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Technical Paper Series

Full Power Hydraulic Actuation, Circuit Design Considerations for Off-Highway Vehicles and Equipment

David E. Keyser MICO, Inc.

Presented at the 10th International Conference on FLUID POWER the future for 5 - 7 April 1993 FULL POWER ACTUATION, CIRCUIT DESIGN CONSIDERATIONS FOR OFF-HIGHWAY VEHICLES AND EQUIPMENT

D. E. Keyser

MICO, Incorporated 1911 Lee Boulevard North Mankato Minnesota USA 56003-2507 FULL POWER HYDRAULIC BRAKE ACTUATION, CIRCUIT DESIGN CONSIDERATIONS FOR OFF-HIGHWAY VEHICLES AND EQUIPMENT

ABSTRACT Standards Organization (ISO) and the Society of Auto- motive Engineers (SAE) can provide recommended The intent of this paper is to create a clear understand- vehicle brake system performance specifications. Infor- ing of full power hydraulic brake actuation system mation on laws that regulate vehicle brake performance design as it relates to off-highway vehicles and equip- can be obtained from Federal, State, and Provincial ment. The paper is divided into four main sections. The Government agencies. Actual vehicle performance is first section outlines six design prerequisites used for determined by the vehicle designer. It will be the vehicle selecting the service and the full power brake designer's responsibility to insure a proper testing actuation system. The second section, Brake Actuation program is defined and conducted to insure validation Systems, includes advantages of a full power brake of the components selected for use in the brake system and a brief description of reverse modulation actuation system. brake systems. Section three is a discussion of open center, closed center and load sensing hydraulic BRAKE TORQUE AND KINETIC ENERGY systems and the integration of a full power brake REQUIREMENTS - The brake torque and kinetic actuation system into these systems. Section three energy required to stop the vehicle is calculated based also explains the operation, related components and on the desired stopping parameters and the vehicle some common problems to be avoided in the actuation specifications. Vehicle specifications include, but are system design process. The fourth section describes not limited to, the gross vehicle weight, vehicle velocity, reverse modulating brake actuation and how it differs static loaded radius of the tires, gear reductions from full power hydraulic brake actuation. between the brake and the ground, the number of braked wheels, the number of brakes to be used and The actual selection of the service brakes is beyond the the road surface. Of the specifications mentioned, scope of this paper. However, it is assumed the vehicle velocity will have the greatest impact on the vehicle's brakes have been properly sized and are fully brake torque and kinetic energy. For example, if vehicle operational. The brakes are referred to throughout to velocity is doubled, the magnitude of the kinetic energy emphasize the importance of their relationship to the is multiplied by a factor of four. Where as, an increase brake actuation system. in vehicle mass will result in a directly proportional increase in kinetic energy, reference 1.

