Paper 12

Representative Testing of Emissions and Fuel Consumption

of Working Machines in Reality and Simulation

Reno Filla

VOLVO CONSTRUCTION EQUIPMENT AB, ESKILSTUNA, SWEDEN

Abstract

Out of necessity, emission and fuel consumption test cycles are a simplified repre-sentation of the real-life use of a vehicle or component that is assumed to be most com-mon. In reality, variations are introduced by both the driver and the environment – and to a lesser degree also by the vehicle itself through performance deviations because of tolerances in the components’ characteristics. However, since such simplified test cy-cles exist and are accepted (or even required by law), OEMs tend to use them also in product development to benchmark their products against the competition, and to make decisions on how to optimize design.

While this approach might give acceptable results for on-road vehicles, it fails to capture reality in the case of versatile working machines. Here, the variety of possible applications cannot be covered by one common application but rather demands a mix of several cycles. This has a large impact on the setup and evaluation of physical and vir-tual testing of working machines, especially those with alternative power systems like hybrids, which will be discussed in the paper.

Attempts to simplify the complexity of real-life applications are made in some test-ing standards and standard proposals, but they over-simplify with the result of prescrib-ing a common cycle that is not representative and which therefore, however tempting, cannot be used for any meaningful benchmarking of emissions and fuel consumption.

This paper has been published as: Filla, R. (2012) “Representative Testing of Emissions and Fuel Consumption of Working Machines in Reality and Simulation”. SAE paper 2012-01-1946. http://papers.sae.org/2012-01-1946 http://dx.doi.org/10.4271/2012-01-1946

Get your facts first and then you can distort them as much as you wish. (Mark Twain)

Representative Testing of Emissions and Fuel Consumption … 3

1 Introduction

For wheel loaders, excavators and similar working machines in construction, agricul-ture, mining, and forestry, the main customer buying criteria are productivity (i.e. mate-rial processed per time unit, commonly expressed in ton/hour) and energy efficiency (i.e. material processed per unit of energy, expressed, for example, in ton/liter standard diesel fuel). These criteria are frequently required to measure, both for company-internal purposes (in order to optimize system design and benchmark against competi-tors) and external purposes (customers benchmarking competing sales offers, as well as possible future legislation).

Similar to the standardized driving cycles for automobiles, people in the nonroad au-tomotive sector have started to develop standardized working cycles. While in the case of automobiles, fuel consumption (expressed in liter/hours, for example) is tested apply-ing the same driving cycles used in exhaust emission testing (like the New European Driving Cycle, NEDC [1] or US Federal Test Procedure 75, FTP-75 [2]), this cannot be done for working machines. Here, exhaust emissions are not measured while using the vehicle (or in this case, machine) but are instead acquired in an engine test bench, where the engine is subjected to a loading cycle with pre-defined torque/speed values (for ex-ample according to the Nonroad Transient Cycle, NRTC [3] or the static ISO 8178 cy-cle [4]). These methods for testing emissions are a compromise and therefore not opti-mal in all possible scenarios, as will be covered later in this paper. More importantly, they cannot be used to also assess fuel consumption, because both productivity and en-ergy efficiency of a working machine are strongly affected by the machine’s power sys-tem design (with the engine only being one contributing part out of several), as well as the way the operator uses the machine to perform work – as demonstrated in [5-7]. This also means that energy efficiency, productivity and operability (i.e. ease of operation) are connected to each other.

We have thus a strong influence of machine specification, working environment and operator behavior on the fuel consumption of a working machine. Practically unavoida-ble variations in the former will lead to undesired, measurable variations in the latter. Instead of embracing these variations and accounting for them by means of statistics and enhanced test designs, the most prominent answer of the engineering community has been to develop less complex test procedures – simplified to the point of the test results being non-representative or even misleading. This will be discussed in the fol-lowing section.

2 Testing Purposes

This paper is concerned with the testing of complete machine systems (even though one particular component might be in the focus). Such testing can in principle be per-formed in reality by physical testing or by means of computer simulation, i.e. virtual testing. Today the boundary between these two extremes is no longer clear. Frequently, hardware-in-the-loop testing is performed, where the tested component interacts with a simulated environment. In this paper we consider such testing as a variant of physical

4 Paper 12 testing. Furthermore there is human-in-the-loop simulation, in which a human operator controls the machine to be tested. We consider this to be a variant of virtual testing. Table 1 lists four main purposes of testing and how this is performed today.

