Towards Low Carbon: A Lightweight Design of Automotive Brake Hub

Abstract

Carbon peaking and carbon neutrality have become important considerations in today’s manufacturing industry. Vehicle lightweight design can reduce carbon emissions and it is an important means to achieve carbon peak and carbon neutrality. In this study, the lightweight design method of automotive brake hub towards low carbon and the calculation method of low-carbon benefit are presented. A brake hub is the core of a drum brake, working together with a friction plate and brake shoe to complete the braking process. The requirements for the safety performance of brake hub are becoming increasingly more stringent in order to improve the stability and safety of the braking process. The brake hub ZD02-151122A manufactured by Anhui Axle Co., Ltd.(Suzhou, China), was used as the research object. The lightweight optimization of the brake hub was designed under the lightweight drive to reduce the shape variables and stress values of the brake hub and to reduce the mass. The proposed optimization scheme changed the chamfering to 45 × 45 and increased the number of bolt holes to eight. Compared with the original brake hub, the maximum strain, maximum stress value, stress concentration coefficient, and mass were reduced by 15.38%, 17.66%, 1.50%, and 17.40%, respectively, which achieved the specified optimization goal of improving mechanical properties and reducing mass. Towards low carbon, the reduction in carbon emissions from the optimized brake hub manufacturer and the vehicle during operation was calculated. For Anhui Axle Co., Ltd., the carbon emission can be reduced by 4.21 × 10⁶ kg per year. Moreover, vehicle exhaust emissions can be reduced by 8.76 × 10⁸ kg if all trucks produced by a medium-sized vehicle assembly company are driven on the road until being scrapped. This study serves as a reference for design optimization and low-carbon benefit analysis of other major automotive components.

1. Introduction

As the global response to climate change continues to grow, carbon peak and carbon neutrality have become a global focus. China has named carbon peak and carbon neutrality as one of the eight major tasks of the central economic work in 2021 [1]. Energy consumption and carbon dioxide emissions of the crucial manufacturing sector account for more than one-third of the world’s total emissions [2]. In 2019, China’s total energy consumption reached 4.86 billion tons of standard coal units [3]. The 14th Five-Year Plan will be the critical period when China’s carbon emissions will peak; moreover, manufacturing is the main sector responsible for China’s carbon emissions, accounting for about 80% of the country’s total emissions. Therefore, the manufacturing industry will inevitably become the main battleground for peak carbon emissions and carbon neutrality. The automotive industry is the crown jewel of the manufacturing industry. As the central representative in pursuing the goal of “carbon peak and carbon neutral” and building a high-value development pattern, the automotive industry is once again at the center of the 2021 inventory. China has already committed to carbon dioxide emissions peaking by 2030 and becoming carbon neutral by 2060 (referred to as the 30·60 Target), which poses both great challenges and opportunities for the automotive industry in China. However, no comprehensive and detailed studies exist on the challenges and strategies for reducing carbon emissions to fulfill the 30·60 Target in the automotive industry [4].

In 2022, the number of cars in China exceeded 307 million, and the annual fuel consumption exceeded 500 million tons, which contributed to the intolerable pollution in the atmosphere. Low carbon has become a new rule in the automobile industry [5]. To achieve a low carbon emission for auto parts and their production, multiple studies have focused on calculating the total carbon emissions of the automobile industry, paid attention to technologies that focus on reducing carbon emissions, and analyzed the impact of carbon policy on the automobile industry. For example, Zhang et al. [6] studied the design process of automobile engines. From the analysis results of the integrated system, the study reported that the raw material procurement stage of the engine has the largest carbon emissions, with the cylinder block being the chief contributor. On the basis of the established evaluation model, the study also proposed optimizations for the structure and materials and verified the feasibility of the integrated system. Lee et al. [7] investigated an eco-control approach to carbon accounting for supply chain management in the automotive industry. Hao et al. [8] created a bottom-up model to consider the energy and environmental impacts of reducing greenhouse gas emissions from the passenger vehicle fleet. Qiao et al. [9] conducted a comparative study on the life cycle of CO₂ emissions from electric and conventional vehicles in China. Wu et al. [10] investigated the identification of barriers, analysis, and solutions for hydrogen fuel cell vehicles for deployment in China, with the goal of carbon neutrality. Du et al. [11] conducted a study that focused on policy making and its impact on the automotive industry in the context of carbon neutrality. Du et al. [12] investigated the costs and potentials of reducing CO₂ emissions in the Chinese transportation sector on the basis of an energy system analysis. The results underscored the carbon peak policy as alternative fuel vehicles (AFV) become more efficient, which increases the overall cost of emission reduction [13]. Since a car consists of many parts, it is important to summarize and highlight the strategic directions and technological paths for low-carbon development of the automotive industry at the component level [14].

