Method for operating a switchable engine mount and motor vehicle

Abstract

Method for operating a switchable motor bearing, in which - the engine mount has: ◯ a chamber; ◯ a separating element (12) which is movable between two positions, namely a separating position in which the separating element (12) separates a fluidic connection between the chamber and another area, and a release position in which the separating element (12) releases the fluidic connection; and ◯ an electrically operated actuator by means of which the separating element (12) can be moved by controlling the actuator; and - the actuator is controlled by means of a pulse width modulated signal, whereby the separating element (12) is moved at least from one of the positions to the other position, characterized in that the pulse width modulated signal is combined with a ramp function, by which an electrical voltage is selectively changed monotonically increasing or monotonically decreasing over at least three voltage values ​​during the control of the actuator, and the at least three voltage values ​​of the ramp function are specified as fractions of an on-board network voltage of the motor vehicle.

Description

[0001] The invention relates to a method for operating a switchable engine bearing according to the preamble of claim 1. The invention also relates to a motor vehicle.

[0002] From DE 103 24 245 A1, a hydraulically damped motor mount is known with an elastomer body that delimits a hydraulic chamber which is divided by a first diaphragm into two sub-chambers filled with hydraulic medium, and with an electrically actuated and suitably controllable actuator with which a force can be periodically exerted on the hydraulic medium and the actuator can act on the hydraulic medium via a second diaphragm provided in a secondary chamber or via a diaphragm delimiting one of the sub-chambers.

[0003] From DE 10 2010 001 004 A1, a method and a device for controlling actuators within a vehicle electrical system are known, which has different operating voltages or changes in vehicle electrical system voltage over time, wherein it is provided that the actuator(s) are controlled with different pulse-width modulated control signals, wherein the pulse width and the period of the control signals are adjustable independently of each other and are adapted depending on the currently applied vehicle electrical system voltage.

[0004] From CN 1 02 148 087 A, a method and a device for controlling an actuator within a vehicle electrical system is known, which provides different operating voltages or temporal and spatial changes in the vehicle electrical system voltage, wherein the actuator(s) are controlled with different pulse-width modulated control signals, wherein the pulse width and the period of the control signals are independently adjustable and are matched to the currently applied vehicle electrical system voltage.

[0005] From CN 1 10 580 997 A, a circuit for electronic control of an electromagnetic actuator of an electromagnetic valve is known, wherein the circuit provides a control signal for the electromagnetic actuator which has a high level and a low level as well as at least one first time interval with a first duty cycle, wherein the time length of the at least one time interval and the size of the at least one duty cycle are designed such that the electromagnetic actuator switches between operating states.

[0006] From DE 34 04 593 A1, a method for operating a switchable motor bearing is known. The motor bearing has a chamber and a separating element, wherein the separating element is movable between two positions: a separating position in which the separating element disconnects a fluidic connection between the chamber and another area, and a release position in which the separating element releases the fluidic connection. The separating element is movable by an electrically operated actuator. The actuator is controlled by means of a pulse-width modulated signal, whereby the separating element is moved at least from one of the positions to the other. The pulse-width modulated signal is combined with a ramp function, whereby an electrical voltage is selectively varied monotonically, either increasing or decreasing, over at least three voltage values ​​during the actuation of the actuator.

[0007] From JP 2010-91 062 A, a method for operating a switchable motor bearing is known. The motor bearing has a chamber and a separating element, wherein the separating element is movable between two positions: a separating position in which the separating element closes a fluidic connection between the chamber and another area, and a releasing position in which the separating element releases the fluidic connection. The separating element is movable by an electrically operated actuator. The actuator is controlled by a pulse-width modulated signal, which moves the separating element from at least one of the positions to the other.

[0008] A control circuit for an electric motor is known from JP H11-247 920 A. The control circuit features a pulsed and amplitude-modulated signal with a stepwise increasing reference voltage and a stepwise increasing pulsed control signal.

