Patent Application
20180051721
The present invention relates to a hydraulic system including a hydraulic actuator that moves bi-directionally.
Generally speaking, in a hydraulic system that electrically controls a hydraulic actuator that moves bi-directionally, a control valve connected to the hydraulic actuator, the control valve including first and second pilot ports, and a pair of solenoid proportional valves that outputs secondary pressures to the first and the second pilot ports, respectively, are used (see Patent Literature 1, for example).
However, the use the pair of solenoid proportional valves increases the cost of the hydraulic circuit. Moreover, in this case, a controller that controls the solenoid proportional valves needs two current generators. This also increases the cost of the controller. Furthermore, since the number of pins of a connector connecting between the controller and the solenoid proportional valves is large, the connector needs to be large-sized.
In view of the above, an object of the present invention is to provide a hydraulic system capable of electrically controlling a hydraulic actuator that moves bi-directionally by using a single solenoid proportional valve.
In order to solve the above-described problems, a hydraulic system according to the present invention includes: a control valve connected to a hydraulic actuator and including a first pilot port to move the actuator in a first direction and a second pilot port to move the actuator in a second direction; a first line that connects between a pilot pressure source and the first pilot port; a solenoid proportional valve provided on the first line; a second line that branches off from the first line at a position upstream of the solenoid proportional valve and that is connected to the second pilot port; a switching valve that is provided on the second line and that shifts between a closing position, in which the switching valve allows the second pilot port to communicate with a tank, and an opening position, in which the switching valve allows the second pilot port to communicate with the pilot pressure source, the switching valve including a spring to keep the switching valve in the closing position and a pilot port to shift the switching valve from the closing position to the opening position; and a third line that connects between the pilot port of the switching valve and a portion of the first line, the portion being positioned downstream of the solenoid proportional valve.
According to the above configuration, the switching valve is positioned in the closing position when a secondary pressure of the solenoid proportional valve is low, and the switching valve is positioned in the opening position when the secondary pressure of the solenoid proportional valve is high. When the switching valve is positioned in the closing position, the control valve is driven by the secondary pressure of the solenoid proportional valve to a first position, in which the control valve causes the actuator to move in the first direction. When the switching valve is positioned in the opening position, the control valve is driven by the differential pressure between the pressure of the pilot pressure source and the secondary pressure of the solenoid proportional valve to a second position, in which the control valve causes the actuator to move in the second direction. This makes it possible to electrically control the hydraulic actuator, which moves bi-directionally, by using the single solenoid proportional valve. Moreover, since the switching valve acts automatically in accordance with the secondary pressure of the solenoid proportional valve, the controller needs only one current generator for the single control valve. This makes it possible to reduce the cost of the controller. Furthermore, since the number of solenoid proportional valves necessary for the single control valve is one, the number of pins of a connector connecting between the controller and the solenoid proportional valve is small. For this reason, a small-sized connector can be used, and the cost can be reduced also in this respect.
The switching valve may be configured to shift from the closing position to the opening position when a pressure led to the pilot port of the switching valve becomes a predetermined pressure or higher, and the predetermined pressure may be a half of a pressure of the pilot pressure source. According to this configuration, in both the case of moving the actuator in the first direction and the case of moving the actuator in the second direction, the control valve can be driven substantially in the same manner.
The solenoid proportional valve may be a direct proportional valve outputting a secondary pressure that indicates a positive correlation with a command current. According to this configuration, when a failure such as an electrical path being cut off occurs, the pressure of the first pilot port and the pressure of the second pilot port of the control valve can be brought to zero, and thereby the actuator can be assuredly prevented from moving.
The above hydraulic system may further include: an operating device that receives a first operation for moving the actuator in the first direction and a second operation for moving the actuator in the second direction, the operating device outputting a first operation signal corresponding to a magnitude of the first operation and a second operation signal corresponding to a magnitude of the second operation; and a controller that feeds the command current to the solenoid proportional valve. The controller may: increase the command current toward a reference current, at which the secondary pressure outputted from the solenoid proportional valve is the predetermined pressure, when the first operation signal increases; and decrease the command current toward the reference current when the second operation signal increases. According to this configuration, the actuator can be moved in accordance with the magnitude of the first operation and the magnitude of the second operation.
