WO2001038151A1

WO2001038151A1 - Force reducing pedal and linkage

Info

Publication number: WO2001038151A1
Application number: PCT/GB2000/004393
Authority: WO
Inventors: Sylvain Cospin
Original assignee: Draftex Industries Limited
Priority date: 1999-11-20
Filing date: 2000-11-17
Publication date: 2001-05-31
Also published as: EP1268246A1; GB9927427D0; GB2356443A; GB2356443B; AU1405701A

Abstract

A control pedal for a vehicle such as a brake pedal comprising an upper member (6) and a lower member (9) one or both of which are formed from a plastics material, and which are hingedly coupled together and in combination form an arm of the pedal, and a foot plate (10) located at a first end of the arm, the distal end of the arm being arranged for pivotal mounting on a vehicle and the hinged coupling between the two members (6, 9) permitting additional movement of the lower member (9) relative to the upper member (6) in the operating direction of the pedal, the pedal further including biasing means (14) arranged to restrict the additional movement when the force applied to the foot pedal is below a predetermined threshold whereby when a force is applied to the foot pedal which is above the predetermined threshold, the lower member (9) comes into contact with a fixed part (17) of the vehicle body.

Description

FORCE REDUCING PEDAL AND LINKAGE

This invention relates to a control pedal and a control linkage for a vehicle.

GB-A-2322836 describes pedals which are designed to deform so that in an accident,

if a driver's foot comes into contact with the pedal, the driver's foot is not injured.

US 4005617 describes a pedal arm which comprises upper and lower members

hingedly coupled together to permit additional movement of the lower member

relative to the upper member, although the purpose of the additional movement is to

provide reduced braking during the initial phase of the braking.

According to the invention there is provided a control pedal, for a vehicle such as a

brake pedal comprising an upper member and a lower member, which are hingedly

coupled together and in combination form an arm of the pedal, and a foot plate located

at a first end of the arm, the distal end of the arm being arranged for pivotal mounting

on a vehicle and the hinged coupling between the two members permitting additional

movement of the lower member relative to the upper member in the operating

direction of the pedal, the pedal further including biasing means arranged to prevent

additional movement until the force applied to the foot pedal exceeds a predetermined

force threshold, characterised in that the lower member comes into contact with a

fixed part of the vehicle body after the additional movement and the additional

movement requires a force applied to the foot pedal against the biasing means which is different from that applied to the foot pedal prior to exceeding the predetermined

force threshold.

According to a second aspect of the invention there is provided a control linkage for

coupling a vehicle control pedal such as a brake pedal to a vehicle mechanism such

as a brake servo, comprising pedal fixing means for coupling to a vehicle pedal,

mechanism fixing means for coupling to a vehicle mechanism to be controlled, and

biasing means arranged to bias the pedal fixing means and mechanism fixing means

into a first position, the linkage is arranged to move towards a second position in

which the pedal fixing means and mechanism fixing means are closer together than

in the first position when a force is applied between the pedal fixing means and

mechanism fixing means which exceeds a predetermined threshold, characterised in

that the movement towards the second position requires a different force for

displacement against the bias between the pedal fixing means and the mechanism

fixing means to be applied which is different from that force required before

exceeding the pre-determined threshold.

According to a third aspect of the invention there is provided a control mechanism,

comprising the combination of a foot pedal and a control linkage for coupling to a

vehicle mechanism such as a brake servo and for applying a force to the vehicle

mechanism, characterised in that the combination is arranged to deform in use when

a force is applied in the operating direction which exceeds a predetermined threshold, o so that the force required to be applied to the foot pedal to operate the vehicle

mechanism prior to deformation is different from the force required to provide further

operation of the vehicle mechanism after deformation whereby the force applied to the

vehicle mechanism is limited to a predetermined maximum applied force.

Embodiments of pedals in accordance with the invention will now be described by

way of example with reference to the drawings in which:

Figure 1 is a perspective view of a known pedal;

Figure 2 is a schematic side elevation of a pedal in accordance with the invention;

Figure 3 is a graph showing force on the foot plate of the pedal illustrated in Figure

2 against pedal deformation;

Figure 4 is a graph showing force on the foot plate of the pedal illustrated in Figure

2 against force on the upper arm of that pedal:

Figure 5 is a schematic side elevation of a buffer in accordance with the invention;

Figure 6 is a schematic side elevation of an alternative pedal in accordance with the

invention; 1/38151

Figure 7 is a schematic cross section through a linkage in accordance with the

invention;

Figure 8 is a schematic cross section through a brake servo mechanism incorporating

the linkage illustrated in Figure 7;

Figure 9 is a schematic cross section through a modified linkage in accordance with

the invention;

Figure 10 is a graph showing force on the foot plate of a pedal connected to the

linkage illustrated in Figure 9;

Figure 11 is a schematic perspective view of a linkage in accordance with the

invention;

Figure 12 is a schematic cross section of the linkage illustrated in Figure 11 ; and

Figure 13 is an exploded view of a pedal, servo mechanism and the linkage illustrated

in Figure 11.

