Vehicle with electrical system and method for operating it

Abstract

Vehicle comprising a first partial electrical system (1) with a first electrical energy storage device (E1), a starter (S) and a generator (G) and a second partial electrical system (2) with a second electrical energy storage device (E2), and wherein the first partial electrical system has an electrical line resistance (R1) between the generator and the first electrical energy storage device, - the first sub-network and the second sub-network can be coupled via an electrical path (3), - the electrical path has a coupling resistance (R2), and - the coupling resistance is greater than the line resistance, where - the electrical path has a first coupling element (S1), and - the first coupling element is electrically connected in series with the coupling resistor, wherein - the vehicle has an engine stop-start function, and - when the starter is activated for a warm start, the first coupling element is open, and wherein - the first sub-network includes at least one high-power consumer (V1), and - when at least one high-performance consumer makes a power demand, the first coupling element is open.

Description

[0001] The invention relates to a vehicle which comprises a first sub-vehicle electrical system with a first electrical energy storage device, a starter and a generator and which comprises a second sub-vehicle electrical system with a second electrical energy storage device, and in which the first sub-vehicle electrical system has an electrical line resistance between the generator and the first electrical energy storage device.

[0002] Modern vehicles with a 14-volt electrical system have a specific generator control system to recover the vehicle's kinetic energy as electrical energy when braking or coasting. This is called recuperation.

[0003] The potential for recuperation can be increased by supplementing the vehicle's electrical system with energy storage devices with high charging acceptance. This is known, for example, from document DE 10 2006 002 985 A1.

[0004] Furthermore, the state of the art describes vehicle electrical systems with recuperation in a sub-system at an elevated voltage level of, for example, 24 volts. Power transfer to the sub-system is achieved by a DC / DC converter, see, for example, JP 2010 081 762 A1.

[0005] US 2002 / 0 158 513 A1 discloses a power supply device for a motor vehicle, comprising a motor generator, an inverter for driving the motor generator, a battery, and a capacitor. The capacitor is directly connected to a DC side of the inverter, and the battery is connected in parallel with the capacitor via a first switching unit. When an engine is started, the energy stored in the capacitor is used, and the switching units are turned off to disconnect the battery.

[0006] Further state of the art is shown in DE 10 2004 016 292 A1 and DE 10 2007 029 479 A1.

[0007] It is an object of the invention to describe an improved vehicle which comprises a first sub-vehicle electrical system with a first electrical energy storage device, a starter and a generator and which comprises a second sub-vehicle electrical system with a second electrical energy storage device, and in which the first sub-vehicle electrical system has an electrical line resistance between the generator and the first electrical energy storage device.

[0008] This object is achieved by a vehicle according to claim 1. Advantageous embodiments and further developments of the invention emerge from the dependent claims.

[0009] According to the invention, the first sub-vehicle network and the second sub-vehicle network can be coupled via an electrical path which has a coupling resistance and which exceeds the line resistance.

[0010] An electrical path is understood to be an electrical circuit that is located electrically between the two sub-vehicle electrical systems. This electrical circuit has the coupling resistance. When current flows through the coupling resistance, the coupling resistance causes a voltage drop across the coupling resistance, so that the electrical potential of the first electrical energy storage device and the electrical potential of the second electrical energy storage device are different. For example, the coupling resistance means that when charging current flows through the generator, a voltage drop across the coupling resistance occurs. As a result, the voltage level of the second energy storage device is always below the voltage level of the first energy storage device. This enables effective overvoltage protection for the second energy storage device. The coupling resistance therefore connects the two sub-vehicle electrical systems and is partially ohmically decoupled.This is also called partial decoupling.

[0011] The electrical path has a coupling element with which the coupling resistor is electrically connected in series.

[0012] The coupling element can, for example, be designed as a switch.

[0013] The vehicle has an engine stop-start function, and when the starter is operated for a warm start, the coupling element is opened.

[0014] In a vehicle with an engine stop-start function, a warm start is the starting of the combustion engine while driving with the engine off, e.g., during a red light at a traffic light. A first-time start at the beginning of a journey is referred to as a cold start.

[0015] It is also provided that the first sub-vehicle network comprises at least one high-power consumer and that the coupling element is opened when the at least one high-power consumer requests power.

[0016] This results in a power output and thus a voltage drop in the first energy storage device when the coupling element is open. The voltage level of the second energy storage device remains stable, so that consumers connected in parallel to the second energy storage device can be supplied with electrical power at a stable voltage.

[0017] In addition, when the vehicle is at rest, the coupling element is open; before the starter is operated for a cold start, the coupling element can be closed in order to charge the first electrical energy storage device; and when the starter is operated for a cold start, the coupling element is opened.

