METHOD FOR OPERATING A DAMPER VALVE FOR CONTROLLING A DAMPER FORCE OF A DAMPER

Abstract

A method for operating a damper valve in order to control a damper force of a damper in an active chassis of a vehicle, wherein the damper valve includes a pilot valve for controlling a main spool. The method includes determining a target pressure necessary for a target damper force, in a first damper chamber of the damper; determining a valve flow through a damper valve inlet of the damper valve on the basis of a damper flow, generated by a damper movement, from the first damper chamber and on the basis of a measured pump flow of a pump; determining a main spool opening distance in such a way that, with an applied main spool flow through the main spool opening distance, the target pressure is present as the back pressure in the first damper chamber.

Claims

1. A method for operating a damper valve of a damper, wherein the damper valve comprises a pilot valve for controlling a main spool, wherein the method comprises: determining a target pressure (F.sub.D) necessary for a target damper force (p.sub.D) in a first damper chamber of the damper; determining a valve flow (Q.sub.V) through a damper valve inlet of the damper valve on the basis of a damper flow (Q.sub.D), generated by a damper movement, from the first damper chamber and on a basis of a measured pump flow (Q.sub.P) of a pump; determining a main spool opening distance (x.sub.HS) in such a way that, with an applied main spool flow (Q.sub.HS) through the main spool opening distance (x.sub.HS), the target pressure (p.sub.D) is present as a back pressure in the first damper chamber; determining a pilot valve flow (Q.sub.PV), which, at the target pressure (p.sub.D) to be set, passes via an inlet throttle in the main spool to the pilot valve and at which the main spool is in a force equilibrium; determining a pilot valve opening distance (x.sub.PV) on the basis of the pilot valve flow (Q.sub.PV); determining an armature position (x.sub.A) on the basis of the main spool opening distance (x.sub.HS) and the pilot valve opening distance (x.sub.PV); and setting the armature position (x.sub.A) by way of an actuator.

2. The method according to claim 1, wherein an actual force of the damper is furthermore determined on the basis of pressures ascertained at the pump, of a damper movement, and/or of a temperature of a damper medium.

3. The method according to claim 2, wherein the armature position (x.sub.A) is controlled on the basis of a deviation of the predetermined target force (F.sub.D) and the measured actual force.

4. The method according to claim 1, wherein the actuator is an electromagnet and a magnetic force necessary for the armature position (x.sub.A) to be set is determined on the basis of a force equilibrium at an armature.

5. The method according to claim 4, wherein a determination of a magnet valve current, which leads to a magnetic force applied by the electromagnet to the armature, is determined on the basis of at least one characteristic map.

6. The method according to claim 1, wherein a specification of the pump flow (Q.sub.P) is determined as a function of the target force (F.sub.D) to be provided, of a driving situation of a vehicle comprising the damper, and/or of a damper movement.

7. The method according to claim 1, wherein the target pressure (p.sub.D) is determined based on a static pressure (p.sub.s) in a second damper chamber, a target damper force (F.sub.D) to be set, and a piston surface between the first damper chamber and the second damper chamber.

8. The method according to claim 7, wherein the static pressure (p.sub.s) is set as a function of an ambient temperature and a position of a piston in a cylinder of the damper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention is explained below in greater detail with reference to the appended FIG. 1. In particular, advantageous embodiments and aspects of the invention are discussed.

[0020] FIG. 1 shows a schematic representation of a damper system of a vehicle.

DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 shows a schematic representation of a damper system of a vehicle, consisting of a damper 20, a damper valve 10, a pump 30, and a pressure reservoir 40. The damper 20 comprises a cylinder 21, which is divided into a first damper chamber 211 and a second damper chamber 212 by a piston 22 having a piston rod 221. The first damper chamber 211 is fluidly connected to the damper valve 10 via a damper valve inlet 16 and the pump 30. The second damper chamber 212 is fluidly connected to the damper 10 via a damper valve outlet 17 and the pressure reservoir 40.

[0022] The damper valve 10 comprises an armature 11, which can be moved by an actuator in the form of an electromagnet 12. The position of the armature 11 is referred to as the armature position x.sub.A. The armature 11 is in this case preloaded by a spring 13. A pilot valve 14, which defines a pilot valve opening 141 to a main spool 15, is provided on the armature 11. The distance between the pilot valve 14 and the main spool 15 is referred to as the pilot valve opening distance x.sub.PV.

[0023] The main spool 15 encloses a main spool volume 153 in the damper valve 10, wherein the main spool volume 153 is fluidly connected to the first damper chamber 211 through the damper valve inlet 16. Furthermore, depending on the position of the main spool 15, a main spool opening 152 is provided between the main spool 15 and the housing of the damper valve 10 so that the main spool volume 153 defined by the main spool 15 is fluidly connected to the damper valve outlet 17 through the main spool opening 152. The distance between main spool 15 and the housing of the damper valve 10, which defines the main spool opening 152, is referred to as the main spool opening distance x.sub.HS. Through the main spool opening 152, a main spool flow Q.sub.HS can thus flow from the main spool volume 153 toward the damper valve outlet 17. Furthermore, the main spool 15 comprises an inlet throttle 151, which likewise represents a fluid connection from the volume enclosed by the main spool 15, toward the pilot valve 14.

