A fail-safe brake by wire braking system for a bicycle

Abstract

A hydraulic braking system for a bicycle, comprises a master cylinder (15) actuated by a manual control lever (14), an electrically controlled changeover valve (19) alternatively connectable either a brake caliper (13) or to a lever force hydraulic simulator (21), and a motor driven hydraulic actuator (25) that is in fluid communication with the brake caliper. An electronic control unit (32) controls the changeover valve and the motor driven hydraulic actuator. The changeover valve (19) is electrically controlled through a solenoid (40) that, when energized by the electronic control unit, sets the changeover valve in fluid communication with the lever force hydraulic simulator (21) and cuts off direct fluid communication between the master cylinder and the brake caliper. A fail-safe spring (41) acts against the force exerted by the solenoid on the changeover valve, whereby in the absence of electric power supplied to the solenoid, the fail-safe spring switches the changeover valve to a fail-safe operational mode in which the master cylinder is fluidically directly connected to the brake caliper.

Description

[0001] A fail-safe brake by wire braking system for a bicycle

[0002] Technical field

[0003] The present invention pertains to a hydraulic brake-by-wire braking system for a bicycle in which the mechanical linkage between the rider and the brake may be completely interrupted by an electronic control system. Specifically, the present invention provides a brake-by-wire system having a fail-safe operational mode.

[0004] Background art

[0005] Brake-by-wire systems allow for more effective integration with hybrid or electric driving technologies, and the possibility for autonomous braking functions. Multiple technologies exist within the automotive industry to enable autonomous control of braking systems. These technologies exist to enable deceleration torque to be applied to the driving wheels of a vehicle either by the traction motors or the brakes in a way which is invisible to the driver. The driver only needs to depress the brake pedal, and the intelligent braking system apportions braking torque between the electric traction system and the hydraulic braking system in the most appropriate manner. By employing such systems, the vehicle manufacturers can enable energy regeneration during vehicle deceleration without relying on any driver skill or input, and hence to increase the driving range and energy efficiency of their vehicles. Additionally, such systems allow autonomous braking without any input from the driver. This enables the design of driver assistance aids such as active cruise control systems, and safety aids such as ‘city braking’, where the brakes are automatically activated in order to avoid hazards detected by a LIDAR or camera system. Such braking systems will be essential in the realisation of fully autonomous vehicles.

[0006] An example of a ‘brake by wire’ system is known from in DE 10 2005 063 691 B3. Known brake by wire systems maintain hydraulic systems to operate the braking system, and as such provide a ‘fail-safe operation mode’ where there is a hydraulic connection between the brake pedal and the brake callipers in the event of system failure. These systems are complex, because they allow for the distribution of pressure to multiple brake hydraulic circuits (to allow brake pressure distribution, multi-channel ABS and ESP functions).

[0007] US 2019 / 0359187 Al discloses a brake operating apparatus for a small vehicle including a bicycle, the brake operating apparatus comprising: a support; an operating member mounted to the support, a detector configured to detect information on input to the operating member, an electric actuator configured to drive the brake apparatus, and an electronic controller configured to control the electric actuator based on a detection result of the detector.

[0008] Summary of the invention

[0009] It is an object of the present invention is to provide an improved and fail-safe brake-by- wire braking system, ensuring effective braking action even in the event of a failure or loss of electric power on an e-bike.

[0010] According to an aspect, the present invention provides a braking system for a bicycle as defined in claim 1. Preferred embodiments are defined in the dependent claims.

[0011] In summary, a hydraulic braking system for a bicycle, comprises a master cylinder actuated by a manual control lever, an electrically controlled changeover valve alternatively connectable either a brake calliper or to a lever force hydraulic simulator. A motor driven hydraulic actuator comprises an electric motor controlling a hydraulic piston that is in fluid communication with the brake calliper. An electronic control unit controls the changeover valve and the motor driven electric actuator. A sensor measuring the amount of actuation of the master cylinder is electrically connected to the electronic control unit. The changeover valve is electrically controlled through a solenoid that, when energized by the electronic control unit, sets the changeover valve in fluid communication with the lever force hydraulic simulator and cuts off direct fluid communication between the master cylinder and the brake calliper. A fail-safe spring acts against the force exerted by the solenoid on the changeover valve, whereby in the absence of electric power supplied to the solenoid, the fail-safe spring switches the changeover valve to a fail-safe operational mode in which the master cylinder is fluidically directly connected to the brake calliper.

