動(dòng)力換檔變速器的進(jìn)一步發(fā)展和電控單元開發(fā)過程的重要性

Dipl.Ing.（FH）Christoph G?bel ZF Friedrichshafen AG－Operations and Technology ZF Group

1 前言

多年來，無級(jí)變速器已成功進(jìn)入市場(chǎng)。但是多檔變速器（通常在部分載荷下?lián)Q檔）仍然是拖拉機(jī)的標(biāo)準(zhǔn)傳動(dòng)方式。這就是為什么會(huì)產(chǎn)生將無級(jí)變速器（功能更多、操作更便捷、更舒適、自動(dòng)控制等）所具有的功能擴(kuò)展到多檔變速器中。

這里部分挑戰(zhàn)來自定義批量生產(chǎn)準(zhǔn)備階段的功能和通過機(jī)械、液壓和電子（硬件和軟件）加以實(shí)現(xiàn)。不斷增加的控制單元、界面、（某些時(shí)候與CAN網(wǎng)絡(luò)的聯(lián)接）功能需要更具創(chuàng)新性的開發(fā)過程，特別是涉及軟件時(shí)。

本文通過實(shí)例敘述拖拉機(jī)用多檔變速器功能的擴(kuò)展和說明必要的軟件開發(fā)過程基本原理。

1 Introduction

For some years now，continuously variable transmissions are introduced successfully on the market.Nevertheless，multistep transmissions（usually shiftable under partial load）remain the standard drive solution for tractors.This is why ideas from continuously variable transmissions（additional functions，easier operation with increased comfort，automation，etc.）are also applied to multistep transmissions more and more.

A particular challenge here is to specify volume－production－ready functions and implement them in mechanics，hydraulics，and electronics（both hardware and software）.The growing number of control units，interfaces，and（in some cases interlinked on e.g.CAN network）functions require more innovative development processes，especially when it comes to software.

This article uses examples to describe expanded functions of multistep transmissions for tractors，and explains basic principles of the necessary software development processes.

2 T7000拖拉機(jī)傳動(dòng)裝置、系統(tǒng)詳細(xì)資料

帶動(dòng)力換檔的拖拉機(jī)具有很多種用于控制各項(xiàng)功能的操作機(jī)構(gòu)和顯示元件?？紤]到當(dāng)今復(fù)雜拖拉機(jī)所具有的范圍廣泛的行駛、作業(yè)和操作功能（圖1），控制系統(tǒng)的人機(jī)工程設(shè)計(jì)就成為一個(gè)重要因素。目前在技術(shù)方面的創(chuàng)新關(guān)注于這些需求并至少向以下目標(biāo)之一前進(jìn)：

·通過自動(dòng)控制的典型程序提高駕駛舒適性

·利用人機(jī)工程設(shè)計(jì)的控制和顯示設(shè)備改善操作舒適性

·提高換檔品質(zhì)

·通過提高最高行駛速度擴(kuò)展拖拉機(jī)使用范圍

·縮短響應(yīng)時(shí)間以優(yōu)化作業(yè)過程

·減少反作用力以提高使用壽命

以下將通過大量實(shí)例論述在不影響安全性和可靠性的前提下這些目標(biāo)是如何實(shí)現(xiàn)的。

2 T7000Tractor Transmission，System Details

Tractors with powershift transmissions feature a large number of operating and display elements for control of the various functions.Considering the extensive range of driving，working，and operating functions of today＇s complex tractors（Figureergonomic design of the control system is a major factor.Today＇s technological innovations address these needs and pursue at least one of the following goals：

·Increasing driving comfort through automation of typical processes

·Increasing operating comfort with ergonomic design of the controls and displays

·Improving shifting comfort

·Expanding the scope of the tractor by increasing the maximum driving speed

·Optimizing working processes through shorter reaction times

·Increasing service life with smaller reaction forces

In the following，various examples are used to illustrate how these goals are achieved without compromising on safety and reliability.

