Operating procedure for an electro-hydraulic vehicle braking system

Abstract

Operating method for an electro-hydraulic braking system of a vehicle with an electrically operated conveying device for the hydraulic medium actuating the brakes, which generates electrical energy by reducing the hydraulic pressure stored in the braking system, characterized in that the generated electrical energy is made available to the electro-hydraulic braking system with priority shortly before the start of a drive unit of the vehicle.

Description

[0001] The invention relates to an operating method for an electro-hydraulic braking system of a vehicle with an electrically driven conveying device for the hydraulic fluid that actuates the brakes, which generates electrical energy by reducing the hydraulic pressure stored in the braking system. Furthermore, the invention relates to an electro-hydraulic braking system of a vehicle for carrying out the operating method according to the invention. For the prior art, reference is made not only to DE 102 08 511 A1, but in particular to DE 10 2012 205 340 A1.

[0002] Vacuum-operated brake boosters are well-known. These systems use a pressure differential to assist the driver's pedal force in operating the vehicle's brakes, independent of the voltage level of the vehicle's electrical system. The necessary vacuum is generated either in the intake manifold of a quantity-controlled internal combustion engine serving as the vehicle's drive unit or by a dedicated vacuum pump.

[0003] Furthermore, electro-hydraulic braking systems are known that require sufficiently high electrical power to fulfill their function. During electrical voltage dips, such as those that can occur particularly during a cold start of an internal combustion engine vehicle, the electrical voltage in the vehicle's electrical system can briefly drop significantly below the usual level.

[0004] Several measures are known to prevent a negative impact of a drop in the electrical voltage in the vehicle's electrical system on the functionality of the vehicle's braking system, which must always be guaranteed. For example, a so-called boost converter can be provided, or the electromagnetically controlled valves used can be dimensioned for even lower supply voltages, all of which are relatively complex. In the aforementioned German patent DE 102 08 511 A1, an auxiliary electric generator coupled directly to the drivetrain at the wheel side is proposed as a solution to such a problem.

[0005] Further prior art regarding electro-hydraulic vehicle braking systems is described in the generic German patent DE 10 2012 205 340 A1 in the form of a method for controlling an electro-hydraulic braking system with at least one brake pressure control function, in particular an anti-lock braking control function, and a further brake pressure control function, which can be controlled, for example, in a "brake-by-wire" operating mode, with a pressure supply device controllable by means of an electronic control unit, which is driven by an electric motor, wherein the electric motor is connected to the vehicle's electrical system for power supply, and which is connected to hydraulically actuated wheel brakes and by means of which the wheel brakes can be hydraulically actuated via at least one pressure control valve. At least the latter features are also present in an electro-hydraulic braking system of the present invention.In the earliest prior art, the pressure supply device comprises a cylinder-piston arrangement with a hydraulic pressure chamber, the piston of which can be displaced relative to a rest position by the electric motor. This can, but does not have to, be implemented in the electro-hydraulic braking system of the present invention in the form of the aforementioned electrically driven conveying device. In the earliest prior art, a regenerative current fed into the electrical grid by the electric motor during a reversing process in generator mode is limited; that is, it is known from this document that electrical energy can be generated in an electro-hydraulic braking system by reducing the hydraulic pressure stored in the braking system by means of the present electrically driven conveying device.

[0006] The present invention aims to demonstrate a further measure, implementable without significant effort, that prevents a negative impact of a drop in electrical voltage in the vehicle's electrical system on the functionality of the vehicle's braking system, which must always be guaranteed (the object of the present invention). The solution consists of an operating method for an electro-hydraulic braking system according to the preamble of claim 1 and is characterized in that the generated electrical energy is made available to the electro-hydraulic braking system primarily, preferably exclusively, shortly before a start, and in particular before a cold start, of the vehicle's drive unit. Advantageous embodiments are the subject of the dependent claims.

[0007] According to the invention, temporary voltage dips can be bridged by utilizing hydraulic energy within the braking system. This is achieved by reducing the hydraulic pressure maintained in the braking system and converting it into electrical energy, for example, via the pump driven by this hydraulic pressure and the electric motor mechanically connected to it, which then operates as a generator. This converted electrical energy can thus compensate for a short-term voltage dip, provided that this electrical energy does not flow into the entire vehicle electrical system, but is primarily, and preferably exclusively, made available to the electro-hydraulic braking system. This ensures that the electrical voltage for the braking system remains at a level at which all system components, including the critical valves, function correctly.

[0008] Such a “voltage-supporting energy conversion” within the braking system, which can be carried out analogously to the state of the art by the conveying device, but alternatively also in other ways, but always by reducing stored hydraulic pressure, is provided in particular for the aforementioned case of a cold start of a drive unit of the vehicle, but can in principle be implemented in all starting processes in which short-term voltage drops are to be feared.

