DE102006055799B4 - Method for regenerative braking of a vehicle with multiple braking systems - Google Patents

Abstract

The invention relates to a method for regenerative braking of a vehicle by means of a hydraulic or pneumatic brake system (7, 9), an electromechanical brake system (6) and a generator, each of the systems (7, 9; 6; 2) using a specific proportion ( R, E, H) contributes to a desired overall deceleration of the vehicle. A braking process can be carried out particularly easily and with a high level of efficiency if the proportion of the electromechanical braking device 6 is controlled as a function of the proportion (R) of the generator 2 .

Description

State of the art

The invention relates to a method for braking a vehicle according to the preamble of patent claim 1 and a control unit according to the preamble of patent claim 11.

The patent specification DE 601 14 140 T2 deals with a system for braking a trailer which has an axle unit and is towed by a vehicle. The system includes at least one electric machine coupled to said axle assembly, at least one sensor operative to measure an attribute of said trailer and generate a first signal representative of said measured attribute, and a controller in communication coupled to said at least one electrical machine and said sensor, said controller being operable to receive a first signal and selectively apply a second signal to said at least one electrical machine based on said first signal, said second signal causing in that said at least one electric machine applies regenerative braking torque to said axle assembly to decelerate said trailer and thereby generate electrical energy.

The Disclosure DE 10 2005 000 194 A1 relates to a vehicle brake device in which front wheel braking power is controlled with fluid pressure braking power and regenerative braking power, while rear wheel braking power is controlled with only fluid pressure braking power, so that regenerative and cooperative braking control is performed.

The disclosure document JP 2006 - 197 757 A aims to provide a regenerative braking controller for vehicles which makes it possible to stabilize vehicle behavior while the vehicle is in a straight-ahead steering state and regenerative braking is performed only on either the front wheels or the rear wheels.

Today, regenerative braking is mainly used in hybrid vehicles to improve vehicle efficiency and save fuel. In addition to the internal combustion engine, hybrid vehicles have an electric machine that is operated either as a motor or as a generator. When the engine is running, the electric machine generates an additional drive torque that drives the combustion engine, e.g. B. supported in an acceleration phase. In generator mode, on the other hand, the kinetic energy released when the vehicle decelerates is converted into electrical energy (recuperation). The electrical energy obtained in this way is stored in an energy store, e.g. B. a battery or a super-cap, stored and can be used in other driving situations such. B. be used to drive the vehicle or to supply electrical consumers. The efficiency of the vehicle can be significantly increased as a result. But even in conventional vehicles that only have a vehicle generator, the energy balance can be improved by regenerative braking.

With regenerative braking, the electric machine or generator generates a drag torque that has a braking effect on the combustion engine. The drag torque is particularly dependent on the current speed of the internal combustion engine. In addition, the drag torque depends on the state of charge or the capacity of the on-board electrical system. With a fully charged energy storage z. B. only very little or no electrical energy is fed into the vehicle electrical system, since the energy store would otherwise be overloaded or voltage-sensitive consumers could be damaged. The drag torque of the generator can therefore fluctuate considerably. This also influences the braking behavior of the vehicle as a whole. In order to avoid this, the hydraulic brake pressure is therefore usually modulated as a function of the generator drag torque. However, this is hydraulically very complex, since a lot of brake fluid has to be pumped back and forth in the brake circuits during a regenerative braking process.

Disclosure of Invention

It is therefore the object of the present invention to create a method for regenerative braking of a vehicle in which the hydraulic or pneumatic effort is significantly lower.

This object is achieved according to the invention by the features specified in patent claim 1 and in patent claim 11 . Further configurations of the invention are the subject matter of dependent claims.

An essential aspect of the invention consists in using an electromechanical braking device, preferably an electromechanical drum brake, and modulating its braking torque in order to compensate for the fluctuating drag torque of the generator. Hydraulic or pneumatic modulation is no longer required. This has the main advantage that fluctuations in the generator drag torque can be compensated much more easily.