圖1 T7000變速器控制系統(tǒng)簡(jiǎn)圖Fig.1 System control schema of atypical T7000transmission application

3 增加舒適性、自動(dòng)操作和安全性方面的功能

3.1 自動(dòng)耕地/道路切換（FRRS）

ZF公司T7000變速器可作為一個(gè)頻繁切換過程自動(dòng)操作的良好實(shí)例。它包括4檔/6檔同步嚙合變速器，并帶有一個(gè)兩速組合式變速器用于耕地/道路工況。在過去，組合式變速器的切換必須在近乎靜止?fàn)顟B(tài)下手動(dòng)完成。而目前該過程可部分實(shí)現(xiàn)自動(dòng)化，其優(yōu)點(diǎn)是：

·方便駕駛員操縱

·可在某一速度范圍內(nèi)進(jìn)行切換

·破損安全操作

組合式變速器切換步驟如下：

駕駛員按下一個(gè)預(yù)選開關(guān)向變速器電控系統(tǒng)提示他所要求切換的工況。

系統(tǒng)檢查以下邊界條件是否滿足：

·同步嚙合換擋桿是否處于空檔

·離合器踏板是否踩下

·行駛速度是否處于速度限制范圍內(nèi)然后，相應(yīng)的電磁閥被激活。位置傳感器確認(rèn)切換成功。

安全功能（定時(shí)鎖、同步嚙合變速器用電磁閥閉鎖和操作失敗后限制重試次數(shù)）防止了非允許的換檔和損害。

3.2 自動(dòng)離合器工作（換檔舒適，CS）

換檔舒適性和主離合器激活功能得到了改善。采用新型的比例控制后，操作過程由先前的開環(huán)控制便成為閉環(huán)控制。踩下離合器踏板操縱主離合器（或向動(dòng)力換檔離合器映射主離合器功能）是一個(gè)經(jīng)常重復(fù)的步驟，它出現(xiàn)在各種主要行駛工況下（起步、倒車、變速換檔、蠕動(dòng)等）。尤其是在離合器結(jié)合過程中，駕駛員必須考慮所有條件（速度、負(fù)載、壓力、速比）。在自動(dòng)控制中，駕駛員按下一個(gè)在換擋桿上的離合器按鈕激活該過程。根據(jù)上述的邊界條件，電子系統(tǒng)估計(jì)適當(dāng)?shù)墓ぷ鳡顟B(tài)并調(diào)整離合器壓力，這具有以下優(yōu)點(diǎn)：

·更舒適的離合器結(jié)合

·較少的駕駛員工作（單手操縱離合器和換檔控制）

·最佳的壓力調(diào)節(jié)降低離合器和傳動(dòng)系統(tǒng)的應(yīng)力

·行駛功能最優(yōu)控制以提高工作性能1）

3 Functions for increasing comfort，automation and safety

3.1 Automated field to road switchover（FRRS）

The T7000transmission from ZF provides a good example of the automation of frequently recurring processes.It combines a 4－speed/6－speedsynchromesh transmission with a 2－speed group transmission for field/road operation.In the past，the synchronized switchover of the groups had to be performed manually and almost at a standstill.Now it’s established，that this procedure is partially automated，with the following benefits：

·Easier for the driver

·Switchover while driving within a certain speed range

·Failsafe operation

The steps for a group switchover are：

The driver presses a preselection key to indicate to the transmission electronics that he wishes to switch groups.

The system checks that the following boundary conditions are met：

·Synchromesh shift lever in neutral

·Clutch pedal depressed

·Driving speed within speed limit

3.3 自動(dòng)動(dòng)力換檔（APS）

同樣自動(dòng)動(dòng)力換檔功能（APS）也已通過新型比例閉環(huán)控制加以改善。

拖拉機(jī)速度在很大程度上取決于當(dāng)前的工況。駕駛員通過確定某一發(fā)動(dòng)機(jī)速度、掛入合適的檔位和選擇合適的動(dòng)力換檔過程來影響速度。

