JPS6234584B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a vehicle equipped with two sets of steerable wheels, in which a driver constantly steers one set of wheels,
The present invention relates to a steering control method for operating the other wheel set following this steering operation. Conventional vehicle steering methods typically involve steering only the front wheels or only the rear wheels; there are exceptions, particularly in long wheelbase vehicles or special purpose vehicles, where multiple axles can be steered. By mechanically or hydraulically coupling these steerable axles to each other, one set of wheels can be steered to an angle proportional to the other set of wheels to maneuver in tight spaces. Aiming for ease of handling, the vehicle was steered to make small turns at low speeds. However, this conventional vehicle steering method is
In both cases, the only input that determined the motion of the vehicle was the steering angle of the steered wheel set, resulting in the following problems. For example, if a vehicle is turning in a steady state, a four-wheeled vehicle can be treated as a two-wheeled vehicle, so in the two-wheeled model shown in Fig. 3, the mass of the vehicle is m,
l is the wheelbase, a is the distance between the front wheels and the center of gravity, b is the distance between the rear wheels and the center of gravity, Cf is the cornering power of the front tires, Cr is the cornering power of the rear tires, δf is the front wheel steering angle , αf is the slip angle of the front tires, αr is the slip angle of the rear tires, V is the vehicle speed, γ is the yaw rate (angular change speed at which the car attempts to change its direction), y is the lateral displacement of the center of gravity, and Yf is the front wheels. Assuming that Yr is the cornering force of the rear wheels, the equation of motion of a vehicle steered using only the steering angle of the front wheels as input is: where Yf=-Cf・αf=-Cf(y/V+aγ/V-δf) Yr=-Cr・αr=-Cr(y/V-bγ/V), and the above formula When we convert Laplace and display it as a matrix, we get From the above equation, the transfer function Gr(S) that indicates the frequency response of the vehicle's yaw rate is: Standardizing the above equation, Gγ(S)=γ(S)/δf(S) =Krω〓 ² /S ² +2ξ〓ω〓S+ω〓 ² (1+ν〓
S) However, Kγ, ξγ, ωγ, and ν are constants. As can be seen from the above equation, a vehicle in which the only input that determines vehicle motion is the steering angle exhibits a first-order lead, second-order delay system response, that is, when the vehicle turns,
There is always a phase lag between the vehicle's yaw rate (angular change rate at which the vehicle attempts to change direction) and the steering operation, and as a result, the change in direction of the vehicle occurs with a delay relative to the steering operation, so the vehicle's There is a problem in that the vehicle characteristics require skill in driving, such as steering while anticipating changes in direction, which gives the driver an unnatural operating feeling. The present invention has been made by focusing on such conventional problems, and includes two sets of wheels that can steer the left and right wheels in conjunction with each other, one of which is steered by the driver, In a vehicle steering control method in which the other wheel set is steered to follow the one wheel set, the other wheel set is steered at a steering angle obtained by proportionally multiplying the steering angular velocity of the one wheel set; The aim is to solve the above problems by improving steering performance. The invention will now be explained with reference to the drawings. FIG. 1 shows one embodiment of the present invention, and FIG. 2 is a block diagram schematically showing FIG. 1, in which 1 is a steering wheel, 2 is a steering column, 3 is a gearbox, and 4 is a pittman arm,
5 is the connecting rod, 6 is the side rod,
7 is a knuckle arm, 8 is a tire, 9 is a suspension, 10 is an engine, 11 is a transmission, 12 is an axle shaft, 13 is a vehicle speed detector attached to the transmission 11, 14
Reference numeral 15 indicates a front wheel steering angular velocity detector attached to the steering cabinet 3, and 15 indicates a load detector attached to the attachment point of the suspension 9 on the vehicle body side. The vehicle speed detector 13, front wheel steering angular velocity detector 14, and load detector 15 are electrically connected to a command circuit 16, and this command circuit 16 is electrically connected to a servo amplifier 17 to electrically drive the servo valve 18. connected to. The servo valve 18 is connected to a hydraulic pump 19 driven by the engine 10 to control the amount of oil. An actuator 21 is coupled to the steering linkage 20 of the rear wheel, and this actuator 2
A servo amplifier 17 is connected to 1 by a hydraulic circuit, and is configured to change the steering angular velocity of the rear wheels by displacement of an actuator 21. A potentiometer 22 is connected to the servo amplifier 17 for detecting the displacement of the actuator 21 and controlling the steering angular velocity in a feedback manner. Next, the motion that occurs in the horizontal plane of the vehicle when the vehicle is steered will be explained. Therefore, when the vehicle is steered, there is a yaw motion in the rotational direction and a sideslip motion in the linear direction, as explained using a simple two-degree-of-freedom model of a two-wheeled vehicle shown in FIG. Third
In the figure, l is the wheelbase, a is the distance between the front wheels and the center of gravity, b is the distance between the rear wheels and the center of gravity,
Cf is the cornering power of the front tires, Cr is the corner cylinder power of the rear tires, δf is the front wheel steering angle, k is the magnification and corresponds to the front and rear wheel steering angle ratio (rear wheel steering angle/front wheel steering angular speed), and αf is The slip angle of the front tires, αr is the slip angle of the rear tires, V is the vehicle speed, γ is the yaw rate, y is the lateral displacement of the center of gravity, y is the lateral displacement speed of the center of gravity, ¨y is the lateral displacement acceleration of the center of gravity, and β is The rear wheel sideslip angle, Yf indicates the cornering force of the front wheels, and Yr indicates the cornering force of the rear wheels. In the model shown in Figure 3, assuming that the mass of the vehicle is m and that the rear wheels are steered in the opposite direction to the front wheels at a steering angle obtained by multiplying proportionally by the steering angular velocity multiplier k of the front wheels, the equation of motion is m(¨ y+V・γ)=Yf
+Yr Iz〓γ=aYf−bYr. Here, it is expressed as Yf=-Cfαf=-Cf(y/V+aγ/V-δf) Yr=-Crαr=-Cr(y/V-bγ/V+k〓δf), and the above formula with S as Laplace operator When we convert Laplace and display it as a matrix, we get By solving the above equation, the transfer function Gγ(S) of yaw rate, which is the time rate of change of yaw motion, is obtained as follows: Gγ(S)=K〓S ² +2ξ〓ω〓S+ω〓 ² /ω〓
² ωγ ² /S ² +2ξ〓ω〓S+ω〓 ^2In the above formula, Therefore, if the rear wheels are steered in proportion to the front wheel steering angular velocity, the yaw rate transfer function Gγ
It can be seen that (S) is expressed by a quadratic lead and quadratic lag system. The phase lag ∠Gγ(S) in the quadratic leading and quadratic lag transfer function Gγ(S) is ∠Gγ(S)=∠S ² +2ξ〓ω〓S+ω〓 ² /ω〓
² −∠S ² +2ξ〓ω〓S+ω〓 ² /ω〓
² , and the phase angles indicated by the first and second terms of the above equation are π/2 and −π/2 at the respective natural frequencies ω〓 and ω〓, as shown in FIG. Therefore, if ω = ω, the phase lead and lag of both will almost match, and both phase angles can be canceled out. As a result, the delay in the yaw rate of the vehicle relative to the driver's steering can be reduced to only a slight phase lag and phase lead due to the difference between ξ〓 and ξ〓, as is clear from the above equation. Therefore, according to the present invention, as a condition for eliminating the yaw rate delay, ω ² 〓=ω 〓 ² , and CfCr/mIz{1 ² /V ² −m(a/Cr -b/C
f)}=1Cf/mkbV Formula for calculating the ratio k of rear wheel steering angle to front wheel steering angular speed By controlling the rear wheels at a steering angle that is the front wheel steering angular velocity multiplied by the above k times, the delay in yaw rate relative to the steering angle steered by the driver can be made extremely small. Figure 5 assumes that the vehicle specifications are constant, that is,
Assuming that the wheelbase l, the distance a between the front wheels and the center of gravity, the distance b between the rear wheels and the center of gravity, the vehicle mass m, and the moment of inertia Iz in formula [1] are constant, formula [1] is

