Abstract:
A knee bolster system is capable of automatic extension and retraction during specified scenarios that are determined based on sensor input. A microprocessor electrically controls an actuator capable of extending at least one telescoping mechanism which is rigidly engaged to a knee bolster pad located in the lower portion of an instrument panel at knee height to an occupant. Each telescoping mechanism houses a plowing mechanism. This plowing mechanism generates reaction forces during actuation.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a knee bolster system and more particularly to an extendable and retractable knee bolster system, including its control logic, with an impact pre-sensing system for an automotive vehicle.  
         BACKGROUND OF THE INVENTION  
         [0002]    The fixed fore-aft location of a knee bolster may constrain how far the lower portion of the instrument panel can be placed forward and away from the knees of an occupant. This constraint can limit comfort for the occupant. The position of current fixed-in place knee bolster systems is also a constraint on interior spaciousness. It is known that utilization of inflatable knee bolster systems brings the location of the lower portion of the instrument panel rearward when preferred. However, such crash triggered inflatable knee bolster systems do not typically retract automatically, and could require complete replacement after actuation. Such replacement is expensive, a cost borne by the consumer.  
         SUMMARY OF THE INVENTION  
         [0003]    In accordance with the present invention, there is provided an extendable and retractable knee bolster system generally positioned in the lower portion of the instrument panel of a vehicle at knee height to an occupant. The knee bolster system has at least one and preferably two telescoping mechanisms secured to a bolster pad. The telescoping mechanism has an outer tube securing rigidly to the vehicle structure at a base end. The outer tube concentrically supports an inner tube capable of linear telescoping movement. The inner tube has a leading end secured to the bolster pad and a trailing portion engaged to a shuttle which operatively connects to a drive device via a rotating screw disposed concentrically within the inner and outer tubes.  
           [0004]    The drive device rotates the screw which is engaged threadably to the shuttle. The shuttle thereby moves or extends the inner tube through a free end of the outer tube. The shuttle comprises part of a plowing mechanism which can help dissipate the energy. Preferably, the plowing mechanism has at least one axially extending groove defined by an outer cylindrical surface of the inner tube and facing an inner cylindrical surface of the outer tube. The groove has a trailing deep end and a leading shallow end. A sphere resides in the deep end and is restricted there during normal extending and retracting motions of the knee bolster pad by a plurality of radially extending fingers engaged to the shuttle. During an impact on the bolster pad, the sphere is thrust into the shallow end and plows into the inner surface of the outer tube causing deformation of the outer tube. The kinetic energy from the impact upon the bolster pad is absorbed into the telescoping mechanism. Examples of ways in which this energy could be absorbed are plowing of the balls and deformation of the tubes.  
           [0005]    Preferably, the knee bolster system is actuated or controlled by a microprocessor which electrically communicates primarily with a plurality of risk sensors and a plurality of imminent impact sensors, and secondarily with a plurality of impact occurrence sensors. By using the outputs of risk sensors and imminent impact sensors as the primary means of triggering deployment, deployment times in the tenths of a second for the extendable/retractable knee bolster invented here rather than thousandths of a second required for impact triggered systems that have been proposed by others are tolerable in some applications. If a fully robust pre-impact sensor is not available, the bolster will automatically extend to the current mandated bolster location if the occupant is unbelted and the car placed in gear. The knee bolster pad will automatically retract if the ignition is off or the transmission is not in gear. In addition, the bolster pad will automatically retract if output signals or setpoints which caused the initial extension are cleared.  
           [0006]    An advantage of the present invention is that through the use of continuous monitoring and forecasting, the knee bolster is able to be stored further from the occupant in so doing permitting a more spacious vehicle interior.  
           [0007]    Another advantage of the present invention is the automatic retraction capability thereby minimizing maintenance costs.  
