Patent Description:
A shovel in which the bleed off of directional control valves each corresponding to one of hydraulic actuators sharing a main pump can be controlled with a single cut valve has been known. (See Patent Document <NUM>.

According to this shovel, the turning acceleration force of an upper turning body when the working radius of a work attachment is small is controlled by increasing the bleed off as the working radius of the work attachment decreases.

The above-described shovel, however, only controls the bleed off with the cut valve to stabilize turning operability, and does not use the cut valve to control the pulsation of the pressure of hydraulic oil within a hydraulic circuit. Therefore, the pulsation of the pressure of hydraulic oil within the hydraulic circuit cannot be controlled.

In view of the above, it is desirable to provide a shovel that can control the pulsation of the pressure of hydraulic oil within a hydraulic circuit.

A shovel according to an embodiment of the present invention includes a lower traveling body, an upper turning body turnably mounted on the lower traveling body, a hydraulic pump mounted on the upper turning body, a hydraulic actuator configured to be driven with hydraulic oil discharged by the hydraulic pump, a bleed valve configured to control the flow rate of a portion of the hydraulic oil discharged by the hydraulic pump, the portion flowing to a hydraulic oil tank without going through the hydraulic actuator, and a control device configured to control the opening area of the bleed valve in accordance with the magnitude of pulsation in the pressure of hydraulic oil supplied from the hydraulic pump to the hydraulic actuator.

The above-described means makes it possible to provide a shovel that can control the pulsation of the pressure of hydraulic oil within a hydraulic circuit.

<FIG> is a side view of a shovel (excavator) according to an embodiment of the present invention. According to the shovel, an upper turning body <NUM> is turnably mounted on a lower traveling body <NUM> through a turning mechanism <NUM>. A boom <NUM> is attached to the upper turning body <NUM>. An arm <NUM> is attached to the end of the boom <NUM>. A bucket <NUM> serving as an end attachment is attached to the end of the arm <NUM>.

The boom <NUM>, the arm <NUM>, and the bucket <NUM> constitute an excavation attachment that is an example of an attachment, and are hydraulically driven by a boom cylinder <NUM>, an arm cylinder <NUM>, and a bucket cylinder <NUM>, respectively. A boom angle sensor S1 is attached to the boom <NUM>, an arm angle sensor S2 is attached to the arm <NUM>, and a bucket angle sensor S3 is attached to the bucket <NUM>.

The boom angle sensor S1 detects the rotation angle of the boom <NUM>. According to this embodiment, the boom angle sensor S1 is an acceleration sensor and can detect the rotation angle of the boom <NUM> relative to the upper turning body <NUM> (hereinafter referred to as "boom angle α"). The boom angle α is zero degrees when the boom <NUM> is lowest and increases as the boom <NUM> is raised, for example.

The arm angle sensor S2 detects the rotation angle of the arm <NUM>. According to this embodiment, the arm angle sensor S2 is an acceleration sensor and can detect the rotation angle of the arm <NUM> relative to the boom <NUM> (hereinafter referred to as "arm angle β"). The arm angle β is zero degrees when the arm <NUM> is most closed and increases as the arm <NUM> is opened, for example.

The bucket angle sensor S3 detects the rotation angle of the bucket <NUM>. According to this embodiment, the bucket angle sensor S3 is an acceleration sensor and can detect the rotation angle of the bucket <NUM> relative to the arm <NUM> (hereinafter referred to as "bucket angle γ"). The bucket angle γ is zero degrees when the bucket <NUM> is most closed and increases as the bucket <NUM> is opened, for example.

Each of the boom angle sensor S1, the arm angle sensor S2, and the bucket angle sensor S3 may alternatively be a potentiometer using a variable resistor, a stroke sensor that detects the stroke amount of a corresponding hydraulic cylinder, a rotary encoder that detects a rotation angle about a link pin, a gyro sensor, a combination of an acceleration sensor and a gyro sensor, or the like.

A boom rod pressure sensor S7R and a boom bottom pressure sensor S7B are attached to the boom cylinder <NUM>. An arm rod pressure sensor S8R and an arm bottom pressure sensor S8B are attached to the arm cylinder <NUM>. A bucket rod pressure sensor S9R and a bucket bottom pressure sensor S9B are attached to the bucket cylinder <NUM>.

The boom rod pressure sensor S7R detects the pressure of the rod-side oil chamber of the boom cylinder <NUM> (hereinafter, "boom rod pressure"), and the boom bottom pressure sensor S7B detects the pressure of the bottom-side oil chamber of the boom cylinder <NUM> (hereinafter, "boom bottom pressure"). The arm rod pressure sensor S8R detects the pressure of the rod-side oil chamber of the arm cylinder <NUM> (hereinafter, "arm rod pressure"), and the arm bottom pressure sensor S8B detects the pressure of the bottom-side oil chamber of the arm cylinder <NUM> (hereinafter, "arm bottom pressure"). The bucket rod pressure sensor S9R detects the pressure of the rod-side oil chamber of the bucket cylinder <NUM> (hereinafter, "bucket rod pressure"), and the bucket bottom pressure sensor S9B detects the pressure of the bottom-side oil chamber of the bucket cylinder <NUM> (hereinafter, "bucket bottom pressure").

A cabin <NUM> that is a cab is provided and a power source such as an engine <NUM> is mounted on the upper turning body <NUM>. A body tilt sensor S4, a turning angular velocity sensor S5, and a camera S6 are attached to the upper turning body <NUM>.

The body tilt sensor S4 detects the tilt of the upper turning body <NUM> relative to a horizontal plane. According to this embodiment, the body tilt sensor S4 is an acceleration sensor that detects the tilt angle of the upper turning body <NUM> about its longitudinal axis and lateral axis. The longitudinal axis and lateral axis of the upper turning body <NUM> are orthogonal to each other and pass through the center point of the shovel that is a point on the turning axis of the shovel, for example.

