WO2008129345A1

WO2008129345A1 - Controller of a skid steered machine

Info

Publication number: WO2008129345A1
Application number: PCT/IB2007/002117
Authority: WO
Inventors: Roger Caillieret
Original assignee: Volvo Compact Equipment Sas
Priority date: 2007-04-19
Filing date: 2007-04-19
Publication date: 2008-10-30

Abstract

The invention relates to a skid steer machine having separate left and right hydraulic propulsion units (32, 34) and a hydraulic control circuit comprising a pilot circuit comprising a controller (38) having a control member (40) and being connected to the left and right main control valves (58L, 58R), characterized in that said controller (38) comprises at least a front left (42a), a front right (42b), a rear left (42c) and a rear right (42d) pilot sensor, and in that each said sensor is connected so that: - front left sensor (42a) controls forward movement of the right propulsion unit (34); - front right sensor (42b) controls forward movement of the left propulsion unit (32); - rear left sensor (42c) controls rearward movement of the left propulsion unit (32); and - rear right sensor (42d) controls rearward movement of the right propulsion unit (34).

Description

CONTROLLER OF A SKID STEERED MACHINE

Technical field

The invention relates to the field of skid steer machines, especially construction equipment machines, such as excavators, mini excavators, loaders, etc., where the machine has at least two separate left and right propulsion units to drive the vehicle, and where the left and right movement of the machine comes as a consequence of a difference in the speed of the left and right propulsion units.

Background art

On figure 1 is depicted a conventional crawler excavator 10. It comprises an upper frame carrying the excavator's superstructure which comprises the driver's cabin 14 and an engine compartment 16. The upper frame carries the machine's main work equipment: a digging assembly 18. Typically, the digging assembly 18 can have boom 20 which is pivotably connected around a horizontal axis on the upper frame. The boom 20 can be lowered and lifted vertically. At the free end of the boom

20, an arm 24 may be pivotably connected around another horizontal axis, and it can be lowered and lifted. At the free end of the arm 24, a working tool, such as bucket

28, is pivotably connected around another horizontal axis.

A lower frame carries the undercarriage of the machine 10, which comprises mainly the drivetrain of the machine. In the example shown, the drive train is in the form of a left and a right endless track 32, 34, but it could also be made of a set of wheels. As it is well-known, the superstructure 12 of the machine can swivel around a vertical axis with respect to the undercarriage thanks to a suitable mechanical link between the upper frame and the lower frame, with the possibility of both frames rotating with respect to each other around a vertical axis.

Most construction equipment machines use a hydraulic pressure system to operate the various working tools 18 carried by the machine, as well as to operate the drive train. The hydraulic pressure system comprises usually a Diesel engine which drives at least one hydraulic pump which itself feeds pressurized fluid to various actuators through hydraulic circuits comprising hydraulic lines, distributors, valves, etc. It is common for such a construction machine to be designed as a skid steer machine. Is such a case the drive train comprises at least two propulsion units, one dedicated to the right side of the machine and the other one dedicated to the left side of the machine. Each propulsion unit therefore drives one endless track (left or right) or a series of synchronous wheels located on one side of the machine. Each propulsion unit is controlled separately by the operator through a specific controller. Each controller controls the corresponding propulsion unit either forwardly or rearward Iy and also controls the speed of the propulsion unit.

In many cases, the propulsion units are hydraulically powered, and they are also piloted through a hydraulic pilot circuit, but an electrical pilot circuit is also possible. In the case of a hydraulic pilot circuit, the controllers comprise each at least one manually operated proportional valve which provides oil pressure to one side or the other of the propulsion unit's power hydraulic circuit, at a varying pressure and/or flow rate.

