On demand machine rimpull adjustment to prevent tire slip

Abstract

A system for proactively controlling rimpull limit of a machine includes a hydraulic system having a lift cylinder to move an implement; a lift cylinder pressure sensor that senses a hydraulic pressure of the lift cylinder and responsively produces a lift cylinder pressure signal; and a controller in operable communication with the power train and the lift cylinder pressure sensor. The controller is configured to receive the lift cylinder pressure signal; determine the rimpull limit based at least in part upon the lift cylinder pressure signal; and adjust the torque of the power train to the rimpull limit.

Claims

1. A method for controlling a wheel loader machine, the wheel loader machine having a hydraulically-driven bucket control system including a lift cylinder and a bucket; and a power train including an engine and producing a torque for moving wheels of the wheel loader machine, the method comprising: automatically increasing a force available at the wheels of the wheel loader machine in response to an increase in pressure in the hydraulically-driven bucket control system, wherein the automatically increasing of the force available at the wheels corresponds to an increasing of a rimpull limit.

2. The method of claim 1, wherein the increase in pressure results from interaction of the bucket with a pile of material.

3. The method of claim 1, further including limiting the force available at the wheels when the wheel loader machine is doing work, prior to automatically increasing the force available at the wheels.

4. The method of claim 1, wherein the increasing of the force available at the wheels is proportional to the increase in pressure in the hydraulically-driven bucket control system.

5. The method of claim 1, wherein the increase in pressure in the hydraulically-driven bucket control system corresponds to an increase in pressure in the lift cylinder.

6. The method of claim 1, wherein the increasing of the rimpull limit is within a range of 60% and 100% of a total available rimpull.

7. The method of claim 1, wherein the increasing of the rimpull limit includes no longer applying the rimpull limit.

8. The method of claim 1, wherein the automatically increasing of the force available at the wheels is based on an input from an operator or controller regarding a ground surface that the wheel loader machine is operated upon.

9. The method of claim 8, wherein the input regarding the ground surface is related to a coefficient of friction of the ground surface.

10. A method for controlling a machine, the machine having a hydraulically-driven implement control system including a lift cylinder and an implement; and a power train including an engine and producing a torque for moving wheels of the machine, the method comprising: automatically increasing a force available at the wheels by increasing a rimpull limit in response to at least one of: an increase in pressure in the hydraulically-driven implement control system, or movement of the implement by the hydraulically-driven implement control system.

11. The method of claim 10, wherein the automatically increasing of the force available at the wheels is in response to at least: the increase in pressure in the hydraulically-driven implement control system, and the movement of the implement by the hydraulically-driven implement control system.

12. The method of claim 11, wherein the increase in pressure results from interaction of the implement with a pile of material.

13. The method of claim 11, wherein the increase in pressure in the hydraulically-driven implement control system corresponds to an increase in pressure in the lift cylinder.

14. The method of claim 11, wherein the movement of the implement by the hydraulically-driven implement control system corresponds to a movement of the lift cylinder.

15. The method of claim 11, wherein the automatically increasing of the force available at the wheels is based on an input from an operator or controller regarding a ground surface that the machine is operated upon.

16. The method of claim 15, wherein the input regarding the ground surface is related to a coefficient of friction of the ground surface.

17. A system for controlling a machine, the system comprising: a hydraulically-driven implement control system including a lift cylinder and an implement; a power train including an engine and producing a torque for moving wheels of the machine; and a controller in operable communication with the hydraulically-driven implement control system, the engine, and the power train, the controller being configured to: automatically increase a force available at the wheels by increasing a rimpull limit in response to an increase in pressure in the hydraulically-driven implement control system.

18. The system of claim 17, wherein the increase in pressure results from interaction of the implement with a pile of material.

19. The system of claim 18, wherein the increase in pressure in the hydraulically-driven implement control system corresponds to a sensed increase in pressure in the lift cylinder.

20. The system of claim 17, wherein the machine is a wheel loader machine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a general schematic view of an exemplary embodiment of a system constructed in accordance with the teachings of this disclosure;

(2) FIG. 2 is a perspective view of an embodiment of an exemplary vehicle in which a system in which the teachings of the disclosure may be used; and

(3) FIG. 3 is a flowchart illustrating exemplary blocks of an exemplary method for preventing tire slip in a machine, in accordance with the teachings of this disclosure.

DETAILED DESCRIPTION

(4) Referring now to the drawings, and with reference to FIG. 1 and FIG. 2, there is shown a machine system of the present disclosure and generally referred to by reference numeral 100. The machine system 100 may comprise one or more wheels 210, a power train 102, a hydraulic system 103, an engine, 104, an implement 211, and a controller 106.

(5) In FIG. 2, an exemplary machine 200, a wheel loader, which incorporates the features of the present invention is shown. The machine 200 includes a frame 201 generally supporting the various assemblies and mechanical systems of the machine 200. The frame 201 supporting a cab assembly 202, axel assemblies 203, a lift assembly 204, and a tilt assembly 205.

