New breed of tractors gear up for take-off

Transcription

1 Stepless transmissions New breed of tractors gear up for take-off Stepless or continuously variable transmissions are the latest development in a push toward efficiency in tractor-based farming operations. Instead of preset gear ratios, tractors with stepless transmissions have an infinite range of ratios to suit any combination of travel speed and engine power. This report outlines the technology and the tractors available. At a glance Stepless transmissions eliminate fixed gear ratios, allowing the operator to choose any desired working ratio. The new technology is claimed to be more fuel-efficient than conventional powershift transmissions, as engine speed and transmission ratio can be fine-tuned to any particular operation. Work rates can be increased as gear ratio changes are made on the run automatically by the tractor s computer. Stepless transmissions are ideal for power take-off work as the tractor s travel speed can be infinitely adjusted while maintaining constant engine and power take-off speed. Engine power is split into both hydrostatic and mechanical power trains to create a continuously variable ratio, while maintaining transmission efficiency. Different stepless transmissions exist in other machinery as beltdrive or fully hydrostatic systems but these are unsuitable for tractors due to inefficient power transfer. Farmers participating in the Kondinin Group review overwhelmingly accepted the new transmissions, with most rating the machines as excellent to operate. When buying a tractor with a stepless transmission, weigh up the increased cost of the machine versus potential savings from increased efficiency and work rate. The power loss through a stepless transmission is roughly the same as for a four-speed powershift transmission. Some control systems will increase available engine power at higher ratios where torque is lower. Ben White Stepless transmissions are more than a passing fad now that five major tractor manufacturers have machines on the Australian market. Kondinin Group engineer Josh Giumelli inspects the transmission found in the Case IH CVX tractor. Farmers can potentially save on fuel costs and cut time off their working day by using tractors fitted with stepless transmissions. The new stepless or continuously variable transmissions (CVT) differ considerably from conventional powershift units by using a infinite range of gear ratios to suit any combination of travel speed and engine power rather than preset gear ratios. Stepless transmissions offer increased power, ease of operation and higher travel speeds which can cut transport times all of which equals considerable fuel savings, even up to 3 per cent as tested by Profi International. Fendt introduced the first tractor with a stepless transmission internationally during 995 with release of the Vario series. Case IH, John Deere, Massey Ferguson and Deutz have all since followed suit and have entered the Australian market (see Table opposite and Table, page 8). Not all manufacturers use their own individual transmission units. For example, Massey Ferguson uses the Vario transmission, Deutz and John Deere s 640 series tractors use a ZF Eccom unit, while John Deere s 700 series is fitted with a different transmission which the company designed. Case IH uses a CVX transmission, the same type as in the Steyr S-Matic series. While some of these tractors share the same transmission, each has its own complex computer system, which controls the gear ratio and engine speed. Why go stepless? Fuel efficiency, ease of operation and time savings are the hallmarks of stepless transmission tractor technology. With a traditional gearbox, engine speed is directly linked to travel speed. For any given gear ratio, the faster the engine speed, the faster the tractor travels. But with a stepless gearbox, engine speed and travel speed are independent. The tractor s computer can save fuel by slowing the engine speed while maintaining travel speed during light work. Likewise, it can increase engine speed and lower the transmission ratio to maintain travel speed while boosting draught when working under more difficult conditions. For example, a conventional tractor operating at eight kilometres per hour could be overloaded if shifted into the next gear Index Case IH CVX transmission 0 Vario transmissions John Deere IVT transmission 4 ZF Eccom transmissions 6 6

2 Stepless transmissions Research Report at 8.8km/h. But if the operator could select the ideal working speed of 8.5km/h by changing the transmission ratio and not increasing the engine speed, the tractor would use less fuel. The stepless transmission allows this to occur. The difference between travelling at 8km/h and 8.5km/h also could reduce a -hour work day by 40 minutes. Extra options for PTO work The stepless transmission allows travel speed to be adjusted while power take-off (PTO) revolutions per minute (rpm) are held constant. In effect, the operator can accelerate and decelerate without changing engine speed. The new technology allows for wider working options as opposed to traditional PTO-driven machinery that requires maintaining a constant engine speed, so the PTO operates at 000rpm, 750rpm or 540rpm. Traditional transmissions limit any ability to fine-tune tractor travel speed, as the throttle needs to stay set. How the transmission works At the heart of the stepless gearbox is two power transmission systems mechanical