Advanced transmission technologies to improve vehicle performance

S.N. Doğan , ... J. Dorfschmid , in Alternative Fuels and Advanced Vehicle Technologies for Improved Environmental Performance, 2014

12.5.4 Conclusion and advantages of AUTOTRONIC

The newly developed belt-driven continuously variable transmission AUTOTRONIC represents an important element of the Mercedes-Benz portfolio and was developed and tested in parallel with the new A-Class. This transmission contributes also significantly to reduce CO 2 emissions and sets new standards of comfort and fuel consumption (reduction up to 9%) in the compact car class. optimal integration into the overall vehicle concept was made possible by the most compact CVT in this torque category. The outstanding ratio spread of 6.41, the greater all-round efficiency of the engine-transmission unit and the drive developed strategy has produced significant improvements with respect to NVH and comfort.

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Mechanical and electrical flywheel hybrid technology to store energy in vehicles

K.R. Pullen , A. Dhand , in Alternative Fuels and Advanced Vehicle Technologies for Improved Environmental Performance, 2014

15.4.4 Mechanical transmission

The simplest way of achieving a pure mechanical continuously variable transmission is to use a slipping clutch in series with a stepped gear box. The gearbox has discrete ratios and at each step the clutch can be slipped to achieve the desired ratio. If a gearbox with a large number of ratios is used the power lost due to the slipping of the clutch can be reduced. Having a large number of gears would be expensive but Read developed a methodology of using a gearbox with a few steps plus a smaller gearbox to create the effect of a large number of gears ( Read, 2010). Beachley suggested such a design as one of the ways to connect the flywheel to the driveline for their flywheel hybrid (Beachley et al., 1981). More recently a digital hydraulic system has been developed by Artemis Intelligent Power Ltd (Artemis, 2012) and has been applied to flywheel transmissions.

The other way of achieving a CVT through purely mechanical means would be by using the planetary gear set (PGS) as a two degrees of freedom device. In the conventional applications it is common to hold one of the elements of the planetary gear set stationary while the other two act as an input or output. However, in case of being used as a CVT all three branches of the PGS would be free to rotate. Since the PGS is a speed coupling device, by determining the speeds of any two branches the third one can be controlled. Diego-Ayala used a simple PGS with a brake to design a flywheel based powertrain (Diego-Ayala et al., 2008).

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Life Cycle Tribology

Toshiki Sato , Kazuhisa Kawata , in Tribology and Interface Engineering Series, 2005

1 Introduction

Additives contained in belt-type CVT(continuously variable transmission) oil are known to form a boundary lubricating film on the contact surface between element and pulley by tribo-chemical reaction. The structure and mechanical properties of this boundary lubricating film greatly affect the friction and wear characteristics between the element and the pulley. Especially, the appropriate value of the friction coefficient is required to improve the power efficiency by preventing the element and the pulley from slipping each other and to reduce wear. Hence the structure and mechanical properties of boundary lubricating film have to be controlled. However, the mechanism of boundary lubrication as well as the influence of the structure and mechanical properties of boundary lubricating film on the friction and wear properties is not fully clarified yet. Therefore to study the structure and mechanical properties of boundary lubricating film is useful to not only improving the tribological characteristics between the element and the pulley but also clarifying the mechanism of boundary lubrication.

In the past, many studies related with the structure of the boundary lubricating film formed from zinc dialkyldithiophosphate (ZDTP) and molybdenum dialkyldithiocarbamate (MoDTC) have been done using the various analytical techniques such as XPS[1-4], AES[5], XANES[6-9], TOF-SIMS[10-11] and TEM[12-13]. Particularly TEM is the most useful technique to analyze the crystal structure of the boundary lubricating film whose thickness is in the range of several tens of nanometers. To observe the boundary lubricating film by using TEM, foil specimen has to be prepared. But it is difficult to make a foil specimen by means of ion milling or electro-polishing because of damaging the boundary lubricating film. Therefore TEM observations of boundary lubricating films were scarcely conducted in the past except for the observation of wear debris, which don't need any sample preparation[12]. Recently FIB (Focused Ion Beam) technique became available to prepare TEM specimen without much damage.

