JPH0751985B2 - Hydraulic continuously variable transmission - Google Patents

Description

Detailed Description of the Invention a. OBJECT OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydraulic continuously variable transmission including a combination of a hydraulic pump and a hydraulic motor, at least one of which is a variable displacement type. The present invention relates to a hydraulic continuously variable transmission that includes a clutch mechanism that connects a discharge side and a suction side of a pump directly to each other in a connected hydraulic closed circuit to put the transmission in a neutral state.

(Prior Art) Various hydraulic continuously variable transmissions including a combination of a hydraulic pump and a hydraulic motor, at least one of which is a variable displacement type, have been conventionally proposed (for example, Japanese Patent Publication No. 32-7159). In such a hydraulic continuously variable transmission, a short-circuit passage that connects the two oil passages that are arranged between the pump and the motor to form an open circuit and that connects the discharge side and the suction side of the pump is formed. It is also known that the clutch control of the transmission is provided by controlling the opening and closing of this short circuit by a clutch valve (for example, Japanese Patent Laid-Open No. 56-95722).

(Problems to be Solved by the Invention) If such a clutch valve is opened and the discharge side and the suction side of the pump are communicated with each other by the above-mentioned short circuit, the motor is not driven even if the pump is rotationally driven, A neutral state is obtained. However, since it is necessary to form the short-circuit path in the transmission and dispose the clutch valve in this short-circuit path, it is not possible to ensure a sufficient cross-sectional area of the short-circuit path due to its configuration, There is a case where the opening area cannot be sufficiently secured. In such a case, even if the clutch valve is opened, a part of the pump discharge oil flows to the motor side, the motor side is driven, and there is a problem that a complete neutral state cannot be obtained.

Furthermore, when the oil temperature is low, the viscosity of this oil is high,
Since the flow path resistance of the short circuit increases, the flow rate through the short circuit is small even if the clutch valve is opened. Even in this case, some of the pump discharge oil also flows to the motor side and a perfect neutral state is obtained. There is a problem that you can not.

In view of such problems, it is an object of the present invention to provide a hydraulic continuously variable transmission having a configuration capable of obtaining a perfect neutral state when necessary.

B. Configuration of the Invention (Means for Solving the Problems) To achieve such an object, a hydraulic continuously variable transmission according to the present invention is provided with a pump discharge passage and a pump suction passage that communicate with a discharge port and a suction port of a hydraulic pump, respectively. And a distribution board having a motor discharge path and a motor suction path, which communicate with the discharge port and the suction port of the hydraulic motor, respectively, and a sliding contact with the distribution plate, and the pump discharge path and the motor according to the rotation of the hydraulic pump and the hydraulic motor. It has a distribution ring that divides and forms a first oil passage that communicates with the suction passage and a second oil passage that communicates with the pump suction passage and the motor discharge passage, and further separates this distribution ring from the distribution board. A neutral state creating means for directly communicating the pump discharge passage and the pump suction passage through a communication space formed between the sliding contact surfaces of the distribution board and the distribution ring, and the hydraulic closed circuit. A short-circuit passage that is provided in parallel with the communication space and short-circuits the pump discharge passage and the pump suction passage through the first oil passage and the second oil passage, and a clutch valve that controls the opening degree of the short-circuit passage. ing. In addition, the neutral state creating means, a hydraulic chamber facing the surface of the distribution ring opposite to the sliding contact surface to generate hydraulic pressure in the direction of slidingly contacting the distribution ring with the distribution disk, and the sliding contact surface side. An inlet passage with a throttle for introducing the acting hydraulic pressure into the hydraulic chamber, an exhaust passage for exhausting the hydraulic pressure from the hydraulic chamber, and the discharge passage is closed when the distribution ring is slidably brought into contact with the distribution board. It is desirable that the opening and closing means is configured to open the discharge path when the is moved away from the distribution board.

