AU631370B2

AU631370B2 - Power assisted steering apparatus and linear force sensor suitable therfor

Info

Publication number: AU631370B2
Application number: AU39486/89A
Authority: AU
Inventors: Warren James Hancock
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-08-10
Filing date: 1989-08-10
Publication date: 1992-11-26
Anticipated expiration: 2009-08-10
Also published as: AU3948689A

Description

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tt 631370 COMMONWEALTH OF AU PATENTS ACT 1952 COMPLETE SPECIFICATION (Original) FOR OFFICE USE Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority: S Related Art: t, ST RA LI A Int. Class This document contains the J amnendmets ailowiv. irnder Section 83 by the Supervising Examiner on and is correct for printing Name of Applicant: WARREN JAMES HANCOCK Address of Applicant: 39 MARGARITA STREET HAMPTON VICTORIA 3188 COMMONWEALTH OF AUSTRALIA Actual Inventor(s): WARREN JAMES HANCOCK Address for Service: Davies Collison Patent Attorneys 1 Little Collins Street Melbourne Victoria 3000 Commonwealth of Australia Complete specification for the invention entitled: Power Assisted Steering Apparatus ad A-4e'r Force- Sensor Suifable TherpCr The following statement is a full description of this invention including the best method of performing it known to me:- M o1.432 1QOs 88 0O1O.gjndat.030,han.1,1 1

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la- 1 2 3 4 6 7 8 9 11 f* 13 14 e* 17 18 19 21 ae S 22 041 23 24 26 S27 28 29 31 32 33 34 36 37 POWER ASSISTED STEERING APPARATUS This invention relates to electric power assisted steering apparatus having particular application to boats, especially those having large outboard motors and stern drives, and to other mobile equipment such as forklift trucks and battery powered vehicles. In a specific aspect, ,^orczethe invention is also concerned with a linear4 diopl2 mont sensor adaptable as a force sensor for power assisted steering apparatus.

Automobiles have, for several decades, been fitted with hydraulic power assisted steering. Usually, an hydraulic pump driven by the motor provides the motive power to an hydraulic cylinder and this is arranged, in parallel with the manual steering system, to assist the driver by reducing manual effort. Special valving, integrated into the steering mechanism, controls hydraulic energy in proportion to the manual effort required, which is measured at the mechanical input from the steering wheel to the steering mechanism.

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890810.gjnspe.007.han. pe,i r i- i i i I -2- A fail-safe attribute is conventionally provided by the mechanical steering system remaining coupled to the output linkage: in the event of hydraulic system failure, manual steering is maintained albeit at greater physical effort. The permanent coupling of the manual steering system also provides force feedback or "feel" to the driver, an important feature for effective vehicle control.

Electric systems could function in a vehicle in a similar manner to hydraulic systems but these are not common.

Electric steering systems have been used in marine craft with some success, and typically employ an electric thruster which provides linear motion from an electrical input. This is coupled directly to the steering linkage, and is S commonly used in autopilot steering systems for large and small boats. The :"drawback with such devices is that electric thrusters are generally constant low Iel le speed devices suitable only for autopilot use in that they will only provide S 15 steering power for slow changes in course direction and are generally disengaged for normal steering use. They have no facility to modulate their .,,force output in response to steering effort input, which limits their responsiveness in matching the variable conditions normally encountered in use.

20 It is accordingly an object of the invention to provide in an embodiment t C application, power assisted steering apparatus suitable, inter alia, for application to boats, especially those with outboard motors and/or stern drives.

In its broadest aspect the invention also provides a linear force sensor which includes a body, and a pair of mutually spaced flexure elements coupled together at spaced locations. Means is provided for mounting the pair of flexure elements to the body. The flexure elements are adapted for attachment in use to a member which in response to an applied force is linearly displaceable in a direction to flex the flexure elements with respect to the mounting means. Further means on the body is adapted to output a signal representative of the amount of flexing and therefore also representativc of said applied force.

