WO2000075618A1

WO2000075618A1 - Method and device for determining during driving the friction between the road and the wheel of a vehicle

Info

Publication number: WO2000075618A1
Application number: PCT/SE2000/001155
Authority: WO
Inventors: Jan Folke Wallenius
Original assignee: Jan Folke Wallenius
Priority date: 1999-06-03
Filing date: 2000-06-02
Publication date: 2000-12-14
Also published as: SE9902036L; SE9902036D0; SE513217C2

Abstract

The invention relates to a method and a device for deciding, during driving of a vehicle, the friction between the road and at least one of the wheels of the vehicle, which wheel is set to a prescribed toe-in/toe-out angle, wherein the mechanical forces to the wheel suspension and wheel setting means caused by the setting angle are sensed by sensors (51). According to the invention, an amplifying of the intended measuring value is obtained by the prescribed toe-in/toe-out value being imparted, instantaneously, an essentially increased value by a mechanism (20) at the same time as measuring is carried out.

Description

Method and device for determining during driving the friction between the road and the wheel of a vehicle.

The present invention relates to a method according to the preamble of the following patent claim 1 and a device for carrying out the method according to the preamble of patent claim 2.

It is very important that the driver, when driving a vehicle on a road which suddenly presents portions that are ice-covered or by other reasons are very slippery, for instance because of pools of water or slippery surfaces, immediately becomes aware of the fact that such conditions are existing.

Since almost 20 years attempts have been carried out to measure the friction between the road and the wheels of a vehicle during driving. Experiments have been carried out with sensors placed at various places in the wheel suspensions and in the different parts of the steering mechanism, as the steering arms, steering drag rods, and steering tie rods. The mechanical forces in these parts have been measured by electrical means or sensors, for instance strain-meters, during moments when the vehicle is turned in one or the other direction, and the measure values received have been processed in computers and have been compensated for disturbing influences by for instance the inclination of the road, changes of speed, and so on. This can be exemplified by the patent publications SE 9500958, WO 88/02483, DE 2947259 and US 5 435 193. The last-mentioned publication has in view only to achieve optimal driving characteristics. As to the design of these known computer devises reference is made to said publications. In some cases the fixed toe-in or toe-out adjustments of the vehicle have been utilized for measuring the arising axial force on the wheels during driving straight forward, which is a desirable method because an indication of slipperiness is most valuable when driving straight forward. An indication of slipperiness first at reaching the entrance of a curve is normally too late for a safe reduction of speed.

None of these experiments, however, seems to have resulted in a useful equipment. The reason might be the disturbances which influence the measuring to such a degree that the desired measuring values are blocked by the disturbances. It is obvious, that a strain-meter mounted on for instance a steering tie rod hardly can distinguish clearly the weak pressure from the ambition of the wheel to straighten out under the influence of the friction when the pressure force has to pass the steering knuckle bearings and a joint between steering arm and steering drag rod and a joint between steering drag rod and an end of the steering tie rod, where the differences between motive friction and static friction probably completely overshadow the demanded compressive force.

The object of the invention is to attain a method and a device that involves a simple and safe solution of the problem to measure the friction between wheels and road of a vehicle that has a certain toe-in/toeout adjustment.

This is achieved, according to the invention, by a method and a device having the characterizing subject matters set forth in claims 1 and 2.

An increase of the decided toe-in/toe-out value is carried out by the invention to a value, that would be unacceptable at normal driving, but here a return to the initial value is carried out as soon as the friction value has been indicated, which means a course of about one second. The course can be started by the driver as a non-recurring sequence, for instance by pressing a button. Preferably, an interval triggering for an adjustable time is carried out when a slippery road is expected, in the same way as the interval cleaning by the windshield cleaner. No noticeable wear of the tires is observed by this.

The sensors may be placed at the same spots as is the case with the previously known devices, but must be well protected for damage and damp. As hinted earlier a sensor should be placed as close to a steering arm as possible in order to avoid that varying friction conditions may disturb the measuring. Hence, according to an embodiment of the invention, a sensor is placed in an axial bore in the ball of a ball coupling between a steering arm and a steering drag rod for sensing the forces directly in the mounting part of the ball, as set forth in claim 4.