[0012] Brief description of the drawings

[0013] In order that the present invention may be well understood there will now be described a few preferred embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which:

[0014] Figure l is a schematic view showing an e-bike with a brake by wire installation;

[0015] Figure 2 is a schematic diagram of braking components and a brake by wire system according to an embodiment of the present invention;

[0016] Figure 3 is a schematic diagram depicting the Brake by Wire system at rest, when no braking is occurring;

[0017] Figure 4 is a schematic diagram showing the system of Figure 3 in an operational condition in which the rider starts to pull on the hand lever;

[0018] Figure 5 is a schematic diagram showing the system of Figure 4 in an operational condition in which the rider is pulling on hand lever, and with brake-by-wire operation;

[0019] Figure 6 shows two diagrams representing brake blending between the electric traction motor and the hydraulic brakes, as a function of time;

[0020] Figure 7 is a schematic diagram showing the system of Figures 3 to 5 during an autonomous braking mode; and

[0021] Figure 8 is a schematic diagram showing the system of Figures 3 to 5 and 7 in a fail-safe braking operational mode.

[0022] Detailed description

[0023] Referring initially to Figures 1 and 2, a bicycle, in this example an e-Bike designated at 10, fitted with a hydraulic brake system. The bicycle 10 has a frame 18 and wheels 11 with associated rotation sensors 10. The wheels are each equipped with brake discs 12 and associated brake callipers 13, which apply a braking torque to the brake discs. A manual control lever 14 (or hand lever) operates a hydraulic master cylinder 15 for generating and controlling pressure within a hydraulic brake circuit 16. The brake callipers 13 are controlled by the hand lever 14 and activated through the hydraulic circuit 16 by a brake by wire unit 17 arranged on the hydraulic circuit between the master cylinder 15 and the brake callipers 13. In an emergency or fail-safe operational mode, the brake callipers can be controlled directly by the hand lever 14 through the master cylinder 15, bypassing the brake by wire unit 17.

[0024] According to a preferred embodiment, the components which compose the brake-by-wire unit, depicted within the dashed boundary in Figure 2, may be conveniently fitted in a housing mounted to the bicycle frame 18.

[0025] The hydraulic brake master cylinder 15 and the hand lever 14 are attached to the bicycle handlebar. The master cylinder 15 may also include a reservoir 33 containing hydraulic fluid at atmospheric pressure. When the rider pulls on the hand lever 14, the master cylinder piston is moved inside a chamber and hydraulic fluid is forced along a pipe towards the brake-by-wire unit and the brake calliper. When the lever is released, a compensation port 34 is opened which opens the cylinder chamber to the reservoir. The hydraulic circuit 16 comprises an upstream line 43 that extends from the master cylinder 15 to a changeover valve 19.

[0026] Designated at 20 is a sensor for measuring the amount of actuation of the master cylinder 15. According to a preferred embodiment, the sensor 20 is a pressure sensor that measures the pressure of the brake fluid downstream of the master cylinder 15, between the master cylinder and the changeover valve 19. The pressure sensor 20 provides a direct measurement of the rider’s braking demand. The changeover valve 19 is preferably a solenoid operated change-over valve, which selectively connects the upstream line 43 from the hydraulic master cylinder 15 either to the brake calliper 13, when the changeover valve 19 is not electrically energised, or to a lever force hydraulic simulator 21, when energised. The changeover valve 19 is spring loaded so that, when de-energised, it returns automatically to the position where the master cylinder is connected to the brake calliper.

[0027] The lever force hydraulic simulator 21 comprises a spring-loaded piston 22 inside a hydraulic chamber 23.

[0028] The changeover valve 19 is electrically controlled through a solenoid 40 that, when energized, exerts a force on the changeover valve 19 setting it in fluid communication with the lever force hydraulic simulator 21 and cutting off direct fluid communication between the master cylinder 15 and the brake calliper 13 through the changeover valve 19. The changeover valve 19 is also associated with a fail-safe spring 41 acting against the force exerted by the solenoid 40, whereby in the absence of electric power supplied to the solenoid 40, the fail-safe spring 41 switches the changeover valve 19 to a fail-safe operational mode in which the master cylinder 15 is fluidically directly connected to the brake calliper 13.