R4The invention therefore provides, in another aspect, power assisted 92617,gjndatl22,harIet,2 i -3steering apparatus which includes first link means adapted to be pivotally connected in use to a steerable body, and a displaceable element for operating the first link means via second link meansto which\the element is mounted, and thereby in use steering the steerable body. This displaceable element comprises a pair of mutually spaced flexure elements which are coupled together at spaced locations and are adapted for attachment in use to a member which in response to a linearly applied force is linearly displaceable in a direction to flex the flexure elements with respect to the second link means.

An electrically powered actuator is coupled to the second link means or to the first link means for assisting the applied force to steer the steerable body. The J apparatus further includes means to monitor flexing of the flexure elements r and to provide a signal representative of the amount of such flexing and therefore of the linearly applied force on the aforesaid member, for initiating activation of the actuator.

The apparatus may be disposed in a boat in which the steerable body is an outboard motor tiller arm, and in which the outboard motor is mounted for vertical tilting about a tilt axis. The actuator is preferably then disposed ahead of the tilt axis and has an output drive member which acts generally parallel to i this axis. The first link means preferably lies generally between the axis and the output drive member.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a somewhat diagrammatic plan view of power assisted steering apparatus in accordance with an embodiment of the invention; Figure 2 is a cross-section on the line 2-2 in Figure 1; and Figure 3 is a cross-section on the line 3-3 in Figure 2.

The illustrated installation includes an outboard motor mounting assembly 12 with an associated steerable body in the form of tiller arm 14.

The tiller arm is hingedly mounted to assembly 12 for angular movement about a vertical axis. The motor mounting assembly is mounted for vertical tilting about a tilt axis 17 on a motor tilt tube 18. In accordance with conventional practice, a manual push/pull 920617,gjndat122,han.Iet3 r, 4 1 2 3 4 6 7 8 9 11 o0 *oo 12 00 13 S 14 15 16 a o o 4 16 17 18 19 20 S 21 0" 22 S 23 23 24 0a 26 04 27 28 29 31 32 33 34 36 se 37 steering cable 20 passes through tube 18 and is coupled to tiller arm 14 via a pivotally mounted primary link 27.

Steering power iinear assistance is provided by an electricallyAgpwer actuator 24 which is also coupled to link 22. The connections to link 22 from cable 20 and the output drive rod 25 of actuator 24 are provided by a secondary link 26 which includes a housing 28 attached to rod 25 and link 22 and a displaceable element 30 attached to the cable.

Actuator 24 comprises an electric motor 32, a recirculating ball screw 34, intervening reduction gearing 36, and output drive rod 25. Screw 34 converts rotary motion to linear motion with high efficiency. It will be noted that actuator 24 extends generally parallel to and in front of motor tilt axis 17 and that primary link 22 lies in and extends along the space between cable 20/axis 17 and actuator 24.

Secondary link 26 is detailed in Figures 2 and 3 and incorporates a force sensor for monitoring the steering force applied to cable- 44 A control circuit 40 for actuator 24/with associated power supply, then actuates the actuator responsive to the applied force so that the power assistance imparted to the primary steering link 22 matches the manual force being applied on cable 20. This matching is achieved by modulating the power supplied to the actuator in accordance with the output of the force sensor.

Housing 28 defines respective bottom and top portions 44, 45. The bottom portion is configured as a split clamp with a main bore 46, a slit 48 and a pair of clamping bolts 49a, 49b by which the housing is clamped ontIutput drive rodAof actuator 24. One of the bolts, 49a, traverses a groove in the rod for preventing longitudinal withdrawal.

The top portion 45 of housing 28 has a knuckle hinge 51 mounting for link,,- and a cavity 50 closed by a side cover plate 52. Displaceable element 30 projects from cavity and includes, within the cavity,, a pair of parallel thin metal flexure elements 54 secured together by spaced pairs of fasteners 55 and held at a fixed separation by sleeved spacers 56 on the fasteners. At the lower or inner end, 890810.gjnspe.007,han.spe, 4

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1 2 3 4 6 7 8 9 11 12 o 13 P 0 p 4 15 16 17 18 19 20 a A4 21 **22 23 24 26 0.0 27 t 28 29 32 33 34 36 fasteners 55 are secured to an internal pedestal 43 on housing 28. The upper fasteners mount a head 58 which projects through an opening 60 in the top of housing 42 and has a transverse bore 62 for pinning element 30 to steering cable 20. Opening 60 is filled about head 58 by a compressible seal 66 to protect the sensor from the external environment whilst allowing linear motion. 54 When a steering force is applied to cable 20, elements 4 are slightly flexed as head 584"4 linearly displaced by the cable. Because of the flexure elements, there is no rotational component of motion introduced at head 58: the head moves strictly parallel to cable axis 17. Such a rotational component of motion would introduce a displacement component spurrious to -the applied force.

