Continuously Variable Transmission and Control

This invention relates to a continuously variable transmission and controls.

Continuously variable ratio transmissions are employed in vehicles to provide efficient drive systems. The transmission ratio can be changed in a continuous manner from a maximum underdrive ratio to a maximum overdrive ratio. This permits the engine to be operated at either the best fuel consumption area or the best performance area. Vehicle speed can be maintained at a substantially constant level while the transmission ratio is varied to attain a desired vehicle speed as requested by an operator.

The most currently used continuously variable transmissions are the flexible belt type due mainly to the advent of the flexible steel belt which runs against steel sheaves. The sheaves of the input and output pulleys are movable axially to adjust the radius at which the belt turns. The sheaves are moved to hydraulic pressure which is distributed from a control valve.

It is an object of this invention to provide an improved control for a continuously variable transmission of the flexible belt type.

In one aspect of this invention, a stepper motor and a control valve are provided to control the speed ratio between an input member and an output member of a flexible belt type continuously variable transmission.

In another aspect of this invention, the stepper motor receives a count signal from the control to establish the commanded position and a speed ratio of the continuously variable transmission through movement of the control valve.

In yet another aspect of this invention, the stepper motor is given a step count to rapidly move the valve to permit a ratio change in an underdrive direction.

FIG. 1 is a schematic representation of a continuously variable transmission and electro-hydraulic controls therefore.

FIG. 2 is a portion of an algorithm which controls the speed ratio within the continuously variable transmission.

FIG. 3 is another portion of the algorithm which controls the speed ratio within the continuously variable transmission.

FIG. 4, is a graph representing the relation between speed ratio and sheave travel and Forcemotor Counts.

FIG. 5 is a diagrammatic representation of a portion of the hydraulic control for a continuously variable transmission.

FIG. 6 is an enlarged view of the hydraulic control shown in FIG. 5.

The schematic representation of FIG. 1 describes a continuously variable transmission generally designated 10 including a torque converter and torque converter clutch 12, a continuously variable transmission (CVT) 14 and a forward/reverse planetary gearset 16 disposed between the torque converter and the CVT 14.

The torque converter 12 is driven by an engine 18 to provide power to the continuously variable transmission 14. The planetary gearset 16 includes a sun gear 20, a ring gear 22 and a compound carrier assembly 24. The ring gear 22 is groundable through a stationary clutch 26 and the carrier 24 and sun gear 20 are interconnectable through a selectively engageable rotating clutch 28.

The carrier 24 is drivingly connected with an output shaft 30 of the torque converter and torque converter clutch 12 and the sun gear 20 is connected through a transmission input shaft 32 with an input member or adjustable sheave assembly 34. The adjustable sheave assembly 34 is connected with an output member or adjustable sheave assembly 36 by means of a flexible belt member 38. These types of devices are well known in the art such that a more elaborate description is not believed necessary for those skilled in the art.

The stationary clutch 26 when engaged will provide a reverse drive between the shaft 30 and the sun gear 20 which will cause the continuously variable transmission 14 to operate at a reverse ratio. The engagement of the rotating clutch 28 will cause a 1:1 drive between the shaft 30 and the input member 34 thereby causing a forward drive within the transmission.

The output member 36 is drivingly connected with a final drive gear 40 which in turn is connected with a final drive gear 42. The final drive gear 42 is drivingly connected with a conventional differential gearset 44 to provide an output from the continuously variable transmission 14.

The sheave assemblies 34 and 36 are controlled by hydraulic pressure in chambers 46 and 48, respectively. The pressure utilized in the chambers 46 and 48 is controlled by an electro/hydraulic control system which includes a conventional positive displacement pump 50 which delivers fluid pressure to a fluid pressure regulator 52. The pressure regulator 52 then establishes the maximum system pressure within the control system and delivers that pressure through a passage 54 to a primary sheave limit valve 56.

The fluid pressure in passage 54 is limited by a line limit valve 60 when the maximum system pressure is satisfied in passage 54 the regulator valve 52 will distribute fluid pressure to a passage 58 which includes the line limit valve 60 for limiting the pressure within the passage 58 to a predetermined amount. The passage 58 communicates with a torque converter clutch control valve 61 and a torque converter clutch valve 62. These two valves operate in a conventional manner and control the pressure and flow of fluid to the torque converter and torque converter clutch assembly 12.

In the position shown, the assembly 12 is in the disengaged or clutch released position and all of the power is transmitted hydro-dynamically in a well known manner. When the torque converter clutch valve 62 is shifted through the control pressure operation, the clutch portion of the assembly 12 is engaged and the engine has a direct drive the planetary gear arrangement 16.

The passage 54 is also connected to a manual valve 66 through a clutch control valve 68 as limited by the valve 60. The manual valve 66 is movable by an operator through a lever 70 to a plurality of operating conditions including Park "P", Reverse "R", Neutral "N", Drive "D", Intermediate "INT" and Low "LO". The lever 70 is manipulated linearly in a slot 72 to the drive positions above enumerated. The slot 72 also has a side or adjacent slot 74 which permits the driver to preselect a number of transmission ratios as will be described later.

