Elektrikle tahrikli bir tarım traktörünün tasarım ve analizi
Design and analysis of agricultural tractor driven with electric motor
Yazar: BELGÜTEY SAVAŞIR
Danışman: PROF. DR. İSMAİL MURAT EREKE ; ÖĞR. GÖR. ORHAN ATABAY
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Otomotiv Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Mühendislik Bilimleri = Engineering Sciences

Özet:
Son yıllardaki petrol kaynaklarındaki azalma insanoğlunu yenilenebilir enerji kullanımına yönlendirmiştir. Özellikle otomotiv sanayindeki petrol ihtiyacı günden güne artmakta olduğu için yenilenebilir enerjilerin kullanımı için çalışmalar hızlandırılmıştır. 
Yapılan literatür araştırmasında, traktörler için yenilenebilir enerji kullanımının binek veya ticari araçlara oranla çok az olduğu gözlemlenmiştir. Traktörlerde son 10 yıla kadar yapılan elektrik motoru uygulamaları genellikle mevcut bir traktörün içten yanmalı motorunun çıkarılıp yerine elektrik motoru ve bataryalar yerleştirilmesi şeklindedir. Önceleri 10-20 kW gücünde ve kısa çalışma süresine sahip olan elektrikli traktör uygulamaları son yıllarda ise birkaç üniversitenin yaptığı çalışmalarda motor gücü 40 kW lara kadar çıkmaktadır. Bazı traktör firmalarının gelecek elektrikli traktör çalışmaları ise 100 kW gücünde ve çok daha uzun süreli çalışmaya imkanı verecektir.
Bu çalışmada dizel motorlu bir traktörden yola çıkılarak, elektrik motorlu bir traktör yapılması için gerekli olan değişiklikler ve performans analizleri ortaya koyulmuştur.
Çalışmada baz olarak New Holland 55HP  bahçe traktörü seçilmiştir. Bu traktörün tam yükte motor güç ve tork eğrilerinden yola çıkarak, ideal güç , ideal çeki ve ideal tork eğrileri çıkarılmıştır.  Daha sonra aktarma organları çevrim oranlarına göre her bir vites kademesi için  güç arz, kuvvet arz ve tork arz değerleri ve eğrileri çıkarılmıştır.
Traktörün seyir dirençleri hesabı için traktörün çalışma koşulları göz önünde bulundurularak 3 tip yol koşulu belirlenmiştir. Bu yol koşulları; normal yolda seyir, tarlada seyir ve toprak işleme koşullarıdır.
Traktörler düşük hızlarda çalıştığı için bu üç yol koşulunda da ivmelenme ve rüzgar dirençleri ihmal edilmiştir. Normal yolda seyir ve tarlada seyirde yuvarlanma  direnci ve yokuş direnci dikkate alınırken, toprak işleme sırasında ise bu seyir dirençlerine ek olarak pulluk çeki kuvveti hesaba katılmıştır.
Belirlenen her üç yol seyir koşuluna göre seyir dirençleri hesaplanmıştır. Bu seyir dirençleri ile motor ideal eğrileri ve motor arz eğrileri karşılaştırılarak, belirlenen yol koşullarının baz olarak seçilen traktör için geçerli olup olmadığı incelenmiştir.
Arz eğrilerine göre belirlenen seyir dirençlerini karşılayabilecek elektrik sistemi belirlenmiştir. Bu sistem mevcut cer dişlisi ve diferansiyel sistemlerini sabit tutarak yeni ve daha küçük iki kademeli bir vites kutusu ile bir elektrik motoru ve bataryadan oluşmaktadır. Elektrik motoru ve vites kutusu seçiminde diferansiyel ve cer dişlisi sabit tutulduğu için belirlenen 3 yol koşulunda hesaplanmış diferansiyel girişinden ihtiyaç duyulan tork ve devir değerlerinin birleşim kümesi dikkate alınmıştır.