and hydrostatic (see Figure ). In simple terms, power from the engine is split into the hydrostatic and mechanical drive trains and then recombined. The hydrostatic system consists of a hydraulic pump and a swash plate-style hydraulic motor. The mechanical system uses one or more planetary gear trains. In some cases (such as in the ZF Eccom and Case IH CVX) clutches and brakes are used to engage and disengage the various planetary elements. A planetary gear train has three elements: a central sun gear; planet gears orbiting the sun gear; and a ring gear surrounding the planets. The planets are attached to the planet carrier, which can also rotate. FIGURE How a stepless transmission works Engine Hydraulic pump with variable output Ring gear Hydraulic motor Sun gear Planet gear Planet carrier Engine power is split into the hydrostatic and mechanical drive trains and then recombined. The hydrostatic system has an hydraulic pump and motor and the mechanical system uses planetary gear trains consisting of a central sun gear, planet gears orbiting the sun gear and a ring gear. Inset: Hydraulic pump flow rate or hydraulic motor displacement is varied by changing the angle of the swash plate or pump or motor (pictured) to alter the piston stroke. A longer piston stroke means a higher pump flow rate or a lower shaft speed from the motor. Oil is not pumped at a zero angle but angling the pump body or swash plate below zero reverses the flow direction. Source: Profi International. Inset: Kondinin Group. Drive can be taken from any element in the planetary gear train but no gear ratio is fixed if all elements are free to rotate. This is where the hydrostatic system works by modifying the rotational speed of the planetary system. To understand the working of the system, compare the action of the planetary gear train to a vehicle s differential system, which is also a type of planetary gear train. A vehicle s differential allows the speed of each rear wheel to change, so the outside wheel can turn faster and the inside wheel turns slower when cornering. The slower one wheel turned, the faster the other would turn, until the slow wheel ceased to turn and the fast wheel would be turning at twice its original speed. If the stationary wheel was then turned in the opposite direction, the speed of the fast wheel would continue to increase. Changing speeds A hydraulic motor alters the speed output of the planetary gear train just as slowing or reversing the direction of one wheel changes the speed of the opposite wheel. To change the speed of the hydraulic motor, the output flow rate of the hydraulic pump is altered by either changing the swash plate angle or the angle of the pump body, which lengthens or shortens the stroke of the pistons (see Figure inset). TABLE Stepless transmissions as reviewed by Kondinin Group Case IH Deutz Make CVX TTV Vario Autopowr IVT Dyna-VT (600 series) (700 series) Transmission origin Steyr S-Matic ZF Eccom Fendt ZF Eccom John Deere Fendt Maximum forward speed (km/h) Number of working ranges Hydraulic pump displacement Variable Variable Variable Variable Variable Variable Hydrostatic motor displacement Fixed Fixed Variable Fixed Fixed Variable Number of planetary gear trains Number of transmission clutches Number of transmission brakes 0 0. Positive engagement clutches (non-friction). Source: Kondinin Group. Fendt John Deere John Deere Massey Ferguson 7

3 Research Report Stepless transmissions Sharing the power load Although fully hydrostatic transmissions are common in harvesters and earthmoving equipment, they are typically inefficient as power is wasted due to friction in the hydraulic oil flow. A tractor fitted with a hydrostatic transmission would be uneconomical to run due to excessive fuel use. TABLE Price list Make and model Case IH CVX $48,500 CVX $56,00 CVX $69,400 CVX 70 4 $88,650 CVX 90 9 $98,550 Deutz TTV $54, $58, $65,000 Fendt Vario $04, $0, $7, $4, $33, $44, $53, $55, $6, $70, $75, $95, $07, $7, $3,76 John Deere $7,8 640S 73 $5, $33, $4, $49, S 00 $57, $35, $43, $5, $78, $88, $9,590 Massey Ferguson $33, $4, $48, Not released Not released Not released 8 * All prices include goods and services tax.. The manufacturer has yet to release prices. Source: Kondinin Group. Power (kw) Price* For this reason, the stepless transmission retains the mechanical components. The power splitting concept of the stepless transmission aims to increase the efficiency of hydrostatic transmission by sharing the power flow with a more efficient mechanical system. Tests reveal a leading edge Independent testing by Profi International and Germany s Nürtingen Technical College has verified tractors fitted with stepless transmissions are more fuel efficient, powerful and save time compared with powershift models. For example, European tests carried out by Profi International comparing the Case IH CS50 and CVX50 tractors (which are basically the same tractor, except the CVX has a stepless transmission) showed a 3% increase in work rate and a 3% decrease in fuel consumption in the stepless model when both tractors were used in cultivation. At higher speeds and towing a five-tonne trailer the CVX50 used 3% less fuel than the CS50 model. This was due to the stepless tractor s ability to reduce engine speed but maintain travel speed under lighter loads. When the trailer weight was increased to about 30t, the CVX50 travelled 6km/h faster, using % less fuel. Germany s Nürtingen Technical College tested two Fendt tractors