GB2090675A - A land vehicle having automatic steering control - Google Patents

Abstract

A land vehicle such as a tractor has steerable wheels operated by a hydraulic cylinder (25), which is controllable manually by a steering wheel (14) or automatically by a system which includes an accelerometer (110). For negotiating bends, for example at the ends of fields, a function generator (113) generates artificial acceleration signals and a comparator (115) compares the output of the accelerometer (110) and the function generator (113), and delivers an error signal. The hydraulic cylinder (25) is actuated to reduce the error signals, this having the effect of steering the vehicle around the bend. <IMAGE>

Description

SPECIFICATION A land vehicle having automatic steering control This invention relates to a steerable motor vehicle.

According to the present invention, there is provided a land vehicle having a steering mechanism and automatic steering control means for controlling the steering mechanism to cause the vehicle to travel along a desired curved path, the steering control means comprising: an accelerometer responsive to acceleration of the vehicle in a direction perpendicularto the normal travel direction of the vehicle; a function generator for generating, on a time base, artificial acceleration signals corresponding to the desired path; and a comparator for comparing the output of the accelerometer and the output of the function generator and for delivering an error signal representing the difference between these outputs, the steering mechanism being continuously adjusted in response to the error signal to cause the vehicle to follow the desired path.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure lisa side elevation of a tractor; Figure 2 is a plan view of a field over which the tractor is to run, indicating the path of the tractor; Figure 3 is a schematic drawing of a monitor of an automatic steering device for the tractor of Figure 1; Figure 4 is a block diagram of the automatic steering device including the monitor of Figure 3; Figure 5 is a diagram indicating the relationship between an actual travel path and a desired travel path; Figure 6 is a further diagram indicating the relationship between an actual travel path and a desired travel path; and Figure 7 illustrates an alternative construction for part of the monitor of Figure 3.

The tractor shown in Figure 1 has steerable front wheels 1, leading rear wheels 2 and trailing rear wheels 3. On each side of the tractor, in this embodiment, a caterpillar 3A extends around the rear wheels 2 and 3. The rotary axles of the rear wheels 2 and 3 on each side of the tractor are rotatably jour nalled in a wheel carrier 4, which is pivotable with respect to the tractor frame about a horizontal pivotal shaft 5 extending transversely of the intended direction of forward travel B. In this embodiment, the shaft 5 is approximately halfway between the wheel axles of the wheels 2 and 3. A driving engine 6 of the tractor and an associated torque converter are located in the region between the rear wheels 2 and 3 on both sides of the tractor in order to minimise the risk of wheelspin and skidding of the driven wheels 2, 3.The rear wheels 2 and 3 are driven by means of a driving mechanism arranged in the hollow wheel carrier 4. In this embodiment the front wheels 1 are not driven. The engine 6 is covered on the top by panels 7 which are inclined upwardly with respect to the direction B: at the front these panels 7 meet a rear wall 8 of a driver's cab 9 having a glass windscreen. The cab is situated in the region bounded by a vertical plane going through the front points of the leading rear wheels 2 and by a vertical plane going through the front points of the front wheels 1.

Away from its junction with the front of the panel 7, the rear wall 8 of the cab 9 and hence its glass windscreen are inclined forwardly and upwardly.

The cab 9 has a roof, which is extended at the rear beyond the joint between the rear wall 8 and the roof 10 to form a shield 11. At the front, the roof 10 terminates at a front wall 12 of the cab 9, which has a glass windscreen which is inclined towards the rear. The rear windscreen is substantially parallel to the front windscreen. Inside the driver's cab 9 there is an upwardly extending console 13 which has a steering wheel 14. A hydraulic steering member coupled with the steering wheel 14 is accommodated in the console 13. Behind the console 13 there is a driver's seat 15. The internal height of the cab 9 is such that the vertical distance between a floor 16 of the cab and the lower side of the roof 10 is great enough to allow a person of normal height (about 1.75 to 1.80 ms) to stand upright in the rear part of the cabin.The tractor is provided at the rear with a three-point lifting device 17 and at the front with a three-point lifting device 18.

