JP5670824B2

JP5670824B2 - Tractor

Info

Publication number: JP5670824B2
Application number: JP2011105342A
Authority: JP
Inventors: 貞治吉田
Original assignee: Kubota Corp
Current assignee: Kubota Corp
Priority date: 2011-05-10
Filing date: 2011-05-10
Publication date: 2015-02-18
Anticipated expiration: 2031-05-10
Also published as: JP2012236454A

Description

本発明は、操向操作自在な前輪を後輪の周速度と同等の周速度で駆動する標準駆動状態と前記後輪の周速度より速い周速度で駆動する増速駆動状態とに切換え自在な前輪変速機構を、前記標準駆動状態にスプリングによって切換え操作され、前記増速駆動状態に油圧アクチュエータによって切換え操作される状態で設け、前記油圧アクチュエータを油圧ポンプに接続する操作油路に、前記油圧ポンプからの油圧を前記油圧アクチュエータに供給する給油位置と前記油圧アクチュエータから油圧を排出する排油位置とに切換え自在な人為選択弁、牽制弁及び自動選択弁を直列に並べて設け、前記牽制弁を、走行用の変速機構が低速伝動状態にあると前記給油位置に自動的に切換え操作され、前記変速機構が高速伝動状態にあると前記排油位置に自動的に切換え操作されるように、前記変速機構に連係させ、前記自動選択弁を、前記前輪が設定切れ角以上の操向状態にあると前記給油位置に自動的に切換え操作され、前記前輪が前記設定切れ角未満の操向状態にあると前記排油位置に自動的に切換え操作されるように、前輪操向機構に連係させたトラクタに関する。 The present invention is switchable between a standard driving state in which the steerable front wheel is driven at a peripheral speed equivalent to the peripheral speed of the rear wheel and an increased driving state in which the front wheel is driven at a peripheral speed faster than the peripheral speed of the rear wheel. A front wheel speed change mechanism is provided in a state that is switched to the standard drive state by a spring and is switched to the speed increasing drive state by a hydraulic actuator, and the hydraulic pump is connected to an operation oil path that connects the hydraulic actuator to the hydraulic pump. An artificial selection valve, a check valve, and an automatic selection valve that can be switched between an oil supply position for supplying hydraulic pressure from the hydraulic actuator to an oil discharge position for discharging hydraulic pressure from the hydraulic actuator are provided side by side in series, When the traveling speed change mechanism is in a low-speed transmission state, the operation is automatically switched to the oil supply position, and when the speed change mechanism is in a high-speed transmission state, the oil discharge position is set. The automatic selection valve is linked to the speed change mechanism so as to be dynamically switched, and the automatic selection valve is automatically switched to the refueling position when the front wheel is in a steering state equal to or greater than a set cutting angle. The present invention relates to a tractor linked to a front wheel steering mechanism so that when the steering wheel is in a steering state less than the set cut angle, it is automatically switched to the oil draining position.

上記したトラクタは、畦際などにおける小旋回半径での旋回走行を可能にしたり、小旋回半径での旋回走行を牽制したりするものである。
すなわち、作業時など低速走行する場合、人為選択弁を給油位置に切換えておけば、畦際などで旋回走行する際、前輪を設定切れ角以上の操向状態に操向操作するだけで小旋回半径で旋回走行できる。つまり、前輪が設定切れ角以上に操向操作されて自動選択弁が給油位置に自動的に切換え操作されることにより、そして変速機構が低速伝動状態に変速されていて牽制弁が給油位置に切換えられていることにより、油圧アクチュエータに油圧が供給されて前輪変速機構が増速駆動状態に切換えられ、前輪が後輪より速い周速度で駆動される。 The above-described tractor enables turning traveling with a small turning radius at the shore or restrains turning traveling with a small turning radius.
In other words, when traveling at low speeds, such as during work, if the artificial selection valve is switched to the refueling position, when turning on the coast, etc., just turn the front wheel to a steered state greater than the set turning angle and make a small turn You can turn with a radius. In other words, when the front wheel is steered beyond the set cut angle, the automatic selection valve is automatically switched to the fueling position, and the speed change mechanism is shifted to the low-speed transmission state and the check valve is switched to the fueling position. As a result, the hydraulic pressure is supplied to the hydraulic actuator, the front wheel speed change mechanism is switched to the speed increasing drive state, and the front wheels are driven at a higher peripheral speed than the rear wheels.

作業時など低速走行する場合でも、人為選択弁を排油位置に切換えておけば、前輪を設定切れ角以上の操向状態に操向操作して自動選択弁が給油位置に切換え操作されても、そして変速機構が低速伝動状態に変速されていて牽制弁が給油位置に切換え操作されていても、人為選択弁が排油位置になっていることにより、油圧アクチュエータに油圧が供給されなくて前輪変速機構が標準駆動状態に維持され、前輪が後輪と同等の周速度で駆動されて旋回半径が標準の旋回半径になる。 Even when driving at low speeds, such as during work, if the artificial selection valve is switched to the oil draining position, the automatic selection valve can be switched to the oiling position by steering the front wheels to a steering state greater than the set cut angle. Even if the speed change mechanism is shifted to a low-speed transmission state and the check valve is switched to the oil supply position, the hydraulic actuator is not supplied with oil pressure because the artificial selection valve is in the oil discharge position. The speed change mechanism is maintained in the standard drive state, the front wheels are driven at the same peripheral speed as the rear wheels, and the turning radius becomes the standard turning radius.

移動時など高速走行する場合、人為選択弁が給油位置に切換えられていても、前輪が設定切れ角以上の切れ角に操向操作されて自動選択弁が給油位置に切換え操作されても、変速機構が高速伝動状態に変速されていて牽制弁が排油位置に切換え操作されていることにより、油圧アクチュエータに油圧が供給されずに前輪変速機構が標準駆動状態に維持され、前輪が後輪と同等の周速度で駆動されて旋回半径が標準の旋回半径になる。 When traveling at high speeds, such as when moving, even if the artificial selection valve is switched to the refueling position, even if the front wheel is steered to a turning angle greater than the set cutting angle and the automatic selection valve is switched to the refueling position, shifting Since the mechanism is shifted to a high-speed transmission state and the check valve is switched to the oil discharge position, the front wheel transmission mechanism is maintained in the standard drive state without supplying hydraulic pressure to the hydraulic actuator, and the front wheels are connected to the rear wheels. Driven at the same peripheral speed, the turning radius becomes the standard turning radius.

特開２００５−２６３１７０号公報JP-A-2005-263170

この種のトラクタとして、従来、例えば特許文献１に記載されたものがあった。特許文献１に記載されたものでは、前輪変速機構を増速駆動状態にバネに抗して切換え操作する油圧アクチュエータとしてのピストン部材を備え、人為選択弁としての自動変速選択バルブ、牽制弁としての牽制バルブ、自動選択弁としての前輪制御バルブを備えている。 Conventionally, for example, this type of tractor is described in Patent Document 1. The one described in Patent Document 1 includes a piston member as a hydraulic actuator that switches a front wheel speed change mechanism against a spring in a speed-up drive state, an automatic speed change selection valve as an artificial selection valve, and a check valve as a check valve. It is equipped with a check valve and a front wheel control valve as an automatic selection valve.

この種のトラクタにあっては、油圧アクチュエータと油圧ポンプに接続する操作油路にリリーフ弁を有するリリーフ油路を接続し、操作油路によって油圧アクチュエータに油圧供給する際の油圧が前輪変速機構をスプリングに抗して増速駆動状態に切換え得る油圧となるように、リリーフ弁によって油圧の設定を行なうように構成され、かつ、前輪変速機構が増速駆動状態に切り換わった後において油圧ポンプから操作油路に供給される油圧をリリーフ油路によって操作油路から排出するように構成される。
油圧ポンプから操作油路に供給される油圧を操作油路から取り出して静油圧式無段変速装置などに供給するのに、リリーフ油路から取り出すよう構成した場合、前輪変速機構を標準駆動状態に維持するよう油圧アクチュエータに対する油圧供給が行われない時においても、リリーフ弁を介して油圧を取り出すことになり、前輪変速機構が標準駆動状態に維持されている際の油圧ポンプの駆動による動力ロスが発生しがちであった。 In this type of tractor, a relief oil passage having a relief valve is connected to an operation oil passage connected to a hydraulic actuator and a hydraulic pump, and the hydraulic pressure when hydraulic pressure is supplied to the hydraulic actuator through the operation oil passage causes the front wheel transmission mechanism to The hydraulic pressure is set by a relief valve so that the hydraulic pressure can be switched to the speed increasing drive state against the spring, and the hydraulic pump after the front wheel transmission mechanism is switched to the speed increasing driving state. The hydraulic pressure supplied to the operation oil passage is configured to be discharged from the operation oil passage by the relief oil passage.
When the hydraulic pressure supplied from the hydraulic pump to the operating oil path is taken out of the operating oil path and supplied to the hydrostatic continuously variable transmission, etc. Even when the hydraulic pressure is not supplied to the hydraulic actuator so as to maintain, the hydraulic pressure is taken out via the relief valve, and there is no power loss due to the drive of the hydraulic pump when the front wheel transmission mechanism is maintained in the standard drive state. Tended to occur.

本発明の目的は、操作油路からの油圧取り出しを動力ロスの発生を抑制しながら行なえるトラクタを提供することにある。 An object of the present invention is to provide a tractor capable of taking out hydraulic pressure from an operation oil passage while suppressing generation of power loss.