           [0008]    An additional advantage of this invention is the enhancement of vehicle entry and egress, since the bolster is stowed when the vehicle is not in gear. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    Preferred exemplary embodiments of the present invention hereinafter shall be described in conjunction with the impending drawings, wherein like numerals denote like elements and wherein:  
         [0010]    [0010]FIG. 1 is a side view of a knee bolster system within a vehicle environment of the present invention;  
         [0011]    [0011]FIG. 2 is a top plane view illustrating two knee bolster systems within the vehicle environment;  
         [0012]    [0012]FIG. 3 is a partial cross-sectional longitudinal view of the knee bolster system;  
         [0013]    [0013]FIG. 4 is a partial broken away view of a telescoping mechanism shown in an initial powered extending state;  
         [0014]    [0014]FIG. 5 is a cross sectional view of the telescoping mechanism taken along line  5 - 5  viewing in the direction of the arrows of FIG. 4;  
         [0015]    [0015]FIG. 6 is a partial broken away view of the telescoping mechanism shown in an initial powered retracting state;  
         [0016]    [0016]FIG. 7 is a cross sectional view of the telescoping mechanism taken along line  7 - 7  viewing in the direction of the arrows of FIG. 6;  
         [0017]    [0017]FIG. 8 is a partial broken away view of the telescoping mechanism shown with an impact absorber portion engaged;  
         [0018]    [0018]FIG. 9 is a cross sectional view of the telescoping mechanism taken along line  9 - 9  viewing in the direction of the arrows of FIG. 8;  
         [0019]    [0019]FIG. 10 is a functional flow chart of the knee bolster system control loop;  
         [0020]    [0020]FIG. 11 is a functional flow chart of a seat belt subroutine of FIG. 10;  
         [0021]    [0021]FIG. 12 is a functional flow chart of a vehicle velocity subroutine of FIG. 10;  
         [0022]    [0022]FIG. 13 is a functional flow chart of an antilock braking system subroutine of FIG. 10;  
         [0023]    [0023]FIG. 14 is a functional flow chart of a mid-range radar subroutine of a crash pre-sensing system found in FIG. 10;  
         [0024]    [0024]FIG. 15 is a functional flow chart of a side radar subroutine of the crash pre-sensing system found in FIG. 10;  
         [0025]    [0025]FIG. 16 is a functional flow chart of a side crash sensor subroutine of FIG. 10;  
         [0026]    [0026]FIG. 17 is a functional flow chart of a vehicle stability enhancement system subroutine of FIG. 10;  
         [0027]    [0027]FIG. 18 is a functional flow chart of a car gear check subroutine of FIG. 10;  
         [0028]    [0028]FIG. 19 is a functional flow chart of a car ignition check subroutine of FIG. 10;  
         [0029]    [0029]FIG. 20 is a functional flow chart of a knee bolster extension and contact check subroutine of FIG. 10; and  
         [0030]    [0030]FIG. 21 is a partial cross-sectional longitudinal view of a second embodiment, specifically a directly driven embodiment of the knee bolster system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    Referring to FIGS. 1, 2 and  3 , the knee bolster system  30  includes an actuator  32  connecting operatively to at least one and preferably two telescoping mechanisms  33 ,  34 . The telescoping mechanisms  33 ,  34  each have a leading end  35  attached to a singular or common elongated knee bolster pad  36 , and a base end  37  attached to a vehicle structure  40 . The knee bolster system  30  generally mounts to the vehicle structure  40  within the lower portion of the dash  38 . A leading surface of the knee bolster pad  36  can be a visual or aesthetically pleasing lower part of the dash  38 . Two knee bolster systems  30  are preferably utilized within a single vehicle, one for a passenger  42  and one for a driver  44 .  
         [0032]    A microprocessor  46  receives the necessary input signals from a variety of external impact indication sensors  48 , and extends the bolster pad  36  when preset limits are reached during certain risk scenarios or actual vehicle impact scenarios. In addition, the microprocessor  46  will initiate a signal to retract the bolster pad  36  after the reasons to extend are alleviated and pre-set delay times have expired. An optional and preferable impact pre-sensing system  50  also communicates with the microprocessor  46 . The pre-impact sensing system  50  receives input signals from sensors which preferably utilize radar to detect the relative speed and distance of approaching objects, thereby forecasting imminent vehicle impact scenarios. Once any one of the sensor output limits are reached, the microprocessor  46  processes an “extend flag” signal causing the actuator  32  to extend the knee bolster pad  36 . When the knee bolster system  30  actuates upon ‘extend flag’ initiation(s) within the control logic of the microprocessor  46 , the actuator  32  actuates, the first and second telescoping mechanisms  33 ,  34  simultaneously extend, and the knee bolster pad  36  projects substantially horizontally toward the knees of the occupants, passenger  42  or driver  44 .  
         [0033]    Referring to FIGS. 2 and 3, the actuator  32  has a drive device  45 , which may be powered pneumatically or electro-magnetically, but is preferably an electric dual drive motor  54  having a dual ended rotor  56 . A first end of rotor  56  engages with a first screw cable  58  and a second end of the rotor  56  engages a second screw cable  60  of the actuator  32 . The first and second screw cables  58 ,  60  are reverse or counter threaded and extend centrally within the respective first and second telescoping mechanisms  33 ,  34 . The first telescoping mechanism  33  substantially parallels the second telescoping mechanism  34 . In order to equalize and minimize cable rotation resistance within the first and second screw cables  58 ,  60 , the rotor  56  of the motor  54  is preferably disposed perpendicular to the longitude of the first and second telescoping mechanisms  33 ,  34 . However, the flexibility of the left and right screw cables  58 ,  60  will enable any orientation of the motor  54  relative to the telescoping mechanisms  33 ,  34 .  
