Structure and Strength Optimization of the Bogdan ERCV27 Electric Garbage Truck Spatial Frame Under Static Loading

Abstract

Taking into account the requirements to reduce the release of harmful emissions into the environment, the EU’s environmental standards when transitioning to the Euro 7 standard in 2025 will actually lead vehicles having to operate without producing emissions in all driving situations. Carmakers believe that the new, much stricter regulations will mark the end of the internal combustion engine era. For example, in 2030, the manufacturer SEAT will cease its activities, leaving behind the Cupra brand, which will be exclusively electric in the future. This trend will apply not only to private vehicles (passenger cars), but also to utility vehicles, which is the subject of our research, namely the spatial tubular frame in the Bogdan ERCV27 garbage truck, presented in the form of a solid model. The peculiarity of the studied model is the installation of a battery block behind the driver’s cabin, causing an additional load to be placed on the spatial frame of the garbage truck, which in terms of its architecture is more like the body of a bus. During the conditions involving various modes of operation of a full-scale Bogdan ERCV27 garbage truck sample, questions about the strength and uniformity of its load-bearing spatial frame inevitably arise, which are decisive, even at the stage of designing and preparing the technical documentation. The main static load mode, which, despite its name, also covers dynamic conditions, was modeled using the appropriate coefficient k_d = 2.0. The maximum stresses on the model during the “bending” mode were 381.13 MPa before structure optimization and 270.5 MPa as a result of the improvement measures. The spatial frame mass was reduced by 4.13%. During the “torsion” mode, the maximum deformation values were 12.1–14.5 mm, which guarantees the normal operation of the aggregates and units of the truck.

1. Introduction

During the conditions involving various exploitation modes of a full-scale garbage truck sample (model Bogdan ERCV27), which is the object of this research, questions about the strength and uniformity of its load-bearing spatial frame inevitably arise, which are decisive, even at the design stage. Therefore, the materials presented in this investigation can be used in further steps in terms of structure optimization of the spatial frame (hereafter, simply “optimization”) in order to increase its mass–mechanical efficiency indicators, namely reducing the equipped mass of the frame, while simultaneously increasing its strength. The analysis of the stress–strain state of the frame body is performed using the finite element method (FEM) in the Ansys Static Structural environment, by applying the appropriate boundary conditions, similar to natural tests. The model is represented by beam rather than solid elements, which is quite effective for use during the initial stages of designing a truck (comparatively, it is simple to change the cross-sections of pipes or the configuration of their connection at the node) and is applicable to practical engineering; moreover, it is atypical in terms of the previous publications that feature solid-state models.

Given that we are dealing with a spatial tubular frame for a garbage truck, which is a novelty for trucks, and not a simple flat truss with longitudinal spars, part of the literature review will be devoted to the closest related structure, namely bus bodies. In paper [1], a bus body frame is created as a research object that is meshed using Hypermesh software. The static strength and stiffness of the bus body frame under four typical working conditions are calculated using the Nastran solver by the authors, as an alternative to the use of the Ansys software in our case. The analysis of the results showed that the strength and stiffness of the bus body frame must meet the design requirements and that the modal frequency was also within the range specified in the design.

It is quite exciting to compare the investigated spatial tubular frame with the comparatively primitive classical truck frame that uses the “ladder”, which is the subject of paper [2]. The authors determined that the maximum stress of the frame was 214 MPa in the full load condition and the maximum stress of the frame was 459 MPa during the lifting condition. Study [3] evaluated the safety performance of a hydrogen fuel cell city bus body frame through finite element analysis under various operating conditions, revealing excessive stress levels during emergency maneuvers, which were subsequently reduced by up to 20.13% through size optimization, ultimately enhancing the strength of the frame, achieving a weight reduction of 106 kg, and meeting the design requirements.

Following the assessment of truck frame research, it makes sense to get acquainted with paper [4], which is dedicated to research on strength test technology and fatigue evaluation methods for bogie frames and body bolsters.