In addition to the simple design of the brake hub itself, good environment-friendly heat dissipation, pollution-free production process, and economic feasibility of product, the safety performance requirements are even more important as they directly determine the quality of the brake hub. Domestic and foreign scholars have studied the mechanical properties as well as the friction and wear of brake hubs. Raj et al. [15] suggested that the brake disc is an important component in the braking system. Moreover, the effect of vane shape on the flow-field and heat transfer characteristics was numerically investigated for different configurations of vanes at different speeds. To elaborate, three types of rotor configurations, namely, circular pillared, modified taper radial, and diamond pillar vanes, were considered for the numerical analysis. Belhocine [16] analyzed the thermomechanical behavior of the dry contact between brake disc and pads during the braking phase using the thermal-structural analysis with coupling to determine the detected deformation and the Von Mises stress in the disc. S. A. Askerov [17] proposed a theoretical analysis to determine the quantitative relationship between abrasion and cracking in brake drum during braking of a wheeled vehicle. V. Gowtham [18] proposed a CAD Model that was based on the required fatigue life cycles. The forces acting on the hub were calculated, and linear static structural analysis of the wheel hub was performed for three different materials using ANSYS Finite Element code V 16.2. The theoretical fatigue strength was compared with the stress obtained from the structural analysis for each material. Güleryüz [19] proposed and analyzed a commercial integrated rotor and hub pair used in heavy-duty vehicles as a benchmark as well as achieved a reduction of 10 kg (15%) in the total weight compared to the base design. M. Nouby [20] proposed a refined finite element (FE) model of the disc brake corner that included the wheel hub and steering knuckle. Experimental modal analysis of the disc brake system was initially used to validate the FE model. Tirovic [21] proposed that the new fingered hub disc design was 8.5% lighter compared to a solid hub disc. Moreover, since it is a single piece cast design, the manufacturing cost is low.

However, there is still insufficient research on the advantages of a low-carbon brake hub in manufacturing and braking due to the short time in which China has formulated the carbon neutrality goal. Meanwhile, many scholars have paid more attention to the basic research on the technologies for reducing carbon emissions from automobiles. Much of the literature on lightweight design focuses on reducing quality and does not address the impact of lightweight on carbon emissions [22,23,24,25]. It is very meaningful to consider carbon emissions while reducing weight [26,27]. The existing literature is even more lacking in terms of the detailed process of brake hub lightweight and the impact of lightweight on carbon emissions.

The proposal presented in this paper is based on the structural parameters of the ZD02-151122A brake hub. The 3D model of the brake hub was created using Pro/E software. Then, a static analysis was performed with ANSYS. On the basis of the analysis results and theoretical principles, a lightweight optimization design scheme for the brake hub was developed. The data from the optimized scheme and original brake hub were compared and analyzed. Moreover, the low-carbon benefit of the lightweight brake hub was analyzed.

