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Now I\’m no engineer but….

Known as GenShocks, the contraptions will mean that motorists will no longer just worry about their suspension, but regard every jolt as potentially cutting the cost of a visit to the filling station.

This in turn means that less fuel is needed to power the electrics.

This is because the devices not only absorb the impact from driving over rough surfaces but convert it into electricity as well.

The power generated from the bumpy ride is then used for the myriad of devices which rely on electricity from the car\’s alternator – such as headlights, windscreen wipers and sound system.

The question is, will it make any difference?

I\’m certainly under the impression (and do correct me if I\’m wrong) that the alternator simply runs at the same speed/power level all the time. When you switch on the lights, it\’s not revving the car more so as to generate more electricity. You\’ve a standard amount of electricity being generated all the time….if you don\’t use it then it\’s just wasted. I think the process is that the alternator runs all the time, feeds it into the battery and then, when you use some, it\’s drawn from the battery.

If this is so then having more electricity being generated elsewhere doesn\’t make any difference, does it?

If the alternator doesn\’t rev the engine to make more power, then making more power elsewhere won\’t not rev the engine and save fuel, will it?

Update….looking at the comments it\’s lucky I don\’t engineer things, isn\’t it?

16 thoughts on “Now I\’m no engineer but….”

  1. My guess it would make a difference, but a negligible one. On Land Rovers we used to replace the belt-driven fan with an electric one to reduce the load on the engine, but these were 1970s engines which were as inefficient as hell and were driving a huge metal fan. Modern engines are too efficient to see much of a difference in fuel consumption by removing such a relatively tiny load as the alternator. The extra weight, complexity, and cost of the equipment and control system would probably render it uneconomical.

    Tim adds: Ah, no, they’re not suggesting getting rid of the alternator. Just that the shock absorbers will feed power to the extant one. Which I don’t think will make any difference at all to the fuel consumption.

  2. Useful on a hybrid, where you’ve already got capacitors and batteries capable of storing the power. 5% fuel saving possible based on manufacturers claims.

  3. Particularly on a smaller car, you are likely to notice an additional load put on the engine when you turn the air conditioning compressor on.

  4. Tim, firstly, the alternators work is, although it is always rotating at the same proportion of engine speed, the higher the load the harder it is to turn. It is therefore absorbing a higher percentage of the engine power as the load increases. This can be particularly noticeable for very high power devices such as air conditioners.

    Secondly, there is undoubtedly some power that could be recovered from shock absorbers, this is currently converted to waste heat. However, it is obviously not very much, as otherwise shock absorbers would have cooling fins.

    The cynical engineer would expect that, like wind turbines, the recovered power would not match the extra cost of installation.

  5. Tim needs to go buy one of those educational toy sets (mostly sold for boys) including an electric motor/generator, rig up the generator to a switch and a lightbulb, wind string around the axle, pull with the switch open and with it closed: and feel the difference.

    Best regards

  6. Tim, take no offence, but I’m afraid I must say that generally, an engineer has a better understanding of economics than an economist has understanding over engineering…

    When you use more electricity in a car, you also burn more fuel. For instance, when you switch on the lights, or other electric appliances, the alternator has to produce more electric energy – otherwise the car battery would be drained. Thus, for every kWh of electric power produced, you need to consume something like 3 kWh worth of fuel.

    This is why I find surprising that in the EU level, the direction of regulation is towards having to have headlights on all the time. Elsewhere, they’ve been regulating towards saving energy, even in very very stupid ways (such as the ban of frosted incandescent light bulbs in Northern Europe – the Portuguese idiot in the ivory tower just didn’t believe that for 10 months in a year, we have a need to heat up our houses, and we just don’t have air conditioning in our homes, so the heat-light ratio of bulbs is really not so hugely relevant for us.)

    Tim adds: OK, but this is the bit I’m not getting. When the engine’s on the alternator is running, the fan belt is going around etc. When you rev the engine this goes around faster. Fine, yes, got that.

    But when you switch on the lights the engine doesn’t start running faster. This is the bit I’m clearly not getting. What is the mechanism by which the need for more electrical power causes the engine to run faster? My assumption is, rather, that you’re producing electrical power through the alternator all the time, power that gets used or not dependent upon whether you’ve got the lights on or not.

  7. Timmy, Roue is correct.

    How *easy* the altenator is to spin depends on how much electrical work it is doing, i.e. how much power it is generating = voltage x amperage. If you disconnect it it spins easily. If you run it through a small resistance, it does maximum work and you couldn’t turn it by hand.