(Operation) In the hydraulic continuously variable transmission having the above-described configuration, when the neutral state creating means is operated to separate the distribution ring in sliding contact with the distribution plate from the distribution plate, the pump discharge path and the motor suction path by the distribution ring. And the pump suction passage and the motor discharge passage are disconnected from each other, and the pump discharge passage and the pump suction passage are directly communicated with each other through the communication space. Therefore, the neutral state can be obtained without using the short-circuit path and the clutch valve as in the conventional case. In this case, the pump discharge passage and the pump suction passage are in direct communication with each other, so that a completely neutral state is achieved. Moreover, if the opening degree of the short-circuit path is controlled by the clutch valve, it is possible to realize the fine gear ratio control based on the half-clutch control of the clutch valve in the communication space. If the neutral state creating means is configured by a hydraulic type that generates hydraulic pressure in the direction in which the distribution ring slides on the distribution board and an opening / closing means that discharges hydraulic pressure from this hydraulic chamber, a more rapid transition to the neutral state. You can control.

(Examples) Hereinafter, preferred examples of the present invention will be described with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram of a continuously variable transmission according to the present invention,
In this figure, a continuously variable transmission T is a constant displacement type swash plate axial plunger type hydraulic pump P driven by an engine E via an input shaft 1 and a variable displacement type swash plate axial plunger type hydraulic pump P connected to an output shaft 2. It has a hydraulic motor M. A pump discharge path La is connected to the discharge port of the hydraulic pump P, and a pump suction path Ld is connected to the suction port. The motor suction path Lb is connected to the suction port of the hydraulic motor M, and the motor discharge path Lc is connected to the discharge port. In a normal state, the pump discharge passage La and the motor suction passage Lb communicate with each other and the motor discharge passage Lc and the pump suction passage Ld communicate with each other by the distribution mechanism D including the distribution plate 80 and the distribution ring 92. , Pump P and motor M
A closed circuit is hydraulically connected to and. In addition, from the pump discharge passage La communicating with the distribution mechanism D to the motor suction passage
The portion up to Lb is called the first circuit oil passage, and the portion from the motor discharge passage Lc to the pump suction passage Ld is called the second circuit oil passage.

A discharge port of a charge pump (replenishment pump) 10 driven by the engine E via a pair of gear sets 9a, 9b is connected to a regulator valve 12 via a pump discharge oil passage L ₁ , and further, this discharge oil The first control oil passage L ₂ is branched from the passage L ₁ . The regulator valve 12 operates according to the oil pressure in the discharge oil passage L ₁ , sets the oil pressure in the discharge oil passage L ₁ and the first control oil passage L ₂ to a predetermined control line pressure P _L, and The hydraulic oil having P _L is supplied to the control valve or the like from the first control oil passage L ₂ .

The amount of oil supplied from the first control oil passage L ₂ to the control valve or the like is smaller than the discharge amount of the charge pump 10. Therefore, the remaining oil is supplied to the first charge oil passage L ₃ by the operation of the regulator valve 12. Sent. If there is still an excessive amount of oil even after being sent to the first charge oil passage L ₃ , it is returned from the drain oil passage L ₄ to the sump 17. In this way, the first charge oil passage L ₃
Is sent to the third circuit oil passage Le having a pair of check valves 3 and 3 through the second charge oil passage L ₅ after being purified through the centrifugal oil filter 4. By the action of the check valves 3,3, the oil is supplied to the low pressure side oil passage of the first and second circuit oil passages.

It should be noted that the first lubricating oil passage L ₆ connected from the second charge oil passage L ₅ to the internal space of the motor cylinder 70 forming the pump case.
Is branched, and a part of the oil supplied to the second charge oil passage L ₅ passes through the check valve 6a arranged in the first lubricating oil passage L ₆ and also through the oil passage L ₆ as described above. Supplied into the interior space. The oil supplied to this internal space lubricates the pump parts and is sent from the second lubricating oil passage L ₇ to the outside for lubrication. The hydraulic oil in the internal space is directly sampled by opening the check valve 6b when the rotation of the motor cylinder 70 is extremely small, that is, when the engine is stopped.
Discharged to 17.

A governor valve 8 is mounted coaxially with the charge pump 10. The governor valve 8 is supplied with hydraulic oil of a predetermined pressure from a control valve (not shown), and the governor valve 8 converts the pressure of this hydraulic oil into governor hydraulic pressure corresponding to the rotational speed of the engine E.

