EP1426499B1 - Method and apparatus for end stroke dampening in hydraulic actuators of mobile working machines - Google Patents

Abstract

The end of stroke damping system may be used for a mobile digging machine with two hydraulic cylinders (10,11). It has a control circuit (15) connected to position (17) and velocity sensors (16) on cylinders and closes throttle valves near the end of the stroke of each piston (18). End switches may be connected to a timer (19) in the control circuit. Three hydraulic pumps (1-3) draw hydraulic fluid from a tank (14) and pass it through three control valves (4-6).

Description

The present invention relates to a method and a device for damping movement of hydraulic cylinders of mobile machines, in particular hydraulic excavators, wherein by means of a position detection device reaching a Vorendstellung the hydraulic cylinder is detected before reaching the end positions of the hydraulic cylinder whose movement speed is reduced and the hydraulic cylinder with only reduced speed in the respective end position is driven. For this purpose, a flow control member for throttling the inlet and / or the drain of the hydraulic cylinder is provided, which is controlled by a control device upon reaching the Vorendstellung correspondingly to throttle the flow rate, which flows into the hydraulic cylinder or from this.

The movement damping or end position deactivation of hydraulic cylinders ensures that the speed of the hydraulic cylinders is reduced shortly before reaching the mechanical end stop, in order to avoid excessive mechanical loading of the steel components due to inertia forces due to the abrupt deceleration and to increase the comfort during work. For such a movement damping hydraulic solutions have already been proposed as well as electrical shutdowns.

A hydraulic solution is shown in FIG 7. As shown therein, the drive of hydraulic cylinders of earthworking machines such as hydraulic excavators and the like is carried out regularly via a hydraulic pump 1 and a downstream directional control valve 4. In the hydraulic cylinder 10 geometric changes 13 are mounted in the end region of the piston and rod when entering the modified geometry 12 of the cylinder housing cause a pressure accumulation of the returning fluid.

The speed of the cylinder is determined by the delivery rate of the hydraulic pump 1 in the inlet to the cylinder. A damping effect arises only when the amount is reduced in the feed to the cylinder. A reduction can only be achieved by either the controller R of the pump 1 or a switched into the hydraulic circuit pressure relief valve 7 responds. The response of the pump controller or the pressure relief valve is achieved by the inlet pressure, which means that the dynamic pressure must increase on the discharge side corresponding to the transmission ratio of the hydraulic cylinder. Depending on the size of the machine, the pressure regulator of the pump or the pressure relief valve responds to between 300 and 350 bar pressure, so that a back pressure of 600 to 700 bar is required on the inlet side of the hydraulic cylinder.

The back pressure is achieved via a restriction at the annular gap and special throttle cross-sections, wherein the throttle effect at the annular gap is highly dependent on the manufacturing tolerances and the viscosity of the fluid. Due to these deviations from the geometry and fluid parameters, there is a high probability that either the back pressure will not be sufficient to activate the control elements or that the back pressure will rise so high that the strength of the cylinder housing is jeopardized.

Because of these shortcomings, an electrical shutdown of the inlet and outlet has already been proposed. In systems with electro-hydraulic feedforward control offers an electrical shutdown, in which a limit switch is provided for each direction of movement of the cylinder. Shortly before reaching the final position of the Cylinder is passed over a corresponding limit switch, by the signal, the control device switches off the corresponding directional control valve. This results in a braking of the movement as a function of the switching speed of the directional control valve.

In this solution, however, is regularly stopped too early or too late, which means on the one hand that the kinematics is not fully utilized or yet the mechanical end stop of the hydraulic cylinder is reached at too high a speed. In the event of uncontrolled shutdown, there are also pressure spikes on the discharge side and lack of filling on the inlet side, which leads to increased stress on the lines and hydraulic components.