The turning angular velocity sensor S5 detects the turning angular velocity of the upper turning body <NUM>. The turning angular velocity sensor S5 is a gyro sensor according to this embodiment, but may alternatively be a resolver, a rotary encoder, or the like.

The camera S6 obtains an image of an area surrounding the shovel. According to this embodiment, the camera S6 includes a front camera attached to the upper turning body <NUM>. The front camera is a stereo camera that captures an image of an area in front of the shovel. The front camera is attached to the roof of the cabin <NUM>, namely, the exterior of the cabin <NUM>, but may alternatively be attached to the ceiling of the cabin <NUM>, namely, the interior of the cabin <NUM>. The front camera can capture an image of an excavation attachment. The front camera may alternatively be a monocular camera.

A controller <NUM> is installed in the cabin <NUM>. The controller <NUM> serves as a main control part that controls the driving of the shovel. According to this embodiment, the controller <NUM> is composed of a computer including a CPU, a RAM, a ROM, etc. Various functions of the controller <NUM> are implemented by the CPU executing programs stored in the ROM, for example.

<FIG> is a block diagram illustrating an example configuration of the drive system of the shovel of <FIG>, indicating a mechanical power transmission line, a hydraulic oil line, a pilot line, and an electric control line by a double line, a thick solid line, a dashed line, and a dotted line, respectively.

The drive system of the shovel mainly includes the engine <NUM>, a regulator <NUM>, a main pump <NUM>, a pilot pump <NUM>, a control valve <NUM>, an operating apparatus <NUM>, a discharge pressure sensor <NUM>, an operating pressure sensor <NUM>, the controller <NUM>, and a proportional valve <NUM>.

The engine <NUM> is a drive source of the shovel. According to this embodiment, the engine <NUM> is, for example, a diesel engine that so operates as to maintain a predetermined rotational speed. The output shaft of the engine <NUM> is coupled to the input shafts of the main pump <NUM> and the pilot pump <NUM>.

The main pump <NUM> supplies hydraulic oil to the control valve <NUM> via a hydraulic oil line. According to this embodiment, the main pump <NUM> is a swash plate variable displacement hydraulic pump.

The regulator <NUM> controls the discharge quantity of the main pump <NUM>. According to this embodiment, the regulator <NUM> controls the discharge quantity of the main pump <NUM> by adjusting the tilt angle of the swash plate of the main pump <NUM> in response to a control command from the controller <NUM>.

The pilot pump <NUM> supplies hydraulic oil to various hydraulic control apparatuses including the operating apparatus <NUM> and the proportional valve <NUM> via a pilot line. According to this embodiment, the pilot pump <NUM> is a fixed displacement hydraulic pump.

The control valve <NUM> is a hydraulic controller that controls the hydraulic system of the shovel. The control valve <NUM> includes control valves <NUM> through <NUM> and a bleed valve <NUM>. The control valve <NUM> can selectively supply hydraulic oil discharged by the main pump <NUM> to one or more hydraulic actuators through the control valves <NUM> through <NUM>. The control valves <NUM> through <NUM> control the flow rate of hydraulic oil flowing from the main pump <NUM> to hydraulic actuators and the flow rate of hydraulic oil flowing from hydraulic actuators to a hydraulic oil tank. The hydraulic actuators include the boom cylinder <NUM>, the arm cylinder <NUM>, the bucket cylinder <NUM>, a left side traveling hydraulic motor 1A, a right side traveling hydraulic motor 1B, and a turning hydraulic motor 2A. The bleed valve <NUM> controls the flow rate of a portion of the hydraulic oil discharged by the main pump <NUM> which flows to the hydraulic oil tank through no hydraulic actuators (hereinafter, "bleed flow rate"). The bleed valve <NUM> may be installed outside the control valve <NUM>.

The operating apparatus <NUM> is an apparatus that an operator uses to operate hydraulic actuators. According to this embodiment, the operating apparatus <NUM> supplies hydraulic oil discharged by the pilot pump <NUM> to the pilot ports of control valves corresponding to hydraulic actuators through a pilot line. The pressure of hydraulic oil supplied to each pilot port (pilot pressure) is a pressure commensurate with the direction of operation and the amount of operation of a lever or pedal (not depicted) of the operating apparatus <NUM> for a corresponding hydraulic actuator.

The discharge pressure sensor <NUM> detects the discharge pressure of the main pump <NUM>. According to this embodiment, the discharge pressure sensor <NUM> outputs the detected value to the controller <NUM>.

The operating pressure sensor <NUM> detects the details of the operator's operation using the operating apparatus <NUM>. According to this embodiment, the operating pressure sensor <NUM> detects the direction of operation and the amount of operation of a lever or pedal of the operating apparatus <NUM> for a corresponding hydraulic actuator in the form of pressure, and outputs the detected value to the controller <NUM>. The details of the operation of the operating apparatus <NUM> may be detected using a sensor other than an operating pressure sensor.

The proportional valve <NUM> operates in response to a control command output by the controller <NUM>. According to this embodiment, the proportional valve <NUM> is a solenoid valve that adjusts a secondary pressure introduced from the pilot pump <NUM> to the pilot port of the bleed valve <NUM> in the control valve <NUM>, in response to an electric current command output by the controller <NUM>. For example, the proportional valve <NUM> operates such that the secondary pressure introduced to the pilot port of the bleed valve <NUM> increases as the electric current command increases.

Next, an example configuration of a hydraulic circuit installed in the shovel is described with reference to <FIG> is a schematic diagram illustrating an example configuration of a hydraulic circuit installed in the shovel of <FIG>. Like <FIG>, <FIG> indicates a mechanical power transmission line, a hydraulic oil line, a pilot line, and an electric control line by a double line, a thick solid line, a dashed line, and a dotted line, respectively.

The hydraulic circuit of <FIG> circulates hydraulic oil from main pumps <NUM> and 14R driven by the engine <NUM> to the hydraulic oil tank via conduits <NUM> and 42R. The main pumps <NUM> and 14R correspond to the main pump <NUM> of <FIG>.