The fourth circuit oil passage Lf having the shuttle valve 110 is connected to the closed circuit. A fifth circuit oil passage Lg having a low pressure relief valve 7 and connected to the oil sump 17 is connected to the shuttle valve 110. Shuttle valve 110
Operates according to the hydraulic pressure difference between the first and second circuit oil passages (motor suction passage Lb and motor discharge passage Lc), and the oil passage on the low pressure side of the first and second circuit oil passages is changed to the fifth circuit oil passage. Connect to road Lg. Thereby, the relief hydraulic pressure of the oil passage on the low pressure side is regulated by the low pressure relief valve 7.

Further, the transmission T is also provided with a main clutch valve CL that controls the opening of an oil passage that short-circuits the first and second circuit oil passages and a direct coupling clutch valve DC that can close the pump discharge oil passage La. ing.

The main clutch valve CL is a clutch valve of a type that has been conventionally used, and in this case, the cross-sectional area of the short-circuit path and the opening area of the clutch valve CL cannot be increased so much due to structural restrictions. , Even if the clutch valve CL is fully opened, the complete neutral state may not be achieved. This problem is particularly great when the oil temperature is low and the viscous resistance is large. Therefore, in this example, in the distribution mechanism D, the distribution ring 92 is forcibly separated from the distribution plate 80, and
The second circuit oil passage (the pump discharge passage La and the pump suction passage Ld) is directly communicated with each other so that a reliable neutral state can be obtained.

Although the detailed structure and operation for this will be described later, the first and second neutral control lines L ₁₁ and L ₁₂ for performing this operation are connected to the distribution mechanism D as shown. Check valves for both neutral control lines L ₁₁ and L ₁₂ respectively
After passing through 121 and 122, it communicates with the third control line L ₁₃ connected to the neutral control valve 130. The neutral control valve 130 is a valve that closes the third neutral control line L ₁₃ when the spool 131 is moved against the spring 132 by receiving the hydraulic pressure sent from the fourth neutral control line L ₁₄ to the hydraulic chamber 134. Is.
When the third neutral line L ₁₃ is closed, the distribution ring 92 is kept in sliding contact with the distribution plate 80, and when the third neutral line L ₁₃ is opened and connected to the drain, the distribution ring 92 is distributed to the distribution plate 80. (The operation will be described later).

It should be noted that the fourth neutral control line L ₁₄ is connected to the hydraulic control valve 140 of the transmission, and when the engine T is in the operating state and the transmission T is in a state other than neutral, the fourth neutral control line L ₁₄ is predetermined. When the transmission T is in the neutral state, the hydraulic pressure of the fourth neutral control line L ₁₄ is reduced. As a result, when the transmission T is in the neutral state,
The distribution ring 92 is separated from the distribution board 80, and the neutral state is surely obtained.

Next, a specific structure of the continuously variable transmission T will be briefly described with reference to FIG.

The continuously variable transmission T includes a hydraulic pump P and a hydraulic motor M coaxially arranged in a space surrounded by the first to fourth cases 5a to 5d. Input shaft 1 of hydraulic pump P
Is coupled to the output shaft Es of the engine E via a coupling 1a. A centrifugal filter 50 is arranged on the inner peripheral side of the coupling 1a.

A drive gear 9a is connected to the input shaft 1 by a spline, and a driven gear 9b meshes with the drive gear 9a. The driven gear 9b is coaxially coupled to the drive shaft 11 of the charge pump 10, and the rotation of the engine E is performed by the pair of gears.
It is transmitted to the drive shaft 11 of the charge pump 10 via 9a and 9b, and the charge pump 10 is driven. The drive shaft 11 penetrates the charge pump 10 and projects to the side opposite to the gear 9b, and is also connected to the governor valve 8. Therefore, the rotation of the engine E is also transmitted to the governor valve 8, and the governor valve 8 produces a governor hydraulic pressure corresponding to the rotation of the engine E.

The hydraulic pump P has a pump cylinder 60 spline-coupled to the input shaft 1 and a plurality of pump plungers 62 slidably fitted into a plurality of cylinder holes 61 circumferentially equidistantly formed in the pump cylinder 60. And is rotationally driven by the power of the engine E transmitted through the input shaft 1.

The hydraulic motor M includes a motor cylinder 70 that is provided so as to surround the pump cylinder 60, and a plurality of motor plungers 72 that are slidably fitted into a plurality of cylinder holes 71 that are formed in the motor cylinder 70 at even intervals on the circumference. The pump cylinder 60 is concentric with the pump cylinder 60 and is relatively rotatable.

