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Title:
AUTOMOTIVE STEERING GEAR CASING
Document Type and Number:
WIPO Patent Application WO/2019/102508
Kind Code:
A1
Abstract:
The present Invention refers to an automotive steering gear easing which allows the prolongation of the axis of the front steered wheels - if the steering gear casing is fitted to a motor vehicle and on curves - to be concurrent at a point P on the prolongation of the axis of the rear wheels no matter what the steering angle.

Inventors:
SCARDI, Francesco Antonio (Via San Magno, 50/B, CORATO, 70033, IT)
Application Number:
IT2018/050224
Publication Date:
May 31, 2019
Filing Date:
November 20, 2018
Export Citation:
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Assignee:
SCARDI, Francesco Antonio (Via San Magno, 50/B, CORATO, 70033, IT)
International Classes:
B62D7/09; B62D3/12
Domestic Patent References:
WO2017037727A12017-03-09
Foreign References:
US4240306A1980-12-23
GB609356A1948-09-29
US4270397A1981-06-02
EP1354783A12003-10-22
KR20130065151A2013-06-19
US3546957A1970-12-15
Attorney, Agent or Firm:
RUSSO, Dimitri (Via Ottavio Serena 37, BARI, 70126, IT)
Download PDF:
Claims:
CLAIMS

1 ) Automotive steering gear casing characterized by a first shaft (5) having a rack (18), a pinion (13) to be connected to a motor vehicle steering wheel and geared to said rack (18), said first shaft (5) being suitable to be connected to a first front steered wheel of a motor vehicle and being fastened - and sliding - to a pair of shafts (8): said first shaft (5) including a pin (9) inserted inside a first cam on a cylinder (4), and characterized in that it includes a second shaft (6), said second shaft (6) being suitable to be connected to a second front steered wheel of a motor vehicle and being fastened - and sliding - to said pair of shafts

(8) , said second shaft (6) including a pin (10) inserted inside a second cam on said cylinder (4), in which during the steering phase the motion of the first shaft (5), powered by the rotation of the motor vehicle steering wheel, causes the rotation of the cylinder (4), through the pin

(9) sliding inside said first cam, and the rotation of the cylinder (4) causing the simultaneous motion of the second shaft (6), through the pin (10) sliding inside the said second cam, said first cam and said second cam being shaped in such a way that the axes of the steered wheels to be connected to said first shaft (5) and to said second shaft (6) are concurrent on a point of the axis passing through the centre of the rear wheels during the steering phase.

2) Automotive steering gear casing characterized by a first shaft (5) having a rack (18), a pinion (13) to be connected to a motor vehicle steering wheel and geared to said rack (18), said first shaft (5) being suitable to be connected to a first front steered wheel of a motor vehicle and being fastened - and sliding - to a pair of shafts (8), said first shaft (5) including a pin (9) inserted inside a first cam on a plate, and characterized in that it includes a second shaft (6), said second shaft (6) being suitable to be connected to a second front steered wheel of a motor vehicle and being fastened - and sliding - to said pair of shafts (8), said second shaft (6) including a pin (10) inserted inside a second cam on said plate, in which during the steering phase the motion of the first shaft (5): powered by the rotation of the motor vehicle steering wheel, causes the motion of said plate, through the pin (9) sliding inside said first cam, and the motion of said plate causing the simultaneous motion of the second shaft (6), through the pin (10) sliding inside said second cam, said first and second cams being shaped in such a way that the axes of the steered wheels to be connected to said first shaft (5) and to said second shaft (6) are concurrent on a point of the axis passing through the centre of the rear wheels during the steering phase.

3) Automotive steering gear casing as claimed in claim one or two in which said first cam and said second cam are curved.

4) Automotive steering gear casing as claimed in claim one or two in which on a X-Y Cartesian plane the shape of the said first cam is determined by a set of discrete points (Xα, Yα) and the shape of the said second cam is determined by a set of discrete point (Xβ, Yβ) where:

- Υβ = Y3 = Y being the ordinate on the X-Y Cartesian plane;

- Χα being the abscissa on the X-Y Cartesian plane coinciding with the shift of the centre of the steering gear casing knuckle E for the first steered wheel and being = s sen

- Xβ being the abscissa on the X-Y Cartesian plane coinciding with the shift of the centre of the steering gear casing knuckle F for the second steered wheel and being = s sen - tang

- p being the distance between the axis passing through the rotation centres of the front steered wheels and the axis passing through the rotation centres of the rear wheels of the motor vehicle in which the steering casing is connected.

