Braking system for a vehicle to control a regenerative braking

An embodiment of a braking system for a vehicle to control a regenerative braking; the braking system is provided with: a plurality of hydraulically operated mechanical brakes; a hydraulic braking circuit connected to the mechanical brakes; a brake pump to raise pressure in the hydraulic braking circuit; a brake pedal mobile between a resting position and a maximal braking position; a connecting cap, which mechanically connects the brake pedal to the brake pump, and is divided into two reciprocally independent parts; an elastic system which tends to push the brake pedal towards the resting position; a position sensor to read the position of a part of the connecting cap integral to the brake pedal; and a pilot system to pilot an energy recovery system for effecting a regenerative braking and uses the position of the part of the connecting cap integral to the brake pedal provided by the position sensor.

PRIORITY CLAIM

The instant application claims priority to Italian Patent Application No BO2008A000651, filed Oct. 23, 2008, which application is incorporated herein by reference in its entirety.

TECHNICAL FIELD

An embodiment of the present invention relates to a braking system for a vehicle to control a regenerative braking.

BACKGROUND

A hybrid vehicle comprises an internal combustion engine, which transmits the torque to the drive wheels by means of a transmission provided with a gearbox, and at least one electric motor which is electrically connected to an electric storage system and is mechanically connected to the drive wheels.

In order to increase the overall energy efficiency during all steps of decelerating, the electric motor may be used as a generator for effecting a regenerative deceleration in which the kinetic energy possessed by the vehicle instead of being completely dissipated into heat generated by friction, is partially converted into electricity which is stored in the electric storage system. For this purpose, when the driver presses the brake pedal, a control unit of the braking system does not initially operate the mechanical brakes and pilots the electric motor as a generator, so that the braking torque is generated only by the electric motor; if the driver presses the brake pedal in a more vigorous manner thus requiring a high braking torque which is higher than the capacity of the electric motor, the control unit of the braking system also operates the mechanical brakes.

In the currently marketed traditional braking systems, the mechanical brakes are hydraulically piloted and the brake pedal directly acts on a brake pump which raises the pressure in a braking circuit with the aid of a servo brake system In order to implement the above-described regenerative braking mode, it has been suggested to suppress the mechanical connection between the brake pedal and the brake pump which raises the pressure in the braking circuit; in this case, the position of the brake pedal is detected by a position sensor and according to the brake pedal position read by the position sensor, the control unit of the braking system pilots the electric motor as a generator and, if needed, also operates the mechanical brakes using an actuator (e.g. an electric actuator) coupled to the brake pump which raises the pressure in the braking circuit.

Suppressing the mechanical connection between the brake pedal and the brake pump which raises the pressure in the braking circuit results, however, in fully redesigning the braking system and thus high costs and long manufacturing times. Furthermore, suppressing the mechanical connection between the brake pedal and the brake pump which raises the pressure in the braking circuit makes it difficult to operate the brakes in case of errors or malfunctioning of the position sensor which reads the position of the brake pedal or in the actuator coupled to the brake pump; therefore, adequate redundancies and adequate diagnostics should be provided to ensure a high degree of vehicle driving safety.

Patent applications WO2005014351A1 and WO2005102804A1, which are incorporated by reference, describe a braking system for a vehicle to control a regenerative braking; the braking system is provided with: a plurality of hydraulically operated mechanical brakes; a hydraulic braking circuit connected to the mechanical brakes; a brake pump to raise pressure in the hydraulic braking circuit; a brake pedal mobile between a resting position and a maximal braking position; a connecting cap, which mechanically connects the brake pedal to the brake pump, and is divided into two reciprocally independent parts; an elastic system which tends to push the brake pedal towards the resting position; a position sensor to read the position of a part of the connecting cap integral to the brake pedal; and a pilot system to pilot an energy recovery system for effecting a regenerative braking using the position of the part of the connecting cap integral to the brake pedal provided by the position sensor The mechanical solution used in patent applications WO2005014351A1 and WO2005102804A1 for implementing the elastic system tending to push the brake pedal towards the resting position is, however, particularly complex and expensive.