The known pedal illustrated in Figure 1 has a pivot tube 1 located at one end of a main

arm 2. At the other end of the main arm 2 is a foot plate 3. The pedal is mounted to a vehicle by the pivot tube 1 and is caused to move about the pivot tube 1 by force

applied to the foot plate 3. A control linkage 5 is pivotally mounted at point 4 partwa}

along the main arm 2. Force applied to the foot plate 3 is multiplied

the lever

arrangement formed by the main arm 2 and the relative locations of the pi\ ot point 4

and pivot tube 1. and is transmitted to a mechanism to be controlled such as a brake

servo or clutch mechanism via the control linkage 5.

In an emergency . a driver may apply a force of the order of 250 deca-newtons to the

foot plate 3. This after multiplication by the lever arrangement, may cause a force of

the order of a 1000 deca-newtons to be applied to the vehicle brake servo. However,

the effort which is required for full operation of the brakes is typically of the order of

18 deca-newtons at the foot plate. Pressure applied at higher levels than this usually

results in the operation of an ABS system or in skidding of one or more wheels of the

vehicle.

Although the high forces generated by the lever system under emergency have no use.

it is necessary to design the braking system and the pedal system to withstand such

high forces. This has implications for the construction of the pedal and braking

system. Plastic materials are not generally used as brake pedals as softer plastic

materials will deform over time from repeated use. Harder plastics may be too brittle

over the full temperature range of the vehicle and so suffer catastrophic fracture with

a resultant loss of brakins function. The invention described below allows a pedal to be used which is made of a material

other than metal (plastics for example) and thus allows the pedal to be lighter and

cheaper to manufacture. A suitable pedal may be based on the pedal described in our

co-pending application GB-A-232551 1.

With reference to Figure 2, a pedal is shown which limits the maximum force

transmitted to a vehicle control system such as the brake or clutch system. This allows

the size and therefore cost, of the braking or clutch system to be reduced.

Furthermore, foot pedals made from plastic materials may also be used. The

maximum force is limited to ensure failure of the pedal does not occur due to the

vehicle operating too far below the glass transition temperature of the plastic material

and so fracturing in use.

The general principle is to direct two different levels of force to different parts of the

vehicle. Part of the force is directed to the mechanism to be controlled and the surplus

force is directed to the body of the vehicle.

With reference to Figure 2, an upper pedal arm 6 is rotatably connected to the vehicle

body about point 7. The upper arm 6 also includes a hinge point 8 for the connection

of a control linkage to transmit force to a mechanism such as a brake servo.

A lower arm 9 has a foot plate 10 which is formed at the lower part of the lower arm 9. The lower arm 9 is hingedly connected to the upper arm 6 by an axle 1 1. A further

connection between the upper and lower arms 6 and 9 is made by co-operating hooks

13 and 12 on the upper and lower arms respectively.

The hooks 12 and 13 permit rotation of the lower arm 9 about the axle 1 1 generally

in the direction A. They prevent such rotation in the opposite direction.

A compression spring 14 is located on lugs 15 and 16 formed respectively on the

upper and lower arms 6 and 9. The compression spring acts against the hooks 12 and

13 and acts to rotate the lower arm 9 in the opposite direction to arrow A.

The compression spring 14 is precompressed so that the upper and lower arms 6 and

9 are held generally in the position shown in Figure 2 until a force is applied to the

foot plate 10 which overcomes the precompression of the spring 14. Thus until the

precompression of the spring 14 is overcome, the pedal acts in a generally

conventional way and transmits effort applied to the foot plate 10 to a control linkage

connected to the pivot point 8.

When excess force is applied to the foot plate 10, the lower arm 9 is allowed to pivot

about axle 1 1 and eventually comes into contact with a part of the vehicle body 17.

The effect of this is shown in the graph of Figure 3. At point A, no effort is applied to the foot plate 10. Along the line A to B, increasing force is applied to the foot plate

but no deformation of the pedal occurs. This situation is shown in Figure 2 where all

force applied to the foot plate 10 is applied to the mechanism of the vehicle which is

being controlled.

