Control system for trailer house car based on cooperation of hinge point damping force and differential braking

Abstract

The application discloses a kind of based on articulated point damping force and differential braking coordination's trailer house car control system, it is related to the steering stability field of trailer house car, including information acquisition module, decision control module and lower layer execution module.The information acquisition module includes various sensors, for gathering driving data and sending to the decision control module;The decision control module includes electronic control unit ECU, electromagnetic relay and current controller;The lower layer execution module includes electromagnetic brake and adjustable damping rod.The decision control module determines the damping coefficient of the adjustable damping rod and the braking force of the electromagnetic brake according to the driving data, and then controls the yaw moment of articulated point damping force and differential braking;The technical scheme disclosed in the application solves the problem of trailer house car instability in snake shape tail swing through multi-actuator cooperative control, and also solves the problems of large speed fluctuation and high energy loss that may be caused by the prior art.

Description

Technical Field

[0001] The present invention relates to the field of handling stability of trailer-type caravans, and in particular to a trailer-type caravan control system based on the coordination of hinge point damping force and differential braking. Background Art

[0002] In recent years, with the rise of tourism culture, people's enthusiasm for self-driving tours has grown, and the popularity of trailer RVs in my country has also increased. However, due to their more complex structure compared to self-propelled RVs, trailer RVs are prone to instability such as tailspin and shimmy during high-speed obstacle avoidance or emergency braking, seriously affecting driving safety and consumer purchasing intentions.

[0003] Existing approaches primarily involve rationally designing the RV's structure and internal layout during the manufacturing phase. These include minimizing the trailer's mass and moment of inertia, increasing the cornering stiffness of the trailer and towing vehicle's rear wheels, and increasing the trailer's wheelbase or the distance from the trailer's front axle to the towing point. However, these methods can only reduce the likelihood of the RV's yaw, but cannot completely eliminate it.

[0004] Differential braking is often used in Europe and the United States to prevent RVs from swaying. Differential braking is a method of controlling the braking force difference between the wheels to generate a yaw torque to maintain stability. However, in some cases, the driving posture of the RV may temporarily fluctuate, and the system will eventually stabilize even without braking. At this time, the electronic control unit (ECU) detects that the RV is unstable and will immediately initiate braking to maintain vehicle stability. This will inevitably cause fluctuations in the RV's speed and energy loss. For RVs traveling at high speeds, the sudden application of braking force may also cause other instability problems such as tire locking. Overall, current anti-sway technologies and methods are somewhat irrational and unsuitable. Summary of the Invention

[0005] Purpose of the invention: To address the instability problems of trailer RVs such as yaw and folding, a trailer RV control system based on the coordination of hinge point damping force and differential braking is proposed. The control mode of damping force and differential braking can be switched under different working conditions, thereby improving the safety and stability of trailer RVs during driving.

[0006] The technical solutions adopted in the present invention are as follows:

[0007] A trailer-type RV control system based on the coordination of hinge point damping force and differential braking is characterized by comprising an information acquisition module, a decision control module and a lower-level execution module.

[0008] The information acquisition module is used to obtain driving data of the trailer caravan and send it to the decision control module; the decision control module includes an electronic control unit ECU, an electromagnetic relay and a current controller; the lower-level execution module includes an electromagnetic brake and an adjustable damping rod, the adjustable damping rod is arranged on both sides of the hinge point between the tractor and the caravan to form a forward-converging isosceles trapezoid, the adjustable damping rod changes the gear according to the current signal of the electromagnetic relay, the zero gear damping coefficient is zero, the higher the gear, the greater the damping coefficient, thereby controlling the damping force of the hinge point, the electromagnetic brake directly controls the braking force of the left and right wheels of the caravan according to the current size of the current controller to form a yaw torque of differential braking; the electronic control unit ECU stores a coordinated stability control method for controlling the hinge point damping force and differential braking, and its specific control process is as follows:

[0009] Step 1: Detecting the longitudinal speed of the RV, and determining the gear position of the adjustable damping rod and the control mode of the differential brake according to the longitudinal speed;

[0010] If the longitudinal vehicle speed is less than the critical vehicle speed 1, the adjustable damping rod is set to zero gear, and the differential brake is set to a multivariable cooperative control mode;

[0011] If the longitudinal vehicle speed is between the critical vehicle speed 1 and the critical vehicle speed 2, the adjustable damping rod is set to a low gear, a middle gear, or a high gear. The speed between the critical vehicle speed 1 and the critical vehicle speed 2 is divided into three intervals from low to high. The first speed interval is set to the low gear, the second speed interval is set to the middle gear, and the third speed interval is set to the high gear. The differential brake is set to a single variable control mode.