2. Materials and Methods (Optimization of Brake Hub Structure under Lightweight Drive)

2.1. Flowchart of Method

This paper built a lightweight design method towards low carbon for the automobile brake hub. Specifically, the finite element method was adopted to analyze the stress, strain, and safety factors of the automobile brake hubs on the basis of their actual stress and to and obtain the corresponding contours. Afterwards, the positions with the smallest stress and strain and the largest safety factors were found on the basis of these contours, which were crucial for the determination of positions that can achieve lightweight. Then, considering the actual working conditions of the automobile brake hub, a lightweight solution was proposed. After the implementation of the scheme on the parts, the finite element method was re-applied to the lightweight parts to explore their changes in stress, strain, safety factor, and mechanical properties, hence verifying the feasibility of the lightweight scheme. Finally, the variations in carbon emissions caused by the mass reduction application of the automobile brake hub were calculated for evaluating the low-carbon benefits generated by the lightweight design and to assess the low-carbon benefits. The flowchart of the proposed method is presented in Figure 1.

2.2. Overview of Brake Hub

A brake hub is the key part of a car brake [28]. Improvements to the safety of the brake hub improve the safety of the entire vehicle, thereby significantly reducing the failure rate of vehicles and the occurrence of traffic accidents [29]. Statistically, more than half of the traffic accidents are caused by brake failure during braking, resulting in a longer braking distance and eventually leading to a series of tragedies [30]. Brake hubs have the shape of a tambourine, as shown in Figure 2. While braking, the brake shoe under the action of the actuator on the outside of the brake is constantly rotating, and the friction disc on the inner surface of the brake presses on the inner wall of the brake hub, producing a significantly large friction torque and forcing the car to complete the braking action. Generally, the brake hub in a car is similar to a metal drum or a small bucket placed on the outside of the hub, and when braking, the bottom of the barrel rubs against the car hub such that the car further slows down and finally stops.

The brake friction torque of brake hub is significantly large during the braking process, which is closely related to the current driving speed and the load of vehicle. There are multiple failure modes of a brake hub, and the main failure modes are cracks. The main reason for cracking is that the temperature of brake hub changes rapidly during the braking process, and stress concentration occurs during the braking process. Stress concentration is mainly caused by the bending moment load (friction between the friction plate and the inner wall of brake hub), which mainly occurs at the flange root corner.

2.3. Stress Analysis of a Brake Hub under Normal Working Conditions

Prior to simulation analysis, the stress on the brake hub is analyzed under normal operating conditions. First, the force $F$ of the brake hub is projected on the X, Y, and Z planes, and then the resultant $F_{xy}$ force from the XOY plane is obtained. Finally, the moment of the force $F_{xy}$ is measured at the intersection of the plane and axis, as shown in Figure 3.

Torque of force on axis is

$$M\left(F_{xy}\right)=F_{xy}\times h$$

(1)

where $M(F_{xy})$ is the torque exerted on the brake hub, N·m; $h$ is the radius of the brake hub, mm; and $F_{xy}$ is the force applied to the brake hub, N.

Considering $M(F_{xy})=$ 8000 N·m and $h$ = 0.32 m, the force can be calculated using Equation (1), as $F_{xy}=$ 25,000 N.

The six connecting bolts used on the brake hub are all special tire bolts that belong to a type of bolt used to make holes. Under the action of torque $T$, each tire bolt is subjected to both shear and extrusion, and the transverse shear force of each bolt is perpendicular to the line between the bolt axis and the geometric symmetry center O of the bolt set (arm $r_i$). It is assumed that the connected piece is a rigid body and that the connecting surface does not deform under the action of torque $T$ and is still in a flat state. Next, it is not difficult to conclude that the shear deformation of the bolt is proportional to the distance between the bolt hole and the geometric symmetry center O of the bolt set, i.e., the bolt farthest from the geometric symmetry center O of the bolt group has the largest shear deformation. The shear stiffness of each bolt is the same, and therefore the greater the shear deformation of a bolt, the greater the working shear force.

$$F_i=F_{max}\left(r_i/r_{max}\right), \forall i=1,2,\dots ,z$$

(2)

where $r_i$ and $r_{max}$ represent the distance between the axis of the i-th bolt and the bolt with the maximum force, respectively, from the geometric symmetry center O of the bolt set, and $F_i$ and $F_{max}$ represent the working shear force of the i-th bolt and the bolt with the maximum force, respectively.

