Abstract:
An improved hydraulic motor system, suitable for driving an automotive cooling fan or the like. The system is driven by grade gerotor set and an idle gerotor set which are stacked between a center plate and against a rear wall of a cylindrical cavity in a front face of a manifold. A fluid-tight chamber is established by securing an end frame can around the stacked gerotor sets and against the perimeter of the manifold cavity. Tightness of the seal is controlled by positioning a resilient cover plate against the end frame can from a position opposite the manifold, and adjustably clamping the resilient cover against the manifold until the resilient cover has undergone a predetermined amount of elastic deformation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to an arrangement of cooperatively driven hydraulic motors for use in powering an automotive cooling fan or the like. Automotive engines are typically supplied with a liquid coolant, which is circulated through a radiator. The radiator is a heat exchanging device which collects heat generated by an internal combustion process and radiates it to the ambient air. Under ideal conditions, the heat transfer would proceed at the rate at which it is generated. Unfortunately, this is easier said than done.  
           [0002]    When an automotive engine is idling, there is no natural airflow across the radiator surfaces, and it is customary to supplement the airflow with forced air from a cooling fan. As an automotive vehicle moves forward from an idle condition and gains speed, it suffers gradually increasing energy losses from air drag, road friction and internal frictional losses. These energy losses are made up by increasing the rate of internal combustion. That in turn increases the rate of heat generation, thereby increasing the work which must be done by the radiator. However, increases in vehicle speed cause an increase in the natural airflow through the radiator. This increase in natural airflow increases natural cooling at a rate which rises faster than the rate of heat generation. As a consequence, the workload on the cooling fan generally decreases with vehicle speed.  
           [0003]    The above energy considerations are discussed in detail in Buschur U.S. Pat. No. 5,561,978. That patent teaches that improved energy efficiency may be achieved by providing an automotive cooling system having a plurality of hydraulic motors which are switched into driving relationship with the cooling fan in response to pressure conditions in the hydraulic fluid supply. By way of example, the Buschur patent teaches a hydraulic motor system comprising two segregated spur gear hydraulic motors, communicating with a hydraulic fluid supply and driving a common fan shaft. It is taught that the fluid supply lines may be connected either in parallel or in series and that one or more clutches may be provided for selectively placing the hydraulic motors into driving relationship with the fan shaft. The patent also suggests the use of gerotor type hydraulic motors.  
           [0004]    [0004]FIG. 1 hereof illustrates a prior art hydraulic motor drive  300  for an automotive cooling fan (not illustrated). The drive unit  300  comprises a first hydraulic motor  302  and a second hydraulic motor  304 , both of which are of the gerotor type. Hydraulic motors  302 ,  304  are supported by a manifold body  306  and are sealed against opposite faces of a coupling block  308 . The assembly is secured to manifold body  306  by four bolts  309   a - 309   d  and an end plate  310 . It is readily apparent that motor system  300  is quite complex, difficult to assemble and susceptible to fluid leakage at approximately a dozen seals to atmosphere. There is a need for an improved dual displacement hydraulic motor system which is more simple to manufacture and easier to maintain.  
         SUMMARY OF THE INVENTION  
         [0005]    This invention provides an improved motor system, suitable for driving an automotive cooling fan or the like. In a first aspect, the motor system has two hydraulic drive mechanisms, circumferentially fixed to a common shaft and surrounded by a common, fluid-tight chamber, In this first aspect, the hydraulic drive mechanisms preferably are gerotor sets, each comprising an inner rotor, circumferentially fixed to the common shaft, and an outer rotor eccentrically positioned about the inner rotor. The fluid-tight chamber is established by securing an end frame can against the perimeter of a manifold cavity. The two gerotor sets are stacked on opposite sides of a center plate, one gerotor set being placed in the manifold cavity, and the center plate and other gerotor set being placed in the can.  
           [0006]    In a second aspect, the invention provides an improved method of preventing leakage of hydraulic fluid from a dual drive hydraulic motor system. The method involves the steps of:  
           [0007]    (1) stacking the hydraulic motor components against a manifold,  
           [0008]    (2) placing a sealing ring around the hydraulic motor components and in contact with the manifold,  
           [0009]    (3) moving an end frame can enclosingly about the hydraulic motor components and into contact with the sealing ring,  
           [0010]    (4) urging a resilient cover plate toward the end frame can from a position opposite the manifold, and  
           [0011]    (5) adjustably clamping the resilient cover against said manifold until the resilient cover has undergone a predetermined amount of elastic deformation.  
           [0012]    It is therefore an object of the invention to provide an improved dual displacement hydraulic motor system which is more simple to manufacture and easier to maintain.  
           [0013]    It is another object of the invention to provide an improved method of assembling a hydraulic motor system.  