自動(dòng)動(dòng)力換檔的目的的將駕駛員從選擇動(dòng)力換檔時(shí)機(jī)中解放出來。而是由系統(tǒng)根據(jù)一些變量自動(dòng)完成該項(xiàng)任務(wù)。行駛策略系統(tǒng)根據(jù)速度、轉(zhuǎn)速梯度、發(fā)動(dòng)機(jī)負(fù)荷和發(fā)動(dòng)機(jī)速度降低等估計(jì)出正確的動(dòng)力換檔時(shí)機(jī)。

駕駛員可根據(jù)特殊的工作狀態(tài)自行選擇換檔閾值。自動(dòng)換檔系統(tǒng)依據(jù)不同的外界負(fù)荷和駕駛員的手動(dòng)操縱（檔位、組合式變速器、行駛方向等）選擇正確的動(dòng)力換檔時(shí)機(jī)。這樣，系統(tǒng)能夠快速識(shí)別最佳換檔點(diǎn)，并具有以下優(yōu)點(diǎn)：

·牽引力或油耗最優(yōu)的檔位

·對(duì)載荷變化系統(tǒng)響應(yīng)更快

·減少駕駛員工作

·增加舒適性

3.4 動(dòng)力換檔操縱品質(zhì)最佳

采用比例控制閥使得動(dòng)力換檔操縱品質(zhì)在換檔舒適性方面實(shí)現(xiàn)盡善盡美。每個(gè)離合器的壓力可單獨(dú)控制。根據(jù)變速器工作條件（例如溫度、負(fù)載、檔位變化、速度），變速器控制器計(jì)算出最佳動(dòng)力換檔順序并實(shí)施之。其它優(yōu)點(diǎn)是提供過載保護(hù)和提高離合器轉(zhuǎn)矩傳遞能力，其結(jié)果是倒車更快速。

3.5 電控同步嚙合換檔撥叉

電控?fù)Q檔撥叉單元是下一級(jí)自動(dòng)控制。該單元的任務(wù)是根據(jù)來自變速器控制器的電信號(hào)在6個(gè)同步嚙合齒輪副間換檔。電控取代機(jī)械執(zhí)行器后換檔撥叉單元的效能大為提高。這意味著操作元件的設(shè)計(jì)變成為線控?fù)Q檔方法，因此更容易實(shí)現(xiàn)。另外無需駕駛員提供相應(yīng)的操縱力而且換檔過程及其精確。除了手動(dòng)操作選擇，依據(jù)換檔策略也可自動(dòng)選擇。換檔撥叉單元由變速器控制器控制。為完成該任務(wù)配備有兩個(gè)結(jié)合/脫開電磁閥、兩個(gè)比例電磁閥和一個(gè)位置傳感器。

3.6 推進(jìn)功率的使用和控制

推進(jìn)功率是額外的預(yù)備功率，在某些工況下將后備功率接入變速器和發(fā)動(dòng)機(jī)。當(dāng)需要單獨(dú)牽引時(shí)推進(jìn)功率提供更大的功率起動(dòng)性能。其意圖是使用帶大功率動(dòng)力輸出軸機(jī)械的輕型車輛。

Then，the corresponding solenoid valve is actuated.

A position sensor transmits a confirmation of successful switchover.

Safety functions（time lock，locking solenoid for synchromesh transmission，and limit to number of re－tries after failure）prevent non－permitted gear changes and damage.

3.2 Automated clutch operation （comfort shift，CS）

The familiar function of comfort shift as well as the actuation of the main clutch has been improved.With the new proportional control the processes which were previously open－loop now have closed－loop control.Pressing the clutch pedal to operate the main clutch（or mapped main clutch functionality to powershift clutches）is a frequently repeated process that occurs in many driving situations（setting off，reversing，gearshifts，inching，etc.）.Especially during clutch engagement，the driver needs to take into account a whole range of conditions（speed，load，compression，speed ratio）.In automatic control，the driver actuates this process by pressing a clutch button on the shift lever.Based on the boundary conditions described above，the electronics calculate the appropriate operating mode and modulate the clutch pressure，resulting in the following advantages：

·More comfortable clutch engagement

·Less work for the driver（clutch and gear shift controls in one hand）

·Optimum pressure modulation reduces stress on clutch and driveline.