- c being the distance between the rotation centres of the front steered wheels of the motor vehicle in which the steering casing is connected;

- β being the angle from the rotation axis of the first steered wheel to the axis passing through the rotation centres of the rear wheels;

- a being the angle from the rotation axis of the second steered wheel to the axis passing through the rotation centres of the rear wheels;

- being the projected length on the road surface of the rod to be connected to the first steered wheel;

- being the projected length on the road surface of the rod to be

connected to the second steered wheel;

- s being the projection on the road surface of the component perpendicular to the axis passing through the rotation centres of the front wheels of the rod which connects the steered wheels hub.

5) Steering gear casing as claimed in claims one, three and four in which the cylinder (4) is held in a central body (3) and it is fitted to a pair of bearings (15) and (16).

6) Steering gear casing as claimed in claim five comprising seals (14) and (17) for its lubricating liquid tight.

7) Steering gear casing as claimed in previous claims comprising a bushing (11) meant for letting the second shaft (6) slide thereinside.

8) Motor vehicle comprising at least a pair of steered wheels, characterized in that it includes a steering gear casing as claimed in any claim 1 to 7, in which said steering gear casing is connected to said pair of steered wheels.

9) Motor vehicle as claimed in claim 8 comprising at least a fuel container, in which said fuel container is placed at a point coincident with the motor vehicle centre of gravity, and in which the cams of the steering gear casing are shaped so as to make the axes of the front steered wheels be concurrent at said point coincident with the motor vehicle centre of gravity.

10) Motor vehicle comprising a pair of front steered wheels and a pair of rear steered wheels, characterized in that it includes a front steering gear casing as claimed in any claim 1 to 7, in which said front steering gear casing is connected to said pair of front steered wheels and a rear steering gear casing as claimed in any claim 1 to 7 , in which said rear steering gear casing is connected to said pair of rear steered wheels.

11 ) Motor vehicle as claimed in claim 10 comprising at least a fuel container, in which said fuel container is placed at a point coincident with the motor vehicle centre of gravity, and in which the cams of the front and rear steering gear casings are shaped so as to make the axes of the front steered wheels and those of the rear steered wheels be concurrent at said point coincident with the motor vehicle centre of gravity.

Description:
AUTOMOTIVE STEERING GEAR CASING

The present invention refers to an automotive steering gear casing which allows the prolongation of the axis of the front steered wheels - if the steering gear casing is fitted to a motor vehicle and on curves - to be concurrent at a point P on the prolongation of the axis of the rear wheels no matter what the steering angle.

The steering gear casings used by ail car manufacturers are devices which transform - through mechanical couplings (as, for example, pinion/rack or any other) - the rotatory motion of the motor vehicle steering wheel into an axial motion of a shaft which is transversaily placed and mechanically connected to the front wheels hubs. In the known type steering gear casings the angles from the axes of each one of the two steered wheels to the prolongation of the axis passing through the rear wheels are equal without the axes being concurrent at a unique point on said prolongation of the axis of the rear wheels, unless very complex and expensive devices are used.

The main aim of the present invention is to provide an automotive steering gear casing in which, during the steering phase, the axes of each one of the two steered wheels are concurrent at a unique point on the prolongation of the axis of the rear wheels.

More specifically, the aim of the invention is to provide an automotive steering gear casing in which the axes of the steered wheels are concurrent at a point on the axis passing through the centre of the rear wheels no matter what the steering angle between 0*and the design maximum steering angle.

Another aim of the invention is to provide an automotive steering gear casing which allows - when it is fitted to a motor vehicle - a uniform tyre wear on the steered wheels and consequently a longer tyre life

A further aim of the present invention is to provide an automotive steering gear casing which allows - when it is fitted to a motor vehicle - a better road holding and greater safety for the motor vehicle. Another aim of the invention is to provide an automotive steering gear casing having a low production cost which makes it suitable to be used on the cheapest types of motor vehicles as well as on the most luxurious ones.