The motor cylinder 70 is composed of first to fourth portions 70a to 70b that are integrally joined in a line in the axial direction. The first portion 70a is rotatably supported by the case 5b via a bearing 79a at the outer periphery of the left end thereof, and the right inner surface is inclined with respect to the input shaft 1 to form a pump swash plate member. A pump swash plate ring 63 is provided on the pump swash plate member. The plurality of cylinder holes 71 are formed in the second portion 70b, and the third portion 70c includes the cylinder holes 61, 71.
It has the distribution board 80 in which the oil path to was formed. Fourth part 70
A gear member GM having first and second drive gears 21 and 22 in d
Is press-fitted and is rotatably supported by the case 5c via a bearing 79b.

On the pump swash plate ring 63, an annular pump shoe is
64 is mounted so that it can rotate and slide, and this pump shoe 64
The pump plunger 62 and the pump plunger 62 are connected via a connecting rod 65 so as to be swingable to some extent. The pump shoe 64 and the pump cylinder 60 are formed with bevel gears 68a, 68b that mesh with each other. Therefore, when the pump cylinder 60 is rotationally driven from the input shaft 1, the pump shoe 64 is also rotationally driven, and the pump plunger 62 is reciprocated according to the inclination of the pump swash plate ring 63, so that oil is sucked and discharged from the suction port. The oil is discharged to the outlet.

Further, the swash plate member 73 facing each motor plunger 72,
It is swingably supported by the second case 5b via a pair of trunnion shafts (swing shafts) 73a protruding from both outer ends thereof in a direction perpendicular to the paper surface. A motor swash plate ring 73b is arranged on a surface of the swash plate member 73 facing the motor plunger 72, and a motor shoe 74 is attached by sliding on the motor swash plate ring 73b. The motor shoe 74 is swingably connected to the end of each motor plunger 72. The swash plate member 73 is located at a position away from the trunnion shaft 73a and has a speed change servo unit via a link member 39.
The piston rod 33 is connected to the piston rod 33, and when the piston rod 33 is moved in the axial direction by the shifting servo unit 30, the swash plate member 73 is swung about the trunnion shaft 73a. .

The fourth portion 70d of the motor cylinder 70 is formed hollow, and the fixed shaft 91 fixed to the pressure distribution plate 18 is inserted into the center of the fourth portion 70d. A distribution ring 92 is attached to the left end of the fixed shaft 91 so as to be liquid-tight and movable in the axial direction, and the axial left end surface of the distribution ring 92 is eccentrically brought into sliding contact with the distribution board 80. There is. The distribution ring 92 divides the hollow portion formed in the fourth portion 70d into an inner oil chamber and an outer oil chamber, the inner oil chamber constitutes the first circuit oil passage La, and the outer oil chamber is It constitutes the second circuit oil passage Lb. In addition, the pressure distribution board 18
Has a shuttle valve 110, a low-pressure relief valve 7, etc., is attached to the right side surface of the third case 5c, and is covered by the fourth case 5d.

This distribution board 80 and the detailed structure in the fourth portion 70d are
It is shown in the figure and will be described below with reference to FIG.

The distribution board 80 is provided with a pump discharge port 81a and a pump suction port 82a, and through the discharge port 81a and a pump discharge passage 81b connected to the discharge port 81a, a cylinder hole 61 of a pump plunger 62 in the discharge stroke is formed. The first circuit oil passage La formed of the inner oil chamber communicates with the cylinder hole 61 of the pump plunger 62 in the suction stroke and the outer oil chamber via the pump suction port 82a and the pump suction passage 82b connected to the pump suction port 82a. The second circuit oil passage Lb is communicated. Further, the distribution board 80 is formed with a communication path 83 communicating with the cylinder hole (cylinder chamber) 71 of each motor plunger 72, and the opening of this communication path 83 is opened on the sliding contact surface with the distribution ring 92. ing.
The communication passage 83 is formed corresponding to each cylinder hole 71, and when the motor plunger 72 in the cylinder hole 71 is in the expansion process, the communication passage 83 becomes a motor suction passage and the motor plunger 72 is In the contraction process, this connecting path 83 becomes a motor discharge path.

