GB2588222A - Braking system with split stroke function for motor vehicles - Google Patents

Abstract

A motor vehicle braking system and method for operation in a brake-by-wire (BBW) mode and a fallback mode. The system comprises a master cylinder 1, which can be actuated by a brake pedal 2 and includes a piston and pressure chamber 1c with outlet a; a brake fluid reservoir 4; a pressure supply generator 5 for actuating wheel brakes 21 in the brake-by-wire mode; a pedal feel simulator 3’ including a pressure chamber, a simulator piston and an elastic element to provide a progressive stroke in the brake-by-wire mode; and a linear stroke valve 14 hydraulically connected between the reservoir 4 and an outlet of either the master cylinder pressure chamber or the simulator pressure chamber (see figure 6), the opening of the respective pressure chamber outlet being delayed by the linear stroke valve until a pre-set linear stroke of the brake pedal is completed. The valve 14 may be closed when the brake pedal is not actuated, opened once pedal travel is detected (e.g. by sensor S1) in brake-by-wire mode, and closed again once a linear stroke is completed, only opening again when the pedal returns to home position.

Description

Description

Braking system with split stroke function for motor vehicles The present invention generally relates to a braking system for motor vehicles, and especially to a braking system with split stroke function.

Currently known electrohydraulic braking ("brake-by-wire") systems comprise a hydraulic actuating unit (a master cylinder with at least one pressure chamber and at least one piston and one spring) which can be actuated by means of a brake pedal, a pressure medium reservoir associated with the hydraulic actuating unit and controlled by an electronic control unit. In such a system, the driver can be decoupled from the direct access to the wheel brakes, this function being used in a "brake-by-wire" operating mode. Pressure is actively build-up in the brake circuits with the aid of a driver-independent pressure generator, usually driven by an electric motor. This is generally done by coupling the pressure chamber of master cylinder to a hydraulic consumer called "pedal feel simulator" (named "simulator" in the following description). Also, a hydraulic fallback mode is provided, in which the driver can decelerate or stop the vehicle by muscular force on actuation of the brake pedal; in this case, the pressure chamber of master cylinder is coupled to one of the hydraulic circuits feeding the brake wheels cylinders. Prior art is published e.g. under EP1802504B1, US9555786B2, The simulator is custom-built for each customer and ensures a specific force versus stroke curve at compression, which accurately reproduces the customer-required force versus stroke curve at pedal. Usually, a simulator comprises a piston, a steel spring, a rubber spring and a pressure piece. The most significant elements playing a role in the modelling the characteristic curve of stroke versus force are the rubber spring element and the pressure piece, which are custom-built for each single different brake pedal characteristic curve.

As shown in the figure illustrating the characteristic curve of stroke versus force of the brake pedal, the stroke is linear only in a first stage that corresponds to the pedal travel required to bring the brake pads in contact with the brake disk and depends on the steel spring design. The simulator reproduces the linear stroke of the brake pedal at the start of the braking phase. Afterwards a transition stage follows, whithin which the stroke is influenced by the design of the pressure piece, whereas for the next stages of progressive force increase, the stroke is accomplished exclusively by the rubber spring's design and volumetric compression.

However, in this context of keeping the stroke versus force characteristic curve as required, the current configuration of simulator is subject to improvement, since there are some disadvantages associated with too many components of a high diversity.

When it comes to limit the number of components, the influence of the steel spring on the final characteristic curve is insignificant. Its purpose is to account for all production tolerances of the piston, pressure piece ad rubber spring and to ensure that in any condition, the piston returns to the initial position and the simulator gap is not affected. The removal of this component will not impact the final characteristic curve.

As for the pressure piece, a high design diversity is present: every adjustement of the linear stroke requires a new pressure piece, which means custom-tailored pressure piece. The result is a massive diversity of unique parts and simulator assemblies which need to be traced individually for each customer during the development and production stages.

The technical problem to be solved is to reduce the size, the number of components of the simulator and their design diversity without affecting its functionality whatsoever.

Therefore, the objective of the invention is to solve the 10 deficiencies of the mentioned prior art and to redesign the brake-by-wire system accordingly.

This objective is achieved according to the invention by means of the technical characteristics mentioned in the independent 15 claims, namely a braking system and a method of operating thereof.

Further advantageous embodiments are the subject matter of the dependent claims.

The present invention is based on the concept of splitting the linear stroke realization from that of the progressive stroke by distributed components across the brake-by-wire system and place them where space is available.