A further aim of the invention is to provide an automotive steering gear casing which may be used together with another, or with several, automotive steering gear casing(s), on motor vehicles having two or more pairs of steered wheels which axes are concurrent at a point of the axis passing through the centres of the rear wheels no matter what the steering angle. The automotive steering gear casings of the present invention are accordingly suitable to be fitted to a motor vehicle having two pairs of steered wheels, a front pair and a rear pair, with respect to the axis inside the wheels quadrilateral, which is perpendicular to the straight direction of travel and coplanar to the drawing plane.

A further aim of the invention is to provide an automotive steering gear casing which allows to reduce the turning radius of the motor vehicle to which it is fitted, so also allowing parking facilities.

The last aim of the invention is to provide a motor vehicle comprising an automotive steering gear casing according to the present invention and having a great road holding.

The said aims are achieved by the automotive steering gear casing according to the present invention, characterised by a first shaft having a rack, a pinion suitable to be connected to a motor vehicle steering wheel and geared to said rack, in which said first shaft being suitable to be connected to a first front steered wheel of a motor vehicle and being fastened - and sliding - to a pair of shafts, said first shaft including a pin inserted inside a first cam on a cylinder, and characterized in that it includes a second shaft, said second shaft being suitable to be connected to a second front steered wheel of a motor vehicle and being fastened - and sliding - to said pair of shafts, said second shaft including a pin inserted inside a second cam on said cylinder, in which during the steering phase the motion of the first shaft, powered by the rotation of the motor vehicle steering wheel, causes the rotation of the cylinder, through the pin sliding inside said first cam, and the rotation of the cylinder causing the simultaneous motion of the second shaft, through the pin sliding inside the said second cam, said first cam and said second cam being shaped in such a way that the axes of the steered wheels to be connected to said first shaft and to said second shaft are concurrent at a point of the axis passing through the centre of the rear wheels during the steering phase.

The above indicated aims are further achieved by the automotive steering gear casing according to the present invention characterised by a first shaft having a rack, a pinion suitable to be connected to a motor vehicle steering wheel and geared to said rack, said first shaft being suitable to be connected to a first front steered wheel of a motor vehicle and being fastened - and sliding - to a pair of shafts, said first shaft including a pin inserted inside a first cam on a plate, and characterized in that it includes a second shaft, said second shaft being suitable to be connected to a second front steered wheel of a motor vehicle and being fastened - and sliding - to said pair of shafts, said second shaft including a pin inserted inside a second cam on said plate, in which during the steering phase the motion of the first shaft, powered by the rotation of the motor vehicle steering wheel, causes the motion of said plate, through the pin sliding inside said first cam, and the motion of said plate causing the simultaneous motion of the second shaft, through the pin sliding inside the said second cam, said first cam and said second cam being shaped in such a way that the axes of the steered wheels to be connected to said first shaft and to said second shaft are concurrent at a point of the axis passing through the centre of the rear wheels during the steering phase.

The above described aims of the invention are further achieved by an automotive steering gear casing in which said first cam and said second cam are curved. The above described aims of the present invention are also achieved by an automotive steering gear casing, in which on a X-Y Cartesian plane the shape of the said first cam is determined by a set of discrete points (Χ α , Y α ) and the shape of the said second cam is determined by a set of discrete point where:

& being the ordinate on the X-Y Cartesian plane;

being the abscissa on the X-Y Cartesian plane coincident with the shift

of the centre of the steering gear casing knuckle E for the first steered wheel and being - s sen

- X β being the abscissa on the X-Y Cartesian plane coincident with the shift of the centre of the steering gear casing knuckle F for the second steered wheel and being = s sen

- p being the distance between the axis passing through the rotation centres of the front steered wheels and the axis passing through the rotation centres of the rear wheels of the motor vehicle in which the steering casing is connected;

- c being the distance between the rotation centres of the front steered wheels of the motor vehicle in which the steering casing is connected;

- β being the angle from the rotation axis of the first steered wheel to the axis passing through the rotation centres of the rear wheels;

- a being the angle from the rotation axis of the second steered wheei to the axis passing through the rotation centres of the rear wheels;

- t α being the projected length on the road surface of the rod to be connected to the first steered wheel;

- t β being the projected length on the road surface of the rod to be connected to the second steered wheel: - s being the projection on the road surface of the component perpendicular to the axis passing through the rotation centres of the front wheels of the rod which connects the steered wheels hub to the steering gear casing.