[0029] When the change-over valve 19 is energised and the master cylinder 15 is connected to the lever force hydraulic simulator 21, and when the rider pulls on the hand-lever 14, brake fluid is pumped into the hydraulic chamber 23 and compresses the spring 24 associated with piston 22. The spring force provided by the lever force hydraulic simulator 21 may be calibrated to give a rise in pressure and hence a rising force at the hand-lever which, to the rider, feels similar to a conventional braking system.

[0030] A first hydraulic line 35 directly connects the changeover valve 19 to the brake calliper. A second hydraulic line 39 connects the changeover valve 19 to the hydraulic chamber 23 of the lever force hydraulic simulator 21.

[0031] The brake by wire unit 17 comprises a motor driven hydraulic actuator 25, which comprises a hydraulic piston 26 that is moved inside a chamber 27 by an electric motor 28. When at rest, the hydraulic piston 26 preferably reacts against a fixed stop 42 which prevents the volume of the chamber 27 from increasing when the brake fluid inside it is pressurised.

[0032] When the electric motor 28 is energised, a mechanical conversion mechanism (for example a reversible screw) converts the rotation of the electric motor into linear motion of the hydraulic piston 26, which is moved away from its fixed stop 42 in order to reduce the volume of chamber 27.

[0033] A one-way valve 29 may be provided on a line 30 of the hydraulic circuit 16 fluidically connecting the lever force hydraulic simulator 21 to the master cylinder 15. The one-way valve 29 prevents the brake fluid from flowing when the master cylinder pressure is greater than the lever force simulator pressure, but allows fluid to flow back to the master cylinder 15 when the master cylinder pressure is less than the lever force simulator pressure.

[0034] Each brake calliper 13 converts hydraulic pressure in the brake circuit into normal force between the brake pads and the relevant brake disc. Preferably, associated with each brake calliper 13 is a pressure sensor 31 which detects the hydraulic pressure at the brake calliper.

[0035] The Brake-by-Wire unit 17 comprises a Brake Control Unit (BCU) 32, which is an electronic unit that receives information from the rotation sensors and the pressure sensors within the braking system, and executes an algorithm which controls the solenoid that activates the changeover valve 19 and the electric motor 28 that operates the motor driven cylinder actuator 25. Particularly, the upstream pressure sensor 20 detects the desired braking effort demanded by the rider and is connected electrically to the BCU 32 to provide information concerning the amount of braking force that the rider wants to actuate the brakes with.

[0036] Optionally, the Brake Control Unit 32 (BCU) may have an integrated Inertial Measurement Unit (IMU), designated at 37, which detects acceleration and orientation of the e-bike. Based on these measurements, and on information made available from the wheel rotation sensors 10, the BCU 32 can energize the electric motor 28 to control the position of the motor driven cylinder actuator 25, in order to prevent roll-over of the bike when the rider brakes excessively on high friction road surfaces, and prevents locking of the controlled wheel when the rider brakes on low friction surfaces.

[0037] A power supply 36 is provided for the Brake by Wire unit 17 by a battery 38. If the unit 17 is fitted to an eBike, it may be powered by the same battery as the traction motor. In the drawings, an electric wire connecting the pressure sensor 20 to the BCU 32 is indicated 20a. Electric wiring connecting the BCU 32 to the changeover valve 19, the motor driven cylinder actuator 25, the calliper pressure sensor 31 and the wheel rotation sensors 10 are designated 19a, 25a, 31a, 10a, respectively.

[0038] Operation of the Brake by Wire system is as follows. Figure 3 depicts a condition in which the braking system is at rest. The rider is not pulling the hand-lever 14, and a compensation port 34 within the master cylinder is open, whereby the master cylinder chamber is connected to the reservoir 33 at atmospheric pressure. The change-over valve 19 is not energised; therefore, brake master cylinder 15 is connected directly to the brake calliper 13 through the first hydraulic line 35.

