TECHNICAL FIELD

The present invention relates to a snow groomer for grooming ski slopes.

More specifically, the present invention relates to a snow groomer comprising a frame; at least one attachment connected movably to the frame; at least one hydraulic assembly comprising at least one actuator for positioning the attachment with respect to the frame, and at least one valve for controlling the actuator; and a pump for supplying the hydraulic assembly.

BACKGROUND ART

The snow groomer normally comprises a hydraulic control device connected to the pump; lines connecting the pump to the attachment hydraulic assembly; and an internal combustion engine connected to and for driving the pump.

In actual use, the pump is controlled by the hydraulic control device as follows.

When the hydraulic assembly actuator is idle, the valve is closed and the pump is controlled by the hydraulic control device so that the pressure in the lines equals a standby pressure.

When the hydraulic assembly actuator is active, the valve is open and the pressure in the lines falls below the standby pressure. When pressure falls below standby pressure, the hydraulic control device acts on the pump to deliver the maximum possible flow rate, which varies depending on the operating conditions, in particular the speed, of the internal combustion engine.

In other words, the instant the actuator is operated, the pump delivers the maximum flow rate, even if the actuator does not need it; in which case, the valve delivers the necessary flow rate to the actuator, and the difference between the maximum flow rate from the pump and the necessary flow rate is drained into a holding tank.

One drawback of the known art lies in the pump delivering the maximum flow rate, even if the actual flow rate demanded by the actuator is lower.

Another drawback of the known art lies in unnecessary operation of the pump, which consists in the valves draining surplus flow into the holding tank, and which subtracts energy from other groomer user devices .

Both drawbacks are compounded by the pump being designed to feed a plurality of hydraulic assemblies, and by each hydraulic assembly possibly comprising more than one valve .

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a snow groomer designed to eliminate the drawbacks of the known art . Another object of the present invention is to provide a snow groomer designed to reduce energy- consumption.

Another object of the present invention is to reduce the degree of unnecessary operation, i.e. reduce the amount of flow drained into the holding tank.

According to the present invention, there is provided a snow groomer comprising a frame; at least one attachment connected movably to the frame; at least one hydraulic assembly comprising at least one actuator for positioning the attachment with respect to the frame, and at least one valve for controlling the actuator; a variable-flow pump for supplying the hydraulic assembly; and a control system for calculating a total flow rate demand of the hydraulic assembly, and controlling the variable- flow pump as a function of the total flow rate demand, so delivery of the variable-flow pump preferably equals the total flow rate demand.

According to the present invention, the variable- flow pump is able to deliver a total flow rate that takes into account total flow rate demand, and so reduce energy consumption of the groomer.

Another object of the present invention is to provide a method of controlling a snow groomer, designed to eliminate the drawbacks of the known art.

According to the present invention, there is provided a method of controlling a snow groomer, comprising the steps of:

- positioning at least one attachment, connected movably to a frame of the snow groomer, by means of a hydraulic assembly comprising at least one actuator for positioning the attachment, and at least one valve for controlling the actuator;

- supplying the hydraulic assembly by means of a variable- flow pump;

calculating a total flow rate demand of the hydraulic assembly; and

- controlling the variable-flow pump as a function of the total flow rate demand, preferably so that delivery of the variable-flow pump equals the total flow rate demand .

BRIEF DESCRIPTION OF THE DRAWINGS

A non- limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which :

Figure 1 shows a top plan view, with parts removed for clarity, of a snow groomer in accordance with the present invention;

Figure 2 shows a schematic view, with parts removed for clarity, of a detail of the Figure 1 snow groomer.

BEST MODE FOR CARRYING OUT THE INVENTION

Number 1 in Figure 1 indicates as a whole a snow groomer for grooming ski slopes, and which comprises a frame 2; an internal combustion engine 3; two independent tracks 4 and 5; two drive wheels 6 and 7 connected to respective tracks 4 and 5; a plurality of attachments 8; a hydraulic drive 9 for powering drive wheel 6; a hydraulic drive 10 for powering drive wheel 7; a hydraulic drive 11 for powering a component 12; and a hydraulic drive 13 for positioning attachments 8.

In the example shown, attachments 8 comprise a shovel connected movably to frame 2; a tiller also connected movably to frame 2; and possibly a winch (not shown) connected movably to frame 2. Each of the accessories 8 described can assume a plurality of positions with respect to frame 2, and which are controlled by hydraulic drive 13. The tiller is equipped with the component 12 - in the example shown, a rotary shaft - which is driven directly by dedicated hydraulic drive 11.

With reference to Figure 2, hydraulic drive 13 comprises a variable-flow pump 14; a hydraulic assembly 15; a tank 16; a pressure sensor 17; a control valve 18; a delivery branch 19; and a return branch 20.

Snow groomer 1 also comprises a control system 21 for controlling hydraulic drive 13.

Variable- flow pump 14 is powered by internal combustion engine 3 via a drive shaft 22, is designed to deliver a maximum flow rate as a function of the speed of internal combustion engine 3, and comprises a regulating device 23 for adjusting delivery between a minimum and maximum flow rate, regardless of the speed of internal combustion engine 3. For example, variable- flow pump 14 is a variable-eccentricity vane pump, in which regulating device 23 adjusts the eccentricity of the vanes as a function of a regulating signal from control system 21.

Hydraulic assembly 15 in Figure 2 is associated with only one attachment 8, e.g. the shovel, and comprises, for example, four actuators 24 - in the example shown, double-acting hydraulic cylinders - for positioning attachment 8; and four valves 25 - in the example shown, four-way, three-position slide valves - for controlling actuators 24.

