diff --git a/utilities/at32f421_freertos_demo/src/TaskLoop.c b/utilities/at32f421_freertos_demo/src/TaskLoop.c
index aea83cb..2fc62a8 100644
--- a/utilities/at32f421_freertos_demo/src/TaskLoop.c
+++ b/utilities/at32f421_freertos_demo/src/TaskLoop.c
@@ -653,27 +653,38 @@ void vd1_task(void)
      *    - 用途: 进入/离开检测判定
      *================================================================*/
 
-    /* 1a. 慢速 IIR — 斜率限幅 */
+    /* 1a. 慢速 IIR — 斜率限幅（参考 CAPVD）*/
     {
-        uint32_t fast_input;  // 快速 IIR 的输入：限幅后的原始值，不经慢速 IIR 滞后
+        uint32_t fast_input;
 
         if (loop1_CAPVD == 0) {
             loop1_CAPVD = loop1_Value;
             fast_input = loop1_Value;
         } else {
-            /* 斜率限幅: 物理车辆不可能让频率瞬间跳变 > MAX_SLOPE_RATE% */
+            /*--- 慢速路径：斜率限幅参考 CAPVD (τ=135ms)，保护基线跟踪 ---*/
             int32_t raw_delta = (int32_t)loop1_Value - (int32_t)loop1_CAPVD;
             int32_t max_step = (int32_t)(loop1_CAPVD * MAX_SLOPE_RATE / 100);
-            if (max_step < 100) max_step = 100;  // 最小限幅，防止 origin 很小时锁死
+            if (max_step < 100) max_step = 100;
             if (raw_delta > max_step)  raw_delta = max_step;
             if (raw_delta < -max_step) raw_delta = -max_step;
             uint32_t clamped_value = (uint32_t)((int32_t)loop1_CAPVD + raw_delta);
             loop1_CAPVD = get_flt_value(clamped_value, loop1_CAPVD);
-            fast_input = clamped_value;
+
+            /*--- 快速路径：斜率限幅参考 CAPVD_fast (τ=28ms)，限幅窗口随快速值扩展
+             *    解决 ALFA_CAP1=18 时 CAPVD 移动太慢限制限幅天花板的问题 ---*/
+            if (loop1_CAPVD_fast == 0) {
+                fast_input = clamped_value;
+            } else {
+                int32_t f_delta = (int32_t)loop1_Value - (int32_t)loop1_CAPVD_fast;
+                int32_t f_max   = (int32_t)(loop1_CAPVD_fast * MAX_SLOPE_RATE / 100);
+                if (f_max < 100) f_max = 100;
+                if (f_delta > f_max)  f_delta = f_max;
+                if (f_delta < -f_max) f_delta = -f_max;
+                fast_input = (uint32_t)((int32_t)loop1_CAPVD_fast + f_delta);
+            }
         }
 
-        /* 1b. 快速 IIR — α=0.5: (old + new) / 2
-         * 输入直接用限幅后的原始值，不经过慢速 IIR，保持 τ≈28ms 的响应速度 */
+        /* 1b. 快速 IIR — α=0.5: (old + new) / 2 */
         if (loop1_CAPVD_fast == 0) {
             loop1_CAPVD_fast = fast_input;
         } else {