I am currently studying How excavators work? and came to know that "In excavators diesel engine is used to drive the hydraulic pump. The high pressure fluid from hydraulic pump is used to run the hydraulic motors which rotates the wheel." Is there any specific reason for using hydraulic motors instead of directly using diesel engine?
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3 Answers
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Yes, because many or most excavators can 360 rotate so getting a classic gearbox/ prop shaft drive to the wherls or tracks would be challenging.
Then sorting the ability to do forwards with one side and reverse at the same time with the other is also difficult without hydraulics.
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2$\begingroup$ Additionally, the hydraulic system is already in place for managing the manipulators. $\endgroup$ Commented Nov 7, 2022 at 14:17
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A hydraulic motor has much greater torque density (torque vs size) compared to electric or diesel engines.
The hydraulic motor works well underwater, while an electric motor needs expensive (and heat retaining) waterproofing and a diesel engine needs air.
The hydraulic motor is simply more durable and efficient, despite any loss from converting from one power source to another.
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$\begingroup$ While most of that is true, the excavators still need a power source to run the hydraulic motor, so it will not be able to function under water if that power source is a combustion engine. Considering the whole powertrain, hydraulic motor is an extra "point of loss", it would be possible to construct a fully electric, or a combustion engine powertrain both of which would have better overall efficiency. Hydraulic system is much simplier, I'll give you that. Durability is simply a question of engineering, it's not dependent on the type of the system. $\endgroup$– Jpe61Commented Nov 9, 2022 at 8:15
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1$\begingroup$ We can't do much better than that link, which clearly rebutts all but your first sentence. $\endgroup$– RobCommented Nov 9, 2022 at 8:47
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$\begingroup$ Where exactly do the hydraulic motors get their power from? Just because a hydraulic motor manufacturer (reseller?) says on the internet that they are superior does not mean they are. Please have some source critisism. $\endgroup$– Jpe61Commented Nov 9, 2022 at 9:46
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$\begingroup$ Hydraulic motors are used in many types of equipment, Unbiased source: researchgate.net/publication/…. 2nd opinion: e-mj.com/features/… and agreement from an electric motor manufacturer: emotorsdirect.ca/knowledge-center/article/… - When the best answer is your own, you should write your own answer. $\endgroup$– RobCommented Nov 9, 2022 at 15:25
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$\begingroup$ @SolarMike has the best anwer. Without hydraulic pressure, the torque density of a hydraulic motor is zero. What do you think produces the hydraulic pressure for hydraulic motors? $\endgroup$– Jpe61Commented Nov 9, 2022 at 17:36
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Having spent over 30 years working in the world of heavy equipement, marine industry, farm industry, construction industry, logging industry etc., my experience has been that electric motors and systems always seem to have a have a way of succumbing to environmental corrosion over time faster than other types of systems, no matter what the engineers or theories might suggest. Sitting in a nice office someplace far away from actual construction world doesn't always cut it. There's a Canadian company (Letourne) that made log stackers using electric drives in each motor...they were a pain to work on and we always wished they were hydraulically driven rather than electric, as it seemed to us that the electric motors were more failure prone and you couldn't easy get repair parts for them or fix them easily in the field. If a hydraulic drive broke down, it was usually as simple as replacing a worn out hydraulic hose, which was cheap and easy and we could fix ourselves on site. Simplicy and realiability seemed to be the benefit of hydraulics, even if they are not as "efficient" as other drive systems, as no one cared about the cost of "efficiency" when two men and a manchine were costing the customer or the company hundreds of dollars per hour if they weren't working... Thus the extra cost of fuel was a mute point. Even the electric drive Letourne had to have a big diesel motor to generate the electricity for the electrical system in the wheels...so I'm not sure they were all that efficient, and thus like the Wankle rotary motor, it just never caught on (for good reason)... Theories and engineering only gets you so far... My best advice is to get out and get some on-site/real world work experience on Tug Boats, farming, logging or construction.
