DE19749548A1 - Method for operating hybrid vehicle - Google Patents

Abstract

The method firstly involves a condenser being charged up by the generator. Secondly, the condenser to at least 2% serves for two seconds in total to operate the electrical loads and/or to charge the battery. A condenser with a discharge/charge power of at least 0.5 kW, preferably 0.7 kW and especially at least 1 kW is installed. A condenser with a cyclically exploitable store of at least 20 kJ and especially at least 28 kJ may be used.

Description

The invention relates to a method for operating a motor vehicle according to the Preamble of claim 1.

To reduce nitrogen oxide emissions in internal combustion engines different ways described. The best known process is the catalytic one Exhaust gas cleaning, in which the nitrogen oxides in particular with hydrocarbons or Carbon monoxide can be reduced. Further measures are taken on the combustion side. H. through exhaust gas recirculation or special combustion chamber designs up to the number of Valves. Furthermore, the raw nitrogen oxide emissions can be reduced if the Internal combustion engine is operated in cheaper operating points. Such a process is known for example from DE 196 39 826 A, according to which the current generator, the one performance-intensive auxiliary unit of the internal combustion engine is, with unfavorable Operating points of the internal combustion engine is de-excited. The necessary supply of electrical consumers take place via the accumulator. This known method can lead to a high number of charge / discharge cycles on the accumulator, whereby this can age faster under certain circumstances.

The object of the invention is to operate an internal combustion engine such that at unfavorable operating conditions, the power consumed in auxiliary units is reduced, however, an excessive number of charge / discharge cycles on the on-board accumulator should be avoided.

In the method described at the beginning, this task is solved with the measures of claims 1 and / or 4.

The subclaims show preferred forms of the method.  

The invention is based on the partial use of the braking energy of a motor vehicle. Around a third of the energy required for vehicle propulsion is - related to the MVEG cycle - in the case of a medium-sized vehicle via the wheel brakes in the form of heat destroyed. Brake energy recovery with the aim of supporting the However, vehicle jacking is not considered to be solely because of storage space and control problems critically assessed. The high theoretically achievable reductions in consumption are due to the double passage through the converter and memory chain significantly reduced there are high costs for the systems, weight gain and space requirements for installation the additional components of such storage systems.

Technically cheaper than the support of vehicle jacking is a continued use of the Braking energy to support subsystems with poorer efficiency than that of vehicle jacking. Such support for accessory drives is from the DE 196 39 826 mentioned at the beginning. Because the power generator on the motor vehicle represents one of the most power-intensive auxiliary units and moreover already with one Accumulator is coupled as an energy store, is a braking energy recovery Support of the electrical system is possible. Other storage media are less suitable because the need for pneumatic and / or hydraulic energy in one Motor vehicle is usually significantly smaller than the electrical energy requirement; moreover are corresponding energy storage to an accumulator with respect to the storage density inferior.

B. Voß, VDI Progress Reports, Series 12, No. 159, 1991 already suggests preferred generator operation in the overrun phases and the greatest possible shutdown of generator operation in the other operating states of the internal combustion engine. Due to the limited charging capacity of the lead accumulators usually used in motor vehicles of 500 W in the best case, even with larger versions (130 Ah) and usual charging conditions of mostly ≧ 80%, only a comparatively small use of the braking energy is possible. In addition, the life of the lead accumulator is severely limited by high-current cyclical loading and unloading. According to the invention, therefore, in addition to the usual accumulator, usually a lead accumulator, a further electrical energy store is provided, which is used specifically for the repeated storage of electrical energy and to support the generator during the operation of the motor vehicle, the support of the generator being of low value until it is completely switched off of the generator (electrical substitution) can take place. The electrical energy store used in this way is advantageously a capacitor which is in particular dimensioned such that it fulfills at least one of the following criteria:

• - The capacitor substitutes at least 2%, especially at least 10%, of Generator power for a total of at least 2 s during its discharge cycle;
• - The capacitor (or other electrical storage) has one Charging / discharging power of at least 0.5 kW and in particular of at least 1 kW;
• - The capacitor (or other electrical storage) has a cyclically usable Storage capacity of at least 20 kJ, in particular at least 30 kJ.

