Abstract:
An arrangement for avoiding rollovers when accelerating motor vehicles, single-track or double-track vehicles such as motorcycles or passenger cars in particular, with an arrangement for comparing a difference in rotational speed between the speed of at least one front wheel or the front axle and the speed of at least one rear wheel or the rear axle of the motor vehicle with an adjustable rotational speed difference threshold value. Also included is an arrangement for detecting a wheel acceleration for at least one front wheel and for at least one rear wheel and an arrangement for activating the vehicle&#39;s propulsion system when the rotational speed difference threshold value is reached or exceeded if the wheel acceleration is simultaneously negative for at least one front wheel and positive for at least one rear wheel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to arrangements and methods for avoiding rollovers when braking or accelerating motor vehicles, single-track or double-track vehicles such as motorcycles or passenger cars in particular. 
     BACKGROUND INFORMATION 
     In order to avoid or reduce the possibility of rollovers during braking or acceleration, conventional vehicles have design features such as a long wheelbase, a low center of gravity, a balanced axle load distribution or low braking or propulsive power. More recently, however, vehicles having a short wheelbase and a significantly higher center of gravity have become increasingly popular. In such vehicles, there is the danger that a rollover or tipping over on or about the front axle will take place, especially on downhill grades. There is also the danger that a vehicle with rear wheel drive will tip backwards about the rear axle when strongly accelerating or when reaching uphill grades, for example. Such difficulties also occur, for example, in motorcycles or racing cars, drag racing cars in particular. In motorcycles, the avoidance of rollovers during acceleration is entirely dependent on the driving skill of the driver. 
     A braking force control system for motor vehicles is known from German Published Patent Application No. 21 33 547 in which a sensor is assigned to each wheel for the measurement of the momentary rotational characteristics, the signals of the sensor being processed in an evaluation circuit and compared with specified rotational deceleration, acceleration and/or slip thresholds, the evaluation circuit emitting signals for operation of the inlet and outlet valves assigned to the wheel if the threshold values are exceeded or not met, as a result of which the braking pressure drops, remains constant or increases in order to avoid wheel locking, an additional logical operation being provided in the evaluation circuit in vehicles having a short wheelbase and a high center of gravity which reduces the pressure on the front wheel brakes if a signal indicating road adherence of the rear wheels does not arrive within a specific waiting period. This printed publication deals exclusively with braking force control systems; arrangements for increasing the safety or handling of a vehicle during acceleration are, however, not dealt with. In addition, the disadvantage of such a braking force control system is that it initiates braking force control only after receiving a signal indicating the lack of road adherence. Due to the elasticity of the tires, this can result in delays in initiating braking force control. 
     An arrangement for the detection of rollovers in vehicles is known from German Published Patent Application No. 196 09 717 in which angular rate sensors measure the angular rate of the vehicle about the yaw axis, the roll axis and the pitch axis, an arrangement being present which signals a rollover event if at least one of the measured angular rate exceeds a specifiable limiting value. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to specify arrangements or methods by which such rollovers can be avoided in an effective manner during braking or acceleration. 
     According to the arrangement of the present invention, a criterion indicating the danger of a rollover can be specified in a simple manner from the determination of the rotational speed difference of at least one front wheel and at least one rear wheel (or the rotational speed difference between the front and rear axle) with a rotational speed difference threshold value and the determination of a wheel acceleration for at least one front wheel and for at least one rear wheel. When a vehicle with rear wheel drive is accelerated, specifically in the event of an impending backwards rollover about the rear axle, the rotational speed of the rear wheels is increased while the rotational speed of the front wheels is reduced simultaneously. When the rotational speed difference threshold value and corresponding acceleration values are reached, control of the vehicle&#39;s propulsion system is triggered (in particular via an anti-spin regulation (ASR)) to reduce the propulsive power, as a result of which an impending backwards rollover can be effectively avoided. A suitable rotational speed difference threshold value can, for example, be determined on the basis of vehicle tests or also by model calculations which are at least based on vehicle geometry. Advantageously, the threshold value describes a state in which no immediate danger of a rollover exists. 
