AU3819102A - Cable reel control system - Google Patents

Description

II

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for Service: Invention Title: Details of Basic Application(s): WILLIAM ROBERT IFIELD WILLIAM ROBERT IFIELD HODGKINSON OLD McINNES Patent Trade Mark Attorneys Levels 3 and 4, 20 Alfred Street MILSONS POINT NSW 2061 CABLE REEL CONTROL SYSTEM Australian Patent Appln No. PR4943 Filed 11 May 2001 The following statement is a full description of this invention, including the best method of performing it known to me:

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2 2824C CABLE REEL CONTROL SYSTEM TECHNICAL FIELD The present invention relates to a control system for use in relation to electric powered mobile vehicles having trailing cables as, for example, are utilized for coal mining shuttle cars.

Although the invention shall be principally described with reference to coal mining shuttle cars it should be appreciated that the invention is not limited to such application.

BACKGROUND

For many years, electrically powered vehicles have been utilized which require cables for the supply of electrical power. To avoid cables being fouled in the wheels of the vehicle, or otherwise causing obstruction, such vehicles are often provided with cable reels. These reels pay out cable as the vehicle moves away from the anchor point for the cable, and reel in the cable as the vehicle moves towards the anchor point for the cable. Such electrically powered vehicles are used extensively in underground coal mining particularly as shuttle cars that carry coal from the cutting face to a conveyor system.

Cable reels, for these vehicles, are typically driven by a fixed displacement hydraulic unit having an output torque proportional to pressure differential. This hydraulic unit is generally connected to the reel via a chain sprocket drive and acts as a motor for the reel in mode and as a pump for the pay out mode with an electric driven pump maintaining the system at a constant pressure.

However, a constant pressure does not produce a constant cable tension since there are frictional losses associated with the system and the effective radius of the reel is continually changing according to whether there is a lot of cable wound on the reel or whether the reel is nearly empty.

The frictional losses in the drive mechanism have a different effect on the cable tension depending on whether the cable is in 'pay out' or 'reel in' mode. In the 'pay out' mode the cable tension is proportional to the theoretical torque of the hydraulic unit, acting as a pump, plus its frictional losses and plus the frictional-losses of the total drive mechanism P Q I' 4 3 2824C so as to give a high cable tension. When in the 'reel in' mode the cable tension is proportional to the theoretical torque of the hydraulic unit, acting as a motor, less its frictional losses and less the frictional losses of the total drive mechanism so as to give a low cable tension.

The net effect of the differences in tension occasioned by switching from the 'reel in' mode to the 'pay out' mode in addition to diameter changes occasioned by the amount of cable wound onto the reel result in variances in cable tension of up to four times or more.

Thus, if the recommended tension for the cable is applied during the 'pay out' mode with a near empty reel, the tension is quite low during the 'reel in' mode with a full reel and a slack cable can result particularly as the vehicle accelerates. This acceleration may be due to normal vehicle acceleration or may be due to bumps in the road but in any case a slack cable may lead to the formation of loops in the cable or to the cable over-wrapping on the reel.

The formation of loops or over-wrapping during the reel in mode will frequently cause a failure of the cable during the pay out mode and it is common for a cable failure to occur on average once for every five thousand tonnes of coal produced. It is also the case that seventy-five percent of all cases of arcing in hazardous zones relate to failures of shuttle car cables.

In the past, as described in US 4,114,827 (Maier), apparatus has been installed to sense whether the reel is in pay out or reel in mode by an arrangement of valves sensing the direction of flow in the high- pressure line to the hydraulic motor. Such sensors then have been used to actuate a switching device to set the hydraulic pressure to the hydraulic drive unit to a relatively low pressure when the cable is being reeled out and to a relatively high pressure when the cable is being reeled in. In such a manner a more constant cable tension is achieved as frictional drive line losses which add to the tension when paying out and subtract from the tension when reeling in can be the subject of compensation by the variance in pressure to the hydraulic drive unit.