The fluctuation in the regenerative component is preferably compensated for at least at the end of a braking process. The proportion of the generator usually decreases sharply when the vehicle is braked to a standstill and the combustion engine is only running at idle speed in the last phase of the braking process. The decreasing generator drag torque is then compensated by an increasing electromechanical braking torque. On the other hand, the braking torque in the initial phase of a braking process can, as before, also be modulated hydraulically or pneumatically. A significant improvement in the technical complexity can already be achieved if the braking torque is modulated at least in the final phase of the braking process using the electromechanical braking device.

According to a preferred embodiment of the invention, only the moment of the electromechanical braking device is modulated during the entire regenerative braking process.

In addition, the braking torque of the hydraulic or pneumatic braking device is preferably limited to a predetermined value. For this z. B. valves of the brake system are controlled accordingly. Due to the limitation of the hydraulic component, a varying hydraulic component does not also have to be taken into account when modulating the electromechanical component. The modulation can thus be significantly simplified.

In principle, the generator is preferably operated in such a way that the proportion of the electrical generator power generated is at a maximum. As a result, a maximum of electrical energy can be recovered.

In order not to overcharge an energy store provided in the vehicle electrical system (e.g. a battery or a super-cap) in recuperation mode, the state of charge of the energy store must be known. It is therefore a facility such. B. is provided known from the prior art state of charge detection that monitors the state of charge of the energy storage. The status detection can e.g. B. be stored as software in a control unit.

If, during a regenerative braking process, a driving dynamics limit situation occurs in which slip control (eg ABS or ESP) has to be carried out, the generator is preferably switched off completely or the proportion of the generator is at least greatly reduced. This is intended to rule out any impairment of the slip control by the generator.

In the case of slip control, various strategies can be used with regard to the necessary modulation of the braking force. According to a first embodiment, for example, the component of the hydraulic or pneumatic braking device can be kept constant and only the electromechanical component can be modulated. The hydraulic component can also be reduced to zero and the braking torque can be modulated solely by means of the electromechanical braking device.

According to a second embodiment, of course, the electromechanical component can also be set to a predetermined constant value and the slip control can be carried out by means of the hydraulic or pneumatic brake device. Here, too, the electromechanical component can be reduced towards zero and the slip control can be carried out exclusively by means of the hydraulic or pneumatic braking device.

Optionally, the slip control could also be carried out by means of both braking devices, i. H. the hydraulic or pneumatic and the electromechanical braking device are carried out simultaneously.

The method described above is preferably software-based and is controlled by a control unit. The control unit preferably comprises a coordinator (software algorithm) which i.a. the distribution of the desired total braking torque to the individual braking systems or the generator is determined.

The presence of a driving dynamics limit situation is usually monitored by a driving dynamics control unit.

character list

• 1 die Bremsmomentenverteilung in einem Fahrzeug gemäß einer ersten Ausführungsform der Erfindung;
• 2 die Bremsmomentenverteilung in einem Fahrzeug gemäß einer zweiten Ausführungsform der Erfindung;
• 3 die Bremsmomentenverteilung vor und nach dem Eintreten einer fahrdynamischen Grenzsituation;
• Fi. 4 die Bremsmomentenverteilung in einer fahrdynamischen Grenzsituation gemäß einer ersten Ausführungsform der Erfindung;
• 5 die Bremsmomentenverteilung in einer fahrdynamischen Grenzsituation gemäß einer ersten Ausführungsform der Erfindung;
• 6 die Bremsmomentenverteilung in einer fahrdynamischen Grenzsituation gemäß einer ersten Ausführungsform der Erfindung;
• 7 ein schematisches Blockschaltbild der wesentlichen Elemente eines Fahrzeugsystems zum regenerativen Bremsen; und
• 8 eine schematische Darstellung eines hydraulisch-elektrischen Radbremse.

The invention is explained in more detail below by way of example with reference to the attached drawings. Show it:

• 1 the braking torque distribution in a vehicle according to a first embodiment of the invention;
• 2 the braking torque distribution in a vehicle according to a second embodiment of the invention;
• 3 the braking torque distribution before and after the occurrence of a driving dynamics limit situation;
• Fi. 4 shows the braking torque distribution in a driving dynamics limit situation according to a first embodiment of the invention;
• 5 the braking torque distribution in a driving dynamics limit situation according to a first embodiment of the invention;
• 6 the braking torque distribution in a driving dynamics limit situation according to a first embodiment of the invention;
• 7 a schematic block diagram of the essential elements of a vehicle system for regenerative braking; and
• 8th a schematic representation of a hydraulic-electric wheel brake.