In all cases (either the flat truck frame is investigated or the spatial tubular frame), the topic of T-joints in the body structure was a particular focus, in this regard it is suggested that you familiarize yourself with [5], where the authors investigated the influence of the welding sequence and welding current on the T-joint strength, based on the integral structure of a bus. The results showed that the welding process had an obvious effect on the T-joint strength. For three selected T-joints, the difference between the maximum and minimum stress values was more than 40% when adopting different welding sequences. The difference between the maximum and minimum stress values was about 30% when taking different welding currents into account.

Returning to spatial frames, it makes sense to mention paper [6], which describes an optimized lightweight frame for intelligent new-energy vehicles. A joint optimization method, based on a multi-objective response surface approximation model and a finite element simulation program, was proposed to realize the lightweight optimization of new-energy vehicle frames. As a result, the weight of the frame was reduced from 25.05 kg to 19.86 kg, a weight reduction of 20.7%, achieving a significant weight reduction effect. Moreover, mass reduction (metal economy) is also part of our garbage truck frame optimization steps, so this paper correlates with our research goals.

The center of gravity (COG) influence on the frame strength is an actual question in our case, taking into account the fact that the compactor position in a garbage truck is variable, which is why it is recommended to research the results in paper [7]. In paper [8], the authors proposed the basic theory of structural reliability combined with bus driving characteristics, the concept of strength reliability for bus body frames, and a calculation method based on the Monte Carlo method.

Study [9], on the battery management system for electric garbage compactor trucks, highlights that the battery mass and configuration significantly impact system stability, making proper estimation of the state-of-charge (SoC) and state-of-health (SoH) critical for managing the battery load distribution and center of gravity.

A frequent aspect related to the boundary conditions of garbage truck loads is associated with compactor mounting brackets. The topic of bracket strength is considered in several studies in regard to the example of a truck frame (as a part of it) [10,11]. In addition, the results in paper [10] indicate that suspension supports experience high levels of stress in six operating conditions and the most dangerous location of the frame always lies at the weld bead between the suspension support and the frame. The primary and secondary stress intensity, along the most dangerous path, decreased by 16.69% in the condition involving a free-hanging left front wheel and by 59.91% in the condition involving a free-hanging right rear wheel. Study [12] examined a 6 ton truck frame, modeled and analyzed using FEA, which showed that the truck frame’s structural strength exceeded the load requirements, allowing for an 8.4% weight reduction, while maintaining the strength of the frame, with the maximum stress reduced from 207.3 MPa to 177.86 MPa. Stress analysis and a strength test involving a 2500 fracturing truck frame is presented in [13].

Japanese garbage truck drivers experience whole-body vibrations, which is linked to lower back pain, and a field study [14] found that diesel truck operations should be limited to 2.5 h per day in current conditions to reduce health risks. Taking into account the transition to electric traction, the issues related to theoretical low-frequency vibrations by a diesel engine have been solved in regard to the electric garbage truck being studied in this article. At the same time, the topic related to the oscillation of batteries, with large masses and a high COG, is an actual issue for future research.

Yield strength is the key indicator that defines the safety factor of the frame; this topic is raised in paper [15], where the authors investigate the improvement to the fatigue strength of a high-strength hot-rolled steel sheet for use in a truck frame. Continuing on the topic of yield strength, publication [16] is dedicated to determining the features of the stressed state in terms of a passenger car frame made using an energy-absorbing material in the girder beam.

Paper [17] utilizes finite element theory and a simplified model to assess the static strength and reliability of a touring car’s frame structure. A finite element model was established to numerically predict the reliability of the structure’s static strength in four frequently encountered operational scenarios, namely bending, torsion, braking, and turning. Boundary conditions applied to a tubular frame, together with the strength–strain results, are the topic of [18]; from the analysis of the results and in regard to the determination of the material to be used, between Aluminum 6061-T6 and Aluminum 6063-T6, that involved a comparison of the stress values, displacement, and safety factors that were relevant in regard to the frame, it can be concluded that the chassis was a tubular type, with the use of pipes that were 34.4 × 26.64 3.38 mm thick and 21.36 × 15.50 mm thick, and that 2.77 mm was the most secure chassis thickness and that the weight was quite light. So, the trend in regard to optimization and the reduction of material parts [19] has actually been implemented nowadays among buses, trucks, and their modifications, like garbage trucks.