·Optimized control of driving functions increases work performance

3.3 Automatic powershift（APS）

Also the established automatic powershift function（APS）has been improved with the new proportional closed－loop control.

The tractor speed depends to a large extent on what it is currently being used for.The driver influences the speed by determining a certain engine speed rate，engaging a suitable synchronous gear，and additionally by selecting an appropriate power－shift stage.

推進(jìn)功率功能具有兩個(gè)必要的特征：

1、帶電控發(fā)動(dòng)機(jī)控制器的現(xiàn)代柴油機(jī)，它能夠采用不同的發(fā)動(dòng)機(jī)特性（轉(zhuǎn)矩曲線）。

2、智能化軟件算法能夠察覺除牽引工況之外所需的附加功率，例如PTO工作、空調(diào)或低效率行車條件。

變速器控制單元根據(jù)諸如尤其速度、變速器速比和各種發(fā)動(dòng)機(jī)輔助驅(qū)動(dòng)等工況決定采用那種功率特性曲線。這里，功率流可根據(jù)工作點(diǎn)而優(yōu)化，這功能僅在幾個(gè)控制單元相互聯(lián)系的情況下才能實(shí)現(xiàn)。

3.7 PTO啟動(dòng)控制

除了車輛行駛外，取力器是拖拉機(jī)上一個(gè)相當(dāng)重要的轉(zhuǎn)換變速器。預(yù)選2檔或4檔PTO速比則是行駛開關(guān)切換過程的一部分。

事實(shí)上經(jīng)改進(jìn)的PTO控制相當(dāng)容易。采用調(diào)節(jié)比例閥控制后，駕駛員僅感覺到有一個(gè)非常平滑的啟動(dòng)。借助于比例閥技術(shù)和變速器控制單元與新開發(fā)軟件的交互作用使得在任何負(fù)載慣量下的啟動(dòng)非常平滑。低慣量的突然啟動(dòng)或高慣量負(fù)荷時(shí)的發(fā)動(dòng)機(jī)停轉(zhuǎn)已成為過去。

該功能能夠保護(hù)部件并提供更高的安全工作環(huán)境。

3.8 機(jī)電駐車制動(dòng)

機(jī)電駐車制動(dòng)改善了操作者的安全性和舒適性。這項(xiàng)創(chuàng)新也擴(kuò)展了變速器現(xiàn)有的功能。像動(dòng)態(tài)制動(dòng)和汽車應(yīng)用等功能將實(shí)現(xiàn)自動(dòng)操作，其結(jié)果是簡(jiǎn)化了手動(dòng)操作的動(dòng)作。

駐車制動(dòng)的實(shí)施和解鎖由駕駛室中的開關(guān)完成，所以駐車制動(dòng)操縱桿已不再需要。當(dāng)開關(guān)切斷點(diǎn)火或離開駕駛室時(shí)，制動(dòng)過程自動(dòng)實(shí)施。

同時(shí)機(jī)電駐車制動(dòng)為駕駛室設(shè)計(jì)提供更多的便利，因?yàn)橥ǔ２捎玫臋C(jī)械推拉式鋼索被電線所替代。

4 軟件開發(fā)過程的重要性

上述現(xiàn)代拖拉機(jī)變速器功能的開發(fā)和改進(jìn)在很大程度上是由軟件所控制。因此，在農(nóng)業(yè)機(jī)械市場(chǎng)上的應(yīng)用正在增大：

·實(shí)現(xiàn)功能的軟件必須視作為一個(gè)“產(chǎn)品”，并且變得日益重要。

·如同硬件，“軟件”產(chǎn)品必須經(jīng)定義、設(shè)計(jì)、開發(fā)、試驗(yàn)和驗(yàn)證。這里有特殊的開發(fā)過程。

多年前ZF公司就認(rèn)識(shí)到軟件開發(fā)和相關(guān)過程的重要性。其結(jié)果是，公司完成了從基于工藝（技工）型企業(yè)到體系系統(tǒng)化、過程導(dǎo)向型工業(yè)的轉(zhuǎn)變。