that share the same engine but one model, the Vario 96, had a stepless transmission while the Favorit 86 was fitted with a four-speed powershift. During mowing tests on undulating ground the Vario 96 covered 8 6% more area and used 0 6% less fuel than the Favorit 86. In this test, the Favorit 86 had to change working ranges continually. PTO speed in the stepless tractor varied by only 5%, while it changed by up to 0% in the powershift tractor. Farmers trials Kondinin Group gauged farmer impressions of stepless transmission tractors at a recent Leibe Group field day at Dalwallinu, Western Australia. Farmers operated a John Deere 780 and the Fendt Vario 74 and 930 model tractors. Most farmers rated the tractors as excellent, particularly for their ease of driving and operating controls. Farmers also praised the degree of control when moving the tractor forward very slowly, the ability to decelerate evenly and quickly from a high speed and the ease of changing between forward or reverse gears. Most people could operate the machines with as little as five minutes tuition, although some found it difficult to adapt to the lack of a clutch pedal. Photos: Josh Giumelli James Erskine, Moora, Western Australia, reviewed the John Deere 780 after operating the machine at the Leibe Group field day held at Dalwallinu, WA. The tractors were considered suitable for spraying and chaser-bin operations and casual workers would be capable of operating the machines with minimum tuition. See Table for tractor prices. The pros and cons Before buying a tractor with a stepless transmission consider the benefits and disadvantages of the technology. Advantages Better fuel economy as the engine can power down under low load. An increased work rate for faster operations. More suited to road work and are usually capable of a top speed of 50 kilometres per hour. Ease of driving as there is no gear shifting or clutch use. Suitable for operations where constant power take-off (PTO) speed is critical. Disadvantages Tractors with stepless transmissions cost 0 0 per cent more than those with a powershift transmission. Some newer models on the market do not have a track record or proof of reliability. There are low or nil fuel savings when working under heavy cultivation in even conditions compared with a powershift tractor.

4 Research Report Stepless transmissions Case develops the CVX transmission Case IH s CVX transmission was developed by Steyr in conjunction with transmission manufacturer ZF and is also used in the Steyr CVT range of tractors (known as the S-Matic). The transmission shares some features with the ZF Eccom unit such as four planetary gear trains and four working ranges but differs in its design and operation. Four clutches are used to select the four different working ranges, with an extra two brake clutches for selecting forward or reverse gears. The clutches engage and disengage various planet carriers, sun and ring gears to transfer mechanical power flow through the planetary gear trains. The clutches are toothed and positively engage rather than the more common friction clutch packs. To understand this transmission it is essential to know how the four clutches operate (see Figure ). Clutch one engages the ring gear in the second planetary to the intermediate shaft. Clutch two engages the sun gear in the second planetary to the intermediate shaft. Clutch three connects the output shaft to the first planet carrier through the shaft that travels through the centre of the transmission. Clutch four links the output shaft to the intermediate shaft, which is connected to the sun gears in the third and fourth planetary gear trains. Engine power is delivered directly to the ring gear in the first planetary gear train. The hydraulic pump is also directly enginedriven and has a variable swash plate angle to alter the output flow rate. The hydraulic motor has a fixed displacement and drives the sun gear in the first planetary. Standing still If the engine turns the ring gear at a set speed and the hydraulic motor turns the sun gear at the same speed but in the opposite direction, the planet carrier and planets will not rotate around the shaft. As a result, the transmission is locked under power, as opposed to a neutral position where the tractor can free-wheel. The first clutch is in the engaged position, which connects the locked output through the ring gear to the intermediate shaft. The forward brake is also engaged on the fourth planetary, which locks the intermediate shaft to the output shaft through the planetary gears and carrier. Moving off in first range With the transmission in the locked position, the hydraulic pump s output is reduced, slowing the speed of the hydraulic motor and the sun gear. The planet carrier will rotate, driving the planets that turn the ring gear. This drives the intermediate shaft and the output is transferred through the fourth planetary to the output shaft. All clutches and brakes are in the same position as when the transmission was in the locked position. As the hydraulic motor continues to reduce its speed, the difference in speed between the sun gear and the ring gear in the first planetary increases, adding speed to the first planet carrier and the tractor as it travels forward. Maximum speed in the first range is reached when the hydraulic pump s swash plate is at a zero angle, which halts the movement of the hydraulic motor and Case IH CVX Evolution series The Case IH CVX Evolution series