TORQUE TRANSMISSION ELEMENT WITH REINFORCED FLUID CONNECTION AND METHOD FOR ITS MANUFACTURING

Abstract

A torque transmission element having a reinforced fluid connection, and a method for its manufacture. The torque transmission element comprises a body element formed from a steel alloy and rotatable about an axis of rotation. The body element includes an outer surface, an inner surface defining a fluid passage through the body, and a fluid connection communicating with the fluid passage. The fluid connection has a contact surface that connects the outer surface of the body to the inner surface of the fluid passage. A pressure load above the yield strength of the steel alloy is applied to the contact surface using a steel mandrel having a hardness greater than 60 HRC. The body element is subjected to a heat treatment process to form a hardened insert after the pressure load has been removed from the contact surface.

Description

INTRODUCTION

[0001] The present disclosure relates to a torque transmitting element having a fluid passage, more particularly to a torque transmitting element having a reinforced fluid port for the fluid passage.

[0002] Modern vehicles with conventional internal combustion engines (ICEs), electric vehicles with electric engines, and hybrid vehicles with both ICEs and electric motors use transmissions, also known as gearboxes and differentials, in the drivetrain to transfer torque from the engines to one or more drive wheels to propel the vehicles. These engines, gearboxes, and differentials consist of multiple torque-transmitting elements, such as rotating shafts and gear elements. For improved fatigue strength and increased fuel efficiency, these torque-transmitting elements have fluid passages to receive and distribute a lubricating fluid, such as engine oils, transmission fluids, and the like.Such internal fluid passages may also be configured to distribute coolant to maintain operation of such engines, transmissions, and / or differentials within rated operating temperatures.

[0003] Lubricating fluids and / or coolants are introduced into and discharged from the fluid passages of the torque-transmitting elements via fluid ports in communication with the fluid passages. These fluid passages are typically formed by drilling or reaming holes or openings through the surfaces of the torque-transmitting elements. During the formation of the openings of the torque-transmitting element, material removal can negatively impact the overall service life and performance of the torque-transmitting element.

[0004] While known torque transmitting elements having fluid connections and methods of manufacturing them serve their purpose, there is a continuing need for torque transmitting elements that have improved endurance and performance. SUMMARY

[0005] According to several aspects, a torque-transmitting element having a reinforced fluid port is disclosed. The torque-transmitting element includes a body member rotatable about an axis, a fluid passage extending through the body, and a fluid port in communication with the fluid passage. The body member has an outer surface, the fluid passage has an inner surface, and the fluid port has a mating surface connecting the outer surface of the body member to the inner surface of the fluid passage. The reinforced port is obtained by applying a predetermined compressive load to the mating surface followed by a final heat treatment process.

[0006] According to an additional aspect of the present disclosure, the body element comprises a metal alloy having an alloy yield point. The predetermined compressive load is above the yield point of the alloy.

[0007] According to another aspect of the present disclosure, the reinforced fluid connection includes a predetermined allowable dimensional tolerance. The predetermined compressive load includes an upper compressive load limit above which the reinforced fluid connection permanently deforms outside the predetermined allowable dimensional tolerance. The predetermined compressive load is below the upper compressive load limit. The predetermined compressive load is between 6 and 8 percent above the yield strength of the alloy.

[0008] According to another aspect of the present disclosure, the metal alloy is a steel alloy.

[0009] According to another aspect of the present disclosure, the heat treatment process includes a carburizing heat treatment process or an induction heat treatment process.

[0010] According to another aspect of the present disclosure, the connection surface defines a frustoconically shaped reinforced fluid port. The torque-transmitting element may be a rotatable shaft or a gear element.

[0011] According to several aspects, a method for manufacturing a torque-transmitting element having a reinforced fluid port is disclosed. The method includes providing a metallic workpiece having a mating surface enclosing an opening to a fluid passage, applying a compressive load to the mating surface using a mandrel, and heat-treating the metallic workpiece. The metallic workpiece has a yield point. The compressive load is above the yield point.

