FORCE REDUCING PEDAL AND LINKAGE

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: 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 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 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.

Inventors: COSPIN SYLVAIN, COSPIN, SYLVAIN
Applicants: COSPIN SYLVAIN, DRAFTEX IND LTD, COSPIN, SYLVAIN, DRAFTEX INDUSTRIES LIMITED
Application year: 2000
Main classification: B60T7
IPC codes: B60T7, G05G1