A cyclically usable storage capacity exists if the storage system can withstand at least 10 ⁵ charge / discharge cycles between 100% and 40% of its nominal storage capacity. The nominal storage capacity is usually at least 50% of the maximum storage capacity of the storage when new.

The preferred storage values of the electrical storage device are only approximate 10% use of braking energy possible due to the high proportion of braking energy in the total consumption of the motor vehicle, however, this means a noticeable Reduction of consumption and NOx emissions. A capacitor as an electrical one Energy storage has the disadvantage of a known lead accumulators much lower storage density (about an order of magnitude smaller) and a high one Self-discharge rate of up to 25% / day, however, is in the method according to the invention suitable because on the one hand because of the significant reduction in the cyclical load on the Lead accumulator during the operation of the internal combustion engine according to the present invention the lead accumulator with less safety reserves, d. H. lighter can be designed, and on the other hand, during the operation of the invention electrical storage (capacitor) operated in relatively short cycles (some Seconds to a few minutes), so that the high self-discharge rate is unproblematic.  

However, the disadvantages of the capacitor do not allow a complete replacement of the conventional motor vehicle battery, but only a parallel use to this.

When using a capacitor as an electrical storage, so-called Gold capacitors (GoldCaps, SuperCaps) becomes a control according to the invention provided the discharge voltage of the capacitor, which is an exponential Has, regulates or stabilizes the voltage curve. This is done advantageously on the for electrical consumers or the charging of the on-board battery (accumulator) Tension. The control is advantageously designed so that it is also low Capacitor output voltage can regulate to a higher voltage. Such Control is for example in Elektor, No. 7-8, 1995, pp. 86/87, battery saving circuit, described. Alternatively, but in particular in addition, the control also serves one Change in the charging voltage of the capacitor, the voltage when charging the Capacitor is increased. The increase is advantageous up to a max. 144 V and especially up to max. 42 V and is preferably at least 1.5 times that usual vehicle electrical system voltage (i.e. at least 21 V). Through this voltage increase one achieves a higher cyclically usable storage capacity of the capacitor; Furthermore the voltage regulation described above can be simplified, for example, such that the discharge of the capacitor is only used up to one Discharge voltage of at least 6 V and in particular at least 9 V.

According to the invention, the electrical system of a motor vehicle is advantageously combined from a starter battery and a capacitor store for braking energy recovery modified. As a result, it is also advantageously achieved that the usually in Motor vehicles rarely used lead acid batteries due to periodic charging / discharging processes is charged, as it is particularly in swing-use machines (parking and Disengaging the internal combustion engine during overrun operation). Of the Capacitor voltage regulator does not need the peak currents during starter operation be designed, but max. on the electrical system load (approx. 100 A), also a lower one Sizing is possible, in which case the lead battery again has low cyclical loads is subjected.

The strategy of power supply, i. H. the partial or complete activation of the Additional storage (capacitor) to supply the power grid is advantageous  Optimized low consumption, while at the same time lower nitrogen oxide emissions can be achieved. Such an optimization is, for example, from DE 195 38 324 A known. The generator is preferably operated fully in the lower part-load range, i. H. of the charged capacitor becomes partial or above the lower partial load range full supply of the on-board electrical system switched on. A balance of consumption the internal combustion engine with and without generator load shows that the specific Generator consumption in the lower partial load range can be lower than the best value of the unit not loaded with the generator.

The connection of the capacitor store under is particularly advantageous Consideration of the state of charge of the capacitor store and the Engine operating point decided. This advantageously ensures that at Falling below a minimum charge level of the electrical storage of the generator in full continuous operation works.