In this paper, structures of the boundary lubricating films formed during the sliding tests in commercial belt-type CVT oil using a vane-on-disc type tester have been studied with AFM, SEM and TEM in combination with FIB technique mentioned above.

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Automotive Engine Materials

R.C. McCune , G.A. Weber , in Encyclopedia of Materials: Science and Technology, 2001

3.2 Continuously Variable Transmissions

In the search for improving fuel economy, automobile manufacturers have developed continuously variable transmissions (CVTs), in which distinctive gear pairings are replaced by drive arrangements where the torque delivered to the wheels varies continuously over the vehicle speed range. Principal current designs utilize either belt-driven sheaves or so-called traction drives which rely on contact between rollers and planar elements. Both types of CVT require extraordinary material durability and finishing in the contact regions. Materials developments for CVTs will focus on improved materials for severe contacts, surface treatments, and advanced lubricants.

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Tribology for Energy Conservation

H.A. Spikes , in Tribology Series, 1998

3 TRACTION DRIVES AND TRACTION FLUIDS

Despite the fact that most vehicle transmissions are based upon fixed ratio gears, it has long been recognised that continuously variable transmissions (CVTs) potentially offer significant energy-saving, by enabling crankcase engines to operate closer to their optimum performance level over a full driving cycle. At present, all vehicle CVTs in use are belt drives and these are limited in torque capability to use in relatively low capacity engines. A number of designs and prototypes exist, however, for vehicle CVTs based on counterformal contact. These offer much higher torque capability and could thus be used in larger-engined cars and even trucks. There are many alternative layouts and a few typical ones are shown in figure 7, of which variants on the toroidal arrangement are probably currently the most favoured.

Figure 7. Types of counterformal contact traction drive

One tribological challenge is to produce lubricants able to provide high friction or "traction" over the wide temperature and pressure range experienced in counterformal, EHD contacts. All fluids appear to shear thin in EHD contacts and, it is generally believed, reach a limiting shear stress and thus a limiting EHD traction coefficient at high pressures and strain rates. For most mineral oils, the limiting fraction coefficient is about 0.05 to 0.07 at room temperature, falling to between 0.03 and 0.05 at 100°C. Synthetic esters and polyalphaolefins generally have even lower traction coefficients. To transmit power through an EHD contact requires higher traction coefficients and there have been considerable efforts over the years to develop synthetic lubricants with very high traction coefficient values, i.e. traction fluids.

This development started in the 1960s and the products of that time, notably the Santotrac fluids are still the most widely-recognised traction fluids (22). It appears that for fluids to have high EHD traction their molecules much be quite bulky and also inflexible. Santotrac fluids are thus based upon two cyclohexyl rings joined by a short, methyl-substituted alkyl chain. Two other more recently-developed traction fluids are Spirobis, also based upon cyclohexyl groups but linked with an ester group (23), and a range of hydrogenated polyaromatic fluids (24). In practice it has not proved possible to develop lubricants with EHD traction coefficients greater than about 0.1 and 0.12 may be a fundamental limit (25).

It has been claimed that the use of traction drives in motor vehicles may offer a 10 to 15% overall fuel saving compared to gear transmissions. To realise this in practice, however, probably needs considerably greater understanding of EHD traction than we currently possess. The problem is not simply to develop fluids with a high limiting traction coefficient but how to maintain a high traction value in moderate pressure contacts and over a wide temperature range, when the limiting value is not reached.

