WO2018022685A1

WO2018022685A1 - Method for control of a ball planetary type continuously variable transmission implementing long term life monitoring

Info

Publication number: WO2018022685A1
Application number: PCT/US2017/043841
Authority: WO
Inventors: Jeffrey M. DAVID; Gordon M. Mcindoe; T. Neil MCLEMORE; Patrick Sexton; Matthew Simister; Robert A. Smithson
Original assignee: Dana Limited
Priority date: 2016-07-29
Filing date: 2017-07-26
Publication date: 2018-02-01

Abstract

Provided herein is a control system for a multiple-mode continuously variable transmission having a ball-type variator. The control system has a transmission control module configured to receive a plurality of electronic input signals, and to determine a mode of operation from a plurality of control ranges based at least in part on the plurality of electronic input signals. The transmission control module includes a CVP control module. The CVP control module is adapted to implement a long term life monitoring process. The long term life monitoring process is configured to evaluate duration of operating time under load at the traction contact location on the ball surface and other traction contact components and adjust control parameters to extend the life of the traction contact locations.

Description

METHOD FOR CONTROL OF A BALL PLANETARY TYPE

CONTINUOUSLY VARIABLE TRANSMISSION IMPLEMENTING LONG TERM LIFE MONITORING

RELATED APPLICATION

The present application claims the benefit of U.S. Provisional

Application No. 62/368,290 filed on July 29, 2016, which is incorporated herein by reference in its entirety.

BACKGROUND

Continuously variable transmissions (CVT) and transmissions that are substantially continuously variable are increasingly gaining acceptance in various applications. The process of controlling the ratio provided by the CVT is complicated by the continuously variable or minute gradations in ratio presented by the CVT. Furthermore, the range of ratios that are available to be implemented in a CVT are not sufficient for some applications. A transmission is capable of implementing a combination of a CVT with one or more additional CVT stages, one or more fixed ratio range splitters, or some combination thereof in order to extend the range of available ratios. The combination of a CVT with one or more additional stages further complicates the ratio control process, as the transmission will have multiple configurations that achieve the same final drive ratio.

The different transmission configurations could for example, multiply input torque across the different transmission stages in different manners to achieve the same final drive ratio. However, some configurations provide more flexibility or better efficiency than other configurations providing the same final drive ratio.

Real world vehicle usage patterns indicate that the variator (CVP) portion of continuously variable transmissions may be subjected to long periods of constant operation at a fixed transmission speed ratio. Therefore, there is a need to monitor and control planet shear stress, cycles at a specific stress level, and location on the planet contact track of those stresses due to long term CVP health concerns. SUMMARY

Provided herein is a computer-implemented control system for a continuously variable transmission having a ball-type variator (CVP), the computer-implemented control system including: a digital processing device including an operating system configured to perform executable instructions and a memory device; a computer program including instructions executable by the digital processing device, the computer program including a software module configured to monitor and control the CVP; an input speed sensor adapted to provide an input speed signal to the software module; and an output speed sensor adapted to provide an output speed signal to the software module, wherein the software module is configured to execute a long term life monitoring process, the long term life monitoring process is configured to calculate and store an estimated life of the CVP and transmit mitigation commands to change the operating condition of the CVP based on the estimated life.

Provided herein is a computer-implemented method for controlling continuously variable transmission having a ball-type variator (CVP) provided with a ball in contact with a first traction ring assembly, a second traction ring assembly, a first sun member, and a second sun member, the method including the steps of: receiving a plurality of data signals provided by sensors located on the CVP, the plurality of data signals including: an input speed signal, an output speed signal, an input torque signal, and a CVP speed ratio signal; calculating and storing a signal indicative of a remaining life expectancy of a contact location between the ball and the first traction ring assembly and a contact location between the ball and the second traction ring assembly;

comparing the remaining life expectancy signal to a stored variable indicative of a total fatigue life; and issuing a plurality of mitigation command signals based on the comparison, wherein the mitigation commands change the operating condition of the CVP.

