EP2580152A1 - Method for determining the probability of a handling truck's tipping over - Google Patents

Abstract

The invention relates to a method for determining the probability of a handling truck's (1) tipping over, said handling truck comprising at least three wheels, the normal force (F_ZVL, F_ZHL) acting in the z direction being determined for at least two wheels in each case, at least two normal forces (F_ZVL, F_ZHL) being compared and the probability of the handling truck's (1) tipping over being determined on the basis of the comparison result.

Description

 Method for determining a probability of tipping on an industrial truck

description

The present invention relates to a method for determining a probability of tipping in an industrial truck, such as a forklift.

State of the art

Forklift trucks (so-called FLT, English: fork-lift truck) from different manufacturers are constructed very similar in terms of the chassis. Predominant are a front-axle drive with a front axle fixed to the body, a rear axle steering with a pendulum axle and an almost complete absence of a suspension (only the tire has elastic properties). The steering is usually carried out as a hydrostatic steering, i. The steering wheel angle is transmitted to the wheel steering angle via hydraulic connecting elements. The lift mast with the fork is mounted in front of the front axle, the driver sits between the axles. The drive of the FLT generates not only the driving torque but also the braking torque via the drive train. A service brake, which acts on all four wheels, is usually not provided.

FLTs are very compact, i. narrow and short, built, very agile and can lift large loads very high. This may result in load bearing, driving and especially on sloping roads possibly high risk of tipping over because of the loads on the fork, the overall center of gravity of the FLTs is greatly shifted and the static and dynamic tipping stability of the FLT u.U. very much reduced, which is not always predictable for the driver.

In the context of this invention, the following terms and definitions are used: l The x-axis points in the direction of travel, the y-axis perpendicular to the right along the front axis. The z-axis is perpendicular to the xy plane and points downwards (legal system). The rotation about the x-axis (longitudinal axis) is referred to as rolling, the rotation about the y-axis (transverse axis) as pitching, and the rotation about the z-axis (yaw axis) as yawing.

DE 103 04 658 A1, to which reference is expressly made for details regarding the stability model underlying a forklift, discloses a device for controlling the driving stability of a forklift and a method for controlling a forklift. Sensors are used to record the load, the inclination of the mast and the lifting frame, the lifting height of the load, the tipping forces acting on the mast and the accelerations acting on the vehicle in the longitudinal and transverse directions and compared with specified limit values. These limit values, which are dependent on the driving state, can not be arbitrarily exceeded by the driver, so that the vehicle generally remains stable regardless of the driving state (cornering, straight ahead, downhill, etc.).

It is desirable to provide an improved method for determining a probability of tilting in order then to be able to react more quickly, if necessary, in order to prevent tilting.

Disclosure of the invention

According to the invention, a method for determining a probability of tipping over of a truck with the features of patent claim 1 is proposed. advantageous

Embodiments are the subject of the dependent claims and the following description.

Advantages of the invention

The invention can purposefully improve the determination of the danger of tipping on industrial trucks by performing a tipping evaluation defined on an axle-specific and / or side-by-side basis. In this case, the normal forces acting on the wheels are compared, wherein based on the normal forces preferably roll and pitch probabilities as tilting probabilities be determined. The determination is based in particular on the forces in the z-direction (normal forces), in a four-wheel device, for example on FZVR. FZVL (normal force front right or left) and F _ZH R, F _zhl (normal force rear right or left). In the dependent claims, inter alia, preferred equations are given to determine certain roll and pitch probabilities. These equations are characterized by their particularly simple shape and still lead to very useful tipping ratings.

In a further preferred embodiment, a counteracting tiltering operation is automatically performed in response to the certain probability of tilting. Expediently, setpoint accelerations in the x and y direction of the industrial truck are determined in order to reduce or eliminate the danger of tipping over. Thus, the reliability can be significantly increased. Damage to man and / or machine can be avoided. In an embodiment, limit values for the lift mast drive to prevent inadmissible fork heights and lift mast inclinations can be specified. As an intervention, the driving speed can also be limited.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings. It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention. The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing.

FIG. 1 shows a schematic representation of a counterweight forklift in a side view.