A first subject-matter of invention is a braking system for motor vehicles using brake fluid applied to one or more wheel brakes, the system being able to operate in a brake-by-wire operating and in at least one fallback operating mode, comprising: - a brake master cylinder, which can be actuated by a brake pedal and having at least one piston and at least one pressure chamber with an outlet, - a brake fluid reservoir hydraulically connected by means of supply lines and a return line, - a pressure supply generator for actuating the wheel brakes in the brake-by-wire operating mode, which is hydraulically connected to the pressure chamber of the brake master cylinder, -a simulator which provides a progressive stroke in the brake-by-wire operating mode and comprises a simulator piston and an elastic element that can be moved or deformed to a limited extent within a simulator pressure chamber with an outlet, and wherein -a linear stroke valve is arranged in hydraulic connection between the brake fluid reservoir and either the outlet of the pressure chamber of master cylinder or the outlet of the simulator pressure chamber, the opening of the respective pressure chamber outlet being delayed by the linear stroke valve until a preset linear stroke of the brake pedal is completed.

The advantages of employing the braking system according to invention are the following: -reduced overall packaging of the brake-by-wire system; - extended range of use, including for vehicles of larger size; - layout flexibility; - improved logistic chain, reduced tolerance chain during manufacturing process; - cost reduction.

A second subject-matter of invention is a method for the operation the mentioned braking system of a vehicle comprising the steps 30 of - providing a brake master cylinder, which can be actuated by a brake pedal and having at least one piston and at least one pressure chamber with an outlet, - providing a brake fluid reservoir hydraulically connected by means of supply lines and a return line, - providing a pressure supply generator for actuating the wheel brakes in the brake-by-wire operating mode, which is hydraulically connected to the pressure chamber of the brake master cylinder, - providing a simulator which provides a progressive stroke in the brake-by-wire operating mode and comprises a simulator piston and an elastic element that can be moved or deformed to a limited extent within a simulator pressure chamber with an outlet, - providing a linear stroke valve in hydraulic connection between the brake fluid reservoir and either the outlet of the pressure chamber of master cylinder or the outlet of the simulator pressure chamber, whereby the opening of the respective pressure chamber outlet is delayed by the linear stroke valve until a preset linear stroke of the pedal is completed.

The advantages of the method for the operation the mentioned braking system according to invention are the following: - significantly reduced costs and shorter lead times for achieving the same linear stroke; - better reproducibility and repeatability of linear stroke across the product range; - the linear stroke can be modified from one pedal apply to the next as a function of sport/comfort mode.

Further special features and advantages of the present invention 30 can be taken from the following description of advantageous embodiments by way of the accompanying drawings.

Fig. 1 is a schematic diagram of a prior art brake-by-wire system, with a known simulator; Fig. 2 shows a sectional view through the known simulator used in the prior art brake-by-wire system; Fig. 3 shows a characteristic curve of stroke versus force at brake pedal; Fig. 4 illustrates a redesigned simulator according to invention; Fig. 5 shows a first embodiment of a brake-by-wire system according to invention; Fig. 6 represents a second embodiment of a brake-by-wire system according to invention; Fig. 7 represents a third embodiment of a brake-by-wire system according to invention.

Prior art simplified "brake-by-wire" system is shown schematically in FIG. 1. The braking system essentially includes a master cylinder 1 (for example, a tandem master cylinder, as it is illustrated in this drawing) which can be actuated by means of a brake pedal 2, interacts with a pedal feel simulator 3, and is supplied with brake fluid from a brake fluid reservoir 4 under atmospheric pressure. The master cylinder 1 has a classic design with two pistons arranged in series, a primary piston 1.1 and a secondary piston 1.2, with their afferent springs, namely a primary piston spring 1.1.1 and a secondary piston spring 1.2.1, as well as sealing rings 1.3. The brake fluid reservoir 4 is hydraulically connected to the master cylinder 1 and communicates with it via compensation ports a'. Brake fluid circulates from and into the tandem master cylinder via hydraulic lines, a cut valve lv can close the hydraulic connection between the tandem master cylinder and the brake circuits (not shown). The master cylinder 1 also communicates with the simulator 3 through an outlet a and via a simulator valve 3v.

The simulator 3 comprises a rubber spring 3.1, a pressure piece 3.2, a simulator piston 3.3, a steel spring 3.4, a sealing ring 3.5. The drawing also shows a linear stroke LS in terms of distance travelled by the simulator piston 3.3.

Fig. 2 shows in detail the configuration of such a known 5 simulator, by highlighting two simulator parameters, extrusion gap g between the pressure piece 3.2 and the piston 3.3, and simulator height H, given by the height of a simulator pressure chamber 3.6 up to a closing cover 3.0. The extrusion gap represents the space between the pressure piece outer diameter 10 and the simulator bore where the rubber spring is extruded at high compression forces. Extrusion gap g is present when the pressure piece 3.2 is guided by the piston 3.3 which may result the rubber spring 3.1 being damaged after endurance test.