The aims of the invention are also achieved by the automotive steering gear casing according to the present invention in which the cylinder is held in a central body and it is fitted to a pair of bearings.

The aims of the invention are further achieved by the automotive steering gear casing according to the present invention comprising seals for its lubricating liquid tight.

Another aim of the invention is to provide an automotive steering gear casing comprising a bushing meant for letting the second shaft slide thereinside. A further aim of the present invention is to provide a motor vehicle comprising a pair of front steered wheels and a pair of rear steered wheels, a front steering gear casing according to the invention, in which said front steering gear casing is connected to said pair of front steered wheels and a rear steering gear casing according to the invention, in which said rear steering gear casing is connected to said pair of rear steered wheels.

At this point, it suffices to connect the two steering gear casings with each other during the straight direction of travel, by attaching one of them to the steering gear casing, and the system is installed.

The last aim of the present invention is to provide a motor vehicle comprising at least one fuel container, in which said container is placed at a point coincident with the motor vehicle centre of gravity (or as close to its centre of gravity as possible), and in which the cams of the front and rear steering gear casings are shaped so as to make the axes of the front steered wheels and those of the rear steered wheels be concurrent at a point on an axis passing through the projection point (on the drawing plane or road surface) of the centre of gravity of the motor vehicle, no matter what the steering angle. The above said aims and advantages, as well as others, as they are better described hereafter, are achieved by the automotive steering gear casing, which is henceforth illustrated in a preferred embodiment - to be possibly further developed and improved - through the attached drawings which show respectively:

Figure 1 , a plan view of a motor vehicle comprising a known type steering gear casing;

Figure 2, a plan view of a motor vehicle on which the steering gear casing according to the present invention is installed (only references E and F are indicated);

Figure 3, a plan view of the cams relevant to a steering to the right according to the present invention;

Figure 4, a plan view of the cams relevant to a full steering (to the right and to the left) according to the present invention;

Figure 5, a side partially sectional view of the steering gear casing according to the present invention;

Figure 6, side views of the shafts of the steering gear casing according to the present invention;

Figure 7, a side view of one of the heads of the steering gear casing according to the present invention:

Figure 8, orthogonal projections of the cylinder of the steering gear casing according to the present invention;

Figure 9, the central body, holding the cylinder with the cams according to the present invention;

Figure 10, orthogonal projections of a shaft of the steering gear casing according to the present invention;

Figure 11 , a side view of a shaft of the steering gear casing according to the present invention; Figure 12, orthogonal projections of the second head of the steering gear casing according to the present invention;

Figure 13, an axonometric view of the steering gear casing according to the present invention;

Figure 14, a plan view od the steering gear casing in a second embodiment of the present invention; this one has the cylinder with the cams on it too;

Figure 15, a plan view of the steering gear casing shown in figure 14;

Figure 16, a plan view of a motor vehicle comprising two steering gear casings according to the invention connected to two pairs of front steered wheels;

Figure 17, a plan view of a motor vehicle comprising two steering gear casings according to the invention connected to two pairs of front and rear steered wheels.

Referring to figures 5 to 13 a first embodiment of the steering gear casing according to the invention is described.

The automotive steering gear casing according to the present invention (see figure 5) includes a first steel shaft 5 having a rack 18, figure 6. The rack 18 is on a side of the shaft 5.

The steering gear casing includes a pinion 13 suitable to be connected to a motor vehicle steering wheel and geared to said rack 18.

The first shaft 5 is to be connected to a first front steered wheel of a motor vehicle and is fastened - and sliding - to a pair of parallel shafts 8, figure 11. The first shaft 5 includes a pin 9 which is inserted inside a first cam on a cylinder 4, figure 8.

The steering gear casing includes a second shaft 6 is to be connected to a second front steered wheel of a motor vehicle.

