More mpg by eliminating belt driven units?


#1

I must wonder to the automotive industry who is constantly seeking more MPG, what if you eliminate the un-neccessary belt driven units and have them just electric motor driven ? Would this result in sufficiently more mpg or would the elecrical load and extra weight negate that savings ?



I’m perfectly pleased with the electric steering on my hybrid Escape and must wonder about the a/c. After all, your refrigerator has an electric compressor.



Since we need less power steering at hiway speed , why have a belt driven pump that’s spinning ten times faster than needed when all the power assist we need already exists at idle ?



Since the air conditioning works perfectly at idle too, why have the clutch connecting at 20,000 rpm ?



What other engine load could be relegated to constant speed electric drive ?


#2

Radiator fans, water pumps, AC compressors, power steering pumps, alternators, etc. can be driven by belts or electric motors. Car manufacturers have taken both routes over the past 50+ years. It takes the same amount of energy to spin a AC compressor, fan, water pump, etc. by belt or motor. Some make more sense powered by belts (AC) and some by electric motors (fans). It’s not just a matter of fuel mileage, but control over the accessory device.

Twotone


#3

Certainly this is happening with hybrids, out of necessity. Electric steering is becoming quite popular, too. As for A/C, I guess the clutch can make up for the drive belt inefficiencies. But I know they carefully size the pullies to handle the expected needs.


#4

Air conditioning takes energy and I would assume it would be about the same whether the compressor is driven by a belt or by an electric motor receiving its power from the alternator. Certainly, the alternator would have to be a very large unit to power a compressor.

However, perhaps the heat from the internal combustion engine that is normally wasted could be put to use. The old Servel gas refrigerators, made up until 1957 cooled by using a gas flame. Carrier perfected a system that used steam to cool passenger railroad cars back in the 1930’s and this system was used into the 1960’s. Originally, the steam was generated by the steam locomotive. When the diesel/electric locomotives came along, a steam generator was incorporated in the locomotive that pulled the cars. Steam lines were run from car to car and attaching the steam lines and air lines were part of the coupling process. The power for the air handling fans came from batteries in each passenger coach. These batteries produced 32 volts and were recharged through a generator driven from the axle on each car. Apparently, this system was not as efficient as having a 480 volt 3 phase generator in the locomotive and cooling and heating the coaches electrically.


#5

There is no free lunch. Most automotive A/C units would need about 100 amps at 15 VDC to power them. This is where electric cars will have big trouble. The accessory loads will kill them…


#6

The boys in Detroit and Japan are not sleeping when it comes to these issues. As a DIY retrofit, well you had better be real good at your hobby.

We will see fully electric AC compressors very soon, and if you think they are expensive now, well no free lunch. Electric power steering seems to be a system that is having developmental trouble. Boost is variable on most current power steering stystems and has been for 15 years already.

It is hard to beat people trained in automotive design, but don’t stop trying.


#7

My refrigerator actually has a belt.


#8

Since the motor is spinning it was easiest to use belts to drive accessories. Now with max mpg the goal there is reason to look at other options. It is a benefit vs costs question in each case.

The alternator doesn’t make sense to use separate motor which takes electricity to generate electriciy.

Power steering really doesn’t draw that much power off the motor, but there are electric power steering systems coming on line. This means even a small decrease in draw off the gas motor means enough of a mpg saving to be worth the extra costs.

The big belt driven radiator fans take a lot of power, but have been increasingly rare on newer models. They probably will be extinct on new cars and trucks in a few years.

The AC compressor is a big draw of power, but would need a significant electric motor that uses power too. On hybrid cars with bigger batteries this system makes sense. The costs benefit ratio on “conventional” cars and trucks isn’t clear. If it means a bigger, or second, battery to make sure the AC is powered it might add more weight and it will put more load on the alternator. This one needs some more engineering work perhaps. It is nice in a hybrid to have the AC working while the gas motor is stopped in traffic or at fuel stops.

With better stronger and more compact electric motors we’ll see more accessories powered by electricity. This might mean more reliable systems, or more expensive repairs of these accessories. We’ll just have to see how it goes.


#9

As others have commented, compressors and pumps take power to operate. It may be more efficient to simply run them directly off the crank than to convert the crank power to electrical power and then convert that to mechanical power. Energy loss is a fact with every conversion.

Another problem exists in application. Operating compressors and pums with electric motors would create sufficient draw from the battery to prolong recharge times after starting. Since cars have to be practical for those who use them primarily for short trips, maintaining full battery charge could become a challenge in real life applications.

Electric fans are common primarily because of transversely mounted engines. The cranks are not oriente such that there exists a practical way of running the fans with them.

Inevitably technology may get around these porblems as hybrid and electric technologies progress. But at the moment operating compressors and pumps with electric motors just isn’t the most practical approach.


#10

Were you the highest bidder for the Hastings refrigerator from Willy Loman’s estate? (Willy Loman was the central character in Arthur Miller’s “Death of a Salesman” who complained about his Hasting’s refrigerator eating belts. He also complained about the carburetor adjustment on his Chevrolet)