Roll control system, device and method for controlling vehicle stability

A roll control system for a vehicle is disclosed. The roll control system includes front and rear stabilizer bars, first and second magnetorheological actuators, and an electronic control system. The first magnetorheological actuator is disposed between the front stabilizer bar and the front suspension on one side of the vehicle, and a first droplink is disposed between the front stabilizer bar and the front suspension on the other side of the vehicle. The second magnetorheological actuator is disposed between the rear stabilizer bar and the rear suspension on one side of the vehicle, and a second droplink is disposed between the rear stabilizer bar and the rear suspension on the other side of the vehicle. The electronic control system is responsive to a vehicle operating characteristic and is in signal communication with the first and second magnetorheological actuators. The first and second actuators are responsive to a control signal from the electronic control system such that they are locked in response to the vehicle undergoing a cornering maneuver, and are unlocked in response to the vehicle not undergoing a cornering maneuver.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to a roll control system, device and method for controlling vehicle stability, and particularly to a magnetorheological actuator for purposes thereof.

A vehicle roll or stability control system may consist of a passive anti-roll bar made up of solid or hollow steel tubes connected between the left and right body suspension points in the front and rear of the vehicle. During cornering at high velocities, the centrifugal forces on the body of a vehicle tend to push the body roll angle toward its stability limit. With a suitably designed anti-roll (stabilizer) bar, the vehicle roll angle may be reduced under such maneuvers and the vehicle roll-over propensity minimized. However, a passive anti-roll bar tends to increase the suspension harshness by transmitting road disturbances such as single wheel pot hole or bump events to the passenger compartment, resulting in a less than desirable ride quality. An active or semi-active roll control system may engage the anti-roll bar only when needed and disengage it otherwise, thereby improving the ride quality. However, typical active roll-control systems require a hydraulic pump and a hydraulic control, thereby driving up system complexity and cost.

While existing anti-roll actuators, roll control systems and methods for controlling vehicle stability are suitable for their intended purpose, there remains a need in the art for improvements that overcome these drawbacks.

BRIEF DESCRIPTION OF THE INVENTION

Embodiments of the invention disclose a roll control system for a vehicle. The roll control system includes front and rear stabilizer bars, first and second magnetorheological actuators, and an electronic control system. The first magnetorheological actuator is disposed between the front stabilizer bar and the front suspension on one side of the vehicle, and a first droplink is disposed between the front stabilizer bar and the front suspension on the other side of the vehicle. The second magnetorheological actuator is disposed between the rear stabilizer bar and the rear suspension on one side of the vehicle, and a second droplink is disposed between the rear stabilizer bar and the rear suspension on the other side of the vehicle. The electronic control system is responsive to a vehicle operating characteristic and is in signal communication with the first and second magnetorheological actuators. The first and second actuators are responsive to a control signal from the electronic control system such that they are locked in response to the vehicle undergoing a cornering maneuver, and are unlocked in response to the vehicle not undergoing a cornering maneuver.

Further embodiments of the invention disclose a magnetorheological actuator having first, second and third portions, and a magnetic field generator. The first and second portions are disposed having a translational degree of freedom with respect to each other, the third portion has a rotational degree of freedom with respect to the first and second portions, the first and third portions are coupled via a translation-to-rotation converter, the second and third portions coupled via a magnetorheological fluid, and the magnetic field generator is in field communication with the magnetorheological fluid. The third portion is rotationally responsive to translational motion between the first and second portions, and the shear stress characteristic of the magnetorheological fluid is responsive to the magnetic field generator, such that a rotational braking action of the third portion results from field excitation at the magnetic field generator.

Yet further embodiments of the invention disclose a stabilizer control system for a vehicle having a suspension with a stabilizer bar and a support. The stabilizer control system includes a plurality of sensors responsive to at least one operating characteristic of the vehicle, a controller responsive to signals from the plurality of sensors, and a magnetorheological actuator disposed between the stabilizer bar and the support. The actuator includes first, second and third portions, and a magnetic field generator. The first and second portions are disposed having a translational degree of freedom with respect to each other, the third portion has a rotational degree of freedom with respect to the first and second portions, the first and third portions are coupled via a translation-to-rotation converter, the second and third portions are coupled via a magnetorheological fluid, and the magnetic field generator is in field communication with the magnetorheological fluid. The third portion is rotationally responsive to translational motion between the first and second portions, the shear stress characteristic of the magnetorheological fluid is responsive to the magnetic field generator, and the magnetic field generator is responsive to an activation signal from the controller. The magnetorheological actuator is responsive to the controller such that an activation signal from the controller causes an increase in the shear strength of the magnetorheological fluid, a rotational braking action at the actuator, and translational motion restraint between the stabilizer bar and the support.