The clutch control valve 68 provides the necessary pressure to engage the clutches 28 and 26. The pressure distributed by the clutch control valve 68 is controlled by a variable bleed solenoid valve 76 which permits the electronic control system to adjust the engaging and disengaging pressure of the clutches 26 and 28.

The fluid pressure in passage 54 is connected to a ratio control valve 84 and through a passage 78 to the primary limit valve 56. This valve 56 limits the pressure distributed to the chamber 46. An actuator control 80 includes a ratio control motor 82, the ratio control valve 84, and a feedback arm 86 which is connected to a portion of the sheave assembly 34. The arm 86 is connected to the movable sheave of the sheave assembly 34 such that the position of the sheave assembly is always known to the control system.

When the control motor 82 is actuated as will be described later, the control valve 84 is manipulated such that fluid pressure is increased at the sheave assembly 34 or decreased at the sheave assembly 34. If the fluid pressure is increased at the sheave assembly 34, the ratio within the continuously variable transmission 14 will change from an underdrive ratio shown toward an overdrive position. If the continuously variable transmission 14 is established at an overdrive or above a minimum underdrive ratio and the pressure at the control valve 84 is relieved, the ratio within the continuously variable transmission 14 will move toward an underdrive ratio.

The pressure output or pressure established by the regulator valve 52 is also variable such that a control function is provided by a pulse width modulated line control valve 88. The line control valve 88 has a pulse width modulated solenoid, which is a well known device, and is adapted to deliver a control pressure through a passage 90 to the regulator valve 52. The pressure in the passage 90 is increased to cause an increase in the output of pressure regulator 52 and decreased to cause a decrease in line pressure.

The ratio within the continuously variable transmission 14 is preferably controlled by a conventional programmable digital computer which is programmed to operate the algorithm shown in FIGS. 2 and 3. Briefly, the algorithm described in FIGS. 2 and 3 provides command signals for the continuously variable transmission 14 as received from the operator through the range selector manual valve 66 and from various engine and vehicle speed signals.

The vehicle provides an engine speed or an input speed to the transmission at a sensor 92 and input speed to the continuously variable transmission 14 at a sensor 94 and an output speed from the continuously variable transmission at a sensor 96. By comparing these various speed signals, the control system can determine if the torque converter clutch is engaged or disengaged and can also determine the actual speed ratio across the continuously variable transmission 14.

The control system determines a desired speed ratio from the various inputs and establishes an output signal which is directed a summing or comparing unit S1. The summing unit S1 compares the desired speed signal as with a commanded speed signal, as will be described in more detail later. The commanded speed signal is stored and also fed back to the summing unit S1 for error correction as will be discussed later. The commanded signal is also directed to a Table SRAC which effects a count for the motor 82.

As seen in FIG. 4, the counts at the motor 82 are equal or comparable with sheave travel. The sheave travel is then also related by the curve C1 with the speed ratio of the continuously variable transmission 14. Thus, the control system, by knowing the count at the Table SRAC will establish the commanded speed ratio at the transmission.

FIG. 5 depicts a portion of the actuator 80. As can be seen, the ratio control motor 82 is connected with a link 100 which is also connected to a valve spool 102 of the valve 84. Feedback link 86 is connected to a hub or rim 104 of the sheave assembly 34. The enlarged portion of the valve 84 is shown in FIG. 6.

The motor 82 is a stepper motor which will respond to the counts as output by the algorithm described above. The valve 84 includes the valve spool 102 which is slidably disposed in a valve bore 106 and urged leftwardly by a spring 108 to maintain the link 100, the valve spool 102, the stepper motor 82 and feedback link 86 in firm contact. The valve bore 106 has a first port 110 which is communicating with the passage 54, a second port 112 which communicates, through valve 56, with the chamber 46 and a third port 114 which communicates with exhaust or with the system sump 116.

When it is desired to move toward an overdrive condition, the motor 82 will receive the proper count input from the algorithm described above such that the valve spool 102 will be moved leftward opening fluid communication between the passage 54 and the chamber 46 to cause the sheave assembly 34 to urge the belt 38 outwardly thereby pulling the belt 38 inwardly in the sheave 36 and accommodating a lesser diameter in sheave 36.

As the sheave assembly 34 is adjusted, the hub 104 will be moved rightward thereby causing the link 100 to pivot and bring the valve spool 102 back toward the neutral position shown. In this position, the fluid pressure from valve 56 is maintained at the chamber 46 to accommodate any fluid leakage which might occur downstream.