Study [20] analyzes the safety and reliability of a mobile pump truck frame in four loading conditions using a finite element model, which showed that while stress and deformation were minimal under full-load bending, emergency turning, and braking, they were significant in torsion conditions, yet all the conditions met the strength requirements, providing valuable design insights. These regimes are correlated with the boundary conditions for the garbage truck calculation presented below.

Finally, it makes sense to turn to publications [21], where the authors presented several strength calculation approaches (mass, damping, and stiffness matrix, etc.), using the Ansys environment. That fundamental knowledge allows us to understand the essence of the processes that take place during calculations in the Ansys environment, which is the main tool for analyzing the strength of the garbage truck frame in our study. It is especially relevant considering the applied method in terms of the frame structure and strength optimization in the current research, namely the iteration approach when n consecutive FE calculations are performed, with the selection of alternative pipe cross-sections or other connections to the nodes. In this regard, the following conditions must be met: the minimization of the total mass and the achievement of uniform strength (a reduction in the difference between the minimum and maximum stress).

Finally, the purpose of the current research is to design an easily applicable and practically efficient methodology for spatial structure strength optimization of a garbage truck frame using a beam modelling approach, which is a precursor to solid simulations and enables the achievement of uniform strength and the minimization of the related mass, with minimal investment of resources.

2. Materials and Methods

From a mathematical point of view, the frame of the electric garbage truck, Bogdan ERCV27 (Figure 1), is a solid body, which in modeling can almost strictly be described as a set of geometrically similar elements, connected in such a way that they form a structure as close as possible in shape to a real body. The frame model produced in the Ansys environment is presented by beams and surfaces, with the structural parts fully corresponding to the drafts (Figure 2) and technical documentation.

The chosen approach to build a beam model, rather than a solid model, is explained by the flexibility in terms of its future optimization, namely that the structural elements (rods) can be easily replaced by others (cross-section).

The rod model consumes a lot less computational resources than solid models, due to a different finite element meshing approach being adopted (which will be demonstrated below).

The beam model produced in the Ansys environment is perfectly suited to the Static Structural Ansys module (Figure 3), in regard to the boundary conditions applied.

A feature of the model is the use of an electric powertrain instead of a traditional internal combustion engine, so we can see a vertical cabinet for the batteries behind the driver’s cabin (Figure 3). The spatial frame itself is fundamentally different from typical primitive truck frames, in that the frame is formed of two longitudinal spars connected by crossbars.

The next step is the meshing of the beam model (Figure 4), which consists of the following:

-

61,233 elements;

-

71,169 nodes.

Unlike solid elements, beam elements correspond, in terms of their two dimensions (height and width), to the cross-section of the pipe and the third parameter (depth) is editable in order to establish the necessary accuracy for the calculation. There is a recommended rule: the depth (mm) must be less than the smallest size of the pipe cross-section. As part of this calculation, a value of 18 mm was set, which was less than the 22.797 mm recommended by the Ansys software. Decreasing this parameter leads to an increase in the calculation time, erasing the advantages of the beam approach compared to the solid model approach.

It is obvious that if a solid model was used instead of a beam model, the number of finite elements would be 10× greater, which would significantly complicate further strength optimization, which consists of many iterations (step-by-step improvements to the structure).

The customer specifies the material of the spatial frame, in this case 1.4003 (stainless ferritic, chromium steel X2CrNi12), although the calculation methodology proposed below assumes the possibility of using any grade of steel, which can be imported into the Ansys Granta EduPack module. Among the characteristics that determine the physical and mechanical properties of the material, those detailed in the following table have the greatest role (

Table 1. X2CrNi12 properties.

Property	Typical
Yield tensile strength (N/mm2)	320
Tensile strength (N/mm2)	530
Modulus of elasticity (GPa)	220
Density (kg/m3)	7700

).

A static calculation is a basic type of structural strength test, which was used even before the creation of solid models (that is also why the model makes sense), drawings, and design documentation. Its main task is to optimize the structure and strength of the spatial frame, reduce the maximum stresses in the model, achieve uniform strength, and improve the capacity of the material. The two main modes of static tests are «bending» and «torsion». They are not related to bending or torsional moments, but are related to the type of load applied and the final deformation of the body. In fact, in each of these load modes, the spatial frame is in a complex loaded state, where tensile and compressive forces, as well as torsional and bending moments, are present, this is called a stress–strain state.