The electrical storage system in a car with direct-injection turbodiesel (66 kW) achieved a consumption and NOx reduction of around 4% (series generator 90 A, MVEG cycle). By increasing the generator power to 120 A the energy utilization is reduced increased in the delay phases, resulting in approximately 145 kJ in the MVEG cycle 90 kJ with 90 A generator of braking energy can be used. This degree of utilization is still below 10% of total braking energy. When using a 320 A generators can recover approx. 600 kJ of braking energy in the MVEG cycle be used, whereby the consumption by approx. 13% and the NOx emission by approx. 12% could be lowered. An increase in generator output to over 500 A (at 14.4 V) makes little sense, since the braking energy stored in this way no longer exceeds the Auxiliary units can be used up completely.

The invention is described below using an exemplary embodiment and drawings described in more detail.  

Show it

Fig. 1 preferred generator operating areas in the engine map;

FIG. 2 shows a decision logic for generator operation;

Fig. 3 is a graph showing the operating logic;

Fig. 4 is an electrical system with braking energy recovery;

5 is a table with the savings function of the generator size. and

Fig. 6 shows a further operating strategy of the electrical system.

The shell diagram of an internal combustion engine shown in FIG. 1 shows the specific consumption in g / kWh as a function of the speed and the torque of the internal combustion engine. The cheapest specific consumption of 223 g / kWh is a relatively low speed and a relatively high torque. The specific fuel consumption at 50 A generator load can be determined directly from this diagram at any point in the performance map. The calculation equation is engine power with generator load × specific fuel consumption - engine power without generator load × specific fuel consumption. As can be seen from the calculations for points A and B (A 'and B' with generator load 50 A), the specific generator consumption is lowest in the lower part-load range 20 , which is shown as a dotted line as the preferred generator operating range.

The charging strategy shown in FIG. 2 can be developed from this. The load torque Md, calculated for example from the engine speed and the fuel injection quantity m, is linked to the state of charge of the capacitor, for example determined from its voltage, in an equation. The curve resulting therefrom is shown in FIG. 3, from which it can be seen that the generator is excited, that is to say supplies current, only at relatively low charge states of the capacitor and essentially at relatively low torques of the internal combustion engine. A thrust query is added to this loading strategy. In the overrun mode of the internal combustion engine, this does not require any fuel in the event of a fuel overrun cutoff, so that here the generator delivers electricity without additional fuel consumption. Accordingly, the dotted area in which the generator is excited to generate electricity and to charge the capacitor is above the curve determined in the overrun mode when the capacitor is at high charge states. In this generator operation, the decision regarding generator operation or shutdown or capacitor charging or discharging is made taking into account the capacitor storage charge state and the engine operating point. This ensures that the generator operates in continuous operation if the capacitor storage state falls below a minimum charge level. The minimum charge state of the capacitor is advantageously chosen such that it is in the range of the limit of the usable capacitor capacitance, since the entire nominal capacitance of the capacitor cannot be used as a result of the exponential voltage drop in the capacitor storage discharge. During the discharge, in particular the semiconductor elements of the voltage converter limit the minimum voltage to approximately 9 V; the upper voltage limit is limited by the maximum voltage of the capacitor and by voltage protection measures.

The electrical system according to the invention is shown schematically in FIG. 4. The generator 2 , which is driven by an internal combustion engine 1 via a belt drive 15 , basically delivers a voltage of 14.4 V, with which a battery 3 is charged and electrical consumers 4 are fed. In addition to the generator 2 , the motor 1 drives a drive axle 6 with wheels 7 via a drive train 16 and a transmission 5 .

A control unit 9 , which contains a DC-DC converter, is also connected to the 14.4 V electrical system 8 . This converts the 14.4 V voltage to 42 V for charging a SuperCap 10 , which is designed for 11 Wh and has a charging / discharging power of 2 KW. SuperCap 10 is charged in the operating states described in FIGS . 2 and 3 (or 6). As soon as these are left, the generator 2 is de-energized via the control unit 9 and an excitation line 11 and at the same time the vehicle electrical system 8 is supplied from the SuperCap 10 via the control unit 9 , the voltage of which can drop to 9 V.