本第１発明は、操向操作自在な前輪を後輪の周速度と同等の周速度で駆動する標準駆動状態と前記後輪の周速度より速い周速度で駆動する増速駆動状態とに切換え自在な前輪変速機構を、前記標準駆動状態にスプリングによって切換え操作され、前記増速駆動状態に油圧アクチュエータによって切換え操作される状態で設け、
前記油圧アクチュエータを油圧ポンプに接続する操作油路に、前記油圧ポンプからの油圧を前記油圧アクチュエータに供給する給油位置と前記油圧アクチュエータから油圧を排出する排油位置とに切換え自在な人為選択弁、牽制弁及び自動選択弁を直列に並べて設け、
前記油圧アクチュエータからの油圧が排出されるタンクを備え、
前記人為選択弁を、人為操作によって前記給油位置と前記タンクに直接つながる前記排油位置とに切換え操作されるように構成し、
前記牽制弁を、走行用の変速機構が低速伝動状態にあると前記給油位置に自動的に切換え操作され、前記変速機構が高速伝動状態にあると前記タンクに直接つながる前記排油位置に自動的に切換え操作されるように、前記変速機構に連係させ、
前記自動選択弁を、前記前輪が設定切れ角以上の操向状態にあると前記給油位置に自動的に切換え操作され、前記前輪が前記設定切れ角未満の操向状態にあると前記タンクに直接つながる前記排油位置に自動的に切換え操作されるように、前輪操向機構に連係させ、
前記排油位置に切換えられた前記人為選択弁によって前記操作油路に対する開き状態に操作されて前記油圧ポンプからの油圧取出しが可能となり、前記給油位置に切換えられた前記人為選択弁によって前記操作油路に対する閉じ状態に操作される人為選択取出し油路と、
前記排油位置に切換えられた前記牽制弁によって前記操作油路に対する開き状態に操作されて前記油圧ポンプからの油圧取出しが可能となり、前記給油位置に切換えられた前記牽制弁によって前記操作油路に対する閉じ状態に操作される牽制取出し油路と、
前記排油位置に切換えられた前記自動選択弁によって前記操作油路に対する開き状態に操作されて前記油圧ポンプからの油圧取出しが可能となり、前記給油位置に切換えられた前記自動選択弁によって前記操作油路に対する閉じ状態に操作される自動選択取出し油路と、
前記油圧アクチュエータに供給される油圧を設定するリリーフ弁を有した状態で、前記操作油路の前記人為選択弁、前記牽制弁及び前記自動選択弁よりも上流側に位置する部位から分岐するように前記操作油路に接続されたリリーフ油路と、
前記人為選択取出し油路、前記牽制取出し油路、前記自動選択取出し油路及び前記リリーフ油路から油圧取出しを行なう油圧取出し油路とを設けてある。 The first aspect of the present invention switches between a standard driving state in which a steerable front wheel is driven at a peripheral speed equivalent to the peripheral speed of the rear wheel and an increased driving state in which the front wheel is driven at a peripheral speed faster than the peripheral speed of the rear wheel. A free front wheel speed change mechanism is provided that is switched to the standard driving state by a spring and is switched to the speed increasing driving state by a hydraulic actuator,
An artificial oil selection valve that is switchable between an oil supply position for supplying the hydraulic pressure from the hydraulic pump to the hydraulic actuator and an oil discharge position for discharging the hydraulic pressure from the hydraulic actuator, to an operation oil path that connects the hydraulic actuator to a hydraulic pump; A check valve and an automatic selection valve are arranged in series,
A tank for discharging hydraulic pressure from the hydraulic actuator;
The human selection valve is configured to be switched to the oil supply position and the oil discharge position directly connected to the tank by human operation,
The check valve is automatically switched to the refueling position when the traveling speed change mechanism is in a low speed transmission state, and automatically to the oil discharge position directly connected to the tank when the speed change mechanism is in a high speed transmission state. Linked to the speed change mechanism so that it is switched to
The automatic selection valve is automatically switched to the refueling position when the front wheel is in a steering state equal to or greater than a set cut angle, and directly into the tank when the front wheel is in a steering state less than the set cut angle. Link to the front wheel steering mechanism so that it is automatically switched to the connected oil drain position ,
The manual selection valve switched to the oil discharge position is operated in an open state with respect to the operation oil passage, and hydraulic pressure can be taken out from the hydraulic pump. The operation oil is switched by the manual selection valve switched to the oil supply position. An artificially selected oil passage that is operated in a closed state with respect to the road;
The operation valve is operated in an open state with respect to the operation oil passage by the check valve switched to the oil discharge position, and hydraulic pressure can be taken out from the hydraulic pump, and the operation valve to the operation oil passage is enabled by the check valve switched to the oil supply position. A check-out oil passage that is operated in a closed state;
The automatic selection valve that has been switched to the oil discharge position is operated in an open state with respect to the operation oil passage, and hydraulic pressure can be taken out from the hydraulic pump, and the operation oil can be extracted by the automatic selection valve that has been switched to the oil supply position. An automatically selected oil passage that is operated in a closed state with respect to the road;
In a state where a relief valve for setting the hydraulic pressure supplied to the hydraulic actuator is provided, a branch is made from a portion located upstream of the artificial selection valve, the check valve and the automatic selection valve in the operation oil passage. A relief oil passage connected to the operation oil passage;
The artificial selection extraction fluid passage, said牽Seito out oil passage is provided with a hydraulic extraction fluid passage for performing hydraulic taken out of the automatic selection extraction oil passage and the relief oil passage.

本第１発明の構成によると、前輪変速機構を標準駆動状態に維持するよう油圧アクチュエータに対する油圧供給が行なわれない場合、人為選択弁、牽制弁及び自動選択弁の３つ又は２つ又は１つが排油位置に切換えられていたり排油位置に切換え操作されたりして、人為選択取出し油路、牽制取出し油路及び自動選択取出し油路の３つ又は２つ又は１つが対応する人為選択弁又は牽制弁又は自動選択弁によって操作油路に対する開き状態に操作されていたり操作されたりする。人為選択取出し油路、牽制取出し油路及び自動選択取出し油路の３つ又は２つが操作油路に対する開き状態に操作されていたり操作されたりした場合、油圧ポンプから操作油路に供給される油圧を、人為選択取出し油路、牽制取出し油路及び自動選択取出し油路のうち、操作油路に最上流側で連通している人為選択取出し油路又は牽制取出し油路又は自動選択取出し油路によって取り出し、この取出し油圧を油圧取出し油路によって取り出すことができる。人為選択取出し油路、牽制取出し油路及び自動選択取出し油路のうちの１つが操作油路に対する開き状態に操作されていたり操作されたりした場合、油圧ポンプから操作油路に供給される油圧を、操作油路に対する開き状態に操作されている人為選択取出し油路又は牽制取出し油路又は自動選択取出し油路によって取り出し、この取出し油圧を油圧取出し油路によって取り出すことができる。 According to the configuration of the first aspect of the present invention, when the hydraulic pressure is not supplied to the hydraulic actuator so as to maintain the front wheel transmission mechanism in the standard driving state, three, two, or one of the artificial selection valve, the check valve, and the automatic selection valve are An artificial selection valve or three or two or one of a manually selected take-out oil passage, a check-out take-out oil passage and an automatically selected take-out oil passage, which are switched to the drain oil position or operated to be switched to the drain oil position, or It is operated or operated in an open state with respect to the operation oil passage by a check valve or an automatic selection valve. The hydraulic pressure supplied from the hydraulic pump to the operating oil passage when three or two of the artificially selected take-out oil passage, the check-out take-out oil passage, and the automatic selection take-out oil passage are operated or operated in an open state with respect to the operation oil passage. Among the manually selected take-out oil passage, the check take-out oil passage, and the automatic select take-out oil passage, by the man-made select take-out oil passage, the check take-out oil passage, or the automatically selected take-out oil passage that communicates with the operation oil passage on the most upstream side. It can take out and this take-out hydraulic pressure can be taken out by a hydraulic take-out oil passage. If one of the artificially selected take-out oil passage, the check-out take-out oil passage, or the automatic select take-out oil passage is operated or operated in an open state with respect to the operation oil passage, the hydraulic pressure supplied from the hydraulic pump to the operation oil passage is increased. Then, it is possible to take out by the manually selected take-out oil passage, the check-out take-out oil passage or the automatically selected take-out oil passage that is operated in the open state with respect to the operation oil passage, and take out the hydraulic pressure from the oil take-out oil passage.

人為選択弁、牽制弁及び自動選択弁が給油位置に切換えられていたり切換え操作されたりした場合、人為選択取出し油路、牽制取出し油路及び自動選択取出し油路が人為選択弁又は牽制弁又は自動選択弁によって操作油路に対する閉じ状態に操作されていたり操作されたりして、操作油路から油圧アクチュエータに油圧が供給され、油圧アクチュエータに供給される油圧がリリーフ弁によって前輪変速機構の増速駆動状態への切換え操作に必要なものに設定され、前輪変速機構がスプリングに抗して増速駆動状態に切換え操作される。前輪変速機構が増速駆動状態に切り換わると、この後、油圧ポンプから操作油路に供給される油圧を、リリーフ油路に排出させてリリーフ油路から油圧取出し油路によって取り出すことができる。 When the selection valve, check valve, and automatic selection valve are switched to the lubrication position or switched, the artificial selection oil passage, the check extraction oil passage, and the automatic selection extraction oil passage are the artificial selection valve, check valve, or automatic. The hydraulic pressure is supplied from the operating oil passage to the hydraulic actuator by being operated in a closed state with respect to the operating oil passage by the selection valve, and the hydraulic pressure supplied to the hydraulic actuator is driven to increase the speed of the front wheel transmission mechanism by the relief valve. It is set to what is necessary for the switching operation to the state, and the front wheel transmission mechanism is switched to the acceleration drive state against the spring. When the front wheel transmission mechanism is switched to the speed increasing drive state, the hydraulic pressure supplied from the hydraulic pump to the operation oil passage can be discharged to the relief oil passage and taken out from the relief oil passage by the hydraulic take-out oil passage.

従って、前輪変速機構が標準駆動状態に維持されている場合、人為選択取出し油路又は牽制取出し油路又は自動選択取出し油によってリリーフ弁を介することなく取り出してリリーフ弁によって発生する取出し抵抗を受けずに済ませ、前輪変速機構が標準駆動状態に維持される場合の油圧ポンプの駆動負荷を軽減できる。 Therefore, when the front wheel speed change mechanism is maintained in the standard drive state, it is not subject to the extraction resistance generated by the relief valve by taking out without the relief valve by the manually selected take-out oil passage or the check take-out oil passage or the automatically selected take-out oil. Therefore, the driving load of the hydraulic pump when the front wheel transmission mechanism is maintained in the standard driving state can be reduced.

本第１発明の構成によると、油圧ポンプから操作油路に供給される油圧を、人為選択弁、牽制弁及び自動選択弁による流動抵抗を受けない状態でリリーフ油路に取り出すことができ、前輪変速機構が増速駆動状態に操作される場合の油圧ポンプの駆動負荷を軽減できる。 According to the configuration of the first aspect of the invention, the hydraulic pressure supplied from the hydraulic pump to the operation oil passage can be taken out to the relief oil passage without being subjected to flow resistance by the artificial selection valve, the check valve, and the automatic selection valve. The driving load of the hydraulic pump when the speed change mechanism is operated in the acceleration drive state can be reduced.

