Abstract:
A brake pedal apparatus including: (a) an operating pedal disposed pivotably about a first axis; (b) a pivot member disposed pivotably about a second axis and connected to the operating pedal via a link mechanism so as to be pivoted about the second axis in response to a depressing operation of the operating pedal; and (c) an output member for receiving an output generated by pivot motion of the pivot member. The link mechanism includes (i) a first connecting link connecting the operating pedal and the pivot member with first play, and (ii) a second connecting link connecting the operating pedal and the pivot member with second play. In a first region before a characteristic switching point of a pedal stroke of the operating pedal, the pivot member is pivoted through the first connecting link, while a lever ratio is changed according to a first lever ratio characteristic. In a second region beyond the characteristic switching point, the pivot member is pivoted through the second connecting link, while the lever ratio is changed according to a second lever ratio characteristic.

Description:
This application is based on Japanese Patent Application No. 2006-155860, the content of which is incorporated hereinto by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates in general to a brake pedal apparatus, and more particularly to such a brake pedal apparatus having a high degree of freedom in setting of a lever ratio characteristic. 
   2. Discussion of Prior Art 
   There is known a brake pedal apparatus having (a) an operating pedal which is disposed pivotably about a first axis, (b) a pivot member which is disposed pivotably about a second axis parallel to the first axis, and which is connected to the operating pedal via a link mechanism so as to be mechanically pivoted about the second axis in response to a depressing operation effected on the operating pedal; and (c) an output member which is to be mechanically pressed or pulled as a result of pivot motion of the pivot member. As an example of such a brake pedal apparatus, Patent Document 1 discloses an apparatus in which a lever ratio representative of a ratio of an output to a depression force acting on the operating pedal is changed in accordance with a pedal stroke. 
   Patent Document 1: JP-H7-205776A 
   Patent Document 2: JP-H10-29510A 
   However, in such a conventional brake pedal apparatus, since a characteristic of change of the lever ratio (lever ratio characteristic) is dependent on connected positions of the link mechanism, it is difficult to largely change the lever ratio halfway during the pedal stroke. Thus, the change in the lever ratio is not necessarily satisfactory. 
   Patent Document 2 discloses a technique of largely changing the lever ratio characteristic by changing a path for transmission of the depression force. According to an arrangement disclosed by this document, in a normal case, the depression force is transmitted from the operating pedal to an input rod of a brake booster via an elastic member. When the depression force applied to the operating pedal is increased, for example, in the event of failure of the brake booster, the depression force is transmitted from the operating pedal directly to the input rod of the brake booster. However, the disclosed arrangement is for changing the lever ratio characteristic in accordance with the depression force, rather than for largely changing the lever ratio in accordance with the pedal stroke during a normal operation of the operating pedal. Further, since the elastic member is arranged to receive the depression force at its portion that is offset from the input rod of the brake booster, the input rod can be easily stuck, thereby causing a risk of deterioration in efficiency of transmission of the depression force and durability of the brake pedal apparatus. 
   The present invention was made in the light of the background art discussed above. It is therefore an object of the invention to provide a brake pedal apparatus which is capable of changing the lever ratio by a large amount halfway during the pedal stroke without considerable deterioration in the efficiency of transmission of the depression force and the durability of the apparatus, and which has a high degree of freedom in setting of the lever ratio characteristic. 
   SUMMARY OF THE INVENTION 
   For achieving the above object, the first invention provides a brake pedal apparatus having: (a) an operating pedal which is disposed pivotably about a first axis; (b) a pivot member which is disposed pivotably about a second axis parallel to the first axis, and which is connected to the operating pedal via a link mechanism so as to be mechanically pivoted about the second axis in response to a depressing operation effected on the operating pedal; and (c) an output member which is to be mechanically pressed or pulled as a result of pivot motion of the pivot member, the brake pedal apparatus is characterized in that: (d) the link mechanism has a pair of first and second connecting links connecting the operating pedal and the pivot member with play; (e) in a first region before a predetermined characteristic switching point of a pedal stroke of the operating pedal, the pivot member is pivoted through via the first connecting link, and a lever ratio is changed according to a lever ratio characteristic  1  that is dependent on connected positions of the first connecting link; and in a second region beyond the predetermined characteristic switching point of the pedal stroke, the pivot member is pivoted through the second connecting link, and the lever ratio is changed according to a lever ratio characteristic  2  that is dependent on a connected position of the second connecting link. 
