GB1590473A

GB1590473A - Pedal-operated brake-applying mechanisms

Info

Publication number: GB1590473A
Application number: GB3711676A
Authority: GB
Original assignee: Girling Ltd
Current assignee: Girling Ltd
Priority date: 1977-09-05
Filing date: 1977-09-05
Publication date: 1981-06-03

Description

(54) IMPROVEMENTS IN PEDAL-OPERATED BRAKE-APPLYING MECHANISMS (71) We, GIRLING LIMITED, a British Company of Kings Road, Tyseley, Birmingham 11, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be par ticularly described in and by the following statement: - This invention relates to improvements in pedal-operated brake-applying mechanisms for use in braking systems of electrically driven vehicles.

In electrically driven vehicles it is advantageous to use the electric motor which normally provides the drive to one pair of wheels to give vehicle retardation when a brake-applying mechanism is operated. This is known as regenerative brake and when operated the electric motor can act partially to re-charge the batteries (or an external electric source if applicable). Such brakes of course make for reduced fuel requirements, and do not wear like friction brakes, but have the disadvantage of not being capable of high braking torques which are sometimes required, for example in emergency conditions. Also the regenerative braking effect disappears below substantially 10 m.p.h. Thus a friction brake is also required to provide the necessary braking torque under such conditions.

It is known to operate a regenerative brake and a friction brake "in series" by means of a single pedal with the pedal being movable in first and second stages of travel, the pedal being movable from an inoperative retracted position through the first stage of travel to actuate the regenerative brake and through the second stage to operate the friction brake.

Desirably the regenerative brake takes all the light duty with which it can cope, thereby avoiding wear of the friction brake, with the friction brake being available when necessary as a supplement for heavier brake applications requiring the generation of a higher braking torque.

A friction brake always has some degree of built in slack and the extent of this degree of slack varies with the state of adjustment of the brake, even when adjustment to compensate for wear is automatic.

Operation of a regenerative brake is controlled by a potentiometer and since, the brake does not wear, the travel of the brake remains substantially constant. It follows therefore that when a regenerative brake and a friction brake are operated in series as described above by means of a single pedal, depending on the state of wear or adjustment of the friction brake the two stages of travel may overlap, or there may be a gap therebetween, which could cause a delay before the friction brake can become operative. This will affect the "feel" or reaction of the pedal at the foot of the driver with the feel varying with the condition of adjustment of the friction brake.

According to our invention in a pedaloperated brake-applying mechanism for a braking system of an electrically driven vehicle having a first regenerative brake and a second friction brake a single pedal is provided for operating both brakes, and the mechansim incorporates a lost-motion device for taking up the clearances of the second brake as the first brake is moved between an "off" and a fully applied condition in response to movement of the pedal through a first stage of travel, the lost-motion device being variable automatically in accordance with the degree of slack in the second brake whereby the clearances of the second brake are completely taken up at a changeover point at which the first brake is fully applied, whereafter the.second brake is applied by continued movement of the pedal in the same direction and in a second stage.

The provision of the variable lost-motion device ensures that operation of the second brake occurs consecutively following operation of the first and without any overlap or delay thereby providing an even pedal "feel" or reaction throughout a common brake-applying sequence.

It is preferably arranged that the first stage of travel is sufficient to take up the braking clearances even when the second brake is in a maximum permissible slack adjustment condition, which may be defined as the condition which occurs when the second brake is fully actuated at the instant the pedal attains its position of maximum travel in a brake-applying direction which is determined by the engagement of the pedal with a stop, for example the floor of the vehicle.

The lost-motion device preferably acts between the pedal and an operating member for the second brake and comprises a thrust transmitting member which is disposed in a gap between the operating member and an abutment on the pedal to reduce the effective length of the gap to a distance which can be taken up during the first stage of pedal travel irrespective of the braking clearances of the second brake so that when the changeover point is reached the thrust from the pedal can be applied directly to the operating member through the thrust member, the effective length of the gap to be taken up during the first stage of pedal travel being determined by the position of the thrust member which, in turn, is controlled by a linkage responsive to the braking clearances In a theoretical case in which the second brake is fully adjusted and no braking clearances are to be taken up before the second brake can be applied, the thrust member will not move during brake application and the effective length of the gap will be reduced only by angular movement of the pedal towards the operating member during the first stage of pedal travel.

In practice some reduction in the effective length of the gap will be necessary during the first stage of pedal travel to compensate for braking clearances, and the linkage is arranged to move the thrust member in a direction to reduce the effective length of the gap during initial movement of the pedal and until, at an intermediate point, the reaction on the second brake, indicating that the clearances have been taken up, becomes greater than the force applied to the linkage from the pedal.

