JPH053727U - Hydraulic control circuit in automatic transmission - Google Patents

Abstract

(57) [Summary] [Purpose] The purpose is to reliably reduce the shock when the modulator valve is activated and the clutch is engaged during the switching operation of the forward / reverse switching lever. [Structure] When the forward / reverse switching lever 6 is switched from a traveling position to a neutral position, the pistons 33, 43, 52 of the respective change valves 30, 31, 41 are springs provided at one end side of the same 33, 43, 52. The oil urged to the other end by 36, 50 and 60 and pressure-fed into the modulator valve 59 is surely discharged to the oil tank 24 via the selector valve 4.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a hydraulic control circuit in an automatic transmission mounted on, for example, a forklift.

[0002]

[Prior Art]

 FIG. 2 shows a hydraulic control circuit of a second-speed automatic transmission mounted on a conventional forklift truck. An oil pump 81 connected to an engine 80 is connected to a selector valve 83 via a regulator valve 82. The spool 84 of the selector valve 83 is connected to a forward / reverse switching lever 85 arranged in the operator's cab, and the forward / reverse switching lever 85 is in the neutral position, first speed forward traveling position, second speed forward traveling position, first speed. It is switched to the reverse drive position and the second speed reverse drive position. When the forward / reverse switching lever 85 is switched to any traveling position, the spool 84 of the selector valve 83 described above moves in the longitudinal direction with respect to the main body 86.

When the forward / reverse switching lever 85 is set to the first forward travel position, as shown in FIG. 3, the oil supplied from the regulator valve 82 passes through the first forward oil passage 87 and advances to the first forward. It is supplied to the clutch 88, and the clutch 88 is connected. Therefore, the forward gear for the first speed of the transmission (not shown) is driven, and the forklift truck travels at low speed. At this time, the clutch pressure of the oil supplied to the clutch 88 is controlled by the first and third change valves 89 and 90 and the modulator valve 91 as shown in FIG. That is, as shown in FIG. 3, the oil branched and flowing from the first speed forward oil passage 87 moves the pistons 92 and 93 of the first and third change valves 89 and 90 to one side, and the modulator valve 91. As a result, the clutch pressure is controlled as shown in FIG.

When the forward / reverse switching lever 85 is set to the second-speed forward drive position, as shown in FIG. 4, the oil supplied from the regulator valve 82 passes through the second-speed forward oil passage 94 and moves to the second-speed forward drive. It is supplied to the clutch 95, and the clutch 95 is connected. Therefore, the forward gear for the second speed of the transmission is driven, and the forklift truck travels at high speed. At this time, the clutch pressure of the oil supplied to the clutch 95 is controlled as shown in FIG. 7 by the first and third change valves 89 and 90 and the modulator valve 91. That is, as shown in FIG. 4, the oil branched from the second speed forward oil passage 94 flows to the other side of the piston 92 of the first change valve 89 and to the one side of the piston 93 of the third change valve 90. By moving and pumping to the modulator valve 91, the clutch pressure is similarly controlled as shown in FIG. 7.

Then, when the forward / reverse switching lever 85 is set to the first speed reverse traveling position, as shown in FIG. 5, the oil supplied from the regulator valve 82 passes through the first speed reverse movement oil passage 96 and is used for the first speed. It is supplied to the reverse clutch 97, which is connected. Accordingly, the reverse gear for the 1st speed of the transmission is driven, and the forklift will travel at a low speed in reverse. At this time, the clutch pressure of the oil supplied to the clutch 97 is controlled by the second and third change valves 98 and 90 and the modulator valve 91 as shown in FIG. That is, as shown in FIG. 5, the oil branched and flowing from the first speed reverse drive oil passage 96 moves the pistons 100 and 93 of the second and third change valves 98 and 90 to the other side, and the modulator valve. By being pressure-fed to 91, the clutch pressure is controlled as shown in FIG.

