Steering column with variable collapse force

Abstract: A method is provided for optimising energy dissipation in a vehicle steering column (12) in a high energy impact. The method includes the steps of: (a) providing a variable energy dissipation system (14) on the vehicle steering column (12); (b) sensing at least one occupant condition; and (c) adjusting the variable energy dissipation system (14) based upon the sensed occupant condition to optimise energy dissipation.

Description: The present invention relates to a method of optimising energy dissipation in a vehicle steering column by adjusting a variable damper based upon sensed occupant conditions in a high energy impact. Steering columns of passenger cars are designed to collapse during a collision in order to dissipate energy of a vehicle occupant engaging the steering wheel. Typically, steering columns are provided with deformable crash features for such energy dissipation. However, the optimum force with which the column should resist collapse depends on whether the driver is belted or unbelted, as well as other occupant factors, and may vary significantly. It is, therefore, desirable to provide a steering column assembly with adjustable damping based upon these various factors, such as occupant weight, crash severity, etc., in order to optimise the energy dissipation characteristics of a collapsible steering column in a vehicle. Prior art attempts at providing a collapsible steering column system with variable energy dissipation or absorption characteristics include: DE 19749970 (Petri AG), which comprises the features mentioned in the preamble of claim 1 and in which axial movement of the steering column is hydraulically damped by controlling fluid flow between two chambers to varying degrees dependant on occupant weight and relative speed; "Computer Monitored Energy Absorbing Steering Column" Research Disclosure, Industrial Opportunities Ltd, Havant, GB, in an energy absorption mechanism is controlled in dependence on driver mass and vehicle speed; US 4,886,295 (Browne), in which hydraulic damping of a collapsible steering column is performed by inflating a bag surrounding part of the column to a pressure depending on driver weight and vehicle approaching speed relative to another vehicle or an obstacle; and DE 24 17 543 (Porsche AG), in which steering column damping is controlled by varying the flow rate of a fluid between two chambers in response to a collision sensor. The present invention provides a method of optimising energy dissipation in a vehicle steering column in a high energy impact, comprising: providing an electronically variable energy dissipation system on the vehicle steering column; sensing at least one occupant condition; and adjusting the variable energy dissipation system based upon said sensed occupant condition to optimise energy dissipation; characterised in that: the step of adjusting the variable energy dissipation system comprises disengaging the variable energy dissipation system if a seat belt is sensed to be buckled; the method further comprising: charging a capacitor to a high voltage when the vehicle ignition is turned on to enable electronic variation of the variable energy dissipation system if power is lost. In its preferred form, the invention provides a method of optimising energy dissipation in a vehicle steering column in a high energy impact, including: (a) providing a variable energy dissipation system on the vehicle steering column; (b) sensing at least one occupant condition; and (c) adjusting the variable energy dissipation system based upon the sensed occupant condition to optimise energy dissipation. The variable energy dissipation system may comprise a hydraulic damper with an electronically variable orifice, or a hydraulic damper with a damping fluid having an effective viscosity which is variable by varying a magnetic field intersecting the damping fluid. Also, the sensed occupant conditions may include crash severity, whether a vehicle seat belt is buckled, the occupant weight, etc. The adjustment of the variable energy dissipation system may comprise disengaging the hydraulic damper or dynamically adjusting the damping rate of the hydraulic damper based upon the sensed occupant conditions. In a preferred embodiment, a capacitor is charged to a high voltage when the vehicle ignition is turned on to enable electronic variation of the variable energy dissipation system in the event power is lost in the vehicle. The invention provides a means for selectively adjusting a variable collapse force of a steering column assembly based upon various sensed occupant conditions. The present invention will now be described further, by way of example, with reference to the accompanying drawing, which shows a schematic view of a variable rate damper attached to a collapsible steering column, and including a control system for adjusting the variable rate damper. Referring to the figure, a steering wheel 10 is attached to a collapsible steering column assembly 12. The collapsible steering column assembly 