GB2179899A - A velocity-differential steering system for four-wheeled vehicles - Google Patents

Abstract

A four-wheeled vehicle is arranged so that two power-driven wheels A1 and A2 are positioned to form a pair on an axis spanning the vehicle's width, with the other two wheels B1 and B2 comprising offset swivel-castors placed fore and aft of this axis and positioned on the vehicle's longitudinal centre-line. Wheels A are coupled together in such a manner that their relative rates of rotation are under control of the driver, who steers the vehicle by means of their velocity-differential, wheels B simply following the resulting direction of motion by castor action. Extreme manoeuvrability is achieved without any conventional mechanical steering system, including a facility for turning the vehicle on the spot about its own vertical axis C, while the scheme also lends itself to incorporation of a flywheel energy-storage device whereby rotational manoeuvres may be effected without the vehicle being otherwise powered. The wheels A may be driven from a single power source via a conical shaft D and slave wheels E; by variable pitch-circle diameter belt pulleys; by a pump and fluid coupling between the wheels, by differential gearing or by separate electric motors. <IMAGE>

Description

SPECIFICATION A velocity-differential steering system for four-wheeled vehicles We, Henry John Frederick Crabbe of 303 Whitehorse Lane, South Norwood, London SE25 6UG, and George Charles Hayward of Forest Edge, Dragons Green Road, Nr. Southwater, Sussex, both British subjects, do hereby declare the invention for whch we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention exploits the geometry of an unconventional road-wheel configuration to achieve steerage of a four-wheel vehicle by means of the relative rotational velocities of its two power-driven wheels, without the need for a separate mechanical steering system.

A number of previous UK patents (especially 841871, 883565, 1171290 and 1270975) have advocated the adoption of a diamond-like road-wheel layout in order to enhance manoeuvrability, the general scheme being as in Fig. 1. Here, the two side-wheels A are power-driven and the front and rear wheels B provide steerage. The latter is achieved by arranging the wheels B1 and B2 are deflected in opposite directions when moved from their neutral positions, so that as B1 is turned clockwise on its steering axis, B2 swivels anticlockwise (as arrowed), and vice versa.Such mirror-image steering-locks facilitate very small overall turning radii for the vehicle, while in the limiting case where the two wheels B have locks of +90 , the axes of all four roadwheels intersect at the vehicle's centre C, enabling rotation on the spot by application of opposed drives to wheels A.

A fuller consideration of the geometry and behaviour of vehicles using this system will be found in the aforementioned patents, and also in the present inventors' co-pending UK patent application No. 8521279, where it is proposed that an offset swivel-castor be used for the rear wheel, with positive steering applied to the front wheel only. This avoids the need for an interwheel steering linkage system, while the rear wheel still follows the vehicle's motion by virtue of its castor-action. Likewise, if a castor is also used for the front wheel, both B1 and B2 will follow whatever direction of motion is imparted to the vehicle by the driven wheels A. Then, if the driver is able to control the relative rotational velocities of the two side-wheels, diret mechanical steering may be abandoned completely.A vehicle employing such a principle (which is the prime claim of this invention) will hereinafter be referred to as having 'velocity-steering'.

In the simplest case, if the wheels B1 and B2 in Fig. 1 were castors with their vertical swivel axes situated forward from the corresponding horizontal wheel axes (at points S), and the side-wheels A were powered so that each rotated at the same velocity, the two castors would trail in line with each other, undeflected, giving forward motion as shown.

Referring now to Fig. 2, if the left-hand sidewheel Al is prevented from revolving while its partner A2 continues to be powered, the vehicle will rotate about a vertical axis passing through the centre of Al, causing the front and rear castors B1 and B2 to pivot on their swivel axes S as they are pulled into position by castor-action, their corresponding wheel axes finally intersecting at the vehicle's centreof-rotation as shown. Likewise, in the extreme case of the two driven wheels A being powered to revolve at the same rate but in opposite directions (Fig. 3), the vehicle will rotate on the spot about its own centre at C, again forcing the two castors B1 and B2 into commensurate positions.