Embodiments of the invention

1 shows a schematic view of the braking torque distribution during a typical braking process, in each case on the front axle VA and the rear axle HA of a vehicle. The vehicle is equipped with hydraulic disc brakes on the front axle. Various braking systems are provided for braking the rear axle HA, each of which contributes a certain proportion H, E, R to the total braking torque. In this exemplary embodiment, the rear wheels each have a combined hydraulic/electromechanical wheel brake, as is exemplified in 8th is shown. This type of wheel brake is also referred to as a DIH brake (DIH: drum in head) and includes a hydraulic disc brake 9 and an electromechanical drum brake 6 in one structural unit.

In 1 the contribution of the hydraulic disk brake 9 is denoted by H and the proportion of the electromechanical drum brake 6 is denoted by E. In recuperation mode, the vehicle generator also generates a drag torque, which also contributes to the deceleration of the vehicle. The portion of the generator 2 is denoted by R here.

The generator is preferably operated in such a way that the highest possible proportion of the desired total deceleration (specified by the driver by actuating the foot brake pedal) is effected by the generator 2 and thus a maximum of energy can be recovered. The portion R generated by the generator is not constant over the course of a braking process, but depends on the speed of the combustion engine and the state of charge or the capacity of the on-board electrical system. With a fully charged battery or Super-Cap, only very little or no electrical energy can be fed into the vehicle electrical system. The drag torque generated by generator 2 can therefore vary relatively greatly.

The fluctuating portion R of the generator 2 is compensated here solely by the electromechanical drum brake. The component H of the hydraulic disk brake 9, on the other hand, is limited to a constant value and held at this value. To limit the hydraulic braking torque H, for example, valves in the hydraulic braking system can be controlled accordingly. The limitation takes place during the entire duration t ₀ of the braking process.

2 shows the proportions H, E, R of the individual braking systems according to a second embodiment. Purely hydraulic braking takes place on the front axle VA. At the beginning of the braking process, the rear axle HA is braked hydraulically and regeneratively. The varying component R of the vehicle generator 2 is initially regulated purely hydraulically. In the initial phase, the electric drum brake 6 makes no contribution. If, after some time, the regenerative component R of the generator 2 is relatively constant, the component H of the disk brake 9 is limited to a fixed value. Only in the final phase t1 of the braking process, in which the proportion R of the generator 2 falls, is the falling proportion R compensated for by the electric drum brake 6 . This procedure is somewhat more complex than the strategy according to 1 , but still much simpler than a purely hydraulic modulation of the braking torque.

3 shows the braking torque distribution in the case of a driving dynamics limit situation in which slip control must be carried out. Purely hydraulic modulation takes place on the front axle VA. As soon as the critical driving situation has been identified, the regenerative component R is reduced on the rear axle HA and the generator 2 is completely deactivated (see time t ₂ ). The hydraulic component H is also reduced to zero. So there remains only the part E of the electromechanical drum brake 6, which is modulated in the following. Optionally, the hydraulic component H could also be kept constant or kept at a lower constant value.

4 shows the braking torque distribution in the case of a slip control according to another embodiment. The graphic describes a braking process without regenerative braking, i.e. without the participation of generator 2. A purely hydraulic modulation takes place on the front axle VA. The component E of the electromechanical drum brake 6 is modulated on the rear axle HA and the hydraulic component H is kept constant. In the case of slip control (from Time t ₂ ) only the electromechanical component E is modulated. The hydraulic component H remains constant as long as the braking torque of the electromechanical brake 6 is greater than zero.

5 shows a further embodiment for a braking torque distribution in the case of a critical driving situation. The distribution of 5 is complementary to that of 4 . As can be seen, the hydraulic braking torque H is controlled here, while the electromechanical component E remains constant.

6 shows a further embodiment for a braking torque distribution in the case of a critical driving situation. In contrast to the embodiments of 4 and 5 Both parts E and H are synchronously modulated here on the rear axle HA. The technical outlay in this exemplary embodiment is naturally somewhat higher than in the previous exemplary embodiments.

