JP4005673B2 - Hydraulic piston device of automatic transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce shift shock and pull-in feeling in initial shift during low load engine operation and improve running stability during shifting. SOLUTION: This device has a piston formed in a twin piston structure with a primary piston 33 and a secondary piston 34 and interiorly packaging in a servo unit 26 connected to a stem 27 to grant braking torque to a 2&4 brake 20. When operating pressure with specified transient characteristic is supplied to a 2&4 servo chamber 41 during shift, only the primary piston 33 with a small area of pressure receiving face 33a fastens the 2&4 brake 20 via the stem 27 with weak fastening force of restrained braking torque at a low operating pressure in initial shift and, when the operating pressure is over a specified pressure, the secondary piston 34 in addition to the primary piston 33 is operated to fasten and fix the 2&4 brake 20. In initial shift, the 2&4 brake 20 is fastened with weak fastening force to reduce shift shock.

Description

【００３０】
表１に示すように、変速段を１速から２速へ変速する際には、フォワードクラッチ２３ａを係合させると共に２＆４ブレーキ２０を締結動作させる。又、２速から３速へ変速させるときは、少なくとも
上記２＆４ブレーキ２０を解放すると共にハイクラッチ１８を結合させる。
【００３１】
図２に示すように、上記２＆４ブレーキ２０は、上記フロントプラネタリギヤ１６のサンギヤ１６ｄと一体回転するリバースクラッチドラム１９ａに巻装されたブレーキバンド２０ａ等で構成されている。
【００３２】
又、符号２０はサーボユニットで、このサーボユニット２０に設けたステム２７の先端が上記ブレーキバンド２０ａの一端にストラット２８を介して連設されている。尚、このブレーキバンド２０ａの他端はアンカエンドピンを介して上記トランスミッションケース２１に固定されている。
【００３３】
又、上記ステム２７の基端がサーボユニット本体２９に進退自在に挿通支持されている。上記ステム２７の基端にはオーバドライブ（ＯＤ）ピストン３０が挿通され、このＯＤピストン３０に対向する上記サーボユニット本体２９の底部にＯＤリテーナ３１が配設され、上記ＯＤピストン３０とＯＤリテーナ３１との間にＯＤサーボ室３２が形成されている。
【００３４】
又、上記ステム２７の中途に、ツインピストンを構成するプライマリピストン３３とセカンダリピストン３４とが下から順に挿通されている。このプライマリピストン３３は、その上端が上記ステム２７の中途に形成された段部２７ａにワッシャ３５を介して掛止され、更に、このプライマリピストン３３の背面と上記ＯＤピストン３０の上方に掛止されたプライマリリテーナ３６との間にＯＤリターンスプリング３７が介装されている。
【００３５】
又、上記セカンダリピストン３４は、その上端が上記ステム２７に形成されたフランジ２７ｂに掛止され、更に、このセカンダリピストン３４の背面と上記プライマリピストン３３の上面との間にプライマリリターンスプリング３８が介装されている。更に、上記セカンダリピストン３４の上面と上記サーボユニット本体２９の上面との間に一対のセカンダリリターンスプリング３９ａ，３９ｂが介装されている。
【００３６】
上記プライマリピストン３３は、外周方向へ２段の段部を有して拡開されており、内周側の側面と上記ＯＤピストン３０の外周とが、上記サーボユニット本体２９の内周に固設するサーボリテーナ４０に摺動自在に支持されている。又、上記プライマリピストン３３の外周が、上記セカンダリピストン３４の袋状に形成された内周面に摺接されている。更に、このセカンダリピストン３４の外周下端面が上記サーボリテーナ４０の上端に掛止されている。
【００３７】
又、上記サーボリテーナ４０と上記プライマリピストン３３の段部３３ａと上記セカンダリピストン３４の外周下端面３４ａと上記サーボユニット本体２９の内壁とで囲繞された領域に、２＆４サーボ室４１が形成されており、上記プライマリピストン３３の段部３３ａ、及びセカンダリピストン３４の外周下端面３４ａが下受圧面を成している。この両下受圧面の面積は、上記セカンダリピストン３４の下受圧面（外周下端面）３４ａがプライマリピストン３３の下受圧面（段部）３３ａよりも広く設定されている。
【００３８】
更に、このセカンダリピストン３４の上受圧面３４ｂと上記サーボユニット本体２９との間に第１リリースサーボ室４２ａが形成され、又、この第１リリースサーボ室４２ａが上記セカンダリピストン３４に穿設された流通孔３４ｃを介して、上記セカンダリピストン３４の底面及び内周面とプライマリピストン３３の上受圧面３３ｂとで郭成された第２リリースサーボ室４２ｂに連通されている。
【００３９】
尚、上記ＯＤサーボ室３２には作動圧４Ａが供給され、２＆４サーボ室４１には作動圧２Ａが供給され、第１リリースサーボ室４２ａには解放圧３Ｒが供給される。又、上記プライマリピストン３３を押圧するプライマリリターンスプリング３８は、上記プライマリピストン３３の下受圧面３３ａにかかる単位面積当たりの圧力が、例えば０．５Kgf/cm²に達したとき撓むように設定され、一方、セカンダリピストン３４を押圧する一対のセカンダリリターンスプリング３９ａ，３９ｂは、上記セカンダリピストン３４の下受圧面３４ａにかかる単位面積当たりの圧力が、例えば４Kgf/cm²に達したとき撓むように設定されている。
