Hybrids cause confusion

7 July 2005

The traditional car magazines - mostly staffed with petrolheads rather than geeks - are having a tough time coming to terms with some new motoring technologies. The current issue of the UK's Test Drive magazine is a good example. It reviews the Lexus RX 400h hybrid 4x4 and dutifully explains that its gear selector will be a bit unfamilar to most drivers:

In addition to the usual Park, Neutral and Drive positions, there's also a B (battery) gear selector that keeps the CVT gearbox locked in electric mode. This whizzes the heavily soundproofed, superbly damped car along in complete, pollution-free silence.

All well and good, except that it's completely wrong. In this car, as in Toyota's Prius MkI and II, the B position is actually a hill-descent mode.
Hybrids use regenerative braking to turn momentum into electrical energy, and to maximise this effect the engine is decoupled from the drivetrain when braking. This is fine in most conditions but on a long or steep downhill road the lack of engine braking can not only be a bit unnerving for the driver, but can also lead to overheated brakes. Hence the B (Braking) mode, which in the Lexus puts both the front and rear electric motors into generator mode, rather than the front alone, beefing up the rolling resistance.
It does make one wonder whether Test Drive actually took the RX for a test drive...
No doubt the mainstream mags will become more familiar with how hybrids actually work in the coming months.

Update: Top Gear magazine cuts through the above confusion nicely in its review of the RX 400h, published last week:
Controls and driving procedures all are as per normal.

Nicely precise journalism from road tester Paul Horrell...

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