A typical algorithm for carrying out static bending strength tests consists of the following stages of loading:

-

The weight of the sprung part of the bus *;

-

The weight of the nodes, aggregates, and body;

-

The payload weight.

* The sprung mass, Ma, includes the mass of the bus excluding the suspension, axles and wheels, that is, those elements located between the body and the road (Figure 5).

When analyzing the static strength, the following rule should be observed: the total stresses in the body element under investigation should not exceed the allowable stresses in terms of the conditions in regard to the strength of the material. To assess the impact of peak loads, the dynamic coefficient (aka the “safety factor”) is introduced:

$$k_d={\displaystyle \frac{{\sigma }_y}{{\sigma }_{max}}}, \mathrm{moreover} {\sigma }_{max}\le {\displaystyle \frac{{\sigma }_y}{k_d}}$$

(1)

where:

${\sigma }_{max}$—is the maximum stress, MPa;

${\sigma }_y$—is the yield strength of the material, MPa;

$k_d$—is the dynamic coefficient (a dimensionless quantity).

The method for determining the dynamic coefficient, k_d, is based on experimental measurements of the vertical accelerations at various points of the sprung mass or vertical forces acting on the side of the suspension elements. So, to simulate operating conditions, where the amplitude of the road surface (asphalt height differences) could differ 2–5 times depending on the quality of the road (their class and appointment), it is advisable to place the k_d value in the range of 1.5–2.0 for the “bending” mode tests and 1.0 for the “torsion” mode tests. From physics, the equation is known as:

$$\overrightarrow{a_k}={\displaystyle \frac{2S}{t^2}},$$

(2)

where:

$\overrightarrow{a_k}$—is the linear acceleration of the wheel center in the vertical direction, m/s²;

$S$—is the path (amplitude of the road surface), m;

$t$—is the time, s.

Let us consider the essence of Equation (2): under the conditions of an absolutely flat road, the value of S (the vertical distance between the maximum protrusion and the depression on the road) will be equal to 0, which means that a_k = 0. Therefore, on an absolutely flat road, the wheel does not undergo vertical oscillations and does not transmit accelerations to the vehicle body. In conditions involving movement at the same speed, but on a low-quality road, for the same allotted time t, the wheel of the vehicle performs a vertical movement S (a movement due to compliance with the suspension), which creates a specific acceleration, a_k. With such a simple example, we understand the influence of road irregularities on the reactions transmitted to the vehicle body.

Practically, the value of the coefficient, k_d = 2.0, means that the garbage truck frame must withstand stresses within the yield tensile strength of the material, which occurs when its total sprung mass increases by 2 times.

The total bending load can be written as follows:

$$\sum P_a=k_d{m}_{s}g,$$

(3)

where:

$\sum P_a$—is the total load on the sprung mass, N;

$m_s$—is the sprung mass, kg;

$g$—is the acceleration due to gravity, m/s².

Summing it up, the following values were taken into account:

-

$k_d=2.0$ for the “bending” mode;

-

$k_d=1.0$ for the “torsion” mode.

All the stress results from our model must be exclusively within the limits of proportionality in terms of the material stress diagram, that is, they must fall within the remit of Hooke’s law, although the “Bilinear Isotropic Hardening” curve was considered in regard to the material characteristics for the correct modeling of plasticity (if it occurs locally).

Given that our body frame, consisting of rods, is in a complex stress–strain state, where tension, compression, twisting, and bending are simultaneously present, a fair and internationally accepted guideline for estimating structural stresses in the Ansys Workbench is the Mises–Hencky model, also known as the form change energy theory.

The theory states that a ductile material begins to fail at points where the Mises stress (${\sigma }_{vonMises})$ becomes equal to the ultimate stress. In most cases, the yield strength (σ_y) is used as the ultimate stress; the safety factor (SF), which defines the margin of safety, must be greater than 1 and can be determined according to the following ratio:

$$SF={\displaystyle \frac{{\sigma }_y}{{\sigma }_{vonMises}}}>1$$

(4)

Based on the data in Table 1, the yield tensile strength is σ_y = 320 MPa, which is the red line we should not exceed in terms of the strength optimization results of the frame.