The conduit <NUM> is a hydraulic oil line that connects the control valves <NUM> and <NUM> and control valves <NUM> and <NUM> placed in the control valve <NUM> in parallel between the main pump <NUM> and the hydraulic oil tank. The conduit 42R is a hydraulic oil line that connects the control valves <NUM> and <NUM> and control valves 175R and 176R placed in the control valve <NUM> in parallel between the main pump 14R and the hydraulic oil tank.

The control valve <NUM> is a spool valve that switches the flow of hydraulic oil in order to supply hydraulic oil discharged by the main pump <NUM> to the left side traveling hydraulic motor 1A and to discharge hydraulic oil discharged by the left side traveling hydraulic motor 1A to the hydraulic oil tank.

The control valve <NUM> is a spool valve that switches the flow of hydraulic oil in order to supply hydraulic oil discharged by the main pump 14R to the right side traveling hydraulic motor 1B and to discharge hydraulic oil discharged by the right side traveling hydraulic motor 1B to the hydraulic oil tank.

The control valve <NUM> is a spool valve that switches the flow of hydraulic oil in order to supply hydraulic oil discharged by the main pump <NUM> to the turning hydraulic motor 2A and to discharge hydraulic oil discharged by the turning hydraulic motor 2A to the hydraulic oil tank.

The control valve <NUM> is a spool valve for supplying hydraulic oil discharged by the main pump 14R to the bucket cylinder <NUM> and to discharge hydraulic oil in the bucket cylinder <NUM> to the hydraulic oil tank.

The control valves <NUM> and 175R are spool valves that switch the flow of hydraulic oil in order to supply hydraulic oil discharged by the main pumps <NUM> and 14R to the boom cylinder <NUM> and to discharge hydraulic oil in the boom cylinder <NUM> to the hydraulic oil tank.

The control valves <NUM> and 176R are spool valves that switch the flow of hydraulic oil in order to supply hydraulic oil discharged by the main pumps <NUM> and 14R to the arm cylinder <NUM> and to discharge hydraulic oil in the arm cylinder <NUM> to the hydraulic oil tank.

A bleed valve <NUM> is a spool valve that controls the bleed flow rate with respect to hydraulic oil discharged by the main pump <NUM>. A bleed valve 177R is a spool valve that controls the bleed flow rate with respect to hydraulic oil discharged by the main pump 14R. The bleed valves <NUM> and 177R correspond to the bleed valve <NUM> of <FIG>.

The bleed valves <NUM> and 177R have a first valve position of a minimum opening area (an opening degree of <NUM>%) and a second valve position of a maximum opening area (an opening degree of <NUM>%). The bleed valves <NUM> and 177R can steplessly move between the first valve position and the second valve position.

Regulators <NUM> and 13R control the discharge quantity of the main pumps <NUM> and 14R by adjusting the swash plate tilt angle of the main pumps <NUM> and 14R. The regulators <NUM> and 13R correspond to the regulator <NUM> of <FIG>. For example, the controller <NUM> reduces the discharge quantity by adjusting the swash plate tilt angle of the main pumps <NUM> and 14R with the regulators <NUM> and 13R in response to an increase in the discharge pressure of the main pumps <NUM> and 14R. This is for preventing the absorbed power of the main pump <NUM> expressed by the product of the discharge pressure and the discharge quantity from exceeding the output power of the engine <NUM>.

An arm operating lever 26A, which is an example of the operating apparatus <NUM>, is used to operate the arm <NUM>. The arm operating lever 26A uses hydraulic oil discharged by the pilot pump <NUM> to introduce a control pressure commensurate with the amount of lever operation to pilot ports of the control valves <NUM> and 176R. Specifically, when operated in an arm closing direction, the arm operating lever 26A introduces hydraulic oil to the right side pilot port of the control valve <NUM> and introduces hydraulic oil to the left side pilot port of the control valve 176R. Furthermore, when operated in an arm opening direction, the arm operating lever 26A introduces hydraulic oil to the left side pilot port of the control valve <NUM> and introduces hydraulic oil to the right side pilot port of the control valve 176R.

A boom operating lever 26B, which is an example of the operating apparatus <NUM>, is used to operate the boom <NUM>. The boom operating lever 26B uses hydraulic oil discharged by the pilot pump <NUM> to introduce a control pressure commensurate with the amount of lever operation to pilot ports of the control valve <NUM> and 175R. Specifically, when operated in a boom raising direction, the boom operating lever 26B introduces hydraulic oil to the right side pilot port of the control valve <NUM> and introduces hydraulic oil to the left side pilot port of the control valve 175R. Furthermore, when operated in a boom lowering direction, the boom operating lever 26B introduces hydraulic oil to the left side pilot port of the control valve <NUM> and introduces hydraulic oil to the right side pilot port of the control valve 175R.

Discharge pressure sensors <NUM> and 28R, which are examples of the discharge pressure sensor <NUM>, detect the discharge pressure of the main pumps <NUM> and 14R, and output the detected value to the controller <NUM>.

Operating pressure sensors 29A and 29B, which are examples of the operating pressure sensor <NUM>, detect the details of the operator's operation on the arm operating lever 26A and the boom operating lever 26B in the form of pressure, and output the detected value to the controller <NUM>. Examples of the details of operation include the direction of lever operation and the amount of lever operation (the angle of lever operation).

Right and left traveling levers (or pedals), a bucket operating lever, and a turning operating lever (none of which is depicted) are operating apparatuses for performing operations for causing the lower traveling body <NUM> to travel, opening and closing the bucket <NUM>, and turning the upper turning body <NUM>, respectively. Like the arm operating lever 26A and the boom operating lever 26B, these operating apparatuses each introduce a control pressure commensurate with the amount of lever operation (or the amount of pedal operation) to the right or left pilot port of a control valve for a corresponding hydraulic actuator, using hydraulic oil discharged by the pilot pump <NUM>. The details of the operator's operation on each of these operating apparatuses are detected in the form of pressure by a corresponding operating pressure sensor like the operating pressure sensors 29A and 29B, and the detected value is output to the controller <NUM>.