[0009] The invention is based on the objective of operating a switchable engine mount in a particularly quiet manner and of providing a motor vehicle with such an engine mount.

[0010] The problem is solved by a method with the features of claim 1 and by a motor vehicle with the features of claim 9. Advantageous embodiments of the invention are described by the dependent claims, the following description, and the figures.

[0011] In conventional motor vehicles, especially those with internal combustion engines, one or more engine mounts are installed between the engine and the vehicle body, thus supporting the engine against the body. An engine mount is designed to dampen the transmission of vibrations both from the engine to the body and vice versa. Vibrations transmitted from the engine to the body differ depending on the engine's operating condition. For example, at idle, i.e., at low engine speed, the engine exhibits a different excitation spectrum than when the vehicle, and therefore the engine, is in dynamic driving mode, i.e., at a higher engine speed than at idle. Therefore, it can be advantageous for the engine mount to also have different damping characteristics, between which it can switch depending on the operating condition.Electrically switchable hydraulic mounts can be used, for example, to provide different damping characteristics. Switching involves moving a movable or movable separating element, which, upon impact with a stop at the end of a switching process, can generate a broadband noise that is transmitted as structure-borne sound through the vehicle body into the passenger compartment and can be perceived as disturbing. A hydraulic mount dampens excitations or vibrations by moving fluid. A hydraulic mount can incorporate an elastically deformable membrane, the expansion of which provides additional space for the fluid.A first aspect of the invention relates to a method for operating a switchable motor bearing, in which the motor bearing comprises: a chamber, a separating element which is movable between two positions, namely a separating position in which the separating element separates a fluidic connection between the chamber and a further area, and a release position in which the separating element releases the fluidic connection, an electrically operable actuator by means of which the separating element can be moved by actuating the actuator, and the actuator is actuated by means of a pulse-width modulated signal, whereby the separating element is moved at least from one of the positions to the other position.The method is characterized by the fact that the pulse-width modulated signal is combined with a ramp function, by which an electrical voltage is selectively changed monotonically increasing or monotonically decreasing over at least three voltage values ​​during the actuation of the actuator.

[0012] The diaphragm expands into the chamber, which, depending on whether the separating element is in the release or disconnect position, may be fluidically connected to another area, such as the vehicle's surroundings, or it may be fluidically sealed off from the surroundings. If the chamber is fluidically sealed, the diaphragm must compress any fluid present in the chamber, such as air, as it expands into it. This means the expansion of the diaphragm counteracts a force. Therefore, if the chamber is fluidly sealed, the engine mount exhibits dynamically stiff damping. In this case, the separating element is in the disconnect position, and the engine mount is thus in a deactivated state. This state is particularly advantageous for the engine mount and the vehicle when the vehicle is in motion, i.e., driving on the road.If the chamber is fluidically open to the environment, pressure equalization between the chamber and the environment can occur when the diaphragm expands into the chamber. In this state, the separating element is in a release position and the engine mount is in an engaged state. In this state, the engine mount exhibits dynamically soft damping. This state is particularly advantageous when the engine is idling, for example, when the vehicle is stopped at a traffic light. To switch between the two states of the engine mount, the separating element is movable between two positions: the release position and the separation position. The actuator can move or guide the separating element between these two positions. The separating element can be designed as a pin or plunger, preferably rotationally symmetrical.To move the separating element from one position to another, the actuator can include an electromagnet, such as a copper coil. When the actuator is energized, the coil is powered, generating a magnetic field that attracts the separating element and moves it from at least one position to the other. For this purpose, the separating element can be partially made of magnetic material, such as nickel, iron, or cobalt, or of magnetic alloys containing these elements. Additionally, the actuator can include a return spring that automatically moves the separating element to a different position when the magnetic field is switched off, due to the spring's restoring force. As is known in the art, the actuator can be controlled by a pulse-width modulated (PWM) signal.The time interval within which the separating element is to be moved from one position to the other, or within which it is to be switched from an on state to an off state and vice versa, can be predefined. Within this time interval, the voltage applied to the actuator or coil to energize it should not rise abruptly from 0% to 100% of the available voltage, nor should it drop abruptly from 100% to 0%. The ramp function ensures that the voltage rises or falls monotonically over the specified time interval. Here, "monotonic," in contrast to "strictly monotonous," is to be understood in the commonly used mathematical sense.

