Electromagnet mounting and control system for a variable camshaft phaser containing magneto-rheological fluid

A magneto-rheological fluid controlled camshaft phaser is provided having a stator with inwardly directed projections which define working spaces therebetween. The stator is adapted to be connected to the crankshaft via a timing gear and chain. A rotor is located radially inside the stator and is connected to the camshaft. Rotor lugs extend radially outwardly from the rotor into the working spaces, dividing them into first and second chambers on each side of the rotor lugs. A magneto-rheological fluid is located in the chambers, and the chambers on each side of each rotor lug are connected via a clearance space between the radially outer surface of the lugs and the inner surface of the stator located between the projections. The rotor is connected to the camshaft. An electromagnetic assembly is mounted adjacent to the stator and includes at least one electromagnet along with at least one ferrous focusing piece. In one embodiment, a plurality of the electromagnets are axially spaced apart from the working chambers holding the magneto-rheological fluid. In another embodiment the electromagnetic is formed by a coil which is radially spaced apart from the working chambers holding the magneto-rheological fluid. In each case, the magnetic field is passed from the electromagnet(s) and the ferrous focusing piece(s) into the phaser via a small air gap spacing between the electromagnet assembly and the moving camshaft phaser.

BACKGROUND

Camshaft phase shifting mechanisms that vary the rotational angle position of a camshaft relative to a crankshaft of an internal combustion engine using pressurized hydraulic fluid to control a rotary actuator, typically using engine oil supplied by the oil pump, are known. However, such hydraulically actuated phasers can have a high oil demand, and the performance can vary depending upon the temperature of the engine oil. Further, such systems require oil flow control valves and complex passages for leading the pressurized hydraulic fluid from the engine oil supply to the rotating, hydraulically actuated camshaft phasing assembly.

In order to address the shortcomings of such pressurized hydraulic fluid actuated camshaft phasing assemblies, it has also been proposed to use a closed hydraulic circuit in an engine camshaft phaser in which the hydraulic circuit employs a magneto-rheological fluid as a hydraulic pressure medium. This is disclosed in PCT/GB02/05464. In this disclosure, a camshaft phaser is provided having a rotor attached to the camshaft and a stator connected to the crankshaft via a timing chain and gear. Hydraulic working chambers are located on opposing sides of two vanes which extend from the rotor into working chambers defined in the stator. The magneto-rheological fluid flows freely between the chambers via passages which connect opposing chambers. The flow of the magneto-rheological fluid through the passage is controlled by the selective application of a magnetic field.

Magneto-rheological fluids are materials that respond to an applied magnetic field with a change in their properties. In this case, the application of a magnetic field causes the magneto-rheological fluid to increase greatly in viscosity to a virtual solid state. Magneto-rheological fluids have a very fast response time and their flow properties change within milliseconds of application or removal of the magnetic field. One example is MRF-122EG from Lord Corp.

In the case of a camshaft phaser, as the rotor, which is typically connected with the camshaft, fluctuates in position relative to the stator within a defined rotational angle based on the travel available to the vanes in the working chambers, when a desired position is achieved, the electromagnet is actuated and the position of the rotor is hydraulically locked relative to the stator due to the passage between the chambers being blocked by the change of state of the magneto-rheological fluid in response to the magnetic force being applied.

DE 102 33 044 A1 also discloses a magneto-rheological fluid actuated camshaft adjuster in which passages between the working chambers are provided via openings defined through the vanes of the rotor. However, in these known prior art devices, it is necessary to provide current to the electromagnet as it rotates with the camshaft adjuster. Further, these prior art solutions change from a low viscosity fluid state when no electromagnetic force is applied to a nearly solid state when the electromagnetic force is applied, making controlled shifting of the phase position of the camshaft relative to the crankshaft more complicated.

SUMMARY

The present invention provides a camshaft phaser using magneto-rheological fluid to maintain the angular position between the camshaft and the crankshaft of an internal combustion engine which addresses these issues with the prior art.

In a first preferred embodiment of the invention, the camshaft phaser includes a stator having inwardly directed projections which define working spaces therebetween. The stator is adapted to be connected to the crankshaft via a timing gear and chain. A rotor is located radially inside the stator and is connected to the camshaft. Rotor lugs extend radially outwardly from the rotor into the working spaces, dividing them into first and second chambers on each side of the rotor lugs. A magneto-rheological fluid is located in the chambers, and the chambers on each side of each rotor lug are connected via a clearance space between the radially outer surface of the lugs and the inner surface of the stator located between the projections. The rotor is connected to the camshaft, preferably via a central bolt. An electromagnetic assembly is mounted adjacent to the stator and includes at least one electromagnet along with at least one ferrous focusing piece. In the first embodiment, a plurality of the electromagnets are axially spaced apart from the working chambers holding the magneto-rheological fluid. In a second preferred embodiment the electromagnetic is formed by a coil which is radially spaced apart from the working chambers holding the magneto-rheological fluid. In each case, the magnetic field is passed from the magnet and the ferrous focusing piece into the phaser via a small air gap spacing between the electromagnet assembly and the moving camshaft phaser.