Table 1. Testing in reality (physical testing) vs. simulation (virtual testing) for different purposes

Purpose Physical testing 1

Virtual testing 2

Legislative / certification X

Benchmark, external use X

Benchmark, internal use X X

Design optimization X X

1) incl. hardware-in-the-loop simulation if that hardware is in the focus 2) incl. human-in-the-loop simulation

Out of necessity, all testing, physical or virtual, is always a simplification of complex reality, either in detail or time. This simplification (or modeling) has to be decided on a case-per-case basis, which requires a reflection on the question to be answered by the testing and the underlying, but not always clearly communicated requirements for the quality of the test results. In other words, before deciding how to test, the engineer has to reflect on what phenomenon is to be tested, what will the test results be used for, and what is the suitable level of detail (i.e. how much deviation from reality is still accepta-ble).

The purposes listed in Table 1 are connected to questions asked by different custom-ers and the answers (i.e. the test results) will be used differently. Therefore, it is under-standable that the tests differ in procedure and scope, because the different purposes set different levels of acceptance for the quality of the test results. It should therefore also be clear that the test cycles differ depending on the purpose.

In the following, each purpose will be examined in more detail. Current test cycles will be discussed and possible improvements will be presented.

Representative Testing of Emissions and Fuel Consumption … 5

3 Testing for Legislative / Certification Purposes

Legislation and non-mandatory certification are focusing on protection of the user (op-erator), society, and the environment. In the context of this paper we are mainly con-cerned with the latter, because test cycles for exhaust emissions of automobiles are also used to measure greenhouse gas emissions and fuel consumption. Naturally, there is temptation to also do so for nonroad machines, such as wheel loaders, excavators and other working machines.

Reports like [8, 9] have revealed how little the formerly used static ISO 8178 test cy-cle [4] managed to capture reality. These reports showed that transients have a high influence on the formation of exhaust emissions and fuel consumption. Not only was the static test cycle incapable of correctly assessing fuel consumption of working ma-chines, it also was too crude an approximation of reality when it came to measuring exhaust emissions.

The next step was to develop a transient test cycle, which was a difficult undertaking since the variety of working machines and their respective applications is huge. Due to practicality reasons the engine was still to be tested in a test bench and again a “one cycle fits them all” approach was chosen, resulting in the synthetic NRTC cycle [3], a time-series of torque/speed values which the engine is to be loaded with. Figure 1 shows how little this cycle manages to capture reality for a specific wheel loader with load-sensing hydraulics, used in short loading cycles.

Figure 1. NRTC vs. real work (short loading cycle) for a specific wheel loader.

6 Paper 12

However, compared to the static ISO 8178 cycle, the NRTC certainly improved the quality of the test results to a level that seems to be acceptable for the regulators of ex-haust emissions. With the practicality demand in mind, as well as the goal to not pre-vent business for smaller OEMs and independent engine manufacturers, it seems to be hard to find a principally better solution.

The almost philosophical challenge with such general test cycles is that they do not cover specific applications very well, with both favorable and unfavorable consequenc-es. The goal with all modeling is to represent reality in a simpler way. For working ma-chines, this goal must be to somehow represent the most common use of the machine, not just one specific component like the engine. Figure 2 shows how in a wheel loader the primary power from the diesel engine is split between hydraulics and drive train in order to create lift/tilt movements of the bucket and traction of the wheels, but is con-nected again when filling the bucket in e.g. a gravel pile, which requires coordinated use of the machine’s main functions (dashed boxes).

Auxiliaries

Bucket

Wheels

Lifting + Breaking/Tilting

Travelling/PenetrationDrive train

Hydraulics

Σ Engine

Linkage

External (+/-)

Gravelpile

Figure 2. Simplified power transfer scheme of a wheel loader during bucket loading [7].

