Mapping temperature compensation limits for PWM control of VCT phasers

Abstract

A variable cam timing (VCT) phaser system including a phaser with an actuator in which the max duty cycle is altered to maintain a constant current in the system based on at least one engine parameter.

Description

BACKGROUND

1. Field of the Invention

The invention pertains to the field of variable camshaft timing systems. More particularly, the invention pertains to methods of operating a pulse-width-modulated (PWM) variable cam timing system at substantially the same actuation rate under different temperature conditions by limiting the duty cycle to different values to compensate for changes in temperature.

2. Description of Related Art

The performance of an internal combustion engine may be improved by the use of dual camshafts, one to operate the intake valves of the various cylinders of the engine and the other to operate the exhaust valves. Typically, one of such camshafts is driven by the crankshaft of the engine, through a sprocket and chain drive or a belt drive, and the other of such camshafts is driven by the first, through a second sprocket and chain drive or a second belt drive. Alternatively, both of the camshafts may be driven by a single crankshaft powered chain drive or belt drive. Engine performance in an engine with dual camshafts may be further improved, in terms of idle quality, fuel economy, reduced emissions or increased torque, by changing the positional relationship of one of the camshafts, usually the camshaft which operates the intake valves of the engine, relative to the other camshaft and relative to the crankshaft, to thereby vary the timing of the engine in terms of the operation of intake valves relative to its exhaust valves or in terms of the operation of its valves relative to the position of the crankshaft.

Consideration of information disclosed by the following U.S. Patents, which are all hereby incorporated by reference, is useful when exploring the background of the present invention.

U.S. Pat. No. 5,002,023 describes a VCT system in which the system hydraulics include a pair of oppositely acting hydraulic cylinders with appropriate hydraulic flow elements to selectively transfer hydraulic fluid from one of the cylinders to the other, or vice versa, to thereby advance or retard the circumferential position of a driven shaft relative to a driving shaft. The control system utilizes a control valve in which the exhaustion of hydraulic fluid from one or another of the oppositely acting cylinders is permitted by moving a spool away from a centered or null position. The movement of the spool occurs in response to an increase or decrease in control hydraulic pressure Pc on one end of the spool, and an oppositely direct mechanical force on the other end, from a compression spring that acts thereon.

U.S. Pat. No. 5,107,804 describes another VCT system in which the system hydraulics includes a vane having lobes within an enclosed housing replacing the oppositely acting cylinders disclosed by the aforementioned U.S. Pat. No. 5,002,023. The vane is oscillatable with respect to the housing, with appropriate hydraulic flow elements to transfer hydraulic fluid within the housing from one side of a lobe to the other, or vice versa, to thereby oscillate the vane with respect to the housing in one direction or the other. The oscillation of the vane in one direction or the other advances or retards the position of a driven shaft relative to a driving shaft. The control system of this VCT system is identical to that divulged in U.S. Pat. No. 5,002,023.

U.S. Pat. Nos. 5,172,659 and 5,184,578 both address the problems of the aforementioned types of VCT systems created by the attempt to balance the hydraulic force exerted against one end of the spool and the mechanical force exerted against the other end. The improved control system disclosed in both U.S. Pat. Nos. 5,172,659 and 5,184,578 utilizes hydraulic force on both ends of the spool. The hydraulic force on one end results from the directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, P_S. The hydraulic force on the other end of the spool results from a hydraulic cylinder or other force multiplier which acts thereon in response to system hydraulic fluid at reduced pressure P_C, supplied by a PWM solenoid. Due to the force at each of the opposed ends of the spool being hydraulic in origin, based on the same hydraulic fluid, changes in pressure or viscosity of the hydraulic fluid will be self-negating, and will not affect the centered or null position of the spool.

U.S. Pat. No. 5,289,805 discloses an improved VCT method which utilizes a hydraulic PWM spool position control and an advanced control algorithm that yields a prescribed set point tracking behavior with a high degree of robustness.

U.S. Pat. No. 5,497,738 shows a control system which eliminates the hydraulic force on one end of a spool resulting from directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure, P_S. The force on the other end of the vented spool results from an electromechanical actuator, preferably of the variable force solenoid type, which acts directly upon the vented spool in response to an electronic signal issued from an engine control unit (ECU). The ECU receives signals from sensors corresponding to camshaft and crankshaft positions and utilizes this information to calculate a relative phase angle in a closed-loop feedback system. The use of a variable force solenoid solves the problem of sluggish dynamic response. The faster response allows the use of increased closed-loop gain, making the system less sensitive to component tolerances and operating environment.