was released during September 003 and is an update of the previous CVX stepless transmission range. The tractors have a power range of 89 9 kilowatts (power take-off) and use six-cylinder, turbocharged, intercooled diesel engines. The stepless CVX transmission shifts between four working ranges automatically to reach a top speed of 50 kilometres per hour. The operator applies the accelerator to move the tractor forward and when released, the machine comes to a controlled stop, including on sloping ground as the transmission prevents the tractor from rolling. The manufacturer s automatic productivity management (APM) system integrates the engine, transmission, power take-off (PTO), hitch and cabin controls. Engine speed and transmission ratio are controlled to deliver power while maintaining a practical level of fuel efficiency. Engine speed is reduced for road transport to improve fuel economy while the transmission ratio is adjusted to maintain travel speed. For paddock operations, the APM will keep the PTO at a constant speed and adjust travel 0 speed using the transmission ratio and not engine speed. Operators can select three speed ranges of 0 4km/h, 0 5km/h and 0 50km/h for better speed control via the accelerator pedal. The main transmission controls are mounted in the right armrest and on the fixed joystick. Three cruise control modes are available and the computer will manage engine speed and transmission ratio to maintain the set travel speed. A monitor on the A-pillar displays travel speed, cruise speed, PTO revolutions per minute, remote hydraulic flow rate and other information. Minimum engine speed can be set using a small knob on the right armrest, which also controls how the transmission responds to load changes. At the minimum setting, the transmission will drop its ratio quickly as soon as the engine speed starts to decrease under load to maintain working speed and ensure maximum power. At the maximum setting, the engine speed will fall to about 600rpm before the transmission ratio decreases for maximum fuel economy. 4 3 Cabin controls in the tractor are: () the + and buttons control travel speed; () is the shuttle reverse; (3) is the hand throttle; and (4) is the cruise control interrupt resume button. Case IH Phone: (0) Fax: (0)

5 Stepless transmissions Research Report sun gear. At this point, the drive is transmitted only by mechanical power. Second range To engage the second range, the first clutch is released and the second clutch is activated. Power now travels from the sun gear through clutch two to the intermediate shaft, lifting the drive ratio. The hydraulic pump is reset to maximum angle (maximum flow) and works its way back to zero flow as speed in the second range increases to maximum (00 per cent mechanical). Power is transferred though the fourth planetary to the output shaft. Third range Power from the planet carrier in the first planetary gear train is now transferred directly to the output shaft, effectively bypassing the second, third and fourth planetary gear trains. Clutch three is used to connect the output shaft to the shaft running through the centre of the intermediate shaft to the planet carrier in the first planetary. The forward brake on the fourth planetary is disengaged to allow the planetary carrier to rotate freely with the output shaft. Speed is varied continuously with the hydrostatic drive. Fourth range Engaging clutch two will transfer power from the second sun gear to the intermediate shaft. FIGURE The Case CVX transmission Source: Profi International. Hydraulic motor Intermediate shaft First planetary Second planetary First clutch Second clutch Clutch three is disengaged and clutch four engaged, which locks the fourth planetary and allows it to rotate as a whole, effectively locking together both the output and intermediate shafts. Reverse action Engaging the reverse brake activates the third planetary, which transfers power from Hydraulic pump Reverse brake Third planetary Fourth planetary Forward brake Fourth clutch Third clutch the third sun gear via the planets to the ring gear (now travelling in the opposite direction). The third ring gear is attached to the fourth planet carrier, which is attached to the output shaft. When the reverse brake is engaged, the forward brake on the fourth planetary will disengage. This space is deliberately blank

6 Research Report Stepless transmissions Vario takes complexity out of stepless style The Vario transmission the least complicated system in use is fitted on both the Fendt Vario and Massey Ferguson Dyna-VT range. Only one planetary gear train is used in conjunction with a variable output hydraulic pump and two variable displacement hydraulic motors. The transmission has two ranges a working range of 0 8 kilometres per hour and a travel range of 0 50km/h. The engine is linked directly to the planet carrier in the planetary gear train (see Figure 3). The planet gears drive the sun gear, which transmits power to the rear wheels and to the ring gear to drive the hydraulic pump. Both hydraulic motors are connected to a collecting shaft on the output side of the transmission. Neutral position When the hydraulic pump is set at a zero angle it will not pump oil but the shaft driving the pump is free to rotate. As a result, the engine-driven planet carrier and the ring gear (which drives the pump) rotate around the sun gear without actually turning it. This means the planetary gear train freewheels without turning