The distribution ring 92 is slidably in contact with the distribution board 80, and is connected to the communication path 83.
Has a recess 92a for communicating with the first circuit oil passage La, and a passage 92b for communicating the communication passage 83 with the second circuit oil passage Lb.
Therefore, when the distribution board 80 is rotated together with the motor cylinder 70, the cylinder hole 71 of the motor plunger 72 in the expansion stroke and the first circuit oil passage La are connected to the cylinder hole 71 of the motor plunger 72 in the contraction stroke and the first circuit oil passage La. 2 circuit oil passage Lb and connecting passage 83
Are communicated with each other.

In this way, a closed hydraulic circuit is formed between the hydraulic pump P and the hydraulic motor M via the distribution board 80 and the distribution ring 92. Therefore, from the input shaft 1 to the pump cylinder
When 60 is driven, the high-pressure hydraulic oil generated by the discharge stroke of the pump plunger 62 is communicated from the pump discharge port 81a to the pump discharge passage 81b, the first circuit oil passage La (inner oil chamber), and the communication state therewith. It flows into the cylinder hole 71 of the motor plunger 72 in the expansion stroke through the path 83 and gives thrust to the motor plunger 72. On the other hand, the hydraulic oil discharged by the motor plunger 72 in the contraction stroke is transferred to the suction stroke via the communication passage 83 communicating with the second circuit oil passage Lb (outer oil chamber), the pump suction passage 82b, and the pump suction port 82a. It flows into a cylinder hole 61 of a pump plunger 62.

The circulation of the hydraulic oil causes the pump plunger 62 in the discharge stroke to move to the motor cylinder via the pump swash plate ring 63.
Reaction torque given to 70 and motor plunger of expansion stroke
The sum of the reaction torque that 72 receives from the motor swash plate member 73 drives the motor cylinder 70 to rotate.

The gear ratio of the motor cylinder 70 to the pump cylinder 60 is given by the following equation.

As can be seen from the above equation, if the swash plate member 73 is swung by the shifting servo unit 30 and the displacement of the hydraulic motor M is changed from 0 to a certain value, the gear ratio is from 1 (minimum value) to a required value ( Maximum value).

On the other hand, as described above, the fourth portion 70 of the motor cylinder 70
d is a gear member having first and second drive gears 21 and 22
The GM is press-fitted and fixed, and the rotational driving force of the motor cylinder 70 is transmitted to the output shaft 28 via the forward / reverse switching device 20. This device 20 includes these first and second drive gears 21,2.
2, a first driven gear 23 that is rotatably supported by the output shaft 28 and that meshes with the first drive gear 21, and a second driven gear 22 that meshes with the second drive gear 22 via an intermediate gear (not shown). A second driven gear 25 rotatably supported on the clutch 28, a clutch hub 26 fixed to the output shaft 28 between the first and second driven gears 23, 25, and an axially slidable clutch hub 26.
And a sleeve 27 that selectively connects the clutch gear 23a or 25a formed on the side surfaces of the driven gears 23 and 25, respectively, and the sleeve 27 is moved left and right by a shift fork 29.

In this forward / reverse switching device 20, when the sleeve 27 is slid to the left in the drawing by the shift fork 29 and the clutch gear 23a of the first driven gear 23 and the clutch hub 26 are connected, the output The shaft 28 is rotated in the direction opposite to the rotating shaft 2, and the wheels are rotated in the forward direction as the continuously variable transmission T is driven. On the other hand, the sleeve 27 is slid to the right by the shift fork 29, and the clutch gear 25a of the second driven gear 25 is moved.
And the clutch hub 26 are connected, the output shaft
28 is rotated in the same direction as the rotating shaft 2, and the wheels are rotated in the reverse direction.

The output shaft 28 is connected to the differential device 100 via the final gear sets 28a and 28b, and the rotational driving force of the output shaft 28 is transmitted to the differential device 100. Then, the rotational drive force divided into the left and right drive shafts 105, 106 by the differential device 100 is
The vehicle is driven by being transmitted to the left and right wheels (not shown).