At that intermediate point the effective lengh of the gap remaining is sufficient to enable the first brake to be fully operated before the second brake is actuated at the changeover point. At the maximum permissible slack condition the intermediate point and the changeover point will coincide.

When the intermediate point is attained further angular movement of the pedal is resisted by a return spring through which the pedal previously acted on the operating member through the linkage.

Preferably the thrust member comprises a wedge which progressively reduces the effective length of the gap as it is moved by the linkage.

Conveniently the linkage comprises a lever which is pivotally connected at one end to a stationary pivot for the pedal and at the opposite end to one arm of a bellcrank of which the other arm is connected to a link to the wedge, the bellcrank itself being pivotally connected to a substantially stationary pivot, and the lever at an intermediate point in its length acting on the operating member, the arrangement being such that the lever moves angularly with the pedal to advance the operating member, at the same time acting through the bellcrank and the link to advance the wedge to reduce the effective length of the gap until the intermediate point is reached, whereafter the pedal moves angularly with respect to the lever until the changeover point is reached.

In one construction the operating member comprises a push-rod for operating the piston in a hydraulic master cylinder for applying the second brake, and an operating member for the first brake comprises a potentiometer to the casing of which the bellcrank is pivotally connected. In such a construction the casing is coupled to the body of the vehicle through a pivotally mounted spring-loaded support link which moves angularly against its spring loading when the pedal is moved angularly to apply the second brake, accompanied by bodily displacement of the casing.

Two embodiments of our invention are illustrated in the accompanying drawings, in which: Figure 1 is a diagrammatic side elevation of pedal-operated brake-applying mechanism; Figure 2 is an end elevation of one practical pedal-operated brake-applying mechanism Figure 3 is a side elevation showing the potentiometer in the "off" position of both brakes; Figure 4 is a view similar to Figure 4 with 50 per cent regenerative braking; Figure 5 is a view similar to Figure 4 but with 000 per cent regenerative braking; Figure 6 is a side elevation of the mechanism of Figure 2 with the potentiometer omitted for clarity and with both brakes in the "off" position, according to Figure 3: : Figure 7 is a view similar to Figure 6 and showing the relative position of the parts equivalent to the pedal position of Figure 4; Figure 8 is a view similar to Figure 7 with the wedge fully advanced and equi valet to the pedal position Figure 5; and Figure 9 is a view similar to Figure 6 following 100 per cent regenerative braking.

In the pedal-operated brake-applying mechanism illustrated in Figure 1 of the drawings a pedal 1 for operating sequentially a first regenerative brake and a second friction brake is pivotally mounted for angular movement about a fixed pivot 2 in a relatively stationary part 3.

The regenerative brake is operated by a potentiometer 4 having a casing 5 which is pivotally connected at its closed end to a pivot 6 with a link 7, and the link 7 is pivotally connected to the stationary part 3 by means of a pivot 8. A tension return spring 9 acts between the pivot 6 and the stationary part. The slider of the potentiorneter is coupled to the pedal 1 by means of a bifurcated fitting 10.

The friction. brake is operated by an hydraulic master cylinder, not shown, through an operating member 11 comprising push-rod 12 which acts on a piston rod 13 through a compression spring 14 located in a cage 15.

The pedal I operates the master cylinder through a variable lost-motion device and a linkage. As illustrated a lever 16 is pivotally connected at one end to the pivot 2, and at an intermediate point in its length to the push-rod 12 through a pivot 17. A bellcrank 18 is pivotally connected at 19 to the casing 5 and one of its arms are pivotally connected to the lever 16 by means of a pivot 20.

A thrust member 21 is guided for sliding movement in a direction transverse to the line of action of the push-rod 12 against an abutment face 22 on the pedal 1 and the wedge is located in a gap between the face 22 and the adjacent end of the push-rod 12.

The outer end of the wedge 21 is connected to the other arm of the bellcrank 18 through a pivotally mounted link 23.

In a normal inoperative position the wedge 21 is in engagement at one edge with the face 22 and at its opposite edge is spaced from the adjacent end of the pushrod 12 by a gap which corresponds to the distance through which the pedal 1 must be moved angularly in a first stage of travel to operate the regenerative brake to 100 per cent regenerative braking and up to a changeover point after which the friction brake is operated by further angular movement of the pedal in the same direction.

When the pedal is operated initially angular movement of the pedal 1 to operate the regenerative brake by moving the slider of the potentiometer 4 is accompanied by angular movement of the lever 16 about the common pivot 2. The lever 16 applies a force to the push-rod 12 and moves the bellcrank 18 in a clockwise direction to move the wedge 21 inwardly to decrease the effective length of the gap to compensate for wear of the friction linings of the friction brake. This continues until, at an intermediate point, the reaction on the friction brake comprising the pressure generated in the master cylinder, which is transmitted back through the rods 13 and 12 and the spring 14, becomes greater than the force applied to the pushrod 12 through the lever 16, indicating that the braking clearances have been taken up.

