Abstract:
A two solenoid pressure modulated ABS relay valve incorporates a quick release valve in the control air circuit to allow a majority of the air in the control cavity to escape directly to ambient. The orifice through the exhaust solenoid need only handle a relatively small volume of air upstream of the quick release valve, i.e., between the quick release diaphragm and the inlet solenoid seat.

Description:
BACKGROUND OF THE INVENTION 
     This application relates to the art of braking systems, and more particularly to an antilock brake system (ABS) modulator relay valve. The invention is particularly applicable to a tractor or tractor-trailer type vehicle equipped with an air braking system in which a vehicle operator generates a control signal to operate a brake control valve. The signal is transmitted to relay valves which communicate compressed air from storage reservoirs to vehicle brakes. It will be appreciated, however, that the invention may relate to similar environments and applications. 
     A modulator relay valve for ABS brake systems typically includes an impermeable or solid walled piston or flexible diaphragm that selectively moves during normal service braking to establish communication among supply, delivery, and exhaust ports. The piston is responsive to a control signal provided, for example, from a foot brake valve or trailer control valve. The piston then selectively activates an inlet/exhaust valve to selectively connect the supply, delivery, and exhaust ports. In response to an antilock control event, a solenoid control assembly provides for a rapid pulsing of the brake application. That is, if an antilock event is sensed, an electronic control unit sends suitable signals to solenoid valve assemblies associated with the modulator. The valve assemblies provide an electro-pneumatic interface between the electronic control unit and the airbrake system. If an impending wheel lockup is sensed, the antilock controller immediately begins to modify brake application using the modulator. Air on one side of the modulator piston is controlled by selectively opening and closing the supply and exhaust solenoid valve assemblies. Coils associated with the respective solenoid valve assemblies are quickly energized or deenergized in a predetermined sequence by the controller. When the solenoid coil is energized, a core or shuttle is moved to either open or close an associated air passage. This either opens or closes the exhaust passage or reapplies air pressure to the brake actuator. By opening or closing the solenoid valves, the anti-lock controller simulates brake “pumping” but at a rate substantially faster than the driver of a vehicle could actually pump the brakes to avoid skidding. 
     To achieve good ABS performance in air brake vehicles, a significant actor is the ability to rapidly exhaust service air from the brake chamber. In known two solenoid relay valve arrangements, control air from a relay valve control cavity is exhausted through an orificed exhaust solenoid passage. As will be appreciated, the orificed exhaust passage is relatively small. One proposed solution is to employ a larger solenoid, i.e., a solenoid having a larger orifice or exhaust passage, so that the passage would not serve as a bottleneck for the exhaust function during an antilock control event. However, a larger solenoid is less efficient and requires additional power to operate. It is for these reasons that present arrangements use an exhaust solenoid of a predetermined size and exhaust the control air from the relay valve control cavity through the exhaust solenoid passage. Thus, any improvement that addresses these concerns would be desirable, particularly if easily incorporated into an existing modulator valve without substantial modification. 
     SUMMARY OF THE INVENTION 
     The present invention contemplates an improved modulator relay valve employing a quick release valve in the control air circuit to allow control air contained therein to escape directly to atmosphere. 
     In accordance with a preferred embodiment of the invention, a quick release valve is interposed between the control cavity and the exhaust solenoid. In this manner, a majority of the control air contained in the cavity is permitted to escape directly to atmosphere through the quick release valve. The exhaust solenoid passage need only exhaust the relatively small volume of air disposed between the quick release diaphragm and the supply solenoid seat. 
     According to another aspect of the invention, the conventional antilock braking system is easily modified to incorporate this improvement. 
     A principal advantage of the invention is the ability to improve ABS performance on air braked vehicles. 
     Another advantage of the invention resides in the ability to achieve improved exhaust of control air from the relay valve control cavity without increasing the size and power constraints associated with the present solenoid valve assembly. 
     Still another advantage of the invention is the ability to easily modify the existing system to incorporate this feature. 
     Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description. dr 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification. The preferred embodiment is illustrated in the accompanying drawings and forms a part of the invention, wherein: 
     FIG. 1 is a schematic representation of a prior art, two solenoid modulating relay valve assembly shown in a normal service application position; 
     FIG. 2 is a view similar to FIG. 1 illustrating the relay valve in a balanced or hold position; 
     FIG. 3 illustrates the prior arrangement in a service application release position; 
     FIG. 4 illustrates ABS operation where the exhaust port of the solenoid assembly is opened to simulate pumping of the brakes; 
     FIG. 5 is a schematic representation of the new invention; and 
     FIG. 6 is a graphical representation of the improved exhaust feature provided by the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1-4 illustrate a conventional pressure modulating relay valve assembly  10  having a housing  12  that communicates with an air supply or pressurized air reservoir  14  and a control valve  16 , which may include a foot-brake valve  18  and a trailer control valve  20  interconnected, for example, by a double-check valve  22 . The relay valve housing  12  also communicates with a service brake chamber  24 . A control port  30  selectively receives an air pressure signal from either the brake valve or trailer control valve. The air passes through an inlet or supply solenoid valve assembly  32  and passage  34  for communication with a control volume or cavity  36  defined by a first or upper face of the piston  38  sealingly received in the housing. The pressurized air acts on the piston and urges it toward a position as shown in FIG. 1 where an inlet/exhaust valve  40  opens communication between the storage reservoir  14  and the brake chamber  24 . That is, a lower side of the relay piston  38  engages and urges the inlet/exhaust valve from associated seat  42 . This establishes communication between the air reservoir  14  and the brake chamber  24  as illustrated by the arrows in FIG.  1 . Thus, supply port  44  communicates with delivery port  46 . The movement of the piston also engages a valve seat  50  to preclude further communication with exhaust port  52 . Consequently, the brake chamber  24  which is normally in communication with the exhaust port, is then actuated or pressurized by the air, as exhibited in FIG.  1 . 