FIG. 2 shows an exemplary control circuit according to a preferred embodiment of the invention. Figure 3 shows schematically the flow of a preferred embodiment of the invention. Although the invention will be explained below with reference to a counterbalance truck, this is purely exemplary. It should be emphasized that the described models are also applicable to other industrial trucks in order to realize the invention.

FIG. 1 shows a counterweight forklift 1 (hereinafter FLT) with a driver's cab 2, a chassis with a front axle 4, a steerable rear axle 6, for example a pendulum axle, and a counterweight 8 arranged in the region of the rear axle 6, schematically from the side. O.E. Let us assume in the following that the origin of the coordinates lies in the center of the front axis, the resulting coordinate axes x, y and z being shown in FIG.

At the front of the FLT a mast 10 is mounted with a tiltable about a tilt axis 12 mast 14. The adjustment of the angle of inclination a of the mast 14 via a tilting device with, for example, two tilting cylinders 16 which are hinged to the vehicle frame and the mast 14. On the frame-shaped mast a fork 17 is slidably guided, wherein the lifting height h _G by means of a schematically indicated lifting cylinder 18 is adjustable. The FLT 1 further comprises a control unit 20, which can be integrated in the vehicle control or designed as an external module. The control unit 20 is arranged to carry out the invention. In the following, simple feasible estimates are explained, which can serve as a starting point for the following description. For further details regarding the determination of different sizes in a forklift, reference is expressly made to DE 103 04 658 A1. It is proposed to measure the state of motion of the FLT in each direction of the space with the aid of, for example, a so-called sensor cube with yaw rate and acceleration sensors, so that a quasi-static movement trajectory of the FLT at the driving level (xy) is determined by the dynamic signal components of the movement. and drive influences are caused, can be separated. Thus, the roadway be estimated in the longitudinal and transverse directions. These estimates may be used to advantage for the model calculations described below.

From the measurement of the empty FLT, the position (X _F LT, V FLT, Z _F _T) of the FLT center of gravity can be determined. For example. For this purpose, inclined planes and load cells can be used for axle load determination, ie such a determination can possibly take place with relatively little effort. As a consequence, the FLT can be regarded as point mass m _FLT . In addition, the moment of inertia of the FLTs can be measured around the vertical axis JZZFLT and thus assumed to be known.

The fork load m _La st and the position of the fork load center can, as described above, estimated or determined eg according to DE 103 04 658 A1. This results in a FLT overall model with two masses with two centers of gravity, which can be combined into a total mass total, a total center of gravity and a total moment of inertia.

The total mass m _Ge samtwird determined to:

mTotal ⁼ m _L ast ⁺ TlFLT · tal The x-center distance to the front axle x _G is determined to:

^ Total ⁼ (ΓΠρ_ * Χρΐ-Τ ~~ ^m Last'XLast) / ITlGesamt-

The vertical distance of the center of _gravity ZG _total from the origin is determined as:

ZTotal ⁼ (TIFLT'ZFLT ⁺ rnL _a st * Zload) / rnTotal

The total moment of inertia JzzTotal of the FLT around the vertical axis is determined as:

^« JzzTotal ⁼ JzzFLT ⁺ TlLast'XLast ² -

As a result, the normal forces on each wheel can be estimated, for example, from sensor signals and using the calculation model explained below by way of example:

A FLT generally has no separate suspension, ie the rear swing axle is hinged unsprung on the FLT structure and the front wheels of the FLT are mounted directly and rigidly on the body. Thus, the FLT structure is mechanically at three points, ie at the front wheels and at the joint of the pendulum axle, fixed. If the roll and pitch angles of the FLT are now measured, the road inclinations in these directions are estimated, and the yaw rate v _Gi , the transverse and longitudinal accelerations a _y and a _{x are} measured, the normal forces can be calculated from the force and torque sums of the FLT structure at the front wheels Fzvi and F _Z V _R are determined as well as the transverse and normal forces F _QH and F _ZH in the joint of the pendulum axle:

(FZVL + FZVR) = + h _S 'Sin ( _P + v)) + m ^« a _x ' h _s -Jy d dt ² ] / (l _v + lH);