Such systems however, are unsatisfactory because the hydraulic unit acting as a pump during the 'pay out' mode must, in most cases, first generate high pressure to cause the switch to low pressure so that high tension occurs as a transient condition. The maximum 2824C reel-in tension is thus limited to avoid an excess tension under this transient condition. In other cases, where the switch is biased to the lower pressure, the sensor must be insensitive to small flows in the high- pressure line to allow for internal leakage at the hydraulic unit.

However, leakage at the hydraulic unit may vary with rotational position and with temperature and the flow that must be permitted to allow for this variation is high.

Significant travel by the vehicle may then occur at low cable tension before the switch to high pressure occurs with untidy and unsafe cable wrapping as result.

Such systems are also unsatisfactory because they tend to be unstable and alternate between the two pressure settings while the vehicle is stationary to produce a 'whip' in the cable and thus a hazard to personnel. This 'whip' is frequently initiated when brakes are applied during the pay out mode where the inertia of the reel causes pay out to continue after the vehicle is stopped.

It is accordingly an object of the present invention to ameliorate one or more of the abovementioned disadvantages with existing cable reeling equipment or at least to provide the market with an alternative.

SUMMARY OF INVENTION According to a first aspect the present invention consists in a control system for winding and unwinding a power supply cable stored on a reel of an electrically powered vehicle, said system comprising within a hydraulic circuit, a hydraulic drive unit coupled to said reel for activating the latter, a hydraulic pump for providing pressurized fluid to activate said hydraulic drive unit, a reservoir for storing fluid, and valve means for controlling the application of pressurized fluid from said pump to said hydraulic drive unit between a low torque mode and a high torque mode, said low torque mode being applied when said vehicle is stationary or said reel is paying out said cable and said high torque mode is applied when said reel is reeling in said cable, said valve means comprising a mode-sense valve to sense whether said system is being switched from a low torque mode to a high torque mode, characterised in that said mode-sense valve senses the pressure drop which occurs in the low pressure return line from the hydraulic drive unit to the reservoir.

2824C Preferably the mode sense valve senses the pressure drop across a "near zero" tolerance flow sensing mechanism located in the low pressure return line.

Preferably the mode sense valve senses the pressure drop across a pair of check valves located in said low pressure return line.

Preferably said electrically powered vehicle is provided with at least one hydraulic brake, and the activation of said brake by pressurised fluid overrides the pressure drop in the low pressure return line sensed by the mode-sense valve.

Preferably said hydraulic brake is a park brake.

Preferably said hydraulic brake is a service brake.

According to a second aspect the present invention consists in a cable reeling system for an electrically powered mobile vehicle wherein there are two torque modes for the hydraulic drive unit to the reel. A low torque is applied while the vehicle is stationary and during the pay-out mode and the switch to high torque occurs immediately when reel-in commences.

This is achieved by actuating a switch from a near zero tolerance flow sensing mechanism in the low-pressure line to the hydraulic unit. By switching to high torque rather than switching to low torque, the excess transient tension during pay-out is avoided and the reel-in tension is then limited only by the tension that arises during the reel in mode. The reel in tension may vary with drum diameter or may be held near constant by a radius compensating system. The change in torque may be achieved through the switch changing the pressure from low to high or by the switch reducing the displacement of a variable displacement motor.

Preferably, the signals from the flow sensing mechanism to the switch are overridden by signals from the park and service brakes to nullify the effects of the small internal leakage from the hydraulic unit and to ensure stability. The override from the service brakes also inhibits excess tension while braking during the reel-in process, particularly with a full reel where the inertia effects are highest.

2824C BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described with reference to the accompanying drawings.

Figure 1 is a schematic of the hydraulic circuit of the control system according to a first embodiment of the invention.

Figure 2 is a schematic of the hydraulic circuit of the control system according to a second embodiment of the invention.

A MODE OF CARRYING OUT INVENTION With reference to figure 1, there is disclosed a schematic representation of a first embodiment of a hydraulic control system associated with a cable reeling system for winding and unwinding a power supply cable stored on a reel of a mobile electrically powered vehicle in accordance with the present invention. It shows the principal components of such a system comprising within a hydraulic circuit, a hydraulic pump 1, a cable reel hydraulic drive unit (motor) 2 and a hydraulic reservoir 3 linked via hydraulic passageways and various valves. Check valves 5 and 6 are situated in the low pressure line to the hydraulic drive unit 2, to achieve switching from a low pressure (torque) to a high pressure (torque) when the cable reel hydraulic drive unit 2 changes from a "pay out" mode or stationary mode to the "reel in" mode.