A method and a device of the type mentioned are known from US 4,896,582. It is proposed, depending on a signal of the control lever, with which the movement of the respective hydraulic cylinder is controlled to delay the end position damping differently. The said control lever signal must e.g. however, with varying loads, it is not necessarily the same as the actual hydraulic cylinder speed, so that the damping control may become inaccurate. Furthermore, GB 1 382 057 shows a hydraulic cylinder in which the throttle speed is controlled independently of the output speed. EP 0 879 969 A2 describes a method of controlling a hydraulic cylinder in which, depending on the time between passing two points, some control parameters, e.g. the length of a braking interval can be changed.

The present invention is therefore based on the object to provide an improved method and an improved device for damping movement of hydraulic cylinders of each type mentioned, avoid the disadvantages of the prior art and further develop the latter in an advantageous manner. Preferably, a drive on the mechanical stop at too high speed safely avoided while still fully exploiting the kinematics of the hydraulic cylinder.

This object is achieved by a method according to claim 1 and a device according to claim 6. Preferred embodiments of the invention are the subject of the dependent claims.

It is therefore provided according to the invention a speed detection device which detects the movement speed of the hydraulic cylinder before reaching the respective end position. The control device, which controls the flow control member for throttling the inlet or outlet, comprises a delay device with the aid of which the start time of the throttling is changed as a function of the detected movement speed. The speed detection device in this case comprises two successively arranged end signal generator, which are passed shortly before reaching the end position of the piston, and a time detection device which detects the time interval between the signals of the two end signal generator. The signal of the time-detecting device, which reproduces said time interval between the signals of the two end signals, forms the speed signal which the control device bases on the control of the flow control element. The detected period of time, which lasts the passing of the two successively arranged Endsignalgeber is then compared in a comparison means of the control device with a predetermined period of time. If the difference is negative, i. the detected time is less than the predetermined time, the fixed, earliest possible start time of the damping is determined by the control device. If the difference is positive, i. the detected time is greater than the predetermined time, the amount of the difference of the delay of the beginning of attenuation is taken as the basis. In particular, the start time may be shifted back by the amount of the determined difference.

The flow control member is thus actuated sooner or later depending on the detected movement speed of the hydraulic cylinder, so that the movement damping or speed reduction of the hydraulic cylinder begins sooner or later. In this case, the motion damping can in particular be adapted to the speed of movement, on the one hand the achievement of the mechanical End stop takes place, on the other hand reaching the end stop but only with the desired minimum speed.

In order to match the motion damping to the sensed speed, basically the throttle velocity of the flow organ, i. the rate at which the flow is shut down can be changed. In order to allow a simple control, however, it is preferably provided in a development of the invention that the throttle speed of the flow control member is predetermined independently of the detected movement speed of the hydraulic cylinder. The adaptation of the motion damping is thus achieved solely by the fact that the initial time of throttling or the actuation time of the flow control member is shifted in dependence on the detected speed. However, it is quite possible here to shift the actuation times of the control elements differently when using a plurality of flow control elements, so that overall a different damping characteristic results. However, the throttle speed can be kept the same for each of the control organs here.

Conveniently, the beginning of damping is delayed with decreasing moving speed of the hydraulic cylinder, i. pushed backwards in time.

The adaptation of the start time of the damping to the movement speed can basically be done in various ways. However, in order to keep the control arrangement simple, the control device is configured in such a way that a fixed starting time is always specified if the detected movement speed is greater than or equal to a predetermined limit speed, ie, the front end position detected by the piston position detection device with a limit speed or overrun at an even greater speed. In this case, the damping is initiated immediately. However, if the movement speed detected in the pre-end position is below the limit speed, the initial time becomes the damping is delayed by a certain period of time. The period of time by which the start time of the damping or the time of actuation of the flow control member is shifted can be set variably by the control device. Preferably, the control means varies the amount of time the damping is shifted in proportion to the detected speed upon reaching the pre-end position.

The speed detection device or its end signal generator can basically be arranged at a different location and assigned to the hydraulic cylinder. In order to provide a simple arrangement and to provide for both end positions only a pair of end signal generator, first and second markings may be provided on the piston rod of the hydraulic cylinder and / or a detection sensor coupled thereto, each corresponding to one of the two end positions and Vorendstellungen of the piston , Both markings can be detected by a correspondingly arranged end signal generator pair. Accordingly, only one detection device is provided for detecting both end positions or only one detection device for detecting the speed when both end positions are reached.