The controller <NUM> receives the outputs of the operating pressure sensors 29A and 29B, etc., and outputs a control command to the regulators <NUM> and 13R to change the discharge quantity of the main pump <NUM> and 14R on an as-needed basis. Furthermore, the controller <NUM> outputs an electric current command to proportional valves 31L1, 31L2, 31R1, and 31R2 to change the opening area of the bleed valves <NUM> and 177R and negative control throttles <NUM> and 18R (hereinafter, "NEG control throttles <NUM> and 18R") on an as-needed basis.

The proportional valves 31L1 and 31R1 adjust a secondary pressure introduced from the pilot pump <NUM> to the pilot ports of the bleed valves <NUM> and 177R in accordance with an electric current command output by the controller <NUM>. The proportional valves 31L2 and 31R2 adjust a secondary pressure introduced from the pilot pump <NUM> to the NEG control throttles <NUM> and 18R in accordance with an electric current command output by the controller <NUM>. The proportional valves 31L1, 31L2, 31R1, and 31R2 correspond to the proportional valve <NUM> of <FIG>.

The proportional valve 31L1 can adjust the secondary pressure so that the bleed valve <NUM> can stop at any position between the first valve position and the second valve position. The proportional valve 31R1 can adjust the secondary pressure so that the bleed valve 177R can stop at any position between the first valve position and the second valve position.

The proportional valve 31L2 can adjust the secondary pressure so that the opening area of the NEG control throttle <NUM> can be adjusted. The proportional valve 31R2 can adjust the secondary pressure so that the opening area of the NEG control throttle 18R can be adjusted.

Here, negative control (hereinafter referred to as "NEG control") adopted in the hydraulic circuit of <FIG> is described.

In the conduits <NUM> and 42R, the NEG control throttles <NUM> and 18R are placed between the most downstream bleed valves <NUM> and 177R and the hydraulic oil tank. The flow of hydraulic oil to the hydraulic oil tank through the bleed valves <NUM> and 177R is restricted by the NEG control throttles <NUM> and 18R. The NEG control throttles <NUM> and 18R generate a control pressure for controlling the regulators <NUM> and 13R (hereinafter referred to as "NEG control pressure"). NEG control pressure sensors <NUM> and 19R are sensors for detecting the NEG control pressure, and output the detected value to the controller <NUM>.

According to this embodiment, the NEG control throttles <NUM> and 18R are variable throttles whose opening area varies in accordance with the secondary pressure of the proportional valves 31L2 and 31R2. For example, the opening area of the NEG control throttles <NUM> and 18R decreases as the secondary pressure of the proportional valves 31L2 and 31R2 increases. Alternatively, the NEG control throttles <NUM> and 18R may be fixed throttles.

The controller <NUM> controls the discharge quantity of the main pumps <NUM> and 14R by adjusting the swash plate tilt angle of the main pumps <NUM> and 14R in accordance with the NEG control pressure. Hereinafter, the relationship between the NEG control pressure and the discharge quantity of the main pumps <NUM> and 14R is referred to as "NEG control characteristic. " For example, the NEG control characteristic may be stored in the ROM or the like as a reference table or may be expressed by a predetermined calculation formula. For example, the controller <NUM> refers to a table representing a predetermined NEG control characteristic, and decreases the discharge quantity of the main pumps <NUM> and 14R as the NEG control pressure increases and increases the discharge quantity of the main pumps <NUM> and 14R as the NEG control pressure decreases.

Specifically, as illustrated in <FIG>, in a standby state where none of the hydraulic actuators in the shovel is in operation, hydraulic oil discharged by the main pumps <NUM> and 14R passes through the bleed valves <NUM> and 177R to reach the NEG control throttles <NUM> and 18R. The flow of hydraulic oil passing through the bleed valves <NUM> and 177R increases the NEG control pressure generated upstream of the negative control throttles <NUM> and 18R. As a result, the controller <NUM> decreases the discharge quantity of the main pumps <NUM> and 14R to a predetermined minimum allowable discharge quantity to control pressure loss (pumping loss) during passage of the discharged hydraulic oil through the conduits <NUM> and 42R. This predetermined minimum allowable discharge quantity is an example of the bleed flow rate, and is hereinafter referred to as "standby flow rate.

When any of the hydraulic actuators is operated, hydraulic oil discharged by the main pumps <NUM> and 14R flows into the operated hydraulic actuator through a control valve corresponding to the operated hydraulic actuator. Therefore, the bleed flow rate reaching the negative control throttles <NUM> and 18R through the bleed valves <NUM> and 177R decreases, so that the NEG control pressure generated upstream of the NEG control throttles <NUM> and 18R is reduced. As a result, the controller <NUM> increases the discharge quantity of the main pumps <NUM> and 14R to supply sufficient hydraulic oil to the operated hydraulic actuator to ensure driving of the operated hydraulic actuator. Hereinafter, the flow rate of hydraulic oil flowing into a hydraulic actuator is referred to as "actuator flow rate. " In this case, the flow rate of hydraulic oil discharged by the main pumps <NUM> and 14R is equivalent to the sum of the actuator flow rate and the bleed flow rate.

According to the configuration as described above, in the case of actuating a hydraulic actuator, the hydraulic circuit of <FIG> can ensure that necessary and sufficient hydraulic oil is supplied from the main pumps <NUM> and 14R to the hydraulic actuator to be actuated. Furthermore, in the standby state, the hydraulic circuit of <FIG> can reduce unnecessary hydraulic energy consumption because the bleed flow rate can be reduced to the standby flow rate.

According to the hydraulic circuit of <FIG>, however, even in the standby state, hydraulic oil of the standby flow rate is constantly supplied to the NEG control throttles <NUM> and 18R. Furthermore, when a hydraulic actuator is being actuated, a certain amount of hydraulic oil is constantly supplied to the NEG control throttles <NUM> and 18R as the bleed flow rate. This is for generating the NEG control pressure and also for making it possible to swiftly change the discharge quantity in accordance with the motion of the hydraulic actuator.

