Method for changing the spring rate of an air spring for a vehicle wheel

Abstract

Method for changing the spring rate of a multi-chamber air spring of a vehicle chassis, for which at least one additional air chamber of the multi-chamber air spring can be selectively coupled to a main air chamber, characterized in that, for this purpose, an electric motor with a downstream self-locking gearbox, controlled by a control unit, adjusts a ball valve installed in a connection between the main air chamber and the additional air chamber.

Description

[0001] The invention relates to a method for changing the spring rate of an air spring at an upper support bearing of a vehicle wheel suspension, which ultimately supports a vehicle wheel in a strut tower of the vehicle, according to the preamble of the first claim.

[0002] Various air spring systems are already known in the prior art. Among them are switchable air springs, which allow for variable spring behavior. These air springs consist of an air bellows with multiple air volumes that can be connected to each other via valves. By opening or closing at least one of the valves, the effective air volume is varied, thus changing the spring rate of the air spring. This results in a shift in the natural frequency of the sprung and unsprung masses.

[0003] The air volume is controlled via solenoid valves. To avoid switching noise, however, controlled deceleration of the valve before reaching its end position is necessary. If this deceleration is implemented electrically, it leads to a high control complexity, and using a pulse-width modulation (PWM) method can cause electromagnetic compatibility (EMC) issues. Further disadvantages arise from the design of the valves. Firstly, the valve can only be in two states: open or closed. Due to this operating principle of a solenoid valve, a continuous current is required to maintain one of the two states. If a spring rate deviating from the nominal spring rate is to be set for an extended period, a constant connection between two air volumes must be maintained.To enable this, a continuous power supply to the valves, and thus a constant energy flow, is necessary. This is disadvantageous because it significantly heats up the power electronics. If these are integrated into central control units, this can lead to cooling problems. As the number of air chambers used increases, so does the number of valves required, which exacerbates the aforementioned disadvantages.

[0004] German patent application DE 103 36 342 A1 describes a multi-chamber air spring system. The aim of this system is to allow for variation of the spring rate. For this purpose, the spring system consists not only of a main air chamber, but also of at least one additional air chamber. Advantageously, two additional air chambers with different volumes are used. To vary the spring rate, the main and additional chambers are connected via a pipe system. To simplify the installation of this system, only one valve is used to connect / disconnect both additional volumes to the main chamber. An electrically actuated multi-way slide valve or a multi-way rotary valve is preferably used for this purpose. To prevent sudden changes in height when the valves are switched, the air volumes are connected to a compressor and venting system, which generates a uniform system pressure.

[0005] Building on this, DE 10 2007 050 187 A1 describes a multi-chamber gas spring system consisting of one main chamber and at least one secondary chamber per wheel. A fluidic connection exists between the secondary chambers and the main chamber. Valves allow the secondary chambers to be connected to or disconnected from the main chamber. The axle stiffness is adjusted depending on the resulting total volume. The valves required to control the total volume can be implemented as switching valves or proportional valves. Proportional valves offer the advantage of continuous variation between the open and closed positions. The valves are actuated electrically by controlling an electromagnet.

[0006] The object of the present invention is to provide a method for changing the spring rate of an air spring for a vehicle wheel, which enables variable spring behavior with as little control effort as possible and in which a permanent current supply to valves in certain control positions is avoided.

[0007] The problem is solved by the features and process steps of the first claim. Further embodiments of the invention are described in the dependent claims.

[0008] The inventive method for changing the spring rate of a multi-chamber air spring of a vehicle chassis, for which at least one additional air chamber of the multi-chamber air spring can be selectively coupled to a main air chamber, is characterized in that, controlled by a control unit, an electric motor with a downstream self-locking gearbox adjusts a ball valve installed in a connection between the main air chamber and the additional air chamber.

[0009] According to the invention, ball valves are proposed for separating the air volumes in a multi-chamber air suspension system. These valves are adjusted by an electric motor with a self-locking gearbox. The electric motor provides the necessary adjustment torque, while the self-locking gearbox prevents the valve from rotating when de-energized. With this type of adjustment, the valve only needs to be energized during the switching process and not for holding the valve in a position. The design and control of a ball valve allows not only for open and closed positions but also for adjusting other connecting cross-sections between the air volumes. This enables the implementation of an adjustable, low leakage, which allows for a very slow pressure equalization between the air volumes. This pressure equalization advantageously prevents abrupt changes in the vertical direction when the valve switches.Additionally, a ball valve makes it possible to switch multiple volumes via one valve.

[0010] A preferred embodiment of the method is characterized in that the control unit is mounted on the ball valve, and in particular, that the control unit, the electric motor, and the transmission form an actuator assembly. This is advantageously space-saving for the vehicle package.

[0011] Since the position of the ball valve needs to be measured and controlled, the control unit for the ball valve is mounted directly on it. For this purpose, it is advantageous to implement the control directly via a so-called private CAN bus and to design the control unit as a so-called smart actuator, i.e., as an actuator assembly. This means that a central master control unit determines the optimal positions for each individual ball valve and communicates these target positions to the respective smart actuators via a private CAN bus. These actuators execute the positioning requests and then report the actual position of their ball valve back to the master control unit. In addition to the private CAN bus connection, the smart actuators then only require a power supply.This type of power supply reduces the path of the electric current through the vehicle, which contributes to a reduced burden in the area of ​​electromagnetic compatibility.

[0012] Therefore, a further preferred embodiment of the inventive method is characterized in that at least one further additional air chamber can be connected to the main air chamber via a further ball valve, whereby a central main control unit determines a position for each ball valve and communicates this respective target position via a direct control line from the main control unit to each actuator assembly, whereupon the latter adjusts the associated ball valve and reports its new position to the main control unit. Additionally, the direct control lines are preferably implemented as a CAN bus.

[0013] Overall, the advantages of this method compared to the prior art are that maintaining a defined valve position requires no energy, continuous adjustment of the valve cross-section is possible, adjustable leakage prevents changes in the height of the air spring during valve switching, switching of multiple air volumes via a ball valve is possible, and reduced electromagnetic compatibility is achieved. Furthermore, the implementation as a smart actuator with control via a private CAN bus can improve the vehicle architecture.

Claims

[1] Method for changing a spring rate of a multi-chamber air spring of a vehicle chassis, for which purpose at least one additional air chamber of the multi-chamber air spring can be coupled to a main air chamber, characterized by that, controlled by a control unit, an electric motor with a downstream self-locking gear adjusts a ball valve built into a connection between the main air chamber and the additional air chamber. [2] Method according to claim 1, characterized by that the control unit is attached to the ball valve. [3] Method according to claim 1 or 2, characterized by that the control unit and the electric motor and the transmission form an actuator assembly. [4] Method according to claim 3, characterized bythat at least one further additional air chamber can be connected to the main air chamber via a further ball valve, in that a central main control unit determines a position for each ball valve and communicates this respective target position via a direct control line from the main control unit to each actuator assembly, whereupon the latter adjusts its associated ball valve and reports its new position to the main control unit. [5] Method according to claim 4, characterized by that the direct control lines are designed as CAN bus.