U.S. Pat. No. 5,657,725 shows a control system which utilizes engine oil pressure for actuation. The system includes a camshaft with a vane secured to an end thereof for non-oscillating rotation therewith. The camshaft also carries a housing which can rotate with the camshaft, and is also oscillatable with the camshaft. The vane has opposed lobes which are received in opposed recesses, of the housing. The recesses have a greater circumferential extent than the lobes, to permit the vane and housing to oscillate with respect to one another, and thereby permit the camshaft to change in phase relative to a crankshaft. The camshaft tends to change direction in reaction to camshaft torque pulses, advancing or retarding the phaser by selectively blocking or permitting the flow of engine oil through the return lines from the recesses by controlling the position of a spool within a spool valve body. The spool is moved within the spool valve body in response to a signal indicative of an engine operating condition from an engine control unit. The spool is selectively positioned by controlling hydraulic loads on its opposing end in response to a signal from an engine control unit. The vane may be biased to an extreme position to provide a counteractive force to a unidirectionally acting frictional torque experienced by the camshaft during rotation.

U.S. Pat. No. 6,247,434 shows a multi-position variable camshaft timing system actuated by engine oil. Within the system, a hub is secured to a camshaft for rotation synchronous with the camshaft. A housing circumscribes and is rotatable with the hub and the camshaft and is further oscillatable with respect to the hub and the camshaft within a predetermined angle of rotation. Vanes extend from the hub into a chamber formed between the housing and the hub, dividing the chamber into advance and retard chambers. A locking device, reactive to oil pressure, prevents relative motion between the housing and the hub. A controlling device controls the oscillation of the housing relative to the hub.

U.S. Pat. No. 6,263,846 shows a control valve strategy for a variable camshaft timing system. The strategy involves an internal combustion engine that includes a camshaft and hub secured to the camshaft for rotation therewith, where a housing circumscribes the hub and is rotatable with the hub and the camshaft, and is further oscillatable with respect to the hub and camshaft. Vanes extend from the hub into a chamber formed between the housing and the hub, dividing the chamber into advance and retard chambers. A configuration for controlling the oscillation of the housing relative to the hub includes an electronic engine control unit, and an advancing control valve that is responsive to the electronic engine control unit and that regulates engine oil pressure to and from the advance chambers. A retarding control valve responsive to the electronic engine control unit regulates engine oil pressure to and from the retard chambers. An advancing passage communicates engine oil pressure between the advancing control valve and the advance chambers, while a retarding passage communicates engine oil pressure between the retarding control valve and the retard chambers.

U.S. Pat. No. 6,938,592 shows a method of adding a dither frequency (a periodic adjustment) to the control signal to always keep the VCT control valve moving a little in order to minimize the effects of hysteresis with regard to valve movement. The dither frequency is adjusted based on varying temperature conditions, since the dither technique is less effective at higher temperatures.

Temperature and voltage may also have an undesirable effect on the phaser actuation rate. Therefore, it would be desirable to have a VCT phaser which could compensate for the temperature and voltage effects on actuation rate.

SUMMARY OF THE INVENTION

A variable cam timing (VCT) phaser system including a phaser with an actuator in which the max duty cycle is altered to maintain a constant current in the system based on at least one engine parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows a schematic of a cam torque actuated phaser of the present invention moving in the null position.

FIG. 1 b shows a schematic of a cam torque actuated phaser of the present invention moving towards the advance position.

FIG. 1 c shows a schematic of a cam torque actuated phaser of the present invention moving towards the retard position.

FIG. 2 shows a schematic of an oil pressure actuated phaser of the present invention in the null position.

FIG. 3 shows a schematic of a torsion assist phaser of the present invention in the null position.

FIG. 4 shows a graph of a temperature compensation map used for duty cycle compensation of a first embodiment.

FIG. 5 shows a method of adjusting the duty cycle for a maximum actuation rate in view of temperature changes of a first embodiment.

FIG. 6 shows an alternate method of adjusting the duty cycle for a maximum actuation rate in view of temperature changes of a first embodiment.

FIG. 7 shows a method of adjusting the duty cycle for a maximum actuation rate in view of voltage changes in a second embodiment.

FIG. 8 shows a graph of duty cycle versus voltage at different constant temperatures.

FIG. 9 shows an alternate method of adjusting the duty cycle for a maximum actuation rate in view of voltage changes in a second embodiment.

FIG. 10 shows a method of adjusting the duty cycle for a maximum actuation rate in view of temperature and voltage changes in a third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanism use one or more “vane phasers” on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a rotor with one or more vanes, mounted to the end of the camshaft, surrounded by a housing with the vane chambers into which the vanes fit. It is possible to have the vanes mounted to the housing, and the chambers in the rotor, as well. The housing's outer circumference forms the sprocket, pulley or gear accepting drive force through a chain, belt, or gears, usually from the crankshaft, or possible from another camshaft in a multiple-cam engine.