It is thus not correct to simply represent such an application with a time series of torque/speed values at the engine, but rather the engine load is a consequence of the power demands at the bucket and the wheels, as well as all the control losses and sys-tem losses in hydraulics and drivetrain. Therefore, a representative cycle for working machines must prescribe the correct application, i.e. the work to be done by the ma-chine.

A consequent realization of this line of argument would require in-use testing of eve-ry machine in each application, which is hardly practical or achievable. It is therefore understandable why the ISO 8178 and later the NRTC approach have been chosen. However, one must also consider that each law, irrespective of its covering taxes or fuel consumption, has not only a regulatory function but also shapes future development by providing direct or indirect incentives or disincentives.

Currently, from an exhaust emissions legislation point of view, there is not only a lack of any direct incentive but actually a presence of an indirect disincentive to realize working machines as diesel-electric hybrids. Various designs are possible [10], but in

Representative Testing of Emissions and Fuel Consumption … 7

all cases the engine used has to be certified using the NRTC test cycle, even though the engine will never be run as transient and with as much part-loading. It would be feasible to build a fully functioning working machine without any expensive exhaust after-treatment system where the exhaust emissions are not exceeding the limits set by the regulation, but it would be illegal since the regulation requires the engine to be certified according to the NRTC test cycle, not according to how it will be utilized in the ma-chine in real life. As a consequence it is not possible to offset the increased costs of a hybrid system by not investing in exhaust after-treatment, even though it might not be needed. Furthermore, where fuel consumption is tested using the NRTC, an electric hybrid would have similar levels as a conventional machine.

Indirect incentives shown by regulations include possibilities for optimization. A drastic (and illegal) version of such optimization would be cycle beating, in which an electronic control unit (ECU) detects that the engine or vehicle is run according to a standardized test cycle, upon which a special control program is activated to provide better test results than would be achievable during normal use. The softer version of such optimization is to design the whole system around the test cycle, instead of focus-ing on real-life use. For example, the NEDC [1] is used to test both exhaust emissions and fuel consumption of automobiles. Two common critiques of its overly simplistic modeling of urban and rural driving are the maximum vehicle speed of 120 km/h and the prescribed maximum acceleration [11]. The former means that, for example, the transmission ratio of the highest gear can be chosen so that a good compromise between high performance and low fuel consumption is achieved when driving according to the test cycle, i.e. never faster than 120 km/h. In reality, most drivers drive faster than that on motorways, even in countries other than Germany (with its famous absence of any speed limit on large parts of its motorway system). On the other hand, the problem with a prescribed acceleration is that this has been chosen to be achievable by the majority of automobiles. Today most cars are actually capable of higher acceleration, due to a more powerful engine, which is, of course, utilized by the driver. The consequence in both cases is that such a car will show significantly higher fuel consumption during real-life use than in testing, according to the NEDC cycle.

When designing a test cycle for regulation, it is therefore important to also reflect on the secondary effects, i.e. what indirect incentives or disincentives are given. However, the main focus should, of course, be on an acceptable representation of reality.

In accordance with Figure 2, a representative cycle for working machines must pre-scribe the correct application, i.e. the work to be done by the machine. But as stated earlier, machine properties like fuel consumption are also dependent on how the opera-tor uses the machine. Revisiting the wheel loader example, the inner loop in Figure 3 shows how the human operator interacts with the machine. In order to fill the bucket, the operator needs to control three motions simultaneously: a forward motion that also exerts a force (traction), an upward motion (lift) and a rotating motion of the bucket to fit in as much material as possible (tilt). This is similar to how a simple manual shovel is used. However, in contrast to a manual shovel, the operator of a wheel loader can only observe and cannot directly control these three motions. Instead, he or she has to use different subsystems of the machine (controlled by a network of electronic control units, ECUs) in order to accomplish the task. The gas pedal controls engine speed,

8 Paper 12 while lift and tilt lever control valves in the hydraulics system ultimately control movement of the linkage's lift and tilt cylinder, respectively. The difficulty lies in that no operator control directly affects only one single motion. The gas pedal controls en-gine speed, which affects both the machine's longitudinal motion and, via the hydraulic pumps, the speeds of the lift and tilt cylinders. The linkage between the hydraulic cylin-ders and the bucket acts as a non-linear planar transmission, and, due to its design, a lift movement will also change the bucket’s tilt angle, and a tilt movement affects the buck-et edge's height above the ground.

