JP4936012B2 - Stroke simulator - Google Patents

Description

  The present invention relates to a stroke simulator used in a brake-by-wire that electronically controls braking of an automobile.

  In the brake-by-wire system, the brake pedal only changes the braking deceleration intended by the driver into an electrical signal, which is irrelevant to the actual braking, but in order to improve the driver's braking feeling, the conventional hydraulic brake The pedal simulator / reaction force relationship that resembles the system is realized by a stroke simulator.

  Conventionally, as this type of stroke simulator, for example, there is one described in Patent Document 1. In this type, metal springs (coil springs) with different spring constants are arranged in three stages in series, and the metal springs are operated in order from the one with the lowest spring constant by the movement of the piston interlocking with the brake pedal. It has a structure that gives nonlinear characteristics.

JP 2003-261014 A

  However, according to the stroke simulator shown in Patent Document 1, the pedal stroke / reaction force relationship (reaction force characteristic) is a straight line bent in two steps in the middle, and smooth nonlinear characteristics cannot be obtained. There was a problem. Also, in the hydraulic brake system, when the brake pedal is depressed rapidly, the reaction force increases rapidly and a feeling of response to the response appears. However, in the configuration that relies on the metal spring, the reaction force characteristics cannot be given speed dependency. It was difficult to realize a feeling of tactile response.

  The present invention has been made in view of the above-described conventional problems, and the object of the present invention is to provide a smooth non-linear characteristic and speed dependency to the reaction force characteristic. The purpose of this invention is to provide a brake simulator for brake-by-wire that greatly contributes to the improvement of the above.

To solve the above problems, the present invention includes within Ke pacing, in order from one side to the other side, arranged a piston for pressing the foam and the foam of closed cell harboring a dilatant fluid, the An input rod extending from the brake pedal is operatively connected to the piston.

  According to the stroke simulator of the present invention, since the closed-cell foam containing the dilatant fluid is used as the reaction force generation mechanism, the reaction force characteristics can be given smooth nonlinear characteristics and speed dependence, There is an effect that greatly contributes to an improvement in brake operation feeling.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a brake simulator for a brake-by-wire as one embodiment of the present invention. In the figure, 1 is a stroke simulator according to the present invention, and 2 is a brake pedal that is rotatably coupled to a fixed portion 3 under a dashboard by a pin 4. The stroke simulator 1 is attached to a vehicle compartment front wall 5 in place of a vacuum booster in a normal hydraulic brake system, and one end portion is coupled to the brake pedal 2 via a clevis 6 inside thereof. The other end of the input rod 7 is inserted.

  The stroke simulator 1 includes a cylindrical casing 10 with a bottom, and the casing 10 extends in front of the vehicle compartment in a state in which a cylindrical portion 10a projecting from the back surface on the opening side is extended into the vehicle interior. It is fixed to the front surface of the wall 5. In this casing 10, a closed-cell foam 12 containing a dilatant fluid 11 to be described later and a piston 13 for pressing the foam 12 are disposed in this order from the bottom side to the opening side. The piston 13 linearly moves on the axis of the casing 10 by slidingly fitting a cylindrical portion 13a provided on the back side thereof with a guide member 14 fixed on the opening side in the casing 10. It has become.

  The other end of the input rod 7 is inserted into the cylindrical portion 13 a of the piston 13. A flange 7a is provided in the middle of the input rod 7. Between the flange 7a and the casing 10, the input rod 7 is constantly urged toward the brake pedal 2 side, and has a relatively small spring constant (soft). ) A return spring 15 is interposed. A spring 16 having a larger spring constant (harder) than the return spring 15 is interposed between the other end of the input rod 7 and the piston 13.

  The closed-cell foam 12 has a truncated cone shape, and the diameter of the top surface is not sufficiently smaller than the diameter of the piston 13. On the other hand, the diameter of the piston 13 is sufficiently smaller than the inner diameter of the casing 10, thereby avoiding the danger of the closed-cell foam 12 being caught between the piston 13 and the casing 10. The dilatant fluid 11 is accommodated in a truncated cone-shaped recess 12 a formed on the base side of the closed-cell foam 12, and its back surface is in contact with the inner bottom of the casing 10. The height of the dilatant fluid 11 is lower than the height of the foam 12, so that there is a predetermined gap between the upper surface of the dilatant fluid 11 and the top surface of the foam 12 (contact surface with the piston 13). A gap is secured.