[0012] According to an additional aspect of the present disclosure, the mating surface defines the fluid port, which has a predetermined allowable tolerance. Applying the compressive load to the mating surface includes applying a limited compressive load to prevent the fluid port from deforming outside the predetermined tolerance. The compressive load is 5 to 6 percent above the yield strength of the metallic workpiece. The metallic workpiece is made of a steel alloy.

[0013] According to several aspects, a method of manufacturing a torque-transmitting element is provided. The method includes providing a workpiece comprising a low-carbon steel alloy, the workpiece having a machined fluid port defined by a mating surface; applying a predetermined compressive load to the mating surface using a mandrel, the predetermined compressive load being above a yield point of the steel alloy; removing the compressive load from the mating surface; and after removing the compressive load from the mating surface, heat-treating the workpiece. The steel alloy has a Rockwell C scale (HRC) hardness of less than 25 prior to heat-treating the workpiece. The predetermined compressive load is 5 to 6 percent above the yield point of the steel alloy.The torque transmission element can be a torque transmission shaft or a gear element.

[0014] According to an additional aspect of the present disclosure, the low carbon steel alloy is selected from a group consisting of a 5120 steel alloy, a 1040 steel alloy, and an 8620 steel alloy.

[0015] According to another aspect of the present disclosure, the mandrel is formed from a tool steel having a hardness greater than 60 HRC and includes a conical or spherical portion operable to apply the compressive load to the mating surface.

[0016] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way; they show: Fig. 1 is a top view illustration of an electric vehicle including an electric drive unit (EDU) according to an exemplary embodiment; Fig. 2 is a cross-sectional view of the EDU having multiple torque transmitting elements according to an exemplary embodiment; Fig. 3A-B show exemplary representations of the torque transmission elements; Fig. 4A-B illustrate the use of a mandrel to apply a compressive load to a surface of a fluid port according to an exemplary embodiment; Fig.5 a detailed view of the fluid connection according to an exemplary embodiment; Fig. 6 an alternative embodiment of a mandrel; and Fig. 7 is a block flow diagram of a method for manufacturing a torque transmitting element having a reinforced fluid connection. DETAILED DESCRIPTION

[0018] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. The illustrated embodiments are disclosed with reference to the drawings, wherein like numerals indicate corresponding parts throughout the several drawings. The figures are not necessarily to scale, and some features may be exaggerated or minimized to show details of particular features. The specific structural and functional details disclosed are not intended to be interpreted in a limiting sense, but rather as a representative basis for teaching one skilled in the art how to practice the disclosed concepts.

[0019] Torque-transmitting elements of vehicle powertrains often have machined openings, such as oil holes, formed in steel blanks for lubrication purposes. Machining these openings could damage the original surface finish and grain pattern in the area surrounding the machined openings and introduce stress buildup, resulting in reduced service life. The following disclosure provides a torque-transmitting element having a reinforced fluid port and a method for applying a compressive load to the surface of the fluid port surrounding the machined openings using a specially designed tool that compressively deforms the material of the port surface.The compression-formed blank undergoes a recrystallization process during a final heat treatment process, which causes a refinement of the grain size, which would improve the surface finish of the fluid connection and provide a remedy for the damage of the surface grain pattern, resulting in improved strength and toughness of the fluid connection and the torque transmission element.

[0020] Fig.1 shows a schematic representation of a non-limiting example of an electric vehicle 100 having an electric drive unit (EDU) 102. The vehicle 100 generally includes a body 104 containing front wheels 106A, 106B and rear wheels 108A, 108B. The front wheels 106A, 106B and the rear wheels 108A, 108B are each located near a corresponding corner of the body 104. The EDU includes three (3) modules: power electronics 110, an electric motor 112, and a transmission 114. The power electronics are responsible for converting the DC voltage from rechargeable batteries (not shown) into a three-phase AC voltage for the overall operation and control of the electric motor 112.The electric motor 112 converts electrical energy into mechanical torque, which is transmitted through the transmission 114 and the mechanical linkages 116 to one or more of the wheels 106A, 106B, 108A and 108B to propel the vehicle 100.