To develop effective traction fluids thus requires accurate rheological models of fluid behaviour in EHD conditions. Over the past few years a number of such models have been proposed which can, in theory at least, be used to predict EHD traction. Unfortunately there are still areas of crucial disagreement between these. Some, based primarily on EHD friction studies, suggest that, as shear stress increases, the fluid first shear thins and then, eventually yields completely at a limiting value of shear stress (26). Others, based on high pressure rheology measurements, indicate that there is, in fact, negligible shear thinning and the fluid in an EHD contact shows Newtonian behaviour up to its limiting shear value (27). Until this, and other features of EHD rheology are resolved, such as the development of a full rheological/thermal model of EHD, it will be difficult to optimise either traction drives or traction fluids.

Progress is being made however. One approach to the problem of EHD rheology is to use molecular dynamics simulation (MDS) to model to flow behaviour of a large ensemble of lubricant molecules at high shear stress (28). This may help resolve the shear thinning question. It is also becoming possible to map the shear stress of EHD films within high pressure contacts using infrared thermography coupled with heat conduction theory which may be able to demonstrate the presence, if any, of time-dependent rheological response within contacts (29). Table 2 lists some areas where research in Tribology may assist in traction fluid development.

Table 2. A few potential contributions of Tribology to the traction drives

Area of Research Possible Benefit
Molecular dynamics simulation of fluids in EHD conditions Reliable models of fluid rheology in EHD
Design of fluids with optimal rheological properties to give high EHD traction
EHD fraction
Mapping friction in EHD contacts Reliable models of fluid rheology in EHD
EHD solutions with realistic rheological model and thermal treatment Prediction of EHD fraction based on measurable fluid properties

It will require the promise of major energy- saving benefits to displace gears by traction drives to any significant extent. The combination of accurate models of EHD traction and an understanding of the molecular origins of the key rheological properties at the core of these models may, in the future, make this possible.

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Flywheel energy storage

Keith R. Pullen , in Storing Energy (Second Edition), 2022

5.2.1 Vehicles for construction and mining

Vehicles in construction and mining are currently powered by diesel engines and hydraulic actuators are used to perform functions of lifting and applying large forces. Flywheels have been investigated for energy storage with mechanical connection via hydraulic or continuously variable transmissions [ 4,31] but this did not go beyond demonstrator stage. As vehicles are electrified in order to eliminate fossil fuels there will be a need for energy storage. If the vehicle has a relatively large battery then it is likely to be able to cope with high power demand without damaging life, but given that the range and speed of these vehicles are low, it is less likely to be the case and short-term added power will be needed. FESS can provide this but will need to compete with ultracapacitors. FESS has the advantage of being more rugged, and so may be a good choice for these applications given the harsh environments.

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The roadmap

Paul Nieuwenhuis , Peter Wells , in The Automotive Industry and the Environment, 2003

16.4 The mechanics of change

Given that we need dramatic change to achieve our roadmap's agenda, how is this brought about? We should not dismiss existing players as potential agents of change. Contrary to popular belief, the existing car industry has, at times, been surprisingly radical and risk seeking. In 1963 Chrysler Corporation embarked on one of the boldest such experiments, when it produced a run of 55 specially designed turbine cars and put 50 of them in the hands of the public (Dixon, 1980; www.turbinecar.com; www.geocities.com/motorcity). Between 1964 and 1966, some 203 ordinary volunteer drivers in 133 cities in 48 states as well as the District of Columbia used the cars on 3-month trial periods. The feedback was considered extremely useful and fed into subsequent generations of Chrysler turbine engines. The turbine project was finally abandoned in the financial crisis of 1979–80 when Chrysler had to call in government help. Government officials considered the turbine programme frivolous and were unwilling to support it.

Other bold technologies reached the market and actually survive to this day. The Wankel engine was a bold technology from a small German company, NSU, and can be said to have cost the firm its independence. The company is now incorporated into the Audi division of the Volkswagen Group, although the Wankel engine itself survives in Mazda's sports cars such as the RX-7 and RX-8, and a number of other applications (Hege, 2001 ). More successful was the automatic continuously variable transmission (CVT). Its principles go back to the dawn of motoring with manual CVT systems used by vehicles such as the belt-driven Fouillaron from 1901 (van der Brugghen, 1988: 61) and the friction-wheel driven Turicum from Switzerland (Schmid, 1978: 244).

