JP7585997B2 - Work vehicles - Google Patents

Description

The present invention relates to work vehicles such as agricultural tractors and lawnmowers, and in particular to work vehicles equipped with a hydraulic clutch that switches between operating and deactivating the PTO.

The PTO drive system for riding lawn mowers includes a blower/mower drive system. For example, a known configuration has a blower drive hydraulic clutch and a mower drive hydraulic clutch for turning the blower on and off, and the blower drive hydraulic clutch and the mower drive hydraulic clutch are turned on and off by a hydraulic control device that uses a solenoid valve and a controller, respectively (Patent Document 1).

JP 2008-154547 A

However, in Patent Document 1, there were problems such as excessive load being placed on each power shaft and shock occurring when the hydraulic clutch for driving the blower or mower was suddenly connected.

In view of the above, the present invention aims to provide a work vehicle that can gradually increase clutch pressure when engaging a PTO hydraulic clutch.

This invention takes the following technical measures to solve the above problems:

The invention described in claim 1 is a work vehicle having a hydraulic clutch 42 in a power transmission path to a PTO shaft 41, and is provided with a PTO valve 55 that switches between a pressure oil supply state to the hydraulic clutch 42 and a pressure oil return state from the hydraulic clutch 42 to a tank. A relief valve 57 is provided in a branch oil path 58 that branches off from a supply oil path 56 from the PTO valve 55 to the hydraulic clutch 42. A two-position changeover valve 59 is disposed midway along the branch oil path 58 to connect or block the branch oil path 58 to the relief valve 57. A first restriction 60 is provided between the two-position changeover valve 59 and the relief valve 57, and when the pressure difference before and after the first restriction becomes a predetermined value or more, the branch oil path 58 is switched to the cutoff side.

The invention described in claim 2 is the invention described in claim 1, in which when the two-position switching valve 59 switches the branch oil passage 58 to the shutoff side, the pressurized oil of this valve 59 is returned from the tank port to the tank via the return oil passage 63, and a second throttle 64 is provided in this return oil passage 63.

The invention described in claim 3 is the invention described in claim 2, in which the downstream of the second throttle 64 is connected to a tank at atmospheric pressure.

The invention described in claim 4 is the invention described in claim 2, wherein the two-position switching valve 59
The two-position changeover valve 59 is provided upstream of the first throttle 60 between the pressure regulator 57 and the relief valve 57.
A pilot passage 65 connected to the upstream side of the second throttle 64 of the return oil passage 63 is connected to a pilot passage 62 which can be switched to the cut-off side of the branch oil passage 58, and the cut-off side of the branch oil passage 58 is maintained by the two-position changeover valve 59 with the pressure upstream of the second throttle 64. A shuttle valve 66 is provided which applies to the two-position changeover valve 59 the higher pilot pressure of either the pilot passage 62 connected to the upstream side of the first throttle 60 or the pilot passage 65 connected to the upstream side of the second throttle 64.

According to the invention described in claim 1, when pressure oil is supplied to the hydraulic clutch 42, the pressure difference before and after the first throttle 60 does not become large during the piston stroke in the hydraulic clutch 42, so the piston member 42c can be moved with the pressure controlled by the relief valve 57. When the stroke end is reached, the pressure upstream of the first throttle 60 rises and the two-position changeover valve 59 switches, the relief valve 57 no longer functions, and the pressure is switched to a high pressure to supply pressure oil to the hydraulic clutch 42, allowing smooth clutch engagement.

According to the invention described in claim 2, in addition to the effect described in claim 1, the two-position switching valve 59 maintains the path from the branch oil passage 58 to the return oil passage 63 at high pressure, so that the branch oil passage 58 can be kept switched to the shutoff side.

According to the invention described in claim 3, in addition to the effect described in claim 2, it is possible to suppress the increase in internal pressure caused by the increase in the oil temperature of the returning pressurized oil, thereby preventing malfunction.