Therefore, in order to fully control the propulsion of the machine, the operator generally needs to act simultaneously on two levers, each acting on one propulsion unit. He can control the forward movement for example by pushing the two levers forwardly to the same extent. To move right or left, he must to the contrary act on both levers but not to the same extent, so that the respective propulsion units do not drive the left and right sides of the machine at the same speed, resulting in the so- called skid-steering of the machine. This way of controlling the machine is not entirely satisfactory, at least in the sense that the operator needs his both hands to precisely control the travel of the machine. Moreover, having two control levers in the cabin of the machine is burdensome in terms of occupied space. Indeed the space available in the cabin is sometimes scarce, especially on compact machines, and/or the space needed for the controls command that they be placed in a location where they are not optimally accessible for the operator.

This is why it has already proposed to replace the two levers by a joystick controller, where a single control lever is movable through a full circular pattern to actuate a respective first and second actuator in either direction. Indeed, hydraulic joysticks have long been used on construction equipment to control the operation of the work implements such as the boom and the bucket.

Nevertheless, it has proven a challenging to design a pilot circuit which could be used to control the drive train of a machine in an ergonomically simple and intuitive fashion for the operator. Document US-5.875.631 discloses a joystick controller for controlling a hydrostatic transmission through control actuators. The joystick controller has four valves, configured as in a diamond, with a front one of them controlling forward movement of both tracks, and rear one of them controlling rearward movement of both tracks. Direction of the machine is controlled through the other two valves which are connected is such a way that it organizes pressure drops in one or the other of the left and right pilot circuits to control a speed reduction in one of the tracks. If the corresponding right or left valve is sufficiently depressed, the track can even see its speed become negative, to achieve on-the-spot turning. This system requires the use of a bleed down type of control system. Moreover, with the proposed controls, it is not very convenient to achieve a real on-the-spot turn where the speed of the left and right tracks have the same value, but in opposite directions. Indeed, such on-the-spot turn condition is obtained only with the joystick lever in a very specific position which is not easy to find: it is basically needed to set the lever at a position which is displaced for example forwardly to give a forward motion to both tracks, and then to move the lever quite extensively to one side, to reduce and invert the speed of one track. But it is then quite difficult to find the correct amount of displacement of the lever to the side to meet the condition of having the same absolute value for the left and right speed. Therefore, achieving true on-the-spot turn is theoretically possible, but it is practically impossible to achieve with a sufficient degree of confidence for the operator. Therefore, it is an object of the invention to provide a skid steer machine where the propulsion units are controlled through a single intuitive and user-friendly controller.

Summary of the invention

According to the above, the invention provides for a skid steer machine having separate left and right hydraulic propulsion units which are independently controlled through a hydraulic control circuit including a controller having a control member, characterized in that said controller comprises at least a front left, a front right, a rear left and a rear right pilot sensor which each deliver a corresponding front left, front right, rear left, and rear right pilot signal representative of the movement of said control member in a corresponding direction, and in that each said sensor is connected so that:

- front left sensor controls a forward movement of the right propulsion unit; - front right sensor controls a forward movement of the left propulsion unit;

- rear left sensor controls a rearward movement of the left propulsion unit; and - rear right sensor controls a rearward movement of the right propulsion unit.

Description of figures

Other aspects and features of the invention will become apparent when reading the following detailed description of the invention with reference to the appended figures wherein:

- Figure 1 is a schematic perspective view of a crawler exactor on which the invention can be applied;

- Figure 2 is a schematic view of how a joystick controller can be implemented in a cabin of a crawler excavator; and

- Figure 3 is a simplified diagrammatic view representing an embodiment of a hydraulic control circuit for the propulsion units of a skid steer machine according to the invention.

Description of the invention

The invention will be hereunder described when applied to a crawler excavator as depicted in Figure 1 and described above. Nevertheless, it could also be implemented in any skid steer machine having hydraulic left and right propulsion units and where the left and right movement of the machine comes as a consequence of a difference in the speed of the left and right propulsion units. Such skid steer machines could be of any type of construction equipment machines, such for example as skid steer loaders or bulldozers, or other types of machines such as leisure vehicles, snow groomers, etc... According to the invention, both left and right propulsion units are to be controlled through a single controller. The controller, as represented in Figures 2 and 3, is for example a joystick-type controller 38 having a control lever which is to be directly hand-actuated by the machine's operator.

