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dmg
Posted: March 29, 2017 12:09 am
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the setup:

got an engine, driving a pump, that drives a motor, that drives a transmission that drives the axles on a wheeled loader.

now, the thing is the owner did get the pump and motor refubrished, confirmed indeed i can measure 350 BAR pressure when its working hard, however it does not really seems to load the engine, and its not quite strong. rather its weak as a whimp.

i found that the pump can manage 350 BAR and at full engine speed will pump 120 L/min, witch is about 70KW of power. but the engine can do a bit past 100 Kw in this loader, so i think the pump and motor are not the original one as it could not possibly ever load the engine properly.

Allso i found that interestingly the hidraulic pump can be reduced in flow, witch is not a bad thing.
however, even when the transmission is in the lowest range the thing is still too fast. so the pump has to be reduced in flow.

i calculated that when the speed would be comfortable, it would only make about 90 liter flow. that means no more engine load than 52 ish Kw... so not loading the engine.

now, i had been asked if i know of a solution.
my solution would be as follows:
throw out the pump and motor, and get new ones.
the pump should be able to make 170 lter/minute, at 350 BAR.
that should give a decent load. and the hydraulic motor should be a variable displacement motor.
the idea is to measure the pressure the pump makes, if it is say.. 320 BAR, increase the fluid capacity /revolution of the motor, if its less (say drops to 280 BAR) increase the fluid capacity /revolution of the motor. the idea is that thisway, when say.. going uphill, supposedly the hydraulics has to work harder, meaning more pressure. in witch case if it can not provide enough tourqe it should increase the fluid needed to make a revolution and that would in return yield higher tourqe. fine and dandy, specially since the mechanical tranny can provide 2 speed ranges.
most probably the high/low pressure at witch the fluid capacity should be changed can be adjusted with a pair of potenciometers, that part is fine and dandy.

but how to :
1. monitor engine load? if the loading arms are operated or the steering, it does take power from the engine, and preventing stalling would be a goal.
2. how could braking be incorporated ? as if you start to apply brakes, that is load on the drivetrain, in witch case the electronics woud increase tourqe at output. witch would make it pretty not decent at all.

does anyone have an idea ?
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kellys_eye
Posted: March 29, 2017 09:50 am
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1. How do you know the engine can do 100kW - nameplate? It could have de-rated significantly over the years.
2. The 100kW rating will be at peak operating revs - do you want/need to run at 'full blast' all the time?
3. Trying to match the hydraulic loading to engine output is an invitation to constant stalling.
4. Matching engine to pump is always a matter of compromise and the manufacturer wouldn't deliberately 'waste' one or the other so they have set the specs for a good reason.

But to answer your last few questions.

Engine loading can be measured by monitoring the engine vacuum. There's bound to be a vacuum sensor on the market these days.

If you over rate the hydraulic pump you WILL stall the engine - have you calculated the loading 170ltr/350bar will give?

Won't the torque be related to the psi rather than the flow rate? By increasing the flow rate you either increase the diameter of the pipework ( dry.gif ) or increase the pressure at which it is operating - since you can't adjust the pipework the flow rate is set by the psi and increasing it will just blow the seals etc.



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dmg
Posted: March 29, 2017 04:58 pm
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170 liter / minute at 350 bar gives allmost 100 kw.
if the engine revs are less than peak, the tourqe is higher than at peak rpm.
usually at half the maximum constant operating speed you see from 15 to 30 % more tourqe.
meanwhile the pump represents a load that linear with the engine rpm.

so i'm not inviting stalling, however i do have to consider when other pumps / loads affect the engine.

that is why i need some methood to monitor if the engine is overloaded or not. as if it is, i should be making the variable displacement motor take more oil / revolution, to make sure everything goes smoothly without any YEEHAA moments biggrin.gif
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dmg
Posted: April 01, 2017 07:51 am
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i sortha think i managed to solve my questions.
its a diesel so measuring vaccum would be pointless. takes the same amount of air allways.

but, i came up with an ingenious solution. i can adjust maually the maximum flow on the pump. the lifting part has an electric enable/disable switch to avoid acciedently dropping stuff while on the move. so i hacked a relay and resistor circuit, when the lifting part is enabled it makes the realy short a small resistor (actually a trim pot for fine tuning) limiting the flow the pump is allowed to make, therefore load on the engine is less. so it won't stall when you are digging in the bucket and lifting it.

braking was a tiny bit harder, along electronic controls this thing has a manual lever to adjust the flowrate. i added a small pneumatic piston to that lever, when you apply the brakes (air brakes) it actuates this piston too, reducing fluid flow to zero gradually.
to slow down the reduction i added a spring counteracting this piston, and the hose that supplys the piston has a manual choke valve i managed to adjust.

so if you apply the brakes the hydraulics actually help witht he braking.
sadly when you start again, and drop the brakes it sometimes does iterfer. brakes did not yet release, however the hydraulics are working full blast.

i allso added some selectable resistors to the pressure sensor (thank god its analog, and linear..) so you can select 3 different target pressures, but after field testing it turned out 2 would had been enough. 1 for work, 1 for driving around unloaded from site to site.

all in all i'm verry statisfied, so is the owner. the machine is utilised to its real maximum, given full blast on the diesel engine and really doing hard work it lets the engine drop to 1800 from 2200, but no more. it does not stall, if you wanted to dig the bucken in, previously it went it a quarter , and the machine stopped, while the diesel engine was verry happy and efforthless. however now, it is digging in hard, revs stop to drop and the machine only slows down (as the hidraulic motor opens up for more fluid / revs) and tourqe rises nicely, it lets now the bucket digg in properly into stuff, fills up nicely, and you can withness the diesel engine working at its best.

we noticed that top speed did improve a lot when driving unloaded, and acceleration in both wrking and driving around is brutal. before this transition it was... more like an old granny on the sunday morning. now it kicks hard. specially in mechanical low range.

i should patent this. sooo mutch better than the original, and requires no computers or controller boards that tend to be expensive when they give up the ghost.
the fuel consumption did increase / workhours, but when testing loading of a truck it actually improve the fuel /work done figure, not to mention its soo mutch faster.

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BlueVanACD2005
Posted: April 01, 2017 12:20 pm
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QUOTE
its a diesel so measuring vaccum would be pointless. takes the same amount of air allways.


Exhaust temperature might help you if you want to measure load. Fully loaded is probably 750-1000 F, idle is probably 250-450 F (just guessing).

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dmg
Posted: April 01, 2017 06:44 pm
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well, currently its done by "guesswork"
i mean the power it takes to turn the pump is in direct relation to pressure and flow.
pressure "seen" by the hidraulic motor is what defines the tourqe it can make, and the flow rate will define the RPM it can do.

fluid flow in liter/min * pressure in BAR /600 = Kw of power.
the diesel engine has a rising tourqe curve as rpm falls.
so i only need to set the initial flow rate, as the pump loads the engine its RPM will fall at a certain point. it will fall untill it gets high enough tourqe to drive the pump, and the tourqe gain is not linear. while power requirements for the pump are, and tied to RPM.

if the revs fall under the rpm of maximum tourqe then the engine is overloaded and will stall.
so my methood was to decrease maximum flow unitll unter full hydraulic load the engine speed drops by 20% of the maximum. surely over time it will have to be adjusted a bit if the engine wears out.

so it turns out it works more than properly with simple guesswork.
i do not need to monitor engine load it seems.
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