Delphi 48-Volt (nonsense)

Bob, do you think that no light-weighting is going on? Conventional vehicles (such as early '70s GM sedans like the Olds 98) have been transformed incrementally over the past four decades. What do you think hydroforming chassis parts is all about, along with Ford's use of aluminum body panels and structural elements on pickup trucks? Use of electrohydraulic steering versus hydraulic is a weight saver, due to the load dynamics that are allowed with a power-electronic controlled pressure system rather than pumps based on pure belt drive. Not to mention the move to smaller-displacement engines with much better power to weight ratios and lighter parts, such as engine blocks, that also require smaller and lighter 12-volt batteries due to better electronic control of spark, fuel, and throttle plates.

If a partial hybrid (i.e. 48 rather than 200 to 400) is another incremental improvement that gives an incremental gain, why knock it?

And even if it is the accountants that see a way to save 200 watts and 200#, why look a gift horse in the mouth?

 

It all depends on where the cost accumulates. The only thing magic about 12V was the simplicity of directly connecting to the battery. The pain of 12V is the cost of copper and gold (connectors). Once the cost savings of direct battery connections vanishes, then the material savings in modern cars becomes significant at higher voltages. However, there is nothing magic about 48V, so I would expect a whole series of different voltages being routed around in the future.

 

How expensive will a 48v mild hybrid system be?

GM is selling a limited number of eAssist pick ups for an additional $500 to $700. Auto start/stop, without regenerative braking, on 12v is now $295 to $500. Full hybrids are still $2000 to $3000, if not more.

 

Yes, but with full hybrid premium you are getting more than fuel economy.

When you add a more sophisticated transmission to a 48V system then price premium suddenly wanishes.

 

Yes, better fuel economy, but at a higher price. Higher fuel prices make that cost a better value, but the higher cost reduces a full hybrids sellability of the lower cost car models.

The $2000 to $3000 is for US pricing compared to the automatic transmission model. A CVT or dual clutch automatic isn't going to substantially close the that gap. Then some full hybrids make use of these traditional transmissions. So they aren't using a transmission more sophisticated than what a 48v mild hybrid system would see.

 

I see the tail wagging the dog here. If 48 volts or any other voltage is used extensively in a vehicle, it is because that is seen as the lowest cost solution for the overall vehicle. It makes no sense to "raise" the cost to insert 48V. 99.9% of consumers are going to look at the bottom line cost and the car maker know this. The reason for looking at higher voltages is simply because the cost of transistors is vastly less than the cost of copper and gold.

 

There is a unique feature of 48 volts - it is the highest voltage that can be connected across the human chest without fatal results. This is a big advantage for high-power systems that must be serviced, and for which one desires servicing modes where the battery will not be disconnected. At higher voltages double-insulation is required which adds to cost and system complexity, and the potential need for galvanic isolation between portions of the electrical system. To guarantee safety with unregulated electrical systems, the target voltage 42 volts is a good compromise. Long-time car guys will know that the distribution voltage for a 12 volt system can be as low as 9 v and as high as 16 or even 18 volts. With that poor regulation applied to 48 volts, the car would be hazardous to humans for most of its time on the road and in the service bay.

 

Completely agree with all the factors. But even the Prius has a high voltage system so multiple voltages are already in play with newer propulsion technologies. That is actually the trend that will continue....to have multiple voltages. 12V has a home, so can 48V, and so can some very high voltages. The common thread is the overall cost function of the final vehicle.

 

Going forward, we are going to see more blurring between what is a standard ICE car and what is a hybrid. Raising CAFE targets and carbon taxes will push this. The are already ICE cars available on the US market that have start/stop or regenerative braking. Combine the two, and you have a mild hybrid. Besides Mazda's, start/stop systems that stick with just one 12v battery run the risk of not being as effective outside the lab over time. They can simply stop operating to preserve a worn battery, or kill the battery early. The system on the Malibu Limited has a second, deep discharge 12v in the trunk, which is probably the minimum needed for start/stop to be effective over time in the real world. The second battery and isolation unit, so the starter battery isn't drawn on while the engine is off, close the cost gap with a mild hybrid system.

Likewise, a regenerative braking system needs larger batteries and different chemistries in order to be worthwhile in actually capturing the brake energy. Well, besides Mazda's. Theirs uses a 25v capacitor, which are much better at absorbing energy in a short time than a battery. Their start/stop system uses precise control of cylinder ignition to restart a warm engine, thus no draw on the starter battery for it. Being Mazda's, other manufacturers aren't likely to implement them though.

The 48v mild hybrid is likely the lowest cost system. Development of 48v accessories was started when 48v was considered become the standard for cars. Switching to that voltage for all the car's systems means not needing a DC-DC converter to step down the hybrid system's voltage for them.

42v might be a good compromise for service and rescue safety, but it may reduce the regen effectiveness.