Further, when the forward / reverse switching lever 85 is set to the second speed reverse traveling position, as shown in FIG. 6, the oil supplied from the regulator valve 82 passes through the second speed reverse oil passage 99 and is used for the second speed. It is supplied to the reverse clutch 101, and the same clutch 101 is connected. Therefore, the reverse gear for the second speed of the transmission is driven to allow the forklift to travel at high speed in reverse. At this time, the clutch pressure is controlled as shown in FIG. 7 by sending the oil under pressure to the modulator valve 91 via the second and third change valves 98 and 90, as described above.

When the forward / reverse switching lever 85 is set to the neutral position, the oil supplied to the first speed forward clutch 88 at the position operated before the neutral position is operated, for example, at the first speed forward traveling position. Is discharged to the oil tank 103 via the drain oil passage 102. Further, the oil pressure-fed to the modulator valve 91 is similarly discharged to the oil tank 103 via the third and first change valves 90 and 89 and the drain oil passage 104.

[0008]

[Problems to be solved by the device]

 However, in the above-mentioned conventional technique, for example, when the forklift is moved forward and then the vehicle is moved backward at a low speed, the oil supplied to the modulator valve 91 is temporarily set to the neutral position with the forward / reverse switching lever 85, and the selector valve 8 is used during forward traveling. The hydraulic path that has passed between the third and first and third change valves 89 and 90 is reversed and discharged to the oil tank 103, the pressure of the modulator valve 91 is reduced, and the forward / reverse switching lever 85 is moved to the low speed reverse drive position. Switched to.

At this time, the pistons 92, 93 of either the first change valve 89 or the third change valve 90 move to the center due to vibrations of the forklift during traveling or for some other reason, and the selector valve 91 moves to the selector valve 91. The oil passage to the valve 83 was sometimes closed. As a result, even if the forward / reverse switching lever 85 is set to the neutral position, the oil from the modulator valve 91 does not drop downstream from the change valve closed by the pistons 92 and 93, and the pressure of the modulator valve 91 is reduced. It only drops to some extent.

Therefore, when the forward / reverse switching lever 85 is switched from the neutral position to the low speed reverse traveling position, the pressure of the modulator valve 91 is high from the neutral position of the forward / reverse switching lever 85, and therefore the first speed is set. The clutch pressure near Ckg / cm ² shown in FIG. 7 is supplied to the reverse clutch 97 for use from the start of the clutch pressure supply. That is, when the forward / reverse switching lever 85 is switched from the neutral position to the first speed reverse traveling position, the modulator valve 91 is incompletely operated, so that the shock at the time of connecting the first speed reverse clutch 97 is large. There was a problem of becoming.

The present invention has been made to solve the above problems, and the purpose thereof is to reliably operate the modulator valve at the time of switching operation of the forward / reverse switching lever and reduce the shock when the clutch is engaged. It is to provide a hydraulic control circuit for an automatic transmission that is used.

[0012]

[Means for Solving the Problems]

 To achieve the above object, in the present invention, an oil pump connected to an engine and driven together with the engine, a plurality of clutches for transmitting the pressure of oil pumped from the oil pump to a transmission, and a vehicle The forward / reverse switching lever for switching the traveling state of the vehicle to stop, forward traveling, or reverse traveling, and the forward / reverse switching lever are connected, and the oil pump is connected to a predetermined clutch based on the operation of the forward / reverse switching lever. A selector valve that supplies oil that is pressure-fed from the clutch, a plurality of change valves that branch from an oil passage that connects the selector valve and each clutch, and a plurality of change valves that are connected to the predetermined clutch from the selector valve. When oil is supplied from the oil pump to the change valve, the piston of the change valve moves to communicate with the selector valve. In a hydraulic control circuit of an automatic transmission including a modulator valve that adjusts the pressure of oil supplied to the predetermined clutch to a set value pressure, an urging means is provided on one end side of each piston of the plurality of change valves, and The essential point is a hydraulic control circuit in an automatic transmission that constantly urges the piston toward the other end, and when the forward / reverse switching lever is neutral, the hydraulic path between the selector valve and the modulator valve is always in the same communication pattern. And

[0013]

[Action]

 Therefore, when the forward / reverse switching lever is switched from the neutral position to the traveling position, the oil pumped from the oil pump driven together with the engine is operated by the selector valve connected to the forward / reverse switching lever to advance the first speed forward clutch. It is supplied to the forward clutch for 2nd speed or the reverse clutch for 1st speed and the reverse clutch for 2nd speed. Then, the oil becomes the clutch pressure to connect the clutch.

