Control apparatus for power assist steering system

• US 4,598,787 A
• Filed: 11/30/1984
• Issued: 07/08/1986
• Est. Priority Date: 11/30/1984
• Status: Expired due to Term

• Current Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: TRW Limited (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Drutchas, Gilbert H.
• Primary Examiner(s): Pekar, John A.
• Application Number:
  US06/676,522
• Time in Patent Office: 585 Days
• Field of Search: 180/79.1, 74/388 PS, 200/30 R, 200/153 L, 200/155 R
• US Class Current: 180/444
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

The invention provides an apparatus for controlling a power assist steering system of the type having an electric assist motor connected to a steering member such as a rack and a steering shaft including first and second coaxial shaft sections rotatable with respect to each other and connected by an elastic member. One of the shaft sections is coupled to the hand wheel and the other to the steering member. A cam operated, reversing switch is coupled across the first and second shaft sections. A drive circuit and the electric assist motor are connected to the reversing switch. A control circuit measures the relative rotation between the two shaft sections and controls the drive circuit. Relative rotation of the two steering shaft sections mechanically controls the reversing switch. The electric assist motor is (i) not electrically connected to the drive circuit when the two shaft sections are in a relative null position, (ii) electrically connected to the drive circuit in one direction when the shaft sections are relatively rotated in a first direction a predetermined amount from the null position, and (iii) electrically connected to the drive circuit in the opposite direction when the shaft sections are relatively rotated in a second direction the predetermined amount from the null position. The control circuit insures that the drive circuit outputs no electrical drive signal until the shaft sections are relatively rotated the predetermined amount. The drive potential increases thereafter as the relative rotation between the shaft sections increases above the predetermined amount.

Claims

1. An apparatus for controlling an electric assist steering system having an electric motor drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal that varies in accordance with the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver, said variance occuring after a predetermined amount of force is applied to the vehicle hand wheel;

means responsive to said output signal from said torsion sensing means for generating a variable amount of electrical drive potential to drive said electric motor, the speed of the electric motor varying in accordance with the output signal of said torsion sensing means; and

switch means connected to said electric motor and to said generating means and mechanically actuatable in response to a predetermined amount of force applied for connecting said variable amount of electrical drive potential to said electric motor when in an actuated condition.

2. The apparatus of claim 1 wherein said generating means comprises:

an actuable semoconductor switching means for, when actuated, connecting a first energy terminal to said switch means;

control means for controlling the actuation of said actuatable semiconductor switching means for a time in accordance with said output signal of said torsion sensing means; and

a second energy terminal connected to said switch means.

3. The apparatus of claim 2 wherein said actuatable semiconductor switching means includes an FET and wherein said control means includes a pulse width modulation circuit for controlling the ON and OFF time of said FET.

4. The apparatus of claim 1 wherein said generating means does not output any electrical drive potential until said torsion sensor means senses force applied to said hand wheel greater than said predetermined amount and wherein said switch means is mechanically actuated before the outputting of any electrical drive potential from said generating means.

5. The apparatus of claim 4 wherein said torsion sensing means includes a potentiometer having an amount of resistance that varies in accordance with the amount of force applied after said force applied is greater than said predetermined value.

6. The apparatus of claim 5 wherein said generating means comprises:

an actuatable semiconductor switching means for, when actuated, connecting a first energy terminal to said electric motor;

control means actuating said actuatable semiconductor switching means for a time in accordance with the amount of resistance of said potentiometer; and

a second energy terminal connected to said switch means.