Auxiliaries

Bucket

Wheels

Lifting + Breaking/Tilting

Travelling/PenetrationDrive train

Hydraulics

Σ Engine

Linkage

External (+/-)

GravelpileOperatorECU

ECU

ECU

ECU

Figure 3. Simplified power transfer and control scheme of a wheel loader

during bucket loading [7].

It is therefore easy to see that, apart from the systems design, fuel consumption of the complete working machine is not only affected by the conditions in the working envi-ronment (material properties, ambient air pressure and temperature etc.) but also by the operator’s behavior, which to a large degree is a consequence of the operator’s skill and experience. This has been discussed in [7] and demonstrated to be clearly the case in [5, 6], also showing that bucket filling is the main source of variation in energy efficiency. Furthermore, it has also been demonstrated that the productivity required of the joint man-machine system has a large impact on energy efficiency: a more aggressive cycle with higher output leads not to proportionally higher fuel consumption. Rather, the rela-tionship between productivity and fuel consumption is non-linear with a clear optimum range, after which energy efficiency suffers severely from increased productivity. This is yet another degree of freedom that has to be taken into account.

In summary, due to all these variations and degrees of freedom, it is practically im-possible to standardize a test cycle for a working machine, even if the application and productivity level were possible to define precisely.

Despite these challenges, efforts are made to define simplified standardized cycles per type of working machine, most prominently the Japanese JCMAS standards H 020 [12] and H 022 [13], also proposed for standardization by ISO. However, these pro-posals and publications advocating them [14] fail to realize just how large an influence the discarded aspects have on the very target of the test: fuel consumption. In brief, the

Representative Testing of Emissions and Fuel Consumption … 9

essence of these standards is to remove the influences of the working environment and operator behavior by demanding the typical working motions to be executed in the air, without any interaction between the tool (e.g. bucket) and the material to be processed (e.g. gravel or soil). By entirely removing the bucket filling phase, which as discussed above is the main source for variation in energy efficiency, and by demanding all mo-tions be executed at maximum speed, the test result variations are kept smaller than what would have been possible in real work. However, in real work the fuel consump-tion is higher than in those test cycles because the interaction between bucket and mate-rial does not only give rise to digging forces but also other dynamic phenomena, which are completely ignored in these standard proposals.

For example, Figure 3 showed how the operator of a wheel loader controls the ma-chine during bucket loading and how in the outer loop the primary power from the die-sel engine is split up between hydraulics and drive train in order to create lift/tilt move-ments of the bucket and traction of the wheels, but is connected again when filling the bucket in e.g. a gravel pile. Figure 4 shows that in this situation, the traction force from the drivetrain, acting between wheels and ground, creates a reaction force between gravel pile and bucket edge, which in turn counteracts lift and tilt forces from hydrau-lics, and vice versa. Since both working systems are already mechanically connected via the engine (see Figure 3), a challenging situation arises in which engine torque is trans-ferred to the wheels to accomplish traction but at the same time counteracts that part of the engine torque that has been transferred through hydraulics to accomplish lifting – in turn requiring even more torque to be transferred.

Figure 4. Force balance during bucket filling (simplified) [7].

The momentary power distribution to drivetrain and hydraulics is specific to the working task at hand. It is controlled by the operator, who ultimately balances the com-plete system and actively adapts to both the machine, the task at hand, and the working place.

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Visualizing test results obtained in earlier studies, Figure 5 shows that the fuel con-sumption rate of a wheel loader (expressed in volume or mass per time unit) is approx-imately 60% higher during bucket filling than the average of a short loading cycle. Ex-pressed in absolute values, bucket filling accounts for 35-40% of the mean total fuel consumption per cycle, yet the time spent filling the bucket is only 25% of the average cycle time.

Figure 5. Fuel consumption during short loading cycle [7].