As best seen in FIG. 6, the valve spool 102 has a central land 118 which is large enough to overlap the port 112. As seen in FIG. 6, the port 112 is essentially line on line with the right edge of land 118 which will permit fluid pressure in port 110 to feed any leakage makeup necessary to maintain the pressure in chamber 46 at the desired level. However, when it is desired to change the ratio of the continuously variable transmission 14 in an underdrive direction, the overlap of land 118 creates a time lag before the pressure within the chamber 46 can be exhausted. This time lapse or lag is compensated by the step count described above in the algorithm.

When the step count occurs, the stepper motor 82 will rapidly move rightward to accommodate the large increase in count command thereby causing the valve spool 102 to move rightward rapidly, quickly opening the communication between the ports 112 and 114 so that the pressure in chamber 46 can be rapidly reduced. This will permit the continuously variable transmission 14 to change ratios in the underdrive direction quite rapidly. The time required for the count change (to cause the valve to move sufficiently to exhaust the chamber 46) is removed from the control cycle thus eliminating the lag which is otherwise present with the valve overlap.

The commanded ratio is then directed to a transmission control module TCM driver which in turn directs the signal to the motor 82 for the movement of the actuator 80. The actuator 80, as described above, adjusts the speed ratio within the continuously variable transmission 14. This signal is then compared at a summing point S2 which compares the actual transmission speed ratio with the commanded transmission speed ratio to determine if an adapt modifier is necessary to bring the control count into accordance with the driver commanded or driver desired count.

The output of the adapt modifier is directed to a summing unit S3 which adds the commanded signal, the count adapt modifier signal and a valve overlap signal from a valve overlap control C2 to provide a signal to the TCM driver. The valve overlap control C2, provides a step count to a transmission control module (TCM DRIVER) which directs the count to the actuator 80. This will cause the control motor 82 to move a predetermined step when the mechanism is shifting in an underdrive direction.

The Ratio Control Algorithm selects the desired ratio the transmission is to operate in from a series of maps. The maps that are used are determined by Transmission Range. Desired ratio determines commanded ratio which is used to set the step count of the ratio control motor. The ratio control motor positions the ratio control valve. The current step count of the motor is saved on powerdown and must remain the same on the next powerup. A control flow logic at the end of this section is included. This algorithm runs at 25 milliseconds on a conventional programmable digital computer.

The desired transmission ratio is selected from Table DTR a function of CVT.sub.-- RANGE. It is stored in the process variable DESIRED.sub.-- SPEED.sub.-- RATIO.

If CVT.sub.-- RANGE indicates REVERSE, the desired speed ratio, DESIRED.sub.-- SPEED.sub.-- RATIO is defined by the constant KE.sub.-- REV.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO.

In Park, Neutral and Drive Range, Desired Speed Ratio is determined by one of three maps dependent upon the state of the pattern select switch. In Intermediate and Low Range, the same maps are used but Desired Speed Ratio is limited to a maximum value defined in calibration tables. In Park, Neutral, Drive, Intermediate and Low Ranges, Detent Desired Speed Ratio determines the desired speed ratio when in the Detent Mode.

When THROTTLE.sub.-- KICKDOWN is requested by the operator, the detent mode is active and desired speed ratio, DESIRE.sub.-- SPEED.sub.-- RATIO, is defined by process variable DESIRED.sub.-- DET.sub.-- SPEED.sub.-- RATIO found in the two-dimensional table KV.sub.-- DET.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO (DDSR) plus a signed adaptive speed ratio DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT found in non-volatile RAM table DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT.sub.-- CELLS (DSRA). The independent variable in these tables DDSR, DSRA is VEHICLE.sub.-- SPEED and the dependent variable is DESIRED.sub.-- DET.sub.-- SPEED.sub.-- RATIO and DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT respectively. As in all tables, the dependent variable (desired speed ratio) is linearly interpolated, a function of the independent variable (vehicle speed).

The detent desired ratio is scheduled to maintain a desired engine RPM. Desired engine speed is determined from the calibration KE.sub.-- DESIRED.sub.-- DET.sub.-- ENGINE.sub.-- RPM.

As previously described, when in the detent mode, desired detent speed ratio is modified by signed adaptive cells DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT.sub.-- CELLS. The independent variable in the table is KPH.sub.-- OUTPUT.sub.-- SPEED and the dependent variable is DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT. If check sum of the adapt cells fail, then all of the adapt cells must reset to their default values of zero.