The flexural displacement of elementsis monitored by an inductive proximity sensor 70 having one part 72 (a tubular fixture open at one end) on the displaceable element and the other f ixed part 73 (a coil) on a printed circuit board 74 at the back of cavity. The board also provides ancillary oscillator and amplifier functions.

Bending of the flexures under applied load changes the relative positions of the two parts of the inductive proximity sensor, and thus this force induced displacement can be readily detected by established techniques sensitive to inductance changes. Note that other displacement sensors could be applied optic), to derive force information. The resultant output signal is conducted to control circuit 40 via cable 76.

An integral external claw 80 on displaceable element head 58 defines a notch 82 which receives a slightly smaller projection 84 on housing 28 to physically limit the movement of element By virtue of the inventive arrangement, it will be appreciated that, while the drawings illustrate a push/pull cable steering system, the invention is applicable to any steering system, e.g. whether mechanical linkage system or a closed circuit hydraulic system. The means is unimportant providing that manual steering can be effected without power 890810. gjnsp. 007.hm.po. 6it d ii 1 2 3 4 6 7 8 9 11 tt 12 t ic 13 f cr 14 16 t t S17 18 19 21 *o 22 23 S" 24 26 1 27 28 29 31 32 33 34 36 37 38 assistance when necessary.

It will be appreciated that, while the forces to be measured extend over a very broad range varying from light forces required for gradual changes of craft direction to high forces generated in rapid emergency manoeuvres, measurements involve only minor displacements at the force sensor. Introduction of large amounts of compliance would affect driver "feel" and could introduce servo system instabilities. Flexures are designed to operate over a range of "normal" forces, reaching a displacement limit if this force is exceeded in either direction. By using dual flexure elements internal motions are kept parallel and externally applied moments can be resisted without incurring erroneous motions of the displacement sensor.

Additional features of the illustrated arrangement include the following: 1. Fail safe. In the event of electric/electronic power failure the manual steering system must be capable of providing the steering function, albeit at greater physical effort, and to do this it must provide sufficient force to drive the power steering system backwards as well as steering the craft. By selecting the mechanical gearing and electric motor size for the actuator to cover this contingency it is possible to provide effective power assistance as well as fail safe operation.

2. The electric motor/gearbox assembly preferably incorporates an electromagnetic brake which resists kick-back forces being transmitted to the driver via the manual steering system. It also reacts the constant load often present in marine steering applications as a result of propeller torque reaction, thus reducing current consumption in the straight-ahead mode. Electrical failure modes may automatically disconnect power to the brake allowing manual steering as described above.

3. Autopilot operation. Having now provided a full time, all electric, power assisted steering system, it is relatively straightforward to input to the electronic controller signals for gradual course changes derived from a 890810,gjnape.007han.ap.6 i 7 1 variety of proprietary navigation equipment such as Radio 2 Direction Finders, Loran C Receivers, Satellite Navigation 3 Aids.

4 4. Speed responsive steering. As in automotive practice, the degree of power assistance required at high 6 speed may be quite different from that required at low 7 speed, for certain craft. With the present arrangement it 8 is again relatively straightforward to modulate the output 9 of the electronic power supply in response to engine speed, craft speed or a combination of both.

11 12 13 14 4 1 t t 16 t t 17 18 19 S21 S4 22 23 S 24 26 27 S' 28 29 31 32 33 34 36 37 38 890a10.gjn8P..007.han.p up.

