GB2365086A

GB2365086A - Electric motor driven wheel brake having pistons pressed together for emergency or auxiliary braking

Info

Publication number: GB2365086A
Application number: GB0117372A
Authority: GB
Inventors: Matthias Schanzenbach; Dieter Blattert
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-07-17
Filing date: 2001-07-17
Publication date: 2002-02-13
Anticipated expiration: 2021-07-17
Also published as: GB0117372D0; GB2365086B

Abstract

A wheel brake device 10 having a rotation/translation conversion gear 28, comprising a spindle 26 and nut 38 which is rotationally driven by an electric motor 48; a hydraulic working piston 16 integral with the spindle 26 which is displaced by the rotation/translation conversion gear 28; and a brake lining piston 12 coaxial with, and which can be displaced hydraulically by the working piston 16. For emergency actuation (eg. hydraulic leakage), or as an auxiliary brake (with valve 22 open), the working piston 16 can also press directly against the brake lining piston 12, the motor being locked by a solenoid brake 50. A reservoir 20 supplies hydraulic fluid via solenoid valve 22 and pressure sensor 24. Monitoring of the pressure and motor shaft angles are compared with desired values to determine a fault in the brake, heating of hydraulic fluid, or for adjusting clearances. A faulty brake is released by opening solenoid valve 22 or by releasing motor solenoid brake 50.

Description

<Desc/Clms Page number 1> DESCRIPTION WHEEL BRAKE DEVICE AND METHOD FOR OPERATION THEREOF The invention relates to wheel brakes of the type comprising an electric motor, having a rotation/translation conversion gear which is rotationally driven by the electric motor, having a working piston which is displaceably received in a working cylinder and which can be displaced by the rotation/translation conversion gear, and having a brake lining piston which is displaceably received in a cylinder, wherein the working cylinder and the cylinder of the brake lining piston are in operative connection. The invention also provides an operating method of the type wherein the wheel brake device comprises an electric motor, a rotation/translation conversion gear which can be rotationally driven by the electric motor, a working piston which is displaceably received in a working cylinder and can be displaced by the rotation/translation conversion gear, and a brake lining piston which is displaceably received in a cylinder, wherein the working cylinder and the cylinder of the brake lining piston are operatively connected.

From DE 195 29 664 Al a wheel brake device of this type is known. The known wheel brake device comprises an electric motor with which a rotation/translation conversion gear can be driven in a rotating manner. The rotation/translation conversion gear of the known wheel brake device is formed as a helical gear. A

hydraulic working piston can be displaced in a working cylinder by the rotation/translation conversion gear. The working cylinder communicates with a cylinder in which a brake lining piston is received in a displaceable manner. By displacement of the working piston in the working cylinder the brake lining piston is displaced in its cylinder, wherein by reason of different cylinder diameters a hydraulic path reduction and force transmission can be achieved. A friction brake lining on a brake body which is rotationally fixed to a vehicle wheel can be pressed by the brake lining piston, for example against a brake disc or brake drum in order to produce a braking force or a braking moment. The known wheel brake device combines an electromechanical drive with a hydraulic drive.

In accordance with a first aspect of the present invention, a rotation/translation conversion gear can be brought into a mechanical connection with the brake lining piston and the brake lining piston can therefore be displaced.

This has the advantage that an auxiliary brake function, independent of the hydraulics, of the wheel brake device can be achieved. A braking force built up in the auxiliary brake function remains unchanged over a long period since the braking force is built up in a purely mechanical manner and a reduction in braking force by leakage losses in the hydraulics is thereby excluded. A further advantage of the wheel brake device in accordance with the invention is its ability to operate in a purely mechanical manner, for example if there is leakage in the hydraulics of

the wheel brake device. In this way a mechanical emergency brake operation is possible when there is a fault in the hydraulics. In contrast to a purely electromechanical wheel brake device the wheel brake device in accordance with the invention has the advantage that it can be readily formed with two or more brake lining pistons and in this way can be produced at low cost, for example even as a fixed caliper brake device.

According to claim 2, a displaceable element of the rotation/translation conversion gear can be displaced into position onto the brake lining piston and in this way the brake lining piston can be displaced mechanically to press the friction brake lining onto the brake body. The displaceable element can be a spindle of a rotation/translation conversion gear formed as a helical gear.

According to claim 3 a further possibility for the mechanical displacement of the brake lining piston is to provide the working piston so as to be displaceable into position onto the brake lining piston.