As the bleed flow rate decreases, an effect due to control of unnecessary hydraulic energy consumption increases, but the flow rate of hydraulic oil flowing to a hydraulic actuator is more likely to vary. In this case, when a pressure variation occurs in a vibration system of the hydraulic system, and a flow rate variation is large relative to the pressure variation, a large vibration results. This is because the damping term of a second-order vibration system is expressed by -∂Q/∂P, where P represents the discharge pressure of the main pump <NUM> (the load pressure of a hydraulic actuator) and Q represents the flow rate of hydraulic oil flowing into a hydraulic actuator. Therefore, when the pressure variation increases because of an increase in the load, it is desirable to increase the bleed flow rate to reduce the flow rate variation of hydraulic oil flowing into the hydraulic actuator. Accordingly, it is inappropriate to reduce the bleed flow rate without exception.

Therefore, a bleed valve controlling part <NUM> of the controller <NUM> achieves both control of unnecessary hydraulic energy consumption and control of pressure pulsation by changing the bleed flow rate in accordance with the magnitude of pressure pulsation.

For example, the bleed valve controlling part <NUM> controls the opening area of the bleed valve <NUM> in accordance with the magnitude of pulsation in the pressure of hydraulic oil discharged by the main pump <NUM>. The bleed valve controlling part <NUM> may also control the opening area of the bleed valve <NUM> in accordance with the magnitude of pulsation in the pressure of hydraulic oil in a hydraulic actuator in operation, such as the boom rod pressure, the boom bottom pressure, the arm rod pressure, or the arm bottom pressure. For example, the bleed valve controlling part <NUM> increases the opening area of the bleed valve <NUM> as the pulsation increases. This is for controlling the pulsation by increasing the damping of the pulsation by increasing the bleed flow rate (including the standby flow rate in the standby state). The bleed valve controlling part <NUM> decreases the opening area of the bleed valve <NUM> as the pulsation decreases. This is for controlling the amount of unnecessarily discarded hydraulic oil by decreasing the bleed flow rate (including the standby flow rate in the standby state).

The bleed valve controlling part <NUM> calculates the magnitude of the pulsation based on information on the pulsation obtained by an information obtaining device. The information on the pulsation includes at least one of, not all being part of the claimed invention, the boom angle α, the arm angle β, the bucket angle γ, the boom rod pressure, the boom bottom pressure, the arm rod pressure, the arm bottom pressure, the bucket rod pressure, the bucket bottom pressure, an image captured by the camera S6, the discharge pressure of the main pump <NUM>, the operating pressure of the operating apparatus <NUM>, etc. The information obtaining device includes at least one of, not all being part of the claimed invention, the boom angle sensor S1, the arm angle sensor S2, the bucket angle sensor S3, the body tilt sensor S4, the turning angular velocity sensor S5, the camera S6, the boom rod pressure sensor S7R, the boom bottom pressure sensor S7B, the arm rod pressure sensor S8R, the arm bottom pressure sensor S8B, the bucket rod pressure sensor S9R, the bucket bottom pressure sensor S9B, the discharge pressure sensor <NUM>, the operating pressure sensor <NUM>, etc. The bleed valve controlling part <NUM> may determine the magnitude of the pulsation in multiple levels. In this case, the bleed valve controlling part <NUM> determines the magnitude of the pulsation in three levels of "large," "medium," and "small" based on the output of the discharge pressure sensor <NUM>, for example. Specifically, it is determined that the magnitude of the pulsation is "large" when the fluctuation range of the pump discharge pressure during a predetermined period of time is more than or equal to a first threshold, it is determined that the magnitude of the pulsation is "medium" when the fluctuation range is less than the first threshold and more than or equal to a second threshold, and it is determined that the magnitude of the pulsation is "small" when the fluctuation range is less than the second threshold.

For example, the bleed valve controlling part <NUM> increases or decreases the opening area of the bleed valve <NUM> by outputting a control command commensurate with the magnitude of the pulsation to the proportional valve <NUM>. For example, the bleed valve controlling part <NUM> increases the opening area of the bleed valve <NUM> by reducing the secondary pressure of the proportional valve <NUM> by decreasing an electric current command to the proportional valve <NUM> as the pulsation increases. This is for controlling the pulsation. Conversely, the bleed valve controlling part <NUM> decreases the opening area of the bleed valve <NUM> by increasing the secondary pressure of the proportional valve <NUM> by increasing an electric current command to the proportional valve <NUM> as the pulsation decreases. This is for controlling the amount of unnecessarily discarded hydraulic oil.

Furthermore, the bleed valve controlling part <NUM> changes the NEG control characteristic in accordance with an increase or decrease in the opening area of the bleed valve <NUM>. According to this embodiment, the bleed valve controlling part <NUM> changes the NEG control characteristic by increasing or decreasing the opening area of the NEG control throttles <NUM> and 18R in accordance with an increase or decrease in the opening area of the bleed valve <NUM>. This is for preventing an increase or decrease in the bleed flow rate from changing the relationship between the amount of lever operation and the actuator flow rate.

For example, the bleed valve controlling part <NUM> shifts the NEG control characteristic more toward a high pulsation time NEG control setting as the pulsation becomes larger, and shifts the NEG control characteristic more toward a low pulsation time NEG control setting as the pulsation becomes smaller.

The standby flow rate is higher and a decrease in the discharge quantity relative to an increase in the NEG control pressure is slower according to the high pulsation time NEG control setting than according to the low pulsation time NEG control setting. That is, with the NEG control pressure being the same, the discharge quantity of the main pump <NUM> is larger according to the high pulsation time NEG control setting than according to the low pulsation time NEG control setting. Furthermore, in the case of achieving the same discharge quantity, the NEG control pressure is higher according to the high pulsation time NEG control setting than according to the low pulsation time NEG control setting. The actuator flow rate, however, is the same irrespective of a difference in the NEG control characteristic with the other conditions including the amount of lever operation being equal. For example, with the other conditions including the amount of boom raising operation being equal, the flow rate of hydraulic oil flowing into the bottom-side oil chamber of the boom cylinder <NUM> is the same irrespective of a difference in the bleed flow rate and a difference in the NEG control characteristic.