Figure 2 shows a field to be covered by the tractor, the boundaries being designated by 81,82, 83 and 84. The entrance to the field is designated by 85.

Having entered the field, the tractor is stationary at a place referenced 86, which is the starting point of the working path. At this place 86, while the tractor is stationary, the desired direction of travel is determined; it is indicated in Figure 2 by the path 87 which is parallel to the field boundary 81. This direction corresponds with the direction B-D indicated in Figure 2, whereas the direction A-C is the direction perpendicular to the direction B-D. The direction A-C corresponds in Figure 2 with the directions of the field boundaries 82 and 84.

A monitor, shown in Figure 3, for the position of the tractor is preferably disposed near or at the centre of gravity of the tractor. Two relatively spaced coaxial bearings 95 are mounted on supports 94 which are rigidly secured to the tractor frame. The bearings 95 receive shafts 96, which are rigidly secured to a gimbal ring 97, which is horizontal in a central position. In the ring 97 are arranged bearings 98 receiving shafts 99, which are fastened to a gimbal ring 100. The shafts 99 are perpendicular to the shafts 96 and are horizontal in their central positions.

The common centreline of the aligned shafts 99 intersects the common centreline of the aligned shafts 96. The gimbal ring 100 lies parallel to a vertical plane which coincides with the vertical longitudinal plane of symmetry of the tractor, when the tractor is standing on level ground. Under these conditions, the shafts 96 are perpendicular to the vertical plane of symmetry of the tractor. To the ring 100 are The drawing(s) originally filed were informal and the print here reproduced is taken from a later filed formal copy.

fastened aligned vertical shafts 101, the common centreline of which intersects those of the shafts 96 and 99 at one point. At the end from the fastening point on the ring 100 each shaft 101 has a bearing 102. The bearings 102 are spaced apart from one another. The outer rings of the bearings 102 hold curved supports 103, which project from the associated bearings 102 on different sides ofthe longitudinal plane of symmetry of the tractor and are connected by their ends away from the bearings 102 to the outer races of bearings 104. The centrelines of the bearings 104 are accurately in line and are inclined to the common centreline of the shafts 101.

In the two bearings 104 isjournalled a shaft 105 of a gyroscope rotor 106. The rotor 106 is located between the bearings 104 and the centre of gravity of the assembly of the shaft 105 and the rotor 106 is accurately located on the common centreline of the shafts 101 at the point of intersection of the centrelines of the shafts 96, 99 and 101.-JVhere one of the shafts 101 is connected to the ring 100 there is a platform 107, and at the opposite side ofthe ring 100 there is a weight 108. The mass of the weight 108 is such that the centre of gravity of the assembly comprising the ring 100, the platform 107 and of the apertures, described later, arranged thereon, and of the weight 108, is located at the point of intersection of the centrelines of the shafts 96, 99 and 101.The rotor shaft 105 and the rotor 106 are, therefore, freely pivotable with respect to the shafts 101.

The platform 107 is provided with a longitudinal accelerometer 109 measuring accelerations in a horizontal direction and in a vertical reference plane coinciding with the vertical longitudinal plane of symmetry of the tractor, when it is standing on level ground, and also with a transverse accelerometer 110 measuring accelerations in a horizontal direction perpendicular to said reference plane. The accelerometers 109 and 110 are of known type, for example in the form of piezo-electrical crystals.