[0018] According to an alternative embodiment, the electrical path has a first coupling element which is electrically connected in parallel with the coupling resistor.

[0019] This allows the coupling resistor to be short-circuited when the first coupling element is closed. The coupling resistor therefore only has an effect when the first coupling element is open.

[0020] If the vehicle has a recuperation function and / or an engine stop-start function, it is particularly advantageous if the first coupling element is open when the starter is operated for a warm start, and in a recuperating state the first coupling element is open, and in a recuperated state the first coupling element is open.

[0021] This means that the effect of the coupling resistance is only used in specific driving phases of the vehicle.

[0022] A recuperation function is understood to mean that when the vehicle is coasting or braking, the vehicle's kinetic energy is fed into the vehicle's electrical system or sub-electrical systems by increasing the generator's output voltage and thus increasing the generator's torque demand on the combustion engine. This is done, for example, to charge an energy storage device. This period is also referred to as the coasting phase or the recuperating state. After a coasting phase, the energy storage device is at least partially charged. This state is referred to as the recuperated state.

[0023] In addition, it is advantageous if the electrical path has a second coupling element, and the second coupling element is connected in series with the coupling resistor and in parallel with the first coupling element.

[0024] This means that when the first coupling element and the second coupling element are open, the two sub-vehicle networks are galvanically isolated via the electrical circuit, and that when the first coupling element is closed, the coupling resistance can be bridged.

[0025] If the vehicle has a recuperation function and / or an engine stop-start function, an advantage is achieved if the first coupling element is open when the starter is actuated for a warm start, the first coupling element is open in a recuperating state, the first coupling element is open in a recuperated state, and the first coupling element and the second coupling element are open in a rest state of the vehicle.

[0026] A vehicle's idle state is defined as a stationary phase in which the vehicle is not in operation. Therefore, a stationary phase with the combustion engine switched off by an engine stop / start function is not considered a idle phase in this document. In a stationary state, both coupling elements can be opened to prevent mutual discharging of the energy storage units while the vehicle is stationary.

[0027] The invention is based on the following considerations: Some vehicles with a 14 V electrical system architecture recover braking energy during overrun phases using a special generator control system. This is called recuperation. The maximum possible generator current is set during overrun phases, which charges the accessible on-board battery, usually a 12 V lead-acid battery. During the subsequent traction phases, this regeneratively generated energy is fed back into the on-board electrical system.

[0028] There are also advanced 14 V architectures where, for recuperation, a specific generator control system charges braking energy into an additional energy storage device that has better charge acceptance than a lead-acid battery. This can be a supercapacitor.

[0029] Alternatively, on-board electrical systems are expanded in series, meaning that sub-on-board electrical systems have a higher nominal voltage. This allows recuperation to occur at increased power.

[0030] Maximum utilization of the recuperation potential, which the generator can provide as power during overrun phases, is often limited by the low charge absorption capacity of the lead-acid battery used for recuperation. Furthermore, recuperation leads to increased cycling of the lead-acid battery, which negatively impacts its service life.

[0031] If the vehicle has an engine stop-start function in addition to the recuperation function, the lead battery is additionally stressed by frequent starts of the combustion engine during driving.

[0032] Today's generators can deliver up to 300 A at 14.8 V. At best, a new and partially discharged lead-acid battery is capable of efficiently absorbing the available power. The partially discharged state and the additional cycling of the lead-acid battery caused by recuperation can further shorten its service life through accelerated aging. Connecting a performance-optimized energy storage device, such as a supercapacitor, in parallel with the lead-acid battery does not mitigate the problem of accelerated aging.

[0033] It is proposed to connect a recuperation storage unit in parallel with the on-board network storage unit, partially ohmically decoupled.

[0034] A preferred embodiment of the invention is described below with reference to the accompanying drawings. Further details, preferred embodiments, and developments of the invention will emerge from these. In detail, schematically Fig. 1 On-board network with ohmic partially decoupled energy storage devices Fig. 1a Voltage and current curve of partially decoupled energy storage systems during recuperation Fig. 2 On-board network with ohmic partially decoupled energy storage devices and serial switches Fig. 3 On-board network with ohmic partially decoupled energy storage units and parallel switch Fig. 4 On-board network with ohmic partially decoupled energy storage devices and with serial switch and parallel switch

[0035] Fig. 1 to 4 show a first sub-vehicle electrical system (1) and a second sub-vehicle electrical system (2) of a vehicle. The first sub-vehicle electrical system comprises a first energy storage device (E1), referred to as the recuperation storage device, and the second sub-vehicle electrical system comprises a second energy storage device (E2), referred to as the on-board electrical system storage device. The first sub-vehicle electrical system also comprises a starter (S) and a generator (G). These components are designed for the 12 V on-board electrical system for motor vehicles, which is familiar to those skilled in the art.