【００４０】
次に、上記構成による本実施の形態の作用について説明する。サーボユニット２６の各サーボ室３２，４１に作用する作動圧４Ａ，２Ａ、及び第１、第２リリースサーボ室４２ａ，４２ｂに作用する解放圧３Ｒが全てドレーンされている状態では、上記各ピストン３０，３３，３４はリターンスプリング３７，３８，３９ａ，３９ｂの付勢力で後退動作し、ステム２７のブレーキバンド２０ａに対する締結を解除している（図２、又は図３の右半分の状態）。
【００４１】
この状態で、変速段を１速から２速へ変速する場合、先ず、サーボユニット２６の２＆４サーボ室４１に作動圧２Ａが供給される。この作動圧２Ａはエンジン負荷の代表であるスロットル開度等に応じて過渡特性が、例えば図７（ａ）に示すように制御される。
【００４２】
そして、上記作動圧２Ａが上昇し、プライマリピストン３３の下受圧面３３ａにかかる圧力が、作動点である例えば０．５Kg/cm²に達すると、この作動圧２Ａがプライマリリターンスプリング３８の付勢力に打ち勝ち、上記プライマリピストン３３は上記プライマリスプリング３８の付勢力に抗して上昇を開始する。このプライマリピストン３３の上端にはワッシャ３５を介してステム２７の段部２７ａが掛止されており、上記プライマリピストン３３の上昇により上記ステム２７が押し上げられる（図３の左半分の状態）。
【００４３】
このとき、上記作動圧２Ａはセカンダリピストン３４の下受圧面３４ａにも作用するが、上記セカンダリピストン３４を押圧付勢する両セカンダリリターンスプリング３９ａ，３９ｂの付勢力が大きいため変位せず、図３の左半分に示すように、ステム２７はプライマリピストン３３によってのみ押し上げられ、セカンダリピストン３４の上端面は上記ステム２７の中途に形成したフランジ２７ｂから相対的に離間する。
【００４４】
又、上記プライマリピストン３３の下受圧面３３ａの面積が小さいため上記ステム２７は、図５に実線で示すように制動トルクの上昇を抑えた比較的緩いステム推力となり、ブレーキバンド２０ａを緩やかに押圧する。その結果、上記作動圧２Ａの過渡特性の下限値を必要以上に下げることなく、リバースクラッチドラム１９ａに対する締結力の急激な変化が抑制され、低エンジン負荷状態における１速から２速への変速時の変速ショックが緩和される。
【００４５】
そして、上記作動圧２Ａが次第に上昇し、やがてセカンダリピストン３４の下受圧面３４ａにかかる圧力が、作動点である例えば４Kgf/cm²に達すると、上記セカンダリピストン３４が上記セカンダリリターンスプリング３９ａ，３９ｂの付勢力に抗して上昇を開始する。このとき、図３の左半分に示すように、上記セカンダリピストン３４の上端面が上記ステム２７の中途に形成したフランジ２７ｂから相対的に離間されているため、先ず、上記セカンダリピストン３４の上昇によりこの空隙が縮小され、やがて、図４の右半分に示すように上記セカンダリピストン３４の上端面が上記ステム２７のフランジ２７ｂに当接すると、このステム２７が、上記プライマリピストン３３の下受圧面３３ａに作用する作動圧２Ａに加え、セカンダリピストン３４の下受圧面３４ａとの広い受圧面積に作用する作動圧２Ａにて押し上げられる。
【００４６】
その結果、図５に実線で示すように、ステム２７はセカンダリピストン３４のアシスト動作によりステム推力の変化が大きくなる。従って、このような高エンジン負荷運転時の作動圧２Ａの高い領域においては、従来と同様、十分な制動トルクでリバースクラッチドラム１９ａを締結することができる。
【００４７】
このように、本実施の形態では、ツインピストンによりステム２７を２段階に押圧するようにしたことで、ステム２７の変速初期におけるステム推力を比較的緩やかに設定することがでできると共に、ブレーキバンド２０ａの締結時には十分な制動トルクを付与することができる。
【００４８】
その結果、図７（ｂ）に示すように、作動圧２Ａの過渡特性が、従来（図１１(b)参照）のように短時間で急激に上昇することがなく、緩やかに設定することが可能となり、又、変速後期ではセカンダリピストン３４がアシスト動作するため、十分な制動トルクを付与することができる。又、同図（ａ）の領域Ｅ’に示すように、初期段階ではプライマリピストン３３のみの作動によりサーボピストン２７を緩やかに上昇させることができるため、変速時の加速度a(m/S²)のピークが抑制され、変速ショックが緩和される。
【００４９】
これに対して、図５に破線で示す従来のシングルピストンでは、作動圧２Ａに比例したステム推力しか得られず、従って変速初期の段階でのステム推力の変化が相対的に大きくなってしまい、変速ショックを抑制することが困難である。
【００５０】
一方、変速段が２速に変速されている状態から、３速へ変速させる場合、先ず、ハイクラッチ１８に対して作動圧３Ｒを供給し、このハイクラッチ１８を結合させ、更に、このハイクラッチ１８の結合が開始された後、セカンダリピストン３４の上面側に形成した第１リリースサーボ室４２ａに上記作動圧３Ｒと同一圧力の解放圧３Ｒを供給する。
【００５１】
すると、上記第１リリースサーボ室４２ａに供給された解放圧３Ｒが上記セカンダリピストン３４の上受圧面３４ｂを押圧すると共に、上記セカンダリピストン３４に穿設された流通孔３４ｃを介して第２リリースサーボ室４２ｂへ供給され、上記プライマリピストン３３の上受圧面４２ｂを押圧する。
【００５２】
上記両ピストン３３，３４は、解放圧３Ｒが作用する上受圧面３３ｂ，３４ｂと作動圧２Ａが作用する下受圧面３３ａ，３４ａとの受圧面積差及びリターンスプリング３８，３９ａ，３９ｂの付勢力との差圧による圧力の釣り合いにより後退する。
【００５３】
このとき、図６に示すように、上記上受圧面３３ｂ，３４ｂの面積が下受圧面３３ａ，３４ａの面積よりも広く設定されているため、ステム２７は変化量の多いステム推力で後退し、図に破線で示す従来のシングルピストンによるステム推力に比し、２＆４ブレーキ２０を速やかに解放する。
【００５４】