All of this is completely ignored in simplified test cycles like JCMAS H 020 and H 022. The official reasoning is that for excavators the overall system efficiency is such that the energy required for raising the boom is approximately the same whether the bucket is full or empty. For wheel loaders the lifting work is approximated by raising a bucket of defined weight. In both approaches the strong power demand of the interac-tion with the material is not included, but for excavators the lifting of an empty bucket means that an ideal hybrid machine with full energy recuperation will have zero energy consumption because in any fully balanced system, energy needs only to be invested in moving the unbalanced mass. For example, in an ideal elevator with zero losses the actual cage is fully balanced, and only the mass of the people inside needs to be lifted, which requires energy. If this ideal elevator only lifts and lowers the cage without any people then no energy is consumed. The same would be valid for an ideal hybrid exca-vator in a JCMAS H 020 test cycle. The reasoning – that it does not matter whether the bucket is full or empty because about the same amount of energy is required anyway – was only ever valid for conventional machines without any balancing of the boom.

In practice, also in a hybrid excavator, some energy would be required for all auxilia-ry systems as well as the engine itself, provided it is not turned off during the test cycle.

Representative Testing of Emissions and Fuel Consumption … 11

But this would be another case of secondary effects of a regulation: an indirect incentive is given to designs that balance the boom of an excavator. In such machines fuel con-sumption is more strongly affected by any load in the bucket than in a conventional excavator (see the loaded/unloaded ratio in Figure 6), but since the JCMAS H 020 cycle demands to test without any bucket load, unrealistically low fuel consumption figures will be the result. Expressed in percent, the test results of a hybrid excavator with bal-anced boom will be much farther off the truth than those of a conventional machine – which would be an unpleasant surprise for a customer.

Energyrequired

∆Ehybr_lift

Ehybr_lift_real

∆Econv_lift

Econv_lift_real

>>+ bucket

load

+ bucketload

Conventional excavator

Hybrid excavator w/ boom balancing

∆Econv_lift

∆Ehybr_lift

Ehybr_lift_real

Econv_lift_real

unlo

aded

(JCM

AS H

020

)

full

buck

et(r

eal l

iftin

g)

Figure 6. Hypothetical fuel consumption results obtained for lifting unloaded vs. fully loaded

bucket.

On top of the problem depicted in Figure 6 comes the absence of energy required for actually digging into the material and filling the bucket. Figure 7 visualizes that when using the JCMAS H 020 cycle, the hybrid excavator appears to be far superior to the conventional machine, while in reality the relative improvement in terms of fuel effi-ciency is significantly smaller due to the energy that needs to be invested in actually filling the bucket, as well as lifting a full bucket instead of an empty one. The surprise for the customer would be even more unpleasant since the “air digging” results for the example given in Figure 7 would have shown a decrease in fuel consumption by ca. 80% (which is 400% increased fuel efficiency), while in reality the hybrid machine “on-ly” shows ca. 50% decreased fuel consumption (100% increased fuel efficiency).

12 Paper 12

Energyrequired

+ bucketload

+ bucketload

Conventional excavator

Hybrid excavator w/ boom balancing

Ehybr_real

Econv_real

unlo

aded

(JCM

AS H

020

)

full

buck

et(r

eal l

iftin

g)

full

buck

et in

cl. d

iggi

ng(r

eal w

ork)

Ehybr_0

Econv_0

+ bucketfilling

+ bucketfilling

>>Ehybr_real

Econv_real

Ehybr_0

Econv_0

Figure 7. Hypothetical fuel consumption results obtained in JCMAS H 020 test cycle vs. reality.

It is not intended to be in the scope of this paper to argue for any specific test cycle for fuel consumption or exhaust emission certification, but we wanted to show the chal-lenges with current approaches. In the following we will review the situation and pro-pose solutions for testing for benchmarking purposes, both external and internal, as well as testing for design optimization, both physical and virtual.

4 Testing for external benchmarking

With automobiles and other light-duty vehicles being more of a consumer product, cus-tomers have to rely on published figures for fuel consumption and greenhouse gases [15-17], only to discover later that, in actual use, the official figures can deviate quite significantly from customers’ personal experience. This will also be the case for the owners of working machines if or when fuel consumption testing according to a specific (and naturally simplified) cycle becomes mandatory.

Professional machine owners above a certain company size generally perform their own testing before placing a substantial purchase order. In the spirit of “nothing beats reality,” they invite several OEMs to their site for a head-to-head comparison between competing products. As mentioned earlier, productivity and energy efficiency are strongly affected by machine specification, working environment, and operator behav-ior. With the working environment the same for all competitors, the strategy is to make sure that each machine is equipped and operated in an optimal way. Therefore, the OEMs are free to tailor their machines to the specific application by configuring them with special tools, tires and any possible optional equipment, provided everything is part of the sales catalogue. In the actual competition the machines are then used by the OEMs’ own expert operators, which ensures that each machine is operated properly.

Representative Testing of Emissions and Fuel Consumption … 13

Whoever can show the lowest total cost of ownership [18] wins the sales order (or at least has a very strong position in the ensuing negotiations).

It can be argued that the use of specifically equipped machines and highly experi-enced operators skews the test results towards more favorable figures, but this is the case for each competing machine. It is also the only possible way for a real “apples to apples” comparison, because if average machines and operators were to be used, the first question to ask is the definition of “average machine” and “average operator.” With the first one only being a commercial matter, since the competing OEM will make sure to adapt the machine to the customer’s specific application in an optimal way, the ques-tion of how to compare the expert operators’ test results with the figures later to be achieved by the customer’s own operators is a more difficult one. Research like the studies reported in [5-7] has shown that there is a significant variation not only between operators of various skill levels, but also for the same operator using the same machine in the same application. This demonstrates the usefulness of professional operating edu-cation, as well as the need for operator assistance functions. With both measures, pref-erably combined, the promise is that any operator can be enabled to use a machine just like an expert.

In summary, the approach described above is the best conceivable one with the high-est possible amount of objectivity. Relying instead on test results from synthetic and simplified test cycles would be a major setback with a potentially huge loss of an OEM’s credibility in the eyes of the customer.

5 Testing for internal benchmarking

In this paper we understand internal benchmarking in the widest sense as an OEM’s internal test activities in order to compare its own machines both with each other and with competitors’ products. In contrast to external benchmarking the receiver of the test results is not an actual customer with a specific application, but rather the OEM itself. The absence of a specific application poses the problem to define the scenario(s) in which the machines are to be used in order to provide results with an acceptable level of quality.

For any benchmarking without a specific target application, the ambition is to some-how cover the complete spectrum of all possible applications – or at least to make a good enough approximation of the spectrum. Many working machines are extremely versatile, making it practically impossible to cover every use case. The solution is to rely on statistics, both in test design and data analysis.

Modern working machines from large OEMs come with data logging onboard. These data are not only very useful for the customers to optimize their respective business but also for the engineers developing these working machines. In the context of this paper logged data can be used to construct a mix of standardized working cycles that is repre-sentative of a whole population of machines in the field. Table 2 describes how to do this.

14 Paper 12 Table 2. Designing a representative mix of standardized working cycles

Step Action

1

Determine characteristic working cycles for the machine type (and size) in question

2 Standardize working cycles for good validity and repeatability

3

Determine characteristic parameter(s) for the machine type (and size) in question

4

Measure characteristic parameter(s) for the standardized work-ing cycles

5

Determine weighing factors for the standardized working cy-cles so that the mix approximates the entire machine popula-tion’s distribution of the characteristic parameter

For example, the characteristic working cycles for a medium-sized wheel loader would be short loading cycle, load & carry, transport and several others. The character-istic parameter could be the machine speed and the average fuel consumption. Having developed standardized test procedures so that each working cycle can be performed in a valid and repeatable manner, the trick is to find weighing factors so that the machine speed distribution and the average fuel consumption of the mix of standardized working cycles approximates the entire machine population. This cycle mix can now be used to test and compare all possible wheel loaders of similar size.

As is the case in external benchmarking, in testing for internal comparisons of energy efficiency it would be a mistake to make use of simplistic test cycles like the JCMAS H 020 and H 022 cycles discussed earlier. The underlying assumption of any benchmark-ing activity is that the results can be translated into the real world. With the JCMAS “air digging” cycles lacking proper man-machine and machine-environment interaction, the results are too skewed to be useful, even if just the ratio of, for example, fuel consump-tion before and after some design optimization was of interest. The example of a hybrid excavator with balanced boom has been discussed earlier, depicted in Figure 7. But the design changes do not have to be as significant as the introduction of a hybrid system in order to provide misleading results in testing according to JCMAS cycles. It could just as well be the case that a lighter boom has been developed or a new hydraulic system with reduced idle and part-load losses. Also in these cases testing, according to JCMAS will lead to a massive overestimation of the fuel efficiency improvement achieved in reality.