   The second invention is, in the brake pedal apparatus of the first invention, characterized in that (a) the first and second connecting links are connected to the operating pedal and the pivot member at a total of four connected positions that are set individually from each other, and in that (b) an elongated hole is provided in one of connecting portions of the operating pedal and the pivot member at which the operating pedal and the pivot member are connected to each of the first and second connecting links, such that the elongated hole provides the play. 
   In the brake pedal apparatus, in the first region before the characteristic switching point, the pivot member is pivoted through the first connecting link whereby the lever ratio is changed according to the lever ratio characteristic  1 . On the other hand, in the second region beyond the characteristic switching point, the pivot member is pivoted through the second connecting link whereby the lever ratio is changed according to the lever ratio characteristic  2 . The lever ratio characteristics  1  and  2  can be set depending on the connected positions of the first and second connecting links and individually from each other. The characteristic switching point, at which the lever ratio characteristic is switched from the lever ratio characteristic  1  to the lever ratio characteristic  2 , can be suitably set depending on the connected positions and the play of the first and second connecting links. 
   Thus, the lever ratio characteristic in the first region and that in the second region can be set independently of each other, and the characteristic switching point as a boundary of the first and second regions can be suitably set. It is therefore possible to incontinuously and largely change the lever ratio at an arbitrary position (characteristic switching point) of the pedal stroke, thereby improving a degree of freedom in setting of the lever ratio characteristic and providing a further excellent braking operation feeling. Further, the depression force is transmitted from the operating pedal to the pivot member through the first connecting link during the first region, and the depression force is transmitted from the operating pedal to the pivot member through the second connecting link during the second region, so that there is no risk of considerable deterioration in efficiency of transmission of the depression force and durability of the brake pedal apparatus, which deterioration would be caused in the event of the stuck due to the offset arrangement as in the above-described Patent Document 2. 
   In the second invention, the total of four connected positions at which the first and second connecting links are connected to the operating pedal and the pivot member are set individually from each other, so that the degree of freedom in setting of the lever ratio characteristics  1  and  2  is high. Further, since the play is established by the elongated hole that is provided in the connecting portion, each of the first and second connecting links is relatively movable within the elongated hole. The lever ratio characteristic is switched between the lever ratio characteristics  1  and  2 , when the first or second connecting link reaches an end portion of the elongated hole. Thus, the switching of the lever ratio characteristic can be stably and smoothly made as the depressing operation of the operating pedal is effected. 
   The first and second regions are set, for example, to correspond to a first half and a second half of the entire pedal stroke, respectively. However, each of the first and second regions does not necessarily have to correspond to a half of the entire pedal stroke, but may be suitably set, for example, such that one of the first and second regions corresponds to about one-third or less of the entire pedal stroke. Further, the lever ratio in the second region may be either larger or smaller than that in the first region. The brake pedal apparatus may be constituted by any one of various arrangements such as an arrangement in which the pedal stroke reaches the second region only when the operating pedal is largely depressed, for example, in case of a so-called “panic brake”, and the lever ratio is drastically increased or reduced in the second region. 
   The first and second connecting links may be are arranged to be parallel to each other, as seen in a front view perpendicular to the first and second axes, for example, in an initial state before a depressing operation is effected on the operating pedal. However, the first and second connecting links do not necessarily have to be parallel to each other. Further, the first and second connecting links may be arranged to intersect with each other, depending on the lever ratio characteristic  1  and the lever ratio characteristic  2 . 
   Further, in addition to the first and second connecting links, a third connecting link may be provided to connect the operating pedal and the pivot member with certain play, so that the pedal stroke of the operating pedal is divided into three regions. According to this arrangement, in the first region, the pivot member is pivoted through the first connecting link in the first region whereby the lever ratio is changed according to the lever ratio characteristic  1 , the pivot member is pivoted through the second connecting link in the second region whereby the lever ratio is changed according to the lever ratio characteristic  2 , and the pivot member is pivoted through the third connecting link in a third region whereby the lever ratio is changed according to a lever ratio characteristic  3 . 