DESIGN PREREQUISITES There are many sources for formula's used to calculate brake torque, kinetic energy and the factors that affect The goal of the brake actuation system designer is to them, two of which are given in references 2 and 3. select the proper components to provide optimum brake performance for a given application. To do this the SERVICE BRAKE CAPACITY - Identifying the designer must start at the vehicle service brakes and service brake capacity is the process of matching the “work backward” to the method of actuation. Specific service brake(s) to the vehicle stopping parameters and design prerequisites for the vehicle brakes as well as brake torque requirements. The available brake torque the brake actuation system must be identified. The six is expressed at a given brake line pressure which key prerequisites that will be discussed are: (1) vehicle allows the designer to identify the proper amount of stopping parameters, (2) the resultant brake torque and brake line pressure required to match the vehicle torque kinetic energy required, (3) service brake capacity, requirements. The service brake capacity information is (4) brake line pressure, (5) brake volume and (6) acquired from the brake and or axle manufacturer and operator input effort. the torque versus pressure relationship is generally a linear function. STOPPING PARAMETERS - The stopping parame- ters are identified as performance attributes associated To avoid the pitfalls of either under-braking or over- with stopping the vehicle. They will include, but are not braking it is important to calculate the actual required limited to, the deceleration rate, stopping distance, torque for the application. Do not assume that the percentage of grade for operation and vehicle velocity. manufacturer's specified maximum brake line pressure Information used in determining these properties can be is the same as the required brake line pressure. procured from professional organizations, government This can be demonstrated in the following examples; agencies and the vehicle designer. one in which the vehicle brake torque requirement is Professional organizations such as the International above the torque limitations of the service brake. In the 1 other, the vehicle torque requirement is below the maximum brake line pressure or maximum desired torque capacity of the service brake. brake torque. Again, there are directing organizations and agencies that make recommendations to assist in Consider a vehicle that requires 680 N-m of brake identifying this value, references 5 and 6. More impor- torque. The torque limitation of the service brake is tantly, the pedal effort must comply with the operator's 450 N-m at a maximum pressure of 70 bar. Supplying ability to effectively control the machine. the maximum 70 bar and consequently generating 450 N-m of brake torque, does not stop the vehicle as required. The vehicle is under-braked. BRAKE ACTUATION SYSTEMS Conversely, consider if the torque requirement is now The system designer can accomplish brake actuation in 110 N-m and the brake is rated for 450 N-m at 70 bar. different ways. One method is the classical method of Supplying the maximum 70 bar will stop the vehicle brake actuation which uses fluid pressure to actuate the immediately (too severely). In this example, the torque braking means. Full power hydraulic brake actuation is requirement is satisfied with 25% of the available pres- a direct means of supplying hydraulic pressure to the sure resulting in aggressive, oversensitive brakes. brakes. This method uses fluid pressure and flow These scenarios will change in magnitude depending generated by the pump of a hydraulic system and on the method of actuation that is selected (reference directs this energy to the service brakes. 4) and the type of brakes on the vehicle. FULL POWER HYDRAULIC BRAKE SYSTEM Through proper brake actuation and circuit design the ADVANTAGES - The full power hydraulic brake system designer can match the actuation circuit to the service has several advantages over traditional brake actuation brakes and avoid poor performance characteristics. systems. These systems are capable of supplying fluid to a range of very small and large volume service BRAKE LINE PRESSURE - The brake line pres- brakes with actuation that is faster than sys- sure, as previously mentioned, is determined by tems. Figure 1 represents a time comparison between a matching the brake torque requirement to the service typical air/hydraulic and full power hydraulic brake brake capacity. By examining the brake torque versus actuation system. brake pressure relationship, the designer can extrapo- Figure 1 late the brake line pressure required to attain brake performance matched to the vehicle stopping parame- ters. The brake line pressure will also used in selection of the hydraulic system pump, determining the system relief valve pressure setting, accumulator dry nitrogen precharge, accumulator charge valve (in open center systems), and the brake modulating valve pressure setting. REQUIRED VOLUME - The brake volume require- ment is critical in determining the method of brake actuation to be used and in component selection. The designer needs to know the minimum, nominal, and maximum volume of fluid required. Different types of actuation components are used in various ranges of brake volume displacements. The brake volume is also used to determine the capacity of the accumulators and the accumulator charge valve charge rate with respect to the desired number of power-on and power-off stops. In open center and load sensing applications that use an accu- mulator charging valve, power-on stops are defined as the number of brake applications that can be attained Response Time between the high and low accumulator charge limit Full Power Brake Actuation settings. Power-off stops are defined as the number of -VS- stops that can be attained between the low accumulator Air/Hydraulic Brake Actuation charge limit setting and the maximum brake line pres- sure with the energy source disconnected. Full power systems can supply significantly higher OPERATOR INPUT EFFORT - Input pedal force brake pressures with relatively low reactive pedal required by the operator is generally expressed as the forces. The reactive pedal force felt by the operator maximum force allowed to generate the desired will be proportional to the brake line pressure being 2 generated. This is referred to as brake pressure modu- OPEN CENTER, CLOSED CENTER AND LOAD lation. Another key design feature of full power systems SENSE SYSTEM INTEGRATION is the ability to control maximum brake line pressure. In addition, because these systems operate with hydraulic Full power hydraulic brake actuation systems will vary oil, filtration can be utilized to provide long component in sophistication with the various types of hydraulic life and low maintenance operation. systems available today; open center, closed center, and load sensing. Because these systems are closed center, by using a properly sized accumulator, emergency power-off OPEN CENTER SYSTEMS - For the purposes of braking that is identical to power-on braking can be this paper, open center systems are considered sys- achieved. These systems can be either dedicated, tems where pump flow circulates to the reservoir at low where the brake system pump supplies only the pressure while the system controls are in a neutral demands of the brake system, or non-dedicated, where position. Actuation of the system controls will then allow the pump supplies the demands of the brake system as pressure to build as a function of resistance within the well as some secondary down stream hydraulic devise. hydraulic system. Another important note is that all seals within these Full power hydraulic brake actuation circuits that are system must be compatible with the fluid medium being used in open center hydraulic systems will contain as a used. minimum; a , a relief valve positioned REVERSE MODULATING BRAKE ACTUATION - between the pump and an accumulator charging valve, Another method of hydraulic brake actuation is reverse an accumulator, a low pressure warning switch, a brake modulation or as it is sometimes referred to, negative modulating valve, and the service brakes, see system braking. The term "reverse modulating" is used be- schematic 1. As is the case with any full power hydrau- cause pressure is decreased to actuate the brake from lic brake actuation system, it is possible to use either a a preset pressure that keeps the brake fully released. dedicated brake pump or divert oil from other hydraulic Reverse modulation uses hydraulic pressure to release sources on the machine, referred to as a non-dedicated a brake that is mechanically applied by springs. Maxi- pump. mum torque is produced when hydraulic pressure is Depending on the requirement, these systems can be absent either intentionally or due to system failure. either single, dual or variations thereof. This paper Section four of this paper discusses the concept of discusses single and dual circuits, only to mention the reverse modulation in further detail and compares it to components that differ between the two. full power hydraulic apply brake actuation.