As shown in the block diagram of Figure 4, the output signals of the accelerometer 109 and 110 are applied to an integrator 111. The output signals of this integrator are a measure for the speed of the centre of gravity of the tractor in its direction of travel (direction B or D, see Figure 2) and for the speed of the centre of gravity of the tractor transverse of the direction of movement (direction A or C, see Figure 2). These speed signals are applied to a second integrator 112. The Output signals of the integrator 112 are a measure for the path covered by the centre of gravity of the tractor in the direction of movement B or D and the path covered by the centre of gravity of the tractor in a direction at right angles to the reference plane, viewed from the starting point 86 (Figure 2), when the measurement at point 86 is chosen to represent the zero point.The output signals of the integrator 112 originating from the accelerometer 109 are applied to a signal generator 113, which comprises a counter assessing the total path covered. The signals originating from the accelerometer 110 at the output of the integrator 112 are again applied to an integrator 114, which trans mits the integral of the path covered appearing at its output to an arithmetic unit 115. The arithmetic unit 115 applies the signals received by it, if necessary through a power amplifier for example, to relays actuating the slide of a hydraulic control valve 116.

The control valve 116 is connected through the steering member 31 with a hydraulic cylinder 25, which steers the front wheels 1. The driver can override the signals applied by the control valve 116 by operating the steering wheel 14.

During travel in the direction B, as is shown in Figure 5, deviations from the desired, rectilinear path 87 will occur. Figure 5 shows the actual path 117 allowed by the tractor. The output signals of the arithmetic unit 115 are fully suppressed within a margin 118 (Figure 5) on either side of the desired path 87 in the direction A or C. While the deviation remains within this margin, the slide of the valve 116 does not respond. The magnitude of the margin 118 on both sides of the desired track 87 is an adjustable factor in the arithmetic unit 115. The magnitude of this margin 118 corresponds to the response sensitivity of the automatic steering system and it is provided in order to avoid excessively rapid responses of the front wheels 1 to deviations and hence to avoid highly unsettling steering and oversteering.As stated above, the arithmetic unit 115 receives signals from the integrator 114, which correspond to the integral of the path covered in the direction A or C respectively at right angles to the desired path of movement 87. This integrated path is designated in Figure 5 by reference numeral 119. As long as the integrated signal 119 stays within the margin 118 set in this direction, no signal will appear at the output of the arithmetic unit 115 and the steering cylinder 25 will not be operated. Therefore, the steering system does not respond to slight deviations transverse ofthe direction 87, which regularly occur randomly to both sides of the direction 87 and which have a comparatively small magnitude and which approximately compensate one another with respect to the direction 87.If, however, a deviation to one side of the line 87, even a small one, has a long duration, a deviation of the direction with respect to the desired path 87 is imminent. A long term deviation of the actually covered path 117 from the line 87 is traced in Figure 6 as well as the integrated track length 119 introduced into the arithmetic unit 115. In this case the integrated track length in the direction A will move beyond the margin 118 at the point 120, although the actual track covered remains within the margin. From point 120 the arithmetic unit 115 applies an output signal to the control valve 116, which corrects the wheels 1 by means of the steering cylinder 25 to an extent such that the actual track covered is corrected into a path 121 indicated by broken lines. By using the integral of the track covered as a control signal an effective response of the steerable wheels to deviations from the desired track 87 is obtained.