7. The apparatus of claim 1 further including first and second coaxial steering shaft sections connected by an elastic member, said force applied causing relative rotation between said steering shaft sections, said switch means comprising:

camming means coupled to said first shaft section;

cam follower means coupled to said second shaft section and biased against said camming means for responding to relative rotation between said first and second shaft sections;

first electrical contacts carried by said cam follower means;

second electrical contacts coupled to said second shaft section, each first electrical contact having an associated second electrical contact;

said cam means, said cam follower means and said first and second electrical contacts arranged to provide (i) no closure between first electrical contacts and their associated second electrical contacts when said first and second shaft sections are in a relative rotational position defining a null position, (ii) closure between some of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in one direction an amount less than a predetermined value from said null position to connect said generating means across said electric motor in one direction, and (iii) closure between the other of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in the other direction an amount less than said predetermined value from said null position to connect said generating means across said electric motor in the other direction.

8. The apparatus of claim 1 further including an input shaft connected to a hand wheel and an output shaft connected to a pinion, said input shaft and said output shaft coaxially aligned, connected by an elastic member and relatively rotatable upon said force applied, said switch means comprising:

camming means connected to one of said shafts for driving a follower;

cam follower means connected to the other of said shafts and operatively contacting said camming means for responding to relative rotation between said input shaft and said output shaft;

first set of switch contacts carried by said cam follower means;

second set of switch contacts connected to said other of said shafts, each first switch contact having an associated second switch contact;

said electric motor electrically connected to one set of switch contacts, said generating means connected to the other set of said switch contacts, relative rotation between said input shaft and said output shaft in one direction contacting some of said first switch contacts with their associated second switch contacts to drive said electric motor in one direction and relative rotation between said input shaft and said output shaft in the other direction contacting the other of said first switch contacts with their associated second switch contacts to drive said electric motor in the other direction.

9. An apparatus for controlling an electric assist steering system having an electric motor means drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

actuatable semiconductor switching means for, when actuated, connecting a first energy terminal to a reversing switch means;

control means for generating a pulse width modulated control signal to control actuation of said actuatable semiconductor switching means, the duty cycle of said control signal varying in response to the output signal from said torsion sensing means;

said reversing switch means operatively connected to said motor means, said actuatable semiconductor switching means and a second energy terminal for connecting said actuatable semiconductor switching means and said second energy terminal to said motor responsive to the direction of said steering maneuver.

10. The apparatus of claim 9 wherein said actuatable semiconductor switching means includes an FET and wherein said control signal controls the ON and OFF time of said FET.

11. The apparatus of claim 9 wherein said control means includes means for not actuating said actuatable semiconductor switching means until said torsion sensor means senses an amount of force applied greater than a predetermined value and wherein said reversing switch means connects said actuatable semiconductor switching means and said second energy terminal to said motor before actuation of said actuatable semiconductor switching means.

12. The apparatus of claim 11 wherein said torsion sensing means includes a potentiometer having an amount of resistance across said potentiometer that varies in accordance with the amount of force applied after said force applied is greater than said predetermined value, said control means actuating said actuatable semiconductor switching means for a time in accordance with the amount of resistance across said potentiometer.

13. The apparatus of claim 9 further including first and second coaxial steering shaft sections connected by an elastic member, said force applied causing relative rotation between said steering shaft sections, said reversing switch means comprising:

camming means coupled to said first shaft section;

cam follower means coupled to said second shaft section and biased against said camming means for responding to relative rotation between said first and second shaft sections;

first electrical contacts carried by said cam follower means;

second electrical contacts coupled to said second shaft section, each first electrical contact having an associated second electrical contact;

said cam means, said cam follower means and said first and second electrical contacts arranged to provide (i) no closure between first electrical contacts and their associated second electrical contacts when said first and second shaft sections are in a relative rotational position defining a null position, (ii) closure between some of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in one direction an amount less than a predetermined value from said null position to connect said semiconductor switching means and said second energy termial across said electric motor means in one direction, and (iii) closure between the other of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in the other direction an amount less than said predetermined value from said null position to connect said semicdnductor switching means and said second energy terminal across said electric motor means in the other direction.