トラクタの全体を示す側面図である。It is a side view which shows the whole tractor. 走行駆動装置を示す概略図である。It is the schematic which shows a traveling drive apparatus. 前輪伝動構造を示す縦断側面図である。It is a vertical side view which shows a front-wheel transmission structure. 増速駆動状態での前輪変速機構を示す縦断側面図である。It is a vertical side view which shows the front-wheel transmission mechanism in the acceleration drive state. 標準駆動状態での前輪変速機構を示す縦断側面図である。It is a vertical side view which shows the front-wheel transmission mechanism in a standard drive state. 前輪変速機構の変速操作を可能にする油圧回路図である。FIG. 3 is a hydraulic circuit diagram that enables a speed change operation of a front wheel speed change mechanism. 第１の別実施構造を備えた油圧回路図である。It is a hydraulic circuit diagram provided with the 1st another implementation structure. 第２の別実施構造を備えた油圧回路図である。It is a hydraulic circuit diagram provided with the 2nd another implementation structure. 第３の別実施構造を備えた油圧回路図である。It is a hydraulic circuit diagram provided with the 3rd another implementation structure.

以下、本発明の実施の形態を図面に基づいて説明する。
図１は、本発明の実施例に係るトラクタの全体を示す側面図である。この図に示すように、トラクタは、左右一対の操向操作及び駆動自在な前輪１，１と左右一対の駆動自在な後輪２，２とによって自走するように構成され、かつ車体前部に設けたエンジン３、運転座席４ａ及びステアリングハンドル４ｂを有した運転部４が装備された自走車を備え、自走車の車体フレーム５の後部を構成するミッションケース６に左右一対のリフトアーム７ａ，７ａによって上下に揺動操作されるように構成して設けられたリンク機構７を備え、ミッションケース６の後部に車体後方向きに突設された動力取り出し軸８を備えており、車体後部にリンク機構７を介してロータリ耕耘装置（図示せず）が連結され、動力取り出し軸８からロータリ耕耘装置にエンジン３の出力を伝達するように構成されることにより、乗用型耕耘機を構成する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side view showing an entire tractor according to an embodiment of the present invention. As shown in this figure, the tractor is configured to be self-propelled by a pair of left and right steering operations and driveable front wheels 1 and 1 and a pair of left and right driveable rear wheels 2 and 2, and a front part of the vehicle body. A self-propelled vehicle equipped with an engine 3, a driver's seat 4a, and a driving unit 4 having a steering handle 4b, and a pair of left and right lift arms on a transmission case 6 constituting the rear part of a body frame 5 of the self-propelled vehicle 7a, a link mechanism 7 configured to swing up and down by 7a, a power take-off shaft 8 projecting rearward of the vehicle body at the rear of the transmission case 6, and Is connected to a rotary tiller (not shown) via a link mechanism 7 and is configured to transmit the output of the engine 3 from the power take-off shaft 8 to the rotary tiller. Opportunity to configure.

車体フレーム５の前部を構成するエンジン支持フレーム９に支持される前輪駆動ケース１０の内部に、左右一対の前輪１，１を差動可能に駆動する前輪差動機構１１を設け、ミッションケース６の後部内に、左右一対の後輪２，２を差動可能に駆動する後輪差動機構１２を設け、前輪差動機構１１及び後輪差動機構１２にエンジン３の出力を伝達して前輪１及び後輪２を駆動する走行駆動装置を図２に示す如く構成してある。 A front wheel differential mechanism 11 that differentially drives the pair of left and right front wheels 1 and 1 is provided in a front wheel drive case 10 supported by an engine support frame 9 that forms the front portion of the vehicle body frame 5. A rear wheel differential mechanism 12 for differentially driving the pair of left and right rear wheels 2 and 2 is provided in the rear portion, and the output of the engine 3 is transmitted to the front wheel differential mechanism 11 and the rear wheel differential mechanism 12. A traveling drive device for driving the front wheels 1 and the rear wheels 2 is configured as shown in FIG.

すなわち、走行駆動装置は、エンジン３の出力軸３ａからの出力を、主クラッチ１３及び伝動軸１４を介して主変速用の静油圧式無段変速装置１５を構成する油圧ポンプＰが備えるポンプ軸１５ａに伝達し、静油圧式無段変速装置１５を構成する油圧モータＭが備えるモータ軸１５ｂによる出力を、副変速用の変速機構１６の入力軸１６ａに伝達し、変速機構１６の出力軸１６ｂの駆動力を、出力軸１６ｂの後端部から後輪差動機構１２の入力ギヤ１２ａに伝達し、副変速用の変速機構１６の出力軸１６ｂの駆動力を、出力軸１６ｂの前端部に設けた出力ギヤＧ７からミッションケース６に装備した前輪用出力軸１７、前輪用出力軸１７の前端部から車体前方向きに延出する伝動軸１８を介して前輪変速機構２０の入力軸２１に伝達し、前輪変速機構２０の出力軸２２の駆動力を、出力軸２２の前端部に設けた出力ギヤＧ１３から伝動軸１９を介して前輪差動機構１１の入力ギヤ１１ａに伝達する。 In other words, the travel drive device includes a pump shaft provided in a hydraulic pump P that constitutes a hydrostatic continuously variable transmission 15 for main transmission via the main clutch 13 and the transmission shaft 14 with the output from the output shaft 3 a of the engine 3. 15a and the output from the motor shaft 15b of the hydraulic motor M constituting the hydrostatic continuously variable transmission 15 is transmitted to the input shaft 16a of the sub-transmission transmission mechanism 16, and the output shaft 16b of the transmission mechanism 16 is transmitted. Is transmitted from the rear end portion of the output shaft 16b to the input gear 12a of the rear wheel differential mechanism 12, and the driving force of the output shaft 16b of the sub-transmission transmission mechanism 16 is transmitted to the front end portion of the output shaft 16b. Transmission from the provided output gear G7 to the input shaft 21 of the front wheel speed change mechanism 20 via the front wheel output shaft 17 mounted on the transmission case 6 and the transmission shaft 18 extending forward from the front end of the front wheel output shaft 17 toward the vehicle body. And front wheels The driving force of the output shaft 22 of the speed mechanism 20, to transmit through the transmission shaft 19 from the output gear G13 provided at the front end portion of the output shaft 22 to the input gear 11a of the front wheel differential mechanism 11.

静油圧式無段変速装置１５は、ミッションケース６の前部に装着されている。前輪用出力軸１７の後端部にクラッチギヤＧ８を一体回転及び摺動操作自在に設けてある。クラッチギヤＧ８は、摺動操作されて出力ギヤＧ７に咬合させられることにより、出力軸１６ｂと前輪用出力軸１７とを連動させるように入り状態になり、摺動操作されて出力ギヤＧ７から離脱することにより、出力軸１６ｂと前輪用出力軸１７の連動を絶つように切り状態になる。トラクタは、クラッチギヤＧ８が入り状態に切換え操作されることにより、前輪１及び後輪２が駆動される四輪駆動状態になり、クラッチギヤＧ８が切り状態に切換え操作されることにより、後輪２が駆動されて前輪１が駆動されない二輪駆動状態になる。 The hydrostatic continuously variable transmission 15 is attached to the front portion of the transmission case 6. A clutch gear G8 is provided at the rear end of the front wheel output shaft 17 so as to be integrally rotatable and slidable. The clutch gear G8 is slid and engaged with the output gear G7, so that the output shaft 16b and the front wheel output shaft 17 are engaged with each other, and the clutch gear G8 is slid and separated from the output gear G7. By doing so, the output shaft 16b and the front wheel output shaft 17 are disconnected so as to be disconnected. The tractor is in a four-wheel drive state in which the front wheel 1 and the rear wheel 2 are driven when the clutch gear G8 is switched to the on state, and the rear wheel is switched by the clutch gear G8 being switched to the off state. 2 is driven and the front wheel 1 is not driven.

動力取り出し軸８にエンジン３の駆動力を伝達する作業駆動装置を、図２に示す如く構成してある。 A work driving device for transmitting the driving force of the engine 3 to the power take-off shaft 8 is configured as shown in FIG.

作業駆動装置は、静油圧式無段変速装置１５のポンプ軸１５ａの駆動力を、ポンプ軸１５ａの後端部から作業クラッチ３０、伝動軸３１、連結スリーブ３２、伝動軸３３及びギヤ機構３４を介して動力取出し軸８に伝達する。作業駆動装置は、ミッションケース６の前端側の下部から車体前方向きに突出するミッド作業装置用の動力取り出し軸３５を備え、この動力取り出し軸３５に、作業クラッチ３０からギヤ機構３６を介して伝動する。 The work drive device supplies the drive force of the pump shaft 15a of the hydrostatic continuously variable transmission 15 to the work clutch 30, the transmission shaft 31, the connecting sleeve 32, the transmission shaft 33, and the gear mechanism 34 from the rear end portion of the pump shaft 15a. To the power take-off shaft 8 via The work drive device includes a power take-out shaft 35 for a mid work device that projects forward from the lower part of the front end side of the transmission case 6 toward the vehicle body, and is transmitted to the power take-out shaft 35 from the work clutch 30 via a gear mechanism 36. To do.

副変速用の変速機構１６は、入力軸１６ａにスプライン嵌合されたシフトギヤＧ１がシフト操作されることによって出力軸１６ｂの駆動速度を作業用の低速側の２段と移動走行用の高速側の１段との計３段階の変速伝動状態に変速するようになっている。 The sub-transmission speed change mechanism 16 shifts the shift gear G1 spline-fitted to the input shaft 16a to change the drive speed of the output shaft 16b on the low speed side for working and the high speed side for moving travel. The speed is changed to a total of three speed transmission states with one speed.