It has proved possible in a preferred embodiment of the invention to attain in one and the same unit of each wheel both the desired toe-in/toeout variation and the requested measuring by a design of the device as set forth in any of claims 6,7 or 8.

The invention is more clearly explained in the following with reference to the attached drawings, which schematically show, by way of example, a number of embodiments of the invention, and in which Figure 1 is a plan view of the steering mechanism and parts of the wheel suspension of a motor vehicle, Figure 2 is a perspective view of a steering worm gear with a device for short-term increases of the toe-in/toe-out adjustment, Figure 3 is a side view, partly in section, of a sensor arranged in a bore in the ball of a ball coupling, and Figure 4a and 4b is a perspective view of a ball coupling with a portion removed for more clearly showing the inner parts of a preferred embodiment of the invention. Figure 5 is a view showing the invention applied to a steering type including a steering rack, Figure 6 is a view showing alternative locations of sensors applied to a front wheel suspension for front wheel drive, and Figure 7 discloses a toe-in variation arrangement in a rear wheel suspension at front wheel drive.

Figure 1 discloses the parts of the front portion of a motor vehicle essential for the explanation of the invention. Left hand and right hand fore wheels 1 and 2, respectively, are rotatably journalled in the usual way on trunnions, not shown, which in turn are pivoted on each a steering knuckle or upright 3,4, respectively, or a corresponding arrangement with link arms. The trunnions are firmly connected to each a steering arm 5,6 for pivoting the trunnions, which arms are provided with each a link ball 7,8 to which one end 9,10 of a link hand and right hand steering drag rod 11,12 is hinged, the other ends 13,14 of which are hinged to a steering gear arm 15 and blind gear arm 16, respectively, which two arms 15,16 are hinged to a tie rod 17. The steering mechanism is so far designed in a conventional manner, and the steering gear arm 15 is pivoting in a steering worm gear 20, which in Fig.l is indicated by a square of dot and dash lines, and which is shown in more detail in Fig.2.

The steering worm gear 20 shown in Fig.2 has an input shaft 21 that is firmly secured to the bottom end 22 of a steering column. The steering gear 20 is designed such that when the steering column is rotated the worm gear, not shown, brings about a swinging motion of the steering gear arm 15. Hence, by the embodiment according to Fig.l a turning of the wheels 1,2 is obtained. The wheels have a toe-in or toe-out adjustment amounting to a few tenths of a degree when driving straight forward, which adjustment is prescribed by the manufacturer. At turn to the left or right the adjustment is changed a little due to the geometry of the fore vehicle for obtaining the best road manners at taking of corners.

The prescribed angular value should, however, according to the invention, be essentially increased for a short time period during the measuring, for instance to a value five times the prescribed. This is achieved by exchanging the steering gear arm shown in Fig.l for the modified arm shown in Fig.2.

The free end of the steering gear arm 15 is, as shown in Fig.2 , provided with an expanding mechanism comprising an adjusting arm 25 journalled movable to and fro along the arm 15, which adjusting arm at the outer end is provided with a centre pin 26 that is directed downward on the drawing and protrudes between two semicircle-shaped recesses in a right hand and a left hand swinging lever 27 and 28, respectively. These levers 27,28 are journalled hinged by bearings 29,30 at the ends of a semicircular yoke 31, which is firmly attached to the end of the steering gear arm 15. The inner end of the adjusting arm is attached to an excentric mechanism 32, which is driven by an electric motor 33 via a gear 34.

The excentric mechanism is designed such, that it when turned one turn moves the adjusting arm 25 from the initial position shown to an outermost postion and back to the initial position. The centre pin 26 is moved outwards and turns the levers 27,28 out from each other and back again. At their outermost ends is one end of the tie rod 17 hinged to the lever 27 by a trunnion 35, and one end of the left hand steering drag rod hinged to the lever 28 by a trunnion 36. The tie rod 17 and the left hand steering drag rod 11 are moved apart a distance corresponding to the desired increase of the angle adjustment for toe-in when the levers 27,28 are expanded. The levers 27,28 are turn towards each other at the return of the adjusting arm 25 to the initial position and the tie rod 17 and the left hand steering^' drag rod are moved toward each other to the initial positions corresponding to the prescribed toe-in adjustment.