SUMMARY

An embodiment of the present invention to provide a braking system for a vehicle to control a regenerative braking, which braking system is free from the above-described drawbacks while being easy and cost-effective to be implemented.

DETAILED DESCRIPTION

InFIG. 1, numeral1indicates as a whole an embodiment of a hybrid vehicle provided with two front wheels2and two rear drive wheels3, which receive the driving torque from a hybrid propulsion system4

The hybrid propulsion system4comprises a thermal internal combustion engine5, which is arranged in a frontal position and is provided with a drive shaft6, a servo controlled transmission7, which transmits the driving torque generated by the internal combustion engine5to the rear drive wheels3, and a reversible electric motor8(i.e. which may work either as an electric motor by absorbing electric energy and generating a mechanical driving torque, and as an electric generator by absorbing mechanical energy and generating electricity) which is mechanically connected to the servo controlled transmission7

The servo controlled transmission7comprises a propeller shaft9which is angularly integral to the drive shaft6on one end and is mechanically connected to a servo controlled gearbox10on the other end, which is arranged in a rear position and transmits the motion to the rear drive wheels3by means of two axle shafts12which receive the motion from a differential gear11. The reversible electric motor8is then mechanically connected to the gearbox10and is piloted by an electric drive connected to at least one battery to store electricity; by way of example, a shaft of the reversible electric motor8may be mechanically connected (meshed either directly or by interposing a speed reducer and/or a clutch) to a primary shaft of the gearbox10or to a secondary shaft of the gearbox10

Furthermore, vehicle1comprises a braking system13, which is provided with four mechanical disc brakes14, each of which is coupled to a respective wheel2or3; each disc brake14comprises a disc15, angularly integral to the respective wheel2or3, and a caliper16to be hydraulically controlled in order to clamp on the disc15. The braking system13is provided with a hydraulic braking circuit17, which is connected to all the calipers16and is provided with a brake pump18to raise the pressure in the hydraulic braking circuit17itself. The brake pump18is controlled by a brake pedal19, which is mechanically connected to the brake pump18for directly acting on the brake pump18, and is provided with a servo brake system20for amplifying the action of the brake pedal19and thus reducing the force which should be exerted on the brake pedal19itself.

As shown inFIG. 2, the brake pedal19is hinged to a chassis of road vehicle1to rotate between a resting position (shown inFIG. 2), in which the braking torque applied to the road vehicle1is null, and a maximal braking position (not shown) in which the braking torque applied to road vehicle1is maximal. A connecting cap21is provided, which mechanically connects the brake pedal19to the brake pump18(by interposing the servo brake system20) and has one end22integral to the brake pedal19and an opposite end22integral to the brake pump18(by interposing the servo brake system20).

The connecting cap21is divided into two reciprocally independent parts21aand21bhaving two respective ends24and25facing each other; in other words, part21aof the connecting cap21has the end22integral to the brake pedal19and the end24, while part21bof the connecting cap21has the end23opposite to end22integral to the brake pump18and the end25. The two ends24and25facing each other of the two parts21aand21bof the connecting cap21are inserted into a tubular base26forming a coupling between the ends24and25themselves; according to three different, reciprocally equivalent embodiments, either both ends24and25are slidingly mounted inside the base26, or the base26is integral to the end24, while end25is slidingly mounted inside the base26, or the base26is integral to the end25, while end24is slidingly mounted inside the base26. As previously mentioned, the function of the tubular base26is to make a coupling between the ends24and25by guiding the mutual movement away or towards the ends24and25while always maintaining the ends24and25themselves facing each other.

An elastic system27which pushes the brake pedal19towards the resting position is included; in the embodiment shown inFIG. 2, the elastic system27comprises a spring28, which is directly coupled to the brake pedal19(i.e. is compressed between the brake pedal19and a chassis of the road vehicle1), and a spring29which is interposed between the two parts21aand21bof the connecting cap21(i.e. is compressed between the end24and the end25and is inserted into the tubular base26). According to a different embodiment (not shown), the elastic system27could comprise either the spring28only or the spring29only.