In a preferred embodiment of the invention the wheel brake device comprises a valve which can open and close and which is attached to the working cylinder and to the cylinder of the brake lining piston (claim 4). When the valve is open a hydraulic operative connection between the working piston and the brake lining piston is released and the brake lining piston can be displaced mechanically by the

rotation/translation conversion gear. Furthermore, the opening of the valve causes the wheel brake device to be released in the event of a fault in its electromechanical drive. The valve is preferably open in a basic position (claim 5).

According to claim 6 the wheel brake device in accordance with the invention comprises a pressure sensor for measuring the hydraulic pressure. For example, a braking force of the wheel brake device can be determined by the pressure sensor since the braking force is at least approximately proportional to the hydraulic pressure.

According to claim 7 the wheel brake device in accordance with the invention comprises a rotational angle sensor for the rotor of the electric motor or the rotation/translation conversion gear. The rotational angle sensor can be used to measure a rotational angle of the rotor of the electric motor or of a rotating part of the rotation/translation conversion gear in terms of full rotations and/or fractions of a rotation. Since the rotational angle is proportional to a displacement path of the rotation/translation conversion gear a displacement path of the rotation/translation conversion gear can be determined.

By correlation of the rotational angle measured by the rotational angle senor and of the hydraulic pressure measured by the pressure sensor it is possible to monitor

the fault-free operation of the wheel brake device. During fault-free operation of the wheel brake device these two values are in a specific relationship to each other in all operating states of the wheel brake device. If, during operation of the wheel brake device in accordance with the invention, the relationship between the two values deviates to a considerable extent with respect to their relationship in a fault-free wheel brake device, it is possible to conclude that there is a fault. Instead of the rotational angle sensor the wheel brake device according to claim 8 can also comprise a path sensor for the displacement path of the rotation/translation conversion gear.

The rotation/translation conversion gear of the wheel brake device in accordance with the invention and according to claim 9 is preferably formed so as to be non- self-locking /so that when the electric motor is not energised a force pressing the friction brake lining against the brake body is reduced to a low value. In this way the wheel brake device can be released if a power supply to the electric motor fails.

In order to maintain an applied braking force in the non-energised state for the auxiliary brake function claim 10 provides a brake with which the rotor of the electric motor or the rotation/translation conversion gear can be locked.

The invention will be explained in more detail hereinunder, by way of example only with the aid of an exemplified embodiment illustrated in the drawing. The single figure shows an axial cross-section of a wheel brake device according to the invention. The drawing is to be understood as a partially simplified schematic illustration.

The wheel brake device 10 in accordance with the invention illustrated in the drawing comprises a brake lining piston 12 which is displaceably received in a cylinder 14. In order to produce a braking moment or a braking force in a manner known per se a friction brake lining (not shown) lying against the brake lining piston 12 can be pressed by the brake lining piston 12 against a brake body (also not shown) for example, a brake disc.

In order to displace the brake lining piston 12 the wheel brake device 10 comprises a working piston 16 which is displaceably received in a working cylinder 18. The working piston 16 is disposed coaxially to the brake lining piston 12, it has a smaller diameter than the brake lining piston 12. The working cylinder 18 and the cylinder 14 of the brake lining piston 12 are hydraulic cylinders which are operationally connected to each other. In the illustrated exemplified embodiment the working cylinder 18 and the cylinder 14 of the brake lining piston 12 form one piece with each other, the working cylinder 18 issues coaxially into the cylinder 14 of the brake lining piston 12. A brake fluid storage

reservoir 20 is connected to the working cylinder 18 and has the working cylinder 18, and therefore also the cylinder 14 of the brake lining piston 12, operatively connected to it by means of a solenoid valve 22. The solenoid valve is formed as a two-port, two-position solenoid valve which is open in its non-energised basic position. Furthermore, a pressure sensor 24 is connected to the working piston 18, by which hydraulic pressure in the working cylinder 18 and the cylinder 14 of the brake lining piston 12 can be measured.

The working piston 16 is a single-piece component of a spindle 26 of a helical gear 28. The helical gear 28 forms a rotation/translation conversion gear. Instead of the helical gear 28 it is also possible to use another rotation/translation conversion gear such as a circulating ball gear or a roll thread drive (not shown). In order for it to be rotationally secured, the spindle 26 comprises a slide spring 30 which lies in an axially parallel groove 32 in the spindle 26 and in an axially parallel groove 34 in a housing 36 of the wheel brake device 10.

