Drum brake device

A drum brake device comprising:

• a driving force generating unit for generating a driving force responsive to application of brakes to a vehicle;
• a first shoe having a first contact surface proximate the inner peripheral surface of a rotary drum and being moved to contact the inner peripheral surface of the drum based on the driving force generated by the driving force generating unit;
• a second shoe having a second contact surface 3a proximate the inner peripheral surface of the drum and being moved in connection with the first shoe;
• a first lever having a contact portion with the first shoe and applying a load on the first shoe toward the inner peripheral surface of the drum based on a driving force of the driving force generating unit;
• a second lever having a contact portion with the second shoe and applying a load to the second shoe toward an inner peripheral surface of the drum based on a driving force of the driving force generating unit;
• a strut connecting the first lever and the second lever;
• an anchor member for receiving an anchor load generated by the first shoe or the second shoe;
• a third lever connected to a portion of the first lever between the connection portion of the first lever with the strut and the contact portion 4 of the first lever with the first shoe to feed back the load applied to the anchor member to the first lever;
• and
• a fourth lever which swings around a predetermined portion and has the anchor member disposed at one side of the predetermined portion and is connected to the third lever at another side of the predetermined portion;
• wherein the second lever swings around the support end portion of the second lever which is opposite to the contact portion thereof with the second shoe across the connection portion thereof to the strut;
• wherein the end portion of the first lever which is opposite to the contact portion with the first shoe across the connection portion to the strut is connected to an output lever to which the driving force of the driving force generating unit is output;
• wherein a distance from a center of the connection portion of the first lever with the strut to a center of the connection portion of the first lever with the third lever is w1, a distance from a center of the connection portion of the first lever with the strut to the contact portion of the first lever with the first shoe is expressed by La, and a distance from a center of the connection portion of the first lever with the strut to a center of the connection portion of the first lever with the output lever is expressed by La×m;
• wherein a distance from a center of the connection portion of the second lever with the strut to a center of the contact portion of the second lever with the second shoe is w1, a distance from a center of the connection portion of the second lever with the strut to a center of the support end portion of the second lever is expressed by n,
• wherein a distance from a center of a swing of the fourth lever to a center of the anchor member is 1, a distance from the center of the swing of the fourth lever to the center of the connection portion of the fourth lever with the third lever is expressed by Lb;
• and
• wherein the radius of the drum is expressed by r;
• wherein if the brakes are applied when the drum is rotated in the first direction F, the first and second contact surfaces contact the inner peripheral surface of the drum and the second shoe as a secondary shoe is pressed by the first shoe as a primary shoe to generate an anchor load which is applied to two portions of the contact portion of the second lever with the second shoe and the anchor member, and in this state, a force applied to the first shoe by the first lever via the contact portion of the first lever with the first shoe be Fa1, a force applied to the second shoe by the first shoe be Fax, a force applied to the second lever by the second shoe via the contact portion of the second shoe with the second lever be Fa2, a load applied to the anchor member by the second shoe be Fan, and a force applied to the first lever by the driving force generating unit be F0;
• further, a straight line passing the center of the drum is a reference line Z, a distance from the center of the anchor member to the reference line Z be an, a distance from the center of the anchor member to the center of the drum is an′, a distance from the contact portion of the first lever with the first shoe to the reference line Z be c1, a distance from a point of the first shoe at which a load is applied to the second shoe to the reference line Z is a1, a distance from a point of the second shoe at which a load is applied by the first shoe to the reference line Z is c2, a distance from the contact portion of the second lever with the second shoe to the reference line Z is a2, and a distance from a point of the second shoe to which a load is applied by the first shoe to the center of the anchor member is h;
• a servo ratio of the first shoe by the force Fa1 applied to the first shoe is BF1 and a servo ratio of the second shoe by the force Fax applied to the second shoe by the first shoe is BF2;
• A1, A2, B1, B2, D2 are expressed by the following equations:
• (Equation 1)
• A1(c2+r×BF2)(c1/a1+BF1×r/a1)
• (Equation 2)
• A2=La(1+m)
• (Equation 3)
• B1=a2−BF2(an−a2) r/h
• (Equation 4)
• B2=La×m(n+1)/n
• (Equation 5)
• D2=(La×m+1)/Lb
• wherein the lever ratios of the first lever, the second lever, and the forth lever are expressed based on a brake effectiveness factor BEFmof, which is expressed by the following equation 6, by the force F0 which the driving force generating unit applies to the first lever in the first direction F;
• Equation 6 is BEFmo =[BF1+{1+(an−a2)(an′×A2+D2×A1)/(an′×B2+D2×B1)/(c1/a1+BF1×r/a1)/h}BF2×(c1/a1+BF1×r/a1)]/{1+(A1×B2−A2×B1)/(an′×B2+D2×B1)/La/Lb}×m.