According to the constraint of torque balance on the bottom plate,

$${\displaystyle \sum }_i^z{F}_i{r}_i=T$$

(3)

According to Equations (2) and (3), the working shear force of the bolt with the maximum force can be obtained as

$$F_{max}=\frac{T{r}_{max}}{{{\displaystyle \sum }}_{i=1}^z{r}_i^2}$$

(4)

Since the connecting surface of the brake hub is round and the six bolt holes are evenly distributed, $r_i$ and $r_{max}$ are equal, resulting in equal $F_i$ and $F_{max}$, $T$ = 8000 N·m, and $r_i$ = $r_{max}$ = 111 mm. $F_{max}$ can be obtained by being substituted into Equation (4)

$$F_{max}=\frac{T{r}_{max}}{{{\displaystyle \sum }}_{i=1}^z{r}_i^2}=\frac{8000\times 0.111}{{0.111}^2\times 6}=\mathrm{12,012} \mathrm{N}$$

(5)

The allowable shear force of ordinary bolts with a diameter of 21 mm is 14,000 N, and the bolts used for the brake hub are custom-made tire bolts with strength and stiffness significantly higher than that of ordinary bolts; therefore, the maximum allowable working shear force is within the appropriate range.

2.4. Simulation Analysis of Brake Hub under Normal Working Conditions

In Pro/E, a 3D model was created according to the 2D drawing of the brake hub of model ZD02-151122A (Figure 4). Then, the model was saved as a solid X_T format and imported into the ANSYS-Workbench environment for analysis.

The statics module was selected from the analysis module in Workbench to perform the statics analysis of the brake hub. The analytical process was as follows:

(1) Determine the brake hub material: The brake hub of ZD02-151122A manufactured by Anhui Axle Co., Ltd., uses HT250, and the compositional content is listed in

Table 1. Compositional content of HT250.

Name	C	Si	Mn	P	S	Cu	Cr
Content	3.3–3.6	1.5–1.9	0.7–0.9	≤0.12	≤0.12	0.4–0.6	0.2–0.4

. The mechanical properties of HT250 are listed in

Table 2. Mechanical properties of HT250 [32,33].

Symbol	Material Property	Values
E	Young’s modulus	2 × 1011 Pa
v	Poisson’s ratio	0.25
SYt	Yield strength	3 × 108 Pa
SUt	Tensile strength	9 × 108 Pa
ρ	Density	6900 kg/m3

[31]. Next, the X_T format entity model converted from the previous step was imported into the Workbench model. According to the data in Table 2, the mechanical properties of HT250 were added to the material library of the software and added to the brake hub.

(2) Meshing: The greater the node number and the cell number, the more accurate the calculation results, but the greater the amount of computation time. For general engineering applications, standard grid is sufficient. The meshing that uses tetrahedral mesh can balance the speed, obtaining the mesh quality that is expected in order to assure the strength of quality, and the user can control the parameter and achieve feasible algorithms. Thus, a standard tetrahedral meshing grid was selected to perform the mesh division for the 3D model of the brake hub, and the partition effect is shown in Figure 5. The node number was 334,321, and the cell number was 217,370.

(3) Add constraint: The inner wall of the brake hub was mainly subjected to torque during the braking process. The braking process was based on enormous frictional forces. The fixed position consisted of six bolt holes, and installation stopped such that the brake hub can be fixed firmly on the axle, as shown in Figure 6.