The adaptive cells, DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT.sub.-- CELLS, may be updated when timer, DETENT.sub.-- ADAPT.sub.-- TIMER, reaches calibration time KE.sub.-- DETENT.sub.-- ADAPT.sub.-- TIME. The timer, DETENT.sub.-- ADAPT.sub.-- TIMER is cleared and started when the detent mode is first entered. It is incremented as long as the detent mode is present and it is stopped when the Detent Mode is exited. When timer, DETENT.sub.-- ADAPT.sub.-- TIMER, reaches calibration time KE.sub.-- DETENT.sub.-- ADAPT.sub.-- TIME, the adaptive cells may be updated. The timer is also cleared and started after an adapt update which allows time for the actual ratio to move to the desired speed ratio before another adapt update is allowed. The actual engine rpm is used in the following equation to determine the engine RPM error, DETENT.sub.-- ENGINE.sub.-- RPM.sub.-- ERROR:

DETENT.sub.-- ENGINE.sub.-- RPM.sub.-- ERROR is a signed number. DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT.sub.-- CELLS is updated by the signed modifier DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MOD found in table KV.sub.-- DETENT.sub.-- ADAPT.sub.-- MODIFIER. The independent variable in the table is DETENT.sub.-- ENGIE.sub.-- RPM.sub.-- ERROR and the dependent variable is DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MOD. When conditions are met to allow an adapt update, the closest vehicle speed cell is updated by adding the signed modifier, determined from table KV.sub.-- DETENT.sub.-- ADAPT.sub.-- MODIFIER (DAM), which has been multiplied by factor KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 0. A percentage of the signed modifier value also updates the two neighboring table positions on either side of the selected cell (vehicle speed) position. The percentage factor is a calibration constant dependent upon cell position. For example, factor KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 1L is used on the cell next to the selected cell on the decreasing vehicle speed side. The value of DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT.sub.-- CELLS is bounded by KE.sub.-- MIN.sub.-- DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT, and KE.sub.-- MAX.sub.-- DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPT.

N--2 cell position: DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx=DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx-1+(DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MODx KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 2L)

N-1 cell position: DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx=DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx-1+(DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MODx KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 1L)

N cell position: DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx=DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPx-1+(DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MODx KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 0)

N+1 cell position: DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx=DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx-1+(DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MODx KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 1H)

N+2 cell position: DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx=DET.sub.-- SPEED.sub.-- RATIO.sub.-- ADAPTx-1+(DETENT.sub.-- RATIO.sub.-- ADAPT.sub.-- MODx KE.sub.-- DET.sub.-- ADAPT.sub.-- FACTOR.sub.-- 2H)

If CVT.sub.-- RANGE indicates DRIVE or PARK or NEUTRAL, desired speed ratio is defined by one of three maps in table DXDR dependent upon the pattern select input which sets NORMAL, SPORT or ECONOMY. When the pattern select is NORMAL, desired speed ratio, DESIRED.sub.-- SPEED.sub.-- RATIO, is equal to DRIVE.sub.-- NORM.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO which is found in the three-dimensional table KA.sub.-- DRIVE.sub.-- NORM.sub.-- DESIRED.sub.-- RATIO (DXDR). When the pattern select is SPORT or ECONOMY, desired speed ratio, DESIRED.sub.-- SPEED.sub.-- RATIO, is equal to DRIVE.sub.-- SPORT.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO or DRIVE.sub.-- ECON.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO, which are found in the three-dimensional table KA.sub.-- DRIVE.sub.-- SPORT.sub.-- DESIRED.sub.-- RATIO DXDR or KA.sub.-- DRIVE.sub.-- ECON.sub.-- DESIRED.sub.-- RATIO (DXDR). The independent variables in the tables are KPH.sub.-- OUTPUT.sub.-- SPEED and THROTTLE, the dependent variables are DRIVE.sub.-- NORM.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO, DRIVE.sub.-- SPORT.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO and DRIVE.sub.-- ECON.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO.

If CVT.sub.-- RANGE indicates DRIVE.sub.-- INT or DRIVE.sub.-- LOW, the desired speed ratio is defined by the DRIVE table and the pattern select, KA.sub.-- DRIVE.sub.-- NORM.sub.-- DESIRED.sub.-- RATIO, KA.sub.-- DRIVE.sub.-- SPORT.sub.-- DESIRED.sub.-- RATIO or KA.sub.-- DRIVE.sub.-- ECON.sub.-- DESIRED.sub.-- RATIO, however, it is limited to a maximum speed ratio. The maximum speed ratio in DRIVE.sub.-- INT is defined in the two-dimensional table KV.sub.-- INT.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT (IDSL). The maximum speed ratio in DRIVE.sub.-- LOW is defined in the two-dimensional table KV.sub.-- LOW.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT (LDSL). The independent variable in the tables is KPH.sub.-- OUTPUT.sub.-- SPEED and the dependent variables are INT.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT and LOW.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT.

For example, in DRIVE.sub.-- INT, DESIRED.sub.-- SPEED.sub.-- RATIO is the DRIVE.sub.-- DESIRED.sub.--SPEED.sub.-- RATIO from Table KA.sub.-- DRIVE.sub.-- DESIRED.sub.-- RATIO or INT.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT from table KV.sub.-- INT.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT, which ever table value contains the lowest speed ratio value. DESIRED.sub.--SPEED.sub.-- RATIO can be less than INT.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT as defined by DRIVE.sub.-- DESIRED.sub.-- SPEED.sub.-- RATIO but it cannot exceed INT.sub.-- DESIRED.sub.-- SR.sub.-- LIMIT.