At this time, the oil pumped from the oil pump is supplied to the clutch, and at the same time, supplied to the modulator valve via the change valve. By supplying the oil to the modulator valve, the clutch pressure supplied to the clutch is gradually adjusted from the low pressure to the set value pressure. Therefore, the shock is reduced when the clutch is engaged.

Further, when the forward / reverse switching lever is operated to switch from the traveling position to the neutral position, the piston is constantly urged to the other end side by the urging means provided at one end side of the piston of the change valve. Therefore, when the forward / reverse switching lever is in the neutral position, the hydraulic path has the same communication pattern, and the oil supplied to the modulator valve is reliably discharged to the outside of the selector valve.

[0016]

【Example】

 An embodiment in which the present invention is embodied in a hydraulic circuit of a 2-speed automatic transmission of a forklift will be described with reference to FIGS.

FIG. 1 shows a hydraulic control circuit of a second-speed automatic transmission mounted on a forklift, and an oil pump 2 connected to an engine 1 is connected with a selector valve 4 via a regulator valve 3. The spool 5 of the selector valve 4 is connected to a forward / reverse switching lever 6 arranged in the operator's cab, and the front / reverse switching lever 6 is in the neutral position, first speed forward traveling position, second speed forward traveling position, first speed. It is possible to switch between the reverse drive position and the second speed reverse drive position. When the forward / reverse switching lever 6 is switched, the spool 5 of the selector valve 4 moves in the longitudinal direction with respect to the main body 7.

The spool 5 of the selector valve 4 is formed in a substantially columnar shape, and a switching portion 8 having a large diameter is formed in the center thereof. Further, an oil inflow hole 9 is formed in the switching portion 8 from the center of the right end surface of the spool 5, and the oil is drained vertically from the upper portion of the switching portion 8 so as to communicate with the oil inflow hole 9. A hole 10 is formed. Then, the oil flows into the oil inflow hole 9 through the regulator valve 3 that is pressure-fed from the oil pump 2, and further the oil flows into the oil discharge hole 10.

On the upper part of the main body 7 of the selector valve 4, a forward port 11 for the first speed, a forward port 12 for the second speed, a drain port 13 for the forward speed, a reverse port 14 for the first speed, a reverse port 15 for the second speed, and The reverse side drain port 16 is transparently provided. When the forward / reverse switching lever 6 is set to the neutral position, the oil discharge hole 10 provided through the switching portion 8 of the spool 5 has the forward port 11 for the first speed and the reverse port 14 for the first speed. It is located in between and is closed by the main body 7.

Further, when the forward / reverse switching lever 6 is set to the first speed forward traveling position, the oil discharge hole 10 of the spool 5 communicates with the first speed forward port 11 penetratingly provided on the main body 7, and the forward / reverse switching is performed. When the lever 6 is set to the second speed forward drive position, the oil discharge hole 10 communicates with the second speed forward port 12.

Further, when the forward / reverse switching lever 6 is set to the 1st reverse traveling position, the oil discharge hole 10 communicates with the 1st reverse passage port 14, and the forward / reverse switching lever 6 is set to the 2nd reverse traveling position. In such a case, the oil discharge hole 10 is adapted to communicate with the second speed reverse drive port 15.