[0024] The mode of operation of the shown damper valve 10 using the method according to aspects of the invention is considered in more detail below. In this case, a pulling force as a damper force F.sub.D is to be applied to the piston 22, which damper force is oriented toward the right in the drawing plane, as indicated by the corresponding arrow on the piston rod 221. Such a force is to be provided to compensate for a disturbance as a result of a movement of the piston 22. To do so, a pressure in the first damper chamber 211 must be increased to a particular target pressure p.sub.D. A disturbance of the piston 22 toward the left induces a damper flow Q.sub.D, which flows from the first damper chamber 211 toward the damper valve inlet 16. A valve flow Q.sub.V flowing through the damper valve inlet 16 is composed of the damper flow Q.sub.D and a pump flow Q.sub.P provided by the pump 30.

[0025] The valve flow Q.sub.V results in a pressure in the main spool volume 153 defined by the main spool 15. The pressure applied there is backed up into the first damper chamber 211 via the corresponding pressure lines so that, with a corresponding control, the back pressure caused must correspond to the target pressure p.sub.D. This back pressure is determined by the main spool flow Q.sub.HS, which arises through the main spool opening 152 as a function of the main spool opening distance x.sub.HS. If there is a large main spool opening distance x.sub.HS and thus a large main spool opening 152, the back pressure is lower.

[0026] The main spool opening distance x.sub.HS is in this case defined by a force equilibrium at the main spool 15. As a result of the inlet throttle 151, a low flow passes through the main spool 15 to the pilot valve 14. The force equilibrium of the main spool 15 is accordingly set through the pressure above and below the main spool 15 as well as a preloading of a spring which is provided accordingly above the main spool 15 and preloads the main spool 15 downward. The opening of the inlet throttle 151 is constant so that a particular pressure within the main spool volume 153 and thus a defined target pressure p.sub.D in the first damper chamber 211 result in a particular flow through the inlet throttle 151. Depending on the opening of the pilot valve 14, the pressure above the main spool 15 can thus be set. In the case of a large pilot valve opening distance x.sub.PV, the pilot valve opening 141 is large, as a result of which a relatively large pilot valve flow Q.sub.PV passes through the pilot valve opening 141. Through the pilot valve flow Q.sub.PV, the pressure drop in the volume above the main spool 15 is set via the inlet throttle 151. In the case of a high pilot valve flow Q.sub.PV, the pressure drop across the inlet throttle 151 is large and the compression force acting downward on the main spool 15 is thus reduced in the volume above the main spool 15. The main spool opening distance x.sub.HS is thereby increased. By closing the pilot valve opening 141, i.e., reducing the pilot valve opening distance x.sub.PV, the pressure above the main spool 15 can be increased, which leads to a lower main spool opening distance x.sub.HS and consequently to a greater back pressure within the main spool volume 153. The pilot valve 14 in turn can be set by the cooperation of the armature 11 and the electromagnet 12.

[0027] It should be noted at this point that a static pressure p.sub.s in the second damper chamber 212 is not critically influenced by the pilot valve flow Q.sub.PV and the main spool flow Q.sub.HS, which flow from the damper valve outlet 17, and is kept constant by the pressure reservoir 40.

[0028] According to the method according to aspects of the invention, based on the illustrated mode of operation of the damper valve 10, the target pressure p.sub.D, required for the target damper force F.sub.D, in the first damper chamber 211 of the damper 20 is determined first. For this purpose, the static pressure p.sub.s in the second damper chamber 212 and the surface of the piston 22 are considered. Subsequently, the valve flow Q.sub.V is determined based on the damper flow Q.sub.D and the pump flow Q.sub.D. In this case, the pump flow Q.sub.D is preferably ascertained as a function of the target force F.sub.D to be provided, of a driving situation of the vehicle, and/or of a damper movement.

[0029] Furthermore, the main spool opening distance x.sub.HS required to generate the back pressure in the main spool volume 153 and thus the corresponding target pressure p.sub.D in the first damper chamber 211 is calculated. In addition, the pilot valve flow Q.sub.PV, which flows out of the main spool volume 153 via the inlet throttle 151, for the corresponding back pressure in the main spool volume 153 is determined. This preferably takes place with the aid of a hydraulic model of the inlet throttle 151. Subsequently, the pilot valve opening distance x.sub.PV is determined, which is necessary in order to establish the force equilibrium at the main spool 15 in order to set the target main spool opening distance x.sub.HS. The armature position x.sub.A required for this purpose is furthermore calculated from the sum of the pilot valve opening distance x.sub.PV and the main spool opening distance x.sub.HS. Preferably, in this case, a known offset of the damper valve, which can be predetermined as the valve setting, is furthermore taken into account.

[0030] In order to ultimately generate the target pressure p.sub.D in the first damper chamber 211, the electromagnet 12 is subsequently controlled in such a way that the armature 11 moves to the calculated armature position x.sub.A. This method enables a corresponding control of the damper force during the detection of the actual force of the damper 20. The actual force is preferably calculated via a hydraulic model from pressures measured at the pump 30, from the damper movement, and from the oil temperature. On the basis of the target-actual force deviations, the magnetic force of the electromagnet 12 for setting the armature position x.sub.A can be adjusted accordingly.

[0031] The magnetic force necessary for the setting of the armature position x.sub.A is calculated from a force equilibrium at the armature 11. Acting on the armature 11 due to the pilot valve flow Q.sub.PV at the pilot valve 141 are a compression force from below upward, the magnetic force itself downward, and the spring force of the spring 13 proportionally to the armature position x.sub.A. This force equilibrium can be changed according to the magnetic force to be set, by specifying the armature position x.sub.A. Deviations between the target and actual forces are directly applied to the magnetic force via a PI controller, whereby the armature position x.sub.A is readjusted. In the last step, the magnetic force is converted into a magnet valve current. This conversion preferably takes place with a characteristic map.