Torque transmitting member with strengthened fluid

Abstract

A torque transmitting member with reinforced fluid ports and a method of making the same. The torque transmitting member includes a body member formed of a steel alloy and is rotatable about a rotational axis. The body member includes an outer surface, an inner surface defining a fluid passage extending through the body, and a fluid port in communication with the fluid passage. The fluid port includes a port surface connecting an outer surface of the body to an inner surface of the fluid channel. A compressive load above the yield point of the steel alloy is applied to the port surface by using a steel mandrel having a hardness greater than 60 HRC. After removing the compressive load from the port surface, the body member is subjected to a heat treatment process to form a hardened layer.

Description

Technical Field

[0001] The present disclosure relates to a torque transmitting member having a fluid passage, and more particularly to a torque transmitting member having an enhanced fluid port for the fluid passage. Background Art

[0002] Modern vehicles with traditional internal combustion engines (ICE), electric vehicles with electric engines, and hybrid vehicles with ICE and electric engines utilize gearboxes (also referred to as transmissions and differentials in the drivetrain) to transfer torque from the engine to one or more drive wheels to propel the vehicle. These engines, transmissions, and differentials are composed of multiple torque transfer components (such as rotatable shafts and gear components). In order to improve durability and enhance fuel efficiency, these torque transfer components have fluid channels to receive and distribute lubricating fluids (such as engine oil, gear oil, etc.). Such internal fluid channels can also be configured to distribute coolant to maintain the operation of such engines, transmissions, and / or differentials within nominal operating temperatures.

[0003] Lubricating fluid and / or coolant is introduced into and discharged from the fluid passages of the torque transfer member through fluid ports that communicate with the fluid passages. These fluid ports are typically formed by drilling or boring holes or openings through the surface of the torque transfer member. When forming the openings of the torque transfer member, removing material may have a negative impact on the overall durability and performance of the torque transfer member.

[0004] While current torque transmitting members having fluid ports and methods of making the same serve their purpose, there remains a need to improve the durability and performance of torque transmitting members. Summary of the invention

[0005] According to several aspects, a torque transfer member with a reinforced fluid port is disclosed. The torque transfer member includes a body member rotatable about an axis, a fluid channel extending through the body, and a fluid port communicating with the fluid channel. The body member includes an outer surface, the fluid channel includes an inner surface, and the fluid port includes a port surface connecting the outer surface of the body member to the inner surface of the fluid channel. The reinforced port is obtained by applying a predetermined compressive load to the port surface and then performing a final heat treatment process.

[0006] In another aspect of the present disclosure, the body member includes a metal alloy having an alloy yield point. The predetermined compressive load is greater than the alloy yield point.

[0007] In another aspect of the present disclosure, the strengthening fluid port includes a predetermined acceptable dimensional tolerance. The predetermined compressive load includes an upper compressive load limit, above which the strengthening fluid port is permanently deformed beyond the predetermined acceptable dimensional tolerance. The predetermined compressive load is less than the upper compressive load limit. The predetermined compressive load is 6% to 8% higher than the yield point of the alloy.

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

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

[0010] In another aspect of the present disclosure, the port surface defines a frusto-conical enhanced fluid port.The torque transmitting member may be a rotatable shaft or a gear member.

[0011] According to several aspects, a method of manufacturing a torque transfer member having a reinforced fluid port is disclosed. The method includes providing a metal workpiece having a port surface surrounding a fluid passage opening, applying a compressive load to the port surface using a mandrel, and heat treating the metal workpiece. The metal workpiece includes a yield point. The compressive load is above the yield point.

[0012] In another aspect of the present disclosure, the port surface defines a fluid port having a predetermined acceptable tolerance. Applying a compressive load to the port surface includes applying a limited compressive load to avoid deformation of the fluid port beyond the predetermined tolerance. The compressive load is 5% to 6% higher than the yield point of the metal workpiece. The metal workpiece is a steel alloy.

[0013] According to several aspects, a method of manufacturing a torque transfer member is provided. The method includes providing a workpiece having a low carbon steel alloy, wherein the workpiece includes a machined fluid port defined by a port surface; applying a predetermined compressive load to the port surface using a mandrel, wherein the predetermined compressive load is above a yield point of the steel alloy; removing the compressive load from the port surface; and heat treating the workpiece after removing the compressive load from the port surface. Prior to heat treating the workpiece, the hardness of the steel alloy is less than 25 Rockwell C hardness (HRC). The predetermined compressive load is 5% to 6% higher than the yield point of the steel alloy. The torque transfer member can be a torque transfer shaft or a gear member.

