1. Field of the Invention
The present invention relates to a traction control system configured to control a driving power applied to a drive wheel according to a degree to which the drive wheel spins.
2. Description of the Related Art
Japanese Laid-Open Patent Application Publication No. Hei. 7-103009 discloses a traction control system in a vehicle, configured to reduce an engine driving power to restore a gripping force of a drive wheel with respect to a road surface when an amount of a slip of the drive wheel with respect to the road surface exceeds a predetermined value. This control system is configured to execute a traction control for reducing the driving power in such a manner that an ignition timing of an engine is retarded with respect to an optimal timing when a monitored value (e.g., increasing rate of an engine speed) exceeds a predetermined value.
In some cases, the driving power of the drive wheel is favorably maintained or increased, even when the monitored value exceeds the predetermined value and the traction control is executed. However, in the conventional traction control system, when the monitored value exceeds the predetermined value, the traction control is executed to restrict the driving power of the drive wheel irrespective of a gripping state of the drive wheel. Thus, the traction control is executed undesirably.
If the ignition timing of the engine is retarded, an imperfect combustion occurs and a fuel gas remains in a cylinder. The remaining fuel gas flows to a catalyst provided inside an engine component such as a muffler, through an exhaust pipe along with other exhaust gas, and is combusted in the catalyst. If the fuel gas has an uneven concentration in the catalyst, a temperature of the catalyst rises locally excessively, which leads to deterioration of the catalyst.