(6) The lift assembly 204 and tilt assembly 205 are pivotally mounted on the machine 200 and in operable communication with the implement 211, wherein the movement of the lift assembly 204 and tilt assembly 205 is translated to the implement 211 in the form a change in a height or an angular tilt of the implement 211. Within this exemplary machine 200, the implement 211 is depicted as a bucket, although other implement 211 types may be utilized.

(7) The axel assemblies 203 are in operable communication with the wheels 210 and in operable communication with the engine 104, wherein rotation of the axel assemblies 203 and wheels 210 is generally powered by the engine 104 through engagement with the power train 102.

(8) The cab assembly 202 may include a plurality of control devices in the form of joysticks, pedals user interfaces, controls and other types of display and input devices to provide input to the controller 106.

(9) While the description and drawings are made with reference to the machine system 100 positioned on a wheel loader, the teachings of the disclosure may be implemented on other machines utilized in earth moving, mining, construction, farming, material handling, transportation, and other similar machines. Accordingly, as a wheel loader is shown, the machine may be a bulldozer or other type of machine.

(10) Referring now back to FIG. 1, the machine system 100 of the present disclosure, the hydraulic system 103 includes a lift cylinder 130 in operable communication with the lift assembly 204 (FIG. 2), wherein the lift cylinder 130 is generally adapted to actuate the lift assembly 204 to change a height of the implement 211 and in the form of a linkage. The lift cylinder 130 may be a rod and cylinder assembly as is known in the art, wherein the lift cylinder 130 generally receives a pressurized fluid from the hydraulic system 103 to actuate the lift assembly 204.

(11) A lift cylinder pressure sensor 131 is deposed on the machine 200 to sense the pressure within the lift cylinder 130 and generate a responsive signal for input into the controller 106. The signal from the lift cylinder 130 generally utilized to calculate a downforce on the wheels 210, wherein the lift cylinder 130 sensed pressure is one of the primary variables used within this calculation. The lift cylinder pressure sensor 131 may be comprised of one or more sensors and be provided from any sensor type known with the art and suitable for the purpose of sensing a pressure.

(12) Accordingly, the lift cylinder 130 pressure is used to determine the force on the wheel 210 during machine 200 work and wherein the machine system 100 controller 106 generally adjusts the machine 200 rimpull by determining a rimpull limit and proactively controlling corresponding power train 102 and engine 104 systems proportionately to the rimpull limit.

(13) Further, one or more sensors may be disposed on the machine 200 and configured as a lift position sensor 240 in operable communication with the controller 106 to send a responsive signal representative of the position of the lift assembly 204. Similarly, one or more sensors may be disposed on the machine 200 and configured as a tilt position sensor 250 in operable communication with the controller 106 to send a responsive signal responsive to the position of the tilt assembly 205.

(14) The controller 106 generally adapted in a most basic form to utilize the lift sensor pressure 130 to determine a limit on the rimpull in proportion to the lift cylinder 130 pressure. Accordingly, this rimpull limit is controlled by adjusting a torque from the engine 104 through the power train 102 and to the wheels 210.

(15) In an advanced implementation, the system 100 of the present disclosure is generally adapted to utilize multiple sensor signals 131, 240, 250 to determine the downforce on the wheels 210 and limit the rimpull accordingly.

(16) The following variables are generally utilized in the system 100 with the below calculations to determine the downforce: F.sub.x: horizontal component of force applied to the implement tip F.sub.y: vertical component of force applied to the implement tip F.sub.cyl: lift cylinder force F.sub.0: lift cylinder force induced by an empty implement lift assembly and tilt assembly linkage weight ΔF.sub.cyl: lift cylinder force induced by external force k.sub.x: lift cylinder force increase due to unit F.sub.x horizontal force k.sub.y: lift cylinder force increase due to unit F.sub.y vertical force W: machine weight μ: coefficient of friction

(17) The force in the lift cylinder is a composite of force induced by an empty linkage weight and external forces.
F.sub.cyl=F.sub.0+ΔF.sub.cyl

(18) Assuming a fixed point of application (implement tip) the cylinder force is the sum of the external force vector components and their respective kinematic gain factors.