In addition, the fixed shaft 91 inserted in the hollow portion of the fourth portion 70d.
A sixth circuit oil passage Lf, which is a short-circuit passage between the first circuit oil passage La and the second circuit oil passage Lb, is formed therein, and a main clutch valve CL capable of controlling the short-circuit passage from fully closed to fully open and A direct coupling clutch valve DC that can control the connection and disconnection of the first circuit oil passage La is provided.

First, the main clutch valve CL will be described. Fixed shaft 91
A short-circuit port 91a that allows the first oil passage La and the second oil passage Lb to communicate with each other is formed on the peripheral wall of the cylindrical main clutch valve body 95 inserted into the hollow portion of the fixed shaft 91. ing. The valve body 95 is rotatable relative to the fixed shaft 91 and has a short-circuit hole 95a that can be aligned with the short-circuit port 91a. By rotating the arm 96 formed at the right end of the valve body 95, the valve body 95 can be rotated to adjust the amount of alignment (overlap) between the short circuit port 91a and the short circuit hole 95a. . The size of this matching portion is determined by the size of the first oil passage La and the second oil passage.
The opening of the short-circuit oil passage (sixth circuit oil passage Lf) with Lb is set. Therefore, the opening degree of the sixth circuit oil passage Lf is controlled from fully open to fully closed by the rotation control of the valve body 95. You can If the opening degree of the sixth circuit oil passage Lf is fully open, the pump discharge port 81a
The hydraulic oil discharged from the first oil passage La from the short-circuit port 91a
Also, the hydraulic motor M flows directly into the second oil passage Lb from the short-circuit hole 95a and into the pump suction port 82a.
Turns off and the main clutch is turned off. Of course, conversely, when the opening degree of the sixth circuit oil passage Lf is fully closed, the main clutch ON state is realized.

In this case, the short-circuit port 91a and the short-circuit hole 95a
There is a limit to increasing the flow passage area of, and when the oil temperature is low, there is a case where a complete neutral state cannot be obtained only by turning off the main clutch CL. Therefore, in this example, the distribution ring 92 is separated from the distribution board 80, and the first circuit oil passage La and the second circuit oil passage Lb are directly communicated with each other so that a reliable neutral state can be realized.

The distribution ring 92 is eccentrically positioned with respect to the fixed shaft 91, and is attached so as to be movable in the axial direction. Further, with the distribution ring 92 attached to the fixed shaft 91, the fixed shaft 91
Two annular hydraulic chambers 93, 94 are formed between the two. These hydraulic chambers 93, 94 are respectively connected to the first circuit oil passage La and the second circuit oil passage Lb via small holes (introduction passages with throttle) 92c, 92d formed in the distribution ring 92, and the fixed shaft 91
It is connected to the first and second neutral control lines (exhaust paths) L ₁₁ and L ₁₂ shown in FIG. 1 through the small holes 91b and 91c formed in the.

Therefore, when the transmission is in the neutral state and the third neutral control line L ₁₃ is communicated with the drain by the neutral control valve 130,
Since the first and second neutral control lines L ₁₁ and L ₁₂ are also communicated with the drain, the hydraulic pressure in the hydraulic chambers 93 and 94 decreases. When the hydraulic pressure in the hydraulic chambers 93, 94 decreases, the distribution ring 92 receives the hydraulic pressures of the first and second circuit oil passages La, Lb and is moved rightward in the figure to separate from the distribution board 80. Therefore, the first circuit oil passage La and the second circuit oil passage Lb are directly communicated with each other, and a reliable neutral state is established.

When the transmission is other than neutral, the hydraulic pressure control valve 140 passes through the fourth neutral control line L ₁₄ and the hydraulic chamber 13
The third neutral control line L ₁₃ is closed by the spool 131 by the hydraulic pressure supplied to 4. In this case, the first and second neutral control lines L ₁₁ and L ₁₂ are also closed, and the hydraulic chambers 93 and 94 are
The hydraulic pressure inside communicates via the small holes 92c and 92d, respectively.
And becomes equal to the hydraulic pressure of the second circuit oil passages La and Lb. Therefore, the oil pressure acting on the distribution ring 92 is balanced and the distribution ring 92
Is urged by a spring 97 and comes into sliding contact with the distribution board 80.