[0009] For the benefit of further development, a higher hydraulic pressure than usual during normal operation can be built up in the brake system before the hydraulic pressure stored in the brake system is released, thus allowing a larger amount of energy to be stored or held in reserve. The actual energy storage, in the form of generating and essentially "locking in" hydraulic pressure, can occur essentially directly before this stored hydraulic pressure is released. Alternatively, hydraulic pressure that will be released later as needed in connection with a start or cold start of the vehicle's drive unit can also be built up in advance, for example, when the vehicle is switched off. Provided the hydraulic brake system is sufficiently leak-tight, this can be achieved in advance.A hydraulic pressure storage unit connected to this can maintain the latter for a longer period of time and selectively call upon it when needed in order to generate electrical energy from it - as described - to bridge a short-term voltage drop.

[0010] Particularly if – as suggested as a possible alternative – the build-up and subsequent release of hydraulic pressure are carried out immediately sequentially before the vehicle's drive unit is started, an electronic control unit in which the inventive method is implemented should be able to detect an impending start, or especially a cold start, with sufficient reliability. At least one cold start is easily achievable via the electronic vehicle data bus, for example, by unlocking the parked and usually locked vehicle. With such or other suitable warning signals, the conversion process presented here can be initiated or carried out within a reasonable timeframe (e.g., on the order of approximately 100 milliseconds).

[0011] Returning to the characteristic feature that the electrical energy generated by a reduction in the hydraulic pressure stored in the braking system is primarily, and preferably exclusively, made available to the electro-hydraulic braking system, it is recommended that, at the moment of a voltage drop in the vehicle's electrical system, the electrical components of the braking system be decoupled from the vehicle's electrical system. This ensures that the generated electrical energy remains within the braking system and its electrical components and cannot flow to other storage devices or consumers in the vehicle's electrical system. Such decoupling can be implemented using standard electro-electronic elements and can advantageously also be achieved using existing components, such as a reverse polarity protection device. Following the aforementioned warning signal during the build-up of hydraulic pressure, the reverse polarity protection device can be closed accordingly.A further claimed electro-hydraulic braking system of a vehicle for carrying out the operating method according to the invention thus has a device that prevents the generated electrical energy from flowing into the electrical on-board network of the vehicle.

[0012] In the interest of an advantageous further development of the method according to the invention, the electric motor of the braking system can, after pressure build-up has taken place, be set into a slight rotary movement corresponding to generator operation shortly before the start of the pressure reduction in order to compensate for its rotor inertia at the beginning of the pressure reduction.

[0013] An electro-hydraulic braking system of a vehicle for carrying out the operating method according to the invention can have a suitable pressure accumulator for the pressurized hydraulic medium, which is formed or provided within the hydraulic braking system itself or which constitutes a separate component. In the former case, actuation of the brake pedal by the driver is required; however, such actuation is required anyway in motor vehicles with an automatic transmission when starting the vehicle's drive unit. If a separate pressure accumulator for the hydraulic medium is provided, which can advantageously be part of a pedal force simulator known to those skilled in the art, then no brake pedal actuation is necessary, and the method according to the invention can then be implemented simply, i.e., without further special adaptation, also in vehicles with manual transmissions.

[0014] The method presented here provides a simple and particularly cost-effective way to support the power supply of an electro-hydraulic braking system. The solution is fully implementable using the components of a state-of-the-art braking system. By compensating for voltage dips during cold starts, the overall system can be designed for a higher minimum voltage. The proposed method poses no safety risk, as any increased brake pressure when the vehicle is stationary has no effect, and the driver advantageously experiences no change in pedal feel, since the pressure is not transmitted to the brake pedal.

Claims

[1] Operating method for an electro-hydraulic braking system of a vehicle with an electrically operated pumping device for the hydraulic fluid that actuates the brakes, which generates electrical energy by reducing the hydraulic pressure stored in the braking system, characterized by , that the generated electrical energy is made available to the electro-hydraulic braking system as a priority shortly before the start of a drive unit of the vehicle. [2] Operating method according to claim 1, characterized by , that a higher hydraulic pressure than usual during operation of the brake system is built up in the brake system before the hydraulic pressure stored in the brake system is reduced. [3] Operating method according to claim 1 or 2, wherein the build-up and subsequent release of hydraulic pressure is carried out immediately consecutively before the start of the vehicle drive unit. [4] Electro-hydraulic braking system of a vehicle for carrying out the operating procedure according to one of the preceding claims, comprising a device preventing the generated electrical energy from flowing into the vehicle's electrical system. [5] Electro-hydraulic braking system of a vehicle for carrying out the operating procedure according to one of claims 1-3 with a pressure accumulator for the pressurized hydraulic medium.