[0012] If the longitudinal vehicle speed is greater than the critical vehicle speed 2, the adjustable damping lever is set to the high gear, and the differential brake is set to the multivariable weighted control mode.

[0013] Step 2: determining whether the RV is unstable based on the driving data; if instability occurs, applying differential braking torque to the left and right wheels according to the degree of instability; if no instability occurs, the braking force is zero;

[0014] Step 3. Return to step 1 and repeat steps 1 to 3.

[0015] Furthermore, the information collection module includes a tractor speed sensor installed on the tractor, a steering wheel angle sensor, an articulation angle sensor installed at the hinge point, and a yaw rate sensor installed on the RV; the driving data includes the longitudinal speed of the tractor, the steering wheel angle, the articulation angle between the tractor and the RV, and the yaw rate of the RV; the steering wheel angle is used to estimate the front wheel angle of the tractor.

[0016] Furthermore, the critical speed 1 and the critical speed 2 are predetermined speed thresholds, and the critical speed 1 is less than the critical speed 2; the critical speed 1 is set as the critical speed for switching between the zero gear and low gear of the adjustable damping rod and the multi-variable collaborative control mode and the single variable control mode, and the critical speed 2 is set as the critical speed for switching between the single variable control mode and the multi-variable weighted control mode.

[0017] Furthermore, the single variable control mode uses the articulation angle of the tractor and the RV as a control variable, with the sole purpose of maintaining the articulation angle deviation between the tractor and the RV within a set articulation angle stability threshold range.

[0018] Furthermore, the multivariable collaborative control mode is that when the articulation angle deviation between the tractor and the RV is within the set articulation angle stability threshold range, the yaw angular velocity of the RV is used as the control variable; when the articulation angle deviation between the tractor and the RV exceeds the stability threshold, the articulation angle of the tractor and the RV is used as the control variable, with the first purpose of maintaining the articulation angle deviation between the tractor and the RV within the set articulation angle stability threshold range, and the second purpose of maintaining the yaw angular velocity deviation of the RV within the set yaw angular velocity stability threshold range.

[0019] Furthermore, the multivariable weighted control mode simultaneously outputs two yaw moments using the articulation angle between the tractor and the RV and the yaw angular velocity of the RV as control variables, and obtains the yaw moment ultimately required by the RV after a certain weighted calculation, with the purpose of simultaneously maintaining the deviation of the articulation angle between the tractor and the RV and the yaw angular velocity of the RV within the set articulation angle stability threshold and the set yaw angular velocity stability threshold.

[0020] Furthermore, the method for determining whether the RV is unstable is as follows: when the yaw rate deviation of the RV or the articulation angle deviation between the tractor and the RV exceeds a respective set instability threshold, the RV is in an unstable state; when the yaw rate deviation of the RV and the articulation angle deviation between the tractor and the RV are both less than a respective set stability threshold, the RV is in a stable state. The specific instability thresholds are:

[0021]

[0022] The stability threshold is:

[0023]

[0024] Wherein, ω2 is the yaw rate of the RV, θ is the articulation angle between the tractor and the RV, ω0 is the ideal yaw rate of the RV, θ0 is the ideal articulation angle between the tractor and the RV,

[0025] The purpose of the discontinuity between the stability threshold and the instability threshold is to prevent the differential braking from frequently intervening and exiting near the stability threshold, causing impact vibration and energy waste; specifically, when the yaw angular velocity deviation of the RV or the articulation angle deviation between the tractor and the RV is between their respective instability threshold and stability threshold, the control mode remains consistent with the previous moment.