変速段を２速から３速へ変速するとき、ニュートラル状態を形成させないために、先ずハイクラッチ１８の係合を開始し、次いで２＆４ブレーキ２０を解放動作させるので、ハイクラッチ１８と２＆４ブレーキ２０とが同時に係合するオーバラップ状態が一時的に生じる。このオーバラップ状態は、変速段が４速に変速された状態と同じであり（表１参照）、駆動力が一時的に低下し易いが、本実施の形態では２＆４ブレーキ２０が速やかに解放されるので、オーバラップ期間が短く、従って、図８（ａ）の領域Ｆ’に示すように、駆動力の一時的な低下を示す期間が短縮され、その分、運転者に付与される不快な引き込み感が緩和される。
【００５５】
尚、本実施の形態では、摩擦ブレーキの一例として、２＆４ブレーキ２０を示したがＬ＆Ｒブレーキ２５等、他の摩擦ブレーキであっても採用可能である。
【００５６】
又、図９に本発明の第２実施の形態を示す。本実施の形態では、自動変速機の各摩擦クラッチを作動させるピストンをツインピストン化したものである。尚、本実施の形態では、摩擦クラッチの一例としてオーバランニング（ＯＶＲ）クラッチ２３ｂを示す。
【００５７】
このＯＶＲクラッチ２３ｂは、ＦＷクラッチドラム２３ｃとＦＷワンウェイクラッチ２４ａとに連設されており、セレクトレバーが３レンジ、２レンジ、１レンジの何れかにセットされた状態で前進走行する際に結合し、上記ＦＷワンウェイクラッチ２４ａの作動を固定するものである。
【００５８】
上記ＯＶＲクラッチ２３ｂの後端に、サーボユニットを構成するＯＶＲクラッチピストン５１が配設されている。このＯＶＲクラッチピストン５１は、プライマリピストン５２とセカンダリピストン５３とを有するツインピストン構造を成し、プライマリピストン５２が上記ＦＷクラッチドラム２３ｃに内装されていると共に、その開口端部が上記ＯＶＲクラッチ２３ｂの後端に当接されている。
【００５９】
又、上記セカンダリピストン５３が、上記プライマリピストン５２に内装されていると共に、その開口端部が上記プライマリピストン５２にスナップリング５４を介して掛止されている。
【００６０】
セレクトレバーが３レンジ、２レンジ、１レンジの何れかにセットされると、上記プライマリピストン５２の背面と上記ＦＷクラッチドラム２３ｃとで形成された第１サーボ室５５ａに、所定過渡特性の作動圧２Ａ’が供給されて、このプライマリピストン５２が押圧されると共に、上記プライマリピストン５２に穿設された流通孔５２ａを経て、上記プライマリピストン５２の内周と上記セカンダリピストン５３の背面とで郭成された第２サーボ室５５ｂに流入されて、このセカンダリピストン５３を押圧する。
【００６１】
そして、上記作動圧２Ａ’が上記プライマリピストン５２を反対方向へ付勢するプライマリリターンスプリング５６に打ち勝つと、上記プライマリピストン５２が上記プライマリリターンスプリング５６の付勢力に抗して前進し、その開口端部がＯＶＲクラッチ２３ｂを押圧する。
【００６２】
このとき、上記ＯＶＲクラッチ２３ｂはプライマリピストン５２のみによる緩い押圧力で係合されるため、係合動作が緩やかになり、結合時のトルクショックが緩和される。
【００６３】
一方、セカンダリピストン５３は、上記プライマリピストン５２よりも大きいばね定数のセカンダリリリーススプリング５７に反対方向へ付勢されているため、上記プライマリピストン５２が動作を開始した際には、未だ動作せず、上記作動圧２Ａ’が所定に上昇し、上記セカンダリリリーススプリング５７の付勢力に打ち勝つと、このセカンダリリリーススプリング５７の付勢力に抗して、図の左方向へ移動し、やがて、上記セカンダリピストン５３の開口端部が、上記スナップリング５４に当接すると、上記このセカンダリピストン５３が上記プライマリピストン５２をアシストし、上記ＯＶＲクラッチ２３ｂを十分な押圧力で結合させる。
【００６４】
その結果、ＯＶＲクラッチ２３ｂは、作動圧２Ａ’の低い作動初期の段階においてはプライマリピストン５２のみの作動による緩やかな締結力で結合させることができるためトルクショックが緩和される。そして、作動圧２Ａ’が上昇し、セカンダリリリーススプリング５７の付勢力に打ち勝つと、上記セカンダリピストン５３が上記プライマリピストン５２をアシスト動作し強い締結力で上記ＦＷワンウェイクラッチ２４ａの作動を固定する。
【００６５】
【発明の効果】
以上、説明したように本発明によれば、摩擦係合要素を係合動作させるピストンを受圧面積の狭いプライマリピストンと受圧面積の広いセカンダリピストンとのツインピストン構造としたので、作動圧の低い初期段階ではプライマリピストンのみにて上記摩擦係合要素をゆっくりと押圧することができ、その結果、低エンジン負荷運転時の変速初期に生じる変速ショックを、作動圧過渡特性の下限値を必要以上に下げることなく緩和することができる。又、上記摩擦係合要素を解放する際には、両ピストンに作用する作動圧を速やかに減少させることができるため、摩擦係合要素の解放タイミングが早くなり、その分、トルク不足によって生じる引き込み感が緩和される。その結果、変速時の走行安定性の向上を図ることができる。
【図面の簡単な説明】
【図１】第１実施の形態による自動変速機の動力伝達列を示す模式図
【図２】同、サーボユニットの断面図
【図３】同、図２の状態別の要部断面図
【図４】同、図２の状態別の要部断面図
【図５】同、作動圧の過渡特性に対するステム推力を示す特性図
【図６】同、解放圧の過渡特性に対するステム推力を示す特性図
【図７】同、１速から２速へ変速する際の加速度（変速ショック）と作動圧の過渡特性との関係を示す図表
【図８】同、２速から３速へ変速する際の加速度（変速ショック）と作動圧の過渡特性との関係を示す図表
【図９】第２実施の形態によるサーボユニットの断面図
【図１０】従来のサーボユニットの断面図
【図１１】従来の１速から２速へ変速する際の加速度（変速ショック）と作動圧の過渡特性との関係を示す図表
【図１２】従来の２速から３速へ変速する際の加速度（変速ショック）と作動圧の過渡特性との関係を示す図表
【符号の説明】
２Ａ，２Ａ’…作動圧
２０…摩擦係合要素（２＆４ブレーキ）
２３ｂ…摩擦係合要素（オーバランニングクラッチ）
２７…ステム
３３，５２…プライマリピストン
３３ａ，３４ａ…受圧面
３４，５３…セカンダリピストン[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic piston device for an automatic transmission that variably controls a brake operating pressure or a clutch operating pressure at the time of shifting according to an operating state.
