Brake booster coupling device

A brake booster coupling device includes: a braking piston, an input piston displaceable by an operation of a brake input element from its starting position by a driver braking distance, a force transmission between the input piston displaced by a driver braking distance below a predefined threshold value and the braking piston is suppressed, and a booster piston displaceable with the aid of the brake booster drive such that the braking piston, which contacts the booster piston, is displaceable with the aid of the brake booster drive from a non-braking position into a braking position; a contact element displaceable by a displacement of the braking piston from the non-braking position into the braking position such that a first contact surface of the contact element contacts a second contact surface of the input piston in such a way that a driver brake force is transmittable to the braking piston.

RELATED APPLICATION INFORMATION

The present application claims priority to and the benefit of German patent application no. 10 2010 003 822.9, which was filed in Germany on Apr. 9, 2010, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a brake booster coupling device.

BACKGROUND INFORMATION

A conventional brake system for a vehicle frequently has a nonlinear relationship between a driver brake force, which a driver exerts on a brake input element of the brake system, and a braking force, which is applied to a braking component situated on a brake master cylinder. In particular, such a brake system, such as the servobrake device discussed in DE 197 22 739 C2, for example, often has a jump-in range which is perceptible to the driver during the operation of the brake input element.

FIGS. 1A and 1Bshow two coordinate systems to illustrate an example of a relationship between a driver brake force and a resulting braking force. The abscissas of the coordinate systems show a driver brake distance z, by which an input piston, which is coupled to the operated brake input element, is displaceable. The ordinate of the coordinate system ofFIG. 1Ashows driver brake force Ff to be applied to displace the input piston by driver brake distance z. In the coordinate system ofFIG. 1B, the ordinate specifies resulting braking force Fe.

As is apparent inFIG. 1A, the driver must apply a minimum force Fm to move the input piston, which is in its starting position (z=0) when the brake input element is not operated, out of this position. During subsequent jump-in range J from the starting position up to a driver brake distance zj, driver brake force Ff to be applied to displace the input piston is comparatively low and nearly constant. In jump-in range J, braking force Fe only increases with a small slope. From driver brake distance zj, driver brake force Ff and braking force Fe become increasingly steeper and subsequently merge into an approximately linear range.

Jump-in range J often results from an air gap between the input piston, which is present in its starting position, and a disc (reaction disc), via which the driver brake force is transmittable from the input piston to a braking piston situated on the brake master cylinder after a displacement of the input piston by driver brake distance zj. Since in this case there is no contact for the force transmission between the input piston and the reaction disc in the event of a driver brake distance less than zj, braking force Fe is typically exerted on the braking piston by a brake booster drive in jump-in range J. The brake booster drive is typically activated in such a way that a booster piston, which is situated on the brake booster drive and contacts the disc, is synchronously moved with the input piston in such a way that a nonzero differential distance does not exist between the input piston and the booster piston.

SUMMARY OF THE INVENTION

The exemplary embodiments and/or exemplary methods of the present invention provide a brake booster coupling device for a vehicle having the features described herein.

The brake booster coupling device expands a brake system having a jump-in range by a blending functionality, so that during the braking, a part of the kinetic energy of the vehicle is convertible into electrical energy with the aid of a generator, without the driver noticing anything thereof because of a vehicle deceleration which deviates from standard behavior and/or because of an altered brake operation feeling. The exemplary embodiments and/or exemplary methods of the present invention therefore combine the advantages of automatic conversion of the kinetic energy of the vehicle into storable electrical energy with good operating comfort of the brake input element for the driver. It is ensured that in the various executable braking actions, which may include braking exclusively with the aid of the hydraulic friction brake, braking exclusively with the aid of the generator, and braking with simultaneous use of the hydraulic friction brake and the generator, a vehicle deceleration which is specified by the driver is reliably maintained, and a routine brake operation feeling is implemented for the driver in all braking actions. In particular, the implemented brake operation feeling corresponds to the standard brake feeling having a jump-in range.

Advantageous specific embodiments and refinements of the brake system according to the present invention are described herein.

Further features and advantages of the exemplary embodiments and/or exemplary methods of the present invention are explained in greater detail hereafter on the basis of the figures.

DETAILED DESCRIPTION

FIGS. 2Aa through 2Hashow schematic views of operating modes of a first specific embodiment of the brake booster coupling device, the coordinate systems ofFIGS. 2Ab through 2Hbshowing a relationship between a driver brake distance and a driver brake force, the coordinate systems ofFIGS. 2Ac through 2Hcshowing a relationship between the driver brake distance and a braking force, and the coordinate systems ofFIGS. 2Ad through 2Hdshowing a relationship between the driver brake force and the braking force. The abscissa of the coordinate systems ofFIGS. 2Ab through 2HbandFIGS. 2Ac through 2Hcis driver brake distance z. The ordinate of the coordinate systems ofFIGS. 2Ab through 2Hband the abscissa of the coordinate systems ofFIGS. 2Ad through 2Hdis driver brake force Ff. Correspondingly, the ordinate of the coordinate systems ofFIGS. 2Ac through 2HcandFIGS. 2Ad through 2Hdis braking force Fe.