(4) Add loads: The brake hub model studied in this paper was ZD02-151122A with a load capacity of 5 t. The inner wall of the brake hub was mainly subjected to torque during braking. The radial force caused by vehicle lateral displacement was ignored. The radial force was too small compared to the friction during braking. Therefore, only the maximum friction force was added. In order to facilitate the simulation, the maximum friction force was converted into the maximum friction moment to realize. The maximum torque under normal braking conditions is 8000 N·m (static), as measured by the technical personnel of Anhui Axle Co., Ltd (Suzhou, China).

(5) Simulating calculation: After setting the above process, the cloud diagram of the stress value, shape variables, and safety factor of the brake hub in this working environment was obtained through a simulation calculation, as shown in Figure 7.

Figure 7 shows that the shape variable increased gradually along the inner wall of the brake drum. The minimum shape variable of the six bolt holes was 4.98 × 10⁻⁵ mm, and the maximum shape variable at the top of the brake hub was 0.013 mm, all within reasonable limits. The stress value decreased gradually along the inner wall of the brake hub. The maximum stress value at the six bolt holes was 35.04 MPa, which was within reasonable limits. The minimum safety factor of the brake hub was 15 with a large margin for the safety factor, which can be optimized.

Let the maximum stress in the cross-section where stress concentration occurs be ${\sigma }_{max}$ and the average stress in the same section be $\sigma$, then the ratio of the two is

$$K={\sigma }_{max}/\sigma$$

(6)

where $K$ is the theoretical stress concentration factor, which reflects the stress concentration degree of the local area. The higher $K$ is, the more likely it is that the stress concentration will occur.

Figure 7 shows the stress distribution of the brake hub at a fixed torque of 8000 N·m, The stress values arranged from small to large were 0.0080 MPa, 3.90 MPa, 7.79 MPa, 11.68 MPa, 15.58 MPa, 19.47 MPa, 23.36 MPa, 27.25 MPa, 31.15 MPa, and 35.04 MPa. The maximum stress ${\sigma }_{max}$ was 35.04 MPa, and the calculated average stress $\sigma$ was 17.52 MPa.

From Equation (6),

$$K={\sigma }_{max}/\sigma =35.04 \mathrm{MPa}/17.52 \mathrm{MPa}=2.00$$

(7)

In the case of torsion, the general range of $K$ was 1.6–4.0. Therefore, the calculated value of $K=$ 2.00 was within a reasonable range of values and met the requirements.

2.5. Optimization Scheme

After the simulation analysis of the original brake hub, the improvement areas were determined according to the analysis of the stress values and shape variables, considering the failure mode of the brake hub that often occurs in the braking process under the overarching principle that the brake hub is lightweight and that safety is not reduced. The optimization goals are improving or achieving constant mechanical properties and reducing mass. The main structure of the brake hub cannot be changed, and the connection between the outer contour and other parts cannot be greatly changed. Therefore, it can only be changed from some auxiliary structures. Driven by optimizing mechanical performance and reducing mass, the methods that can be used are reducing convex platform and ribs and removing the structure and reducing the number of ribs. At the same time, the optimization design must also take into account the actual situation of the brake hub. Consequently, the identified improvements modify the size of the outer circle chamfering of the brake hub and change the number of bolt holes of the brake hub.

The original outer circle chamfering of the brake hub was 35 × 35, which was increased to 45 × 45. The size of the bolt hole cannot be changed due to the limitations of the wheel hub, as it cannot be modified. Only the number of bolt holes can be changed. The number of the original brake hub bolt holes was six. Too many bolt holes will also increase the manufacturing cost of the cars. Therefore, the number of bolt holes proposed for the modification was eight. The comparison of the 3D models of the brake hub before and after optimization is shown in Figure 8.

2.6. Comparison before and after Optimization of the Brake Hub

An FE analysis was performed for the optimized brake. The steps were the same as stated earlier. The deformation and stress cloud diagram of the optimized brake hub is shown in Figure 9.