[0002]
[Prior art]
In general, in an automatic transmission mounted on a vehicle such as an automobile, control is performed to automatically change the gear position according to the acceleration / deceleration of an accelerator pedal and the vehicle speed. And engagement or disengagement with respect to a frictional engagement element such as a clutch.
[0003]
For example, in Japanese Patent Application Laid-Open No. 61-119852, a brake drum connected to a sun gear of a planetary gear device is fastened by a brake, which is an example of a friction engagement element, when shifting the speed stage from the first speed to the second speed. Techniques to do this are disclosed.
[0004]
The operation of the brake device disclosed in this prior art will be described with reference to the drawing of FIG.
A band servo piston 4 is pivotally attached to the base of a stem 3 for fastening or releasing a brake band 2 wound around a brake drum 1 connected to a sun gear of a planetary gear device. Between the band servo piston 4 and the retainer 5 An actuating servo chamber 6 is formed. When the operating pressure 2A acting on the actuating servo chamber 6 is drained, the band servo piston 4 is moved backward by the urging force of the return spring 7 to release the brake, and the actuating servo chamber When the operating pressure 2A acts on 6, the band servo piston 4 pushes up the stem 3, and the brake band 2 connected to the stem 3 fastens and fixes the brake drum 1. As a result, the planetary gear unit sun gear is fixed and the gear position is changed from the first speed to the second speed.
[0005]
From this state, when the release pressure 3R acts on the release servo chamber 8 formed at a position facing the operation servo chamber 6 with the band servo piston 4 interposed therebetween, the band sabot piston 4 is The brake band 2 releases the brake drum 1 by retreating from the pressure balance due to the differential pressure between the operating pressure 2A and the release pressure 3R.
[0006]
The transient characteristic (shelf pressure) of the operating pressure 2A is set on the basis of the throttle opening, which is representative of the engine load. Since the operating pressure 2A is set low, the shift shock is reduced.
[0007]
[Problems to be solved by the invention]
By the way, the area of the pressure receiving surface that receives the operating pressure 2A of the band support piston 4 is set to a value that allows the brake drum 1 to be fastened against the engine torque (maximum torque) output when the throttle valve is fully opened. Designed. Therefore, in order to avoid a shift shock in the operation region where the engine torque is small, as shown in FIG. 11B, the lower limit value of the transient characteristic of the working pressure 2A is set low, and the transient characteristic at the initial stage of the shift is set. Must be set moderately. Further, in order to apply a braking torque sufficient to fasten the brake drum 1, it is necessary to change the transient characteristics in the later stage of the shift relatively large.
[0008]
However, since the lower limit value of the transient characteristic of the operating pressure 2A is inevitably derived from the capability of the hydraulic control system, it cannot be further reduced and has a limit. As a result, in the shift control during the low engine load operation, the thrust of the band servo piston 4 with respect to the stem 3 becomes excessive with respect to the engine torque, and the shift shock may not be sufficiently reduced.
[0009]
That is, as shown in a region E of FIG. 11A, in the slow acceleration operation in which the acceleration a hardly changes, the area of the pressure receiving surface of the band servo piston 4 is large, so the operating pressure 2A is lowered at the initial stage of operation. Even if the value is set, the fastening force to the brake drum 1 becomes excessive, and a sudden torque fluctuation occurs on the output side. This torque fluctuation causes the longitudinal acceleration a (m / S) of the vehicle body. ² ) Changes in a short time, and this is transmitted to the passenger as a shift shock.
[0010]
When shifting the gear stage from the second speed to the third speed, the release pressure 3R flows into the release chamber 8 and the brake band 2 releases the brake drum 1 and at the same time, the engine output is transmitted to the planetary gear of the planetary gear unit. The high clutch is engaged.
[0011]
The high clutch pressure for operating the high clutch and the release pressure 3R often use the same hydraulic pressure, and if the brake drum 1 is released before the high clutch is engaged as a shift timing, the engine Since the output is not transmitted to the planetary gear device, the engine temporarily turns into a neutral state and the engine rotation is blown up, so that the release operation of the brake drum 1 is started after the high clutch engagement operation is started. The accumulator characteristic for the band servo piston 4 is set.
[0012]
However, in the overlap state where both the high clutch and the brake drum 1 are engaged, the shift stage is the same as when the fourth speed is set, and the drive is caused by insufficient torque as shown in the region F in FIG. The power may temporarily decrease, which may give the driver an unpleasant pull-in feeling. FIG. 2B shows transient characteristics (shelf pressure) of the release pressure 3R and the high clutch pressure H / C.