For initiating this movement of the tie rod 17 and of the steering drag rod 11 there is a trigger device 40 connected to the motor 33 by a conduit 41. The trigger device 40 is placed close to the driver and has a button 42. When the button is pressed the motor 33 is started. The motor is arranged to turn the excentric mechanism 32 one turn in about one second and then stop with the arm 25 in withdrawn position for about 10 seconds and so on in the same way with 10 seconds intervals until a repeated pressing of the button 42 brings the motor 33 to stop with the arm 25 in withdrawn position.

The interval 10 seconds may be too long or too short in dependence of the state of the road, and therefore the trigger device 40 may have a knob 43 for setting a suitable interval. Such a trigger device may be of a kind similar to the device used for the intermittent drive of wind screen cleaners.

At each such change of the angular adjustment of the wheels the stresses have to be measured by a sensor, for instance a strain meter, at some point between each steering arm 5,6 and the steering gear arm 15. According to a preferred embodiment of the invention, which results in an as far as possible undisturbed measuring value, there is a sensor placed in an axial bore in each link ball 7 and 8 on the respective steering arm 5 and 6 on the respective steering arm 5 and 6, as shown in Fig.3.

Fig.3 discloses left hand steering arm 5, to which a link ball 7 is secured. One end of the left hand steering drag rod 11 is hinged to the link ball 7 in the usual way. The link ball has an axial bore 50 in which a sensor 51 comprising a strain meter is mounted for indicating arising bending strain at the point of attachment of the link ball to the steering arm 5. From the sensor 51 a signal conduit 52 leads to a computer device 53. A corresponding sensor is placed in the link ball 8 on the right hand steering arm 6 and is connected the computer device 53 by a second conduit 52. An indicating device 54 close to the driver is connected to the device 53 via a conduit 55.

The sensors 51 measure at each short increase of the toe-in adjustment of the wheels 1,2 the strain arising when an axial pressure is formed against the wheels from the road. As the sensors 51 measure the strain directly at the steering arms 5,6 varying friction values of the joints cannot disturb the measuring values of the sensors 51. There are, however, a number of other disturbing sources which can be indicated by sensors and need treatment in the computer device. These measures are clearly described in the publications mentioned in the introduction, to which it is referred in order not to weigh the specification down with matters that are of common knowledge in this connection. Speed, acceleration, retardation and turning of the steering wheel for example are factors that usually are measured and compensated for, all in order to achieve measuring values that are as exact as possible concerning indicated friction values at driving straight forward and at cornering.

Vehicles equipped with steering rack and pinion do not have the steering gear shown in Fig.l and Fig.2, and, accordingly, the shown device for variation of the toe-in/toe-out adjustment is not applicable in such a case. In that case the connection between the steering arms and each end of the steering rack must have a device for the toe-in/toe-out variation as well as a device with sensors, in which case the arrangement of one of the steering arms shown in Fig.4a is a preferred solution of this problem.

As shown above, a link ball 7 is attached to the steering arm 5. A link socket 60 partly surrounding the ball is by a central connecting part 61 connected to a hub 62 enclosing the upper part of the link socket 60, which hub 62 has a cylindrical exterior wall. The hub 62 is located in a housing 63, which is firmly attached to the steering drag rod 11. A ring-shaped space is formed between a cylindrical interior wall of the housing 63 and the exterior wall of the hub 62, in which space an excentric sleeve 64 is rotatably journalled displacing the hub 62 in a revolving motion due to the fact that the hub 62 is prevented from turning in relation to the housing 63 by a tongue 65 protruding from the hub 62 and positioned between two knobs 66 on the housing 63. The exterior wall of the excentric sleeve is provided with a ring-shaped ridge 67 with teeth cooperating with a tangential screw worm 68, which is driven by an electric motor 69 attached to the housing 63. To the connecting part 61 are sensors, preferably strain meters 51, attached for sensing the forces in the connecting part 61 when the electric motor turns the excentric sleeve 64 one turn from prescribed toe-in/toe-out adjustment to maximum change and back to the initial value. The signals from the sensors are transmitted by conduits 52 to the computer device 53 and further on by the conduit 55 to the indicating device 54.