14. The apparatus of claim 9 further including an input shaft connected to a hand wheel and an output shaft connected to a pinion, said input shaft and said output shaft coaxially aligned, connected by an elastic member and relatively rotatable upon said force applied, said reversing switch means comprising:

camming means connected to one of said shafts for driving a follower;

cam follower means connected to the other of said shafts and operatively contacting said camming means for responding to relative rotation between said input shaft and said output shaft;

first set of switch contacts carried by said cam follower means;

second set of switch contacts connected to said other of said shafts, each first switch contact having an associated second switch contact;

said electric motor electrically connected to one set of switch contacts, said semiconductor switching means and said second energy terminal connected to the other set of said switch contacts, relative rotation between said input shaft and said output shaft in one direction contacting some of said first switch contacts with their associated second switch contacts to drive said electric motor in one direction upon actuation of said semiconductor switch means and relative rotation between said input shaft and said output shaft in the other direction contacting the other of said first switch contacts with their associated second switch contacts to drive said electric motor in the other direction upon actuation of said semiconductor switching means.

15. An apparatus for controlling an electric assist steering system having electric motor means drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

means for generating a variable amount of electrical drive energy for driving said electric motor means responsive to said output signal from said torsion sensing means, said generating means not outputting any electrical drive energy until the output signal from said torsion sensing means reaches a predetermined value; and

switch means for connecting said generating means to said motor means in response to the direction of said steering maneuver prior to said generating means outputting any electrical drive energy.

16. The apparatus of claim 15 wherein said generating means comprises:

an actuatable semiconductor switching means for, when actuated, connected a first energy terminal to said switch means;

a second energy terminal connected to said switch means; and

control means for controlling the actuation of said actuatable semiconductor switching means responsive to said output signal from said torsion sensing means and preventing actuation of said actuatable semiconductor switching means until the torsion sensing means output signal reaches said predetermined value, said switch means making said connections to said motor means prior to actuation of said semiconductor switching means.

17. The apparatus of claim 16 wherein said actuatable semiconductor switching means includes an FET and wherein said control means includes a pulse width modulation circuit for controlling the ON and OFF time of said FET.

18. The apparatus of claim 17 wherein said torsion sensing means includes a potentiometer having an amount of resistance across said potentiometer that varies in accordance with the amount of force applied after said force applied is greater than said predetermined amount.

19. The apparatus of claim 15 further including first and second coaxial steering shaft sections connected by an elastic member, said force applied causing relative rotation between said steering shaft sections, said switch means comprising:

camming means coupled to said first shaft section;

cam follower means coupled to said second shaft section and biased against said camming means for responding to relative rotation between said first and second shaft sections;

first electrical contacts carried by said cam follower means;

second electrical contacts coupled to said second shaft section, each first electrical contact having an associated second electrical contact;

said cam means, said cam follower means and said first and second electrical contacts arranged to provide (i) no closure between first electrical contacts and their associated second electrical contacts when said first and second shaft sections are in a relative rotational position defining a null position, (ii) closure between some of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in one direction an amount less than a predetermined value from said null position to connect said generating means across said electric motor means in one direction, and (iii) closure between the other of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in the other direction an amount less than said predetermined value from said null position to connect said generating means across said electric motor means in the other direction.

20. The apparatus of claim 15 further including an input shaft connected to a hand wheel and an output shaft connected to a pinion, said input shaft and said output shaft coaxially aligned, connected by an elastic member and relatively rotatable upon said force applied, said switch means commprising:

camming means connected to one of said shafts for driving a follower;

cam follower means connected to the other of said shafts and operatively contacting said camming means for responding to relative rotation between said input shaft and said output shaft;

first set of switch contacts carried by said cam follower means;

second set of switch contacts connected to said other of said shafts, each first switch contact having an associated second switch contact;

said electric motor means electrically connected to one set of switch contacts, said generating means connected to the other set of said switch contacts, relative rotation between said input shaft and said output shaft in one direction contacting some of said first switch contacts with their associated second switch contacts to connect said generating means across said electric motor means in one direction and relative rotation between said input shaft and said output shaft in the other direction contacting the other of said first switch contacts with their associated second switch contacts to connect said generating means across said electric motor means in the other direction.