詳述すれば、入力軸１６ａの前後には大径遊嵌ギヤＧ２と小径遊嵌ギヤＧ３が装着され、出力軸１６ｂには大径遊嵌ギヤＧ２に常時咬合する小径ギヤＧ４と小径遊嵌ギヤＧ３に常時咬合する大径ギヤＧ５が固着されている。出力軸１６ｂにはシフトギヤＧ１に直接咬合可能な中径ギヤＧ６が固着されている。シフトギヤＧ１を後方にシフトしてそのボス部を小径遊嵌ギヤＧ３のボス部に咬合連結することで、小径遊嵌ギヤＧ３と大径ギヤＧ５とのギヤ比での伝動により、低速伝動状態の第１速がもたらされる。シフトギヤＧ１を前後中間位置にまでシフトして中径ギヤＧ６に直接咬合させることで、シフトギヤＧ１と中径ギヤＧ６とのギヤ比での伝動により、低速伝動状態の第２速がもたらされる。低速伝動状態の第２速は、低速伝動状態の第１速より高速である。シフトギヤＧ１を前方にシフトしてそのボス部を大径遊嵌ギヤＧ２のボス部に咬合連結することで、大径遊嵌ギヤＧ２と小径ギヤＧ４とのギヤ比での伝動により、低速伝動状態の第１及び第２速よりも高速の高速伝動状態がもたらされる。 More specifically, a large-diameter loosely fitted gear G2 and a small-diameter loosely-fitted gear G3 are mounted on the front and rear of the input shaft 16a, and a small-diameter gear G4 and a small-diameter loosely-fitted on the output shaft 16b are always meshed with the large-diameter loosely fitted gear G2. A large-diameter gear G5 that always meshes with the gear G3 is fixed. A medium-diameter gear G6 that can be directly meshed with the shift gear G1 is fixed to the output shaft 16b. By shifting the shift gear G1 rearward and engaging the boss portion with the boss portion of the small-diameter loose fitting gear G3, the transmission in the low-speed transmission state is caused by the transmission in the gear ratio between the small-diameter loose fitting gear G3 and the large-diameter gear G5. The first speed is provided. By shifting the shift gear G1 to the front-rear intermediate position and directly meshing with the medium-diameter gear G6, the transmission at the gear ratio between the shift gear G1 and the medium-diameter gear G6 provides the second speed in the low-speed transmission state. The second speed in the low-speed transmission state is higher than the first speed in the low-speed transmission state. By shifting the shift gear G1 forward and engaging the boss portion with the boss portion of the large-diameter free-fit gear G2, a low-speed transmission state is achieved by transmission in the gear ratio between the large-diameter free-fit gear G2 and the small-diameter gear G4. Thus, a high-speed transmission state that is faster than the first and second speeds is provided.

図３に示すように、クラッチハウジング４０には主クラッチ１３を収容する乾式のクラッチ室４１と、このクラッチ室４１と隔絶された湿式（オイルバス潤滑式）の変速室４２とが備えられており、この変速室４２に、前輪変速機構２０が装備されている。 As shown in FIG. 3, the clutch housing 40 includes a dry clutch chamber 41 that houses the main clutch 13, and a wet (oil bath lubrication) transmission chamber 42 that is isolated from the clutch chamber 41. The transmission chamber 42 is equipped with the front wheel transmission mechanism 20.

図２，３，４，５に示すように、前輪変速機構２０は、変速室４２に入力軸２１と出力軸２２を車体前後向きにかつ平行に設け、入力軸２１の後端側と出力軸２２とに亘って摩擦クラッチ５１を備える増速伝動機構５０を設け、入力軸２１の前端側と出力軸２２とに亘って咬合いクラッチ５６を備える標準伝動機構５５を設けて構成してある。 As shown in FIGS. 2, 3, 4, and 5, the front wheel speed change mechanism 20 is provided with an input shaft 21 and an output shaft 22 in the shift chamber 42 in parallel with the vehicle body in the longitudinal direction. 22, a speed increasing transmission mechanism 50 including a friction clutch 51 is provided, and a standard transmission mechanism 55 including an engagement clutch 56 is provided between the front end side of the input shaft 21 and the output shaft 22.

増速伝動機構５０は、入力軸２１に一体回転自在に設けた大径ギヤＧ９と、この大径ギヤＧ９に常時咬合された状態で出力軸２２に相対回転自在に支持される小径遊転ギヤＧ１１とを備えている。増速伝動機構５０を構成する摩擦クラッチ５１は、小径遊転ギヤＧ１１に一体回転自在に設けたスプラインボス部５２と出力軸２２に一体回転自在に設けたクラッチドラム５３とに亘って設けた多板式の摩擦クラッチ本体５１ａを備え、この摩擦クラッチ本体５１ａがクラッチドラム５３に内装した油圧アクチュエータとしての油圧ピストン５４によって加圧操作されることにより、入り状態に切り換え操作され、小径遊転ギヤＧ１１と出力軸２２とをスプラインボス部５２、摩擦クラッチ本体５１ａ及びクラッチドラム５３を介して一体回転するように連動させる。摩擦クラッチ５１は、摩擦クラッチ本体５１ａの油圧ピストン５４による加圧操作が解除されることにより、スプリング５９によって切り状態に切換え操作され、小径遊転ギヤＧ１１と出力軸２２の相対回転を可能にする。 The speed increasing transmission mechanism 50 includes a large-diameter gear G9 that is integrally rotatable with the input shaft 21, and a small-diameter idle gear that is supported by the output shaft 22 so as to be relatively rotatable with the large-diameter gear G9 constantly engaged. G11. The friction clutch 51 that constitutes the speed increasing transmission mechanism 50 includes a spline boss portion 52 that is provided so as to be integrally rotatable with the small-diameter idler gear G11 and a clutch drum 53 that is provided so as to be integrally rotatable with the output shaft 22. A plate-type friction clutch main body 51a is provided. When the friction clutch main body 51a is pressurized by a hydraulic piston 54 as a hydraulic actuator built in the clutch drum 53, the friction clutch main body 51a is switched to the on state, and the small-diameter idle gear G11 and The output shaft 22 is interlocked so as to rotate integrally through the spline boss portion 52, the friction clutch main body 51a, and the clutch drum 53. When the pressurizing operation by the hydraulic piston 54 of the friction clutch main body 51a is released, the friction clutch 51 is switched to the cut state by the spring 59, and the relative rotation of the small-diameter free-wheeling gear G11 and the output shaft 22 is enabled. .

標準伝動機構５５は、入力軸２１に一体回転自在に設けた小径ギヤＧ１０と、この小径ギヤＧ１０に常時咬合された状態で出力軸２２に相対回転自在に支持される大径遊転ギヤＧ１２とを備えている。標準伝動機構５５を構成する咬合いクラッチ５６は、大径遊転ギヤＧ１２の側部に設けたクラッチ爪５６ａ、及びクラッチドラム５３のボス部５３ａにスプライン係合を介して一体回転及び摺動操作自在に支持されるシフト部材５７に設けたクラッチ爪５６ｂを備えている。シフト部材５７と油圧ピストン５４とは、クラッチドラム５３に設けたピン孔を摺動自在に挿通する連結ピン５８によって一体摺動自在に連結されている。咬合いクラッチ５６は、クラッチドラム５３に内装したスプリング５９の弾性復元力による油圧ピストン５４及び連結ピン５８を介してのシフト部材５７の摺動操作によって大径遊転ギヤＧ１２のクラッチ爪５６ａとシフト部材５７のクラッチ爪５６ｂとが咬合い操作されることにより、入り状態に切換え操作され、大径遊転ギヤＧ１２と出力軸２２とをシフト部材５７及びクラッチドラム５３を介して一体回転するように連動させる。咬合いクラッチ５６は、油圧ピストン５４によるスプリング５９に抗して、かつ連結ピン５８を介してのシフト部材５７の摺動操作によって大径遊転ギヤＧ１２のクラッチ爪５６ａとシフト部材５７のクラッチ爪５６ｂとの咬合いが解除されることにより、切り状態に切換え操作され、大径遊転ギヤＧ１２と出力軸２２の相対回転を可能にする。 The standard transmission mechanism 55 includes a small-diameter gear G10 provided to be rotatable integrally with the input shaft 21, and a large-diameter free-wheeling gear G12 that is supported by the output shaft 22 so as to be relatively rotatable while being constantly engaged with the small-diameter gear G10. It has. The occlusal clutch 56 constituting the standard transmission mechanism 55 is integrally rotated and slidably operated through spline engagement with a clutch pawl 56a provided on the side of the large-diameter idle gear G12 and a boss 53a of the clutch drum 53. A clutch pawl 56b provided on a shift member 57 that is freely supported is provided. The shift member 57 and the hydraulic piston 54 are slidably coupled together by a coupling pin 58 that is slidably inserted through a pin hole provided in the clutch drum 53. The bite clutch 56 shifts with the clutch pawl 56a of the large-diameter free-wheeling gear G12 by the sliding operation of the shift member 57 via the hydraulic piston 54 and the connecting pin 58 by the elastic restoring force of the spring 59 built in the clutch drum 53. By engaging the clutch pawl 56 b of the member 57, it is switched to the engaged state so that the large-diameter free-wheeling gear G 12 and the output shaft 22 rotate integrally through the shift member 57 and the clutch drum 53. Interlock. The bite clutch 56 opposes the spring 59 by the hydraulic piston 54, and the clutch pawl 56a of the large-diameter idle gear G12 and the clutch pawl of the shift member 57 by the sliding operation of the shift member 57 via the connecting pin 58. When the engagement with 56b is released, switching to the cut state is performed, and the large-diameter free-wheeling gear G12 and the output shaft 22 can be rotated relative to each other.

従って、前輪変速機構２０は、油圧ピストン５４による摩擦クラッチ５１の入り状態への切換え操作によって増速駆動状態に切換え操作され、スプリング５９による咬合いクラッチ５６の入り状態への切換え操作によって標準駆動状態に切換え操作される。 Therefore, the front wheel speed change mechanism 20 is switched to the speed increasing drive state by the switching operation to the engagement state of the friction clutch 51 by the hydraulic piston 54, and is in the standard driving state by the switching operation to the engagement state of the engagement clutch 56 by the spring 59. Is switched to.

図４は、増速駆動状態での前輪変速機構２０を示す縦断側面図である。この図に示すように、前輪変速機構２０は、出力軸２２及びバルブケーシング６０の内部を通る操作油路６１からクラッチドラム５３の縦壁部５３ｂと油圧ピストン５４の間に油圧が供給されると、油圧ピストン５４が油圧によってスプリング５９に抗して縦壁部５３ｂから離れる側に摺動操作され、摩擦クラッチ本体５１ａが油圧ピストン５４によって加圧操作されて摩擦クラッチ５１が入り状態に切換え操作されることで増速駆動状態に切り換わる。この場合、油圧ピストン５４が連結ピン５８を介してシフト部材５７をクラッチドラム５３の縦壁部５３ｂが位置する側に摺動操作して咬合いクラッチ５６が切り状態になる。前輪変速機構２０は、増速駆動状態に切り換わると、変速機構１６から入り状態のクラッチギヤＧ８、前輪出力軸１７、伝動軸１８を介して入力軸２１に伝達される駆動力を増速伝動機構５０によって出力軸２２に伝達し、出力軸２２の駆動力を出力ギヤＧ１３から伝動軸１９を介して前輪差動機構１１に伝達して、左右一対の前輪１，１の平均周速度が左右一対の後輪２，２の平均周速度より速い平均周速度になるようにして左右前輪１を駆動する。 FIG. 4 is a longitudinal side view showing the front wheel speed change mechanism 20 in the speed increasing drive state. As shown in this figure, when the front wheel speed change mechanism 20 is supplied with hydraulic pressure between the vertical wall portion 53 b of the clutch drum 53 and the hydraulic piston 54 from the operation oil passage 61 passing through the output shaft 22 and the inside of the valve casing 60. The hydraulic piston 54 is slid to the side away from the vertical wall 53b against the spring 59 by hydraulic pressure, the friction clutch body 51a is pressurized by the hydraulic piston 54, and the friction clutch 51 is switched to the on state. To switch to the accelerated drive state. In this case, the hydraulic piston 54 slides the shift member 57 to the side where the vertical wall portion 53b of the clutch drum 53 is located via the connecting pin 58, and the engagement clutch 56 is turned off. When the front wheel speed change mechanism 20 is switched to the speed increasing drive state, the driving force transmitted from the speed change mechanism 16 to the input shaft 21 through the engaged clutch gear G8, the front wheel output shaft 17 and the transmission shaft 18 is speed up transmission. The mechanism 50 transmits the output force to the output shaft 22, and the driving force of the output shaft 22 is transmitted from the output gear G 13 to the front wheel differential mechanism 11 via the transmission shaft 19. The left and right front wheels 1 are driven such that the average peripheral speed is higher than the average peripheral speed of the pair of rear wheels 2 and 2.