Thus, the bleed valve controlling part <NUM> calculates the magnitude of the pulsation and outputs a control command commensurate with the magnitude of the pulsation to the proportional valve <NUM>. The proportional valve <NUM> actuates the bleed valve <NUM> to increase or decrease the bleed flow rate. According to this configuration, the controller <NUM> can control the pulsation by increasing the bleed flow rate when the pulsation is large. Furthermore, the controller <NUM> can control the amount of unnecessarily discarded hydraulic coil by decreasing the bleed flow rate when the pulsation is small.

Furthermore, referring to <FIG>, the control valves <NUM>, <NUM>, <NUM>, and <NUM>, which control the flow of hydraulic oil from the main pump <NUM> to hydraulic actuators, are connected in parallel to one another between the main pump <NUM> and the hydraulic oil tank. The control valves <NUM>, <NUM>, <NUM>, and <NUM>, however, may alternatively be connected in series between the main pump <NUM> and the hydraulic oil tank. In this case, whichever valve position the spool of each control valve is switched, the conduit <NUM> can supply hydraulic oil to an adjacent control valve placed on the downstream side without being interrupted by the spool.

Likewise, the control valves <NUM>, <NUM>, 175R, and 176R that control the flow of hydraulic oil from the main pump 14R to hydraulic actuators are connected in parallel to one another between the main pump 14R and the hydraulic oil tank. The control valves <NUM>, <NUM>, 175R, and 176R, however, may alternatively be connected in series between the main pump 14R and the hydraulic oil tank. In this case, whichever valve position the spool of each control valve is switched, the conduit 42R can supply hydraulic oil to an adjacent control valve placed on the downstream side without being interrupted by the spool.

Next, a process of increasing or decreasing the bleed flow rate (hereinafter, "bleed flow rate increasing/decreasing process") by the bleed valve controlling part <NUM> is described with reference to <FIG> and <FIG>. <FIG> illustrates a flowchart of an example of the bleed flow rate increasing/decreasing process. The bleed valve controlling part <NUM> repeatedly executes this process at predetermined control intervals while the shovel is in operation. <FIG> illustrates a temporal transition of the pump discharge pressure and a proportional valve characteristic during execution of the bleed flow rate increasing/decreasing process during the boom raising operation. The proportional valve characteristic means the relationship between the operating pressure of the boom operating lever 26B and the target secondary pressure of the proportional valve <NUM>. For example, like the NEG control characteristic, the proportional valve characteristic may be stored in the ROM or the like as a reference table or may be expressed by a predetermined calculation formula. According to the illustration of <FIG> and <FIG>, the proportional valve characteristic is selected from a high pulsation time proportional valve setting and a low pulsation time proportional valve setting. With the operating pressure of the boom operating lever 26B being the same, the target secondary pressure of the proportional valve <NUM> is lower according to the high pulsation time proportional valve setting than according to the low pulsation time proportional valve setting. That is, with the operating pressure of the boom operating lever 26B being the same, the opening area of the bleed valve <NUM> is larger according to the high pulsation time proportional valve setting than according to the low pulsation time proportional valve setting. Furthermore, with the operating pressure of the boom operating lever 26B being the same, the opening area of the NEG control throttle is larger according to the high pulsation time proportional valve setting than according to the low pulsation time proportional valve setting.

First, the bleed valve controlling part <NUM> determines whether the pressure pulsation of hydraulic oil flowing through the hydraulic circuit is large (step ST1). According to the illustration of <FIG>, the bleed valve controlling part <NUM> determines whether the fluctuation range of the discharge pressure of the main pump <NUM> during a predetermined period of time is greater than a predetermined threshold based on the output of the discharge pressure sensor <NUM>. In response to determining that the fluctuation range is greater than the predetermined threshold, the bleed valve controlling part <NUM> determines that the pressure pulsation of hydraulic oil flowing through the conduit <NUM> is large. The same applies to the pressure pulsation of hydraulic oil flowing through the conduit 42R. The following description, which is about the pressure pulsation of hydraulic oil flowing through the conduit <NUM>, also applies to the pressure pulsation of hydraulic oil flowing through the conduit 42R.

In response to determining that the pressure pulsation is large (YES at step ST1), the bleed valve controlling part <NUM> selects the high pulsation time proportional valve setting as the proportional valve characteristic of the proportional valves 31L1 and 31L2 and selects the high pulsation time NEG control setting as the NEG control characteristic (step ST2). According to the illustration of <FIG>, at each of time t1 and time t3, the bleed valve controlling part <NUM> determines that the pressure pulsation is large, and selects the high pulsation time proportional valve setting as the proportional valve characteristic of the proportional valves 31L1 and 31L2 and selects the high pulsation time NEG control setting as the NEG control characteristic.

In response to determining that the pressure pulsation is not large (NO at step ST1), the bleed valve controlling part <NUM> selects the low pulsation time proportional valve setting as the proportional valve characteristic of the proportional valves 31L1 and 31L2 and selects the low pulsation time NEG control setting as the NEG control characteristic (step ST3). According to the illustration of <FIG>, at time t2, the bleed valve controlling part <NUM> determines that the pressure pulsation is not large, and selects the low pulsation time proportional valve setting as the proportional valve characteristic of the proportional valves 31L1 and 31L2 and selects the low pulsation time NEG control setting as the NEG control characteristic.