For axial displacement of the spindle 26 together with the working piston 16 forming one piece therewith, the helical gear 28 comprises a nut 38 with which the spindle 26 is engaged. The nut 38 is rotatably mounted with an angular roller bearing 40 in the housing 36 and is supported in an axial manner in the housing 36 by the angular roller bearing 40. The spindle drive 28 is non-self-locking, ie. axial pressure on the spindle 26 means that the nut 38 can be rotated and the spindle 26

can be axially displaced.

The nut 38 of the helical gear 28 forms one piece with a toothed wheel 42 which meshes with a toothed wheel 44 of smaller diameter. The two toothed wheels 42, 44 form a toothed wheel gear. The smaller toothed wheel 44 is attached in a rotationally fixed manner to a motor shaft 46 of an electric motor 48. The electric motor 48 comprises an integrated rotational angle sensor (not shown in the drawing) for its motor shaft 46. A solenoid-operated brake is flange-mounted onto the electric motor 48 and is hereinunder designated as solenoid brake 50.

The solenoid brake 50 has a stable brake position in which it locks the motor shaft 46. In order for the solenoid brake 50 to be released it is energised. The solenoid brake 50 can be formed in a bistable manner, ie. it remains non-energised both in the braking position and in a released position and is only energised in order to switch between the braking position and the released position and inverse. Solenoid brakes 50 of this type are known pre se to the person skilled in the art both in the monostable and in the bistable form in numerous designs and for this reason no more detail will be given at this point as to the construction of the solenoid brake 50.

The toothed wheel gear 42, 44 is a mechanical reduction gear, wherein a moment transmission from the electric motor 48 to the nut 38 of the helical gear 28 takes place. By reason of the smaller diameter of the working piston 16 there is also a

hydraulic reduction in the displacement path and an increase in the force from the working piston 16 to the brake lining piston 12.

Operation of the wheel brake device In order to actuate the wheel brake device 10 the solenoid brake 50 is released, the solenoid valve 22 is closed and the electric motor 48 is energised in an application direction. By means of the toothed wheel gear 42, 44, the nut 38 of the helical gear 28 is made to rotate and displaces the spindle 26 together with the working piston 16, forming one piece therewith, in the direction of the brake lining piston 12. The working piston 16 forces brake fluid out of the working cylinder 18 into the cylinder 14 of the brake lining piston 12 and thereby displaces the brake lining piston 12. In this way there is a force transmission from the working piston 16 to the brake lining piston 12 in proportion to their two diameters. By means of the brake lining piston 12 the friction brake lining (not shown) is pressed in a manner which is known pre se against the brake body (not shown) and in this way a braking moment or braking force is exerted onto the brake body.

In order to reduce the braking force and to reset the wheel brake device 10 the electric motor 48 is energised in a reverse rotational direction, so that by means of the toothed wheel gear 42, 44 and the helical gear 28, the working piston 16 and therefore also the brake lining piston 12 are pushed back. The hydraulic pressure

in the working cylinder 18 and in the cylinder 14 of the brake lining piston 12 is measured by the pressure sensor 24. Since the hydraulic pressure is proportional to a force with which the brake lining piston 12 presses the friction brake lining against the brake body, the pressing force of the friction brake lining against the brake body and therefore the braking force of the wheel brake device 10 can be determined from the hydraulic pressure measured by the pressure sensor and can be adjusted to a desired value.

Auxiliary brake function, emergency brake function For use as an auxiliary brake the working piston 16 is displaced in the manner described above, when the solenoid brake 50 is released by energising of the electric motor 48, until it contacts the brake lining piston 12. In this way the solenoid valve 22 remains open so that brake fluid forced from the working piston 16 exits into the brake fluid storage reservoir 20. The brake lining piston 12 is further displaced with the working piston 16 lying against the brake lining piston 12 until the friction brake lining (not shown) lies against the brake body. Further energising of the electric motor 48 means that, by reason of the working piston 16 lying against the brake lining piston 12, the friction brake lining presses against the brake body and thus a braking force is built up. The solenoid brake 50 is brought into its braking position and locks the motor shaft 46. The energising of the electric motor 48 can be terminated, by means of the toothed wheel gear 42,

44 the solenoid brake SO holds the nut 38 of the spindle gear 28 in a rotationally fixed manner and thereby also locks the spindle 26 and the working piston 16. The braking force applied by energising of the electric motor 48 is retained when the electric motor 48 is non-energised. The braking force is applied mechanically by the position of the working piton 16 on the brake lining piston 12 without the hydraulic effect of the braking fluid and is maintained so that the applied braking force is not reduced by any leakage losses.