Like the first shaft 5, the second shaft 6 is fastened - and sliding - to said pair of shafts 8. The second shaft 6, figure 10, includes a pin 10 inserted inside a second cam on said cylinder 4, figure 8.

The shafts 5 and 6 are mutually telescopic and have a vent hole 12 : they slide on the steel shafts 8, figure 11 (the latter are two, they are parallel to each other e to the axis of the steering gear casing) and each determines the motion of the wheel to which it is connected.

During the steering phase, the operation of the steering wheel causes the rotation of the pinion 13 which engages the rack 18 on the side of the shaft 5. The shaft 5, through the pinion-rack device positioned in the head 1, figure 7, and indicated in figure 5, moves on the shafts 8 and through the pin 9, inserted inside the first one of the two cams on the cylinder 4, makes the latter rotate.

The cylinder 4 with its cams, thanks to the method object of the present invention, allows the axes of the rear wheels to be concurrent at a point of the axis passing through the centre of the rear wheels during the steering phase. The cylinder 4, fitted to the bearings 15 and 16 ; is positioned in the cylindrical frame 3, figure 9, and in turn, while rotating, makes the shaft 6 move through the pin 10 inserted inside the second cam.

The first and second cams are shaped in such a way that the axes of the steered wheels to be connected to said first shaft 5 and to said second shaft 6 are concurrent at a point of the axis passing through the centre of the rear wheels during the steering phase.

The head 1 houses the pinion-rack device which activates the shaft 5. Furthermore the head 2, figure 12, includes a bushing 11 inside which the shaft 6 slides. Both the heads are fastened to the central body 3 by means of the screws 19. The seals 14 and 17 guarantee that the lubricating liquid inside the steering gear casing is properly tightened. This liquid, for both models, may be put inside the steering gear casing during the assembly operations or through a cap which is not shown neither on the scheme nor on the model and which may always be fitted.

The heads 1 and 2 are manufactured of a light metallic alloy, for example an aluminium alloy.

The ratio between the number of the rack teeth and the number of the pinion teeth indicates the number of turns that the steering wheel will have to perform in order to accomplish a full steering.

In another embodiment of the present invention the cylinder 4 may be replaced by a moving plate with the cams on it.

In figures 14 and 15 the steering wheel according to the present invention is described in a second embodiment. The steel shaft 14, powered by the steering wheel, rotates on the bearings 15 and 17 and by means of a pair of gears 25 (one, the pinion, at the end of the shaft 14 and the other, the rack, at the end of the cylinder 4, also in steel) makes the cylinder 4 rotate. The cylinder 4, which in turn rotates on the bearings 20 and 22, is inside the cylindrical frame in a light alloy 3.

The mutually telescopic steel shaft 5 and 6, which have a vent hole 13, can in turn slide on the steel shafts 8 (the latter are two, they are parallel to each other and to the axis of the steering gear casing and are secured in the light alloy heads 1 and 2). Pins 9 and 10 are at the end of the shafts 5 and 6 (inner side).

Said shafts are assembled in such a way that the pins are each inside one of the cams on the cylinder 4,

In the head 1the shaft 14 is assembled and secured by means of the light alloy cap 24 and relevant seal 18.

The shafts 5 and 6 pass through the bushings 11 and 12 fitted on the (light alloy) heads 1 and 2 and are connected to the relevant wheels.

The seals 19 and 23 guarantee that the lubricating liquid inside the steering gear casing is properly tightened. The heads 1 and 2 are secured to the central body 3 by means of the screws 26 (only the axes are shown).

By powering the steering wheel, the shaft 14 is obviously made to rotate, the latter, in turn, making the cylinder 4 rotate, and the shafts 5 and 6 move to the right or to the left depending on the direction of rotation of the steering wheel. It is noted that the ratio between the number of teeth of the cylinder portion (arc) which includes the cams and the number of the pinion 14 teeth indicates the number of turns that the steering wheel will have to perform in order to accomplish a full steering.

Referring to figures 1 to 4 the procedure for determining the shape of the cams of the steering wheel according to the invention is here below illustrated.