The brake booster coupling device which is schematically shown inFIGS. 2Aa through 2Hais coupled to a brake master cylinder10having at least one hydraulic brake circuit (not shown). For example, brake master cylinder10may be a tandem brake master cylinder. As described in greater detail hereafter, an inner volume of brake master cylinder10is changeable in such a way that a desired internal pressure is settable in brake master cylinder10and in at least one wheel brake cylinder of the hydraulically connected brake circuit. In this way, a desired hydraulic braking torque may be exerted on at least one assigned wheel with the aid of the at least one wheel brake cylinder.

The at least one brake circuit which cooperates with brake master cylinder10may be assigned, for example, to exclusively one wheel, the wheels of one axle of the vehicle, at least two wheels situated on one side of the vehicle, or two wheels situated diagonally on the vehicle. The brake booster coupling device described hereafter is not restricted to a specific embodiment of the brake circuits which cooperate with brake master cylinder10.

The brake booster coupling device is advantageous in particular in the case of an arrangement in a (regenerative) brake system having a generator12, with the aid of which a generator braking torque is exertable on at least one wheel. All known specific embodiments of a generator for converting a kinetic energy of a vehicle into storable electrical energy are usable together with the brake booster coupling device. A more precise description of usable generator12will therefore be dispensed with here.

The (regenerative) brake system which is equipped with the brake booster coupling device has at least one brake input element (not shown), such as a brake pedal. An input piston14of the brake booster coupling device may be coupled to the brake input element in such a way that input piston14is displaceable by a driver brake distance z in relation to brake master cylinder10in the event of an operation of the brake input element by the driver of the vehicle. Input piston14may be designed as an input rod or include an input rod, for example. However, it is to be noted that input piston14is not restricted to an approximately rod-shaped form. Instead, input piston14may be understood as a force transmission component of arbitrary form, which is displaceable in the direction toward brake master cylinder10in the event of an operation of the brake input element by the driver.

A braking piston16of the brake booster coupling device may be displaceably situated/coupled onto brake master cylinder10. Braking piston16, which is coupled to brake master cylinder10, may be at least partially pushed into brake master cylinder10with an exertion of force. Therefore, an internal pressure in brake master cylinder10is settable according to the desired hydraulic braking torque with the aid of braking piston16.

Braking piston16may be understood as an output rod, for example. The (regenerative) brake system described here is not restricted to an approximately rod-shaped braking piston16, however. Instead, braking piston16may be understood as any displaceable braking component of a brake master cylinder10, with the aid of which a desired internal pressure is implementable in brake master cylinder10.

In order to allow a driver of a vehicle which is equipped with the brake system described here to have good operating comfort of the brake operation element in the event of a braking action, the brake system also has a brake booster drive (not shown). The brake booster drive may include at least one electric motor. The advantages listed hereafter are not restricted to equipping the brake system with an electromechanical brake booster, however. A vacuum brake booster may also be used as an alternative or supplement to an electromechanical brake booster. The brake booster drive may thus also be understood as a drive, which is not designed as an electric motor, for providing a booster force Fv.

The brake booster drive is connectable via a booster piston18of the brake booster coupling device to braking piston16in such a way that booster force Fv is transmittable via booster piston18to braking piston16to set a desired internal pressure in brake master cylinder10. Booster piston18may be connected via at least one spring20to a surrounding housing22. In this way, undesired displacement of booster piston18may be prevented during non-operation of the brake booster drive. Brake master cylinder10may also be connected to housing22. Since the technology according to the present invention does not impair the arrangement of the brake master cylinder in a vehicle, it is not discussed in greater detail here.

Input piston14may be at least partially situated inside a cavity in booster piston18. Braking piston16may also at least partially protrude into a cavity of booster piston18. The brake booster coupling device described here is not restricted to such an arrangement of pistons14,16,18to one another, however.

Optionally, braking piston16may be connected via a spring unit, such as illustrated intermediate spring24, to booster piston18. In the implementation of the brake system described here, however, intermediate spring24or a corresponding spring unit between input piston16and booster piston18may also be dispensed with.

FIG. 2Aashows a position of pistons14,16, and18in the case of non-operation of the brake input element. Since driver brake force Ff, which is exerted on brake input element, is equal to zero (seeFIG. 2Ab), input piston14is present in its starting position (z=0), in which it is decoupled from braking piston16. Decoupling of input piston14from braking piston16may be understood to mean that there is no direct contact of input piston14on braking piston16and no indirect connection, via a component which contacts braking piston16, for a force transmission between pistons14and16. In particular, input piston14is spaced apart in its starting position from a contact element26, which is displaceably situated on braking piston16. An air gap28exists between a first contact surface32of contact element26, which is oriented toward input piston14, and a second contact surface30of input piston14, which is oriented toward contact element26. A starting width b for air gap28is definable as the spacing between contact surfaces30and32.

As explained in greater detail hereafter, the brake booster coupling device described here has the advantage that jump-in range J, which is perceptible to the driver during the operation of the brake input element, is predefinable differently from starting width b of air gap28. In particular, a high executable degree of recuperation may be implemented via starting width b of air gap28and may be blended so it is not perceptible to the driver. Starting width b of air gap28may correspond to a maximum executable degree of recuperation, jump-in range J, which is perceived by the driver, simultaneously being impaired hardly or not at all by the particularly wide layout of air gap28having a high starting width b. The desired standard brake operation feeling during the operation of the brake input element, e.g., a pedal feeling, is therefore implementable having a what may be a jump-in range J in spite of a high executable and blendable degree of recuperation/generator braking torque.