   The total of four connected positions at which the first and second connecting links are connected to the operating pedal and the pivot member may be different from each other. However, one of the operating pedal and the pivot member may have a common connecting portion that provides both of the connecting portions of the one of the operating pedal and the pivot member at which the one of the operating pedal and the pivot member are connected to the respective first and second connecting links (through a common connecting pin, for example). In this case, the play may be provided in each of the connecting portions of the other of the operating pedal and the pivot member at which the other of the operating pedal and the pivot member are connected to the respective first and second connecting links. 
   In the second invention, the elongated hole providing the play is provided in one of the connecting portions of the operating pedal and the pivot member at which the operating pedal and the pivot member are connected to each of the first and second connecting links. However, the first invention may be carried out, for example, with an arrangement in which the elongated holes are provided in both of the operating pedal and the pivot member, or with an arrangement in which the play is provided by a cutout and/or an engaging protrusion. Further, the elongated hole providing the play may be provided in the first connecting link and/or the second connecting link, so that the play is provided by engagement of the elongated hole with a connecting pin that is provided in the operating pedal and/or the pivot member. The elongated hole may take any one of various shapes such as straight linear shape and arcuate shape. 
   The output member is provided by, for example, a rod of a brake booster that is to be pressed in response to a depressing operation effected on the operating pedal. However, the output member may be provided by a brake cable that is to be pulled in response to the depressing operation. Further, the present invention is applicable also to an electric brake system in which a braking force is controlled by electrically detecting load applied to the output member and displacement of the output member. 
   The brake pedal apparatus of the present invention is advantageously applied to a service braking system. However, the brake pedal apparatus can be applied to a parking braking system, too. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view schematically showing a brake pedal apparatus as an embodiment of the present invention. 
       FIGS. 2A and 2B  are views showing in enlargement a link mechanism portion of the embodiment of  FIG. 1 , wherein  FIG. 2A  shows a state in which the operating pedal is in its initial position, while  FIG. 2B  shows a state in which the operating pedal is depressed to a characteristic switching point. 
       FIGS. 3A-3C  are views explaining a lever ratio characteristic of the embodiment of  FIG. 1 , wherein  FIG. 3A  explains a lever ratio RL 1  in a first region,  FIG. 3B  explains a lever ratio RL 2  in a second region, and  FIG. 3C  shows an example of the lever ratio characteristic in the entirety of the pedal stroke. 
       FIG. 4  is a view corresponding to  FIG. 2A , explaining another embodiment of the present invention and showing in enlargement the link mechanism portion of the another embodiment while the operating pedal is in the initial position. 
       FIG. 5  is a view corresponding to  FIG. 2A , explaining still another embodiment of the present invention and showing in enlargement the link mechanism portion of the still another embodiment while the operating pedal is in the initial position. 
       FIGS. 6A and 6B  are views corresponding to the views of  FIGS. 2A and 2B , and explaining still another embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   There will be described in detail embodiments of the present invention, with reference to the drawings. 
     FIG. 1  is a front view schematically showing an embodiment of the invention in the form of a brake pedal apparatus  10  that is to be used for a service braking system of a vehicle. The front view of  FIG. 1  shows the brake pedal apparatus  10  as installed on the vehicle, and is a view as seen in a lateral direction of the vehicle. This brake pedal apparatus  10  is provided in brackets  12 ,  14  that are integrally fixed to a body of the vehicle. An operating pedal  18  is provided in the bracket  12 , so as to be pivotable about an axis of a first support shaft  16  that is substantially horizontal. The brackets  12 ,  14  are connected through a second support shaft  20  on which a pivot member  22  is mounted to be pivotable about an axis of the second support shaft  20 . A link mechanism  24  is provided to bridge between the operating pedal  18  and the pivot member  22 . The first and second support shafts  16 ,  20  are held in parallel to each other, and the axes of the first and second support shafts  16 ,  20  correspond to a first axis and a second axis, respectively. 