The forward side drain port 13, the second speed forward port 12 and the first speed forward port 11 are communicated by a forward side communication passage 17 formed by the main body 7 and the spool 5 on the left side of the switching unit 8. The reverse side drain port 16, the second speed reverse port 15 and the first speed reverse port 14 are formed by a reverse side communication passage 18 formed by the body 5 and the spool 5 on the right side of the switching unit 8. It is in communication.

The first speed forward port 11 is connected to the first speed forward clutch 20 via a first speed forward oil passage 19, and the second speed forward port 12 is connected to the second speed forward oil passage 21. It is connected to the forward clutch 22 for the second speed via. The forward drain port 13 communicates with an oil tank 24 via a drain oil passage 23.

On the other hand, the first speed reverse drive port 14 is connected to the first speed reverse drive clutch 26 via the first speed reverse drive oil passage 25, and the second speed reverse drive port 15 is connected to the second speed reverse drive oil passage. It is connected via 27 to a reverse clutch 28 for the second speed. The reverse side drain port 16 communicates with the oil tank 24 via a drain oil passage 29. That is, when the forward / reverse switching lever 6 is switched from the neutral position to the forward or backward traveling position, the oil pumped from the oil pump 2 causes the clutch corresponding to the switching position of the forward / backward switching lever 6. Is supplied to the clutch and the clutch is adapted to be engaged.

Further, a first change valve 30 branched from the first-speed forward oil passage 19 is connected to the first-speed forward clutch 20, and the first change valve 30 is connected to the second-speed forward clutch. The clutch 22 is also connected via a second speed forward oil passage 21. Further, a second change valve 31 branched from the first speed reverse oil passage 19 is connected to the first speed reverse clutch 20, and the second change valve 31 is connected to the second speed reverse clutch 28. Both are connected through a second speed reverse drive oil passage 27.

The first change valve 30 connected to the first-speed forward clutch 20 and the second-speed forward clutch 22 via the first-speed forward oil passage 19 and the second-speed forward oil passage 21 is the main body of the main body. A piston 33 is arranged so as to be movable in the longitudinal direction with respect to 32, and the inside of the main body 32 is divided by the piston 33 into a first-speed forward oil supply chamber 34 and a second-speed forward oil supply chamber 35. The first-speed forward oil supply chamber 34 is connected to the first-speed forward oil passage 19 via a first-speed inlet port 37. That is, the first speed forward movement port 11 of the selector valve 4 and the first speed forward movement oil supply chamber 34 of the first change valve 30 are communicated with each other.

On the other hand, the second speed forward oil supply chamber 35 of the first change valve 30 is connected to the second speed forward oil passage 21 via a second speed side inflow port 38. That is, the second speed forward port 12 of the selector valve 4 and the second speed forward oil supply chamber 35 of the first change valve 30 are in communication with each other. Further, a forward discharge port 39 is transparently provided at the center of the upper portion of the main body 32 of the first change valve 30, and the forward discharge port 39 is connected to a third change valve 41 via a forward oil passage 40. Has been done.

A spring 36 as an urging means is disposed in the first-speed forward oil supply chamber 34 of the first change valve 30. The spring 36 causes the piston 33 to move in the leftward direction, that is, 2 When the forward drive oil supply chamber 35 is pressed and the forward / reverse switching lever 6 is neutral, the forward drive discharge port 39 and the first speed forward oil supply chamber 34 are always in communication with each other.

The second change valve 31 connected to the first speed reverse clutch 26 and the second speed reverse clutch 28 via the first speed reverse oil passage 25 and the second speed reverse oil passage 27 is a main body. A piston 43 is arranged so as to be movable in the longitudinal direction with respect to 42, and the piston 43 divides the inside of the main body 42 into a reverse speed oil supply chamber 44 for the first speed and a reverse speed oil supply chamber 45 for the second speed. The 1st speed reverse oil supply chamber 44 is connected to the 1st speed reverse oil passage 25 via the 1st speed inflow port 37. That is, the first reverse gear port 14 of the selector valve 4 and the first reverse gear oil supply chamber 44 of the second change valve 31 are communicated with each other.

