ROAD MACHINES FIELD OF THE INVENTION

This invention relates generally to an active rollover prevention system for construction and road machinery, and more particularly, to an active rollover prevention system for a compactor with an eccentric vibrator. BACKGROUND TO THE INVENTION

Conventional active rollover prevention systems are adapted for standard automotive vehicles with a rigid single frame, a conventional steering system and a suspension system adapted for a relatively smooth roads.

However these conventional active rollover prevention systems cannot be used on construction and road machines which generally work on rough, unstable and uncompacted soil, which causes a wide margin of error for conventional active rollover prevention systems. Moreover, the operation of some construction and road machines can significantly interfere with the operation of conventional active rollover prevention systems. For instance, in the case of a Compactor with an eccentric vibrator, the eccentric vibrator generates a periodic hammering force which interferes with the angle and acceleration sensors used in conventional active rollover prevention systems.

Construction and road machines are prone to falling over because of their articulation and high centre of gravity, and the results are often fatal for the drivers. Thus, there is an urgent need for an active rollover prevention system for construction and road machinery. SUMMARY OF THE INVENTION

The object of the present invention is to provide an active rollover prevention system for construction and road machinery that will prevent the machinery from falling over. According to the present invention there is provided an active rollover prevention system for construction and road machines, the system comprising: (a) means for sensing the pitch, tilt and articulation angles of the machine; (b) means for sensing the speed of the machine;

(c) means for comparing the pitch, tilt and articulation angles against pre-determined safe operating speed using an information processing unit;

(d) means for reducing the speed of the machine if it exceeds the pre- determined safe operating speed for the pitch, tilt and articulation angles

(e) means for warning the driver of the machine that the machine has exceeded the pre-determined safe operating speed or angle; and

(f) means for re-positioning an attachment of the machine to a safe- operating position if the machine exceeds the pre-determined safe operating speed or angle.

Preferably, inclinometers are the means for sensors used for measuring the pitch and tilt angles.

More preferably, the front section of the machine and the rear section of the machine have separate inclinometers.

It is preferred that the pitch and tilt angle sensor readings are corrected for the effects of dynamic forces on those sensors prior to the readings use in the determination of the safe operating speed.

It is preferred that a positioning sensor is used to measure the articulation angle of the machine.

Preferably, speed sensors are used to measure the velocity of the machine.

More preferably, the front section of the machine and the rear section of the machine have separate speed sensors. Preferably the speed sensors readings are compared with the joystick positioning sensor of the machine prior to the readings use in the determination of the safe operating speed. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a soil compactor, which is an example of a machine on which the present invention may be used.

Fig. 2 is a side view of the soil compactor of Fig. 1 shown pitched at an angle. Fig. 3 is a front perspective view of the soil compactor of Fig. 1 shown tilted at an angle. Fig. 4 is a top perspective view of the soil compactor of Fig. 1 shown articulated at various angles. Fig. 5 is a flow chart showing the operation of the active rollover prevention system for construction and road machinery according to the present invention. Fig. 6 is a graph showing the variation of the eccentric force (eforce) generated by the weight within the eccentric vibrator of the machine of Fig. 1 over one period of time. Fig. 7 is a graph showing the variation of neutral force applied by the surface to the machine of Fig. 1. Fig. 8 is a graph showing the variation of the safe working tilt angle for a machine of Fig. 1 over with time. Fig. 9 is a graph showing the relationship between the radius of turning, the speed and the tilt angle of the machine of Fig. 1 working on positive camber. Fig. 10 is a graph showing the relationship between the radius of turning, the speed and the tilt angle of the machine of Fig. 1 working on negative camber. DETAILED DESCRIPTION OF THE INVENTION

The active rollover prevention system 20 of the present invention can be used on a machine 10 such as a Compactor which is shown in Fig. 1.