(F _ZVL -F _Z V _R ) = {m '[a cos (<p _R + <p) + g * sin (<p _R + (p)] + J _xx ^» ö ² (p / öt ²

F _QH = {Jzz'dvci dt + M'L _v '[a ^_y' cos (9R + 9) + g'sin (<p _R + (p)]} / (l + l _{H v);}

F _ZH = - nva _y 'sin (<p _R + <p) - (F _Z V _R + F _Z V _L );

The normal forces at the front wheels result to:

F _Z VR = 1/2 '[(FZVL + FZVR) - (FZVL-FZVR)]

FZVL ⁼ [(FZVL ⁺ FZVR) - ZV]

The normal forces at the rear wheels F _ZHL and F _ZHR result in:

FzHL -FQH * hpG S _WH + FzH / 2

Parameter:

m: total mass FLT in [kg]

9: gravitational acceleration [m / s ² ]

 IH: longitudinal distance of the rear axle to the center of gravity [m]

lv: longitudinal distance of the front axle to the center of gravity [m]

a _x : longitudinal acceleration [m / s ² ]

hs: height center of gravity above ground [m]

h _P : height center of gravity over joint pendulum axis [m]

hpG: height of joint swing axle over ground [m]

S _W V: gauge front [m]

S _W H: rear track [m]

Jyy: Moment of inertia in pitch [kgm ² ]

J: Moment of inertia in roll direction [kgm ² ] φ _κ : roll angle [rad]

φ: road inclination in roll direction [rad]

ψ _Ρ : pitch angle [rad]

ψ: road inclination in pitch direction [rad]

v _Gi : yaw rate

This is a preferred way to determine the normal forces on the wheels. It is understood, however, that the normal forces are in principle also determinable in other ways, e.g. with the help of reductions or extensions of the above equations.

According to the invention, it has been recognized that FLTs tend to tip prematurely on one axle while the other still remains on the ground. The probability of tipping, here pitch probability, is therefore expediently determined axle-wise, for example as Rov _A for the front axle and RQHA for the rear axle, according to the following preferred relationship: RQVA ⁼ (FZVR-FZVLV (FZV ⁺ FZVL)

RQHA ⁼ (FZHR-FZHL) / (FZHR ⁺ FZHL) -

In the longitudinal direction, a similar assessment of the probability of tipping, here rolling probability, take place. It is intended to evaluate the left-hand FLT side with a roll probability R _L L separately from the right-hand side with a roll probability R _L R:

RLL ⁼ (FZVL-FZHL) / (FZVL ⁺ FZHL)

RLR ⁼ (FZVR-FZHR) / (FZVR ⁺ FZHR) - It is also intended to determine a total rolling probability R _L :

(FZVL ⁺ FZVR-FZHL-FZHRV (FZVL ⁺ FZVR ⁺ FZHL ⁺ FZHR)

If one of the determined tilting probabilities reaches a value close to an amount of 1, then only one very small normal force acts on at least one wheel, so that it is recognized that the FLT is about to tip over. If the amount of certain tilting probabilities remains close to zero, there is no risk of tipping over. In a preferred embodiment, a tilting counteracting intervention is performed automatically. For example, the need for a corrective intervention can be derived from the amounts for the risk of tipping near 1. As a threshold, a value of eg

 0.9 can be used. In this case, it is also advantageous to include the time duration in which such values are observed into the definition of the start of intervention, for example via suitable filter algorithms, so that high tilting risks must be determined over a defined period of time in order to trigger an intervention start.

In the condition for the end of the control, a time dependency also expediently, in order to prevent premature shutdown of the procedure. Otherwise, due to oscillating switch-on and switch-off conditions, the FLT can swing up with a high probability of overturning. It is also possible to set the turn-off threshold (e.g., at 0.8) for interventions to be lower than the turn-on threshold (e.g., at 0.9).