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

[0015] In another aspect of the present disclosure, the mandrel is formed of a tool steel having a hardness greater than 60 HRC and includes a tapered portion or a spherical portion operable to apply a compressive load to the port 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 intended 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 illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0018] Figure 1 is a plan view of an electric vehicle having an electric drive unit (EDU) according to an exemplary embodiment;

[0019] Figure 2 is an illustration of a cross-sectional view of an EDU having a plurality of torque transmitting members according to an exemplary embodiment;

[0020] Figure 3A and Figure 3B is a diagram of an exemplary torque transmitting member;

[0021] Figure 4A and Figure 4B is an illustration of applying a compressive load on a surface of a fluid port using a mandrel according to an exemplary embodiment;

[0022] Figure 5 is a detailed view of a fluid port according to an exemplary embodiment;

[0023] Figure 6 is an alternative embodiment of a mandrel; and

[0024] Figure 7 is a block flow diagram of a method of manufacturing a torque transmitting member having enhanced fluid ports. DETAILED DESCRIPTION

[0025] 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 accompanying drawings, wherein like reference numerals represent corresponding parts in the several drawings. The drawings are not necessarily drawn 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 as limiting, but rather as a representative basis for teaching those skilled in the art how to practice the disclosed concepts.

[0026] Torque transfer components of vehicle transmission systems typically have machined openings for lubrication purposes, such as oil holes formed in a green steel workpiece. Machining of these openings may damage the original surface integrity and grain flow in the area surrounding the machined openings and introduce high stresses, thereby shortening the service life. The following disclosure provides a torque transfer component with a reinforced fluid port, and a method of applying a compressive load to the fluid port surface around the machined opening using a specially designed tool that will compressively deform the port surface material. The compressively deformed green material undergoes a recrystallization process in a final heat treatment process, resulting in a refinement of the grain size, which will improve the fluid port surface finish and provide a remedy for surface grain flow damage, thereby improving the strength and toughness of the fluid port and torque transfer component.

[0027] Figure 1 1 is a schematic diagram 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 having front wheels 106A, 106B and rear wheels 108A, 108B. The front wheels 106A, 106B and the rear wheels 108A, 108B are each rotatably positioned near a respective corner of the body 104. The EDU includes three (3) modules: a power electronics device 110, an electric motor 112, and a transmission 114. The power electronics device is responsible for converting a direct current (DC) voltage from a rechargeable battery (not shown) into a three-phase alternating current (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 to one or more of the wheels 106A, 106B, 108A, 108B through a gearbox 114 and a mechanical linkage 116 to propel the vehicle 100.

[0028] Figure 2 1 is an illustration of a cross-sectional view of the EDU 102. The motor 112 includes a stator 124, a rotor 126 rotatable relative to the stator 124, a rotor shaft 128 splined to the rotor 126, and a first gear member 130 splined to the rotor shaft 128. The first gear member 130 meshes with a second gear member 132 splined to a torque transfer shaft 134. The torque transfer shaft 134 is rotatably supported by a rolling element bearing 136. The torque transfer shaft 134 includes a third gear member 138 meshed with a torque distribution gear mechanism 140 (also referred to as a differential unit 140).

[0029] In operation, the motor 112 generates torque that is output through the rotor shaft 128. The torque transfer shaft 134 then transmits 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-106B, 108A-108B to propel the vehicle 100. The torque transfer shaft 134 undergoes a heat treatment process to form a hardened layer to improve wear resistance while retaining the toughness and ductility of the mild steel core. The heat treatment process may include carburizing, in which carbon atoms are diffused into the surface of the mild steel shaft to form a carbon-rich layer and quench hardening. In an alternative embodiment, the heat treatment process may include induction heating of the high carbon steel core and quench hardening.

[0030] Although vehicle 100 is described as a passenger car, other examples of vehicles include, but are not limited to, land vehicles such as motorcycles, trucks, sport utility vehicles (SUVs), and recreational vehicles (RVs), as well as non-land vehicles including watercraft and aircraft. It should be understood that although an electric vehicle is described, the disclosure of torque-transmitting members (such as torque-transmitting shafts and gear members) also applies to torque-transmitting members on conventional internal combustion vehicles and hybrid vehicles.

