BR-102024017488-A2 - METHOD FOR MEASURING SCREW SLIP IN FRONT ACCESSORY DRIVE SYSTEMS OF HYBRID VEHICLES WITH FLEX-FUEL ENGINES AND BELT-DRIVEN STARTER GENERATOR AND AUXILIARY SLIP TEST DEVICE

Abstract

This invention focuses on intelligently correlating CAE simulation with physical tests and understanding the level of accuracy of the simulation when compared to a real joint. This correlation can be used to improve virtual models and parameters, such as friction coefficients, which are more accurately represented and can provide reliability for subsequent simulations. This is achieved by comparing the results of finite element calculations with progressive load tests on real joints, making it possible to refine numerical models and reliably guarantee the mechanical strength of the bolts under all stresses, even the most complex ones related to engine hybridization technologies.

Inventors

• BERNANDO MENDES MARTINS COSTA
• ROGERIO GONDIM COSTA
• HENRIQUE FERNÃO DIAS DE SOUSA AMARAL
• GIULIANO MARCO ROSA

Assignees

• STELLANTIS AUTOMOVEIS BRASIL LTDA

Dates

Publication Date

20260310

Application Date

20240826

Claims (9)

1. 1. A method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, characterized by comprising the following steps: ultrasonic clamping force measurement; assembly and positioning; progressive load application; slippage monitoring; and model refinement.
2. 2. A method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, according to claim 1, characterized in that, in the ultrasonic tightening force measurement step, a screw from the same batch as the screw under test undergoes a calibration process, in which a machined screw and a dedicated device are used to measure the relationship between screw elongation and tightening load, and with this calibration information, the screw elongation can be measured using ultrasound on the assembled components, allowing the determination of the tightening load as the screw is tightened.
3. 3. Method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generator, according to claim 1, characterized in that, in the assembly and positioning stage, the joint under physical test is mounted with a known load, as simulated by finite element simulation (CAE), preferably using an ultrasonic measurement of the screw for this stage, with the load range varying depending on the external forces and CAE estimates, with values above 0 kN up to at least 100 kN, wherein a hydraulic actuator is mounted in the direction of the expected maximum external load, as found in the calculations or measurements, this actuator support allowing the joint to slide and move, not rigidly fixed to the joint, and using an auxiliary slippage test device (1) intended for applying force to the joint.
4. 4. A method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, according to claim 1, characterized in that, during the progressive load application stage, the load starts at zero and increases progressively as the actuator advances, wherein the test control parameter is the actuator speed, which can vary from 0.1 mm/s to a maximum of 0.5 mm/s, avoiding impact loads; and the load is the result of the actuator's advance and is only measured, not controlled, with the test continuing until one of these conditions occurs: the load reaches a limit value and slippage did not occur, or the actuator displacement reaches a limit value, both limits being defined based on CAE estimates, with an estimate of 2 times the expected slippage load and stopping 2 mm after slippage.
5. 5. A method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, according to claim 4, characterized in that, even in the progressive load application stage, for each sample, the tensioner and the motor block are replaced for each test, ensuring that the contact profile can be accurately compared with the simulation results.
6. 6. A method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, according to claim 1, characterized in that, in the slippage monitoring stage, the load and displacement are monitored in real time, detecting the start of slippage and verifying the predictions of virtual simulations, wherein slippage is defined as an abrupt change in the load x displacement curve, indicating that the load limit for the static friction coefficient has been reached.
7. 7. A method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, according to claim 1, characterized in that, in the model refinement stage, a graph comparing load and displacement is generated, allowing the analysis and identification of slippage loads, and the comparison of CAE results and test results may indicate the need to adjust the model parameters, especially the friction coefficient values, until the virtual values correlate with the real test, allowing virtual iterations in order to provide better accuracy.
8. 8. Method for measuring screw slippage in front accessory drive systems of hybrid vehicles with flex-fuel engines and belt-driven starter generators, characterized by allowing a real calculation of the coefficient of friction value, based on the measurement of compression forces and external forces.
9. 9. Auxiliary slip test device (1), for applying the method as defined in claims 1 to 8, characterized by comprising a metal rod (2) provided, at one of its ends, with a threaded extension (3) incorporating a nut (4) and a vertically positioned "C" washer (5).

