DRAFT FORCE DETECTION ON A VEHICLE HAVING A LINKAGE

Abstract

A vehicle control system for controlling the height of a linkage on a vehicle having a continuously variable transmission (CVT) in which the linkage is automatically raised and lowered depending on a draft force detected by the vehicle including an input draft force detected by sensors in the CVT or driveline is inputted into the control system and the system further processes said input draft force to provide an output draft force upon which movement of the linkage is based and the control system processes the input draft force by compensating the input draft force detected during acceleration or deceleration and/or compensating the input draft detected whilst travelling along a slope, and/or equalising the input draft force by applying a ramp function, and/or reducing the input draft force when the linkage is at a predetermined height.

Claims

1. A vehicle control system for a vehicle having a continuously variable transmission (CVT), for controlling the height of a linkage on the vehicle and/or on an implement coupled with the vehicle, in which the linkage is automatically raised and lowered depending on a draft force detected by the vehicle, wherein an input draft force detected by sensors in the CVT or a driveline is inputted into the control system and said system further processes said input draft force to provide an output draft force upon which movement of the linkage is based, wherein said control system processes the input draft force by at least one of the following: compensating the input draft force detected during acceleration or deceleration, compensating the input draft detected while travelling along a slope, equalizing the input draft force by applying a ramp function, and reducing the input draft force when the linkage is at a predetermined height.

2. The vehicle control system as claimed in claim 1, wherein the input draft force detected during acceleration or deceleration is compensated by taking the draft force applied to the mass of the vehicle into account for a given acceleration/deceleration value.

3. The vehicle control system as claimed in claim 2, wherein the mass of the vehicle is stored electronically and accessed by the control system.

4. The vehicle control system as claimed in claim 2, wherein the mass of the vehicle can be varied by the operator.

5. The vehicle control system as claimed in claim 1, wherein to compensate the input draft force while travelling along a slope, the control system receives the angle of the slope, calculates a component of the drag force for that angle and takes that component into account to determine the output draft force.

6. The vehicle control system as claimed in claim 1, wherein the control system sets a maximum output draft force when the input draft force exceeds a pre-determined value and the maximum output draft force is ramped down when the linkage is moved above a pre-determined height.

7. The vehicle control system as claimed in claim 6, wherein the pre-determined height is selected at a height where an attached implement cannot contact the ground.

8. An agricultural tractor comprising the vehicle control system as claimed in claim 1.

9. A control method for a vehicle having a continuously variable transmission (CVT), the control method for controlling the height of a linkage on the vehicle and/or on an implement coupled with the vehicle, the control method comprising the steps of: detecting an input draft force by sensors in the CVT or driveline; processing said input draft force to provide an output draft force upon which movement of the linkage is based; and raising and lowering the linkage based on the output draft force, wherein the step of processing comprises at least one of the following: compensating the input draft force detected during acceleration or deceleration, compensating the input draft detected whilst travelling along a slope, equalizing the input draft force by applying a ramp function, and reducing the input draft force when the linkage is at a predetermined height.

10. A controller for a vehicle configured to carry out the method as claimed in claim 9.

11. A computer program product comprising a non-transitory storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing the steps of the method as claimed in claim 9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention will now be described, by way of example only, with reference to the following drawings in which:

[0052] FIG. 1 is a side view of a tractor,

[0053] FIG. 2 is side view of a tractor showing a linkage at the rear in accordance with the invention,

[0054] FIG. 3 is a flow chart showing the steps involved in determining a draft force in accordance with the invention,

[0055] FIG. 4 shows a graph and a respective values table with reference to one of the steps shown in FIG. 3,

[0056] FIG. 5 shows a graph referring to one of the steps shown in FIG. 3,

[0057] FIG. 6 is a side view of a tractor for control of a linkage on a trailed implement, in accordance with a further aspect of the invention, and

[0058] FIG. 7 is a side view of a tractor for control of a linkage on a semi-mounted implement, in accordance with a further aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0059] Referring to the drawings, an agricultural tractor 1 has a driveline 2 having a combustion engine 3, a continuously variable transmission, (CVT), T of the hydrostatic-mechanical split type and a rear axle housing 300. Combustion engine 3 is connected to the CVT, T by chassis part 310. Rear wheels 2a and front wheels 2a are driven by driveline 2.

