JP2016011633A - Hydraulic drive system with fail-safe - Google Patents

Abstract

A fail-safe hydraulic drive system having a simple configuration is provided. A fail-safe hydraulic drive system (1) electrically controls a discharge flow rate from a hydraulic pump (2) using an electromagnetic proportional valve (4). A regulator 3 that adjusts the tilt angle of the hydraulic pump 2 includes a servo cylinder 31 , a spool 32 , a horsepower control piston 36 and a flow rate control piston 35 . A primary pressure is led to the proportional solenoid valve 4 through a primary pressure line 41 , and a secondary pressure is led from the proportional solenoid valve 4 to the pressure receiving chamber 37 for the flow control piston 35 . The proportional solenoid valve 4 reduces the secondary pressure as the command current increases. A branch line 5 supplies primary pressure to a pressure receiving chamber 39 for a horsepower control piston 36 , and the branch line 5 is blocked or communicated with the pressure receiving chamber 39 by a switching valve 6 . The switching valve 6 has a pilot port for moving from the blocking position to the communicating position, and the secondary pressure from the electromagnetic proportional valve 4 is introduced to this pilot port. [Selection drawing] Fig. 1

Description

  The present invention relates to a hydraulic drive system that electrically controls the flow rate of hydraulic oil discharged from a hydraulic pump, and relates to a fail-safe hydraulic drive system that can function safely in the event of a failure such as a breakage of an electrical system.

  2. Description of the Related Art Conventionally, a hydraulic drive system that electrically controls the flow rate of hydraulic oil discharged from a hydraulic pump using an electromagnetic proportional valve is known. As shown in FIG. 4A, the hydraulic drive system is generally a positive type in which the command current to the electromagnetic proportional valve and the discharge flow rate have a positive correlation. In such a hydraulic drive system, measures are taken when the electromagnetic proportional valve stops operating during a failure. For example, Patent Document 1 discloses a hydraulic drive system 100 with fail-safe as shown in FIG.

  Specifically, the hydraulic drive system 100 includes a variable displacement hydraulic pump 110, a regulator 120 that adjusts the tilt angle of the hydraulic pump 110, an electromagnetic proportional valve 130, and a switching valve 140. The regulator 120 includes a servo cylinder 121 coupled to the swash plate of the hydraulic pump 110, a spool 122 that drives the servo cylinder 121, a horsepower control piston 124 that operates the spool 122, and a flow rate control piston 123. Further, the regulator 120 includes two pressure receiving chambers 126 and 127 for the horsepower control piston 124 and a pressure receiving chamber 125 for the flow rate control piston 123.

  The discharge pressure Pd of the hydraulic pump 110 is guided to one pressure receiving chamber 126 for the horsepower control piston 124, and the horsepower control piston 124 moves the spool 122 in the flow rate reduction direction when the discharge pressure Pd increases. The other pressure receiving chamber 127 communicates with the tank in normal times.

  A flow rate control pressure is guided to the pressure receiving chamber 125 for the flow rate control piston 123, and the flow rate control piston 123 moves the spool 122 in the direction of increasing the flow rate when the flow rate control pressure increases. The electromagnetic proportional valve 130 receives the primary pressure Psv and outputs a secondary pressure as the flow control pressure. The horsepower control piston 124 and the flow rate control piston 123 are configured to move the spool 122 with priority given to control of the discharge flow rate to be small.

  At normal times, a relatively large secondary pressure is output from the electromagnetic proportional valve 130, so that the switching valve 140 is maintained at the left side in FIG. 3, and the secondary pressure from the electromagnetic proportional valve 130 is used for the flow control piston 123. The pressure receiving chamber 125 is guided. On the other hand, at the time of a failure, the secondary pressure from the electromagnetic proportional valve 130 becomes substantially zero, so that the switching valve 140 is switched to the state on the right side in FIG. As a result, the pilot pressure Pp is guided to the pressure receiving chamber 125 for the flow control piston 123 and the primary pressure Psv is guided to the pressure receiving chamber 127 for the horsepower control piston 124. When the primary pressure Psv is guided to the pressure receiving chamber 127, the horsepower control characteristic is shifted from the line A to the line B as shown in FIG. 4B, and the upper limit of the discharge flow rate Q at each discharge pressure Pd is kept low.