Fig. 3 shows a characteristic curve of stroke versus force at brake pedal, which is substantially determined by a function which can be specified in an electronic control unit (not illustrated) that controls the operation of the brake-by-wire system. The characteristic curve has four distinctive stages: the first stage (linear stroke) corresponds to the pedal travel required to bring the brake pads in conctact with the brake disk; the dedicated component responsible for realization of the linear stroke is the simulator steel spring. A transition stage follows, ensured by the design of the pressure piece, then the force increases progressively by means of the rubber spring design, and finally the force increases also progressively and more accentuated, which stage is accomplished by volumetric compression of rubber spring.

Fig. 4 shows an illustrative embodiment of a redesigned simulator 3', basically with similar closing cover 3.0, rubber spring 3.1 and sealing ring 3.5, but with a redesigned simulator piston 3'.3 which travels into a reshaped simulator pressure chamber 3'.6. By elimination of some of previous parts (pressure piece 3.2, steel spring 3.4), the redesigned simulator 3' gets a reduced height H'. By comparison, for example the total reduction in height in this case is by 11,9 mm from a total of 59 mm, which represents 20% -a significant decrease of size. This is caused 5 by the elimination of the initial linear stroke of 3,6 =and the shortening of the piston with the same height since there's no need to cover this stroke, and the elimination of the pressure piece thickness. This reduced height allows flexibility in the layout of this compact redesigned simulator 3' within the system, 10 without affecting whatsoever its main function of providing the progressive stroke, as mentioned.

Among other advantages, it has to be mentioned that, at the same time, the simulator bore is machined in a single step with cost advantages from manufacturing side and conservation of the rubber spring's integrity by elimination of extrusion gap. The piston diameter remains unchanged, but the diameter of the cover 3.0 is reduced, meaning the redesigned simulator 3' occupies a smaller area and volume, increasing the clearance to the neighboring components of the braking system. The resulting design is much more compact and simplified compared to prior art design, allowing flexibility in choosing its location in order to reach the most compact system package.

Fig. 5 shows a first embodiment of a braking system according to the invention. In essence, the inventive brake-by-wire system includes an electro-hydraulic module 22 (delimited by the dashed line in Fig. 5)and brake circuits I and II within a housing 20. The brake circuits I and II correspond to vehicle wheels provided with wheel brakes 21, the wheels being referenced by FL -front left wheel, RR -rear right wheel, FR-front right wheel and RL -rear left wheel. The electro-hydraulic module 22 comprises an inlet valve 15 and an outlet valve 16 for each wheel brake 21, each valve 15, 16 being hydraulically connected in pairs to one another and to the wheel brakes 21. The inlet valves 15 are supplied with pressures by means of supply lines 12, pressures derived from pressure supply generator 5 (in normal, ,brake-by-wire" operating mode) or from master cylinder 1 (in fallback operating mode). The outlet valves 16 are connected to the brake fluid reservoir 4 by a return line 13.

Apart from the electro-hydraulic module 22, the housing 21 also accommodates a master cylinder 1 (which, in this case, is illustrated also as a tandem master cylinder) actuated by a brake pedal 2 and hydraulically connected to a redesigned pedal feel simulator 3,, as previously described; a pressure supply generator 5 that comprises an electric motor 6, a pressure charter 7 and a piston 8; a multitude of sensors: a travel displacement sensor Sl, motor-related sensors 52 and 53, pressure sensors 54 and 55; as well as a multitude of valves: check valves 1,v, lffv and 9, block valves 17 and sequence valves 18, and a linear stroke valve 14, which is shown as a normally closed, two positions hydraulic valve.

An electronic control unit 10 is used to control the electro-hydraulic module 22, the electric motor 6 and the electrically actuated valves of the braking system, for example the block valves 17 and sequence valves 18, check valve l'v and simulator valve 3v.

The master cylinder 1 communicaes with the brake fluid reservoir 4 via compensation ports a' through corresponding compensation lines 11; at least one pressure chamber lc accommodates a piston spring and an afferent piston (not referenced), and supplies pressures to wheel brakes 21 via an outlet a.

In the normal braking function of the braking system ("brake by wire" operating mode) , the master cylinder 1 and hence the vehicle driver are decoupled from the wheel brakes by the closed block valves 17, and supply lines 12 are connected via the opened sequence valves 18 to the pressure supply generator 5, which supplies the system pressure for actuating the wheel brakes 21.

