CN210436959U

CN210436959U - System for position control of vehicle

Info

Publication number: CN210436959U
Application number: CN201921159255.7U
Authority: CN
Inventors: W·鲍尔
Original assignee: FSP Fluid Systems Partners Holding AG
Current assignee: Accor fortos Group Co.,Ltd.
Priority date: 2018-07-26
Filing date: 2019-07-23
Publication date: 2020-05-01
Anticipated expiration: 2029-07-23
Also published as: WO2020020718A1; DE102018118062A1; CN110774852A

Abstract

A system for position control of a vehicle, the vehicle having a plurality of wheels, the system comprising: a plurality of height-adjustable spring assemblies, each spring assembly (41a, 41b,41c,41 d) being assigned to at least one wheel (51a, 51b,51c,51 d); a position sensor (44) for determining a height position (Ha, Hb, Hc, Hd) of the at least one spring assembly (41a, 41b,41c,41 d) and for outputting at least one height position signal; a force sensor for determining a force acting on the at least one spring assembly (41a, 41b,41c,41 d) and for outputting at least one force signal; characterized in that at least one spring assembly (41a, 41b,41c,41 d) is adjusted based on the force signal and the height position signal.

Description

System for position control of vehicle

Technical Field

The utility model relates to a system for vehicle position control.

Background

A method and a system for position control are known from DE 1814124 a 1.

In the prior art, vehicles with hyperstatic suspensions are generally standard. Thus, for example, each passenger car with four wheels and therefore four contact points on the ground is statically overdetermined with respect to the contact forces acting there. This is because three points of contact are sufficient to maintain the vehicle chassis in a stable position relative to the ground. However, four contact points (at each corner of the vehicle) are specifically selected to improve lateral leaning stability.

Theoretically, with four contact points, when the ground is perfectly flat and all four wheels are perfectly arranged on the vehicle, the springs of the spring suspension have exactly the same spring rate, and the wheel comprising the tire is also exactly the same in geometry and internal pressure, the force distribution is ideally evenly distributed.

The fact that the above conditions can never be complied with is self-evident. Thus, in the case of all vehicles having at least four contact points and no adjustable length spring assembly (i.e., no position control), there is a distribution that deviates from the ideal distribution of contact forces. This is generally the case for all commercial passenger cars. What is accepted here is the fact that the contact force deviates from the ideal distribution and therefore also the possible traction on the wheel deviates from the ideal situation. It is also accepted that under contact forces that are not ideally distributed, the suspension behavior is not uniform, e.g., the vehicle acts on the diagonal of heavier loads in a "rolling" manner (especially in the case of progressive suspensions and load-dependent spring rates).

In the case of sports cars, it is crucial for the maximum traction of the sports car that the load distribution is optimized on the wheel load scale, since the suspension strut is adjusted in length, so that the vehicle (on a completely flat ground) has an ideal wheel load distribution (resulting from the position of the center of gravity). In the case of a vehicle center of gravity located on the vehicle-longitudinal-center axis and having a horizontal contact area, the sum of the wheel loads is therefore the same on the first diagonal (from the center point of the left front wheel to the center point of the right rear wheel) and on the second diagonal (from the center point of the right front wheel to the center point of the left rear wheel).

There are vehicles in which the height of individual wheels or wheel sets is adjustable. The height adjustment or height position adjustment can be carried out in a spring assembly which holds the individual wheels on the chassis in a spring-mounted manner. In the case of a vehicle with individual height adjustment of all wheels, it is important to comply with the conditions required for an ideal wheel load distribution when adjusting the height.

However, for most such vehicles, this is not possible, since such vehicles typically have mechanical roller stabilization (e.g. torsional stabilizer), so that the wheel load distribution is generated by the stabilizer effect, and the two wheels of the axle are adjusted together in height, e.g. pneumatically (truck) or hydropneumatically (e.g. snowdrop). Thus, there is only one degree of freedom per axle for height adjustment, so that the wheel load distribution cannot be optimized or can only be achieved by means of support roller stabilization.

In the case of a vehicle without mechanical roller stabilization, whereby the roller stabilization is completely dependent on spring elements, the wheel load distribution can be optimized. By way of example, mention may be made here of self-propelled field sprayers, the individual wheels of which are pneumatically adjusted over their length to a given set point length or set point height position. However, known control methods do not produce ideal results and may therefore lead to poor traction behaviour.

SUMMERY OF THE UTILITY MODEL

Starting from this prior art, it is an object of the present invention to provide an improved method for vehicle position control. In particular, the effect of the method is to give the vehicle a better traction behaviour and greater roller stability and a better suspension behaviour. Furthermore, a corresponding system for vehicle position control is provided.