[0013]
Note that a shift shock during low engine load operation may occur due to torque fluctuations before and after engagement even when a friction clutch such as a forward clutch or an overrunning clutch is engaged.
[0014]
In view of the above circumstances, the present invention alleviates shift shock and pull-in feeling at the initial stage of gear shifting during low engine load operation without unnecessarily lowering the lower limit value of the operating pressure having transient characteristics, and stabilizes running during gear shifting. It is an object of the present invention to provide a hydraulic piston device for an automatic transmission that improves performance.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, a hydraulic piston device of a first automatic transmission according to the present invention is an automatic transmission that changes an operating pressure with respect to a piston that engages a frictional engagement element along a transient characteristic. It consists of a primary piston with a small pressure receiving area and a secondary piston with a large pressure receiving area. A primary return spring that urges the primary piston; and a secondary return spring that urges the secondary piston and deflects at an operating pressure higher than the operating pressure at which the primary return spring bends. The secondary piston assists in addition to the primary piston as the return spring becomes higher than the biasing force. A hydraulic piston device for an automatic transmission.
[0016]
The hydraulic piston device of the second automatic transmission is the hydraulic piston device of the first automatic transmission, wherein the friction engagement element is a brake, and the both pistons are inserted into a stem connected to the brake, The operating pressure is higher than the operating pressure at which the primary return spring is bent and lower than the operating pressure at which the secondary return spring is bent. When the operating pressure is low, the primary piston presses the stem. Ru It is characterized by that.
[0017]
The hydraulic piston device of the third automatic transmission is the hydraulic piston device of the first automatic transmission, wherein the friction engagement element is a clutch, the primary piston is connected to the clutch, and the secondary piston is connected to the secondary piston. The primary piston can be moved forward and backward, The operating pressure is higher than the operating pressure at which the primary return spring is bent and lower than the operating pressure at which the secondary return spring is bent. When the operating pressure is low, the primary piston presses the clutch Ru It is characterized by that.
[0018]
That is, in the hydraulic piston device of the first automatic transmission, the piston that engages the friction engagement element is composed of a primary piston having a small pressure receiving area and a secondary piston having a large pressure receiving area, and a low operating pressure at the initial stage of shifting. Occasionally, the friction engagement element is engaged only with a primary piston with a small pressure receiving area, and the secondary piston with a large pressure receiving area is assisted in addition to the primary piston as the operating pressure gradually increases along the transient characteristics. Then, the friction engagement element is fastened and fixed.
[0019]
In the hydraulic piston device of the second automatic transmission, in the hydraulic piston device of the first automatic transmission, the friction engagement element is a brake, and a stem that is connected to a brake band that constitutes the brake is provided at the initial stage of shifting. When the operating pressure is low, the thrust is transmitted slowly to the stem while suppressing the braking torque by pressing only with the primary piston having a small pressure receiving area. Then, as the operating pressure increases, the brake is fastened by assisting the secondary piston having a large pressure receiving area in addition to the primary piston.
[0020]
In the hydraulic piston device of the third automatic transmission, in the hydraulic piston device of the first automatic transmission, the friction engagement element is a clutch, and only a primary piston having a small pressure receiving area is used at a low operating pressure in the initial stage of gear shifting. The clutch is slowly pressed against the increase in the operating pressure, and the secondary piston having a large pressure receiving area is assisted in addition to the primary piston in accordance with the increase in the operating pressure, thereby engaging the clutch.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 to 8 show a first embodiment of the present invention. FIG. 1 shows a power transmission train of an automatic transmission employed in the present embodiment.
[0022]
In this power transmission train, a torque converter 11, an oil pump 12, and a multistage transmission 13 are arranged from the input side, and driving force from the engine output shaft 14 passes through the torque converter 11 and the input shaft of the multistage transmission 13. 15 and the oil pump 12 is driven by the driving force from the engine.
[0023]
In the multi-stage transmission 13, a front planetary gear 16 and a rear planetary gear 17 are provided side by side on the input shaft 15, and each planetary gear 16 (17) includes a planetary carrier 16a (17a) and a ring gear 16b (17b). ), A pinion gear 16c (17c), and a sun gear 16d (17d).
[0024]
Further, in front of the front planetary gear 16, friction engagement elements such as a high clutch 18, a reverse clutch 19, and a 2 & 4 brake 20 are arranged in parallel.
[0025]
A planetary carrier 17 a of the rear planetary gear 17 rotates integrally with the ring gear 16 b of the front planetary gear 16 and is connected to the output shaft 22.
[0026]
Further, a forward (FW) clutch drum 23c is disposed on the outer periphery of the planetary gears 16 and 17, and the FW clutch drum 23c rotates integrally with the front planetary carrier 16a and is connected to the low one-way clutch 24b. . Further, a forward clutch 23a, which is an example of a friction engagement element, is interposed between the FW clutch drum 23c and the ring gear 17b of the rear planetary gear 17 via a FW one-way clutch 24a. Further, the FW one-way clutch 24a And the FW clutch drum 23c are connected to each other via an overrunning (OVR) clutch 23b which is an example of a friction engagement element. The OVR clutch 23b has a FW one-way clutch 24a when the select lever is set to a travel range (first speed, second speed, third speed,...) Other than the D (drive) range and the R (reverse) range. The operation of the is fixed.
[0027]
The low one-way clutch 24 that engages and disengages the planetary carrier 16a of the front planetary gear 16 and the transmission case 21 to the side of the rear planetary gear 17, and the low and reverse that prevents the low one-way clutch 24 from idling. An (L & R) brake 25 is arranged in parallel.
[0028]
The multi-stage transmission 13 having such a configuration has four forward speeds and one reverse speed, and includes the high clutch 18, the reverse clutch 19, the forward clutch 23a, the 2 & 4 brake 20, and the L & R brake 25. The gear position is set by the engagement or release operation.