           [0014]    Other and further objects and advantages of the invention will be apparent from the following specification, with its appended claims, and the attached drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is an exploded perspective drawing of a prior art hydraulic motor system;  
         [0016]    [0016]FIG. 2 is an exploded perspective drawing of a hydraulic motor system according to the present invention;  
         [0017]    [0017]FIG. 3 is a side elevation drawing of the hydraulic motor system, sectioned to show an axially extending hydraulic fluid return channel in a side wall of a can;  
         [0018]    [0018]FIG. 4 is a side elevation drawing of the hydraulic motor system, sectioned to show an enclosed, axially extending, hydraulic fluid return passage and a radially extending notch which feeds hydraulic fluid thereto;  
         [0019]    [0019]FIG. 5 is a side elevation drawing of the hydraulic motor system, sectioned to illustrate clamping of a cover plate;  
         [0020]    [0020]FIG. 6 is a schematic illustration of an offset cylindrical cavity in a front face of a manifold;  
         [0021]    [0021]FIG. 7 is an illustration of a center plate; and  
         [0022]    [0022]FIG. 8 is a side elevation drawing of the hydraulic motor system, sectioned to show a path for conveying hydraulic fluid between a manifold and an idle gerotor set. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    The improved hydraulic motor system is illustrated in the exploded perspective drawing of FIG. 2 shown therein are a manifold  1 , an end frame  2  and a cover plate  3 . Four threaded bolts  4   a - 4   d,  preferably of the MIO type, extend through cover plate  3  and engage manifold  1  to clamp end frame  2  therebetween. A shaft  50  extends from manifold  1  through end frame  2  and cover plate  3  for engagement with an automotive cooling fan (not illustrated). An idle gerotor set  8 , comprising inner and outer idle rotors  31 ,  36 , respectively, is stacked on shaft  50  inside a circular opening  53  in eccentric ring  6 . Idle gerotor set  8  is stacked between end frame  2  and a center plate  5 . Also, a grade gerotor set  9 , comprising inner and outer grade rotors  21 ,  26 , respectively, is stacked on shaft  50  between center plate  5  and manifold  1 . Outer grade rotor  26  is received within a cylindrical cavity  51  in manifold  1 , as illustrated on FIG. 3. Inner grade rotor  21  and inner idle rotor  31  are circumferentially fixed to shaft  50  by axially extending rectangular teeth. Circular opening  53  and cylindrical cavity  51  are positioned eccentrically with respect to the axis of shaft  50 . Alignment is maintained between the above-described parts by means of a pair of alignment pins  20 ,  20  extending parallel to shaft  50 .  
         [0024]    Note also that when end frame  2  is positioned on manifold  1 , the pins  20  eccentrically align ring  6 , center plate  5  and manifold  1 , thereby reducing human errors and facilitating reduction of assembly time.  
         [0025]    Numerous interface seals required by the prior art configuration of FIG. 1 are eliminated through use of the metal to metal stack construction as shown in FIGS. 2 and 3. In the present invention, clamped surfaces at interface A (between end frame  2  and eccentric ring  6 ), interface B (between eccentric ring  6  and center plate  5 ) and interface C (between center plate  5  and manifold body  1 ) define the principle fluid boundaries to enclosed operation pockets for gerotor sets  8  and  9 . (Details on the passage of oil through the stacked plate interfaces to the two gerotor sets are shown in FIGS.  6 - 8 ). Leakage past the interfaces is captured by an overall cylindrical can  10  integral to end frame  2 . This leakage hydraulic fluid is collected within the can and channeled radially through grooves created by chamfers  11  on center plate  5  and eccentric ring  6 . and further on to axial channel  12  in the interior wall of can  10 . Leakage hydraulic fluid is then carried out of the general motor area and vented to near atmospheric pressure through notch  13  (FIG. 4) on the face of manifold  1  and passage  14  as shown on FIG. 4. Given that the restriction to hydraulic fluid flow through interfaces A, B and C is considerably tighter than through notch  13  and passage  14  the pressure within the can  10  is low. Thus, multiple high pressure seals required in the prior art are replaced by one low pressure seal  15  in this invention.  
         [0026]    Requirements for traditional dowels in the construction are eliminated by dividing the alignment feature provided by close tolerance dowels into two functions. Referring now to FIG. 5, the can  10  which is an extension of end frame  2  provides centerline to centerline alignment to eccentric ring  6  and center plate  5 . Further, the interface ID  16  allows alignment through interface OD  17  on manifold  1 . These features facilitate the alignment of bearings  18  and  19  on shaft  50 , given that proper tolerances have been established and maintained.  
         [0027]    Referring again to FIG. 3, one alignment pin  20  feeds through all parts as shown to provide proper angular alignment for port timing to the two gerotor sets. The second alignment pin  20  (shown on FIG. 2) is used on the remote side of the motor stack to better balance and provide initial alignment prior to the introduction of can  10  during assembly. In this manner, both the centerline alignment and angular positioning of parts may be accomplished without traditional multiple tight tolerance dowels between each interface of the hydraulic stack.  