The controller 38 is installed preferably in the machine's cabin 14 preferably in front of the operator when he is in a work position. Indeed, in the following, the orientation of the controller 38 will be discussed with reference to the position and orientation of the operator. More precisely, it will refer to the most probable/frequent position and orientation of the operator when he will have to operate the propulsion of the machine.

Conventionally, the operator of a crawler excavator is seated in the cabin 14, facing the front side of the machine so he has direct sight on the main working equipment 18. In other words, the sagittal plane of the operator is substantially aligned with the longitudinal front to rear axis X-X of the cabin. One particular aspect of an excavator as described above is the possibility for the cabin to swivel with respect to the drive train. Therefore, the longitudinal front to rear axis X-X of the cabin does not necessarily correspond to the longitudinal front to rear axis of the undercarriage which carries the tracks. In other machines, such as skid steer loaders, the two axes are always aligned, and the sagittal plane of the operator is usually aligned with these two axes. Nevertheless, in some machines, the operator might have a different orientation when working, or he could even occupy one of several orientations, depending on the task he is performing. In the forthcoming description, it will be assumed that the operator will be placed as conventionally in an excavator cabin, as shown schematically on Figure 2, on which the cabin is represented aligned with the undercarriage carrying the tracks. Therefore, the notions of front and rear, and of left and right, will be those conventional with this operator placement. Preferably, the controller 38 will be placed centrally in front of the operator, but the controller could also be located in front of him but offset transversally on one side.

The controller could be of another type than a joystick-type controller, especially with a different sort of control member. Indeed, the control member could simply be a plate which the operator could operate either with his hands, or even with his feet, simply pressing more or less on different parts of the plate. The control member, whatever its form, could also be indirectly actuated by the operator, for example through some kind of linkage mechanism.

According to the invention, the controller 38 has at least four pilot sensors 42a, 42b, 42c, 42d which are each able to deliver a pilot signal, each signal being representative of the displacement of the control member in one direction. Preferably, the pilot signal will be proportional to the displacement, either linearly proportional or not, so that to each position, of the control member, or at least to several positions, will correspond a different value of the pilot signal. This proportionality can be either continuous or can vary by steps, or can be a combination of both. The control member 40 is displaceable with respect to the sensors, which are for example attached to a controller base fixed in the cabin. In the depicted embodiment, the control member is mounted on a spherical joint or on an equivalent mechanism (not shown). It could also be mounted so as to slide with respect to a base member along two dimensions. A combination of a sliding movement in one direction of a rotating movement around the same direction can also be used. All in all, the control member can be displaced along at least two dimensions and can therefore occupy any position within the two dimensions.

In the depicted embodiment, the control member cannot activate more than two of the four sensors simultaneously, and it cannot activate two diametrically opposed sensors simultaneously. Nevertheless, some embodiments of the invention may involve for example that two diametrically opposed sensors are activated simultaneously, for example in opposite ways.

The pilot circuit driven by the controller can either be hydraulic or electric. If the pilot circuit is electric, the sensors will deliver each a pilot electric signal which is representative of the movement of said controller lever, and the main control valves which feed the hydraulic propulsion units will preferably be solenoid valves driven in accordance to these pilot signals.

In the depicted embodiment, the pilot circuit is hydraulic, and the main control valves are hydraulic pressure controlled valves. Moreover, in the depicted embodiment, the controller will for example be a joystick controller 38 similar to the