In particular, the object is solved by a method of positioning a vehicle having wheels, wherein in each case at least some of the wheels are connected to a chassis in a spring-mounted manner by means of a spring assembly. The method comprises the following steps:

a. determining an actual height position of at least one wheel relative to the chassis, in particular using at least one position sensor;

b. calculating at least a first correction value for a spring assembly assigned to at least one wheel using the setpoint height position;

c. measuring and/or calculating at least one wheel load force, such as a spring load and/or a wheel contact force, of at least one wheel, in particular by using at least one (force) sensor;

d. calculating at least a second correction value taking into account the wheel load force;

e. the height position of the at least one wheel is adjusted based on the first and/or second correction values.

The vehicle may be a commercial vehicle or a work machine, such as a field sprayer, in particular a self-propelled field sprayer. The spring assembly creates a connection between the chassis or body (e.g., in a self-supporting body) and each wheel.

A central aspect of the invention is to take into account not only the actual height position but also the wheel load force (e.g. contact force of the wheel on the ground) for adjusting the height position of the at least one wheel. In this respect, the individual spring assemblies can be controlled such that the individual wheels adopt a (nearly) optimal position relative to the chassis. At the same time, the wheel contact force can be optimized substantially as the spring load.

In other words, according to the invention, the (pure) position control or height control of the individual wheels is superimposed with the control regarding the wheel contact force. A hybrid control is thus produced which, on the one hand, keeps the vehicle in a predetermined position relative to the ground (for example parallel to the ground) and, on the other hand, adjusts the wheel contact force corresponding to a desired distribution. The superposition of the two controls can be carried out in such a way that the setpoint height position of the individual wheel or of a partial number of wheels is first determined on the basis of the position control. The setpoint height position can be corrected by means of a correction value which is determined by the control of the wheel contact force/spring load of all wheels or selected wheels.

In the present invention, there is no distinction between the terms adjustment and control. In this regard, adjustment in the narrow sense may mean control, and control may mean adjustment as well.

In an embodiment, an ideal load profile is calculated based on a plurality of wheel load forces. An actual load distribution may also be calculated, wherein the at least one second correction value is calculated based on a comparison of the ideal load distribution and the actual load distribution. In theory, an "ideal load profile" may be defined, and the latter may be used as a basis for the control/regulation according to the invention. A dynamic determination of the ideal load distribution is preferably carried out, wherein for example the load state of the vehicle is taken into account.

In order to determine the at least one correction value, in particular the at least one second correction value, the current spring load of some or all wheels or spring assemblies can be determined. Wheel load forces may also be generally considered.

In an embodiment, the at least one spring assembly may comprise a pneumatic and/or hydraulic and/or hydropneumatic spring assembly. In step c), the wheel load force (e.g. spring load) may then be calculated based on the measured load bearing pressure. Additionally or alternatively, in step e), the height position adjustment is performed by adjusting the pressure and/or volume in a spring assembly assigned to at least one wheel. According to the utility model discloses, can directly carry out the strength measurement with the help of the force sensor on the spring unit. Alternatively, the measurement can be made indirectly by pressure measurement on the load-bearing element (suspension cylinder, pneumatic suspension bellows, etc.).

The vehicle may comprise at least four wheels and the spring load of at least one pair of wheels may be calculated, said wheels being located at the first and/or second diagonal already mentioned. In this regard, the spring load of the spring assembly assigned to each diagonal wheel may be measured directly or indirectly. The spring load can thus be determined with a specific diagonal pressure sensor. Alternatively or in addition, individual spring loads on individual wheels may be measured, and based on these measurements (total) spring loads for the respective diagonals may be determined.

The required control loop can thus be kept relatively simple.

In principle, it is also possible to adjust or control asymmetrically. Preferably, a first spring load of a first pair of wheels on a first diagonal is calculated, and a second spring load of a second pair of wheels on a second diagonal is calculated, wherein the first diagonal intersects the second diagonal. In an embodiment, the wheels located on the diagonal are arranged offset relative to each other in the direction of travel.

By comparing the wheel load forces (e.g. spring loads) with each other and with a limit value, at least one wheel with a greater spring load can be determined. According to the invention, the wheels can be retracted (alternatively or in addition, less weight-loaded wheels can also be extended). Finally, this means that the more heavily loaded wheels are assigned such height positions: the height position results in the wheel adopting a position in which the wheel axle is closer to the reference plane of the vehicle. The load on the other wheels is thus increased and the load is thus adapted to the ideal situation.

In an embodiment, it is determined that a plurality of wheels (e.g. a pair of wheels) have a higher spring load, for example on the diagonal already described. By comparing the calculated wheel load forces (e.g. spring loads), a pair of wheels with a higher spring load can be determined for each pair of wheels. Alternatively or in addition, an adjustment to the limit value can also be carried out here. In step e), at least one wheel, preferably both wheels, on the diagonal with the higher spring load may be retracted. The control algorithm becomes more stable. Alternatively or additionally, a diagonal wheel with less load is projected.