Provided herein is a computer-implemented method for extending operational life of traction components in a ball-type variator (CVP) having a plurality of balls in contact with a first traction ring assembly and a second traction ring assembly, the computer-implemented method including: receiving a plurality of data signals indicative of the operating condition of the CVP, the data signals including an input speed signal, an output speed signal, an input torque signal, and a CVP speed ratio signal; counting, by computer, the number of rotations of the balls during operation of the CVP; determining a plurality of discrete traction contact patch regions on the surface of the balls, wherein the discrete traction contact patch region corresponds to a location on the ball surface contacting the first traction ring assembly and the second traction ring assembly; calculating and storing a normal force at each discrete traction contact patch region to form a normal force distribution, wherein the normal force is based in part on the input torque signal and the CVP speed ratio signal; estimating a fatigue life expectancy based in part on the normal force distribution, wherein the fatigue life expectancy is indicative of cumulative operation of the CVP; and commanding a change in operating condition of the CVP based on the fatigue life expectancy.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Novel features of the preferred embodiments are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present embodiments will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the preferred embodiments are utilized, and the accompanying drawings of which:

Figure 1 is a side sectional view of a ball-type variator.

Figure 2 is a plan view of a carrier member that used in the variator of Figure 1.

Figure 3 is an illustrative view of different tilt positions of the ball-type variator of Figure 1. Figure 4 is a block diagram schematic of a transmission control system that could be implemented in a vehicle.

Figure 5 is a flow chart depicting a long term dither control process that is implementable in the transmission control system of Figure 4.

Figure 6 is a schematic diagram of the traction contact patch locations of the variator of Figure 1.

Figure 7 is a graph depicting bin contact stress distribution.

Figure 8 is a graph depicting bin subsurface shear stress distribution.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electronic controller is described herein that enables electronic control over a variable ratio transmission having a continuously variable ratio portion, such as a Continuously Variable Transmission (CVT), Infinitely

Variable Transmission (IVT), or variator. The electronic controller could be configured to receive input signals indicative of parameters associated with an engine coupled to the transmission. The parameters could include throttle position sensor values, accelerator pedal position sensor values, vehicle speed, gear selector position, user-selectable mode configurations, and the like, or some combination thereof. The electronic controller could also receive one or more control inputs. The electronic controller could determine an active range and an active variator mode based on the input signals and control inputs. The electronic controller could control a final drive ratio of the variable ratio transmission by controlling one or more electronic actuators and/or solenoids that control the ratios of one or more portions of the variable ratio transmission.

The electronic controller described herein is described in the context of a continuous variable transmission, such as the continuous variable transmission of the type described in U.S. Patent Application Number 14/425,842, entitled "3-Mode Front Wheel Drive And Rear Wheel Drive Continuously Variable Planetary Transmission" and Patent Cooperation Treaty Application Number PCT/US16/030930, entitled "Control Method of Synchronous Shifting of a Multi- Range Transmission Comprising a Continuously Variable Planetary

Mechanism", each assigned to the assignee of the present application and hereby incorporated by reference herein in its entirety. However, the electronic controller is not limited to controlling a particular type of transmission but rather, is optionally configured to control any of several types of variable ratio transmissions.

Provided herein are configurations of CVTs based on a ball-type variator, also known as CVP, for continuously variable planetary. Basic concepts of a ball-type Continuously Variable Transmissions are described in United States Patent No. 8,469,856 and 8,870,711 incorporated herein by reference in their entirety. Such a CVT, adapted herein as described

throughout this specification, includes a number of balls (planets, spheres) 1 , depending on the application, two ring (disc) assemblies with a conical surface contact with the balls, as input (first) traction ring assembly 2 and output (second) traction ring assembly 3, and an idler (sun) assembly 4 as shown on FIG. 1. In some embodiments, the output traction ring assembly 3 includes an axial force generator mechanism. The balls are mounted on tiltable axles 5, themselves held in a carrier (stator, cage) assembly having a first carrier member 6 operably coupled to a second carrier member 7. The first carrier member 6 rotates with respect to the second carrier member 7, and vice versa. In some embodiments, the first carrier member 6 is substantially fixed from rotation while the second carrier member 7 is configured to rotate with respect to the first carrier member, and vice versa. In one embodiment, the first carrier member 6 is provided with a number of radial guide slots 8. The second carrier member 7 is provided with a number of radially offset guide slots 9, as illustrated in FIG. 2. The radial guide slots 8 and the radially offset guide slots 9 are adapted to guide the tiltable axles 5. The axles 5 are adjustable to achieve a desired ratio of input speed to output speed during operation of the CVT. In some embodiments, adjustment of the axles 5 involves control of the position of the first 6 and second carrier members 7 to impart a tilting of the axles 5 and thereby adjusts the speed ratio of the variator. Other types of ball CVTs also exist, like the one produced by Milner, but are slightly different.