     According to another arrangement of the present invention, sensors or switches, limit switches, for example, are attached to the vehicle&#39;s front axle. The position of the front axle in relation to the road surface or in relation to the rear axle can be determined in a simple manner via such limit switches so that in this case also the engine control unit can be activated or propulsive power can be reduced, via an ASR system in particular. In principle, two types of limit switches can be used. The first type of limit switch is a discrete limit switch which simply differentiates whether or not the limit position has been reached. As long as the limit position has not been reached, such limit switches do not generate a signal. Only if the limit position is reached is a signal emitted. In addition, limit switches which emit a continuous-value signal can be provided. Such a continuous-value signal can be analyzed as a measure of the position of the sprung mass (vehicle body) in relation to the unsprung mass (wheel, axle components) or of spring travel at a particular moment. The use of such limit switches makes it possible to detect a braking rollover or even an acceleration rollover solely via a limit switch assigned to an axle of the vehicle. In fact, with a limit switch of this type, it is possible to detect the direction of movement of the sprung mass or the magnitude of the rebound rates, i.e., the changes of the spring travels. If a single limit switch is used, the dynamic characteristics of the vehicle must also be taken into account. The use of level sensors, such as those used in connection with headlight leveling control, is also possible as an alternative to limit switches. 
     According to another arrangement of the present invention, at least one angular rate sensor is provided to detect a rotation of the vehicle about its rear axis. When angular rate sensors are used to detect an impending rollover, the rotational speed about the corresponding vehicle axle is compared with an associated threshold value. Moreover, the rotational speed is integrated over time and thus the angle of rotation about the corresponding vehicle axis is determined. This angle of rotation is also compared with an associated threshold value. If the rotational speed or the angle of rotation are greater than the associated threshold values, the danger of rollover is recognized. 
     Advantageously, the characterizing features of the devices specified according to the present invention can be combined in any manner. This makes it possible to achieve increased reliability or safety in the avoidance of motor vehicle rollovers during acceleration. 
     According to another arrangement of the present invention, rollovers during braking can be avoided easily and reliably. During braking, the state of the vehicle at the start of a rollover is characterized by very strong braking action and by the fact that the vehicle begins to tip frontwards about the front axle. As a result, the rotational speed of the rear wheels which, for example, can be acted upon by an ABS/ASR system, drops to zero due to the abrupt loss of the frictional connection. Owing to the elasticity of the tires, however, this loss of frictional connection does not take place at the same time as the actual start of the rollover motion. However, the switches or sensors detecting the movement or the limit position of the unsprung axle components make it possible to initiate a reduction of the braking action appropriate to the situation already with partial or total rebound, i.e., already before the rear wheels lose frictional connection. In particular, ABS/ASR systems can be used for such reduction. Rollovers during acceleration can be avoided in an analogous manner, since the direction of movement of the unsprung components in relation to the sprung components detected by the switches or sensors is merely the opposite. 
     According to an advantageous embodiment of the arrangement according to the present invention, at least one active speed sensor is provided which is mechanically linked to at least one rear wheel or the rear axle of the vehicle. This makes it possible to detect reliably a loss of frictional connection of the rear wheels which are in particular affected by an ABS or ASR system, via which an effective criterion for the activation of an ABS or ASR system is made available. Such ABS systems can, for example, reduce the braking pressure or braking force in the front wheel brakes until the rear wheels turn again or a control time limiting value is exceeded, thus ensuring that the vehicle, due to its inertia, is no longer in the process of rolling over but rather comes to a complete standstill. This also ensures that the vehicle does not continue to “creep” forward, which would extend the braking distance in a disadvantageous manner. Particularly in combination with the method of the present invention of attaching sensors or switches to determine the limit position of at least one unsprung axle component, the result is a safe and reliable system to avoid motor vehicle rollovers, resulting in a significant increase of vehicle safety. 
     Advantageously, the arrangement of the present invention for avoiding rollovers during braking has an angular rate sensor and an arrangement to activate the braking control system in the event a predetermined angular rate is reached or exceeded (i.e., at least reached). 
     The arrangements of the present invention to avoid rollovers during braking can be used with all braking systems, including braking systems operated with non-liquid or non-gaseous transmission media. 
     It proves to be particularly advantageous that angular rate sensors attached to the rear axle can be used both for the detection of impending rollovers during braking as well as during acceleration. 
     The arrangements of the present invention for the prevention of rollovers can, as mentioned, be used advantageously in combination with ABS and ASR systems. A corresponding expansion of such ABS or ASR systems can be easily implemented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a diagrammatic representation of the use of limit switches to detect an impending rollover of a vehicle. 