[0031] Figure 3A and Figure 3B A non-limiting example of a rotatable torque transfer member is shown, such as a gear member 300A and an output shaft 300B disposed about rotational axes A, A', respectively. Each torque transfer member 300A, 300B includes an internal passage 302A, 302B configured to convey a fluid and at least one fluid port 304A, 304B, 306A. A fluid port is defined as the area surrounding an inlet opening or an outlet opening of a fluid passage. The fluid ports 304A, 304B are shown as being perpendicular to the rotational axes A, A', respectively. The fluid port 306A is located at Figure 3A 304A, 304B, 306A are shown parallel to the rotation axis A. Each fluid port 304A, 304B, 306A may be an inlet port or an outlet port. The fluid may be a lubricating fluid such as gear oil or a coolant such as ethylene glycol.

[0032] Figure 4A A cross-sectional view of a portion of a torque transfer member 400 is shown, the torque transfer member 400 having a fluid port 402 surrounding an opening 404 leading to a fluid passage 408 and a spindle 450 having a tapered portion 452 spaced from the fluid port 402. The torque transfer member 400 can be a torque transfer member of the gear member 300A or the torque transfer shaft 300B. The torque transfer member 400 includes an inner surface 406 defining the fluid passage 408 and an outer surface 410 defining the opening 404.

[0033] Just like Figure 5As shown, the fluid port 402 includes a chamfered port surface 412 that intersects the outer surface 410 and the inner surface 406 of the fluid passage 408 to define a frusto-conical fluid port 402. Figure 4A , Figure 4B and Figure 5 , the fluid port 402 is in communication with the fluid passage 408. The tapered portion 452 of the mandrel 450 includes a form factor capable of abutting the port surface 412 of the fluid port 402, such as Figure 4B shown.

[0034] The mandrel 450 is made of tool steel having a hardness greater than 60 Rockwell C hardness (HRC) and a contact portion 452 operable to abut the port surface 412 of the fluid port 402. The non-restrictive contact portion 452 shown includes a taper having a space angle α between 30° and 60°. The mandrel 450 can be mounted on a press (not shown) that is operable to press the mandrel 450 onto the port surface 412 of the fluid port 402. During the pressing process, the torque transfer member 400 is supported without any movement. Prior to heat treatment, the port surface 412 of the fluid port 402 is pressed to yield the material and change the grain flow characteristics in the region 470, which improves durability (i.e., increases fatigue life).

[0035] Figure 7 is a block flow diagram of a method of manufacturing a rotatable torque transfer component having enhanced fluid ports for improved durability (method 700). Figure 7 and Figure 4A , Figure 4B and Figure 5 , the method 700 begins at frame 702, in which a green state torque transfer member 400 is provided. The torque transfer member 400 can be formed of a metal alloy, including but not limited to 5120, 1040, 8620 steel alloys. The green state means that the torque transfer member 400 has not undergone a final hardening heat treatment process and has a hardness of less than 25 HRC. In the non-limiting embodiment shown, the torque transfer member 400 includes a fluid channel 408 and a fluid port 402 surrounding an opening 404 that communicates with the fluid channel 408. The fluid port 402 includes a port surface 412 that defines a frustoconical fluid port 402 surrounding the opening 404. Relative to the outer surface 410 of the torque transfer member 400 at the intersection between the outer surface 410 and the port surface 412, the port surface 412 includes an angle β between 30 degrees and 60 degrees.

[0036] Proceeding to box 704, the mandrel 450 has a tapered portion 452 capable of abutting the port surface 412 of the fluid port 402. The mandrel 450, which is axially aligned with the opening 404, is moved axially toward the opening 404 until the tapered portion 452 presses against the port surface 412. In other words, the tapered portion 452 of the mandrel 450 presses against the port surface 412 of the frusto-conical fluid port 402.

[0037] Proceeding to box 706, a predetermined compressive load is applied to the port surface 412 by the tapered portion 452 of the mandrel 450. A sufficient amount of force F is applied to the port surface 412 by the mandrel 450 until the compressive load acting on the port surface 412 exceeds the yield point of the metal alloy, but is less than the amount of force required to deform the port surface 412 of the fluid port 402 beyond an acceptable tolerance. The yield point is defined as the point on the stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, the metal alloy will deform elastically and return to its original shape after the applied stress is removed. Once the yield point is exceeded, part of the deformation will be permanent and irreversible, referred to as plastic deformation.