[0026] Furthermore, the degree of instability is measured based on the RV yaw rate deviation |ω0-ω2| and the articulation angle deviation |θ0-θ| between the tractor and the RV. The greater the deviation, the greater the degree of instability. The RV yaw rate deviation |ω0-ω2| is the difference between the ideal RV yaw rate ω0 and the RV yaw rate ω2. The articulation angle deviation |θ0-θ| between the tractor and the RV is the difference between the ideal articulation angle θ0 between the tractor and the RV and the articulation angle θ between the tractor and the RV. The ideal RV yaw rate ω0 and the ideal articulation angle θ0 between the tractor and the RV can be obtained from the steady-state RV yaw rate gain and the steady-state articulation angle gain between the tractor and the RV:

[0027]

[0028]

[0029] Among them, K1 and K2 are the stability factors of the trailer caravan; they are determined by structural parameters and usage conditions, L1 is the wheelbase of the tractor, v is the longitudinal speed of the caravan, and δ is the front wheel angle of the tractor, which is obtained by the ratio of the steering wheel angle to the steering system angle transmission ratio.

[0030] Furthermore, the yaw moment is obtained through PID control, specifically:

[0031]

[0032] Where u(t) is the curve of the yaw torque required for differential braking changing with time; e(t) is the function of ω0-ω2 or θ0-θ with respect to time. When the yaw angular velocity of the RV is used as the control target, e is ω0-ω2; when the articulation angle between the tractor and the RV is used as the control target, e is θ0-θ; K P is the proportional coefficient; T i is the integration time; T d The yaw moment is obtained and then distributed to the left and right wheel braking forces of the RV, specifically:

[0033]

[0034] Among them, F xbl is the left wheel braking force, F xbr is the braking force of the right wheel, and B is the wheelbase of the RV. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a system structure diagram of the present invention;

[0036] Figure 2 A top view diagram of the installation position of each module;

[0037] Figure 3 Flowchart selected for the mode of the present invention.

[0038] 1-RV yaw rate sensor, 2-articulation angle sensor, 3-steering wheel angle sensor, 4-tractor speed sensor, 5-RV information exchange unit, 6-tractor information exchange unit, 7-electronic control unit ECU, 8-electromagnetic relay, 9-current controller, 10-adjustable damping rod, 11-electromagnetic brake. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] like Figure 1 As shown, a trailer RV control system based on the coordination of hinge point damping force and differential braking includes an information acquisition module, a decision control module and a lower-level execution module.

[0041] like Figure 2 As shown, the information acquisition module includes a tractor speed sensor 4 and a steering wheel angle sensor 3 mounted on the tractor, an articulation angle sensor 2 mounted at the hinge point, and a motorhome yaw rate sensor 1 mounted on the motorhome. The tractor speed sensor 4 detects the longitudinal speed of the tractor; the steering wheel angle detected by the steering wheel angle sensor 3 is used to estimate the front wheel angle of the tractor; the articulation angle sensor 2 detects the articulation angle between the tractor and the motorhome; and the motorhome yaw rate sensor 1 detects the yaw rate of the motorhome.

[0042] The decision control module includes an electronic control unit ECU7, an electromagnetic relay 8 and a current controller 9; the lower-level execution module includes an electromagnetic brake 11 and an adjustable damping rod 10. The adjustable damping rod 10 is arranged on both sides of the hinge point between the tractor and the RV to form a forward-converging isosceles trapezoid. The adjustable damping rod 10 changes the gear according to the current signal of the electromagnetic relay 8. The damping coefficient of zero gear is zero. The higher the gear, the greater the damping coefficient, thereby controlling the damping force of the hinge point. The electromagnetic brake 11 directly controls the braking force of the left and right wheels of the RV according to the current size of the current controller 9 to form a yaw torque of differential braking.

[0043] The RV yaw rate sensor 1 is connected to the input end of the RV information exchange unit 5, and is used to send the collected RV yaw rate to the electronic control unit ECU7. The electromagnetic relay 8 and the current controller 9 are connected to the output end of the RV information exchange unit 5, and are used to receive the control signal sent by the electronic control unit ECU7. The RV information exchange unit 5 completes information exchange with the tractor information exchange unit 6 via wireless means.

[0044] The input and output ends of the tractor speed sensor 4, steering wheel angle sensor 3, articulation angle sensor 2 and tractor information exchange unit 6 are directly connected to the electronic control unit ECU7. The electronic control unit ECU7 processes the various data collected by the sensors and sends the control signals to the middle-level control module and the lower-level execution module through the tractor information exchange unit 6 and the RV information exchange unit 5.