The command current when the first operation signal is maximum may be lower than the reference current, and the command current when the second operation signal is maximum may be higher than the reference current. According to this configuration, unstable action of the switching valve at a pressure close to the predetermined pressure can be avoided.
For example, the operating device may include an operating lever, and each of the first operation signal and the second operation signal may indicate an inclination angle of the operating lever.
The present invention makes it possible to electrically control a hydraulic actuator that moves bi-directionally by using a single solenoid proportional valve.
In the example shown in
The control valve 3 is connected to a main pressure source 11 by a supply line 21, and is connected to a tank 13 by a tank line 22. The control valve 3 is driven between a neutral position in which the control valve 3 blocks all the lines 21 to 24 connected to the control valve 3 and a first position (left-side position in
To be more specific, the control valve 3 includes: a first pilot port 3a to drive the control valve 3 from the neutral position to the first position to move the actuator 15 in the first direction A; and a second pilot port 3b to drive the control valve 3 from the neutral position to the second position to move the actuator 15 in the second direction B.
The first pilot port 3a is connected to a pilot pressure source 12 by a first line 41. The first line 41 is provided with a solenoid proportional valve 5. That is, a secondary pressure outputted from the solenoid proportional valve 5 is led to the first pilot port 3a. The solenoid proportional valve 5 is connected to the tank 13 by a tank line 44.
A controller 7 feeds a command current I to the solenoid proportional valve 5. In the present embodiment, as shown in
Returning to
The switching valve 6 shifts between a closing position in which the switching valve 6 allows the second pilot port 3b to communicate with the tank 13 and an opening position in which the switching valve 6 allows the second pilot port 3b to communicate with the pilot pressure source 12. In the present embodiment, the switching valve 6 is a pilot valve, and includes a spring 62 to keep the switching valve 6 in the closing position and a pilot port 61 to shift the switching valve 6 from the closing position to the opening position. The pilot port 61 is connected by a third line 43 to the first line 41 at a position downstream of the solenoid proportional valve 5.
The switching valve 6 may be a single valve connected to piping. However, as indicated by a two-dot chain line of
The switching valve 6 is configured to shift from the closing position to the opening position when a pressure led to the pilot port 61 of the switching valve 6, i.e., the secondary pressure outputted from the solenoid proportional valve 5, becomes a predetermined pressure α or higher. Accordingly, as shown in
Therefore, as shown in
In the present embodiment, the predetermined pressure α, which causes the switching valve 6 to shift from the closing position to the opening position, is the half of the pressure Pp of the pilot pressure source 12. The term “half” herein means a range that is substantially equal to Pp/2 (a range that covers ±20% from Pp/2). Accordingly, as shown in
Returning to
The operating device 8 is, for example, an electrical joystick that includes an operating lever. In this case, each of the first operation signal Sa and the second operation signal Sb indicates an inclination angle of the operating lever. However, as an alternative example, the operating device 8 may be an operating valve that outputs a first pilot pressure corresponding to the inclination angle of the operating lever when the operating lever is inclined to one side and outputs a second pilot pressure corresponding to the inclination angle of the operating lever when the operating lever is inclined to the other side. In this case, a pair of pressure sensors that measures the first and the second pilot pressures may be provided, and the measured first and second pilot pressures may be inputted to the controller 7. As another alternative example, the operating device 8 need not be limited to one including the operating lever, but may be one including a handle that receives turning operations as the first operation and the second operation.
The controller 7 does not feed the command current I to the solenoid proportional valve 5 when neither the first operation signal Sa nor the second operation signal Sb is outputted from the operating device 8. On the other hand, when the first operation signal Sa is outputted from the operating device 8, the controller 7 feeds the command current I to the solenoid proportional valve 5 in accordance with the first operation signal Sa as shown in
To be more specific, when the first operation signal Sa increases, the controller 7 increases the command current I from the minimum current I1 toward the reference current I0, and when the second operation signal Sb increases, the controller 7 decreases the command current I from the maximum current I2 toward the reference current I0. In this manner, the actuator 15 can be moved in accordance with the magnitude of the first operation and the magnitude of the second operation.