Between the neutral condition of forward motion (Fig. 1) and the above extremes of one-wheel drive and opposed drive (Figs. 2 and 3), there will be a span of steering options involving castor displacements ranging from about 45" down to one degree or less, the latter being the approximate lower deflection limit used in practical steering. For velocity-steering to apply, these deflections must be generated by a corresponding range of different rotation rates at the two driven wheels, and in the case of a rhombus wheel layout having the 1.5/1 diagonal aspect-ratio employed in Fig. 1, the velocity differentials on Al and A2 will range from 5/1 for 45" deflection down to 1.025/1 for one degree.

If means can be devised whereby a steering-wheel or its equivalent can be used to exercise control over the velocity differential between the two driven wheels over a range of this order, it therefore becomes possible to steer a vehicle entirely by such means. This removes at one stroke all the perennially vexing problems generated by mechanical steering systems, and the associated cost and complexity in manufacture and maintenance. However, in order that the vehicle may be steered while coasting as well as when powered,, a continuously variable coupling ratio must ;be in operation between the two side-wheels whenever the vehicle is moving, regardless of the power drive.

Suitable systems could involve: (i) a frictional link between the two wheels as shown schematically in Fig. 4, where a mirror-image conical shaft D transmits drive from the power source P to the road-wheels A via a pair of slave-wheels E, while also being movable laterally as arrowed to afford a continuously variable coupling ratio; (ii) a variation on the above where a pair of variable pitch-circle diameter belt-pulleys take the place of the conical shaft; (iii) use of a fluid turbo-coupling between the two wheels, with variations of its hydraulic gear-ratio used to effect the required velocity differential, possibly allied with overall power drive from a motor-operated pump; (iv) a modified differential gear in which rotation of the planet bevels is brought under separate control to act as a servo-mechanism commanding the two half-axle velocities; or (v) use of a separate electric motor-generator for each driven wheel, with divided and cross-connected windings whose multiple series/parallel switching configurations facilitate tight electromechanical coupling at digitally stepped velocity ratios.

Whichever system is employed, it should be possible to enhance fine control of the velocity differential by means of an electronically operated servo-system which monitors the final wheel velocities and applies appropriate corrections, while in cases where the facility for turning on the spot is to be included, means must be incorporated for applying opposed drives to the two wheels. There may also be emergency situations requiring some modification of the normal control system, as when rapid swerving motions are needed at high speed, or one of the powered wheels spins due to ice, mud, or other abnormal road conditions.The former could be met by arranging that the decelerated side-wheel be decoupled from the power source and momentarily braked whenever the steering-wheel is defiected very swiftly, while a fail-safe override could cope with a one-sided loss of traction by removing motive power from both driven wheels and/or deflecting one or both castors as necessary. Such refinements could be integrated with the above servo-system and commanded by a mini-computer to provide the driver with instant steering control at all times.

A velocity-steered vehicle need not employ a true rhombus wheel layout of the sort assumed in Fig. 1, since whatever the distance of the front and rear castors from the sidewheels' axis (and assuming them still to be situated on the vehicle's longitudinal bisector), they will continue to follow the motion path dictated by the drive wheels' differential. Thus if other design factors require it, a longitudinally asymmetrical wheel layout ma9 be chosen, where the front castor B1 is either further from or nearer to the A-A axis than its rear partner B2. Alternatively, in some cases it may be appropriate to choose a very compressed wheel layout, such as a square whose diagonals form the vehicle's longitudinal and lateral bisectors, to provide the base for a circular or near-circular superstructure.

Regarding categories of vehicle to which this invention may be applied, although the foregoing paragraphs primarily concern its use in domestic motorcars, it could also be employed in invalid carriages, delivery floats, industrial vehicles concerned with the handling of materials, or indeed in any other application where manoeuvrability is at a premium, large steering-locks are required without expenditure of manual effort, or avoidance of mechanical steering mechanisms is desired. Assuming, in cars, the application of appropriate design criteria in relation to the dynamics of vehicles with a single front wheel, it could be worth exploiting the potential for aerodynamic streamlining offered by the narrow front and rear contours made possible by the single wheel in each position.