(19) $\Delta F_{\mathrm{cyl}}=F_x{k}_x+F_y{k}_y{F}_y=\frac{\Delta F_{\mathrm{cyl}}-F_x{k}_x}{k_y}$

(20) The gain factors and empty bucket cylinder force are each a function of lift and tilt position which can be expressed as lookup maps.
k.sub.x=f.sub.1(lift,tilt)
k.sub.y=f.sub.2(lift,tilt)
F.sub.0=f.sub.3(lift,tilt)

(21) To avoid slipping the horizontal force must be less than the product of the coefficient of friction and the total vertical load on the tires.
F.sub.x<μ(W+F.sub.y)
Substituting for F.sub.y and solving for F.sub.x

(22) $F_x<\mu \left(W+\frac{\Delta F_{\mathrm{cyl}}{F}_x{k}_x}{k_y}\right)F_x<\mu \frac{{\mathrm{Wk}}_y+\Delta F_{\mathrm{cyl}}}{k_y+k_x\mu }$
Finally substituting for ΔF.sub.cyl we have the horizontal force limit expressed in terms of current cylinder force, linkage position, and assumed coefficient of friction

(23) $F_{\mathrm{xlimit}}=\mu \frac{{\mathrm{Wk}}_y+F_{\mathrm{cyl}}-F_0}{k_y+\mu k_x}$

(24) Based upon this above calculation, F.sub.xlimit is the rimpull limit for a given machine 200 based upon the system 100. Accordingly, the machine 200 can approach a pile with the implement 211 and wherein the controller 106 will adjust the rimpull based upon the lift cylinder 130 pressure and adjust the rimpull limit as the pressure increases. Accordingly, the rimpull limit is generally adjusted between a range of 60% and 100% of the total available rimpull based upon the pressure of the lift cylinder 130, although the limit can be reduced below 50%. As the pressure sensed 131 on the lift cylinder 130 increases, the rimpull limit is proportionately increased towards 100% of the total available rimpull to ensure efficient usage of the machine 200 hydraulic system 103.

(25) The controller 106 may receive an input 161 for the coefficient of the friction (“μ”) within the above calculation. Accordingly, the machine 200 operator may make an adjustment to the rimpull limit based upon a given ground surface, wherein the input 161 is adjusted to the actual friction of a given surface the machine 200 is operated upon.

(26) Depending on the power train 102 system of a given machine 200 the rimpull limit will be adjusted utilizing a different mechanism. For a machine 200 having a power train 102 type with an impeller clutch torque converter 120 the controller 106 will control the rimpull limit through a clutch pressure of the impeller clutch 121. For a machine 200 having a power train 102 type with an electric motor with a continuously variable transmission (“CVT”) 122 the controller 106 will control the rimpull limit through electric motor current 123. For a machine 200 having a power train 102 powered through hydraulics and having a hydrostatic CVT 124 the controller 106 will control the rimpull limit through variator displacement 125. For a machine 200 having a power train 102 type with a torque converter 126 the controller 106 will control the rimpull limit though engine 104 speed.

(27) In use, a user of the machine system 100 on the machine will generally implement the system 100 to prevent tire wear where the controller 106 will set the rimpull limit on demand based upon the lift cylinder pressure 130 sensed pressure 131. As the user approaches a pile of material to be moved the rimpull limit is reduced in proportion to the lift cylinder 130 pressure. As there is no material in the implement 211, the pressure within the lift cylinder 130 is relatively low and the torque provided to the wheels 210 is limited. As the user pushes into the pile with the machine 200 implement 211, the lift cylinder 130 pressure increases and the controller 106 correspondingly and proportionately increases the rimpull limit. As material is added to the implement 211 downforce increases on the wheels 210 and the rimpull no longer needs to be limited.

INDUSTRIAL APPLICABILITY

(28) Referring now to FIG. 3, an exemplary flowchart is illustrated showing sample method steps that may be followed in setting an on demand rimpull limit for a machine 200 to prevent tire slip during machine 200 use. The method 300 may be practiced with more or less method steps and is not limited to the order shown. While in the flowchart, the controller 106 processes operational parameters to determine if the machine 200 and implement 211 are doing work, wherein the rimpull of the wheels 210 is limited to prevent tire slip.

(29) The initial method step 301 includes, receiving by a controller 106, operational parameters. The operational parameters may include sensed data related to weight and positioning of the implement 211 and input 161 related to the friction of the surface the machine 200 is operated upon.

(30) In one embodiment of the present disclosure, the controller 106 receives a pressure signal 131 from the lift cylinder 130. In an alternate embodiment, the controller 106 receives a pressure signal 131 from the lift cylinder 130 and a signal from the position sensor 240 of the lift assembly 204. In an alternate embodiment, the controller 106 receives a pressure signal 131 from the lift cylinder 130, a signal from the position sensor 240 of the lift assembly 204, and a signal from the position sensor 250 of the tilt assembly.

(31) After the controller 106 receives the given operational parameters at step 301, the controller 106 identifies, through a calculation, the downforce needed at the wheels 210 of the machine 200 to prevent wheel 101 slip at step 302.

(32) Based upon this downforce, the controller 10 then limits the rimpull of the machine 200 at step 303. Throughout the use of the machine 200, step 302 is repeated and wherein step 303 is continually processed on demand to prevent wheel 101 slip during machine 200 use.