   The operating pedal  18 , when a pedal pad  26  provided in its lower end portion is depressed by a driver of the vehicle, is pivoted clockwise about the first support shaft  16  as seen in  FIG. 1 , thereby causing the pivot member  22  to be mechanically pivoted counterclockwise about the second support shaft  20 , through the link mechanism  24  that is connected to an upper end portion of the operating pedal  18 . A rod  30  of a brake booster is connected to an upper end portion of the pivot member  22 , so as to be pivotable relative to the pivot member  22  about an axis of a connecting pin  28  that is parallel to the second support shaft  20 . As a result of the pivot motion of the pivot member  22 , the rod  30  is mechanically pressed leftward as seen in  FIG. 1 , and pushes a push rod of a master cylinder (not shown), for generating a hydraulic brake pressure. The rod  30  is biased to project outwardly of the brake booster. Therefore, when the pedal pad  26  is released from the depressing operation effected thereon, the biasing force of the rod  30  causes the pivot member  22  to be pivoted back clockwise about the second support shaft  20 , and the operating pedal  18  to be pivoted back counterclockwise about the first support shaft  16  so as to be held in its initial position as shown in  FIG. 1 . It is noted that the rod  30  corresponds to an output member. 
   As shown in  FIGS. 2A and 2B , the link mechanism  24  is equipped with a pair of first and second connecting links  32 ,  34  that are provided to bridge between an upper end portion of the operating pedal  18  and a lower end portion of the pivot member  22 . Each of the first and second connecting links  32 ,  34  is provided by a pair of members that are disposed on opposite sides of the operating pedal  18  or pivot member  22  (on front and rear sides of drawing sheet of  FIGS. 2A and 2B ). The first and second connecting links  32 ,  34  are integrally connected at their longitudinally opposite end portions to the operating pedal  18  and the pivot member  22  through connecting pins  36 ,  38 ,  40 ,  42  that are parallel to the first and second support shafts  16 ,  20 . The connecting pins  36 ,  40  connecting the first and second connecting links  32 ,  34  to the operating pedal  18  are pivotably received in respective holes formed in the operating pedal  18 , so as to be connected to certain portions of the operating pedal  18 . Meanwhile, the connecting pins  38 ,  42  connecting the first and second connecting links  32 ,  34  to the pivot member  22  are movably received in respective straight-linear-shaped elongated holes  44 ,  46  formed in the pivot member  22 , so that certain play is provided by the elongated holes  44 ,  46 . 
   The first and second connecting links  32 ,  34  are connected to the operating pedal  18  and the pivot member  22  at connected positions (positions of the connecting pins  36 ,  38 ,  40 ,  42 ) that are determined such that the first and second connecting links  32 ,  34  are parallel to each other in a state, as shown in  FIG. 2A , in which the operating pedal  18  is in its initial position. The elongated holes  44 ,  46  are parallel to each other and have respective lengths such that, in the state of the initial position of the operating pedal  18 , the elongated hole  44  overlaps with the first connecting link  32  while the elongated hole  46  is aligned with an extension of the second connecting link  34 . In this state of the initial position, the connecting pin  38  is held in contact with an end portion of the elongated hole  44 , and the pivot member  22  is biased clockwise about the second support shaft  20  by a biasing force of the rod  30 , whereby the operating pedal  18  is biased counterclockwise about the first support shaft  16  through the first connecting link  32 , so as to be held in the initial position. When the operating pedal  18  is depressed, the pivot member  22  is pivoted counterclockwise about the second support shaft  20  through the first connecting link  32  whereby the rod  30  is pressed leftward. The elongated hole  46  provided for the connection of the second connecting link  34  with the pivot member  22  provides certain play in a direction of the depressing operation of the operating pedal  18 , i.e., in the counterclockwise direction about the second support shaft  20  in the state of initial position shown in  FIG. 2A , so that the connecting pin  42  of the second connecting link  34  is merely moved within the elongated hole  46  until the operating pedal  18  reaches the characteristic switching point shown in  FIG. 2B  as a result of the depressing operation effected on the operating pedal  18 . 