Table 1 shows the operating relationship of each clutch and brake during shifting.
[0029]
[Table 1]

[0030]
As shown in Table 1, when shifting the gear stage from the first speed to the second speed, the forward clutch 23a is engaged and the 2 & 4 brake 20 is engaged. When shifting from 2nd gear to 3rd gear, at least
The 2 & 4 brake 20 is released and the high clutch 18 is connected.
[0031]
As shown in FIG. 2, the 2 & 4 brake 20 includes a brake band 20a wound around a reverse clutch drum 19a that rotates integrally with the sun gear 16d of the front planetary gear 16.
[0032]
Reference numeral 20 denotes a servo unit, and the tip of a stem 27 provided in the servo unit 20 is connected to one end of the brake band 20a via a strut 28. The other end of the brake band 20a is fixed to the transmission case 21 via an anchor end pin.
[0033]
The base end of the stem 27 is inserted into and supported by the servo unit main body 29 so as to be able to advance and retract. An overdrive (OD) piston 30 is inserted through the proximal end of the stem 27, and an OD retainer 31 is disposed at the bottom of the servo unit main body 29 facing the OD piston 30, and the OD piston 30 and the OD retainer 31. An OD servo chamber 32 is formed between the two.
[0034]
Further, in the middle of the stem 27, a primary piston 33 and a secondary piston 34 constituting a twin piston are inserted in order from the bottom. The upper end of the primary piston 33 is hooked on a step portion 27 a formed in the middle of the stem 27 via a washer 35, and is further hooked on the back surface of the primary piston 33 and above the OD piston 30. An OD return spring 37 is interposed between the primary retainer 36 and the primary retainer 36.
[0035]
The upper end of the secondary piston 34 is hooked on a flange 27b formed on the stem 27, and a primary return spring 38 is interposed between the back surface of the secondary piston 34 and the upper surface of the primary piston 33. It is disguised. Further, a pair of secondary return springs 39 a and 39 b are interposed between the upper surface of the secondary piston 34 and the upper surface of the servo unit main body 29.
[0036]
The primary piston 33 is expanded with two steps in the outer peripheral direction, and the inner peripheral side surface and the outer periphery of the OD piston 30 are fixed to the inner periphery of the servo unit main body 29. The servo retainer 40 is slidably supported. The outer periphery of the primary piston 33 is in sliding contact with the inner peripheral surface of the secondary piston 34 formed in a bag shape. Further, the outer peripheral lower end surface of the secondary piston 34 is hooked on the upper end of the servo retainer 40.
[0037]
A 2 & 4 servo chamber 41 is formed in a region surrounded by the servo retainer 40, the step portion 33a of the primary piston 33, the outer peripheral lower end surface 34a of the secondary piston 34, and the inner wall of the servo unit main body 29. The step 33a of the primary piston 33 and the outer peripheral lower end surface 34a of the secondary piston 34 form a lower pressure receiving surface. The area of both lower pressure receiving surfaces is set such that the lower pressure receiving surface (outer peripheral lower end surface) 34 a of the secondary piston 34 is wider than the lower pressure receiving surface (step portion) 33 a of the primary piston 33.
[0038]
Further, a first release servo chamber 42a is formed between the upper pressure-receiving surface 34b of the secondary piston 34 and the servo unit body 29, and the first release servo chamber 42a is formed in the secondary piston 34. The second release servo chamber 42 b defined by the bottom surface and the inner peripheral surface of the secondary piston 34 and the upper pressure receiving surface 33 b of the primary piston 33 is communicated with the second release servo chamber 42 b through the circulation hole 34 c.
[0039]
The OD servo chamber 32 is supplied with operating pressure 4A, the 2 & 4 servo chamber 41 is supplied with operating pressure 2A, and the first release servo chamber 42a is supplied with release pressure 3R. The primary return spring 38 that presses the primary piston 33 has a pressure per unit area applied to the lower pressure receiving surface 33a of the primary piston 33 of, for example, 0.5 kgf / cm. ² On the other hand, the pair of secondary return springs 39a and 39b that press the secondary piston 34 is set to bend when the pressure per unit area applied to the lower pressure receiving surface 34a of the secondary piston 34 is, for example, 4 kgf / cm. ² It is set to bend when it reaches.
[0040]
Next, the operation of the present embodiment having the above configuration will be described. Each servo chamber 32, 4 of the servo unit 26 1 In a state where the operating pressures 4A and 2A that act and the release pressure 3R that acts on the first and second release servo chambers 42a and 42b are all drained, the pistons 30, 33, and 34 have return springs 37, 38, Retraction is performed by the urging force of 39a and 39b, and the fastening of the stem 27 to the brake band 20a is released (the state of the right half in FIG. 2 or FIG. 3).
[0041]
In this state, when shifting the gear position from the first speed to the second speed, first, the operating pressure 2A is supplied to the 2 & 4 servo chamber 41 of the servo unit 26. The operating pressure 2A has a transient characteristic controlled as shown in FIG. 7A, for example, in accordance with a throttle opening, which is representative of engine load.
[0042]
Then, the operating pressure 2A increases, and the pressure applied to the lower pressure receiving surface 33a of the primary piston 33 is the operating point, for example, 0.5 kg / cm. ² , The operating pressure 2A overcomes the urging force of the primary return spring 38, and the primary piston 33 starts to rise against the urging force of the primary spring 38. A stepped portion 27a of the stem 27 is hooked on the upper end of the primary piston 33 via a washer 35, and the stem 27 is pushed up by the rising of the primary piston 33 (the state of the left half in FIG. 3).
[0043]
At this time, the operating pressure 2A also acts on the lower pressure receiving surface 34a of the secondary piston 34, but is not displaced because the urging forces of the secondary return springs 39a and 39b that press and urge the secondary piston 34 are large, and FIG. As shown in the left half, the stem 27 is pushed up only by the primary piston 33, and the upper end surface of the secondary piston 34 is relatively separated from the flange 27 b formed in the middle of the stem 27.