The simulator 3' is connected to the brake circuits by the opened simulator valve 3v and through a segment line 19, and the vehicle driver is given a familiar brake pedal feel.

In a fallback operating mode of the braking system, e.g. in the event of a failure of the electric energy supply of the entire braking system, the simulator 3' is disconnected from the brake circuits by the normally closed simulator valve 3v, and the pressure supplying device 5 is separated from the supply lines 12, by the normally closed sequence valves 18. The brake master cylinder 1 is connected by supply lines 12 to the normally open block valves 17 and further on by supply lines 12.1, 12.2 and hence to the wheel brakes 21, with the result that the vehicle driver can build up pressure directly in the wheel brakes 21 by actuating the brake pedal 2.

In both fallback mode and normal brake mode with the brake pedal in initial position, the linear stroke valve 14 is not actuated and its state is closed. In normal mode, once the pedal travel is detected, the delay in pressure buildup is achieved by energizing the linear stroke valve 14, opening the outlet of the master cylinder chamber l'c to the reservoir 4. After the pedal travel sensor Si detects that the desired linear stroke is completed, it triggers the linear stroke valve 14 to close and to remain closed until the pedal reach the initial position; to achieve low energy consumption, the linear stroke valve 14 remain closed (de-energized) as long as the pedal 2' is in initial position. Only when the pedal travel is detected, the linear stroke valve 14 is energized in the open position and kept as such until the desired linear stroke is achieved.

II

A second embodiment of a braking system accord ing to the invention is shown schematically in Fig. 6. In this case, the linear stroke valve 14 connects the simulator pressure chamber 3'.6 to the brake fluid reservoir 4. The advantage consists into the possibility to flush the simulator pressure chamber 3'.6 with brake fluid and eliminate the residual air. This in turn offers flexibility in the configuration of the layout of the electro-hydraulic module allowing to place the pressure supply generator 5 above the simulator 3' and still be able to bleed the simulator 3'.

An third embodiment of the inventive braking system is shown schematically in FIG. 7. The third illustrative embodiment employs a single-piston master cylinder 1' and a redesigned simulator 3' as previously described, where the linear stroke valve 14 is hydraulically connected between the outlet of a pressure chamber l'c of the master cylinder lr and the supply line 12. The introduction of the linear stroke valve 14 results into delaying the pressure buildup in the master cylinder chamber l'c until the necessary linear stroke of the pedal is completed. Thus, linear stroke valve connects and controls the opening of the outlet of the master cylinder chamber l'c to the brake fluid reservoir 4.

In this case, by employing a redesigned simulator 3', the total reduction in height is for example by 20.7 mm from a total of 64.5 mm, which represents 32% -also a significant decrease of size. The simplified design for the simulator 3' combined with the use of the linear stroke valve 14 in the hydraulic arrangement shown in Fig. 7 offers the possibility to have smaller dimensions (volume) for an extra-large variant of rubber spring. If in the prior art design (Fig. 1), the brake fluid volume sent by the master cylinder to the simulator affects the rubber spring dimensions (since the compression of the rubber spring is proportional with said volume), now, with the inventive solution (shown in Fig. 4 and Fig. 7), the volume delivered by the master cylinder to have the linear stroke at pedal is sent to the brake fluid reservoir 4 and only the volume necessary to compress the rubber spring is delivered to the simulator 3'. Moreover, the linear stroke valve 14 is implemented and adjusted as required entirely by software and not by hardware components anymore.

However, while certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.

List of reference numbers a outlet of pressure chamber a' compensation port g extension gap H, H' simulator height I, II brake circuit Si -56 sensors 1, 1' master cylinder 1.1 primary piston l'.1 piston 1.2 secondary piston 1.3 sealing rings 1.1.1 primary piston spring 1.2.1 secondary piston spring lc, l'c master cylinder chamber lv master cylinder cut valve Inv check valve 2, 2' brake pedal 3, 3' pedal feel simulator 3.0 closing cover 3.1 rubber spring 3.2 pressure piece 3.3, 3.3' piston 3.4 steel spring 3.5 sealing rings 3.6, 3'.6 simulator pressure chamber 3v, 3'v simulator valve 4 brake fluid reservoir 5 pressure supply generator 6 electric motor 7 pressure chamber of pressure supply generator 8 piston 9 check valve 12, 12.1, 12.2 14 19, 19' electronic control unit/ECU pressure compensation lines supply line return line linear stroke valve inlet valve outlet valve block valve sequence valve line segment housing wheel brake electro-hydraulic module