On the other hand, the second speed reverse oil supply chamber 45 of the second change valve 31 is connected to the second speed reverse oil passage 27 via a second speed inflow port 47. That is, the second speed reverse drive port 15 of the selector valve 4 and the second speed reverse drive oil supply chamber 45 of the second change valve 31 are communicated with each other. Further, a reverse discharge port 48 is provided in the center of the upper portion of the main body 42 of the second change valve 31, and the reverse discharge port 48 is connected to the third change valve 41 via a reverse oil passage 49. It is connected to the.

A spring 50 as an urging means is disposed in the reverse gear oil supply chamber 45 for the second speed of the second change valve 31. The spring 50 causes the piston 43 to move in the leftward direction, that is, for the first speed. When the reverse travel oil supply chamber 44 is pressed and the forward / reverse travel switching lever 6 is in the neutral position, the reverse travel discharge port 48 and the second reverse oil supply chamber 45 are always in communication with each other.

Like the first and second change valves 30 and 31, the third change valve 41 is formed of a main body 51 and a piston 52, and the inside of the main body 51 is moved by the piston 52 to a forward oil supply chamber 53. And a reverse oil supply chamber 54. The forward movement oil supply chamber 53 is connected to the forward movement oil passage 40 via a forward movement side inflow port 55. That is, the forward discharge port 39 of the first change valve 30 and the forward oil supply chamber 53 of the third change valve 41 are in communication with each other.

On the other hand, the reverse travel oil supply chamber 54 of the third change valve 41 is connected to the reverse travel oil passage 49 via a reverse travel side inlet port 56. That is, the reverse drive discharge port 48 of the second change valve 31 and the reverse drive oil supply chamber 54 of the third change valve 41 communicate with each other. Further, a modulator discharge port 57 is provided at the center of the upper portion of the main body 42 of the third change valve 41, and the modulator discharge port 57 is communicated with a modulator valve 59 via a modulator oil passage 58.

A spring 60 as a biasing means is disposed in the forward oil supply chamber 53 of the third change valve 41, and the spring 60 causes the piston 52 to move in the leftward direction, that is, the reverse oil supply chamber 54. When the forward / reverse switching lever 6 is in the neutral position, the modulator discharge port 57 and the forward oil supply chamber 53 are always in communication with each other.

In the modulator valve 59, the forward / reverse switching lever 6 is switched from the neutral position to any traveling position, and the oil discharge hole 10 of the selector valve 4 and any port transparently provided in the main body 7 are connected. When communicating, the pressure of the oil (clutch pressure) supplied from the port communicating with the oil discharge hole 10 is increased to Akg / cm ^{2 in the} modulator valve characteristic diagram shown in FIG. 7 via each change valve. .. When the clutch pressure reaches Akg / cm ² , the modulator valve 59 presses the oil by a piston (not shown) built in the modulator valve 59, and the modulator valve 59 presses the Akg / cm ² The clutch pressure is further increased to Bkg / cm ² . Then, when the clutch pressure reaches arrives in Bkg / cm ^2, the modulator valve 59, once the raise the clutch pressure to Ck g / cm ² is set value pressure, the oil pump 2 to hold the pressure It is designed to control the clutch pressure that is sent from.

That is, the clutch to which the clutch pressure is supplied when the forward / reverse switching lever 6 is switched from the neutral position to the traveling position is Akg / cm ² when the clutch pressure starts to be supplied, and Bkg / cm ² when the pressure is adjusted. ² , and finally, the clatch pressure of Ckg / cm ² , which is the set pressure, is supplied.

The first speed forward clutch 20 is connected to a first speed forward gear (not shown) of the transmission, and clutch pressure is supplied to the first speed forward clutch 20 to connect the first speed forward clutch 20. In this case, the forward gear for the first speed of the transmission is driven, and the forklift is adapted to travel at a low speed. Further, the second speed forward clutch 22 is connected to a second speed forward gear (not shown) of the transmission, and the clutch pressure is supplied to the second speed forward clutch 22 so that the second speed forward clutch 22 is provided. When connected, the forward gear for the second speed of the transmission is driven so that the forklift travels at high speed.