The detection devices may preferably be integrated in the hydraulic cylinder, in particular be arranged in the region of the collar of the hydraulic cylinder, through which the piston rod emerges.

According to a particularly advantageous embodiment of the invention may also be provided a separate from the hydraulic cylinder, but coupled thereto detection sensor, which moves in accordance with the movement of the hydraulic cylinder. In particular, here can be provided a rotary rotary disk having two markings of the aforementioned type. The position of the markings can be detected by corresponding end signal generator.

Fig. 1:

eine schematische Darstellung eines hydraulischen Antriebssystems für zwei Hydraulikzylinder eines Hydraulikbaggers mit einer Vorrichtung zur Bewegungsdämpfung nach einer vorteilhaften Ausführung der vorliegenden Erfindung, wobei das Antriebssystem als Dreipumpensystem dargestellt ist,

Fig. 2:

ein Stromzeitdiagramm, das den Verlauf des Ansteuerstroms für die Wegeventile des hydraulischen Antriebs aus Fig. 1 zur Erreichung der gewünschten Bewegungsdämpfung zeigt,

Fig. 3:

die Anordnung der Endsignalgeber zur Erfassung einer Vorendstellung und Geschwindigkeit des Kolbens des Hydraulikzylinders nach einer Ausführung der Erfindung, bei der vier Endsignalgeber vorgesehen sind, die eine Markierung an der Kolbenstange erfassen,

Fig. 4:

eine schematische Darstellung einer mit der Kolbenstange des Hydraulikzylinders gekoppelten Detektionsscheibe sowie die zugehörige Anordnung der Endsignalgeber einer Erfassungseinrichtung zur Erfassung der Vorendstellung und der Geschwindigkeit des Hydraulikzylinders für beide Bewegungsrichtungen,

Fig. 5:

eine schematische Darstellung einer in den Hydraulikzylinder integrierten Einrichtung zur Erfassung der Kolbenstellung und der Kolbengeschwindigkeit,

Fig. 6:

eine schematische Darstellung einer in den Hydraulikzylinder integrierten Einrichtung zur Erfassung der Vorendstellung und der Geschwindigkeit des Kolbens des Hydraulikzylinders nach einer weiteren Ausführung der Erfindung, und

Fig. 7:

eine schematische Darstellung eines hydraulischen Einpumpenantriebs eines Hydraulikzylinders mit hydraulischer Bewegungsdämpfung nach dem Stand der Technik.

The invention will be explained in more detail with reference to preferred embodiments and associated drawings. In the drawings show:

Fig. 1:

1 is a schematic representation of a hydraulic drive system for two hydraulic cylinders of a hydraulic excavator with a device for damping movement according to an advantageous embodiment of the present invention, wherein the drive system is shown as a three-pump system,

Fig. 2:

a current time diagram showing the course of the drive current for the directional valves of the hydraulic drive of Figure 1 to achieve the desired motion damping,

3:

the arrangement of the end signal generator for detecting a Vorendstellung and speed of the piston of the hydraulic cylinder according to an embodiment of the invention, in which four end signal generator are provided which detect a mark on the piston rod,

4:

a schematic representation of a coupled to the piston rod of the hydraulic cylinder detection disc and the associated arrangement of the end signal generator of a detection device for detecting the Vorendstellung and the speed of the hydraulic cylinder for both directions of movement,

Fig. 5:

a schematic representation of an integrated device in the hydraulic cylinder for detecting the piston position and the piston speed,

Fig. 6:

a schematic representation of an integrated device in the hydraulic cylinder for detecting the Vorendstellung and the speed of the piston of the hydraulic cylinder according to a further embodiment of the invention, and

Fig. 7:

a schematic representation of a hydraulic Einpumpenantriebs a hydraulic cylinder with hydraulic motion damping according to the prior art.