The working principle of such a CVP of FIG. 1 is shown in FIG. 3. The CVP itself works with a traction fluid. The lubricant between the ball and the conical rings acts as a solid at high pressure, transferring the power from the input ring, through the balls, to the output ring. By tilting the balls' axes, the ratio is changed between input and output. When the axis is horizontal, the ratio is one, as illustrated in FIG. 3, when the axis is tilted, the distance between the axis and the contact point change, modifying the overall ratio. All the balls' axes are tilted at the same time with a mechanism included in the carrier and/or idler. Embodiments disclosed herein are related to the control of a variator and/or a CVT using generally spherical planets each having a tiltable axis of rotation that is adjustable to achieve a desired ratio of input speed to output speed during operation. In some embodiments, adjustment of said axis of rotation involves angular misalignment of the planet axis in a first plane in order to achieve an angular adjustment of the planet axis in a second plane that is substantially perpendicular to the first plane, thereby adjusting the speed ratio of the variator. The angular misalignment in the first plane is referred to here as "skew", "skew angle", and/or "skew condition". In one embodiment, a control system coordinates the use of a skew angle to generate forces between certain contacting components in the variator that will tilt the planet axis of rotation. The tilting of the planet axis of rotation adjusts the speed ratio of the variator.

Real world vehicle usage patterns indicate that the variator (CVP) portion of continuously variable transmissions may be subjected to long periods of constant operation at a fixed transmission speed ratio. This concentrates wear on a narrow range of the planet traction surface. Long term monitoring and control for durability addresses long term CVP health concerns by monitoring planet shear stress, cycles at a specific stress level, and location on the planet contact track of those stresses. This information is used to calculate the remaining life for a given contact track location. Once it is determined that a region of the traction surface is approaching low remaining life multiple mitigation strategies can be employed. For example, mitigation strategies include, but are not limited to, random dither of the speed ratio within a fixed bound under steady state cruising, establishment of an avoidance region, or a ratio specific torque limit. In some embodiments, the mitigation strategy could result in a limp home mode that enables an end of life CVP to remain functional in a limited manner. As used here, the terms "operationally connected," "operationally coupled", "operationally linked", "operably connected", "operably coupled", "operably coupleable", "operably linked," and like terms, refer to a relationship (mechanical, linkage, coupling, etc.) between elements whereby operation of one element results in a corresponding, following, or simultaneous operation or actuation of a second element. It is noted that in using said terms to describe inventive embodiments, specific structures or mechanisms that link or couple the elements are typically described. However, unless otherwise specifically stated, when one of said terms is used, the term indicates that the actual linkage or coupling will take a variety of forms, which in certain instances will be readily apparent to a person of ordinary skill in the relevant technology.

For description purposes, the term "radial", as used herein indicates a direction or position that is perpendicular relative to a longitudinal axis of a transmission or variator. The term "axial" as used herein refers to a direction or position along an axis that is parallel to a main or longitudinal axis of a transmission or variator.

It should be noted that reference herein to "traction" does not exclude applications where the dominant or exclusive mode of power transfer is through "friction." Without attempting to establish a categorical difference between traction and friction drives herein, generally, these are understood as different regimes of power transfer. Traction drives usually involve the transfer of power between two elements by shear forces in a thin fluid layer trapped between the elements. The fluids used in these applications usually exhibit traction coefficients greater than conventional mineral oils. The traction coefficient (μ) represents the maximum available traction forces that would be available at the interfaces of the contacting components and is a measure of the maximum available drive torque. Typically, friction drives generally relate to transferring power between two elements by frictional forces between the elements. For the purposes of this disclosure, it should be understood that the CVTs described here could operate in both tractive and frictional applications. As a general matter, the traction coefficient μ is a function of the traction fluid properties, the normal force at the contact area, and the velocity of the traction fluid in the contact area, among other things. For a given traction fluid, the traction coefficient μ increases with increasing relative velocities of

components, until the traction coefficient μ reaches a maximum capacity after which the traction coefficient μ decays. The condition of exceeding the maximum capacity of the traction fluid is often referred to as "gross slip condition". Traction fluid is also influenced by entrainment speed of the fluid and temperature at the contact patch, for example, the traction coefficient is generally highest near zero speed and decays as a weak function of speed. The traction coefficient often improves with increasing temperature until a point at which the traction coefficient rapidly degrades.

As used herein, "creep", "ratio droop", or "slip" is the discrete local motion of a body relative to another and is exemplified by the relative velocities of rolling contact components such as the mechanism described herein. In traction drives, the transfer of power from a driving element to a driven element via a traction interface requires creep. Usually, creep in the direction of power transfer, is referred to as "creep in the rolling direction." Sometimes the driving and driven elements experience creep in a direction orthogonal to the power transfer direction, in such a case this component of creep is referred to as "transverse creep."