In general, there are a number of situations in which it is determined that a wheel with a higher wheel load force is preferred, wherein the wheel with the higher wheel load force is retracted. Thus, for example in tilting, it is advantageous that the centre of gravity is not remote from the surface, but is closer to the surface after adjustment.

When there are multiple wheels (e.g. in the case of a mobile crane), for example 6, 8, 10 or 12, at least two wheels may be combined into a group. It is conceivable to consider the set of wheels as a single imaginary wheel. For example, a (single) second correction value for at least two wheels of the set may be calculated. According to the utility model discloses, can form a plurality of groups. For example, in the case of a three-axle vehicle, the two left-hand wheels and the right-hand wheel in each case can be combined into a group.

Step c) may comprise a plurality of measurements for determining the load force of at least one wheel, preferably a plurality of measurements being combined to form one measurement value. It is feasible to determine the mean or median value. A low pass filter may also be used in order to combine multiple measurements. The combination of the values can be carried out continuously, wherein values or a number of values which have been determined over a period of time can always be combined. The time period considered when using a low-pass filter may be longer than half a second, for example, preferably longer than one second. The time period may also be longer, e.g. longer than 3s or 5 s. The time period may also be dynamically adapted to the travelling behaviour of the vehicle, such as the speed.

The initially mentioned object is also solved by a computer readable storage medium comprising instructions for implementing the method having been described, which method has several or all of the specifically described features.

Furthermore, the initially mentioned object is solved by a system for position control of a vehicle having at least one computing unit and at least one computer readable memory, wherein the memory contains previously defined instructions.

The initially mentioned object is also solved by a system for position control of a vehicle having a plurality of wheels, wherein the system comprises:

-a plurality of height adjustable spring assemblies, each assigned to at least one wheel;

-a position sensor for determining the height position of the at least one spring assembly and for outputting at least one height position signal;

a (force) sensor for determining (directly or indirectly) the force acting on the at least one spring assembly and for outputting at least one force signal;

wherein the system is intended to adjust at least one spring assembly based on said force signal and said height position signal.

The sensor, in particular the force sensor, may be any sensor suitable for measuring the force acting on the respective spring assembly. The force determination may be made indirectly by a position sensor and/or a capacitive sensor.

Similar advantages also exist for these systems, such as those already explained in connection with the method.

The core idea here is primarily that the position control of the spring assembly (constant distance to the ground) can be improved by taking into account also the wheel contact force at the respective set point position.

The plurality of height adjustable spring assemblies may be mechanically coupled to the wheel, particularly the wheel axle, indirectly or directly. The mentioned position sensors may be angle sensors indicating the position of the wheel axle relative to the piston or chassis or the respective suspension point. They may also be linear sensors that indicate the position of the hydraulic piston relative to the hydraulic cylinder. It is obvious to a person working in the field that there are many possibilities to determine and indicate the height position, wherein this indication ultimately provides information about how far the spring assigned to the spring assembly is retracted or extended due to the action of force. The height position signal finally indicates the measured value in digital or analog form, so that it can be further processed, for example, by a computing unit.

In another aspect, the force sensor measures the force acting on the spring assembly and/or the respective wheel. In an embodiment, the wheel contact force is determined, or if appropriate only the longitudinal force of the spring element.

In an embodiment, a hydraulic or hydropneumatic suspension is used, wherein the force measurement is preferably made by pressure measurement. The force signal reproduces the measured force in digital or analog form, so that it can preferably be processed by the computing unit. However, according to the present invention, the described control loop can also be implemented without the use of a calculation unit. For example, control according to the present invention may be implemented with analog electrical, hydraulic, and/or mechanical logic circuits (differential pressure sensors, mechanical lowpass, etc.)

As previously mentioned, the system is intended to adjust at least one spring assembly based on the force signal and the height position signal. The use of both parameters can be done continuously or only occasionally.

As previously mentioned, the system may be position controlled, wherein at least one spring assembly is adjusted to a set point position or a set point height position using a height position signal. The setpoint position may be predetermined, for example, in the factory defined by the driver or by dynamic calculations.

In an embodiment, at least one memory is provided, wherein preferably each spring assembly stores at least one set point height position.

In one embodiment of the present invention, the set point height position may be altered based on user input. User input may be made via one or more operating elements, such as a touch screen.

Based on the at least one force signal, a correction value of the at least one spring assembly can be calculated, by means of which correction value the setpoint values of the at least two spring assemblies are adapted. The calculation of the correction value is preferably based on a plurality of force signals, which are averaged, for example, over a predetermined time interval. For example, a low-pass filter can be applied in order to filter out the measurement fluctuations on the basis of the oscillation cycle of the suspension. The resulting averaged and/or filtered force signal can then be used to calculate a correction value.