The electromagnet(s) are connected to the engine control unit (ECU) and are activated using pulse width modulation (PWM) signals. As the signals increase from 0% to a maximum of 100%, the viscosity of the magneto-rheological fluid becomes thicker, until it is nearly solid at 100% PWM signal. This allows the position of the rotor to be adjusted relative to the stator with some control by continuously adjusting the viscosity of the magneto-rheological fluid using the ECU. As the movement of the rotor relative to the stator occurs based on the camshaft torsional forces provided via engagement and disengagement of the cam lift surfaces with the respective lifters, in a 0% PWM signal state, this can result in rapid fluctuation between the maximum adjustment positions of the rotor relative to the stator, which is limited only by the stops created by the stator projections. Using the PWM signal control and gradually increasing the signal from 0% to gradually increase the viscosity of the magneto-rheological fluid prevents such rapid fluctuating movements of the rotor relative to the stator and, using feedback position sensing of the camshaft to the ECU, allows the ECU to lock the rotor (and hence the camshaft) into a desired position with a higher accuracy.

In the first preferred embodiment, the electromagnets are held via a mounting plate spaced axially apart from the phaser.

In the second preferred embodiment, the mounting plate holds the electromagnet in a radially spaced apart position around the camshaft phaser.

Preferably, the spaces between the stator and rotor are sealed using o-ring and/or combination o-ring/lip seals in order to prevent the magneto-rheological fluid from escaping from the phaser as well as to prevent air from entering the phaser. The mounting plates for the electromagnets can be made of any suitable metallic or polymeric material, and may be molded.

In the second embodiment of the invention with the radially spaced electromagnet, preferably the support plate includes a support ring that is spaced apart from the radial outer surface of the stator and in or upon which an electromagnetic coil is wound. A ferrous focusing ring is mounted inside the support ring to focus the electromagnetic field toward the working chambers with the magneto-rheological fluid.

In the both preferred embodiments, an alignment feature is provided for accurate placement of the electromagnetic support assembly around the phaser10. In one preferred embodiment, this alignment feature is designed to wear off rapidly, and may be made of a low density polymeric material.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Certain terminology is used in the following description for convenience only and is limiting. The words “front,” “rear,” “upper” and “lower” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to the directions toward and away from the parts referenced in the drawings. A reference to a list of items that are cited as “at least one of a, b or c” (where a, b or c represent the items being listed) means any single one of the items a, b or c, or combinations thereof. The terms “camshaft”, “phaser” and “adjuster” are used interchangeably. Magneto-rheological fluid is also referred to as “MR fluid.” The terminology includes the word specifically noted above, derivatives thereof and words of similar import.

Referring toFIGS. 1-6, a first embodiment of a magneto-rheologically actuated camshaft phaser10is shown. As show in detail inFIGS. 1 and 2, the camshaft phaser10includes a stator12which is connected to a timing gear or pulley14for connection to the crankshaft of an internal combustion engine via a traction element, such as a timing chain or belt, or a gear stage drive. As shown most clearly inFIG. 2, the stator12includes inwardly directed projections16which define working spaces18for the magneto-rheological fluid. A rotor20is located within the stator12and includes an outer surface on which the inwardly directed projection16of the stator are slidingly supported. Rotor lugs22extend radially outwardly from the rotor20into the working spaces18defined by the stator12, dividing the working spaces18into a first set of chambers24and a second set of chambers26, with the first and second sets of chambers24,26being located on opposite sides of the rotor lugs22. While three sets of chambers24,26and lugs22are shown, this number can be varied. The rotor20preferably includes a timing pin28which can be received in the front end of a camshaft30of an internal combustion engine, as shown in the phantom lines inFIG. 1. A helical spring32is connected between the stator12and the rotor20in order to equalize the force required to advance or retard a timing position of the rotor20relative to the stator12. The spring32is held to the rotor20via a spring retainer34which preferably also acts as a trigger wheel for a position or timing sensor52connected to the engine control unit (ECU)50. Preferably, a space is provided between the radially outer surface of the rotor lugs22and the inner surface of the stator12in the working spaces18as shown inFIG. 2. This allows the MR fluid to move between the first set of chambers24and the second set of chambers26when no electromagnetic field is applied and the MR fluid has a low viscosity.

Preferably, the timing gear14, the stator12and the rotor20are formed of non-ferromagnetic material, such as aluminum, in order not to interfere with the magnetic circuit described in more detail below. The MR fluid fills the first and second sets of chambers24,26. Preferably seals36are disposed on each side of the rotor20in order to seal the first and second sets of chambers24,26to prevent the MR fluid from escaping. The seals36can be o-ring seals, lip seals or a combination of an o-ring seal including one or more lip seals extending therefrom, as illustrated.

As shown in detail inFIG. 1, an electromagnetic assembly40is mounted to the engine behind the camshaft phaser10. The electromagnetic assembly40includes a mounting plate41having a plurality of electromagnets44located in magnet mounting holes42. Ferrous focusing discs45are located on the camshaft phaser facing sides of the electromagnets44. Mounting holes46are provided in the plate41for mounting the electromagnetic assembly40to the engine in a position behind the camshaft phaser10. A clearance opening48is provided into which the front of the camshaft30extends for attachment to the rotor20of the camshaft phaser10. The electromagnets44are preferably inserted from the backside of the plate41, and the ferrous focusing discs45for focusing the electromagnetic radiation are located on the front side in close proximity to stator12.