The desired relative angular position between the camshaft and the crankshaft is determined by a controller 36, which may be further controlled by an ECU. The controller may be a microprocessor, computer, application specific integrated circuit (ASIC), digital electronics, analog electronics, or any combination thereof. The controller 36 is coupled to an actuator 38 which is capable of adjusting the spool 54 and thus the phaser to vary the relative angular position between the camshaft and the crankshaft. The controller 36 receives input from a temperature sensor 40, a battery 37, and the ECU 39. Alternatively, the controller 36 may be part of the ECU 39. The controller is preferably a Motorola Model No. 68332 microcontroller. The temperature sensor 40 is preferably a sensor in the main oil gallery, which supplies oil to the actuator 38 and/or phaser. The temperature sensor may also be present in other parts of the engine and measure an associated temperature such as, the engine block, the engine compartment, the radiator, and the cooling system. The battery 37 may provide voltage to run the controller 36 and enable the controller 36 to monitor the voltage or the controller 36 will only monitor the voltage from the battery 37. The ECU 39 provides additional input regarding other engine parameters to the controller 36, such as the angular position of the camshaft relative to the crankshaft and thus spool position.

The controller 36 is configured to adjust an actuator control parameter, such as the duty cycle of the actuator 38, based on input from the temperature sensor 40, the battery, and the ECU in order to achieve a substantially constant actuation rate. The controller may also further adjust the duty cycle based on whether the ECU supplies input to move the phaser to a null position, a retard position, or an advance position.

The actuator 38 may be a flow control switch which receives a pulse-width-modulated (PWM) signal from the controller 36 to vary the current which allows varying amounts of pressurized hydraulic fluid 56 to drive the spool 54 against an opposing force, here illustrated as spring 64. The lands of the spool 54 and the characteristics of the spring 64 may be chosen so that at some nominal value of current, for example 0.6 amps, the spool 54 will be in the null position, as shown in FIGS. 1a, 2, and 3, locking the vane 46 in a position. At 1 amp, the spool will be fully moved to an advance position, and at 0.2 amps, the spool will be moved to a full retard position. The duty cycle that corresponds to the null position, the full advance position, and the full retard position will vary based on the current outputted, but ideally, based on current, 0.2 amps corresponds to a 20% duty cycle, 0.6 amps corresponds to 60%, and 1.0 amp corresponds to 100% duty cycle. As explained below, if the current is greater than 1 amp, the maximum duty cycle will be adjusted to being the maximum current back to 1 amp. It should be noted that vane 46 may be stopped at any position and does not need to be in the position specifically shown in FIGS. 1a, 2 and 3. Since the vane 46 is not being driven in this position, the actuation rate of the vane 46 is zero.

The controller 36 and actuator 38 may be used with any of the following phasers: cam torque actuated, oil pressure actuated, torsion assist, a hybrid phasers as shown in FIGS. 1a through 3 and discussed below. For the discussion of the phasers, it is assumed that the current outputted is equal to 1 amp and the maximum duty cycle of 100% does not need to be altered.

Cam torque actuated (CTA) phasers use torque reversals in the camshaft, caused by the forces of opening and closing engine valves to move the vane. Control valves are present to allow fluid flow from chamber to chamber causing the vane to move, or to stop the flow of oil, locking the vane in position. The CTA phaser has oil input to make up for losses due to leakage, but does not use engine oil pressure to move the phaser. CTA phasers have shown that they provide fast response and low oil usage, reducing fuel consumption and emissions. However, in some engines, i.e. 4-cylinder engines, the torsional energy from the camshaft is not sufficient to actuate the phaser over the entire speed range of the engine, especially when the rpm is high and optimization of the performance of the phaser in view of engine operating conditions (e.g. the amount of available cam torque) is necessary.

FIGS. 1 a through 1c show a cam torque actuated phaser (CTA) of the present invention. Torque reversals in the camshaft caused by the forces of opening and closing engine valves move the vane 46. The advance and retard chambers 50, 52 are arranged to resist positive and negative torque pulses in the camshaft and are alternatively pressurized by the cam torque. The control valve 51 in a CTA system allows the vane 46 in the phaser to move, by permitting fluid flow from the advance chamber 50 to the retard chamber 52 or vice versa, depending on the desired direction of movement, as shown in FIGS. 1a through 1c.

When the controller 36 increases the current, from 0.6 amps or in increases the duty cycle from 60% to 1 amp or 100%, then the actuator 38 will increase the pressure of the oil driving the spool 54 against the spring 64, the actuator moving the spool to the left in FIG. 1c until the force of the actuator 38 balances the force of the spring 64, and depending on the duty cycle or current chosen, a particular actuation rate of the phaser vane will be set in a second direction, here illustrated as a counter-clockwise or retarding direction, opposite the first direction.