Description

FIELD OF THE INVENTION [0001] The present invention relates to the technical field of the automotive industry, focusing more specifically on hybrid vehicles with flex-fuel engines equipped with a front-end accessory drive system (FEAD), such as alternators and pumps, and also equipped with belt-start generators (BSG). BACKGROUND OF THE INVENTION [0002] The idea of using a pulley and belt system to drive automotive engine accessories emerged in the late 1960s when, in addition to the dynamo/alternator, some belts also began to drive the water pump. In the 1980s and 1990s, the system began to incorporate automatic tensioning devices, and more durable belts were developed, with the integration of FEAD (Fuel Energy Efficiency Drive) with electronic control systems emerging at the end of this period. The BSG (Belt and Gear System) concept emerged in the early 2000s, combining the function of a starter motor and alternator in a single component, using a belt to drive a generator that provides starting support and assists in energy recovery during vehicle deceleration. Within this premise, BSG began to be implemented in hybrid and high-efficiency vehicles after 2005, experiencing rapid and widespread expansion and integration with hybrid technologies to this day. BSG has become part of start-stop systems and other energy-efficient technologies, and FEAD, of which BSG is a part, has evolved with the introduction of low-friction belts and other technical advancements. BSG is increasingly integrated into hybrid and electric systems, emphasizing the development of more efficient and sustainable systems, with reduced weight, increased energy efficiency, and reduced emissions. Despite all the positive aspects stemming from the technological evolution described, hybrid vehicles with FEAD systems and BSG present significant challenges, since in these vehicles the BSG system can interact with other highly complex components, such as electric motors and energy management systems. This interaction can make maintaining the reliability and durability characteristics of the bolted joints of the vehicle's powertrain more complex. Therefore, it is necessary to create a method that ensures bolted joints can withstand the increased loads to which they are subjected for the reasons described, preventing failures and increasing the reliability of the system. For a better understanding of the proposed invention, it is necessary to initially understand the concepts of sliding and adhesion in a bolted engine joint, which will be explained in more detail below. [0003] Slippage occurs when external forces exceed the frictional resistance holding the joint together, causing relative movement between the joint surfaces. This is a dangerous situation for the components, as it can impose excessive loads on the bolt, resulting in loosening and failure. Frictional force is achieved through the tension of the bolt as it is tightened, resulting in compressive loads on the joint components. Thus, at a basic level, the amount of force that can be exerted by a bolt is a function of its cross-sectional area and its maximum tensile stress. The tensile stress area is determined by the dimensions of the bolt, and the tensile stress is derived from the yield strength of the bolt material, adjusted by a safety factor. Given this context, some joints may present design challenges, for example, with high external forces but restricted to the use of a small bolt, which, in turn, will result in a maximum possible clamping load. To calculate the clamp load targets, the first step is to know the external forces to which the joint will be subjected and their directions. The methods for finding these loads can vary widely, such as virtual analysis using Computer-Aided Engineering (CAE), Excel spreadsheets, dedicated calculation software, or even actual field measurements. These are beyond the scope of this methodology, but the result for all should be the same information. These loads are used in CAE simulations, which also require, as input, several other joint parameters, such as material properties, component dimensions, component constraints, and especially friction coefficients between interfaces. Accuracy in this last piece of data is crucial for a realistic result, but it is not always precise, as interfaces have different materials and surface finishes that can lead to different friction coefficients. [0004] This invention focuses on intelligently correlating CAE simulation with physical tests and understanding the level of accuracy of the simulation when compared to a real joint. This correlation can be used to improve virtual models and parameters, such as friction coefficients, which represent them more accurately and can provide reliability for subsequent simulations. The way it is done is by comparing the results of finite element calculations with progressive load tests on real joints, making it possible to refine the numerical models and reliably g