At this intermediate point the lever 16 is prevented from moving angularly any further and similarly the wedge 21 is held against movement in a direction to reduce the gap still further. Further travel of the pedal 1 in the same direction moves the slider of the potentiometer further to increase the regenerative braking to 100 per cent at the changeover point at which the wedge 21 engages with the push-rod 12 to actuate the master cylinder and thereby apply the friction brake.

When the changeover point is reached the slider of the potentiometer cannot be moved any further in that direction.

Further movement of the pedal 1 is therefore accompanied by bodily movement of the casing 5 with the link 7 moving angularly about the pivots 6 and 8 against the loading of the return spring 9.

In the practical construction illustrated in Figures 2 to 9 the potentiometer 4 is carried by and is angularly movable with the pedal 1 which acts on the slider of the potentiometer 4 through a bellcrank 25 of which one arm is coupled by the spring 9 to the stationary part 3 and the other arm is coupled to the pedal 1.

As the pedal is moved angularly the bellcrank 25 is moved angularly in an anticlockwise direction to operate the slider until, as shown in Figure 5, at 100 per cent regenerative braking a pivoted connection 26 between the bellcrank 25 and the casing 5 engages with the casing 5. Thereafter the spring 9 extends to permit further angular movement of the pedal.

The piston-rod 13 is connected by a pivot 27 to the lever 16, and the push-rod 12 engages with the pivot 27 being urged into engagement with it all the time by the compression spring 14 which acts between an abutment flange 28 on the push-rod 12 and a radial flange 29 on a cylindrical extension 30 of the pedal 1. The push-rod 12 works through an opening surrounded by the flange 29 and the projecting portion of the push-rod 12 carries an enlarged head 31 which engages with the outer face of the flange 29 to limit inward movement of the push-rod 12 under the influence of the spring 14.

The wedge 21 is guided through diametrically opposed elongate slots 32 in the wall of the extension 30 and through an axially extending slot 33 in the push-rod 12. The inner ends of the slots 32 are defined by an abutment flange or platform 34 of the pedal 1, and the slots 32 and 33 are substantially equal in length to the width of the thicker, outer end of the wedge 21.

The thinner, inner end of the wedge 21 is integral with an extension 35 of constant section which traverses the cylindrical extension 30 when the pedal is in the inoperative position illustrated in Figures 3 and 6. In this position the wedge 21 is completely withdrawn from the extension 30.

It will be appreciated therefore that the length of the slot 33 minus the thickness of the extension 35 represents the lost-motion which it to be taken up during the first stage of travel of the pedal to achieve 100 per cent regenerative braking as the changeover part, assuming that no braking clearances of the friction brake are to be taken up during that pedal movement. This condition is illustrated in Figure 9 from which it will be observed that the wedge 21 has remained in the same initial position as Figure 6.

Figures 7 and 8 indicate adjustment requirements. As illustrated in Figures 4 and 7 where 50 per cent regenerative braking has been achieved the wedge 21 has entered the slot 32 to reduce the lost-motion or the effective length of the slot 32 and, at 100 per cent regenerative braking where the operating rod 13 has moved further to take up all the clearances of the friction brake, as shown in Figures 5 and 8, the wedge has entered the slot 32 still further.

The construction and operation of the embodiment of Figures 2 to 9 is otherwise the same as that of Figure 1 and corresponding reference numerals have been applied to corresponding parts.

WHAT WE CLAIM IS:- 1. A pedal-operated brake-applying mechanism for a braking system of an electrically driven vehicle having a first regenerative brake and a second friction brake, in which a single pedal is provided for operating both brakes, and the mechanism incoporates a lost-motion device for taking up the clearances of the second brake as the first brake is moved between an "off" and a fully applied condition in response to movement of the pedal through a first stage of travel, the lost-motion device being variable automatically in accordance with the degree of slack in the second brake whereby the clearances of the second brake are completely taken up at a changeover point at which the first brake is fully applied, whereafter the second brake is applied by continued movement of the pedal in the same direction and in a second stage.

2. A pedal-operated brake-applying mechanism according to Claim 1, in which the arrangement is such that the first stage of travel is sufficient to take up the braking clearances when the second brake is in a maximum permissible slack adjustment condition in which the second brake is fully actuated at the instant the pedal attains its position of maximum travel in a brakeapplying direction which is determined by the engagement of the pedal with a stop.