At least some of the spring assemblies may comprise hydraulic cylinders, wherein, for adjusting the height position of the spring assemblies, fluid is delivered by means of at least one pump and/or fluid (in particular oil) is discharged by means of at least one valve. It may thus involve volume control.

The utility model discloses a position control's system for vehicle, the vehicle has a plurality of wheels, a serial communication port, the system includes:

-a plurality of height adjustable spring assemblies, each spring assembly being assigned to at least one wheel;

a force sensor for determining a force acting on the at least one spring assembly and for outputting at least one force signal;

at least one spring assembly is adjusted based on the force signal and the height position signal.

Wherein the vehicle has at least one computing unit and at least one memory.

Wherein the at least one spring assembly is adjusted to a set point height position based on the height position signal.

Wherein at least two spring assemblies are individually position controlled.

Wherein the system comprises: a computing device that computes at least one correction value for at least two spring assemblies based on the at least one force signal; and an adjusting device which adjusts the setpoint height position of the at least two spring assemblies by means of the correction value.

Wherein the force signal is a plurality of force signals.

Wherein the at least one memory stores at least one set point height position.

Wherein the at least one memory stores at least one set point height position for each spring assembly.

Wherein at least some of the spring assemblies comprise hydraulic cylinders, wherein, for adjusting the height position of the respective spring assembly, fluid is delivered by means of at least one pump and/or fluid is discharged by means of at least one valve.

Wherein the fluid is oil.

Drawings

The invention is explained in more detail with the aid of several embodiment examples with reference to the attached schematic drawings with more details.

In a single picture:

fig. 1 shows a schematic plan view of a working machine according to the invention with four wheels and position control by means of a height-adjustable spring assembly;

FIG. 2 shows a schematic diagram of a control device implementing position control in a work machine;

FIG. 3 shows a schematic circuit diagram of a hydraulic system for adjusting the two spring assemblies of FIG. 1;

FIG. 4 shows a schematic front view of the work machine of FIG. 1;

fig. 5 shows a schematic diagram of a series of control algorithms.

List of reference numerals:

10,11 hydraulic unit

12 first connection

13a,13b pump

14 second connection

15 pot

16 third connection

17a,17b pressure accumulator

18 fourth connection

19a,19b hydraulic cylinder

20 rising branch

21 reduced branching

22 valve

23 electric motor

24 piston

25 second throttle valve

26 switch valve

27 first throttle valve

28 pressure limiting valve

29,30 control loop

31 fluid source

32 bypass line

33 suspension branch

34 connecting branch

35 pressure limiting branch

40 position control system

41a,41b,41c,41d spring assembly

44 position sensor

45 pressure sensor

50 working machine

51a,51b,51c,51d wheel

60 control computer

62 memory

64 calculation unit

Diagonal line D1 and D2

E reference plane

Height position of Ha, Hb, Hc, Hd wheel

Sa, Sb, Sc, Sd set point height position

k1, k2 correction values

K1, K2 node.

Detailed Description

Fig. 1 shows a schematic plan view of a work machine 50 having four wheels, i.e., a left front wheel 51a, a right front wheel 51b, a left rear wheel 51d, and a right rear wheel 51 c.

Wheels

51a,51b,51c,51d are each connected to the chassis of work machine 50 by

spring assemblies

41a,41b,41c,41d, respectively. The

spring assemblies

41a,41b,41c,41d include springs or

hydraulic cylinders

19a,19b (see fig. 3) that allow each

wheel

51a,51b,51c,51d to be spring-mounted. According to the present disclosure,

spring assemblies

41a,41b,41c,41d are adjustable in their height so that each

wheel

51a,51b,51c,51d may assume a predetermined position relative to the chassis of work machine 50. In this specification, the position is represented as a height position Ha, Hb, Hc, Hd, which represents a distance from a point, line or plane of the chassis.

Fig. 4 shows exemplary definition options for the height positions Ha, Hb, Hc, Hd. Reference plane E here passes through the underside of the chassis of work machine 50. The height position Ha of the right front wheel 51a is then measured as the distance of the wheel axle from the reference plane E. Accordingly, the height position Hb of the left front wheel 51b is defined as the distance of the wheel axle of the left front wheel 51b from the reference plane E. Alternatively, when the vehicle is standing on a completely flat ground, the reference plane may be defined such that it passes through the wheel contact points of the vehicle (here work machine 50).

Fig. 1 shows virtual diagonals D1 and D2, with wheel 51a and wheel 51c on a first diagonal D1 and wheel 51b, wheel 51D on a second diagonal D2.

In an example of embodiment of the present invention, the height position Ha, Hb, Hc, Hd of each

wheel

51a,51b,51c,51d is adjusted such that the

respective wheel

51a,51b,51c,51d assumes the set point height position Sa, Sb, Sc, Sd (fig. 5). These setpoint height positions Sa, Sb, Sc, Sd may be predetermined. In an example of embodiment, during ongoing operation, correction factors k1 (first diagonal D1) and k2 (second diagonal) are applied to the height positions Ha, Hb, Hc, Hd.