[0039] According to a preferred embodiment, if any residual pressure is contained within the chamber of the lever force simulator, the one-way valve 29 will be opened and brake fluid transferred to the master cylinder 15 until the pressure is equalised. Hence, all parts of the hydraulic system are at atmospheric pressure.

[0040] When the rider starts to pull on the hand lever 14 (Figure 4), the compensation port 34 within the master cylinder closes and pressure rise is measured by the pressure sensor 20, which sends the BCU 32 a signal indicative of the required amount of pressure and therefore of the amount of braking force to be exerted. In order to commence the ‘brake- by-wire’ function, the BCU 32 energises the solenoid of the change-over valve 19. Consequently, the change-over valve 19 connects the master cylinder 15 connected to the lever force simulator 21, while cutting off direct fluid communication from the changeover valve 19 to the brake calliper 13 through the first hydraulic line 35.

[0041] As the rider continues to pull against the hand-lever (Figure 5), brake fluid is moved from the master cylinder 15 through the change-over valve 19 into the chamber 23 of the lever force simulator 21, where the piston 22 is displaced, the spring 24 is compressed, and hydraulic pressure is generated. Hence the rider feels resistance at the hand lever 14 which is proportional to lever travel. The pressure sensor 20 detects a further pressure increase, which is transmitted to the BCU 32. The master cylinder pressure signal is used as a demand signal for a closed loop pressure control function, where the electric motor 28 of the motor driven hydraulic actuator 25 is energised in order to actuate the piston 26 and generate pressure in the brake calliper circuit, and the resulting pressure is monitored by the calliper pressure transducer 31, and fed back into the control loop to the BCU 32.

[0042] Optionally, the pressure demand signal from the master cylinder pressure sensor 20 may be multiplied by a gain value, so that the pressure demanded from the closed loop pressure control algorithm is greater than the pressure generated within the master cylinder. Hence, the brake by wire system may fulfil the function of providing powered assistance to the rider during the braking manoeuvre.

[0043] Additionally, signals from the wheel speed sensors and from the Inertial Measurement Unit 37 are monitored, and the pressure demand may be further modified. For example, the pressure demand may be reduced in order to prevent the bicycle from rolling over on a high friction surface or from locking its wheel on a low friction surface. If the bicycle is fitted with an eDrive system which can apply a braking torque to the wheel whilst recharging the battery, the BCU 32 may communicate with the eDrive control system to negotiate sharing of the braking torque between the hydraulically operated friction brakes and the traction motor, in order to optimise energy usage within the bicycle. In this arrangement, the pressure demand signal could be reduced in order to make an allowance for the vehicle deceleration provided by the electric traction motor. Figure 6 illustrates the concept of ‘brake blending’ where both the electric traction motor and the hydraulic brake system contribute to give the deceleration rate demanded by the rider.

[0044] Using the data connection to other systems within the bicycle, the braking system may be configured to allow the bicycle to brake autonomously (Figure 7). For example, a LIDAR or camera system (not shown) mounted to the bicycle or to the rider’s crash helmet may be capable of detecting an imminent collision between the bicycle and another road user, and may request an emergency stop from the brake-by-wire system. When the emergency stop is requested, the BCU 32 autonomously energises the change-over valve 19, and actuates the motor driven hydraulic actuator 25 to generate pressure in the brake calliper circuit. Schematically indicated by a double arrow “D” are data exchanged between the BCU 32 and other systems in the vehicle which may include an electric eDrive unit, LIDAR or camera system.

[0045] Embodiments may provide that the wheel speed sensors and the Inertial Measurement Unit are also monitored in order to modify the autonomously generated pressure demand signal, in order to prevent the bike from rolling over or the wheels from locking. When the BCU 32 detects a condition indicative of an imminent wheel locking, it may execute an algorithm which operates the motor driven hydraulic actuator 25 in order to reduce the hydraulic pressure on the brake at the affected wheel, thus reducing the braking force on this wheel, so that the wheel remains braked but can rotate. As known this process is repeated continuously during braking, several times per second, preventing the vehicle from skidding.