The Driver Commanded Gear Mode (DCG Mode) is entered when the Range is DRIVE and the input DRIVER.sub.-- COMMAND.sub.-- GEAR is true. In the DCG Mode the transmission is manually upshifted and downshifted by the driver. There are a maximum of 6 gears, each of which are assigned a speed ratio.

In the DCG Mode, DESIRED.sub.-- SPEED.sub.-- RATIO is set by DCG.sub.-- SPEED.sub.-- RATIO. DCG.sub.-- SPEED.sub.-- RATIO is found in the calibration table KV.sub.-- DCG.sub.-- SPEED.sub.-- RATIO (DCG) as a function of COMMANDED.sub.-- GEAR. COMMANDED.sub.-- GEAR is determined by DESIRED.sub.-- GEAR and calibration limits. Both COMMANDED.sub.-- GEAR and DESIRED.sub.-- GEAR are limited to the calibration constant KE.sub.-- DCG.sub.-- GEAR.sub.-- NUMBER which is the maximum number of discrete gear steps available in DCG Mode. The minimum number of gear steps is 1.

When the DCG Mode is first entered, the current ACTUAL.sub.-- SPEED.sub.-- RATIO is compared to each DCG.sub.-- SPEED.sub.-- RATIO found in the table KV.sub.-- DCG.sub.-- SPEED.sub.-- RATIO. DCG.sub.-- ERROR.sub.-- x (wherex=1,2,3,4,5,6) is equal to DCG.sub.-- SPEED.sub.-- RATIO.sub.-- x minus COMMANDED.sub.-- SPEED.sub.-- RATIO. If DCG.sub.-- ERROR.sub.-- x is zero or less than KE.sub.-- DCG.sub.-- ERROR.sub.-- LIMIT for a calibration, set DESIRED.sub.-- GEAR equal to the associated value. If DCG.sub.-- ERROR.sub.-- x does not satisfy the above condition, set DESIRED.sub.-- GEAR equal to the associated gear value of DCG.sub.-- ERROR.sub.-- x where DCG.sub.-- ERROR.sub.-- x is a negative number closest to zero. When entering DCG Mode, DCG.sub.-- MIN.sub.-- GEAR is set to one and DCG.sub.-- MAX.sub.-- GEAR is set to the calibration constant KE.sub.-- DCG.sub.-- GEAR.sub.-- NUMBER which is the maximum number of discrete gear steps available in DCG Mode.

When exiting DCG Mode, DESIRED.sub.--SPEED.sub.-- RATIO is determined by the maps described previously.

Each time the driver input indicates upshift, DESIRED.sub.-- GEAR is incremented one step. When the driver input indicates downshift, DESIRED.sub.-- GEAR is decremented one step. Again DESIRED.sub.-- GEAR is limited to a maximum found in calibration constant KE.sub.-- DCG.sub.-- GEAR.sub.-- NUMBER and to a minimum of 1. COMMANDED.sub.-- GEAR is set to DESIRED.sub.-- GEAR within DCG.sub.-- MAX.sub.-- GEAR and DCG.sub.-- MIN.sub.-- GEAR limitations.

A gear display output, not shown, follows DESIRED.sub.-- GEAR. The gear display and DESIRED.sub.-- GEAR will temporarily show a driver input even when outside the limits DCG.sub.-- MAX.sub.-- GEAR and DCG.sub.-- MIN.sub.-- GEAR which is bounded by 1 and KE.sub.-- DCG.sub.-- GEAR.sub.-- NUMBER. COMMANDED.sub.-- GEAR is always limited to a minimum of the value of DCG.sub.-- MIN.sub.-- GEAR and a maximum of DCG.sub.-- MAX.sub.-- GEAR. If a driver commands a downshift less than DCG.sub.-- MIN.sub.-- GEAR or an upshift greater than DCG.sub.-- MAX.sub.-- GEAR, DESIRED.sub.-- GEAR follows the signal for a calibratable amount of time, KE.sub.-- DESIRED.sub.-- DISPLAY.sub.-- TIME. When a driver commands a downshift less than DCG.sub.-- MIN.sub.-- GEAR or an upshift greater than DCG MAX.sub.-- GEAR, timer, DCG.sub.-- DISPLAY.sub.-- TIMER is initialized and started. Once the timer is complete, DESIRED.sub.-- GEAR is again limited by DCG.sub.-- MIN.sub.-- GEAR. If another driver command occurs outside the limit before the timer is complete, the DESIRED.sub.-- GEAR is decremented or incremented again and the timer restarted. If DCG.sub.-- MIN.sub.-- GEAR or DCG.sub.-- MAX.sub.-- GEAR changes due to the gear limit calibrations (not a driver initiated shift), DESIRED.sub.-- GEAR and COMMANDED.sub.-- GEAR are immediately bounded by these limits and the timer is not used.