         [0034]    Preferably, the left and right screw cables  58 ,  60  each have a rigid screw portion disposed concentrically and extended longitudinally within the respective telescoping mechanisms  33 ,  34 . First and second shuttles  62 ,  64  are engaged threadably to and are concentric with the rigid portions of the first and second screw cables  58 ,  60  from within the respective telescoping mechanisms  33 ,  34 . The first shuttle  62  is therefore reverse threaded relative to the second shuttle  64 . The first shuttle  62  engages the leading end  35  of the first telescoping mechanism  33  and the second shuttle  64  engages the leading end  35  of the second telescoping mechanism  34 . The counter-rotation of the first and second screw cables  58 ,  60  cause the first and second shuttles  62 ,  64  to translate linearly up and down the longitudinal length of the first and second screw cables  58 ,  60 , thereby causing the telescoping mechanisms  33 ,  34  to move longitudinally between a retracted position  65 , see FIGS. 3 and 4, and an extended position  67 , see FIG. 6.  
         [0035]    Referring to FIGS. 3, 4 and  6 , the base end  37  is part of an outer tube  66  of the telescoping mechanism  33 ,  34  and rigidly attaches to the vehicle structure  40  via a tubular boss  68 . The outer tube  66  slideably and concentrically supports from within an inner tube  70 . The leading end  35  is part of the inner tube  70  which protrudes outward through a free end  74  of the outer tube  66 . The leading end  35  interconnects to the bolster pad  36  by a bracket  76 .  
         [0036]    A trailing portion  78  of the inner tube  70  engages the shuttle  62 ,  64 . Trailing portion  78  has an outer cylindrical face  80  having a circumference or diameter equal to or slightly less than the circumference or diameter of an inner cylindrical face  82  of the outer tube  66 . From the outer cylindrical face  80 , the trailing portion  78  extends radially inward, forming at the axial ends an annular leading surface  84  and an annular trailing surface  86  or the trailing portion of the inner tube  70 . The outer cylindrical face  80  extends axially between and substantially perpendicular to the leading surface  84  and the trailing surface  86 . The trailing portion  78  is disposed concentrically to and substantially radially outward from the shuttle  62 ,  64 .  
         [0037]    Referring to FIGS.  4 - 7 , the interaction between the shuttle  62 ,  64 , the trailing portion  78  of the inner tube  70 , and the inner cylindrical face  82  of the outer tube  66  function as a plowing mechanism  88  which deforms the outer tube  66  when a force brought on by the forward motion of the knees of an occupant  42 ,  44  impacts the bolster pad  36 . Mechanism  88  has a plurality of crevices  90  formed into the trailing portion  78 , and communicating longitudinally through a radial inner face  92  and radially through the trailing end surface  86  of the trailing portion  78 . Each crevice  90  extends forwardly from the trailing end surface  86  to a contact end surface  94 .  
         [0038]    An elongated tapered groove  96  forms axially into the trailing portion  78  through the outer cylindrical face  80 . Groove  96  communicates and aligns circumferentially with, and radially inward from each crevice  90 . A deep end  100  of groove  96  trails and tapers radially outward to a shallow end  102 . A sphere  104  of the plowing mechanism  88 , preferably metallic and of a harder material than the outer tube  66 , resides in the deep end  100  of the groove  96 . The diameter of the sphere  104  is equal to or slightly less than the depth of the groove  96  at the deep end  100 .  
         [0039]    A tubular mid portion  106  of shuttle  62 ,  64  forms axially between and radially inward of a hex shaped forward stop member  108  and a rearward stop member  110 . The axial length of the tubular mid portion  106  substantially equals the length of the groove  96  minus the diameter of the sphere  104 . Extending radially outward from the rearward stop member  110  is at least one and preferably a plurality of fingers  112 . Each finger  112  extends into the respective crevice  90 . The finger  112  generally aligns axially between the deep end  100  and the shallow end  102  of the groove  96 . Furthermore, finger  112  extends radially into the deep end  100 , but falls short of extending into the shallow end  102 . The axial length of the tubular mid portion  106  permits full axial translation or movement of the finger  112  within the groove  96  from the sphere  104  to the shallow end  102 .  
         [0040]    To minimize friction within the telescoping mechanism  34  when extending and retracting, at least one bearing ring  114  extends circumferentially and is disposed between the inner face  82  of the outer tube  66  and the outer face  80  of the inner tube  70 . Preferably, one ring  114  seats slightly axially rearward of the deep end  100  and another ring  114  seats just forward of the shallow end  102  of the groove  96  within the trailing portion  78 .  
         [0041]    Motor Driven Extending State  
         [0042]    Referring to FIGS. 4 and 5, when the knee bolster system  30  is in a motor driven extending state  116  the shuttle  62 ,  64  is advancing forward. The fingers  112  also advance forward within the respective crevice  90  until the fingers  112  contact or engage the contact end surface  94 . The sphere  104  remains in the deep end  100  of groove  96 . With engagement of the fingers  112  to the contact end surface  94 , the trailing portion  78  of the inner tube  70  is pushed in the forward or extended direction. This extension continues until either the first and second screw cables  58 ,  60  cease rotating, or the knees of an unbelted passenger  42  or driver  44  impact the bolster pad  36  and in so doing engaging the plowing mechanism  88 .  