Contact element26may be a tappet which is connected via a restoring spring34to braking piston16, for example. In particular if the tappet is used as contact element26, a brake booster coupling device with an air gap28having a large starting width b is implementable in a simple way. In this case, the tappet may protrude at least partially into a cavity of braking piston16. Further features of the advantageous arrangement/coupling of contact element26on braking piston16and/or brake master cylinder10are explained in greater detail hereafter.

In the case of non-operation of the brake input element, force transmission also does not occur from the brake booster drive (not shown) to braking piston16. The motor of the brake booster may be deactivated/turned off in this operating mode. Braking force Fe is therefore equal to zero (seeFIG. 2Ac) and braking piston16is present in its non-braking position at a braking distance s=0.

A starting position in relation to braking piston16is also definable for a contact element26, which is displaceable in relation to braking piston16, having a relative displacement distance r between braking piston16and contact element26equal to zero. If contact element26is deformable in relation to braking piston16, a relative distance of the first contact surface may accordingly also be definable in relation to braking piston16.

The brake booster coupling device optionally also includes a pedal force partial simulator which is situated on input piston14. The pedal force partial simulator which is schematically shown here includes at least one roller36, which is pressed with the aid of a simulator spring38against input piston14. A path40of the at least one roller36runs along input piston14, which is shaped in such a way that simulator force Fs, which is exerted by roller36on input piston14, is variable according to a desired pedal feeling. The at least one path40may be shaped in such a way that associated roller36has a minimum spacing to a central longitudinal axis of input piston14and/or a maximum spacing to surrounding housing22if input piston14is present in its starting position. Further sections of the at least one path will be discussed during the description of the following figures.

In order to displace input piston14out of its starting position (at z=0), the driver must exert a relatively low driver brake force Ff equal to a minimum force Fm on the brake operation element. Within jump-in range J from the starting position (at z=0) to a driver brake distance zj, the input piston is displaceable with the aid of a small and what may be (nearly) constant driver brake force Ff. For the driver, this is associated with the advantage that he does not have to execute a force-intensive movement to lightly brake his vehicle.

FIG. 2Bashows a position of pistons14through18and contact element26to one another in the case of a driver brake distance z42within jump-in range J. In this operating mode of the brake booster coupling device, a force transmission from input piston14to braking piston16is prevented because of air gap28between contact surfaces30and32, however. It is to be noted that in the case of a driver brake distance z within jump-in range J, there is no direct contact between pistons14and16for a force transmission. The driver therefore does not directly brake using driver brake force Ff transmitted to input piston14into brake master cylinder10in the case of a driver brake distance z within jump-in range J.

Optionally, the brake system which is equipped with the brake booster coupling device may already be controllable in the case of a driver brake distance z within jump-in range J in a braking mode exclusively having a hydraulic braking torque, in a braking mode exclusively having a generator braking torque, and/or in a braking mode having a hydraulic braking torque and a generator braking torque, as described in greater detail hereafter. As an alternative thereto, the brake system may also be designed in such a way that in the case of a driver brake distance z within jump-in range J, only hydraulic braking is performed because of the comparatively low vehicle deceleration requested by the driver.

A braking action, which is executed without generator12, is schematically shown inFIG. 2Ba. A booster force Fv is exerted on booster piston18with the aid of the brake booster drive. Control electronics may be configured for the purpose of activating the brake booster drive in such a way that provided booster force Fv corresponds to the braking command of the driver predefined with the aid of driver brake force Ff.

With the aid of booster force Fv, braking piston16, which is coupled to booster piston18, is displaced from its non-braking position (at s=0) by a braking distance44into at least one braking position in brake master cylinder10. The internal pressure in brake master cylinder10is increased until a counter force Fg equal to braking force Fe acts on braking piston16. The pressure increase in brake master cylinder10causes a corresponding hydraulic braking torque on the wheels assigned to the connected brake circuits.

Contact element26, which is situated on braking piston16, is displaceable and/or deformable during a displacement of braking piston16out of the non-braking position into at least one braking position (having a nonzero braking distance s44) in such a way that first contact surface32of contact element26is transferable in relation to braking piston16in a direction toward second contact surface30of input piston14. During a displacement of input piston14within jump-in range J, current width b1of the air gap or the spacing between contact surfaces30and32is below starting width b in spite of the displacement of braking piston16in a direction oriented away from input piston14.

For example, displaceable contact element26may be connected via a hydraulic feedback unit to brake master cylinder10for this purpose. Such a hydraulic feedback unit is implementable, for example, in that braking piston16is provided with a passage opening (not shown), via which a braking gas or braking fluid exchange is possible between the internal volume of brake master cylinder10and a surface of contact element26. In this case, a pressure increase in the brake master cylinder also causes a displacement force (not shown), which displaces contact element26in relation to braking piston16from its starting position (at r=0) by a relative displacement distance46.