[0045] like Figure 3 As shown, the control system for a trailer caravan based on the coordination of hinge point damping force and differential braking includes the following steps:

[0046] Step 1: Detecting the longitudinal speed of the RV, and determining the gear position of the adjustable damping rod and the control mode of the differential brake according to the longitudinal speed;

[0047] If the longitudinal vehicle speed is less than the critical vehicle speed 1, the adjustable damping rod is set to zero gear, and the differential brake is set to a multivariable cooperative control mode;

[0048] If the longitudinal vehicle speed is between the critical vehicle speed 1 and the critical vehicle speed 2, the adjustable damping rod is set to a low gear, a middle gear, or a high gear. The speed between the critical vehicle speed 1 and the critical vehicle speed 2 is divided into three intervals from low to high. The first speed interval is set to the low gear, the second speed interval is set to the middle gear, and the third speed interval is set to the high gear. The differential brake is set to a single variable control mode.

[0049] If the longitudinal vehicle speed is greater than the critical vehicle speed 2, the adjustable damping lever is set to the high gear, and the differential brake is set to the multivariable weighted control mode.

[0050] Step 2: determining whether the RV is unstable based on the driving data; if instability occurs, applying differential braking torque to the left and right wheels according to the degree of instability; if no instability occurs, the braking force is zero;

[0051] Step 3. Return to step 1 and repeat steps 1 to 3.

[0052] The critical speed 1 and the critical speed 2 are predetermined speed thresholds, and the critical speed 1 is less than the critical speed 2; the critical speed 1 is set as the critical speed for switching between the zero gear and low gear of the adjustable damping rod and the multi-variable collaborative control mode and the single variable control mode, and the critical speed 2 is set as the critical speed for switching between the single variable control mode and the multi-variable weighted control mode.

[0053] The single variable control mode uses the articulation angle of the tractor and the RV as the control variable, with the sole purpose of maintaining the articulation angle deviation of the tractor and the RV within the set articulation angle stability threshold range; the multivariable coordinated control mode uses the yaw angular velocity of the RV as the control variable when the articulation angle deviation of the tractor and the RV is within the set articulation angle stability threshold range; when the articulation angle deviation of the tractor and the RV exceeds the stability threshold, the articulation angle of the tractor and the RV is used as the control variable to maintain the articulation angle deviation of the tractor and the RV within the set articulation angle stability threshold range. The first purpose is to maintain the yaw rate deviation of the RV within the set yaw rate stability threshold range, and the second purpose is to maintain the yaw rate deviation of the RV within the set yaw rate stability threshold range; the multivariable weighted control mode is to simultaneously output two yaw moments with the articulation angle of the tractor and the RV and the yaw rate of the RV as control variables, and obtain the yaw moment finally required by the RV after a certain weighted operation, so as to simultaneously maintain the articulation angle of the tractor and the RV and the yaw rate deviation of the RV within the set articulation angle stability threshold range and the set yaw rate stability threshold range.

[0054] The specific method for determining whether the RV is unstable is as follows: when the yaw rate deviation of the RV or the articulation angle deviation between the tractor and the RV exceeds the respective set instability thresholds, the RV is in an unstable state; when the yaw rate deviation of the RV and the articulation angle deviation between the tractor and the RV are both less than the respective set stability thresholds, the RV is in a stable state. The specific instability thresholds are:

[0055]

[0056] The stability threshold is:

[0057]

[0058] Among them, ω2 is the yaw rate of the RV, θ is the articulation angle between the tractor and the RV, ω0 is the ideal yaw rate of the RV, θ0 is the ideal articulation angle between the tractor and the RV,

[0059] The purpose of the discontinuity between the stability threshold and the instability threshold is to prevent the differential brake from frequently engaging and disengaging near the stability threshold, causing impact vibration and energy waste. Specifically, when the RV yaw rate deviation or the articulation angle deviation between the tractor and RV is between their respective instability threshold and stability threshold, the control mode remains consistent with the previous moment. The ideal RV yaw rate ω0 and the ideal articulation angle θ0 between the tractor and RV can be obtained from the steady-state RV yaw rate gain and the steady-state articulation angle gain between the tractor and RV:

[0060]

[0061]

[0062] Among them, K1 and K2 are the stability factors of the trailer caravan; they are determined by structural parameters and usage conditions, L1 is the wheelbase of the tractor, v is the longitudinal speed of the caravan, and δ is the front wheel angle of the tractor, which is obtained by the ratio of the steering wheel angle to the steering system angle transmission ratio.