To attain full control of all calculations of the values measured by the sensors is it necessary to receive a signal representing the steering angle of the front wheels. Such a signal can be obtained in various ways, for instance by measuring the turning movements of the steering column. A very preferable measuring device is shown in Fig.4b, which shows the same link ball as in Fig.4a with the sensors 51 and accompanying parts omitted in order not to conceal the arrangement of a permanent magnet 94 with a south pole S and a north pole N fitted in a transversal bore 93 in the link ball 7. To the link socket 60 partly surrounding the ball is a ring-shaped Hall- element 95 attached and provided with connection conduits (not shown) to the computer device 53, Fig.l. The magnet field lines 96 of the permanent magnet 94 pass through a Hall element, that in a known manner very exactly indicates the turning movements of the magnet field lines 96 when the link ball 7 and accordingly the permanent magnet 94 turns in relation to the link socket 60.

Modern cars are often provided with pinion and rack steering. Fig.5 discloses such a steering adapted to the invention. A pinion 70 adapted to be turned by a steering column cooperates with teeth on a to and fro journalled rack 71. On the rack are two steering rods 72,73 journalled with two ends facing each other and being right hand and left hand threaded, respectively, and connected with each other by a correspondingly threaded sleeve 74, which is rotatably but not movably mounted on the rack 71. The other ends of the steering rods 72,73 are hinged to the steering drag rods 11,12 described above. The sleeve 74 is rotatably mounted for a momentary increase of the toe-in angle adjustment an turning angle corresponding to the change of angular adjustment and back again by an actuating mechanism, which may be a hydraulic piston or an electric motor. Also sensors may be arranged here on the rods 72,73.

The description has up to now been adapted mainly to rear wheel driven vehicles. In front wheel driven vehicles it is necessary also to take into consideration the forces on the front wheel suspension and the steering means caused by the drive shafts, which forces must be subtracted from the measure values described above. A front wheel suspension of the MacPherson type and front wheel drive is shown in Fig.6. A front wheel 1 is journalled on a hub 80 which is attached to a steering nuckle 81 which is hinged partly in a bottom ball and socket joint 82, partly in a spring leg 83. A steering knuckle arm 84 is attached to the hub 80, in which a drive shaft 85 is rotatably journalled. The forces caused by the torque of the drive shaft are here indicated by a strain meter located in the bottom ball and socket joint 82 in the same manner as described above in connection to Fig.3. As an alternative the sensors may be located on the arms 86,87 of the wheel suspension link 88 that keeps the wheel 1 in place and takes up the brake and drive forces or in their hinges 89,90.

In order to avoid in case of front wheel drive the complication of measurements and calculations, as described above, it may be suitable, as an alternative, to arrange a possibility of toe-in variation of the non-driven rear wheels and place the sensors on suitable places in the rear wheel suspension, for instance as shown in Fig.7. Here the rear wheels are suspended in the usual way on obliquely backwards directed swinging arms 100,101 which are journalled on shafts 102,103. The inner ends of the shafts are journalled pivotal a few degrees in the horizontal plane by joints 104,105. The outer ends of the shafts 102,103 are fixed in excentric sleeves 106,107, which by electric motors, not shown, can be rotated in synchronism such that the shafts 102,103 when necessary can be pivoted a short distance in the directions indicated by arrows and back again. The forces on the arms 100,101, caused by the changed toe-in adjustment, are indicated by sensors 108,109 positioned on the arms, as described above.

The invention is of course not limited to the here shown and described embodiments but may be modified in various ways within the limits of the invention defined by the claims. Hence, the steering gear can of course have a ball- nut mechanism. Also the mentioned mechanism for a short change of the wheel adjustment, also called the splay of wheel, can be varied in many ways. The shown excentric mechanisms can be replaced by a screw mechanism to be screwed to and fro. Also a simple hydraulic device may be possible.