The main idea in terms of the relevant materials is to form an effective and easily applicable methodology for forming boundary conditions, which can become an available tool for such a purpose, including for use by employees of design bureaus. At the same time, there is a wide list of outstanding issues for future studies: the influence of the compactor dynamics on the stress of the garbage truck frame in regard to the formation of the corresponding differential equations for multifactorial mathematical modeling; determining the effect of the COG and the mass of the batteries behind the driver on the cabin vibrations, and UNECE R66 and 29 compliance, etc.

3. Boundary Condition Formulations

In order to fix our spatial model frame (Figure 3), it is necessary to apply supports to it (fixed ones and displacements). The supports are applied to the flanges of the pneumatic cylinders forming the suspension, which are connected to the corresponding welded trusses in the frame to receive the vertical load and limit the movement of the body as a whole, relative to the other axes.

The scheme of the model fixation for the “bending” mode involves setting movement restrictions on all wheels (Figure 6), but with different types of support.

In contrast to the “bending” mode, which involves resting the vehicle on all the wheels and loading with a dynamic coefficient of k_d = 2.0 or so, the “torsion” mode (Figure 7) corresponds to movement at low speeds through an incline, with one of the wheels hanging out (usually the wheel of the least loaded axle). Also, the “torsion” mode can correspond to the case of hanging the wheel out in a static position (pit, open hatch, etc.). In this case, the vehicle rests on three wheels (if the total number of wheels is four), or on five wheels if the total number is six, etc. The dynamic coefficient is k_d = 1.0 because there is no velocity or it is reduced to zero.

Applying the supports to the tubular frame of the garbage truck in the Ansys Static Structural environment is carried out using the “displacement” and “fixed support” types fixed to the mounting platforms of the flanges of the pneumatic suspension cylinders (marked in red—Figure 8), according to the “bending” and “torsion” mode schemes (Figure 6 and Figure 7).

Additionally, the acceleration according to the k_d value is applied to the model (Figure 9): 19,613 mm/s² for the “bending” mode, with k_d = 2.0, and nominal Earth gravity, g, for the “torsion” mode.

The masses of the aggregates (powertrain, batteries, equipment, etc.; a total of 41 grouped masses) are applied to the actual installation locations, according to the technical documentation; for example, the compactor rests on eight supports and has three centers of mass (Figure 10), according to the scheme (red arrows in Figure 2):

-

The compactor itself;

-

The garbage in it;

-

The loading device in the rear overhang;

4. Results

4.1. “Bending” Mode

The strength analysis is performed according to several criteria, the main feature of which is the assessment of the stress amount. According to the stress map, the maximum value was 381.13 MPa (marked as Max in Figure 11), which exceeds the yield strength of the material 1.4003, the yield tensile strength = 320 MPa (Table 1).

The maximum stress area (Figure 11) corresponds to the location of the cross-beam between the two rear axles, on which two of the eight supports for the compactor rest (marked orange in Figure 12).

Let us analyze the stress–strain state of the rods from the central part of the frame (between the cabin and the central axis). The maximum value was 131 MPa and was recorded in the slope of the floor base (Max in Figure 12). The rest of the beams are characterized by stresses in the range of 70–80 MPa. That is, if additional loading in this area with other masses is not planned, then the safety margin can be considered sufficient.

The front (cabin) load-bearing part received a stress of no higher than 179 MPa (observed in the left spar), which is absolutely normal from the point of view of the margin at the yield point (Max in Figure 13):

The uniform strength of the frame can be estimated using the safety factor, which is physically equal to the ratio of the yield strength of the material to the actual stress value in this area of the frame. A value of 1 means that the actual stresses are equal to the yield strength; a value less than 1 means that the strength is insufficient; values greater than 1 mean that the safety margin has been exceeded (Figure 14).

