I wonder if this would work, or if it would ever happen..

Imagine having an axillary engine on a truck, to power the alternator, power steering, and AC pump. It would sit under the box somewhere, and maybe be a 10 hp 1 cylinder motor. It would drive the alternator 100% of the time, and have electric clutches on the AC and power steering pump.

The engine bay would no longer contain the alternator, AC junk, or even batteries. Just the engine, cooling system, water pump and fan.
There is a TON of room under these trucks, and it seems like this would work great.

Disadvantages:
-Longer electrical cables going to APU.
-Extension hoses for AC system.
-Extension hoses for power steering.
-Extra system / equipment to maintain.
-Cost

Advantages:
-APU always runs alternator at full output capability.
-APU always able to provide full power steering output regardless of main engine RPM.
-Steering pump, alternator, AC pump all running at optimum efficiency all the time.
-Fuel economy.


So just imagine this; the APU could shed it's excess heat into the main engine, how many times to you leave a truck parked somewhere and leave it running for heat, or AC? Now you could do this, but it wouldn't be as hard on the main engine, plus it would burn less fuel. Main engine would remain warm for when you start it and drive away.

Since the APU would start in the 'RUN' position, when cranking the main engine over, the alternator system would already be charging at full capacity.

The truck could run things like inverters, while camping, without running the main engine. In essence, could be used as a generator when needed.

Because the belt driven equipment would all be running at optimum speed all the time, driving down the highway should yield better fuel economy, because no power is being wasted spinning things faster than they need to go.
From what I've read, a reefer unit on a highway trailer burns about a gallon an hour, but they are much larger engines that what this would take.
Everyone is so concerned about idling trucks, well this would eliminate the need to idle a big engine all the time, while still enjoying heat and AC, plus keeping the main engine warm and ready to go.

What you think- potential, or way too much engineering and cost for the gains?
If ford offered it in super duty, would you spend an extra couple 1000$ for it?

 

Add to disadvantages:
APU dies, no power steering
APU dies, no A/C
APU dies, no alternator
If the cooling systems are intertwined, if one springs a leak, both are down.

I had an 8kW genset on my last big truck. None of the systems were intertwined at all, and that was a good thing. Rooftop A/C and heat on the sleeper was fine, and I could run the block heater on the main engine if needed. It also powered my water heater for the shower, refrigerator on 120v, and microwave/convection oven. Yes, it was a big sleeper.

 

I think you're about to invent the hybrid.