  The closed cell foam 12 is configured such that the internal closed cell forms a fine gas chamber and generates a gas reaction force similar to that of the air spring, and the closed cell has a volume ratio of 70 to 90. %. Here, the foam 12 is made of a rubber sponge, and is manufactured by kneading a foaming agent that generates gas by thermal decomposition at a high temperature into a rubber (base material) and foams it during heat molding. As the foaming agent, one that normally decomposes and generates nitrogen gas is used, and most of the closed cells are nitrogen gas. In the present embodiment, the type of the rubber material as the base material is arbitrary as long as it can be heat-molded and can create closed cells by adding a foaming agent. Examples of such rubber materials include urethane rubber (U), nitrile rubber (NBR), and ethylene / propylene rubber (EPDM), which have large energy absorption, but have a wide operating temperature range (hard to be cured at low temperatures), and It is desirable to use silicon rubber because the compression set is small.

  The dilatant fluid 11 is a material having a characteristic (dilatancy) in which shear stress, that is, deformation resistance increases as the deformation speed increases, and here, silicon putty is used. The silicon putty as the dilatant fluid 11 is formed by slimming silicon oil with boric acid water or borax, and has high durability. The dilatant fluid 11 strongly resists fast deformation, but has a free shape for slow deformation and follows the deformation of the foam 12.

Here, if the entire closed cell foam 12 housed in the casing 10 is regarded as an air spring (air cylinder) 10A, the stroke simulator 1 has a spring system as shown in FIG. In this spring system, if the cylinder cross-sectional area is A, the air volume is V, the initial air volume is V0, the initial cylinder length is Xa, the displacement of the piston 13 is X2, and the initial air pressure is P0, V = A × (Xa− X2), V0 = A × Xa, so the cylinder air pressure P is as shown in (1) below.
P = P0 * V0 / V = P0 * Xa / (Xa-X2) (1)

On the other hand, the air reaction force F2 of the air cylinder 10A is given by the following formula (2). Therefore, when P in the formula (1) is substituted for this, the formula (3) is obtained.
F2 = A × (P−P0) (2)
F2 = AP0 × {Xa / (Xa−X2) −1}
= AP0 * X2 / (Xa-X2) (3)

  That is, the air reaction force F2 of the air cylinder 10A is zero as the reaction force F is balanced between P and P0 at the initial piston displacement X2 = 0 as shown by the thick solid line in FIG. 3, and as the piston displacement X2 increases. The hyperbola becomes asymptotic to the perpendicular of the cylinder length Xa. In this case, if the cross-sectional area A of the air cylinder is changed, the reaction force F2 becomes strongly non-linear (slope change is abrupt) as shown by the thin solid line in FIG. When the cross-sectional area A is too large, the nonlinearity is weak (gradient change is slow) as shown by the broken line in FIG.

  By the way, the reaction force F1 requested by the user, that is, the relationship between the input displacement X1 and the reaction force F1 is as shown by a thick solid line in FIG. 4, and an appropriate cross-sectional area A is given by the above equation (3). When the air reaction force F2 obtained by selection is overlapped, the reaction force F2 becomes a characteristic close to the reaction force characteristic requested by the user.

On the other hand, the spring constant K1 of the soft return spring 15 is determined in accordance with the gradient of the small stroke portion in relation to the reaction force characteristic requested by the user shown in FIG. Further, the spring constant K2 of the hard spring 16 is determined in accordance with the gradient of the large stroke (high pedaling force) portion of the reaction force characteristic of the same user request. When the hard spring 16 is provided in series with the air cylinder 10A, the relationship of F2 = K2 (X1-X2) is established between the air reaction force F2, the input displacement X1, and the piston displacement X2. When this is modified, X2 = X1-F2 / K2, and when this is substituted into the above equation (3), the following equation (4) is obtained.
F2 = AP0 * (X1-F2 / K2) / (Xa-X1 + F2 / K2) (4)
F2 ² + {XK2 × (Xa−X1) + AP0} × F2−AP0 × X1 × K2 (5)

  Here, since F1 = F2 + K1 × X1, the reaction force F1 with respect to the input displacement X1 when the air cylinder sectional area A is given by the above equation (5) can be calculated, as shown by the thick solid line in FIG. It is possible to obtain characteristics that approximately match the reaction force characteristics requested by the user.

