MOTOR VEHICLE HAVING A RECUPERATIVE BRAKING MODE

A hydraulic brake for a motor vehicle in which one inlet valve and one outlet valve, configured in the switchable fashion, is respectively made available for at least one wheel, wherein the inlet valve is fluidly coupled to the outlet valve downstream of the inlet valve via a brake pressure line, and wherein a hydraulic accumulator for storing hydraulic fluid is made available downstream of the outlet valve. The hydraulic accumulator is reaction-free in a recuperative braking mode. The brake pressure line is coupled to a piston of a brake lining of a friction brake of the wheel via a valve arrangement, wherein the valve arrangement has a first valve which opens only towards the piston, and a second valve which opens only towards the brake pressure line, and wherein an opening pressure of the first valve is higher than a residual pressure brought about by the hydraulic accumulator.

SUMMARY

Illustrative embodiments relate to a hydraulic brake for a motor vehicle. The hydraulic brake has an inlet valve and an outlet valve, which is designed to be switchable, for each wheel, wherein a brake pressure line, via which the inlet valve and the outlet valve are coupled to one another and which leads to a piston of a brake pad of a friction brake of the wheel, is provided downstream of the inlet valve. A hydraulic accumulator for storing hydraulic fluid is provided downstream of the outlet valve. Illustrative embodiments also include a motor vehicle having the disclosed hydraulic brake.

DETAILED DESCRIPTION

To integrate the hydraulic brake described in a recuperative system, the displaced volume of hydraulic fluid has to be guided into the hydraulic accumulator via the outlet valve when the brake pedal is actuated so that brake pressure does not build up at the piston of the brake pad. However, the hydraulic accumulator produces a residual pressure in the brake pressure line, which presses on the piston of the brake pad of the brake disk of the wheel via the opened outlet valve. This impairs the efficiency with regard to the energy recovery in the recuperative braking mode.

A recuperative brake system for which the disclosed hydraulic brake is suitable is known, for example, from DE 10 2012 023 345 A1. According to this, for a regenerative braking procedure, a pressure reduction valve is opened for each brake after the actuation of a brake pedal and the activation of a generator so that a hydraulic fluid flows from the wheel brakes and thereby lowers the brake pressure in the wheel brakes. The hydraulic braking torque is therefore not built up to the same extent as the total braking torque, which additionally comprises the generator torque.

It is known from DE 10 2012 203 779 A1 that, in purely regenerative or recuperative braking, a build up of brake pressure in a brake circuit of a brake system is limited to a response pressure of a storage volume of the brake circuit. This takes place by controlling a wheel outlet valve of the brake circuit so that brake fluid is displaced out of the master brake cylinder and the first brake circuit and into the storage volume of the brake circuit via the wheel outlet valve.

The disclosed embodiments prevent the loss of efficiency described at the outset owing to the reaction of the hydraulic accumulator on the piston of the brake pad.

A hydraulic brake for a motor vehicle is provided. In the hydraulic brake, an inlet valve and an outlet valve, which is designed to be switchable, are provided in each case for at least one wheel. A brake pressure line, which couples the inlet valve hydraulically or fluidically to the outlet valve, is provided downstream of the inlet valve (and upstream of the outlet valve). In a manner known per se, a brake pressure can be built up in the brake pressure line via the inlet valve by closing the outlet valve, which brake pressure then acts on a piston of a brake pad of a friction brake of the wheel and thereby brings about a braking effect of a brake disk of the wheel in a known manner. A low pressure accumulator or hydraulic accumulator for storing hydraulic fluid is furthermore provided downstream of the outlet valve in the hydraulic brake.