In figure 1 the plan of a motor vehicle is schematically shown. In this plan we suppose that the axes of the wheel are parallel to the road surface and that the pins of the steered wheels rotate around two stub axles A and B perpendicular to the road surface. In its curve ride attitude (for example a steering to the right), the angle between the axis of the left front wheel and the axis passing through C and D (see figure 2) is indicated with α and the angle between the axis of the right front wheel and the axis passing through C and D is indicated with β\ it follows that to ensure that the axes of the steered wheels are concurrent at a point P of the axis passing through C and D, the angle β has to be larger than the angle σ. The point P is called instant centre of rotation and it travels on the prolongation of CD following the changes in the curve ride attitude. Figure 1 illustrates the projection of the mechanism which connects the traditional steering gear casing to the wheels both on the drawing plane and on the plane perpendicular to it. In this figure, EF is the RS projection, it is parallel to AB and is therefore coplanar to the drawing plane, GE and FH are the UR and SV bars projection on the drawing plane and are parallel to AB during the straight direction of travel. Figure 2 does not show the steering gear casing but only its references E and F (knuckles) with EF - which is figure 1 RS projection - parallel to AB and therefore coplanar to the drawing plane; elements GM and HN of figure 1 have been replaced in figure 2 by the components GA and HB projections on the drawing plane, the latter being integral with, respectively, the stub axles A and B and perpendicular to AB.

Referring to figure 2 and indicating with:

- p the pitch (distance between AB and CD),

- c the distance between A and B (rotation centres of the front wheels).

- a the angle between the left front wheel and the axis passing through C and D,

- β the angle between the right front wheel and the axis passing through C and D,

- Y the angle between the right front wheel and the axis passing through the centres of the rear wheels,

by means of trigonometrical relationships the following is derived:

Once γ mx is set as the maximum value of the steering angle of the inner wheel, β mx takes its complementary value.

If we consider a sequence of design values (for example, every half-degree) from 0 to β mx , the following sequence is derived:

Through the relationship (1 ) we are able to obtain the corresponding sequence:

Furthermore:

-.to being the length of E G,

- t β being the length of F H,

- s being the length of A G = B H. During a turn, for example a steering to the right, at a certain time the axes of the front wheels form, as said before, angles a and β with the axis passing through C and D. It follows that at a certain time (always referring to figure 2) the point F moves to F β and X β indicates, in absolute terms, the distance F F β (with coincides with F); E moves to E« and X«

indicates, in absolute terms, the distance

E a coincides with E).

By means of trigonometrical relationships the following formulations are obtained:

Once the size of the chassis is set, the maximum steering angle of the inner wheel, the size of the steering gear casing (distance EF = RS), the length of the bars constituting the mechanism, it is obviously possible to write ~ in addition to the a and β sequences of values - the Χ α and X β sequences. The values of the X α and X β are then noted on a drawing plane and combined with a sequence of ordinates (Y α = Y β = Y) assigned by a constant pitch (for example every 0,5 - 0,875 - 1 - 1 ,5 mm), two sets of points

By connecting the points X α - Y and, separately, the points X β - Y, a graph is obtained, in which two polygonal lines comparable to two curves, one for X α and one for X β , are represented.

It is recalled that the corresponding X α and X β values must have the same ordinate and that the more numerous the points, the greater the curve continuity. In fact, in the described case an every half-degree β sequence has been adopted; if an every quarter-of-a-degree sequence had been adopted the points for determining the graph curves of figure 4 would redouble so producing a greater curve continuity and so on.

Here below the procedure for calculating the shape of the cams in a known type of motor vehicle is illustrated.

In particular, being the distance c (AB) = 1225 mm, the pitch p = 2460, the arm s = 130 mm, the bar projection the distance E F (length of the steering gear casing) = 524 mm, the steering angle of the right front wheel γ mx = 60°, to which the maximum angle between the axis of the inner wheel and CD, that is β mx = 30°, corresponds, the following sequence can be written;

in which, as said before, = 0 (abscissa of F) and X α = 0 (abscissa of E) correspond to the straight ride attitude. Once the said values are noted on a drawing sheet, a graph is obtained, in which two polygonal lines comparable to two curves are represented (figure 3).