For description purposes, the terms "prime mover", "engine," and like terms, are used herein to indicate a power source. Said power source could be fueled by energy sources including hydrocarbon, electrical, biomass, solar, geothermal, hydraulic, and/or pneumatic, to name but a few. Although typically described in a vehicle or automotive application, one skilled in the art will recognize the broader applications for this technology and the use of alternative power sources for driving a transmission including this technology.

Those of skill will recognize that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein, including with reference to the transmission control system described herein, for example, could be implemented as electronic hardware, software stored on a computer readable medium and executable by a processor, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

Skilled artisans could implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present embodiments. For example, various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein could be implemented or performed with a general purpose processor or processing device, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device/discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor could be a microprocessor, but in the alternative, the processor could be any conventional processor, controller, microcontroller, or state machine. A processor could also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Software associated with such modules could reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD- ROM, or any other suitable form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor reads information from, and write information to, the storage medium. In the alternative, the storage medium could be integral to the processor. The processor and the storage medium could reside in an ASIC. For example, in one embodiment, a controller for use of control of the IVT includes a processor (not shown).

In some embodiments, the control system for a continuously variable transmission described herein includes a digital processing device, or use of the same. In further embodiments, the digital processing device includes one or more hardware central processing units (CPU) that carry out the device's functions. In still further embodiments, the digital processing device further comprises an operating system configured to perform executable instructions. In some embodiments, the digital processing device is optionally connected a computer network. In further embodiments, the digital processing device is optionally connected to the Internet such that it accesses the World Wide Web. In still further embodiments, the digital processing device is optionally connected to a cloud computing infrastructure. In other embodiments, the digital processing device is optionally connected to an intranet. In other embodiments, the digital processing device is optionally connected to a data storage device.

In some embodiments, the device includes a storage and/or memory device. The storage and/or memory device is one or more physical

apparatuses used to store data or programs on a temporary or permanent basis. In some embodiments, the device is volatile memory and requires power to maintain stored information. In some embodiments, the device is non-volatile memory and retains stored information when the digital processing device is not powered. In further embodiments, the non-volatile memory comprises flash memory. In some embodiments, the non-volatile memory comprises dynamic random-access memory (DRAM). In some embodiments, the non-volatile memory comprises ferroelectric random access memory (FRAM). In some embodiments, the non-volatile memory comprises phase- change random access memory (PRAM). In other embodiments, the device is a storage device including, by way of non-limiting examples, CD-ROMs, DVDs, flash memory devices, magnetic disk drives, magnetic tapes drives, optical disk drives, and cloud computing based storage. In further embodiments, the storage and/or memory device is a combination of devices such as those disclosed herein.

In some embodiments, the digital processing device includes an input device to receive information from a user. In some embodiments, the input device is a keyboard. In some embodiments, the input device is a pointing device including, by way of non-limiting examples, a mouse, trackball, track pad, joystick, or stylus. In some embodiments, the input device is a touch screen or a multi-touch screen. In other embodiments, the input device is a microphone to capture voice or other sound input. In other embodiments, the input device is a video camera or other sensor to capture motion or visual input. In still further embodiments, the input device is a combination of devices such as those disclosed herein.

In some embodiments, the control system disclosed herein includes at least one computer program, or use of the same. A computer program includes a sequence of instructions, executable in the digital processing device's CPU, written to perform a specified task. Computer readable instructions may be implemented as program modules, such as functions, objects, Application Programming Interfaces (APIs), data structures, and the like, that perform particular tasks or implement particular abstract data types. In light of the disclosure provided herein, those of skill in the art will recognize that a computer program may be written in various versions of various language. Referring now to FIG. 4, in one embodiment, a transmission controller 100 includes an input signal processing module 102, a transmission control module 104 and an output signal processing module 106. The input signal processing module 102 is configured to receive a number of electronic signals from sensors provided on the vehicle and/or transmission. The sensors optionally include temperature sensors, speed sensors, position sensors, among others. In some embodiments, the signal processing module 102 optionally includes various sub-modules to perform routines such as signal acquisition, signal arbitration, or other known methods for signal processing. The output signal processing module 106 is optionally configured to