12 is provided with a variable energy dissipation system 14 and a control system 16 for adjusting the variable energy dissipation system 14 as desired in a high energy impact. Preferably, the variable energy dissipation system 14 includes first and second hydraulic damper mechanisms 18,20 integrated therein, or supplementally attached thereto. The damping rate of the hydraulic damper mechanisms 18,20 may be adjusted by an electronic controller 22 by any of several means. The size of the damping orifice can be changed either mechanically or, for higher speed, piezoelectrically. For example, a piezoelectrically variable hydraulic damper may be obtained from Active Control eXperts, Inc. of Troy, Michigan, sold under the name "K2 BIKE SmartShock." Alternatively, a fixed orifice can be used with an electrorheological or magnetorheological fluid as the damping fluid. Electrorheological materials are suspensions of micron-sized polarisable particles, while magnetorheological fluids are similar suspensions of iron-based particles. The effective viscosity of these fluids is changeable, which exhibit large rheological changes when subjected to strong electric fields. The effective viscosity of the fluid is changeable by the application of an electric or magnetic field in the vicinity of the orifice. The electric or magnetic field may be created by a voltage supply or an electromagnet. As illustrated in the figure, at least three pieces of information are available to the electronic controller 22 from sensors which may be present in the vehicle for other reasons. Depending upon implementation, any combination of these, as well as input from a variety of miscellaneous sensors, may be used. The belted condition of the driver is obtained by a seat belt sensor. The driver's mass is determined by a weight sensor in the seat, and the severity of the collapse is determined from the air bag accelerometer module, perhaps supplemented by the speedometer reading at the beginning of the crash. An example of a miscellaneous sensor that may be used is a seat track position sensor that may provide further information regarding the driver and his relationship to the steering wheel. From this data, the controller 22 determines what the optimum damping should be. Various degrees of sophistication can be used. The simplest is no more than "on" or "off," based on whether the driver is belted or unbelted. If belted, the collapsible steering column is used alone with no supplemental damping. If unbelted, the steering column collapse force is supplemented by the damping mechanism 14. In this case, the damping mechanism 14 need not be controllable, but could simply be kept in an engaged or disengaged condition by either a mechanical latch or a bypass valve in the damper, whose position is determined on the basis of the signal from the seat belt sensor. Since this position would be determined before the crash, high speed switching would not be necessary. In fact, hydraulic damping itself would not be necessary. Alternatively, a supplemental crushable member could be used. However, to avoid the use of mechanical latches, it may still be preferable to use an electrically adjustable damper. In this case, the controller 22 could be a very simple circuit. A step up in sophistication from this approach is to use driver mass and/or crash severity to determine intermediate levels of damping. A more sophisticated approach yet changes the damping dynamically during the crash according to a previously defined protocol determined on the basis of bio-mechanical considerations. An alternative method for determining the damping, one that does not rely on a measurement of driver mass, is to mount an accelerometer on a particular portion of the vehicle such as the steering wheel or the collapsible portion of the steering column; or, alternatively, to derive velocity and/or acceleration from a sensor that measures piston movement in the damper. The controller 22 then adjusts the damping of the dampers 18, 20 as necessary to limit the acceleration (which is related to the acceleration of the driver when he or she is in contact with the steering wheel through the air bag) to that which results in a predetermined occupant deceleration value. In the latter two cases, the damping rate must be adjusted very quickly. In the case of electrorheological or magnetorheological fluids, the rate of change of effective viscosity is very rapid, being limited primarily by the build-up time of the field. Changing the field rapidly requires high power, but since the collision time is short, not much energy. This power is provided, in accordance with the invention, by charging a capacitor to a high voltage when the ignition is turned on. The energy in the capacitor is then available for creating the electric or magnetic field, or to activate a piezoelectric orifice. With an additional capacitor to power the electronics, this would assure fail-safe operation even if battery power failed. Another feature provided by the system is the possibility of improving noise and