More specifically, in moving towards the retard position of the phaser, as shown in FIG. 1c, the spool valve 51 is internally mounted within the rotor 42 and includes a sleeve 53 for receiving a spool 54 with lands 54a, 54b, and a biasing spring 64. An actuator 38, preferably a pulse width modulated (PWM) solenoid, moves the spool 54 within the sleeve 53. In the position shown, spool land 54b blocks line 62, and lines 60 and 58 are open. Camshaft torque pressurizes the advance chamber 50, causing fluid in the advance chamber 50 to move into the retard chamber 52. Fluid exiting the advance chamber 50 moves through line 58 and the fluid moves and into the spool valve 51 between spool lands 54a and 54b. From the spool valve 51, fluid move back into line 60, through check valve 51 into line 62 supplying fluid to the retard chamber 52, moving the vane 46 in the direction shown by the arrow.

Makeup oil is supplied to the phaser from supply S to make up for leakage and enters line 55 and moves through inlet check valve 57 to the spool valve 51. From the spool valve fluid enters line 60 through either of the check valves 59, 61, depending on whether fluid travels to the advance chamber 50 or the retard chamber 52.

When the controller 36 reduces the current, from 0.6 amps or reduces the duty cycle from 60% to 0.2 amps or 20%, respectively, then the actuator 38 will reduce the pressure of the oil driving the spool 54 against the spring 64 and the spring force will bias the spool 54 to the right in FIG. 1b until the force of the actuator 38 balances the force of the spring 64, and depending on the duty cycle chosen, a particular actuation rate of the vane will be set in a first direction, here illustrated as a clockwise or advancing direction. The actuation rate of the vane is the rotational speed at which the vane 46 is moving. Based on setting the spool 54 for a desired actuation rate with a given duty cycle, the vane 46 position may be carefully dialed in by allowing the vane 46 to move for a preset time period. The actuation rate multiplied by the time period will give a desired change in phaser position.

In the position shown, spool land 54a blocks the exit of fluid from line 58, and lines 60 and 62 are open. Camshaft torque pressurizes the retard chamber 52, causing fluid in the retard chamber 52 to move into the advance chamber 50. Fluid exiting the retard chamber 52 moves through line 62 and into the spool valve 51 between lands 54a and 54b. From the spool valve 51, the fluid enters line 60 and travels through open check valve 59 into line 58 and the advance chamber 50, moving the vane 46 in the direction shown by the arrow.

Makeup oil is supplied to the phaser from supply to make up for leakage and enters line 55 and moves through inlet check valve 57 to the spool valve 51. From the spool valve 51 fluid enters line 60 through either of the check valves 59, 61, depending on whether fluid travels to the advance chamber 50 or the retard chamber 52.

FIG. 1 a shows the phaser in null or a central position where the spool lands 54a, 54b block lines 58 and 62, respectively and vane 46 is locked into position. Makeup oil may be provided to the chambers 50, 52 as necessary. In the null or central position, the actuation rate is zero. However, the force from the actuator 38 on the spool must balance the force of the spring 64, to maintain the spool in a central position.

FIG. 2 shows a schematic of an oil pressure actuated phaser. In an oil pressure actuated phaser, engine oil pressure is applied to one side of the vane 46 or the other by a control valve 51. Oil from the opposing chamber is exhausted back to oil sump through one of lines 63, 65. The applied engine oil pressure alone is used to move the vane 46.

FIG. 3 shows a schematic of a torsion assist phaser, which may also be used with the control system of the present invention. In torsion assist phasers, the engine oil pressure is the main force in which moves the vane 46 in the desired direction. A check valve 57 is added in the oil supply line 55 to block oil pressure. The check valve blocks oil pressure pulses due to torque reversals caused by changing load conditions from propagating back into the oil system, prevents drainage of oil from the phaser when the engine is stopped, and stops the vane from moving backwards due to torque reversals. In this type of system, however, motion of the vane due to forward torque effects is permitted. Alternatively, two check valves may be added in the supply line to each of the chambers. U.S. Pat. No. 6,883,481 and U.S. Pat. No. 6,763,791 also disclose torsion assist phasers and are hereby incorporated by reference.

The control system of the present invention described above may also be used with a hybrid phaser, which is a CTA phaser with proportional oil pressure as discussed in U.S. Pat. No. 6,997,150 which is hereby incorporated by reference

Ideally, the actuation rate of the vane would be constant for a given duty cycle. Unfortunately, however, the relationship between actuation rate and duty cycle may change under differing temperature conditions. As the temperature increases, the actuation rate at a given duty cycle tends to increase. An example of this relationship is shown in FIG. 4 which graphically illustrates a first embodiment of the present invention. The system is designed so that at a nominal temperature 1, a first actuation rate curve 66 is present. As the temperature is increased to a temperature 2 and to a further temperature 3, the actuation rate curves may change to curves 68 and 70 respectively. These actuation curves 66, 68, 70 may be determined empirically during development of the VCT phaser. Although the example actuation curves 66, 68, 70 are shown as continuous curves, they may be discreet points in other embodiments, and for the purposes of choosing values from such discreet points, algorithms for rounding or interpolating may be used. The benefit to programming, storing, or making the data actuation rate curve data available to the controller 36 is that a duty cycle may be set to achieve a desired actuation rate AD based on the current temperature conditions.