     FIG. 2 represents a balance or hold position where air is still communicated from the brake trailer control valve to the port  30 , thus pressurizing the upper side of the piston. Likewise, the second or underside of the piston has reached the state where air pressure, in conjunction with the biasing force of spring  54 , provides for inlet/exhaust valve  40  to be seated against both valve seat  42  and valve seat  50 . 
     In FIG. 3, control pressure above the relay piston is exhausted as the valve  60  opens and air pressure is removed from the control port  30 . The control piston also unseats from the valve seat  50  thus establishing communication between the brake chamber  24  and exhaust port  52 . In this manner, the service brakes are released until the next brake application is demanded by the operator. 
     FIG. 4 is representative of the antilock mode of the relay valve. Again, when an antilock controller senses impending wheel lock, electrical signals are sent to the supply solenoid  32  and exhaust solenoid  70 . By selectively opening and closing the solenoids, brake pumping is simulated. More particularly, the supply solenoid is normally open and when closed prevents control line pressure from port  30  from further pressurizing control cavity  36 . On the other hand, the exhaust solenoid  70  is normally closed. When opened, the exhaust solenoid provides a path for air pressure from the control volume  36 , though passage  34 , and through the restricted orifice to reach ambient pressure (as represented by the deflected shape of exhaust diaphragm  71 ). 
     Because of the restricted orifice  72  through the exhaust solenoid assembly, a need exists for improved ABS performance and the ability to rapidly exhaust air from the control volume. FIG. 5 illustrates the provision for a large exhaust passage  74  from the control cavity to an exhaust side of a diaphragm  76  of a quick release valve  78 . As will be appreciated, the exhaust paths represented by passage  34  in the prior art embodiment of FIGS. 1-4 are preferably plugged to the exhaust solenoid. FIG. 5 shows a pressure modulating relay valve assembly  10 ′. Also, analagous to the features shown in FIGS. 1-4, FIG. 5 includes an air supply or pressurized air reservoir  14 ′, control valve  16 ′, foot-brake valve  18 ′, trailer control valve  20 ′, double check valve  22 ′, service brake chamber  24 ′, control port  30 ′, supply solenoid valve assembly  32 ′, control cavity  36 ′, piston  38 ′, inlet/exhaust valve seat  42 ′, supply port  44 ′, delivery port  46 ′, exhaust port  52 ′, spring  54 ′, valve  60 ′, exhaust solenoid  70 ′, exhaust diaphragm  71 ′, and orifice  72 ′. The additional passage  74  is cross-drilled in the housing to provide a large diameter passage  74  from the control volume to the exhaust side of the quick release valve  78 . There is still a communication path between the supply side of the quick release diaphragm and the exhaust solenoid as represented by the arrow in FIG.  5 . The exhaust solenoid need only exhaust a relatively small volume of air upstream of the quick release diaphragm  76 . The majority of the control air in the control cavity  36 ′ escapes directly to ambient through passage  74  and the quick release valve  78 . This effectively achieves the rapid exhaust desired for improved ABS performance. 
     FIG. 5 shows the modulator relay assembly of the present invention in ABS exhaust mode, with the air in control cavity  36 ′ being exhausted to ambient past valve seat  82  of the quick release valve  78 . ABS exhaust is initiated by simultaneous movement of supply solenoid  32 ′ to seal against supply solenoid seat  80  so as to cut off air pressure coming from control port  30 ′, along with actuation of exhaust solenoid  70 ′ to exhaust the air volume between diaphragm  76  and supply solenoid seat  80 . This action removes the pressure from the upstream side of diaphragm  76  so that it is unseated from valve seat  82  to allow rapid exhaust of the air in control cavity  36 ′ through passage  74 . When the modulator is in the ABS build or hold modes where rapid exhaust through quick release valve  78  is not desired, the supply solenoid valve assembly air pressure from control port  30 ′ maintains the diaphragm  76  in a position sealed against valve seat  82  so that no air is exhausted past quick release valve  78 . 
     FIG. 6 is a graphic representation of the improvement achieved with the present invention. Particularly, voltages are depicted by curve  90  in the graph. The solenoid current is represented by curve  92 . The representative distinction between the embodiment of FIGS. 1-4 and that of FIG. 5 is best exemplified by a comparison of the air pressure curves  94 ,  96 . Although the air pressure decreases rapidly as illustrated by curve  94 , indicating release of air pressure in the control cavity upon energization of the exhaust solenoid, curve  96  has a steeper slope and more quickly exhausts the air pressure therefrom. Incorporating the quick release valve  78  and the large diameter passage  74  results in the increased slope and improved performance desired for ABS performance. 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to other upon reading and understanding of this specification. For example, alternative designs of a quick release valve assembly can be used to rapidly and efficiently exhaust air from the control volume. The present invention is intended to include such modifications and alterations in so far as they come within the scope of the appended claims or the equivalents thereof.