An emergency brake function is possible in a similar manner to the auxiliary brake function. If the hydraulic transfer of the displacement of the working piston 16 to the brake lining piston 12 fails, for example as a result of insufficient brake fluid or because of leakage, the working piston 16 can be pushed into position on the brake lining piston 12 and the brake lining piston 12 can be mechanically displaced by the working piston 16 which lies against it.

Operational monitoring The hydraulic pressure measured by the pressure sensor 24 and the rotational angle of the motor shaft 46 measured by the integrated rotational angle sensor of the electric motor 48 are in a specific relationship of dependency with each other in every operating condition of the wheel brake device 10. The rotational angle therefore means a number of full rotations and/or a fraction of a rotation. If, for

example in order to build up a braking force, when the solenoid valve 22 is closed, the electric motor 48 is energised and its motor shaft 46 thus made to rotate, the working piston 16 and the brake lining piston 12 are displaced. Until the friction brake lining comes into position on the brake body only a low hydraulic pressure is built up. As soon as the friction brake lining lies against the brake body the hydraulic pressure increases as the motor shaft 46 continues to turn. This dependency of the hydraulic pressure upon the rotational angle of the motor shaft 46 is exploited to provide operational monitoring of the wheel brake device 10. In addition, the hydraulic pressure actually prevailing and the rotational angle of the motor shaft 46 are measured and compared with desired values in a fault-free wheel brake device 10. If the measured values deviate by more than a fixed permissible tolerance from the desired values, this indicates a fault in the wheel brake device 10. This operational monitoring can also take place when a vehicle fitted with the wheel brake device 10 in accordance with the invention is not moving. The operational monitoring of the wheel brake device 10 can be carried out automatically, for example when the engine of the vehicle is started up before travel commences.

Heating of the brake fluid during braking can be determined in the following manner: If the brake fluid is heated in the working cylinder 18 and in the cylinder 14 of the brake lining piston 12 by frictional heat during braking, then the brake fluid expands. The hydraulic pressure is above the known hydraulic pressure

which would prevail with cold brake fluid and with the same rotational angle of the motor shaft 46. From the increased hydraulic pressure it is possible to conclude that there is an increase in temperature or to calculate this increase. In this way a warning can be given promptly before the hydraulic fluid reaches a critical temperature.

Even during unbraked travel it is possible to check whether the brake fluid is heated. This may be the case if there is little or insufficient clearance, ie. when the friction brake lining lies continuously against the brake body as a result of a mechanical fault. In order to check such an increase in temperature of the brake fluid the solenoid valve 22 is closed when the wheel brake device 10 has not been operated, and the hydraulic pressure is measured by the pressure sensor 24. If the brake fluid is heated, the brake fluid expands and the hydraulic pressure increases. Determination of clearance Clearance is determined during the above-described operation of the wheel brake device 10 by monitoring the hydraulic pressure using the pressure sensor 24. Until the friction brake lining comes into position on the brake body there is little increase in the hydraulic pressure and the hydraulic pressure remains approximately constant. As soon as the friction brake lining lies against the brake body the hydraulic pressure increases. From the number of rotations of the motor

shaft 46 it is possible to determine the displacement path of the brake lining piston 12 travelled until the pressure increases, ie. until the friction brake lining comes into position on the brake body, and therefore to determine the clearance. If the clearance is too great, for example as a result of a worn brake lining, it is adjusted in that during release of the wheel brake device 10 the motor shaft 46 is turned back less than it has been rotated during application of the wheel brake device 10 in the application direction.

The spacing of the working piston 16 from the brake lining piston 12 can be determined in the following manner: By energising the electric motor 48 the working piston 16 is displaced in the direction of the brake lining piston 12 when the solenoid valve 22 is opened. In this way the working piston 16 forces braking fluid out of the working cylinder 18, whereby the hydraulic pressure is somewhat increased. As soon as the working piston 16 contacts the brake lining piston 12 and displaces it the brake lining piston 12 with the larger diameter draws brake fluid into the working cylinder 18 or the cylinder 14 of the brake lining piston 12, the hydraulic pressure falls to a negative pressure. From the number of rotations of the motor shaft 16 until the hydraulic pressure falls when the working piston 16 contacts the brake lining piston 12 the displacement path travelled by the working piston 16 and therefore the original spacing between the working piston 16 and the brake lining piston 12 can be determined and adjusted when the working piston 16 is returned.