According to the embodiment of figure 1, the mode-sense valve 4 senses whether the system is stationary, "paying out" or "reeling in" by sensing the pressure drop across check valves 5 and 6.

Relief valve 7 is set by pilot valve 8 to a low pressure while the vehicle is stationary with no flow through either check valve 5 or 6, and during the "pay out" mode when the pressure drop through check valve 6 assists the spring in valve 4. While the vehicle is moving towards the cable anchor in a "reel-in" mode, flow through check valve 5 is sensed by mode-sense valve 4 and relief valve 7 is then set by pilot valve 9 to a high pressure "reel in" setting. Valve 9 may be varied by some means to compensate for variation in effective cable reel diameter.

2824C Actuation of the service brake 16 of the vehicle applies pressure to valve 4 via check valve 11 assisting the spring load and ensures that relief valve 7 is set to the lower setting as set by pilot valve 8. Actuation of the park brake 17 dumps the pilot line via check valve opposing the spring in valve 4 and also ensures that the relief valve 7 is set to the lower setting as set by valve 8. When the park brake 17 is applied and the pilot line is dumped, valve 12 moves to a restricted flow condition and this provides a control of reel speed that is beneficial on start-up to minimize or eliminate cable whip and is also beneficial when first loading the cable onto the reel.

The connection to the brakes via check valves 10 and 11 is important to override the flow sensing by the check valves 5 and 6 during two situations. To override the effects, including instability, of any leakage that may occur through the hydraulic drive unit 2 while the vehicle is stationary, and to avoid excess cable tension that may otherwise occur due to the inertia of the reel while braking during the "reel in" process.

Figure 2 shows an alternative embodiment where the system pressure is controlled via a pressure-reducing valve 20 in place of the relief valve 7. This embodiment is useful in providing means to dump pump 1 by using a check valve 13 and sequence valve 14 during the pay-out mode.

Claims (7)

1. A control system for winding and unwinding a power supply cable stored on a reel of an electrically powered vehicle, said system comprising within a hydraulic circuit, a hydraulic drive unit coupled to said reel for activating the latter, a hydraulic pump for providing pressurized fluid to activate said hydraulic drive unit, a reservoir for storing fluid, and valve means for controlling the application of pressurized fluid from said pump to said hydraulic drive unit between a low torque mode and a high torque mode, said low torque mode being applied when said vehicle is stationary or said reel is paying out said cable and said high torque mode is applied when said reel is reeling in said cable, said valve means comprising a mode-sense valve to sense whether said system is being switched from a low torque mode to a high torque mode, characterised in that said mode- sense valve senses the pressure drop which occurs in the low pressure return line from the hydraulic drive unit to the reservoir.

2. A control system as claimed in claim 1 wherein the mode-sense valve senses the pressure drop across a "near zero" tolerance flow sensing mechanism located in the low pressure return line.

3. A control system as claimed in claim 1 wherein the mode-sense valve senses the pressure drop across a pair of check valves located in said low pressure return line.

4. A control system as claimed in claim 1 wherein said electrically powered vehicle is provided with at least one hydraulic brake, and the activation of said brake by pressurised fluid overrides the pressure drop in the low pressure return line sensed by the mode-sense valve.

A control system as claimed in claim 4 wherein said hydraulic brake is a park brake.

6. A control system as claimed in claim 4 wherein said hydraulic brake is a service brake. 9 2824C

7. A control system as claimed in claim 5, wherein a flow restriction valve is located between said hydraulic pump and said hydraulic drive unit, and said flow restriction valve moves to a restricted flow mode when said park brake is actuated. Dated this 3 rd day of May 2002 WILLIAM ROBERT IFELD BY: HODGKINSON OLD McINNES Patent Attorneys for the Applicant