In a particularly advantageous specific embodiment, the brake booster coupling device also includes a lever48, via which contact element26is connected to booster piston18. This ensures in a simple way a particularly advantageous maintenance of a linear displacement movement of contact element26in relation to braking piston16in the event of a pressure increase in brake master cylinder10. However, the design of the coupling device is not restricted to equipment with such a lever48.

The at least one path40of the pedal force partial simulator may be shaped in such a way that the at least one roller36moving along it does not execute a relative movement with respect to surrounding housing22during a displacement movement of input rod14within jump-in range J. This may also be described in such a way that in this case, the spacing between roller36and housing22is kept (nearly) constant, and roller36is therefore not displaced against the force of simulator spring38. This causes, as explained in greater detail hereafter, a uniformly low friction between roller36and braking piston14. During a displacement movement of the braking piston in jump-in range J, the pedal force partial simulator therefore does not cause any substantial simulator force Fs, which the driver must additionally exert as driver brake force Ff on the brake input element. Such a pedal force partial simulator therefore ensures a pleasant brake operation feeling for the driver, who must only exert a small driver brake force Ff on the brake input element for light braking of his vehicle within jump-in range J.

FIG. 2Cashows a position of pistons14through18and contact element26to one another in the case of an operating mode in which the driver operates the brake operating element beyond jump-in range J, which is perceptible to him. The driver therefore perceives an increase of the force counteracting his brake operation from driver brake distance zj, after the displacement of input piston14beyond jump-in range J, which is perceptible to the driver. From driver brake distance zj, the driver must exert a driver brake force Ff, which is elevated in relation to jump-in range J, on the brake input element because of the increased counteracting force for a further displacement of input piston14. The brake operation feeling which is perceptible by the driver therefore corresponds to a routine standard.

Nonetheless, after the displacement of input piston14beyond jump-in range J, air gap28still exists between contact surfaces30and32. Even if current width b2of air gap28or the spacing between contact surfaces30and32is below starting width b, a force transmission from input piston14to braking piston16via contact element26is nonetheless prevented.

In order that the driver perceives a standard brake operation feeling during the operation of the brake input element in spite of air gap28between contact surfaces30and32and is not irritated by an unusually large jump-in range J, the at least one path40is shaped in such a way that the at least one roller36traveling along it contacts a bulge after a displacement of input piston14beyond jump-in range J, or from the driver brake distance zj, and therefore is pressed into a closer spacing to housing22against the force of simulator spring38upon a further increase of driver brake distance z. As explained in greater detail hereafter, this causes an increase of simulator force Fs, which the driver perceives as an increase of driver brake force Ff to be applied by him. This ensures the standard brake operating feeling for the driver.

In this way, various possibilities are feasible for executing the vehicle deceleration desired by the driver even in the event of a stronger braking of the vehicle outside jump-in range J. The option is between braking of the vehicle by braking into the brake master cylinder with the aid of the brake booster, braking of the vehicle with the aid of a generator braking torque, or braking of the vehicle with the aid of a combination of direct braking into brake master cylinder10with the aid of the brake booster and a generator braking torque. The selection of the executed braking action may be carried out under consideration of a charge state of the internal-vehicle storage unit, such as the vehicle battery, and/or a current vehicle speed which is suitable for advantageous operation of generator12. The blending procedures described in greater detail hereafter are simultaneously executable for blending of the generator braking torque which is unnoticeable by the driver.

The advantage of equipping the brake system described here with the brake booster coupling device is that the various possibilities for executing the vehicle deceleration are also executable in the case of stronger braking of the vehicle, without the driver perceiving which of the executable braking actions is applied as a result of a changed brake operation feeling. The driver is therefore not irritated by an unfamiliar brake operation feeling. This ensures good operating comfort of the brake input element with an advantageous option for recharging the storage unit as needed and/or under consideration of the current vehicle speed.

However, an operating mode is shown inFIG. 2Cain which use of generator12for braking the vehicle is dispensed with, for example, because of a completely charged energy storage. Instead, a hydraulic braking torque which is adapted to the current operation of the brake pedal by the driver is set at the wheels via direct braking with the aid of booster force Fv via booster piston18and braking piston16.

FIGS. 2Da through 2Gashow the advantages of an enlargement of a mechanical (actual) decoupling range by providing the brake booster coupling device with an air gap28having a comparatively large starting width b between components14and26, which are present in their starting position, in relation to jump-in range J for the driver. It is apparent that the brake input element is also decoupled from brake master cylinder10after a displacement of input piston14beyond jump-in range J, or also in a driver braking distance range beyond driver braking distance zj, in such a way that the possibility of using generator12having a generator braking torque Mgen still exists, without the driver noticing feedback therefrom. In particular, generator braking torque Mgen may be varied, and may assume values of 0 g (FIG. 2Da), 0.1 g (FIG. 2Ea), 0.2 g (FIG. 2Fa), or 0.3 g (FIG. 2Ga), for example. The values listed here are to be understood as only exemplary. Of course, intermediate values between listed generator braking torques Mgen is also implementable.

