Rib Design for Improving the Local Stiffness of Gearbox Housing for Agricultural Electric Vehicles
Round 1
Reviewer 1 Report
Rib Design for Improving the Local Stiffness of Gearbox Housing for Agricultural Electric Vehicles
Interesting and relevant work for vibration reduction of the gearbox for agricultural electric vehicles. For the prediction of the gearbox dynamic behavior, it’s local stiffness in the defined frequency range was characterized and evaluated with the help finite element model. The obtained results were analyzed and validated experimentally (using MAC values). The shape and differently tested dimensions of the ribs have been technically and constructively improved or optimized by means of the detected local changes in stiffness, and from this a most efficient rib shape is determined. With the experimental modal analysis (EMA), the assembled FE model was updated, to ensure the determined stiffness values according to the rib design. As a result, the rigidity of the transmission housing has been improved through an efficient rib design and the problem of noise emission in agricultural electric vehicle drives has been optimized. For example, the results show that by means of the frequency response analysis performed in modified gearboxes, the maximum acceleration amplitude in the frequency range of interest is about 1.87 dB lower than the original model values, and the rate of increase in strength was about 43.3%.
The scope of the work is very detailed, and the methods are most often well explained alongside some mentioned in the comments below. This work is certainly valuable for industrial users and researchers working in the field of mechanics and component design.
Before admission, it is recommended to consider the following suggestions: to specify the terms, symbols and abbreviations used in a nomenclature.
Comments for author File: 
Comments.pdf
Author Response
Interesting and relevant work for vibration reduction of the gearbox for agricultural electric vehicles. For the prediction of the gearbox dynamic behavior, it’s local stiffness in the defined frequency range was characterized and evaluated with the help finite element model. The obtained results were analyzed and validated experimentally (using MAC values). The shape and differently tested dimensions of the ribs have been technically and constructively improved or optimized by means of the detected local changes in stiffness, and from this a most efficient rib shape is determined. With the experimental modal analysis (EMA), the assembled FE model was updated, to ensure the determined stiffness values according to the rib design. As a result, the rigidity of the transmission housing has been improved through an efficient rib design and the problem of noise emission in agricultural electric vehicle drives has been optimized. For example, the results show that by means of the frequency response analysis performed in modified gearboxes, the maximum acceleration amplitude in the frequency range of interest is about 1.87 dB lower than the original model values, and the rate of increase in strength was about 43.3%.
The scope of the work is very detailed, and the methods are most often well explained alongside some mentioned in the comments below. This work is certainly valuable for industrial users and researchers working in the field of mechanics and component design.
Before admission, it is recommended to consider the following suggestions: to specify the terms, symbols and abbreviations used in a nomenclature.
MDPI-Applied Sciences does not have a form or requirement for nomenclature. I searched and reviewed other published papers in this journal, but the nomenclature was not written in most of them. In my manuscript, terms, symbols and abbreviations are explained in detail below each formula and sentence. I think it is easier for the reader to understand.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper focuses on the case study for the rib parameters to improve the dynamic behaviour of the gearbox housing. It is written at the sufficient level, well organised and logically divided into sections. However, in the reviewer’s opinion, the scientific level and the novelty is low. In the reviewer’s opinion, manuscript is not suitable for the scientific journal and it is much more aimed to the engineering field. Basically, the FEM model is presented, its validation with respect to the usual EMA and the case study of the dynamical response of the modified system with different combination of rib parameters is shown. Moreover, the problem may should be treated by the automatized optimisation process and not only by the case study of the chosen combination of parameters.
Notes and questions:
In the text, “analytical” modal analysis is mentioned several times. However, FEM-based "numerical" modal analysis is used. The parametric study was used to find an “optimal” design of the rib. Hence, only a table with limited number of parameter combinations was tested. Why the parametric optimisation with appropriate constrains was not used? This would lead to the true optimum. Authors note that electric powertrain noise includes high frequency factors. However, only the range of 1-3 kHz is analysed with no comment of this restriction. Since the system is tuned in this range only, other resonant frequencies outside this range can change and even grow up. The hearing range is up to 16kHz. English should be improved.Author Response
Comments and Suggestions for Authors
The paper focuses on the case study for the rib parameters to improve the dynamic behaviour of the gearbox housing. It is written at the sufficient level, well organised and logically divided into sections. However, in the reviewer’s opinion, the scientific level and the novelty is low. In the reviewer’s opinion, manuscript is not suitable for the scientific journal and it is much more aimed to the engineering field.