System Schematic 1

Single Closed Center Brake Circuit in a Non-Dedicated Open Center Hydraulic System

3 CLOSED CENTER SYSTEM - Defined as systems may include an isolation check valve in place of the where the fluid is static at full system pressure until the accumulator charging valve, see system schematic 2. system controls are actuated at which time the closed The check valve will prevent accumulator pressure loss center system will allow fluid flow to be initiated at load in the event of an energy source failure. It is important induced pressure. The full power hydraulic brake circuit in closed center systems to be sure the pump can fulfill that is incorporated in a closed center hydraulic system all of the volume demand requirements. The recovery is usually a non-dedicated circuit. The pressure com- rate of the brake system must be considered under full pensated pump that supplies fluid to the brake system flow demands on the pump, references 5 and 6. The will almost always supply fluid to some other system pump should be sized so that it can satisfy the recovery requirement as well. In these circuits the brakes will rate of the brake system accumulators as well as the operate off of the pump displacement and the accumu- secondary system requirements. The brakes should lators will act as the energy source for the power-off never suffer a lack of fluid. braking requirements. Pressure compensated systems

System Schematic 2

Dual Closed Center Brake Circuit in a Non-Dedicated Closed Center Hydraulic System

If the designer elects to use a dedicated closed center Load sense systems are similar to the open center sys- system then consideration must be given to the fre- tems with respect to the components they require for quency of brake actuation. The concern is the potential integrating brake actuation systems. In both the open of a pressure compensated pump to operate at design center and load sense brake systems the accumulator speed while in a zero stroke condition, displacing little acts as the primary fluid source for brake actuation. The or no fluid for the time interval between brake actua- accumulator also provides the fluid source for power-off tions. In these conditions the pump may fail due to heat brake actuation. The difference comes in the form of the generated due to a lack of cooling flow. pump and the charge valve that is used, see system schematic 3. The load sense system will operate as a LOAD SENSING SYSTEMS - By definition the load flow and pressure on demand system. The control sense systems are very similar to the closed center section of the load sense accumulator charge valve system because fluid is static when the system controls sends a pilot signal to the pump when fluid is required. are in a neutral position. One exception is that the load Since load sense hydraulic pumps are generally high sense system is at a significantly lower stand-by pres- efficiency piston equipment, the concern over low sure in neutral as compared to the higher compensated speed operation is not as great. pressure of the closed center system.