21. An apparatus for controlling an electric assist motor in an electric power assist steering system having first and second coaxial steering shaft sections connected by an elastic member, said apparatus comprising:

camming means coupled to said first shaft section;

cam follower means coupled to said second shaft section for responding to relative rotation between said first and second shaft sections;

first electrical contacts carried by said cam follower means;

second electrical contacts coupled to said second shaft section, each first electrical contact having an associated second electrical contact;

said cam means, said cam follower means and said first and second electrical contacts arranged to provide (i) no closure between first electrical contacts and their associated second electrical contacts when said first and second shaft sections are in a relative rotational position defining a null position, (ii) closure between some of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in one direction an amount less than a predetermined value from said null position, and (iii) closure between the other of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in the other direction an amount less than said predetermined value from said null position.

22. The apparatus of claim 21 wherein said cam follower means is in electrical communication with said first electrical contacts carried thereby and said apparatus further includes:

internal brush members carried by said second shaft section, each internal brush member having said cam follower means pivotally and slidably mounted thereto and in electrical brush surface contact therewith;

means for biasing said cam follower means against said camming means;

post members coupled to said second shaft section, each post member carrying at least one of said second electrical contacts and in electrical communication therewith;

a plurality of electrical connecting rods, each of said brush members and each of said post members having a connecting rod operatively connected thereto, said rods extending parallel with the axis of rotation of said first and second shaft sections;

a plurality of axially spaced slip rings, each slip ring being operatively connected to one of said connecting rods;

a plurality of communication brushes, each slip ring having an associated communication brush; and

means to bias each of said communication brushes against its associated slip ring.

23. The apparatus of claim 22 further including:

drive means operatively coupled to a first and a second communication brush;

said electric assist motor having first and second connection terminals operatively connected to a third and fourth communication brush, respectively;

said electric assist motor (i) not electrically connected to said drive means when said first and second shaft sections are in said null position, (ii) connected to said drive means in one direction when said first and second shaft sections are relatively rotated in said one directon an amount less than said predetermined value, and (iii) connected to said drive means in another direction when said first and second shaft sections are relatively rotated in said other direction an amount less than said predetermined value.

24. The apparatus of claim 23 further including sensing means for sensing the relative rotation between said first and second shaft sections.

25. The apparatus of claim 24 wherein said drive means includes control means for controlling the amount of said effective drive potential responsive to said sensing means.

26. The apparatus of claim 25 wherein said control means permits no effective drive potential to be outputted from said drive means until said first and second shaft sections are relatively rotated by an amount equal to said predetermined value.

27. The apparatus of claim 21 wherein said cam means includes a plurality of cam faces and wherein said cam follower means includes a plurality of cam followers, each cam follower associated with at least one cam face.

28. A control apparatus for use in a power assist steering system of the type having an electric assist motor mechanically coupled to a steering member and having a steering shaft including first and second coaxial shaft sections rotatable with respect to each other and coupled to each other by an elastic member, one of said shaft sections coupled to an operator steering wheel and the other of said shaft sections coupled to said steering member, said apparatus comprising:

cam means fixed to said first shaft section and having first and second cam faces; and

cam followers, each of said cam faces having an associated cam follower, each cam follower coupled to said second shaft section and carrying first and second electrical contacts, each of said electrical contacts having associated mating electrical contacts, said first and second electrical contacts and their associated mating electrical contacts of each cam follower defining first and second electrical switches associated with such cam follower, said electric assist motor coupled to each electrical switch of each cam follower; and

electrical drive means connected across the switches associated with one of said cam followers and the switches associated with the other of said cam followers;

said electric switches arranged to provide (i) no electrical connections of said electrical drive means to said electric assist motor when said first and second shaft sections are in a relative rotational position defining a null position, (ii) electrical connections of said electrical drive means across said electric assist motor in one direction when said first shaft section is rotated in one direction an amount less than a predetermined value from said relative null position, and (iii) electrical connections of said electrical drive means across said electric assist motor in the other direction when said first shaft section is rotated in the other direction an amount less than said predetermined value from said relative null position.