When the temperature is temperature 1, actuation rate AD is achieved by setting the duty cycle to DC1. If the temperature is increased to temperature 2, then a duty cycle value of DC2 would achieve the actuation rate AD. Similarly, if the temperature is increased to temperature 3, then a duty cycle value of DC3 would achieve the actuation rate AD. In other words, the duty cycle is varied based on temperature to maintain a constant actuation rate. For simplicity, duty cycles are mapped for only three temperatures in the embodiment of FIG. 4, however, any number of temperatures may be mapped in other applications. The temperature map values may be stored in a non-volatile memory (NVM), read-only memory (ROM), or populated into a volatile memory, such as a random access memory (RAM) as needed.

FIG. 5 shows the steps for a method of adjusting the duty cycle of the actuator 38, preferably a PWM solenoid of a phaser as shown in FIGS. 1 through 3, based on temperature changes only, using a temperature limit curve. In a first step 72, the maximum actuation rate is set by the ECU 39. Then, the temperature is determined by a sensor 40, preferably in the main oil gallery in step 73 and sent to the controller 36. Next, a temperature limit curve is selected in step 74 by controller 36. The temperature limit curve may be a continuous relationship or a set of discreet points. In step 75, a new max duty cycle is calculated and then compared in step 76 to the current duty cycle stored in the controller 36 and adjusted in step 77, if necessary, based on the temperature limit curve selected in step 74. The controller 36 then uses this duty cycle when activating the actuator 38. If the duty cycle is the same, the method restarts at step 73.

Optional actions may be taken prior to adjusting the duty cycle in step 77. Rather than always having to select the duty cycle curve, particularly if the temperature was not changing or had reached a steady state, a current duty cycle table may be populated in step 80 with various actuation rates based on the last changed temperature. No change would be necessary if the temperature has not changed. Since discreet values are likely to be used in the step 74 of selecting a temperature curve or in step 80 of populating a duty cycle table, step 82 of interpolating the values populated into the current temperature limit curve may be performed. Similarly, the duty cycle rate may be interpolated in step 84 in order to determine the desired actuation rate for the actuation rate adjustment in step 77.

Alternative to using a temperature limit curve is to determine the maximum duty cycle by equation (1.1), calculated in controller 36 at a constant voltage. $\begin{array}{cc}\left[\frac{1}{\frac{V_0}{\left[R_0*\alpha \left(\Delta T\right)\right]+R_0}}\right]*100=\mathrm{Max}\mathrm{DC}& \left(1.1\right)\end{array}$ Where:

• R₀ is the Initial Resistance at starting temperature;
• ΔT is the change in temperature from a starting temperature to a final temperature;
• α is the Temperature coefficient of resistance; and
• V₀ is the initial voltage

For example, if the starting temperature of the main oil gallery is 20° C., the initial resistance is 6 ohms, the temperature coefficient of resistance is for copper, due to the windings in the controller, the voltage is 14 volts, and the temperature increases to 135° C., the maximum duty cycle (MaxDC) would be calculated as follows: $\begin{array}{cc}\left[\frac{1}{\frac{14}{\left[6*\mathrm{.0039}\left(115\right)\right]+6}}\right]*100=\mathrm{Max}\mathrm{DC}& \left(1.1\right)\end{array}$ 62.08%=MaxDC at 135° C. Therefore, the maximum duty cycle would be set at 62.08% in order to receive the maximum current output of 1.0 amp.

FIG. 6 shows the steps for a method of adjusting the duty cycle of a PWM solenoid of a phaser as shown in FIGS. 1 through 3 based on temperature changes only, using equation (1.1) calculated in controller 36. In a first step 72, the maximum actuation rate is set by the ECU 37. Then, the temperature is determined by a sensor 40, preferably in the main oil gallery in step 173 and the initial resistance is at the initial starting temperature is determined and sent to the controller 36. The temperature and the initial resistance at the initial starting temperature is inputted into step 175 and a new duty cycle is determined, preferably using equation (1.1) in the controller 36. In step 176, the new max duty cycle is compared to the current duty cycle stored in the controller 36 and adjusted if necessary in step 177. The controller 36 then uses this duty cycle when activating the actuator 38. If the duty cycle is the same, the method restarts at step 173.

In a second embodiment, the controller varies the duty cycle sent to the actuator 38, preferably a PWM solenoid is varied based on voltage only in the phasers shown in FIGS. 1 through 3. The voltage is preferably from a battery in the engine. Based on the system designed, the current outputted as a result of the voltage is reduced (if necessary) to a maximum current that is non-detrimental to the both the system as a whole and the solenoid valve through the duty cycle of the PWM solenoid or actuator 38. For the examples in this application, the maximum amount of current used with the system is 1 amp. One amp of current corresponds to full movement of the spool in a direction from a null position of the spool. While 1 amp was chosen as the maximum current of the system, other values may be chosen. Table 1 shows a range of voltages at a constant temperature and the current originally outputted from the system and the max percent duty cycle used to maintain the one amp maximum set.