只有當(dāng)合適的開發(fā)過程被確立后，再現(xiàn)性、可追溯性、定量和傳輸可靠性等各種需要才能滿足。公司還必須在合適工具和過程高效管理、過程控制等方面提供支持。所有這一切的基礎(chǔ)是由現(xiàn)代化高效工具所支持的精致的工作流程管理。

The purpose of the automatic powershift is to free the driver from having to select the powershift stage.Instead the system automatically takes over this task depending on a number of variables.The driving strategy system calculates the right powershift stage according to the speed，rpm gradient，engine load，and engine speed reduction.

The driver has the option of setting shift thresholds himself according to the specific working situation.The automatic system selects the right powershift stage not only in the case of different external loads，but also when the driver makes manual changes（synchromesh gear，group，direction of travel）.In this way，the system identifies the optimal operating point faster，leading to the following advantages：

·Optimum gear in terms of tractive force or fuel consumption

·Faster system response to load changes

·Less work for the driver

·Increased comfort.

3.4 Quality of powershift operations in perfection

It’s for the use of proportional controlled valves excellently due to，that the quality of powershift operations reaches perfection regarding shifting comfort.The pressure for each clutch can be controlled individually.According to the transmission operating conditions（e.g.temperature，load，gear transition，speed）the best powershifting sequence will be calculated by the transmission controller and carried out.Further advantages are the overload protection and the increased transfer capability of the clutches，which results，for example，in quicker reversing.

3.5 Electronically controlled synchromesh gearshifter

The electronically controlled gear－shifter unit represents the next grade of automation.The job of this unit is to shift all 6synchromesh gears according to electrical signals from the transmission controller.The gear－shifting unit is more efficient in case of electronically control instead of mechanic actuation.This means that the design of the oper－ating element is changed to the method shift by wire and therefore easier for realization.Further advantages are e.g.no relevant operating force necessary by the driver and highest operating preciseness.Additional to manual operating selection also automatic selection following the shift strategy is possible.The gear－shifter unit is controlled by the transmission controller.For this task two on/off solenoid valves，two proportional solenoid valves and a position sensor are used.

軟件開發(fā)步驟與變速器應(yīng)用場(chǎng)合（轎車、商用車、非公路車輛）大體無關(guān)。所有ZF軟件工程師都在聯(lián)合電子部門工作。這意味著他們能夠充分利用各部門間的協(xié)調(diào)優(yōu)勢(shì)。他們特別關(guān)注功能的再利用、軟件模塊、程序、功能的安全性和整個(gè)工作流程。

這里給出的V型（圖2）模塊是軟件開發(fā)過程的基礎(chǔ)。它描述了軟件開發(fā)過程中各階段工作的詳細(xì)執(zhí)行順序以及文檔和相應(yīng)工具方面的支持。

為確保公司軟件開發(fā)工作的效率不變，我們經(jīng)常進(jìn)行內(nèi)部和外部評(píng)估。分析和評(píng)估過程的強(qiáng)項(xiàng)和弱點(diǎn)，因而能夠不斷升級(jí)。

這里顯示了ZF公司今后繼續(xù)為車輛應(yīng)用開發(fā)復(fù)雜軟件的能力。

3.6 Usage and control of boost power

Boost power is the provision of extra power in certain operating situations by tapping into the power reserves in the transmission and the engine.The boost power provides the power take－off more performance when this would be needed for traction alone.The established intention was to use a lightweight basic vehicle in combination with powerful PTO－shaft machines.

圖2 V型模塊軟件開發(fā)Fig.2 V－model of software development

Two features are necessary for the boost power function：

1.A modern diesel engine with an electronic engine controller that allows different engine characteristics（torque curves）to be used

2.An intelligent software algorithm which detects an additional power requirement beyond the traction work itself，e.g.PTO in operation，air conditioning system，or low－effectiveness driving conditions.

The transmission control unit determines which power characteristic curve is applied depending on conditions such as travel speed，transmission ratio，and use of various engine－driven auxiliaries.In this way，the power flow can be optimized according to the operating points，a function that is only possible with the interconnection of several control units.