7 shows a schematic representation of the essential components of a motor vehicle braking system designed for regenerative braking. The overall system here includes three sub-brake systems, namely a hydraulic brake system with components 7 (hydraulic unit) and 9 (disc brakes), an electromechanical drum brake 6 and a generator 2, which can be switched on in recuperation mode. Each of the sub-brake systems is connected to a central control unit 1, which determines the level of the shares of the individual sub-brake systems in the total braking torque and controls or regulates the sub-brake systems accordingly. For this purpose, the control unit 1 includes special software 8 (coordinator).

During a braking process, as exemplified in the 1 until 6 was shown, the desired setpoint deceleration or a variable proportional thereto is first determined. For this purpose, a sensor system 5, such as a pedal value sensor, is provided, which transmits the driver's request in the form of a setpoint value, such as B. a target torque M _set or a target deceleration a _set to the control unit 1 outputs. With an automatically initiated braking, as z. B. can be requested by a brake assistance system, the target size z. B. provided by another control unit (not shown). The coordination algorithm then decides what proportion of the total braking torque is caused by the individual sub-braking systems 6, 9, 2 and whether, if necessary, a regenerative braking process involving generator 2 should be carried out.

The proportion R, E, H depends on the current driving situation, the desired total braking torque and - in the case of regenerative braking - the capacity of the on-board electrical system, in particular the battery or a super-cap. The information about the type of braking process (with or without slip control) is supplied to control unit 1 by an external ESP or ABS control unit 10 . The current state of charge or capacity of the battery 4 is supplied to the control unit by a battery state detection device.

The operating state of the generator 2 and in particular the active power output are adjusted by means of a pulse-controlled inverter 3 (PWR).

8th shows an example of a combined hydraulic/electric brake, which is also referred to as a DIH brake (DIH: drum in had). The DIH brake includes a hydraulic disc brake with a brake disc 11 and brake shoes 15, which can work, for example, according to the floating caliper principle.

The brake shown also includes an electromechanical drum brake, which is denoted here overall by the reference number 6 . The electromechanical drum brake 6 includes brake shoes 13 which are actuated by means of an electric drive 14 . The brake shoes 13 interact with the friction surface of a brake drum 12, which is connected to the brake disc 11 as a structural unit.

The electromechanical drum brake 6 is preferably also used as an automatic parking brake.

Claims (11)

Method for regenerative braking of a vehicle, in which a target variable (M _target , a _target ), which represents a desired total braking torque, is determined and distributed proportionally to at least one electromechanical braking device (6) and a generator (2), each of which has a Share (H,E,R) of the total braking torque, characterized in that the share (E) of the electromechanical braking device (6) is modulated as a function of the share (R) of the generator (2) in order to compensate for fluctuations in the generator share ( R) to compensate. procedure after claim 1 , characterized in that the proportion (E) of the electromechanical braking device (6) is regulated at least in a final phase (t ₁ ) of a braking process. procedure after claim 2 or 3 , characterized in that the proportion (E) of the electrome chanical braking device (6) during the entire braking process (t ₀ ) is regulated. Method according to one of the preceding claims, characterized in that the vehicle has a hydraulic or pneumatic braking device (7, 9) which also effects a proportion (H) of the total braking torque. procedure after claim 4 , characterized in that the hydraulic or pneumatic portion (H) is limited to a predetermined constant value. Method according to one of the preceding claims, characterized in that the generator component (R) is reduced when a driving dynamics limit situation occurs and is preferably reduced completely to zero. procedure after claim 4 , characterized in that the hydraulic or pneumatic component (H) is kept constant when a dynamic driving situation occurs and the electromechanical component (E) is modulated. procedure after claim 4 , characterized in that the electromechanical component (E) is kept constant when a dynamic driving situation occurs and the hydraulic or pneumatic component (H) is modulated. procedure after claim 4 , characterized in that when a driving dynamics limit situation occurs, the electromechanical component (E) and the hydraulic or pneumatic component (H) are regulated. Method according to one of the preceding claims, characterized in that the desired total deceleration (M _desired , a _desired ) is distributed to the individual braking systems (2, 6, 7, 9) by means of a coordinator (8). Control unit comprising means for carrying out one of the previously claimed methods.

Images