Figure 9 shows that after the optimized brake hub, the maximum deformation variable was 0.011 mm, and the maximum stress was 28.85 MPa. The eight changed bolt holes were still evenly distributed; therefore, $r_i$ and $r_{max}$ were equal. Moreover, $F_i$ and $F_{max}$ were equal. Therefore, Equations (4) and (5) give

$$F_{max}=\frac{T{r}_{max}}{{{\displaystyle \sum }}_{i=1}^z{r}_i^2}=\frac{8000\times 0.111}{{0.111}^2\times 8}=9009 \mathrm{N}$$

(8)

After changing to eight bolt holes, the stress values of the brake hub arranged from small to large were 0.0041 MPa, 3.21 Mpa, 6.41 MPa, 9.62 MPa, 12.82 MPa, 16.03 MPa, 19.23 MPa, 22.44 MPa, 25.65 MPa, and 28.85 MPa. The maximum stress ${\sigma }_{max}$ was 28.85 MPa, and the calculated average stress $\sigma$ was 14.43 MPa. Moreover, the following can be derived from Equation (6):

$$K={\sigma }_{max}/\sigma =28.85 \mathrm{MPa}/14.63 \mathrm{MPa}=1.97$$

(9)

Comparing the data of the modified eight-bolt-hole brake hub with that of the original brake hub data, it can be seen that the comprehensive performance of the brake hub with eight bolt holes was much better than that of the original hub in terms of shape variables and stress values. The shape variable and stress value improved by 12.3% and 17.6%, respectively. The maximum working shear also reduced from 12012 N to 9009 N; moreover, the theoretical stress concentration coefficient $K$ also changed slightly, from 2.00 to 1.97, which showed that the stress concentration at the bolt hole also improved. In summary, it is safe to increase the number of bolt holes from six to eight and the outer circle chamfering from 35 × 35 to 45 × 45.

In summary, the brake hub was optimized for lightweight drive by setting the chamfering of the outer circle to 45 × 45 and changing the number of bolt holes to eight. The three-dimensional (3D) model of the brake hub was established to compare the mass before and after optimization. Moreover, this was combined with the simulation results based on the mechanical properties (maximum strain, maximum stress, stress concentration factor) study conducted, as discussed above. The comparison of parameters before and after optimization is listed in

Table 3. Comparison of the parameters before and after brake hub optimization under lightweight drive constraint.

Items Plan		Internal Chamfer R/mm	Number of Bolt Holes	Maximum Strain/mm	Maximum Stress/MPa	Stress Concentration Factor $\mathit{K}$	Mass/kg
Before optimization	Parameters	35	6	0.013	35.04	2.40	24.20
After optimization (change in the number of chamfering and bolt holes)	Parameters	45	8	0.011	28.85	1.97	19.99
	Variable quantity	10	2	0.002	6.19	0.43	4.21
	Optimization degree	28.57%	33.33%	15.38%	17.67%	17.92%	17.40%

.

Table 3 shows that after brake hub optimization under lightweight drive constraint, the mass was reduced by 4.21 kg to 17.4%; the maximum strain and maximum stress were optimized, and the optimization degrees reached 12.7% and 17.66%, respectively. The safety factor was reduced; the reduction was 17.8%, still within the safe range of being acceptable. The optimization goal of improving or achieving constant mechanical properties and reducing mass was achieved. The lightweight method that increased the outer circle and the number of bolt holes was appropriate.

Anhui Axle Co., Ltd. has used the optimization results to produce the brake hub, which has been applied to the vehicle axle and achieved good results. The comparison of the product of the brake hub before and after optimization and applied on the vehicle axle is shown in Figure 10.

The connection stability was better after the change to eight bolt holes.

Note that after reducing the fillet corners and increasing the number of bolt holes, the optimization effect was obvious after the combination. Compared to prior optimization, each parameter was optimized to different degrees. Consequently, the goal of lightweight optimization, namely, the reduction of stresses and strains and the reduction of mass, was achieved.