         [0043]    Motor Driven Retracting State  
         [0044]    Referring to FIGS. 6 and 7, when the knee bolster system  30  is in a motor driven retracting state  118 , the shuttle  62 ,  64  is retracting in a rearward direction. As in the extending state  116  the sphere  104  remains in the deep end  100  of the groove  96 , but unlike the extending state  116 , the sphere  104  remains in the deep end  100  due to sphere  104  contact with the finger  112 . During initial motored retraction  118  after extension, the finger  112  which was once in contact with the contact end surface  94  now moves axially rearward within the crevice  90  until the lip  108  of the shuttle  62 ,  64  engages the leading surface  84  of the trailing portion  78 . With continuing rotation of the first screw cable  58  or second screw cable  60 , the inner tube  70  begins retracting. The finger  112  resides forward of and contacts the sphere  104  prior to the inner tube  70  moving with respect to the outer tube  66 , thereby preventing the sphere  104  from moving forward into the shallow end  102  of the groove  96 . This finger obstruction assures that the plowing mechanism  88  does not engage. In other words the finger  112  assures that the sphere  104  will not enter the shallow end  102  and wedge between the outer tube  66  and the inner tube  70 . Retraction of the inner tube  70  will cease when the motor  54  is deenergized or the inner tube is in the fully retracted position.  
         [0045]    Plowing Mechanism Engagement State  
         [0046]    Referring to FIGS. 8 and 9, the knee bolster system  30  is capable of repeated extending and retracting actuations unless the energy absorber or plowing mechanism  88  has been engaged. Engagement of the plowing mechanism portion  88  will occur when sufficient force is exerted against the front surface of the bolster pad  36  independent of how far it is extended. The necessary force is gauged so that the knees of the occupant  42 ,  44  experience a force within specified tolerance levels. The plowing mechanism  88  will essentially stop extension or forward movement of the inner tube  70  and permit a limited retraction or rearward movement, thereby creating a cushioning effect. When actuated, and regardless of the rotation of the first or second screw cable  58 ,  60 , the trailing portion  78  is thrust forward relative to the occupant  42 ,  44  or rearward in relation to the shuttle  62 ,  64 . The lip  108  therefore departs from the leading surface  84  and the contact end surface  94  then impacts the fingers  112 . Because the fingers  112  have moved forward within respective crevices  90 , the fingers  112  no longer obstruct movement of sphere  104 . The retracting movement of the trailing portion  78  of the inner tube  70  causes the sphere  104  to wedge forward or move forward within the groove  96  into the shallow end  102 . Since the depth of shallow end  102  is less than the diameter of the sphere  104  the sphere  104  distorts or causes plastic deformation of the outer tube  66  as it plows into the inner face  82 . This lateral distortion absorbs the energy of the longitudinally moving inner tube  74 . The relative softness between the preferable metals, or alternative plastics, of the outer tube  66 , the inner tube  70 , and the sphere  104  are selected to minimize reaction forces.  
         [0047]    System Logic  
         [0048]    The following list provides a brief alphabetical description of terminology&#39;s and abbreviations found within FIGS. 10 through 21:  
                                       ABS:   Anti-lock Braking System       ABS = N   Is a logic step wherein the ABS initiated signal is “not set” indicating the           ABS has not been in control of the braking function while the vehicle is           traveling in excess of 50 km/hr, within the last 10 seconds.       ABS = Y   Is a logic step wherein the ABS initiated signal is “set” indicating the           ABS has taken over the braking function while the vehicle is traveling at           speeds in excess of 50 km/hr within the last 10 seconds.       B = N:   Is a logic step wherein the belted signal is not “set” indicating the           occupant is not belted. This logic step will trigger a slow extend flag       B = Y:   Is a logic step wherein the belted signal is “set” indicating or suggesting           the occupant is belted.       E/R:   Extendable/Retractable       KB:   Knee Bolster       E1 = N:   Is a logic step wherein the risk of front impact signal is not “set”           indicating the imminence of an impact has not been detected by a mid-           range radar system within the last 10 seconds       E1 = Y:   Is a logic step wherein the risk of front impact signal is “set” indicating           that a mid-range radar has determined sometime within the last 10           seconds that an impact is imminent.       E2 = N:   Is a logic step wherein the risk of side impact signal is “not set” indicating           the imminence of a side impact has not been detected by a side radar           system within the last 10 seconds.       E2 = Y:   Is a logic step wherein the risk of side impact signal is “set” indicating           that a side radar system has determined sometime within the last 10           seconds that a side impact is imminent.       E3 = N:   Is a logic step wherein an impact occurrence signal is “not set” indicating           a side impact has not been detected within the last 10 seconds.       E3 = Y:   Is a logic step wherein an impact occurrence signal is “set” indicating that           a side impact has been detected within the last 10 seconds.       E4 = N:   Is a logic step wherein a vehicle spin or rollover signal is “not set”           indicating a vehicle spin or rollover has not been detected within the last           10 seconds.       E4 = Y:   Is a logic step wherein a vehicle spin or rollover signal is “set” indicating           a vehicle spin or rollover has been detected within the last 10 seconds.       extend flag:   Is a logic signal triggered by a condition or logic step which will cause           slow or fast extension of the knee bolster.       SIR:   Supplemental inflatable restraint (air bag).       T:   Timer, with a duration of ten seconds.       T1:   Timer one, with a duration of ten seconds.       T2:   Timer two, with a duration of ten seconds.       T3:   Timer three, with a duration of three seconds.       T5:   Timer five, with a duration of ten seconds.       T6:   Timer six, with a duration of ten seconds.       T7:   Timer seven, with a duration of ten seconds.       V:   Velocity in km/hr       VV = Y:   Is a logic step wherein the upper velocity limit is “set.” This logic step is           initially triggered when the vehicle exceeds 140 km/hr for more than 10           seconds and will cause a slow extend flag to trigger.       VSES:   Vehicle Stability Enhancement System, may include but is not necessarily           limited to vehicle rollover and yaw rate sensors.                  