As shown inFIG. 1, the rear wall of the stator12is preferably formed via the timing gear wheel, and the electromagnets44are placed with a small axial clearance to allow rotation of the phaser10within contacting the ferrous discs45. The placement of the electromagnets44is directly aligned with the working chambers24,26and, based on the rotational speed of the phaser, four uniformly spaced electromagnets is believed to be sufficient for maintaining the state of the MR fluid when the electromagnets44are activated by the PWM signal from the ECU.

A second embodiment of the invention is shown inFIGS. 7-10, in which the phaser10is as described above. However, in this case the electromagnet assembly60provides a single ring-shaped electromagnet that entirely radially encompasses the stator12of the phaser10in the region of the working chambers24,26. As shown inFIGS. 8-10, the electromagnet assembly60includes a housing62having mounting holes68for mounting the electromagnet assembly in position at the front of the camshaft phaser10. The housing62includes a support ring63in or around which the electromagnetic coil64is wound. A ferrous focusing ring66is radially inwardly located from the coil64and is used to focus the electromagnetic radiation toward the first and second sets of chambers24,26in order to activate the MR fluid. The housing62can be made of a non-ferrous or polymeric material and can be cast or molded.

In view of the small radial clearance desired between the ferrous ring66and the outside of the stator12, the electromagnet support assembly60must be closely aligned with the phaser10to prevent interference or contact between the phaser10and the ferrous ring66. This can be accomplished with thin, wear away spacers which are located on the ferrous disks45or the ferrous ring66, which are preferably a low density polymeric material.

In operation, the separate electromagnets44of the electromagnet assembly40or the electromagnetic coil64of the electromagnet assembly60are connected to the ECU for the engine, and the magnetic field strength is varied by the ECU50from 0% to 100% using a PWM signal from the ECU50. The position of the rotor20(and hence the camshaft) relative to the stator12is measured via the sensor52from the trigger wheel34. The ECU actuates the electromagnet(s)44,64using the PWM signal from the ECU50. The signal can be increased from 0%, at which the MR fluid is at its lowest viscosity, to a maximum of 100%, where the viscosity of the MR fluid becomes so high that the fluid is nearly solid at 100% PWM signal. With the 100% PWM signal, the phase angle position between the rotor20and the stator12is fixed.

The electromagnetic radiation from the electromagnet(s)44,64passes either through the radial cover or end face of the stator12to the first and second sets of chambers24,26in order to activate the MR fluid. By slowly increasing the PWM signal to the electromagnet(s)44,64, the viscosity of the MR fluid can be gradually increased. This has the advantage of acting as a variable effect damper to damp the movements created between the rotor and the stator due to the different forces experienced by the camshaft30during its rotation. During the engine cycle, the camshaft experiences reversing torques that act alternately in directions to advance and to retard the phase of the camshaft relative to the crankshaft depending upon whether the cams on the camshaft are in a lift cycle (to open a valve) or a closing cycle (allowing the valve to close via the valve spring). If the PWM signal is at 0% to the electromagnet(s)44,64, the rotor20is allowed to move freely by the MR fluid passing between the first and second sets of chambers24,26via the space between the radially outer surface of the rotor lugs22and the facing inner surface of the stator12. As the PWM signal to the electromagnet(s)44,64increases from 0%, the viscosity of the MR fluid increases, creating a greater damping action, slowing the alternating movement of the rotor20due to the alternating torques experienced by the camshaft30. The position/timing sensor52continuously reads the position of the camshaft30and, based on input regarding the position of the crankshaft, it can increase the PWM signal as required, creating a greater damping effect by the MR fluid and allowing the position of the rotor20to be more accurately measured due to the higher damping of the movement. As the desired timing position is reached, the PWM signal increases to 100%, changing the state of the MR fluid to a nearly solid form in a matter of milliseconds, thus locking the angular position of the rotor20relative to the stator12.

In a preferred embodiment of the invention, the outer cover of the stator12is formed as a deep drawn aluminum part which can be welded, mechanically fastened or otherwise connected to the timing gear14.

This arrangement provides a MR fluid actuated camshaft phaser10that allows dependable, accurate and reliable positioning of a camshaft phase angle relative to a crankshaft without the use of pressurized engine oil. This avoids the changes in operation seen in the previously known hydraulically actuated camshaft phasers due to changes in oil temperature. As the MR fluid controlled phaser10is entirely independent of the engine oil circuit, it provides improved phaser performance.

Both embodiments of the invention also address the need to activate the MR fluid within the rotating phaser10from a stationary electromagnet connected to the ECU in order to receive the PWM signal.

Those skilled in the art will appreciate that various modifications can be made to the MR fluid controlled phaser10as well as the electromagnet assemblies40and60described above which would still fall within the scope of the present invention.