In the brake system described here having the brake booster coupling device, a degree of recuperation of up to 100% is feasible. Such a degree of recuperation of 100% may be understood to mean that the brake booster drive remains passive (Fv=0), while generator12brakes at 100% (seeFIG. 2Ga). The brake booster drive is therefore operable, at least in the case of a driver braking distance z of input piston14below predefined threshold value zs, in a non-recuperation mode having a degree of recuperation equal to zero and in at least one recuperation mode having a degree of recuperation not equal to zero.

As is clear on the basis ofFIGS. 2Dbthrough 2 Gb, the driver does not notice the different degrees of recuperation. Therefore, for example, a change may be made from a first degree of recuperation having a first generator braking torque Mgen to a second degree of recuperation having a different second generator braking torque, without the driver feeling feedback. This ensures an advantageous adaptation of the currently executed degree of recuperation to the charge state of the storage unit and/or to the current vehicle speed without irritation of the driver.

It is also recognizable on the basis of the described figures that in the case of a driver braking distance z within the mechanical (actual) decoupling range, which is enlarged in relation to jump-in range J perceptible to the driver, the presence of air gap28between input piston14and contact element26is independent of the degree of recuperation/generator braking torque Mgen, independent of a relative position/a relative distance x1, x2, and x3of input piston14in relation to booster piston18, and independent of a relative position of input piston14in relation to braking piston16. Therefore, booster force Fv provided by the brake booster (not shown) may be varied without this resulting in undesired closing of air gap28.

As may also be recognized on the basis ofFIGS. 2Da through 2Ga, it is ensured in a specific embodiment of the advantageous design/coupling of contact element26in the case of a driver braking distance z within the mechanical (actual) decoupling range that also in the case of different degrees of recuperation, a width b3of air gap28, which is independent of the set degree of recuperation/generator braking torque Mgen, of a relative distance x1, x2, and x3of booster piston18in relation to input piston14, and/or of a relative distance of braking piston16in relation to braking piston14, is provided as the spacing between contact surfaces30and32. The brake booster coupling device may therefore be configured in such a way that in the case of a driver braking distance z within the mechanical (actual) decoupling range, a current width b1, b2, and/or b3of air gap28is independent of the existing degree of recuperation, of a relative distance x1, x2, and x3of booster piston18in relation to input piston14, and/or of a relative distance of braking piston16in relation to input piston14. This may also be paraphrased that, in the case of a driver braking distance z within the mechanical (actual) decoupling range, current width b1, b2, and/or b3of the air gap is a function of driver braking distance z. A variation of the degree of recuperation therefore does not result in a change of current width b1, b2, and/or b3of air gap28.

It is noted once again here that in the brake system shown here having the brake booster coupling device, the brake booster drive need not be activated in such a way that a uniform relative position of input piston14in relation to booster piston18is always regulated. Instead, relative position/relative distance x1, x2, and x3of input piston14may be intentionally varied in relation to booster piston18in such a way that a total braking torque desired by the driver, which is made up of a generator braking torque Mgen and/or a hydraulic braking torque, is present at the vehicle wheels. In particular, the lever ratio described in greater detail hereafter may also be used to set the desired internal pressure in brake master cylinder10.

FIG. 2Hashows the brake booster coupling device in the case of a driver braking distance z equal to a predefined threshold value zs, for example, at a total braking torque of 0.4 g, at which input piston14contacts contact element26. The air gap is closed. Therefore, from a driver braking distance z equal to threshold value zs, a contact exists between input piston14and contact element26, via which driver brake force Ff is transmittable to braking piston16.

This may also be described in such a way that second contact surface30of input piston14, which is displaced by a driver braking distance z from threshold value zs, contacts first contact surface32of contact element26in such a way that driver brake force Ff is transmittable by input piston14, which is displaced by driver braking distance z from threshold value zs, via contact element26to braking piston16, which is present in a position range including the non-braking position and the at least one braking position. In addition to an advantageous standard braking feeling, reliable closing of the air gap is therefore also ensured by touching of contact surfaces30and32in the case of a specific driver braking distance zs independently of the current degree of recuperation. Due to the touch contact between input piston14and contact element26, the driver has the possibility from driver braking distance z equal to threshold value zs of braking directly into brake master cylinder10and therefore rapidly increasing the hydraulic braking torque exerted on the wheels, in order to bring the vehicle to a standstill in a comparatively short time. After the closing of the air gap, operation of generator12need no longer occur and the vehicle deceleration is exclusively hydraulically executed.

Using the closing of the air gap, the pedal force partial simulator generates its highest simulator force Fs. If driver braking distance z increases beyond threshold value zs with higher driver brake force Ff, the pedal force partial simulator advantageously reduces its simulator force Fs continuously to 0. For this purpose, path40assigned to the at least one roller36may be shaped in such a way that roller36contacts a stretch of path40in the case of a further displacement of input piston14beyond threshold value zs, which has a decreasing slope in relation to housing22and/or in the direction toward spring38, which goes to zero. In contrast to a conventional full simulator, the pedal force partial simulator described here therefore does not require actuating energy at high driver brake forces Ff. This is advantageous in particular if the brake booster drive fails and the driver must apply all of the actuating energy.

FIGS. 3A through 3Cshow a force flow in various operating modes of the brake system ofFIG. 2.