Desirably, a command current I3 when the first operation signal Sa is a maximum signal 51 is lower than the reference current I0, and a command current I4 when the second operation signal Sb is a maximum signal S2 is higher than the reference current I0. The reason for this is that unstable action of the switching valve 6 at a pressure close to the predetermined pressure α, which causes the switching valve 6 to shift from the closing position to the opening position, can be avoided.
As described above, in the hydraulic system 1A according to the present embodiment, the switching valve 6 is positioned in the closing position when the secondary pressure of the solenoid proportional valve 5 is low, and the switching valve 6 is positioned in the opening position when the secondary pressure of the solenoid proportional valve 5 is high. When the switching valve 6 is positioned in the closing position, the control valve 3 is driven by the secondary pressure of the solenoid proportional valve 5 to the first position, and when the switching valve 6 is positioned in the opening position, the control valve 3 is driven by the differential pressure between the pressure Pp of the pilot pressure source 12 and the secondary pressure of the solenoid proportional valve 5 to the second position. This makes it possible to electrically control the hydraulic actuator 15, which moves bi-directionally, by using the single solenoid proportional valve 5. Moreover, since the switching valve 6 acts automatically in accordance with the secondary pressure of the solenoid proportional valve 5, the controller 7 needs only one current generator for the single control valve 3. This makes it possible to reduce the cost of the controller 7. Furthermore, since the number of solenoid proportional valves 5 necessary for the single control valve 3 is one, the number of pins of a connector connecting between the controller 7 and the solenoid proportional valve 5 is small. For this reason, a small-sized connector can be used, and the cost can be reduced also in this respect.
In the present embodiment, the solenoid proportional valve 5 is a direct proportional valve, and the switching valve 6 is normally kept in the closing position. Therefore, when a failure such as an electrical path being cut off occurs, the pressure Pa of the first pilot port 3a and the pressure Pb of the second pilot port 3b of the control valve 3 can be brought to zero, and thereby the actuator 15 can be assuredly prevented from moving.
Next, a hydraulic system 1B according to Embodiment 2 of the present invention is described with reference to
In the present embodiment, the switching valve 6 is provided with an assist passage 63 for assisting in keeping the switching valve 6 in the opening position when the switching valve 6 shifts from the closing position to the opening position. It should be noted that, desirably, a pushing force applied through the assist passage 63 is sufficiently less than the urging force of the spring 62, which serves to return the switching valve 6 from the opening position to the closing position.
The above configuration makes it possible to obtain an advantageous effect that the switching valve 6 shifted to the opening position can be stably kept in the opening position in addition to the advantageous effects obtained in Embodiment 1.
Next, a hydraulic system 1C according to Embodiment 3 of the present invention is described with reference to
Also in the present embodiment, the same advantageous effects as those obtained in Embodiment 1 can be obtained except when a failure occurs. When a failure occurs, both the pressure Pa of the first pilot port 3a and the pressure Pb of the second pilot port 3b of the control valve 3 are brought to the pressure Pp of the pilot pressure source 12, and thereby the actuator 15 is prevented from moving.
The present invention is not limited to the above-described Embodiments 1 to 3. Various modifications can be made without departing from the spirit of the present invention.
For example, in Embodiment 3, similar to Embodiment 2, the switching valve 6 may be provided with the assist passage 63 for assisting in keeping the switching valve 6 in the opening position when the switching valve 6 shifts from the closing position to the opening position. It should be noted that, desirably, a pushing force applied through the assist passage 63 is sufficiently less than the urging force of the spring 62, which serves to return the switching valve 6 from the opening position to the closing position.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-050466 | Mar 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/001229 | 3/7/2016 | WO | 00 |