As Figure 1 shows, the hydraulic cylinders 10 and 11, which may be, for example, the lifting cylinder of a hydraulic excavator, driven by a hydraulic drive having three hydraulic pumps 1, 2 and 3, which can be controlled via a regulator R respectively. The three hydraulic pumps 1, 2 and 3 are connected via a respective directional control valve 4, 5 and 6 with the hydraulic cylinders 10 and 11, which are also connected in parallel. Through the directional control valves 4, 5 and 6, the inlets and outlets of the hydraulic cylinders 10 and 11 can be separated from the respective pumps 1, 2 and 3 and shut off or brought into flow communication with the pump in a conventional manner, wherein the flow direction is reversible so that the hydraulic cylinders can be extended and retracted. Upstream of the directional control valves 4, 5 and 6 are in the outgoing of the pumps 1, 2 and 3 pressure lines pressure relief valves 7, 8 and 9, can be drained via the hydraulic fluid in the tank 14. Also, the directional control valves 4, 5 and 6 are connected via corresponding lines to the tank 14 in order to guide in the closed position, the pumped by the pump fluid and in the corresponding switching position of the hydraulic cylinders returning fluid in the tank.

The directional control valves 4, 5 and 6 are controlled by an electronic control device 15 to control the movement of the hydraulic cylinders 10 and 11.

The movement of the hydraulic cylinders 10 and 11 is monitored on the one hand by a position detection device 17, which indicates the approach of the piston rod at its two end positions, in particular indicates the achievement of a preliminary end position. On the other hand, the velocity of the piston rod of the hydraulic cylinders 10 and 11 is detected by means of a speed detection device 16 when they reach said pre-end position.

The speed detection and the detection of the preliminary end can be done in various ways. FIG. 3 shows a speed detection device 16 in the simplest form. The speed detection takes place in each of the Vorendstellungen the piston of the hydraulic cylinder by means of two limit switches S ₁ and S ₂ or S ₃ and S ₄ . On the piston rod 18, a mark is attached, which is detected by the limit switches S ₁ to S ₄ , when the piston rod is moved past it. The limit switches can be mechanical switches or inductive sensors. The limit switches S ₁ to S ₄ are associated with a time detection device 19 in the control device 15, which determines the time span that lapses over the successively arranged limit switches S ₁ and S ₂ or S ₃ and S ₄ . The time taken to overrun a limit switch pair is a measure of the piston speed when the pre-end position is reached.

A simplified solution of a speed detection device 16 is shown in FIG 4. Here, the limit switches S ₁ and S _{2 are} not arranged directly on the hydraulic cylinder or not directly associated with the piston rod 18, but are attached to the fulcrum of appropriate equipment, the hydraulic cylinders 10 and 11 relative to each other to be moved. For example, the rotary detection disc 20 with a moving part such. B. be connected to the bucket with the bearing block of a hydraulic excavator or be formed by a part of the bearing block. The limit switches in the form of inductive sensors S ₁ and S ₂ can with the counterpart, z. B. the stem of the hydraulic excavator connected. The markers 21, 22 are mounted on the detection disc 20 so that they reach the limit switches S ₁ and S ₂ when the hydraulic cylinder reaches one of its Vorendstellungen.

A further preferred embodiment of a speed detection device 16 is shown in FIG 5. In this embodiment, the path of the piston via markings on the cylinder rod or piston rod 18 and corresponding limit switches or sensors S ₁ and S _{2 is} detected over the entire path of the piston. The sensors S ₁ and S ₂ are located in the unpressurized region of the piston rod bearing. Such a relative measuring system is expediently provided with a reference zero, which is run over at least once each time the machine is started.

For the present motion damping is preferred in comparison to the training shown in Figure 6, the position and speed detection device 16 and 17. The way of the piston rod 18 is detected only in the region of the two end positions, which is quite sufficient for hydraulic cylinders, in which only the Movement damping according to the invention should take place. The limit switches S ₁ and S ₂ are in turn integrated in the region of the piston rod bearing in the hydraulic cylinder and detect markings on the piston rod 18, which are provided in the end regions thereof. If the markers 21 or 22 reach the limit switches or end signal transmitters S ₁ and S ₂ , they emit a signal, so that the reaching of the preliminary end position of the piston is indicated in the previously described manner and, on the other hand, the velocity of the piston present or detected . can be determined.