図５は、標準駆動状態での前輪変速機構２０を示す縦断側面図である。この図に示すように、前輪変速機構２０は、クラッチドラム５３の縦壁部５３ｂと油圧ピストン５４の間に供給されて油圧ピストン５４を縦壁部５３ｂから離れる側に操作している油圧が操作油路６１によって排出されると、油圧ピストン５４がスプリング５９によってクラッチドラム５３の縦壁部５３ｂが位置する側に摺動操作され、シフト部材５７が連結ピン５８及び油圧ピストン５４を介して作用するスプリング５９によってクラッチドラム５３の縦壁部５３ｂから離れる側に摺動操作されて咬合いクラッチ５６を入り状態に切換え操作することで標準駆動状態に切り換わる。この場合、摩擦クラッチ５１がスプリング５９による油圧ピストン５４の摺動操作によって切り状態に切り換わる。前輪変速機構２０は、標準駆動状態に切り換わると、変速機構１６から入り状態のクラッチギヤＧ８、前輪出力軸１７、伝動軸１８を介して入力軸２１に伝達される駆動力を標準伝動機構５５によって出力軸２２に伝達し、出力軸２２の駆動力を出力ギヤＧ１３から伝動軸１９を介して前輪差動機構１１に伝達して、左右一対の前輪１，１の平均周速度が左右一対の後輪２，２の平均周速度と同等（あるいは若干速い周速度）の平均周速度になるようにして左右前輪１を駆動する。 FIG. 5 is a longitudinal side view showing the front wheel transmission mechanism 20 in the standard drive state. As shown in this figure, the front wheel transmission mechanism 20 is operated by hydraulic pressure that is supplied between the vertical wall portion 53b of the clutch drum 53 and the hydraulic piston 54 to operate the hydraulic piston 54 away from the vertical wall portion 53b. When discharged by the oil passage 61, the hydraulic piston 54 is slid to the side where the vertical wall portion 53b of the clutch drum 53 is located by the spring 59, and the shift member 57 acts via the connecting pin 58 and the hydraulic piston 54. The spring 59 is slid to the side away from the vertical wall portion 53b of the clutch drum 53, and the engagement clutch 56 is switched to the on state to switch to the standard drive state. In this case, the friction clutch 51 is switched to the disconnected state by the sliding operation of the hydraulic piston 54 by the spring 59. When the front wheel speed change mechanism 20 is switched to the standard drive state, the drive power transmitted from the speed change mechanism 16 to the input shaft 21 via the clutch gear G8, the front wheel output shaft 17 and the transmission shaft 18 that are engaged is standard transmission mechanism 55. Is transmitted to the output shaft 22, and the driving force of the output shaft 22 is transmitted from the output gear G 13 to the front wheel differential mechanism 11 via the transmission shaft 19, and the average peripheral speed of the pair of left and right front wheels 1, 1 is The left and right front wheels 1 are driven so that the average peripheral speed is equal to (or slightly faster than) the average peripheral speed of the rear wheels 2 and 2.

図６は、前輪変速機構２０の変速操作を可能にする油圧回路図である。図５，６に示すように、前輪変速機構２０の変速操作を可能にする油圧回路は、前記油圧ピストン５４と油圧ポンプ６５の吐出部とを接続する操作油路６１に人為選択弁６６、牽制弁６７及び自動選択弁６８を直列に並べて設けて、人為選択弁６６に油圧取出し側端部７０ａが接続された人為選択取出し油路７０と、牽制弁６７に油圧取出し側端部７１ａが接続された牽制取出し油路７１と、自動選択弁６８に油圧取出し側端部７２ａが接続された自動選択取出し油路７２と、操作油路６１の人為選択弁６６、牽制弁６７及び自動選択弁６８より上流側に位置する部位に接続されたリリーフ油路７３とを備えて、人為選択取出し油路７０の排出側端部７０ｂと牽制取出し油路７１の排出側端部７１ｂと自動選択取出し油路７２の排出側端部７２ｂとリリーフ油路７３の排出側端部７３ｂのそれぞれに上流側が接続された油圧取出し油路７４を備えて構成してある。 FIG. 6 is a hydraulic circuit diagram that enables a speed change operation of the front wheel speed change mechanism 20. As shown in FIGS. 5 and 6, the hydraulic circuit that enables the speed change operation of the front wheel speed change mechanism 20 includes a manipulating valve 66 and a check valve in the operation oil passage 61 that connects the hydraulic piston 54 and the discharge portion of the hydraulic pump 65. The valve 67 and the automatic selection valve 68 are arranged in series, and the artificial selection take-out oil passage 70 in which the hydraulic take-out side end portion 70a is connected to the artificial selection valve 66 and the hydraulic take-out side end portion 71a is connected to the check valve 67. The check take-out oil passage 71, the automatic selection take-out oil passage 72 in which the hydraulic pressure take-out side end 72 a is connected to the automatic selection valve 68, the artificial selection valve 66, the check valve 67 and the automatic selection valve 68 in the operation oil passage 61. A relief oil passage 73 connected to a portion located on the upstream side, a discharge-side end portion 70b of the artificially selected take-out oil passage 70, a discharge-side end portion 71b of the check-out take-out oil passage 71, and an automatically selected take-out oil passage 72. Discharge side end 7 Upstream to the respective discharge-side ends 73b of the b and the relief oil path 73 are constituted comprising a hydraulic extraction fluid passage 74 connected.

操作油路６１は、前輪変速機構２０の出力軸２２の内部に形成された軸内油路６１ａと、人為選択弁６６、牽制弁６７及び自動選択弁６８が装備されたバルブケーシング６０の内部に形成されたケーシング内油路６１ｂと、ケーシング内油路６１ｂと前輪操向機構８０の吐出部８１とを接続する前輪変速機構側の給油路６１ｃと、前輪操向機構８０のポンプポート部８２と油圧ポンプ６５の吐出部とを接続する油圧ポンプ側の給油路６１ｄとを備えて構成してある。 The operation oil passage 61 is provided in an inside oil passage 61 a formed in the output shaft 22 of the front wheel transmission mechanism 20, and in a valve casing 60 equipped with an artificial selection valve 66, a check valve 67 and an automatic selection valve 68. The formed casing internal oil passage 61b, the oil supply passage 61c on the front wheel speed change mechanism side connecting the casing internal oil passage 61b and the discharge portion 81 of the front wheel steering mechanism 80, and the pump port portion 82 of the front wheel steering mechanism 80, An oil supply passage 61d on the hydraulic pump side that connects the discharge portion of the hydraulic pump 65 is provided.

前輪操向機構８０は、ステアリングハンドル４ｂが回転操作されることにより、コントロールバルブ８４が操作され、パワーシリンダ８５が油圧ポンプ６５からの油圧によって駆動されてピットマンアーム８６を揺動操作するようにパワステアリング形式になっている。前輪操向機構８０には、ポンプポート部８２からコントロールバルブ８４に至る給油路とコントロールバルブ８４から吐出部８１に至る排油路とに接続され、リリーフ弁８７ａが備えられたリリーフ油路８７を設けてある。 The front wheel steering mechanism 80 is operated so that the control valve 84 is operated by rotating the steering handle 4b, and the power cylinder 85 is driven by the hydraulic pressure from the hydraulic pump 65 to swing the pitman arm 86. Steering type. The front wheel steering mechanism 80 has a relief oil passage 87 connected to an oil supply passage from the pump port portion 82 to the control valve 84 and an oil discharge passage from the control valve 84 to the discharge portion 81 and provided with a relief valve 87a. It is provided.

人為選択弁６６は、運転部４に設けた操作具６６ａ（図１参照）の人為操作によって給油位置Ａと排油位置Ｂとに切換え操作される。人為選択弁６６は、給油位置Ａに切換え操作されると、油圧ポンプ６５からの油圧を油圧ピストン５４に供給するように、操作油路６１におけるケーシング内油路６１ｂの人為選択弁６６より上流側の部位と下流側の部位とを連通させる。人為選択弁６６は、排油位置Ｂに切換え操作されると、油圧ピストン５４から油圧を排出するように、ケーシング内油路６１ｂの人為選択弁６６より下流側の部位をミッションケース６への排油路７５に連通させる。人為選択弁６６は、排油位置Ｂに切換え操作されると、人為選択取出し油路７０をケーシング内油路６１ｂの人為選択弁６６より上流側の部位に対する開き状態に切換え操作し、人為選択取出し油路７０による操作油路６１からの油圧取出しを可能にする。人為選択弁６６は、給油位置Ａに切換え操作されると、人為選択取出し油路７０を操作油路６１におけるケーシング内油路６１ｂに対する閉じ状態に切換え操作する。 The artificial selection valve 66 is switched between the oil supply position A and the oil discharge position B by an artificial operation of an operation tool 66a (see FIG. 1) provided in the operation unit 4. The artificial selection valve 66 is upstream of the artificial selection valve 66 in the casing oil passage 61b in the operation oil passage 61 so that the hydraulic pressure from the hydraulic pump 65 is supplied to the hydraulic piston 54 when switched to the oil supply position A. This part is communicated with the downstream part. When the manual selection valve 66 is switched to the oil discharge position B, the portion downstream of the human selection valve 66 of the oil passage 61b in the casing is discharged to the transmission case 6 so that the hydraulic pressure is discharged from the hydraulic piston 54. The oil passage 75 is communicated. When the manual selection valve 66 is switched to the oil discharge position B, the manual selection take-out oil passage 70 is switched to an open state with respect to a portion upstream of the human selection valve 66 in the casing oil passage 61b. The hydraulic pressure can be taken out from the operation oil path 61 by the oil path 70. When the manual selection valve 66 is switched to the oil supply position A, the manual selection take-out oil passage 70 is switched to a closed state of the operation oil passage 61 with respect to the casing oil passage 61b.