[0021] Fig.Figure 2 shows a cross-sectional view of the EDU 102. The electric motor 112 includes a stator 124, a rotor 126 rotatable relative to the stator 124, a rotor shaft 128 meshed with the rotor 126, and a first gear member 130 meshed with the rotor shaft 128. The first gear member 130 meshes with a second gear member 132 meshed with a torque transmitting shaft 134. The torque transmitting shaft 134 is rotatably supported by rolling bearings 136. The torque transmitting shaft 134 includes a third gear member 138 meshed with a torque distribution gear mechanism 140, also referred to as a differential unit 140.

[0022] During operation, the electric motor 112 generates a torque output through the rotor shaft 128. The torque transfer shaft 134 then transfers the torque from the rotor shaft 128 to the differential unit 140, which then selectively distributes the torque to one or more of the vehicle wheels 106A-B and 108A-B to drive the vehicle 100. The torque transfer shaft 134 is subjected to a heat treatment process to form a hardened insert for wear resistance while maintaining the toughness and ductility of a low-carbon steel core. The heat treatment process may include carburization, in which carbon atoms are diffused into the surface of a low-carbon steel shaft to form a high-carbon insert, and quench hardening.According to an alternative embodiment, the heat treatment process may comprise induction heat treatment of a high carbon steel core and quench hardening.

[0023] Although vehicle 100 is illustrated as a passenger vehicle, other vehicle examples include, but are not limited to, land vehicles such as motorcycles, trucks, off-road vehicles (SUVs), and recreational vehicles (RVs), as well as non-land vehicles including vessels and aircraft. It should be appreciated that while an electric vehicle is described, the disclosure of torque-transmitting elements such as torque-transmitting shafts and gear elements is also applicable to those on conventional internal combustion engine vehicles and hybrid vehicles.

[0024] The Fig. 3A and Fig.3B show non-limiting examples of rotatable torque-transmitting elements, such as a gear member 300A and an output shaft 300B, arranged about a rotational axis A and A', respectively. Each of the torque-transmitting elements 300A, 300B includes a network of internal passages 302A, 302B configured to conduct a fluid, and at least one fluid port 304A, 304B and / or 306A. A fluid port is defined as the area surrounding an inlet or outlet opening of a fluid passage. The fluid ports 304A, 304B are shown as being perpendicular to the rotational axis A and A', respectively. The fluid port 306A is shown in Fig. 3A parallel to the rotational axis A. The individual fluid ports 304A, 304B, and 306A can be inlet ports or outlet ports. The fluid can be a lubricating fluid such as a gear oil or a coolant such as ethylene glycol.

[0025] Fig.4A shows a cross-sectional view of a portion of a torque-transmitting member 400, which includes a fluid port 402 surrounding an opening 404 of a fluid passage 408, and a mandrel 450 having a tapered portion 452 spaced from the fluid port 402. The torque-transmitting member 400 may be the gear member 300A or the torque-transmitting shaft 300B. The torque-transmitting member 400 has an inner surface 406 defining the fluid passage 408 and an outer surface 410 defining the opening 404.

[0026] How best in Fig. 5, the fluid port 402 has a tapered connection surface 412 that intersects the outer surface 410 and the inner surface 406 of the fluid passage 408 to define a conical fluid port 402. In the Fig. 4A, Fig. 4B and Fig.5, the fluid port 402 is in communication with the fluid passage 408. The conical portion 452 of the mandrel 450 has a shape factor capable of abutting against the mating surface 412 of the fluid port 402, as shown in Fig. 4B is shown.

[0027] The mandrel 450 is made of a tool steel with a hardness on the Rockwell C scale (HRC) greater than 60 and has a contact portion 452 operable to abut against the mating surface 412 of the fluid port 402. The contact portion 452, shown non-limitingly, has a conical shape with an opening angle α of 30 to 60 degrees. The mandrel 450 can be mounted on a press-fitting device (not shown) operable to press the mandrel 450 onto the mating surface 412 of the fluid port 402. The torque-transmitting element 400 is mounted so as to be motionless during the pressing process. The connection surface 412 of the fluid connection 402 is pressed to cause the material to flow and change the grain distribution properties in this area 470 prior to heat treatment, resulting in improved fatigue strength (i.e., increased fatigue life).