JP 2005-146969 A

  However, in the hydraulic drive system with failsafe 100 shown in FIG. 3, it is necessary to use a 6-port valve as the switching valve 140. Therefore, there is a demand for a fail-safe hydraulic drive system that operates with a simpler structure and is more difficult to stick and operates reliably.

  Further, since the switching valve 140 is switched at a low pressure at the time of failure, there is a problem that it is easy to stick due to contamination or the like. Therefore, a fail-safe hydraulic drive system that is difficult to stick is desired.

  Therefore, an object of the present invention is to provide a fail-safe hydraulic drive system that has a simple configuration and is less likely to cause malfunction due to a stick.

  In order to solve the above-mentioned problem, the inventors of the present invention are so-called normally closed proportional valves that increase the secondary pressure as the command current increases. The inventors have come up with the idea that the configuration can be simplified by using a so-called normally open proportional valve that lowers the secondary pressure as the command current increases. The present invention has been made from such a viewpoint.

  That is, the fail-safe hydraulic drive system of the present invention includes a hydraulic pump that discharges hydraulic oil at a flow rate corresponding to a tilt angle, a servo cylinder that changes the tilt angle of the hydraulic pump, and a small tilt angle. A spool that moves in a flow rate decreasing direction that drives the servo cylinder and a flow rate increasing direction that drives the servo cylinder so that the tilt angle increases, and the spool when the discharge pressure of the hydraulic pump increases A horsepower control piston that moves the spool in the flow rate reduction direction, a flow rate control piston that moves the spool in the flow rate increase direction when the flow control pressure increases, and an electromagnetic proportional valve that outputs a secondary pressure as the flow control pressure An electromagnetic proportional valve that decreases the secondary pressure as the command current increases, and a pressure receiving pressure for the flow rate control piston from the electromagnetic proportional valve A secondary pressure line that directly leads the secondary pressure to the primary pressure line, a primary pressure line that leads the primary pressure to the electromagnetic proportional valve, and a branch from the primary pressure line that leads the primary pressure to the pressure receiving chamber for the horsepower control piston. A switching valve capable of switching between a branch line, a shut-off position that blocks the branch line from the pressure receiving chamber for the horsepower control piston, and a communication position that communicates the branch line with the pressure receiving chamber for the horsepower control piston; A switching valve having a pilot port for moving the switching valve from the blocking position to the communication position against a biasing force of the spring, and a spring for maintaining the switching valve in the blocking position; And a pilot line connecting the secondary pressure line and the pilot port of the switching valve.

  According to the above configuration, since the secondary pressure that is somewhat small is normally output from the electromagnetic proportional valve, the switching valve is maintained at the shut-off position by the biasing force of the switching valve spring. Thereby, the primary pressure is not led to the pressure receiving chamber for the horsepower control piston. Since the secondary pressure from the electromagnetic proportional valve is guided to the pressure receiving chamber for the flow control piston, it is possible to perform electrical flow control according to the command current to the electromagnetic proportional valve. On the other hand, at the time of failure, since the secondary pressure output from the electromagnetic proportional valve becomes substantially equal to the primary pressure, the switching valve is switched to the communication position. As a result, the primary pressure is guided to the pressure receiving chamber for the horsepower control piston. A secondary pressure almost equal to the primary pressure is also introduced to the pressure-receiving chamber for the flow control piston, but the primary pressure and the discharge pressure are applied to the horsepower control piston, and the horsepower control piston has a tilt angle that is greater than that of the flow control piston. Only the horsepower control is performed. Thus, the hydraulic actuator can be driven with a certain amount of horsepower even during a failure. Furthermore, since a valve with a small number of ports can be used as the switching valve, a simple configuration can be realized. In addition, since the solenoid valve is switched from the shut-off position to the communication position with a high pressure at the time of failure, malfunction due to the stick is unlikely to occur.

  For example, in the above-described fail-safe hydraulic drive system, when a pilot-type operation valve for operating a hydraulic actuator is operated, the higher the pilot pressure output from the operation valve, the smaller the command current becomes. A control device for feeding to the proportional valve may be further provided.

  According to the present invention, it is possible to provide a fail-safe hydraulic drive system that operates reliably with a simple configuration.