I do not think that the scientific novelty of my paper is lacking for the following reasons. 1) Model updating: In other papers, there is little description of the validation process of the FE model, but this manuscript suggests a model updating method for more accurate FE model validation. Using this method, we construct a FE model with little error. 2) Selection process for design reinforcement part(stiffness weak point): Using the driving point frequency response analysis, we proposed a method to find the stiffness weak points of the housing and a method to evaluate the local stiffness of each point. Like the reviewer's opinion, these methods can be used more in the engineering field, but I can't agree with the low scientific level because the above methods are presented through an objective and reasonable process.
Basically, the FEM model is presented, its validation with respect to the usual EMA and the case study of the dynamical response of the modified system with different combination of rib parameters is shown. Moreover, the problem may should be treated by the automatized optimisation process and not only by the case study of the chosen combination of parameters.
After reviewing a number of related papers, the automation process is convenient for optimization but it is used at the concept design level. Therefore, in this study, the design reinforcement part (stiffness weak points) was identified and the position of the rib installation was selected. Then, the detail design of the rib shape was conducted through the parameter study. This method is widely used for rib design in existing papers, and in order to consider detail design and manufacturing possibility, it was determined that it was right to optimize the rib shape by manual method according to the designer's judgment.
Notes and questions:
In the text, “analytical” modal analysis is mentioned several times. However, FEM-based "numerical" modal analysis is used.
As noted by the reviewer, it has been modified in manuscript. (analytical -> FEM-based numerical)
The parametric study was used to find an “optimal” design of the rib. Hence, only a table with limited number of parameter combinations was tested. Why the parametric optimisation with appropriate constrains was not used? This would lead to the true optimum.
After reviewing a number of related papers, the automation process is convenient for optimization but it is used at the concept design level. Therefore, in this study, the design reinforcement part (stiffness weak points) was identified and the position of the rib installation was selected. Then, the detail design of the rib shape was conducted through the parameter study. This method is widely used for rib design in existing papers, and in order to consider detail design and manufacturing possibility, it was determined that it was right to optimize the rib shape by manual method according to the designer's judgment. In this study, the maximum value of the rib shape was limited in consideration of the size of the original housing, and the parameter study was conducted by dividing the dimensions within the shape limit range. Therefore, it can be seen that the optimized rib shape was derived in consideration of the possibility of design modification.
Authors note that electric powertrain noise includes high frequency factors. However, only the range of 1-3 kHz is analysed with no comment of this restriction. Since the system is tuned in this range only, other resonant frequencies outside this range can change and even grow up. The hearing range is up to 16kHz.
In my paper, I mentioned: "The tests were conducted in the free end condition, and the frequency range of interest was set within 3000 Hz from the excitation frequency information of the gearbox." In more detail, the fundamental frequency of excitation due to the gear mesh at the rated speed (2650 rpm) of the gearbox is about 618 Hz. Even considering the 5th harmonic component, it is 3091Hz, so it was determined that the validation of the FE model for vibration analysis was sufficient to review up to 3200Hz. I have added this to manuscript.
English should be improved.
This manuscript has been proofread in English. Certification of English editing is attached below.
Author Response File: Author Response.docx
Reviewer 3 Report
Dear Authors,
in my opinion some little changes are suggested:
- Fig. 4, where FRFs of the housing are reported, should be isolated and magnified in order to improve the readability
- Fig. 5 should be improved either in terms of quality or with an alternative way to show the results
It could be very interesting a multiphysic analysis where the operating temperature of the mechanical assembly is taken into account (material properties variation).
Author Response
In my opinion some little changes are suggested:
- Fig. 4, where FRFs of the housing are reported, should be isolated and magnified in order to improve the readability
- Fig. 5 should be improved either in terms of quality or with an alternative way to show the results.
As noted by the reviewer, it has been modified in manuscript. The figure 4 of "FRFs of the housing" is separated and enlarged to improve readability. The figure 6 of "MAC results between EMA and FEA" was modified about the contour legend and numbers at axes that was not previously displayed.
It could be very interesting a multiphysic analysis where the operating temperature of the mechanical assembly is taken into account (material properties variation).
Multi-physic analysis can be conducted considering the operating temperature of the gearbox housing, but the operating temperature of the gearbox housing is about 70 ° C, the stiffness characteristics of the housing do not change significantly in this range of temperature. So the study was conducted without consideration of the operating temperature.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
As noted in my previous review, the paper is well and clearly written. Moreover, all of the remarks noted in „notes and questions“ of my previous review were clarified and explained by the author so the paper was improved.
My main objection was that the level of scientific novelty since the paper introduces an engineering application of the widely-used methods. However, after reading an author’s explanation and after more in-depth exploration of the similar papers, I can state that contrary to the abovementioned, it has its significance and it may be helpful to the researchers in the specific application field. With respect to that and considering the author’s clear response to all my notes, I suggest the paper to be published in the present form.