Thereafter, the bleed valve controlling part <NUM> determines the target secondary pressure of the proportional valves 31L1 and 31L2 based on the selected proportional valve setting (step ST4). According to the illustration of <FIG>, the bleed valve controlling part <NUM> refers to a table associated with the proportional valve setting, and determines the target secondary pressure according to the operating pressure output by the operating pressure sensor 29B. That is, the target secondary pressure differs depending on the then condition of the shovel including the magnitude of the pulsation, operation details, etc. Furthermore, the opening area of each of the bleed valve <NUM> and the NEG control throttle <NUM> is uniquely determined according to the secondary pressure.

Thereafter, the bleed valve controlling part <NUM> outputs an electric current command commensurate with the target secondary pressure to the proportional valves 31L1 and 31L2 (step ST5). For example, in response to receiving an electric current command commensurate with the target secondary pressure determined with reference to a table associated with the high pulsation time proportional valve setting, the proportional valves 31L1 and 31L2 reduce a secondary pressure acting on the pilot ports of the bleed valve <NUM> and the NEG control throttle <NUM> to the target secondary pressure. Therefore, the opening area of each of the bleed valve <NUM> and the NEG control throttle <NUM> increases to increase the bleed flow rate, so that the responsiveness of the NEG control pressure increases and the damping of the pressure pulsation increases. As a result, it is possible to damp the pulsation of the boom bottom pressure during the boom raising operation. The illustration of <FIG> shows that the high pulsation time proportional valve setting is selected so that the pressure pulsation of hydraulic oil discharged by the main pump <NUM>, namely, hydraulic oil flowing into the bottom-side oil chamber of the boom cylinder <NUM>, is damped during the period between time t1 and time t2 and the period after time t3. At this point, the bleed valve controlling part <NUM> refers to the table of the high pulsation time NEG control setting to determine the target discharge quantity of the main pump <NUM> commensurate with a current NEG control pressure, and outputs a control command commensurate with the target discharge quantity to the regulator <NUM>. The main pump <NUM> is so controlled by the regulator <NUM> as to achieve the target discharge quantity.

Alternatively, for example, in response to receiving an electric current command commensurate with the target secondary pressure determined with reference to a table associated with the low pulsation time proportional valve setting, the proportional valves 31L1 and 31L2 increase a secondary pressure acting on the pilot ports of the bleed valve <NUM> and the NEG control throttle <NUM> to the target secondary pressure. Therefore, the opening area of each of the bleed valve <NUM> and the NEG control throttle <NUM> decreases to decrease the bleed flow rate. As a result, it is possible to control unnecessary hydraulic energy consumption during the boom raising operation. The illustration of <FIG> shows that the low pulsation time proportional valve setting is selected during the period before time t1 and the period between time t2 and time t3. At this point, the bleed valve controlling part <NUM> refers to the table of the low pulsation time NEG control setting to determine the target discharge quantity of the main pump <NUM> commensurate with a current NEG control pressure, and outputs a control command commensurate with the target discharge quantity to the regulator <NUM>. The main pump <NUM> is so controlled by the regulator <NUM> as to achieve the target discharge quantity.

According to this configuration, even with the same operating pressure, the bleed valve controlling part <NUM> can cause the target secondary pressure of the proportional valve <NUM> to differ between when the pressure pulsation is large and when the pressure pulsation is small. That is, the bleed valve controlling part <NUM> can cause the bleed flow rate to differ between when the pressure pulsation is large and when the pressure pulsation is small. Therefore, when the pressure pulsation is large, it is possible to damp the pressure pulsation by increasing the bleed flow rate, and when the pressure pulsation is small, it is possible to control unnecessary hydraulic energy consumption by reducing the bleed flow rate.

According to the example illustrated in <FIG> and <FIG>, the bleed valve controlling part <NUM> determines whether the pressure pulsation is large based on the detected value of the discharge pressure sensors <NUM> and 28R that detect the discharge pressure of the main pump <NUM> and 14R. The bleed valve controlling part <NUM>, however, may alternatively determine whether the pressure pulsation is large based on the detected value of a pressure sensor that detects the pressure of hydraulic oil in the hydraulic circuit, such as the boom rod pressure sensor S7R, the boom bottom pressure sensor S7B, the arm rod pressure sensor S8R, the arm bottom pressure sensor S8B, the bucket rod pressure sensor S9R, or the bucket bottom pressure sensor S9B.

Next, another example of the bleed flow rate increasing/decreasing process is described with reference to <FIG> is a flowchart of another example of the bleed flow rate increasing/decreasing process. The bleed valve controlling part <NUM> repeatedly executes this process at predetermined control intervals while the shovel is in operation.

First, the bleed valve controlling part <NUM> calculates the magnitude of the pressure pulsation of hydraulic oil flowing through the hydraulic circuit as the degree of pulsation (step ST11). According to the illustration of <FIG>, the bleed valve controlling part <NUM> calculates the fluctuation range of the discharge pressure of the main pump <NUM> during a predetermined period of time as the degree of pulsation that represents the magnitude of the pressure pulsation of hydraulic oil flowing through the conduit <NUM>, based on the output of the discharge pressure sensor <NUM>. The same applies to the pressure pulsation of hydraulic oil flowing through the conduit 42R. The following description, which is about the pressure pulsation of hydraulic oil flowing through the conduit <NUM>, also applies to the pressure pulsation of hydraulic oil flowing through the conduit 42R.

Thereafter, the bleed valve controlling part <NUM> determines the target secondary pressure of the proportional valves 31L1 and 31L2 in accordance with the degree of pulsation and the operating pressure (step ST12). According to the illustration of <FIG>, the bleed valve controlling part <NUM> determines the target secondary pressure according to the calculated degree of pulsation and the operating pressure output by the operating pressure sensor 29B.

Thereafter, the bleed valve controlling part <NUM> outputs an electric current command commensurate with the target secondary pressure to the proportional valves 31L1 and 31L2 (step ST13). The proportional valves 31L1 and 31L2 adjust a secondary pressure acting on the pilot ports of the bleed valve <NUM> and the NEG control throttle <NUM> to the target secondary pressure. Therefore, when the opening area of each of the bleed valve <NUM> and the NEG control throttle <NUM> is increased, it is possible to increase the responsiveness of the NEG control pressure and to increase the damping of the pressure pulsation. As a result, it is possible to damp the pulsation of the boom bottom pressure during the boom raising operation. When the opening area of each of the bleed valve <NUM> and the NEG control throttle <NUM> is reduced, it is possible to control unnecessary hydraulic energy consumption.