4 Accumulators System Schematic 3

A1 Inverted A2 Shuttle Low Dual Modulating Valve Pressure Warning Switch SW

T

P P

T T A A Dual Accumulator Charging Valve P O Relief Valve Pump Dual Dual Closed Center Brake Brake System Circuit in a Non-Dedicated

Filter Load Sense Hydraulic System

OPERATION, RELATED COMPONENTS, AND must be taken into consideration when the designer ASSOCIATED PROBLEMS - In the open center specifies the accumulator(s) to be used in the system. hydraulic system an accumulator charging valve, either single or dual, is used in conjunction with an accum- The dual accumulator charging valve performs essen- ulator and a modulating brake valve. The valve tially the same functions as the single charging valve. automatically halts charging when the accumulator When the dual accumulator charging valve is used in pressure reaches its high limit. When the accumulator a dual hydraulic brake system each individual axle is pressure reaches its low limit, the charging valve diverts controlled separately by a modulating valve and an a small amount of fluid from the main open center accumulator. One dual charging valve charges both hydraulic system to charge the accumulator. However, accumulators, see system schematic 4. The primary in a non-dedicated system if the downstream open advantage of the dual charging valve over the single center circuit causes the hydraulic system pressure charging valve is that if half of the brake system fails to rise over the high accumulator charge limit, the the remaining half will continue to function. accumulator will be charged to this higher value. This

Accumulators System Schematic 4

A1 Inverted A2 Shuttle Low Dual Modulating Valve Pressure Warning Switch SW

T

P P

T T A A Dual Accumulator Charging Valve P O Relief Valve Pump Dual Closed Center Brake Dual Brake Circuit in a Dedicated Open System Center Hydraulic System Filter

5 The charged accumulator supplies pressurized fluid to be capable of handling the full pump displacement and the brake modulating valve. These can also be either the required pressure for the actuation system. single or dual depending on the application. Modulating power brake valves of closed center design are used The number of power-off stops can be varied by chang- for controlling output pressures to the brake system. ing the accumulator size, dry nitrogen pre-charge, fluid The valves are considered closed center because they pressure in the accumulator, or by increasing the pres- block the fluid at the pressure port of the modulating sure differential between the low accumulator charge valve while in the brake release position. Fluid remains limit and the maximum brake line pressure. static at accumulator pressure until the operator de- The accumulator has two purposes in the full power presses the brake pedal. This action causes the brake hydraulic brake actuation systems: (1) To provide valve to modulate fluid out to the brakes and provide reserve oil for power-off controlled braking and (2) the braking means. The operator can modulate pres- when used in an open center or load sense system with sure in the brake system by increasing or decreasing a charging valve, the accumulator provides the reserve pressure as required in proportion to the input force on volume and pressure necessary for pump unloading. the brake pedal. As previously mentioned in this text The accumulator should be of adequate size to accom- the maximum brake line pressure can be adjusted and modate the volume and leakage conditions of the brake controlled to prevent over-pressurizing the system. system. It is necessary that the accumulator have suffi- Low pressure warning switches are used to sense cient oil volume between the high and low limits of the accumulator pressure and warn the operator through charging valve to minimize the charging cycles. some audible or visual device in the event the pressure Accumulator oil capacity, dry nitrogen precharge pres- in the accumulator decays to an unsafe operating level. sure, and the initial oil pressure are also evaluated to These switches are typically set at a pressure below the limit charge cycle frequency, thus reducing heat and low accumulator charge limit yet higher than the enhancing pump life, references 7 and 8. pressure required to satisfy the secondary stopping The advantages and disadvantages of various pump requirements. This value is defined by the directing designs are beyond the scope of this paper. It is impor- organizations and agencies that regulate the brake tant however, that brake system designers be informed system recovery rate, the number of power-off stops, about various pump capabilities while evaluating and operator warning devices, references 5 and 6. methods of supplying oil to brake actuation circuits. Because the full power hydraulic brake system is Most pumps can deliver constant flow and pressure dependant on accumulated volume and pressure, the capable of sustaining a full power brake system while power-off stopping confines of the system must be rotating at a constant high speed. It is recommended considered to assure the operator can stop safely in the that pump efficiency be strongly considered when used event the energy source (engine or pump) fails. in variable RPM, engine driven mobile equipment. The number of power-off stops is determined with the In dedicated brake systems the pump supplies only the energy source off or disconnected. To determine the demands of the brake system. Typically, long periods of number of power-off stops in an open center system, time can elapse between brake applications. As pre- lower the accumulator fluid pressure to the pressure viously discussed there are concerns over using a that equals the low limit of the accumulator charging dedicated pressure compensated pump in a closed valve. While counting the number of applications, apply center brake actuation system. the brakes fully and release, repeatedly, until the point where the accumulator fluid pressure is no longer In the non-dedicated closed center brake system where sufficient to supply the pressure required to attain the the pressure compensated pump supplies fluid to both maximum brake line pressure. The number of brake the brake circuit and some secondary requirement, this applications between the low limit of the charge valve concern is not as great. The secondary requirement will and maximum brake line pressure is considered the usually allow the pump to function from zero stroke to power-off stopping capacity of the system. The charge full stroke and cycle more frequently. rate of the accumulator charge valve is determined by By using the pressure compensated pump with an the desired recovery rate of the application. The low accumulator charge valve in an open center circuit, the charge valve limit is determined by the maximum brake charge valve will unload the pump allowing the pump to line pressure and the number of power-off stops that displace fluid at low pressure differential. This combina- are desired. The high limit of the charge valve is deter- tion of components works especially well for the mined by the pressure differential band widths available variable RPM mobile equipment application. from the accumulator charge valve manufacturer. The minimum relief valve pressure setting is determined by the high charge valve limit. Relief valves must be incor- porated into the system to protect the pump and other controls from over-pressurization. The relief valve must