1 is a hydraulic circuit diagram of a fail-safe hydraulic drive system according to an embodiment of the present invention. (A) is a graph showing the relationship between the pilot pressure Pp output from the operation valve and the command current I to the electromagnetic proportional valve in the hydraulic drive system shown in FIG. 1, and (b) is a graph showing the relationship between the command current I and the electromagnetic proportional valve. A graph showing the relationship between the secondary pressure P2, (c) a graph showing the relationship between the secondary pressure P2 and the discharge flow rate Q, and (d) a graph showing the relationship (input / output characteristics) between the command current I and the discharge flow rate Q. is there. It is a hydraulic-circuit figure of the conventional hydraulic drive system with a fail safe. (A) is a graph which shows the input-output characteristic of a general conventional hydraulic drive system, (b) is a graph which shows the horsepower characteristic of the hydraulic drive system shown in FIG.

  FIG. 1 shows a hydraulic drive system 1 with a fail safe according to an embodiment of the present invention. The hydraulic drive system 1 is mounted on a construction machine such as a hydraulic excavator or a hydraulic crane, and supplies hydraulic oil to various hydraulic actuators (not shown).

  Specifically, the hydraulic drive system 1 includes a variable displacement hydraulic pump 2, a regulator 3 that adjusts the tilt angle of the hydraulic pump 2, an electromagnetic proportional valve 4, and a switching valve 6. The hydraulic drive system 1 also includes a control device 7 that supplies a command current I to the electromagnetic proportional valve 4.

  The hydraulic pump 2 discharges hydraulic oil at a flow rate corresponding to the tilt angle. In this embodiment, a swash plate pump whose tilt angle is defined by the angle of the swash plate 21 is employed as the hydraulic pump 2. However, the hydraulic pump 2 may be an oblique pump whose tilt angle is defined by the angle of the oblique axis.

  The regulator 3 includes a servo cylinder 31 that changes the tilt angle of the hydraulic pump 2, a spool 32 that adjusts a control pressure for driving the servo cylinder 31, and a sleeve 33 that houses the spool 32. The servo cylinder 31 is connected to the swash plate 21 of the hydraulic pump 2. The spool 32 and the sleeve 33 constitute a pressure adjusting valve 34 for the servo cylinder 31.

  More specifically, the spool 32 drives the servo cylinder 31 so that the tilt angle of the hydraulic pump 2 decreases when the spool 32 moves in the flow rate reduction direction (rightward in FIG. 1) (when switched to the left position). At the same time, the servo cylinder 31 is driven so that the tilt angle of the hydraulic pump 2 is increased when it moves in the flow rate increasing direction (leftward in FIG. 1) (when switched to the right position). The sleeve 33 is connected to the servo cylinder 31 by the first lever 3a. The pump discharge pressure Pd acts on the small diameter side of the servo cylinder 31, and the pressure adjustment valve 34 adjusts the large diameter side of the servo cylinder 31. Pressed control pressure acts. The control pressure output from the pressure adjustment valve 34 is adjusted so that the force (pressure × servo cylinder pressure receiving area) acting from both sides of the servo cylinder 31 is balanced. In this way, the pressure adjustment valve 34 operates so that the relative position (metering characteristic) between the spool 32 and the sleeve 33 is constant. In this way, the sleeve 33 moves following the movement of the spool 32.

  The regulator 3 includes a flow rate control piston 35 and a horsepower control piston 36 that operate the spool 32. The flow rate control piston 35 and the horsepower control piston 36 are connected to the spool 32 via the second lever 3b and the third lever 3c, respectively. Further, the regulator 3 includes two pressure receiving chambers 38 and 39 for the horsepower control piston 36 and a pressure receiving chamber 37 for the flow rate control piston 35.

  The discharge pressure Pd of the hydraulic pump 2 is guided to one pressure receiving chamber 38 for the horsepower control piston 36. The horsepower control piston 36 moves the spool 32 in the flow rate decreasing direction when the discharge pressure Pd increases, and moves the spool 32 in the flow rate increasing direction when the discharge pressure Pd decreases. The other pressure receiving chamber 39 is connected to the switching valve 6 by a downstream line 52.

  A flow control pressure is guided to the pressure receiving chamber 37 for the flow control piston 35. The flow rate control piston 35 moves the spool 32 in the flow rate increasing direction when the flow rate control pressure increases, and moves the spool 32 in the flow rate decreasing direction when the flow rate control pressure decreases. The horsepower control piston 36 and the flow rate control piston 35 are configured to move the spool 32 with priority given to the one that restricts the discharge flow rate Q (that is, the direction that commands a small flow rate).

