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California’s new ZEV rule introduces the BEVx; ARB staff expects these vehicles to play a longer-term role than plug-in hybrids

On Friday 27 January, the California Air Resources Board (ARB) adopted the new Advanced Clean Cars (ACC) package that sets out the regulatory emissions and technology requirements for light-duty automobiles through model year 2025. (Earlier post.) The Zero Emission Vehicle (ZEV) regulation—one of the three main regulatory packages that constitute ACC—introduces a new regulatory vehicle category: the BEVx, or a battery-electric vehicle with a small “limp-home” range extending engine or APU (auxiliary power unit)—i.e., not a series-hybrid type vehicle such as the Chevrolet Volt equipped with a full-capability engine.

Under the ACC, ARB will award BEVx credits on the same basis as BEVs—i.e., on zero-emission miles (the simplified ZEV credit scheme under the ACC is a linear one based on those zero-emission miles). BEVx vehicles can provide up to 50% of the pure ZEV requirement for manufacturers, and so they may emerge as a significant vehicle type.

In the Initial Statement of Reasons (ISOR) published prior to the Board meeting, ARB staff noted that “some manufacturers” proposed this new class of advanced vehicles for separate treatment as part of the ZEV program. (During the public hearing on the ACC rule package, comments from ARB staff and the Board indicated that BMW was particularly interested in this classification.)

The basic rationale, according to ARB staff, is that such a vehicle has the potential to expand the BEV market beyond current market estimates by giving interested customers an extra measure of confidence about range, and if successful, would add substantial zero-emission vehicle miles traveled (VMT) to the overall California fleet.

It was suggested during the hearing that such a vehicle might even deliver more all-electric miles than a battery-only electric vehicle, as the availability of the range-extending engine could preclude drivers reserving battery charge to ensure they actually make it home.

The BEVx would have reduced performance while operating in APU (auxiliary power unit) mode—i.e., while using the range extender to find a charging location. Most of these vehicles are expected to have a zero-emission range of 80 miles or greater.

This vehicle has substantially more range than currently announced PHEVs, ARB staff noted, with electric range comparable to full function BEVs and will probably require ground-up BEV design.

Manufacturers believe that the APU will be a relatively high-cost option on top of an existing, full function (100+ mile), BEV. BEVs are expected to play an important role in ARB’s long-term emissions reduction strategy, but the market for current technology BEVs might be limited.

While the APU within the vehicle may evolve during this transition, from gasoline to advanced biofuels to hydrogen, it is reasonable to believe that this proposed vehicle may help meet ARB’s long-term GHG and criteria pollutant emissions reduction goals.

Staff expects BEVxs to play a longer-term role than TZEVs [ transitional zero emission vehicle; most commonly a plug-in hybrid PHEV] because of their improved zero emission mileage potential. These vehicles would be particularly well suited to use of low upstream GHG fuels that might be more expensive, since the predominant operating cost would be offset by relatively low-cost electricity. In addition to potential for emerging alternative fuel use, there is an opportunity to explore engine technologies that are advantageous but otherwise unsuitable for application in conventional vehicles.

Engine technology applied to existing PHEVs is derived from small conventional production gasoline engines, but highly specialized APUs for BEVxs may eventually spin off and evolve in completely different directions. Future BEVxs with highly specialized engine and fuel technologies could be optimized to drive cost, weight, size, and emissions down and make these specialized BEVx APUs suitable for more affordable and therefore more widespread application. Lotus Engineering and other automotive design firms have been developing hybrid-specific APUs and have several unique concepts under development already.


ARB staff suggested that the BEVx market may appeal to drivers who would not otherwise consider a BEV with the same range. Since staff considers these vehicles full function BEVs with short range APUs, it stressed the importance of having the minimum range for eligibility be equivalent to full function BEVs in the marketplace.

Basic criteria for these vehicle include:

  1. the APU range is equal to or less than the all-electric range;

  2. engine operation cannot occur until the battery charge has been depleted to the charge-sustaining lower limit;

  3. a minimum 80 miles electric range; and

  4. super ultra low emission vehicle (SULEV) and zero evaporative emissions compliant and TZEV warranty requirements on the battery system.

ARB expects—but is not at this point requiring— manufacturers to incorporate further performance limits on charge-sustaining APU mode operation, including speed restrictions.

For the 2012 through 2017 model years, BEVxs will be referred to as Type I.5x and Type IIx vehicles, to fit in with the pre-2018 nomenclature for ZEVs. Type I.5x and Type IIx vehicles will receive the same credits as Type I.5 and Type II ZEVs: 2.5 and 3 credits, respectively. Up to 50% of the portion of the ZEV requirement that must be met with pure ZEVs may be met with these Type I.5x and Type IIx vehicles.

ARB staff has committed to studying PHEV and BEVx user-behavior to find a more refined attribute-based methodology that can better correlate with desirable zero-emission VMT (vehicle miles traveled) and emissions reductions.


  • ARB Staff Report: Initial Statement Of Reasons Advanced Clean Cars 2012 Proposed Amendments To The California Zero Emission Vehicle Program Regulations



One issue not considered that this forces the battery to carry a 10 year warranty on capacity.. that could be expensive since the pack would need a low SOC usage such as the Volt and probably a refrigerated liquid cooling system. There goes the simplicity and low cost of a Leaf and back into the $40k territory

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