[0044]
Further, since the area of the lower pressure receiving surface 33a of the primary piston 33 is small, the stem 27 becomes a relatively loose stem thrust that suppresses an increase in braking torque as shown by a solid line in FIG. 5, and gently presses the brake band 20a. To do. As a result, a rapid change in the engagement force with respect to the reverse clutch drum 19a is suppressed without unnecessarily lowering the lower limit value of the transient characteristic of the operating pressure 2A, and a shift from the first speed to the second speed is performed in a low engine load state. The shift shock is reduced.
[0045]
Then, the operating pressure 2A gradually increases, and eventually the pressure applied to the lower pressure receiving surface 34a of the secondary piston 34 is the operating point, for example, 4 kgf / cm. ² The secondary piston 34 starts to rise against the urging force of the secondary return springs 39a and 39b. At this time, as shown in the left half of FIG. 3, the upper end surface of the secondary piston 34 is relatively separated from the flange 27 b formed in the middle of the stem 27. When this gap is reduced and eventually the upper end surface of the secondary piston 34 comes into contact with the flange 27b of the stem 27 as shown in the right half of FIG. 4, the stem 27 becomes the lower pressure receiving surface 33a of the primary piston 33. In addition to the operating pressure 2A acting on the secondary piston 34, it is pushed up by the working pressure 2A acting on a wide pressure receiving area with the lower pressure receiving surface 34a of the secondary piston 34.
[0046]
As a result, as shown by the solid line in FIG. 5, the stem 27 has a large change in stem thrust due to the assist operation of the secondary piston 34. Therefore, the reverse clutch drum 19a can be fastened with sufficient braking torque in the region where the operating pressure 2A during the high engine load operation is high as in the conventional case.
[0047]
As described above, in the present embodiment, the stem 27 is pressed in two stages by the twin piston, so that the stem thrust in the initial stage of the shift of the stem 27 can be set relatively gently, and the brake band can be set. Sufficient braking torque can be applied at the time of fastening of 20a.
[0048]
As a result, as shown in FIG. 7B, the transient characteristic of the operating pressure 2A does not increase rapidly in a short time as in the prior art (see FIG. 11B), and can be set gently. In addition, since the secondary piston 34 performs an assist operation in the latter stage of the shift, a sufficient braking torque can be applied. Further, as shown in a region E ′ of FIG. 5A, in the initial stage, the servo piston 27 can be gently raised only by the operation of the primary piston 33, so that the acceleration a (m / S during shifting) ² ) Peak is suppressed and the shift shock is alleviated.
[0049]
On the other hand, in the conventional single piston shown by the broken line in FIG. 5, only the stem thrust proportional to the operating pressure 2A can be obtained, and therefore the change in the stem thrust at the initial stage of the shift becomes relatively large. It is difficult to suppress shift shock.
[0050]
On the other hand, when shifting from the state where the gear stage is shifted to the second speed to the third speed, first, the operating pressure 3R is supplied to the high clutch 18, the high clutch 18 is coupled, and the high clutch 18 is further coupled. 18 is started, a release pressure 3R having the same pressure as the operating pressure 3R is supplied to the first release servo chamber 42a formed on the upper surface side of the secondary piston 34.
[0051]
Then, the release pressure 3R supplied to the first release servo chamber 42a presses the upper pressure receiving surface 34b of the secondary piston 34, and the second release servo via the flow hole 34c formed in the secondary piston 34. The pressure is supplied to the chamber 42b and presses the upper pressure receiving surface 42b of the primary piston 33.
[0052]
The pistons 33 and 34 have a difference in pressure receiving area between the upper pressure receiving surfaces 33b and 34b on which the release pressure 3R acts and the lower pressure receiving surfaces 33a and 34a on which the operating pressure 2A acts, and the urging force of the return springs 38, 39a and 39b. Retreats due to the balance of pressure due to the differential pressure.
[0053]
At this time, as shown in FIG. 6, since the area of the upper pressure receiving surfaces 33b, 34b is set larger than the area of the lower pressure receiving surfaces 33a, 34a, the stem 27 is retracted by a stem thrust with a large amount of change, Compared with the stem thrust by the conventional single piston shown by the broken line in the figure, the 2 & 4 brake 20 is quickly released.
[0054]
When shifting the gear stage from the 2nd speed to the 3rd speed, in order not to form a neutral state, first the engagement of the high clutch 18 is started and then the 2 & 4 brake 20 is released, so the high clutch 18 and the 2 & 4 brake 20 An overlap condition occurs in which the two engage simultaneously. This overlap state is the same as the state in which the gear stage is shifted to the fourth speed (see Table 1), and the driving force tends to temporarily decrease, but in this embodiment, the 2 & 4 brake 20 is released quickly. Therefore, the overlap period is short. Therefore, as shown in the region F ′ in FIG. 8A, the period during which the driving force is temporarily reduced is shortened, and the unpleasant feeling given to the driver correspondingly. The feeling of pulling is reduced.
[0055]
In the present embodiment, the 2 & 4 brake 20 is shown as an example of the friction brake, but other friction brakes such as the L & R brake 25 can also be adopted.
[0056]
FIG. 9 shows a second embodiment of the present invention. In this embodiment, the piston that operates each friction clutch of the automatic transmission is made into a twin piston. In the present embodiment, an overrunning (OVR) clutch 23b is shown as an example of a friction clutch.
[0057]
The OVR clutch 23b is connected to the FW clutch drum 23c and the FW one-way clutch 24a, and is coupled when the select lever is set to travel in the 3rd range, the 2nd range, or the 1st range. The operation of the FW one-way clutch 24a is fixed.