   Therefore, between the initial position shown in  FIG. 2A  and the characteristic switching point shown in  FIG. 2B , a depression force applied to the operating pedal  18  is transmitted to the pivot member  22  through the first connecting link  32 , while a lever ratio is changed according to a lever ratio characteristic  1  (first lever ratio characteristic) that is dependent on the connected positions in which the first connecting link  32  is connected to the operating pedal  18  and the pivot member  22 . That is, as shown in  FIG. 3C , in a first region in which the pedal stroke of the operating pedal  18  does not yet reach the characteristic switching point SP 1 , the depression force is transmitted by the first connecting link  32  while the lever ratio is changed according to the lever ratio characteristic  1 . In this first region, the lever ratio RL 1  is expressed by the following expression (1) where “L” represents a pedal arm length corresponding to a distance from the first support shaft  16  to the pedal pad  26 , “R 1 ” represents a moment length corresponding to a distance from the first support shaft  16  to the first connecting link  32 , “R 2 ” represents a moment length corresponding to a distance from the second support shaft  20  to the first connecting link  32 , and “R 3 ” represents a moment length corresponding to a distance from the second support shaft  20  to the rod  30 , as shown in  FIG. 3A . Thus, the lever ratio RL 1  is continuously changed as the moment lengths R 1 , R 2 , R 3  are changed in accordance with the pedal stroke. It is noted that the lever ratio characteristic  1  shown in  FIG. 3C  is merely an example and does not necessarily correspond to the lever ratio RL 1  shown in  FIG. 3A .
 
 RL 1=( L/R 1)×( R 2/ R 3)  (1)
 
   On the other hand, when the pedal stroke of the operating pedal  18  reaches the characteristic switching point shown in  FIG. 2B , the connecting pin  42  of the second connecting link  34  is brought into contact with an end portion of the elongated hole  46  while the connecting pin  38  of the first connecting link  32  is separated from the above-described end portion of the elongated hole  44 , so that the pivot member  22  comes to be pivoted counterclockwise about the second support shaft  20  through the second connecting link  34 , whereby the rod  30  is pressed leftward by the pivot member  22 . The elongated hole  44  provided for the connection of the first connecting link  32  with the pivot member  22  provides certain play in a direction opposite to the direction of the depressing operation of the operating pedal  18 , i.e., in the clockwise direction about the second support shaft  20 , so that the connecting pin  38  of the first connecting link  32  is merely moved within the elongated hole  44  when the operating pedal  18  is further depressed from the characteristic switching point in the state of the characteristic switching point shown in  FIG. 2B . The elongated hole  44  is provided with a size sufficient to provide certain play between the hole  44  and the connecting pin  38  even where the operating pedal  18  is strongly depressed. 
   Therefore, beyond the characteristic switching point shown in  FIG. 2B , the depression force applied to the operating pedal  18  is transmitted to the pivot member  22  through the second connecting link  34 , while the lever ratio is changed according to a lever ratio characteristic  2  (second lever ratio characteristic) that is dependent on the connected positions in which the second connecting link  34  is connected to the operating pedal  18  and the pivot member  22 . That is, as shown in  FIG. 3C , in a second region in which the pedal stroke of the operating pedal  18  exceeds the characteristic switching point SP 1 , the depression force is transmitted by the second connecting link  34  while the lever ratio is changed according to the lever ratio characteristic  2 . In this second region, the lever ratio RL 2  is expressed by the following expression (2) where “L” represents the pedal arm length corresponding to the distance from the first support shaft  16  to the pedal pad  26 , “r 1 ” represents the moment length corresponding to the distance from the first support shaft  16  to the second connecting link  34 , “r 2 ” represents the moment length corresponding to the distance from the second support shaft  20  to the second connecting link  34 , and “r 3 ” represents the moment length corresponding to the distance from the second support shaft  20  to the rod  30 , as shown in  FIG. 3B . Thus, the lever ratio RL 2  is continuously changed as the moment lengths r 1 , r 2 , r 3  are changed in accordance with the pedal stroke. It is noted that the lever ratio characteristic  2  shown in  FIG. 3C  is merely an example and does not necessarily correspond to the lever ratio RL 2  shown in  FIG. 3B .