[Equation] where A and B are constants, and a characteristic curve showing the relationship between the vehicle speed V and the magnification k of the rear wheel steering angle to the front wheel steering angular speed, which is determined based on the actual vehicle specifications, is shown. In the embodiment shown in FIGS. 1 and 2, the vehicle speed V is detected by the vehicle speed detector 13, the front wheel steering angular velocity is detected by the front wheel steering angular velocity detector 14, and the vehicle weight of the front and rear wheels is detected by the load detector 15. By knowing the vehicle weights mf and mr of the front and rear wheels, the distances a and b between the front and rear wheels and the center of gravity can be found from the relationship a=l×mr/m, b=l×mf/m, and also, The vehicle weight is determined by mf + mr, and the moment of inertia is determined by, for example, determining the weights mf ₁ , mf ₂ , mr ₁ , mr ₂ on each wheel, and calculating the distance from the center of gravity to the axle by r ₁ , r ₂ , r ₃ , By finding r ₄ , it can be found from the relationship Iz=mf ₁ ×r ² ₁ +mf ₂ ×r ² ₂ +mr ₁ r ₃ ² +mr ₂ m ₄ ⁴ . From the measured values thus obtained, the command circuit 16
In the formula [1], the magnification k of the rear wheel steering angle with respect to the front wheel steering angular velocity is determined, and the rear wheel steering angle is determined from this magnification k and the measured value detected by the front wheel steering angular velocity detector 14, and this value is transmitted to the servo amplifier 17 as a command signal. The servo amplifier 17 outputs a control current to the servo valve 18, whereby the servo valve controls the amount of oil supplied from the hydraulic pump 19 to the actuator 21 and the amount of oil returned to the oil tank 23, thereby controlling the displacement of the actuator 21. do. Note that the command circuit 16 can be constructed of either an analog circuit or a digital circuit. In addition, since the change in vehicle load is small compared to changes in other factors in a vehicle with a small payload, such as a passenger car, the change in vehicle load can be ignored as shown in equation [1'] above. Therefore, it is not necessary to detect it, and for vehicles such as trucks where load changes cannot be ignored, formula [1] can be used in consideration of load changes.