6 REVERSE MODULATING BRAKE ACTUATION Although a non-traditional method of braking a vehicle, a separate method of actuation. The complexity of such spring applied hydraulic release brakes are becoming systems will be apparent when the designer considers increasingly important to off-highway equipment design- the number of valves, switches, hoses and connectors ers, and engineers. For this reason it is important to that are involved. understand the difference between the conventional full power hydraulic apply brake actuation system and the Spring applied hydraulic release brake systems, on the spring applied hydraulic release brake actuation sys- other hand, may consist of a single circuit, providing tem. To obtain brake performance as recommended by service, secondary and parking functions with a com- the many accepted brake standards (references 5 and mon brake(s). The actuation circuit used to control this 6), a conventional hydraulic brake actuation system brake will require limited control hardware and plumb- may require independent service, secondary and park- ing. Consequently, this brake system will be easy to ing brake circuits. These circuits provide braking in the maintain, troubleshoot and is cost effective. event of any single failure in the service brake system. In each of the system schematics 5, 6, and 7, the brake Service brake actuation systems are commonly split to actuation circuits will differ only relating to the charging add redundancy to a system. In addition, parking of a brake accumulator. functions typically require an independent brake and

System Schematic 5

Low Pressure Warning Switch

MICO MICO Single Reverse Accumulator Modulating Charging Valve Valve

T

P A A T

P O To Power Beyond

Closed Center Actuation Circuit/Open Center Spring Apply/Hydraulic Charging System Release Brakes

This is relative to the type of system they are integrated operator applies the brake valve, pressure from the with. As shown in these schematics the brake actuation accumulator is blocked in a closed center condition circuit is considered as closed center. Closed center while fluid in the brake is exhausted to the reservoir. because the fluid pressure is supplied to the brake which maintains a brake release condition. When the

7 System Schematic 6

MICO Reverse Modulating Valve

Low Pressure Warning Switch

Closed Center Actuation Circuit/Pressure Compensated System

Spring/Apply Hydraulic Release Brake

In a spring applied hydraulic release brake actuation modulating brake valve. The reverse modulating power circuit the primary purpose of the accumulator is to brake valve is used for modulating the pressure in the provide power-off controlled braking in the event the brake system by increasing or decreasing pressure in energy source becomes disabled. The charged accu- the brake system in direct proportion to the input force mulator supplies pressurized fluid to the reverse from the operator via the brake pedal.