 
         [0049]    Referring to FIG. 10, the control system for the knee bolster system  30  will not initiate and therefore the knee bolster pad  36  will not actuate if the ignition is off. Turning the ignition on initiates the knee bolster system  30  which then proceeds to perform a system malfunction check. The timers of a plurality of process sensor outputs  48  are “set” to zero, but not “started” until specifically initiated by a subroutine. Each process sensor output  48  has at least one associated subroutine, the subroutines together comprise the control loop  140 . Each subroutine can singularly initiate an extend flag signal which will cause the knee bolster system  30  to extend the knee bolster pad  36 . Every subroutine which has initiated an extend flag signal must initiate a retract flag signal before the knee bolster system  30  retracts the knee bolster pad  36  (unless the vehicle is parked, is in neutral or reverse gear, or the ignition is off).  
         [0050]    The plurality of process sensor outputs  48 , or the control loop  140  may be separated into five categories of outputs. The first category or risk outputs  150  entail sensors which detect vehicle operating conditions that pose a risk should an impact occur, but not necessarily a higher likelihood of a crash. The risk outputs  150  comprise the seatbelt interlock sensor or subroutine  152 , see FIG. 11 and the wheel rotation rate/vehicle velocity sensor or subroutine  154 , see FIG. 12. The second category is an operating condition that indicates a higher likelihood of an impact. This category is comprised of the ABS sensor or subroutine  156 , see FIG. 13. The third category or imminent impact outputs  160  entail sensors which detect that an impact will occur and comprise the mid range radar sensor or subroutine  162 , see FIG. 14, and the side radar sensor or subroutine  164 , see FIG. 15. The imminent impact outputs  160  rely on the pre-impact sensing system  50  to communicate with the microprocessor  46 . The fourth category or impact occurrence outputs  170  entail output sensors which detect an actual impact occurrence (or unstable vehicle control) and comprise a side impact sensor or subroutine  172 , see FIG. 16, and a VSES sensor or subroutine  174 , see FIG. 17. The risk outputs  150  are assigned “slow” extend flags, and the higher likelihood of an impact, imminent impact and impact occurrence outputs  156 ,  160 ,  170  are assigned “fast” extend flags by the microprocessor  46 . The fifth category or retract flag outputs  180  function to override existing extend flags from the first four categories which include  150 ,  156 ,  160  and  170 , if specific conditions are met. The retract flag outputs  180  comprise a vehicle gear sensor or subroutine  182 , see FIG. 19 and an ignition sensor or subroutine  184 , see FIG. 20. Vehicle gear subroutine  182  overrides any existing extend flags and retracts the knee bolster pad  36  if the vehicle is either shifted into park, neutral or reverse gear. The ignition subroutine  184  overrides any existing extend flags and retracts the knee bolster pad  36  if the vehicle ignition is off.  
         [0051]    Referring to FIGS. 10 and 11, the seat belt loop subroutine  152  checks to see if the right front seat is occupied by a full-sized passenger. If so occupied the subroutine checks to see if the right front occupant is belted. If belted, the subroutine  152  acts as it would without a passenger  42  and checks to see if the logic step “B=Y” is set. If set, the pad  36  has not been extended from previous subroutine  152  executions and returns to the loop  140 . If not set, the subroutine  152  sets the logic step “B=Y” indicating no passenger  42  or the passenger  42  is belted and turns off the slow extend flag prior to returning to the loop  140 .  