3.7 PTO start－up control

Apart from the vehicle drive，the power takeoff drive is one of the most important conversion transmissions in tractors.The pre－selection for 2to 4PTO gear ratios is part of the drive switching on and off processes.

Also，the fact that the PTO control has been improved has made handling easier.With the regulated proportional valve control the driver experiences a smoother start－up.The interaction with the new software development for the transmission control unit enables a smooth start－up with the proportional valve technology for each implement inertia.Sudden start－off with low inertia or engine stalling with high inertia implements have become a thing of the past.This function protects the components and implements and meets higher safety oper－ation.

3.8 Electro－mechanical Parking Brake

The electro－mechanical parking brake improves safety and comfort for the operator.This innovation also extends the transmissions’existing range of functions.Functions like dynamic braking and auto apply will automate and，as a result，simplify a variety of actions，which have so far been manual.

The parking brake is applied and released by a switch in the driver’s cab，so the parking brake lever used so far is no longer required.The brake is automatically applied upon switching off the ignition or leaving the driver’s cab.

Also the electro－mechanical parking brake offers more flexibility for the design of the cabin because the normally used mechanical push－pull cable is replaced by electrical wire.

4 The Importance of Software Development Processes

Many of the newly developed and improved functions in modern tractor transmissions as described above are wholly or partly controlled by software.Consequently，there is an increasing realization on the agricultural machinery market of the following points：

·Software for the implementation of functions must be seen as a"product"，and is becoming increasingly important.

·Just like hardware，the"software"product must be specified，designed，developed，tested，and validated.There are specific development processes for this.

ZF recognized the importance of SW development and the associated processes many years ago.As a result，the company initiated and completed the transition from a craft－based（"artisan"）company to a systematically structured，process－oriented industrial player.

A whole range of requirements such as reproducibility，traceability，quantifiability，and delivery reliability can only be met when suitable develop－ment processes have been installed.We also have to provide support with the right tools and efficient process management，including process controlling.The basis for this is a tailored workflow management also supported by modern effective tools.

The software development procedure is mainly unrelated to the transmission application （passenger car，commercial vehicle，off－road machinery，…）.All ZF software engineers work together in the Corporate Electronics department.This means they can make the most of interdepartmental synergies.They focus in particular on function reuse，SW modules，processes，functional safety and the entire workflow.

The V－model shown here（Figure2）provides the basis for the SW development process for all applications.It describes the individual work stages to be carried out in a defined order during software development，supported by documents and appropriate tools.

To secure the sustained effectiveness of our SW development work，we regularly carry out internal and external assessments.These analyze and evaluatethestrenthsandweaknessesofthe process，so it can be continually upgraded.

This gives ZF the capacity，also in the future，to continue to develop complex SW for all vehicle applications.

［1］ Cappellaro T.，Geiger R.，Grad K.und Gruhle W.－D.：Weiterentwicklung an Lastschaltgetriebe und die Bedeutung des Entwicklungsprozesses von elektronischen Steuerungen.VDI－MEG TAGUNG Landtechnik 2004.

［2］ Renius，K.－Th.u.M.Martinus：Motoren und Getriebe bei Traktoren.In：Jahrbuch Agrartechnik 16 （2004）S.60－66u.S.234－235.Münster：Landwirtschaftsverlag 2004.

［3］ Grad，K.：Stand und Neuheiten bei Traktorgetrieben unter besonderer Berücksichtigung der Anforderungen der alpinen Landwirtschaft.7.FAT/BLT－Tagung Landtechnik im Alpenraum，F(xiàn)eldkirch 11.－12.Mai 2004.Langfassung unter：http：//www.blt.bmlfuw.gv.at.

［4］ Feulner，P.，M.Sieger und F.K?nig：Workflow－Management in der Software－Entwicklung，Effizienzsteigerung durch Wiederverwendung von Prozessen.VDI－Tagung Elektronik im Kraftfahrzeug，Baden－Baden 2004.

［5］ Bilder：ZF