the output shaft. Moving forward If the hydraulic pump is moved from its zero angle, it will start to pump oil to the hydraulic motors. The motors are set on their maximum angle and at this maximum displacement they will turn the collecting shaft slowly when supplied with oil. As the tractor moves, the sun gear will rotate, mechanically transferring some of the engine s power through the planetary gear train. At slow operation speeds, most power is transferred hydrostatically. As the pump angle increases, more oil is pumped, the collecting shaft turns more quickly and the tractor travels faster. As the speed of the collecting shaft increases, so too does the sun gear, which means more power is transferred mechanically. Going faster The pump is at maximum displacement when its body is angled at 45 degrees. To increase tractor speed further, the hydraulic motors are angled back from 45 degrees, reducing their displacement but increasing the speed at which they turn the collecting shaft. The tractor continues to accelerate and the mechanical power share increases. As the tractor travels even faster, the angle of the hydraulic motors approaches zero. At this point, the hydraulic pump ceases to drive the motors as they have zero displacement and the pump cannot supply oil with the motors in this position. But the collecting shaft is free to rotate, so all power is transferred mechanically Fendt Vario series The 995 release of the Fendt tractor equipped with a Vario transmission was the forerunner of all stepless tractors. There are now 5 models in the 400, 700, 800 and 900 series. The clutch pedal fitted to the Vario actually operates a hydraulic proportional valve in the transmission, which acts the same as a conventional clutch would. This allows the service brakes to be applied when the engine speed is less than 300 revolutions per minute, without loading the transmission. To move, the operator selects one of the two working ranges (0 8 kilometres per hour or 0 50km/h), presses the switch on the back of the joystick, then accelerates. The switch is a safety feature to prevent accidental operation of the tractor. To increase the transmission ratio, the operator holds the joystick forward while applying the throttle and the tractor can now accelerate to the maximum transmission ratio. Alternatively, the joystick can be bumped to shift the ratio up or down in steps. To slow the tractor, pull back the joystick to lower the transmission ratio. Holding the joystick in position will make the tractor stop quickly. With the tractor stationary, pull back the joystick for reverse travel. Changing from forward to reverse also can be carried out automatically with the tractor travelling at speed by tapping the joystick to the left the tractor will stop, then reverse its direction. The ratio of forward to reverse speed can be adjusted. At default, the ratio is set at :, which means the tractor will travel at the same speed in reverse as it will in forward gear. But the reverse mode can be set to operate either slower or faster than the forward speed. (The John Deere Autopowr series also has this option.) Two cruise control speeds can be stored and activated by tapping the joystick to the right to either increase or decrease travel speed to the preset level, irrespective of engine speed or changing load. The acceleration rate is set by a fourposition toggle on the side of the joystick. This also controls how quickly the tractor moves through its transmission ratios. For slow operations (such as inching up to an implement), the setting is left on position one for improved control. The 800 and 900 series Vario tractors use an advanced engine and transmission management system called TMS, which actively selects the most appropriate engine speed for the transmission ratio in use. The TMS also makes adjustments for the acceleration rate selected on the joystick and the tractor load. The 700 series tractors will soon be fitted with engines incorporating an electrical rather than mechanical governor, which will allow the TMS control system to be installed. 4 The joystick () moves forward or backward to change the transmission ration, while () sets the acceleration rate and a button (3) selects the working range of I or II. The cruise control is set via the monitor (4). Agco Australia Phone: Fax: (03)

7 Stepless transmissions Research Report and the tractor travels at top speed for that range. Changing ranges The Vario transmission has two ranges, which can be changed on-the-go. But the control system can block the change (for example, if there is engine overload changing from low to high range). The lower range of 0 8km/h is used for paddock operations, while the higher 0 50km/h range is used for transport. FIGURE 3 The Vario stepless transmission Hydraulic motor Planetary gear train Reverse action To change the direction of the collecting shaft and the travel direction of the tractor, the hydraulic pump body is moved back past zero to a negative angle. This reverses the flow of oil, with the discharge side of the pump now becoming the suction side. With a reversed oil flow, the hydraulic motors will turn in the opposite direction, rotating the collecting shaft in reverse. To increase the reverse speed, the pump can be angled to a maximum of 30 degrees. Hydraulic pump Collecting shaft Source: Profi International. Two-speed range Hydraulic pump Massey Ferguson Dyna-VT Massey Ferguson has released the Dyna- VT tractor range consisting