[0028] Fig.7 shows a block diagram of a method for manufacturing a rotatable torque transmitting element having a reinforced fluid port with improved fatigue strength (method 700). According to Fig. 7 and the Fig. 4A, Fig. 4B and Fig.5, the method 700 begins at block 702 by providing a torque-transmitting member 400 in the green state. The torque-transmitting member 400 may be formed from a metal alloy, including, but not limited to, steel alloys 5120, 1040, and 8620. Green state means that the torque-transmitting member 400 has not undergone a final hardening treatment process and has a hardness of less than 25 HRC. According to the non-limiting embodiment, the torque-transmitting member 400 has a fluid passage 408 and includes a fluid port 402 defining an opening 404 in communication with the fluid passage 408. The fluid port 402 has a connection surface 412 defining a frustoconically shaped fluid port 402 surrounding the opening 404.The connection surface 412 includes an angle β between 30 and 60 degrees with respect to the outer surface 410 of the torque transmission element 400 at the interface between the outer surface 410 and the connection surface 412.

[0029] The method continues in block 704, where a mandrel 450 has a conical portion 452 capable of abutting against the mating surface 412 of the fluid port 402. The mandrel 450 is axially aligned with the opening 404 and is moved axially toward the opening 404 until the conical portion 452 is pressed against the mating surface 412. In other words, the conical portion 452 of the mandrel 450 is pressed against the mating surface 412 of the frustoconically shaped fluid port 402.

[0030] The method continues in block 706, where a predetermined compressive load is applied to the mating surface 412 by the conical portion 452 of the mandrel 450. A sufficient amount of force F is applied by the mandrel 450 to the mating surface 412 until the compressive load acting on the mating surface 412 exceeds the yield strength of the metal alloy, but is less than the amount of force required to deform the mating surface 412 of the fluid port 402 outside of the allowable tolerances. The yield strength is defined as the point on a stress-strain curve that indicates the limit of elastic behavior and the onset of plastic behavior. Below the yield strength, the metal alloy deforms elastically and then returns to its original shape when the applied load is removed.Once the yield point is exceeded, part of the deformation is permanent and irreversible and is called plastic deformation.

[0031] It is preferred to apply a force that produces a compressive stress of 5 to 6 percent above the yield point of the metal alloy. While the mandrel having a conical shaped section is shown, a mandrel having a Fig. 6, instead of the conical-shaped portion 652, a spherically shaped portion may be provided. The spherically shaped portion creates a concave curvature 654 in the surface of the plastically deformed fluid port 402, further increasing the strength of the fluid port 402 by distributing the load across the fluid port 402.

[0032] In block 708, the mandrel 450 is removed, and the torque-transmitting element 400 is subjected to a final heat treatment process, such as carburizing and quench hardening, or induction heat treatment and quench hardening. The plastically deformed blank metal alloy of the fluid port 402 undergoes a recrystallization process during the heat treatment process. Recrystallization causes a refinement of the grain size, which improves the toughness of the surface 412 of the fluid port 402, including the immediate areas 470 or the areas 470 of the torque-transmitting element 400 surrounding the fluid port 402.