  The pressure receiving chamber 37 for the flow rate control piston 35 is connected to the electromagnetic proportional valve 4 by a secondary pressure line 42, and the electromagnetic proportional valve 4 is connected to the auxiliary pump 25 by a primary pressure line 41. That is, the primary pressure P <b> 1 from the auxiliary pump 25 is guided to the electromagnetic proportional valve 4 by the primary pressure line 41.

  The electromagnetic proportional valve 4 outputs a secondary pressure P2 as the flow rate control pressure. The secondary pressure P2 is directly and constantly guided from the electromagnetic proportional valve 4 to the pressure receiving chamber 37 by the secondary pressure line 42. As shown in FIG. 2B, the electromagnetic proportional valve 4 decreases the secondary pressure P2 as the command current I increases. When the secondary pressure P2 decreases, the flow control piston 35 moves the spool 32 in the flow rate reduction direction. For this reason, the relationship between the secondary pressure P2 and the discharge flow rate Q is as shown in FIG. 2C, and the relationship between the command current I and the discharge flow rate Q is as shown in FIG.

  As shown in FIG. 2D, the hydraulic drive system 1 is a negative type in which the command current I to the electromagnetic proportional valve 4 and the discharge flow rate Q have a negative correlation. For this reason, when the pilot type operation valve for operating the hydraulic actuator (not shown) is operated, the control device 7 generates the pilot pressure Pp output from the operation valve as shown in FIG. The higher the value, the smaller the command current I is sent to the electromagnetic proportional valve 4.

  Returning to FIG. 1, the primary pressure line 41 is connected to the switching valve 6 by the upstream line 51. That is, the upstream line 51 and the downstream line 52 described above constitute the branch line 5 that branches from the primary pressure line 41 and guides the primary pressure P1 to the pressure receiving chamber 39 for the horsepower control piston 36.

  The switching valve 6 is switched between a blocking position where the branch line 5 is blocked from the pressure receiving chamber 39 for the horsepower control piston 36 and a communication position where the branch line 5 is communicated with the pressure receiving chamber 39 for the horsepower control piston 36. In the present embodiment, the tank line 55 is also connected to the switching valve 6, and the downstream line 52 is communicated with the tank line 55 when the switching valve 6 is located at the shut-off position.

  More specifically, the switching valve 6 includes a spring 62 for maintaining the switching valve 6 in the cutoff position, and a pilot for moving the switching valve 6 from the cutoff position to the communication position against the urging force of the spring 62. A port 61 is provided. The pilot port 61 is connected to the secondary pressure line 42 by a pilot line 43. That is, the secondary pressure P <b> 2 from the electromagnetic proportional valve 4 is guided to the pilot port 61.

  As shown in FIG. 2B, the spring 62 determines a threshold value for determining a failure time (switching the switching valve 6) based on the secondary pressure P <b> 2 from the electromagnetic proportional valve 4. For example, as shown in FIG. 2C, the secondary pressure P2 includes a low pressure side dead zone and a high pressure side dead zone that do not affect the discharge flow rate Q. The threshold is preferably equal to or greater than the minimum value of the high-pressure side dead zone and less than the maximum value of the secondary pressure P2. Needless to say, the maximum value of the secondary pressure P2 is substantially equal to the primary pressure P1. As the threshold value for switching the switching valve 6, a high pressure value close to the primary pressure P1 is used, so that the urging force of the spring 62 can be set sufficiently large. For this reason, at the time of failure, it is possible to reliably prevent the switching valve 62 from sticking and causing a malfunction due to contamination or the like.

  Next, the operation of the hydraulic drive system 1 will be described.

  Since the secondary pressure P <b> 2 that is somewhat small is output from the electromagnetic proportional valve 4 in normal times, the switching valve 6 is maintained in the cutoff position by the urging force of the spring 62. As a result, the primary pressure is not guided to the pressure receiving chamber 39 for the horsepower control piston 36, and the pressure in the pressure receiving chamber 39 becomes substantially zero. Accordingly, only the discharge pressure Pd guided to the pressure receiving chamber 38 acts on the horsepower control piston 36, and the horsepower control based on only the discharge pressure Pd is performed. Since the horsepower control by the horsepower control piston 36 is set to a very high horsepower, for example, a horsepower larger than the engine horsepower, as in the line A in FIG. 4B, the discharge flow rate Q is not normally limited. . That is, at the normal time, the discharge flow rate Q is controlled only by the flow control piston 35. Since the secondary pressure P2 from the electromagnetic proportional valve 4 is guided to the pressure receiving chamber 37 for the flow control piston 35, an electric flow control according to the command current I to the electromagnetic proportional valve 4 can be performed. .