[0063] The adjustable damping rod increases the damping ratio of the trailer RV. When the tractor and the RV rotate relative to each other, the adjustable damping rod can reduce the yaw angular velocity of the RV and suppress the increase of the articulation angle, thereby reducing the number of differential braking interventions and thus reducing the speed fluctuation and energy consumption of the RV.

[0064] In summary, the trailer RV control system based on the coordinated hinge damping force and differential braking can improve steering flexibility at low speeds; at medium and high speeds, the damping force can reduce oscillations, and the differential braking can ensure the rapid convergence of various system parameters. The combination of the two can significantly improve the stability of the system.

[0065] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A trailer caravan control system based on the coordination of hinge point damping force and differential braking, characterized in that: Including information collection module, decision control module and lower-level execution module, The information acquisition module is used to obtain driving data of the trailer caravan and send it to the decision control module; the decision control module includes an electronic control unit ECU, an electromagnetic relay and a current controller; the lower-level execution module includes an electromagnetic brake and an adjustable damping rod, the adjustable damping rod is arranged on both sides of the hinge point between the tractor and the caravan to form a forward-converging isosceles trapezoid, the adjustable damping rod changes the gear according to the current signal of the electromagnetic relay, the zero gear damping coefficient is zero, the higher the gear, the greater the damping coefficient, thereby controlling the damping force of the hinge point, the electromagnetic brake directly controls the braking force of the left and right wheels of the caravan according to the current size of the current controller to form a yaw torque of differential braking; the electronic control unit ECU stores a coordinated stability control method for controlling the hinge point damping force and differential braking, and its specific control process is as follows: Step 1: Detecting the longitudinal speed of the RV, and determining the gear position of the adjustable damping rod and the control mode of the differential brake according to the longitudinal speed; If the longitudinal vehicle speed is less than the critical vehicle speed 1, the adjustable damping rod is set to zero gear, and the differential brake is set to a multivariable cooperative control mode; If the longitudinal vehicle speed is between the critical vehicle speed 1 and the critical vehicle speed 2, the adjustable damping rod is set to a low gear, a middle gear, or a high gear. The speed between the critical vehicle speed 1 and the critical vehicle speed 2 is divided into three intervals from low to high. The first speed interval is set to the low gear, the second speed interval is set to the middle gear, and the third speed interval is set to the high gear. The differential brake is set to a single variable control mode. If the longitudinal vehicle speed is greater than the critical vehicle speed 2, the adjustable damping lever is set to the high gear, and the differential brake is set to a multivariable weighted control mode; Step 2: determining whether the RV is unstable based on the driving data; if instability occurs, applying differential braking torque to the left and right wheels according to the degree of instability; if no instability occurs, the braking force is zero; Step 3. Return to step 1 and repeat steps 1 to 3.

2. A trailer RV control system based on the coordination of hinge point damping force and differential braking according to claim 1, characterized in that: The information acquisition module includes a tractor speed sensor installed on the tractor, a steering wheel angle sensor, an articulation angle sensor installed at the hinge point, and a yaw rate sensor installed on the RV; the driving data includes the longitudinal speed of the tractor, the steering wheel angle, the articulation angle between the tractor and the RV, and the yaw rate of the RV; the steering wheel angle is used to estimate the front wheel angle of the tractor.

3. The control system for a trailer caravan based on the coordination of hinge point damping force and differential braking according to claim 1, characterized in that: The critical vehicle speed 1 and the critical vehicle speed 2 are predetermined vehicle speed thresholds, and the critical vehicle speed 1 is lower than the critical vehicle speed 2.

4. The trailer RV control system based on the coordination of hinge point damping force and differential braking according to claim 1, characterized in that: The single variable control mode uses the articulation angle of the tractor and the RV as a control variable, with the sole purpose of maintaining the deviation of the articulation angle between the tractor and the RV within a set articulation angle stability threshold range.