         [0028]    [0028]FIG. 6 shows cylindrical cavity  51 , as viewed from interface C, with end frame  2 , idle gerotor set  8  and center plate  5  being removed. The figure shows kidney-shaped inlet and outlet ports  23 ,  25  respectively for circulating hydraulic fluid through grade gerotor set  9 . High pressure hydraulic fluid is admitted from inlet port  23  to grade gerotor set  9  between inner grade rotor  21  and outer grade rotor  26 . Projections of inner grade rotor  21  and outer grade rotor  26  are indicated by dotted lines on FIG. 6. Projections of inner and outer idle rotors  31 ,  36 , respectively are also shown in dotted lines. Projections of inlet and outlet ports  33 ,  35  respectively for circulating hydraulic fluid through idle gerotor set  8 , are indicated in phantom lines.  
         [0029]    Outer rotors  26 ,  36  each have one more tooth than their associated inner rotors  21 ,  31  respectively. This plus the eccentric positioning of outer rotors  26 ,  36  causes an outer rotor sliding action which creates continuously opening and closing pockets  57  at each outer rotor tooth, as the gerotor pairs rotate. For each complete rotation of an outer rotor, the pocket  57  at each outer rotor tooth progresses through a cycle between fully opened and substantially closed conditions. The pockets generally increase in size while overlapping an inlet port and decrease in size while overlapping an outlet port.  
         [0030]    As hydraulic fluid fills the space between inner and outer grade rotors  21 ,  26  all pockets  57  which overlap inlet port  23  rise to high pressure, and grade gerotor set  9  rotates CW (when viewed in an axially rearward direction looking from end frame  2  toward manifold  1 , as in FIG. 6). All pockets  57  which overlap outlet port  35  are at low pressure. When taken in aggregate, this creates a large force imbalance bearing force F 1  on the inner grade rotor, as shown. This force is transferred to shaft  50  resulting in deflection and frictional loads at bearings  18 ,  19  (FIG. 5). However, the fluid flow direction is reversed for idle gerotor set  8 . This produces an oppositely acting bearing force F 2 . The two resultant shaft loads oppose each other greatly reducing shaft deflection and net bearing load. The fluid flow through idle gerotor set  8  also produces a net CW torque on shaft  50 , even though the radial force F 2  is opposite F 1 . This is due to the fact that outer grade rotor  26  and outer idle rotor  36  are radially offset in opposite directions from the axis of shaft  50 .  
         [0031]    A solenoid  52  (FIG. 2) controls the flow of hydraulic fluid to gerotor sets  8  and  9 . The timing of the flow sequence to gerotor sets  8  and  9  may be in accordance with the teachings of Buschur 5,561,978, which is incorporated herein and made a part hereof. The connections to grade gerotor set  9  run more or less directly to ports  23 ,  25 . FIGS. 7 and 8 show the connections to idle gerotor set  8 . FIG. 7 is a view of the front face  74  of plate  5 . That figure shows the inlet and outlet ports  33  and  35  respectively for idle gerotor set  8 . Hydraulic fluid flows to inlet port  33  via an internal supply passage  46  connected to an opening  43  on the rear face  76  of center plate  5 . Upon entry into inlet port  33 , the hydraulic fluid causes CW rotation of gerotor set  8 , meanwhile undergoing pocketed flow from inlet port  33  to outlet port  35 . Thereafter, the flow path through center plate  5  is via an internal passage  48  to a rear face opening  45 .  
         [0032]    [0032]FIG. 8 is a sectioned side elevation view of an assembled hydraulic motor system, according to the present invention. Shown there are passages  71  and  73  in manifold  1 . Passages  71 ,  73  are in communication with openings  43 ,  45 . This completes the flow path between manifold  1  and idle gerotor set  8 .  
         [0033]    Referring again to FIG. 5, attention is directed at cover plate  3 . This element should be fabricated from a resilient material. Any one of a wide range of materials would be suitable, but ferrous stock is preferred due to its relatively low cost and its temperature insensitive modulus of elasticity. Cover  3  has two important functions.  
         [0034]    First, cover  3  serves as a massive wave washer allowing a predictable axial clamping load to be applied to the motor stack to resist pressure forces and prevent leakage at the stack interfaces. During assembly, a relatively light torque load (&lt;10 N-m) is applied to each of bolts  4   a - 4   d  to seat the cover plate in a starting position. Then each bolt is turned a set number of degrees, thereby deflecting the cover plate. This applies a predetermined clamping pressure to interfaces A, B, and C (FIG. 3). The only significant variables thus determining the resultant clamping load are the thickness and modulus of the plate and pitch of the bolt threads, all of which are highly controllable. Given that the cover plate is not a perfect washer shape due to packaging issues, the drive angles of the four bolts are modified to allow a uniform clamping load around the clamp load circle. Significant deflection of the plate is desirable as it then easily compensates for any long term creep of the threads.  
         [0035]    The second design function of cover plate  3  is to allow manipulation of the location of the resultant clamping loads on the motor stack caused by the bolt tensile loads. It is apparent that bolts  4   a - 4   d  must be placed outside the seal perimeter as defined by seal  15  resulting in clamping loads outside the desired clamp load circle and increasing the diameter of the disk which hydraulic loads can attempt to deflect. However, cover plate  3  transfers the loads generated by the bolts to a circular area inside the arrows F 3 , thereby minimizing bending moments applied to the stacked motor elements.  
         [0036]    While the form of apparatus and the method herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus and method, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.