TABLE 1
		Initial		New Max
Voltage	Temperature	Current	Max Duty Cycle	Current Output
9 V	40° C.	1.36 amps	73.3%	1.0 amp
12 V	40° C.	1.82 amps	55.0%	1.0 amp
15 V	40° C.	2.27 amps	44.0%	1.0 amp
18 V	40° C.	2.73 amps	36.7%	1.0 amp
(Assuming an initial resistance of 6.6 ohms).

The maximum duty cycle for a change in voltage may be calculated using equation (2.1). $\begin{array}{cc}\left[\frac{1}{\frac{V_0+\Delta V}{R_0}}\right]*100=\mathrm{Max}\mathrm{DC}& \left(2.1\right)\end{array}$ Where:

• V₀ is the Voltage initial;
• R₀ is the Resistance initial; and
• ΔV=is the change in voltage.

For example, if the voltage changes from outputting 9 volts to 12 volts with an initial resistance of 6.6 ohms at a constant temperature of 40° C., the maximum duty cycle (MaxDC) would be calculated as follows: $\begin{array}{cc}\left[\frac{1}{\frac{V_0+\Delta V}{R_0}}\right]*100=\mathrm{Max}\mathrm{DC}\left[\frac{1}{\frac{9+3}{6.6}}\right]*100=\mathrm{Max}\mathrm{DC}& \left(2.1\right)\end{array}$ 55%=MaxDC at 12V and a constant temperature of 40° C.

The max duty cycle at 12 volts and a constant temperature 40° C. is 55% to insure that only 1 amp of current is received by the actuator 38. The max duty cycle for other voltages are listed in Table 1.

FIG. 7 shows steps for a method of a method of adjusting the duty cycle of a PWM solenoid of a phaser as shown in FIGS. 1 through 3 based on voltage changes only, using equation (2.1) which is calculated in controller 36. In a first step 72, the maximum actuation rate is set by the ECU 37. Then, the voltage outputted by the battery is determined and the initial resistance at the constant temperature is determined in step 273. Next, in step 275, the new maximum duty cycle is determined in the controller 36, preferably using equation (2.1). In step 276, the new max duty cycle is compared to the current duty cycle stored in the controller 36 and adjusted if different in step 277. The controller 36 then uses the new adjusted duty cycle from step 277 when actuating actuator 38. If the duty cycle is the same, the method restarts at step 273.

Alternatively, as shown in FIGS. 8 and 9, a voltage curve may also be used to determine the maximum duty cycle. In a first step 72, of a method of adjusting the duty cycle of a PWM solenoid of a phaser as shown in FIGS. 1 through 3, the maximum actuation rate is set by the ECU 37. Then, the voltage outputted by the battery is determined and the constant temperature is determined in step 373. Next, in step 374, a voltage curve, as shown in FIG. 8 is selected by controller 36 and is used to determine a new duty cycle. The voltage curve may be a continuous relationship or a set of discreet points. In step 375, the new max duty cycle is compared to the current duty cycle stored in the controller 36 and adjusted if different in step 377. The controller 36 then uses the new adjusted duty cycle from step 377 when actuating actuator 38. If the duty cycle is the same, the method restarts at step 373. The duty cycle rate may be interpolated in step 384 in order to determine the desired actuation rate for the actuation rate adjustment in step 377.

In a third embodiment, the duty cycle of the actuator 38, preferably a PWM solenoid of a phaser as shown in FIGS. 1 through 3 is varied based on voltage and temperature. The voltage is preferably from a battery in the engine. Based on the system designed, the current outputted as a result of the voltage and temperature is altered to a maximum current that is non-detrimental to the both the system as a whole and the solenoid valve through the duty cycle of the PWM solenoid or actuator 38. For the examples in this application, the maximum amount of current used with the system is 1 amp. One amp of current corresponds to movement of the spool in a first direction from null and may be the advancing direction. As the temperature changes, the voltage from the battery changes, thus the amps outputted also changes due to resistance. In order to maintain the maximum actuation rate of the phaser, the current outputted from the varying voltage and temperature is altered back to 1 amp by varying the duty cycle as in previous embodiments.

The initial current as the voltage and temperature change may be calculated using equation (3.1). $\begin{array}{cc}\left[\frac{1}{\frac{V_0+\Delta V}{\left[R_0*\alpha \left(\Delta T\right)\right]+R_0}}\right]*100=\mathrm{Max}\mathrm{DC}& \left(3.1\right)\end{array}$ Where:

• V₀ is the Initial Voltage;
• R₀ is the Initial Resistance;
• ΔV is the Change in Voltage;
• ΔT is the Change in Temperature; and
• α is the Temperature coefficient of resistance.