29. The apparatus of claim 28 further including spring bias means coupled to each cam follower to bias said cam followers against their associated cam faces.

30. The apparatus of claim 29 further including sensing means for generating an electrical signal in response to the amount of relative rotation between said first and second shaft sections.

31. The apparatus of claim 30 further including control means for controlling an amount of effective drive potential from said electrical drive means responsive to the output signal of said sensing means.

32. The apparatus of claim 31 wherein said control means controls said electrical drive means to output substantially no effective drive potential across said electric assist motor until said first and second shaft sections are rotated with respect to each other by an amount equal to said predetermined value.

33. An apparatus for controlling an electric motor in an electric assist steering system having an input shaft connected to a hand wheel and an output shaft connected to a pinion, said input shaft and said output shaft coaxially aligned, connected by an elastic member and relatively rotatable upon applied steering torque, said apparatus comprising:

camming means connected to one of said shafts for driving a follower;

cam follower means connected to the other of said shafts and operatively contacting said camming means for responding to relative rotation between said input shaft and said output shaft;

first set of switch contacts carried by said cam follower means;

second set of switch contacts connected to said other of said shafts, each first switch contact having an associated second switch contact;

said electric motor electrically connected to one set of switch contacts, and

electric drive means for energizing said electric motor electrically connected to the other set of said switch contacts;

relative rotation between said input shaft and said output shaft in one direction contacting some of said first switch contacts with their associated second switch contacts to drive said electric motor in one direction and relative rotation between said input shaft and said output shaft in the other direction contacting the other of said first switch contacts with their associated second switch contacts to drive said electric motor in the other direction.

34. The apparatus of claim 33 further including torsion sensing means for measuring the amount of said applied steering torque.

35. The apparatus of claim 34 further including control means operatively connected to said torsion sensing means and said electrical drive means for controlling said electrical drive means responsive to the sensed amount of torque.

36. The apparatus of claim 35 wherein said control means includes means to prevent said electric drive means from outputting a drive signal for said electric motor until said torsion sensing means senses a predetermined amount of applied torque.

37. The apparatus of claim 36 wherein said electric drive means includes an FET and said control means includes a pulse width modulation circuit controlling the ON and OFF duty cycle of said FET.

38. The apparatus of claim 33 wherein said camming means includes two diametrically opposed cam faces and said cam follower means includes two cam followers, each cam face having an associated cam follower operatively biased thereagainst, each cam follower carrying two first switch contacts.

39. An apparatus for controlling an electric assist steering system having an electric motor drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

means for generating a variable amount of electrical drive potential for driving said electric motor in accordance with the output signal of said torsion sensing means; and

switch means connected to said electric motor and to said generating means and mechanically actuatable in response to a predetermined amount of force applied for connecting said variable amount of electrical drive potential to said electric motor when in an actuated condition;

said generating means comprising an actuatable semiconductor switching means including an FET for, when actuated, connecting a first energy terminal to said switch means, control means including a pulse width modulation circuit for controlling the ON and OFF time of said FET in accordance with said output signal of said torsion sensing means, and a second energy terminal connected to said switch means.

40. An apparatus for controlling an electric assist steering system having an electric motor drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver, said torsion sensing means including a potentiometer having an amount of resistance that varies in accordance with the amount of force applied after said force applied is greater than a predetermined value;

means for generating a variable amount of electrical drive potential for driving said electric motor in accordance with the output signal of said torsion sensing means, said generating means including means for not permitting outputting of any electrical drive potential until said torsion sensor means senses an amount of force applied greater than said predetermined value; and

switch means connected to said electric motor and to said generating means and mechanically actuatable in response to a predetermined amount of force applied for connecting said variable amount of electrical drive potential to said electric motor when in an actuated condition, said switch means being mechanically actuated before the outputting of any electrical drive potential from said generating means.

