JP3623105B2 - Travel transmission for work vehicle - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a traveling transmission that uses a hydrostatic continuously variable transmission (hereinafter abbreviated as HST) used in a work vehicle such as a tractor.
[0002]
[Prior art]
A neutral valve is connected to the drive oil passage that connects the axial plunger type variable displacement pump and the constant displacement motor, so that the motor will not be driven and rotated even if the pump is not returned to the neutral point exactly. The area is secured. This neutral valve is interposed between the motor drive oil passage and the drain oil passage, and incorporates a valve body such as a poppet that operates using the pressure of the motor drive oil passage as a pilot pressure.
[0003]
This valve body is spring-biased in the valve-opening direction that connects the motor drive oil passage and the drain oil passage, so that the discharge amount from the pump is reduced and the pilot pressure (pressure of the motor drive oil passage) is reduced. When the pressure drops, the valve opens with a spring so that even if a small amount of oil is discharged from the pump, it is not supplied to the motor.When the discharge from the pump increases and the pilot pressure rises, it closes against the spring. The valve operates to supply the entire amount of oil discharged from the pump to the motor, and FIG. 5 shows the characteristics of a conventional neutral valve. This shows the relationship between the flow rate Q passing through the neutral valve and the effective pressure P, and some hysteresis is given between the process of increasing and decreasing the flow rate. In the example, the vehicle body is set to start moving when the effective pressure P is 35 to 40 kg / cm @ 2.
[0004]
[Problems to be solved by the invention]
The neutral valve has a built-in throttle that operates when oil from the motor drive oil passage is allowed to pass when the valve is opened. The neutral valve is pumped from the neutral state (the pump discharge is zero or very small). If the discharge amount is increased, that is, if the speed change lever, shift pedal, etc. are operated from the neutral position to the speed increasing side and the aircraft is started, the differential pressure before and after the throttle will increase as the pump discharge amount increases. And the differential pressure (effective pressure) acts as a pilot pressure that operates the valve body in the valve closing direction. In this case, when the effective pressure reaches the vicinity of the pressure at which the vehicle body starts to move, the valve body closes, the amount of oil passing through the neutral valve becomes zero, and the pressure in the motor drive oil passage increases rapidly. Therefore, there was a tendency to give some shock to starting on a flat surface or a road surface with a low driving load.
[0005]
In addition, if the speed change lever, speed change pedal, or the like is decelerated from a certain travel shift position to a neutral position, the pressure in the motor drive oil passage decreases as the pump discharge decreases, and the pressure in the motor drive oil passage decreases. The valve body of the neutral valve that was held in the closed state with the pilot pressure as the pilot pressure is opened by the spring force, but according to the conventional example, the pressure of the motor drive oil passage is near the pressure at which the vehicle body starts moving When the pressure drops to the level, the neutral valve body suddenly closes and operates, and the vehicle body stops at once, so-called "shaking" may be experienced.
[0006]
The present invention has been made paying attention to such points, and it is an object of the present invention to provide a traveling transmission that can suppress a shock at the time of aircraft start and a “shake” at the time of aircraft stop.
[0007]
[Means for Solving the Problems]
[Configuration, operation and effect of the invention according to claim 1]
[0008]
(Structure) The invention according to claim 1 incorporates a valve body in which a pump discharge pressure is applied as a pilot pressure for valve closing into a neutral valve in a hydrostatic continuously variable transmission, and more than a throttle provided in the neutral valve. An orifice is provided in the input oil passage on the upper side,
In the relationship between the flow rate that passes through the neutral valve and the effective pressure that presses the valve body in the valve closing direction based on the differential pressure across the throttle, the process of transitioning from the open state to the closed state of the neutral valve; , Giving hysteresis between the transition from the closed state to the open state ,
The effective pressure at which the neutral valve is completely closed is set higher than the effective pressure at which the vehicle body starts to move and the effective pressure at which the neutral valve starts to operate in the valve opening direction from the closed state.