The direct coupling clutch valve DC is provided in the center of the hollow main clutch valve body 95, and is a piston shaft that is movable in the axial direction.
85, a shoe 86 attached to the tip of the piston shaft 85, and a pilot spool located inside the piston shaft 85.
It consists of 84 and. A servo mechanism is provided between the piston shaft 85 and the pilot spool 84, and the piston shaft 85 follows the pilot spool 84 and is moved in the axial direction. Therefore, if the pilot spool 84 is moved to the left to move the piston shaft 85 to the left and the shoe 86 closes the pump discharge passage 81b, the direct connection state between the hydraulic pump P and the hydraulic motor M is realized.

C. EFFECTS OF THE INVENTION As described above, according to the present invention, by operating the neutral state creating means to separate the distribution ring in sliding contact with the distribution plate from the distribution plate, the pump discharge path and the motor suction by the distribution ring. The communication with the passage and the communication between the pump suction passage and the motor discharge passage can be removed, and the pump discharge passage and the pump suction passage can be directly communicated with each other. Therefore, the neutral state can be obtained without using the short-circuit path and the clutch valve as in the conventional case. In this case, the pump discharge path and the pump suction path are directly communicated with each other, so that the neutral state can be reliably realized. Moreover, if a short-circuit passage for short-circuiting the pump discharge passage and the pump suction passage through the first and second oil passages is provided in parallel with the communication space, and the opening degree of the short-circuit passage is controlled by the clutch valve. It is also possible to perform fine gear ratio control based on half-clutch control or the like. If the neutral state creating means is configured by a hydraulic chamber that generates hydraulic pressure in the direction of sliding the distribution ring to the distribution board and an opening / closing means that discharges hydraulic pressure from the hydraulic chamber, a pulling force or the like is applied to the distribution ring. As compared with the case of detaching from the distribution board by a simple operation, the transition control to the neutral state can be performed more quickly with a simple and compact structure.

[Brief description of drawings]

FIG. 1 is a hydraulic circuit diagram of a hydraulic continuously variable transmission according to the present invention, FIG. 2 is a sectional view of the hydraulic continuously variable transmission, and FIG. 3 is an enlarged sectional view showing a part of this transmission. It is a figure. 1 ... Input shaft, 20 ... Forward / reverse switching device 80 ... Distribution board, 81b ... Pump discharge passage 92 ... Distribution ring, 95 ... Clutch valve body 130 ... Neutral control valve

Claims (2)

[Claims] 1. A hydraulic pump connected to an input shaft, a hydraulic motor connected to an output shaft, and a hydraulic closed circuit hydraulically connecting the hydraulic pump and the hydraulic motor to each other. In a hydraulic continuously variable transmission in which at least one of a hydraulic pump and a hydraulic motor is of a variable displacement type, a pump discharge passage and a pump suction passage communicating with a discharge port and a suction port of the hydraulic pump, and a discharge of the hydraulic motor. A distribution board formed with a motor discharge passage and a motor suction passage, which communicate with the outlet and the suction opening, respectively, and a sliding contact with the distribution board, and the pump discharge passage and the motor suction passage according to the rotation of the hydraulic pump and the hydraulic motor. A distribution ring that divides and forms a first oil passage that communicates with the second oil passage that communicates with the pump suction passage and the motor discharge passage; Is arbitrarily moved in a direction away from the distribution plate with which the distribution ring is in sliding contact, and the pump discharge path and the pump suction path are directly communicated with each other through a communication space formed between the distribution plate and the sliding contact surface of the distribution ring. A neutral state creating means; and a short-circuit path that is provided in parallel with the communication space in the hydraulic closed circuit and short-circuits the pump discharge path and the pump suction path through the first oil path and the second oil path, and A hydraulic continuously variable transmission, comprising: a clutch valve that controls an opening degree of a short-circuit path. 2. The neutral state creating means faces a surface of the distribution ring opposite to the sliding contact surface, and generates a hydraulic pressure in a direction of slidingly contacting the distribution ring with the distribution board. An introduction path with a throttle for introducing the hydraulic pressure acting on the sliding contact surface side into the hydraulic chamber, a discharge path for discharging the hydraulic pressure from the hydraulic chamber, and the sliding ring for sliding the distribution ring onto the distribution plate. The hydraulic continuously variable transmission according to claim 1, further comprising: an opening / closing unit that closes the discharge passage and opens the discharge passage when moving the distribution ring away from the distribution board. Machine.