3. A pedal-operated brake-applying mechanism according to Claim 1 or Claim 2 in which the lost-motion device acts between the pedal and an operating member for the second brake and comprises a thrust transmitting member which is disposed in a gap between the operating member and an abutment on the pedal to reduce the effective length of the gap to a distance which can be taken up during the first stage of pedal travel irrespective of the braking clearances of the second brake so that when the changeover point is reached the thrust from the pedal can be applied directly to the operating member through the thrust member, the effective length of the gap to be taken up during the first stage of pedal travel being determined by the position of the thrust member which, in turn, is controlled by a linkage responsive to the braking clearances.

4. A pedal-operated brake-applying mechanism according to Claim 3, in which the linkage is arranged to move the thrust member in a direction to reduce the effective length of the gap during intitial movement of the pedal and until, at an intermediate point, the reaction on the second brake, indicating that the clearances have been taken up, becomes greater than the force applied to the linkage from the pedal.

5. A pedal-operated brake-applying mechanism according to Claim 4, in which a return spring is arranged to resist further angular movement of the pedal when the intermediate point is attained, the pedal previously acting, up to the intermediate point, on the linkage through the return spring.

6. A pedal-operated brake-applying mechansim according to any of Claims 3 to 5, in which the thrust member comprises a wedge which progressively reduces the effective length of the gap as it is moved by the linkage.

7. A pedal-operated brake-applying mechanism according to Claim 6, in which the linkage comprises a lever which is pivotally connected at one end to a stationary pivot for the pedal and at the opposite end to one arm of a bellcrank of which the other arm is connected through a link to the wedge, the bellcrank itself being pivotally connected to a substantially stationary pivot and the lever at an intermediate point in its lengh acting on the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 12. The inner ends of the slots 32 are defined by an abutment flange or platform 34 of the pedal 1, and the slots 32 and 33 are substantially equal in length to the width of the thicker, outer end of the wedge 21. The thinner, inner end of the wedge 21 is integral with an extension 35 of constant section which traverses the cylindrical extension 30 when the pedal is in the inoperative position illustrated in Figures 3 and 6. In this position the wedge 21 is completely withdrawn from the extension 30. It will be appreciated therefore that the length of the slot 33 minus the thickness of the extension 35 represents the lost-motion which it to be taken up during the first stage of travel of the pedal to achieve 100 per cent regenerative braking as the changeover part, assuming that no braking clearances of the friction brake are to be taken up during that pedal movement. This condition is illustrated in Figure 9 from which it will be observed that the wedge 21 has remained in the same initial position as Figure 6. Figures 7 and 8 indicate adjustment requirements. As illustrated in Figures 4 and 7 where 50 per cent regenerative braking has been achieved the wedge 21 has entered the slot 32 to reduce the lost-motion or the effective length of the slot 32 and, at 100 per cent regenerative braking where the operating rod 13 has moved further to take up all the clearances of the friction brake, as shown in Figures 5 and 8, the wedge has entered the slot 32 still further. The construction and operation of the embodiment of Figures 2 to 9 is otherwise the same as that of Figure 1 and corresponding reference numerals have been applied to corresponding parts. WHAT WE CLAIM IS:-

1. A pedal-operated brake-applying mechanism for a braking system of an electrically driven vehicle having a first regenerative brake and a second friction brake, in which a single pedal is provided for operating both brakes, and the mechanism incoporates a lost-motion device for taking up the clearances of the second brake as the first brake is moved between an "off" and a fully applied condition in response to movement of the pedal through a first stage of travel, the lost-motion device being variable automatically in accordance with the degree of slack in the second brake whereby the clearances of the second brake are completely taken up at a changeover point at which the first brake is fully applied, whereafter the second brake is applied by continued movement of the pedal in the same direction and in a second stage.

operating member, the arrangement being such that the lever moves angularly with the pedal to advance the operating member, at the same time acting through the bellcrank and the link to advance the wedge to reduce the effective length of the gap until the intermediate point is reached, whereafter the pedal moves angularly with respect to the lever until the changeover point is reached.

8. A pedal-operated brake-applying mechanism according to Claim 7, in which the operating member comprises a pushrod for operating the piston of an hydraulic master cylinder for applying the second brake, and an operating member for the first brake comprises a potentiometer to the casing of which the bellcrank is pivotally connected.

9. A pedal-operated brake-applying mechanism according to Claim 8, in which the casing is coupled to the body of the vehicle through a pivotally mounted springioaded support link which moves angularly against its spring loading when the pedal is moved angularly to apply the second brake, accompanied by bodily displacement of the casing.

10. A pedal-operated brake-applying mechanism substantially as herein described with reference to and as illustrated in Figure 1 of the accompanying drawings.

11. A pedal-operated brake-applying mechanism substantially as herein described with reference to and as illustrated in Figures 2 to 9 of the accompanying drawings.