Further, the first-speed reverse clutch 26 is connected to a first-speed reverse gear (not shown) of the transmission, clutch pressure is supplied to the first-speed reverse clutch 26, and the first-speed reverse clutch is supplied. When 26 is connected, the reverse gear for the first speed of the transmission is driven and the forklift is adapted to travel at a low speed. Further, the second speed reverse clutch 28 is connected to a second speed reverse gear (not shown) of the transmission, and clutch pressure is supplied to the second speed reverse clutch 28 to connect the second speed reverse clutch 28. In this case, the reverse gear for the second speed of the transmission is driven to drive the forklift at a high speed.

Next, the operation of the hydraulic circuit of the automatic transmission for the second speed having the change valves configured as described above will be described. First, when the engine 1 is started and the oil pump 2 is driven, the oil is pumped from the oil pump 2, and the oil flows through the regulator valve 3 from the oil inlet hole 9 of the selector valve 4 to the oil outlet hole 10. Is supplied to. Then, when the forward / reverse switching lever 6 is switched from the neutral position to the first speed forward traveling position in order to drive the forklift forward at a low speed, the spool 5 of the selector valve 4 correspondingly moves within the main body 7 as well. Moving to the left, the oil discharge hole 10 communicates with the first speed forward port 11.

Since the oil discharge hole 10 and the first speed advancing port 11 communicate with each other, the oil pressure-fed from the oil pump 2 is transferred from the oil discharge hole 10 to the first speed advancing port 11 and the first speed advancing oil passage. After being supplied to the first side forward clutch 20 via 19, the first change valve 30 is supplied to the first side forward oil supply chamber 34 from the first speed side inflow port 37. The oil supplied to the first-speed forward oil supply chamber 34 passes through the forward discharge port 39, the forward oil passage 40, and the forward oil inlet chamber 55 of the third change valve 41. It is pumped to 53. Then, the oil pressure-fed to the forward oil supply chamber 53 is pressure-fed to the modulator valve 59.

That is, by supplying the oil to the modulator valve 59, the clutch pressure shown in FIG. 7 is generated in the first speed forward clutch 20. Therefore, when the forward / reverse switching lever 6 is switched from the neutral position to the first speed forward traveling position, the first speed forward clutch 20 is not connected at a clutch pressure of Ckg / cm ² which is the set value pressure at one time, Since the clutches are gradually connected with high clutch pressure, it is possible to reduce the shock at the start of low-speed forward travel of the forklift.

Further, when the forward / reverse switching lever 6 is switched from the 1st forward traveling position to the 2nd forward traveling position in order to move the forklift from the low speed forward traveling to the high speed forward traveling, the oil discharge of the selector valve 4 is performed. The hole 10 communicates with the second speed forward port 12. Since the oil discharge hole 10 and the second speed forward port 12 are communicated with each other, the oil pressure-fed from the oil pump 2 is supplied to the second speed forward clutch 22 and the oil discharge hole 10 is used for the second speed. It is supplied to the second-speed forward oil supply chamber 35 from the second-speed inlet port 38 of the first change valve 30 via the second-speed forward oil passage 21 and the second-speed forward oil passage 21. The piston 33 of the first change valve 30 is pressed rightward against the biasing force of the spring 36 by the pressure of the oil supplied to the second-speed forward oil supply chamber 35, and the second-speed forward oil supply is supplied. The chamber 35 communicates with the forward discharge port 39.

Since the second-speed forward oil supply chamber 35 and the forward-movement discharge port 39 communicate with each other, the oil supplied to the second-speed forward oil supply chamber 35 is transferred from the forward-movement discharge port 39. The oil is fed from the advancing-side inflow port 55 of the third change valve 41 to the advancing oil supply chamber 53 via the advancing oil passage 40. Then, the oil supplied to the forward oil supply chamber 53 is pressure-fed from the modulator discharge port 57 to the modulator valve 59 via the modulator oil passage 58.