Daha sonra çıkarılan ve eklenen sistemlerin kütleleri karşılaştırılmış ve toplam traktör kütlesi ve ağırlık merkezini değiştirmeyecek şekilde maksimum batarya kütlesi hesaplanmıştır.
Belirlenen üç seyir koşulu için  düşük güç , orta güç ve tam güçten oluşan sürüş döngüleri belirlenmiştir. Bu sürüş döngüleri normal yolda %60 düşük güç, %30 orta güç ve %10 yüksek güçte , tarlada seyirde %80 orta güç ve %20 yüksek güçte  ve toprak işlemede ise %20 orta güç ve %80 yüksek güçte çalışıyormuş varsayımı yapılmıştır.
Hesaplamalara göre içten yanmalı motorlu traktörün normal yolda çalışma süresi, tarlada seyir çalışma süresi, toprak işleme çalışma süresi hesaplanmıştır. Aynı sürüş çevrimleri elektrik motorlu traktör için kullanılarak pil veya akü seçeneklerinin çalışma süreleri ve batarya fiyatları hesaplanmıştır. Bütün bu incelemeler ışığında çalışma süresi, fiyatı ve paketlenebilirlik açısından 7 farklı batarya tipi incelenmiştir.
Bu çalışmada hedeflenen içten yanmalı bir traktörün elektirkli traktöre dönüştürülmesi teknik olarak ve parasal olarak fizibilitesinin çıkarılmasıdır.

Abstract:
Nowadays,  decrease in energy  resources and its negative effect on fuel cost  make mankind investigate and use less cost effective and green energy sources. Automotive industry has the most effective examples. Recently, the world?s biggest automotive companies have observed that need and have come a long way  to reduce the petroleum addiction and the exhaust emissions. However, in literature researches it was observed that very little renewable energy applications had been performed for agricultural tractors  compared to passenger car and commercial vehicles.
Up until the last ten years, electric motor application studies for agricultural tractor were based on using an electric motor and battery pack instead of an internal combustion engine and fuel system. 
In the first electric tractor studies, maximum 5-15 kW power was achieved with short range. Nowadays some  universities  have studied to increase electric tractor power and range. With those studies tractor power has been increased to 40 kW. Not only universities but several agricultural tractor manufacturers also has been studying for electric tractors. Latest and most important developement has been performed by New Holland. New Holland declared that a new product's motor power and torq would be up to 100kW  and 1200 N.m .
In the thesis, the main idea was to show required changes and performance analysis of electric garden tractor considering the working condition of the garden tractor with an internal combustion engine. 
New Holland 55HP garden tractor has been selected as a reference vehicle. According to the reference vehicle's power - torq curves and values, ideal force , ideal torq and ideal power curves have been created. Afterwards, according to transmission, planet gear box,  differential and traction gear drive ratio, engine torq and power supply curves have been created for each gear.
Three different road and process types have been determined to calculate road resistance considering garden tractor road conditions. Those road condition are called as normal road driving conditions, transport in the field driving road condition and soil cultivation process driving condition.  
Normal road driving condition is composed of field road and mountain road. In addition, normal road driving condition has maximum 40% inclination angle and maximum allowable speed limit is 40 km/h which are specified by Repuclic of Turkey General Directorate for Highways. 
Generally a driver uses this driving condition when he travels from village to field where he performs cultivation process. It has been assumed that a tractor is used without a trailer. In this study only rolling resistance and gradient resistance have been taken into account for normal road  driving condition  in order to calculate  total road resistances.  
Transport in field driving condition is composed of field road. It has been assumed that transport in field driving condition  has maximum 100% inclination angle and maximum achievable speed limit is 25 km/h for garden tractor which was determined after various of surveys and calculations according to reference vehicle. 
Drivers only transports in the field without using trailer. In this study only rolling resistance and gradient resistance have been taken into account for transport in field driving condition in order to calculate total road resistances  which is same as normal road driving condition. Only difference is rolling resistance coefficent. Field rolling resistance coefficent has been selected bigger than normal road coefficient due to soil deflection and wheel skid.     