"4TH5 Hydraulic pilot control" from Bosch Rexroth AG. In such a controller, the sensors 42a-d are in the form of hydraulic proportional valves which deliver an oil pressure which is proportional to the displacement of the control member. When the controller is installed in a vertical position, the valves 42a-d are arranged substantially vertically, parallel one to the other, and they each have one contact portion on which the control member can mechanically push to operate the valves. The contact portions of the valves are arranged substantially along a "square" configuration or along a "diamond" configuration when viewed from the top, depending on the orientation of the controller around its vertical axis. The control member can be represented as a X shaped cross member 46 extending in a substantially horizontal plane, the centre of the cross being coupled to the base through a spherical ball joint located on an axis which is equidistant to each of the valves contact portions. This cross member 46 is preferably equipped with a lever 44 extending vertically, or slightly angled for ergonomic reasons as shown on the pictures. Various levers, with various shapes and possible additional functions can be adapted. As represented in Figure 2 and 3, the controller 38 is mounted in the cabin so that, at least in a work configuration of the cabin, the controller is located so as to have two front sensors 42a, 42b on the one hand, and two rear sensors 42c, 42d on the other hand which are aligned substantially parallel to the vertical transversal plane of the operator, that is a plane perpendicular to the operator's sagittal plane.

Moreover, the controller is oriented so as to have left sensors 42a, 42c on the one hand, and the right sensors 42b, 42d on the other hand which are aligned substantially parallel to the sagittal plane of the operator, which is defined as a vertical plane dividing the body of the operator in two symmetrical left and right halves. When combined together, these two properties result in the controller 38 having a control member 40 extending substantially vertically, with the pilot sensors

42a-d being in a "square" or 'rectangular" configuration, rather than in a "diamond" configuration, with a front left sensor 42a, a front right sensor 42b, a rear left sensor

42c and a rear right sensor 42d. With this specific configuration of the controller 38, when the operator pushes the control member forwardly, he will tend to depress simultaneously the two front sensors 42a, 42b, and when pulling the control member rearwardly, he will tend to act simultaneously on the two rear sensors 42c, 42d. Similarly, when the operator pushes the control member to the left, he will tend to act simultaneously on the two left sensors 42a, 42c, and when pulling the control member right, he will tend to depress simultaneously the two right sensors 42b, 42d.

When the operator pushes the control member 40 forwardly and leftwardly, he will tend to act only on the front left sensor 42a if he pushes the control member exactly at 45 degrees (in the case of a "square" configuration), or on both the front left sensor 42a and one of the front right 42b or rear left 42c sensor, depending on his action on the control member 40 on one side or the other of this 45 degree axis. Similar functioning can be derived "mutatis mutandis" from the above for the operation of the control member in the other three quadrants.

It will now be described in a very simplistic way an embodiment of a propulsion unit power hydraulic circuit which can be controlled through the above mentioned controller 38 (and its corresponding pilot circuit) to achieve a simple and intuitive control of the machine's travel. The power hydraulic circuit will only be described as to its main functions and components, the skilled man in the art being able to design a true operative hydraulic circuit according to this general plan. As an example, each left and right propulsion unit comprises a hydraulic motor

48L, 48R. Each motor has at least two hydraulic ports 48Lf, 48Lb and 48Rf, 48Rb. The two hydraulic ports are to be connected one to a hydraulic pressure source 50 and the other to a hydraulic tank 52. In the embodiment of Figure 3, the hydraulic pressure source 50 comprises a pump 54 with a pressure regulator 56. Regarding the left motor 48L, it will be appreciated that, if the port 48Lf is connected to the pressure source 50 (the other port 48Lb being then connected to the hydraulic tank 52), then the left motor 48L will drive the left propulsion unit so as to tend to move the machine forwardly. Conversely, if the port 48Lb is connected to the pressure source 50 (the other port 48Lf being then connected to the hydraulic tank 52), then the left motor will drive the left propulsion unit so as to tend to move the machine backwardly, i.e. rearwardly.

Similarly, regarding now the right motor 48R, if the port 48Rf is connected to the pressure source 50 (the other port 48Rb being then connected to the hydraulic tank 52), then the motor 48R will drive the right propulsion unit so as to tend to move the machine forwardly. Conversely, if the port 48rb is connected to the pressure source 50 (the other port 48Rf being then connected to the hydraulic tank 52), then the motor 48R will drive the right propulsion unit so as to tend to move the machine backwardly, i.e. rearwardly.

