Controlling the electrical system of a motor vehicle

Abstract

Method (200) for operating an electrical on-board network (115) of a motor vehicle (105), wherein the method (200) comprises the following steps: Determine (205) that a voltage of the vehicle electrical system (115) is below a predetermined threshold value while electric current from the vehicle electrical system (115) flows through a consumer (130) on board the motor vehicle (105); Lowering (210) a voltage applied to the consumer (130) in order to reduce the current flowing through the consumer (130); and continuously increasing (220) the voltage applied to the consumer (130) at a predetermined rate of change.

Description

[0001] The present invention relates to a vehicle electrical system. In particular, the invention relates to the control of an electrical consumer connected to the vehicle electrical system.

[0002] A motor vehicle's electrical system is designed to provide a predetermined voltage to a multitude of electrical consumers. If current flows through several low-impedance consumers, the voltage of the electrical system can drop. A safety-critical component connected to the electrical system as a consumer, such as an electric power steering or an electromechanical clutch actuation, can only operate safely above a predetermined voltage. A non-safety-critical consumer should therefore preventively receive less current if the voltage in the electrical system is dangerously low.

[0003] To achieve this, the voltage at the non-safety-critical load can be gradually reduced until it draws a sufficiently low current. Control oscillations must be avoided, for example, when multiple loads are controlled in a similar manner. Nevertheless, the current through the load must be reduced within a specified time, for example, in the range of approximately 10 ms. A corresponding control method can be complex, and a control device may require expensive components.

[0004] US 2017 / 0187319 A1 concerns a technology for temporarily switching off a consumer of an electrical supply network in the event of an overload of the network.

[0005] DE 10 2016 214 112 A1 proposes to operate a consumer in an on-board electrical system with reduced power if the voltage of the on-board electrical system falls below a predetermined threshold value

[0006] DE 10 2016 123 063 A1 shows a sequence-controlled distribution of power to different loads in an on-board network.

[0007] DE 10 2014 007 548 A1 proposes having multiple consumers in an on-board electrical system check whether the on-board voltage falls below a predetermined threshold. If this is the case, the respective consumer can reduce its power consumption itself.

[0008] One object of the invention is to provide an improved technology for controlling a motor vehicle's electrical system. The invention achieves this object by means of the subject matter of the independent claims. Subclaims specify preferred embodiments.

[0009] A method for operating an electrical system of a motor vehicle comprises steps of determining that a voltage of the electrical system falls below a predetermined threshold while electrical current from the electrical system flows through a load on board the motor vehicle; lowering a voltage applied to the load to reduce the current flowing through the load; and continuously increasing the voltage applied to the load at a predetermined rate of change.

[0010] The load preferably has a voltage-dependent current consumption. The load can be a substantially resistive load, for example in the form of an electric heater for a window, a mirror, or an interior. The load can also be substantially inductive and comprise, for example, a drive motor for an air conditioning compressor, a pump, or a servomotor. More preferably, the load is a non-safety-relevant load that can be operated in a limited manner, at least for a short time, without impairing a safety-relevant function, in particular longitudinal or lateral control or an accident avoidance or safety system.

[0011] By lowering the voltage at the load, the on-board electrical system can be quickly relieved, allowing its voltage to return above the threshold. Gradually increasing the voltage at the load can be easier to control than a conventional gradual decrease. The proposed control can be robust against control oscillation or other undesirable control effects that could stress or contaminate the voltage of the on-board electrical system.

[0012] The voltage applied to the load can be reduced by a predetermined amount or to a predetermined value. The reduction is preferably carried out abruptly, i.e., as quickly as possible. The voltage applied to the load can then be increased from zero or a value close to zero. This can sustainably relieve the load on the vehicle electrical system. The load can be operated within a voltage range in which its current consumption can be satisfied by the vehicle electrical system without the vehicle voltage exceeding the threshold value.

[0013] This can also ensure that the consumer remains essentially switched off if the voltage of the vehicle electrical system has not yet exceeded the threshold due to the voltage reduction at the consumer. In this case, the system can automatically wait until the voltage rises above the threshold again, for example, due to another consumer being switched off or an increased supply of electrical energy.

[0014] The voltage increase can occur continuously or in several discrete steps. For discrete increases, more than three steps are preferably used, and more preferably more than approximately 10 steps. The number of steps can be so large that it can practically be considered a continuous increase. This can be the case, for example, with approximately 100 or 200 steps.

[0015] The voltage at the load can be increased until the current flowing through the load reaches a predetermined value. This allows an additional termination condition for the voltage increase to be defined. If at least one condition exists that prevents further increase, the voltage at the load can be kept constant. The predetermined value can be static or determined dynamically, for example, depending on the voltage of the vehicle electrical system or a current flowing through another load.