Additional embodiments of the invention disclose a method of controlling a vehicle stabilizer system, the system having a plurality of sensors responsive to at least one operating characteristic of the vehicle, a controller responsive to the sensors, and an actuator responsive to the controller and disposed between a first part and a second part of the vehicle suspension. A signal is received at the controller from the plurality of sensors, the sensor signal is analyzed, and an activation signal generated in response thereto. The actuator is activated in response to the activation signal so as to cause a braking action at the actuator and restraint of motion between the first and second parts of the vehicle suspension.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention utilizes magnetorheological (MR) actuators with locking and unlocking capability on two sides of each of the front and rear stabilizer bars of a vehicle. An alternative embodiment utilizes one magnetorheological actuator on one side of each of the front and rear stabilizer bars. The front and rear stabilizer bars preferably have increased stiffness compared to the standard passive stabilizer bar used in a typical vehicle. An electronic control module (controller) is used with a vehicle lateral accelerometer, a steering angle sensor and a vehicle speed sensor. In response to the vehicle speed, steering angle and lateral acceleration, the control module may or may not send an activation signal to lock or unlock the actuators. During cornering, the actuators are controlled to be in a locked condition that engages the stabilizer bars and reduces vehicle roll angle. In the absence of cornering, the actuators are controlled to be in an unlocked condition thereby de-coupling the stabilizer bars from the rest of the suspension of the vehicle for improved ride performance.

FIG. 1is an exemplary embodiment of a vehicle100having a front suspension system105, a front (preferably high stiffness) stabilizer bar110, a rear suspension system115, and a rear (preferably high stiffness) stabilizer bar120. Roll-control (stabilizer) actuators200connect each end of front and rear stabilizer bars110,120to portions of front and rear suspension systems105,115, respectively. WhileFIG. 1depicts vehicle100having four roll-control actuators200, embodiments of the invention may employ only two roll-control actuators200, with one actuator on one side of each of front and rear stabilizer bars110,120. In an embodiment having only one roll control actuator200per stabilizer bar on one side of vehicle100, the other side of the respective stabilizer bar on the other side of the vehicle is coupled to the respective suspension system via a suspension droplink, generally shown as numeral200in the figures but understood to mean a droplink when used in that context.

Embodiments of the invention may use any one of several different types of magnetorheological roll-control actuators200depending on the packaging space. An exemplary magnetorheological (MR) roll-control actuator200is an actuator that utilizes a minimum amount of MR fluid222and achieves the required locking force while transmitting minimum force during an unlocked condition. In an embodiment, the amount of MR fluid222used is equal to or less than about 50 cc (cubic centimeters), and preferably equal to or less than about 10 cc, compared with more than 100 cc used in other MR actuator type devices. However, it is also within the scope of this invention to use linearly translating MR actuators that use greater than about 50 cc of MR material.

Reference is now made toFIGS. 2 and 3, whereFIG. 2depicts a cross-section block representation andFIG. 3depicts a cutaway cross-section detail view of MR actuator200. In general, MR actuator200utilizes a magnetorheological fluid222dispensed in an annular space225between two concentric cylinders274,276where it is subjected to a controllable magnetic field. Under zero magnetic field, the fluid222can be sheared easily producing little resistance to rotation, whereas under higher magnetic fields, the fluid222exhibits a high yield stress that resists rotation and therefore generates significant opposing torque on a rotor255within MR actuator200.

Referring toFIG. 2, MR actuator200includes first205, second210and third215portions. First and second portions205,210are disposed having a translational degree of freedom parallel to axis201with respect to each other, and third portion215is disposed having a rotational degree of freedom about axis201with respect to the first and second portions205,210. First and third portions205,215are coupled via a translation-to-rotation converter220, second and third portions210,215are coupled via a magnetorheological fluid222within annulus225, and a magnetic field generator230is in field communication with the magnetorheological fluid222within annulus225. Third portion215is rotationally responsive to translational motion between the first and second portions205,210, and the shear stress characteristic of the magnetorheological fluid222within annulus225is responsive to magnetic field generator230, such that a rotational braking action of third portion215results from field excitation at magnetic field generator230.

In an embodiment, first portion205includes a tube235having a ball nut240, third portion215includes a shaft245having a ball screw250at one end and a magnetic rotor ring255at an opposing end,. and second portion210includes a housing260receptive of ball nut240, shaft245and magnetic field generator230. Ball screw250is engagingly disposed at ball nut240for rotational motion therebetween, and magnetic rotor ring255is disposed within the magnetorheological fluid222at annulus225for fluid communication therebetween.