The measurement with the sensors can be carried out with respect to only one wheel, but, of course, best safety is obtained if the measurement is carried out with respect to one pair of wheels. Also the short change of adjustment of the wheel set can be carried out on only one wheel but should preferably be carried out on both wheels of a pair of wheels.

In two of the shown embodiments are the sensors 51 positioned in the ball-and-socket joints at the steering arms. Another position of the sensors 51, which involves a concentration of all the equipment to one place, is on the swinging levers 27,28, where the sensors easily can be attached and accompanying conduits together with sensors and the mechanism for angular adjustment are concentrated to one equipment unit.

Claims

C A I M S

1. Method for deciding, during driving of a vehicle, the friction between a road and at least one of the wheels (1,2) of the vehicle, which wheel is adjusted to a prescribed toe-in/toe-out angle with respect to the longitudinal direction of the vehicle, wherein the mechanical forces to the wheel suspension and the wheel adjustment means caused by said adjustment angle are measured by sensors (51,-108,109) and fed to a computer device (53) which is connected to an indicating device (54) adjacent to the driver for indicating friction values, and especially occurring low friction values, characterized in that the set toe-in/toe-out value during a short time period is imparted an essentially increased value and a return back to the initial value at the same time as said measurement is carried out.

2. Device for carrying out the method according to claim 1, for deciding during the driving of the vehicle the friction between a road and at least one of the wheels (1,2) of the vehicle, which wheel is set with a prescribed toe-in/toe-out value with respect to the longitudinal direction of the vehicle, comprising one or more sensors (51;108,109) for sensing the mechanical forces to the wheel suspension of the vehicle and wheel adjustment, caused by said adjustment angle, which sensors (51;108,109) give rise to signals, which are fed to a computer device (53) arranged to indicate on an indicating device (54) placed adjacent to the driver measured friction values, especially low friction values, characterized by a device (26-28;64; 72-74) for increasing during a short time period the set toe-in/toe-out value and restoring same to the initial value at the same time as said sensing takes place.

3. Device according to claim 2, characterized in that the device (26-28;64; 72-74) for increasing the set toe-in/toe-out value and restoring same is controlled in dependence of the sensed friction value to stop said increase at a value corresponding to beginning skidding.

4. Device according to claim 2, characterized by an excentric mechanism (32;64) included in the steering mechanism, which excentric mechanism is driven by a drive means (33;69) that is designed, at activation, to turn the excentric mechanism (32;64) one turn and thereby during a short time period increase said adjustment angle to a maximum value and restore said adjustment.

5. Device according to claim 2, 3 or 4, characterized by an axial bore (50) in a link ball (7,8) located between a steering arm (5,6) and a steering drag rod (11,12), in which bore (50) a sensor (51) is positioned for sensing the forces at the point of attachment of the link ball (7,8).

6. Device according to any of claims 2-4, comprising a steering gear with a link ball for each of the steered wheels, characterized in that a link socket (60) partly surrounding a ball (7,8) is situated in a surrounding hub (62) in which the link socket is connected to the hub by a central connecting part (61) to which the sensors (51) are attached, and which hub (62) is enclosed in a housing (63) actuated by the steering gear, in which housing the hub (62) is movable to and fro by an excentric mechanism (64) driven by an electric motor (69) and affecting the toe-in/toeout value.

7. Device according to claim 6, characterized in that the hub (62) has a cylindrical exterior wall and is connected non-turnable to said housing (63) , said housing has a cylindrical interior wall , and that an excentric sleeve (64) is rotatably journalled in a ring shaped space between said walls rotatable by a gear (68) driven by an electric motor (69).

8. Device according to claim 6 or 7, characterized in that the link ball (7,8) is attached to a steering arm (5,6) and the housing (63) of the link socket cooperating with the link ball is attached to a steering drag rod (11,12) .

9. Device according to any of claims 2-8, characterized by a trigger device (40) which at fixed intervals activates the device ( 26-28; 64; 72- 74) for increasing and then resetting said angular adjustment.