vibration characteristics under normal driving conditions by using the dampers to damp axial and radial steering column vibrations. The latter mode might be damped by canting the dampers by a few degrees with respect to the steering column. In the discussion so far, the controllable dampers have been used to supplement the crush resistance of the steering column itself. Normally, the steering column would be designed according to methods well known to the state of the art, to provide a mechanical crush force that in this case would be the minimum needed (e.g., low-speed crash, belted driver). The controllable damping would then provide an extra damping force when needed for an unbelted driver or severe crash. An important difference to note between mechanical crush and hydraulic damping is that the former force is more or less independent of the crash speed, while the latter increases as crash speed increases. Thus, even in the simplest control mode, the hydraulic damping provides an "automatic" adjustment for crash speed: the more severe the crash, the greater the crush resistance. Of course, if the damping is electronically adjusted, any damping profile can be chosen within the range of the dampers. Alternatively, the mechanical crush resistance could be eliminated entirely, and the hydraulic dampers used to provide the total crush resistance. In this case, the steering column would normally be held in the fully extended position by a shear pin or some other device that would prevent the dampers from collapsing under normal use. The damping would be set to a nominal value. For a magnetorheological fluid damper, the magnetic field required to do this could be provided by a permanent magnet, with the electromagnet increasing or decreasing the nominal field as required. This has a fail-safe advantage that if all electrical power fails, the steering column collapse would revert to a nominal rate. It has a further advantage that the magnetic field need only be shifted from a nominal value, rather than generated from a zero value, so that the time and energy needed to establish the correct field is minimised. An advantage of putting all the collapse-resistance in the dampers is derived from the fact that in a crash the steering column is usually pushed not only forward but also upward. For maximum effectiveness, the dampers could be oriented along the direction of force of the driver, rather than along the axis of the steering column.

Claims: A method of optimising energy dissipation in a vehicle steering column in a high energy impact, comprising: providing an electronically variable energy dissipation system (14) on the vehicle steering column (12); sensing at least one occupant condition; and adjusting (22) the variable energy dissipation system (14) based upon said sensed occupant condition to optimise energy dissipation; characterised in that : the method further comprising: charging a capacitor to a high voltage when the vehicle ignition is turned on to enable electronic variation of the variable energy dissipation system if power is lost. A method as claimed in claim 1, wherein said step of providing a variable energy dissipation system comprises providing a hydraulic damper (18,20) with an electronically variable orifice. A method as claimed in claim 2, wherein said electronically variable orifice comprises a piezoelectrically controlled valve. A method as claimed in claim 1, wherein said step of providing a variable energy dissipation system comprises providing a hydraulic damper (18,20) with a damping fluid having an effective viscosity which is variable by varying a magnetic field intersecting the damping fluid. A method as claimed in claim 1, wherein said step of providing a variable energy dissipation system comprises providing a hydraulic damper (18,20) with a damping fluid having an effective viscosity which is variable by varying an electric field intersecting the damping fluid. A method as claimed in claim 1, wherein said step of sensing at least one occupant condition comprises a) sensing vehicle deceleration, b) the weight of a seat occupant, c) vehicle speed or d) whether a vehicle seat belt is buckled. A method as claimed in claim 1, wherein said variable energy dissipation system (14) comprises a hydraulic damper (18,20) and the step of sensing at least one occupant condition comprises: sensing vehicle occupant weight; sensing deceleration of a particular portion of the steering column assembly (12); determining an estimated driver deceleration based on the sensed occupant weight and sensed vehicle deceleration; and varying the damping rate of the damper (18,20) based upon said estimated driver deceleration.

Inventors: ABRAMOSKI EDWARD JOSEPH, BROWN LEONARD MURRAY, HEDDERLY GREGORY THOMAS, STEPHAN CRAIG HAMMANN, TEKELLY JOSEPH PAUL, ABRAMOSKI, EDWARD JOSEPH, BROWN, LEONARD MURRAY, HEDDERLY, GREGORY THOMAS, STEPHAN, CRAIG HAMMANN, TEKELLY, JOSEPH PAUL
Applicants: FORD GLOBAL TECH INC, FORD GLOBAL TECHNOLOGIES, INC.
Application year: 2000
Main classification: B62D1
IPC codes: B62D1