    The lights run off the main electricity supply of the car. If you turn the lights on, the altenator will begin to charge the battery more (either because the voltage of the battery drops or because the car is clever and disconnects the altenator via relays when charging is not needed), and will be harder to turn, hence will require more petrol to turn the engine.

    Really, conservation of energy works.

    You can try it yourself with a DC toy motor (say from a broken scalextrix), which functions exactly as an altenator does. If you have one. It will spin easily. However if you connect the two terminals with a paperclip, it won’t.

  8. “But when you switch on the lights the engine doesn’t start running faster.”

    You ride a bike, Tim. Cadence and work aren’t the same, are they? On the flat, nice and easy, going up hill you have to work harder.

    When the alternator draws power, it becomes harder to turn, so the engine has to work harder: more turning force means more fuel in the cylinder until a maximum, and then the engine speed has to change. It’s just like a bike.

    The mechanism by which the alternator becomes harder to turn requires and understanding of Maxwell’s laws, back EMF, and those force diagrams that map to your thumb and fingers (you can tell when students reach the motor / dynamo question in an exam!)

    I’ve forgotten the details now (is it left hand for dynamos and right for motors?). But I merely do that specialization thing you talk about – and let someone else worry about it.

  9. Tim, the guys are right about the alternator, the more load you place on it the harder the engine works to turn it. Try this: sit in your stationary car with thecengine at idle. Switch on lights on full beam and you’ll notice the engine speed dio for a second until the fuel system can react and pour a bit more fuel in to restore the speed.

    Shock absorbers don’t absorb the bump from the road, springs do. Shock absorbers damp the action of the spring so you don’t bounce along. The energy removed from the system by this action escapes as heat. It seems reasonable that this energy could instead be turned into electricity. Not much, but enough to recover the cost of the generator, which is all that is needed.

  10. I’m no engineer either but I have a different problem with the system.

    When a shock absorber is compressed it stores energy and when it rebounds it releases it. Newton’s third law. If you add a turbine in there to harvest energy you are simply adding another layer of resistance not capturing stored energy.

    So some energy is lost as heat and you might capture that, but are they really saying up to 6% of the fuel used by a car goes into heating up the suspension?

    Surely more fuel could be saved by simply making the roads smoother instead of the diabolical state they are currently in.

  11. Winston writes: “When a shock absorber is compressed it stores energy and when it rebounds it releases it.”

    No; as written above by Marksany, 2.5 hours earlier, that is what springs do. The shock absorbers take out energy, and convert it into heat. The ‘proposed’ mechanism takes out energy and converts it to electricity, to reduce that needed from either the battery or from the petrol engine via the alternator.

    Is there a blog for people interested (and possibly competent) in both economics and engineering?

    Best regards

  12. The problem I could see with it would be having a constant load on you shock absorber generators. If this varies then the amount of damping would vary as well. If you have no electrical load your car could wallow around like a big American car. Switch on all the gadgets and it would stiffen up like an F1 car.

    And alternators aren’t little dynamos like you fit to a bike. They generate a fair bit of electricity. I would imagine a big car would have 1kW or more.

    I wish your engineering was right Tim, because if it was you would have discovered perpetual motion.

    Tim adds: Ah, no, my misunderstanding wasn’t that bad, I know about perpetual motion. No, what I thought was that the alternator is always on, the alternator is always generating the same amount of power, and that power was either used or dumped if it wasn’t used. That is, that the alternator was always generating enough power to run your CD, your lights, etc, and you either used it or you didn’t.

    Silly perhaps, but not silly enough to lead to accusations of having discovered perpetual motion.

  13. I think this technology has arisen from electronically controlled dampers which change the degree of damping under control of an ECU. I don’t think they plan to replace the alternator, but supplement it.

    Nigel, I imagine a blog for engineers who understand economics or economists who understand engineering would be catering to a very small audience!

    The thing with Tim is, he knows he doesn’t know, so he asks the questions. I wish my non-engineers managers would do that. Instead they pretend they know and tell me to do stupid things.

  14. Mark. Many year ago, I learned of one definition of engineer: “Someone who can make for sixpence, what any fool can make for a shilling.”

    Thus, I view any true engineer as also something of an economist (in both ‘punny’ senses).

    Best regards

  15. This is going nowhere, the cost of the equipment will outweigh the savings made. A better source of recycling automotive energy would be regenerative braking (as a lot of eco demonstrator cars have) and an exhaust gas turbogenerator (approx 30% of fuel energy goes down the exhaust)

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