For example, the equations given above may be for a target size, here e.g. maximum allowable lateral acceleration ayumvA or ayumHA. For this purpose, desired values RovAum or RoHAUm are specified, e.g. as a fixed quantity or as a time-variable variable with a sliding adjustment to the actual value:

ayLimVA = {^ Αυσ, · 8 «ν · 1/2 ^ · (ΐΗ · οο8 (ψρ + ψ) + h _S 'Sin ( _P +)) +

+ ax'hs-jyy / nrrd dt ² } +

+ Jzz / rrvihs-hpJ'dVGi / dt - Jxx / m-hs '(l _v + l _H j'o St ² ] / (h _s ^» l _H + l _y ' h _P ) -

- g ^" sin (<p _R + (p)} /

/ COS (<pR + (p)) ayLimHA = [RQHAm ^, s _W H '{g * [cos (p +) »((lv + lH) ^, cos (9R + 9) -l _H ) -

- ax'hs + Jyy / m'ö dt ² }] - {J _zz / m'öv _Gi / öt + l _v 'g * sin (9R + 9)}' h _PG ^» 2] /

/ [lv * pG * 2 "COS _((R p + <p) + RaHALim'SwH 'v + ^ lH SiniipR + i)]

In a preferred embodiment, the smaller of the lateral acceleration values is selected and used for the limiting value formation:

ayLim ⁼ min {ayLimVA; a LimHA}. In a further preferred embodiment, the lateral acceleration, for example by means of steering and / or drive interventions, is now regulated so that the specific limit value is not exceeded. According to the invention, it has been found that the effectiveness of a lateral acceleration control can be improved. For example. results from the dynamic behavior of the FLTs when driving forward a poor controllability of the lateral acceleration, ie the gain of the lateral acceleration loop can not be chosen very large. Therefore, in a preferred embodiment, a second control loop is established via the yaw rate v _G i of the FLT. In this case, the task is transmitted to the yaw rate control loop to generate quasi-stationary movement behavior of the FLT in the sense of a subordinate control loop. Thus, the target value v _G iso of the yaw rate control is assumed on the assumption that the slip angle gradient of the FLT should become small

VGiSo = ayso / v,

where v is the longitudinal velocity of the FLT.

The control circuit over the yaw rate is used in particular to regulate additional dynamic portions of the movement behavior. An exemplary control loop is illustrated below with reference to FIG. FIG. 2 schematically shows a control loop structure 200 for regulating a lateral acceleration a _y and a yaw rate v _Gi . For this purpose, the control loop 200 is supplied with corresponding setpoints aysoii and v _GiS oii as reference variables. The setpoints are each fed to a comparison element, to which the instantaneous actual values a _y and v _Gi are also supplied as control variables. The comparison elements determine the respective control deviation.

The lateral acceleration control deviation is fed to a yaw rate controller 201, the yaw rate deviation is fed to a yaw rate controller 202. The two control elements each determine a manipulated variable, for example a steering movement, which are summed up and supplied with a possible disturbance variable L _{w to} a lateral acceleration control path 203 and a yaw rate control path 204. The actual values a _y and v _Gi resulting from the controlled systems are, as already mentioned, used as a control variable for comparison with the respective reference variable. The statements made above regarding the lateral acceleration a _y apply in a correspondingly adapted manner for the longitudinal acceleration a _x . In an embodiment of the invention, based on the roadway inclination, the load weight and the center of gravity of the load, a permissible longitudinal acceleration a _x u _{m is determined} from the inversion of the equation for the pitch probability and the actual longitudinal acceleration is limited to this value, for example via a drive intervention.

If it is optionally recognized that the mast is not in a lowered state, the travel speed is expediently limited to low values. If it is determined in the load identification that there is a load on the fork that would lead to (static) overturning of the FLT with the existing (ascertained) road inclination above a certain lifting height, the lifting height is expediently limited accordingly. This can be done, for example, by limiting the switching through of the control valves of the lifting mast, so that the lifting mast can not be moved to critical heights. Alternatively or additionally, the driver at the driver's seat, the criticality of the load, for example visually or acoustically, are displayed.

The sequence of a preferred embodiment of the invention will be explained schematically with reference to FIG. In a block 301, necessary parameters are determined, for example estimated or measured. These include the roadway inclination in the longitudinal and transverse directions, which can be estimated, for example, from center of gravity signals. Furthermore, the recorded fork load and the fork load dimension are determined, which can be estimated for example due to Hubmastsignalen. On the basis of these and in particular further immutable variables, the total center of gravity of the loaded FLT is determined in a block 302.