of the Perkins-engined 7465, 7475 and 7480 series based on the Fendt Vario transmission. Larger tractors the 7485, 7490 and 7495 series using Sisu engines will be released during 004. While the tractors use the Vario transmission with two forward ranges of 0 8 kilometres per hour and 0 50km/h, the operator interface and computer control system are different. Pushing the armrest lever forward will move the tractor, pushing it forward further will increase speed or pulling it back will decelerate the tractor. The left shuttle lever selects the tractor s travel direction and can be used to change the transmission ratio. The controls also can be changed to allow all operations to be carried out via the foot pedal. When operating the tractor with the armrest lever, a dial controls the way engine speed and transmission ratio interact or how forward speed is altered, depending on any drop in engine speed. If the dial is set to the power take-off (PTO) position and the engine speed reduces, the transmission ratio will lower to maintain engine speed and a constant PTO speed. If set at the opposite extreme (a trailer logo), the computer allows engine speed to fall considerably before reducing the ratio. Several settings are available for general draughting and towing. The tractor s cruise control can memorise two forward speeds in each range and direction as well as a start-up speed in forward and reverse. The cruise control is adjustable using two dials located on the console. When operating the machine using the foot pedal the tractor can use one of three modes power, eco or forager (PTO). The power mode allows engine speed to increase and be maintained at the rated speed. The transmission ratio is changed based on the engine load. The eco mode maximises fuel economy by increasing the transmission ratio rather than engine speed under light loads. The forager mode is used for PTO operations and holds the engine speed constant regardless of the tractor s forward speed. Acceleration in forager mode is via the transmission instead of engine speed. Agco Australia Phone: Fax: (03) The transmission speed lever () on this tractor controls the ratio but is not used to select forward or reverse, while two buttons () select the preset cruise control speeds. Inset: This dial (3) controls engine and transmission responses. 3

8 Research Report Stepless transmissions John Deere introduces IVT tractor range The John Deere infinitely variable transmission (IVT) incorporates two planetary gear sets to enable seamless shifting at up to 40 kilometres per hour and contains only two clutches and one brake, making it one of the more simple transmissions in use. The ITV uses a mechanical drive train (see Figure 4). Power from the engine drives the sun gears in both planetary gear trains, as well as the hydraulic pump. Moving the swash plate through 45 degrees in either direction varies the pump s output but the hydraulic motor has a fixed displacement. For the tractor to move, power needs to be transferred through the planetary gear carrier to the clutch pack. FIGURE 4 John Deere s infinitely variable transmission (IVT) Source: Profi International. Hydraulic motor Hydraulic pump First planetary Front axle Reverse brake Second planetary Low range clutch High range clutch To PTO Standing still With the engine turning the first sun gear and driving the hydraulic pump, the hydraulic motor can rotate the ring gear at the same speed in the opposite direction. This means that while the planetary gear will rotate, the planetary carrier stands still and the tractor will not move. The transmission can stay locked at any engine speed as the hydraulic pump can adjust its displacement to keep the ring gear speed equal and opposite to the sun gear. 4 This space is deliberately blank Moving off To start moving, the hydraulic pump s flow rate is reduced, causing the hydraulic motor and ring gear to operate slower. The planet gears start to rotate the planetary carrier, which drives the tractor through the clutch pack (shown in green in Figure 4). The slower the hydraulic flow rate, the faster the tractor travels. When the pump s flow rate slows to zero, the swash plate angle also will be zero. If the swash plate is rotated past this point, the pump starts to drive (becomes a hydraulic motor) and is driven by the hydraulic motor, which is now operating as a pump. In this situation, the ring gear is turning in the same direction as the sun gear and the tractor accelerates. Switching ranges The clutch pack can alternate drives (high or low gear) between the two planetary gear sets to increase the transmission s speed range. The outer low-range clutch disengages and the inner high-range clutch engages, which switches off the first planetary gear train in favour of the second gear train. Reverse action To select reverse, the inner and outer clutches are both released. A brake is engaged on the outer ring gear of the second planetary gear train that will drive the clutch pack through two sets of planet gears (shown as grey and pink in Figure 4), causing it to rotate in reverse. The control system of the IVT 700 series tractor is similar to the John Deere 600 Autopowr tractors (see page 7). John Deere Phone: Fax: (07) The John Deere IVT tractor (pictured top) features the cabin controls (below) of a () transmission ratio control lever, which is also used to select between ranges one and two, () speed control knob, which is also used to set the cruise control.