Selective connection of the ports 48Lf, 48Lb, 48Rf, and 48Rb to the pressure source 50 or to the hydraulic tank 52 is controlled independently for each motor 48L and 48R through a respective left and right main control valve 58L, 58R.

The hydraulic circuit being only described in its main functions and components, the main control valves 58L and 58R are each shown on Figure 3 as a 4 way, three positions proportional directional spool valve which is biased to a neutral center position. The illustrated valves are of the closed center type, but, depending on the exact hydraulic layout, open-centered valves could also be used. Each valve is hydraulically piloted (by the pilot hydraulic circuit as will be explained hereunder) to one or the other of a forward position (where the port 48Lf, 48Rf of the respective motor is connected to the pressure source while the other port 48Lb, 48Rb is connected to the tank - thereby driving the corresponding motor 48L, 48R forwardly) or a backward position (where the port 48Lb, 48Rb of the respective motor is connected to the pressure source while the other port 48Lf, 48Rf is connected to the tank - thereby driving the corresponding motor 48L, 48R backwardly). The F and B arrows shown on Figure 3 indicate in which direction it is necessary to move the spool of the each valve to bring it to the corresponding forward or backward position. Each main control valve 58L 58R has therefore two pilot pressure ports, one 58Lf, 58Rf where the pilot pressure tends to move the spool valve to its forward position and the other R8Lb, 58Rb which tends to move the spool valve to its backward position. The position of each spool valve is proportional to the ratio between the pilot pressures applied on its two pilot pressure ports, and the hydraulic pressure delivered to the motor hydraulic ports is proportional to the position of the spool valve. The pilot hydraulic circuit comprises of course the above described controller 38 which controls a pressure/flow of hydraulic pressure to each one of the pilot pressure ports of the main control valves. The pilot hydraulic circuit has a pressure source which is in fact derived from the main pressure source 50 through a pressure/flow restrictor 60, but it could have it own independent pressure source. The controller 38 is connected to the main control valves in the following manner:

- front left sensor 42a is connected to the forward pilot port 58Rf of the right main valve 58R;

- front right sensor 42b is connected to the forward pilot port 58Lf of the left main valve 58L;

- rear left sensor 42c is connected to the rearward pilot port 58Lb of the left main valve 58L;

- rear right sensor 42d is connected to the rearward pilot port 58Rb of the right main valve 58R. . With the above construction of the power and pilot hydraulic circuits, it is achieved the claimed invention that:

- front left sensor controls forward movement of the right propulsion unit;

- front right sensor controls forward movement of the left propulsion unit;

- rear left sensor controls rearward movement of the left propulsion unit; - rear right sensor controls rearward movement of the right propulsion unit.

With respect to the operator's point of view, the following is achieved by the above described construction: when the operator pushes the control lever forwardly straight, both tracks are controlled forwardly and the machine travels forwardly straight ahead; if he then inclines slightly the control lever to the left or to the right, the speed of respectively the left or the right track will decrease, achieving a corresponding light left or right turn respectively, still traveling forwardly; - when the operator pulls the control lever rearwardly straight, both tracks are controlled rearwardly and the machine travels rearwardly straight; if he then inclines slightly the control lever to the left or to the right, the speed of respectively the right or the left track will decrease in absolute value, causing the machine to rotate on itself towards the left or right; - when the operator displaces the control lever purely transversally to the left or to the right, the two tracks are controlled in reverse directions but with the same absolute speed value, so that the machine turns exactly on itself, achieving a true on-the spot turn, respectively to the left or to the right. Therefore, according to the above, the invention provides for a skid steer machine where the propulsion units are controlled through a single intuitive and user- friendly controller, including the possibility to command true on-the-spot turning of the machine, with a simple and inexpensive hydraulic layout, and especially using a standard off-the-shelf controller.