System Schematic 7 Accumulator

Low Pressure Warning Switch A SW

LS T MICO Reverse Modulating Valve

MICO Single Accumulator Closed Center Actuation Charging P Valve Circuit/Load Sense Charge System

Spring Apply/Hydraulic Release Brake

Further detailed explanation of reverse modulation and through additional technical papers, references 9 and spring applied hydraulic release brakes can be gained 10.

8 COMPARING DESIGN PREREQUISITES - To Volume Requirements - The oil volume capacity of effectively design the actuation portion of the spring the brake must also be determined prior to brake applied hydraulic release brake circuit, the same design actuation circuit design. Volume requirements may be prerequisites used in the conventional full power referred to in terms of maximum (worn) brake and hydraulic brake actuation systems must be known. normal (new) brake displacement. As the brake lining However, there may be differences in the interpretation material wears, piston travel increases. As piston travel of these criteria: (1) vehicle stopping parameters, (2) increases volume increases. Brake system components the resultant brake torque, (3) service brake capacity, such as the accumulator, hoses, and valves will be (4) pressure requirement of the brake, (5) volume sized according to this brake volume requirement. requirement of the brake, and (6) input pedal force requirement. Additionally, the designer must also con- Pedal Force - As is the case with the hydraulic apply sider (7) actuation (response) time, and (8) secondary brake actuation, input pedal force may be expressed as and parking requirements. a maximum value required to generate the maximum brake torque. This again is dictated by the application, Stopping Parameters - The stopping parameters will the operators ability to safely control the vehicle and the be identical to the parameters previously discussed for organizations and agencies that make recommenda- the conventional full power systems. This is because tions to assist in identifying this maximum value. they are defined for the vehicle and not for the method of actuation. Response Time - Response time or actuation time with respect to a spring applied hydraulic release brake Brake Torque and Kinetic Energy Requirements - system, is a time interval initiated by pedal movement, Torque and energy requirements that are calculated to resulting in a full brake application. This is directly satisfy the specifications of the application will again be related to oil volume capacity and full release pressure based on the stopping parameters and vehicle specifi- of the brake. Physical plumbing size, hose, fittings and cations as previously discussed. adapters will affect the response time of the brakes. Oil must be exhausted quickly from the brake and the Service Brake Capacity - Considerations for match- actuation circuit to reduce the response time and ing the service brake to the vehicle requirement are for optimize braking performance. the most part the same. However, because the spring applied hydraulic release brake relies on the forces Secondary / Parking - The secondary (emergency) generated in the springs to provide the braking means, and parking features of the brake actuation circuit must the selection and flexibility found in hydraulic apply be reviewed. In the case of emergency braking, a "fail- brakes may not be as plentiful. In these types of appli- ure mode analysis" will help determine component cations the need to over-brake may be required. selection; for example, if the energy source became disabled, and there were no provisions to maintain Pressure Requirements - As the name implies, the brake system pressure, the brakes will be energized spring applied hydraulic release brake is mechanically and bring the machine to an uncontrolled stop. How- actuated by springs and is dependant on hydraulic ever, by using an accumulator, reserve oil stored in the pressure to keep it released. Therefore, the brake accumulator will be available so the operator can bring actuation circuit, in a normal released mode, must the machine to a controlled stop. maintain sufficient pressure to allow the spring applied hydraulic release brake to fully release. The reverse System schematic 8 illustrates a MICO park/secondary modulating brake valve regulates this pressure to a safe control valve which has been incorporated to provide level above the "full release pressure" of the brake. The two functions: (1) A two position three way valve for brake, in a full release condition, has maximum running manual park actuation of the brake; this could be a clearance between the rotating and stationary plates. modulated valve or the on/off valve as shown. When "Initial release pressure" refers to the brake condition this valve is shifted to the apply position the brake is where the rotating and stationary plates make initial opened to the tank and the pressure supply is blocked. contact and minimal torque is developed. "Full apply In this apply position, the brake may remain actuated pressure" suggests a maximum brake applied condition, for an indefinite period of time, with or without supply normally occurring at zero pressure. The full release pressure from the accumulator. (2) A trigger valve to pressure, initial release pressure and full apply pressure allow an automatic emergency actuation of the brake must be determined prior to design of the brake actua- system when accumulator pressure drops below a pre- tion circuit. Because this brake design is dependant on determined level. Although brake actuation is a direct the forces of the springs to discharge fluid from the response to a loss of pressure, there are certain brake, it is desirable to have a high full release pressure government regulations that may require this feature to work with. This allows the designer a wider pressure due to stopping time restrictions, reference 11. range to modulate, thus providing better quality pres- sure modulation and brake performance.