Each valve 25 is associated with a respective actuator 24, and comprises a servocontrol 26, and a block 27 for controlling valve 25 and servocontrol 26. Block 27 of valve 25 is designed to determine the flow rate between valve 25 and respective actuator 24, and to control valve 25 by means of servocontrol 26.

Pressure sensor 17 monitors the difference in pressure between delivery branch 19 and return branch 20, and controls control valve 18 to drain fluid into tank 16 when the pressure difference exceeds a given threshold value. This is a precautionary measure to prevent a dangerous build-up in pressure along delivery branch 19.

Control system 21 comprises a control unit 28; a control member 29, normally a joystick; a selector 30; and a speed sensor 31.

Control unit 28 is connected to internal combustion engine 3 to acquire the speed of internal combustion engine 3; and to blocks 27 of valves 25 to sense the flow rates from valves 25 to actuators 24 and to control servocontrols 26.

Functionally, in fact, blocks 27, though integrated in respective valves 25, also form an integral part of control system 21.

In an embodiment not shown in the drawings, each hydraulic assembly comprises only one actuator and one valve .

In actual use, control system 21 controls operation of snow groomer 1, as regards use of attachments 8, to optimize energy consumption of groomer 1. More specifically, control system 21 controls positioning of attachments 8 with respect to frame 2; calculates a total flow rate demand of hydraulic assemblies 15; and controls delivery from variable- flow pump 14 accordingly. In a preferred embodiment of the present invention, control system 21 controls variable-flow pump 14 so that the delivery from variable-flow pump 14 substantially, and in fact, equals total flow rate demand .

Control system 21 determines the flow rates between valves 25 and actuators 24 by means of blocks 27; and, by means of control unit 28, accordingly calculates the total flow rate demand of hydraulic assemblies 15.

Attachments 8 are operator-controlled using control member 29, which supplies control unit 28 with a control signal related to, in fact indicating, the desired flow rates between valves 25 and actuators 24; and control unit 28 calculates the total flow rate demand of hydraulic assemblies 15 as a function of the control signals related to the desired flow rates.

Control member 29 in the example shown is a joystick, which can assume a plurality of operating positions within a given range; and the control signal indicating the desired flow rates between valves 25 and actuators 24 depends on the operating position of control member 29. In other words, control member 29 regulates the desired flow rates and, therefore, the operating speed of actuators 24 within a given operating speed range .

In other words, control system 21 acquires the sensed and desired flow rates at a given instant; and immediately determines the total flow rate demand accordingly, to carry out the operator-requested operations .

In a variation not shown of the present invention, the control unit calculates total flow rate demand on the basis of the desired flow rates only, and more specifically as substantially the sum of the desired flow rates.

In another variation not shown of the present invention, the control unit calculates total flow rate demand on the basis of the sensed flow rates only, and more specifically as substantially the sum of the sensed flow rates.

At least one of the operating speed range limits can be adjusted by the operator using selector 30, which, in a preferred embodiment, reduces total flow rate demand by a given percentage. That is, selector 30 reduces each desired flow rate so that the reduction is not made at the expense of the actuator 24 with the higher resistive load. For example, each desired flow rate is reduced by the same percentage .

In a preferred embodiment of the present invention, total flow rate demand varies with the travelling speed of snow groomer 1. In the example shown, total flow rate demand increases alongside an increase in travelling speed, so that the operating speed of the attachments is related to travelling speed. Operation-wise, control system 21 senses the travelling speed of snow groomer 1, and recalculates the total flow rate demand of hydraulic assembly 15, e.g. recalculates the desired flow rates, accordingly .

Variable-flow pump 14 is actually characterized by a maximum delivery, which depends on its construction and dimensional characteristics and its operating speed. In the example shown, the operating speed of variable- flow pump 14 is related to the speed of internal combustion engine 3.

Control unit 28 acquires the operating speed of variable- flow pump 14 to determine its maximum delivery.

Control unit 28 compares the total flow rate demand with the maximum delivery, and, if total flow rate demand exceeds maximum delivery, recalculates total flow rate demand to equal maximum delivery, by reducing the desired flow rate of each actuator 24 so that the reduction is not made at the expense of the actuator 24 with the higher resistive load. For example, each desired flow rate is reduced by the same percentage.

In an alternative embodiment, not shown, of the present invention, the control member is connected directly to the valves, as opposed to the control unit, and acts directly on the valves to regulate the desired flow rate. The control unit senses the delivery from the valves, and calculates total flow rate demand accordingly. More specifically, total flow rate demand is substantially equal to the total sensed delivery, and may be recalculated on the basis of the travelling speed of the groomer, the operator selector settings, and the maximum delivery of the variable-flow pump, as in the previous embodiment .

Accordingly, variable- flow pump 14 can be regulated in three ways : - by closed-loop control as a function of sensed flow rates only; that is, the control system acquires the sensed flow rates, calculates a total flow rate demand substantially equal to the sum of the sensed flow rates, and acts on the variable-flow pump to deliver the calculated total flow rate demand;

- by open-loop control as a function of desired flow rates only; that is, the control system acquires the desired flow rates, calculates a total flow rate demand substantially equal to the sum of the desired flow rates, and acts on the variable-flow pump to deliver the calculated total flow rate demand; and

- by closed- loop control as a function of sensed flow rates and desired flow rates; that is, control system 21 acquires the sensed and desired flow rates, compares them, determines total flow rate demand from the comparison, and acts on variable-flow pump 14 to deliver the total flow rate demand.

The present invention obviously also extends to embodiments not described in the above detailed description, and to equivalent embodiments within the protective scope of the accompanying Claims .