[0046] In the event of an electrical failure (Figure 8), the electrically controlled BCU 32 cannot monitor the pressure sensor 20, and is not able to activate either the change-over valve 19 or the motor driven hydraulic actuator 25. Because the change-over valve 19 is spring loaded, the master cylinder 15 is connected hydraulically to the brake calliper 13 when the changeover valve is not activated. Hence, when the rider pulls the hand lever 14, brake fluid is transmitted from the master cylinder 15 through the change-over valve 19 to the calliper hydraulic line 35, where pressure is applied to both the calliper and to the piston 26 of the motor driven hydraulic actuator 25. Because the piston 26 within the motor driven hydraulic actuator 25 is resting against its fixed stop, the piston 26 does not move when hydraulic pressure is applied to it, and hence the motor driven cylinder actuator 25 does not absorb any brake fluid and cause excessive angular displacement of the hand-lever 14. The hydraulic pressure is applied to the calliper, and hence the rider can achieve safe deceleration of the bicycle.

[0047] In Figure 6, the upper diagram shows the bicycle’s velocity decrease as a function of time; the lower diagram shows the rider’s braking demand DEM, the deceleration DEC from the electric tractions motor and the DEH deceleration from the hydraulic brake system.

Claims

CLAIMS1. A braking system for a bicycle, comprising: a master cylinder (15) actuatable by a manual control lever (14); a hydraulic circuit (16) fluidically connecting the master cylinder (15) to at least one brake calliper (13); a lever force hydraulic simulator (21) comprising a spring-loaded piston (22) sliding within a hydraulic chamber (23); an electrically controlled changeover valve (19) fluidically connected to the master cylinder (15) and selectively and alternatively fluidically connectable either to the at least one brake calliper (13) through a first hydraulic line (35), or to the lever force hydraulic simulator (21) through a second hydraulic line (39); a motor driven hydraulic actuator (25) comprising an electric motor (28) controlling a hydraulic piston (26) within a chamber (27) that is in fluid communication with the second hydraulic line (39); an electronic control unit (32) for controlling the changeover valve (19) and the motor driven electric actuator (25); a sensor (20) for measuring the amount of actuation of the master cylinder (15), the sensor (20) being electrically connected to the electronic control unit (32); wherein the changeover valve (19) is electrically controlled through a solenoid (40) that, when energized by the electronic control unit (32), exerts a force on the changeover valve (19) setting it in fluid communication with the lever force hydraulic simulator (21) and cutting off direct fluid communication between the master cylinder (15) and the at least one brake calliper (13) through the changeover valve (19); and wherein the changeover valve (19) is associated with a fail-safe spring (41) acting against the force exerted by the solenoid (40), whereby in the absence of electric power supplied to the solenoid (40), the fail-safe spring (41) switches the changeover valve (19) to a fail-safe operational mode in which the master cylinder (15) is fluidically directly connected to the at least one brake calliper (13).

2. A braking system according to claim 1, wherein the sensor (20) for measuring theamount of actuation of the master cylinder (15) is a pressure sensor for detecting pressure of brake fluid delivered by the master cylinder (15) to the hydraulic circuit (16).

3. A braking system according to claim 1, wherein the lever force hydraulic simulator (21), the electrically controlled changeover valve (19), the motor driven hydraulic actuator (25), and the electronic control unit (32) compose a brake-by-wire unit (17) which is mountable on a bicycle frame (18).

4. A braking system according to claim 1, wherein the motor driven hydraulic actuator(25) comprises a chamber (27) slidingly accommodating the hydraulic piston (26), and wherein a fixed stop (42) determining an end of stroke position for the hydraulic piston(26) when in said fail-safe operational mode.

5. A braking system according to claim 1, further comprising a line (30) of the hydraulic circuit (16) fluidically connecting the lever force hydraulic simulator (21) to the master cylinder (15) and a one-way valve (29) provided in said line (30) that prevents brake fluid from flowing when the pressure of the brake fluid in the master cylinder (15) is greater than the pressure of the brake fluid in the lever force simulator (21), but allows the brake fluid to flow back to the master cylinder (15) through said line (30) when the pressure in the master cylinder (15) is less than the pressure in the lever force simulator (21).

6. A braking system according to claim 1, wherein the electronic control unit (32) is configured to process the pressure demand signal from the pressure sensor (20) by multiplying this signal by a gain value, so that the pressure demanded from a closed loop pressure control algorithm is greater than the pressure generated within the master cylinder (15), whereby the braking system provides powered assistance to the rider during braking.

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