According to the invention described in claim 4, in addition to the effect described in claim 2, pilot pressure leakage can be reduced whether the branch oil passage 58 is switched to the blocking side by the two-position switching valve 59 or the switching is maintained.

1 is a side view of a riding lawnmower according to an embodiment of the present invention. FIG. 2 is an overall hydraulic circuit diagram of the riding lawnmower of FIG. 1 . FIG. 3 is a hydraulic circuit diagram for the PTO hydraulic clutch of FIG. 2 . 1 is a hydraulic circuit diagram relating to a PTO hydraulic clutch of a work vehicle according to an embodiment of the present invention.

Below, an embodiment of the present invention will be described in detail with reference to the drawings.

A side view of the riding lawnmower 1 of this embodiment is shown in Figure 1.

The vehicle body 1 is equipped with front wheels 2, 2 and rear wheels 3, 3 at the front and rear, respectively, and a mower 5 for cutting grass with a cutting blade 4 is provided below the front of the vehicle body 1 and in front of the front wheels 2, 2, constituting a so-called front mower. A steering column 7 is erected on the floor 6 above the front of the vehicle body 1, and a steering handle 8 is provided on the top of the column 7. A driver's seat 9 is also provided behind the handle 8.

The frame structure of the vehicle body 1 is detailed below. It consists of a floor frame 10 that supports the floor 6 and the cockpit 9 from the front, a transmission case 12 that receives power from the engine 11 and houses a transmission system that drives the traveling speed change device (e.g., HST) and the mower 5, a safety guard frame 13 that is fixed to the upper part of the transmission case 12, and a pair of left and right side frames 14L, 14R that are connected to the lower end of the transmission case 12 and support the engine 11, etc.

The floor frame 10 has a U-shaped front when viewed from above, supports the column 7 at the front, and is provided at the rear to support the cockpit 9 and various levers and other operation boxes, with the left and right rear ends connected in an overlapping state to the left and right side surfaces 13L, 13R of the safety guard frame 13. The left and right support pillars 15L, 15R of the safety guard 15 are connected to the left and right side surfaces 13L, 13R of the safety guard frame 13, and the upper ends of these left and right support pillars 15L, 15R are connected to the head frame 15H. L-shaped case connection parts 13aL, 13aR are provided on the left and right lower sides of the safety guard frame 13, and are fixedly connected to the upper and rear surfaces of the transmission case 12, respectively, to obtain a strong rigid structure.

The transmission case 12 is part of the frame structure of the vehicle body 1 as described above, and the travel transmission cases 12aL, 12aR, which house the transmission endless belts and gears to the front wheels 2, 2, are mounted to the left and right ends of the transmission case 12 in a manner that allows transmission.

The upper frame 17 is constructed at a position slightly higher than the height of the engine 11. When viewed from above, the upper frame 17 is U-shaped, with a curved portion at the rear and the left and right front ends connected to nearby frames.

As shown in FIG. 1, behind the safety guard 15 and above the upper frame 17, a collector 32 is provided that collects grass cut via a lifting mechanism. The lifting mechanism includes a parallel-link lifting arm 33 and a lifting cylinder mechanism 34, one end of which is connected to safety guard frames 13L, 13R that support the safety guard 15, and the other end of which is connected to a collector frame 35 on which the collector 32 can be placed. The grass cut by the mower 5 is blown by a blower (not shown) and collected in the collector 32 via a bellows hose 36.

Next, the transmission mechanism inside the transmission case 12 is equipped with an HST 40, and is configured to transmit infinitely variable power to the front and rear wheels 2, 3. In addition, the transmission mechanism inside the transmission case 12 is branched to form a PTO that drives the mower 5, and the PTO shaft 41 is equipped with a hydraulic clutch 42, allowing the power to be turned on and off.

In FIG. 2, the rotational power of the engine 11 drives the pump 44 of the HST circuit 43, and the rotation of the motor 45 is controlled by swash plate control to output a variable speed, as is well known.