During a deceleration (not in detent/kickdown mode), downshifting will occur automatically at the vehicle speeds found in calibration constants KE.sub.-- DCG.sub.-- DOWNSHIFT.sub.-- 65, KE.sub.-- DCG.sub.-- DOWNSHIFT.sub.-- 54, KE.sub.-- DCG.sub.-- DOWNSHIFT.sub.-- 43, KE.sub.-- DCG.sub.-- DOWNSHIFT.sub.-- 32, KE.sub.-- DCG.sub.-- DOWNSHIFT.sub.-- 121. These calibrations set DCG.sub.-- MAX.sub.-- GEAR when not in kickdown mode to a gear value which limits COMMANDED.sub.-- GEAR and DESIRED.sub.-- GEAR. For example if the vehicle speed is less than KE.sub.-- DCG.sub.-- DOWNSHIFT.sub.-- 65, DCG.sub.-- MAX.sub.-- GEAR is set to 5. In the detent/kickdown mode, downshifting will occur automatically below the vehicle speeds found in calibration constants KE.sub.-- DCG.sub.-- DETENT.sub.-- 65, KE.sub.-- DCG.sub.-- DETENT.sub.-- 54, KE.sub.-- DCG.sub.-- DETENT.sub.-- 43, KE.sub.-- DEG.sub.-- DETENT.sub.-- 32, KE.sub.-- DCG.sub.-- DETENT.sub.-- 21. These calibrations set DCG.sub.-- MAX.sub.-- GEAR in detent/kickdown mode to a gear value which limits COMMANDED.sub.-- GEAR and DESIRED.sub.-- GEAR. When DCG.sub.-- MAX.sub.-- GEAR is set due to one of the above calibrations, the value of DCG.sub.-- MAX.sub.-- GEAR is incremented when vehicle speed is equal to or above the calibration plus KE.sub.-- DCG.sub.-- MAX.sub.-- DELTA. For example, if in the kickdown mode and vehicle speed is less than KE.sub.-- DCG.sub.-- DETENT.sub.-- 43, DCG.sub.-- MAX.sub.-- GEAR is set to 3. When vehicle speed is greater than or equal to KE.sub.-- DCG.sub.-- DETENT.sub.-- 43 plus KE.sub.-- DCG.sub.-- MAX.sub.-- DELTA, DCG.sub.-- MAX.sub.-- GEAR is then set to 4. With DCG.sub.-- MAX GEAR set to 4, a driver initiated upshift will allow DESIRED.sub.-- GEAR and COMMANDED.sub.-- GEAR to equal 4.

In both kickdown and non kickdown mode, overspeed protection is available resulting in automatic upshifts. If vehicle speed is greater than or equal to calibration constants KE.sub.-- DCG.sub.-- OVERSPD.sub.-- 12, KE.sub.-- DCG.sub.-- OVERSPD.sub.-- 23, KE.sub.-- DCG.sub.-- OVERSPD.sub.-- 34, KE.sub.-- DCG.sub.-- OVERSPD.sub.-- 45, KE.sub.-- DCG.sub.-- OVERSPD.sub.-- 56, DCG.sub.-- MIN.sub.-- GEAR is set to a gear value which limits COMMANDED.sub.-- GEAR and DESIRED.sub.-- GEAR. When DCG.sub.-- MIN.sub.-- GEAR is set due to one of the above calibrations, the value of DCG.sub.-- MIN.sub.-- GEAR is decremented (minimum of 1) when vehicle speed is less than the calibration minus KE.sub.-- DCG.sub.-- OVERSPD.sub.-- DELTA. For example, if vehicle speed is greater than KE.sub.-- DCG.sub.-- OVERSPD.sub.-- 12, DCG.sub.-- MIN.sub.-- GEAR is set to 2. When vehicle speed is less than KE DCG.sub.-- OVERSPD.sub.-- 12 minus KE.sub.-- DCG.sub.-- OVERSPD.sub.-- DELTA, then DCG.sub.-- MIN.sub.-- GEAR is set to 1. With DCG.sub.-- MIN.sub.-- GEAR set to 1, a driver initiated downshift will allow DESIRED.sub.-- GEAR and COMMANDED.sub.-- GEAR to equal 1.

Commanded speed ratio is determined from the error between desired speed ratio and the last commanded speed ratio. This error is used to determine the rate at which commanded speed ratio converges to desired speed ratio. The commanded speed ratio is used to look up the count of the ratio control actuator. Commanded speed ratio calculation is frozen if vehicle speed is less than KE.sub.-- RATIO.sub.-- CONTROL.sub.-- FREEZE.sub.-- LOW.sub.-- VS because speed signals are noisy at the low vehicle speeds of approximately three (3) kph.