According to this configuration, the bleed valve controlling part <NUM> can steplessly (seamlessly) determine the target secondary pressure of the proportional valves 31L1 and 31L2 in accordance with the magnitude of the pressure pulsation. Therefore, it is possible to damp the pressure pulsation by increasing the bleed flow rate as the pressure pulsation increases, and it is possible to control unnecessary hydraulic energy consumption by decreasing the bleed flow rate as the pressure pulsation decreases.

As described above, the shovel according to an embodiment of the present invention includes the bleed valve <NUM> that controls the bleed flow rate and the controller <NUM> that controls the opening area of the bleed valve <NUM> in accordance with the magnitude of the pulsation of the pressure of hydraulic oil discharged by the main pump <NUM>. Therefore, when the pulsation is large, it is possible to increase the damping of the pressure pulsation by increasing the bleed flow rate by increasing the opening area of the bleed valve <NUM>. As a result, it is possible to control the pulsation of the pressure of hydraulic oil flowing through the hydraulic circuit. Furthermore, when the pulsation is small, it is possible to control unnecessary hydraulic energy consumption by decreasing the bleed flow rate by decreasing the opening area of the bleed valve <NUM>.

A preferred embodiment of the present invention is described in detail above. The present invention, however, is not limited to the above-described embodiment. Variations, replacements, etc., may be applied to the above-described embodiment without departing from the scope of the present invention, as defined in the appended claims.

For example, according to the above-described embodiment, the NEG control throttles <NUM> and 18R are variable throttles whose opening area changes in accordance with the secondary pressure of the proportional valves 31L1 and 31L2. Furthermore, the NEG control throttles <NUM> and 18R are so configured as to decrease the opening area as the secondary pressure of the proportional valves 31L1 and 31L2 increases, for example. The NEG control throttles <NUM> and 18R, however, may alternatively be fixed throttles as illustrated in <FIG>. In this case, the proportional valves 31L2 and 31R2 may be omitted.

According to the illustration of <FIG>, when the opening area of the bleed valves <NUM> and 177R increases to increase the bleed flow rate reaching the NEG control throttles <NUM> and 18R, the NEG control pressure generated by the NEG control throttles <NUM> and 18R, which are fixed throttles, increases. Therefore, the bleed valve controlling part <NUM> changes the NEG control characteristic by adjusting the movement of the regulators <NUM> and 13R, that is, adjusting the swash plate tilt angle of the main pumps <NUM> and 14R, instead of increasing or decreasing the opening area of the NEG control throttles <NUM> and 18R, in accordance with an increase or decrease in the opening area of the bleed valve <NUM>. This is for preventing an increase or decrease in the bleed flow rate from changing the relationship between the amount of lever operation and the actuator flow rate.

According to this configuration, a shovel including the hydraulic circuit illustrated in <FIG> can achieve the same effects as achieved by a shovel including the hydraulic circuit illustrated in <FIG>.

Furthermore, according to the above-described embodiment, the control valves <NUM>, <NUM>, <NUM>, and <NUM> that control the flow of hydraulic oil from the main pump <NUM> to hydraulic actuators are connected in parallel to one another between the main pump <NUM> and the hydraulic oil tank through the conduit <NUM>. The control valves <NUM>, <NUM>, <NUM>, and <NUM>, however, may alternatively be connected in series between the main pump <NUM> and the hydraulic oil tank. For example, the control valves <NUM>, <NUM>, <NUM>, and <NUM> may be connected in series through a first center bypass conduit. In this case, whichever valve position the spools of the control valves are switched, hydraulic oil flowing through the first center bypass conduit is not interrupted by any spools. Therefore, whichever valve position the spool of each control valve is switched, hydraulic oil flowing through the first center bypass conduit can reach an adjacent control valve placed on the downstream side.

Likewise, the control valves <NUM>, <NUM>, 175R, and 176R may alternatively be connected in series between the main pump 14R and the hydraulic oil tank. For example, the control valves <NUM>, <NUM>, 175R, and 176R may be connected in series through a second center bypass conduit. In this case, whichever valve position the spools of the control valves are switched, hydraulic oil flowing through the second center bypass conduit is not interrupted by any spools. Therefore, whichever valve position the spool of each control valve is switched, hydraulic oil flowing through the second center bypass conduit can reach an adjacent control valve placed on the downstream side.

According to this configuration, a shovel including the above-described hydraulic circuit can achieve the same effects as achieved by shovels including the hydraulic circuits illustrated in <FIG> and <FIG>.

Claim 1:
A shovel comprising:
a lower traveling body (<NUM>);
an upper turning body (<NUM>) turnably mounted on the lower traveling body (<NUM>);
a hydraulic pump (<NUM>, <NUM>, 14R) mounted on the upper turning body (<NUM>);
a hydraulic actuator configured to be driven with hydraulic oil discharged by the hydraulic pump (<NUM>, <NUM>, 14R) ;
a bleed valve (<NUM>, <NUM>, 177R) configured to control a flow rate of a portion of the hydraulic oil discharged by the hydraulic pump (<NUM>, <NUM>, 14R), the portion flowing to a hydraulic oil tank without going through the hydraulic actuator; wherein the shovel comprises:
an information obtaining device configured to obtain information on pulsation that is a repetitive increase and decrease in a pressure of hydraulic oil supplied from the hydraulic pump (<NUM>, <NUM>, 14R) to the hydraulic actuator, the information including an amplitude of the pulsation; and
a control device (<NUM>) configured to control an opening area of the bleed valve (<NUM>, <NUM>, 177R) in accordance with a magnitude of the pulsation calculated based on the information obtained by the information obtaining device.