[Formula] However, for A and B', a magnification k that is a constant may be used. Furthermore, in a vehicle where phase delay becomes a problem only at high vehicle speeds, the value of the ratio k may be a constant value that is compatible with a predetermined high vehicle speed. As described above, according to the present invention, there are provided two sets of wheels capable of steering the left and right wheels in conjunction with each other, one set of wheels is steered by the driver, and the other set of wheels is steered by the driver. In the steering control method for a vehicle that steers by following the wheel set, the other wheel set is steered at a steering angle obtained by multiplying the steering angular velocity of the one wheel set in proportion to the steering angle when turning. The effect is that the phase difference between the driver's steering angle and the yaw rate generated in the vehicle can be significantly reduced, and a natural operating feeling can be given to the driver.

[Brief explanation of the drawing]

1 is a perspective view showing the arrangement of a device used to carry out the present invention, FIG. 2 is an explanatory block diagram of the device shown in FIG. 1, FIG. 3 is an explanatory diagram of the operation when the vehicle turns, FIG. 4 is a characteristic curve diagram showing the phase delay between the yaw rate and the steering operation when the vehicle turns, and FIG. 5 is a characteristic curve diagram showing the relationship between the rear wheel steering angle/front wheel steering angular velocity multiplier k and the vehicle speed. 1... Steering wheel, 2... Steering column, 3... Steering gear box, 4
... Pitman arm, 5 ... Connecting rod, 6 ... Side rod, 7 ... Knuckle arm, 8 ... Tire, 9 ... Suspension, 10
...Engine, 11 ...Transmission, 1
2...Axle shaft, 13...Vehicle speed detector,
14... Front wheel steering angular velocity detector, 15... Load detector, 16... Command circuit, 17... Servo amplifier, 18... Servo valve, 19... Hydraulic pump, 20... Rear wheel steering linkage, 21
...actuator, 22...potentiometer, 23...oil tank.

Claims (1)

[Scope of Claims] 1. Two wheel sets capable of steering the left and right wheels in conjunction with each other, one wheel set is steered by the driver, and the other wheel set follows the one wheel set. A vehicle in which two sets of wheels can be steered, characterized in that the other wheel set is steered at a steering angle obtained by multiplying the steering angular velocity of the one set of wheels in proportion to the steering angular velocity of the other set of wheels. steering control method. 2 The magnification k of the proportional multiplier is (However, V is the vehicle speed, and A and B are constants.) The method according to claim 1, wherein the steering is determined by: 3 The magnification k of the proportional multiplier is (However, V is the vehicle speed, m is the vehicle weight, and A and B' are constants.) The method according to claim 1, wherein the steering is determined by: