Driving patterns and optimum design

The standard legislative driving patterns were the preferred driving patterns for the optimisation of powertrain component sizes to get optimum FE. Generally seven standard driving patterns, namely, UDDS, HWFET, US06, FTP, NEDC, ECE- EUDC, and LA92 were considered in the reviewed literature [49-60], as shown in Table 3.4. The usage of these standard driving patterns in the reviewed literature indicates their importance in the design of powertrain components of HEVs. The probable reason for choosing the standard driving patterns is due to wider acceptability of those driving patterns and therefore easy to understand the improvements of designs based on those standard driving patterns. Real-world driving patterns specific to a location such as TEH-Car based on Tehran city [55] was also considered for the selection of optimum combination of powertrain components.

Table 3.4: Driving patterns considered in literature

Reference Driving patterns

UDDS HWFET US06 FTP ECE-

EUDC

NEDC LA92 Real-

world [49]     [51]  [52]     [54]  [55]   TEH-Car [57]   [58]  [59]   

[50] Combination of Urban and Highway (names were not mentioned) [53] Combination of FTP and HWFET

[56] Combination of UDDS and HWFET [60] Combination of FTP and HWFET

Although standard legislative driving patterns were commonly used by researchers, the standard legislative driving patterns are not sufficient to predict the entire variations in the real-world driving patterns. The standard legislative driving patterns are useful for comparative studies of vehicles. However to predict actual performance on road, it is more logical to evaluate the optimum designs over real- world driving patterns.

It could be seen from Table 3.4 that some literature [51], [54], [58] limited their study to one driving pattern only, whereas, some others [49], [52], [55], [57], [59] considered more than one driving pattern. The majority of studies, [49], [51], [52], [54], [55], [57-59] considered one driving pattern at a time to find an optimum combination of powertrain components over that driving pattern only. The studies which considered one driving pattern obviously found only a single optimum design. The reason behind the selection of any particular driving pattern was not explained in those literatures. It might be due to the objective of those literatures where the main objective was to compare a particular optimisation method as compared to another optimisation method in terms of optimum FE and/or emissions and therefore, the selection of driving pattern was of little significance. However the studies [49], [52], [55], [57], [59] which investigated more than one driving pattern, also considered only one driving pattern at a time for the optimisation of powertrain component sizes; found different sets of optimum powertrain components, one for each driving pattern. In other words, powertrain components were optimum only over a given driving pattern. It was found that a set of optimum powertrain components over a driving pattern was not optimum over other driving patterns [52], [55], [57], as shown in Table 3.5.

Table 3.5: Optimum component sizes over different driving patterns

Reference Components Optimum sizes over driving patterns Variation

in sizes, %

[52] ICE power, kW UDDS: 46, HWFET: 44, LA92: 50, US06: 54 18.5

Motor power, kW UDDS: 48, HWFET: 51, LA92: 52, US06: 82 41.5 Battery power, kWh UDDS: 4.8, HWFET: 4.6, LA92: 5.2, US06: 6 23.3

[55] ICE power, kW FTP: 42.6, ECE-EUDC: 36.9, TEH-Car: 41.4 13.4

Motor power, kW FTP: 12.8, ECE-EUDC: 15.8, TEH-Car: 13.5 19.0

Battery module FTP: 13, ECE-EUDC: 17, TEH-Car: 14 23.5

[57] ICE power, kW FTP: 40.7, ECE-EUDC: 36.9 9.3

Motor power, kW FTP: 12.2, ECE-EUDC: 14.9 18.1

Battery module FTP: 13, ECE-EUDC: 15 13.3

Where,

ܸܽݎ݅ܽݐ݅݋݊݅݊ݏ݅ݖ݁ݏ, % =൫ܯ ܽݔ݅݉ ݑ݉௣௔௥௔௠ ௘௧௘௥_{ܯ ܽݔ݅݉ ݑ݉}−ܯ ݅݊݅݉ ݑ݉௣௔௥௔௠ ௘௧௘௥൯

௣௔௥௔௠ ௘௧௘௥ ∗ 100

The first study [52] found 18.5, 41.5, and 23.3% variation in the maximum power of the ICE, motor, and battery, respectively among the UDDS, HWFET, LA92, and US06 driving patterns, as shown in Table 3.5. The second study [55] found 13.4, 19.0, and 23.5% variation in the maximum power of the ICE, the maximum power the motor, and number of the battery modules, respectively among the FTP, ECE- EUDC and TEH-Car driving patterns, as shown in Table 3.5. The third study [57] found 9.3, 18.1, and 13.3% variation in the maximum power of the ICE, the maximum power of the motor, and number of the battery modules, respectively between the FTP and ECE-EUDC driving patterns, as shown in Table 3.5.

Although FE is generally evaluated over a single driving pattern during the optimisation of powertrain components, four studies were found that used a

combination of two driving patterns for the evaluation of FE [50], [53], [56], [60], as shown in Table 3.4. Two studies [53], [60] considered a combination of urban driving pattern (FTP-75) and highway driving pattern (HWFET) for the evaluation of FE. Similarly, another study considered a combination of urban driving pattern, UDDS and highway driving pattern, HWFET [56]. Another study also considered a combination of urban and highway driving patterns [50], though the names of those driving patterns were not discussed. Although those studies [50], [53], [56], [60] considered a combination of two driving patterns for the evaluation of FE, the usage of the combined driving patterns for the optimisation was not explained. It is logically better to consider urban and highway driving patterns together to represent the actual driving patterns of the real-world, but it is also required to consider different driving styles of urban and highway to represent real-world driving conditions more realistically. When there is a combination of driving patterns, different sequence of driving patterns are possible and each sequence might affect the optimum component sizes. Even though a combination of urban and highway driving patterns were considered for study, the effect of sequence of driving patterns on optimum component sizes was not studied.

As different optimum designs of powertrain components are available for different driving patterns, the natural question would be which design to choose from the available designs for real-world application. Therefore, a designer’s decision is required to select a design from available designs.