The relationship between the driving pattern and the emissions

In the different sections above it has been underlined that the fuel consumption “savings” in a hybrid vehicle compared to a conventional vehicle are largest at low speeds and loads of the vehicle. A question was raised as to whether this is also true for the emissions. In order to get an indication, despite the lack of specific data needed, the emission data generated at US EPA was used for this purpose, in addition to that it was of interest to present emission values from tests according to the FTP-75 driving cycle. Results from the tests carried out by US EPA are summarized in Table 23 and Table 24. It should be observed that the values presented here are converted to SI units.

Table 23. Result from emission tests according to the US EPA FTP-75 test procedure.

Test date FID HC NMHCE CO NOx CO2 Fc Net charg. *

g/km g/km g/km g/km g/km l/100 km Amp-h.

980403 0.037 0.037 0.249 0.031 112.5 4.95 -0.285

980417 0.031 0.025 0.249 0.031 110.0 4.84 -0.252

980423 0.037 0.031 0.249 0.044 113.1 4.98 -0.132

980424 0.037 0.031 0.249 0.031 108.1 4.77 -0.038

*Negative values are related to the net charges of the battery during the driving cycle.

Source: Hellman et al., 1998.

Table 24. Result from emission tests according to the US EPA HFET test procedure.

Test date* FID HC NMHCE CO NOx CO2 Fc Net charg.**.

g/km g/km g/km g/km g/km l/100 km Amp-h.

980403 0.025 0.025 0.186 0.031 110.0 4.835 -0.488

980403 0.025 0.025 0.186 0.037 101.9 4.472 -0.08

980417 No analysis No analysis No analysis No analysis No analysis No analysis -0.444

980417 0.006 0.006 0.124 0.025 103.2 4.534 -0.052

980423 0.006 0.006 0.124 0.037 111.97 4.905 -0.37

980423 0.006 0.006 0.124 0.031 103.8 4.572 -0.014

980424 0.012 0.012 0.124 0.025 110.0 4.838 -0.338

980424 0.012 0.012 0.062 0.031 102.6 4.520 -0.097

*The first value in each column of HFET (Highway Fuel Economy Test – a test for measurement of fuel consumption) refers to the first test of FTP-75, the second value to the second FTP-75 test and so on (compare the test dates in the tables). In this case measurement of emissions and fuel consumption have also been carried out for the preparatory driving according to the HFET cycle, which is not a common procedure.

** Negative values are related to the net charges of the battery during the driving cycle. Source: Hellman et al., 1998.

The result of the tests carried out by EPA show that the emissions of HC at FTP-75 are, on average, more than 40% larger than the values presented by Toyota (Table 23) but as an average approximately 50% less than the Toyota values when driving according to the HFET cycle. It should be kept in mind that the data presented by Toyota were generated according to the Japanese 10-15 mode cycle (see Section 8.1.2).

The emission of CO does not vary for the FTP-75 tests and is at the same level as the CO emission values reported by Toyota. For the HFET cycle the average values are nearly 50%

less than the values reported by Toyota (compare Table 23 with table 24).

On average, the emission of NOx is 0.034 g/km for the FTP-75 tests and 0.031 g/km for the HFET tests i.e. 37% and 24% respectively higher levels than the Toyota NOx values.

Comparing the results from FTP-75 (which represent a lower average speed than the HFET cycle) with the results from the HFET cycle there is an indication of a negative correlation between the average speed and the emissions i.e. the emission levels are higher at a lower average speed than at a higher speed.

According to the tests carried out by US EPA the fuel consumption is considerable higher than data reported by Toyota (see also Section 8.2.3)

Since there is a good potential for obtaining low emission levels and high fuel efficiency, the hybrid vehicle alternative can be seen as a more attractive alternative today than an electric vehicle. However, the development of the future may give the answer as to which of the alternative hybrid or electric vehicle is more attractive. If there will be a successful development and reasonable cost of fuel cell vehicles which work like a electric vehicle, the answer may be definitely “electric vehicle”.

In line with the ranking for best fuel economy (see Section 8.1.4) the ranking can be carried out for the emission performance for conventional vehicles. To keep it simple, the ranking is carried out only for the emissions of NOx and particles. The result of such a ranking will be as follows:

Conventional otto engine with TWC emission control.

Advanced otto engine with direct injection (stoichiometric, EGR and TWC) Advanced otto engine with direct injection (lean-burn, EGR and deNOX) Diesel engine (direct injection)

Comments: It is possible to carry out a similar ranking even for other emission components than for NOx and particles but then the picture will be more complicated depending on the technology used for emission control etceteras and it has been excluded for reasons of space.

13 SUMMARY OF COSTS

A more thoroughly costs estimates was not really included in the enquiry for the preparation this report since there is no on-going production of hybrid electric vehicles and that the extra costs involved for the hybrid vehicles therefore are difficult to estimate. One cannot, however, ignore the fact that this type of vehicle involves the cost of a double driving system. Since there must also be batteries in the system the cost are further increased in the case of the batteries having to be very large. A cautious estimation is that, if a conventional vehicle, with the size of the Toyota Prius, now costs 150,000 Swedish crowns a cost up to 100,000 Sw.cr.

would have to be added for a hybrid vehicle, even if there was a relatively large-scale production (10 000 units per year). Chrysler has estimated that their prototype (PNGV) would cost 15,000 dollars more (approximately 140,000 Sw.cr. in year 2000 exchange rate). This is however a considerable improvement on the previous prognosis from the same manufacturer of +60,000 dollars. To this it can be added that the difference in the actual cost for a Ford Focus flexible fuel vehicle and a Toyota Prius (both of them are to be sold in Sweden) is approximately 80 000 Swedish crowns (approximately $8 400 in the today’s exchange rate).

A calculation of cost given by Mercedes for their previously mentioned hybrid system (see section 8.2.1) is shown in Figure 43.

Figure 43. Cost of various driving systems. Source Mercedes Benz.

Comparison of production costs for various types of driving system (basis for calculations: 10,000 units) Conventional driving system 100%, Convention driving system with EZEV emission level 124% , Series hybrid (EZEV) 204%, Electric vehicle (ZEV) 226%, Source Mercedes Benz

As can be seen in Figure 43 the cost of a driving system for both a hybrid vehicle and a purely electric vehicle exceed the cost of a conventional driving system. In the future and when larger series are involved, the extra cost could probably be reduced to ca 25,000 Sw.cr., but even this extra cost can be too high to be able to motivate a large-scale use of the technique.

It can be seen from the figure that a conventional driving system developed to meet the EZEV limits would be considerably less expensive. Since the parallel hybrid system has the potential

of being considerably cheaper than the series hybrid system, this would be a strong reason for it being more successful in the short and relatively long-term.

The opinion of the authors concerning the hybrid system for passenger vehicles is that the extra cost of series hybrids will be far too high, within the foreseeable future (to 2010) for it to be able to compete with a conventional driving system. Even if a parallel hybrid system can be somewhat cheaper, it seems that the extra cost even for that system is also a considerable hinder. A number of technical break-throughs must thus take place for the hybrid system to be able to compete with a conventional system for passenger vehicles. The great potential for reduced fuel consumption will however probably lead to a great deal of interest for these driving systems in the future.