The commanded speed ratio error is determined in the following equation:

Table KV.sub.-- COM.sub.-- ERROR.sub.-- SR.sub.-- RATE (CESR) modifies the last COMMANDED.sub.-- SPEED.sub.-- RATIO. KV.sub.-- COM.sub.-- ERROR.sub.-- SR.sub.-- RATE is a two-dimensional tables with COMMANDED.sub.-- SR.sub.-- ERROR as the independent variable and DELTA.sub.-- COM.sub.-- SR.sub.-- PER.sub.-- SEC the dependent variable. DELTA.sub.-- COM.sub.-- SR.sub.-- PER.sub.-- SEC is multiplied by the loop time to give DELTA.sub.-- COM.sub.-- SR.sub.-- PER.sub.-- LOOP. The new COMMANDED.sub.-- SPEED.sub.-- RATIO is determined by the following equation:

The driven position of the ratio control actuator is stored in counts. The controller keeps track of the counts in process variable COUNT saving the value at powerdown. The actual count follows COMMANDED.sub.-- COUNT as rapidly as pulses can occur. If COUNT check sum has been compromised, then COUNT is reset to KE.sub.-- RATIO.sub.-- MOTOR.sub.-- DEFAULT.sub.-- COUNT. COMMANDED.sub.-- COUNT is determined by looking up the base actuator count, ACTUATOR.sub.-- COUNT, which is then modified by an adapt value, COUNT.sub.-- ADAPT.sub.-- CELL and an underdrive step count if conditions permit.

During power up and when conditions do not permit adding in an underdrive step count, the following equation is used:

During power up, the actual position of ratio control actuator, COUNT, is not updated for KE.sub.-- RATIO.sub.-- MOTOR.sub.-- WAIT.sub.-- TIME.

The base actuator count, ACTUATOR.sub.-- COUNT, is found in table KV.sub.-- SR.sub.-- ACTUATOR.sub.-- COUNT (SRAC). The independent variable in table KV.sub.-- SR.sub.-- ACTUATOR.sub.-- COUNT is COMMANDED.sub.-- SPEED.sub.-- RATIO, the dependent variable is ACTUATOR.sub.-- COUNT.

When speed ratio is commanded to move toward underdrive, a signed step value is added each loop to the commanded count in order to quickly position the ratio control valve in an exhaust position (due to valve overlap). The step is not added when desired and commanded speed ratio are close to equal.

When commanded speed ratio error, COMMANDED.sub.-- SR.sub.-- ERROR, is less than the signed value of KE.sub.-- SR.sub.-- ERROR.sub.-- COUNT.sub.-- ADD, a signed calibration value KE.sub.-- STEP.sub.-- COUNT.sub.-- VALUE is added to ACTUATOR.sub.-- COUNT and process variable flag STEP.sub.-- COUNT.sub.-- ADDED is set.

When commanded speed ratio error, COMMANDED.sub.-- SR.sub.-- ERROR, becomes greater than the signed value of KE.sub.-- SR.sub.-- ERROR.sub.-- COUNT.sub.-- CLEAR while process variable STEP.sub.-- COUNT.sub.-- ADDED is set, KE.sub.-- STEP.sub.-- COUNT.sub.-- VALUE is no longer used in determining COMMANDED.sub.-- COUNT and process variable STEP.sub.-- COUNT.sub.-- ADDED is cleared.

The Step Count Adapt system is in place to adjust for offsets when actual ratio does not match commanded ratio. An offset can occur if the actuator does not move upon a count change or if an offset exists in the primary pulley link. Actuator step count adapt cell is kept in non-volatile ram, if its check sum has been compromised, then it gets reset to zero.

Actuator step count adapt cell, COUNT.sub.-- ADAPT.sub.-- CELL, calculation is frozen if vehicle speed is less than KE.sub.-- RATIO.sub.-- CONTROL.sub.-- FREEZE.sub.-- LOW.sub.-- VS because speed signals are noisy and unreliable at the low vehicle speeds.

When commanded speed ratio is near desired speed ratio for a calibration amount of time, the error between commanded speed ratio and actual speed ratio can modify the actual count. The speed ratio error is defined as the difference between commanded speed ratio and actual speed ratio as shown in the following equation:

The adaptive cell, COUNT.sub.-- --ADAPT.sub.-- CELL, may be updated when timer, COUNT.sub.-- ADAPT.sub.-- TIMER, reaches calibration time KE.sub.-- COUNT.sub.-- ADAPT.sub.-- TIME. The timer, COUNT.sub.-- ADAPT.sub.-- TIMER is cleared and started when COMMANDED.sub.-- SR.sub.-- ERROR is greater than or equal to KE.sub.-- COUNT.sub.-- ADAPT.sub.-- LOW and less than KE.sub.-- COUNT.sub.-- ADAPT.sub.-- HIGH. The timer is incremented as long as commanded speed ratio error, COMMANDED.sub.-- SR.sub.-- ERROR, is within the calibration band and it is stopped if it falls out side the band. Timer COUNT.sub.-- ADAPT.sub.-- TIMER is cleared and started when COMMANDED.sub.-- SR.sub.-- ERROR again is within the calibration band. When timer, COUNT.sub.-- ADAPT.sub.-- TIMER, reaches calibration time KE.sub.-- COUNT.sub.-- ADAPT.sub.-- TIME, the adaptive cell may be updated. The timer is also cleared and started after an adapt update which allows time for the actual ratio to move to the desired speed ratio before another adapt updated is allowed.

