Electric steering gear

A steering assembly for turning the steerable wheels of a vehicle upon rotation of the vehicle steering wheel, said assembly comprising:

• means for mechanically coupling the vehicle steering wheel with the steerable wheels of the vehicle including,
• an input shaft connected to said steering wheel of rotation therewith,
• a pinion gear,
• a torsion member resiliently connecting said input shaft to said pinion gear, and
• a steering member having rack teeth thereon drivingly engaged by said pinion gear and connected to said steerable wheels of said vehicle, rotary motion of said pinion gear axially driving said steering member to turn said steerable wheels;
• torsion sensing means for providing an electric signal having a value which varies as a function of the amount of input torque applied to said steering wheel;
• speed sensing means for sensing the speed of the vehicle and for providing an electric signal indicative thereof;
• electronic control means connected to said torsion sensing means including speed decoder means for providing a plurality of coded electric signals, each coded signal being indicative of the vehicle being within a particular range of vehicle speeds, memory means for storing a plurality of look-up tables, each vehicle speed range having an associated look-up table, each look-up table having a control value corresponding to a value of the signal provided by said torsion sensing means, means for selecting a look-up table responsive to said coded electric signal indicative of the vehicle being within a particular range of vehicle speeds, means for selecting a control value from a selected look-up table responsive to the value of the signal provided by said torsion sensing means, and means for generating a pulse width modulated signal having a duty cycle controlled by said control value from said selected look-up table;
• an electric power assist motor drivably connected to at least one of said input shaft, said pinion gear or said steering member for assisting movement thereof, the amount of assist being a function of electrical current flow through the motor;
• and
• signal generating means for sequentially generating control values from a minimum assist value to a maximum assist value within a predetermined amount of time, said means for generating a pulse width modulated signal having a duty cycle responsive to the smaller of (i) the control value from said selected look-up table, or (ii) the control value generated by said signal generating means.

A method of controlling a vehicle power assist steering assembly having a vehicle steering wheel mechanically coupled to steerable wheels of the vehicle, power assist means for assisting a vehicle operator in a steering maneuver with an amount of assist available being responsive to an electrical control signal, a torque sensor for providing an electrical signal having a value indicative of applied steering torque, and a speed sensor for providing an electrical signal indicative of vehicle speed, said method comprising the steps of:

• (a) storing a plurality of addressable look-up tables, each table being associated with a particular vehicle speed range and each table having a control value corresponding to a value of the torque sensor signal;
• (b) determining which one of the plurality of speed ranges the vehicle is at from the speed sensor signal;
• (c) addressing an appropriate look-up table in response to the determined vehicle speed range;
• (d) selecting a control value from the addressed look-up table in response to the value of the torque sensor signal;
• (e) sequentially generating control values from a minimum assist value to a maximum assist value within a predetermined amount of time;
• and
• (f) generating said electrical control signal in response to the smaller of (i) the control value selected from said selected look-up table, or (ii) the control value being sequentially generated.

A steering assembly for turning the steering wheels of a vehicle upon rotation of the vehicle steering wheel, said assembly comprising:

• means for mechanically coupling the vehicle steering wheel with the steerable wheels of the vehicle;
• torsion sensing means for providing an electric signal having a value which varies as a function of the amount of input torque applied to said steering wheel;
• speed sensing means for sensing the speed of the vehicle and for providing an electric signal indicative thereof;
• electronic control means connected to said torsion sensing means and to said speed sensing means, said electronic control means including speed decoder means for providing a plurality of coded electric signals, each coded signal being indicative of the vehicle being within a particular range of vehicle speeds, memory means for storing a plurality of look-up tables, each vehicle speed range having an associated look-up table, each look-up table having a control value corresponding to a value of the signal provided by said torsion sensing means, means for selecting a look-up table responsive to said coded electric signal indicative of the vehicle being within a particular range of vehicle speeds, means for selecting a control value from a selected look-up table responsive to the value of the signal provided by said torsion sensing means, and means for generating a pulse width modulated signal having a duty cycle controlled by said selected control value from said selected look-up table;
• an electric assist motor for providing steering assist to aid a vehicle operator in a steering maneuver, the amount of assist being responsive to the electric control signal;
• and
• solid state electrical switches for switchably connecting an electrical drive potential to said electric power assist motor, said electrical switches being controlled by said pulse width modulated signal, the amount of current supplied to said electric power assist motor being proportional to the duty cycle of the pulse width modulated signal, said electronic control means further including temperature sensing means for sensing case temperature of said solid state electrical switches, means for folding back the duty cycle of said pulse width modulated signal responsive to the temperature sensed by said temperature sensing means such that the current supplied to said electric assist motor decreases as the sensed case temperature increases.