Work machine 50 has a control computer 60 to execute the control algorithm.

The control computer 60 includes a memory 62 and a computing unit 64 (see fig. 2). The memory 62 may store all instructions required to implement the method according to the invention. In addition, the memory 62 may store data required to perform the method. For example, the data may be the set point height positions Sa, Sb, Sc, Sd. Furthermore, the memory 62 may be used to store intermediate results, thereby storing the intermediate results for subsequent processing steps.

In a (further) example of embodiment, the set point height position Sa, Sb, Sc, Sd may be adjusted by the driver or user. To this end, work machine 50 may include a twist handle (e.g., with a potentiometer) or a touch screen. According to the present invention, a plurality of options for inputting the setpoint height position Sa, Sb, Sc, Sd are conceivable.

The calculation unit 64 carries out the method according to the invention and ensures that the necessary measured values (for example, force signals and/or position signals) are read out from the sensors and the actuators are set accordingly.

To this end, the control computer 60 is communicatively connected to

spring assemblies

41a,41b,41c,41d (see fig. 2) and the fluid source 31 (fig. 2 or 3), wherein each spring assembly includes a position sensor 44 and a pressure sensor 45 (in this regard, see also the position sensor and pressure sensor 45 illustrated in fig. 3).

In the described example of embodiment, the

spring assemblies

41a,41b,41c,41d form a hydraulic system.

The example of an embodiment of the hydraulic system represented in fig. 3 may be used as a suspension system in a work machine 50, and more particularly for achieving position control or adjustment according to the present disclosure, wherein each

wheel

51a,51b,51c,51d or each

spring assembly

41a,41b,41c,41d may be individually controlled or adjusted. The present invention is not limited to the hydraulic system shown in fig. 3, which is only for a more detailed explanation.

Fig. 3 schematically shows a hydraulic system with two

control circuits

29,30 for

spring assemblies

41a and 41 b. According to an example of embodiment, also in order to adjust the

spring assemblies

41c and 41d accordingly, a further control circuit (not shown in fig. 3) is provided. The

control loops

29,30 may be configured differently. The present invention is not limited to a four-loop system, but may include a single control loop or two control loops or more than four control loops, e.g., six, eight or more control loops. The following explanations relating to the first control loop 29 apply analogously to the second control loop 30 and all further control loops. With regard to the reference numerals of the corresponding components of the control loop, reference is made to the list of reference numerals.

The second control circuit 29 includes a hydraulic cylinder 19 a. The hydraulic unit 10 is rigidly fixed, for example screwed or welded, to the hydraulic cylinder 19 a.

As can be seen in fig. 3, the hydraulic cylinder 19a and the fluid source 31 are fluidly connected by a line, in particular a pipe, or a hose connection. The supply of hydraulic fluid to the hydraulic cylinder 19a is controlled by this fluid connection. The pressure load delivery volume required for the stroke of hydraulic cylinder 19a is provided by fluid source 31. The hydraulic system is designed according to the displacement principle, wherein a fluid source 31 delivers hydraulic fluid into the hydraulic cylinder 19a for upward adjustment of the position, i.e. for raising the hydraulic cylinder 19a (the later height position is higher than the previous height position).

The fluid source 31 comprises a switchable or controllable or adjustable pump drive 13 a.

For example, the switchable fluid source 31 may be a fixed displacement pump, i.e. a pump with a constant displacement volume per revolution. Switchability of the fluid source 13a is typically achieved by a drive element (e.g., motor 23) connected to the fluid source 13 a. The motor 23 connected to the fixed displacement pump is switched on and off for the lifting operation. Alternatively, a fixed displacement pump may be coupled to the motor 23 by a coupling, if desired. Other options are also possible.

The hydraulic unit 10 forms a hydraulic block with a first connection 12, which is or can be connected to a pump drive 13a, in particular to a pump driven by an electric motor. The hydraulic unit 10 comprises a second connection 14, which is or can be fluidly connected to a tank 15. Tank 15 belongs to a fluid source 31. Alternatively, a common tank may be used with other systems. The third connection 16 of the hydraulic unit 10 is or can be connected to an accumulator 17a, for example a membrane accumulator. Such pressure accumulators are known per se.

The fourth connection 18 is connected to a hydraulic cylinder 19 a. As can be seen in fig. 3, the fourth connection 18 is connected directly to the hydraulic cylinder, i.e. without an intervening hose connection. For this purpose, the hydraulic unit 10 is directly or generally rigidly connected to the wall of the hydraulic cylinder 19, wherein the fourth connection 18 is made directly through the wall. This is represented in fig. 3 by the fact that the system boundary (dashed line) of the hydraulic unit 10 coincides with the wall of the hydraulic cylinder 19.