ACTUAL.sub.-- SPEED.sub.-- RATIO.sub.-- ERROR is a signed number. COUNT.sub.-- ADAPT.sub.-- CELL is updated by the signed modifier COUNT.sub.-- ADAPT.sub.-- MOD found in table KV.sub.-- COUNT.sub.-- ADAPT.sub.-- MODIFIER (CAM). The independent variable in the table is ACTUAL.sub.-- SPEED.sub.-- RATIO.sub.-- ERROR and the dependent variable is COUNT.sub.-- ADAPT.sub.-- MOD. When conditions are met to allow an adapt update:

It is possible for the process variables COMMANDED.sub.-- COUNT and COUNT to exceed the variable range if a number of lost counts occur. This section describes the "reset" of COUNT.sub.-- ADAPT.sub.-- CELL, COMMANDED.sub.-- COUNT and COUNT.

The following conditions must be true to enable the reset:

1) ICOMMANDED.sub.-- COUNTI>KE.sub.-- COMMANDED.sub.-- COUNT.sub.-- RESET.sub.-- THRESH (absolute value of COMMANDED.sub.-- COUNT)

2) VEHICLE.sub.-- SPEED=0 continuously for KE.sub.-- ZERO.sub.-- VEHICLE.sub.-- SPEED.sub.-- TIME

The reset action is to set the adapt variable, COUNT.sub.-- ADAPT.sub.-- CELL to zero, recalculate COMMANDED.sub.-- COUNT with the zero value of COUNT.sub.-- ADAPT.sub.-- CELL and set COUNT equal to COMMANDED.sub.-- COUNT.

COUNT.sub.-- ADAPT.sub.-- CELL=0 COMMANDED.sub.-- COUNT=ACTUATOR.sub.-- COUNT+KE.sub.-- STEP.sub.-- COUNT.sub.-- VALUE+COUNT.sub.-- ADAPT.sub.-- CELL (COMMANDED.sub.-- COUNT=ACTUATOR.sub.-- COUNT+KE.sub.-- STEP.sub.-- COUNT.sub.-- VALUE+0) COUNT=COMMANDED.sub.-- COUNT

When the vehicle is stopped the stepper motor is frozen which will allow the reset without interfering with the normal ratio function. When vehicle speed is equal to 0, process variable ZERO.sub.-- VEHICLE.sub.-- SPEED.sub.-- TIMER is rest and started. When vehicle speed becomes greater than 0, process variable ZERO.sub.-- VEHICLE.sub.-- SPEED.sub.-- TIMER frozen. When the reset action takes place, COMMANDED.sub.-- COUNT must be recalculated and COUNT set equal to COMMANDED.sub.-- COUNT without the stepper motor moving.

The process variables listed below need slew capability through instrumentation. On power up, the process variables will use the normal algorithm (a slew value that is present prior to power down is not saved and will be cleared for the next power up). The actual process variable in use, whether calculated or slewed, must be displayed when viewing the process variable with instrumentation.

The process variable DESIRED.sub.--SPEED.sub.-- RATIO must be able to be slewed which will override the normal ratio determination.

The process variable COMMANDED.sub.-- COUNT must be able to be slewed which will override the normal commanded count determination.

The DCG Mode can be enabled by the manual modifier V.sub.-- DCG.sub.-- MODE.sub.-- MAN. If V.sub.-- DCG.sub.-- MODE.sub.-- MAN is equal to 0, then the DCG Mode is entered or exited by the state of DRIVER.sub.-- COMMAND.sub.-- GEAR. If V.sub.-- DCG.sub.-- MODE.sub.-- MAN is anything other than 0, the DCG Mode is enabled.

The process variable COMMANDED.sub.-- GEAR must be able to be slewed when in the DCG Mode (either by the switch or the manual modifier), which will override the normal desired gear determination. COMMANDED.sub.-- GEAR is limited to a maximum found in calibration constant KE.sub.-- DCG.sub.-- GEAR.sub.-- NUMBER and to a minimum of 1 but is not restricted by DCG.sub.-- MAX.sub.-- GEAR and DCG.sub.-- MIN.sub.-- GEAR limitations.

The process variable COUNT.sub.-- ADAPT.sub.-- CELL must be able to be slewed which will override the normal adapt determination. The non-volatile ram value of COUNT.sub.-- ADAPT.sub.-- CELL must also be able to be initialized to value found in V.sub.-- COUNT.sub.-- ADAPT.sub.-- MAN.