FIG. 3Ashows a first force flow50from the brake booster drive (not shown) into brake master cylinder10in the operating mode already shown inFIG. 2Ba. The driver therefore has the possibility in jump-in range J of indirectly building up a hydraulic braking torque on the wheels of his vehicle with the aid of the brake booster drive. A force flow for the direct transmission of driver brake force Ff to contact element26is prevented because of air gap28.

FIG. 3Bshows that, in addition to first force flow50for braking into the brake master cylinder with the aid of booster force Fv, a second force flow52is also possible to relay driver brake force Ff to braking piston16via contact element26in the case of a closed air gap. The driver may thus also brake directly into brake master cylinder10with the aid of driver brake force Ff in the operating mode shown inFIG. 2Ha. This relieves the brake booster drive during generation of a high hydraulic braking torque. The brake booster drive may therefore be designed cost-effectively and require less installation space.

A third force flow54for transmitting driver brake force Ff to braking piston16in the event of a failed brake booster drive is shown inFIG. 3C. The driver must only bridge the relatively small driver braking distance range with the aid of a comparatively low driver brake force Ff via intermediate spring force Fz and the friction in order to be able to brake directly into brake master cylinder10. Therefore, rapid braking of the vehicle is also executable after a failure of the brake booster drive.

FIGS. 4A through 4Eshow two cross sections, a coordinate system, and two schematic views to explain a second specific embodiment of the brake booster coupling device.

FIG. 4Aschematically shows a cross section along the axis of driver braking distance z through the brake booster coupling device. The brake system has an input piston14, which is designed as a pressure pin, a braking piston16, which is equipped with a stop rod60, a booster piston18, which is equipped with a hardened ring62, and a contact element26, which is designed as a tappet having a conical surface, and which is connected to booster piston18via a lever48, which is situated rotatably around a rotational axis64with the aid of a friction bearing or a bearing plate. The tappet has a stop66, which contacts stop rod60in a starting position. Reference is made to the above-described specific embodiment with respect to the cooperation of these components.

The input piston, which is designed as a pressure pin, may have a recess into which a ball joint70of an input rod68protrudes. Ball joint70may be situated on an inner contact area of the recess in such a way that input rod68may execute a pivot movement within the recess. This ensures a reliable force transmission from a brake input element (not shown) to the input piston.

In this specific embodiment, an outer sleeve72of input piston14is also shaped in such a way that it has at least one path40for a roller (plain roller)36of a pedal force partial simulator in each case. Reference is made to the above-described specific embodiment and toFIG. 4Cdescribed hereafter with respect to the various sections of path40.

FIG. 4Bshows a cross section through the pedal force partial simulator perpendicularly to the axis of driver braking distance z. In the specific embodiment described here, simulator spring38, which cooperates with a roller36, is oriented radially away from roller36. Each of rollers36and simulator springs38is situated in a cavity of a housing74having a spray wall76. One roller36and simulator spring38cooperating therewith may be inserted into a separate hole of a ring housing78in each case, which is situated inside the opening in housing74. These holes may also alternatively be formed directly in housing74. A pressure part80may additionally be situated between a roller36and simulator spring38cooperating therewith.

As is apparent inFIG. 4B, each of rollers36may be situated rotatably around its axis in ring housing78with the aid of a pin82and a needle roller84. Pressure part80may rotate freely in the hole. Pressure part80having roller36thus orients itself in relation to input piston14having paths40according to the exemplary embodiments and/or exemplary methods of the present invention. This may also be paraphrased that a centering action is generated because of the concave contact line of each roller36in longitudinal section and outer sleeve72in cross section.

In the illustrated specific embodiment, pedal force partial simulator includes two rollers36having associated simulator springs38, which may be situated offset by 180°. The brake system described here is not restricted to a number of two rollers36, simulator springs38, and paths40, however. For example, the pedal force partial simulator may also have three rollers36, which are situated offset by 120°. This ensures that rollers36and springs38do not generate lateral forces.

The mode of operation of the pedal force partial simulator will be explained once again on the basis of the coordinate system ofFIG. 4C. The abscissa and the ordinate of the coordinate system ofFIG. 4Cshow driver braking distance z and driver brake force Ff.

To initiate a braking action, the driver must displace input piston14out of its starting position via an operation of the brake input element. This is implementable in that the driver exerts a comparatively small driver brake force Ff equal to a minimum force Fm on the brake input element.

During a subsequent jump-in range J, which is perceived by the driver, the driver may only exert this comparatively small driver brake force Ff on his brake input element to increase the total braking torque. In this operating mode, above-described air gap28exists between braking piston14and contact element26, so that direct braking of the driver into the brake master cylinder is suppressed. Instead, with the aid of the brake booster drive and/or with the aid of the generator in the above-described way, the total braking torque desired by the driver may be exerted as the generator braking torque and/or hydraulic braking torque on the wheels. Since there is no direct coupling between input piston14and brake master cylinder10in this operating mode, the driver is not irritated because of a brake operation feeling which changes as a result of the applied braking mode.

It is to be noted once again that during jump-in range J, which is perceptible by the driver, roller36running on the at least one path40is not moved against simulator spring38and therefore no (essential) simulator force Fs is generated. This is implementable, for example, in that the associated section of outer sleeve72is designed to be cylindrical, the cylinder length corresponding to perceived jump-in range J.