Claims (8)

1. Patent claims 1. A braking system for motor vehicles using brake fluid applied to one or more wheel brakes, the system being able to operate in 5 a brake-by-wire operating and in at least one fallback operating mode, comprising: - a brake master cylinder, which can be actuated by a brake pedal and having at least one piston and at least one pressure chamber with an outlet, -a brake fluid reservoir hydraulically connected by means of supply lines and a return line, - a pressure supply generator for actuating the wheel brakes in the brake-by-wire operating mode, which is hydraulically connected to the pressure chamber of the brake master cylinder, - a simulator which provides a progressive stroke in the brake-by-wire operating mode and comprises a simulator piston and an elastic element that can be moved or deformed to a limited extent within a simulator pressure chamber with an outlet, and wherein - a linear stroke valve is arranged in hydraulic connection between the brake fluid reservoir and the outlet of the pressure chamber of master cylinder, the opening of the pressure chamber outlet being delayed by the linear stroke valve until a preset linear stroke of the brake pedal is completed.
2. 2. A braking system for motor vehicles using brake fluid applied to one or more wheel brakes, the system being able to operate in 30 a brake-by-wire operating and in at least one fallback operating mode, comprising: - a brake master cylinder, which can be actuated by a brake pedal and having at least one piston and at least one pressure chamber with an outlet, - a brake fluid reservoir hydraulically connected by means of supply lines and a return line, - a pressure supply generator for actuating the wheel brakes in the brake-by-wire operating mode, which is hydraulically connected to the pressure chamber of the brake master cylinder, - a simulator which provides a progressive stroke in the brake-by-wire operating mode and comprises a simulator piston and an elastic element that can be moved or deformed to a limited extent within a simulator pressure chamber with an outlet, and wherein - a linear stroke valve is arranged in hydraulic connection between the brake fluid reservoir and the outlet of the simulator pressure chamber, the opening of the simulator pressure chamber outlet being delayed by the linear stroke valve until a preset linear stroke of the brake pedal is completed.
3. 3. A method for the operation of the braking system claimed in 20 claim 1, comprising the steps of, - providing a brake master cylinder, which can be actuated by a brake pedal and having at least one piston and at least one pressure chamber with an outlet, - providing a brake fluid reservoir hydraulically connected by means of supply lines and a return line, - providing a pressure supply generator for actuating the wheel brakes in the brake-by-wire operating mode, which is hydraulically connected to the pressure chamber of the brake master cylinder, -providing a simulator which provides a progressive stroke in the brake-by-wire operating mode and comprises a simulator piston and an elastic element that can be moved or deformed to a limited extent within a simulator pressure chamber with an outlet, - providing a linear stroke valve in hydraulic connection between the brake fluid reservoir and the outlet of the pressure chamber of master cylinder, whereby the opening of the pressure chamber outlet is delayed by the linear stroke valve until a preset linear stroke of the pedal is completed.
4. 4. The method as claimed in claim 3, further comprising the step that, when the brake pedal is not actuated, the linear stroke valve is closed.
5. 5. The method as claimed in claim 4 further comprising in that, in the brake-by-wire operating mode and during the brake pedal apply, once a travel of pedal is detected, the linear stroke valve is energized, opening the outlet of the pressure chamber to the brake fluid reservoir.
6. 6. The method as claimed in claim 5, further comprising in that, once the linear stroke is completed, the linear stroke valve closes and remain closed until the brake pedal gets back into home 20 position.
7. 7. A method for the operation of the braking system claimed in claim 2, comprising the steps of, - providing a brake master cylinder, which can be actuated by a brake pedal and having at least one piston and at least one pressure chamber with an outlet, - providing a brake fluid reservoir hydraulically connected by means of supply lines and a return line, - providing a pressure supply generator for actuating the wheel brakes in the brake-by-wire operating mode, which is hydraulically connected to the pressure chamber of the brake master cylinder, - providing a simulator which provides a progressive stroke in the brake-by-wire operating mode and comprises a simulator piston and an elastic element that can be moved or deformed to a limited extent within a simulator pressure chamber with an outlet, and -providing a linear stroke valve in hydraulic connection between the brake fluid reservoir and the outlet of the simulator pressure chamber, whereby the opening of the outlet of simulator pressure chamber is delayed by the linear stroke valve until a preset linear stroke of the pedal is completed.
8. 8. The method as claimed in claim 7, further comprising the step that, in the brake-by-wire operating mode and during the brake pedal apply, once a travel of pedal is detected, the linear stroke valve is energized, opening the outlet of the simulator pressure chamber to the brake fluid reservoir.