controls a revolution speed of the prime mover (<NUM>) and tilting of the first hydraulic pump (<NUM>, 21a), wherein
the construction machine includes
a first pressure sensor (<NUM>, 27a) that detects a pressure of the first hydraulic pump (<NUM>, 21a),
a first bleed-off adjusting device (<NUM>, 25a) that is enabled to adjust a bleed-off flow rate of the first hydraulic pump (<NUM>, 21a), and
an input device (<NUM>) that gives an instruction for measurement of a leakage flow rate of the first hydraulic pump (<NUM>, 21a), and
the controller (<NUM>)
is connected to the operation device (<NUM>), the first pressure sensor (<NUM>, 27a), the first bleed-off adjusting device (<NUM>, 25a), and the input device (<NUM>), and is programmed to determine an operated state of the operation device (<NUM>) on a basis of an input signal from the operation device (<NUM>), convert a detected signal from the first pressure sensor (<NUM>, 27a) into a pressure value, and output a control signal based on a control command value to the first bleed-off adjusting device (<NUM>, 25a), and
is configured to, in a case where the controller (<NUM>) determines that the operation device (<NUM>) is in a non-operated state and where a measuring command is inputted from the input device (<NUM>), measure the pressure of the first hydraulic pump (<NUM>, 21a) while changing the control command value for the first bleed-off adjusting device (<NUM>, 25a) in a state in which a flow rate of the first hydraulic pump (<NUM>, 21a) is maintained, and calculate the leakage flow rate of the first hydraulic pump (<NUM>, 21a) on a basis of the control command value for the first bleed-off adjusting device (<NUM>, 25a) at a time that the pressure of the first hydraulic pump (<NUM>, 21a) is stabilized at a predetermined pressure.