From a driver braking distance zj, the driver notices an accustomed increase of driver brake force Ff to be applied. This standard increase of the driver brake force from driver braking distance zj is implementable although air gap28also exists between input piston14and contact element26in the operating mode of a driver braking distance z between zj and threshold value zs. For this purpose, simulator force Fs is generated with the aid of the pedal force partial simulator. This is implementable, for example, in that path40is shaped for the section which is contacted by roller36in the case of a driver braking distance z between zj and threshold value zs in such a way that the rotation of the section of the path around the axis of driver braking distance z is equal to a truncated cone in a first approximation.

The actual (mechanical) decoupling range is therefore greater than jump-in range J, which is perceived by the driver, and which ends upon reaching driver braking distance zj. The actual (mechanical) decoupling range is concealable with the aid of the pedal force partial simulator, in that the pedal force partial simulator generates a maximum value for simulator force Fs outside perceived jump-in range J.

The increased actual (mechanical) decoupling range in relation to perceived jump-in range J may be used for blending a generator braking torque. For example, a generator braking torque of 0.1 g may be blended in the case of a driver braking distance z1and a generator braking torque of 0.2 g may be blended in the case of a driver braking distance z2. In a specific embodiment, the actual (mechanical) decoupling range may be enlarged enough that a generator braking torque of 0.3 g is blendable in the case of a driver braking distance z3.

After driver braking distance z3, air gap28is closed in the case of a driver braking distance z equal to a threshold value zs. As already described above, direct braking of the driver into the brake master cylinder is therefore possible from driver braking distance zs. Simulator force Fs of the pedal force partial simulator therefore may decrease from driver braking distance zs and finally goes to zero. This reduces driver brake force Ff to be applied by the driver in the case of a large driver braking distance z.

The reduction of simulator force Fs from driver braking distance zs is implementable, for example, in that in this section of path40, outer envelope72is shaped as a truncated cone having a decreasing slope, which goes to zero.

In the case of a driver braking distance increase from driver braking distance z having the slope which goes to zero, envelope72may be shaped as a cylinder, the cylinder length corresponding to maximum possible driver braking distance z (axial distance) of input piston14. This ensures that roller36runs on the cylinder and no (essential) simulator force Fs is generated.

In summary, a particularly advantageous path40is shaped in such a way that roller36, in the case of a driver braking distance z of input piston14between the starting position of input piston14and driver braking distance zj, contacts a first section of path40having a small slope α (in particular if intermediate spring24is omitted to reduce costs and/or installation space), in the case of a driver braking distance z of input piston14between driver braking distance zj and threshold value zs, contacts a second section of path40having an increasing slope α, and/or in the case of a driver braking distance z of input piston14from threshold value zs, contacts a third section of path40having a decreasing slope α which goes to zero.

The relationship between a spring force F38of simulator spring38, a slope α of path40(wedge angle), and simulator force Fs is shown on the basis ofFIG. 4D. (Slope α corresponds to a quotient of a change of path40perpendicularly to the axis of driver braking distance z through a change of path40parallel to the axis of driver braking distance z.) The following equation applies (equation 1):
Fs=tan α·F38,  (Equation 1)
spring force F38rising with increasing displacement of roller36perpendicularly to the axis of driver braking distance z.FIG. 4Eshows a schematic view to explain the mode of operation of the lever system made of input piston14and support piston18. The lever ratios are given by lever lengths h2aand h1a. In order to ensure advantageous booster behavior of the brake booster drive, the lever ratios may be set accordingly.

For example, the booster ratio of the brake booster drive may have a defined value during operation, this transmission ratio being able to remain constant over the entire operating range. This may also apply if the effective length of the lever arms changes with pivot angle β. The following equation (equation 2) may apply for booster ratio a:

a=h⁢⁢2⁢ah⁢⁢1⁢a=h⁢⁢2⁢bh⁢⁢1⁢b;(Equation⁢⁢2)
so that a may remain constant, h2abeing a spacing of pivot point64of lever48and the contact surface of contact element26in a neutral position of contact element26, h1abeing a spacing of booster piston18(or ring62) in a neutral position of contact element26, h2bbeing a spacing of pivot point64of lever48and the contact surface of contact element26in an end position of contact element26, and h1bbeing a spacing of booster piston18(or ring62) in an end position of contact element26.

As long as pivot point90is located on a linear lever48, transmission ratio a remains constant with the change of pivot angle β. Equation 2 may be ensured in that the contact between lever48and contact element26and the contact between lever48and ring62are designed in the form of a tooth engagement, which may correspond to the tooth engagement of a pinion and a toothed rack. Tooth engagements have the advantage that, independently of pivot angle β, the effective length of the lever arms and the effect of the force transmission (engagement angle) remain constant and the friction losses are relatively small.

An engagement angle of 0° which may exists between lever48and ring62. Since the tooth flank of a toothed rack is typically a plane, the counter flank may be designed as a simple, hardened ring62. This is cost-effective and does not require position-bound installation. The tooth engagement between lever48and contact element26(tappet) has an engagement angle of 25°, for example. The counter flank is the lateral surface of a cone having the cone angle 25° and therefore is not a plane, but rather a curved surface. This curvature is technically handled like a strongly crowned gearing. Since contact element26having the cone is a simple rotating part, it does not require position-bound installation. Overload of the lever is preventable in that contact element26, which may be configured as a tappet, stops against output rod60.