The hydraulic unit 10 comprises a raising branch 20 and a lowering branch 21 and optionally further branches having other functions, such as a suspension branch 33, a connecting branch 34 and a pressure limiting branch 35.

The rising branch 20 comprises a conduit from a first connection 12, which is or can be connected to the pump drive 13a, to a first node K1, at which first node K1 the falling branch 21 is fluidly connected to the rising branch 20 or branches off from the rising branch 20. Fig. 3 shows that only a check valve 22 is arranged in the rising branch 20, which check valve 22 prevents hydraulic fluid from leaving the hydraulic unit 10 when the line or hose connection between the hydraulic unit 10 and a fluid source 31 arranged spaced apart from the hydraulic unit 10 is interrupted or not tight.

The connecting branch 34 is arranged downstream of the rising branch 20 in the flow direction.

The connecting branch 34 comprises a line or channel of the hydraulic unit 10 functionally belonging to both the rising branch 20 and the falling branch 21. The connecting branch 34 is therefore characterized by hydraulic fluid flowing through the conduit or passage of the connecting branch 34 in both directions, more precisely in the direction towards the hydraulic cylinder 19a during the lifting operation and in the direction away from the hydraulic cylinder 19a during the lowering operation.

The connecting branch 34 connects both the raising branch 20 and the lowering branch 21 to the hydraulic cylinder 19 a.

The connecting branch 34 extends from the first node K1 to the fourth connection 18 and comprises the fourth connection 18, which fluidly connects the hydraulic cylinder 19a to the hydraulic unit 10.

The suspension branch 33 is fluidly connected to the hydraulic cylinder 19a and includes a first throttle 25 arranged downstream of the second node K2. Furthermore, the suspension branch 33 comprises a pressure accumulator 17a, for example a membrane pressure accumulator.

The lowering branch 21 comprises a line or a channel through which hydraulic oil alone flows during the lowering operation, which hydraulic oil is delivered out of the hydraulic cylinder 19 a. The flow takes place in a single flow direction and more precisely in the line of the lowering branch 21 in the direction towards the tank 15. During lowering, i.e. when the hydraulic cylinder 19a is adjusted downwards, the lowering branch 21 has the function of discharging or partially discharging the hydraulic fluid present in the hydraulic cylinder 19 a. A switching element or a control element is provided in the lowering branch 21 in order to change the lowering speed of the hydraulic cylinder 19 a. Since no power is supplied to the system during the lowering operation, relatively less throttling losses occur.

In particular, the lowering branch 21 comprises a line which leads from the first node K1 and comprises the second connection 14, which is or can be connected to the tank 15. The lowering branch 21 comprises a switch valve 26. The on-off valve 26 is a proportional valve seat that controls the volume flow from the hydraulic cylinder 19a to the tank 15. Other valves are possible.

The second throttle valve 27 is disposed upstream of the on-off valve 26 in the flow direction.

The pressure-limiting branch 35 comprises a bypass line 32 which connects the connecting branch 34 with the lowering branch 21, bypassing the switching valve 26. In particular, the pressure-limiting branch 35 connects the connecting branch 34 between the node K1 and the node K2 with the point of the lowering branch 21 arranged downstream of the on-off valve 26. The pressure limiting branch 35 comprises a pressure limiting valve 28, which pressure limiting valve 28 opens when there is an excessive pressure in the connecting branch 34 in order to protect the hydraulic cylinder 19a from damage. Excessive pressure may occur, for example, due to an impact that acts on the hydraulic cylinder 19a from the outside when traveling on an uneven surface.

The

control circuits

29,30 are supplied with hydraulic fluid from a single fluid source 31. The illustrated principle can be used for a single control circuit or for a plurality of control circuits, for example for six or more control circuits, wherein a corresponding number of pumps or a corresponding number of separate volume flows are provided. In the example shown, two pumps are provided which are respectively assigned to the

control circuits

29, 30. Both pumps are driven jointly by an electric motor 23. Additional pumps with additional motors 23 may be provided for the third and fourth control circuits.

The hydraulic system shown in fig. 3 is intended only as an example for adjusting the height positions Ha, Hb of the

wheels

51a,51b, respectively. It operates as follows:

the motor 23 is turned on to raise the vehicle axle or change the height position Ha, Hb of the

wheel

51a or 51 b. Hydraulic fluid is fed into the

hydraulic units

10,11, more precisely into the respective lifting branch 20 and connecting branch 34 of the two

hydraulic units

10,11, in each case via the first connection 12. Hydraulic fluid is fed from the respective lifting branch 20 via the connection branch 34 via the fourth connection 18 into the hydraulic cylinder 19a of the wheel 51a and/or into the hydraulic cylinder 19b of the wheel 51 b. The piston 24 is extended to raise the vehicle. Thereby changing the height positions Ha, Hb of the

wheels

51a,51b, respectively.