As shown in FIG. 3, the hydraulic clutch 42 provided in the power transmission path to the PTO shaft 41 has alternating driving side multi-plate plates 42a and driven side multi-plate plates 42b that are slidable in the axial direction, and when the piston member 42c advances in the axial direction while pressing the driving side plate 42a due to an increase in back pressure, the driving side multi-plate plate 42a and the driven side multi-plate plate 42b are pressed together in a predetermined manner to enable power transmission. Pressurized oil from the hydraulic pump 46 is introduced into the PTO control valve 48 via a pressure reducing valve 47, and the hydraulic clutch 42 is supplied or discharged by switching the PTO control valve 48, allowing power to be switched on and off.

As shown in the detailed view of FIG. 3, the PTO control valve 48 is in the form of a three-position switching valve and has solenoids 48a and 48b on both sides. First, the solenoid 48a is excited, and the pressure oil supplied from the pressure reducing valve 47 is supplied to the hydraulic clutch 42 from port B via the supply oil passage 49. After the clutch stroke is reached, the solenoid 48b is switched to excitation, and the pressure oil supplied from port A is supplied to the hydraulic clutch 42 from the joint supply oil passage 49. When the solenoid 48a is excited and pressure oil is supplied from port B, a throttle 50 is provided in the return path to the tank port T to enable pressure reduction control until the stroke end is reached. On the other hand, when the solenoid 48b is excited and pressure oil is supplied from port A, the return path to the tank port T is blocked, so the entire amount and total pressure are supplied to the hydraulic clutch 42. Therefore, there is little risk of sudden power connection when the clutch is engaged.

However, in the case of the PTO control valve 48 in Figures 2 and 3, there is a large variation in the output pressure and flow rate due to the pressurized oil during the piston stroke, and a time lag occurs between when the piston reaches the end of the stroke and when full pressure is applied. In light of these circumstances, we have made the improvements shown in Figure 4.

In FIG. 4, a two-position switching PTO valve 55 is provided that is equipped with a solenoid 55a and switches between a pressure oil supply state to the hydraulic clutch 42 and a tank return state of the pressure oil from the hydraulic clutch 42. A relief valve 57 is provided by branching a supply oil line 56 from the PTO valve 55 to the hydraulic clutch 42, and a two-position switching valve 59 is disposed in the middle of the branch oil line 58 to connect or block the oil line to the relief valve 57. A first throttle 60 is provided on the upstream side of the relief valve 57, i.e., between the two-position switching valve 59 and the relief valve 57. A pilot circuit 61 is provided on the downstream side of the first throttle 60, which biases the two-position switching valve 59 to the branch oil line 58 connection side by the pressure on the downstream side, and a pilot path 62 is provided on the upstream side that can switch the two-position switching valve 59 to the branch oil line 58 cut-off side by receiving the pressure on the upstream side, and when the pressure difference before and after the first throttle 60 becomes equal to or greater than a predetermined value, the branch oil line 58 is switched to the cut-off side.

Therefore, when the solenoid 55a of the PTO valve 55 is excited to supply pressurized oil to the hydraulic clutch 42, the pressure difference before and after the first orifice 60 does not become large during the piston stroke in the hydraulic clutch 42, so the piston member 42c can be moved with the pressure controlled by the relief valve 57. When the stroke end is reached, the pressure upstream of the first orifice 60 rises and the two-position changeover valve 59 switches, the action of the relief valve 57 is eliminated, and the pressure is switched to a high pressure to supply pressurized oil to the hydraulic clutch 42, allowing smooth clutch engagement.

When the two-position changeover valve 59 switches the branch oil passage 58 to the shutoff side, the pressurized oil of this valve 59 flows back to the tank from the tank port via the return oil passage 63, and a second throttle 64 is provided in this return oil passage 63. With this configuration, the two-position changeover valve 59 can maintain the state in which the branch oil passage 58 is switched to the shutoff side because the route from the branch oil passage 58 to the return oil passage 63 is maintained at high pressure. In addition, the downstream of the second throttle 64 is configured to communicate with the tank at atmospheric pressure, which suppresses the internal pressure rise caused by the rise in the oil temperature of the returning pressurized oil, etc., and prevents malfunction.