9 Parking and emergency functions may be easily integrated into a spring applied hydraulic release brake actuation system. A typical solenoid or manual two- position three-way directional valve may be used to control parking functions.

System Schematic 8 Accumulator Low Pressure Warning Switch

MICO Park/Secondary Valve MICO Single Accumulator Charging Valve T

A

MICO P O Reverse To Power Modulating Beyond Valve

Closed Center Actuation Circuit with Park Secondary Valve/Open Center Charge System Spring Apply/Hydraulic NOTE: Release Brake This diagram depicts a braking system which may be claimed in United States patent no. 4,893,879 which is neither owned nor licensed by MICO, Inc.

SUMMARY This paper reviewed basic concepts involved in design- existing hydraulic systems, being aware of potential ing full power hydraulic brake actuation systems for problems in the brake actuation design and many other off-road vehicles and equipment. The design process is variables. It is the vehicle designer's responsibility to in- challenging and complex with operator safety being the sure a proper testing program is defined and conducted primary concern. The reliability and economy of the to insure validation of the components selected. design depends directly upon the quality of the data and the accuracy of the system designer. It is essential to have a thorough understanding of not only components and circuits but also the many laws, Designing a brake actuation circuit involves many organizations and agencies that regulate vehicle brak- factors including analyzing design prerequisites, ing and system design. The importance of planning determining brake system needs based on vehicle cannot be overemphasized. specifications, integrating actuation circuits into

10 REFERENCES 1) "Vehicle Braking", 1987 Pentech Press Ltd., 7) "Analyzing Hydraulic Systems", Parker Hannifin by A.K. Baker Fluid Power Bulletins - #0222 and "Fluid Power 2" - #0226 2) "Mechanics of Vehicles", 1957 Penton Publishing Co. by Jaroslav J. Taborek 8) "Design Engineers Handbook", Parker Hannifin Fluid Power Bulletin - #0224 3) "Designing the Brake System Step By Step", 1976 SAE publication, 760637, by Fred W. Cords and 9) "Design Considerations of Spring Apply - Hydraulic John B. Dale Release Cooled Service Brakes for Off-Road Use", 1992 SAE publication, 920907, by G.T. 4) "Hydraulic Brake Systems and Components for DeWald Off-Highway Vehicles and Equipment", 1992 National Fluid Power Association Technical Paper 10) "Reverse Modulating Brake Valves, Circuit Design Series, I92-1.4, by D.E. Keyser and K. Hogan Considerations and Applications", 1992 SAE publication, 920908, by D.E. Keyser and 5) "Surface Vehicle Braking Systems Manual", SAE R.P. Middendorf HS-24/92, ISBN 1-56091-279-0 11) "Automatic Emergency-Parking Brakes",United 6) "Earth-Moving Machinery - Wheeled Machines - States of America Federal Register, Department Performance Requirements and Test Procedures Of Labor, Mine Safety and Health Administration, for Braking Systems", ISO 3450-1985(E) 30 CFR Part 75

11 MICO, Incorporated 1911 Lee Boulevard North Mankato, MN U.S.A. 56003-2507 Tel: +1 507 625 6426 Fax: +1 507 625 3212

Reprinted by permission of Kluwer Academic Publishers

Form No. 80-950-098 1993-08-01 www.mico.com