Greater efficiency drives demand for automated transmissions

  • 29-Apr-2009 11:39 EDT
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ZF AS-Tronic automated transmissions have gained the company's TopoDyn automatic shift program selection to sense engine load and gradient.

Tightening global emissions limits and cost control have been key factors in driving up the share of automated transmissions fitted to commercial vehicles. Transmission manufacturers now offer a broader range of automated products than before.

According to Udo Markfeld, Head of Transmission Product Development for medium-range trucks at ZF of Germany, the demand for automated truck transmissions in Western Europe depends on the respective markets and the use of the vehicle. “We even see some countries where our customer, the OEM, is offering automated transmissions as the standard transmission. In other countries, you will see a different share, but the trend is definitely going above 50%,” he said.

Markfeld believes that vehicle manufacturers are caught in a spiral. “Fuel-consumption reduction is always an issue. In addition now, the market is under pressure from emissions regulations, and this gives additional pressure on the pursuit of fuel-consumption reduction," he explained. "This then means that we are challenged to provide an optimum driving strategy. That’s the point where an automated transmission can deliver some advantages for OEMs.”

As far as the introduction of Euro-VI compliant engines by 2013 is concerned, Markfeld does not expect to see a significant change from current transmissions. “There are no great changes in the torque capacity of these engines and more or less no change in the characteristics,” he said. “This means, for us, there is no significant impact on the mechanical part of the transmission, but for Euro VI there are additional demands on the driving strategy of the transmission, which influences us.

“If you go back to the introduction of the Euro-V engines, the situation was quite different," Markfeld continued. "With Euro V, we saw an increase of torque capacity and a change of the torque characteristics.”

For ZF, that point was the trigger for the introduction of a new range of six- and nine-speed transmissions.

More recently, at the IAA Commercial Vehicles Show at Hanover, Germany, last fall, ZF launched a new torque converter six-speed automatic transmission, named the ZF PowerLine. Designed for commercial vehicles, buses, and pickup trucks with a gross vehicle weight (GVW) of up to 15 ton (14 t), the transmission is due to enter production in 2010 in the U.S. Torque capacity covers the range between 600 and 1000 N·m (443 and 738 lb·ft).

ZF claims that the PowerLine can provide better fuel economy than competitive transmissions. Features include a torque converter that offers early closing of the converter lock-up clutch. Consequently, it will operate for shorter periods in hydraulic power transmission mode.

The PowerLine transmission has a mass of 140 kg (309 lb) and measures approximately 650 mm (25.6 in) long. Both the hydraulic control unit and the sensors are integrated into the transmission. The design life cycle is 700,000 km (435,000 mi) and transmission oil needs changing every 120,000 km (74,500 mi). Filter changes are not required.

The first customer for the PowerLine transmission will be Nissan.

ZF has also introduced TopoDyn, the gearshift control strategy previously available with the company’s automatic transmissions. TopoDyn is now available with the AS Tronic series of automated transmissions. ZF claims fuel-consumption savings of up to 5% for TopoDyn.

Instead of leaving the driver to switch between economy, normal, and power gearshifting modes, TopoDyn uses existing sensors to determine gradient and power requirements. The system will then select the most appropriate shift program to suit the road conditions. It will also select the power mode to keep the engine operating in the optimum speed range for retarders and engine brake systems during hill descents.

Beyond hardware, developments also include incorporating the transmission in driveline network systems. ZF is looking at three subject areas for a networking project: compensation for load transfer, alterations to driving dynamics, and an autonomous driving mode, where the driver could hand over control of the vehicle to automated systems inside a depot, for instance.

Load-transfer compensation can be introduced by networking electronically controlled dampers and the ZF AS Tronic automated manual transmission (AMT). By connecting the two systems via a data bus and a common electronic control unit, the pitching motion that can accompany a gearshift could be reduced. For trucks that may be equipped with an air-suspended driver’s seat, electronically controlled air-suspended cab and axles, there is great potential to improve comfort. Similarly reducing the pitching motion for buses can greatly improve the ride comfort for passengers.

If an active steering system is also similarly networked, then the vehicle could be remotely guided around a depot. This could help to reduce accidental damage and cut fuel consumption, while freeing up the driver for other work.

Allison Transmissions dominates the global bus market, supplying more automatic transmission systems than any rival. Like ZF, the company is working on an adaptive gearshift pattern, named Load Based Shifting Schedule (LBSS). The system is currently under development for European OEMs.

Using existing sensors on the vehicle that supply data regarding gradient and engine load, LBSS can switch automatically between economy and performance modes to improve efficiency and reduce fuel consumption and emissions.

European Marketing Manager Manlio Alvaro told Automotive Engineering International, “In a duty cycle there is always the need to offer the best compromise between the minimum fuel burned, but at the same time, you want to do your task. So you want to find the right balance, and in the case of load-based shifting, the features will allow the vehicle to automatically select the calibration required, based on the grade, based on the vehicle load. Do you need a calibration that will shift earlier or keep the engine speed as low as possible, or achieve the minimum performance required to meet the condition of the road?”

Allison has recently taken about a 10% stake in U.K.-based Torotrak, which has spent many years developing an infinitely variable transmission (IVT). Variants are currently in production for ride-on lawn mowers and forklift trucks. Torotrak claims 94% efficiency for the system.

The deal gives Allison license rights to Torotrak’s IVT technology, as well as options over global manufacturing and sales exclusivity in the truck and bus market for vehicles below 14-t (15-ton) GVW. Similar options for heavier vehicles will be available at a later date. Tata and an unnamed European truck manufacturer have already acquired rights for heavier vehicles.

Torotrak’s own research with a small city bus, supplied by U.K. bus manufacturer Optare, has demonstrated fuel-consumption savings of almost 20% when fitted with an IVT from a large SUV, having been subject to basic calibration.

Under the deal, Allison will manufacture IVT transmissions under license. “That’s the plan at the moment,” Torotrak CEO Dick Elsy told AEI. “Cleary, Allison is very highly integrated and make everything themselves. I don’t know ultimately what their plans are, but I think it is pretty safe to assume that they will be wanting to manufacture a significant amount of this product themselves.”

Daimler was among the first vehicle manufacturers to introduce automated transmissions in its vehicles, launching the Electronic Power Shift (EPS) system in 1985. The company launched its PowerShift 2 transmission in the European Actros heavy-truck range last year, and now the latest recipient of the system is the Mercedes Actros construction vehicle range, for which PowerShift 2 has been modified and branded PowerShift Offroad.

One feature is the “Power Offroad” mode for occasions where the driver needs to maintain maximum power delivery. PowerShift Offroad incorporates gradient sensors. When maintaining traction off highway, the sensors will ensure that as an incline becomes steeper, the system will quickly shift down the gears to maintain momentum. It also helps to minimize stress applied to the clutch.

In “Power Offroad” mode, upward gearshifts are also made to ensure that momentum is not lost. The system ensures that with upward changes, the engine speed continues to increase and is maintained for longer.

Compared with the “Power Offroad” mode provided with on-highway Actros models, the driver can switch the mode on or off manually. For on-highway Actros models, the system will automatically switch off after a pre-set time.

To cater for the harsh off-highway environment, PowerShift Offroad transmissions are equipped with forged steel linkages developed specifically for this version of the transmission. Daimler has acknowledged that many construction vehicles also have to travel further on highway; the construction Actros is now equipped with higher final drive ratios for more fuel-efficient highway cruising.

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