However, the real breakthrough came in 1958 with the launch of the Dutch DAF 600 small car. This used an automatic CVT system involving rubber belts on variable diameter pulleys controlled by the engine vacuum. This 'Variomatic' system worked well and in addition to providing continuously variable automatic drive, as a side effect it also offered traction control and – up to and including the DAF 55 of 1968–72 – a limited slip differential effect. The system was only available on DAF cars and their derivatives, and after the sale of DAF's car business to Volvo, these were the Volvo 66 and 340. In all, this spanned a production period from 1958 to 1990. However, a specialist transmission company, Van Doorne's Transmissie (VDT) was spun off from the DAF company in the 1970s and this developed a steel-belted version that could be adapted to any powertrain. This system is now fitted to a range of cars, particularly from Japan, and in 2002 over one million belts were produced, prompting the commissioning of a second plant in Japan. Although this represents fitment to just 2   % of global car production, it represents more than 90   % of CVT systems fitted, and around 5   % of automatic transmissions.

By 2002 the system had been fitted to Subaru, Nissan, Honda, Ford, Fiat, Volvo, MG, Rover and Lancia production cars, as well as several experimental cars. Although by that time the VDT company was owned by Bosch of Germany, the technology had become well established. The rubber belt version, meanwhile, became more of a commodity transmission and is now fitted to motorcycles, French 'voitures sans permis' and some offroad vehicles such as quad bikes and skidoos. The high risk DAF took with the CVT technology can be shown by the fact that it remained a niche player and had to sell out to Volvo in the 1970s. Only when Volvo adapted the 340 model to take conventional manual gearboxes and offered these in the market as well did sales of the car take off. However, throughout the production life of the 340, around 15   % were delivered with CVT. The alternative Torotrak infinitely variable transmission (IVT) is also coming close to reaching the market now that most problems have been overcome, and a chain-driven CVT developed by ZF was launched in the Audi A6 in 2001.

In terms of time scale for the introduction of new automotive technologies we can take the adoption of Budd technology itself as an example. With Dodge as an early adopter around 1915 and Citroën around 1923/4, the main roll-out of this technology occurred in the course of the 1920s and 1930s, during which time many of the non-adopters perished. A further boost came with increased car demand after the Second World War, and by the 1960s the system was dominant. In fact, by about 1935 the tide had turned in its favour, meaning a critical roll-out period of some 20 years. Hie belt-driven CVT was developed in about three years in the late 1950s (van der Brugghen, 1988:129) and entered the market from 1958. However, true penetration to any significant level was not reached until the late 1990s – hence a 40 year roll-out, or adoption of the technology. The Wankel engine was developed during the 1950s and like DAF's CVT found early adopters in its own products at NSU in the 1960s. Full roll-out never really occurred as it remained a marginal automotive technology, and is now only used by Mazda on one model, since Audi-NSU abandoned it in 1977, having sold over 37000 R080s (Sedgwick, 1986:147).

Using Rogers' (1995: 262) theory of the diffusion of innovations and applying it to firms, it can be argued that Buddism has reached virtually all adopter categories, from Innovators (Dodge, Citroën), via Early Adopters (Ford, Chevrolet, Morris, Fiat), via the Early Majority (Renault, Opel), to the Late Majority (Toyota, Nissan, Alfa-Romeo) and the Laggards, who are those that never adopted it (Aston Martin, Lotus, Ferrari). Wankel technology did not move beyond the innovation stage (NSU, Citroën and Mazda), although several firms experimented with it, among them GM and Mercedes-Benz. Continuously variable transmission has moved from the Innovators (DAF), via Early Adopters (Fiat, Ford, Subaru) to the Early Majority phase. It may be that a truly globalised world would allow a faster roll-out of new technologies than these historical examples illustrate. Even globalisation sceptics regard the free exchange of intellectual capital among nations as desirable. In the current global car industry, fewer larger firms could aid faster adoption of new technologies worldwide.