牽制弁６７は、給油位置Ａと排油位置Ｂとに切換え自在に構成され、連係機構９０によって副変速用の変速機構１６に連係されている。連係機構９０は、牽制弁６７を、変速機構１６の人為操作自在な変速レバー１６ａに連係させることによって変速機構１６に連係させている。牽制弁６７は、変速機構１６が低速伝動状態の第１速及び第２速に変速された場合、連係機構９０によって給油位置Ａに自動的に切換え操作され、変速機構１６が高速伝動状態に変速された場合、連係機構９０によって排油位置Ｂに自動的に切換え操作される。 The check valve 67 is configured to be switchable between an oil supply position A and an oil discharge position B, and is linked to a transmission mechanism 16 for auxiliary transmission by a linkage mechanism 90. The linkage mechanism 90 is linked to the speed change mechanism 16 by linking the check valve 67 to the speed change lever 16 a of the speed change mechanism 16 that can be manually operated. The check valve 67 is automatically switched to the fuel supply position A by the linkage mechanism 90 when the speed change mechanism 16 is shifted to the first speed and the second speed in the low speed transmission state, and the speed change mechanism 16 is shifted to the high speed transmission state. If it is, the linkage mechanism 90 automatically switches to the oil discharge position B.

牽制弁６７は、給油位置Ａに切換え操作されると、油圧ポンプ６５からの油圧を油圧ピストン５４に供給するように、操作油路６１におけるケーシング内油路６１ｂの牽制弁６７より上流側の部位と下流側の部位とを連通させる。牽制弁６７は、排油位置Ｂに切換え操作されると、油圧ピストン５４から油圧を排出するように、操作油路６１におけるケーシング内油路６１ｂの牽制弁６７より下流側の部位をミッションケース６への排油路７５に連通させる。牽制弁６７は、排油位置Ｂに切換え操作されると、牽制取出し油路７１をケーシング内油路６１ｃの牽制弁６７より上流側の部位に対する開き状態に切換え操作し、牽制取出し油路７１による操作油路６１からの油圧取出しを可能にする。牽制弁６７は、給油位置Ａに切換え操作されると、牽制取出し油路７１を操作油路６１におけるケーシング内油路６１ｂに対する閉じ状態に切換え操作する。 When the check valve 67 is switched to the oil supply position A, the upstream side of the check valve 67 of the casing oil passage 61b in the operation oil passage 61 is configured to supply the hydraulic pressure from the hydraulic pump 65 to the hydraulic piston 54. And the downstream part are communicated. When the check valve 67 is switched to the oil discharge position B, the portion of the operation oil passage 61 on the downstream side of the check valve 67 of the oil passage 61b in the casing is discharged to the transmission case 6 so that the hydraulic pressure is discharged from the hydraulic piston 54. The oil is connected to the oil drain passage 75. When the check valve 67 is switched to the oil discharge position B, the check take-out oil passage 71 is changed to an open state with respect to a portion upstream of the check valve 67 of the oil passage 61c in the casing. The hydraulic pressure can be taken out from the operation oil passage 61. When the check valve 67 is switched to the oil supply position A, the check take-out oil passage 71 is switched to a closed state with respect to the casing oil passage 61 b in the operation oil passage 61.

自動選択弁６８は、給油位置Ａと排油位置Ｂとに切換え自在に構成され、連係機構９１によって前輪操向機構８０に連係されている。連係機構９１は、自動選択弁６８に連動された電動アクチュエータ（図示せず）を制御する制御手段９１ａと、前輪操向機構８０にピットマンアーム８６の揺動角を検出するように設けた回転ポテンショメータで成る揺動角センサ９１ｂとを備えて構成してある。制御手段９１ａは、揺動角センサ９１ｂによる検出角を基に前輪１の切れ角を検出し、この検出結果を基に電動アクチュエータを制御することによって自動選択弁６８を切換え操作する。 The automatic selection valve 68 is configured to be switchable between an oil supply position A and an oil discharge position B, and is linked to the front wheel steering mechanism 80 by a linkage mechanism 91. The linkage mechanism 91 includes a control means 91a for controlling an electric actuator (not shown) linked to the automatic selection valve 68, and a rotary potentiometer provided in the front wheel steering mechanism 80 so as to detect the swing angle of the pitman arm 86. And a rocking angle sensor 91b. The control means 91a detects the turning angle of the front wheel 1 based on the detection angle by the swing angle sensor 91b, and switches the automatic selection valve 68 by controlling the electric actuator based on the detection result.

従って、自動選択弁６８は、前輪１が直進位置から設定切れ角以上の操向状態にある場合、連係機構９１によって給油位置Ａに自動的に切換え操作され、前輪１が設定切れ角未満の操向状態にある場合、連係機構９１によって排油位置Ｂに自動的に切換え操作される。実施例では、設定切れ角として３５度を設定してあり、前輪１の設定切れ角未満の操向状態は、直進向きから３５度までの揺動範囲で揺動操作された状態となる。 Accordingly, the automatic selection valve 68 is automatically switched to the fuel supply position A by the linkage mechanism 91 when the front wheel 1 is in a steering state equal to or greater than the set cut angle from the straight traveling position, and the front wheel 1 is operated to be less than the set cut angle. When in the directional state, the linkage mechanism 91 automatically switches to the oil discharge position B. In the embodiment, 35 degrees is set as the set turning angle, and the steering state less than the setting turning angle of the front wheel 1 is a state where the swing operation is performed within the swing range from the straight direction to 35 degrees.

自動選択弁６８は、給油位置Ａに切換え操作されると、油圧ポンプ６５からの油圧を油圧ピストン５４に供給するように、操作油路６１におけるケーシング内油路６１ｂの自動選択弁６６より上流側の部位と下流側の部位とを連通させる。自動選択弁６８は、排油位置Ｂに切換え操作されると、油圧ピストン５４から油圧を排出するように、ケーシング内油路６１ｂの自動選択弁６８より下流側の部位をミッションケース６への排油路７５に連通させる。自動選択弁６８は、排油位置Ｂに切換え操作されると、自動選択取出し油路７２をケーシング内油路６１ｂの自動選択弁６８より上流側の部位に対する開き状態に切換え操作し、自動選択取出し油路７２による操作油路６１からの油圧取出しを可能にする。自動選択弁６８は、排油位置Ｂに切換え操作されると、自動選択取出し油路７２を操作油路６１におけるケーシング内油路６１ｂに対する閉じ状態に切換え操作する。 The automatic selection valve 68 is upstream of the automatic selection valve 66 of the casing oil passage 61b in the operation oil passage 61 so that the hydraulic pressure from the hydraulic pump 65 is supplied to the hydraulic piston 54 when switched to the oil supply position A. This part is communicated with the downstream part. When the automatic selection valve 68 is switched to the oil discharge position B, the portion downstream of the automatic selection valve 68 of the oil passage 61b in the casing is discharged to the transmission case 6 so that the hydraulic pressure is discharged from the hydraulic piston 54. The oil passage 75 is communicated. When the automatic selection valve 68 is switched to the oil discharge position B, the automatic selection take-out oil passage 72 is changed to an open state with respect to a portion upstream of the automatic selection valve 68 of the oil passage 61b in the casing to perform automatic selection take-out. The hydraulic pressure can be taken out from the operation oil path 61 by the oil path 72. When the automatic selection valve 68 is switched to the oil discharge position B, the automatic selection take-out oil passage 72 is switched to a closed state with respect to the casing oil passage 61 b in the operation oil passage 61.

油圧取出し油路７４の吐出側端部は静油圧式無段変速装置１５が備えるチャージ油路７６の入力ポート７６ａに接続されており、油圧取出し油路７４は、人為選択取出し油路７０、牽制取出し油路７１及び自動選択取出し油路７２によって操作油路６１から取出された油圧、及びリリーフ油路７３によって操作油路６１から排出された油圧を取出して静油圧式無段変速装置１５に補充用の作動油として供給する。 The discharge-side end of the hydraulic take-out oil passage 74 is connected to an input port 76a of a charge oil passage 76 provided in the hydrostatic continuously variable transmission 15. The hydraulic take-out oil passage 74 is a manually selected take-out oil passage 70, a check. The hydraulic pressure taken out from the operation oil passage 61 by the take-out oil passage 71 and the automatic selection take-out oil passage 72 and the hydraulic pressure discharged from the operation oil passage 61 by the relief oil passage 73 are taken out and replenished to the hydrostatic continuously variable transmission 15. Supplied as hydraulic fluid.

静油圧式無段変速装置１５のチャージ油路７６は、油圧ポンプＰと油圧モータＭを接続する一対の駆動回路１５ｃ，１５ｃにわたって接続されたメインチャージ油路部７６ｂと、前記メインチャージ油路部７６ｂと入力ポート７６ａを接続する導入油路部７６ｃとを備えている。メインチャージ油路部７６ｂは、導入油路部７６ｃが接続している部位から一方の駆動回路１５ｃに至る油路部分と導入油路部７６ｃが接続している部位から他方の駆動回路１５ｃに至る油路部分とのそれぞれに並列接続の状態で介装された逆止弁７７ａ、リリーフ弁７７ｂ及び絞り７７ｃを備えている。導入油路部７６ｃのメインチャージ油路部７６ｂに接続している部位と入力ポート７６ａとの間に、リリーフ弁７８ａを備えたドレン油路７８が接続されている。 The charge oil passage 76 of the hydrostatic continuously variable transmission 15 includes a main charge oil passage portion 76b connected across a pair of drive circuits 15c, 15c connecting the hydraulic pump P and the hydraulic motor M, and the main charge oil passage portion. 76b and an introduction oil passage 76c that connects the input port 76a. The main charge oil passage portion 76b extends from the portion where the introduction oil passage portion 76c is connected to the one drive circuit 15c and the portion where the introduction oil passage portion 76c is connected to the other drive circuit 15c. A check valve 77a, a relief valve 77b, and a throttle 77c are provided in a state of being connected in parallel with each of the oil passage portions. A drain oil passage 78 including a relief valve 78a is connected between a portion of the introduction oil passage portion 76c connected to the main charge oil passage portion 76b and the input port 76a.

リリーフ油路７３の取出側端部は、操作油路６１におけるケーシング内油路１ｂの自動選択弁６８に接続する部位と前輪操向機構８０の吐出部８１に接続する部位との間に接続されている。 The take-out side end of the relief oil passage 73 is connected between a portion connected to the automatic selection valve 68 of the oil passage 1b in the casing in the operation oil passage 61 and a portion connected to the discharge portion 81 of the front wheel steering mechanism 80. ing.