[0009]
(Operation) According to the above configuration, when the pump discharge amount is increased from the neutral state where the neutral valve is open, the oil in the motor drive oil passage flows into the drain oil passage through the neutral valve. However, since the orifice is located in the input oil passage on the upper side of the throttle of the neutral valve, the amount of oil flowing into the neutral valve is suppressed by the resistance of the orifice even if the pump discharge amount increases, and the difference in the throttle of the neutral valve The pressure rise becomes slow. In other words, the sudden operation in the valve closing direction of the valve body in the neutral valve is suppressed, and the neutral valve is completely closed after the pressure of the motor drive oil passage becomes high, that is, after the vehicle body starts moving, Start without shock.
[0010]
In addition, when a deceleration operation from a certain traveling speed change state to neutral is performed, the oil pressure decreases as the oil amount in the motor drive oil passage decreases, and the neutral valve operates in the open circuit direction. The orifice provided in the oil passage serves as a resistance for the operation of a valve body such as a poppet incorporated therein, and the opening operation is slowed down. As a result, the vehicle body is stopped without “shaking”.
[0011]
(Effect) Therefore, according to the invention according to claim 1, it is possible to smoothly start and stop without a shock at the time of airframe start and “shake” at the time of airframe stop.
[0012]
[Configuration, operation and effect of invention of claim 2]
[0013]
(Structure) According to a second aspect of the present invention, in the first aspect of the present invention, the orifice is formed in a plug that is detachably incorporated in the input port of the valve body.
[0014]
(Operation) According to the above configuration, a plurality of types of plugs having orifices with different opening degrees are prepared, and this is replaced with an input port of the valve body to form a neutral valve with different characteristics. Can do.
[0015]
(Effect) Therefore, according to the invention according to claim 2, it becomes easy to provide orifices having different opening degrees corresponding to different starting torques depending on the weight of the airframe, the type of attachment to be attached, and the like. By using a neutral valve in a state suitable for the above specifications, it is possible to smoothly start and stop without shock or “shake”.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates an agricultural tractor as an example of a work vehicle including a traveling transmission apparatus according to the present invention. This agricultural tractor is provided with an engine 4 at the front of a vehicle body 3 having front wheels 1 and rear wheels 2, and transmits engine output to a hydrostatic continuously variable transmission (hereinafter abbreviated as HST) 5. The transmission output of the HST 5 is transmitted to the gear mission case 6 to drive the rear wheel 2, and the front wheel 1 is driven in synchronization with the rear wheel 2, and a part of the engine output is branched directly without passing through the HST 5. Is transmitted to the PTO shaft 7 at the rear of the vehicle body.
[0017]
FIG. 2 shows the HST hydraulic circuit. In the figure, 11 is an axial plunger type pump configured as a variable capacity driven by engine output, 12 is an axial plunger type motor configured as a fixed capacity, and 13 is a forward rotation drive (forward drive). ), A motor drive oil passage that becomes high pressure, 14 is a motor drive oil passage that becomes high pressure when the motor 12 is driven in reverse rotation (reverse drive), and 15 is a trochoid arranged coaxially with the pump 11 and driven. Type charge pump, 16 is a charge relief valve that restricts the charge pressure, 17 is a check and high pressure relief valve that restricts the maximum pressure of the oil passage 13 for driving the motor and allows the flow of charge oil into the oil passage 13, 18 is a check-and-high-pressure relay that limits the maximum pressure of the oil passage 14 for driving the motor and allows the flow of charge oil into the oil passage 14. 19 is a case relief valve for limiting the hydraulic pressure in the case, 20 is a neutral valve connected to the motor drive oil passage 13, 21 is a neutral valve connected to the motor drive oil passage 14, and 22 is a filter for purifying the charge oil. , 23 is a filter for purifying the intake oil, 24 is an oil cooler for cooling the return oil, and the hydraulic circuit configuration itself is general.
[0018]
In the present invention, an orifice 25 is provided in each input oil passage of the neutral valve 20 for forward movement and the neutral valve 21 for backward movement.