     FIG. 2 shows a diagrammatic representation of the use of level sensors to detect an impending rollover of a vehicle. 
     FIG. 3 shows a diagrammatic perspective view of a motor vehicle equipped with an ABS/ASR system and angular rate sensors according to the present invention. 
     FIG. 4 shows a block diagram for the basic representation of the arrangements according to the present invention. 
     FIG. 5 shows a flow chart illustrating the mode of functioning of the arrangements according to FIG. 4 or the methods according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1, a wheel  1  is coupled to a sprung mass, the vehicle body  3  in particular, via an axle component  4  and a spring suspension  2 . Corresponding to its movement in relation to vehicle body  3 , axle component  4  acts upon a limit switch  103 . Limit switch  103  is connected via conductor leads to a control unit  104 . 
     For the following explanation of the drawing, it is assumed that wheel  1  is a front wheel of a motor vehicle and accordingly axle component  4  is an axle component of the front axle of the vehicle. Moreover, it is assumed that the vehicle (not shown) has rear wheel drive. It should be noted that these assumptions are made solely for reasons of clarity of the representation and are applicable by analogy to a front wheel drive. 
     If the motor vehicle is accelerated too strongly, the front axle area (in the case of rear wheel drive) tends to lift off the road surface. As a result (upward movement of the sprung mass or vehicle body  3 ), limit switch  103  is brought into its closed position so that a corresponding signal is sent to control unit  104 . In the event of a lifting off or backwards rollover of the vehicle, which is indicated by the position of the limit switch, control unit  104  is now capable of initiating suitable control measures. Accordingly, a backwards rollover about the rear axle of the motor vehicle can be appropriately detected and prevented via limit switches arranged in the rear axle area. 
     Level sensors for determining the position of a vehicle body in relation to a road surface are schematically identified as  8  in FIG.  2 . Such level sensors are used, for example, in headlight leveling control systems. Level sensors  8  are connected to a control unit  104  which can initiate suitable control measures in the event of an impending rollover of the motor vehicle indicated by the level sensor. 
     The control units of FIGS. 1 and 2 are, for example, control units of an ABS/ASR system, as is schematically shown in FIG. 3, or control units interacting with an ABS/ASR control unit. 
     In the system shown in FIG. 3, each wheel of the motor vehicle is provided with a (schematically shown) rotational speed sensor  101 . For the proper control of the braking pressure applied to each wheel  1 , the measured values of the wheel speed sensors  101  can be supplied to a control unit  104   a  of a hydraulic unit  10 . In addition, the motor vehicle is provided with (schematically shown) angular rate sensors  102  which detect a tipping behavior of the vehicle (rotation about the front or rear axle) in particular. The measured values determined by sensors  102  can be supplied to control unit  104   a  mounted on hydraulic unit  10  and an additional engine management control unit  104   b . In the event of an impending forwards or backwards rollover of the vehicle under excessive acceleration or sudden braking (represented by the signals of angular rate sensors  102 ), the interaction of the named control units brings about a modulation of the braking force of wheels  1  and/or an engine management by influencing, for example, a throttle actuator  14 , fuel injectors  15  or an ignition module  16 . The signal of an accelerator pedal sensor  17  may be sent to the control units as an additional sensor variable. A rollover of the motor vehicle under acceleration is avoided by comparing the rotational speeds of at least one front wheel  1  detected by wheel speed sensors  101  and of at least one rear wheel  1  with an adjustable rotational speed difference threshold value. Moreover, the differentiation by time of the measured values of wheel speed sensors  101  brings about a determination of the wheel acceleration of at least one front wheel and of at least one rear wheel. If it is now determined that when the rotational speed difference threshold value is reached or exceeded (i.e., at least reached), the wheel acceleration is simultaneously negative for at least one front wheel and positive for at least one rear wheel, hydraulic unit  10  or the engine management system is activated for the generation and implementation of appropriate correction signals or corrections. 
     The tilt rates or angular rates determined by angular rate sensors  102  may be provided additionally or alternatively to the named limit switches  103  or level sensors  8  in order to determine whether a rollover is impending. An appropriate combined analysis of the respective sensor signals, for example, makes a redundant system available for the monitoring of a rollover, which increases the safety and reliability. It is also possible to detect an impending tipping state of the motor vehicle exclusively on the basis of the signals generated by wheel speed sensors  101 . For this purpose, it is determined whether the wheel speed on the front or rear axle suddenly drops as a result of which a loss of frictional connection of the wheels with the road can be represented. An impending rollover can be concluded from such a loss of frictional connection. 