It could also be the case that the newer design, for example a wheel loader, shows lower losses in the bucket-filling phase than the older version, perhaps due to a new transmission design. With bucket filling not included in JCMAS “air digging” a com-parison of the test results will not confirm the improvement in fuel efficiency that will be apparent in real work.

Representative Testing of Emissions and Fuel Consumption … 15

The conclusion must therefore be that “nothing beats reality” in internal benchmark-ing, as well. The previously described approach with a representative mix of several real working cycles appears to be the best possible for a serious comparison of different machines.

There is, however, still the variation induced by the operator’s behavior to be taken into account. Following the findings in [5, 6] the conclusion must be to test each ma-chine in each working cycle by several operators with various levels of skill/experience and at various levels of productivity. Statistical methods of a higher sophistication than just calculation of the average have then to be employed in the analysis of the test data in order to show the robustness of the machine system towards variations in productivi-ty and operating style.

Going back to the beginning of this paper, Table 1 indicates that internal benchmark-ing might also be performed virtually, i.e. by means of computer simulation. However, if the comparison were to include competitors’ products, then the problem arises of how to obtain the large amount of data necessary to correctly model these machines and to validate them. This hardly seems practical. If instead the internal benchmarking were to include only own products, then in principal all an OEM needs to do is to model all test cycles contained in the application mix, including proper man-machine and machine-environment interaction. However, this is a major undertaking, as will become apparent in the following section, in which we discuss the simulation of test cycles for the pur-pose of optimizing design for specific use cases.

6 Testing for Design Optimization

The previously described approaches for benchmarking require a significant amount of time and resources, which makes them impractical in the actual design phase. For a quick and inexpensive verification of a design change’s effects, it is arguably better to concentrate on the one or few specific working cycles in which fuel consumption is considered to be affected the most.

For example, with reference to Figure 3, it has been described how the operator of a wheel loader has to work in order to efficiently perform bucket filling. If a design change involved a new control algorithm or optimized hardware in the hydraulic system or drivetrain, then it would be correct to limit testing in the design phase to short load-ing cycles, where the interaction between hydraulics and drivetrain is most pronounced.

Since engineers in this phase are less concerned with the big picture than the effects of a specific change, it might even be appropriate to use simplistic test cycles like JCMAS H 020 and H 022, provided no extrapolation to real work is done. However, one problem is still present: Provided a correlation factor can be found to correlate the fuel consumption of performing real work to the result of the simplified test cycle, that correlation factor will be specific for the machine type, size and architecture. It is prob-able that a design change will also lead to a change in the correlation factor. This would require new time and resource-consuming test series to establish the size of the new correlation factor, before “air digging” again could be used with at least some level of

16 Paper 12 confidence. It is therefore arguably easier and less expensive to just use the machine in real working cycles.

In the design phase we can also find computer simulation being used intensively. The absence of man-machine and machine-environment interaction in the JCMAS test cy-cles also means that they are easy to perform virtually, since only a machine model is required. However, just as in physical testing the results obtained with “air digging” do not represent reality – in order to do that, the simulation would need to include both an environmental model and an operator model. A detailed account of past and present research activities in these areas would exceed the scope of this paper. We therefore refer the reader to [7] and [19].

7 Summary It has been discussed in this paper that fuel consumption of a working machine is strongly influenced by machine specification, working environment, and operator be-havior. Practically unavoidable variations in the latter will lead to undesired, measura-ble variations in the former. These variations need to be accounted for by means of sta-tistics and thought-through test designs. Depending on the purpose of testing (legislative/certification, external benchmarking, internal benchmarking, or design op-timization), proper approaches can be found without using overly simplified test cycles that lead to non-representative or even misleading test results.