For example, if the initial temperature and voltage of the system were −40° C. and 10 volts respectively, with the initial resistance determined to be 5 ohms for the system, the actuator has copper windings, and the system changed to 20° C. and 12 volts, the max duty cycle based on the initial current and the current maximum of 1 amp would be calculated as follows using equation (3.1). $\begin{array}{cc}\left[\frac{1}{\frac{V_0+\Delta V}{\left[R_0*\alpha \left(\Delta T\right)\right]+R_0}}\right]*100=\mathrm{Max}\mathrm{DC}\left[\frac{1}{\frac{10+2}{\left[5*\mathrm{.0039}\left(60\right)\right]+5}}\right]*100=\mathrm{Max}\mathrm{DC}& \left(3.1\right)\end{array}$ 51.4%=MaxDC at 12V and 20° C.

While not shown in the above example, the duty cycle may also be calculated for other positions of the spool, such as null position and for other temperatures and voltages.

FIG. 10 shows the steps for a method of adjusting the duty cycle of a PWM solenoid of a phaser as shown in FIGS. 1 through 3 based on temperature and voltage changes. In a first step 72, the maximum actuation rate is set by the ECU. Then, the temperature, the voltage, and the initial resistance at the temperature measured is determined in step 473. The temperature may be measured by a sensor 40, which is preferably in the main oil gallery. Next, in step 474a, a temperature limit curve and a voltage curve are selected by the controller 36. The temperature limit curve and the voltage curve may be continuous relationships or sets of discreet points. In step 475, a new max duty cycle is determined and then compared in step 476 to the current duty cycle stored in the controller 36. If the new duty cycle is the same as the current duty cycle, the method is repeated starting at step 473. If the new duty cycle differs from the current duty cycle, the duty cycle is adjusted in step 477, and the new duty cycle is used when activating actuator 38.

Step 474 may be removed from the method, and in step 475, the new max duty cycle may be determined by using equation (3.1) calculated in the controller 36. In another alternative, the max duty cycle for a system with both voltage and temperature changes may be determined using the temperature limit curve or the voltage curve and equations (2.1) and (1.1) for the other.

Optional actions may be taken prior to adjusting the duty cycle in step 477. Rather than always having to select the duty cycle curve, particularly if the temperature and/or voltage was not changing or had reached a steady state, a current duty cycle table may be populated in step 480 with various actuation rates based on the last changed temperature or voltage. No change would be necessary if the temperature and voltage have not changed. Since discreet values are likely to be used in the step 474 of selecting a temperature curve or a voltage curve or in step 480 of populating a duty cycle table, step 482 of interpolating the values populated into the current temperature limit curve or voltage curve may be performed. Similarly, the duty cycle rate may be interpolated in step 484 in order to determine the desired actuation rate for the actuation rate adjustment in step 477.

Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.

Claims

1. A method of maintaining a constant actuation rate in an engine comprising the steps of: a) setting a maximum actuation rate and sending the rate to a controller; b) determining at least one engine control parameter and sending the at least one engine control parameter to the controller; c) using the at least one engine control parameter to determine a new duty cycle in the controller; d) comparing the new duty cycle to a current duty cycle in the controller; and e) adjusting and outputting the new duty cycle from the controller to an actuator.

2. The method of claim 1, wherein the at least one engine control parameter is voltage.

3. The method of claim 1, wherein the at least one engine control parameter is temperature.

4. The method of claim 3, wherein the temperature is from a pressurized source of fluid, a coolant system, engine block, engine compartment, radiator, or a cooling system.

5. The method of claim 1, wherein the at least one engine control parameters are temperature and voltage.

6. The method of claim 1, wherein the actuator is a pulse width modulated solenoid.

7. The method of claim 1, wherein determining the new duty cycle comprises the steps of selecting a temperature limit curve.

8. The method of claim 1, wherein determining the new duty cycle comprises the step of selecting a voltage curve.

9. The method of claim 1, wherein determining the new duty cycle comprises the steps of selecting a voltage curve and selecting a temperature limit curve.

10. The method of claim 1, wherein the new duty cycle is a maximum duty cycle and is determined by equation:

11. A method of maintaining a constant actuation rate in an internal combustion engine comprising the steps of: a) setting a maximum actuation rate of a variable cam timing system and sending the rate to a controller; b) determining at least one engine control parameter and sending the at least one engine control parameter to the controller; c) using the at least one engine control parameter to determine a new maximum duty cycle in the controller; d) comparing the new maximum duty cycle to a current duty cycle in the controller; and e) adjusting and outputting the new maximum duty cycle from the controller to an actuator, such that the actuator positions a control valve of a variable cam timing phaser of the variable cam timing system, altering the phase of the variable cam timing system.