The control device 15 shown in Figure 1 actuates the directional control valves 4, 5 and 6 when reaching the Vorendstellungen depending on the speed detected here as follows:

As FIG. 2 shows, a movement of the hydraulic cylinders 10 and 11 is initiated by the control of the directional control valves 4, 5 and 6 at point P1. The drive current is first increased to a 10% value such as 10, so that the start of movement of the hydraulic cylinder can be assumed in point 2. The pressure build-up and the acceleration of the hydraulic cylinders 10 and 11 take place along the control ramp between the points P2 and P3. The hydraulic cylinders reach their maximum speed at 90% drive current I ₉₀ , which is reached at point P3 of the diagram of Figure 2. From there, the maximum current Imax goes to point P4, so that the hydraulic pistons drive at full speed.

If the piston is accordingly driven to one of its end positions, the first end signal transmitter S ₁ , which is first in the direction of movement, is run over. In the diagram point P5 according to Figure 2, the hydraulic cylinder is still driven at full speed, the first end signal generator S ₁ emits its signal. Here Depending on the equipment component, a control piston of one of the directional control valves 4 or more control pistons several way valves 4 and 5 abruptly controlled, so that the corresponding drive current for these directional control valves abruptly from point P5 to point P6, ie falls to zero. The control pistons follow the current according to their dynamic characteristic.

The remaining control pistons are further driven with initially full drive current Imax until the second end signal generator S _{2 is} run over and emits its corresponding signal. In the time detection device 19 of the control device 15 while the time t _{K is} determined, which was needed to pass over both end signal generator S ₁ and S ₂ . A comparison and subtraction device 23 in the control device 15 compares the detected value t _{K of} the time span, which is a measure of the speed of the hydraulic cylinder, with a predetermined value t _S. If the detected time t _{K is} less than or equal to the value t _S , the damping process takes place along the line between the points P7, P8, P9, P10, P11, P12. This means that the detected piston speed was greater than or equal to a limit speed. The damping process is initiated immediately.

However, if the detected time t _K is greater than the predetermined value t _S , the damping takes place with a time delay, along the line between the points P7 ', P8', P9 ', P10', P11 'and P12'. The time offset t _F is thereby selected by the control device 15 proportional to the time overflow of t _S , ie proportional to the amount by which the detected time t _{K is} greater than the predetermined time t _S.

The non-delayed damping process along the line between the points P7 and P12 and the time-delayed damping process along the line between the points P7 'to P12' can be described as follows:

First of all, the drive current for the remaining directional control valves 6 to n, ie for the directional control valves which were not retracted as soon as the first end signal generator S _{1 has been} traveled over, is reduced to the jump value I _S. By the jump The control piston of the directional control valves are suddenly brought into a position from which a braking effect on the discharge side of the hydraulic cylinders 10 and 11 takes place.

The braking then takes place along the damping ramp from the point P8 to the point P9 or from the point P8 'to the point P9'. Depending on the number of remaining control pistons, a piston continues along the damping ramp up to the points P11 and P11 ', where it is then switched off in each case, ie. the current is reduced to zero, as indicated by the points P12 and P12 '.

The remaining control piston of the one-way valve is driven along a control ramp from the point P9 to the point P10 or P9 'and P10', where it then reaches the outlet flow I _A in point P10. With the discharge flow it is possible to reach the end position with full cylinder force.

The control is initiated at point P13 by releasing the manual control. The current runs along the jump ramp from point P13 to point P14 and is then cut off along the line from point P14 to point P15.

It is understood that the damping process in the opposite direction proceeds according to the same scheme. The detection and direction detection takes place in the reverse direction.