A position sensor30to read the position of the part21aitself is coupled to the part21aof the connecting cap21integral to the brake pedal19. In the embodiment shown inFIG. 2, the position sensor30is mounted at an intermediate portion of the part21aof the connecting cap21; in other words, the position sensor30has a mobile slider31integral to part21aand a fixed reader32, which is arranged close to the mobile slider31for reading the position of the mobile slider31. The position sensor30may include a mechanical connection between the mobile slider31and the fixed reader32(e.g. when the position sensor30is a potentiometer), or the position sensor30may be of the contactless type and therefore not include any mechanical connection between the mobile slider31and the fixed reader32(e.g. when the position sensor30is of the inductive type). Alternatively, the position sensor30could be mounted on the brake pedal19(i.e. the mobile slider31of the position sensor30is integral to the brake pedal19) or the position sensor30could be mounted on the tubular base26(i.e. the mobile slider31of the position sensor30is integral to a portion of the spring29) for detecting the reciprocal distance between the two ends24and25(i.e. for detecting the compression degree of spring29).

Finally, a pilot system33is provided, which receives the reading from the position sensor30and is adapted to pilot the electric motor8as a generator for effecting a regenerative braking; in particular, the pilot system33uses the position of part21aof the connecting cap21integral to the brake pedal19provided by the position sensor30for controlling the operation of the electric motor8as a generator, so that the braking torque absorbed by the electric motor8is inversely proportional to the distance existing between the two parts21aand21bof the connecting cap21(i.e. between the two ends24and25facing each other of parts21aand21b) In other words, the greater the distance between the two parts21aand21b(i.e. between the two ends24and25), the lower the braking torque absorbed by the electric motor8

The operation of the braking system13is described below according toFIG. 2.

When the driver does not press the brake pedal19, the brake pedal19is pushed and maintained in the resting position (shown inFIG. 2) by the elastic system27, at which the distance between the two parts21aand21b(i.e. between the two ends24and25) is maximal. Under these conditions (i.e. when the distance between the two parts21aand21bis maximal), the reading provided by the position sensor30is higher than a predetermined threshold and the pilot system33does not pilot the electric motor8as a generator for creating a braking torque (or, in other words, the braking torque generated by the electric motor8is null)

When the driver starts depressing the brake pedal19, the brake pedal19itself moves, compressing the springs28and29of the elastic system27and gradually approaching the two parts21aand21b(i.e. between the two ends24and25); under these conditions, the pilot system33pilots the electric motor8as a generator for creating a gradually increasing braking torque according to the approach degree between the two parts21aand21b(i.e. the closer the two parts21aand21b, the greater the intensity of the braking torque absorbed by the electric motor8working as a generator). The maximal braking force absorbable by the electric motor8working as a generator may be obtained when the two parts21aand21b(i.e. the two ends24and25) are at a minimum distance from each other (i.e. are very close but do not touch each other yet).

It is worth noting that until this moment, the movement of the brake pedal19does not determine any mechanical action of part21bof the connecting cap19, and thus on the brake pump18. If the driver further depresses the brake pedal19, the movement of the brake pedal19takes part21in contact with part21b(i.e. takes end24in contact with end25); from this moment, a further pressure on the brake pedal19(i.e. a further depressing of the brake pedal19) is transmitted by part21ato part21b, and from this to the brake pump18of the hydraulic braking circuit17, which thus raises the pressure in the hydraulic braking circuit17thus determining the operation of the disc brakes14. In other words, in this circumstance, the braking system13behaves like a traditional braking system in which there is a direct mechanical connection (determined by joining the two parts21and21bof the connecting cap21) between the brake pedal19and the brake pump18of the hydraulic braking circuit17.