The machine 10 is articulated between its rear section 12 and front section 14 which houses a drum 16 comprising a vibrator which generates a periodic hammering force to compact soil or asphalt. The drum 16 has protrusions as illustrated in Figs. 1 , 2 and 4 if compacting soil, or the drum may also be smooth as shown in Fig. 2 to compact asphalt.

The principles described in respect of the present invention may also be adapted and applied to other construction and road machines such as articulated trucks, backhoe loaders, cold planers, feller bunchers, forest machines, forwarders, hydraulic excavators, knuckle-boom loaders, material handlers, motor graders, multi terrain loaders, off-highway tractors, off-highway trucks, paving equipment, pipelayers, road reclaimers, scrapers, skid steer loaders, skidders, telehandlers, track loaders, track-type tractors, underground mining machines, wheel dozers, wheel excavators and wheel loaders.

The data which is monitored by the system 20 includes the velocity υ of the machine 10, the pitch angle α shown in Fig. 2, the tilt angle β (also referred to as the 'oscillation' or 'roll' angle) shown in Fig. 3, and the articulation angle φ shown in Fig. 4.

Particularly in the case of Compactors which have smooth drums (such as the machine 10 shown in Fig. 3), the rollers on the rear section 12 of the machine 10 can spin at a higher velocity (υjon a slippery section of a road, than the velocity of the rollers on the front section 14 of the machine 10 (υ ₂ ) , or vice versa. The average velocity (υ _a )of U ₁ and υ ₂ may be used in calculations.

The x-axis forces which act on the machine 10 include the radial force generated by the acceleration around the turning circle of the machine 10, less the neutral force in the direction vertical to the area on which the machine 10 contacts the ground, less the sine component of the tilt angle of the force generator by the eccentric vibrator, and plus (if the machine 10 is sliding down the hill) or minus (if the machine 10 is sliding up the hill) the cosine component of the tilt angle for the static force of the friction generated between the machine 10 and the ground. This is shown in the equation below:

∑ ^F * = M-^- - N sin β - mrco ² sin(ωt)sin β T f cos β

The y-axis forces which act on the machine 10 are the cosine component of the pitch angle of the force of the acceleration on the machine 10, plus the neutral force in the direction vertical to the area on which the machine 10 contacts the ground, plus the cosine component of the pitch angle of the force generator by the eccentric vibrator, and plus (if the machine 10 is sliding down the hill) or minus (if the machine 10 is sliding up the hill) the sine component of the tilt angle for the static force of the friction generated between the machine 10 and the ground. This is shown in the equation beiow:

]T F _y = -Mg cos α + N cosβ + mrω ² sin(ωt)cos β + f _μ sin β

In respect of the equation for ∑ F _x and ∑ F _y :

• M = the mass of the machine 10 (in kilograms); • m = the mass of the weight inside of the eccentric vibrator 16;

• r = the radius of the eccentric vibrator 16;

• υ _a = the average velocity of the rear section 12 and the front section 14 of the machine 10;

• N = the neutral force in the direction vertical to the area on which the machine 10 contacts the ground;

• R = the radius of the spiral of the machine 10 when it rolls;

• ω = the vibrator frequency of the eccentric vibrator (in radians per second);

• f _μ = static friction force of the machine 10 on the ground; • t = time (in seconds);

• β = the tilt angle of the machine 10; and

• α = the pitch angle of the machine 10.

The first component of the lateral force F _x is M^- which is the radial force on the machine 10 when turning in a circle of radius R (in metres), which is equal to the mass of the machine 10 multiplied by its radial acceleration, and is denoted with the symbol "c" (for reasons which will become clear below) having the following equation:

C = M -^ R

The second component of the lateral force F _x on the machine 10, IM sin β , is the neutral force on the ground of the machine 10, in a direction vertical to the ground.