At point B, the force applied to the foot plate 10 is just enough to overcome the

precompression of the spring 14. This is preferably adjusted to occur at a point where

all the force necessary to operate the vehicle mechanism has already been applied via

the pivot point 8. Thus the pedal is allowed to deform by compression of the spring

14. At point C, the lower arm 9 comes into contact with the part of the vehicle 17 and

the deformation of the pedal ceases. All further force applied to the foot plate 10 is

transmitted to the vehicle body at 17.

Figure 4 shows the force transmitted by the pedal against the force applied to the foot

plate 10. The reference letters used are the same as those used in Figure 3. Thus it will

be seen that beyond point C (at which point the lower arm 9 is in contact with the

vehicle body at 17) no additional force is transmitted to the vehicle mechanism.

In order to adjust the maximum force transmitted to the vehicle mechanism, the point

at which the lower arm 9 comes into contact with the vehicle body at 17 may be

adjusted, for example, by providing an adjustable buffer of the form shown in Figure

5. By adjusting the height of the buffer, the point at which the pedal comes into contact with the buffer may be adjusted which has the effect of adjusting the position

of point C in graph 4. The buffer may include side wings 17 and 18 which serve to

centralise the pedal laterally.

It will be appreciated that the compression spring 14 may be replaced by any generally

resilient compressible material or biasing means. Typical examples are a leaf spring,

a gas spring, a torsion spring, a tension spring, a torsion bar or elastomeric washers.

Figure 6 shows an alternative arrangement for the pedal in which a tension spring 20

is used. In this case, it is not necessary to have inter-engaging hooks 12 and 13 since

the spring does not need to be held in compression. Instead, the spring is pretensioned

and is held in this state by abutting surfaces 22 and 24 on the upper and lower arms

6 and 9 respectively.

With reference to Figure 7, a force reducing effect may instead be achieved using a

generally conventional pedal 50 having a foot plate 52 which pivots on the vehicle

body at pivot point 54. The leverage provided by the pedal 50 is applied to a brake

servo 56 via a control linkage 58.

The control linkage 58 is operable to transmit force from the pedal 50 to the servo 56

until a predetermined maximum force is reached at which point the distance between

the pedal fixing point 60 and the servo fixing point 62 at the distal end of the linkage 58 begins to reduce. This allows the pedal 50 to come into contact with a part of the

vehicle 17 as described above.

In order to achieve this effect, the control linkag 58 has an outer member 64 which

carries the servo fixing means 62 and an inner member 66 slidably mounted within the

outer member 64. The inner member 66 carries the pedal fixing means 60. A wall 68

formed across the inside of the outer member 64 provides an end stop and locating

lugs 70 for a compression coil spring 72. The other end of the coil spring 72 acts on

the inner member 66 to bias the inner member 66 away from the servo fixing point 62.

The inner member 66 is held within the outer member 64 by formations 74. Thus the

coil spring 72 is held under precompression.

When a force is applied to the foot plate 52 of the pedal 50 which (after taking

account of the lever ratios of the pedal ) is sufficient to overcome the precompression

of the coil spring 72. the inner member 66 begins to telescope into the outer member

64. This corresponds to point B on the graph of Figure 3. Thereafter, force continues

to be transmitted to the servo 56 and at the same time, the pedal moves towards the

part of the vehicle 17. At point C. the pedal 50 comes into contact with the part of the

vehicle 17 and no additional force is transmitted to the brake servo 56.

Figure 8 shows a modification in which the servo fixing means 62 is dispensed with and instead the linkage 58 forms an integral part of the servo mechanism 56.

With reference again to Figure 4, it is noted that at point B, the maximum force

necessary to operate the brake servo is applied. However, additional force is applied

to the brake servo until the pedal reaches the part of the vehicle 17. In order to reduce

this additional, unnecessary force, a modified linkage 58 may be used as shown in

Figure 9. This includes a damper arrangement 80 coupled effectively in series with

the compression spring 72. The effect of this damper 80 is shown in the graph of

Figure 10. It will be seen that the additional force transmitted between the point B at

which the spring 72 begins to compress and the point C at which the pedal 50 reaches

the part of the vehicle 17, is much reduced. This provides dual-rate resistance to pedal

movement and allows further cost savings to be made in the manufacture of the brake

servo and braking system. The damper arrangement 80 could be replaced by another

spring or other biassing means.

Figure 1 1 shows one form of the linkage 58. A typical cross-section is shown in

Figure 12.

Figures 13 shows the linkage 58 of Figure 13 in an exploded view ready for assembly

to a pedal 50 and a brake servo 56.