After receiving the first calculation results, a huge set of measures was taken to modify the structure of the frame (selection of alternative cross-sections, change the wall thickness, introduction of additional links, etc.); more than 50 changes in the structure of the frame were applied. Some of them are shown below (Figure 15), the application of which finally improved the total uniform strength and spread of the stress concentrators. By the way, not all the steps focused on strengthening the elements; practice has shown that it is often necessary to weaken certain elements. For example, here are a few steps that were taken (Figure 15): (a) the configuration of the roof dome with the same cross-section was changed (40 × 40 × 2); (b) channels 80 × 40 × 4 were added; (c) 3 mm thick stiffeners (scarves) were added in the front suspension mounting brackets; (d) the thickness of the sheets on the reverse side was reduced to 6 mm; (e) the thickness of the suspension brackets was increased to 8 mm; and (f) the thickness of the sheets in the rear axle suspension mounting bracket was increased to 8 mm.

As a result of the optimization measures to improve the uniform strength of the frame, we achieved a reduction in the maximum stress level to 270.5 MPa (marked as Max in Figure 16), which is completely normal compared with the yield tensile strength = 320 MPa (Table 1). This value is found in regard to the load-bearing crossbar in the central axle wheel attachment of the garbage truck. In general, the central axle is always the most loaded axle and at the same time the driving one, this is typical for all trucks, one can say, without exception. For us, this is a good sign, because, despite the innovative structure of the frame, we get the same results in terms of the stress–strain state characteristics of a classic truck, which simplifies the relevant optimization approaches.

The safety factor map becomes much more uniform as a result of the optimization, almost the entire rear end has at least a 5× strength reserve (Figure 17):

In addition, due to optimization measures implemented, the equipped mass of the frame was reduced by 4.13%.

4.2. “Torsion” Mode

The “torsion” mode traditionally produces smaller stress values due to k_d = 1.0, but is more important from the point of view of displacement estimation. The optimized model demonstrated high rigidity, which can be estimated by the maximum deformations for each torsion case: 14.5 mm in the case of the front left wheel hanging (Figure 18a) and 12.1 mm for the hanging of the rear right wheel (Figure 18b).

The behavior in the case of hanging the rear wheel (Figure 18b) seems interesting, namely the stiffness of the frame is so high in the rear part that the maximum deformations are actually detected in the front of the frame (the front overhang of the cabin). In addition, it is a very positive sign when taking into account the fact that the compactor position in a garbage truck is variable (its position changes when the boot device opens and its center of mass moves, creating extra bending moments).

The most difficult case is the diagonal hanging of the wheels of the garbage truck (when two wheels located opposite each other are hung from different axes): 29.9 mm when the truck stands on the front right and rear left wheels (Figure 19a) and 40.8 mm when the truck stands on the front right and middle left wheels (Figure 19b).

In the case of a classic installation of an internal combustion engine, the truck frame must be rigid enough to ensure the normal operation of the joints in the power plant; the relative movements of the installation points of the engine and transmission should not exceed 10–15 mm. In our case, we observed movements of 12.1 mm and 14.5 mm in extreme cases, when one of the wheels is hanging (Figure 18).

It is possible to observe values around 30–40 mm in the case of oblique diagonal wheel hanging (Figure 19), but it is fair to validate the deformations in the control points, where the aggregates are installed, but not on the edge of the frame (bumper or part of the mudguard attachment). In addition, there is no solid connection between the gearbox, engine, and axes in electric vehicles; thus, we can consider that the total deformations found after the optimization measures have been implemented are admissible, which proves the high total rigidity of the frame. One of the cabin rigidity factors is the relative displacement of the corners of the windshield armhole, which should not exceed 10–15 mm. The front part of the frame passed this point, but the displacements did not exceed the specified value. Actually, this is one of the safety factors considered by the driver, along with a frontal crash test (NCAP, ECE R94) and normal ventilation and microclimate ISO standards, which affect the driver’s reactions and fatigue, etc. All of these aspects form the overall safety in terms of the operation of the garbage truck.