[0058]
An OVR clutch piston 51 constituting a servo unit is disposed at the rear end of the OVR clutch 23b. The OVR clutch piston 51 has a twin piston structure having a primary piston 52 and a secondary piston 53. The primary piston 52 is built in the FW clutch drum 23c, and its open end is the same as that of the OVR clutch 23b. It is in contact with the rear end.
[0059]
The secondary piston 53 is housed in the primary piston 52, and the opening end of the secondary piston 53 is hooked on the primary piston 52 via a snap ring 54.
[0060]
When the select lever is set to any one of the 3 range, 2 range and 1 range, the first servo chamber 55a formed by the back surface of the primary piston 52 and the FW clutch drum 23c has an operating pressure with a predetermined transient characteristic. 2A ′ is supplied, the primary piston 52 is pressed, and the inner periphery of the primary piston 52 and the back surface of the secondary piston 53 are formed through a flow hole 52a formed in the primary piston 52. Then, the secondary piston 53 is pressed into the second servo chamber 55b.
[0061]
When the operating pressure 2A ′ overcomes the primary return spring 56 that biases the primary piston 52 in the opposite direction, the primary piston 52 moves forward against the biasing force of the primary return spring 56, and its open end The portion presses the OVR clutch 23b.
[0062]
At this time, since the OVR clutch 23b is engaged by a loose pressing force only by the primary piston 52, the engagement operation becomes gentle and the torque shock at the time of coupling is alleviated.
[0063]
On the other hand, since the secondary piston 53 is biased in the opposite direction by the secondary release spring 57 having a spring constant larger than that of the primary piston 52, when the primary piston 52 starts operating, the secondary piston 53 does not operate yet. When the operating pressure 2A ′ rises to a predetermined level and overcomes the urging force of the secondary release spring 57, it moves to the left in the figure against the urging force of the secondary release spring 57, and eventually the secondary piston 53 The secondary piston 53 assists the primary piston 52, and the OVR clutch 23b is coupled with a sufficient pressing force when the open end of the second ring 53 comes into contact with the snap ring 54.
[0064]
As a result, the OVR clutch 23b can be coupled with a moderate engagement force by the operation of only the primary piston 52 at the initial stage of operation where the operating pressure 2A ′ is low, so that the torque shock is alleviated. When the operating pressure 2A ′ rises and overcomes the urging force of the secondary release spring 57, the secondary piston 53 assists the primary piston 52 and fixes the operation of the FW one-way clutch 24a with a strong fastening force.
[0065]
【The invention's effect】
As described above, according to the present invention, the piston for engaging and engaging the friction engagement element has a twin piston structure of a primary piston having a small pressure receiving area and a secondary piston having a large pressure receiving area. At this stage, the friction engagement element can be slowly pressed only by the primary piston, and as a result, the shift shock that occurs at the beginning of the shift during low engine load operation is lowered more than necessary. Can be relaxed without any problems. Further, when releasing the friction engagement element, the operating pressure acting on both pistons can be quickly reduced, so the release timing of the friction engagement element is advanced, and the pull-in caused by the torque shortage correspondingly. The feeling is eased. As a result, it is possible to improve the running stability during shifting.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a power transmission train of an automatic transmission according to a first embodiment.
FIG. 2 is a sectional view of the servo unit.
3 is a cross-sectional view of the main part according to the state of FIG.
4 is a cross-sectional view of the main part according to the state of FIG.
FIG. 5 is a characteristic diagram showing stem thrust with respect to transient characteristics of operating pressure.
FIG. 6 is a characteristic diagram showing stem thrust with respect to a transient characteristic of release pressure.
FIG. 7 is a chart showing a relationship between acceleration (shift shock) and a transient characteristic of operating pressure when shifting from the first gear to the second gear.
FIG. 8 is a chart showing the relationship between acceleration (shift shock) and transient characteristics of operating pressure when shifting from 2nd gear to 3rd gear.
FIG. 9 is a sectional view of a servo unit according to a second embodiment.
FIG. 10 is a sectional view of a conventional servo unit.
FIG. 11 is a chart showing a relationship between acceleration (shift shock) and a transient characteristic of operating pressure when shifting from the first speed to the second speed in the related art.
FIG. 12 is a chart showing a relationship between acceleration (shift shock) and a transient characteristic of operating pressure when shifting from the second speed to the third speed in the related art.
[Explanation of symbols]
2A, 2A '... Working pressure
20 ... friction engagement element (2 & 4 brake)
23b ... Friction engagement element (overrunning clutch)
27 ... Stem
33, 52 ... Primary piston
33a, 34a ... pressure receiving surface
34, 53 ... Secondary piston

Claims (3)

In an automatic transmission that changes an operating pressure for a piston that engages and operates a frictional engagement element along a transient characteristic,
The piston is composed of a primary piston with a small pressure receiving area and a secondary piston with a large pressure receiving area ,
A primary return spring that biases the primary piston, and a secondary return spring that biases the secondary piston and bends at an operating pressure higher than the operating pressure at which the primary return spring is deflected,
The hydraulic piston device for an automatic transmission, wherein the secondary piston assists in addition to the primary piston as the operating pressure increases beyond the urging force of the secondary return spring . The friction engagement element is a brake;
Insert both pistons into the stem connected to the brake,
The primary piston that <br/> you press the stem when the actuation pressure is the primary return spring flexes higher than the working pressure and the secondary return spring flexes operation lower than pressure lower working pressure The hydraulic piston device for an automatic transmission according to claim 1. The friction engagement element is a clutch;
The primary piston is connected to the clutch;
The secondary piston is mounted on the primary piston so as to freely advance and retract,
The primary piston that <br/> you press the clutch when the operating pressure is the primary return spring flexes higher than the working pressure and the secondary return spring flexes operation lower than pressure lower working pressure The hydraulic piston device for an automatic transmission according to claim 1.

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