A steering assembly for turning the steerable wheels of a vehicle upon rotation of the vehicle steering wheel, said assembly comprising:

• means for mechanically coupling the vehicle steering wheel with the steerable wheels of the vehicle;
• torsion sensing means for providing an electric signal having a value which varies as a function of the amount of input torque applied to said steering wheel;
• speed sensing means for sensing the speed of the vehicle and for providing an electric signal indicative thereof;
• electronic control means connected to said torsion sensing means and to said speed sensing means, said electronic control means including speed decoder means for providing a plurality of coded electric signals, each coded signal being indicative of the vehicle being within a particular range of vehicle speeds, memory means for storing a plurality of look-up tables, each vehicle speed range having an associated look-up table, each look-up table having a control value corresponding to a value of the signal provided by said torsion sensing means, means for selecting a look-up table responsive to said coded electric signal indicative of the vehicle being within a particular range of vehicle speeds, means for selecting a control value from a selected look-up table responsive to the value of the signal provided by said torsion sensing means, and means for generating pulse width modulated signal having signal having a duty cycle controlled by said selected control value from said selected look-up table;
• an electric assist motor for providing steering assist to aid a vehicle operator in a steering maneuver, the amount of assist being responsive to the electric control signal;
• and
• solid state electrical switches for switchably connecting an electrical drive potential to said electric power assist motor, said electrical switches being controlled by said pulse width modulated signal, the amount of current supplied to said electric power assist motor being proportional to the duty cycle of said pulse width modulated signal, said electronic control means further including current sensing means for sensing the actual current through said electric power assist motor, means responsive to said current sensing means for limiting the duty cycle of said pulse width modulated signal to a predetermined maximum limit.

A steering assembly for turning the steerable wheels of a vehicle upon rotation of the vehicle steering wheel, said assembly comprising:

• means for mechanically coupled the vehicle steering wheel with the steerable wheels of the vehicle including,
• an input shaft connected to said steering wheel for rotation therewith,
• a pinion gear,
• a torsion member resiliently connecting said input shaft to said pinion gear, and
• a steering member having rack teeth thereon drivingly engaged by said pinion gear and connected to said steerable wheels of said vehicle, rotary motion of said pinion gear axially driving said steering member to turn said steerable wheels;
• torsion sensing means for providing an electric signal having a value which varies as a function of the amount of input torque applied to said steering wheel;
• speed sensing means for sensing the speed of the vehicle and for providing an electric signal indicative thereof;
• electronic control mean connected to said torsion sensing means including speed decoder means for providing a plurality of coded electric signals, each coded signal being indicative of the vehicle being within a particular range of vehicle speeds, memory means for storing a plurality of look-up tables, each vehicle speed range having an associated look-up table, each look-up table having a control value corresponding to a value of the signal provided by said torsion sensing means, means for selecting a look-up table responsive to said coded electric signal indicative of the vehicle being within a particular range of vehicle speeds, means for selecting a control value from a selected look-up table responsive to the value of the signal provided by said torsion sensing means, and means for generating a pulse width modulated signal having a duty cycle controlled by said control value from said selected look-up table;
• an electric power assist motor drivably connected to at least one of said input shaft, said pinion gear or said steering member for assisting movement thereof, the amount of assist being a function of the duty cycle of the drive signal;
• and
• solid state electrical switches for switchably connecting an electrical drive potential to said electric power assist motor, said electrical drive potential to said electric power assist motor, said electrical switches being controlled by said pulse width modulated signal, the amount of current supplied to said electric power assist motor being proportional to the duty cycle of the pulse width modulated signal, said electronic control means further including temperature sensing means for sensing case temperature of said electrical switches, means for folding back the duty cycle of said pulse width modulated signal responsive to the temperature sensed by said temperature sensing means such that current supplied to said electric power assist motor decreases as the sensed case temperature increases.