41. The apparatus of claim 40 wherein said generating means comprises:

an actuatable semiconductor switching means for, when actuated, connected a first energy terminal to said electric motor;

control means actuating said actuatable semiconductor switching means for a time in accordance with the amount of resistance of said potentiometer; and

a second energy terminal connected to said switch means.

42. An apparatus for controlling an electric assist steering system having an electric motor drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

first and second coaxial steering shaft sections connected by an elastic member, force applied to a vehicle hand wheel causing relative rotation between said steering shaft sections;

torsion sensing means for providing an output signal indicative of the amount of force applied to said vehicle hand wheel to accomplish a steering maneuver;

means for generating a variable amount of electrical drive potential for driving said electric motor in accordance with the output signal of said torsion sensing means; and

switch means connected to said electric motor and to said generating means and mechanically actuatable in response to a predetermined amount of force applied for connecting said variable amount of electrical drive potential to said electric motor when in an actuated condition, said switch means including, camming means coupled to said first shaft section, cam follower means coupled to said second shaft section and biased against said camming means for responding to relative rotation between said first and second shaft sections, first electrical contacts carried by said cam follower means, second electrical contacts coupled to said second shaft section, each first electrical contact having an associated second electrical contact, said cam means, said cam follower means and said first and second electrical contacts arranged to provide (i) no closure between first electrical contacts and their associated second electrical contacts when said first and second shaft sections are in a relative rotational position defining a null position, (ii) closure between some of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in one direction an amount less than a predetermined value from said null position to connect said generating means across said electric motor in one direction, and (iii) closure between the other of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in the other direction an amount less than said predetermined value from said null position to connect said generating means across said electric motor in the other direction.

43. An apparatus for controlling an electric assist steering system having an electric motor drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

an input shaft connected to a hand wheel and an output shaft connected to a pinion, said input shaft and said output shaft coaxially aligned, connected by an elastic member and relatively rotatable upon said force applied;

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

means for generating a variable amount of electrical drive potential for driving said electric motor in accordance with the output signal of said torsion sensing means; and

switch means connected to said electric motor and to said generating means and mechanically actuatable in response to a predetermined amount of force applied for connecting said variable amount of electrical drive potential to said electric motor when in an actuated condition, said switch means comprising

camming means connected to one of said shafts for driving a follower,

cam follower means connected to the other of said shafts and operatively contacting said camming means for responding to relative rotation between said input shaft and said output shaft,

first set of switch contacts carried by said cam follower means,

second set of switch contacts connected to said other of said shafts, each first switch contact having an associated second switch contact,

said electric motor electrically connected to one set of switch contacts, said generating means connected to the other set of said switch contacts, relative rotation between said input shaft and said output shaft in one direction contacting some of said first switch contacts with their associated second switch contacts to drive said electric motor in one direction and relative rotation between said input shaft and said output shaft in the other direction contacting the other of said first switch contacts with their associated second switch contacts to drive said electric motor in the other direction.

44. An apparatus for controlling an electric assist steering system having an electric motor means drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

actuatable semiconductor switching means including an FET for, when actuated, connecting a first energy terminal to a reversing switch means;

control means including a pulse width modulation circuit for controlling the ON and OFF time of said FET in response to the torsion sensing means output signal;

said reversing switch means operatively connected to said motor means, said actuatable semiconductor switching means and a second energy terminal for connecting said actuatable semiconductor switching means and said second energy terminal to said motor responsive to the direction of said steering maneuver.