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Claims

1. A linear force sensor comprising: a body; a pair of mutually spaced flexure elements coupled together at spaced locations; means mounting said pair of flexure elements to said body, said flexure elements being adapted for attachment in use to a member which in response to an applied force is linearly displaceable in a direction to flex the flexure elements with respect to said mounting means; and means on said body adapted to output a signal representative of the amount of said flexing and therefore also representative of said applied force.

2. A sensor according to claim 1 wherein said body provides a housing for 15 said flexure elements, said housing including an opening through which means extends to provide said attachment to a linearly displaceable member.

3. A sensor according to claim 2 further comprising compressible seal means in said opening about said extending means. 900,0o

4. A sensor according to claim 2 or 3 further comprising co-operating means on said body and on said extending means for limiting the movement of said extending means in response to said applied force.

5. A sensor according to claim 2, 3 or 4 wherein said housing comprises one or a pair of pivotably coupled link means.

6. A sensor according to claim 5 wherein said housing further includes clamp means for securing the housing to a drive rod of a power assisting actuator.

7. A sensor according to any preceding claim wherein said pair of flexure 920617,gjndat22hbamlet8 i. i II x~ it i elements are a pair of thin metal flexure elements secured together in spaced parallel relationship.

8. A sensor according to any preceding claim wherein said means adapted to output a signal comprises an inductive proximity sensor.

9. Power assisted steering apparatus comprising: first link means adapted to be pivotally connected in use to a steerable body; a displaceable element for operating said first link means via second Secjna= fneiovoS link means,to which said element is mounted, and thereby in use steering said steerable body, which element comprises a pair of mutually spaced flexure elements which are coupled together at spaced locations and are adapted for 6 attachment in use to a member which in response to a linearly applied force is S 15 linearly displaceable in a direction to flex the flexure elements with respect to said second link means; an electrically powered actuator coupled to said second link means or to I said first link means for assisting said applied force to steer said steerable body; and means to monitor flexing of said flexure elements, and to provide a signal representative of the amount of said flexing and therefore of said linearly applied force on said member, for initiating activation of said actuator.

Steering apparatus according to claim 9 wherein said second link means is pivotably connected to said first link means and is also coupled to said actuator.

11. Steering apparatus according to claim 9 or 10 wherein said linearly displaceable member comprises a push/pull steering cable.

12. Steering apparatus according to claim 9, 10 or 11 further comprising support means, and a steerable body hingedly mounted to said support means, i920616,gjndatl22,han.let,9 L ^y said first link means being pivotably connected to the steerable body.

13. Steering apparatus according to any one of claims 9 to 12 disposed in a boat in which said steerable body is an outboard motor tiller arm, and in which the outboard motor is mounted for vertical tilting about a tilt axis, wherein said actuator is disposed ahead of said tilt axis and has an output drive member which acts generally parallel to said axis, and wherein the first link means lies generally between said axis and said output drive member. S 10

14. A steering apparatus according to any one of claims 9 to 13 wherein said second link means provides a housing for said flexure elements, said i housing including an opening through which means extends to provide said 4' attachment to said linearly displaceable member.

15. A steering apparatus according to claim 14 further comprising compressible seal means in said opening about said extending means. 4e io:.

16. A steering apparatus according to claim 14 or 15 further comprising co- operating means on said housing and on said extending means for limiting the movement of said extending means in response to said applied force.

17. Steering apparatus according to claim 14, 15 or 16 wherein said housing further includes clamp means for securing the housing to a drive rod of said power actuator.

18. A steering apparatus according to any one of claims 9 to 17 wherein said pair of flexure elements are a pair of thin metal flexure elements secured together in spaced parallel relationship.

19. A steering apparatus according to any one of claims 9 to 18 wherein said means to monitor flexing comprises an inductive proximity sensor.

L -11 Power assisted steering apparatus substantially as hereinbefore described with reference to the accompanying drawings.

21. A linear force sensor substantially as hereinbefore described with reference to the accompanying drawings. DATED this 16th June, 1992 WARREN JAMES HANCOCK 10 By his Patent Attorneys V; Davies Collison 0* 0 .0 o e I 920617,gjndat.122,hanIet,11