Abstract:
A trailer brake system constructed and arranged to effect the relay of a brake signal from the tractor and an automatically generated brake signal of an electronic control device of the trailer to one or more additional trailers in an expanded vehicle train. In one embodiment, the brake signal is relayed to an additional coupled trailer in the form of an electrical signal via an electrical interface. In another embodiment, the brake signal is relayed to an additional trailer by means of a valve device. In yet another embodiment, the brake signal is relayed to an additional trailer by means of a combination of electrical signal transmission and valve device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to an improved trailer brake system for an expanded vehicle train including a tractor and multiple trailers, such as, for example, semitrailers or drawbar trailers, coupled in series thereto. 
     A brake system of the general type under consideration is described in EP 1188634 A2. In the conventional brake system described in EP 1188634 A2, an electronic control device is provided that is capable of, among other things, preventing wheel lock or apportioning braking force as a function of axle load. 
     Also, the electronic control device can generate an automatic brake signal, even without brake actuation by the vehicle train operator, to brake individual vehicle wheels or all wheels to effect handling stability control or prevent rollover of the vehicle train about its longitudinal axis. 
     Furthermore, for braking an additional trailer coupled to the first or preceding trailer to form an expanded vehicle train, brake pressure generated on the basis of brake actuation by the vehicle operator is typically relayed via the first trailer to the brake system of the attached additional trailer. 
     If, however, the first trailer is equipped with a brake system having a conventional electronic control device of the type described above, an automatic brake signal from the electronic control device has no braking effect on the additional trailer. Consequently, the electronic control function corresponding to the automatic brake signal, an example being a vehicle rollover prevention function, cannot be completely effective. Also, with the automatic braking of the first trailer, the handling stability behavior of the vehicle train can change in an undesired way if the additional trailer pushes on the first or preceding trailer. 
     SUMMARY OF THE INVENTION 
     Generally speaking, it is an object of the present invention to provide a trailer brake system that overcomes the disadvantages of conventional systems and that permits safe handling of an expanded vehicle train and efficient use of the brake systems of all coupled trailers. 
     As a preliminary matter, it should be understood that the term “brake signal” as used herein can include both an electrical signal, which can be formed, for example, as a digital data signal, or a pressure (i.e., brake pressure) signal. 
     The present invention, described in greater detail hereinafter, provides, in a simple and cost-effective manner, the capability to coordinate the relay to one or more additional trailers in an expanded vehicle train of (i) a brake signal from the tractor, initiated either by the vehicle operator or automatically by an electronic system in the tractor, and (ii) an automatically generated brake signal of the electronic control device of the trailer brake system. 
     In accordance with a first embodiment of the present invention, relaying of the automatic brake signal to an additional coupled trailer is provided in the form of transmission of electrical signals, for example over a data bus. This embodiment is particularly cost-effective, since it does not require any particularly complex hardware. 
     In accordance with a second embodiment of the present invention, the brake signal can be relayed to an additional trailer by means of a valve device. This has the advantage that a trailer having a brake system that can be actuated exclusively by pneumatic control (that is, no electrical interface is present to receive the brake signal as an electrical signal) can be coupled as an additional trailer. Thus, the second embodiment offers diversity and flexibility in use. 
     A combination of the first and second embodiments is also advantageous. Such a combination enables use independent of the nature of the brake system of the additional trailer(s). 
     Still other objects and advantages of the present invention will in part be obvious and will in part be apparent from the specification. 
     The present invention accordingly comprises the features of construction, combination of elements, and arrangements of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the present invention, reference is had to the following description taken in connection with the accompanying drawings in which: 
         FIGS. 1 to 4  are schematic diagrams depicting embodiments of a trailer brake system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawing figures, where like reference numerals are used for corresponding parts, the trailer brake system in accordance with an embodiment of the present invention depicted in  FIG. 1  is provided with a reservoir coupling head  1  and a brake coupling head  2 . Coupling heads  1 ,  2  are used for connection to corresponding pressurized fluid ports of the vehicle tractor. 