Summarizing the above description, a discontinuity (i.e. a mechanical interruption), which is enclosed in the tubular base26and is coupled to the position sensor30, is inserted along the connecting cap21. When the driver depresses the brake pedal19, the connecting cap21does not firstly act in a mechanical manner on the brake pump18due to the separation of part21aof the connecting cap21from part21b; only by applying a relatively high force on the brake pedal19, the contact between the two parts21aand21bof the connecting cap21is determined, and thus the thrust is transmitted to the brake pump18. The signal of position sensor30is sent to the pilot system33which pilots the electric motor8as a generator for effecting a regenerative braking; the resulting braking torque is managed so as to be approximately proportional to the signal of the position sensor30, so that the driver may control the deceleration of road vehicle1. When the two parts21aand21bof the connecting cap21are in contact, the brake pedal19mechanically acts on the brake pump18thus activating the disc brakes14; in this circumstance, the electric motor8is piloted to absorb all the braking torque made available by the regeneration to which the disc brakes14will add the torque lacking in order to brake the road vehicle1.

The disc brakes14may have a smaller size as compared to a similar conventional braking system because part of the braking energy is supplied by the electric motor8. In some cases, the battery connected to the electric motor8is fully charged (i.e. is no longer capable of storing further electricity) and thus the electricity generated by the electric motor8with the regenerative braking is in excess; in this cases, the electricity generated by the electric motor8with the regenerative braking may be dissipated in the form of heat by using one or more electric resistors.

An embodiment of the above-described braking system13has many advantages. First, an embodiment of the above-described braking system13is simple and rapid to be implemented even in an existing vehicle1, because it is entirely similar to a traditional braking system and the only structural change to be made includes cutting the connecting cap21into two parts21and21b. Furthermore, an embodiment of the above-described braking system13is particularly compact, because it only requires the insertion of tubular base26, position sensor30and elastic system27, and these components are small in size and easily placeable because they may correctly work in several positions.

The braking torque absorbed by the electric motor8working as a generator may be maximized before the intervention of the mechanical disc brakes14and thereby the energy efficiency may be maximized. Moreover, the value of the braking torque absorbed by the electric motor8working as a generator varies from zero to a maximal value and is controlled by the driver depressing the brake pedal19(i.e. intuitively and ergonomically).

Finally, in an embodiment of the above-described braking system13, the mechanical connection between the brake pedal19and the brake pump18which raises the pressure in the braking circuit is maintained, and therefore the braking system13intrinsically has the same safety degree as a traditional braking system. In other words, in case of failure to the position sensor30or the pilot system33, and therefore in the absence of braking action of the electric motor8, the only drawback encountered by the user is a feeling of longer idle stroke of the brake pedal19(i.e. the brake discs14will not work until part21aof the connecting cap21comes in contact with part21b).

One or more of the other methods described below may be used either alternatively or in combination with the above for activating/deactivating and adjusting the action of the electric motor8for effecting a regenerative braking.

An ON/OFF type switch which is used to recognize the step of braking, e.g. for controlling the switching on of the brake lights or for managing the servo controlled transmission7, is coupled to the brake pedal19; such a switch may also be used to control the activation and deactivation of the regenerative braking, which in this case is of the ON/OFF type.

A position sensor which is used to control the activation and deactivation of the regenerative braking is coupled to an accelerator pedal; in particular, when the accelerator pedal is released, a threshold (a reference movement value of the acceleration pedal) may be determined, beyond which the regenerative braking is activated. Alternatively, then the accelerator pedal is released, a reference releasing speed threshold of the accelerator pedal may be determined, beyond which the regenerative braking is activated.

The brake oil pressure value in the hydraulic braking circuit17may be used to activate/deactivate the regenerative braking; in other words, the regenerative braking is activated when the brake oil pressure is higher than a threshold value and the intensity of the braking torque absorbed by the electric motor8is proportional to the brake oil pressure. The brake oil pressure may be measured by a dedicated pressure sensor or a reading carried out by an ABS system and normally made available over the CAN network may be used.

In an embodiment of the above-described systems, there is always a concomitance between the regenerative braking action operated by the electric motor8and the dissipative braking action operated by the disc brakes14, i.e. both the regenerative braking action and the dissipative braking action are simultaneously activated. When a relatively modest braking torque is required (i.e. which may be generated only by the electric motor8), the dissipative braking action operated by the disc brakes14may be either limited or suppressed by using the relief valves of the ABS system which locally remove the pressure from the disc brakes14.