9 Research Report Stepless transmissions ZF Eccom transmission clocks up high speed The ZF Eccom transmission has four working ranges incorporating four planetary gear trains, four clutches and one brake to achieve working speeds of up to 50 kilometres per hour. Figure 5 shows how the engine s power is delivered to the ring gear in the first planetary gear train, which also doubles as the planetary carrier for the second planetary gear train. The hydraulic pump is driven from the far right of the engine shaft. The hydraulic pump has a variable displacement and drives the fixed displacement hydraulic motor, which, in turn, rotates the sun gear (shown in dark blue in Figure 5) in the first planetary gear train. The ZF Eccom transmission is used in both the John Deere 600 Autopowr series and Deutz TTV series of tractors. Standing still If the hydraulic motor (at engine speed) rotates the sun gear in the first planetary train in the opposite direction to the ring gear, the planetary carrier (shown in red in Figure 5) in the first planetary train will rotate at half the engine speed. The planetary carrier is attached to a large drum-like element surrounding the first three planetary gear trains and also serves as the ring gear in the second planetary, as well as the carrier in the third planetary gear train. The second planetary carrier (attached to the engine shaft) rotates at engine speed. But because the ring gear in the second planetary gear train is rotating at half the engine speed, the result is that the sun gears of planetaries two and three (which are linked) rotate at twice the engine speed. As the carrier in the third planetary train is attached to the red drum, it rotates at half the engine speed. When this is engaged with the third sun gear in the centre rotating at double the engine speed, the third ring gear is stationary. Even though the ring gear is not rotating, it is engaged through the first clutch to the sun gear of the fourth planetary set. Because the brake on the fourth planetary s ring gear is engaged, the transmission output is locked and the tractor stands still. Moving off Applying the transmission brake appears complicated but it allows the tractor to move by varying the speed of the hydraulic motor. By reducing the pump output and slowing the drive from the hydraulic motor, the first planetary s sun gear slows, causing the first carrier and drum to accelerate, which causes the sun gears of the second and third planetaries (linked) to decelerate. As a result, the third ring gear (which was stationary) rotates. The brake on the fourth ring gear is still applied, so drive is transferred from the sun gear to the carrier in the fourth planetary and the tractor moves off. First working range As the speed of the hydraulically driven sun gear in the first planetary is reduced, the tractor accelerates. When the output of the pump reaches zero and the sun gear stops rotating, the drive is fully mechanical. The pump then reverses flow, which also reverses the hydraulic motor and the sun gear direction to increase tractor acceleration. At maximum reverse pump flow, all components in the first three planetary gear trains rotate at engine speed. This is the maximum speed in the first working range or about 6km/h. Second working range When the tractor needs to accelerate faster than 6kmh, the second clutch engages, the first The Deutz TTV tractor range uses the ZF Eccom stepless transmission with a maximum speed of 50 kilometres per hour. All tractors are fitted with a liquid-cooled, six-cylinder, turbocharged, intercooled Deutz diesel engine. The transmission operates in either a manual, power take-off (PTO) or automatic mode, which is selected by a button on the armrest. The tractor reverts to automatic mode as a default on start-up. In automatic mode, the engine speed is controlled by the computer, depending on travel speed and power required. The operator selects the travel direction using a button on the joystick or a shuttle lever mounted on the steering column. To start travelling, the operator presses the foot throttle and holds the joystick forward. Pulling the joystick back will slow the tractor. To set a constant travel speed for paddock operations, push the joystick forward until the desired speed is displayed on the monitor. The tractor will accelerate to this speed when the foot throttle is fully depressed. In PTO mode, the hand throttle controls PTO speed, while the foot throttle controls the travel speed using the transmission only. 6 Deutz TTV Agrotron The maximum travel speed is determined using the joystick. The cruise control button can be used to store the current travel speed. The tractor can return to this speed after headland turning or other operations. The auto dial controls the engine speed response. In the Ecomax position, the engine revolutions per minute are maintained at rpm, depending on power requirements. In the Powermin mode, the engine speed will not fall below 800rpm under load. The operator also can set the mode dial to any position between the two extremes. In manual mode, the foot and hand throttles work similarly to those of conventional tractors. The transmission ratio is changed as in auto mode but the computer does not control engine speed. Manual operation is more suited to transport and yard work. If more power is required, the operator can reduce the transmission ratio and increase engine speed. The monitor on the A-pillar displays both the current travel speed and the maximum speed possible under full throttle in the current ratio. The Deutz cabin features () a joystick that moves forward or backward to control the transmission ratio; () hand throttle; (3) shuttle reverse; (4) mode select; (5) economy power dial; and (6) acceleration rate. An active standstill mode will only operate when the transmission is in auto mode and will hold the tractor stationary on a slope as soon as the foot throttle is released. In manual mode, the tractor reverts to neutral and the hand-brake needs to be applied. Landpower Australia Phone: (03) Fax: (03)