[0013] This offers the advantage that the separating element strikes each stop at a lower speed and therefore with a lower impulse or final impulse. A first stop can be provided for reaching the release position and a second stop for reaching the disconnect position. The lower final impulse at each stop reduces the noise generated during impact compared to an abrupt increase or decrease in voltage across the coil from 0 to 100% and vice versa. Thus, the higher the final impulse, the louder or more pronounced the impact noise, and vice versa.

[0014] Furthermore, the inventive method is characterized by the fact that the at least three voltage values ​​of the ramp function are specified as fractions of the vehicle's electrical system voltage.

[0015] In other words, at least three voltage values, both during the switch-on and switch-off processes, should be preset as fractions, for example, as mathematical fractions or percentages of a currently available vehicle electrical system voltage. For the purposes of this invention, "available vehicle electrical system voltage" refers to the maximum available voltage. This maximum voltage can vary over time depending on several factors, such as the ambient temperature, battery temperature, and / or the electrical power consumed by the vehicle's electrical systems. In particular, the maximum available voltage can range between 9.4 volts and 16.7 volts.

[0016] By specifying the voltage values ​​as a fraction of the currently available on-board voltage, the advantage arises that the absolute on-board voltage can be disregarded and no absolute voltage values ​​need to be specified that may not be achievable if, for example, the available on-board voltage is below a specified voltage value.

[0017] The invention also includes embodiments that offer additional advantages.

[0018] In a further development of the invention, the method is characterized in that, in order to move the separating element from the separating position to the release position, the electrical voltage is changed monotonically increasing over at least three voltage values.

[0019] The movement of the separating element from the separation position to the release position is called the switching-on process. During the switching-on process, the separating element is moved along a defined path from the separation position to the release position. At the end of the switching-on process, the separating element should be in the release position, thus establishing the fluidic connection between the chamber and the surrounding area. This allows pressure equalization between the chamber and the surrounding area, and the motor bearing should exhibit a dynamically soft damping characteristic. During the switching-on process, the separating element can be moved against a restoring force from the return spring and, in the switched-on state, is held in the release position against the force of the tensioned return spring by the magnetic force of the coil.A voltage increase across three voltage levels at the actuator or coil means that the voltage is not increased directly across two voltage levels, for example, from 0 to 100% of a vehicle electrical system voltage, but rather that the voltage increases from 0 to 100% over a defined period. Specifically, the third voltage level, which lies between 0 and 100%, can be reached within a specified time. The time it takes to reach this voltage level between 0 and 100% can be determined based on a predetermined duty cycle. For example, a duty cycle of 0.2 to 1.0 seconds, or more specifically 0.3 to 0.5 seconds, can be specified for the switch-on process. The voltage increase can, for example, rise linearly over the duty cycle, with the third voltage level being reached after the specified time.

[0020] This results in the advantage that the separating element has a lower impact velocity and therefore a lower final impulse when reaching the release position, resulting in a lower impact noise than if the separating element is accelerated directly from the separation position with 100% of an available on-board voltage, i.e. the resulting magnetic field, throughout the entire switching-on process.

[0021] In a further development of the invention, the method is characterized in that the electrical voltage is increased stepwise over at least three voltage values ​​to move the separating element from the separating position to the release position.

[0022] Stepped in this context means that at least one voltage value between 0 and 100% of the available vehicle electrical system voltage is to be kept constant for a predetermined period during the switch-on process, i.e., within the switch-on time. With at least three voltage values, at least one step in the rising voltage curve is thus provided. A step is to be understood here as a plateau in the voltage curve over time in the mathematical sense. According to the invention, up to 10 voltage values ​​for 10 steps can be specified, each with a minimum duration of 0.1 seconds or 100 milliseconds between 0 and 100% of the available vehicle electrical system voltage.