If instead of the three pumps 1, 2 and 3 only one pump is used to supply the hydraulic cylinders, it will be understood that when the first end signal generator S _{1 is passed,} the control piston of the corresponding directional control valve is not yet switched off. The Gesamtprozedere then takes place depending on the speed from the crossing of the second Endsignalgebers S _2nd In principle, n pumps can be used.

Claims (11)

1. Method for damping the movement of hydraulic cylinders (10, 11) of mobile working machines, in particular hydraulic excavators, in which the movement speed of a hydraulic cylinder (10, 11) is reduced before the said cylinder reaches one of its end positions and the hydraulic cylinder (10, 11) is moved to the respective end position at a reduced speed, with the inflow and/or outflow of the hydraulic cylinder (10, 11) being throttled by means of a flow-control element (4, 5, 6) in order to reduce the speed,
   characterized in that
   two end signal transmitters (S₁, S₂) which are arranged in series are crossed before the respective end positions are reached, and the time period (t_K) between the times at which the two end signal transmitters (S₁, S₂) are crossed is detected in order to detect the movement speed of the hydraulic cylinder (10, 11), with a time difference (δt) being determined from the detected time period (t_K) and a prespecified time period (t_S), and a delay (t_F) of the starting time (P7') of the damping being determined as a function of the time difference (δt).
2. Method according to the preceding claim, with the throttling speed of the flow-control element (4, 5, 6) being prespecified independently of the detected movement speed of the hydraulic cylinder (10, 11).
3. Method according to either of the preceding claims, with the start (P7, P7') of damping being delayed at a decreasing detected movement speed.
4. Method according to one of the preceding claims, with a fixed start time (P7) being prespecified when the detected movement speed is greater than or equal to a prespecified limit speed, and the start time (P7') is performed with the delay (t_F) with respect to the fixed start time (P7) when the detected movement speed is less than the prespecified limit speed.
5. Method according to one of the preceding claims, with the delay (t_F) being selected to be proportional to the time difference (δt).
6. Apparatus for damping the movement of hydraulic cylinders of mobile working machines, in particular hydraulic excavators, in accordance with the method according to one of the preceding claims, having a position-detection device (17) for detecting a front end position of the hydraulic cylinder (10, 11), a flow-control element (4, 5, 6) for throttling the inflow and/or outflow of the hydraulic cylinder (10, 11), and a control device (15) for actuating the flow-control element (4, 5, 6) when the front end position is reached, characterized in that a speed-detection device (16) for detecting the movement speed of the hydraulic cylinder when the front end position is reached has two end signal transmitters (S₁, S₂), which are arranged in series, and a time-detection device (19) which detects the time period (t_K) between the signals from the two end signal transmitters (S₁ and S₂), and the control device (15) has a comparison device (23) for comparing the detected time period (t_K) with a prespecified time period (t_S) and for forming the difference between the two time periods (t_K, t_S), and a delay device with a delay transmitter which prespecifies the delay (t_F) with which the flow-control element (4, 5, 6) is actuated as a function of the specific difference.
7. Apparatus according to the preceding claim, with one of the end signal transmitters (S₁, S₂) simultaneously forming the position-detection device (17).
8. Apparatus according to either of the preceding Claims 6 and 7, with first and second markers (21, 22) being provided on the piston rod (18) of the hydraulic cylinder (10, 11) and/or a detection transmitter (20) coupled to the latter, the said markers each corresponding to one of the two front end positions and it being possible for the position-detection device (17) and/or the speed-detection device (16) to detect them both.
9. Apparatus according to one of the preceding Claims 6 to 8, with the speed-detection device (16) being integrated in the hydraulic cylinder (10, 11).
10. Apparatus according to one of Claims 6 to 8, with the speed-detection device (16) being arranged separately from the hydraulic cylinder (10, 11) and being associated with a detection transmitter (20).
11. Apparatus according to one of the preceding Claims 6 to 10, with the position-detection device (17) being associated with an articulation point between the two components of the movement train which is driven by the hydraulic cylinder (10, 11), and the position of the two components in relation to one another being detected.

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