45. An apparatus for controlling an electric assist steering system having an electric motor means drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver, said torsion sensing means including a potentiometer having an amount of resistance across said potentiometer that varies in accordance with the amount of force applied after said force applied is greater than a predetermined value;

actuatable semiconductor switching means for, when actuated, connecting a first energy terminal to a reversing switch means;

control means for controlling the actuation of said actuatable semiconductor switching means for a time in response to the amount of resistance across said potentiometer, said control means including means for not actuating said actuatable semiconductor switching means until said torsion sensor means senses an amount of force applied greater than said predetermined value;

said reversing switch means operatively connected to said motor means, said actuatable semiconductor switching means and a second energy terminal for connecting said actuatable semiconductor switching means and said second energy terminal to said motor responsive to the direction of said steering maneuver, aaid reversing switch means connecting said actuatable semiconductor switching means and said second energy terminal to said motor before actuation of said actuatable semiconductor switching means.

46. An apparatus for controlling an electric assist steering system having an electric motor means drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

first and second coaxial steering shaft sections connected by an elastic member, force applied to a vehicle hand wheel causing relative rotation between said steering shaft sections;

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

actuatable semiconductor switching means for, when actuated, connecting a first energy terminal to a reversing switch means;

control means for controlling the actuation of said actuatable semiconductor switching means for a time in response to the torsion sensing means output signal;

said reversing switch means operatively connected to said motor means, said actuatable semiconductor switching means and a second energy terminal for connecting said actuatable semiconductor switching means and said second energy terminal to said motor responsive to the direction of said steering maneuver, said reversing switch means including, camming means coupled to said first shaft section, cam follower means coupled to said second shaft section and biased against said camming means for responding to relative rotation between said first and second shaft sections, first electrical contacts carried by said cam follower means, second electrical contacts coupled to said second shaft section, each first electrical contact having an associated second electrical contact, said cam means, said cam follower means and said first and second electrical contacts arranged to provide (i) no closure between first electrical contacts and their associated second electrical contacts when said first and second shaft sections are in a relative rotational position defining a null position, (ii) closure between some of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in one direction an amount less than a predetermined value from said null position to connect said semiconductor switching means and said second energy terminal across said electric motor means in one direction, and (iii) closure between the other of said first electrical contacts and their associated second electrical contacts when said first and second shaft sections are relatively rotated with respect to each other in the other direction an amount less than said predetermined value from said null position to connect said semiconductor switching means and said second energy terminal across said electric motor means in the other direction.

47. An apparatus for controlling an electric assist steering system having an electric motor means drivably connected to a steering member to assist in driving said steering member, said apparatus comprising:

an input shaft connected to a hand wheel and an output shaft connected to a pinion, said input shaft and said output shaft coaxially aligned, connected by an elastic member and relatively rotatable upon said force applied;

torsion sensing means for providing an output signal indicative of the amount of force applied to a vehicle hand wheel to accomplish a steering maneuver;

actuatable semiconductor switching means for, when actuated, connecting a first energy terminal to a reversing switch means;

control means for controlling the actuation of said actuatable semiconductor switching means for a time in response to the torsion sensing means output signal;

said reversing switch means operatively connected to said motor means, said actuatable semiconductor switching means and a second energy terminal for connecting said actuatable semiconductor switching means and said second energy terminal to said motor responsive to the direction of said steering maneuver, said reversing switch means including camming means connected to one of said shafts for driving a follower, cam follower means connected to the other of said shafts and operatively contacting said camming means for responding to relative rotation between said input shaft and said output shaft, first set of switch contacts carried by said cam follower means, second set of switch contacts connected to said other of said shafts, each first switch contact having an associated second switch contact, said electric motor electrically connected to one set of switch contacts, said semiconductor switching means and said second energy terminal connected to the other set of said switch contacts, relative rotation between said input shaft and said output shaft in one direction contacting some of said first switch contacts with their associated second switch contacts to drive said electric motor in one direction upon actuation of said semiconductor switch means and relative rotation between said input shaft and said output shaft in the other direction contacting the other of said first switch contacts with their associated second switch contacts to drive said electric motor in the other direction upon actuation of said semiconductor switching means.