3. Results and Discussion (Low-Carbon Benefit Analysis of the Lightweight Brake Hub after Optimization)

The lightweight brake hub neither changed the structure of the original brake hub nor added a new process. The chamfering was changed from 35 × 35 to 45 × 45, and the number of bolt holes was changed from six to eight. After optimization, the mass of each brake hub was reduced by 4.21 kg.

The reduced steel consumption caused by the lower brake hub mass and the reduced carbon emissions of production enterprises are expressed in Equation (10) as

$$Q_m=n{\eta }_{\Delta }{m}_{\Delta }$$

(10)

where $Q_m$ is the reduction of carbon emissions from production enterprises due to lightweight optimization (kg); $n$ is the annual output of brake hub from the production enterprise; ${\eta }_{\Delta }$ is the carbon emission coefficient of steel industry, and ${\eta }_{\Delta }=$ 1.7–2.2 for the blast-converter process; and $m_{\Delta }$ is the change in mass for lightweight mass of a brake hub (kg).

Considering Anhui Axle Co., Ltd. (a medium-sized axle manufacturing and processing enterprise), as an example with an annual output of 5 × 10⁶ sets of brake hubs, $n=$ 5 × 10⁶, ${\eta }_{\Delta }=$ 2.0, and $m_{\Delta }=$ 4.21 kg. Substituting these into Equation (10), it can be calculated that the lightweight braking hub will reduce the carbon emissions $Q_m=$ 4.21 × 10⁶ kg for Anhui Axle Co., Ltd.

After the application of the lightweight brake hub in the car, the car exhaust carbon dioxide emissions were the most direct [34,35]. The relationship between the carbon dioxide emissions of a car and the reduction of vehicle mass can be expressed by Equation (11) as

$$Q_w=L{\eta }_w{m}_w$$

(11)

where $Q_w$ is the lightweight brake hub caused by the carbon dioxide emissions from the vehicle exhaust (kg); ${\eta }_w$ is the emission coefficient per kilometer (km⁻¹), and $L$ is the vehicle kilometers traveled (km); and $m_w$ is the mass that causes the reduction in carbon emissions from the vehicle (kg). By the lightweight scheme in this paper,

$$m_w=n_o(m_{\Delta }-m_o)$$

(12)

$n_o$ is the number of brake hubs owned by the vehicle, and $m_o$ is the lightweight of a brake hub leading to the increase in the mass of other parts of the automobile (kg); in this paper $m_o$ is the newly added mass of two bolts.

According to Equation (11), in conjunction with the aforementioned research results on the lightweight design of the brake hub, the low-carbon benefit of a truck with the brake hub in its entire life cycle can be calculated. Let us assume ${\eta }_w=$ 5 × 10⁻⁵ km⁻¹ as the experience value. The truck had a total of 20 brake hubs with a weight loss of 4.21 kg per hub. The newly added mass of two bolts $m_o=0.73$ kg. Therefore, the total weight of the vehicle was reduced by 83.47 kg with mandatory mileage scrapping 7 × 10⁵ km. Substituting ${\eta }_w=$ 5 × 10⁻⁵ km⁻¹, $m_w=$ 83.47 kg, and $L=$ 7 × 10⁵ km into Equation (11), $Q_w=$ 2.92 × 10³ kg, and the emission reduction effect was relatively obvious. If a medium-sized vehicle assembly enterprise equips the annual production of all trucks (about 3 × 10⁵ vehicles) with the proposed lightweight brake hub, 8.76 × 10⁸ kg of reduction in emissions will be achieved.

Therefore, the proposed lightweight brake hub can reduce the carbon emissions from brake hub manufacturers and operating vehicles.