従って、作業時など低速走行する場合、クラッチギヤＧ８を入り状態に切換えて自走車を四輪駆動状態に切換えておけば、そして人為選択弁６６を給油位置Ａに切換えておけば、畦際などで旋回走行する際、前輪１を設定切れ角以上の切れ角に操向操作するだけで小旋回半径で旋回走行できる。 Therefore, when traveling at a low speed such as during work, if the self-propelled vehicle is switched to the four-wheel drive state by switching the clutch gear G8 to the engaged state, and the artificial selection valve 66 is switched to the fueling position A, For example, when the vehicle turns, the vehicle can turn with a small turning radius simply by steering the front wheel 1 to a turning angle greater than the set turning angle.

すなわち、前輪１が設定切れ角以上に操向操作されると、自動選択弁６８が連係機構９１によって給油位置Ａに自動的に切換え操作され、変速機構１６が低速伝動状態の第１速又は第２速に変速されていて牽制弁６７が連係機構９０によって給油位置Ａに切換えられていることにより、油圧ポンプ６５からの油圧が操作油路６１によって油圧ピストン５４に供給され、油圧ピストン５４に供給される油圧がリリーフ油路７３が有するリリーフ弁７３ａによって前輪変速機構２０の増速駆動状態への切換えに必要な油圧に設定されることにより、前輪変速機構２０が油圧ピストン５４によって増速駆動状態に切換えられ、前輪１が後輪２より速い周速度で駆動される。前輪変速機構２０が増速駆動状態に切換えられると、この後、リリーフ油路７３がリリーフ弁７３ａによって開き操作されて操作油路６１からリリーフ油路７３に油圧が排出され、リリーフ油路７３に排出された圧油が油圧取出し油路７４によってリリーフ油路７３から取出されて静油圧式無段変速装置１５に補充用の作動油として供給される。 That is, when the front wheel 1 is steered beyond the set turning angle, the automatic selection valve 68 is automatically switched to the fueling position A by the linkage mechanism 91, and the speed change mechanism 16 is in the first speed or the first speed in the low speed transmission state. Since the speed is changed to the second speed and the check valve 67 is switched to the oil supply position A by the linkage mechanism 90, the hydraulic pressure from the hydraulic pump 65 is supplied to the hydraulic piston 54 through the operation oil passage 61 and supplied to the hydraulic piston 54. The hydraulic pressure is set to a hydraulic pressure necessary for switching the front wheel speed change mechanism 20 to the speed increasing drive state by the relief valve 73 a included in the relief oil passage 73, so that the front wheel speed change mechanism 20 is in the speed increasing drive state by the hydraulic piston 54. And the front wheel 1 is driven at a faster peripheral speed than the rear wheel 2. When the front wheel speed change mechanism 20 is switched to the speed increasing drive state, the relief oil passage 73 is then opened by the relief valve 73 a, and the hydraulic pressure is discharged from the operation oil passage 61 to the relief oil passage 73. The discharged pressure oil is taken out from the relief oil passage 73 by a hydraulic take-out oil passage 74 and supplied to the hydrostatic continuously variable transmission 15 as supplementary hydraulic fluid.

作業時など低速走行する場合でも、人為選択弁６６を排油位置Ｂに切換えておけば、前輪１を設定切れ角以上の切れ角に操向操作して自動選択弁６８が連係機構９１によって給油位置Ａに切換え操作されても、旋回半径が標準の旋回半径になる。 Even when traveling at a low speed, such as during work, if the artificial selection valve 66 is switched to the oil discharge position B, the automatic selection valve 68 is refueled by the linkage mechanism 91 by steering the front wheel 1 to a cutting angle greater than the set cutting angle. Even when the operation is switched to the position A, the turning radius becomes the standard turning radius.

すなわち、変速機構１６が低速伝動状態の第１速又は第２速に変速されていて牽制弁６７が連係機構９０によって給油位置Ａに切換え操作されていても、人為選択弁６６が排油位置Ｂになって人為選択取出し油路７０が操作油路６１に対する開き状態になっていることにより、油圧ポンプ６５から操作油路６１に供給される油圧が人為選択取出し油路７０によって取出されて油圧ピストン５４に供給されず、前輪変速機構２０がスプリング５９によって標準駆動状態に維持されて前輪１が後輪２と同等の周速度で駆動される。このとき、人為選択取出し油路７０によって操作油路６１から取出された油圧が、油圧取出し油路７４によって人為選択取出し油路７０から取出されて静油圧式無段変速装置１５に補充用の作動油として供給される。 That is, even if the speed change mechanism 16 is shifted to the first speed or the second speed in the low-speed transmission state and the check valve 67 is switched to the oil supply position A by the linkage mechanism 90, the man-made selection valve 66 is in the oil discharge position B. Since the artificially selected take-out oil passage 70 is open with respect to the operation oil passage 61, the hydraulic pressure supplied from the hydraulic pump 65 to the operation oil passage 61 is taken out by the man-made select take-out oil passage 70 and hydraulic piston. The front wheel speed change mechanism 20 is maintained in the standard driving state by the spring 59 and the front wheel 1 is driven at the same peripheral speed as the rear wheel 2 without being supplied to 54. At this time, the hydraulic pressure taken out from the operation oil passage 61 by the manually selected take-out oil passage 70 is taken out from the man-made select take-out oil passage 70 by the hydraulic take-out oil passage 74 and replenished to the hydrostatic continuously variable transmission 15. Supplied as oil.

移動時など高速走行する場合、人為選択弁６６が給油位置Ａに切換えられていても、前輪１が設定切れ角以上の切れ角に操向操作されて自動選択弁６８が連係機構９１によって給油位置Ａに切換え操作されても、旋回半径が標準の旋回半径になる。 When traveling at a high speed, such as when moving, even if the artificial selection valve 66 is switched to the refueling position A, the front wheel 1 is steered to a turning angle equal to or greater than the set cutting angle, and the automatic selection valve 68 is refueled by the linkage mechanism 91. Even if the operation is switched to A, the turning radius becomes the standard turning radius.

すなわち、変速機構１６が高速伝動状態に変速されていて牽制弁６７が連係機構９０によって排油位置Ｂに切換え操作されて牽制取出し油路７１が操作油路６１に対する開き状態になっていることにより、油圧ポンプ６５から操作油路６１に供給される油圧が牽制取出し油路７１によって取出されて油圧ピストン５４に供給されず、前輪変速機構２０がスプリング５９によって標準駆動状態に維持されて前輪１が後輪２と同等の周速度で駆動される。このとき、牽制取出し油路７１によって操作油路６１から取出された油圧が、油圧取出し油路７４によって牽制取出し油路７１から取り出されて静油圧式無段変速装置１５に補充用の作動油として供給される。 That is, the speed change mechanism 16 is shifted to the high speed transmission state, the check valve 67 is switched to the oil discharge position B by the linkage mechanism 90, and the check take-out oil passage 71 is open with respect to the operation oil passage 61. The hydraulic pressure supplied from the hydraulic pump 65 to the operation oil passage 61 is taken out by the check take-out oil passage 71 and is not supplied to the hydraulic piston 54, and the front wheel transmission mechanism 20 is maintained in the standard drive state by the spring 59 so that the front wheel 1 is Driven at the same peripheral speed as the rear wheel 2. At this time, the hydraulic pressure taken out from the operation oil passage 61 by the check take-out oil passage 71 is taken out from the check take-out oil passage 71 by the hydraulic take-out oil passage 74 and is supplied to the hydrostatic continuously variable transmission 15 as replenishing hydraulic oil. Supplied.

前輪１が設定切れ角未満の操向状態にある場合、人為選択弁６６及び牽制弁６７が給油位置Ａに切換えられていても、自動選択弁６８が連係機構９１によって排油位置Ｂに切換え操作されていて自動選択取出し油路７２が自動選択弁６８によって操作油路６１に対する開き状態に切換えられており、油圧ポンプ６５から操作油路６１に供給される油圧が自動選択取出し油路７２によって操作油路６１から取出され、自動選択取出し油路７２に取出された油圧が油圧取出し油路７４によって自動選択取出し油路７２から取出されて静油圧式無段変速装置１５に補充用の作動油として供給される。 When the front wheel 1 is steered less than the set cutting angle, the automatic selection valve 68 is switched to the oil discharge position B by the linkage mechanism 91 even if the artificial selection valve 66 and the check valve 67 are switched to the oil supply position A. The automatic selection take-out oil passage 72 is switched to the open state with respect to the operation oil passage 61 by the automatic selection valve 68, and the hydraulic pressure supplied from the hydraulic pump 65 to the operation oil passage 61 is operated by the automatic selection take-out oil passage 72. The oil pressure taken out from the oil passage 61 and taken out to the automatically selected take-out oil passage 72 is taken out from the automatically selected take-out oil passage 72 by the oil pressure take-out oil passage 74 and used as supplementary hydraulic oil for the hydrostatic continuously variable transmission 15. Supplied.

つまり、倍速作動条件が成立した時のみ、油圧ピストン５４に必要な圧力を立てて前輪変速機構２０を増速駆動状態に切換え、不成立の条件では油圧ピストン５４に圧力を立てないで前輪変速機構２０を標準駆動状態に切換える油圧回路になっている。 That is, only when the double speed operation condition is satisfied, the necessary pressure is applied to the hydraulic piston 54 to switch the front wheel transmission mechanism 20 to the speed increasing drive state. When the condition is not satisfied, the pressure is not applied to the hydraulic piston 54 and the front wheel transmission mechanism 20 is not set. It is a hydraulic circuit that switches to the standard drive state.

図７は、第１の別実施構造を備えた油圧回路図である。この図に示すように、第１の別実施構造を備えた油圧回路では、リリーフ油路７３を、操作油路６１の自動選択弁６８と牽制弁６７との間に位置する部位に接続してある。 FIG. 7 is a hydraulic circuit diagram provided with a first alternative embodiment structure. As shown in this figure, in the hydraulic circuit having the first different implementation structure, the relief oil passage 73 is connected to a portion located between the automatic selection valve 68 and the check valve 67 of the operation oil passage 61. is there.