The third component of the lateral force F _x , mrω ² sin(ωt) , is the eccentric vibrator force (denoted "eforce(t)"), which is equal to the mass (in kilograms) of the machine 10, multiplied by the radius (in metres) of the weight within the eccentric vibrator, multiplied by the square of the angular frequency (in Hertz) of the weight within the eccentric vibrator, multiplied by the sinusoidal variation of the angular frequency ω (in radians per second) of the weight within eccentric vibrator, with time (in seconds).

The variation of the eccentric vibrator force on the machine 10, eforce, (which is measured in Newtons) over 0.015 seconds (which is equal to one period) is shown in Fig. 6, and indicates that the eccentric vibrator generates a cyclical positive, then a negative force on the machine 10. The last component of the lateral force F _x , f _μ cos β , is the static friction force of the machine 10 on the ground.

The radial force and eccentric vibrator force are used in the calculation of the neutral force from the ground to the machine 10, denoted by "N", which is given by the equation:

Where: • μ _s = the friction coefficient of the surface that the machine 10 is running on;

• c = the radial force (in Newtons);

• G = force of gravity, 9.8 metres per square second;

The variation of the eccentric force (generated by the weight within the eccentric vibrator 16 on the machine 10) with time is shown in Fig. 6, over one period.

The system 20 of the present invention is shown in the flowchart of Fig. 2.

Before feeding data to the main program 4, the data is validated (i.e. corrected for errors) using sub-programs 1 , 2 and 3.

Referring to the sub-program 1 on Fig. 5, at least one tilt sensor (also known as an 'inclination' sensor') must be used to measure the measure the tilt angle of the machine 10. However, the centrifugal force and the sliding effect of the machine 10 may create an error within the tilt sensor. In order to find the real value of the tilt angle of the surface on which the machine 10 is running, a correction must be applied to the initial reading from the tilt sensor (B) using the formula (within sub-program 1 ) shown below:

β = β _read i _n g ± Δβ = β _readlng ± arctar| ³ _{R g} j

Where:

_• β = the tilt angle of the ground on which the machine 10 is running;

_• υ _a = the average velocity of the rear section 12 and front section 14 of the machine 10 (in metres per second); • R = radius of articulation or 'turning circle' of the machine 10 (in metres);

• B = the acceleration as measured by the tilt sensor (in metres per square second); and • g = the rate of gravity, which is 9.8 metres per square second.

The plus or minus of the Δβ depends on whether the road on which the machine 10 is travelling has a positive or negative camber.

Some roads are not flat, but are sloped at an angle. If the road is sloping towards the direction in which the machine 10 is turning, then the road has a 'positive' camber. If the road is sloping away from the direction in which the machine 10 is turning, then the road has a 'negative' camber.

Sensors on the machine 10 read the tilt angle and the articulation angle of the machine 10, and then the main program 4 (shown in Fig. 5) uses these readings to determine whether the road has a positive or negative camber. 'T ' is the tilt angle that the machine 10 can at work without rolling, based on the friction force of the machine 10 on the road. If the friction force on the machine 10 is zero, then T is also zero. It is given by the equation: Where

• μ ₅ = the static friction coefficient of the surface that the machine 10 is running on.

If the road has a positive camber, then the upper tilt angle limit P ₁ at which the machine 10 can operate is given by:

If the road has a positive camber, then the lower tilt angle limit p ₂ at which the machine 10 can operate is given by: P ₂ = P _o - T If the road has a negative camber, then the upper tilt angle limit β ₃ at which the machine 10 can operate is given by: β ₃ = -β _θ + T

If the road has a negative camber, then there will be no lower tilt angle limit.

Where β ₀ is the tilt angle as a result of the centrifugal force applied to the machine 10 by the sloping surface on which it is running, and is given by the equation:

Where:

• υ _a = the average velocity of the machine 10 (in metres per second);

• R = radius of articulation or turning circle of the machine 10 (in metres); and • g = the rate of gravity, which is 9.8 metres per square second.