The desired path 87 can be set initially at the entr ance 85 with the aid of a unique direction indication by a beacon 122, which is disposed at or slightly outside the field boundary 82 in line with the desired track 87. A beacon may be temporarily erected at point 86 so that at the entrance 85 the driver is in a position, for example, with the aid of a direction fin der, to position the vertical longitudinal plane of symmetry of the tractor in coincidence with the vertical plane containing the line of connection between the beacons 86 and 122. Previousiy the gyroscope has been caused to rotate in known manner about its shaft 105 with a speed of at least 10,000 rev/min.The shape of the brackets 103 is such that the angle between the centreline of the rotor shaft 105 and the common centreline of the shafts 101 is accurately equal to 900 minus the angle corresponding to the geographical latitude of the region where the tractor is used. The centreline of the rotor shaft 105 will, therefore constantly line up parallel to the rotary axis of the globe. The brackets 103 may be adjustable so that the angle between the rotor shaft 105 and the centreline of the shafts 101 can be varied so that the direction of the rotor shaft 105 can be set parallel to the direction of the rotary axis of the earth whatever the geographical latitude where the tractor is to be used.By the adjustment of this direction of the rotor shaft 105 corrections which might otherwise be necessary as a result of rotation of the earth during the time of the job and as a result of the distance thus covered on the global surface become redundant so that stabilisation of the platform 107 is achieved in a most simple manner. Since the direction of the rotor shaft 105 is maintained, the top of the platform 107 will remain accurately horizontal and deviations of the indications of the accelerometers 109 and 110 will be eliminated. Sincethesup- ports 94 are secured to the tractor frame, turning of the tractor about the rotor shaft will result in a turn of the ring 97 and the ring 100 about the rotor shaft, whilst the gyroscope rotor 106 and the shaft 105 will deflect with respect to the rest of the tractor.This deflection is allowed because the supports 103 are freely rotatable by means of the bearings 102 with respect to the shafts 101. The centreline of the shafts 99 remains in the vertical longitudinal plane of symmetry of the tractor and the plane of the ring 100 remains in a vertical position. The movements of the tractor about the centreline of the shafts 96 and also those about the centreline of the shafts 99 do not affect the vertical position oftheshafts 101 and the horizontal position of the top surface of the platform 107. After initial adjustment of the tractor with respect to the beacon 122 (or the beacons 86 and 122) the tractor is set in motion and the path 87 is followed within the two margins 118 in the manner described above.

The distance between the points 86 and 89 (Figure 2) is previously measured accurately and this value is registered as the final value in the abovementioned counter arranged in the signal generator 113. When the tractor arrives at point 89, the length of the path covered in the direction B counted by the counter corresponds with this predetermined value of the measured length between points 86 and 89.

The counter is arranged so that it stops and is reset, whilst the application of the signal emanating from the integrator 114 to the arithmetic unit 115 is stopped by the signal generator 113 (line 113 A). Atthe same instant a previously programmed signal is produced in the signal generator 113, this signal being as a function oftime, equal to a signal at the output of the integrator 112, which would have been produced by the accelerometer 110, if the tractor had made a turn the same as that between the point 89 and the terminal point 123, but in the opposite direction.This signal is introduced via the line 124 (Figure 4) into the arithmetic unit 115, which assesses in this case, after the counterofthe signal generator 113 stops, deviations from the desired bend programmed in the signal generator and applies correction signals to the control valve 16. Contrary to the behaviour of the arithmetic unit 115 during the straight forward travel, in which an integrated path is kept within a margin, the real desired path without a margin is chosen as a measure with a view to high accuracy for travelling through bends. Therefore, the output of the arithmetic unit 115 applies a correction signal to the control-valve 116 even for small deviations so that the tractor faithfully follows the curve indicated in Figure 2 between the points 89 and 123 by means of the steering cylinder 25.It should be noted that the travel of the centre of gravity of the tractor along this curve is completely independent of any skidding of the tractor wheels with respect to the ground. Therefore, with correct programming of the signal generator 113, the direction of the tractor at point 123 is precisely parallel to the direction of the track 87.

At the end of the artificial signal produced as a function of time in the signal generator 113 during travel through the bend 89 to 123, the signal of the accelerometer 109 is again allowed via the integrators 111 and 112 into the signal generator 113, after which the path 91 (Figure 3) is covered in the same way as the path 89 described above.Since the distance between the points 123 and 92 (Figure 2) is equal to the distance between the points 86 and 89, the counter in the signal generator 113, which starts counting again at point 123, has counted again the predetermined distance between points 86 and 89, when the tractor has arrived at point 92, at which instant the input signal of the signal generator 113 originating from the accelerometer 109 is again blocked and the artificial signal for travelling through the bend is again produced in the signal generator 113, but in the opposite sense, that is to say, with the inverse sign. After each field length has been covered, the signal is applied alternately with different polarities via the line 124 to the arithmetic unit 115.