[0016] The voltage applied to the load can preferably only be increased as long as the voltage of the vehicle electrical system is at least a predetermined amount above the threshold value. This prevents the load from consuming so much current that the voltage of the vehicle electrical system returns to the threshold value, which could necessitate a further reduction in the voltage of the load. The predetermined amount is typically in a range of approximately 0.1 V to approximately 1 V.

[0017] The voltage at the load can be increased to a maximum of a predetermined value. This predetermined value is typically within the range of a nominal voltage or the actual voltage of the vehicle's electrical system. When the load is controlled by a semiconductor, the voltage applied to the load can be lower than the vehicle's voltage by a typical semiconductor voltage, for example, 0.4 V or 0.7 V.

[0018] The maximum current flowing through the load may exceed a predetermined value. In other words, it is preferably a load that can draw a large current from the vehicle electrical system. The specific value can be selected appropriately, even dynamically, to ensure a sensible selection of the load. A method described herein can be implemented for multiple loads, in particular for all loads with a predetermined current consumption.

[0019] According to a further aspect of the invention, a control device for an electrical system of a motor vehicle comprises: a voltage controller for providing a voltage for a consumer from the electrical system; a sensing device for determining a voltage of the vehicle electrical system; a processing device configured to determine whether the voltage of the vehicle electrical system falls below a predetermined threshold value; to reduce the voltage supplied to the load in order to reduce the current flowing from the vehicle electrical system through the load; and to gradually increase the voltage supplied to the load as long as the voltage of the vehicle electrical system is above the threshold value.

[0020] The processing device can be configured to fully or partially execute a method described herein. For this purpose, the processing device can comprise a programmable microcomputer or microcontroller, and the method can be in the form of a computer program product with program code means. The computer program product can also be stored on a computer-readable data carrier. Features or advantages of the method can be transferred to the device, or vice versa.

[0021] The control device can further comprise a further sensing device for determining a current flowing through the load. The processing device can be configured to control the voltage applied to the load as a function of the current flowing through the load. In particular, the voltage at the load can only be increased if the current flowing through it is below a predetermined value. This value can be determined as a function of the voltage of the vehicle electrical system, before or after an undervoltage is determined.

[0022] The invention will now be described in more detail with reference to the accompanying figures, in which: Fig. 1 a system; and Fig. 2 shows a flow diagram of a procedure.

[0023] Fig. 1 shows a system 100 comprising a motor vehicle 105 and a control device 110. An electrical system 115 is provided on board the motor vehicle 105, which is typically supplied by a rechargeable energy storage device 120 and / or a generator 125, which may be driven, for example, by a drive motor. The electrical system 115 is configured to supply current of a predetermined voltage, the on-board voltage, to one or more consumers 130 on board the motor vehicle 105. The on-board voltage is typically a direct voltage with a nominal value of, for example, approximately 12 V. A valid range of the on-board voltage may be within a predetermined range around the nominal value, for example, approximately 11.8 - 12.3 V. An undervoltage of the on-board voltage up to a predetermined threshold value, which is typically below the stated range, can be tolerated.If the on-board voltage falls below the threshold, the electrical load on the vehicle electrical system 115 is reduced. A typical threshold value for a nominal on-board voltage of 12 V is approximately 11 V.

[0024] A load 130 shown as an example can be controlled by the control device 110 by changing the voltage applied to it. The load 130 has a voltage-dependent current consumption and is typically configured to draw substantial electrical energy from the vehicle electrical system 115. The load 130 considered here is preferably not safety-critical; thus, the motor vehicle 105 can be operated safely, even if the load 130 operates at reduced power or not at all, at least for a short time. During normal operation, the load 130 is typically powered directly from the vehicle electrical system 115's on-board voltage. Should the load 130 internally require a voltage higher than the vehicle's on-board voltage, it is assumed herein that it includes a suitable voltage converter (step-up converter).

[0025] The control device 110 preferably comprises a processing device 135, more preferably a first sampling device 140 for sampling a voltage of the vehicle electrical system 115 and / or a second sampling device 145 for sampling a current flowing through the load 130. The control device 110 further comprises a voltage controller 150 configured to control a voltage applied to the load 130 continuously or in discrete steps in order to influence a current flowing through the load 130.

[0026] It is proposed that the control device 110 significantly reduce the voltage applied to the load 130 as soon as the on-board voltage of the vehicle electrical system 115 drops below an above-mentioned, predetermined threshold. Subsequently, the voltage at the load 130 should be gradually increased. However, the increase should only occur as long as one or more predetermined conditions are met. One such condition may include the on-board voltage being above a further predetermined threshold, which may be slightly above the above-mentioned threshold. Another condition may be met as long as a current flowing through the load 130 does not exceed a predetermined threshold. This threshold can be determined depending on the on-board voltage before or after the undervoltage is determined.

[0027] Fig.Figure 2 shows a flowchart of a method 200 for controlling a consumer 130 that is mounted on board a motor vehicle 130 and is supplied with electrical energy from an on-board electrical system 115. The method 200 can be executed, in particular, by means of a control device 110.