To lower the vehicle axle, the two switching valves 26 are energized or de-energized depending on the desired switching position. Depending on the switching position of the two switching valves 26, the respective volume flow is fed back via the connecting branch 34 via the lowering branch 21 via the second connection 14 into the tank 15. The piston 24 retracts and the vehicle axle is lowered.

When only the right wheel 51a is raised or retracted (the height position Ha becomes smaller), the motor 23 is opened and the on-off valve 26 of the spring assembly 41b is energized. When only the left wheel 51b is raised, the motor 23 is turned on, and in turn the right switching valve 26 of the spring assembly 41a is energized. In general, in order to lift only the first wheel or only the first side, the respective lifting function of the other, second wheel or other, second side is deactivated by opening the lowering branch 21 of the

hydraulic unit

10,11 of the second wheel or second side.

When only the left wheel 51a is lowered, only the left switch valve 26 is energized, and conversely when only the right wheel 51a is lowered, only the right switch valve 26 is energized. Fig. 3 shows only one variant of how the

spring assemblies

41a,41b,41c,41d are controlled in order to change in each case the respective height position Ha, Hb, Hc, Hd of the

wheels

51a,51b,51c,51 d.

Fig. 5 schematically shows an implementation of a control or regulation method according to the invention. Here, in a first step, for example, the set point height positions Sa, Sb, Sc, Sd of the

respective wheels

51a,51b,51c,51d are read out from the memory 62 (step "read Sa, Sb, Sc, Sd").

Based on the signals of the pressure sensors 45 of the

respective spring assemblies

41a,41b,41c,41D, correction values k1 and k2 for one of the diagonals D1 and D2 (see fig. 1), respectively, are determined (step "determine k1, k 2").

In the next step, the actual height positions Ha, Hb, Hc, Hd of the

respective wheels

51a,51b,51c,51d are measured or determined (step "measure Ha, Hb, Hc, Hd"). The measurement is based on the position sensor 44 of the

respective spring assembly

41a,41b,41c,41 d. The foregoing two steps may be performed in any order or simultaneously.

In one or more subsequent steps, it is determined for each

spring assembly

41a,41b,41c,41d, respectively, whether the measured height position Ha, Hb, Hc, Hd coincides in position with the setpoint (Sa + k1, Sc + k1 or Sb + k2, Sd + k2) corrected by the correction value k1, k2 (see step "if Sa + k 1.

If there is a deviation here, an adjustment of the

divergent spring assemblies

41a,41b,41c,41d is carried out, respectively (see step "adjustment 41 a"). For this purpose, the control computer 60 outputs corresponding control or regulating signals, which can be implemented by means of the hydraulic system described in fig. 3. This results in the height position being adjusted to the desired correct set point position. If no adjustment of the

respective spring assemblies

41a,41b,41c,41d is required (e.g., Sa + k1 corresponds to Ha), the adjustment steps for the

respective spring assemblies

41a,41b,41c,41d may be skipped or omitted. It is clear that in each case two correction values enter the height position adjustment of the

respective spring assembly

41a,41b,41c,41 d. The first correction value takes into account the difference between the actual and setpoint height position, the second correction value k1, k2 being based on a measurement of the wheel load force and/or a calculation of an optimal wheel load distribution. According to the invention it is irrelevant whether the individual values are calculated separately or combined in a correction value that includes everything.

After comparison/checking and possible adjustment of the height positions Ha, Hb, Hc, Hd of all

spring assemblies

41a,41b,41c,41d, a renewed determination of the correction values k1, k2 is carried out (step "determine k1, k 2"). Thereby creating a control loop in which continuous adjustment to the optimal position control is made.

The steps of checking the height position Ha, Hb, Hc, Hd of the

spring assembly

41a,41b,41c,41d and its adjustment can be performed in parallel or, according to the invention, in any order. In the example of embodiment, the adjustment of the respective height positions Ha, Hb, Hc, Hd is started in a parallel process as shown in fig. 5, wherein the next step of fig. 5 is performed immediately after the start of the process. In the sequence as shown in fig. 5, therefore, no feedback of the effect of successful adjustment of the respective height positions Ha, Hb, Hc, Hd is waited for.

In the example of embodiment, a correction value k1, k2 is calculated in each control cycle, which is preferably selected to be proportional to the calculated pressures of the two diagonals D1, D2.

The wheel contact forces acting on the

wheels

51a,51b,51c,51D can thus be determined relatively easily by pressure for the first diagonal D1 and the second diagonal D2:

pressure of first diagonal D1:

where PHR denotes the measured pressure of the spring assembly 41c of the right rear wheel 51c, and PVL denotes the measured pressure of the spring assembly 41a of the left front wheel 51 a.