Figure 7 illustrates a further refinement of this automatic steering system. The bearings 102 are omitted and the supports 103 are rigidly secured to the shafts 101. The shaft 101 is pivotable by means of bearings 125 with respect to the ring 100 and the platform 107, the bearings 125 being arranged in the ring 100. The shaft 101 projects through one of the bearings 125 above the platform 107 and carries at the top a platform 126, which is perpendicular to the shaft 101 and hence parallel to the platform 107. The platform 126 is pivotable about the centreline of the shaft 101 and is fixable in a plurality of positions relative to the shaft 101. This adjustability (not shown) is accessible from the outside. The platform 126 is provided with an accelerometer 127, which measures accelerations in a horizontal direction orthogonal to the path 87.Owing to this adjustability of the platform 126 the measuring direction of the accelerometer 127 can be set in a fixed position reia tire to the direction of the global axis (the direction of the plane containing the centrelines of the shafts 101 and 105) for measuring in a direction perpen dicularto that of the desired path 87,91,93. This additional accelerometer 127 is indicated in Figure 4 by broken lines and is also connected to the integrators 111 and 112, which forthis purpose each have an additional channel. The output signal of the integrator 112 from the channel corresponding to the accelerometer 127 is applied via the line 128 indicated by broken lines to the arithmetic unit 115.

Since the tractor is set at point 86 accurately in the direction ofthe desired path 87 and the correct angle between the measuring direction of the accelerometer 127 and the plane going through the shafts 101 and 105 is adjusted so that this measuring direction is perpendicular to the path 87, this measuring direction is maintained even during turning, since the accelerometer 127 is coupled with the gyroscope and the tractor turns about the centreline of the shafts 101 with respect to the accelerometer 127.

During the travel along the track between the points 86 and 89 (Figure 2) the accelerometer 127 will measure the same value as the accelerometer 110, but, whereas the signal of the accelerometer 110 is replaced during the run through bends by an artificial signal, the accelerometer 127 continues measuring the accelerations in the direction A-C even during bends. When the tractor has arrived at point 123, the output of the integrator 112 corresponding to the accelerometer 127 will have a value corresponding to the actual distance indicated in Figure 2 by refer ence numeral 129. The desired distance between the paths 87 and 91 (for example, 0.75 m in this case of ploughing) may be previously set in the signal generator and be inserted through a line 130 (Figure 4) into the arithmetic unit 115 afterthetermination of the bend at point 123.The measured value emanating from the accelerometer 127 can then be compared in the arithmetic unit 115 with the desired value set in the signal generator 113, the latter value setting a datum (path 87 in Figures 5 and 6) towards which the tractor automatically steers. For the desired path 93 the desired value of the distance 129 is multiplied by a factor 2 after the second bend starting at point 92 is made.

The automatic steering programme terminates after a previously determined number of bends, this number being counted by a separate counter in the signal generator 113.

It should be noted that the signal produced at points 89 and 123 and terminated respectively in the signal generator 113 can be coupled with a pulse generator for lifting or lowering the implement respectively by actuating the lifting device 17 and/or 18. In this way a very accurate automatic steering system and a method of carrying out agricultural jobs with the aid of a tractor are obtained, in which the driver need not exert any controfand may be absent. If the driver is present, he can stand upright in the rear part of the tractor in order to observe the behaviour ofthe hitched implement or implement.

The described arrangement makes the tractor able to follow accurately parallel straight paths. This is conducive to the quality of the job to be accomplished. For example, in the case of a seed drill it is ensured that the rows of plants are accurately straight and parallel to one another, which is very important for subsequent treatments of these rows of plants by machines having to pass between the rows. In harvesting, losses are minimized. The tractor driver, who can oversee the general behaviour of the tractor, is able to give more attention to the behaviour of the implement hitched to the tractor.

Claims (1)

1. A land vehicle having a steering mechanism and automatic steering control means for controlling the steering mechanism to cause the vehicle to travel along a desired curved path, the steering control means comprising: an accelerometer responsive to acceleration of the vehicle in a direction perpen diculartothe normal travel direction of the vehicle; a function generator for generating, on a time base, artificial acceleration signals corresponding to the desired path; and a comparatorforcomparing the output of the accelerometer and the output of the function generator and for delivering an error signal representing the difference between these outputs, the steering mechanism being continuously adjusted in response to the error signal to cause the vehicle to follow the desired path.

2. A vehicle as claimed in claim 1, in which the steering devide in controllable by a manually operated steering wheel which, when operated, overrides the automatic steering of the vehicle.

3. A vehicle as claimed in claim 1 or 2, in which the measuring direction of the accelerometer is kept horizontal by a gyroscope, the rotor of which is freely rotatable with respect to the inner gimbal ring of a gimbal suspension.

4. A vehicle as claimed in claim 3, in which the accelerometer is fixed to the inner gimbal ring.

5. A vehicle as claimed in claim 3 or4, in which the inner gimbal ring is freely pivotable with respect to the outer gimbal ring about an axis which is located in the vertical, longitudinal plane of symmetry of the vehicle and extends substantially horizontally.

6. A vehicle as claimed in any one of claims 3 to 5, in which the inner gimbal ring lies parallel to a vertical plane.

7. A vehicle as claimed in claim 5 or 6, in which the outer gimbal ring is freely pivotable with respect to the rest of the vehicle about an axis which extends perpendicular to the vertical longitudinal plane of symmetry of the vehicle.

8. A vehicle as claimed in any one of the preceding claims, in which the accelerometer is a transverse accelerometer, the measuring direction of which is horizontal and perpendicularto the vertical longitudinal plane of symmetry of the vehicle, a longitudinal accelerometer also being provided, the measuring direction of which is horizontal and parallel to that plane of symmetry.

9. A vehicle as claimed in any one of the preceding claims, in which means are provided for causing the vehicle to follow two straight paths which are parallel to and spaced from each other, the steering control means, in operation, causing the vehicle to transfer from one straight path to the other.

10. Avehicle as claimed in claim 9, in which a further accelerometer is provided, the measuring direction of which is maintained in a constant orientation with respect to a given geographical direction.

11. A vehicle as claimed in claim 10, in which, by means of the further accelerometer, displacement of the vehicle in a direction perpendicular to the straight paths travelled by the vehicle is measured.

12. A vehicle as claimed in claim 9 or 10, in which the signal from the further accelerometer is integrated twice to provide a distance signal to which the steering mechanism is responsive for correcting the distance between the two straight paths.

13. A vehicle as claimed in any one of claims 9 to 12, in which the measuring direction of the further accelerometer during operation is fixed with respect to the direction of the axis of a gyroscope.

14. A vehicle as claimed in claim 13, in which the measuring directions of the further accelerometer is adjustable and fixable in any one of a plurality of positions with respect to the direction of the gyroscope axis.

15. A vehicle as claimed in any one of the preceding claims, in which the vehicle comprises at least one lifting device which can be actuated automatically when the steering control means causes the vehicle to negotiate a bend.

16. A vehicle as claimed in any one of the preceding claims, which is a tractor.

New or amended claims:

1. A land vehicle having a steering mechanism and automatic steering control means for controlling the steering mechanism to cause the vehicle to travel along a desired curved path, the steering control means comprising: an accelerometer responsive to acceleration of the vehicle in a direction perpen dicularto the travel direction of the vehicle; a function generator for generating, on a time base, artificial signals equal to signals which would derive from the accelerometer during travel of the vehicle along a path which is in conformity with the desired curved path; and a comparator for comparing signals deriving from the accelerometer with the artificial signals generated by the function generator and for delivering an error signal representing the difference between these signals, the steering mechanism being continuously adjusted in response to the error signal to cause the vehicle to follow the desired path.