To prevent a buildup of brake pressure in the brake pressure line during regenerative or recuperative braking, it is possible to switch the outlet valve to an open position during the actuation of a brake pedal so that brake fluid can escape from the brake pressure line and into the hydraulic accumulator through the outlet valve. However, in the manner described at the outset, the residual pressure of the hydraulic accumulator then reacts in the brake line as a result of the outlet valve. The residual pressure in the hydraulic accumulator is produced, for example, by a pressure spring, which exerts a static pressure on the hydraulic fluid stored in the hydraulic accumulator. To now prevent this residual pressure from also acting on the piston of the brake pad, it is provided that the brake pressure line is coupled to the piston of the brake pad via a valve arrangement. The valve arrangement here has two valves, a first valve which only enables a flow in the direction of the piston and a second valve which only enables a flow in the direction of the brake pressure line. An opening pressure of the first valve which is directed from the brake pressure line towards the piston in the flow-enabling direction is higher than the residual pressure brought about by the hydraulic reservoir. As a result of the opening pressure of the first valve being higher than this residual pressure, the hydraulic accumulator is not able to transfer the residual pressure to the piston of the brake pad because this is arranged fluidically downstream with respect to the valve arrangement.

During the regenerative or recuperative braking mode, the outlet valve of the hydraulic brake can be brought into an open position without the hydraulic accumulator thereby reacting on the piston of the brake pad of the friction brake with its residual pressure. It is therefore possible for the brake pad to remain free of contact with the brake disk so that a loss of efficiency is not produced during the recuperative braking mode as a result of the brake pad rubbing against the brake disk.

To implement the recuperative braking mode, a further development provides that, depending on a signal signaling a recuperative braking mode, i.e., signaling the activity of an electric machine in generator mode, for example, the outlet valve is switched to an open position so that a fluid flow produced upstream of the inlet valve by an actuated brake pedal is discharged through the inlet valve, past the valve arrangement, through the outlet valve and into the hydraulic accumulator. The valve arrangement does not influence the recuperative braking mode.

According to a further development, the opening pressure of the first valve is in a range of 1 bar to 3 bar. In hydraulic braking mode when brake pressure is built up in the brake pressure line to operate the friction brake, the driver is unable to feel any resistance of the valve arrangement during hydraulic braking owing to the relatively low opening pressure of the first valve.

According to a further development, an opening pressure of the second valve is in a range lower than 0.8 bar. The restoring or return of the brake pad into the rest position and the end of a hydraulic braking procedure is not hindered or delayed by the valve arrangement.

According to a further development, the valve arrangement is integrated in a valve block. The valve block provides that the inlet valve and the outlet valve, together with at least one further inlet valve and at least one further outlet valve for a further wheel in each case, are integrated in the valve block. The valve arrangement is then likewise integrated in this valve block. The valve block can be provided as an installation part and this valve block is already designed to be non-reactive with regard to the piston of the brake pad in a recuperative braking mode. Such a valve block can be, for example, an integral part of an electronic stability control (ESC) which should be realized with as few components as possible, namely according to the so called 2-box principle based on a main valve and the valve block.

According to an alternative further development, the valve arrangement is designed as an individually mountable intermediate piece via which the brake pressure line and the friction brake are mechanically coupled. For example, such an intermediate piece can be screwed to the described valve block, i.e., to an output of the brake pressure line integrated in the valve block. This further development is beneficial in that the valve arrangement can be integrated in an existing brake circuit as a retrofit part.

According to an alternative further development, the valve arrangement is integrated in a brake caliper of the friction brake. The friction brake is itself protected against the reaction of the hydraulic accumulator and its residual pressure.

According to a further development, the first valve and the valve in the valve arrangement are hydraulically connected in parallel, i.e., the valve arrangement has a common first connection for connecting both the first valve and the second valve to the brake pressure line and a common second connection for connecting both the first valve and the second valve to the friction brake. In other words, starting from the first connection, a branched hydraulic line is provided, which fluidically couples the first connection both to the first valve and to the second valve. Equally, the second connection is fluidically coupled both to the first valve and to the second valve via a branched hydraulic line. The further development is beneficial in that the total of four valve openings of the two valves can be connected to a hydraulic circuit via only two connections.

To realize a robust and, in terms of its manufacture, economical embodiment of the hydraulic brake, a further development provides that the first valve and/or the second valve are formed by a spring-mounted ball valve in each case. Small control lines are then required to control the valve positions of the valves.

According to a further development, it is provided that a valve arrangement is only provided for two wheels in each case, for example, the two rear wheels or the two front wheels. Alternatively, it is provided that a valve arrangement is provided for four wheels of the motor vehicle in each case. In other words, for at least one axle of the motor vehicle (front axle, rear axle), a valve arrangement of the type described is provided for its two wheels in each case.