electronically communicate to a variety of actuators and sensors. In some embodiments, the output signal processing module 106 is configured to transmit commanded signals to actuators based on target values determined in the transmission control module 104. The transmission control module 104 optionally includes a variety of sub-modules or sub-routines for controlling continuously variable transmissions of the type discussed here. For example, the transmission control module 104 optionally includes a clutch control sub- module 108 that is programmed to execute control over clutches or similar devices within the transmission. In some embodiments, the clutch control sub- module implements state machine control for the coordination of engagement of clutches or similar devices. The transmission control module 104 optionally includes a CVP control sub-module 110 programmed to execute a variety of measurements and determine target operating conditions of the CVP, for example, of the ball-type continuously variable transmissions discussed here. It should be noted that the CVP control sub-module 110 optionally incorporates a number of sub-modules for performing measurements and control of the CVP. One sub-module included in the CVP control sub-module 110 is described herein.

Referring now to FIG. 5, in some embodiment, the CVP control sub- module 110 is configured to implement a long term life monitoring process 120. The long term life monitoring process 120 begins at a start state 121 and proceeds to a block 122 where a number of signals are received. In some embodiments, the signals include an input speed signal, an output speed signal, an input torque signal, and a CVP speed ratio signal. The long term life monitoring process 120 proceeds to a block 123 where a command to run a cycle counter is issued. As described in more detailed herein, a cycle counter is implemented to track the number of ball or planet rotations. The long term life monitoring process 120 proceeds to a block 124 where calculations are performed to determine discrete traction contact locations on the surface of the balls. As used herein, the terms "traction contact location", "contact location", "contact patch", and "contact patch region" refer to a location on the ball surface in contact with the firsl traction ring, the second traction ring, or the sun ring(s). The long term life monitoring process 120 proceeds to a block 125 where calculations are performed to determine the normal force distribution in the contact patch regions based in part on the input torque signal. The long term life monitoring process 120 proceeds to a block 126 where calculations are performed to determine the remaining life per contact patch region based in part on the normal force distribution determined in the block 125. The long term life monitoring process 120 proceeds to an evaluation block 127 where the remaining life of the contact patch region determined in the block 126 is compared to a stored variable indicative of a fatigue life expectancy of the contact patch region. When the evaluation block 127 returns a false result, the long term life monitoring process 120 returns to the block 122. When the evaluation block 127 returns a positive result, indicating that the contact patch region is nearing the end of the fatigue life expectancy for rolling contact fatigue, the long term life monitoring process 120 proceeds to a block 128 where mitigation commands are issued and transmitted to other sub-modules in the CVP control sub-module 110. The long term life monitoring process 120 ends at an end state 130.

Referring to FIG. 6 and still referring to FIG. 5, in some embodiments, a cycle counter is implemented to track the number of planet (or ball) rotations as in the block 123 of the long term life monitoring process 120. In some embodiments, the surface velocity of rolling contact on the traction ring is calculated first. This is done with the traction radius and the ring speeds as follows.

Reaction = Rsun + RplanetO- + COs(cc_x)), Where Reaction 'S the traction radius, R_sun is the radius of the sun component, R_pi_anet '^s the radius of the ball, and a_x is the angle of the traction contact with respect to the longitudinal axis of the CVP.

Vring = ^ring * 2π * R_traction where V_ring is the velocity of the traction ring, and N_ring is the speed (rpm) of the traction ring.

In some embodiments, the radius of planet to ring and planet to sun contact surfaces are calculated from the tilt angle of the ball as follows.

Rpi = ^Rpianet^cos(.^ai + y)_> where R_pl is the radius of the planet to the first traction ring, R_pi_anet '^{s tne} radius of the ball, a is the angle of the first traction contact with respect to the longitudinal axis, and γ is the tilt angle of the ball axis of rotation.

Rp2 = R_Pianet^C0S(_. ^a2 ~ y)> where R_p2 is the radius of the planet to the second traction ring, and a₂ is the angle of the second traction contact with respect to the longitudinal axis of the CVP.

Rsi = Rpianet^cos(_. ^as ~ y). where R_sl is the radius of the planet to the first sun member, and a_s is the angle of the first sun contact with respect to the longitudinal axis of the CVP.

Rs2 = R_Pianet^C0S(^as + /). where R_s2 is the radius of the planet to the second sun member, and a_s is the angle of the second sun contact with respect to the longitudinal axis of the CVP. In some embodiments, the circumference of the individual planet contact tracks is found. The planet cycles are determined from ring surface velocity and the distance traveled in one planet rotation multiplied by the elapsed time, where dt is the software loop execution rate. The cycle counter for the sun contact is proportional to the relative contact circumference and the ring cycle counter.