 
 RL 2=( L/r 1)×( r 2/ r 3)  (2)
 
   The lever ratio characteristics  1  and  2  can be set depending on the connected positions of the first and second connecting links  32 ,  34  (positions of the connecting pins  36 ,  38 ,  40 ,  42 ) and individually from each other. The characteristic switching point SP 1 , at which the lever ratio characteristic is switched from the lever ratio characteristic  1  to the lever ratio characteristic  2 , can be suitably set by adjusting the connected positions of the first and second connecting links  32 ,  34  and the length of the elongated hole  46 . In the present embodiment, the characteristic switching point SP 1  is set such that the lever ratio characteristic is switched between the lever ratio characteristics  1  and  2  in an intermediate position of the pedal stroke during an ordinary braking operation. 
   Thus, in the brake pedal apparatus  10  of the present embodiment, the lever ratio characteristic in the first region and that in the second region can be set independently of each other, and the characteristic switching point SP 1  as a boundary between the first and second regions can be suitably set. It is therefore possible to incontinuously and largely change the lever ratio at an arbitrary position (characteristic switching point SP 1 ) of the pedal stroke, thereby improving a degree of freedom in setting of the lever ratio characteristic and providing a further excellent braking operation feeling. 
   Further, the depression force is transmitted from the operating pedal  18  to the pivot member  22  through the first connecting link  32  during the first region, and the depression force is transmitted from the operating pedal  18  to the pivot member  22  through the second connecting link  34  during the second region, so that there is no risk of considerable deterioration in efficiency of transmission of the depression force and durability of the brake pedal apparatus, which deterioration would be caused in the event of the stuck due to the offset arrangement as in the above-described Patent Document 2. 
   Further, in the present embodiment, the total of four connected positions at which the first and second connecting links  32 ,  34  are connected to the operating pedal  18  and the pivot member  22  are set individually from each other, so that the degree of freedom in setting of the lever ratio characteristics  1  and  2  is high. 
   Further, since the play is established by each of the elongated holes  44 ,  46 , each of the first and second connecting links  32 ,  34  is relatively movable within a corresponding one of the elongated holes  44 ,  46 . The lever ratio characteristic is switched between the lever ratio characteristics  1  and  2 , when the connecting pin  42  of the second connecting link  34  reaches the end portion of the elongated hole  46 . Thus, the switching of the lever ratio characteristic can be stably and smoothly made as the depressing operation of the operating pedal  18  is effected. 
   In the above-described embodiments, the connected positions at which the first and second connecting links  32 ,  34  are connected to the operating pedal  18  and the pivot member  22  are set such that the first and second connecting links  32 ,  34  are held in parallel to each other in the initial state. However, as in a link mechanism  50  shown in  FIG. 4 , the connected positions may be set such that the first and second connecting links  32 ,  34  are unparallel to each other in the initial state. Each of the elongated holes  44 ,  46  is elongated in a direction that may be determined such that each of the elongated holes  44 ,  46  provides certain play during the depressing operation of the operating pedal  18 , namely, such that each of the elongated holes  44 ,  46  has a predetermined dimension as measured in a circumferential direction about a center in the form of the axis of the second support shaft  20 . 
   In the above-described embodiments, the total of four connected positions at which the first and second connecting links  32 ,  34  are connected to the operating pedal  18  and the pivot member  22  are different from each other. However, as in a link mechanism  60  shown in  FIG. 5 , the operating pedal  18  may have a common connecting portion that provides both the connecting portions of the operating pedal  18  at which the operating pedal  18  is connected to end portions of the respective first and second connecting links  32 ,  34  that are located on the side of the operating pedal  18 , through a single connecting pin  62 . 
   In the above-described embodiments, the elongated hole  44  is provided in the pivot member  22 . However, as in a link mechanism  70  shown in  FIGS. 6A and 6B , an elongated hole  72  may be provided in the operating pedal  18 , such that the connecting pin  36  of the first connecting link  32  is connected to the operating pedal  18  with certain play existing between the first connecting link  32  and the operating pedal  18 , while the connecting pin  38  of the first connecting link  32  is connected to a certain portion of the pivot member  22 . Similarly, the elongated hole  46  provided for the connection of the second connecting link  34  may be provided in the operating pedal  18  rather than in the pivot member  22 . Further, such elongated holes may be provided in both of the operating pedal  18  and the pivot member  22 . 
   The embodiments of the present invention have been described in detail with reference to the drawings. However, the described embodiments are merely embodied forms, and the present invention can be embodied with various modifications and improvements on the basis of knowledge of those skilled in the art.