[0038] Preferably, the force is applied to produce a compressive load of 5% to 6% above the yield point of the metal alloy. Although the mandrel is shown as having a tapered portion, the mandrel may have a Figure 6 A spherical portion is shown in place of the conical portion 652. The spherical portion implements a concave curvature 654 in the surface of the plastically deformed fluid port 402, thereby further enhancing the strength of the fluid port 402 by distributing stress around the fluid port 402.

[0039] Proceeding to box 708, the mandrel 450 is removed and the torque transfer member 400 is subjected to a final heat treatment process, such as carburizing and quench hardening, or induction heating and quench hardening. The plastically deformed green state metal alloy of the fluid port 402 is subjected to a recrystallization process during the heat treatment process. Recrystallization causes a refinement of the grain size, which increases the toughness of the surface 412 of the fluid port 402, including the direct region 470 or region 470 of the torque transfer member 400 surrounding the fluid port 400.

[0040] Tables 1 and 2 below are the durability test results of the transmission system main shaft. Table 1 shows the durability test results of the transmission system main shaft that has not been tested by method 700. Table 2 shows the durability test results of the transmission system main shaft that has been tested by method 700.

[0041]

[0042] Table 1

[0043]

[0044] Table 2

[0045] The durability test was a fatigue test with maximum, minimum and average torsional loads of 3952, 50 and 2001 Newton meters (NM) respectively, with corresponding cyclic load amplitudes, minimum load to maximum load ratio R = -1 (complete reverse load) amplitudes, and R = 0 load ranges of 1951, 2776.5 and 3926.92 respectively. The test plan was designed to run until the structural integrity of the test drive system main shaft failed due to fracturing or fracture.

[0046] Referring to Table 1, the test transmission system spindles to which method 700 was not applied experienced failures between 141,150 and 615,255 cycles. Referring to Table 2, the test transmission system spindles to which method 700 was applied experienced failures at more than 1,249,973 cycles. It should be understood that two (2) of the tests in Table 2 were intentionally stopped due to high cycle counts without failure. Compared to Table 1, Table 2 clearly shows that the test transmission system spindles to which method 700 was applied were more robust than the test transmission system spindles to which method 700 was not applied.

[0047] 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 fall within the scope of the present disclosure. These variations should not be regarded as departing from the spirit and scope of the present disclosure.

Claims

1. A torque transfer member having an enhanced fluid port, comprising: a body member rotatable about an axis, wherein the body member comprises an outer surface; a fluid passage extending through the body member, wherein the fluid passage includes an inner surface; and an enhanced fluid port in communication with the fluid passage, wherein the enhanced fluid port includes a port surface connecting an outer surface of the body member to an inner surface of the fluid passage; and The enhanced fluid port is obtained by applying a predetermined compressive load to the port surface and performing a heat treatment process.

2. The torque transmission member according to claim 1, wherein: The heat treatment process is applied after applying the predetermined compressive load to the port surface.

3. The torque transmission member according to claim 2, wherein: The body member includes a metal alloy having an alloy yield point; and wherein the predetermined compressive load is greater than the alloy yield point.

4. The torque transmitting member according to claim 3, wherein: The enhanced fluid port includes a predetermined acceptable dimensional tolerance; The predetermined compressive load includes an upper compressive load limit above which the enhanced fluid port will deform beyond the predetermined acceptable dimensional tolerance; and The predetermined compression load is less than the compression load upper limit.

5. The torque transmission member according to claim 3, wherein: The predetermined compressive load is 6% to 8% higher than the alloy yield point.

6. The torque transmitting member according to claim 3, wherein: The metal alloy is a steel alloy.

7. The torque transmitting member according to claim 3, wherein: The heat treatment process includes one of the following: a carburizing heat treatment process and an induction heating treatment process.

8. The torque transmitting member according to claim 3, wherein: The fluid channel extends radially perpendicular to the rotation axis.

9. The torque transmitting member according to claim 3, wherein: The torque transmitting member is one of: a shaft and a gear member.

10. The torque transmitting member according to claim 3, wherein: The port surface defines a frusto-conical intensification fluid port.

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