That is, the clutch pressure controlled by the modulator valve 59 is generated in the second speed forward clutch 22 by the connection with the modulator valve 59. When the clutch pressure is generated in the second speed forward clutch 22, the second speed forward clutch 22 starts to be connected. At this time, the clutch pressure is regulated by the modulator valve 59 as in the case of the low speed forward running, and the second speed forward clutch 22 is connected at a clutch pressure of Ckg / cm ² , which is the set pressure at one time. Instead, the clutch is gradually connected with a high clutch pressure, so that it is possible to reduce the shock when the forklift starts traveling at high speed.

When the forklift is traveling from the high speed forward traveling or the low speed forward traveling to the low speed backward traveling, the forward / reverse switching lever 6 is switched from the second forward traveling position or the first forward traveling position to the neutral position. Manipulate. When the forward / reverse switching lever 6 is switched from the second-speed forward traveling position or the first-speed forward traveling position to the neutral position, the piston 33 of the first change valve 30 is urged by the spring 36 so that the second-speed forward drive lever can be operated. It is pressed into the advancing oil supply chamber 35.

Then, the discharge port of each change valve is surely opened, and the oil pressure-fed into the modulator valve 59 during forward traveling falls out into the forward communication passage 17. The oil that has fallen out into the forward communication passage 17 is discharged from the forward drain port 13 to the oil tank 24 via the drain oil passage 23.

Subsequently, the forward / reverse switching lever 6 is switched from the neutral position to the reverse traveling position for the first speed to connect the oil discharge hole 10 and the reverse port 14 for the first speed. The oil from the oil pump is supplied to the reverse oil supply chamber 44 for the first speed of the second change valve 31 because the oil discharge hole 10 and the reverse port 14 for the first speed are communicated with each other. Then, the pressure of the oil supplied to the reverse speed oil supply chamber 44 for the first speed pushes the piston 43 to the right side, that is, the reverse speed oil supply chamber 45 for the second speed, against the biasing force of the spring 50. Oil is supplied from the reverse speed oil supply chamber 44 for the first speed to the reverse speed oil supply chamber 54 of the third change valve 41. The piston 52 of the third change valve 41 is pressed against the urging force of the spring 60 toward the forward oil supply chamber 53 side by the pressure of the oil supplied to the reverse oil supply chamber 54.

Then, the oil pumped from the oil pump 2 is supplied from the reverse oil supply chamber 54 to the modulator valve 59 and the first speed reverse clutch 26. That is, the clutch pressure controlled by the modulator valve 59 is supplied to the reverse clutch 26 for the first speed, as in the case of the forward running, and the shock at the start of the low speed backward running of the forklift can be reduced.

Further, when the forklift is moved from the low speed reverse drive to the high speed reverse drive, the forward / reverse switching lever 6 is operated to switch to the second speed reverse drive position so that the oil discharge hole 10 and the second speed reverse port 15 are connected. By communicating with each other, the oil pumped from the oil pump 2 is supplied to the modulator valve 59 and the second speed reverse clutch 28. That is, the clutch pressure controlled by the modulator valve 59 is supplied to the reverse clutch 28 for the second speed, and it is possible to reduce the shock at the start of the low speed reverse travel of the forklift.

When the forklift is traveling from high speed backward travel or from low speed backward travel to low speed forward travel, the forward / reverse switching lever 6 is once switched to the neutral position, as in the case of switching from forward travel to reverse travel. The oil pressure-fed into the modulator valve 59 is caused to flow backward through the oil passages and the change valves, and is dropped into the reverse communication passage 18 to reduce the pressure of the modulator valve 59. As described above in detail, according to the hydraulic circuit of the automatic transmission for the second speed according to the present embodiment, the spring is provided in the oil supply chamber on one side of each change valve, so that when the forward / reverse switching lever 6 is neutral, Since the piston of each modulator valve is pressed toward the oil supply chamber on the left side, the modulator valve 59 and the selector valve 4 are surely in communication with each other.