     Via reservoir coupling head  1 , a reservoir pressure of the tractor is injected into the brake system of the trailer. This reservoir pressure is guided via a check valve  26  to a compressed air reservoir tank  27  of the trailer. 
     The pressure of reservoir coupling head  1  is further guided to a combined park/release safety valve  3 . The park/release safety valve  3  is used for manual control of the vehicle parking brake function or for releasing the parking brake in emergencies. Valve  3  is further used as a trailer brake valve with break safeguard, meaning that automatic braking of the trailer is initiated in the event of a defect in or a break in the pneumatic lines by which the trailer is in communication with the tractor. 
     The brake signal is fed via brake coupling head  2  as a brake pressure signal from the tractor to the brake system of the trailer. The brake signal of the tractor is influenced, for example, by brake actuation by the vehicle train operator. In the presence of an electronically controlled brake system in the tractor, the brake signal from the tractor is also influenced by electronic control functions, such as the vehicle electronic stability control function (ESC) or the braking force distribution function. 
     The brake system according to the embodiment of the present invention depicted in  FIG. 1  also contains electrical terminals  20 ,  21 ,  22  that can handle electrical brake signals from the tractor (e.g., a tractor having an electronically controlled brake system). 
     The brake system depicted in  FIG. 1  is also provided with an electronic control device  7 , which is connected to the electrical signals fed via terminals  20 ,  21 ,  22 . The electronic control device, which is advantageously designed as a mechatronic device, is provided with an integrated valve part to which park/release safety valve  3 , a further reservoir tank  4  and brake cylinders  9 ,  11 ,  12  are connected. Furthermore, control device  7  is connected via electrical lines  18 ,  19  to speed of rotation sensors  23 , via which the speeds of rotation of wheels of the trailer are measured. 
     Brake cylinders  11 ,  12  equipped with a spring actuator are also connected pneumatically via an overload protection valve  8  to control device  7  and to reservoir tank  27 . 
     In vehicle trains expanded through the addition of a further trailer (e.g., to expand cargo capacity), the pressure signals from the first trailer are relayed to the additional trailer—that is, the reservoir coupling head of the added trailer is connected to reservoir tank  27  of the first trailer and the brake coupling head of the added trailer is connected to pneumatic line  5  in communication with brake coupling head  2  of the first trailer. Also, the electrical signals are typically relayed to the added trailer via a plug connection  10 . 
     Besides performing other control functions, electronic control device  7  effects automatic braking of the trailer upon recognition of a critical driving condition, such as, for example, a potential rollover of the trailer about its longitudinal axis (rollover risk can be reduced by reducing vehicle speed). In the case of a critical driving condition, electronic control device  7  automatically generates a brake signal by injecting brake pressure into brake cylinders  9 ,  11 ,  12 . 
     A two-way valve  25  is provided in the brake system according to the embodiment of the present invention depicted in  FIG. 1  for relaying automatic brake signals of electronic control device  7 . Two-way valve  25  is designed as a type of double check valve, to the effect that it delivers the higher of two input pressures at its output. 
     According to  FIG. 1 , the brake pressure signal of the wheel brake of one wheel of the right side of the vehicle and the brake pressure signal of the wheel brake of one wheel of the left side of the vehicle are connected to the two inputs of two-way valve  25 . Preferably, the wheels of the primary axle of the trailer are used for this purpose. 
     At its output, two-way valve  25  delivers the higher of the two brake pressures to a trailer control valve  24 . Trailer control valve  24  corresponds, for example, to commercial trailer control valves, as are also used in tractor vehicles for control of the brake systems of trailers. Accordingly, trailer control valve  24  is in communication with reservoir tank  27  and, at its reservoir output, delivers a reservoir pressure signal for the additional trailer to a reservoir coupling port  16 . Furthermore, the trailer control valve is in communication with overload protection valve  8  and with brake coupling head  2 . At a further output, trailer control valve  24  delivers, to a brake coupling port  17 , the respective higher value of the brake pressure value received from the tractor via brake coupling head  2  and the brake pressure value received from two-way valve  25 . 