  On the other hand, at the time of failure, the secondary pressure output from the electromagnetic proportional valve 4 becomes substantially equal to the primary pressure, so that the switching valve 6 is switched to the communication position. As a result, the primary pressure P <b> 1 is guided to the pressure receiving chamber 39 for the horsepower control piston 36. Further, the secondary pressure P <b> 2 that is substantially equal to the primary pressure is also introduced into the pressure receiving chamber 37 for the flow rate control piston 35. By applying the primary pressure P1 and the discharge pressure Pd to the horsepower control piston 36, the horsepower control piston 36 is operated, and the horsepower control is performed. That is, since the horsepower control piston 36 tries to make the tilt angle smaller than that of the flow rate control piston 35, only the horsepower control is performed. Thereby, at the time of a failure, a hydraulic actuator (not shown) can be driven with a certain amount of horsepower, for example, a horsepower smaller than the engine horsepower.

  Moreover, in this embodiment, since a valve with few ports can be used as the switching valve 6, a simple structure is realizable.

  Further, the biasing force of the spring 62 can be set sufficiently large, and the solenoid valve 6 is switched from the shut-off position to the communication position at a high pressure at the time of failure, so that the switching valve 62 sticks due to contamination or the like and malfunctions. Can be reliably prevented.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, although not shown, the hydraulic drive system 1 may be incorporated into one of two hydraulic supply lines of a double pump system. In this case, the regulator 3 may include another pressure receiving chamber for the horsepower control piston 36, and the discharge pressure of the counterpart hydraulic pump may be guided to the pressure receiving chamber.

  The hydraulic drive system of the present invention can be applied to various hydraulic circuits.

DESCRIPTION OF SYMBOLS 1 Hydraulic drive system with fail safe 2 Hydraulic pump 31 Servo cylinder 32 Spool 35 Flow control piston 36 Horsepower control piston 37-39 Pressure receiving chamber 4 Electromagnetic proportional valve 41 Primary pressure line 42 Secondary pressure line 43 Pilot line 5 Branch line 6 Switching valve 61 Pilot port 7 Control device

Claims (2)

A hydraulic pump that discharges hydraulic oil at a flow rate corresponding to the tilt angle;
A servo cylinder for changing the tilt angle of the hydraulic pump;
A spool that moves in a flow rate decreasing direction that drives the servo cylinder so that the tilt angle decreases and a flow rate increasing direction that drives the servo cylinder so that the tilt angle increases;
A horsepower control piston that moves the spool in the flow rate reduction direction when the discharge pressure of the hydraulic pump rises;
A flow control piston that moves the spool in the flow rate increasing direction when the flow control pressure rises;
An electromagnetic proportional valve that outputs a secondary pressure as the flow control pressure, and an electromagnetic proportional valve that decreases the secondary pressure as the command current increases;
A secondary pressure line that directly leads the secondary pressure from the electromagnetic proportional valve to the pressure receiving chamber for the flow control piston;
A primary pressure line for guiding the primary pressure to the electromagnetic proportional valve;
A branch line that branches from the primary pressure line and guides the primary pressure to a pressure receiving chamber for the horsepower control piston;
A switching valve capable of switching between a blocking position for blocking the branch line from the pressure receiving chamber for the horsepower control piston and a communication position for connecting the branch line to the pressure receiving chamber for the horsepower control piston. And a switching valve having a pilot port for moving the switching valve from the blocking position to the communication position against the urging force of the spring;
A pilot line connecting the secondary pressure line and the pilot port of the switching valve;
A hydraulic drive system with fail-safe.   When a pilot-type operation valve for operating a hydraulic actuator is operated, the control device further supplies a smaller command current to the electromagnetic proportional valve as the pilot pressure output from the operation valve is higher. The hydraulic drive system with a fail safe according to claim 1.

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