In a block 303, the four forces acting on one wheel-in the present case-are determined. In a block 304, as explained above, based on the normal forces, various tilting probabilities R, such as those shown in FIG. Rolling probabilities and pitch probabilities, certainly.

In a step 305, the determined tilting probabilities are evaluated by, for example, being compared with a predetermined threshold value. It can also be considered how long and by how much the respective probability of tipping exceeds first threshold. If it is determined in this evaluation that there is no danger of tipping over, the method returns to the starting point 301.

However, if it is determined that there is a risk of tipping over, a tamper-evident intervention is automatically performed in step 306. This intervention may consist in particular of regulating a transverse and / or longitudinal acceleration and / or a yaw rate-as explained above.

In a subsequent step 307, it is checked whether a predetermined overturning condition still exists, for example by checking whether a certain tilting probability has fallen below a second threshold value. The first and second threshold values may be different in particular. If the tilt condition continues, the engagement 306 continues to be performed, but if the condition is no longer present, it returns to the starting point 301. Also in the evaluation in step 307, it is advantageously taken into account how long the second threshold value has been undershot in order to prevent rocking.

Claims

claims

1. A method for determining a probability of tipping an industrial truck (1) having at least three wheels, wherein the normal force acting in the z-direction (FZVL.F _ZH L) is determined for at least two wheels,

wherein at least two normal forces (Fzv _L , F _ZH L) are compared and the probability of tipping the truck (1) is determined based on the comparison result.

2. A method according to claim 1, wherein for determining the at least two normal forces (FZVL, FZHL), a roll angle and a pitch angle of the industrial truck and / or

a road inclination in x and y direction are determined.

3. Method according to claim 1, wherein a yaw rate (v _Gi ), a lateral acceleration (a _y ) and a longitudinal acceleration (a _x ) are determined to determine the at least two normal forces (FZVL .F _ZH L).

4. The method according to any one of the preceding claims, wherein for determining a rolling probability of the truck (1) the normal forces on an axle (4, 6), in particular front and / or rear axle, are compared.

5. The method of claim 4, wherein a roll probability RQVA for the front axle (4) and / or R _QH A for the rear axle (6) are determined to:

RQVA ⁼ (FZVR-FZVLV (FZVR ⁺ FZVL)

RQHA ⁼ (FZHR-FZHL) / (FZHR ⁺ FZHL)

With

 FZVR. FZ L: normal force front right or left

FZHR. F _Z HL: normal force rear right or left

6. The method according to any one of the preceding claims, wherein for determining a pitch probability of the truck (1) the normal forces (FZVL. F _Z HL) on one side, in particular the right and / or left side, are compared.

7. The method of claim 6, wherein a pitch probability R _LL for the left side and / or R _LR for the right side are determined to: RLL - (FZVL-FZHL) / (FZVL ⁺ FZHL)

RLR ⁼ (FZVR-FZHRV (FZVR ⁺ F2HR)

With

 FZVR. FZ L: normal force front right or left

F _ZH R, FZHL- normal force rear right or left

8. The method of claim 6, wherein a total pitch probability R _{L is} determined to:

RL ⁼ (FZVL ⁺ FZVR-FZHL-FZHR) / (FZVL ⁺ FZVR ⁺ FZHL ⁺ FZHR)

With

 FZVR. FZVL: normal force front right or left

F _Z HR. F _Z HL: normal force rear right or left

A method according to any one of the preceding claims, wherein a certain tilt probability is compared with a threshold value and, based on the comparison, a tamper-evident engagement is automatically performed.

10. The method of claim 9, wherein in the comparison is also taken into account in addition, how long and by how much each determined probability of tilt exceeds the threshold.

11. The method of claim 9 or 10, wherein as engagement a lateral acceleration (a _y ), in particular for the rear and or front axle (4, 6), and / or a longitudinal acceleration (a _x ) is regulated.

12. The method of claim 1 1, wherein additionally a yaw rate (v _G i) is controlled.

13. computer unit (20) which is adapted to perform a method according to any one of the preceding claims.