12. The method of claim 11, wherein the at least one engine control parameter is voltage.

13. The method of claim 11, wherein the at least one engine control parameter is temperature.

14. The method of claim 13, wherein the temperature is from a pressurized source of fluid, a coolant system, engine block, engine compartment, radiator, or a cooling system.

15. The method of claim 11, wherein the at least one engine control parameters are temperature and voltage.

16. The method of claim 11, wherein the actuator is a pulse width modulated solenoid.

17. The method of claim 11, wherein determining the new maximum duty cycle comprises the step of selecting a temperature limit curve.

18. The method of claim 11, wherein determining the new maximum duty cycle comprises the step of selecting a voltage curve.

19. The method of claim 11, wherein determining the new maximum duty cycle comprises the steps of selecting a voltage curve and selecting a temperature limit curve.

20. The method of claim 11, wherein the new maximum duty cycle is determined by equation:

21. The method of claim 11, wherein the variable cam timing phaser comprises: a housing with an outer circumference for receiving drive force; a rotor for connection to a camshaft coaxially located within the housing having at least one vane, wherein the housing and the rotor define at least one chambers, separated by the vane into an advance chamber and a retard chamber, the vane being capable of rotation to shift relative angular position of the housing and the rotor; and a control valve coupled to the actuator and in connection with the advance chamber and the retard chamber for directing fluid flow to shift the relative angular position of the rotor relative to the housing.

22. The method of claim 21, wherein the control valve allows fluid to flow between the advance chamber and the retard chamber.

23. The method of claim 22, further comprising at least one check valve between the advance chamber and the retard chamber and the control valve for blocking reverse fluid flow.

24. The method of claim 21, further comprising a passage in fluid communication with a pressurized fluid source.

25. The method of claim 24, further comprising a check valve in the passage.

26. A variable cam timing system for an internal combustion engine comprising: a phaser having: a housing with an outer circumference for receiving drive force; a rotor for connection to a camshaft coaxially located within the housing having at least one vane, wherein the housing and the rotor define at least one chambers, separated by the vane into an advance chamber and a retard chamber, the vane being capable of rotation to shift relative angular position of the housing and the rotor; and a control valve in connection with the advance chamber and the retard chamber for directing fluid flow to shift the relative angular position of the rotor relative to the housing; a controller receiving input from at least one engine parameter, and an engine control unit and outputting a new duty cycle based on the at least one engine parameter and the engine control unit to an actuator coupled to the control valve for positioning the control valve, such that the angular position of the housing relative to the rotor of variable cam timing phaser of the variable cam timing system is altered.

27. The variable cam timing system of claim 26, wherein the control valve allows fluid to flow between the advance chamber and the retard chamber.

28. The variable cam timing system of claim 27, further comprising at least one check valve between the advance chamber and the retard chamber and the control valve for blocking reverse fluid flow.

29. The variable cam timing system of claim 26, further comprising a passage in fluid communication with a pressurized fluid source.

30. The variable cam timing system of claim 29, further comprising a check valve in the passage.

31. The variable cam timing system of claim 26, wherein the engine control unit provides the angular phase position between the housing and the rotor.

32. The variable cam timing system of claim 26, wherein a method of determining the new duty cycle comprises the steps of: a) setting a maximum actuation rate of a variable cam timing system from the engine control unit and sending the rate to a controller; b) determining the at least one engine control parameter and sending the at least one engine control parameter to the controller; c) using the at least one engine control parameter to determine the new maximum duty cycle in the controller; d) comparing the new maximum duty cycle to a current duty cycle in the controller; and e) adjusting and outputting the new maximum duty cycle from the controller to an actuator, such that the actuator positions a control valve of a variable cam timing phaser of the variable cam timing system, altering the phase of the variable cam timing system.

33. The variable cam timing system of claim 32, wherein the at least one engine control parameter is voltage.

34. The variable cam timing system of claim 32, wherein the at least one engine control parameter is temperature.

35. The variable cam timing system of claim 34, wherein the temperature is from a pressurized source of fluid, a coolant system, engine block, engine compartment, radiator, or a cooling system.

36. The variable cam timing system of claim 32, wherein the at least one engine control parameters are temperature and voltage.

37. The variable cam timing system of claim 32, wherein the actuator is a pulse width modulated solenoid.

38. The variable cam timing system of claim 32, wherein determining the new maximum duty cycle comprises the step of selecting a temperature limit curve.

39. The variable cam timing system of claim 32, wherein determining the new maximum duty cycle comprises the step of selecting a voltage curve.

40. The variable cam timing system of claim 32, wherein determining the new maximum duty cycle comprises the steps of selecting a voltage curve and selecting a temperature limit curve.

41. The variable cam timing system of claim 32, wherein the new maximum duty cycle is determined by equation:

42. The variable cam timing system of claim 32, wherein the controller is part of the engine control unit.