We have conducted more case research to confirm the suggested method lightweight design to achieving low-carbon. The application of this method to automobile parts has achieved good low-carbon benefits. The lightweight design scheme and carbon emission benefit are shown in

Table 4. The application of lightweight design to achieving low carbon on automobile parts.

No.	Part Name	Lightweight Design Scheme	Reduced Weight		Simulation Parameters Proportion of Change (%)				Carbon Emission Benefit (kg)		Reference
			Mass (kg)	Proportion of Change (%)	Stress	Displacement (or Strain)	Safety Factor	Fatigue Life	A Truck	An Enterprise
1	Axle hub	Removed the step	−4.74	−5.54	+29.5	+103	−22.8	--	--	--	[22]
2	Special axle Hub	Widened wheel hub, reduced thickness and stiffeners	−71.25	−7.52	+64.4	+59.8	−39.1	--	4.99 × 105	--	[28]
3	Wheel hub	Added holes, grooves	−1.4	−11.77	+3.58	+34.91	−3.46	−26	1.02 × 103	2.56 × 107	Anhui Axle Co., Ltd.
4	Brake hub	Increased chamfering and bolt holes	−4.21	−17.40	−17.67	−15.38	−17.92	--	2.92 × 103	8.76 × 108	This paper

.

4. Conclusions

In this study, on the basis of ANSYS finite element analysis software, the proposed lightweight design of ZD02-151122A automobile brake hub was examined with regards to achieving low-carbon emissions. The primary conclusions are as follows:

(1) On the basis of the results of stress and strain analysis, the improvement areas were determined. The identified improvements modified the size of the outer circle chamfering and changed the number of bolt holes of the brake hub. Following this, a lightweight optimization scheme was proposed in which the outer circle chamfering was increased to 45 × 45 and the number of bolt holes was set to eight.

(2) After implementing the lightweight brake hub modifications, the maximum strain variable decreased from 0.013 to 0.011 mm, a reduction of 15.38%. The maximum stress value decreased from 35.04 to 28.85 MPa, a decrease of 17.67%. The stress concentration coefficient decreased from 2.00 to 1.97, corresponding to a decrease of 1.5%. Moreover, the mass was reduced from 24.20 to 19.99 kg, a decrease of 17.40%. Therefore, the optimization goal of improving or achieving constant mechanical properties and reducing mass was achieved.

(3) A lightweight brake hub is critical to reducing the carbon emissions from brake hub manufacturers and operating vehicles. Considering Anhui Axle Co., Ltd., with an annual production of 500,000 sets of brake hubs as an example, the proposed lightweight brake hub can reduce the carbon emissions of the company by 4.21 × 10⁶ kg per year. If all freight cars (about 300,000 vehicles) produced by a medium-sized vehicle assembly company are equipped with the proposed lightweight brake hub and are driven on the road until they are scrapped, the total reduction in vehicle exhaust emissions reaches 8.76 × 10⁸ kg. The lightweight design of automotive brake hub can bring about huge low-carbon benefits. It provides feasible ideas and methods for the challenges and strategies for reducing carbon emissions to fulfill the 30·60 Target in the automotive industry.

In the optimization design proposed in this paper, the influence of temperature, wear, and other factors on the brake hub during the braking process was ignored, and only the static analysis of the brake hub was performed in order to obtain the optimal combination scheme. In fact, the braking process of the brake hub is a significantly complicated process. The relationship between molding parts, automobile exhaust, and carbon emissions is also complex and dynamic. The analysis results presented in this paper are only a simplification of the actual working conditions. The optimization scheme will increase production costs by machining two more holes and assembling two more bolts. The processing time of a single brake hub will be slightly prolonged accordingly. In view of the fact that the brake hub is produced in batches and has high production and assembly efficiency, these factors are ignored in calculating the carbon emission benefits. Consequently, the next step is to analyze the low-carbon benefits of the automobile operation and manufacturing process from the proposed lightweight structural change of the brake hub from the perspective of the entire automobile and its dynamic life cycle process.