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APPLICATIONS – TRANSPORTATION | Hybrid Electric Vehicles: Overview

H. Kabza , in Encyclopedia of Electrochemical Power Sources, 2009

Honda

The second largest selling HEV after the Toyota Prius is the Honda Civic Hybrid. It constitutes a parallel hybrid configuration based on the IMA (Integrated Motor Assist) concept Honda had introduced with the 'Insight' in 1999. In the 2006 Civic Hybrid, a 158   V permanent magnet synchronous EM is mounted between a 1.3   L four-cylinder gasoline engine capable of 70   kW power and 123 Nm max. torque and a continuously variable transmission (CVT). The EM can deliver a maximum power of 15  kW and maximum torque of 103   Nm in motor mode and take up 15.5   kW and 123   Nm, respectively, in regeneration mode. With that the IMA powertrain can deliver up to 85kW and 167   Nm. The battery is a Ni–MH system with a rated capacity of 5.5   Ah enabling short-distance low-speed cruising. Fulfilling the emission requirements of Euro IV, the 1.3 t vehicle accelerates from 0 to 100   km   h−1 within 12   s, allows a top speed of 185   km   h−1, and gives a fuel economy of 4.6   L/100   km corresponding to 109   g   CO2  km−1.

A very similar solution had been applied to the Honda Accord Hybrid that was introduced in 2004, with the EM mounted between a V6 3.0   L gasoline engine and a five-speed automatic transmission.

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Biolubricant product development

Jan C.J. Bart , ... Stefano Cavallaro , in Biolubricants, 2013

10.4.1 Mechanical-dynamic test methods for lubricants

Mechanical-dynamic lubricant testing is an essential element in the development of modern lubricants [7]. The wide range of tribological, mechanical-dynamic test machines and test methods stretches from field tests under real conditions to small laboratory instruments. Table 10.3 shows the various tribological system categories within lubricant testing.

Table 10.3. Tribological system categories within lubricant testing a

Category Test
Type Operating conditions System
I b Field trial Normal or extended Original equipment
II b Test laboratory with complete equipment (vehicle) or plant Close to normal or extended Original equipment
III b Test laboratory with plant or construction elements Normal or extended Original equipment
IV c Standard construction elements or scaled down plant Normal or extended Original equipment; experimental samples
V c Test equipment Close to normal Experimental sample
VI c Simple laboratory test equipment Bench test Experimental sample
a
Classification according to DIN 50322 [13].
b
Customer or field trial or trial under similar conditions.
c
Experiment with model system.

Simple mechanical-dynamic lubricant test machines are the four-ball apparatus, Reichert's friction-wear balance, Brugger rig, Falex test machines, Timken test machine, high-frequency reciprocating test machines, low-velocity friction apparatus (LVFA) and diesel injector apparatus. For details concerning performance tests for gear applications, roller bearing applications, synchroniser applications, automatic transmissions, continuously variable transmissions (CVT) and hydraulic fluid applications, see Bartels [7]. High repeatability is a basic prerequisite for satisfactory reproducibility of a test result. Comparison of existing test conditions with real conditions is important in assessing the relevance of results obtained in tribological lubricant tests.

Standardised tribological, mechanical-dynamic test rigs and test methods play a decisive role in the development of lubricants and additives. Standardised test methods are the basic means of achieving the required performance of OEM specifications for lubricants. A variety of additional in-house methods complete the range of modern tribological, mechanicaldynamic testing. This is the case for the CEC engine tests which do not allow comprehensive testing of all required oil properties. OEM-specific, long-term performance tests for developing oils are part of these engine tests. The engine tests have been supplemented by radionuclide techniques (RNT) [14, 15]. The advantages of this technology lie in the on-line monitoring of wear in defined running conditions and in selective examination of critical engine components. For details on engine oil tests, see ref. [16].

