Theoretical Calculations and Experimental Studies of Power Loss in Dual-Clutch Transmission of Agricultural Tractors
Round 1
Reviewer 1 Report
The scientific work, which is the subject of the article submitted for review, addresses a topic of practical utility. The research design is well elaborated, but in order to be a work of adequate quality I recommend the authors to consider the following issues:
- The article should contain photographs of the construction of the test stand. The description of the lab stand does not show the practical realization of it;
- there is no information on how the tests were carried out, how long the test stand was in operation for each experiment or after how long the oil temperature was measured;
- it would have been interesting to measure the power loss for different types of oil or perhaps cooling and keeping the oil at an optimum operating temperature;
- I think that the power losses are high, therefore I recommend the authors to check carefully the results obtained. It would have been interesting if the transmission efficiency was calculated and correlated with oil temperature;
- Based on the results obtained, the authors should present concrete proposals for improving the operation of these transmissions.
In conclusion, in view of the issues presented, I consider that the paper could be accepted for publication provided that the authors resolve the observations specified above.
Author Response
Answers to Review #1
The article should contain photographs of the construction of the test stand. The description of the lab stand does not show the practical realization of it;
- Figure 2.(b) has been added
there is no information on how the tests were carried out, how long the test stand was in operation for each experiment or after how long the oil temperature was measured;
- Related descriptions have been added in lines 215-222.
“The test procedure is as follows. The speed of the input motor is slowly increased over 120 seconds from 0 to 2200 rpm. When the speed reaches 2200rpm, the torque of the output motor is increased by 200Nm to reach the target load level. While maintaining the target load for 1 minute, the torque and rpm of the input and output sections are measured by the sensor. The oil temperature was maintained in the range of 50 to 90 °C, which is the normal operating temperature of the tractor. Motor and sensor specifications are shown in Table2.”
it would have been interesting to measure the power loss for different types of oil or perhaps cooling and keeping the oil at an optimum operating temperature;
- In this study, the effect of oil temperature or type was not confirmed because it was a study to see the effect of transmission oil level. Efficiency tests for oil temperature and type are planned to be performed in subsequent studies.
I think that the power losses are high, therefore I recommend the authors to check carefully the results obtained. It would have been interesting if the transmission efficiency was calculated and correlated with oil temperature;
- As can be seen from equations (3) to (5) and equations (9) to (11), power loss is proportional to oil viscosity. Therefore, the viscosity relationship according to temperature in the text is defined by ASTM D34 and reflected in the calculation formula. The related contents are added and explained in lines 337-342 of manuscripts as below.
“In the tests of 3.1km/h and 3.6km/h, the oil temperatures were 69.3℃ and 50.7℃, respectively, showing a difference of 18.6℃. As a result of calculating viscosity by the ASTM D341 method, the kinematic viscosity of the oil is 33.2 cSt and 63.61 cSt, respectively, for the tests of 3.1 km/h and 3.6 km/h. As the viscosity increases, it can be seen that the drag torque increases and resulting in a larger speed-dependent power loss.”
Based on the results obtained, the authors should present concrete proposals for improving the operation of these transmissions.
- Related descriptions have been added in lines 331-336 of manuscript as below.
“Through this study, it was confirmed that the error between the theoretical calculation and the measured value of power loss was reduced by considering the oil level change caused by the oil circulation of the transmission. Therefore, in order to improve the efficiency of the transmission, the rotation speed of the internal components and the oil lubrication condition must be considered together. For example, gears with high rotation speeds should be located in positions that are not submerged in oil. Rotating components that are inevitably immersed in oil need to be designed with a small outer diameter and width to minimize power loss.”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript entitled “Theoretical Calculations and Experimental Studies of Power Loss in Dual-Clutch Transmission of Agricultural Tractors” by Hyoung-Jong Ahn et al. calculated the power loss of an agricultural tractor DCT using the ISO standard and viscous fluid theory and measured the power loss of the DCT for each gear step using a 3-axis dynamometer measurement system. The calculated power loss and measurement results were compared and analyzed, with the calculation results reflecting the oil levels considering the characteristics of the agricultural tractor DCT reviewed. The components accounting for the largest portion of the total power loss were the gears and bearings, with the efficiency calculated to be highest at 5.5 km/h, the fastest speed in the max traction force range. Additionally, while the load-dependent power loss was not significantly affected by the oil level, the speed-dependent power loss was affected by the locally varying oil level owing to oil circulation. And confirmed that to predict the efficiency of agricultural transmissions, the oil level reflecting the transmission structure characteristics, oil circulation, and the operating characteristics of the transmission component—such as rotation speed and deviation—must be considered. However, there are some points that need attention in order for the article. I would like to recommend a revision is required for the reasons listed below:
1. It is only mentioned in 2.2.1 that the gears are cylindrical gears, and the types of other gears in the article are not clear.
2. With the increase of vehicle speed, the theoretical power loss calculated in case 2 does not increase completely, which is different from the measured results and needs further explanation.
3. In line226, the max. traction force range is it a proper noun
4. The development of a power loss measurement system is mentioned in the abstract, but the article does not further explain the universality of the power loss measurement system, nor does it mention the power loss measurement system in the conclusion.
Author Response
Answers to Review #2
It is only mentioned in 2.2.1 that the gears are cylindrical gears, and the types of other gears in the article are not clear.
-According to ISO/TR 14179-1, the power loss of bevel gears is also the same as that of cylindrical gears, and the same formulas as Equations (2)-(5) are applied. The difference is that the definitions of terms such as M, Helix angle, and tooth profile are redefined and applied to bevel gears. Therefore, to avoid any misunderstanding for the reader, the word “cylindrical” has been removed from the sentence line 165 “Power loss of the cylindrical gear and shaft”. In addition, the β value of Nomenclature was written together as helix angle and spiral angle.
With the increase of vehicle speed, the theoretical power loss calculated in case 2 does not increase completely, which is different from the measured results and needs further explanation.
- There was an error in which the graphs (a) and (b) of Figure 4, Figure 7 and Figure 8 were reversed. In this regard, misaligned figures have been corrected.
In line226, the max. traction force range is it a proper noun.
- “the max. traction force range” is not a proper noun. Incorrect font application has been corrected.
The development of a power loss measurement system is mentioned in the abstract, but the article does not further explain the universality of the power loss measurement system, nor does it mention the power loss measurement system in the conclusion.
- A dynamometer is a common device for simultaneously measuring the torque and rotational speed (RPM) of drive line so that its instantaneous power may be calculated. Therefore, the phrase “Based on the ISO standard and fluid viscosity theory, a test system was developed to calculate the power losses.” on line 18 of the abstract is misleading. Therefore, it was replaced with the phrase “Power loss was calculated based on ISO standards and fluid viscosity theory, and tests were performed to verify.”
Author Response File: Author Response.pdf