     Based on FIGS. 4 and 5, the options made available according to the present invention to avoid rollovers during braking or acceleration for motor vehicles will now be explained in a more general form. 
     In FIG. 4, wheel speed sensors which supply rotational speeds n ij  as signals are identified as  101 . The index i identifies front (v) or rear (h) and the index j identifies left (l) or right (r). It would also be conceivable to consider one wheel speed sensor per vehicle axis. An angular rate sensor is identified as  102  The angular rate determined with this angular rate sensor is identified as ω 1 , the index i representing front or rear axle. A limit switch is identified as  103 . The signal detected by a particular limit switch is identified as ELS i , the index i again representing front or rear axle. It is conceivable to assign several limit switches to one axle, for example, one limit switch  103  per wheel. 
     Signals n ij , ω i , and ELS i  are sent to a control unit  104  which emits signals or variables S i   1  to control an actuating system  105  (e.g., ABS/ASR or engine management system). For this purpose, control unit  104  forms the timing difference of the detected rotational speed d/dt (n ij ) to detect an acceleration of the motor vehicle. Control unit  104  receives signals or variables S i   2  as feedback from actuating system  105 . 
     In the case of acceleration with an impending rollover (impending rollover about the rear axle of the vehicle with rear wheel drive, for example), the throttle actuator or ignition point is influenced via actuating system  105 , resulting in a reduction of engine torque. In the braking case, i.e., in the case of an impending rollover about the front axle in particular, the valves assigned to the wheel brake cylinders are influenced, resulting in a reduction of braking pressure. 
     As an alternative or as a supportive measure, level sensors may be used in addition to limit switches  103 . If level sensors are used, a value recorded by the level sensor during the application is detected which characterizes the rollover danger of the vehicle (the situation in this case corresponds, for example, to the situation in which limit switches  103  have either reached their particular limit stop or are about to do so). This value can be used as a threshold value in the monitoring system according to the present invention. 
     The sequence of monitoring impending rollovers will now be explained in detail with the aid of FIG.  5 . 
     The start of the process is identified as  201 . Measured variables and sensor variables are supplied in a step  202 . 
     For example, values n ij  and d/dt (n ij ) are supplied in step  202  for the analysis of wheel speed difference and wheel acceleration in the case of an impending acceleration rollover. The values ELS i are supplied for the analysis of limit switches in the case of an acceleration rollover or braking rollover monitoring. Correspondingly, level sensor signals are supplied for the analysis of level sensors. If angular rate sensors are used to monitor an acceleration rollover or a braking rollover, ω i  or the cited integral of ω i  over time is supplied in step  202 . Finally, appropriate wheel speed values can be supplied in the case of analysis of wheel speeds to determine a loss of frictional connection for the situation of a braking rollover or an acceleration rollover. 
     In the subsequent step  203 , a check is made of whether a rollover is impending or not. The check conditions listed below can be combined in any desired sequence for an impending acceleration rollover or braking rollover. 
     If a wheel speed difference between at least one front wheel and at least one rear wheel is detected which is greater than a threshold value and there are corresponding wheel acceleration (negative wheel acceleration of the front wheels and positive wheel acceleration of the rear wheels), an appropriate action is taken in step  204 . If the named threshold value is not reached and/or the corresponding wheel accelerations are not reached, there is a branching to step  205  with no action being taken. 
     A corresponding branching to step  204  takes place if, for example, a limit switch with signal values 0.1 outputs the value ELS i =1. If continuous-value limit switches are used, an action according to step  204  is taken in the event that ELS i  is greater than a threshold value. A corresponding control takes place for measured values obtained from level sensors. 
     When angular rate sensors are used, action according to step  204  is taken if the detected angular rate ω i  about the front or rear axle and an integral of ω i  over time are greater than a threshold value; otherwise, consistent with step  205 , no action is taken. 
     If only the wheel speeds of the front or rear axle are analyzed (in the case of monitoring a rollover over the front axle or the rear axle of the vehicle to recognize frictional connection of the wheels), step  204  is activated if a corresponding threshold value is exceeded; otherwise step  205  is activated.