[0060] A three-point linkage 400 is attached to the rear axle housing 300 and mainly consists of two lower lifting arms 401 to which an implement is attached. A plough 500 with ground engaging means 501 is attached to lower lifting arms 401. An additional top link 402 connects the implement 500 to the tractor 1. The top link 402 is of a hydraulic type adjustable in length to adjust the inclination of the plough 500 with the ground. The lower lifting arms 401 can be pivoted about axis A by respective hydraulic actuating cylinders 403 which move rocker arm 404 and lift rod 405. The height of the lifting arms can thus be changed by pivoting the lifting arms about axis A. By height of the linkage, it is meant the height of a part of the lifting arms relative to the ground. The hydraulic actuating cylinders 403 are supplied with an actuating fluid by a control valve 406. Control valve 406 controls which chamber 403a (to lift the implement) or chamber 403b (to lower the implement) of the hydraulic actuating cylinders 403 is charged with fluid. Control valve 406 is connected to a pump 407 which is driven by combustion engine 3 and connected to a fluid tank 108.

[0061] The position of the lower lift arms 401 is indirectly measured by a position sensor 409 which senses the position of a cam 410 attached to rocker arm 404.

[0062] An additional pressure sensor 411 is provided to measure the fluid pressure in the chamber 403a of the hydraulic actuating cylinders 403. The fluid in chamber 403a is compressed when the implement weight is fully taken up by the three-point linkage 400 and therefore a pressure increase indicates movement of the implement to a high position for transportation.

[0063] A tractor control unit 13 is provided to control various functions of the vehicle. The control unit 13 is electronically connected to various components such as the transmission and display and input devices via a CAN-BUS system, for example. The control unit 13 also contains software to drive the electronic linkage control system. The control unit 13 is connected to an input and display device 14 in the tractor cab 5 to receive inputs from the operator and to show information to the operator. The input and display device 14 includes a means to adjust and display parameters relating to the electronic linkage control system, such as the mix controller or the depth controller described above.

[0064] Position sensor 409, control valve 406 and pressure sensor 411 are connected to the control unit 13.

[0065] As described in WO2013/053645 of the applicant, the driveline 2 or transmission T a, which may be of hydrostatic mechanical split type transmission, contains sensors to determine various driving parameters such as draft force, vehicle speed, driving direction or vehicle stand still.

[0066] As draft force is constantly measured in the system, this parameter can be used to control the linkage based on an increased draft force applied by the implement.

[0067] So, by monitoring the draft force which is already done for transmission control and protection purposes, an increase or decrease of the draft or pull force can be detected and processed by the electronic linkage control system to provide modes such as draft, intermix or position control modes.

[0068] The draft force signal is fed into a tractor control unit 13 which is programmed to lift, or lower the linkage in response to the change as programmed.

[0069] In accordance with the invention, the control system with reference to FIG. 3 will now be described. The detected draft force as measured by the draft sensing means in the CVT, T is processed in a series of steps to provide a corrected draft force reading which takes account of the following conditions: when the vehicle is travelling uphill, when the vehicle is travelling downhill or, when the tractor is accelerating whilst the tractor is in the draft control mode. If these conditions are not taken into account, the detected draft force may result in unnecessary lifting and lowering of the linkage and an attached implement which may be dangerous.

[0070] Each of the steps is described by processing the draft force. A draft force F.sub.draft in is used to describe the value inputted into each step. A draft force F.sub.draft out is used to describe the value outputted from each step (that is after it has been processed by that step). The draft force F.sub.draft out from one step may then be used as an inputted value F.sub.draft in for a subsequent step and so on for a number of steps.

[0071] In a first step S1, the tractor control system will receive the detected draft force F.sub.draft in from the draft sensing means in the CVT as is known in the art. For this step, F.sub.draft in is simply the detected draft force from the CVT, T which increases when, the tractor experiences a higher resistance to the direction of travel, for example when a plough encounters a rock during ploughing.

[0072] But as the draft force F.sub.draft in from the CVT may also increase during acceleration or deceleration of the tractor or when travelling uphill or downhill, the draft force F.sub.draft in, in accordance with the invention, is further processed by at least one further step to ensure that the linkage is correctly adjusted in accordance with the draft force.

[0073] In a second step S2, the control system adapts the detected draft force F.sub.draft in by taking the force due to the inertia of the tractor F.sub.inertia into account. F.sub.inertia is calculated using the equation:

F.sub.inertia=M.sub.tractor×a.sub.tractor cvt×f

where M.sub.tractor is the mass of the tractor and is known from the factory settings and accessed from an electronic storage device connected to control unit 13; a.sub.tractor cvt is the acceleration of the tractor as determined by the CVT, and f is a factor which takes the relevance of inertia into account.

[0074] Factor f is entered by an operator using input device 14. Factor f is introduced to enable the operator to vary the tractor mass over a small range for the purpose of calculations performed by the control system. The mass of the tractor M.sub.tractor is usually a set value entered into a tractor control system during manufacture which cannot be changed by the operator, since its value is relied upon to control safety critical systems of the tractor such as anti-skid brakes. However; the mass of the tractor may change during operation, for example, if an additional ballast is attached to the tractor wheels, or to the tractor frame. This additional mass influences the behaviour during acceleration or deceleration and therefore must be taken into account when determining the drag force. Factor f therefore enables the mass of the tractor to be taken into account for the purpose of determining the drag force without affecting safety critical functions on the tractor.

[0075] The draft force outputted from step S2, F.sub.draft out, is calculated by subtracting the force of inertia F.sub.inertia from the detected draft force F.sub.draft in:

F.sub.draft out=F.sub.draft in−F.sub.inertia

If the tractor is accelerating, the acceleration of the tractor a.sub.tractor cvt determined by the CVT, T would show a positive value so that the output draft force F.sub.draft out is decreased. If the vehicle is decelerating, the acceleration of the tractor a.sub.tractor cvt determined by the CVT, T would show a negative value so that the output draft force F.sub.draft out is increased.

[0076] In a third step, S3 the draft force F.sub.draft out calculated in step S2 is used as the draft force F.sub.draft in. In this step, F.sub.draft in is further corrected to provide a draft force F.sub.draft out which takes into account the slope that the tractor is travelling along. This prevents any unintended movement of the linkages which may be caused by a change in draft force when driving up or down a slope.

[0077] The inclination of the slope α is measured from a gyroscope on the tractor. Typically, a gyroscope is included as part of the guidance system receiver 412 of the tractor. Alternatively, any sensor determining the inclination of the tractor relative to the ground may be used whether part of an existing system or used only for this purpose.

[0078] Using the formula:

F.sub.slope=M.sub.tractor×G×sin α

Where F.sub.slope is the draft force measured when the tractor is travelling along a slope (uphill or downhill), M.sub.tractor is the mass of the tractor and is known from the factory settings and accessed from an electronic storage device connected to control unit 13, and G is the force due to gravity.

[0079] The draft force due to the slope F.sub.draft out is corrected using the absolute value of F.sub.slope (as F.sub.slope may be negative or positive depending on uphill or downhill driving) in the following formula:

F.sub.draft out=F.sub.draft in+F.sub.slope

(when the tractor is travelling downhill to increase the output draft force F.sub.draft out) or

F.sub.draft out=F.sub.draft in−F.sub.slope

(when the tractor is travelling uphill to decrease the output draft force F.sub.draft out)

[0080] If there is no slope, that is the tractor is travelling horizontally, then α is 0 and there is no F.sub.slope and step S3 is omitted by the control system.

[0081] Similar to the factor f described in step S2, the operator may input a factor f to adapt the mass of the tractor for determining the draft force in step S3, for example, if additional ballast is attached.

[0082] In a fourth step, S4 the control system normalizes the draft force F.sub.draft in (by means of a ramp function to make the control function more stable).

[0083] As shown in the graph and value table in FIG. 4, the draft force is measured periodically, for example, every 8 milliseconds. If the draft force F.sub.draft in (shown in the graph of FIG. 4 by the solid line), exceeds a certain value, of say 100 kN, the draft force is normalized to reduce the corresponding height adjustments of the linkage which would otherwise render the tractor unstable. The normalized force F.sub.draft out from step S4 is shown by the broken line in FIG. 4.

[0084] For example, if the draft force F.sub.draft out from step S3 determines a value of 80 kN, this value is used as F.sub.draft in for step S4. Step S4 will not change the value (since it is under 100 kN) and accordingly a F.sub.draft out value of 80 kN will be determined and used for the next step, S5. If the draft force F.sub.draft in for step S4 is 150 kN, as shown in the next time period in FIG. 4, the output force from step S4 will be an equalized draft force F.sub.draft out of 120 kN. If the next F.sub.draft in into step S4 is 200 kN, step S4 will only add 20 kN so that F.sub.draft out is 140 kN. In the same manner, a value of 250 kN in the next measurement results in a draft force F.sub.draft out of 160 kN being determined.

[0085] If the next draft force, F.sub.draft in is 200 kN, F.sub.draft out is calculated as 180 kN. The last draft force F.sub.draft in value shown in FIG. 4 is 150 kN which is lower than the previous F.sub.draft out of 180 KN. In this case, the draft force F.sub.draft out is reduced by 20 KN so that so that draft force F.sub.draft out of 160 kN is forwarded to step S5.

[0086] By reducing the increase in draft force for draft force F.sub.draft in values above a predetermined value, the draft force F.sub.draft out forwarded to the next step is reduced so that movement of the linkage is smoother than forwarding the draft forced received by a preceding step.

[0087] In a fifth step, S5 as is known in the art, if the draft force F.sub.draft in exceeds a predetermined value, the control system defaults to a maximum draft force F.sub.draft out . This has the effect that for draft forces F.sub.draft in above a pre-determined force, a maximum draft force value F.sub.draft out will be used in another subsequent step.

[0088] In a sixth step, S6 the control system reduces the maximum draft force at a predetermined lifting height as shown in the graph in FIG. 5. Above a predetermined linkage height H1 which is indicative of a linkage holding an implement in a transport position, the control system reduces the draft force F.sub.draft in by using a linear ramp-down. For example, a linkage lifting height of 80% of the full lifting height may be defined as the predetermined height H1. When a draft force F.sub.draft in which would ordinarily result in moving the linkage above H1, the control system in step S6 works to continuously reduce the draft force until a maximum height H2 is reached. In between heights H1 and H2, the maximum draft force (at which the control system would stop to automatically change the height depending on the draft force) decreases with increasing height. In practice, the higher the height of pre-determined height H1 the less movement of the linkage there is in reaction to the draft force detected. This leads to a smoother adjustment of the linkage height as shown in FIG. 5.

[0089] In a seventh step S7, the operating condition of the tractor is checked in accordance with the applicant's prior art EP 15177251.4. If the operating condition of the tractor is correct the draft force F.sub.draft out will be progressed to a subsequent step.

[0090] In an eight step S8, the draft force signals may be standardized for compliance with other control systems on the tractor, as is known in the art.

[0091] It must be understand that the steps S2, S3, S4 and S6 may be used completely, partly or in the same or a different order without leaving the scope of the invention. For example, for a tractor having a low mass, the influence of slope and inertia may be so minor so that the steps S2 and S3 may be omitted. This may reduce computing capacity and hardware requirements.

[0092] In a further embodiment of the invention, in FIG. 6 a tractor 10 is shown which is coupled with a trailed implement 600 via a tow bar 200 or other suitable trailer connection. The trailed implement 600, which may comprise a plough or other similar tillage or soil cultivation apparatus, is provided with ground- or soil-engaging means 602, which are supported using at least one implement wheel 603. The height of the soil-engaging means 602, and accordingly their engagement with the ground, is controlled through actuation of an implement-mounted linkage or lift cylinder 604 coupled to the implement wheel 603, but it will be understood that other implement linkage configurations may be used. The actuation of the linkage 604 is controlled via a suitable communication connection with the tractor control unit 13 (shown in FIG. 2), in a similar manner as described above for a linkage-mounted implement.

[0093] In a further embodiment of the invention, in FIG. 7 a tractor 10 is shown which is coupled with a semi-mounted implement 700 via the lower lifting arms 401. The semi-mounted implement 700, which may comprise a plough or other similar tillage or soil cultivation apparatus, is also provided with ground- or soil-engaging means 702, which are partly supported using at least one implement wheel 703. The height of the soil-engaging means 702, and accordingly their engagement with the ground, is controlled through actuation of an implement-mounted linkage or lift cylinder 704 coupled to the implement wheel 703 and the lower lifting arms 401 conjointly, but it will be understood that other implement linkage configurations may be used. The actuation of the linkage 704 is controlled via a suitable communication connection with the tractor control unit 13 (shown in FIG. 2), in a similar manner as described above for a linkage-mounted implement.

[0094] The invention provides a suitable control method for a vehicle control system for a vehicle having a CVT, to control the raising and lowering of a linkage provided on the vehicle or on an implement coupled with the vehicle. The invention may be provided as a controller for use in a vehicle, the controller arranged to perform the steps of the method. Additionally or alternatively, the invention may be provided as a computer program product comprising a non-transitory storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing the steps of the method as outlined above.

[0095] The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.