[0028] In a step 205, it can be determined that the voltage of the vehicle electrical system 115 is below a predetermined threshold. This is also referred to as an undervoltage of the vehicle electrical system 115. If the vehicle electrical system 115 voltage is above the threshold, step 205 can be repeated as often as desired.

[0029] If the on-board voltage is below the threshold value, a voltage applied to the load 130 can be reduced in a step 210. The reduction is preferably carried out by at least 50%, preferably at least 80%, and in a further preferred embodiment by 100%, thus corresponding to switching off the load 130. After the reduction, a predetermined time can elapse before the next step is carried out. The predetermined time can be permanently assigned to the load 130. If several loads 130 connected to the on-board electrical system 115 are controlled in a manner described herein, the predetermined times can in particular be selected differently, so that the following steps can be carried out in a staggered manner for the various loads 130.

[0030] In a subsequent step 215, one or more criteria can be checked. The criterion indicates whether the voltage applied to load 130 can be increased or not. One possible criterion is met if the current flowing through load 130 from vehicle electrical system 115 is below a predetermined threshold. Another possible criterion is met if the voltage of vehicle electrical system 115 is above a predetermined threshold, which may be higher than the threshold in step 205.

[0031] If at least one of the checked criteria is not met, method 200 can end or start again from the beginning. Otherwise, if all criteria are met, the voltage applied to load 130 can be increased in a step 220. The increase is preferably performed by a predetermined amount, which can, for example, be in the range of approximately 0.1 V. The voltage can also be increased continuously, for example, at a predetermined rate of change.

[0032] In a step 225, a check can then be performed to determine whether the voltage applied to load 130 has reached a predetermined value. This value can, in particular, correspond to the vehicle's on-board voltage or be below it by a predetermined amount. However, the value can also be fixed. Once the value is reached, the power reduction of load 130 can be considered complete. Method 200 can end or be repeated.

[0033] Otherwise, if the voltage at load 130 does not reach the value, load 130 continues to operate at a reduced voltage and thus at a reduced current. In this case, method 200 can return to step 215 to check for a possible voltage increase. However, method 200 can also return to the beginning to check beforehand whether a further voltage reduction is necessary. Reference symbol 100 systems 105 Motor vehicle 110 Control device 115 electrical system 120 energy storage units 125 Generator 130 consumers 135 Processing device 140 first sensing device (voltage of the vehicle electrical system) 145 second sensing device (current through the consumer) 150 Voltage control 200 procedures 205 Determine undervoltage 210 Reduce voltage at the consumer 215 criterion met? 220 Increase voltage 225 voltage normal?

Claims

[1] Method (200) for operating an electrical system (115) of a motor vehicle (105), the method (200) comprising the following steps: Determining (205) that a voltage of the vehicle electrical system (115) is below a predetermined threshold value while electrical current flows from the vehicle electrical system (115) through a consumer (130) on board the motor vehicle (105); Lowering (210) a voltage applied to the load (130) to reduce the current flowing through the load (130); and continuously raising (220) the voltage applied to the load (130) at a predetermined rate of change. [2] Method (200) according to claim 1, wherein the continuous increase (220) of the voltage applied to the consumer (130) occurs when the voltage of the vehicle electrical system (115) is above the threshold value. [3] Method (200) according to claim 1 or 2, wherein the voltage applied to the load (130) is raised (220) from a value close to zero. [4] Method (200) according to one of the preceding claims, wherein the voltage at the load (130) is increased (220) until the current flowing through the load (130) reaches a predetermined value. [5] Method (200) according to one of the preceding claims, wherein the voltage applied to the consumer (130) is only increased (220) as long as the voltage of the vehicle electrical system (115) is above the threshold value by a predetermined amount. [6] Method (200) according to one of the preceding claims, wherein the voltage at the load (130) is raised (220) to a maximum of a predetermined value. [7] Method (200) according to one of the preceding claims, wherein a maximum current flowing through the load (130) exceeds a predetermined value. [8] Control device (110) for an electrical system (115) of a motor vehicle (105), comprising: a voltage controller (150) for providing a voltage for a consumer (130) from the electrical system (115); a sampling device (140) for determining a voltage of the electrical system (115); a processing device (135) which is configured to determine when the voltage of the electrical system (115) has fallen below a predetermined threshold value; to reduce the voltage supplied to the consumer (130) in order to reduce a current flowing from the electrical system (115) through the consumer (130); and to continuously increase the voltage supplied to the consumer (130) at a predetermined rate of change. [9] Control device (110) according to claim 8, characterized bythat the control device (110) is designed to continuously increase the voltage supplied to the consumer (130) as long as the voltage of the vehicle electrical system (115) is above the threshold value. [10] Control device (110) according to claim 8 or claim 9, further comprising a further sensing device (145) for determining a current flowing through the load (130).

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