A more detailed description of MR actuator200will now be made with reference toFIG. 3. In an embodiment, first, second and third portions205,210,215form a linear-to-rotary conversion device made up of ball screw250and ball nut240, where ball nut240is attached to a lower tube235, and ball screw250is attached to cylindrical magnetic rotor ring255through a non-magnetic support disc262. Tube235is attached to a lower ball joint264, which is attached to one end of torsion bar110or120(seeFIG. 1). An upper ball joint266of MR actuator200is secured within a housing top cover268, and is attached to a support portion280, such as a strut for example, of vehicle suspension system105or115(seeFIG. 1). While upper and lower ball joints264,266are described and illustrated having specific attachment arrangements, it will be appreciated that upper and lower ball joints264,266may be attached to different parts of vehicle100depending on the type of suspension employed (see front and rear suspensions105,115inFIGS. 7 and 8, for example). Ball screw250is secured to rotate within a non-magnetic housing260and housing top cover268by means of a bushing270and a thrust ball bearing272. As ball nut240travels up and down with tube235due to vehicle body movements, ball screw250rotates in one direction or the other, along with magnetic rotor ring255and attached support disc262. Magnetic rotor ring255is disposed within two soft magnetic stator portions, an inner core274and an outer ring276, that are secured to housing260. Inner core274carries an encapsulated magnetic coil (magnetic field generator)230. The annulus225formed between magnetic rotor ring255and inner and outer stator portions274,276is filled with magnetorheological fluid222that is prevented from leaking out of MR actuator200by using static O-ring seals278between stator portions274,276and housing260.

When an electrical current is passed through coil230from an external source such as the vehicle battery125(depicted inFIG. 4), a magnetic field is produced in the radial direction with respect to axis201across annulus225between stator portions274,276and magnetic rotor ring255. The middle portion257of the rotor ring255and the middle portion259of cylinder274are made up of substantially non-magnetic material (such as, stainless steel, aluminum, brass, for example) or made of such thickness that it prevents significant amount of magnetic flux being diverted away from the outer portion of annulus225(depicted inFIG. 2). The strength of the magnetic field or flux density within MR fluid222determines the shear stress characteristics of MR fluid222, thereby controlling the degree of torque that acts to resist the rotation of magnetic rotor ring255. The resulting magnetic flux lines261that traverse annulus225are depicted inFIG. 2. The resistance torque acting on magnetic rotor ring255translates to a force that resists the linear movement of ball nut240and attached lower tube235. By the appropriate selection of the pitch of ball screw250, the axial and radial dimensions of stator portions274,276and magnetic rotor ring255, the number turns of coil230, the maximum current through coil230, and an MR fluid222with a suitable concentration of iron particles, a force sufficient to lock the translation movement of torsion bar110or120may be generated by activated MR actuators200. Similarly, the above noted parameters may be chosen in such a way as to achieve minimum force generation when the current through coil230is set to zero, thereby resulting in a de-coupled operation of stabilizer bar110,120for a quality ride.

The utilization of MR actuator200in a stabilizer control system300will now be described with reference toFIG. 4. In an embodiment, stabilizer control system300, also herein referred to as a roll control system, includes a plurality of sensors305,310,315, a controller320, at least one MR actuator200, and front and rear stabilizer bars110,120. Sensors305,310,315and controller320may also be herein referred to as an electronic control system. In an embodiment, the plurality of sensors includes a vehicle speed sensor305, a steering angle sensor310, and a lateral accelerometer315, which are responsive to the respective operating characteristic of vehicle100. Controller320is responsive to signals from the plurality of sensors305,310,315for generating an activation signal that causes an increase in the shear strength of the MR fluid222, a rotational braking action at magnetic rotor ring255of MR actuator200, a locking condition at translation-to-rotation converter220, and translational motion restraint of stabilizer bar110and/or120.

In an embodiment, and with reference toFIGS. 5 and 6, the activation signal from controller320is active (ON) in response to the vehicle speed (V) being equal to or greater than a first threshold value (th-1), and at least one of; the magnitude of a steering angle change (δ) from a neutral position being equal to or greater than a second threshold (th-2), and the magnitude of the vehicle lateral acceleration (α) being equal to or greater than a third threshold (th-3), whereby an active (ON) signal causes the locking condition discussed previously. In the embodiment illustrated byFIG. 5, speed V must equal or exceed threshold th-1, and either steering angle change δmust equal or exceed threshold th-2 or lateral acceleration a must equal or exceed threshold th-3, for the activation signal to be ON. In the embodiment illustrated byFIG. 6, all three vehicle operating characteristics must equal or exceed the respective threshold value for the activation signal to be ON.