Claims

1. A control pedal for a vehicle such as a brake pedal, comprising an upper

member (6) and a lower member (9), which are hingedly coupled together and in

combination form an arm of the pedal, and a foot plate (10) located at a first end of

the arm, the distal end of the arm being arranged for pivotal mounting on a vehicle and

the hinged coupling between the two members (6,9) permitting additional movement

of the lower member (9) relative to the upper member (6) in the operating direction

of the pedal, the pedal further including biasing means (14) arranged to prevent the

fixed part of the vehicle body after the additional movement and the additional

movement requires a different force applied to the foot pedal against the biasing

means (14) which is different from that applied to the foot pedal prior to exceeding

the predetermined force threshold.

2. A control pedal according to claim 1, wherein the biasing means (14) is a

compression spring and wherein the upper and lower members (6,9) include co¬

operating formations (12,13) which restrain movement of the lower member (9)

relative to the upper member (6) in a direction opposite to the operating direction of

the pedal.

3. A control pedal according to claim 1 or claim 2, wherein the cooperating formations (12,13) are arranged to hold the lower member (9) in position once a

predetermined position relative to the upper member (6) has been reached during the

additional movement.

4. A control pedal according to any preceding claim, wherein the biasing means

(14,20) is a tension spring (20) connected between upper and lower members (6,9).

5. A control pedal according to any preceding claim, including a buffer for fixing

to the vehicle body and arranged to receive the lower member (9) when the lower

member (9) comes into contact with the vehicle body.

6. A control pedal according to claim 5, wherein the buffer includes guide

formations (18) extending generally away from the vehicle body arranged to reduce

lateral movement of the lower member (9) when this is in contact with the buffer.

7. A control pedal according to claim 5 or claim 6, wherein the buffer is

adjustable to vary the point in the travel of the lower member (9) at which the lower

member (9) comes into contact with the buffer.

8. A control pedal according to any of claims 1 to 3 or 5 to 7, wherein the biasing

means (14,20) is selected from the group containing a block of elastomeric material,

a gas spring, a torsion spring, a torsion bar and a leaf spring.

9. A control pedal according to any preceding claim, wherein the upper and lower

members (6,7) are hingedly connected by a flexible plastics material.

10. A control pedal according to any preceding claim wherein the biassing means

(14,20) has a spring constant which varies depending on the rate of movement of the

lower member (9) relative to the upper member (6), the force applied to the foot plate

( 10) and/or the distance between the lower member (9) and the fixed part of the

vehicle body (17).

11. A control pedal according to any preceding claim, wherein one or both of the

upper and lower members (6,9) are formed from a plastics material.

12. A control linkage (58) for coupling a vehicle control pedal such as a brake

pedal (50) to a vehicle mechanism such as a brake servo (56), comprising pedal fixing

means (60) for coupling to a vehicle pedal, mechanism fixing means (62) for coupling

to a vehicle mechanism to be controlled, and biasing means (72) arranged to bias the

pedal fixing means (62) and mechanism fixing means into a first position, the linkage

(58) is arranged to move towards a second position in which the pedal fixing means

(60) and mechanism fixing means (62) are closer together than in the first position

when a force is applied between the pedal fixing means (60) and mechanism fixing

means (62) which exceeds a predetermined threshold, characterised in that the

movement towards the second position requires a force for displacement against the bias between the pedal fixing means (60) and the mechanism fixing means (62) to be

applied which is different from that force required before exceeding the pre¬

determined threshold.

13. A linkage (58) according to claim 12, including a generally cylindrical outer

member (64) and a generally cylindrical inner member (66) slidably mounted within

the outer member (64). the pedal fixing means (60) being formed at one end of the

inner or outer member (60,62) and the mechanism fixing means (62) being formed at

one end of the other of the inner or outer member (60,62) whereby the movement

towards the second position is achieved by the inner member (66) sliding into the

outer member (64).

14. A linkage (58) according to claim 13, including a compression spring (72)

arranged to provide a biasing force between the inner and outer members (64,66)

directed towards the first position.

15. A linkage (58) according to any of claims 12 to 14. further including damping

means (80) arranged to vary the rate of movement from the first to the second position

for a given applied force between the pedal fixing means (60) and mechanism fixing

means (62).

16. A linkage (58) according to any of claims 12 to 15, which forms an integral part of a brake servo mechanism (56).

17. A control mechanism, comprising the combination of a foot pedal (50) and a

control linkage (58) for coupling to a vehicle mechanism such as a brake servo (56)

and for applying a force to the vehicle mechanism, characterised in that the

combination is arranged to deform in use when a force is applied in the operating

direction which exceeds a predetermined threshold, so that the force required to be

applied to the foot pedal (50) to operate the vehicle mechanism prior to deformation

is different from the force required to provide further operation of the vehicle

mechanism after deformation whereby the force applied to the vehicle mechanism is

limited to a predetermined maximum applied force.