The circumference of the first traction ring contact patch is

P circumf erence _r ~ * ^pl -

The circumference of the second traction ring contact patch is

P circumf erence _r2 ^ T * Rp2 -

The circumference of the first sun contact patch is P_Circumf erence _si = 2n * R_sl.

The circumference of the second sun contact patch is P_Circumference_s2 = 2n * R_s2.

The number of cycles at the first traction ring contact patch is

Ncycles rl * ^t.

r circumf erence _rl

The number of cycles at the second traction ring contact patch is

N_Cycles_r2 ⁼ „ ^~ * dt.

r circumf erence rl

The number of cycles at the first sun contact patch is

P 'ringcircumf erence_si

" cycles_sl cycles rl _D

r circumf erence n

The number of cycles at the second sun contact patch is

j. P ringcircumf erence_sl

"cycles_s2 "cycles_r2 * _D

^circum f erence rl Planet Contact Location and Bin Discretization

The traction patch contact width travels along a curved surface bounded by the gamma angle. Arc length of this surface is calculated as:

Lore = ^{ai+ a} *^Ymax * ^vi net _> where D_planet is the diameter of the ball. Transverse patch radius (b) ranges from a predetermined minimum value to a predetermined maximum value as a function of load. The peak contact stress has an elliptical distribution within that patch width. Utilizing an n point parabolic distribution across the minimum patch width, bin_width, results in the following calculation for the required number of bins, N_bins. Note that n sets minimum number of points to calculate stress distribution for the minimum load case. At maximum load the number of point used in the distribution grows. This is directionally correct, as it is the higher stress point that must be distributed accurately given that the planet life under high stress is lowest.

n * L_arc

Nbins = -^r ■ _ ^orc

vin_Wi_dth— —

'*bins

Arc length, number of bins, and bin width are all static calculations affected only by drive geometry. During operation the number of bins affected by the contact stress is a dynamic quantity that changes with load, for example input torque. For an equal parabolic distribution the number of affected bins, ^Nbins_affected_> should be rounded up to the nearest odd integer.

Table 1 below shows the results of the above calculation methods applied to an example CVP for a range of n-point distributions.

Table 1 : n - point Parabolic Stress Distribution Parameters For example purposes in the analysis that follows the 3-point minimum parabolic stress distribution resulting in 399 total bins is used. The bins are illustrated as dashed lines in FIG. 6. It should be appreciated that

implementation in a controller would balance the need for computational efficiency versus desired solution accuracy. Bin location convention is as shown in FIG. 6. For both ring contact tracks bin 1 is located nearest the R1 axle end of the planet, while bin 399 is nearest the R2 axle end of the ball. Therefore, at full overdrive R1 will contact at bin 1. Conversely, at full underdrive R2 will contact at bin 399.

Sun Contact Location and Bin Discretization

Referring still to FIG. 6, the sun s1 and sun s2 contact tracks can overlap (not simultaneously) the same region of the planet depending upon ratio. For the purposes of planet discretization the two sun contacts are transposed onto the upper region and included in the 399 bin discretization process. Thus, for a given ratio there are four unique contact points tracked simultaneously as they move across the planet surface.

For the purposes of sun life estimation, the contact is assumed to take place always on the same region of the sun with a constant center and a varying width as a function of load. Sun contact load will affect a region from 3 - 15 bins in width depending on load.

Contact Stress Distribution

Referring now to FIGS. 7 and 8, subsurface shear stress is used as the dominant factor in determination of remaining life. Rolling contact fatigue failure theory attributes the primary failure mode to subsurface shear stress induced crack propagation. The shear stress is concentrated at the center of the contact ellipse below the contact surface along the z-axis. The crack then propagates to the surface and initiates spalling, ultimately leading to failure. Peak stress, a_maXi is defined at the center of the contact ellipse, then the stress distribution n steps from the center, σ_0±η, is found with the following parabolic regressio

Concern is with the distribution in the y direction only across the width of the contact surface, therefore x = 0, leaving the following equation in terms of discrete bin steps and current contact patch width.

The net result is a traveling stress wave moving across the width of the planet contact track surface as ratio changes with both a variable width (3 - 15 bins) and a variable amplitude ( 0 - Omax). This is shown in FIG. 7 where max load is the drive design limit and min load is preload only. It should be appreciated that the mathematical model of stress at the contact location is a function of the operating torque being transmitted through the CVP and the speed ratio of the CVP.

Subsurface shear stress shows a similar parabolic distribution as seen in FIG. 8. A negative sign convention is used for shear stress in this plot to visualize the fact that is occurs below the surface.