More particularly, the curve relevant to the left front wheel is indicated with a (X α ) and the curve relevant to the right wheel is indicated with b (X β ). Said curves refer to a steering to the right. In a steering to the left,, the two curves are the same as those of the steering to the right, but they are reversed and down the axis X passing through X α = 0 and X β = 0, namely in the second quadrant. These curves, combined with those of the steering to the right, trace the curve shape as shown in sfigure 4 referred to the full steering.

Any line parallel to the axis X of course intercepts the said curves at two points having abscissa X α and X β . The said values uniquely position the two steered wheels, so that their axes meet at a point of the axis passing through the rear wheels. Now the said curves just have to be noted (by connecting the points wich constitute them) on a metal cylinder surface having an appropriate thickness, by means of a milling system (or whatever else) in order to obtain the cams suitably wide and thick so that they are made to pass on the said cylinder.

Through the described method it is therefore possible to draw the cams for that type of vehicle and to exactly assemble the steering gear casing which ensures, as explained before, that the prolongations of the axes of the front steered wheels are concurrent at a point of the prolongation of the axis passing through the centres of the rear wheels no matter what the steering angle between 0° and the maximum steering angle, which is 60° in our example. In order to make it easier to understand the invention and the method used for determining the cams, one of its embodiments (to be illustrative and not limiting) is below described.

In the assembly of the present model (steering gear casing with both the knuckles fitted and in the straight ride attitude), with reference to figure 15, considering that:

I = design length of the steering gear casing,

I 1 = design distance between the knuckle and the outer face of the knuckle, l 3 = design height of the bushings,

the following must be:

l 2 at least 1 or 2 mm greater than the absolute value of X α min = X β max, l 4 becomes equal to already known

l 5 , which is the distance between X α - 0 and X β = 0 and has to be at least 2 mm smaller than

U - 4X α min - h

where h is the height of the cylindrical head being one with the shaft.

The steering gear casing according to the present invention may be adopted on any motor vehicle provided with one (or more) pair(s) of steered wheels. For example, in figure 2 a motor vehicle having a steering gear casing connected to the pair of front steered wheels is illustrated. We suppose that the axes of the steered wheels rotate around four stub axles A, B, C, D perpendicular to the drawing plane.

As shown in figure 16, once the following factors are set:

-the length of the steering gear casings,

-the dimensions of the mechanism connecting with the relevant wheels in the straight ride attitude

-the distance between the axis passing through A and B and the axis passing through E and F (pitch p-T),

-the distance between the axis passing through C and D and the axis passing through E and F (pitch P2),

-the distance between the centres of rotation of the two pairs of steered wheels c equal to each other (AB = CD),

-the value of the maximum steering angle of one of the inner wheels (for example, in the present case, the wheel which rotates around B),

and once we have indicated with ch, β 1 , α 2 and β 2 the angles formed by each steered wheel with the axis of the rear wheels, all concurrent at P, we can write the following sequences of values: the sequence of β 1 (with β 1mx complementary of the design maximum steering angle), the sequence of on by means of the mathematical expression (1) where α, β and p become a 1 , β 1 p 1 , the sequences of X P i. and X by means of the expression (2) where the indexes β and a become β 1 and oh.

We are thus able to determine the relevant cams and therefore to assemble the steering gear casing relevant to the wheels which rotate around A and B. After that, through the trigonometrical relationships:

tang α 2 = (p 2 / pi) tang α 1 (3)

We are then able to determine the sequence of a 2 from the sequence of ai (which we know) by means of the expression (3), the sequence of β 2 by means of the expression (4), the sequences of Χβ 2 and Xa 2 by means of the expression (2) where the indexes β and a become β 2 and a 2 .

It is therefore possible to determine the relevant cams and to assemble the steering gear casing relevant to the wheels which rotate around C and D. The corresponding values of must have the same ordinate.

In other words, the pitch as chosen for the ordinates must be the same for all four curves necessary for tracing and obtaining the cams of the two cylinders. And then the two steering gear casings are fitted and phase adjusted in the straight ride attitude and reciprocally connected through a mechanical hydraulic (or other) system.