すなわち、リリーフ油路７３の取出側端部が操作油路６１の自動選択弁６８と牽制弁６７の間の部位に接続されている。リリーフ油路７３の排出側端部７３ｂが、油圧取出し油路７４の上流側のうちの牽制取出し油路７１の排出側端部７１ｂに接続している部位と自動選択取出し油路７２の排出側端部７２ｂに接続している部位との間に接続されている。 That is, the take-out side end portion of the relief oil passage 73 is connected to a portion of the operation oil passage 61 between the automatic selection valve 68 and the check valve 67. The portion where the discharge side end 73 b of the relief oil passage 73 is connected to the discharge side end 71 b of the check take-out oil passage 71 in the upstream side of the hydraulic take-out oil passage 74 and the discharge side of the automatic selection take-out oil passage 72. It connects between the site | parts connected to the edge part 72b.

図８は、第２の別実施構造を備えた油圧回路図である。この図に示すように、第２の別実施構造を備えた油圧回路では、リリーフ油路７３を、操作油路６１の牽制弁６７と人為選択弁６６との間に位置する部位に接続してある。 FIG. 8 is a hydraulic circuit diagram having a second alternative embodiment structure. As shown in this figure, in the hydraulic circuit having the second different implementation structure, the relief oil passage 73 is connected to a portion located between the check valve 67 and the artificial selection valve 66 in the operation oil passage 61. is there.

すなわち、リリーフ油路７３の取出側端部が操作油路６１の人為選択弁６６と牽制弁６７の間の部位に接続されている。リリーフ油路７３の排出側端部７３ｂが、油圧取出し油路７４の上流側のうちの人為選択取出し油路７０の排出側端部７０ｂに接続している部位と牽制取出し油路７１の排出側端部７１ｂに接続している部位との間に接続されている。 That is, the take-out side end portion of the relief oil passage 73 is connected to a portion of the operation oil passage 61 between the artificial selection valve 66 and the check valve 67. The discharge side end 73 b of the relief oil passage 73 is connected to the discharge side end 70 b of the artificial selection take-out oil passage 70 on the upstream side of the hydraulic take-out oil passage 74 and the discharge side end of the check take-out oil passage 71. It connects between the part connected to the part 71b.

図９は、第３の別実施構造を備えた油圧回路図である。この図に示すように、第３の別実施構造を備えた油圧回路では、リリーフ油路７３を、自動選択弁６６、牽制弁６７及び人為選択弁６６のうちの最下流側に位置する弁６６よりも下流側の部位で操作油路６１に接続してある。 FIG. 9 is a hydraulic circuit diagram having a third alternative embodiment structure. As shown in this figure, in the hydraulic circuit having the third separate implementation structure, the relief oil passage 73 is provided on the most downstream side of the automatic selection valve 66, the check valve 67 and the artificial selection valve 66. It is connected to the operation oil passage 61 at a site downstream of the operation oil.

すなわち、リリーフ油路７３の取出側端部が操作油路６１の人為選択弁６６と油圧ピストン５４の間の部位に接続されている。リリーフ油路７３の排出側端部７３ｂが、油圧取出し油路７４の人為選択取出し油路７０の排出側端部７０ｂに接続している部位と静油圧式無段変速装置１５の入力ポート７６ａに接続している部位の間に接続されている。 That is, the take-out side end portion of the relief oil passage 73 is connected to a portion of the operation oil passage 61 between the artificial selection valve 66 and the hydraulic piston 54. The discharge side end 73b of the relief oil passage 73 is connected to the portion connected to the discharge side end 70b of the artificially selected take-off oil passage 70 of the hydraulic take-out oil passage 74 and the input port 76a of the hydrostatic continuously variable transmission 15. Connected between connected parts.

〔別実施例〕
（１）上記した各実施例では、人為選択弁６６より上流側に牽制弁６７が位置し、牽制弁６７より上流側に自動選択弁６８が位置する配列で人為選択弁６７、牽制弁６７及び自動選択弁６８を操作油路６１に設けた例を示したが、人為選択弁６６が最上流側に位置する配列や、牽制弁６７が最上流側に位置する配列など、人為選択弁６６、牽制弁６７及び自動選択弁６８が並ぶ順序が種々異なる配列を採用して実施してもよい。 [Another Example]
(1) In each of the above-described embodiments, the artificial selection valve 67, the check valve 67, and the check valve 67 are arranged in an arrangement in which the check valve 67 is located upstream from the artificial selection valve 66 and the automatic selection valve 68 is located upstream from the check valve 67. Although an example in which the automatic selection valve 68 is provided in the operation oil passage 61 is shown, the artificial selection valve 66, such as an arrangement in which the artificial selection valve 66 is located on the most upstream side, an arrangement in which the check valve 67 is located on the most upstream side, etc. An arrangement in which the check valve 67 and the automatic selection valve 68 are arranged in a different order may be adopted.

（２）上記した実施例では、油圧取出し油路７４を静油圧式無段変速装置１５に対して油圧供給するよう構成した例を示したが、リフトアーム７ａを昇降操作する油圧シリンダに供給するよう構成したり、アースブレイカーなどの各種の油圧駆動型の作業装置の駆動用に供給するよう構成したりして実施してもよい。 (2) In the above-described embodiment, the hydraulic take-out oil passage 74 is configured to supply hydraulic pressure to the hydrostatic continuously variable transmission 15. However, the lift arm 7a is supplied to a hydraulic cylinder that moves up and down. It may be configured to be configured so as to be supplied for driving various hydraulically driven working devices such as an earth breaker.

（３）上記した実施例では、牽制弁６７を副変速用の変速機構１６に連係させた例を示したが、主変速用の変速機構としての静油圧式無段変速装置１５に連係させて実施してもよい。 (3) In the above-described embodiment, the example in which the check valve 67 is linked to the sub-transmission transmission mechanism 16 is shown. However, the check valve 67 is linked to the hydrostatic continuously variable transmission 15 as the main transmission transmission mechanism. You may implement.

（４）上記した実施例では、牽制弁６７と変速機構１６が機械式の連係機構９０によって連係される例を示したが、電気式の連係機構によって連係されるように構成してもよい。 (4) In the above-described embodiment, the example in which the check valve 67 and the speed change mechanism 16 are linked by the mechanical linkage mechanism 90 has been described. However, the check valve 67 and the transmission mechanism 16 may be linked by an electric linkage mechanism.

（５）上記した実施例では、自動選択弁６８と前輪操向機構８０が電気式の連係機構９１によって連係される例を示したが、カム機構やリンク機構を採用した機械式の連係機構によって連係されるように構成してもよい。 (5) In the above-described embodiment, the example in which the automatic selection valve 68 and the front wheel steering mechanism 80 are linked by the electric linkage mechanism 91 has been shown. However, by the mechanical linkage mechanism employing a cam mechanism or a link mechanism. You may comprise so that it may cooperate.

本発明は、乗用型耕耘機を構成するトラクタの他、暗渠形成機や肥料散布機など各種の作業機を構成するトラクタに利用できる。 INDUSTRIAL APPLICATION This invention can be utilized for the tractor which comprises various working machines, such as a culvert formation machine and a manure spreader other than the tractor which comprises a riding type tiller.

１前輪
２後輪
１６変速機構
２０前輪変速機構
５４油圧アクチュエータ
５９スプリング
６１操作油路
６５油圧ポンプ
６６人為選択弁
６７牽制弁
６８自走選択弁
７０人為選択取出し油路
７１牽制取出し油路
７２自動選択取出し油路
７３リリーフ油路
７３ａリリーフ弁
７４油圧取出し油路
８０前輪操向機構
Ａ給油位置
Ｂ排油位置
DESCRIPTION OF SYMBOLS 1 Front wheel 2 Rear wheel 16 Transmission mechanism 20 Front wheel transmission mechanism 54 Hydraulic actuator 59 Spring 61 Operation oil path 65 Hydraulic pump 66 Artificial selection valve 67 Check valve 68 Self-propelled selection valve 70 Artificial selection extraction oil path 71 Checking extraction oil path 72 Automatic selection Take-out oil passage 73 Relief oil passage 73a Relief valve 74 Hydraulic take-out oil passage 80 Front wheel steering mechanism A Oil supply position B Oil discharge position

Claims

A front wheel transmission mechanism capable of switching between a standard driving state in which the steerable front wheel is driven at a peripheral speed equivalent to the peripheral speed of the rear wheel and an acceleration driving state in which the front wheel is driven at a peripheral speed faster than the peripheral speed of the rear wheel. , Provided by switching to the standard driving state by a spring, and switching to the accelerated driving state by a hydraulic actuator.
An artificial oil selection valve that is switchable between an oil supply position for supplying the hydraulic pressure from the hydraulic pump to the hydraulic actuator and an oil discharge position for discharging the hydraulic pressure from the hydraulic actuator, to an operation oil path that connects the hydraulic actuator to a hydraulic pump; A check valve and an automatic selection valve are arranged in series,
A tank for discharging hydraulic pressure from the hydraulic actuator;
The human selection valve is configured to be switched to the oil supply position and the oil discharge position directly connected to the tank by human operation,
The check valve is automatically switched to the refueling position when the traveling speed change mechanism is in a low speed transmission state, and automatically to the oil discharge position directly connected to the tank when the speed change mechanism is in a high speed transmission state. Linked to the speed change mechanism so that it is switched to
The automatic selection valve is automatically switched to the refueling position when the front wheel is in a steering state equal to or greater than a set cut angle, and directly into the tank when the front wheel is in a steering state less than the set cut angle. Link to the front wheel steering mechanism so that it is automatically switched to the connected oil drain position ,
The manual selection valve switched to the oil discharge position is operated in an open state with respect to the operation oil passage, and hydraulic pressure can be taken out from the hydraulic pump. The operation oil is switched by the manual selection valve switched to the oil supply position. An artificially selected oil passage that is operated in a closed state with respect to the road;
The operation valve is operated in an open state with respect to the operation oil passage by the check valve switched to the oil discharge position, and hydraulic pressure can be taken out from the hydraulic pump, and the operation valve to the operation oil passage is enabled by the check valve switched to the oil supply position. A check-out oil passage that is operated in a closed state;
The automatic selection valve that has been switched to the oil discharge position is operated in an open state with respect to the operation oil passage, and hydraulic pressure can be taken out from the hydraulic pump, and the operation oil can be extracted by the automatic selection valve that has been switched to the oil supply position. An automatically selected oil passage that is operated in a closed state with respect to the road;
In a state where a relief valve for setting the hydraulic pressure supplied to the hydraulic actuator is provided, a branch is made from a portion located upstream of the artificial selection valve, the check valve and the automatic selection valve in the operation oil passage. A relief oil passage connected to the operation oil passage;
The artificial selection extraction fluid passage, said牽Seito out oil passage, the automatic selection extraction oil passage and a tractor is provided with a hydraulic extraction fluid passage for performing hydraulic taken out of the relief oil passage.