5. The control system for a trailer caravan based on the coordination of hinge point damping force and differential braking according to claim 2, characterized in that: The multivariable collaborative control mode is that when the articulation angle deviation between the tractor and the RV is within the set articulation angle stability threshold range, the yaw angular velocity of the RV is used as the control variable; when the articulation angle deviation between the tractor and the RV exceeds the stability threshold, the articulation angle of the tractor and the RV is used as the control variable, with the first purpose of maintaining the articulation angle deviation between the tractor and the RV within the set articulation angle stability threshold range, and the second purpose of maintaining the yaw angular velocity deviation of the RV within the set yaw angular velocity stability threshold range.

6. The trailer caravan control system based on the coordination of hinge point damping force and differential braking according to claim 2, characterized in that: The multivariable weighted control mode simultaneously outputs two yaw moments using the articulation angle between the tractor and the RV and the yaw angular velocity of the RV as control variables, and obtains the yaw moment ultimately required by the RV after weighted calculation, with the purpose of simultaneously maintaining the articulation angle between the tractor and the RV and the yaw angular velocity deviation of the RV within the set articulation angle stability threshold and the set yaw angular velocity stability threshold.

7. The trailer caravan control system based on the coordination of hinge point damping force and differential braking according to claim 2, characterized in that: The method for determining whether the RV is unstable is as follows: when the yaw rate deviation of the RV or the articulation angle deviation between the tractor and the RV exceeds the respective set instability thresholds, the RV is in an unstable state; when the yaw rate deviation of the RV and the articulation angle deviation between the tractor and the RV are both less than the respective set stability thresholds, the RV is in a stable state. The specific instability thresholds are: The stability threshold is: Wherein, ω2 is the yaw rate of the RV, θ is the articulation angle between the tractor and the RV, ω0 is the ideal yaw rate of the RV, θ0 is the ideal articulation angle between the tractor and the RV, The purpose of the discontinuity between the stability threshold and the instability threshold is to prevent the differential braking from frequently intervening and exiting near the stability threshold, causing impact vibration and energy waste; specifically, when the yaw angular velocity deviation of the RV or the articulation angle deviation between the tractor and the RV is between their respective instability threshold and stability threshold, the control mode remains consistent with the previous moment.

8. The control system for a trailer caravan based on the coordination of hinge point damping force and differential braking according to claim 7, characterized in that: The degree of instability is measured based on the RV yaw rate deviation |ω0-ω2| and the articulation angle deviation |θ0-θ| between the tractor and the RV. The greater the deviation, the greater the degree of instability. The RV yaw rate deviation |ω0-ω2| is the difference between the ideal RV yaw rate ω0 and the RV yaw rate ω2. The articulation angle deviation |θ0-θ| between the tractor and the RV is the difference between the ideal articulation angle θ0 between the tractor and the RV and the articulation angle θ between the tractor and the RV. The ideal RV yaw rate ω0 and the ideal articulation angle θ0 between the tractor and the RV can be obtained from the steady-state RV yaw rate gain and the steady-state articulation angle gain between the tractor and the RV: Among them, K1 and K2 are the stability factors of the trailer caravan; they are determined by structural parameters and usage conditions, L1 is the wheelbase of the tractor, v is the longitudinal speed of the caravan, and δ is the front wheel angle of the tractor, which is obtained by the ratio of the steering wheel angle to the steering system angle transmission ratio.

9. The control system for a trailer caravan based on the coordination of hinge point damping force and differential braking according to claim 6, characterized in that: The yaw moment is obtained through PID control, specifically: Where u(t) is the curve of the yaw torque required for differential braking changing with time; e(t) is the function of ω0-ω2 or θ0-θ with respect to time. When the yaw angular velocity of the RV is used as the control target, e is ω0-ω2; when the articulation angle between the tractor and the RV is used as the control target, e is θ0-θ; K P is the proportional coefficient; T i is the integration time; T d The yaw moment is obtained and then distributed to the left and right wheel braking forces of the RV, specifically: Among them, F xbl is the left wheel braking force, F xbr is the braking force of the right wheel, and B is the wheelbase of the RV.

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