It suffices to connect one of the steering gear casings with the steering wheel of the vehicle and the system is installed. In the event of more than two pairs of steered wheels it is necessary to use several steering gear casings (as many as the pairs of steered wheels) and to repeat the same reasoning.

Figure 17 shows a motor vehicle having two steering gear casings according to the present invention, each for every pair of steered wheels.

In figure 17 the plan of a motor vehicle is schematically shown. We suppose that the axes of the wheels are parallel to the drawing plane and that the pins of the steered wheels rotate around four stub axles A,B S C and D perpendicular to the drawing plane. Z is an axis parallel to the sides AB and CD, inside the quadrilateral ABCD, coplanar to it and - in the straight ride attitude - perpendicular to the travel direction.

We project both the axis Z and the axes of the four steered wheels on the drawing plane.

ch, β ΐ5 α 2 and β 2 are the angles between the axis of each one of the four wheels and the axis Z, all concurrent at a point P of the axis Z.

Pi is the distance of A B from the axis Z, p 2 is the distance of C D from the axis Z, c is the distance between A and B equal to the distance between C and D. Through short trigonometrical relationships we obtain:

Once the following factors are set:

-the length of the steering gear casings,

-the dimensions of the mechanism connecting with the relevant wheels in the straight ride attitude

- the value of the maximum steering angle of one of the inner wheels (for example, in a steering to the right, the inner wheel which rotates around B), we obtain:

- the sequence of β 1 , we give this sequence (with β 1mx complementary of the design maximum steering angle),

- α 1 by means of the expression (1 ) where the indexes α, β, p become α 1 , β 1 , P 1 ,

- the sequence of β 1 , X β1 and X«i by means of the expression (2) where the indexes β and a become β 1 and cu.

The above sequences allow us to determine the cams of the cylinder and therefore to assemble the steering gear casing relevant to the front wheels. Then, we can determine:

- the sequences of a 2 by means of the expression (5),

- the sequence of ch which we already know,

- β 2 by means of the expression (1 ),

- the sequence of α 2 where the indexes α, β, p become

- X β2 and Xcs2 by means of (2) where the indexes β and σ become β 2 and α 2 . it is then possible to trace the cams of the cylinder and to assemble the steering gear casing relevant to the rear wheels. The corresponding values of must have the same ordinate.

In other words, the pitch as chosen for the ordinates (for example 1.5, 2, 2.5 mm) must be the same for ail four curves necessary for tracing and obtaining the cams of the two cylinders. Aiso in this case the steering gear casings are fitted, phase adjusted in the straight ride attitude and reciprocaily connected through a mechanical, hydraulic (or other) system. By connecting the front steering gear casing with the steering wheel of the vehicle, the system is installed.

The above presented configuration allows the axes of the steered wheels to meet at a point of the axis passing through the centre of the rear wheels {in the event of one or more pairs of front steered wheels) or at a point of the axis inside the wheels quadrilateral and perpendicular to the straight direction of travel (in the event of two pairs of steered wheels: one front pair and one rear pair) no matter what the steering angle between 0° and the design maximum steering angle.

The steering gear casing according to the invention allows - when it is fitted to a motor vehicle - a uniform tyre wear on the steered wheels for ail the systems, a better road holding for ail the systems and therefore greater safety, a reduced turning radius and hence parking facilities (double steering gear casing system: one front casing and one rear casing), a reasonable cost of the system and therefore the possibility to use it on all types of vehicles (the cheapest ones as well as the most luxurious ones), a great road holding of motor vehicles (motor racing vehicles and others), in the event of two pairs of steered wheels: one front pair and one rear pair

Always referring to figure 17, by placing the fuel and oil containers in the centre of gravity position and knowing the pilot's weight and position, it is possible to determine with sufficient precision the centre of gravity of the motor vehicle. Alternatively, by placing a mass sliding on an axis which moves according to the fuel and oil consumption so as to keep constant (as far as possible) the centre of gravity position: G is the projection of the said point - inside the quadrilateral A-B-C-D of figure 17 - on the drawing plane (road surface); by making the axis Z pass through G (in the event of the four steered wheels: two front wheels and two rear wheels) and by assembling the steering gear casing with respect to the said axis, we obtain a system wich gives the motor vehicle a great road holding, in addition to the benfits as described before.