[0019]
FIG. 3 shows a detailed structure of the cross section of the neutral valves 20 and 21. The neutral valves 20 and 21 are fitted and fixed to the valve body 27 screwed into the case of the HST 5, a poppet (valve element) 29 that slides at the input port 28, a spring 30 that slides and biases the valve body 27, The fixed spring receiver 31, the spring receiver 32 that is externally fitted to the poppet 29, the plug 33 that is screwed into the input port 28, etc., and the poppet 29 is slid to the movement limit by the spring 30, A passage for communicating the input port 28 and the oil discharge port 34 provided in the valve body 27 is formed in the throttle 35. The orifice 25 is formed as a small-diameter hole formed in the plug 33.
[0020]
FIG. 4 shows the relationship between the flow rate Q passing through the neutral valves 20 and 21 having the above-described configuration and the effective pressure P that presses the poppet 29 in the valve closing direction based on the differential pressure before and after the throttle 35. A large hysteresis is given between the process of increasing and decreasing the flow rate. In addition, the vehicle body 3 is set to start moving when the effective pressure P is 35 to 40 kg / cm ² .
[0021]
Therefore, when the pump discharge amount is increased from the neutral state in which the neutral valves 20 and 21 are opened to the forward side, the pressure at the upper side of the throttle 35 in the forward side neutral valve 21 increases, and the vehicle body 3 starts moving. Even when the vehicle body 3 starts to move, the pressure rises slowly, and the vehicle speed gradually increases. When the poppet 29 is completely closed, the flow rate passing through the neutral valve 20 becomes zero, the entire amount of pressure oil from the pump 11 is supplied to the motor 12, and traveling at a speed corresponding to the discharge amount is performed.
[0022]
In addition, when a deceleration operation from a certain forward travel shift state to neutral is performed, the hydraulic pressure is reduced as the amount of oil in the motor drive oil passage 13 is reduced, but the neutral valve 20 is reduced to a set pressure. After the valve is kept closed until the set pressure is lowered, the poppet 29 starts to be displaced in the valve opening direction by the spring 30, and the flow rate flowing from the input port 28 to the oil discharge port 34 gradually increases. Eventually, the pressure in the oil passage 13 for driving the motor decreases to a pressure near the pressure at which the vehicle body 3 starts moving, and the vehicle body 3 stops.
[0023]
[Another embodiment]
The opening of the orifice 25 is configured to be adjustable by a needle valve that is advanced and retracted by a screw, or a plurality of types of plugs 33 having different orifice openings are prepared in advance, the weight of the vehicle body, the type of attachment to be attached, etc. The neutral valves 20 and 21 having specifications corresponding to the conditions in which the vehicle body is used may be configured and implemented.
[Brief description of the drawings]
FIG. 1 is an overall side view of an agricultural tractor. FIG. 2 is a hydraulic circuit diagram of a hydrostatic continuously variable transmission. FIG. 3 is a sectional view showing a neutral valve in an open state. FIG. 4 is a diagram showing the characteristics of a neutral valve used in the present invention. FIG. 5 is a diagram showing the characteristics of a conventional neutral valve.
5 Hydrostatic continuously variable transmission 20 Neutral valve 21 Neutral valve 25 Orifice 27 Valve body 28 Input port 33 Plug

Claims (2)

A valve body in which pump discharge pressure is given as a pilot pressure for closing the valve is incorporated into a neutral valve in the hydrostatic continuously variable transmission, and an orifice is provided in the input oil passage on the upper side of the throttle provided in the neutral valve .
In the relationship between the flow rate that passes through the neutral valve and the effective pressure that presses the valve body in the valve closing direction based on the differential pressure across the throttle, the process of transitioning from the open state to the closed state of the neutral valve; , Giving hysteresis between the transition from the closed state to the open state ,
The effective pressure at which the neutral valve is completely closed is set higher than the effective pressure at which the vehicle body starts to move and the effective pressure at which the neutral valve starts to operate in the valve opening direction from the closed state. Car travel transmission. The traveling transmission apparatus for a work vehicle according to claim 1, wherein the orifice is formed in a plug that is detachably incorporated in an input port of the valve body.

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