As a further refinement, versions of a velocity-steered vehicle which included sufficient freedom on the castors to facilitate rotation on the spot, might with advantage incorporate a laterally disposed flywheel energy-storage system whose rotational axis is made coincident with the vehicle's own vertical axis of rotation-midway between the driven wheels.

In addition to the known benefits of such flywheels, this could provide rotation on the spot simply by freeing the two side-wheels and momentarily coupling the flywheel to the vehicle. But care would have to be taken to balance the vehicle dynamically in relation to its axis of rotation.

Subject to any constraints imposed by the suspension system, all the above variants are subservient to the general principles covered by this invention. These concern the use of four road-wheels on powered vehicles ,arranged so that two driven wheels are posed tioned to form a pair of an axis spanning the vehicle's width and equally spaced from its longitudinal bisector, the other two wheels taking the form of offset swivel-castors which are placed fore and aft of this axis with their vertical swivels positioned on or near the same longitudinal bisector. The two laterally positioned wheels are so coupled and powered that their relative rotational velocities are under the driver's control and determine the vehicle's direction of motion, the wheels at the front and rear simply following that direction by castor-action.

Claims (1)

1. A four-wheeled vehicle in which two power-driven road-wheels share an axis set across the vehicle's width and are positioned at or near the vehicle's sides, the rotary motions of these two wheels being linked in such a manner that the ratio of their angular velocities is variable by the driver in order to effect steering, with the other two road-wheels situated fore and aft of the driven wheels' axis and comprising offset swivel-castors whose vertical swivel axes are located on or near the vehicle's longitudinal centre-line, these front and rear wheels being free to adopt whatever deflection angles may be dictated by the vehicle's direction of motion, the latter as determined by the driven wheels' relative velocities.

2. A vehicle according to claim 1 in which controlled differential motion of the driven wheels (whether it be achieved by frictional couplings, gears, hydraulics, electro-mechanics, or other means) encompasses a condition where one or other wheel is held stationary while its partner is powered, in order to provide a vehicle turning-circle centred on the locked wheel.

3. A vehicle according to claims 1 or 2 in which the two driven wheels can be powered to revolve in opposite directions, in order that the vehicle may be rotated on the spot about a vertical axis which bisects the line joining said wheels.

4. A vehicle according to claims 1-3 in which a servo monitoring system is employed to ensure close correspondence between the intended and actual relative velocities of the two driven wheels, and which may also cope with emergency road and driving conditions by removing power from and/or applying braking to one, other or both of the driven wheels and/or by deflecting one or both castors.

5. A vehicle according to claims 1-4 fitted with a horizontally disposed flywheel which acts as a dynamic stabilizer and inertial energy store, and whose rotational axis is made coincident with the vehicle's own vertical axis of rotation as defined in claim 3, so that by means of a suitable controlled coupling system its energy may be drawn upon for vehicle rotation purposes.

6. A powered four-wheeled vehicle substantially as described herein with reference to Figs. 1-3 of the accompanying drawings.

CLAIMS Amendments to the claims have been filed, and have the following effect: Claims 1 above have been deleted or textually amended.

New or textually amended claims have been filed as follows:

1. A four-wheeled motorcar, delivery float, or materials-handling vehicle, in which two power-driven road-wheels share an axis set across the vehicle's width and are positioned at or near the vehicle's sides, the rotary motions of these two wheels being linked in such a manner that the ratio of their angular velocities is variable by the driver in order to effect steering, with the other two road-wheels situated fore and aft of the driven wheels' axis and comprising offset swivel-castors whose verticle swivel axes are located on or near the vehicle's longitudinal centre-line, these front and rear wheels being free to adopt whatever deflection angles may be dictated by the vehicle's direction of motion, the latter determined by the driven wheels' relative velocities.