Claims

1. A skid steer machine having separate left and right hydraulic propulsion units (32, 34) which are independently controlled through a hydraulic control circuit including a pilot circuit comprising a controller (38) having a control member (40), characterized in that said controller comprises at least a front left (42a), a front right (42b), a rear left (42c) and a rear right (42d) pilot sensor which each deliver a corresponding front left, front right, rear left, and rear right pilot signal representative of the movement of said control member in a corresponding direction, and in that each said sensor is connected so that:

- front left sensor (42a) controls a forward movement of the right propulsion unit (34);

- front right sensor (42b) controls a forward movement of the left propulsion unit (32); - rear left sensor (42c) controls a rearward movement of the left propulsion unit (32); and

- rear right sensor (42d) controls a rearward movement of the right propulsion unit (34).

2. A skid steer machine according to claim 1 , characterized in that said hydraulic control circuit further includes left and right main control valves (58L, 58R) to independently control the forward or rearward movement of the left and right hydraulic propulsion units, and in that said pilot sensors (42a-d) of said controller (38) are connected to the left and right main control valves.

3. A skid steer machine according to claim 2, characterized in that the front left (42a) and the front right sensors (42b) are connected respectively to the right (58R) and to the left (58L) main control valves to control the forward movement respectively of the right and of the left hydraulic propulsion units.

4. A skid steer machine according to any preceding claim, characterized in that the pilot sensors (42a-d) deliver a pilot signal proportional to the amount of movement of the control member (40).

5. A skid steer machine according to any preceding claim, characterized in that only two controller pilot sensors (42a-d) can be activated simultaneously.

6. A skid steer machine according to any preceding claim, characterized in that the controller (38) is a joystick type controller with a lever-like control member (40).

7. A skid steer machine according to any of claims 1 to 6, characterized in that the left and right main control valves (58L, 58R) comprise each a proportional directional control valve with a displaceable spool, said spool being movable from a central neutral position in either one of two opposite directions, depending on the relative magnitude of two pilot signals fed to the two opposite sides of the spool.

8. A skid steer machine according to any preceding claim, characterized in that the pilot circuit is hydraulic.

9. A skid steer machine according to claim 8, characterized in that the controller sensors (42a-d) comprise each a proportional valve which delivers a pilot pressure which is representative of the movement of said control member (40) in said corresponding direction.

10. A skid steer machine according to claims 8 or 9 in combination with claim 2, characterized in that the main control valves (58R, 58L) are hydraulically piloted.

11. A skid steer machine according to any of claims 1 to 7, characterized in that the pilot circuit is electric.

12. A skid steer machine according to claim 11 , characterized in that the joystick controller sensors deliver each a pilot electric signal which is representative of the movement of said controller lever in said corresponding direction.

13. A skid steer machine according to claims 11 or 12 in combination with claim 2, characterized in that the main control valves are solenoid valves.

14. A skid steer machine according to any preceding claim, characterized in that the control member (40) is movable through a full circular pattern to control the two hydraulic propulsion units.

15. A skid steer machine according to any preceding claim, characterized in that the left and right movement of the machine comes as a consequence of a difference in the speed of the left and right propulsion units.

16. A skid steer machine according to any preceding claim, characterized in that the machine comprises a cabin (14) for an operator, and in that the controller (38) is mounted in the cabin so that, at least in a work configuration of the cabin, the controller (38) is located so that the front sensors (42a, 42b) on the one hand and the rear sensors (42c, 42d) on the other hand are aligned substantially perpendicularly to a sagittal plane of the operator.

17. A skid steer machine according to any preceding claim, characterized in that the machine comprises a cabin (14) for an operator, and in that the controller (38) is mounted in the cabin so that, at least in a work configuration of the cabin, the controller (38) is located so that the left sensors (42a, 42c) on the one hand and the right sensors (42b, 42d) on the other hand are aligned substantially parallel to the sagittal plane of the operator.

18. A skid steer machine according to claims 16 or 17, characterized in that the cabin (14) is rotatably mounted on an undercarriage which carries the hydraulic propulsion units (32, 34).

19. A skid steer machine according to any preceding claim, characterized in that each propulsion unit (32, 34) drives an endless track member or a series of synchronous wheels.