[0036] The wires of the first sub-network are shown as solid lines. The electrical resistances of the wires, called line resistances, are shown in Fig. 1 to 4 without loss of generality as the first resistor (R1).

[0037] The first sub-network and the second sub-network each comprise a group of electrical consumers (V1, V2).

[0038] The vehicle features powertrain functions designed to reduce CO2 emissions and fuel consumption. These include a recuperation function for recovering braking energy and an engine stop / start function for shutting off the combustion engine during stationary phases.

[0039] With state-of-the-art recuperation functions, the generator's output voltage is increased to 14.5 V - 15.0 V during overrun, i.e., when fuel injection is absent during braking or when the vehicle is coasting to a stop, so that a high supply of charging power is available for an energy storage device in the vehicle's electrical system when the vehicle dissipates kinetic energy. Higher voltage levels are avoided to minimize the aging effects of lead-acid batteries as energy storage devices.

[0040] The vehicle may also be a hybrid vehicle, in which the combustion engine is switched off even during driving. In both vehicles with engine stop-start functionality and hybrid vehicles, the number of engine starts is significantly higher compared to a conventional vehicle, relative to the mileage.

[0041] The first energy storage device is ideally designed as an energy storage device with high charge acceptance and cycle stability. This could be a supercapacitor or a module made of supercapacitors.

[0042] The second energy storage unit is ideally designed as a high-energy storage unit. A secondary battery using lead-acid technology is therefore advantageous. However, the lead-acid battery limits the maximum increase in the generator output voltage during overrun, as lead-acid batteries are susceptible to corrosion when exposed to overpotentials.

[0043] According to Fig. 1 to 4, the first sub-vehicle electrical system and the second sub-vehicle electrical system are connected via an electrical path (3). The electrical path includes a second electrical resistor (R2), also referred to as the coupling resistor. The second resistor (R2) is several times greater than the first resistor (R1). The coupling resistor can be implemented as a separate component or as a line resistor in the electrical path. In state-of-the-art vehicle electrical systems, the first resistor has a very low resistance, amounting to a few mΩ, while the second resistor is at least twice the first resistor.

[0044] In Fig. 1, the recuperation storage unit and the on-board power supply unit are directly connected via the second resistor. However, the second resistor does not result in a free potential equalization between the units; instead, the two units are at least partially decoupled in terms of their electrical potentials. This is referred to as partial decoupling.

[0045] Due to the partial decoupling, the output voltage at the generator U gen to over 15 V. The power delivered by the generator at increased recuperation voltage during coasting, the recuperation power, initially feeds the power-optimized energy storage device (E1) with current I1. The second energy storage device is charged with current I2. The potential U1 applied to the first energy storage device is proportional to U gen-(R1 · (I1+I2)). Due to the second resistor, the potential U2 applied to the second energy storage device is additionally reduced by the value I2 · R2 compared to the potential. The potential increase at the second energy storage device due to the increase in the output voltage at the generator is therefore dampened compared to the potential increase at the first energy storage device. This has several advantages: Using a supercapacitor as a recuperation storage device effectively utilizes the recuperation potential and, consequently, the fuel-saving potential, without overcharging the on-board power supply battery. The higher the potential U1, the greater the power that can be absorbed by a supercapacitor. In addition, the resistor R2 protects the on-board power supply battery from an excessively high potential U2 and thus from overcharging during recuperation.In addition, the recuperation storage absorbs the additional cyclization caused by recuperation, which, in the case of increasing cyclization of the on-board network battery, leads to a shortening of its service life.

[0046] If the recuperation battery (E1) is fully charged during a coasting phase, it will initially still have a high voltage level after the coasting phase. During further vehicle operation, a discharge occurs via the resistors (R1, R2) by supplying the electrical consumers (V1 and / or V2) or by charging the on-board battery.

[0047] When the on-board power supply battery (E2) is charged, a voltage drop occurs across the resistor (R2), so that the on-board power supply battery remains protected from excessive voltage even after a coasting phase. This means that the voltage swing, i.e., the potential difference, of a performance-optimized energy storage device (E1), such as a supercapacitor, is increased during and after coasting compared to normal operation at a standard generator output voltage and compared to the voltage swing of the on-board power supply battery, such as a lead-acid battery.Due to this fact, further advantages are associated with the partial decoupling: If the consumers (V1) are consumers that have a high power requirement, such as the starter (S) or chassis control systems that intervene in the on-board network for a short time when there is a high power requirement, the increased voltage level of the recuperation storage device contributes to the voltage stabilization of the on-board network without the increased voltage level "penetrating" the on-board network battery, which is critical for the on-board network battery.