         [0052]    If the right front seat is occupied by an “adult” and the right front occupant is not belted, and either the SIR is deployed or the vehicle is not in a forward gear, and the logic step “B=Y” is set, the subroutine  152  returns to the loop. If the logic step “B=Y” is not set, the signal is then set and the subroutine  152  returns to the loop  140 . This logic assures that the knee bolster pad  36  does not extend after the SIR has been deployed or the vehicle is not in the forward gear. This is so, because if the SIR has already deployed. If the car is in park, a passenger may desire to move about within the vehicle compartment, and an extended pad  36  would get in the way at a time when it is not needed, hence the slow extend flag is not turned on.  
         [0053]    If the logic step “B=N” is set indicating the slow extend flag has been turned on in a previous subroutine  152  execution, and, both, the SIR is not deployed and the vehicle is in a forward gear, the subroutine  152  returns to the loop since the knee bolster pad  36  is already extended. If logic step “B=N” is not set, then “B=N” is set and the slow extend flag is turned on since the right front occupant is not belted, the SIR is not deployed, and the vehicle is in a forward gear. If the pad  36  is not yet extended from previous executions, it will extend upon initiation of the slow extend flag from the subroutine  152 .  
         [0054]    Referring to FIGS. 10 and 12, the vehicle velocity subroutine  154  first checks to see if the vehicle velocity is greater than approximately one hundred and forty kilometers per hour. If yes, timer T 2  and timer T 3  are set to zero, the subroutine  154  then checks to see if logic step “VV=Y” is set. If set, this indicates the slow extend flag has been previously executed and the subroutine  154  returns to the loop  140 . If “VV=Y” is not set, subroutine  154  checks to see if timer T 1  is greater than zero. If no, timer T 1  is started and the subroutine  154  returns to the loop  140 . The slow extend flag will not be turned on until approximately ten seconds have elapsed with the vehicle traveling over one hundred and forty kilometers per hour. If timer T 1  is greater than zero but less than approximately ten seconds, the subroutine  154  again returns to the loop  140 . If timer T 1  is greater than ten seconds the slow extend flag turns on. Timer T 1  is then set back to zero, logic step “VV=Y” is set, indicating the slow extend flag is on, and the subroutine  154  returns to the loop  140 .  
         [0055]    If the vehicle velocity is not greater than approximately one hundred and forty kilometers per hour the subroutine  154  checks to see if the logic step “VV=Y” is set. If set, the subroutine  154  checks to see if the vehicle velocity is less than approximately one hundred and ten kilometers an hour. If yes, and timer T 2  is greater than zero, indicating at the previous subroutine execution(s) the vehicle velocity was also less than one hundred and ten kilometers per hour, the subroutine  154  checks to see if the vehicle velocity is less than approximately ninety kilometers an hour. If timer T 2  is not greater than zero, then the vehicle velocity has only recently dropped below one hundred and ten kilometers per hour, and timer T 2  is started. After starting or assuring timer T 2  has previously been started, the subroutine  154  checks to see if the vehicle velocity is less than approximately ninety kilometers per hour. If yes, and timer T 3  is greater than zero indicating the vehicle velocity was less than ninety kilometers per hour at the previous subroutine execution, and timer T 2  is greater than approximately ten seconds or timer T 3  is greater than approximately three seconds then timer T 1 , timer T 2  and timer T 3  are reset to zero and the slow extend flag is turned off. Logic step “VV=N” is set indicating the vehicle velocity has been under the ninety kilometers per hour set point for a prescribed duration of time (i.e. three seconds) or the vehicle velocity has been under the one hundred and ten kilometers per hour set point for a prescribed period of time (i.e. ten seconds) and therefore the extended knee bolster pad  36  should be retracted. The knee bolster pad  36  will retract provided no other extend flags are “on” from the other subroutines. This sort of control logic prevents unnecessary or irritating extending and retracting oscillations of the knee bolster pad  36 .  
         [0056]    Continuing with subroutine  154  logic, if the vehicle velocity is not less than ninety kilometers per hour but is less than one hundred and ten kilometers per hour then timer T 3  is set to zero. Subroutine  154  again checks to see if timer T 2  is greater than ten seconds or timer T 3  is greater than three seconds. If neither, then the subroutine  154  returns to the loop  140 . If one is, then as before, timer T 1 , timer T 2  and timer T 3  are set to zero, the slow extend flag is turned off, logic step “VV=N” is set, and the subroutine  154  returns to the loop  140 .  
         [0057]    If the vehicle velocity is less than ninety kilometers per hour and timer T 3  is not greater than zero seconds, indicating the vehicle velocity has recently fallen below ninety kilometers per hour, then timer T 3  is started. Subroutine  154  checks to see if timer T 2  is greater than ten seconds. If no, then subroutine  160  returns to the loop  140 . If yes, timer T 1 , timer T 2  and timer T 3  are set to zero, the slow extend flag is turned “off” and logic step “VV=N” is set. The subroutine  154  then returns to the loop  140 .  