That is, when the forward / reverse switching lever 6 is set to the neutral position, all the oil supplied to the modulator valve 59 and the oil passage falls out to the forward communication passage 17 or the reverse passage 18 of the selector valve 4. When the forward / reverse switching lever 6 is switched from the neutral position to the forward traveling position or the reverse traveling position, the clutch pressure supplied to the clutch is the actuation of the modulator valve 59. Is regulated by. Therefore, the shock at the time of engaging the clutch is surely reduced.

The present invention is not limited to the above-mentioned embodiment, and may be configured as follows, for example, within the scope of the invention. In the above-described embodiment, the spring as the urging means arranged in each change valve is arranged in the oil supply chamber on the right side of each change valve in FIG. 1, but if either one of the oil supply chambers is used, It may be arranged in the left oil supply chamber.

[0053]

[Effect of the device]

 As described above in detail, according to the present invention, when the forward / reverse switching lever is switched, the modulator valve is surely operated, and the shock when the clutch is engaged is reduced.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a 2-speed automatic transmission according to an embodiment of the present invention.

FIG. 2 is a hydraulic circuit diagram of a conventional 2-speed automatic transmission.

FIG. 3 is a hydraulic circuit diagram of a second-speed automatic transmission showing a state in which the forward / reverse switching lever is switched to the first-speed forward drive position from the state of FIG.

FIG. 4 is a hydraulic circuit diagram of a second-speed automatic transmission showing a state in which the forward / reverse switching lever is switched from the state of FIG. 3 to a second-speed forward drive position.

5 is a hydraulic circuit diagram of a second-speed automatic transmission showing a state in which the forward / reverse switching lever is switched to the first-speed reverse traveling position from the state of FIG. 2;

FIG. 6 is a hydraulic circuit diagram of a second-speed automatic transmission showing a state in which the forward / reverse switching lever is switched from the state of FIG. 5 to a second-speed reverse traveling position.

FIG. 7 is a characteristic diagram of a modulator valve.

[Explanation of symbols]

1 ... Engine, 2 ... Oil pump, 4 ... Selector valve, 6 ... Forward / reverse switching lever, 20 ... 1st forward clutch, 22 ... 2nd forward clutch, 26 ... 1st backward clutch, 28 ... 2nd forward Reverse clutch, 30 ... First change valve as change valve, 31 ... Second change valve as change valve, 33 ... Piston, 3
6 ... Spring as biasing means, 41 ... Third change valve as change valve, 43 ... Piston, 5
0 ... Spring as biasing means, 52 ... Piston, 5
9 ... Modulator valve, 60 ... Spring as biasing means

Claims (1)

Claims for utility model registration: 1. An oil pump connected to an engine and driven together with the engine; a plurality of clutches for transmitting the pressure of oil pumped from the oil pump to a transmission; A forward / reverse switching lever for switching the traveling state to stop, forward traveling, or reverse traveling, and a forward / reverse switching lever, which is connected to the forward / reverse switching lever and pumped from the oil pump to a predetermined clutch based on the operation of the forward / reverse switching lever. A selector valve for supplying oil, a plurality of change valves branched from an oil passage connecting the selector valve and each clutch, an oil pump connected to the plurality of change valves, and connected to the predetermined clutch with an oil pump When the oil from is supplied, it communicates with the selector valve by the movement of the change valve piston. A hydraulic control circuit for an automatic transmission comprising a modulator valve for adjusting the pressure of the oil supplied to the predetermined clutch to a set value pressure, wherein a biasing means is provided at one end side of each piston of the plurality of change valves, A hydraulic control circuit in an automatic transmission for constantly urging the piston toward the other end so that the hydraulic path between the selector valve and the modulator valve is always in the same communication pattern when the forward / reverse switching lever is in a neutral position.