Release in the event of a fault The wheel brake device 10 can be released in two ways in the event of a fault. On the one hand when the wheel brake device 10 is activated the solenoid valve 22 can be opened and in this way the wheel brake device 10 can be released even if, for example the helical gear 28 is blocked. If the working piston 16 lies against the brake lining piston 12 then the second possibility for releasing the wheel brake device 10 is to release the solenoid brake 50. When the wheel brake device 10 has been actuated and the solenoid brake 50 released, the brake lining piston 12 pushes back the working piston 16 and the spindle 26 of the non-self-locking spindle gear 28 until the braking force exerted on the brake body by the friction brake lining has been reduced to a residual braking force.

Claims

CLAIMS 1 Wheel brake device having an electric motor, a rotation/translation conversion gear which is rotationally driven by the electric motor, a working piston which is displaceably received in a working cylinder and which can be displaced by the rotation/translation conversion gear, and a brake lining piston which is displaceably received in a cylinder, the working cylinder and the cylinder of the brake lining piston being in operative connection, wherein the rotation/translation conversion gear can be brought into a mechanical connection with the brake lining piston and the brake lining piston can therefore be displaced.
2 Wheel brake device according to claim 1, wherein a displaceable element of the rotation/translation conversion gear can be displaced into position onto the brake lining piston.
3 Wheel brake device according to claim 1, wherein the working piston can be displaced into position onto the brake lining piston.
4 Wheel brake device according to claim 1, wherein a valve is attached to the working cylinder and/or to the cylinder of the brake lining piston.

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5 Wheel brake device according to claim 4, wherein the valve is open in a basic position.
6 Wheel brake device according to claim 1, wherein the wheel brake device comprises a pressure sensor connected to the working cylinder and the cylinder of the brake lining piston.
7 Wheel brake device according to claim 1, wherein the wheel brake device comprises a rotational angle sensor with which a rotational angle of a rotor of the electric motor or of the rotation/translation conversion gear can be measured.
8 Wheel brake device according to claim 1, wherein the wheel brake device comprises a path sensor with which a displacement path of the driven element of the rotation/translation conversion gear can be measured.
9 Wheel brake device according to claim 1, wherein the rotation/translation conversion gear is non-self-locking.
10 Wheel brake device according to claim 9, wherein the wheel brake device comprises a brake with which a rotor of the electric motor or of the rotation/translation conversion gear can be locked.

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11 Wheel brake device according to claim 10, wherein the brake has a stable braking position.
12 Wheel brake device according to claim 10, wherein the brake is a solenoid brake.
13 Method for operating a wheel brake device, wherein the wheel brake device comprises an electric motor, a rotation/translation conversion gear which can be rotationally driven by the electric motor, a working piston which is displaceably received in a working cylinder and can be displaced by the rotation/translation conversion gear, and a brake lining piston which is displaceably received in a cylinder, the working cylinder and the cylinder of the brake lining piston being operatively connected, wherein hydraulic pressure in the working cylinder and/or in the cylinder of the brake lining piston and a displacement path of a displaceable driven element of the rotation/translation conversion gear are measured and that the two measurement values are compared with desired values for the two measurement values in a fault-free wheel brake device.
14 Method according to claim 13, wherein when the wheel brake device is actuated the hydraulic pressure in the working cylinder and/or in the cylinder of the brake lining piston is measured and compared with a desired value.

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15 Method according to claim 13, wherein a valve is attached to the working cylinder and/or to the cylinder of the brake lining piston, and that when the wheel brake device is not actuated the valve is closed and the hydraulic pressure in the working cylinder and/or in the cylinder of the brake lining piston is monitored for an increase in pressure
16 Method according to claim 13, wherein when the wheel brake device is actuated the progression over time of the hydraulic pressure in the working cylinder and/or in the cylinder of the brake lining piston is monitored and a displacement path of the driven element of the rotation/translation conversion gear up to a kink point in the pressure progression at the transition from an approximately constant low hydraulic pressure to an increasing hydraulic pressure is measured.
17 Method according to claim 13, wherein when the brake is released and the valve is opened the electric motor is rotationally driven in an application direction, that the progression over time of the hydraulic pressure is measured and that the displacement path of the driven element of the rotation/translation conversion gear up to the transition of the hydraulic pressure from an excess pressure to a negative pressure is measured. 18 Method according to claim 13, wherein in order to actuate the wheel brake

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device the brake is opened, the valve is closed and the electric motor is energised in an application direction. 19 Method according to claim 13, wherein in order to release the wheel brake device the brake is opened and the electric motor is energised in a reverse rotational direction with the valve closed. 20. Method according to claim 13, wherein the brake is released for emergency actuation of the wheel brake device and the electric motor is energised in an application direction with the valve open. 21. Wheel brake device substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing. 22. Method for operating a wheel brake device substantially as hereinbefore described with reference to the accompanying drawing.