         [0058]    If logic step “VV=Y” is set indicating the slow extend flag has previously been initiated and the vehicle velocity is not less than one hundred and ten kilometers per hour, timer T 2  and timer T 3  are set to zero. The slow extend flag remains until approximately ten seconds after the vehicle velocity drops below one hundred and ten kilometers per hour, or until approximately three seconds after the vehicle velocity drops below ninety kilometers per hour, which ever occurs sooner. If logic step “VV=Y” is not set and the vehicle speed is less than one hundred and forty kilometers per hour, subroutine  154  checks to see if timer T 1  is greater than zero. If “no,” then subroutine  154  returns to the loop  140 . If “yes,” timer T 1  is set to zero and subroutine  154 , again, returns to the loop  140 . In other words, the extend flag has not been previously initiated during prior subroutine executions, nor should it be now since the set point speed has not exceeded one hundred and forty kilometers per hour.  
         [0059]    Referring to FIGS. 10 and 13, the ABS subroutine  156  will initiate an extend flag if both the ABS is on and the vehicle velocity is over approximately fifty kilometers per hour. Subroutine  156  begins execution by checking to see if the ABS is on. If yes, the subroutine  156  checks to see if the vehicle speed is over approximately fifty kilometers per hour. If yes, and the logic step “ABS=Y” is set, then the subroutine  156  returns to the loop  140  because the extend flag has been previously initiated. If “ABS=Y” is not set, the subroutine  156  sets timer T 7  to zero, initiates the extend flag, and sets logic step “ABS=Y.” 
         [0060]    If the vehicle speed is not over fifty kilometers per hour, and the logic step “ABS=Y” is not set then the subroutine  156  returns to loop  140  and will not initiate the extend flag. If logic step “ABS=Y” is set indicating the extend flag has previously been turned on, yet the ABS is not presently on or the vehicle speed is not over fifty kilometers per hour, and timer T 7  is not greater than zero, then timer T 7  is started and the subroutine  170  returns to the loop  140 . Starting timer T 7  begins an approximate ten second countdown prior to turning off the extend flag. If timer T 7  is greater than zero, yet less than ten seconds, the countdown was previously started and the subroutine  156  returns to the loop  140 . If timer T 7  is greater than ten seconds, the countdown has expired, the timer T 7  is set to zero, a logic step “ABS=N” is set, and the extend flag is turned off prior to returning to the loop  140 .  
         [0061]    Referring to FIGS. 10 and 14, the pre-impact sensing system  50  mid range radar subroutine  162  checks to see if a risk (imminent impact) has been detected. An affirmative risk detection means that an object has been detected within approximately twenty meters that it is at a sufficiently high relative velocity so that an impact is unavoidable. If yes, the subroutine  162  checks if logic step “E1=Y” has been previously set indicating a fast extend flag has been previously initiated. If set, the subroutine returns to the loop  140 . If not set, then logic step “E1=Y” is set, the fast extend flag initiated, and a timer T is set to zero (but not started). This loop indicates that an impact is imminent and the knee bolster system is preparing or actuating in advance.  
         [0062]    If a risk has not been detected and logic step “E1=Y” is not set, the subroutine  162  returns to the loop  140 . If a risk does not exist, yet logic step “E1=Y” is set and timer T is equal or set to zero, then the timer T is started. This begins a countdown prior to turning off the fast extend flag. If the accumulated time on timer T is greater than ten seconds, the countdown has elapsed and timer T is reset to zero, the fast extend flag is turned off, a logic step “E1=N” is set, and the subroutine  162  returns to the loop  140 . The setting of “E1=N” indicates that a risk condition has not been detected for a duration of at least ten seconds. On the other hand, if logic step “E1=Y” is set and the elapsed time on timer T is greater than zero but less than ten seconds the fast extend flag remains on and the subroutine  162  returns to the loop  140 .  
         [0063]    Referring to FIGS. 10 and 15, the pre-impact sensing system  50  side radar sub-routine  164  routine logic is similar to the mid range radar subroutine  162 . The side radar subroutine  164  checks to see if a risk (imminent side impact) has been detected. An affirmative risk detection like the mid range radar means that an object has been detected within approximately 20 meters and at a sufficiently high relative velocity so that a side impact is unavoidable. If yes, the subroutine  164  checks if logic step “E2=Y” has been previously set indicating a fast extend flag has been previously initiated. If set, the subroutine  164  returns to the loop  140 . If not set, the logic step “E2=Y” is set, the fast extend flag initiated, and a timer T 4  is set to zero but not started. This loop indicates that an impact is imminent from the side and the knee bolster system is preparing or actuating in advance.  
