Casappa Concept of Electro-Hydraulic Load Sensing System

Previously on iHydrostatics N23, hydraulic start-stop concepts and solutions for on-highway vehicle proposed by Rexroth, Poclain and Line have been summarized and compared. This technology has opened a window for hydraulics to the wide on-highway market. You couldn’t miss it. Reply N23 in Wechat iHydrostatics to get this episode. Any questions are always welcomed, iEditor encourages you to leave your comments in iHydrostatics Interest Tribe (iHydrostatics兴趣部落).


Casappa MVP Series Pump Shown on Bauma 2014
In this new post, iEditor would like to discuss an electro-hydraulic load sensing system proposed by Casappa. Combining with angle sensor, electro-hydraulic torque control function can be easily achieved.

1Load Sensing HistoryAs we talk about load sensing system, it has been developing into the third generation due to the stricter emission reduction requirement. Each generation has its own characteristics as summarized below:
1st1st Gen.: Hydro-Mechanical LSIn the first generation, LS pump is introduced plus a tranditional valve with pressure compensator before the main valve spool.


First Generation LS System [1]

2nd2nd Gen.: Flow SharingIn the second generation, the system allows a proportional distribution of the flow demand to the hydraulic lines even in case of pump saturaton. [2] The main difference from first generation is the compensator position which is after the main valve spool.


Second Generation LS System [1]
3rd3rd Gen.: Electro-Hydraulic LSBasically, the electro-hydraulic LS system is an integration of electronic components to a standard hydro-mechanical LS system. [2] The main innovation of this solution focuses on the pump control, which allows to program the control strategy in the controller.

Third Generation LS System [3]

2Casappa Electro-Hydraulic LSBased on the concept of third generation LS system, Casappa has proposed a complete solution with a new developed pressure electronic control (PEC) for MVP pump. This proportional regulator is to replace the hydro-mechanical pressure limiter. [2]

Casappa MVP pump with Pressure Electronic Control (PEC) [2]
This type of control is a pressure control, not a flowrate direct control. With this type of control, the pump outlet pressure is proportional to the control current. The load sensing function is realized by an electronic control unit (Walvoil CED 100X) reading the instantaneous measurement of two pressure transducers, being the first transducer on the pump outlet line, the second one on the valve LS port. The CED 100X current output controls the proportional relief valve, regulating the pump outlet pressure according to the instantaneous LS pressure.[2]


Walvoil CED 100X [2]

By adopting this configuration, more advantages benefit from this solution:
– Increased functionality by variable setting of LS pressure
– Increased safety by pump displacement can be put to zero
– Energy saving by variable LS setting
– Load-induced oscillations transmitted to the hydraulic circuit can be reduced by electronic filtering

3Casappa Electro-Hydraulic LS PlusMoreover, based on Casappa third generation solution, torque control can be easily obtained by simply adding an angular transducer to read the instantaneous swash plate angle. Plus the measured outlet pressure, absorbed torque can be calculated with the two signals.

Casappa MVP Pump with Angle Sensor and PEC [2]
The highlighted advantage of this solution is the variable torque setting compared to hydro-mechanical torque limiter. This advantage can help the pump perfectly match the engine characteristics at any working conditions which has been approved both in the lab and on the real machine. [2]

Torque and Flowrate Diagram Measured on Test Bench [2]
From the result done on the test bench, we can see the pump controlled by the hydraulic limiter has a “double parabolic” torque diagram due to the double spring hydro-mechanical regulator; the electro-hydraulic control, instead, limits the torque more precisely even at different engine speeds. [2]

Modified Kubota KX 161-3; Casappa MVP PECA as Mounted on the Machine [2]
Comparison test has also been done on Kuota mini-excavator. From the result measured on this test bed, it has clearly shown that the electro-hydraulic system has variable torque setting to accommodate different working conditions. Energy has obviously saved with this advantage. Detailed test result can be obtained in the reference [2].

4Casappa MVP PECA VS. Danfoss S45 ETLIf you still remember Danfoss S45 ETL solution shared in post N7/N8, then you can have the chance to compare the two solutions by yourself. They all can achieve variable torque setting with electronic control, but the configuration is different from each other.


Danfoss S45 ETL [4]

REFERENCES[1] Rexroth M9 Valve Training Maunal.
[2] Antonio Lettini, Marc Havermann. Improved Functionalities and Energy Saving Potential on Mobile Machines Combining Electronics with Flow Sharing Valve and Variable Displacement Pump. 7th IFPC, Aachen 2010.
[3] Andrea Vacca. Project Systems September.
[4] S45 ETL data sheet.

STATEMENTS[1]. Copyright of the pictures, videos and paragraphs quoted in this post belong to the original author.
[2]. iHydrostatics is only the platform to share but not create information, iHydrostatics post is NOT intended for academic research.
[3]. This post reprint should be noted with “iHydrostatics Original”.