This also applies to the pressure of the second diagonal D2:

where PVR represents the measured pressure of the spring assembly 41b of the right front wheel 51b and PHL represents the measured pressure of the spring assembly 41d of the left rear wheel 51 d.

The correction value k1, k2 may then be determined as follows, when PD1< PD 2:

k1＝0；

k2＝-1*PD2/PD1*maxK，

where maxK represents the maximum correction possible in a given system.

Accordingly, when PD1> PD 2:

k1＝-1*PD2/PD1*maxK；

k2＝0。

in an example of embodiment, an ideal wheel load profile is calculated based on a wheel load force (e.g. spring load or wheel contact force). This ideal wheel load profile is compared with the actual wheel load profile. The adjustment of the correction values k1, k2 may be performed based on the result of this comparison.

In an example of embodiment, the optimal correction values k1, k2 are approximated step by step (e.g., with a constant step size). Therefore, in the case where the actual force proportional to the pressure is not calculated, when PD1> PD2 (then k2 is preferably set to zero), the correction value k1 may be gradually decreased.

Accordingly, in the example of this embodiment, when PD2> PD1 (then k1 is preferably set to zero), the correction value k2 may be decreased in a stepwise manner.

The step width may have any value suitable for the system to be controlled. For example, when PD1> PD2, k1 may be set to-1 at the first control step. If the first diagonal D1 is still more heavily loaded than the second diagonal D2 in the subsequent control step, k1 is set to-2. Therefore, with the constant correction value k2 being 0, the correction value k1 is gradually increased or decreased.

Accordingly, when PD1< PD2, k2 may be set to-1 at the first control step. If the second diagonal D2 is still more heavily loaded than the first diagonal D1 in the subsequent control step, k2 is set to-2. Therefore, with the constant correction value k1 being 0, the correction value k2 is gradually increased or decreased.

In the example of embodiment, the increase or decrease of the correction value k1 or k2 is only made when the pressure difference and thus the force difference are significant. According to the present invention, a pressure difference or force difference of more than 3% or more than 5% or more than 10% may be considered significant. Thus, in the previous example, the k1 value was only reduced when PD1> PD2 x 1.1 occurred (at least 10% difference). This may be applied to the correction value k 2.

In some or all of the described embodiments. A low-pass filter can be used to determine the height position Ha, Hb, Hc, Hd and/or the wheel load force (in particular the spring load), so that a series of previous values are always taken into account for determining the current value. An implementation of a corresponding low-pass filter is described by way of example in DE19748224B 4.

Many variations of the invention will occur to those skilled in the art and it is hereby stated that such variations are in accordance with the invention.

Claims

1. A system for position control of a vehicle (50), said vehicle (50) having a plurality of wheels (51a, 51b,51c,51 d), characterized by,

the system comprises:

-a plurality of height adjustable spring assemblies (41a, 41b,41c,41 d), each spring assembly (41a, 41b,41c,41 d) being assigned to at least one wheel (51a, 51b,51c,51 d);

-a position sensor (44) for determining a height position (Ha, Hb, Hc, Hd) of the at least one spring assembly (41a, 41b,41c,41 d) and for outputting at least one height position signal;

-a force sensor for determining a force acting on the at least one spring assembly (41a, 41b,41c,41 d) and for outputting at least one force signal;

at least one spring assembly (41a, 41b,41c,41 d) is adjusted based on the force signal and the height position signal.

2. The system for position control of a vehicle (50) according to claim 1, characterized in that the vehicle (50) has at least one calculation unit (64) and at least one memory (62).

3. A system for position control of a vehicle (50) according to claim 1, characterized in that at least one spring assembly (41a, 41b,41c,41 d) is adjusted to a set point height position (Sa, Sb, Sc, Sd) based on the height position signal.

4. A system for position control of a vehicle (50) according to claim 3, characterized in that at least two spring assemblies (41a, 41b,41c,41 d) are individually position controlled.

5. System for position control of a vehicle (50) according to any of claims 1 to 4, characterized by at least one memory (62) storing at least one set point height position (Sa, Sb, Sc, Sd).

6. A system for position control of a vehicle (50) according to claim 5, characterized in that said at least one memory (62) stores at least one set point height position (Sa, Sb, Sc, Sd) for each spring assembly (41a, 41b,41c,41 d).

7. System for position control of a vehicle (50) according to any of claims 1 to 4, characterized in that at least some of the spring assemblies (41a, 41b,41c,41 d) comprise hydraulic cylinders (19a, 19b), wherein for adjusting the height position (Ha, Hb, Hc, Hd) of the respective spring assembly (41a, 41b,41c,41 d) fluid is delivered by means of at least one pump (23) and/or fluid is discharged by means of at least one valve (26).

8. The system for position control of a vehicle (50) of claim 7, wherein the fluid is oil.