Third and last determined driving condition in this thesis is soil cultivation process driving condition. According to reference vehicle, It has been calculated that maximum inclination angle is 100% and maximum speed is 10 km/h for soil cultivation process driving condition. In addition to rolling resistance and inclination resistance, plough draft force has been considered for this driving condition.  
For all three determined driving conditions, acceleration resistance and drag resistance have been neglected due to the fact that tractors are used in low speed.
Road resistances for all three pre-defined road conditions have been calculated. Next, these resistance values have been compared to both engine ideal and engine supply curves in order to assess the validity of the road conditions for the selected reference tractor.
Following this assessment, an electrical system has been specified which is able to meet the road resistances that are determined via supply curves. This system; by keeping current traction gear and differential system, consists of a new and smaller two-stage gear box, an electric motor and battery.
Since the differential and traction gear have been kept constant for the selection of electric motor and gear box, the set of calculated torque and revolution values which are required by the differential inlet have been considered for three road conditions.
According to these information, internal combustion engine-driven tractor has been modelled in CAD stage. Dimensions of the internal combustion tractor parts , which have been used as a base, have been roughly estimated. While passing to electric motorized system, air induction system, engine cooling system,engine,transmission box and the fuel tank have been taken out and instead of them, electrical motor driver unit and electrical motor whose dimensions have been taken from a catalog and transmission box and cooling system but with the acceptance of half size and mass from the accurate system have been added. For the battery mass, the net mass has been calculated with the assumption of the tractor mass of added and taken out systems and the unchangable center of gravity.
Concerning the  battery mass, it was decided to keep the center of gravity and the total mass of the vehicle same with original design.  Therefore, change in the mass of the system proir to battery addition had to be approximately equal to the mass of the battery unit which was calculated as 700 kg. 
According to the calculated battery mass, several battery alternatives have been evaluated. In order to make this evalation, drive cycles have been determined for 3 different driving conditions.  
First of all, the fuel consumption and maximum driving time with the full fuel tank were calculated for the internal combustion engine tractor. After that, each drive cycle was used for electric tractor and maximum driving time was calculated.
For each drive cycle the following assumptions were made regarding the the road conditions:
It has been assumed that during cruise on normal road driving condition, in the 60% of time to deplete the full fuel tank the engine runs at low power (6kW) , in 30% it runs at medium power (15kW) and in the remaining 10% it runs at high power (40,9 kW).
It has been assumed that during transport in field driving condition, in the 80% of time to deplete the full fuel tank the engine runs at medium power (15kW) and in the remaining 20% it runs at high power (40,9 kW).
It has been assumed that during soil cultivation process driving condition, in the 20% of time to deplete the full fuel tank the engine runs at medium power (15kW) and in the remaining 80% it runs at high power (40,9 kW).
A tractor working with internal combustion engine which is driven on the normal road driving condition, transport in field driving condition and soil cultiviation process driving condition are estimated in accordance with calculations.The same driving cycle is used for electrically operated tractor to find out working time of  accumulators and batteries. In line with those examinations,time of driving on the normal road,driving on the field and soil culvitation on the field; besides,with regard to  price of  batteries and capable of packing are chosen  the most feasible battery option. 
LiNiMnCo battery pack has been selected and 230 LiNiMnCo battery has been packaged to the tractor. Both electric tractor's working time and tractor driven with internal combustion engine's working time for each driving condition have been compared and it has been calculated that  electric tractor's working time is approximately half of reference vehicle's working time.
Result of  the thesis is that even it is technically possible to design a tractor driven with electric vehicle, according to add on battery pack cost and working time for each determined driving condition, electric tractor cannot fulfill customer's expectation. However, battery pack technology has been developed year by year. Maybe with future battery packs working time will increase and cost will decrease. It is believed that this thesis will be milestone for future electric tractor studies.