     The added trailer can be coupled analogously via two pneumatic lines to coupling ports  16 ,  17  and via an electrical line to terminal  10 . As a result, the brake system of the added trailer can behave the same way as the brake system of the first trailer with respect to braking initiated by both the vehicle train operator and by automatic brake signals. It should be appreciated that designing the brake system of the added trailer in the same way permits expansion of the vehicle train with additional trailers. 
     The brake system according to the embodiment of the present invention depicted in  FIG. 2  corresponds to the brake system described herein on the basis of  FIG. 1 , except for the differences discussed hereinafter. 
     According to  FIG. 2 , a second two-way valve  29  is connected via a first input to the output side of two-way valve  25 . The second input of second two-way valve  29  is in communication with brake coupling head  2 . On the output side, second two-way valve  29  delivers the higher of the two pressures present at its input ports to its output, just as in the embodiment depicted in  FIG. 1 . The use of second two-way valve  29 , however, permits a more cost-effective implementation of the brake system than if trailer control valve  24  were used. 
     According to one advantageous configuration, a quick-release valve  30  is provided on the output side of second two-way valve  29 . Quick-release valve  30  permits faster depressurization in the downstream pressure line of the additional trailer in communication with brake coupling port  17  if the brakes are to be released. 
     The embodiment of the inventive brake system depicted in  FIG. 3  corresponds to the brake system described herein on the basis of  FIG. 2 , except for the differences discussed hereinafter. 
     According to  FIG. 3 , an additional pressure-limiting valve  31  is provided between second two-way valve  29  and quick-release valve  30 . By this configuration, the danger of wheel lock of the further trailer can be reduced, especially in the use of an additional trailer that is not equipped with a braking system with anti-lock functionality. Pressure-limiting valve  31  can also be integrated structurally into second two-way valve  29  or quick-release valve  30 . 
     The embodiment of the inventive brake system depicted in  FIG. 4  corresponds to the brake system described herein on the basis of  FIG. 2 , except for the differences discussed hereinafter. 
     According to  FIG. 4 , the brake signal relayed to the added trailer is generated by a valve device  32 ,  33  activated by electronic control device  7  by means of an electrical signal. For this purpose, electronic control device  7  is connected via electrical lines to valve device  32 ,  33 . 
     In the embodiment depicted in  FIG. 4 , valve device  32 ,  33  comprises two solenoid valves. Solenoid valve  32  is designed as a 3/2-way valve. In its operating position illustrated in  FIG. 4 , a port  34  in communication with solenoid valve  33  is in communication with atmosphere. Thus, port  34  is being vented. In a second operating position, port  34  is in communication with reservoir tank  27 . Solenoid valve  33  is designed as a 2/2-way valve. It has a shutoff position and a passing position. Solenoid valve  33  is in communication with two-way valve  29 . Via valve device  32 ,  33 , and by appropriate magnet activation, the pressure signal delivered to two-way valve  29  can be optionally increased, decreased or held at a current value. 
     While the embodiment of the present invention depicted in  FIG. 4  employs valve device  32 ,  33 , it should be appreciated that alternatives thereto that permit optional adjustment of the pressure signal delivered to two-way valve  29 , such as, for example, a proportional valve, can be used. 
     Accordingly, the present invention achieves an improved trailer brake system for an expanded vehicle train that coordinates the relay to one or more additional trailers of a brake signal from the tractor and an automatically generated brake signal of the electronic control device of the trailer brake system. The present invention is particularly advantageous in that it can be implemented in a simple and cost-effective manner. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained, and since certain changes may be made in the above constructions without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.