Without being repetitive, it follows that a similar parabolic distribution can be calculated for contact normal force, contact stress, subsurface shear stress, resultant shear stress depth, resultant subsurface tensile stress, etc. The model is configurable to calculate any of the above as necessary for

implementation of a specific fatigue life model. An example of a fatigue life model is presented below. Additional implementations of other well-known fatigue life models are possible.

Remaining Life Index

Life remaining is calculated of each of the 399 planet contact bins and each of the 15 sun s1 and sun s2 contact bins. The sun contact is often the first to wear based on the static distribution of stress (stress on edges of sun contact may intermittently fall to zero while center of contact always experiences stress of some level). There are some specific duty cycles where a planet would fail before the sun. For example, extended operation at a specific ratio such that a ring and sun contact the same planet track location may satisfy this criteria.

Fatigue life model based on normal force distribution across contact patch width is computed as follows.

L = fatigue life (1e6 cycles)

Qc = dynamic normal force capacity (N)

Q = normal force (N)

In some embodiments, the life equation is implemented as a 1-d lookup table across the range of expected normal force values between preload only and full load capacity and then life remaining is computed as in the block 126 of the long term life monitoring process 120. In some embodiments, Q_c is optionally correlated with durability test data to establish a value for use in a real time implementation.

The life consumed is ^Ncycl es

L_consumed =

L

The life remaining is L 'remaining = 1 - ∑L, consumed · Control and Mitigation Strategy

Examples of potential mitigation strategies to lower the input torque to the CVP are provided herein. Engine torque limiting is the primary option if the life limit is reached by the sun as a ratio change does not alter the sun contact point. An engine torque limit can be determined real time based on the minimum remaining life component as follows:

Teng imit ⁼ Tnin(L_sll L_s2, Lp f (index)) -

Limiting the engine torque supplied to the CVP reduces the input torque to the CVP.

The minimum sun 1 and sun 2 life is a static quantity (non-ratio dependent) whereas the planet life is a function of the current ratio command and is computed real time based on the four indices of specific planet contact tracks. Additionally, based on a minimum remaining life a random dither function is enabled to distribute life across a broader region of contact (applies to planet only, sun contact is fixed and is likely the constraint driving minimum life limits). This is optionally enabled globally or as a function of a specific index value to avoid low life regions of the planet only. Specific implementation of the dither function is described in Patent Cooperation Treaty Application Number PCT/US17/015037, which is hereby incorporated herein. For example, dither of speed ratio is either random, sinusoidal, or step functions. In some embodiments, the dither enable function is used to specify a ratio change command (direction of which is based on specific operating conditions) until such time as dither enable is false after reaching a portion of the planet with sufficient remaining life. Software optionally establishes a ratio avoidance zone from this or could allow the ratio to cycle into and out of the low life zone repeatedly, thus mimicking the appearance of random dither. Coordination between engine and transmission controls is optionally used to suppress the driver perception of the dither function (manipulation of TCC slip, throttle servo intervention, etc.).

It should be noted that the description above has provided dimensions for certain components or subassemblies. The mentioned dimensions, or ranges of dimensions, are provided in order to comply as best as possible with certain legal requirements, such as best mode. However, the scope of the embodiments described herein are to be determined solely by the language of the claims, and consequently, none of the mentioned dimensions is to be considered limiting on the inventive embodiments, except in so far as any one claim makes a specified dimension, or range of thereof, a feature of the claim.

The foregoing description details certain preferred embodiments. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the preferred embodiments are practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the embodiment with which that terminology is associated. While preferred embodiments of the present embodiments have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the preferred embodiments. It should be understood that various alternatives to the embodiments described herein could be employed in practice. It is intended that the following claims define the scope of the preferred embodiments and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

WHAT IS CLAIMED IS:

1. A computer-implemented control system for a continuously variable transmission having a ball-type variator (CVP), the computer- implemented control system comprising:

a digital processing device comprising an operating system configured to perform executable instructions and a memory device;

a computer program including instructions executable by the digital processing device, the computer program comprising a software module configured to monitor and control the CVP;

an input speed sensor adapted to provide an input speed signal to the software module; and

an output speed sensor adapted to provide an output speed signal to the software module,

wherein the software module is configured to execute a long term life monitoring process, the long term life monitoring process is configured to calculate and store an estimated life expectancy of the CVP and transmit command signals to change the operating condition of the CVP based on the estimated life.