5. Discussion

Under the pressure of the EU’s environmental standards relating to the transition to electric traction, even garbage trucks are undergoing a frame change from the classic flat “ladder” type to a spatial structure due to a forced layout change. For example, the garbage truck we studied has a cabinet for installing batteries behind the driver’s cabin, which occupies the entire width of the truck, and this requires ensuring sufficient lateral stability of the vehicle, which a classic narrow frame on spars cannot provide. Another reason is that the classic frame is much higher and this significantly increases the height of the center of the mass, which is unsafe for a heavy battery block (2030 kg). Thus, a change in the powertrain type requires fundamental changes in the frame structure, namely a transition to spatial tubular trusses with an integrated cabin, which is significantly stiffer and can absorb higher loads. Speaking of optimization, it can be said for certain that this process is endless; despite dozens of iterations performed within the framework of our research, you can always try to achieve even better structural stability or further reduce the mass. The complexity of the process lies in the fact that the same element behaves differently when the “bending” or “torsion” mode is applied, which is why the proposed method of using a beam model, rather than a solid one, is suitable. In conjunction with the proposed boundary conditions, such an approach turned out to be very effective, it uses a minimum of computing capabilities and allows changes to the structure of the frame to be implemented quickly.

Being equipped with an electric motor, garbage trucks automatically fall under the UNECE R100 rules concerning the approval of vehicles with regard to specific requirements for the electric powertrain, which can be ignored in regard to the use of diesel power. Therefore, the studied truck should withstand the applied horizontal acceleration of 6.6 g in the direction of motion and 5 g perpendicular to it, which will be the topic of future research. It is also necessary to consider the UNECE R29 and NCAP rules regarding the cabin strength in frontal impact conditions; the additional mass of the batteries (2030 kg) behind the cab with a relatively high COG (center of gravity) creates large inertial loads (acceleration reaches 20 g), which in principle are absent in a truck with a diesel engine. The COG and cab weight also affect side rollovers (UNECE R66), which requires FEA for vehicle certification and is a possible area of further research.

6. Conclusions

The main results of the conducted research are as follows:

• The development a really helpful practical method of designing spatial frames for road vehicles, even before the formation of design documentation, which allows structural changes to be made relatively easily, with a large number of iterations aimed at increasing the strength of the truss. This goal was achieved, thanks to the use of a combination of models made from beams instead of solid elements and the application of adequate boundary conditions; the calculation process in the Ansys Static Structural environment is minimal in terms of resource requirements and flexible enough to conduct dozens of consecutive analyzes by making changes to the design;
• The basic calculation modes for “bending” and “torsion” are sufficient to comprehensively analyze the structure of the frame from the point of view of uniform strength and compliance with the strength conditions relative to the yield point. Taking into account the dynamic coefficient k_d = 2.0, the maximum stresses of the model were 381.13 MPa before optimization and 270.5 MPa as a result of the improvement measures. A significantly increased uniform strength was achieved based on the results of the map of the indicator “safety factor” and the mass was reduced by 4.13%;
• The “torsion” mode, after the optimization measures had been implemented, did not reveal unacceptable values in terms of deformations that would make normal operation of the units impossible (the maximum values were 12.1–14.5 mm, depending on the side of the suspended wheel). The relative displacement of the corners of the windshield armhole did not exceed 10–15 mm, which allowed the glass to fit on the glue. The diagonal hanging mode was more dangerous (deformation over 30 mm), but the probability of such a situations was minimal; in addition, we are dealing with an electric powertrain, not an internal combustion engine, where there were tight tolerances on the relative movements of the transmission and engine;
• The global conclusion is that the transition from internal combustion engines to electric units totally changes the rules of the game; you cannot install an electric powertrain behind the driver to house heavy batteries on a classic truck frame, especially for such a special purpose vehicle as a garbage truck, the resulting hybrid would have layout conflicts and would demonstrate its inefficiency. That is why the development of methods for analyzing the strength of spatial beam frames is a promising direction in modern science and engineering;
• Considering how the space truss in a garbage truck differs conceptually from the classic spar frame in trucks and the stress and deformation results that were obtained as a result of the bending and torsion regime, it definitely makes sense to conduct further certification studies, particularly in regard to the UNECE R29 and NCAP (frontal impact), UNECE R66 (side rollover), and UNECE R100 (electric battery frame safety) rules.