Fig. 9 shows the variation of the upper tilt angle limit β _x as a result of the addition of tilt angle β ₀ (from the centrifugal force applied to the machine 10), and the tilt angle T (as a result of the friction force), over 0.015 seconds (i.e. one period). The tilt angle depends on the radius of the turning circle (R) of the machine 10 in metres, the speed at which the machine 10 is travelling ( υ ) in metres per second, and the time (t) in seconds. That is, β(R, υ, t), which is depicted in Fig. 9, where time and the radius of the turning circle are held constant in order to depict the variation of ^ ₁ in two dimensions. Fig. 9 shows that the upper tilt angle limit P ₁ at which the machine 10 can operate before rolling, when travelling on a road with positive camber, decreases as the speed ( υ) of the machine 10 is increases. Likewise, Fig. 10 shows that the upper tilt angle limit p ₃ (t) at which the machine 10 can operate before rolling, when travelling on a road with negative camber, also decreases as the speed of the machine 10 increases.

Referring to the sub-program 2 on Fig. 5, sensors measure the articulation angle φ (refer to Fig. 3) between the rear section 12 and front section 14 of the machine 10.

An articulation sensor reads the angle φ of the machine 10, however in order check that the articulation sensor is reading correctly, the system 20 checks to see if the oil pressure switch is on, which indicates that the steering is in use, and thereby that the machine 10 is articulated.

Speed sensors read the velocity on rear section 12 and the front section 14 of the machine 10. Likewise the position of the joystick of the hydrostatic drive, determines the driving speed of the machine 10.

Firstly, sub-program 3 (on Fig. 5) compares the velocity readings from the speed sensor, with the driving speed from the joystick of the machine 10, to ensure that the sensors are working accurately.

Secondly, sub-program 3 compares the speed of the roller on the rear section 12 with the speed of the roller of front section 14 of the machine 10, and if the speed of the roller on the rear section 12 is less than one quarter of the speed of the roller of front section 14 (or vice versa), then this indicates that one of the speed sensors is not giving accurate readings.

The absolute value of the readings of the front speed sensor and the rear speed sensor, should be less than halve of the average velocity, otherwise an error 3 occurs:

When error 3 occurs driver of the machine 10 will be alerted, and velocity signals will not be sent to the main program 4. The pitch sensor will provide inaccurate readings when the machine 10 is accelerating or decelerating, or going uphill or downhill. Micro-switches within the joystick of the hydrostatic drive detect whether the machine 10 is moving forward and in reverse. The change in velocity over time will determine whether the machine 10 is accelerating or decelerating.

Thirdly, sub-program 3 corrects the pitch sensor readings using the following equation:

α Where:

• υ = the first differential of the average velocity (or acceleration); and

• g = the rate of gravity, which is 9.8 metres per square second.

The main program 4 then compares the velocity sensor readings V ₁ and υ ₂ to see if they are greater than the critical lateral sliding velocity υ _c at which the machine 10 is likely to roll.

If the velocity sensor readings for D ₁ and υ ₂ are greater than the critical lateral sliding velocity υ _c , then the data is transferred to the controller 5.

If U ₁ and υ ₂ have reached the critical velocity, then the controller 5 sends a signal for the machine 10 to be put in drive limp mode 9, in which the machine 10 slows to down to a crawl.

If O ₁ and υ ₂ reach the danger velocity, then the controller 5 sends:

• a warning signal 6 to the driver of the machine 10,

• a signal to the drive control unit 7 to reduce the speed of the machine 10, • a signal to the attachment control unit 8 to turn the attachment off,

For instance, in the case of the compactor, the attachment is the eccentric vibrator, and in the case of a loader the attachment is the bucket. If the height of the bucket is reduced the centre of gravity of the machine 10 is also reduced, which in turn reduces the chance of a rollover. If O ₁ and υ ₂ reach the danger velocity and the driver sharply turns the steering of the machine 10, then the drive limp mode 9 will automatically come into effect.