  In the present embodiment, since the closed cell foam 12 is housed in the casing 10, in order to obtain the same air reaction force F2 as the air cylinder 10A described above, the foaming is performed on the air cylinder length Xa (FIG. 2). What is necessary is just to set the height of this foam 12 so that it may become the value which multiplied the reciprocal number of the rate. As an example, when the foaming rate is 80%, the height is 1.25 × Xa. Further, the area of the top surface of the foam 12 (the contact surface with the piston 13) is set to a size that matches the cross-sectional area A of the air cylinder 10A.

  In the stroke simulator 1 configured as described above, when the driver depresses the brake pedal 2, the input rod 7 moves, the piston 13 moves forward, and the closed-cell foam 12 is compressed. At this time, if the input is gentle, the dilatant fluid 11 in the foam 12 is freely deformed, so that it is substantially the same as the air spring, and is similar to the hydraulic brake system as shown by the thick solid line in FIG. Force characteristics (smooth nonlinear characteristics). Further, since the return spring 15 is arranged in parallel with the foam 12, desired hysteresis characteristics can be obtained together with the hysteresis characteristics of the foam itself. At this time, since there is a large space between the closed-cell foam 12 and the casing 10, the foam 12 is also deformed in the diameter expansion direction. Furthermore, since the hard spring 16 exists between the piston 13 and the input rod 7, the rigidity at the time of a high pedaling force is lower than when both are directly connected, and as a result, an unnatural feeling of wall contact is eliminated.

  On the other hand, when the brake pedal 1 is rapidly depressed, the reaction force characteristics are the same as those in the case of the gentle input described above until the foam 12 is crushed by a predetermined thickness. However, if the foam 12 is crushed more than a predetermined thickness, the input is directly transmitted to the dilatant fluid 11 and its deformation speed increases, so that its deformation resistance increases, and the reaction force F as shown by the thin line in FIG. Increase rapidly. That is, the reaction force characteristic is given speed dependency, and as a result, a desired tactile response can be obtained. When the input displacement is returned to 0, the dilatant fluid 11 returns to its original shape with a delay due to the restoring force of the foam 12, but the foam 12 quickly recovers due to the gas pressure of the closed cells, so the piston 13, that is, the brake There is no delay in returning to pedal 2.

  As described above, according to the stroke simulator 1, not only a smooth non-linear characteristic is imparted to the reaction force characteristic, but also a clear hysteresis characteristic and speed dependency are imparted, so that the driver feels brake operation (pedal feeling). Is good. Further, since the closed-cell foam 12 is used as an air spring, a seal as in a general-purpose air cylinder that encloses air in the cylinder is not necessary.

  The dilatant fluid 11 contained in the closed-cell foam 12 may be embedded in the foam 12 as a sphere as shown in FIG. 6 (A), or as shown in FIG. 6 (B). Alternatively, it may be enclosed in a spherical rubber bag 20 and stored in the recess 12 a of the foam 12. In the former case, the speed dependency is lower than in the above embodiment, and in the latter case, the shape restoring speed of the dilatant fluid 11 is increased by the rubber bag 20.

It is sectional drawing which shows the structure of the stroke simulator as one Embodiment of this invention. It is a schematic diagram which shows the spring system in this stroke simulator. It is a graph which shows the reaction force characteristic in this air cylinder. It is a graph which compares the reaction force characteristic of a user request | requirement with the reaction force characteristic of an air cylinder, and shows the determination procedure of the spring constant based on the reaction force characteristic of a user request | requirement. It is a graph which shows the reaction force characteristic of this stroke simulator. It is sectional drawing which shows the other installation structure of the dilatant fluid in this stroke simulator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stroke simulator 2 Brake pedal 7 Input rod 10 Casing 11 Dilatant fluid 12 Closed-cell foam 13 Piston 15 Return spring 16 Reaction force spring

Claims (3)

A brake-by-wire for the stroke simulator that generates a reaction force in the direction of pushing back the brake pedal according to the pedal stroke, in Ke pacing, in order from one side to the other side, the foam and the foam of closed cell harboring a dilatant fluid A stroke simulator characterized in that a piston for pressing a body is disposed, and an input rod extending from a brake pedal is operatively connected to the piston. The spring having a larger spring constant than a return spring that constantly biases the input rod toward the brake pedal is interposed between the piston and the input rod. Stroke simulator. The stroke simulator according to claim 1 or 2, wherein the closed-cell foam has a space in the casing that can be deformed in an expanding direction.

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