FIGS. 5A and 5Bshow two cross sections to illustrate a third specific embodiment of the brake booster coupling device.

In the cross section through the brake booster coupling device parallel to the axis of driver braking distance z ofFIG. 5A, a partial area of a housing100may also be seen. The illustrated brake system additionally includes a sealing ring102, (optional) a ring104, and parts of a protective envelope106(bellows). A pinion (drive shaft)108may also be situated on booster piston18.

Contact element26represents a hydraulic piston. The (right) front side of contact element26facing toward the input piston is contact surface32, the (left) front side facing toward brake master cylinder10is effective piston surface xy1. The ratio of ring piston surface xy2of braking piston16to piston surface xy1determines booster ratio a (similarly to lever ratio a). Otherwise, reference is made to the above-described specific embodiments with respect to the mode of operation of the individual components.

As is apparent on the basis of the cross section through the pedal force partial simulator perpendicularly to the axis of driver braking distance z ofFIG. 5B, simulator springs38are stretched between two pins82, which are offset by 180°, of both rollers36in the illustrated specific embodiment. A first simulator spring38connects a first end of pin82of the first roller to an opposing first end of pin82of second roller36. Correspondingly, second simulator spring38connects the second end of pin82of first roller36to the second end of pin82of second roller36.

In this specific embodiment, holes do not have to be formed in ring housing78for simulator springs38. In addition, simulator springs38in a larger and more robust design are usable. This reduces the manufacturing costs for the pedal force partial simulator and increases its service life.

FIGS. 6A and 6Bshow two cross sections to illustrate a fourth specific embodiment of the brake booster coupling device.

The brake system which is schematically shown inFIGS. 6A and 6Bvia a cross section through the brake booster coupling device parallel to the axis of driver braking distance z and via a cross section through the pedal force partial simulator perpendicularly to the axis of driver braking distance z ensures the above-described advantages. A further listing of these advantages will be dispensed with here.

FIGS. 7athrough 7dshow a schematic illustration and three coordinate systems to illustrate a fifth specific embodiment of the brake booster coupling device. The abscissa of the coordinate systems ofFIGS. 7band 7cis driver braking distance z. The ordinate of the coordinate system ofFIG. 7band the abscissa of the coordinate system ofFIG. 7dis driver brake force Ff. Correspondingly, the ordinate of the coordinate systems ofFIGS. 7cand 7dis braking force Fe.

In the brake booster coupling device which is schematically shown inFIG. 7a, contact element26is designed as a bellows, which may have a liquid filling. Contact element26may be a metal bellows, for example. In particular, a spring may be inserted into the bellows.

Booster piston18has an inner ring attachment120, on which contact element26is situated. A first part122of contact element26having a greater first diameter perpendicularly to the axis of driver braking distance z is situated between inner ring attachment120and braking piston16. A second part124of contact element26having a smaller second diameter perpendicularly to the axis of driver braking distance z is at least partially situated inside an inner recess of inner ring attachment120and is oriented away from braking piston16in relation to first part122.

Since the inner volume of contact element26also remains constant in the case of a displacement of braking piston16, a reduction of a first height h1of first part122parallel to the axis of driver braking distance z, which is associated with a displacement movement of the booster piston in the direction toward brake master cylinder10, causes an increase of a second height h2of second part124, which runs parallel to the longitudinal axis of driver braking distance z, in such a way that sum h1+h2increases. Therefore, a displacement movement of booster piston18in the direction toward the brake master cylinder is also associated with a reduction of air gap28between contact surfaces30and32. The brake system described here therefore ensures the above-described advantages. Furthermore, contact element26, which is designed as a bellows, ensures that in contrast to a disc (reaction disc), greater air gaps (strokes) are bridgeable.

It is to be noted that the brake booster coupling device shown using the described figures is not restricted to an application in a brake system having a specific maximum possible degree of recuperation. The brake booster coupling device may also be designed in such a way that because of the starting width of air gap28, at most a generator braking torque of 0.2 g or 0.1 g is blendable. In particular, in this case the actual (mechanical) decoupling range and jump-in range J which is perceived by the driver may be identical. Such a specific embodiment is implementable with little outlay, a pedal force partial simulator being able to be dispensed with. This reduces the costs and/or increases the compactness of the brake system.

In particular, in the case of a maximum blendable generator brake torque of 0.05 g, a rubber disc (reaction disc) may also be used as contact element26. The maximum blendable generator braking torque may be increased in that the air gap between the rubber disc and input piston14is expanded slightly. Jump-in range J may particularly be selected in such a way that the rubber disc is not mechanically overloaded.

The exemplary embodiments and/or exemplary methods of the present invention therefore ensure a brake booster coupling device for a brake system having a maximum blendable generator braking torque, which is freely selectable in a range between 0.05 g and 0.4 g. Independently of the selected maximum blendable generator braking torque/degree of recuperation, a good blending capability is also ensured in the event of a decoupling of the input piston outside (desired) jump-in range J perceived by the driver.