Definitions/Abbreviations

CAFE Corporate Average Fuel Economy

ECU Electronic Control Unit

EPA US Environmental Protection Agency

FTP-75 US Federal Test Procedure 75

GHG Greenhouse Gas

ISO International Organization for Standardization

JCMAS Japan Construction Mechanization Association

NEDC New European Driving Cycle

References

[1] DieselNet, “Emission Test Cycles: ECE 15+ EUDC / NEDC”. http://dieselnet.com/standards/cycles/ece_eudc.php

Representative Testing of Emissions and Fuel Consumption … 17

[2] DieselNet, “Emission Test Cycles: FTP-75”. http://www.dieselnet.com/standards/cycles/ftp75.php

[3] DieselNet, “Emission Test Cycles: Nonroad Transient Cycle (NRTC)”. http://dieselnet.com/standards/cycles/nrtc.php

[4] DieselNet, “Emission Test Cycles: ISO 8178”. http://dieselnet.com/standards/cycles/iso8178.php

[5] Frank, B., Skogh, L., Alaküla, M., “On wheel loader fuel efficiency difference due to operator behaviour distribution”, Proceedings of the 2nd Commercial Vehicle Technology Symposium, Kaiserslautern, Germany, March 14-15, 2012.

[6] Frank, B., Skogh, L., Filla, R., Fröberg, A., Alaküla, M., “On Increasing Fuel Ef-ficiency by Operator Assistant Systems in a Wheel Loader”, Proceedings of 2012 International Conference on Advanced Vehicle Technologies and Integration VTI 2012, China, July 16-19, 2012.

[7] Filla, R. (2011) “Quantifying Operability of Working Machines”. Doctoral thesis, Linköping University, Linköping, Sweden, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-70394

[8] JTI, “Engine load pattern and engine exhaust gas emissions from off-road vehicles and methods to reduce fuel-consumption and engine exhaust gas emissions / Jord-bruks- och anläggningsmaskiners motorbelastning och avgasemissioner – samt metoder att minska bränsleförbrukning”. JTI report no. 308, ISSN 1401-4963, 2002. http://www.jti.se/index.php?page=publications

[9] JTI, “Development of relevant work cycles, emission factors and reduction of fuel consumption for working machines / Utveckling av relevanta arbetscykler och emissionsfaktorer samt reducering av bränsleförbrukning för arbetsmaskiner (EMMA)”. JTI report no. 309, ISSN 1401-4963, 2002. http://www.jti.se/index.php?page=publications

[10] Filla, R. (2009) “Hybrid Power Systems for Construction Machinery: Aspects of System Design and Operability of Wheel Loaders”. Proceedings of ASME IMECE 2009, vol. 13, pp 611-620, 2009. http://dx.doi.org/10.1115/IMECE2009-10458

[11] Wikipedia, “New European Driving Cycle – Criticism. http://en.wikipedia.org/wiki/New_European_Driving_Cycle

[12] Japan Construction Mechanization Association, “Earth-moving machinery – Test methods for energy consumption – Hydraulic excavators,” JCMAS Standard H 020, Rev. Sep. 2010.

18 Paper 12 [13] Japan Construction Mechanization Association, “Earth-moving machinery – Test

methods for energy consumption – Wheeled loaders,” JCMAS Standard H 022, Rev. Sep. 2010.

[14] AVL, “Methods to calculate and declare fuel consumption for heavy non road mobile machinery, part II”. Commissioned by The Swedish Transport Administra-tion, 2011. http://goo.gl/frbmH

[15] EPA, “Fuel Economy – Regulations and Standards”. http://www.epa.gov/fueleconomy/regulations.htm

[16] DieselNet, “Emission Standards – United States, Cars: Fuel Economy”. http://dieselnet.com/standards/us/fe.php

[17] DieselNet, “Emission Standards – European Union, Cars: Greenhouse Gas Emis-sions”. http://dieselnet.com/standards/eu/ghg.php

[18] Volvo CE, “How much does your equipment really cost?”. http://goo.gl/gc28I

[19] Filla, R. (2012) “Simulating Operability of Wheel Loaders: Operator Models and Quantification of Control Effort”. Proceedings from the 2nd Commercial Vehicle Technology Symposium, Kaiserslautern, Germany, March 14-15, 2012.

(Internet links updated and verified on August 3, 2012)