2. The computer-implemented control system of Claim 1 , wherein the long term life monitoring process is configured to receive a signal indicative of an input torque to the CVP. 3. The computer-implemented control system of Claim 2, wherein the long term life monitoring process is configured to calculate a signal indicative of a CVP speed ratio based on the input speed signal and the output speed signal. 4. The computer-implemented control system of Claim 3, wherein the long term life monitoring process is configured to calculate a normal force distribution on the ball at a plurality of traction contact locations.

5. The computer-implemented control system of Claim 4, wherein the command signals to change the operating condition of the CVP include a command to change an input torque to the CVP. 6. The computer-implemented control system of Claim 5, wherein the command signals to change the operating condition of the CVP include a command to change the CVP speed ratio.

7. A computer-implemented method for controlling a continuously variable transmission having a ball-type variator (CVP) provided with a ball in contact with a first traction ring assembly, a second traction ring assembly, a first sun member, and a second sun member, the method comprising the steps of:

receiving a plurality of data signals provided by sensors located on the CVP, the plurality of data signals comprising:

an input speed signal,

an output speed signal,

an input torque signal, and

a CVP speed ratio signal;

calculating and storing a signal indicative of a remaining life of a contact location between the ball and the first traction ring assembly and a contact location between the ball and the second traction ring assembly;

comparing the remaining life signal to a stored variable indicative of a fatigue life expectancy; and

issuing a plurality of mitigation command signals based on the comparison, wherein the mitigation commands change the operating condition of the CVP.

8. The computer-implemented method of Claim 7, wherein issuing a plurality of mitigation command signals further comprises commanding a reduction in input torque to the CVP.

9. The computer-implemented method of Claim 7, wherein issuing a plurality of mitigation command signals further comprises commanding a change in speed ratio of the CVP.

10. The computer-implemented method of Claim 7, further comprising the step of counting the number of rotations of the ball at the contact between the ball and the first traction ring assembly and at the contact between the ball and the second traction ring assembly.

11. The computer-implemented method of Claim 10, further comprising the step of determining a plurality of contact patch regions, wherein the contact path regions correspond to the contact between the ball and the first traction ring assembly and the contact between the ball and the second traction ring assembly.

12. The computer-implemented method of Claim 7, further comprising the step of calculating and storing a signal indicative of a remaining life expectancy of a contact location between the ball and the first sun member and a contact location between the ball and the second sun member.

13. A computer-implemented method for extending operational life of traction components in a ball-type variator (CVP) having a plurality of balls in contact with a first traction ring assembly and a second traction ring assembly, the computer-implemented method comprising:

receiving a plurality of data signals indicative of the operating condition of the CVP, the data signals comprising an input speed signal, an output speed signal, an input torque signal, and a CVP speed ratio signal;

counting, by computer, the number of rotations of the balls during operation of the CVP;

determining a plurality of discrete traction contact patch regions on the surface of the balls, wherein the discrete traction contact patch region corresponds to a location on the ball surface contacting the first traction ring assembly and the second traction ring assembly; calculating and storing a normal force at each discrete traction contact patch region to form a normal force distribution, wherein the normal force is based in part on the input torque signal and the CVP speed ratio signal;

estimating a fatigue life expectancy based in part on the normal force distribution, wherein the fatigue life expectancy is indicative of cumulative operation of the CVP; and

commanding a change in operating condition of the CVP based on the fatigue life expectancy.

14. The computer-implemented method of Claim 13, wherein commanding a change in operating condition of the CVP further comprises commanding a reduction in input torque to the CVP.

15. The computer-implemented method of Claim 13, wherein commanding a change in operating condition of the CVP further comprises commanding a change in speed ratio of the CVP.

16. The computer-implemented method of Claim 13, wherein commanding a change in operating condition of the CVP further comprises commanding a random dither in the speed ratio of the CVP. 7. The computer-implemented method of Claim 13, wherein determining a plurality of discrete traction contact patch regions further comprises calculating a traction patch contact width based in part on the size of the ball and an angle of the contact location between the ball and the first traction ring assembly and the second traction ring assembly.

18. The computer-implemented method of Claim 17, wherein determining a plurality of discrete traction contact patch regions further comprises determining a quantity of discrete traction contact patch regions based in part on the input torque of the CVP.

19. The computer-implemented method of Claim 13, wherein estimating a fatigue life expectancy further comprises calculating the subsurface shear stress at the traction contact patch region.

20. The computer-implemented method of Claim 15, wherein commanding a change in speed ratio of the CVP further comprises rotating a CVP carrier member to change a tilt angle of each ball.