As already mentioned, disclosed embodiments also include a motor vehicle. The disclosed motor vehicle has an embodiment of the disclosed hydraulic brake. The disclosed motor vehicle is therefore set up for an efficient recuperative braking mode.

The disclosed motor vehicle may be designed as an automobile, in particular, as a truck or car.

A further development of the motor vehicle enables the recuperative braking mode in that an electric machine is designed to brake the motor vehicle in the recuperative braking mode by converting kinetic energy of the motor vehicle into electrical energy. A computing device is designed to initiate the recuperative braking mode depending on an actuation of a brake pedal of the motor vehicle, as is known per se, and, with this, to signal the recuperative braking mode to the hydraulic brake via a signal. The outlet valve can then be opened in the manner described, for example, as a result of the signal. The computing device can be provided, for example, by a control device of the motor vehicle. The computing device can comprise, for example, a microcontroller or a microprocessor.

In the exemplary embodiment, the described components of the embodiment each represent individual features of the disclosure which can be regarded independently of one another and which also develop the disclosure independently of one another in each case and can therefore be also viewed, individually or in a combination other than that shown, as an integral part of the disclosure. The embodiment described can also be supplemented by others of those features of the disclosure which have already been described.

Functionally identical elements are each denoted by the same reference signs in the figures.

FIG. 1shows a bird's eye view of a motor vehicle1which can be, for example, an automobile, in particular, a car. Wheels2, part of a hydraulic brake3, a computing device4and an electric machine5are shown.

The electric machine5can be a drive motor of the motor vehicle1. It can also be provided that the motor vehicle1additionally or alternatively has an internal combustion engine, which is not illustrated inFIG. 1. The electric machine5can also be designed, for example, as a starter-generator. The electric machine5can be mechanically coupled to two of the wheels2, for example, to thereby brake the coupled wheels2in generator mode and thereby enable a recuperative braking mode of the motor vehicle1.

Of the hydraulic brake3, a control device6, a valve block7, friction brakes8for the rear wheels and hydraulic lines9are shown inFIG. 1. The valve block7can have an inlet valve10and an outlet valve11for each friction brake8, which are fluidically coupled to one another by a brake pressure line12in each case. The friction brakes8and the associated inlet valve10and outlet valve11are differentiated inFIG. 1by the following reference signs for the vehicle wheels: HR—rear right, HL—rear left. Friction brakes3(not illustrated) can equally be provided by the hydraulic brake3for the front wheels VR—front right—and VL—front left.

The respective brake pressure line12is fluidically coupled in each case to a piston14of one of the friction brakes8here via a valve arrangement13and, for example, via one of the hydraulic lines9. The piston14acts on brake pads15, which can be arranged, for example, in a brake caliper16of the friction brake. When the piston14is acted upon by a brake pressure, the brake pads15rub against a brake disk17of the friction brake8and thereby brake the respective wheel2.

Each of the valve arrangements13can be integrated in the valve block7. The valve arrangements13can alternatively be arranged on a connection18of the valve block7and, to this end, be provided as an intermediate piece for connecting the valve block7and the hydraulic line9. The valve arrangements13can equally also be provided in each case as an intermediate piece between the hydraulic line9and the brake caliper16. Finally, each valve arrangement13can also be integrated in the brake caliper16of the respective friction brake8in each case.

To brake the motor vehicle1via a recuperative braking mode, the electric machine5is switched to generator mode by the computing device4. To this end, the computing device4can be designed, for example, as a control device. The computing device4furthermore signals via a signal19to the control device6of the hydraulic brake3that the recuperative braking mode has been initiated. The control device6then implements the control procedure (described below) in the hydraulic brake3to realize the recuperative braking mode as efficiently as possible. Please refer to the followingFIG. 2for explanation.