With this type of operation, different emissions and consumption savings can be achieved depending on the generator power. These are compiled in FIG. 5, and it is also found that mechanical decoupling of the generator has practically no advantages over electrical de-excitation of the generator. When a 320 A generator is used, approx. 600 kJ braking energy is used again in the MVEG cycle by feeding it into the vehicle electrical system, which results in a consumption saving of approx. 13% and a NOx emission reduction of approx. 12%. The measurements were carried out on a 66 kW turbo diesel direct injector installed in a compact car (Golf III).

In FIG. 6, a much simpler control strategy is depicted. Here the charging / discharging behavior of the capacitor is outlined in a short driving cycle. The driving cycle represents a section of an overall driving cycle and begins with a constant drive at 50 km / h. The motor vehicle is decelerated to 30 km / h after approx. 20 s in order to be accelerated again to 50 km / h after another constant travel. The vehicle then continues its speed at a constant 50 km / h. The generator nominal current (maximum power) is 110 A at 50 km / h and 80 A at 30 km / h. During the constant driving phase, the generator supplies the on-board electrical system with 25 A and the almost fully charged battery of the on-board electrical system with approx. 2 A charging current. During the deceleration, the largely discharged capacitor is switched on when the overrun mode begins or when the brake is actuated. Since the nominal generator current is below the maximum charging current that can be absorbed by the capacitor (here 140 A), the entire energy provided by the generator via the on-board power supply can be stored in the amount of approx. 10 kWs, corresponding to approx. 2.8 Wh. The subsequent constant travel at 30 km / h does not represent an "unfavorable" operating state, so the capacitor is not discharged here. The subsequent acceleration is considered an "unfavorable" operating state of the internal combustion engine, so that here the generator is de-energized and the on-board electrical system, including the battery charging current, is supplied by the discharged capacitor via control electronics. At the end of the acceleration process, the generator is excited again and the partially discharged capacitor is disconnected.

Claims (12)

1. A method for operating a motor vehicle with an internal combustion engine, an accumulator, electrical consumers and a power generator that serves to charge the accumulator and to operate the electrical consumers, characterized in that a capacitor is charged via the current generator during a first operation of the motor vehicle , and that during a second operating condition the charged capacitor serves at least 2% for a total of 2 s for operating the electrical consumers and / or for charging the accumulator. 2. The method according to claim 1, characterized in that a capacitor with a Discharge / charging power of at least 0.5 kW, preferably 0.7 kW and in particular at least 1 kW is used. 3. The method according to claim 1 or 2, characterized in that a capacitor with a cyclically usable memory of at least 20 kJ and in particular at least 28 kJ is used. 4. Method for operating a motor vehicle with an internal combustion engine, a battery, electrical consumers and a power generator that the Charging the battery and operating the electrical consumers, characterized in that during a first operating condition of the Electric vehicle is charged via the power generator, that during a second operating condition the charged electrical storage to operate the electrical consumers and / or to charge the battery serves, the electrical storage a charging / discharging power of at least 0.5 kW and / or a cyclically usable memory of at least 20 kJ.   5. The method according to any one of the preceding claims, characterized in that in the first operating condition the generator compared to the second Operating condition a lower theoretical specific fuel consumption Has. 6. The method according to any one of the preceding claims, characterized in that the first operating condition is an overrun phase, a braking phase or a phase, in the internal combustion engine a maximum of 20% of its maximum speed-related performance is required. 7. The method according to any one of the preceding claims, characterized in that the second operating condition depends on the state of charge of the capacitor or of the electrical storage and / or from the operating point of the Internal combustion engine and / or NOx emissions from the Internal combustion engine is. 8. The method according to any one of the preceding claims, characterized in that a gold capacitor is used as a capacitor or memory. 9. The method according to any one of the preceding claims, characterized in that a power generator with an output of at least 1.5 kWh, in particular at least 2 kWh is used. 10. The method according to any one of the preceding claims, characterized in that a control device is provided which detects the charging voltage of the capacitor or electrical storage increased. 11. The method according to any one of the preceding claims, characterized in that a control unit is used that the discharge voltage of the capacitor or electrical storage adapts to the voltage required for the consumer.