[0023] This offers the advantage that the acceleration of the separating element, and thus its final velocity and final impulse, as well as the duration of the switching process, can be controlled.

[0024] In a further development of the invention, the method is characterized in that, in order to move the separating element from the release position to the separation position, the electrical voltage is changed monotonically decreasing over at least three voltage values.

[0025] Moving the disconnecting element from the enable position to the disconnect position is called the switch-off process. Similar to the previously described switch-on process, the voltage can drop linearly from 100% to 0% of the available on-board voltage during the switch-off process within a predetermined switch-off duration. During the switch-off process, the disconnecting element can be moved from the enable position to the disconnect position by the restoring force of the return spring.

[0026] In the off state, the fluidic connection between the outer area and the chamber is interrupted, and the motor bearing exhibits a dynamically stiff damping characteristic. A duration of 0.2 to 1.0 seconds, particularly 0.3 to 0.5 seconds, can be specified for the off process, within which the disconnecting element is to be moved from the release position to the disconnected position. During the off process, a person skilled in the art must take into account that, due to self-induction, the magnetic force of the coil decreases more slowly than the voltage applied to the coil. The decreasing magnetic force due to the voltage drop can counteract the restoring force. It must also be considered that the restoring spring can exert a maximum restoring force at the beginning of the off process.The ramp-like drop in voltage reduces the final pulse of the disconnecting element when the disconnect position is reached, compared to an immediate switch-off or shutdown of the voltage from 100% to 0% of the vehicle electrical system voltage.

[0027] The monotonous voltage drop over at least three voltage levels during the switch-off process means that at least one voltage level between 100% and 0% of the vehicle electrical system voltage is held constant for a predetermined period. In the switch-off state, i.e., when the isolating element is in the disconnected position, the fluidic connection between the chamber and the surrounding area is interrupted, and therefore pressure equalization between the chamber and the surrounding area is not possible when the diaphragm expands into the chamber.

[0028] In a further development of the invention, the method is characterized in that the electrical voltage is gradually reduced over at least three voltage values ​​to move the separating element from the release position to the separation position.

[0029] Similar to the stepwise increase in voltage during the switch-on process, this system provides for at least one voltage value between 100% and 0% to be held constant for a predetermined duration during the switch-off process. A total of up to 10 voltage values ​​between 100% and 0% of the available vehicle electrical system voltage can be specified. Each voltage value can be assigned or predefined a duration, which can be a minimum of 0.1 seconds. Holding individual voltage values ​​constant results in a stepped voltage curve.

[0030] This offers the advantage that the final impulse of the separating element can be controlled and, in particular, reduced when the separating position is reached, so that the noise generated when the separating element strikes the separating position can be reduced, compared to an abrupt or immediate switching off or reduction of the voltage from 100% to 0%.

[0031] In a further development of the invention, the method is characterized in that at least one of the at least three voltage values ​​is assigned a time period during which the at least one voltage value is provided.

[0032] As previously described, each voltage value for the stepped voltage curve, both during the switch-on and switch-off processes, should be assigned a duration during which that voltage value is held constant. Different durations should be assignable to individual voltage values, particularly those between 0 and 100% of the available vehicle electrical system voltage. When specifying the individual durations and the total duration, it must be ensured that the sum of the durations of a switching process—that is, the switch-on and switch-off processes—does not exceed the specified switching duration.

[0033] This offers the advantage that the movement or acceleration, and thus the final impulse, of the separating element at the end of each switching process—that is, when the separating element moves from a release position to a release position and vice versa—can be controlled. This reduces noise generation at the end of each switching process.

[0034] In a further development of the invention, the method is characterized in that a respective duration of a respective voltage value of the switching-off process and / or the switching-on process is specified depending on a movement of the separating element and / or a preload and / or spring stiffness of a return spring.

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