In view of the foregoing, embodiments of the invention may perform a method of controlling a vehicle stabilizer system300by, receiving at controller320signals from sensors305,310,315, analyzing the signals and generating an activation signal in response thereto, and activating MR actuator200in response to the activation signal so as to cause an increase in the shear strength of MR fluid222, a rotational braking action at magnetic rotor ring255of MR actuator200, a locking condition at translation-to-rotation converter220, and translational motion restraint of stabilizer bar110and/or120. In an embodiment, stabilizer system includes stabilizer bars110,120connected to suspensions105,115of vehicle100, a plurality of sensors305,310,315responsive to at least one operating characteristic of vehicle100, controller320, and MR actuator200.

FIGS. 7 and 8depict more detailed isometric views of portions of suspension105,115of vehicle100with an actuator such as MR actuator200, andFIGS. 9 and 10depict exemplary configurations of MR actuator200with exemplary dimensions. In response to actuator200being powered (locked), stabilizer bars110,120are effectively connected to suspension systems105,115, respectively, and in response to actuator200not being powered (free sliding), stabilizer bars110,120are effectively disconnected from suspension systems105,115, respectively. A locked actuator200results in a stiffer riding vehicle100, while a free sliding actuator200results in a softer riding vehicle100.

Exemplary actuator forces for MR actuator200in front suspension system105having two force members and no side forces, are: a maximum holding force of about 2 to about 6 kN (kilo-Newtons) under very low velocity (such as about equal to zero velocity for example) when powered; and, a low damping force such as about 20 to about 600 N (Newtons) at a velocity of about 1 m/sec when not powered.

Exemplary actuator forces for MR actuator200in rear suspension system115having two force members and no side forces, are: a maximum holding force of about 2 to about 6 kN under very low velocity (such as about equal to zero velocity for example) when powered; and, a low damping force such as about 20 to about 600 N at a velocity of about 1 m/sec when not powered.

In view of the foregoing examples, actuator200is effectively locked for axial loads equal to or less than about 6 kN, or alternatively equal to or less than about 2 kN, when the activation signal is ON, and actuator200is effectively unlocked for axial loads equal to or greater than about 20 N, or alternatively equal to or greater than about 600N, when the activation signal is OFF. However, it will be appreciated that the locked and unlocked actuator forces disclosed herein are exemplary only, and that such disclosure is not intended to be limiting in any way.

An exemplary MR actuator200may exhibit some of the following: a maximum velocity when not powered of 4 meters/sec at an input voltage of 12 VDC; a minimum tensile/compression strength when not powered (at maximum extended and compressed positions) of about 6 to about 12 kN; suitability for use at an operating temperature range of −40 degrees Celsius to +130 degrees Celsius; suitability for use at a maximum temperature for continuous operation of 110 degrees Celsius; an absence of MR fluid leakage, seal hardening, or hydraulic stacking at operating temperatures; functionality under exposure to dust (with or without a dust shield), dirt, corrosion, gas, oil, cleaners, and other vehicle fluids; durability over 10 years or 100,000 miles of use, whichever occurs first. As disclosed, some embodiments of the invention may include some of the following advantages: a low cost automotive roll-control system absent the requirement of a hydraulic pump or hydraulic power; lower system cost as a result of small MR fluid usage; lower system cost due to the elimination of gas springs, high-pressure seals and special rod and tube finishes required to minimize abrasion in a telescopic MR damper-type device; reduced roll gain (roll gain being a measure of the amount of roll angle experienced by the vehicle during a turn, or alternatively, the measure of roll angle as a function of lateral axel acceleration); improved ride comfort and quality; de-coupling of the anti-roll (stabilizer) bar from a single wheel event; reduced head toss during a vehicle maneuver; the ability to increase the structural stiffness of the anti-roll (stabilizer) bars by activating and de-activating stabilizer actuators; utilization of an MR actuator that provides a minimum force in the off-state for a given lock-up force; utilization of an MR actuator that has a fast response time on the order of 10 milliseconds, consumes zero or an insubstantial amount of power under normal driving conditions when the roll-bar is unlocked or disengaged, and requires less than 25 Watts of power during the time the roll-bar is locked or engaged during a transient maneuver; the ability to be utilized in semi-active roll control systems with controllable roll rate; reduced package size due to the elimination of hydraulic pump, accumulator and hydraulic lines; the ability to control the vehicle roll rate as a function of vehicle dynamics; and increase in vehicle stability due to reduced vehicle roll angle during cornering; the ability to be utilized for controlling vehicle stability in vehicle oversteering conditions; improved vehicle ride quality during straight driving; minimal parasitic power consumption due to the absence of electrical or hydraulic power demand under normal driving operation; and, a significant reduction in roll gain from about 4 degrees per g-force to about 2 degrees per g-force.