10 Stepless transmissions Research Report clutch disengages and the hydrostatic drive to the first sun gear is reversed. This causes the linked second and third sun gears to increase in speed to twice the engine speed. The second clutch connects the drive to the fourth sun gear (shown in yellow in Figure 5) and to the transmission output, doubling the tractor s speed range to km/h. Third working range With the second clutch engaged, the third clutch will engage and the brake disengages. All of the four planetary gear sets are rotating together at the same speed, with the hydrostatic speed variation operating only on the first planetary gear train. In this range, the tractor can accelerate to 4km/h. Fourth working range The fourth range will increase the tractor s maximum speed to about 50km/h by releasing the third clutch and engaging the fourth clutch. The second clutch remains engaged. In this mode, the hydraulic motor can accelerate both the first and second sun gears to twice the speed of the engine. Engaging the second and fourth clutches transfers power to the output shaft, which will rotate at the speed of the two sun gears. FIGURE 5 The ZF Eccom stepless transmission Source: Profi International. Hydraulic motor Fourth clutch First planetary Second planetary Third planetary Selecting reverse The selection of forward or reverse occurs on the output shaft of the gearbox, using two clutches (forward and reverse). When the Hydraulic pump Reverse clutch First clutch Second clutch Third clutch Fourth planetary Forward clutch Front axle drive clutch PTO shaft To rear axle reverse clutch engages and the forward clutch is disengaged, a gear is effectively eliminated from the drive train, resulting in a reversal of the shaft driving the rear axle. John Deere 600 Autopowr series An earlier version of the John Deere stepless transmission tractors is the 600 Autopowr series tractors fitted with the ZF Eccom transmission. These tractors appeared on the market before the John Deere 700 series fitted with the manufacturer s own infinitely variable transmission (IVT). The transmission speed control lever on the right armrest only has a single speed wheel on top, which fine-tunes the travel speed. To move the tractor, the operator uses the left shuttle control, moving it from either neutral or park to forward or reverse before applying the foot throttle. The gear ratio is increased by pushing forward the speed control lever. A gate in the centre of the lever s movement arc separates the two working ranges (in reality, the transmission shifts through four ranges to reach a maximum speed of 50 kilometres per hour). The speed selector wheel on top of the speed control lever can fine-tune the tractor s travel speed. The operator can program two set speeds into the transmission simply by shifting the control lever to the end of the slot in either range and dialling in a speed with the speed selector wheel. A six-position dial on the right armrest controls how the transmission responds to varying loads. Position zero on the dial indicates manual mode where operators can control the transmission using just the speed control lever and either hand or foot throttle. In position one, the engine speed has to drop by 30 per cent before the transmission control reduces the gearbox ratio. In position two, this is reduced to an 8% engine speed drop. Position three is ideal for power take-off (PTO) operations, as the gearbox ratio will lower as soon as the engine speed reduces by 5%. This means PTO shaft speed can be held at a constant speed as it is directly linked to engine speed. Positions four and five allow for more efficient operation such as in the transport mode when higher travel speeds are required without the need for high engine speeds. The computer will determine the power required and reduce the engine speed accordingly. This needs to occur in conjunction with an increase in transmission ratio to maintain travel speed. The transmission control also can adjust the speed ratio between forward and reverse travel. At default, the ratio is set at :, which means the tractor will travel at the same speed in reverse as in forward travel. But reverse can be set to operate at either 70% slower or 30% faster than the forward travel speed. John Deere Phone: Fax: (07) The Autopowr series features a () transmission ratio control lever, which is also used to select between ranges one and two; () speed control knob, which is also used to set the cruise control; (3) hand throttle; (4) Autopowr selector dial; and (5) engine speed control for PTO work. Acknowledgements Profi International; Leibe Group, WA; Jolly and Sons, WA; Donnie and Co, WA; Agco and CNH Australia. About the author Josh Giumelli is an engineer with Kondinin Group s research team. josh@kondinin.com.au 3 7