FIG. 2again shows the hydraulic brake3in more detail using the example of an individual wheel2. In addition to the elements illustrated inFIG. 1, a brake pedal20, a brake booster21, a master cylinder22, a hydraulic accumulator23and a pump24are further shown. As a result of a brake pedal actuation25of the brake pedal2, a fluid flow26of a brake fluid27is produced in a manner known per se by the master cylinder22. Owing to, or depending on, the signal19, the control device6switches the inlet valve10and the outlet valve11to an open position, whereby the fluid flow26from the master cylinder22arrives in the brake pressure line12through the inlet valve10. The fluid flow26flows past the valve arrangement13through the outlet valve11and into the hydraulic accumulator23. The hydraulic accumulator23therefore receives the volume of hydraulic fluid which has been displaced in the master cylinder22through the actuation25of the brake pedal20. The hydraulic accumulator23can have a spring28which generates or builds up a residual pressure29which reacts in the brake pressure line12as a result of the opened outlet valve11. As a result of the valve arrangement13remaining closed here, brake pressure is not built up on the piston14, i.e., the residual pressure29does not act on the piston14.

Owing to the valve arrangement13, the reaction of the hydraulic accumulator23on the piston14of the friction brake8as a result of the residual pressure29is therefore prevented. The reason for this is the design of the valve arrangement13, which is described below in conjunction withFIG. 3.

In this regard,FIG. 3again shows the arrangement comprising the hydraulic accumulator23, the valve arrangement13and the friction brake8for the two rear wheels HR, HL. For the sake of clarity, the respective outlet valve11has not been shown since it is in an open position in any case during the recuperative braking mode and does not act on the hydraulic circuit of the hydraulic brake3.

The valve arrangement13has a first valve30and a second valve31. The valves30,31can be a spring-mounted ball valve in each case. In other words, the valves30,31may be non-return valves. The first valve30has a flow-enabling direction32which is aligned from the brake pressure line12towards the piston14of the friction brake8. The second valve31has a flow-enabling direction33which is aligned from the piston14towards the brake pressure line12. A brake pressure can be transferred from the brake pressure line12to the piston14via the first valve30. The brake pressure on the piston14can be reduced via the second valve31. The first valve30has an opening pressure34which may be higher than 1 bar, in particular, higher than 1.5 bar, although, in particular, lower than 10 bar, in particular, lower than 5 bar. The opening pressure34is generally higher than the residual pressure29which is produced by the spring28of the hydraulic accumulator23. The opening pressure35of the second valve31may be lower than 1 bar, in particular, lower than 0.5 bar.

As a result of the first valve30having an opening pressure34which is higher than the residual pressure29and the second valve31having a flow-enabling direction33which is in opposition to the residual pressure29, the residual pressure29does not act on the piston14during the recuperative braking mode in spite of the opened outlet valve11. Therefore, the valve arrangement13prevents the brake pads15from being pressed against the brake disk17of the friction brake8as a result of the residual pressure29. A loss of efficiency owing to friction is therefore prevented.

In each valve arrangement13, the valves30,31can be connected to the brake pressure line12via a respective common first connection36. The two valves30,31can be connected to the friction brake8via a common second connection37.

The valve arrangement illustrated inFIG. 1toFIG. 3is merely to be seen as an example of the operating principle. At least two or even all four friction brakes8of the wheels2can be equipped depending on the hydraulic implementation. The threshold pressure valves, i.e., the valves30,31, can be integrated, for example, in an electronic stability control ESC in the valve block7, or provided on the brake pressure line12in the hydraulic line9or they can be arranged in the brake caliper16. The valve arrangement13described does not influence the function of the hydraulic accumulator23since the valve arrangement13is not arranged in the flow path of the brake pressure line12.

Each valve arrangement13represents a hydraulic component which is mounted on the brake line connection, on or in the valve block7, in the direction of the wheel. This component opens the passage to the wheel only when a pressure of, for example, 1 to 2 bar is applied, so that it does not produce a residual braking torque on the friction brake8in this phase. This component also acts during normal braking but, owing to the opening pressure which is selected for the first valve30, it does not cause a hindrance to braking which can be felt by the driver.

All in all, therefore, the example shows how a threshold-pressure-dependent switching device can be provided in conjunction with a 2-box brake system.

LIST OF REFERENCE SIGNS