[0033] Tables 1 and 2 below show the fatigue test results of a test drivetrain main shaft. Table 1 shows the fatigue test results of a test drivetrain main shaft that did not undergo Method 700. Table 2 shows the fatigue test results of a test drivetrain main shaft that did undergo Method 700. Table 1 Results of the fatigue strength test of the main shaft without application of the method Sample ID Test load (Nm) Cycles Maximum load Minimum load Medium load amplitude R=-1 amplitude R=0 area SN10 3952 50 2001 1951 2776,75 3926,92 145504 SN11 3952 50 2001 1951 2776,75 3926,92 615255 SN12 3952 50 2001 1951 2776,75 3926,92 434536 SN15 3952 50 2001 1951 2776,75 3926,92 523134 SN16 3952 50 2001 1951 2776,75 3926,92 141150 SN17 3952 50 2001 1951 2776,75 3926,92 429082 SN20 3952 50 2001 1951 2776,75 3926,92 849626 SN21 3952 50 2001 1951 2776,75 3926,92 189943 SN22 3952 50 2001 1951 2776,75 3926,92 407164 Table 2 Results of the fatigue strength test of the main shaft using the method Sample ID Test load (Nm) Cycles Maximum load Minimum load Medium load amplitude R=-1 amplitude R=0 area SN1 3952 50 2001 1951 2776,75 3926,92 1577577 SN2 3952 50 2001 1951 2776,75 3926,92 stopped at 1 million SN3 3952 50 2001 1951 2776,75 3926,92 1785272 SN4 3952 50 2001 1951 2776,75 3926,92 1249973 SN5 3952 50 2001 1951 2776,75 3926,92 1602846 SN6 3952 50 2001 1951 2776,75 3926,92 stopped at 3 million

[0034] The fatigue test consists of a fatigue test with maximum, minimum, and average torsional loads of 3952, 50, and 2001 Newton meters (Nm), and therefore a cyclic load amplitude, with a load amplitude ratio of minimum to maximum load R = -1 (fully reversed load) or R = 0 in a load range of 1951, 2776.5, and 3926.92 Nm. The test sequence is designed to be carried out until the structural integrity of the test drive train main shaft fails by cracking or breaking.

[0035] Referring to Table 1, the test drivetrain mainshaft that did not undergo Method 700 failed between 141,150 and 615,255 cycles. Referring to Table 2, the test drivetrain mainshaft that did undergo Method 700 failed for more than 1,249,973 cycles. Note that two (2) of the tests in Table 2 were intentionally aborted due to the high number of cycles without failure. Compared to Table 1, Table 2 clearly shows that the test drivetrain mainshaft that did undergo Method 700 is more robust than the test drivetrain mainshaft that did not undergo Method 700.

[0036] The description of the present disclosure is merely exemplary in nature, and variations that do not depart from the general meaning of the present disclosure are intended to be within the scope of the present disclosure. Such variations should not be regarded as a departure from the spirit and scope of the present disclosure.

Claims

[1] Torque transmission element having a reinforced fluid connection and comprising: a body member rotatable about an axis, the body member having an outer surface; and a fluid passage extending through the body member, the fluid passage having an inner surface; wherein the reinforced fluid port is in communication with the fluid passage, the reinforced fluid port having a mating surface connecting the outer surface of the body member to the inner surface of the fluid passage; and the reinforced fluid connection is obtained by applying a predetermined compressive load to the connection surface and applying a heat treatment process. [2] A torque transmission element according to claim 1, wherein applying the heat treatment process follows the application of the predetermined compressive load to the connecting surface. [3] A torque transmitting element according to claim 2, wherein the body member comprises a metal alloy having an alloy yield point; and wherein the predetermined compressive load is above the yield point of the alloy. [4] Torque transmission element according to claim 3, wherein: the reinforced fluid connection has a specified permissible dimensional tolerance; the specified pressure load includes an upper pressure load limit above which the reinforced fluid connection deforms outside a specified permissible dimensional tolerance; and the specified pressure load is lower than the upper pressure load limit. [5] Torque transmission element according to claim 3, wherein the predetermined compressive load is 6 to 8 percent above the yield point of the alloy. [6] Torque transmission element according to claim 3, wherein the metal alloy is a steel alloy. [7] The torque transmission element according to claim 3, wherein the heat treatment process comprises a carburizing heat treatment process or an induction heat treatment process. [8] Torque transmission element according to claim 3, wherein the fluid passage extends radially perpendicular to the axis of rotation. [9] Torque transmission element according to claim 3, wherein the torque transmission element is a shaft or a gear element. [10] The torque transmitting element of claim 3, wherein the interface defines a frustoconically shaped reinforced fluid port.

Images