         [0064]    If a risk has not been detected and logic step “E2=Y” is not set, the sub-routine  164  returns to the loop  140 . If a risk does not exist logic step “E2=Y” is set and timer T 4  is equal or set to zero, then the timer T 4  is started. This begins the count down toward turning off the fast extend flag. If the accumulated time on timer T 4  is greater than ten seconds, the count has elapsed and timer T 4  is reset to zero, the fast extend flag is turned off, a logic step “E2=N” is set, and the subroutine  164  returns to the loop  140 . Setting “E2=N” indicates that a risk has not been detected for a duration of at least ten seconds. On the other hand, if logic step “E2=Y” is set and a lapse time on timer T 4  is greater than zero but less than ten seconds, the fast extend flag remains on and the subroutine  164  returns to the loop  140 .  
         [0065]    Referring to FIGS. 10 and 16, a side impact subroutine  172  works or flows logically in much the same way as the mid range subroutine  162  or the side radar subroutine  164 . The questions of risk detection found in the control logic of subroutines  162  or  164  are replaced with an impact detection check in subroutine  172 . Likewise, referring to FIG. 17, a vehicle spin or rollover subroutine  174  is shown. The impact detection check of subroutine  172  is replaced with a vehicle spin or rollover detection check within subroutine  174 . Otherwise the control logic steps although independent from one subroutine to the next, are generally the same.  
         [0066]    Referring to FIGS. 10 and 18, a vehicle gear subroutine  182  checks to see if the vehicle transmission is in neutral, park or reverse gear position. If no, subroutine  182  returns to the loop  140 . This means that the subroutine  182  will not override any existing extend flags from other subroutines and set an overriding retract flag itself. If the vehicle is in neutral, park or reverse gear position subroutine  182  checks to see if any one or more of the logic steps “VV, E, E1, E2, E3, E4, ABS or B=Y” have been set. If no, the subroutine  182  returns to the loop  140  indicating that no extend flags have been initiated from any of the other subroutines. If yes, the subroutine  182  sets a retract flag. Prior to returning to loop  140  subroutine  182  also sets T and T 1  through T 7  to zero.  
         [0067]    Referring to FIGS. 10 and 19, ignition subroutine  184  checks to see if the vehicle ignition is off. If the ignition is not off, the subroutine  184  returns to the loop  140 . If the ignition is off, the subroutine reacts the same way as subroutine  182  did when the vehicle was found to be in neutral, park or reverse gear position.  
         [0068]    Referring to FIGS. 10 and 20, an extend knee bolster subroutine  190  checks to see if an extend flag is on from any one or more of the subroutines  152 ,  154 ,  156 ,  162 ,  164 ,  172 ,  174 ,  182 , and  184 . If an extend flag does exist, subroutine  190  checks to see if logic step “E=Y” is set. If yes, sub-routine  190  returns to loop  140 . If no, subroutine  190  checks to see if a fast extend flag is on. If yes, the knee bolster pad  36  is extended quickly, if no, the knee bolster pad  36  is extended slowly. During either fast or slow extension, subroutine  190  checks to see if a load set point from a load limit switch has been reached. If no, subroutine  190  checks to see if knee bolster pad  36  is fully extended. Again if no, the bolster pad continues to extend until either the bolster pad  36  is fully extended or the limit switch has detected a load. If a load is detected indicating the pad  36  has contacted the knees of an occupant, the extension is stopped and logic step “E=Y” is set and subroutine  190  returns to the loop  140 .  
         [0069]    Referring to FIG. 21, a second embodiment of the present invention is shown. The drive device  245  mounts rigidly to the base end  237  of the outer tube  266 . The drive device  245  is an electric motor having the rotor  256  aligned concentrically to the inner tube  270  and shuttle  262 . The rotor  256  engages rigidly and co-linearly to the screw  258 . The rotor  256  and the screw  258  can be one straight unitary piece.  
         [0070]    Accordingly, it should thus be apparent that there has been provided in accordance with the present invention an extendable and retractable knee bolster system that achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of preferred exemplary embodiments and that the invention is not limited to the specific embodiments shown. Various changes and modifications will become apparent to those skilled in the art. For example, although the actuator  43  includes an electric motor for a drive device  44 , the actuator may also be a pneumatic actuated cylinder or a rod which extends electro-magnetically. As another example, means other than the ball and shuttle mechanism could be used for locking the stroking elements and generating a stroking/crushing force under knee loading in a vehicle impact. One alternative means would be to use a rachet-type mechanism operative on extension and released upon retraction. A second alternative means would be to use an MRF (magnetorheological fluid) damper as the stroking element. In an MRF damper, stroking force is proportional to the applied current. In this application the applied current would be set to zero when extending and retracting and switched to an appropriate high level consistent with the desired stroking force during knee loading associated with an impact event. It can also be appreciated that the time delays, velocity setpoints and distance setpoints found within the various subroutines may be substantially altered and are for example purposes only in order to describe the logic flow of various subroutines. All such changes and modifications are intended to come within the scope of the appended claims.