[0048] Out of Fig. Figure 1a clearly shows the beneficial effect of partial decoupling with a resistance (R2) of 3 mΩ and a resistance (R1) of 1.5 mΩ. The increase in the generator output voltage to 16 V during a coasting phase is shown. By charging a supercapacitor (E1) as a recuperation storage device, its full charge is already achieved during the coasting phase, which leads to a drop in current I1 at a voltage level U1 of the storage device (E1). The voltage U2 at the on-board power supply battery, which is designed as a 12 V lead battery, only increases to 14.8 V, with the current I2 during the entire coasting phase reaching a maximum of only approximately 10% to 50% of the maximum current I1 during the coasting phase, depending on the charge capacity of the on-board power supply battery, its temperature, and its state of charge. After the coasting phase (“coasting on” after “coasting off” in Fig. 1a) the voltage U1 is higher than the voltage U2, which leads to a further charge of the storage (E2) from the storage (E1).

[0049] A second embodiment in Fig. 2 corresponds to the first embodiment except for one switch (S1) in Fig. 1. The switch (S1) is connected directly in series with the resistor (R2) so that the on-board power supply battery and the electrical consumers (V2) can be separated from the "rest" of the on-board power supply. In a vehicle with an engine stop-start function, the switch (S1) can be opened to start the combustion engine using the starter motor (S). This ensures that the on-board power supply battery and the electrical consumers (V2) are protected from a voltage drop resulting from the high power demand of the starter motor. In addition, the switch (S1) is opened when the vehicle is stationary to prevent the on-board power supply battery from discharging if the recuperation storage device is designed as a supercapacitor.A supercapacitor generally has a significantly higher self-discharge rate than a lead-acid battery. Therefore, when a supercapacitor and a lead-acid battery are connected in parallel during an extended standstill phase, the switch (S1) is opened to prevent the lead-acid battery from discharging via the supercapacitor. For a cold start, i.e., starting the combustion engine at the beginning of a journey instead of a warm start during a journey, the switch (S1) can be closed to precharge the supercapacitor, which has self-discharged after a prolonged standstill period, via the vehicle's electrical system battery. The cold start can be performed from the precharged supercapacitor with the switch (S1) open.

[0050] A further third embodiment is in Fig. 3. This differs from the first embodiment in Fig.1 merely by a switch (S2) connected in parallel with the resistor (R2). In this embodiment, the resistor (R2) can be bridged by the switch (S2), so that when the switch (S2) is closed, a two-storage vehicle electrical system is created without partial decoupling and with a direct connection between the storage devices. The switch (S2) is opened in order to utilize the advantages of a partially decoupled vehicle electrical system according to the first embodiment. This particularly applies to operating states when the combustion engine is started by the starter (S) in a vehicle with an engine stop-start function and during and after overrun phases during overrun operation of a vehicle with a regeneration function. During normal driving operation, without starts by the starter and without a voltage increase at the generator output or at the recuperation storage device, the switch (S1) can be closed in order to prevent a power loss via the resistor (R2).

[0051] According to a fourth embodiment, the electrical path includes a first switch (S3) in series with the resistor (R2) and a second switch (S2) connected in parallel with the series connection of the resistor (R2) and the first switch (S1). With this embodiment, when using a supercapacitor as recuperation storage and a lead battery as the on-board power supply battery, the advantages of the second embodiment can be combined with the advantages of the third embodiment. This means that when the vehicle is stationary, in addition to the first switch (S3), the second switch (S2) is also opened. During normal driving, the first switch (S3) and the second switch (S2) are closed. The second switch (S2) is preferably opened when the combustion engine is started by the starter (S) in a vehicle with an engine stop-start function and during overrun phases and after overrun phases in a vehicle with a regeneration function.

Claims

[1] Vehicle comprising a first sub-vehicle network (1) with a first electrical energy store (E1), a starter (S) and a generator (G) and a second sub-vehicle network (2) with a second electrical energy store (E2), and in which the first sub-vehicle network has an electrical line resistance (R1) between the generator and the first electrical energy store, wherein - the first sub-network and the second sub-network can be coupled via an electrical path (3), - the electrical path has a coupling resistance (R2), and - the coupling resistance is greater than the line resistance, where - the electrical path has a first coupling element (S1), and - the first coupling element is electrically connected in series with the coupling resistor, whereby - the vehicle has an engine stop-start function, and - when the starter is operated for a warm start, the first coupling element is opened, and - the first sub-network comprises at least one high-performance consumer (V1), and - when there is a power demand from at least one high-power consumer, the first coupling element is opened. [2] Vehicle according to claim 1, characterized by , that - when the vehicle is at rest, the first coupling element is open, - before the starter is actuated for a cold start, the first coupling element can be closed in order to charge the first electrical energy storage device, and - when the starter is operated for a cold start, the first coupling element is opened.

Images