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Automakers' Powertrain Options for Hybrid and Electric Vehicles

Fabio Orecchini , Adriano Santiangeli , in Electric and Hybrid Vehicles, 2010

2.2.1 Honda integrated motor assist

The hybrid technology of Honda is characterised by the integrated motor assist (IMA) system with a petrol-electric hybrid engine, stop&start and brake energy regeneration. It was the first carmaker to commercialise a hybrid vehicle outside Japan in 1999 with the coupé Insight (first generation of the IMA system), and is now present in the European market with two models, Civic Hybrid and the new Insight.

Nickel-metal hydride (NiMH) batteries are adopted, and are recharged both through the petrol engine and the recovery of kinetic energy during deceleration. The electric motor supports the heat engine and provides the additional power during acceleration that allows the ICE to work at a more efficient rpm.

The hybrid system of Honda Civic Hybrid includes a four-cylinder i-VTEC petrol engine (1.3   l) of 70   kW at 6,000   rpm with the support of an electric motor of 15   kW at 2,000   rpm that allows a 30% torque increase as well as a power increase. With an overall power of 85   kW, the consumption is 4.6   l per 100   km, with CO2 emissions amounting to 109   g/km in the European homologation combined cycle.

The new Insight has adopted the fifth generation of IMA with an extremely thin electric motor [always included between the heat engine – 65   kW at 5800 rpm – and continuously variable transmission (CVT)] (10  kW power at 1,500   rpm) (Fig. 22.1). The engine-generator, placed in the front bonnet of the vehicle is connected to the 100.8-V Ni-MH battery pack, which is conversely located, with the intelligent power unit (IPU), in the rear underbody of the vehicle (Fig. 22.2). It is endowed with a stop&start system as well as with the brake energy regeneration systems; its consumption under the European combined cycle amounts to 4.4   l per 100   km, with CO2 emissions of 101   g/km.

Figure 22.1. IMA System (Integrated Motor Assist).

Figure 22.2. 2010 Honda Insight: hybrid system layout.

In the Insight the electric motor provides the necessary power when higher performances are requested, and acts as a generator during deceleration and braking, allowing all-electric operation in particular motion conditions. In fact, the variable cylinder management (VCM) technology is also used to block the valve mechanism in the four cylinders when proceeding at low constant speed. In this way, Insight automatically shifts to the 'electric only' all-electric mode, reducing the pumping losses of all the cylinders, up to an official range of nearly 2   km.

Obviously, also the transmission system plays a major role in hybrid powertrain in consideration of the global efficiency of the system. The Insight adopts an evolution of the high torque CVT of civic hybrid, with a lower gear ratio (4,200 vs. 3,937), which improves standing starts.

A further system installed on the Insight, which aims at contributing to reducing consumption and CO2 emissions, is the Ecological Drive Assist System (Eco Assist), which shows drivers whether their driving style is low-consumption, and provides assistance to 'educate' drivers to an 'Eco Drive'.

A step forward, again linked to the IMA system, is the CR-Z hybrid (sport hybrid) presented at the 2010 NAIAS in Detroit (Fig. 22.3). The subsequent step is represented by the adoption of the IMA system on compact Honda Jazz as well as the development of another hybrid system for medium–large vehicles. It is not a 'light' IMA hybrid system, but probably a new full-hybrid system, supporting the driving of large-size SUV and sedans also in all-electric mode.

Figure 22.3. Honda CR-Z.

On the CR-Z the IMA system includes a traditional four-cylinder 1.5 i-VTEC and a 10-kW electric motor. The result is a power of 91   kW and a robust torque of 174   Nm, already available at only 1,500   rpm. These are nearly the same values as Honda Civic 1.8, but with CO2 emissions of 117   g/km and a range of 20   km/l.

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