In addition, a pilot path 65 connected to the upstream side of the second throttle 64 of the return passage 63 is connected to a pilot path 62 that is provided upstream of the first throttle 60 between the two-position switching valve 59 and the relief valve 57 and can switch the two-position switching valve 59 to the branch oil passage 58 blocking side, and the branch oil passage 58 blocking side is maintained by the pressure upstream of the second throttle 64 by the two-position switching valve 59. A shuttle valve 66 is provided to apply the higher pilot pressure to the two-position switching valve 59, either the pilot path 62 connected to the upstream side of the first throttle 60 or the pilot path 65 connected to the upstream side of the second throttle 64. This makes it possible to reduce pilot pressure leakage regardless of whether the two-position switching valve 59 is switching to the branch oil passage 58 blocking side or maintaining the switching state.

In the above embodiment, the PTO hydraulic clutch of a lawnmower was described, but the clutch can also be applied to PTO hydraulic clutches of agricultural tractors, industrial vehicles, etc.

In the hydraulic circuit of FIG. 2, a portion of the pressure oil to the pressure reducing valve 47 is introduced into the steering-linked hydraulic circuit 70. The steering-linked hydraulic circuit 70 operates the steering cylinder 71 in conjunction with the turning steering of the steering wheel 8, contributing to the steering of the front wheels.

In addition, the pressurized oil that bypasses the steering-linked hydraulic circuit 70 is introduced into the lift hydraulic circuit 72. The lift cylinder mechanism 34 is configured to extend and retract by switching the lift hydraulic circuit 72.

41 PTO shaft 42 hydraulic clutch 55 PTO valve 57 relief valve 58 branch oil passage 59 two-position changeover valve 60 first throttle 62 pilot passage 63 return oil passage 64 second throttle 65 pilot passage 66 shuttle valve

Claims (4)

A work vehicle having a hydraulic clutch (42) in a power transmission path to a PTO shaft (41), a PTO valve (55) that switches between a pressure oil supply state to the hydraulic clutch (42) and a pressure oil return state from the hydraulic clutch (42) to a tank, a relief valve (57) in a branch oil path (58) that branches off a supply oil path (56) from the PTO valve (55) to the hydraulic clutch (42), a two-position switching valve (59) that connects or cuts off the branch oil path (58) to the relief valve (57) is disposed midway in the branch oil path (58), a first throttle (60) is provided between the two-position switching valve (59) and the relief valve (57), and when the pressure difference before and after the first throttle (60) becomes a predetermined value or more, the branch oil path (58) is switched to the cut-off side. The work vehicle according to claim 1, in which when the two-position changeover valve (59) switches the branch oil passage (58) to the shutoff side, the pressurized oil of this valve (59) is returned from the tank port to the tank via the return oil passage (63), and a second throttle (64) is provided in this return oil passage (63). A work vehicle as described in claim 2, in which the downstream of the second throttle (64) is connected to a tank at atmospheric pressure. 3. The work vehicle according to claim 2, further comprising a pilot path (65) connected to the upstream side of a second throttle (64) of the return oil path (63) connected to a pilot path (62) that is provided upstream of a first throttle (60) between the two-position changeover valve (59) and the relief valve (57) and that can switch the two-position changeover valve (59) to a branch oil path (58) cut-off side, and configured so that the branch oil path (58) cut-off side is maintained by the two-position changeover valve (59) with the pressure upstream of the second throttle (64), and further comprising a shuttle valve (66) that applies to the two-position changeover valve (59) the pilot pressure which is higher, either the pilot path (62) connected to the upstream side of the first throttle (60) or the pilot path (65) connected to the upstream side of the second throttle (64).

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