# A Review of Recent Advances in Roll Stability Control in On-Road and Off-Road Vehicles
## 5 Roll Stability Control in Off-Road Vehicles
### Active Roll Stability Control Methods
#### 5.3.2 Direct Torque Control  
Direct torque control methods, including active suspensions, single-axis momentum flywheels, and single-frame control moment gyroscopes, have been shown to effectively reduce rollover torque in agricultural machinery, enhancing operational safety. In tractor applications, [PERSON] et al. [42] improved safety by equipping a tractor with an active suspension system, allowing independent actuator control of height. This system significantly enhanced posture control during omnidirectional rollover tests, effectively preventing rollover and improving stability on rugged terrain. [PERSON] et al. [131] proposed a novel rollover risk control method combining a single-axis momentum flywheel and an active steering system. Their nonlinear dynamic model and stability criteria demonstrated that this system reduced the tilt angle by 40%, enhancing tractor stability on complex terrains. Further advancements were made by [PERSON] et al. [132], who developed an active anti-rollover control method using a single-frame control moment gyroscope to address rollover during steering on slopes, as shown in Figure 8a. Their nonlinear dynamic model, coupled with a SMC gyroscope rotor precession velocity controller, significantly improved stability and reduced the peak tilt angle by 42%, outperforming traditional PID control. Additionally,  
Figure 7: Representative leveling control systems in agricultural machinery: (**a**) active attitude adjustment system for tractors in hilly and mountainous terrains [128]; (**b**) articulated omnidirectional leveling system [13]; (**c**) omnidirectional leveling system based on sliding mode synchronous control [12]; (**d**) adaptive leveling system based on four-point adjustable tracked chassis [130].  
[PERSON] et al. [133] introduced a semi-active suspension system utilizing hydraulic-pneumatic mechanisms and an LQG optimal control algorithm. This system, validated using a Kalman filter state observer, effectively reduced the cab's vertical acceleration by nearly 49%, offering a cost-effective solution for tractor vibration control.  
The operational stability of various agricultural machines has drawn increasing attention. [PERSON] et al. [134; 135] developed an active suspension control system for sprayer boom machinery, integrating electro-hydraulic servos and multi-sensor fusion to enhance boom attitude control. Tests showed that the system significantly reduced boom tilt oscillations at resonance, with a standard deviation of tilt angle of only 38% of that of the chassis, demonstrating strong terrain adaptability and disturbance rejection. [PERSON] et al. [136] proposed a dynamic model for counterweight forklifts, analyzing instability using bifurcation theory and introducing a new rollover indicator for steering and obstacle-crossing scenarios. They further designed a staged hydraulic control strategy and adaptive model predictive control system, which improved rollover prevention through coordinated adjustment of the cylinder force and steering ratio. [PERSON] et al. [137] developed a hydraulic active control system for trapezoidal sprayer suspensions using a feedforward PID controller. Experimental results showed superior tracking at 0.2 Hz compared to traditional PID, with field tests indicating a chassis tilt of 3.896\({}^{\circ}\) and a boom tilt of just 0.453\({}^{\circ}\), confirming effective real-time boom stabilization.